EN ISO 4042:2022

SLOVENSKI STANDARD
01-september-2022
Nadomešča:
SIST EN ISO 4042:2018
Vezni elementi - Sistemi galvanskih prevlek veznih elementov (ISO 4042:2022)
Fasteners - Electroplated coating systems (ISO 4042:2022)
Verbindungselemente - Galvanisch aufgebrachte Überzugsysteme (ISO 4042: 2022)
Fixations - Systèmes de revêtements électrolytiques (ISO 4042: 2022)
Ta slovenski standard je istoveten z: EN ISO 4042:2022
ICS:
21.060.01 Vezni elementi na splošno Fasteners in general
25.220.40 Kovinske prevleke Metallic coatings
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

EN ISO 4042
EUROPEAN STANDARD
NORME EUROPÉENNE
June 2022
EUROPÄISCHE NORM
ICS 21.060.01 Supersedes EN ISO 4042:2018
English Version
Fasteners - Electroplated coating systems (ISO 4042:2022)
Fixations - Systèmes de revêtements électrolytiques Verbindungselemente - Galvanisch aufgebrachte
(ISO 4042: 2022) Überzugsysteme (ISO 4042: 2022)
This European Standard was approved by CEN on 4 February 2022.

CEN members are bound to comply with the CEN/CENELEC Internal Regulations which stipulate the conditions for giving this
European Standard the status of a national standard without any alteration. Up-to-date lists and bibliographical references
concerning such national standards may be obtained on application to the CEN-CENELEC Management Centre or to any CEN
member.
This European Standard exists in three official versions (English, French, German). A version in any other language made by
translation under the responsibility of a CEN member into its own language and notified to the CEN-CENELEC Management
Centre has the same status as the official versions.

CEN members are the national standards bodies of Austria, Belgium, Bulgaria, Croatia, Cyprus, Czech Republic, Denmark, Estonia,
Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway,
Poland, Portugal, Republic of North Macedonia, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland, Turkey and
United Kingdom.
EUROPEAN COMMITTEE FOR STANDARDIZATION
COMITÉ EUROPÉEN DE NORMALISATION

EUROPÄISCHES KOMITEE FÜR NORMUNG

CEN-CENELEC Management Centre: Rue de la Science 23, B-1040 Brussels
© 2022 CEN All rights of exploitation in any form and by any means reserved Ref. No. EN ISO 4042:2022 E
worldwide for CEN national Members.

Contents Page
European foreword . 3

European foreword
This document (EN ISO 4042:2022) has been prepared by Technical Committee ISO/TC 2 "Fasteners" in
collaboration with Technical Committee CEN/TC 185 “Fasteners” the secretariat of which is held by BSI.
This European Standard shall be given the status of a national standard, either by publication of an
identical text or by endorsement, at the latest by December 2022, and conflicting national standards
shall be withdrawn at the latest by December 2022.
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. CEN shall not be held responsible for identifying any or all such patent rights.
This document supersedes EN ISO 4042:2018.
Any feedback and questions on this document should be directed to the users’ national standards
body/national committee. A complete listing of these bodies can be found on the CEN website.
According to the CEN-CENELEC Internal Regulations, the national standards organizations of the
following countries are bound to implement this European Standard: Austria, Belgium, Bulgaria,
Croatia, Cyprus, Czech Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland,
Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Republic of
North Macedonia, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland, Turkey and the
United Kingdom.
Endorsement notice
The text of ISO 4042:2022 has been approved by CEN as EN ISO 4042:2022 without any modification.

