ISO 4991:2024

Steel castings for pressure purposes

This document covers steel castings for pressure containing parts. It includes materials which are used for the manufacture of components subject to pressure vessel codes and components not subject to codes. This document relates to castings manufactured from unalloyed and alloyed steel grades (characterized by their chemical composition given in Table 1, and mechanical properties in Tables 2, 3, 4 and 5). NOTE Annex D gives information on ISO grade designation and available UNS numbers which are similar to the ISO grade designation.

Pièces moulées en acier pour service sous pression

General Information

• Status: Published
• Publication Date: 21-Nov-2024
• ICS: 77.140.30 - Steels for pressure purposes
• ICS: 77.140.80 - Iron and steel castings
• Technical Committee: ISO/TC 17/SC 11 - Steel castings
• Drafting Committee: ISO/TC 17/SC 11 - Steel castings
• Current Stage: 6060 - International Standard published
• Start Date: 22-Nov-2024
• Due Date: 12-Jan-2025
• Completion Date: 22-Nov-2024

Relations

• Revises: ISO 4991:2015 - Steel castings for pressure purposes
• Effective Date: 06-Jun-2022

Overview

ISO 4991:2024 - Steel castings for pressure purposes is the fourth edition international standard that specifies requirements for steel castings used in pressure-containing parts. It applies to unalloyed and alloyed cast steels characterized by the chemical composition (Table 1) and mechanical properties (Tables 2–5). The standard covers castings manufactured for components that are both subject to pressure‑vessel codes and components not subject to codes. Annex D links ISO grade designations to similar UNS numbers.

Keywords: ISO 4991:2024, steel castings, pressure purposes, pressure vessel, chemical composition, mechanical properties.

Key technical topics and requirements

• Scope and materials: Defines grades of cast steel for pressure service (composition limits in Table 1) and associated mechanical property requirements (Tables 2–5).
• Heat treatment: Specifies required heat‑treatment types and symbols (for example +N normalized, +QT quenched and tempered, +AT solution treated) and refers to Table 6 for guidance.
• Welding: Welding is permitted with requirements for procedure and welder qualification; welding procedures follow ISO 11970 and welders shall be qualified per ISO 9606‑1. Annex B provides welding conditions.
• Inspection and testing:
  • Manufacturing sampling and test‑block procedures (test blocks heat treated with the casting).
  • Mechanical testing: tensile tests per ISO 6892‑1 (room temperature) and ISO 6892‑2 (elevated temperature) when required; impact testing per ISO 148‑1 where specified.
  • Non‑destructive testing (NDT): purchaser specifies NDT method, area and acceptance criteria (as per ISO 4990).
  • Marking and traceability: heat numbers/serials and manufacturer identification required.
• Supplementary requirements: Additional inspections/tests available when individually specified by purchaser (see Annex A). Ferrite content determination for austenitic/duplex grades via ISO 13520.
• Special additions: This edition adds a higher‑temperature cast steel grade (550 °C–700 °C range) and two duplex grades suitable up to 250 °C; welder qualification requirements were expanded.

Practical applications and users

ISO 4991:2024 is used to specify and procure steel castings for pressure components such as pressure‑vessel parts, valves, pump casings, flanges and other pressure‑containing cast components. Typical users include:

• Foundries and casting manufacturers
• Pressure‑vessel designers and fabricators
• Procurement and quality engineers specifying material and inspection requirements
• Welding supervisors and qualified welders
• Third‑party inspectors and certification bodies

Related standards and annexes

• Normative references: ISO 4990, ISO 6892‑1/2, ISO 148‑1, ISO 11970, ISO 9606‑1, ISO 13520.
• Informative annexes: Annex B (welding conditions), Annex C (creep properties), Annex D (UNS numbers similar to ISO grades).

ISO 4991:2024 provides a comprehensive framework for specifying, producing and inspecting steel castings intended for pressure service, ensuring material traceability, mechanical performance and appropriate testing for safe pressure‑containing components.

Standards Content (Sample)

International
Standard
ISO 4991
Fourth edition
Steel castings for pressure purposes
2024-11
Pièces moulées en acier pour service sous pression
Reference number
© ISO 2024
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: [phone]
Email: [e-mail]
Website: www.iso.org
Published in Switzerland
ii
Contents Page
Foreword .iv
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Information to be supplied by the purchaser . 1
5 Heat treatment . 2
6 Welding . 2
7 Requirements . 2
7.1 Chemical composition .2
7.2 Mechanical properties .2
8 Inspection and testing . 3
8.1 General .3
8.2 Sampling .3
8.3 Formation of test lots . .3
8.4 Non-destructive testing .3
8.5 Marking .3
9 Supplementary requirements . 3
Annex A (normative) Supplementary requirements .11
Annex B (informative) Welding conditions .13
Annex C (informative) Creep properties .15
Annex D (informative) UNS cast grades similar to ISO cast grades .18
Bibliography .20

