ISO 20198:2026

Metallic materials — Steel — Method of test for the determination of brittle crack arrest temperature (CAT)

This document specifies a test method for the determination of the brittle crack arrest temperature (CAT). This document is applicable to either ferritic or bainitic, or both steel base metals with a body-centred cubic (BCC) crystal lattice structure that exhibit ductile to brittle transition behaviour. The applicable materials are rolled steel plates. This document is intended for steels with a tensile strength of 950 MPa or less and a thickness greater than 6 mm but not exceeding 200 mm. The range of arrest temperatures is between − 196 °C and + 100 °C. This document also specifies the requirements for test method and test procedures when using the isothermal crack arrest test to judge valid test results under isothermal conditions and in order to determine the crack arrest temperature.

Matériaux métalliques — Acier — Méthode d'essai pour la détermination de la température d'arrêt de la fissure fragile (CAT)

General Information

• Status: Published
• Publication Date: 12-May-2026
• ICS: 77.040.10 - Mechanical testing of metals
• Technical Committee: ISO/TC 164/SC 4 - Fatigue, fracture and toughness testing
• Drafting Committee: ISO/TC 164/SC 4 - Fatigue, fracture and toughness testing
• Current Stage: 6060 - International Standard published
• Start Date: 13-May-2026
• Due Date: 18-Apr-2026
• Completion Date: 13-May-2026

Overview

ISO 20198:2026 specifies a standardized test method for determining the brittle crack arrest temperature (CAT) in metallic materials, specifically focusing on ferritic and bainitic steels. This international standard applies to rolled steel plates with a body-centred cubic (BCC) crystal lattice structure, which exhibit a ductile-to-brittle transition. The CAT test is relevant for steels with a maximum tensile strength of 950 MPa and thicknesses ranging from over 6 mm up to 200 mm, within a temperature range of −196 °C to +100 °C. The document also provides detailed requirements for isothermal crack arrest tests and the associated test procedures to ensure valid and reliable results.

Key Topics

• Scope and Applicability:

  • Focuses on ferritic and bainitic rolled steel plates.
  • Applicable to steels with tensile strength ≤ 950 MPa and thickness between >6 mm and ≤200 mm.
  • Arrest temperature range of −196 °C to +100 °C.

• Test Equipment and Calibration:

  • Use of hydraulic or mechanical testing machines capable of applying the requisite tensile load.
  • Calibration requirements refer to ISO 7500-1 for static uniaxial testing machines.
  • Precise temperature control and measurement, using calibrated thermocouples according to ASTM E220-19.

• Test Methods:

  • Isothermal crack arrest tests under controlled temperature conditions.
  • Brittle crack initiation methods include both impact (drop-weight or air gun) and double tension tab plate techniques.
  • Strict requirements on test piece configurations, side grooves, and embrittled zones (created via electron beam welding or local temperature gradient techniques).

• Test Procedure:

  • Accurate pre-loading and meticulous temperature control.
  • Detailed procedures for crack initiation, propagation, and observation of fracture surfaces to judge arrest or propagation.
  • Clear criteria for result validation, including multiple test pieces for statistical reliability.

Applications

The test method defined in ISO 20198:2026 is vital for industries where steel structures are exposed to low temperatures and high mechanical stresses, such as:

• Shipbuilding: Ensuring structural plates in vessels can arrest brittle cracks and prevent catastrophic failure, particularly in cold environments.
• Civil Engineering and Infrastructure: Assessing steel plates used in bridges, offshore platforms, and pressure vessels for their ability to resist brittle fracture propagation.
• Automotive and Transport: Relevant for heavy vehicles, railway carriages, and containers using high-strength rolled steels.
• Material Research and Quality Control: Enabling manufacturers to evaluate and certify new steel grades for critical applications, enhancing safety and longevity through robust material property assessment.

Related Standards

ISO 20198:2026 is complemented by several related documents for comprehensive testing of steel materials:

• ISO 20064:2019: Metallic materials - Steel - Method of test for the determination of brittle crack arrest toughness, Kca. Provides a related method for evaluating the lowest temperature at which crack propagation stops under a temperature gradient.
• ISO 7500-1: Metallic materials - Calibration and verification of static uniaxial testing machines - Ensures accurate force application during testing.
• ASTM E220-19: Standard Test Method for Calibration of Thermocouples by Comparison Techniques - Supports precise temperature measurements during fracture testing.

By following ISO 20198:2026, organizations ensure consistent, repeatable, and internationally recognized test results, supporting material selection, compliance, and safety for a broad range of engineering applications.

