ISO 4955:2016

INTERNATIONAL ISO
STANDARD 4955
Fourth edition
2016-05-01
Heat-resistant steels
Aciers réfractaires
Reference number
ISO 4955:2016(E)
©
ISO 2016

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ISO 4955:2016(E)

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ISO 4955:2016(E)

Contents Page
Foreword .iv
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 2
4 Designation . 2
5 Information to be supplied by the purchaser. 2
6 Classification of grades . 3
7 Requirements . 3
7.1 Manufacturing process. 3
7.2 Delivery condition . 3
7.3 Chemical composition . 4
7.4 Mechanical properties . 4
7.4.1 Mechanical properties at room temperature . 4
7.4.2 Mechanical properties at elevated temperatures . 4
7.5 Surface quality . 4
7.6 Internal soundness . 5
7.7 Dimensions and tolerances on dimensions and shape . 5
8 Inspection, testing and conformance of products. 5
8.1 General . 5
8.2 Inspection procedures and types of inspection documents . 6
8.3 Specific inspection and testing . 6
8.3.1 Extent of testing . 6
8.3.2 Selection and preparation of samples and test pieces . 6
8.4 Test methods . 6
8.5 Retest . 7
9 Marking . 7
Annex A (informative) Technical information on heat- and creep-resistant steels .21
Annex B (informative) Data for creep strength to 1 % plastic strain and creep rupture strength .28
Annex C (informative) Designations of the steels given in Table 2 and of comparable grades
covered in various designation systems .33
Annex D (informative) Applicable dimensional International Standards.36
Bibliography .37
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ISO 4955:2016(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 meaning of ISO specific terms and expressions related to conformity
assessment, as well as information about ISO’s adherence to the WTO principles in the Technical
Barriers to Trade (TBT) see the following URL: Foreword - Supplementary information
The committee responsible for this document is ISO/TC 17, Steel, Subcommittee SC 4, Heat treatable and
alloy steels.
This fourth edition cancels and replaces the third edition (ISO 4955:2005), which has been technically
revised.
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INTERNATIONAL STANDARD ISO 4955:2016(E)
Heat-resistant steels
1 Scope
This International Standard specifies requirements for the grades listed in Table 2, which are
usually employed for products for which the resistance to the effects of hot gases and the products of
combustion at temperatures in the region above 550°C and/or to long-term mechanical stress is the
main requirement.
NOTE 1 Grades mentioned in this International Standard may also be used for corrosion and creep resistant
purposes.
This International Standard is applicable to the following:
— flat products;
— bars, sections, rod, semi-finished products and forgings.
NOTE 2 Hammer-forged semi-finished products (blooms, billets, slabs, etc.), seamless rolled rings and
hammer-forged bars are in the following, covered under semi-finished products or bars and not under the term
“forgings”.
NOTE 3 Not all of the grades included in this International Standard are necessarily available in all
product forms.
NOTE 4 In Table 2, two alloys are listed in addition to the steels since they belong to the heat resistant grades.
NOTE 5 Heat resistant wire in the cold worked condition is covered by ISO 16143-3.
NOTE 6 Corrosion resistant stainless steels for which resistance to corrosion is of primary importance are
covered by ISO 16143-1 and ISO 16143-2.
NOTE 7 Heat-resistant steels for valves are covered by ISO 683-15.
In addition to this International Standard, the general technical delivery requirements of ISO 404 are
applicable.
2 Normative references
The following documents, in whole or in part, are normatively referenced in this document and are
indispensable for its application. For dated references, only the edition cited applies. For undated
references, the latest edition of the referenced document (including any amendments) applies.
ISO 377, Steel and steel products — Location and preparation of samples and test pieces for mechanical testing
ISO 404, Steel and steel products — General technical delivery requirements
ISO 4885, Ferrous products — Heat treatments — Vocabulary
ISO/TS 4949, Steel names based on letter symbols
ISO 6506-1, Metallic materials — Brinell hardness test — Part 1: Test method
ISO 6892-1:2009, Metallic materials — Tensile testing — Part 1: Method of test at room temperature
ISO 6929, Steel products — Vocabulary
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ISO 4955:2016(E)

ISO 9443, Heat-treatable and alloy steels — Surface quality classes for hot-rolled round bars and wire
rods — Technical delivery conditions
ISO/TR 9769, Steel and iron — Review of available methods of analysis
ISO 10474, Steel and steel products — Inspection documents
ISO 14284, Steel and iron — Sampling and preparation of samples for the determination of chemical
composition
ISO 15510, Stainless steels — Chemical composition
ISO 20723, Structural steels — Surface condition of hot-rolled sections — Delivery requirements
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 377, ISO 404, ISO 4885,
ISO 6929, ISO 14284 and the following apply.
