CEN/TR 10347:2006

Guidance for forming of structural steels in processing

This CEN Technical Report provides guidance for forming during processing of structural steel products conforming to EN 10025 Parts 2 to 6 and EN 10149 Parts 2 and 3. This Technical Report covers hot and cold forming processes and local hot forming used in flame-straightening operations.
This Technical Report does not cover the special measures necessary for the fabrication of structural components that are subjected predominantly to alternating stresses or that come into contact with aggressive media.

Hinweise für das Umformen von Baustählen bei der Verarbeitung

Guide pour le formage des aciers de construction lors de leur mise en oeuvre

Vodilo za oblikovanje konstrukcijskih jekel med predelavo

General Information

• Status: Published
• Publication Date: 11-Apr-2006
• ICS: 77.140.10 - Heat-treatable steels
• Technical Committee: ECISS/TC 103 - Structural steels other than reinforcements
• Drafting Committee: ECISS/TC 103 - Structural steels other than reinforcements
• Current Stage: 6060 - Definitive text made available (DAV) - Publishing
• Start Date: 12-Apr-2006
• Due Date: 25-Jul-2006
• Completion Date: 12-Apr-2006
• Ref Project: SIST-TP CEN/TR 10347:2006 - Guidance for forming of structural steels in processing

Overview

CEN/TR 10347:2006 - "Guidance for forming of structural steels in processing" is a CEN Technical Report that gives practical guidance for forming operations on structural steel products manufactured to EN 10025 (Parts 2–6) and EN 10149 (Parts 2–3). It covers hot forming, cold forming, and local hot forming used in flame-straightening, and explains effects of forming on mechanical properties, heat treatment needs, and process verification. The report does not address special fabrication measures for components mainly subjected to alternating stresses or exposed to aggressive media.

Key topics and requirements

• Scope and definitions: Clear definitions of hot forming, cold forming and flame-straightening and the temperatures typically associated with each process.
• Hot forming guidance:
  • Recommended temperature window for hot forming (generally above ~900 °C but below ~1050 °C, preferably ≤1020 °C).
  • Advice on heating rates, holding times, cooling (air cooling recommended), and when post-forming heat treatment (normalizing) is required or may be omitted.
  • Need for temperature monitoring and process verification, especially when heat treatment is not repeated after forming.
• Cold forming guidance:
  • Suitability of EN 10025 and EN 10149 steels for cold forming and cautions about forming in the 200–380 °C range.
  • Effects of strain hardening: increased yield strength, reduced ductility/toughness, and potential welding limitations.
  • When stress-relief or renormalizing may be necessary after extensive cold forming.
• Flame-straightening guidance:
  • Describes flame-straightening patterns (hot points, lines, wedges) and limits on flame-straightening temperatures (generally keep ≤ ~700 °C to avoid austenitization and property degradation).
  • Emphasis on rapid, local heating and restraint techniques to control shape change and material effects.

Practical applications and users

This Technical Report is practical for:

• Structural steel fabricators and welders performing bending, pressing, bending radii, inductive bending or flame-straightening.
• Steel manufacturers advising on process compatibility and delivery conditions.
• Structural engineers, quality managers and inspectors planning fabrication sequences, heat treatment, or process verification.
• Procurement teams specifying steel grades and order options for enhanced formability.

Practical takeaways:

• Select steel grades and order options tailored for forming (EN 10025 provides special grades/options).
• Perform pre-production trials or manufacturer consultation for unfamiliar forming operations.
• Monitor and control temperatures; plan post-forming heat treatments when required.

Related standards

• EN 10025 (Parts 2–6) - structural steel product delivery conditions and grades
• EN 10149 (Parts 2–3) - high-strength steels for cold forming
• EN 1011-2 - welding guidance (related revision history)
• EN 1993-1-10 - links cold forming degree to toughness requirements

Keywords: CEN/TR 10347:2006, guidance for forming, structural steels, hot forming, cold forming, flame-straightening, EN 10025, EN 10149, heat treatment, steel fabrication.

