Fasteners - Mechanical properties of corrosion-resistant stainless steel fasteners - Part 6: General rules for the selection of stainless steels and nickel alloys for fasteners (ISO 3506-6:2020)

This document specifies general rules and provides technical information on stainless steels and their properties, which are relevant when using other parts of the ISO 3506 series. It includes specifications for corrosion-resistant stainless steels and nickel alloys, which are suitable for the manufacture of fasteners.
It applies to austenitic, martensitic, ferritic and duplex (austenitic-ferritic) stainless steel grades and nickel alloys for fasteners, and is intended to be used together with the relevant parts of the ISO 3506 series.
Common designations of stainless steels and nickel alloys used for fasteners are given in Annex A.

Verbindungselemente - Mechanische Eigenschaften von Verbindungselementen aus nichtrostendem Stahl - Teil 6: Allgemeine Regeln für die Auswahl von nichtrostenden Stählen und Nickellegierungen für Verbindungselemente (ISO 3506-6:2020)

Fixations - Caractéristiques mécaniques des fixations en acier inoxydable résistant à la corrosion - Partie 6: Règles générales pour la sélection des aciers inoxydables et des alliages de nickel pour les fixations (ISO 3506-6:2020)

Le présent document spécifie les règles générales et fournit des informations techniques sur les aciers inoxydables et leurs propriétés qui sont adéquates pour l'utilisation des autres parties de l'ISO 3506. Il comprend des spécifications pour les aciers inoxydables et les alliages de nickel résistant à la corrosion, qui sont appropriés pour la fabrication de fixations.
Il s'applique aux grades d'aciers inoxydables austénitiques, martensitiques, ferritiques et duplex (austéno-ferritique) ainsi qu'aux alliages de nickel pour les fixations, et il est destiné à être utilisé conjointement avec les autres parties pertinentes de l'ISO 3506.
Les désignations courantes des aciers inoxydables et des alliages de nickel utilisés pour les fixations sont données à l'Annexe A.

Vezni elementi - Mehanske lastnosti korozijsko odpornih nerjavnih jekel - 6. del: Splošna pravila za izbiro nerjavnih jekel in nikljevih zlitin za pritrdilne elemente (ISO 3506-6:2020)

General Information

Status
Published
Public Enquiry End Date
17-May-2022
Publication Date
11-Jul-2022
Technical Committee
Current Stage
6060 - National Implementation/Publication (Adopted Project)
Start Date
01-Jul-2022
Due Date
05-Sep-2022
Completion Date
12-Jul-2022

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SLOVENSKI STANDARD
SIST EN ISO 3506-6:2022
01-september-2022

Vezni elementi - Mehanske lastnosti korozijsko odpornih nerjavnih jekel - 6. del:

Splošna pravila za izbiro nerjavnih jekel in nikljevih zlitin za pritrdilne elemente

(ISO 3506-6:2020)

Fasteners - Mechanical properties of corrosion-resistant stainless steel fasteners - Part

6: General rules for the selection of stainless steels and nickel alloys for fasteners (ISO

3506-6:2020)
Verbindungselemente - Mechanische Eigenschaften von Verbindungselementen aus

nichtrostendem Stahl - Teil 6: Allgemeine Regeln für die Auswahl von nichtrostenden

Stählen und Nickellegierungen für Verbindungselemente (ISO 3506-6:2020)

Fixations - Caractéristiques mécaniques des fixations en acier inoxydable résistant à la

corrosion - Partie 6: Règles générales pour la sélection des aciers inoxydables et des

alliages de nickel pour les fixations (ISO 3506-6:2020)
Ta slovenski standard je istoveten z: EN ISO 3506-6:2022
ICS:
21.060.01 Vezni elementi na splošno Fasteners in general
77.120.40 Nikelj, krom in njune zlitine Nickel, chromium and their
alloys
77.140.20 Visokokakovostna jekla Stainless steels
SIST EN ISO 3506-6:2022 en,fr,de

2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

---------------------- Page: 1 ----------------------
SIST EN ISO 3506-6:2022
---------------------- Page: 2 ----------------------
SIST EN ISO 3506-6:2022
EN ISO 3506-6
EUROPEAN STANDARD
NORME EUROPÉENNE
June 2022
EUROPÄISCHE NORM
ICS 21.060.01
English Version
Fasteners - Mechanical properties of corrosion-resistant
stainless steel fasteners - Part 6: General rules for the
selection of stainless steels and nickel alloys for fasteners
(ISO 3506-6:2020)

Fixations - Caractéristiques mécaniques des fixations Verbindungselemente - Mechanische Eigenschaften

en acier inoxydable résistant à la corrosion - Partie 6: von Verbindungselementen aus nichtrostendem Stahl -

Règles générales pour la sélection des aciers Teil 6: Allgemeine Regeln für die Auswahl von

inoxydables et des alliages de nickel pour les fixations nichtrostenden Stählen und Nickellegierungen für

(ISO 3506-6:2020) Verbindungselemente (ISO 3506-6:2020)
This European Standard was approved by CEN on 20 June 2022.

CEN members are bound to comply with the CEN/CENELEC Internal Regulations which stipulate the conditions for giving this

European Standard the status of a national standard without any alteration. Up-to-date lists and bibliographical references

concerning such national standards may be obtained on application to the CEN-CENELEC Management Centre or to any CEN

member.

This European Standard exists in three official versions (English, French, German). A version in any other language made by

translation under the responsibility of a CEN member into its own language and notified to the CEN-CENELEC Management

Centre has the same status as the official versions.