3.1
heat resistant steels
heat resistant steels of this International Standard are used at above 550°C (wustite point) due to their
excellent resistance to the effects of hot gases and products of combustion, as well as their resistance
to the influence of molten salts and molten metals but also showing good mechanical properties during
short and long-term stressing
3.2
creep resistant grades
steels, nickel- or cobalt-alloys with a minimum of 8 % chromium, which are characterised by good
mechanical behaviour at temperatures above 500 °C under long-range service conditions, i.e. primarily
by creep strength to 1 % plastic strain or creep rupture strength during long-time stressing
4 Designation
For the steel grades covered by this International Standard, the steel names as given in the tables are
allocated in accordance with ISO/TS 4949.
For the steel grades covered by this International Standard, the steel numbers as given in the tables are
allocated in accordance with ISO 15510.
5 Information to be supplied by the purchaser
It shall be the responsibility of the purchaser to specify all requirements that are necessary for products
under this specification. Such requirements to be considered include, in the order listed, but not limited
to, the following:
— the desired quantity;
— the product form;
— the number of the appropriate dimensional standard (see Annex A), the nominal dimensions, plus
any choice of requirements;
— the type of material (grade);
— the number of this International Standard (ISO 4955);
— the name or number of the steel grade;
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ISO 4955:2016(E)

— if, for the relevant steel in Tables 6 and 7 for the mechanical properties, more than one treatment
condition is covered, the symbol for the desired heat treatment;
— the desired process route, including surface finish (see 7.2, 7.5 and Table 4, footnote d);
— if a verification of internal soundness is required, the requirements have to be agreed at the time of
enquiry and order;
— any further optional test agreed between the manufacturer and purchaser at the time of enquiry
and order;
— the type of inspection document and its designation in accordance with ISO 10474 (see 8.2).
EXAMPLE 1 ton of plates according to ISO 9444-2 with a specified thickness of 5,0 mm, a specified width
of 1 200 mm, with trimmed edges (T) and a specified length of 2 500 mm made of a steel grade with the name
X8NiCrAlTi32–21 (4876–088–00-I) as specified in ISO 4955, in process route 1U and inspection certificate 3.1 as
specified in ISO 10474:
1 t plate ISO 9444-2 — 5,0 × 1200T × 2500
Steel ISO 4955 — X8NiCrAlTi32–21 + 1U
ISO 10474 — 3.1
or
1 t plate ISO 9444-2 — 5,0 × 1200T × 2500
Steel ISO 4955 — 4876-088-00-I + 1U
ISO 10474 — 3.1
6 Classification of grades
Heat-resistant steels covered in this International Standard are classified according to their structure
into the following:
— austenitic grades;
— ferritic grades;
— martensitic grades;
— precipitation hardening grades.
7 Requirements
7.1 Manufacturing process
Unless a special steelmaking process is agreed when ordering, the steelmaking process shall be at the
discretion of the manufacturer. When he so requests, the purchaser shall be informed what steelmaking
process is being used.
7.2 Delivery condition
The products shall be supplied in the delivery condition agreed in the order by reference to the process
route given in Tables 4 and 5 (see also Annex A) and where different alternatives exist to the treatment
conditions given in Tables 6 and 7.
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7.3 Chemical composition
7.3.1 The chemical composition requirements given in Table 2 apply with respect to the chemical
composition of the cast analysis.
7.3.2 The product analysis may deviate from the limiting values for the cast analysis given in Table 2 by
values listed in Table 3.
7.4 Mechanical properties
7.4.1 Mechanical properties at room temperature
The mechanical properties at room temperature as specified in Tables 6 and 7 apply for the relevant
specified heat treatment condition. This does not apply to the process route 1U (hot rolled, not heat-
treated, not descaled). If, by agreement at the time of ordering, the products are to be supplied in a non-
heat-treated condition, the mechanical properties specified in Tables 6 and 7 shall be obtainable from
reference test pieces which have received the appropriate heat treatment (simulated heat treatment).