Keywords: ISO 20198:2026, brittle crack arrest temperature, CAT, rolled steel plates, ferritic steel, bainitic steel, isothermal crack arrest test, metallic materials, fracture testing, standard methods, temperature control, steel toughness, structural safety.

Standards Content (Sample)

International
Standard
ISO 20198
First edition
Metallic materials — Steel
2026-05
— Method of test for the
determination of brittle crack
arrest temperature (CAT)
Matériaux métalliques — Acier — Méthode d'essai pour la
détermination de la température d'arrêt de la fissure fragile
(CAT)
Reference number
© ISO 2026
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Published in Switzerland
ii
Contents Page
Foreword .v
Introduction .vi
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Symbols . 2
5 Test equipment . 2
5.1 General .2
5.2 Testing machine . .3
5.2.1 Force implementation .3
5.2.2 Calibration of the testing machine .3
5.2.3 Loading direction .3
5.2.4 Loading distance .3
5.3 Methods for initiating brittle cracks .3
5.3.1 Impact type method .3
5.3.2 Double tension tab plate type method .3
6 Test pieces . 3
6.1 Configurations and dimensions of test pieces with side grooves .3
6.1.1 General .3
6.1.2 Side grooves .4
6.1.3 Number of test pieces .4
6.2 Configurations of extension plates and tab plates .5
6.2.1 General .5
6.2.2 Extension plates .5
6.2.3 Tab plates .5
6.3 Welding of test piece and extension plates .5
6.4 Impact type crack initiation .6
6.5 Double tension type crack initiation .6
6.6 Embrittled zone setting .6
6.7 Side grooves for embrittled zone preparation .7
6.8 Regulation of embrittled zone .7
7 Test method . 8
7.1 Pre-loading .8
7.2 Temperature measurement and control .8
7.2.1 Temperature control plan .8
7.2.2 Temperature measurement .8
7.2.3 EBW embrittlement .9
7.2.4 LTG embrittlement.9
7.2.5 Double tension type crack initiation test piece. 12
7.3 Loading and brittle crack initiation . 12
8 Test procedures .12
8.1 Pre-test procedures . 12
8.2 Impacting procedures . 13
8.3 Procedures after testing . 13
8.4 Observation of fracture surfaces . 13
9 Test validation judgement, judgement of “arrest” or “propagate” and CAT determination . 14
9.1 Brittle crack initiation and validation .14
9.2 Crack path examination and validation . 15
9.3 Fracture surface examination, crack length measurement and validation . 15
9.4 Final test judgement of “arrest”, “propagate” or “invalid" .16
9.5 T , T and CAT determination .17
test arrest
iii
9.5.1 Test determination .17
9.5.2 Target determination .17
9.5.3 CAT determination .17
10 Test report . 17
Bibliography . 19

iv
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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This document was prepared by Technical Committee ISO/TC 164, Mechanical testing of metals, Subcommittee
SC 4, Fatigue, fracture and toughness testing.
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.

v
Introduction
This document is applicable to either ferritic or bainitic, or both steel base metals which exhibits ductile to
brittle transition behaviour. This document provides a test method for determining the brittle crack arrest
[1]
temperature (CAT) using wide plates with a local temperature-gradient (LTG) and electron beam welding
[2][3]
(EBW) test pieces of isothermal type.
2 2
Recently, rolled steel plates with tensile strengths ranging from 570 N/mm to 720 N/mm and thicknesses
[4][5]
between 50 mm and 100 mm are commonly used for the upper deck structures of container carriers .
The International Association of Classification Societies (IACS) has developed the requirements for these
[6][7]
steel plates with brittle crack arrest properties . The brittle crack arrest properties can be evaluated by
the test method of determining either the brittle crack arrest toughness K or the crack arrest temperature
ca
(CAT). Reference [8] is a test method to evaluate the lower bound crack arrest toughness under plane strain
conditions.
The test method for the determination of brittle crack arrest toughness,K , of steel plates with a temperature
ca
gradient is specified in ISO 20064. The K test method applies varying stress levels and temperature
ca
gradients depending on the test conditions to determine the crack length and the temperature at which the
crack arrest occurs, and then derives the K value at the arrest temperature. On the other hand, the CAT
ca
test is a method that assesses the go and no-go behaviour of brittle cracks under iso-thermal conditions and
[9]
design stress .
vi
International Standard ISO 20198:2026(en)
Metallic materials — Steel — Method of test for the
determination of brittle crack arrest temperature (CAT)
1 Scope
This document specifies a test method for the determination of the brittle crack arrest temperature (CAT).
This document is applicable to either ferritic or bainitic, or both steel base metals with a body-centred cubic
(BCC) crystal lattice structure that exhibit ductile to brittle transition behaviour. The applicable materials
are rolled steel plates. This document is intended for steels with a tensile strength of 950 MPa or less and
a thickness greater than 6 mm but not exceeding 200 mm. The range of arrest temperatures is between −
196 °C and + 100 °C.
This document also specifies the requirements for test method and test procedures when using the
isothermal crack arrest test to judge valid test results under isothermal conditions and in order to determine
the crack arrest temperature.
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 7500-1, Metallic materials — Calibration and verification of static uniaxial testing machines — Part 1:
Tension/compression testing machines — Calibration and verification of the force-measuring system
ISO 20064:2019, Metallic materials — Steel — Method of test for the determination of brittle crack arrest
toughness, K
ca
ASTM E220-19, Standard Test Method for Calibration of Thermocouples By Comparison Techniques
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 20064 and the following apply.
ISO and IEC maintain terminology databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at https:// www .electropedia .org/
3.1
arrest temperature
temperature at the point where a brittle crack is arrested in the test temperature
[SOURCE: ISO 20064:2019, 3.5, modified — "in the temperature gradient type arrest toughness test" is
revised to "in the test temperature."]
3.2
brittle crack arrest temperature
CAT
lowest temperature at which running brittle crack is arrested