CEN members are the national standards bodies of Austria, Belgium, Bulgaria, Croatia, Cyprus, Czech Republic, Denmark, Estonia,

Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway,

Poland, Portugal, Republic of North Macedonia, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland, Turkey and

United Kingdom.
EUROPEAN COMMITTEE FOR STANDARDIZATION
COMITÉ EUROPÉEN DE NORMALISATION
EUROPÄISCHES KOMITEE FÜR NORMUNG
CEN-CENELEC Management Centre: Rue de la Science 23, B-1040 Brussels

© 2022 CEN All rights of exploitation in any form and by any means reserved Ref. No. EN ISO 3506-6:2022 E

worldwide for CEN national Members.
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SIST EN ISO 3506-6:2022
EN ISO 3506-6:2022 (E)
Contents Page

European foreword ....................................................................................................................................................... 3

---------------------- Page: 4 ----------------------
SIST EN ISO 3506-6:2022
EN ISO 3506-6:2022 (E)
European foreword

The text of ISO 3506-6:2020 has been prepared by Technical Committee ISO/TC 2 "Fasteners” of the

International Organization for Standardization (ISO) and has been taken over as EN ISO 3506-6:2022 by

Technical Committee CEN/TC 185 “Fasteners” the secretariat of which is held by BSI.

This European Standard shall be given the status of a national standard, either by publication of an

identical text or by endorsement, at the latest by December 2022, and conflicting national standards

shall be withdrawn at the latest by December 2022.

Attention is drawn to the possibility that some of the elements of this document may be the subject of

patent rights. CEN shall not be held responsible for identifying any or all such patent rights.

Any feedback and questions on this document should be directed to the users’ national standards body.

A complete listing of these bodies can be found on the CEN website.

According to the CEN-CENELEC Internal Regulations, the national standards organizations of the

following countries are bound to implement this European Standard: Austria, Belgium, Bulgaria,

Croatia, Cyprus, Czech Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland,

Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Republic of

North Macedonia, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland, Turkey and the

United Kingdom.
Endorsement notice

The text of ISO 3506-6:2020 has been approved by CEN as EN ISO 3506-6:2022 without any

modification.
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SIST EN ISO 3506-6:2022
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SIST EN ISO 3506-6:2022
INTERNATIONAL ISO
STANDARD 3506-6
First edition
2020-04
Fasteners — Mechanical properties
of corrosion-resistant stainless steel
fasteners —
Part 6:
General rules for the selection of
stainless steels and nickel alloys for
fasteners
Fixations — Caractéristiques mécaniques des fixations en acier
inoxydable résistant à la corrosion —
Partie 6: Règles générales pour la sélection des aciers inoxydables et
des alliages de nickel pour les fixations
Reference number
ISO 3506-6:2020(E)
ISO 2020
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SIST EN ISO 3506-6:2022
ISO 3506-6:2020(E)
COPYRIGHT PROTECTED DOCUMENT
© ISO 2020

All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may

be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting

on the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address

below or ISO’s member body in the country of the requester.
ISO copyright office
CP 401 • Ch. de Blandonnet 8
CH-1214 Vernier, Geneva
Phone: +41 22 749 01 11
Fax: +41 22 749 09 47
Email: copyright@iso.org
Website: www.iso.org
Published in Switzerland
ii © ISO 2020 – All rights reserved
---------------------- Page: 8 ----------------------
SIST EN ISO 3506-6:2022
ISO 3506-6:2020(E)
Contents Page

Foreword ........................................................................................................................................................................................................................................iv

Introduction ..................................................................................................................................................................................................................................v

1 Scope ................................................................................................................................................................................................................................. 1

2 Normative references ...................................................................................................................................................................................... 1

3 Terms and definitions ..................................................................................................................................................................................... 1

4 Groups and grades of stainless steels ............................................................................................................................................. 2

4.1 General ........................................................................................................................................................................................................... 2

4.2 Stainless steel group A (austenitic structure) .............................................................................................................. 2

4.2.1 General...................................................................................................................................................................................... 2

4.2.2 Grade A1 .................................................................................................................................................................................. 3

4.2.3 Grade A2 .................................................................................................................................................................................. 3

4.2.4 Grade A3 .................................................................................................................................................................................. 3

4.2.5 Grade A4 .................................................................................................................................................................................. 3

4.2.6 Grade A5 .................................................................................................................................................................................. 3

4.2.7 Grade A8 .................................................................................................................................................................................. 3

4.3 Stainless steel group C (martensitic structure) .......................................................................................................... 4

4.3.1 General...................................................................................................................................................................................... 4

4.3.2 Grade C1 .................................................................................................................................................................................. 4

4.3.3 Grade C3 .................................................................................................................................................................................. 4

4.3.4 Grade C4 .................................................................................................................................................................................. 4

4.4 Stainless steel group F (ferritic structure) — Grade F1 ...................................................................................... 4

4.5 Stainless steel group D (austenitic-ferritic structure) .......................................................................................... 4

4.5.1 General...................................................................................................................................................................................... 4

4.5.2 Grades D2 and D4............................................................................................................................................................ 5

4.5.3 Grades D6 and D8............................................................................................................................................................ 5

4.6 Stainless steels and nickel alloys for elevated and high temperatures ................................................... 5

5 Chemical composition specifications for stainless steels and nickel alloys ...........................................5

6 Resistance to stress corrosion cracking ....................................................................................................................................... 8

7 Resistance to pitting and crevice corrosion ............................................................................................................................. 9

8 Resistance to intergranular corrosion ........................................................................................................................................... 9

9 Susceptibility to formation of intermetallic compounds ........................................................................................11

10 Magnetic permeability properties of stainless steels .................................................................................................12

Annex A (informative) Common designations of stainless steels and nickel alloys used for

fasteners .....................................................................................................................................................................................................................13

Bibliography .............................................................................................................................................................................................................................20

© ISO 2020 – All rights reserved iii
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SIST EN ISO 3506-6:2022
ISO 3506-6:2020(E)
Foreword

ISO (the International Organization for Standardization) is a worldwide federation of national standards

bodies (ISO member bodies). The work of preparing International Standards is normally carried out

through ISO technical committees. Each member body interested in a subject for which a technical

committee has been established has the right to be represented on that committee. International

organizations, governmental and non-governmental, in liaison with ISO, also take part in the work.

ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of

electrotechnical standardization.

The procedures used to develop this document and those intended for its further maintenance are

described in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the

different types of ISO documents should be noted. This document was drafted in accordance with the

editorial rules of the ISO/IEC Directives, Part 2 (see www .iso .org/ directives).

Attention is drawn to the possibility that some of the elements of this document may be the subject of

patent rights. ISO shall not be held responsible for identifying any or all such patent rights. Details of

any patent rights identified during the development of the document will be in the Introduction and/or

on the ISO list of patent declarations received (see www .iso .org/ patents).