7.4.2 Mechanical properties at elevated temperatures
The mechanical properties at elevated temperature as specified in Table 8 apply for each specified
heat treatment condition. This does not apply to the process route 1U (hot rolled, not heat-treated, not
descaled) and to semi-finished products.
The tensile test at elevated temperature shall be carried out at temperature of interest only when
agreed at the time of enquiry and order.
If, by agreement at the time of ordering, the products are to be supplied in a non-heat-treated condition,
the mechanical properties specified in Table 8 shall be obtainable from reference test pieces which have
received the appropriate heat treatment (simulated heat treatment).
7.5 Surface quality
Availability, and the determination of the types of process route and surface finish (for flat products,
see Table 4 and for long products, see Table 5) most suited to a particular case, should be discussed
with the manufacturer.
The general surface appearance with respect to soundness and surface finish shall be consistent with
good production practice, for the grade and quality ordered, as determined by visual inspection.
When flat products are delivered in coil form, the degree and extent of imperfections may be expected
to be higher, due to the impracticability of removing short lengths of coil.
Flat products delivered with hot-rolled or cold-rolled finishes (see Table 4) shall, unless otherwise
agreed, be supplied with only one surface inspected to the required finish (the prime surface). In
such instances, the manufacturer should indicate the prime surface, by marking the material or the
packaging, or by some other agreed method. The default method is to mark the prime surface, and
to make this surface the top surface of plates, sheets and cut lengths, or the outside surface of coiled
products.
For long products, the available surface finishes are given in Table 5. Slight surface imperfections,
inherent to the production process, are permitted. Exact requirements concerning the maximum depth
of acceptable discontinuities for bars, rods and sections in the relevant conditions are given in Table 1.
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ISO 4955:2016(E)

Table 1 — Maximum depth of acceptable discontinuities for bars, rods and sections
a
Conditions Product forms Permissible depth of discontinuities Max. % of delivered weight in
excess of permissible depth of
discontinuities
1U, 1C, 1E, 1D Sections To be agreed upon at the time of enquiry and order on the basis of ISO 20723.
1U, 1C, 1E, 1D Rounds and rod Specified at the time of enquiry and order, otherwise ISO 9443 class 1 za2.
b
1X Rounds —  max. 0,2 mm for d ≤ 20 mm 1 %
—  max. 0,01 d for 20 < d ≤ 75 mm
—  max. 0,75 mm for d > 75 mm
Hexagons —  max. 0,3 mm for d ≤ 15 mm 2 %
—  max. 0,02 d for 15 < d ≤ 63 mm
Other bars —  max. 0,3 mm for d ≤ 15 mm 4 %
—  max. 0,02 d for 15 < d ≤ 63 mm
1G Rounds Technically defect free by manufacture. 0,2 %
a
Depth of discontinuities is understood as being the distance, measured normally to the surface, between the bottom of
the discontinuities and that surface.
b
At the time of enquiry and order, it may be agreed that the product shall be delivered with a surface that is technically
defect free by manufacture. In this case, also the maximum % of delivered weight in excess of permissible depth of
discontinuities shall be agreed.
7.6 Internal soundness
For the internal soundness, where appropriate, requirements together with the conditions for their
verification may be agreed at the time of enquiry and order, if possible, with reference to other
International Standards (e.g. ISO 17577 for flat products of thickness equal to or greater than 6 mm).
7.7 Dimensions and tolerances on dimensions and shape
7.7.1 The dimensions and the tolerances on dimensions and shape are to be agreed at the time of
enquiry and order, as far as possible with reference to the dimensional International Standards listed in
Annex D. The ordered dimensions shall, where applicable, include the minimum machining allowances.
7.7.2 If none of the International Standards listed in Annex D is applicable, then the dimensions
and tolerances should be agreed at the time of enquiry and order on the basis of regional or national
standards.
8 Inspection, testing and conformance of products
8.1 General
The manufacturer shall carry out appropriate process control, inspection and testing to ensure that the
delivery complies with the requirements of the order.
This includes the following:
— a suitable frequency of verification of the dimensions of the products;
— an adequate intensity of visual examination of the surface quality of the products;
— an appropriate frequency and type of test to ensure that the correct grade of steel is delivered.
The nature and frequency of these verifications, examinations and tests are determined by the
manufacturer, based on the degree of consistency that has been determined by the evidence of his
quality system. In view of this, verifications by specific tests for these requirements are not necessary
unless otherwise agreed upon.