iii
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
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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 document 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).
ISO draws attention to the possibility that the implementation of this document may involve the use of (a)
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rights in respect thereof. As of the date of publication of this document, ISO had not received notice of (a)
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Any trade name used in this document is information given for the convenience of users and does not
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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 17, Steel, Subcommittee SC 11, Steel castings.
This fourth edition cancels and replaces the third edition (ISO 4991:2015), which has been technically
revised.
The main changes are as follows:
— grade names and numbers have been corrected;
— a cast steel grade for higher temperature applications (550 °C to 700 °C) has been added;
— two austenitic-ferritic stainless steel (duplex) grades have been added for pressure parts up to 250 °C;
— the application temperature range of some special steels has been extended;
— qualification requirements for welders have been added.
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
International Standard ISO 4991:2024(en)
Steel castings for pressure purposes
1 Scope
This document covers steel castings for pressure containing parts.
It includes materials which are used for the manufacture of components subject to pressure vessel codes
and components not subject to codes.
This document relates to castings manufactured from unalloyed and alloyed steel grades (characterized by
their chemical composition given in Table 1, and mechanical properties in Tables 2, 3, 4 and 5).
NOTE Annex D gives information on ISO grade designation and available UNS numbers which are similar to the
ISO grade designation.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content are
requirements for 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 148-1, Metallic materials — Charpy pendulum impact test — Part 1: Test method
ISO 4885, Ferrous materials — Heat treatments — Vocabulary
ISO/TS 4949, Steel names based on letter symbols
ISO 4990, Steel castings — General technical delivery requirements
ISO 6892-1, Metallic materials — Tensile testing — Part 1: Method of test at room temperature
ISO 6892-2, Metallic materials — Tensile testing — Part 2: Method of test at elevated temperature
ISO 9606-1, Qualification testing of welders — Fusion welding — Part 1: Steels
ISO 11970, Specification and qualification of welding procedures for production welding of steel castings
ISO 13520, Determination of ferrite content in austenitic stainless steel castings
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 4885, ISO/TS 4949 and ISO 4990 apply.
ISO and IEC maintain terminological databases for use in the standardization at the following addresses:
— ISO Online browsing platform: available at https:// www .iso .ort/ obp.
— IEC Electropedia: available at https:// www .electropedia .org/
4 Information to be supplied by the purchaser
Materials specified in this document shall conform to the applicable requirements of ISO 4990, including the
supplementary requirements listed in Annex A that are specified in the enquiry and purchase order.

5 Heat treatment
The type of heat treatment shall conform with Table 6 for the specified grades. The temperatures given are
for information only.
When a grade may be delivered at different strength levels depending on the type of heat treatment (see
Table 2), the purchaser shall state at the time of enquiry and order the type of heat treatment required.
The symbols for the type of heat treatment are as follows:
— +N normalized
— +QT quenched and tempered
— +AT solution treated
NOTE For definitions, see ISO 4885.
6 Welding
Welding is permitted, unless otherwise agreed. All the welds shall conform to the same criteria for non-
destructive testing as the relevant part of the casting. Welding shall be carried out in accordance with
ISO 11970, and the welding personnel for permanent joining of components shall be qualified according to
ISO 9606-1.
The welding conditions are given in Annex B.
7 Requirements
7.1 Chemical composition
An analysis of each heat shall be made by the manufacturer to determine the contents of the specified
elements.
The chemical composition shall comply with the values given in Table 1.
Permissible deviations for the product analysis are specified in ISO 4990.
7.2 Mechanical properties
The mechanical properties shall comply with the values given in Tables 2, 3, 4 and 5.
Mechanical properties shall be measured on test pieces taken from test blocks (according to ISO 4990).
The tensile tests at room temperature shall be carried out in accordance with ISO 6892-1 and, if specified,
impact tests in accordance with ISO 148-1.
If required by agreement at the time of enquiry and order, impact energy properties at low temperature
shall conform with Table 3.
If required by agreement at the time of enquiry and order, impact energy values at room temperature shall
conform with Table 4.
If required by agreement at the time of enquiry and order, verification of the elevated temperature proof
stress values shall be carried out at elevated temperatures in accordance with ISO 6892-2. In such a case, the
values shall conform with Table 5.
Creep resistance mean values are given for information, for some grades in Annex C.