Any trade name used in this document is information given for the convenience of users and does not

constitute an endorsement.

For an explanation of the voluntary nature of standards, the meaning of ISO specific terms and

expressions related to conformity assessment, as well as information about ISO's adherence to the

World Trade Organization (WTO) principles in the Technical Barriers to Trade (TBT), see www .iso .org/

iso/ foreword .html.
This document was prepared by Technical Committee ISO/TC 2, Fasteners.
A list of all parts in the ISO 3506 series can be found on the ISO website.

Any feedback or questions on this document should be directed to the user’s national standards body. A

complete listing of these bodies can be found at www .iso .org/ members .html.
iv © ISO 2020 – All rights reserved
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SIST EN ISO 3506-6:2022
ISO 3506-6:2020(E)
Introduction

When revising ISO 3506-1 and ISO 3506-2, annexes common to several parts have been withdrawn and

included in this document in order to avoid uncessery repetition and to ease further revision of parts as

necessary (these annexes have also been technically revised). This document replaces:

— ISO 3506-1:2009, Annexes B, C, D, E, G and H, and
— ISO 3506-2:2009, Annexes A, B, C, D, F and G.

The ISO 3506 series consists of the following parts, under the general title Fasteners — Mechanical

properties of corrosion-resistant stainless steel fasteners:
— Part 1: Bolts, screws and studs with specified grades and property classes
— Part 2: Nuts with specified grades and property classes
— Part 3 : Set screws and similar fasteners not under tensile stress
— Part 4 : Tapping screws

— Part 5 : Special fasteners (also including fasteners from nickel alloys) for high temperature applications

— Part 6: General rules for the selection of stainless steels and nickel alloys for fasteners

1) It is intended to revise ISO 3506-3 and ISO 3506-4 in the future in order to include the reference to ISO 3506-6.

2) Under preparation.
© ISO 2020 – All rights reserved v
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SIST EN ISO 3506-6:2022
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SIST EN ISO 3506-6:2022
INTERNATIONAL STANDARD ISO 3506-6:2020(E)
Fasteners — Mechanical properties of corrosion-resistant
stainless steel fasteners —
Part 6:
General rules for the selection of stainless steels and nickel
alloys for fasteners
1 Scope

This document specifies general rules and provides technical information on stainless steels and their

properties, which are relevant when using other parts of the ISO 3506 series. It includes specifications

for corrosion-resistant stainless steels and nickel alloys, which are suitable for the manufacture of

fasteners.

It applies to austenitic, martensitic, ferritic and duplex (austenitic-ferritic) stainless steel grades and nickel

alloys for fasteners, and is intended to be used together with the relevant parts of the ISO 3506 series.

Common designations of stainless steels and nickel alloys used for fasteners are given in Annex A.

2 Normative references

The following documents are referred to in the text in such a way that some or all of their content

constitutes requirements of this document. For dated references, only the edition cited applies. For

undated references, the latest edition of the referenced document (including any amendments) applies.

ISO 3506-1, Fasteners — Mechanical properties of corrosion-resistant stainless steel fasteners — Part 1:

Bolts, screws and studs with specified grades and property classes

ISO 3506-2, Fasteners — Mechanical properties of corrosion-resistant stainless steel fasteners — Part 2:

Nuts with specified grades and property classes

ISO 3506-5 , Fasteners — Mechanical properties of corrosion-resistant stainless steel fasteners — Part 5:

Special fasteners (also including fasteners from nickel alloys) for high temperature applications

3 Terms and definitions

For the purpose of this document, terms and definitions specified in ISO 3506-1, ISO 3506-2 and

ISO 3506-5 apply.

ISO and IEC maintain terminological databases for use in standardization at the following addresses:

— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at http:// www .electropedia .org/
3) Under preparation.
© ISO 2020 – All rights reserved 1
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SIST EN ISO 3506-6:2022
ISO 3506-6:2020(E)
4 Groups and grades of stainless steels
4.1 General
The ISO 3506 series deals with stainless steel grades of the following groups:
— austenitic steel A1 to A5 and A8,
— martensitic steel C1, C3 and C4,
— ferritic steel F1,
— duplex (austenitic-ferritic) steel D2, D4, D6 and D8.

Stainless steels cover a great variety of materials providing different corrosion resistant properties and

different functional properties. A specific fastener manufactured from stainless steel shall be carefully

chosen by taking into account all the conditions in the expected environment of the bolted joint.

The condition of the surface of the fasteners (passivated, surface roughness, etc.) can influence the

capacity of the fastener to resist corrosion.

In special cases, it is advised to consult an experienced fastener manufacturer and/or stainless steel

metallurgist in order to make the appropriate choice for a given application.

Corrosion depends on several factors related to the fasteners themselves, the design of the bolted joint,

service environment, surface and material conditions, mechanical stresses, temperature and corrosion

caused by contact between dissimilar metals (known as galvanic corrosion or contact corrosion), etc.

NOTE When combining different stainless steel grades, the corrosion resistance of the assembly depends on

the lowest corrosion resistance grade.

When stainless steel fasteners are intended to be used in a high or low temperature environment:

— austenitic stainless steels are suitable for service environment typically down to –196 °C and up to

+300 °C;

— martensitic stainless steels are suitable for service environment typically down to −40 °C and up to

+230 °C;

— ferritic stainless steels are suitable for service environment typically down to −20 °C and up to

+250 °C;

— duplex stainless steels are suitable for service environment typically down to −40 °C and up to

+280 °C.
4.2 Stainless steel group A (austenitic structure)
4.2.1 General

Several grades of austenitic stainless steels (A1 to A5 and A8) are included in the ISO 3506 series.

They are generally classified as chromium-nickel austenitic grades (A1 to A3) and chromium-nickel-

molybdenum austenitic grades (A4 to A8).

Austenitic stainless steels cannot be hardened by quenching; the mechanical properties of the fasteners

are usually achieved by work hardening. Copper may be added in order to enhance the plasticity of the

austenitic matrix (see chemical compositions specified in ISO 3506-1 and ISO 3506-2).