Standards Content (Sample)

SLOVENSKI STANDARD
01-september-2006
Vodilo za oblikovanje konstrukcijskih jekel med predelavo
Guidance for forming of structural steels in processing
Hinweise für das Umformen von Baustählen bei der Verarbeitung
Guide pour le formage des aciers de construction lors de leur mise en oeuvre
Ta slovenski standard je istoveten z: CEN/TR 10347:2006
ICS:
77.140.10
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

TECHNICAL REPORT
CEN/TR 10347
RAPPORT TECHNIQUE
TECHNISCHER BERICHT
April 2006
ICS 77.140.10
English Version
Guidance for forming of structural steels in processing
Guide pour le formage des aciers de construction lors de Hinweise für das Umformen von Baustählen bei der
leur mise en oeuvre Verarbeitung
This Technical Report was approved by CEN on 13 March 2006. It has been drawn up by the Technical Committee ECISS/TC 10.
CEN members are the national standards bodies of Austria, Belgium, Cyprus, Czech Republic, Denmark, Estonia, Finland, France,
Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Romania,
Slovakia, Slovenia, Spain, Sweden, Switzerland and United Kingdom.
EUROPEAN COMMITTEE FOR STANDARDIZATION
COMITÉ EUROPÉEN DE NORMALISATION
EUROPÄISCHES KOMITEE FÜR NORMUNG
Management Centre: rue de Stassart, 36  B-1050 Brussels
© 2006 CEN All rights of exploitation in any form and by any means reserved Ref. No. CEN/TR 10347:2006: E
worldwide for CEN national Members.

Contents Page
Foreword .3
1 Scope .4
2 Terms and definitions.4
3 General principles.4
4 Hot forming.5
5 Cold forming.7
6 Flame-straightening.8
Bibliography.11