8 Inspection and testing
8.1 General
For all products ordered to the requirements of this document, specific inspection and testing is required.
8.2 Sampling
Test blocks shall be heat treated in production furnaces to the same procedure as the castings they represent.
Test pieces shall not be cut from the test block until the latter has been heat treated.
8.3 Formation of test lots
The formation of test lots shall be carried out in accordance with ISO 4990.
8.4 Non-destructive testing
The following information shall be given at the time of enquiry and order in accordance with ISO 4990:
— non-destructive testing required,
— area to be tested,
— acceptance criteria.
8.5 Marking
Castings shall be marked for material identification.
a) Heat numbers or serial numbers that are traceable to heat numbers, shall be marked on all castings.
b) For small castings, it may be agreed at the time of the enquiry and order that they may be batched and
that their identification is marked on a label attached to each batch.
c) Castings shall be marked with the manufacturer's identification or symbol except where other
provisions have been made between the manufacturer and purchaser.
d) When more than one heat treatment type is available, the heat treatment applied shall be marked with a
suffix added to the grade designation (see Table 2).
9 Supplementary requirements
This document also specifies supplementary requirements, which may be applied to steel castings. These
requirements are provided for use when additional testing or inspection is desired and apply only when
individually specified by the purchaser.
A list of supplementary requirements which may be used at the option of the purchaser is given in ISO 4990
and in Annex A.
If ferrite determination is required for austenitic and austenitic-ferritic grades, it may be made using
ISO 13520.
Table 1 — Chemical composition, in percent, mass fraction
Grade designation C Si Mn P S Cr Mo Ni V Cu Other
Name Number max. max. max.
a a b
GP240GH 1.0619 0,18–0,23 0,60 0,50–1,20 0,030 0,020 0,30 max. 0,12 max. 0,40 max. 0,03 max. 0,30 max.
a a b
GP280GH 1.0625 0,18–0,25 0,60 0,80–1,20 0,030 0,020 0,30 max. 0,12 max. 0,40 max. 0,03 max. 0,30 max.
b
G17Mn5 1.1131 0,15–0,20 0,60 1,00–1,60 0,020 0,025 0,30 max. 0,12 max. 0,40 max. 0,03 max. 0,30 max.
G20Mn5 1.6220 0,17–0,23 0,60 1,00–1,60 0,020 0,020 0,30 max. 0,12 max. 0,80 max. 0,03 max. 0,30 max.
G18Mo5 1.5422 0,15–0,20 0,60 0,80–1,20 0,020 0,020 0,30 max. 0,45–0,65 0,40 max. 0,050 max. 0,30 max.
G20Mo5 1.5419 0,15–0,23 0,60 0,50–1,00 0,025 0,020 0,30 max. 0,40–0,60 0,40 max. 0,050 max. 0,30 max.
G17CrMo5–5 1.7357 0,15–0,20 0,60 0,50–1,00 0,020 0,020 1,00–1,50 0,45–0,65 0,40 max. 0,050 max. 0,30 max.
G17CrMo9–10 1.7379 0,13–0,20 0,60 0,50–0,90 0,020 0,020 2,00–2,50 0,90–1,20 0,40 max. 0,050 max. 0,30 max.
G12MoCrV5–2 1.7720 0,10–0,15 0,45 0,40–0,70 0,030 0,020 0,30–0,50 0,40–0,60 0,40 max. 0,22–0,30 0,30 max.
G17CrMoV5–10 1.7706 0,15–0,20 0,60 0,50–0,90 0,020 0,015 1,20–1,50 0,90–1,10 0,40 max. 0,20–0,30 0,30 max.
G25NiCrMo3 1.6553 0,23–0,28 0,80 0,60–1,00 0,030 0,025 0,40–0,80 0,15–0,30 0,40–0,80 0,03 max. 0,30 max.
G25NiCrMo6 1.6554 0,23–0,28 0,60 0,60–0,90 0,030 0,025 0,70–0,90 0,20–0,30 1,00–2,00 0,03 max. 0,30 max.
G17NiCrMo13–6 1.6781 0,15–0,19 0,50 0,55–0,80 0,015 0,015 1,30–1,80 0,45–0,60 3,00–3,50 0,05 max. 0,30 max.
G9Ni10 1.5636 0,06–0,12 0,60 0,50–0,80 0,020 0,015 0,30 max. 0,20 max. 2,00–3,00 0,05 max. 0,30 max.
G9Ni14 1.5638 0,06–0,12 0,60 0,50–0,80 0,020 0,015 0,30 max. 0,20 max. 3,00–4,00 0,05 max. 0,30 max.
GX15CrMo5 1.7365 0,12–0,19 0,80 0,50–0,80 0,025 0,025 4,00–6,00 0,45–0,65 - 0,05 0,30 max.
GX10CrMoV9–1 1.7367 0,08–0,12 0,20–0,50 0,30–0,60 0,030 0,010 8,00–9,50 0,85–1,05 0,40 max 0,18–0,25 - Nb 0,06–0,10
N 0,03–0,07
Al 0,02 max.
Ti 0,01 max.
Zr 0,01 max.
GX15CrMo9–1 1.7376 0,12–0,19 1,00 0,35–0,65 0,030 0,030 8,00–10,00 0,90–1,20 0,40 max. 0,05 0,30 max.
GX8CrNi12–1 1.4107 0,10 max. 0,40 0,50–0,80 0,030 0,020 11,50–12,50 0,50 max. 0,80–1,50 0,08 max. 0,30 max.
GX23CrMoV12–1 1.4931 0,20–0,26 0,40 0,50–0,80 0,030 0,020 11,30–12,20 1,00–1,20 1,00 max. 0,25–0,35 0,30 max. W 0,50 max.
GX3CrNi13–4 1.6982 0,05 max. 1,00 1,00 max. 0,035 0,015 12,00–13,50 0,70 max. 3,50–5,00 0,08 max. 0,30 max.
GX4CrNi13–4 1.4317 0,06 max. 1,00 1,00 max. 0,035 0,025 12,00–13,50 0,70 max. 3,50–5,00 0,08 max. 0,30 max.
GX4CrNiMo16–5-1 1.4405 0,06 max. 0,80 1,00 max. 0,035 0,025 15,00–17,00 0,70–1,50 4,00–6,00 0,08 max. 0,30 max.
GX2CrNiN19–11 1.4487 0,03 max. 1,50 2,00 max. 0,035 0,030 18,00–20,00 - 9,00–12,00 - 0,50 max. 0,12 ≤ N ≤ 0,20
GX2CrNi19-11 1.4309 0,03 max 1,50 2,00 max. 0,035 0,025 18,00-20,00 - 9,00-12,00 - 0,50 max. N 0,20 max.
GX5CrNi19–10 1.4308 0,07 max. 1,50 1,50 max. 0,040 0,030 18,00–20,00 - 8,00–11,00 - 0,50 max.
GX5CrNiNb19–11 1.4552 0,07 max. 1,50 1,50 max. 0,040 0,030 18,00–20,00 - 9,00–12,00 - 0,50 max. 8xC ≤ Nb ≤ 1,00
GX2CrNiMoN19–11–2 1.4409 0,030 max. 1,50 2,00 max. 0,035 0,030 18,00–20,00 2,00–2,50 9,00–12,00 - 0,50 max. 0,12 ≤ N ≤ 0,20
GX5CrNiMo19–11–2 1.4408 0,07 max. 1,50 1,50 max. 0,040 0,030 18,00–20,00 2,00–2,50 9,00–12,00 - 0,50 max.
GX5CrNiMoNb19–11–2 1.4581 0,07 max. 1,50 1,50 max. 0,040 0,030 18,00–20,00 2,00–2,50 9,00–12,00 - 0,50 max. 8xC ≤ Nb ≤ 1,00