Stainless steel grades A2 and A4 with carbon content lower than 0,030 % may be identified by adding

the letter L to the grade, i.e. A2L and A4L, respectively. Stainless steel grades A2 and A4 with carbon

4) –196 °C is a limit for testability corresponding to liquid nitrogen at a normal atmosphere pressure.

2 © ISO 2020 – All rights reserved
---------------------- Page: 14 ----------------------
SIST EN ISO 3506-6:2022
ISO 3506-6:2020(E)

content above 0,030 % and/or exposed to high temperatures (either during the manufacturing process,

welding process or in the service environment) can have a higher susceptibility to intergranular

corrosion; see Clause 8. In these cases, the purchaser may choose stainless steel grades A2L or A4L,

or stabilized stainless steels A3 or A5 including titanium or niobium. A8 is a highly alloyed austenitic

stainless steel with corrosion resistance much higher than A1 to A5.

Austenitic steels in the annealed state are usually non-magnetic; however, cold working occurring during

the fastener manufacture can create some residual magnetism; see Clause 10. Where low magnetic

permeability is an important consideration, the advice of a stainless steel expert should be sought.

4.2.2 Grade A1

Stainless steels of grade A1 are specially designed for machining. Due to high sulfur content, this grade

has lower resistance to corrosion than corresponding stainless steels with normal sulfur content. This

grade is neither suitable for use in non-oxidizing acids and agents, nor in an environment with chloride

(e.g. in swimming pools using chloride as a cleaning agent, or marine environments).

4.2.3 Grade A2

Stainless steels of grade A2 are the most frequently used stainless steel. This grade is not suitable for

use in non-oxidizing acids and agents, or in an environment with chloride (e.g. in swimming pools using

chloride as a cleaning agent, or marine environments).
4.2.4 Grade A3

Stainless steels of grade A3 have properties similar to grade A2, but with increased resistance to

temperature (typically up to 350 °C). They are stabilized by addition of titanium or niobium that

combines with carbon and nitrogen. This grade is neither suitable for use in non-oxidizing acids and

agents, nor in an environment with chloride (e.g. in swimming pools using chloride as a cleaning agent,

or marine environments).
4.2.5 Grade A4

Stainless steels of grade A4, often known as “acid proof steels”, are molybdenum alloyed which gives

a considerably better resistance to corrosion. This grade may be used in some environments where

chloride is present; however, it is still not suitable in swimming pools using chloride as a cleaning agent,

or many marine environments.
4.2.6 Grade A5

Stainless steels of grade A5 are stabilized stainless steels with properties of grade A4, but with increased

resistance to temperature (typically up to 350 °C). Stainless steels of grade A5 have properties similar

to grade A4 and are resistant to many acids. They are stabilized by addition of titanium or niobium that

combines with carbon and nitrogen. This grade may be used in some environments where chloride is

present; however, it is still not suitable in swimming pools using chloride as a cleaning agent, or many

marine environments.
4.2.7 Grade A8

Stainless steels of grade A8 are known as “6 % Mo” stainless steels. They have a high level of resistance

to all forms of corrosion including pitting, crevice and stress corrosion cracking. They are suitable for

use in swimming pools using chloride as a cleaning agent. However, there can be specific requirements

and/or regulations for buildings and construction. Grade A8 is also suitable for applications in marine

environments.
© ISO 2020 – All rights reserved 3
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SIST EN ISO 3506-6:2022
ISO 3506-6:2020(E)
4.3 Stainless steel group C (martensitic structure)
4.3.1 General

Three grades of martensitic stainless steels (C1, C3 and C4) are included in the ISO 3506 series. They

can be hardened by quenching and tempering. Mechanical properties increase when the carbon

content rises, inducing the necessary rise of chromium content in order to achieve a suitable corrosion

resistance.

Martensitic grades C1, C3 and C4 normally have a lower corrosion resistance than austenitic grades.

However, other martensitic steels with improved corrosion resistance (see Table A.2) can also be used

for special fasteners.

Caution should be taken when using martensitic stainless steels at sub-zero temperatures due to their

poor impact strength and ductility.
Martensitic steel grades are always highly magnetic.
4.3.2 Grade C1
Stainless steels of grade C1 have limited resistance to corrosion.
4.3.3 Grade C3

Stainless steels of grade C3 have limited resistance to corrosion, though better resistance than C1.

4.3.4 Grade C4

Stainless steels of grade C4 are similar to grade C1 but with a lower resistance to corrosion due to their

sulfur content. They are primarily intended for machining.
4.4 Stainless steel group F (ferritic structure) — Grade F1

One single ferritic stainless steel grade F1 is included in the ISO 3506 series. The steels within F1 can

be hardened by work hardening (cold working); however, the cold working effect has a lower efficiency

than for austenitic stainless steels. F1 steels are always magnetic.

When lower corrosion resistance than provided by grades A2 or A3 is suitable for the planned

application, stainless steel grade F1 can be a good economical compromise. However, grade F1 should

not be used at temperatures lower than −20 °C because ferritic stainless steels have poor impact

strength and ductility.
4.5 Stainless steel group D (austenitic-ferritic structure)
4.5.1 General

Duplex stainless steel is a mixture of ferrite and austenite grains with a ferrite content typically 40 %

to 60 % by volume.

In the solution annealed condition, the strength of duplex stainless steels is significantly higher than

the strength of austenitic stainless steels and can be further increased by cold working, but ductility

could then be lower.

Four grades of duplex stainless steels (D2, D4, D6 and D8) are included in the ISO 3506 series: the higher

the digit in the grade, the better the corrosion resistance. Families of duplex stainless steel are usually

described as follows:

— “lean-duplex” (D2 and D4) with lower alloying content (specifically nickel and molybdenum);

4 © ISO 2020 – All rights reserved
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SIST EN ISO 3506-6:2022
ISO 3506-6:2020(E)
— “standard-duplex” (D6);
— “super-duplex” (D8) with higher alloying content.

Duplex stainless steels have much improved resistance to stress corrosion cracking when compared to

austenitic stainless steels A1 to A5.