3.3
defect line fraction
total occupation ratio of the projected defect part to the total thickness
Note 1 to entry: The counting procedure for the defect line fractions is shown in Figure 8.
3.4
shear lip
fracture surface generated by ductile fracture adjacent to the front and back surfaces of a steel plate
[SOURCE: ISO 20064:2019, 3.15]
4 Symbols
For the purposes of this document, the symbols given in Table 1 apply.
Table 1 — Symbols
Symbol Unit Description
a mm Arrested crack length including mechanical notch
arrest
a mm Length of mechanical notch at the test piece edge
MN
B mm Test piece thickness
E J Total strain energy stored in tab plates and pin chucks
t
F kN Applied force
L mm Test piece length
L mm Minimum length between the test piece edge and the electron beam welding zone front
EB-min
Length between the test piece edge and the electron beam welding zone front appeared on
L mm
EB-s1,-s2
both sides of the test piece
L mm Local temperature gradient zone length associated with brittle crack propagation
LTG
L mm Side groove length
SG
Brittle crack arrest temperature at each test condition (target test temperature at which valid
T °C
arrest
brittle crack arrest behaviour is observed)
T °C Target test temperature
target
T °C Defined test temperature
test
W mm Test piece width
5 Test equipment
5.1 General
5.1.1 The testing equipment may be of the hydraulic or mechanical type. The testing equipment shall have
sufficient capacity to provide a tensile load equivalent to two-thirds of the specified minimum yield strength
of the steel being tested.
5.1.2 The temperature control system shall be capable of maintaining the temperature within ±2 °C from
T in the specified region of the test piece.
target
5.1.3 To initiate the brittle crack, an impact method such as a drop weight or air gun type can be used,
along with a double tension tab plate type method.
5.1.4 The testing machine is used to apply tensile force to an integrated test piece, while the impact
equipment is used to initiate a brittle crack on the test piece.

5.2 Testing machine
5.2.1 Force implementation
Using a testing machine with pin type loading, tensile force may be either hydraulically or mechanically
applied to an integrated test piece by force or displacement control. To ensure a uniform stress distribution
across the plate width, the centres of the loading pins on both sides shall be aligned with the neutral axis of
the integrated test piece.
5.2.2 Calibration of the testing machine
The force-measuring system of the testing machine shall be calibrated in accordance with ISO 7500-1, class
1, or better.
The accuracy of the load cells shall be 1 % of the full scale or less.
5.2.3 Loading direction
The testing machine may be oriented either horizontal or vertical. In the case of the horizontal setups, the
test piece surfaces shall be positioned either perpendicular or parallel to the ground.
5.2.4 Loading distance
The loading distance shall be at least 3,4 W or more to prevent force drop caused by a stress wave reflection
at the loading pins before the brittle crack is arrested. The distance between the loading pins can influence
the force drop associated with crack propagation.
5.3 Methods for initiating brittle cracks
5.3.1 Impact type method
For the initiation of brittle cracks, an impact force can be applied to a wedge mounted on the notch of the
test piece, using either a drop-weight type method or an air gun type method. Refer to 6.4 for detailed
requirements of the impact type method.
NOTE The drop-weight type method applies an impact force to the wedge by freely dropping a weight from a
predetermined. The air gun type method applies an impact force to the wedge by introducing a predetermined gas
pressure into a piston-sealed cylinder and then releasing the lock of the piston.
5.3.2 Double tension tab plate type method
Another method for initiating brittle cracks is the double tension method, as specified in 6.5, including
the test piece and requirements. A force or displacement control system can be used to apply load to the
secondary loading tab. However, a hydraulic-type loading system is recommended. Although a pin-type
method is preferred for applying the load, alternative methods may also be used.
6 Test pieces
6.1 Configurations and dimensions of test pieces with side grooves
6.1.1 General
The configuration of the standard test piece, which includes a mechanical notch, is shown in Figure 1 a).
The detailed configuration and dimensions of the standard test piece, including the recommended shape of
the side groove, are shown in Figure 1 b). A mechanical notch of the same length shall be introduced at the
opposite edge to prevent bending movement by aligning the net-section centre with the loading axis.

