Guidelines for specifying Charpy V-notch impact prescriptions in steel specifications

ISO/TS 7705:2017 gives guidelines for specifying Charpy V-notch impact prescriptions in steel specifications.

Lignes directrices pour la spécification des prescriptions d'énergie de rupture sur éprouvette Charpy à entaille en V dans les normes d'acier

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Status
Published
Publication Date
18-Jul-2017
Current Stage
9020 - International Standard under periodical review
Start Date
15-Jul-2020
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ISO/TS 7705:2017 - Guidelines for specifying Charpy V-notch impact prescriptions in steel specifications
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TECHNICAL ISO/TS
SPECIFICATION 7705
First edition
2017-07
Guidelines for specifying Charpy
V-notch impact prescriptions in steel
specifications
Lignes directrices pour la spécification des prescriptions d’énergie de
rupture sur éprouvette Charpy à entaille en V dans les normes d’acier
Reference number
ISO/TS 7705:2017(E)
ISO 2017
---------------------- Page: 1 ----------------------
ISO/TS 7705:2017(E)
COPYRIGHT PROTECTED DOCUMENT
© ISO 2017, Published in Switzerland

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ii © ISO 2017 – All rights reserved
---------------------- Page: 2 ----------------------
ISO/TS 7705:2017(E)
Contents Page

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

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

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

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

4 General features of Charpy V-notch impact test .................................................................................................................. 1

4.1 Toughness testing methods in design codes and in steel specifications ............................................... 1

4.2 Historical background to the Charpy V-notch impact test ................................................................................ 1

4.3 The Charpy V-notch impact test in relation to other tests ................................................................................ 2

4.4 Factors influencing impact properties ............................................................................................................................... 2

4.5 The Charpy V-notch impact test as a powerful tool for delivery control in

steel specifications ............................................................................................................................................................................... 3

5 Information to be gained from the impact test ..................................................................................................................... 3

6 Subsize test pieces .............................................................................................................................................................................................. 6

7 Recommendations for specifying impact strength requirements in steel specifications ........7

7.1 Selection and preparation of samples and test pieces .......................................................................................... 7

7.1.1 Selection and preparation of samples ........................................................................................................... 7

7.1.2 Cutting and machining ................................................................................................................................................ 7

7.2 Number of test pieces to be taken per sample and specific requirements ......................................... 7

7.3 Location of test pieces ...................................................................................................................................................................... 7

7.4 Interpretation of test results ....................................................................................................................................................... 8

Bibliography ................................................................................................................................................................................................................................ 9

© ISO 2017 – All rights reserved iii
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ISO/TS 7705:2017(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 on 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 the following

URL: w w w . i s o .org/ iso/ foreword .html.

This document was prepared by Technical Committee ISO/TC 17, Steel, Subcommittee SC 20, General

technical delivery conditions, sampling and mechanical testing methods.

This first edition of ISO/TS 7705 cancels and replaces ISO/TR 7705:1991, which has been technically

revised.
iv © ISO 2017 – All rights reserved
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TECHNICAL SPECIFICATION ISO/TS 7705:2017(E)
Guidelines for specifying Charpy V-notch impact
prescriptions in steel specifications
1 Scope

This document gives guidelines for specifying Charpy V-notch impact prescriptions in steel

specifications.
2 Normative references
There are no normative references in this document.
3 Terms and definitions
No terms and definitions are listed in this document.

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

— ISO Online browsing platform: available at http:// www .iso .org/ obp
— IEC Electropedia: available at http:// www .electropedia .org/
4 General features of Charpy V-notch impact test
4.1 Toughness testing methods in design codes and in steel specifications

Tests for evaluating the toughness of steel can be divided into two categories: notch toughness tests

and fracture toughness tests based on fracture mechanics.

Notch toughness tests are used to measure the ability of a material to absorb energy and deform

plastically in the presence of a mechanical notch. The Charpy V-notch impact test and the drop weight

test are typical examples of small scale tests which are used for evaluations of notch toughness. They

are often used to determine the ductile to brittle transition temperature of a material and to give a

qualitative estimate of the material’s toughness. Due to relatively good reproducibility and low cost

these methods are highly suitable for use as delivery tests for steel consignments.

Fracture toughness tests such as the crack-tip opening displacement (CTOD) test (see ISO 12135) are

fracture mechanics tests which are generally concerned with the determination of critical crack sizes

which can appear without causing fracture in a material loaded to a specific stress level. Fracture

mechanics tests are very complicated and expensive to carry out. They are primarily used to examine

the behaviour of pressurized or structural components with respect to safety rules, etc. Therefore,

fracture mechanics testing is primarily connected with design codes and not with steel specifications.

For these reasons, only notch toughness tests are dealt with in these guidelines for steel specifications.

4.2 Historical background to the Charpy V-notch impact test

When welded structures, especially heavy ones such as bridges and ships, were first developed on an

industrial scale, and especially when the fabrication methods called for joining heavy segments by

welding, problems with brittle fractures became more common. This was especially evident during the

Second World War when the USA began to produce welded ships of the Liberty and Victory type, where

a large number of failures occurred due to brittle fractures.
© ISO 2017 – All rights reserved 1
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ISO/TS 7705:2017(E)

An empirical relationship based on many tests was found between the Charpy V-notch impact energy

and service fractures. The work initiated by the USA was continued by the International Institute of

Welding (IIW) who provide recommendations and a classification system for steels according to their

susceptibility to brittle fracture after welding.

Originally the USA required an impact energy value of 15 footpounds (ft lb) for a standard

10 mm x 10 mm V-notch impact test piece. This was later increased to 20 ft lb. The IIW converted these

figures into metric units and referred the impact energy value to the cross-section under the notch,

which gave a figure of 3,5 kg m/cm corresponding to 20 ft lb. Later the units were transformed into SI

units. This gave the value of 27 J (20 ft lb).

In 1953 Pellini compared the Charpy V-notch impact test with an explosion crack starter test intended

to simulate the service performance of higher quality steels. Pellini recommended impact energy of

20 ft lb (27 J) instead of the earlier used 15 ft lb.

Wells also simulated service conditions at the starting point of a brittle fracture crack by using a

wide plate test. The intention of this test, which could not be used as an acceptance test for a steel

consignment, was to include in a big plate specimen the stresses existing in a weld, the influence of

plate thickness, the type of defect, etc. The results of wide plate tests were also compared with Charpy

V-notch impact values.

Today 27 J is generally used for unalloyed steels. In some cases, for instance for fine grain steels or

quenched and tempered steel grades, this level can be 27 J or alternatively fixed to a higher level (40 J)

according to the requirements for specific steels and intended applications. Impact test requirements

are included in the product standard.
4.3 The Charpy V-notch impact test in relation to other tests
Originally the Charpy impact test was p
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