INTERNATIONAL ISO
STANDARD 4042
Fourth edition
2022-06
Fasteners — Electroplated coating
systems
Fixations — Systèmes de revêtements électrolytiques
Reference number
ISO 4042:2022(E)
ISO 4042:2022(E)
© ISO 2022
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: +41 22 749 01 11
Email: copyright@iso.org
Website: www.iso.org
Published in Switzerland
ii
ISO 4042:2022(E)
Contents Page
Foreword .v
Introduction . vi
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 2
4 General characteristics of the coating . 2
4.1 Coating metals or alloys and main purposes . 2
4.2 Build-up of basic electroplated coating systems . 3
4.3 Coating systems and coating processes . 4
4.4 Internal hydrogen embrittlement . 4
4.4.1 General . 4
4.4.2 Fasteners with hardness up to 360 HV . 5
4.4.3 Fasteners with hardness above 360 HV and up to 390 HV . 5
4.4.4 Fasteners with hardness above 390 HV . 5
4.4.5 Fasteners in accordance with ISO 898-1, ISO 898-2 and ISO 898-3 . 6
4.4.6 Case-hardened fasteners . . . 7
4.4.7 Work hardened fasteners and fasteners with threads rolled after heat
treatment . 8
4.4.8 Fasteners with bainitic structure . 9
4.5 Baking . 9
5 Corrosion protection and testing .9
5.1 General . 9
5.2 Neutral salt spray test (NSS) for zinc-based coating systems . 10
5.3 Sulfur dioxide test (Kesternich test) . 11
5.4 Bulk handling, automatic processes such as feeding and/or sorting, storage and
transport .12
6 Dimensional requirements and testing .12
6.1 General .12
6.2 Fasteners with ISO metric thread .12
6.2.1 Coating thickness .12
6.2.2 Gaugeability and assemblability . 13
6.3 Other fasteners . 13
6.4 Test methods for thickness determination . 14
7 Mechanical and physical properties and testing .16
7.1 General . 16
7.2 Appearance . 16
7.3 Corrosion resistance related to temperature . 16
7.4 Torque/clamp force relationship . 16
7.5 Determination of hexavalent chromium . 16
8 Applicability of tests .17
8.1 General . 17
8.2 Tests mandatory for each lot . 17
8.3 Tests for in-process control . . 17
8.4 Tests to be performed when specified by the purchaser. 17
9 Designation system .17
9.1 General . 17
9.2 Designation of electroplated coating systems for the order . 18
9.3 Examples of designation of hexavalent chromium free electroplated coating
systems for fasteners . 20
9.4 Designation of fasteners with electroplated coating systems for labelling . 21
iii
ISO 4042:2022(E)
10 Ordering requirements for electroplating .21
11 Storage conditions .22
Annex A (informative) Design and assembly aspects for joints with coated fasteners .23
Annex B (informative) Hydrogen embrittlement consideration .31
Annex C (informative) Corrosion protection related to zinc coatings with chromate
conversion coatings .36
Annex D (informative) Coating thickness and thread clearance for ISO metric threads .37
Annex E (informative) Coating systems tested in accordance with ISO 9227, NSS —
Evaluation of cabinet corrosivity for the neutral salt spray test . 44
Annex F (informative) Obsolete designation codes for electroplated coating systems on
fasteners according to ISO 4042:1999 .54
Bibliography .57
iv
ISO 4042:2022(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 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 2, Fasteners, Subcommittee SC 14, Surface
coatings, in collaboration with the European Committee for Standardization (CEN) Technical Committee
CEN/TC 185, Fasteners, in accordance with the Agreement on technical cooperation between ISO and
CEN (Vienna Agreement).
This fourth edition cancels and replaces the third edition (ISO 4042:2018), which has been technically
revised. The main changes are as follows:
— in Clause 1, a statement has been added that the requirements of this document for electroplated
fasteners have precedence over other documents dealing with electroplating;
— all references to ISO 2081 and ISO 19598 have been removed because ISO 4042 is a self-containing
document for the purpose of fasteners;
— in 4.4, the measures to prevent internal hydrogen embrittlement for nuts, flat washers and case-
hardened screws have been completely revised;
— in 6.4, the reference areas for thickness determination have been more clearly specified;
— wording in the whole document has been improved to be more accurate, especially for complex
topics.