The test piece thickness, B, shall be equal to the thickness of the steel being tested. The test piece with W,
should range between 350 mm and 1,000 mm. The width of the standard test piece should be 500 mm. The
width to thickness ration, W/B, shall be not less than 5. The test piece length, L, should be at least 500 mm or
W, whichever is greater.
6.1.2 Side grooves
Side grooves shall be machined on both surfaces of the test piece to facilitate proper propagation of the
brittle crack and to minimize crack deviation and branching. To ensure a smooth transition, the ends of
the side grooves shall be machined with a gradual reduction in depth, with a curvature radius equal to or
greater than the groove depth.
The side-groove depth shall be equal to or less than 0,1 B. The side groove shall be at least 150 mm, which
is the required embrittled zone length. The side groove depth, tip radius and opening angle should not be
strictly regulated. Instead, they should be appropriately chosen to avoid the formation of shear lips exceeding
1 mm in thickness on either side.
6.1.3 Number of test pieces
A minimum of three sets of valid test pieces shall be prepared to ensure a validated test result, as required
in 9.5.3.1.
Dimensions in millimetres
a) General configuration of the standard test piece,
including the recommended shape of the mechanical notch

b) Detailed configuration and dimensions of the standard test piece,
including the recommended shape of the side groove
Key
1 side groove
Figure 1 — Standard test piece configuration
6.2 Configurations of extension plates and tab plates
6.2.1 General
For the definitions and typical examples of the dimensions of the extension plates and tab plates, refer to
ISO 20064:2019, Figures 7 and 8.
As for loading pins, either the single-pin type or the double-pin type shall be used.
6.2.2 Extension plates
The tolerances of extension plate dimensions shall be in accordance with those as specified in ISO 20064:2019,
6.2.2.
6.2.3 Tab plates
The tab plates shall be in accordance with those as specified in ISO 20064:2019, 6.2.3.
6.3 Welding of test piece and extension plates
The test piece, extension plates and tab plates shall be connected by welding. The welds shall have sufficient
strength to withstand the full magnitude of the applied force. Welding of a test piece and extension
plates shall be carried out in compliance with the requirements of the flatness (angular distortion, linear
misalignment) of the weld between a test piece and an extension plate, and the accuracy of loadings in
ISO 20064:2019, 6.3.
6.4 Impact type crack initiation
6.4.1 Test pieces shall be prepared in accordance with the requirements from 6.1 to 6.3.
6.4.2 A V-shape notch for brittle crack initiation shall be machined on the test piece edge of the impact
side. The total machined notch length shall be 29 mm ± 1 mm. A saw-cut notch radius may be machined in
the range of between 0,1 mm and 1 mm in order to control a brittle crack initiation during testing. The notch
edge shape shall be designed so that a brittle crack shall be initiated by impact but not initiated during force
increase prior to reaching the specified force value.
6.4.3 The requirements for side grooves are described in 6.7. The recommended cross-section of the side
groove is also shown in Figure 1 b).
6.5 Double tension type crack initiation
6.5.1 A double tension type arrest test piece consists of a main plate and a secondary loading tab. The
main plate serves as the test plate for evaluating crack arrest toughness, while the secondary loading tab
functions as a crack starter plate to facilitate the initiation and propagations of a brittle crack to run into
the main plate. After applying a predetermined applied force and a temperature gradient to the main plate,
a secondary force shall be exerted on the secondary loading tab using a secondary loading device. This
process is intended to initiate a brittle crack and promote its propagation into the main plate.
6.5.2 In a double tension type test, the secondary loading tab plate may be cooled further to facilitate
easier initiation of a brittle crack.
6.5.3 The test piece configuration and test procedures for the double tension type arrest test method
should conform to ISO 20064:2019, Annex D.
6.6 Embrittled zone setting
6.6.1 An embrittled zone shall be introduced to ensure that the initiation of a running brittle crack.
electron beam welding (EBW) or local temperature gradient (LTG) may be used to create the embrittled
zone. Other method, including laser welding of creating an
...