It is not recommended to use duplex stainless steels for application outside the temperature range of

−40 °C to +280 °C.
4.5.2 Grades D2 and D4

D2 and D4 are “lean-duplex” characterized by their molybdenum content below 2 %, and even below 1 %.

With respect to pitting and crevice corrosion, D2 has at least an equivalent corrosion resistance

compared to A2, and D4 has at least an equivalent corrosion resistance compared to A4.

4.5.3 Grades D6 and D8

D6 is a “standard-duplex” with molybdenum content above 2,5 %, which has improved corrosion

resistance when compared to A1 to A5 and D4, particularly with respect to pitting and crevice

corrosion.
D8 is a
...

SLOVENSKI STANDARD
oSIST prEN ISO 3506-6:2022
01-april-2022

Vezni elementi - Mehanske lastnosti korozijsko odpornih nerjavnih jekel - 6. del:

Splošna pravila za izbiro nerjavnih jekel in nikljevih zlitin za pritrdilne elemente

(ISO 3506-6:2020)

Fasteners - Mechanical properties of corrosion-resistant stainless steel fasteners - Part

6: General rules for the selection of stainless steels and nickel alloys for fasteners (ISO

3506-6:2020)
Verbindungselemente - Mechanische Eigenschaften von Verbindungselementen aus

nichtrostendem Stahl - Teil 6: Allgemeine Regeln für die Auswahl von nichtrostenden

Stählen und Nickellegierungen für Verbindungselemente (ISO 3506-6:2020)

Fixations - Caractéristiques mécaniques des fixations en acier inoxydable résistant à la

corrosion - Partie 6: Règles générales pour la sélection des aciers inoxydables et des

alliages de nickel pour les fixations (ISO 3506-6:2020)
Ta slovenski standard je istoveten z: prEN ISO 3506-6
ICS:
21.060.01 Vezni elementi na splošno Fasteners in general
77.120.40 Nikelj, krom in njune zlitine Nickel, chromium and their
alloys
77.140.20 Visokokakovostna jekla Stainless steels
oSIST prEN ISO 3506-6:2022 en,fr,de

2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

---------------------- Page: 1 ----------------------
oSIST prEN ISO 3506-6:2022
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oSIST prEN ISO 3506-6:2022
INTERNATIONAL ISO
STANDARD 3506-6
First edition
2020-04
Fasteners — Mechanical properties
of corrosion-resistant stainless steel
fasteners —
Part 6:
General rules for the selection of
stainless steels and nickel alloys for
fasteners
Fixations — Caractéristiques mécaniques des fixations en acier
inoxydable résistant à la corrosion —
Partie 6: Règles générales pour la sélection des aciers inoxydables et
des alliages de nickel pour les fixations
Reference number
ISO 3506-6:2020(E)
ISO 2020
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oSIST prEN ISO 3506-6:2022
ISO 3506-6:2020(E)
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© ISO 2020

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ii © ISO 2020 – All rights reserved
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oSIST prEN ISO 3506-6:2022
ISO 3506-6:2020(E)
Contents Page

Foreword ........................................................................................................................................................................................................................................iv

Introduction ..................................................................................................................................................................................................................................v

1 Scope ................................................................................................................................................................................................................................. 1

2 Normative references ...................................................................................................................................................................................... 1

3 Terms and definitions ..................................................................................................................................................................................... 1

4 Groups and grades of stainless steels ............................................................................................................................................. 2

4.1 General ........................................................................................................................................................................................................... 2

4.2 Stainless steel group A (austenitic structure) .............................................................................................................. 2

4.2.1 General...................................................................................................................................................................................... 2

4.2.2 Grade A1 .................................................................................................................................................................................. 3

4.2.3 Grade A2 .................................................................................................................................................................................. 3

4.2.4 Grade A3 .................................................................................................................................................................................. 3

4.2.5 Grade A4 .................................................................................................................................................................................. 3

4.2.6 Grade A5 .................................................................................................................................................................................. 3

4.2.7 Grade A8 .................................................................................................................................................................................. 3

4.3 Stainless steel group C (martensitic structure) .......................................................................................................... 4

4.3.1 General...................................................................................................................................................................................... 4

4.3.2 Grade C1 .................................................................................................................................................................................. 4

4.3.3 Grade C3 .................................................................................................................................................................................. 4

4.3.4 Grade C4 .................................................................................................................................................................................. 4

4.4 Stainless steel group F (ferritic structure) — Grade F1 ...................................................................................... 4

4.5 Stainless steel group D (austenitic-ferritic structure) .......................................................................................... 4

4.5.1 General...................................................................................................................................................................................... 4

4.5.2 Grades D2 and D4............................................................................................................................................................ 5

4.5.3 Grades D6 and D8............................................................................................................................................................ 5

4.6 Stainless steels and nickel alloys for elevated and high temperatures ................................................... 5

5 Chemical composition specifications for stainless steels and nickel alloys ...........................................5

6 Resistance to stress corrosion cracking ....................................................................................................................................... 8

7 Resistance to pitting and crevice corrosion ............................................................................................................................. 9

8 Resistance to intergranular corrosion ........................................................................................................................................... 9

9 Susceptibility to formation of intermetallic compounds ........................................................................................11

10 Magnetic permeability properties of stainless steels .................................................................................................12

Annex A (informative) Common designations of stainless steels and nickel alloys used for

fasteners .....................................................................................................................................................................................................................13

Bibliography .............................................................................................................................................................................................................................20

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oSIST prEN ISO 3506-6:2022
ISO 3506-6:2020(E)
Foreword

ISO (the International Organization for Standardization) is a worldwide federation of national standards

bodies (ISO member bodies). The work of preparing International Standards is normally carried out

through ISO technical committees. Each member body interested in a subject for which a technical

committee has been established has the right to be represented on that committee. International

organizations, governmental and non-governmental, in liaison with ISO, also take part in the work.

ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of

electrotechnical standardization.

The procedures used to develop this document and those intended for its further maintenance are

described in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the

different types of ISO documents should be noted. This document was drafted in accordance with the

editorial rules of the ISO/IEC Directives, Part 2 (see www .iso .org/ directives).