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8.2 Inspection procedures and types of inspection documents
8.2.1 Products complying with this International Standard shall be ordered and delivered with one of
the inspection documents as specified in ISO 10474. The type of document shall be agreed upon at the
time of enquiry and order. If the order does not contain any specification of this type, a test report 2.2
shall be issued.
8.2.2 If, in accordance with the agreements made at the time of enquiry and order, a test report is to be
provided, this shall cover the following:
a) a statement that the material complies with the requirements of the order;
b) the results of the cast analysis for all elements specified for the type of steel supplied.
8.2.3 If, in accordance with the agreements in the order, an inspection certificate 3.1 or 3.2 is to be
provided, the specific inspections and tests described in 8.3 shall be carried out and their results shall be
certified in the document.
In addition to the details in 8.2.2, the document shall cover the following:
a) the results of the mandatory tests marked in the second column of Tables 9 and 10 by an “m”;
b) the results of any optional test or inspection agreed when ordering.
8.3 Specific inspection and testing
8.3.1 Extent of testing
The tests to be carried out, either mandatorily (m) or by agreement (o) and the composition and size
of the test units, and the number of sample products, samples and test pieces to be taken are given in
Tables 9 and 10.
8.3.2 Selection and preparation of samples and test pieces
8.3.2.1 The general conditions for selection and preparation of samples and test pieces shall be in
accordance with ISO 377 and ISO 14284.
8.3.2.2 The samples for the tensile test shall be taken in accordance with Figures 1 to 3. Samples
from flat products shall be taken in such a way that they are located halfway between the centre and a
longitudinal edge.
The samples shall be taken from products in the delivery condition. If agreed, the samples may be taken
from flat products before flattening or from bars before straightening.
For samples to be given a simulated heat treatment, the conditions for annealing shall be agreed.
8.3.2.3 Samples for the hardness test, where requested, shall be taken from the same locations as those
for the tensile test.
8.4 Test methods
8.4.1 Unless otherwise agreed when ordering, the choice of a suitable physical or chemical method of
analysis to determine the product analysis is at the discretion of the manufacturer. In cases of dispute,
the analysis shall be carried out by a laboratory approved by the two parties. In these cases, the reference
method of analysis shall be agreed, where possible, with reference to ISO/TR 9769.
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8.4.2 The tensile test at room temperature shall be carried out in accordance with ISO 6892-1, taking
into account for flat products the additional or deviating conditions specified in Figure 3, footnote a. It
shall be performed under controlled conditions in accordance with ISO 6892-1:2009, Clause 5.
Unless otherwise agreed, the tensile strength and elongation after fracture shall be determined and,
in addition, for ferritic, martensitic, precipitation-hardening, austenitic free-cutting and austenitic-
ferritic steels, the 0,2 % proof strength, and for austenitic steels, the 0,2 % and 1 % proof strength.
8.4.3 The Brinell hardness test shall be carried out in accordance with ISO 6506-1.
8.4.4 Dimensions and dimensional tolerances of the products shall be tested in accordance with the
requirements of the relevant dimensional International Standards given in Annex D.
8.5 Retest
See ISO 404.
9 Marking
9.1 The products shall be marked with the manufacturer’s trademark or symbol and the steel name
or number. The product shall also be marked with the cast number, thickness or dimension (and if an
inspection, certificate is requested) an identification number related to the inspection certificate.
9.2 Unless otherwise agreed, the method of marking and the material of marking shall be at the option
of the manufacturer. Its quality shall be such that it shall be durable for at least one year, can withstand
normal handling and can be stored in unheated storage under cover. The corrosion resistance of the
product shall not be impaired by the marking.
9.3 Each unit shall be marked:
— for flat products as an alternative, for items that are wrapped, bundled or boxed, or where the
surface is ground or polished, the marking may be applied to the packaging or to a tag securely
attached to it;
— for semi-finished products, bars, sections and forgings by means of labels attached to the bundle
or, by agreement at the time of enquiry and order, by inking, adhesive labels, electrolytic etching or
stamping;
— for rods, by means of a label attached to the coil.