Table 1 (continued)
Grade designation C Si Mn P S Cr Mo Ni V Cu Other
Name Number max. max. max.
GX2CrNiMoN22–5-3 1.4470 0,030 max. 1,00 2,00 max. 0,035 0,025 21,00–23,00 2,50–3,50 4,50–6,50 - 0,50 max. 0,12 ≤ N ≤ 0,20
GX2CrNiMoCuN26–5-3–3 1.4451 0,030 max. 1,00 1,50 max. 0,035 0,025 25,00–27,00 2,50–3,50 5,00–7,00 - 2,75–3,50 0,12 ≤ N ≤ 0,22
GX2CrNiMoN26–7-4 1.4469 0,030 max. 1,00 1,00 max. 0,035 0,025 25,00–27,00 3,00–5,00 6,00–8,00 - 1,30 max. 0,12 ≤ N ≤ 0,22
GX2NiCrMo28–20–2 1.4458 0,030 max. 1,00 2,00 max. 0,035 0,025 19,00–22,00 2,00–2,50 26,00–30,00 - 2,00 max. N ≤ 0,20
GX10NiCrSiNb32-20 1.4859 0,05 to 0,15 0,50-1,50 2,00 max. 0,040 0,030 19,00-21,00 0,50 max. 31,00-33,00 - 0,50 max. 0,50 ≤ Nb ≤ 1,50
c
GX2CrNiMoCuN25-6-3-3 1.4517 1,00 1,00 1,50 max. 0,035 0,025 24,00-26,50 2,50-3,50 5,00-7,00 - 2,75-3,50 0,12 ≤ N ≤ 0,22
c
GX2CrNiMoN25-7-3 1.4417 1,00 1,50 1,50 max. 0,030 0,020 24,00-26,00 3,00-4,00 6,00-8,50 - 1,00 max. 0,12 ≤ N ≤ 0,25,
W 1,0 max.
a
For each reduction of 0,01 % carbon below the maximum specified, an increase of 0,04 % manganese above the maximum specified will be permitted to a maximum of 1,40 %.
b
%Cr + %Mo + %Ni + %V + %Cu ≤ 1,00 %.
c
For this steel grade a minimum value of the “pitting index” may be required as Pi = Cr +
...