Attention is drawn to the possibility that some of the elements of this document may be the subject of

patent rights. ISO shall not be held responsible for identifying any or all such patent rights. Details of

any patent rights identified during the development of the document will be in the Introduction and/or

on the ISO list of patent declarations received (see www .iso .org/ patents).

Any trade name used in this document is information given for the convenience of users and does not

constitute an endorsement.

For an explanation of the voluntary nature of standards, the meaning of ISO specific terms and

expressions related to conformity assessment, as well as information about ISO's adherence to the

World Trade Organization (WTO) principles in the Technical Barriers to Trade (TBT), see www .iso .org/

iso/ foreword .html.
This document was prepared by Technical Committee ISO/TC 2, Fasteners.
A list of all parts in the ISO 3506 series can be found on the ISO website.

Any feedback or questions on this document should be directed to the user’s national standards body. A

complete listing of these bodies can be found at www .iso .org/ members .html.
iv © ISO 2020 – All rights reserved
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oSIST prEN ISO 3506-6:2022
ISO 3506-6:2020(E)
Introduction

When revising ISO 3506-1 and ISO 3506-2, annexes common to several parts have been withdrawn and

included in this document in order to avoid uncessery repetition and to ease further revision of parts as

necessary (these annexes have also been technically revised). This document replaces:

— ISO 3506-1:2009, Annexes B, C, D, E, G and H, and
— ISO 3506-2:2009, Annexes A, B, C, D, F and G.

The ISO 3506 series consists of the following parts, under the general title Fasteners — Mechanical

properties of corrosion-resistant stainless steel fasteners:
— Part 1: Bolts, screws and studs with specified grades and property classes
— Part 2: Nuts with specified grades and property classes
— Part 3 : Set screws and similar fasteners not under tensile stress
— Part 4 : Tapping screws

— Part 5 : Special fasteners (also including fasteners from nickel alloys) for high temperature applications

— Part 6: General rules for the selection of stainless steels and nickel alloys for fasteners

1) It is intended to revise ISO 3506-3 and ISO 3506-4 in the future in order to include the reference to ISO 3506-6.

2) Under preparation.
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oSIST prEN ISO 3506-6:2022
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oSIST prEN ISO 3506-6:2022
INTERNATIONAL STANDARD ISO 3506-6:2020(E)
Fasteners — Mechanical properties of corrosion-resistant
stainless steel fasteners —
Part 6:
General rules for the selection of stainless steels and nickel
alloys for fasteners
1 Scope

This document specifies general rules and provides technical information on stainless steels and their

properties, which are relevant when using other parts of the ISO 3506 series. It includes specifications

for corrosion-resistant stainless steels and nickel alloys, which are suitable for the manufacture of

fasteners.

It applies to austenitic, martensitic, ferritic and duplex (austenitic-ferritic) stainless steel grades and nickel

alloys for fasteners, and is intended to be used together with the relevant parts of the ISO 3506 series.

Common designations of stainless steels and nickel alloys used for fasteners are given in Annex A.

2 Normative references

The following documents are referred to in the text in such a way that some or all of their content

constitutes requirements of this document. For dated references, only the edition cited applies. For

undated references, the latest edition of the referenced document (including any amendments) applies.

ISO 3506-1, Fasteners — Mechanical properties of corrosion-resistant stainless steel fasteners — Part 1:

Bolts, screws and studs with specified grades and property classes

ISO 3506-2, Fasteners — Mechanical properties of corrosion-resistant stainless steel fasteners — Part 2:

Nuts with specified grades and property classes

ISO 3506-5 , Fasteners — Mechanical properties of corrosion-resistant stainless steel fasteners — Part 5:

Special fasteners (also including fasteners from nickel alloys) for high temperature applications

3 Terms and definitions

For the purpose of this document, terms and definitions specified in ISO 3506-1, ISO 3506-2 and

ISO 3506-5 apply.

ISO and IEC maintain terminological databases for use in standardization at the following addresses:

— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at http:// www .electropedia .org/
3) Under preparation.
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oSIST prEN ISO 3506-6:2022
ISO 3506-6:2020(E)
4 Groups and grades of stainless steels
4.1 General
The ISO 3506 series deals with stainless steel grades of the following groups:
— austenitic steel A1 to A5 and A8,
— martensitic steel C1, C3 and C4,
— ferritic steel F1,
— duplex (austenitic-ferritic) steel D2, D4, D6 and D8.

Stainless steels cover a great variety of materials providing different corrosion resistant properties and

different functional properties. A specific fastener manufactured from stainless steel shall be carefully

chosen by taking into account all the conditions in the expected environment of the bolted joint.

The condition of the surface of the fasteners (passivated, surface roughness, etc.) can influence the

capacity of the fastener to resist corrosion.

In special cases, it is advised to consult an experienced fastener manufacturer and/or stainless steel

metallurgist in order to make the appropriate choice for a given application.

Corrosion depends on several factors related to the fasteners themselves, the design of the bolted joint,

service environment, surface and material conditions, mechanical stresses, temperature and corrosion

caused by contact between dissimilar metals (known as galvanic corrosion or contact corrosion), etc.

NOTE When combining different stainless steel grades, the corrosion resistance of the assembly depends on

the lowest corrosion resistance grade.

When stainless steel fasteners are intended to be used in a high or low temperature environment:

— austenitic stainless steels are suitable for service environment typically down to –196 °C and up to

+300 °C;

— martensitic stainless steels are suitable for service environment typically down to −40 °C and up to

+230 °C;

— ferritic stainless steels are suitable for service environment typically down to −20 °C and up to

+250 °C;

— duplex stainless steels are suitable for service environment typically down to −40 °C and up to

+280 °C.
4.2 Stainless steel group A (austenitic structure)
4.2.1 General

Several grades of austenitic stainless steels (A1 to A5 and A8) are included in the ISO 3506 series.

They are generally classified as chromium-nickel austenitic grades (A1 to A3) and chromium-nickel-

molybdenum austenitic grades (A4 to A8).

Austenitic stainless steels cannot be hardened by quenching; the mechanical properties of the fasteners

are usually achieved by work hardening. Copper may be added in order to enhance the plasticity of the

austenitic matrix (see chemical compositions specified in ISO 3506-1 and ISO 3506-2).