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ISO 4955:2016(E)

Table 2 — Chemical composition (cast analysis)
a
Designation % (mass fraction)
Name ISO-number C Si Mn P S Cr Ni N Others
Austenitic steels for heat resistant applications
X6CrNiSiNCe19–10 4818–304– 0,04 to 1,00 to 1,00 0,045 0,015 18,0 to 9,0 to 0,12 to Ce: 0,03 to 0,08
15-E 0,08 2,00 20,0 11,0 0,20
X15CrNiSi20–12 4828–305– 0,20 1,50 to 2,00 0,045 0,030 19,0 to 11,0 to 0,10 —
09-I 2,50 21,0 13,0
X7CrNiSiNCe21–11 4835–308– 0,05 to 1,40 to 0,80 0,040 0,030 20,0 to 10,0 to 0,14 to Ce: 0,03 to 0,08
15-U 0,10 2,00 22,0 12,0 0,20
X18CrNi23–13 4833–309– 0,20 1,00 2,00 0,045 0,030 22,0 to 12,0 to 0,10 —
08-I 24,0 15,0
X8CrNi25–21 4845–310– 0,10 1,50 2,00 0,045 0,015 24,0 to 19,0 to 0,10 —
08-E 26,0 22,0
X15CrNiSi25–21 4841–314– 0,20 1,50 to 2,00 0,045 0,015 24,0 to 19,0 to 0,10 —
00-E 2,50 26,0 22,0
X8NiCrAlTi32–21 4876–088– 0,05 to 1,00 1,50 0,015 0,015 19,0 to 30,0 to — Al: 0,15 to 0,60
00-I 0,10 23,0 34,0 Ti: 0,15 to 0,60
Cu: 0,70
X6NiCrSiNCe35–25 4854–353– 0,04 to 1,20 to 2,00 0,040 0,015 24,0 to 34,0 to 0,12 to Ce: 0,03 to 0,08
15-E 0,08 2,00 26,0 36,0 0,20
Austenitic steels for creep resistant applications
Mo: 0,80 to 1,20
X10CrNiMoMnNbV 4982–215– 0,06 to 0,20 to 5,50 to 14,0 to 9,0 to V: 0,15 to 0,40
0,035 0,015 0,10
B15–10–1 00-E 0,15 1,00 7,0 16,0 11,0 Nb: 0,75 to 1,25
B: 0,003 to 0,009
X7CrNi18–9 4948–304– 0,04 to 1,00 2,00 0,045 0,030 17,0 to 8,0 to — —
09-I 0,10 19,0 11,0
X7CrNiTi18–10 4940–321– 0,04 to 1,00 2,00 0,045 0,030 17,0 to 9,0 to — Ti: 5 × C to 0,80
09-I 0,10 19,0 12,0
c
X7CrNiNb18–10 4912–347– 0,04 to 1,00 2,00 0,045 0,030 17,0 to 9,0 to — Nb: 10 × C to 1,20
09-I 0,10 19,0 12,0
4961–347– 0,04 to 0,30 to 15,0 to 12,0 to — Nb: 10 × C to 1,20
X8CrNiNb16–13 1,50 0,035 0,015
77-E 0,10 0,60 17,0 14,0
4918–316– 0,04 to 16,0 to 12,0 to 0,10 Mo: 2,00 to 2,50
X6CrNiMo17–13–2 0,75 2,00 0,035 0,015
09-E 0,08 18,0 14,0
X7NiCrWCuCoNbN 4990–310– 0,04 to 0,40 0,60 0,025 0,015 21,5 to 23,5 to 0,20 to Co: 1,0 to 2,0
B25–23–3-3–3-2 35-U 0,10 23,5 26,5 0,30 Cu: 2,5 to 3,5
Nb: 0,40 to 0,60
W: 3,0 to 4,0
B: 0,002 to 0,008
Ferritic steels for heat resistant applications
X10CrAlSi7 4713–503– 0,12 0,50 to 1,00 0,040 0,0150 6,0 to 8,0 — — Al: 0,50 to 1,00
72-E 1,00
X2CrTi12 4512–409– 0,03 1,00 1,00 0,040 0,015 10,5 to — — Ti: 6 × (C+N) to
d
10-I 12,5 0,65
X6Cr13 4000–410– 0,08 1,00 1,00 0,040 0,030 12,0 to 1,00 — —
08-I 14,0
X10CrAlSi13 4724–405– 0,12 0,70 to 1,00 0,040 0,015 12,0 to 1,00 — Al: 0,70 to 1,20
77-I 1,40 14,0
Elements not quoted in this table shall not be intentionally added to the steel without the agreement of the purchaser, except for finishing the cast. All
appropriate precautions shall be taken to avoid the addition of such elements from scrap or other mater
...