Foreword
This Technical Report (CEN/TR 10347:2006) has been prepared by Technical Committee ECISS/TC 10
"Structural steels – Grades and qualities", the secretariat of which is held by NEN.
In the ECISS/TC 10 meeting of 8 and 9 December 1998 it was decided with Resolution
ECISS/TC 10 no 2/1998 to publish ECSC IC 2 as a CEN report. The part on welding in ECSC IC 2 has been
revised by CEN/TC 121 and has resulted in EN 1011-2. The part on formability has been revised in this CEN
Technical Report.
1 Scope
This CEN Technical Report provides guidance for forming during processing of structural steel products
conforming to EN 10025 Parts 2 to 6 and EN 10149 Parts 2 and 3. This Technical Report covers hot and cold
forming processes and local hot forming used in flame-straightening operations.
This Technical Report does not cover the special measures necessary for the fabrication of structural
components that are subjected predominantly to alternating stresses or that come into contact with aggressive
media.
2 Terms and definitions
For the purposes of this Technical Report, the following terms and definitions apply.
2.1
hot forming
forming at temperatures in the austenite range, generally around 900 °C depending on the chemical
composition of the steel grade
2.2
cold forming
forming up to the highest temperature permissible for stress relieving, generally in the range of 530 °C to
580 °C
NOTE See the relevant part of EN 10025 (e.g. 7.3.1.1 of EN 10025-1:2004 and 7.4.1.1 of EN 10149-1:1995).
2.3
flame-straightening
local quick heating of a component with a short holding time (generally less than one minute) at the flame-
straightening temperature
2.4
flame-straightening temperature
highest temperature arising in the component during flame-straightening
3 General principles
With rising minimum yield strength values for structural steels and with an increasing wall thickness of
structural steel products, extra care needs to be taken during subsequent processing of steel products.
Furthermore, the technical delivery conditions of steel products complying with EN 10025 and EN 10149 will
depend on the actual process route used by the steel product manufacturer.
In general, suitable steel grades for the special forming situation should be selected. EN 10025 also defines
special steel grades for cold forming and additional options for ensuring forming properties which should be
preferably used. In cases which are not covered by these order options the steel manufacturer should be
consulted. All steel grades of EN 10149 are suitable for cold forming.
In individual cases outside of the specific guidance given here, especially when using structural steels for the
first time, forming should be based on prior experience. This may be based on pre-production procedure trials
undertaken by the fabricator or on documented trials undertaken by the steel product manufacturer.
If a manufacturer wants to ensure that the hot forming, cold forming or flame-straightening process intended to
be applied will not detrimentally influence the mechanical properties of the structure, a process verification
should be performed.
NOTE Temperatures referred to in this Technical Report are measured at the steel product surface and not
somewhere in the furnace. Allowance should be made for the fact that the temperatures in the product may not be uniform.
4 Hot forming
4.1 General
4.1.1 The following products can generally be subjected to hot forming:
� non alloy structural steels supplied as-rolled for normalizing by the purchaser (see 7.3.1.3 of
EN 10025-2:2004) or supplied in the normalized delivery condition conforming to EN 10025-2;
� normalized fine-grain structural steels conforming to EN 10025-3 and EN 10149-3;
� structural steels with improved atmospheric corrosion resistance supplied as-rolled for normalizing by the
purchaser (see 7.3.1.3 of EN 10025-5:2004) or supplied in the normalized delivery condition conforming
to EN 10025-5.
It is not envisaged that thermomechanical rolled steel grades conforming to EN 10025-2, EN 10025-4 and
EN 10149-2 or quenched and tempered steels conforming to EN 10025-6 should require further processing by
hot forming. The strength properties of thermomechanical rolled steel grades, the material condition of which
is not achievable or reproducible by a heat treatment alone, are impaired by hot forming during further
processing.
For quenched and tempered steels the necessary heat treatment after hot forming is very difficult to reproduce.
4.1.2 Where special hot forming operations are performed, e.g. hole flanging or inductive bending, the steel
product manufacturer should be consulted. Process verification for induction bending should ensure that both
the steel and the process are matched.
4.1.3 Where only local heating to hot forming temperature is involved, other than flame-straightening,
attention should be paid to the fact that, apart from the region heated in regular fashion to normalizing
temperature, areas appear with temperatures between the lower limiting temperature for normalizing and the
upper limiting temperature for stress relieving. In these areas, the material properties can be impaired,
depending on the heating technique, temperature, and duration involved.
The area heated into the two phase regime ferrite-austenite is experienced to be particularly critical for both
strength and toughness.
4.2 Temperature during hot forming
To carry out hot forming, the work piece should be heated above 900 °C, but not above 1050 °C, preferably
not above 1020 °C. After reaching the planned temperature for the work piece, holding at that temperature to
ensure a uniform temperature in the work piece is only necessary if stipulated in the relevant steel product
standard.
NOTE 1 The temperature of 900 °C relates to the lower temperatures for normalizing.
NOTE 2 For quenched and tempered steels see 4.1.1.
Heating rates should be as fast as possible and holding times should be as short as possible. For this reason,
work pieces should not be heated in a pile.
During hot forming, the temperature should not drop below the lower limit of admissible temperatures as given
in Table 1. In particular, when the product thickness is small (less than 15 mm) the heat flow from the work
piece to the forming devices should be taken into account during hot forming.
After hot forming, the work piece should generally be cooled in air, in order to ensure a minimum of
deformation due to internal stresses. The cooling rate should be kept as similar as possible to the one applied
to the original product.
In general, the cooling rate after hot forming depends on the shape and wall thickness of the component. In
particular, the cooling rate of products with a small thickness is significantly higher when the work piece is
cooled in contact with the forming devices than in contact with air. For this reason, retarded cooling or
tempering may be necessary in special cases for normalized steel grades with minimum yield strength values
equal to or greater than 420 MPa and small wall thickness (less than 15 mm). Details should be obtained from
the steel product manufacturer.
The temperature should be monitored in all hot forming operations in order to ensure that, during the forming
operation, the highest allowable temperature is not exceeded (see 4.3.2). This is of particular importance
where the heat treatment of the work piece is not intended to be repeated after forming.
4.3 Heat treatment after hot forming
4.3.1 Heating to a temperature greater than about 50 K above the transformation temperature Ac , at
which austenitization is completed, in particular if combined with a long holding time, leads to grain growth and
thereby impairs the toughness properties and the yield strength. For this reason, after hot forming the finished
component should be heat treated generally in accordance with the advice of the steel product manufacturer
or the relevant steel product standard.
It is essential that normalized steel grades are renormalized. This is of particular importance where fabrication
processes require the normalizing of the component after hot forming. Under these circumstances, a
normalized steel product could be ordered in the 'as-rolled' delivery condition. The steel product manufacturer
should be consulted for advice.
4.3.2 With normalized steel grades, normalizing after hot forming may be omitted in the following cases:
a) After single-step hot forming, normalizing of the finished component may be omitted if the process has
been undertaken within the limits given in Table 1.
Table 1 — Criteria for omitting renewed heat treatment after single-step hot forming
Test temperature for Steel grade Maximum temperature Lowest temperature at the end of
verification of Charpy before hot forming hot forming with the degree of hot
a
impact energy for
...