Stainless steel grades A2 and A4 with carbon content lower than 0,030 % may be identified by adding

the letter L to the grade, i.e. A2L and A4L, respectively. Stainless steel grades A2 and A4 with carbon

4) –196 °C is a limit for testability corresponding to liquid nitrogen at a normal atmosphere pressure.

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oSIST prEN ISO 3506-6:2022
ISO 3506-6:2020(E)

content above 0,030 % and/or exposed to high temperatures (either during the manufacturing process,

welding process or in the service environment) can have a higher susceptibility to intergranular

corrosion; see Clause 8. In these cases, the purchaser may choose stainless steel grades A2L or A4L,

or stabilized stainless steels A3 or A5 including titanium or niobium. A8 is a highly alloyed austenitic

stainless steel with corrosion resistance much higher than A1 to A5.

Austenitic steels in the annealed state are usually non-magnetic; however, cold working occurring during

the fastener manufacture can create some residual magnetism; see Clause 10. Where low magnetic

permeability is an important consideration, the advice of a stainless steel expert should be sought.

4.2.2 Grade A1

Stainless steels of grade A1 are specially designed for machining. Due to high sulfur content, this grade

has lower resistance to corrosion than corresponding stainless steels with normal sulfur content. This

grade is neither suitable for use in non-oxidizing acids and agents, nor in an environment with chloride

(e.g. in swimming pools using chloride as a cleaning agent, or marine environments).

4.2.3 Grade A2

Stainless steels of grade A2 are the most frequently used stainless steel. This grade is not suitable for

use in non-oxidizing acids and agents, or in an environment with chloride (e.g. in swimming pools using

chloride as a cleaning agent, or marine environments).
4.2.4 Grade A3

Stainless steels of grade A3 have properties similar to grade A2, but with increased resistance to

temperature (typically up to 350 °C). They are stabilized by addition of titanium or niobium that

combines with carbon and nitrogen. This grade is neither suitable for use in non-oxidizing acids and

agents, nor in an environment with chloride (e.g. in swimming pools using chloride as a cleaning agent,

or marine environments).
4.2.5 Grade A4

Stainless steels of grade A4, often known as “acid proof steels”, are molybdenum alloyed which gives

a considerably better resistance to corrosion. This grade may be used in some environments where

chloride is present; however, it is still not suitable in swimming pools using chloride as a cleaning agent,

or many marine environments.
4.2.6 Grade A5

Stainless steels of grade A5 are stabilized stainless steels with properties of grade A4, but with increased

resistance to temperature (typically up to 350 °C). Stainless steels of grade A5 have properties similar

to grade A4 and are resistant to many acids. They are stabilized by addition of titanium or niobium that

combines with carbon and nitrogen. This grade may be used in some environments where chloride is

present; however, it is still not suitable in swimming pools using chloride as a cleaning agent, or many

marine environments.
4.2.7 Grade A8

Stainless steels of grade A8 are known as “6 % Mo” stainless steels. They have a high level of resistance

to all forms of corrosion including pitting, crevice and stress corrosion cracking. They are suitable for

use in swimming pools using chloride as a cleaning agent. However, there can be specific requirements

and/or regulations for buildings and construction. Grade A8 is also suitable for applications in marine

environments.
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oSIST prEN ISO 3506-6:2022
ISO 3506-6:2020(E)
4.3 Stainless steel group C (martensitic structure)
4.3.1 General

Three grades of martensitic stainless steels (C1, C3 and C4) are included in the ISO 3506 series. They

can be hardened by quenching and tempering. Mechanical properties increase when the carbon

content rises, inducing the necessary rise of chromium content in order to achieve a suitable corrosion

resistance.

Martensitic grades C1, C3 and C4 normally have a lower corrosion resistance than austenitic grades.

However, other martensitic steels with improved corrosion resistance (see Table A.2) can also be used

for special fasteners.

Caution should be taken when using martensitic stainless steels at sub-zero temperatures due to their

poor impact strength and ductility.
Martensitic steel grades are always highly magnetic.
4.3.2 Grade C1
Stainless steels of grade C1 have limited resistance to corrosion.
4.3.3 Grade C3

Stainless steels of grade C3 have limited resistance to corrosion, though better resistance than C1.

4.3.4 Grade C4

Stainless steels of grade C4 are similar to grade C1 but with a lower resistance to corrosion due to their

sulfur content. They are primarily intended for machining.
4.4 Stainless steel group F (ferritic structure) — Grade F1

One single ferritic stainless steel grade F1 is included in the ISO 3506 series. The steels within F1 can

be hardened by work hardening (cold working); however, the cold working effect has a lower efficiency

than for austenitic stainless steels. F1 steels are always magnetic.

When lower corrosion resistance than provided by grades A2 or A3 is suitable for the planned

application, stainless steel grade F1 can be a good economical compromise. However, grade F1 should

not be used at temperatures lower than −20 °C because ferritic stainless steels have poor impact

strength and ductility.
4.5 Stainless steel group D (austenitic-ferritic structure)
4.5.1 General

Duplex stainless steel is a mixture of ferrite and austenite grains with a ferrite content typically 40 %

to 60 % by volume.

In the solution annealed condition, the strength of duplex stainless steels is significantly higher than

the strength of austenitic stainless steels and can be further increased by cold working, but ductility

could then be lower.

Four grades of duplex stainless steels (D2, D4, D6 and D8) are included in the ISO 3506 series: the higher

the digit in the grade, the better the corrosion resistance. Families of duplex stainless steel are usually

described as follows:

— “lean-duplex” (D2 and D4) with lower alloying content (specifically nickel and molybdenum);

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oSIST prEN ISO 3506-6:2022
ISO 3506-6:2020(E)
— “standard-duplex” (D6);
— “super-duplex” (D8) with higher alloying content.

Duplex stainless steels have much improved resistance to stress corrosion cracking when compared to

austenitic stainless steels A1 to A5.

It is not recommended to use duplex stainless steels for application outside the temperature range of

−40 °C to +280 °C.
4.5.2 Grades D2 and D4

D2 and D4 are “lean-duplex” characterized by their molybdenum content below 2 %, and even below 1 %.

With respect to pitting and crevice corrosion, D2 has at least an equivalent corrosion resistance

compared to A2, and D4 has at least an equivalent corrosion resistance compared to A4.

4.5.3 Grades D6 and D8

D6 is a “standard-duplex” with molybdenum content above 2,5 %, which has improved corrosion

resistance when compared to A1 to A5 and D4, particularly with respect to pitting and crevice

corrosion.
D8 is a “super-duplex” and has a corrosion resistance comparable to A8.
4.6 Stainless steels and nickel alloys for elevated and high temperatures

Elevated temperatures refer to the temperature range of 300 °C to 550°C, and high temperatures refer

to temperatures above 550 °C:

— for high temperature applications, fasteners require a sufficient resistance to oxidation and high

temperature corrosion, as well as long-term creep resistance at the service temperature;

— for elevated temperature applications, time-dependent properties are generally not considered to

be critical.

Stainless steels and nickel alloys for elevated and high temperature applications are dealt with in

ISO 3506-5.
5 Chemical composition specifications for stainless steels and nickel alloys

Chemical composition for stainless steel fasteners is specified in ISO 3506-1 for bolts, screws and studs,

ISO 3506-2 for nuts, ISO 3506-3 for set screws, ISO 3506-4 for tapping screws and ISO 3506-5 for special

fasteners for high temperature applications. Tables 1 to 3 give the most widely used standardized

materials, included in ISO 15510, EN 10269 and/or DIN 267-13.
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oSIST prEN ISO 3506-6:2022
ISO 3506-6:2020(E)

Table 1 — Chemical composition of austenitic stainless steels (ISO 3506-1 to ISO 3506-4)

Chemical composition Corres-
ponding
Cast analysis, mass fraction in %
ISO number fastener
(maximum values unless stated otherwise)
grade/
symbol
C Si Mn P S Cr Mo Ni Cu N Nb Ti
Austenitic stainless steels
17,0 to 8,0 to
4305-303-00-I 0,12 1,00 2,00 0,060 ≥0,15 — 1,00 0,10 — — A1
19,0 10,0
17,5 to 8,0 to
4301-304-00-I 0,07 1,00 2,00 0,045 0,030 — — 0,10 — — A2
19,5 10,5
17,5 to 8,0 to
4307-304-03-I 0,030 1,00 2,00 0,045 0,030 — — 0,10 — — A2/A2L
19,5 10,5
17,5 to 8,0 to 0,12 to
4311-304-53-I 0,030 1,00 2,00 0,045 0,030 — — — — A2/A2L
19,5 11,0 0,22
17,0 to 8,0 to 1,00 to
4567-304-98-X 0,08 1,70 2,00 0,045 0,030 — — — — A2
19,0 10,5 3,00
17,0 to 8,0 to 3,00 to
4567-304-30-I 0,040 1,00 2,00 0,045 0,030 — 0,10 — — A2
19,0 10,5 4,0
17,0 to 9,0 to 5 × C to
4541-321-00-I 0,08 1,00 2,00 0,045 0,030 — — — — A3
19,0 12,0 0,70
17,0 to 9,0 to 10 × C
4550-347-00-I 0,08 1,00 2,00 0,045 0,030 — — — — A3
19,0 12,0 to 1,00
16,0 to 2,00 to 10,0 to
4401-316-00-I 0,08 1,00 2,00 0,045 0,030 — 0,10 — — A4
18,0 3,00 13,0
16,5 to 2,00 to 10,0 to
4404-316-03-I 0,030 1,00 2,00 0,045 0,030 — 0,10 — — A4/A4L
18,5 3,00 13,0
16,5 to 2,00 to 10,0 to 0,12 to
4406-316-53-I 0,030 1,00 2,00 0,045 0,030 — — — A4/A4L
18,5 3,00 12,5 0,22
16,5 to 2,00 to 10,0 to 3,00 to
4578-316-76-E 0,040 1,00 2,00 0,045 0,015 0,10 — — A4
17,5 2,50 11,0 3,5
16,5 to 2,00 to 10,5 to 5 × C to
4571-316-35-I 0,08 1,00 2,00 0,045 0,030 — — — A5
18,5 2,50 13,5 0,70
19,0 to 6,0 to 24,0 to 0,50 to 0,15 to
4529-089-26-I 0,020 0,75 2,00 0,035 0,015 — — A8
21,0 7,0 26,0 1,50 0,25
19,5 to 6,0 to 17,5 to 0,50 to 0,18 to
4547-312-54-I 0,020 0,70 1,00 0,035 0,015 — — A8
20,5 7,0 18,5 1,00 0,25
20,0 to 6,0 to 23,5 to 0,18 to
4478-083-67-U 0,030 1,00 2,00 0,040 0,030 0,75 — — A8
22,0 7,0 25,5 0,25

Elements not quoted shall not be intentionally added to the stainless steel without the agreement of the purchaser, other than for

the purpose of finishing the heat. All reasonable precautions shall be taken to prevent the addition, from scrap or other material used in

manufacture, of such elements which affect the hardenability, mechanical properties and applicability.

The stainless steel grades are those which are nearest to the composition ranges specified in ISO 3506-1 and ISO 3506-2; however,

inclusion in this table does not necessarily imply full conformance.
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oSIST prEN ISO 3506-6:2022
ISO 3506-6:2020(E)

Table 2 — Chemical composition of martensitic, ferritic and duplex stainless steels (ISO 3506-1

to ISO 3506-4)
Chemical composition Corres-
ponding
Cast analysis, mass fraction in %
ISO number fastener
(maximum values unless stated otherwise)
grade/
C Si Mn P S Cr Mo Ni Cu N Nb Ti symbol
Martensitic stainless steels
0,08 to 11,5 to
4006-410-00-I 1,00 1,50 0,040 0,030 — 0,75 — — — — C1
0,15 13,5
0,16 to 12,0 to
4021-420-00-I 1,00 1,50 0,040 0,030 — — — — — — C1
0,25 14,0
0,26 to 12,0 to
...

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