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
ISO 4042:2022(E)
Introduction
ISO 4042:1999 was completely revised to take into account new developments related to hexavalent
chromium free passivations, application of sealants and top coats, requirements for functional
properties as well as results of research work to minimize the risk of hydrogen embrittlement. This
revision was published in 2018.
The last editions of ISO 2081:2018 as well as ISO 19598:2016, which are general standards for
electroplating, are not adequate to cover the requirements for electroplated fasteners dealt with in
ISO 4042, especially with regard to hydrogen embrittlement and baking. Therefore, a new revision
of ISO 4042:2018 was necessary to delete all references to these two general standards to avoid any
contradictions.
For electroplated nuts, flat washers, and case-hardened screws, measures to mitigate the risk of
hydrogen embrittlement, especially in relation to baking, have been revised to be consistent with
revisions of ISO 898-2 and ISO 2702, and to reflect findings from the latest research works. For
electroplated flat washers in accordance with ISO 898-3, it is generally accepted that tensile stress
resulting from intended and unintended bending in service may increase the risk of hydrogen
embrittlement. An appropriate test method to simulate such a scenario is currently under investigation.
vi
INTERNATIONAL STANDARD ISO 4042:2022(E)
Fasteners — Electroplated coating systems
1 Scope
This document specifies requirements for steel fasteners with electroplated coatings and coating
systems. The requirements related to dimensional properties also apply to fasteners made of copper or
copper alloys.
It also specifies requirements and gives recommendations to minimize the risk of hydrogen
embrittlement, see 4.4 and Annex B.
It mainly applies to fasteners with zinc and zinc alloy coating systems (zinc, zinc-nickel, zinc-iron) and
cadmium, primarily intended for corrosion protection and other functional properties:
— with or without conversion coating,
— with or without sealant,
— with or without top coat,
— with or without lubricant (integral lubricant and/or subsequently added lubricant).
Specifications for other electroplated coatings and coating systems (tin, tin-zinc, copper-tin, copper-
silver, copper, silver, copper-zinc, nickel, nickel-chromium, copper-nickel, copper-nickel-chromium)
are included in this document only for dimensional requirements related to fasteners with ISO metric
threads.
The requirements of this document for electroplated fasteners take precedence over other documents
dealing with electroplating.
This document applies to steel bolts, screws, studs and nuts with ISO metric thread, to other threaded
fasteners and to non-threaded fasteners such as washers, pins, clips and rivets.
NOTE Electroplating is also applied to stainless steel fasteners, e.g. for the purpose of lubrication in order to
avoid galling.
Information for design and assembly of coated fasteners is given in Annex A.
This document does not specify requirements for properties such as weldability or paintability.
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 1456, Metallic and other inorganic coatings — Electrodeposited coatings of nickel, nickel plus
chromium, copper plus nickel and of copper plus nickel plus chromium
ISO 1463, Metallic and oxide coatings — Measurement of coating thickness — Microscopical method
ISO 1502, ISO general-purpose metric screw threads — Gauges and gauging
ISO 1891-2, Fasteners — Terminology — Part 2: Vocabulary and definitions for coatings
ISO 2082, Metallic and other inorganic coatings — Electroplated coatings of cadmium with supplementary
treatments on iron or steel
ISO 4042:2022(E)
ISO 2093, Electroplated coatings of tin — Specification and test methods
ISO 2177, Metallic coatings — Measurement of coating thickness — Coulometric method by anodic
dissolution
ISO 2178, Non-magnetic coatings on magnetic substrates — Measurement of coating thickness — Magnetic
method
ISO 3497, Metallic coatings — Measurement of coating thickness — X-ray spectrometric methods
ISO 3613, Metallic and other inorganic coatings — Chromate conversion coatings on zinc, cadmium,
aluminium-zinc alloys and zinc-aluminium alloys — Test methods
ISO 4521, Metallic and other inorganic coatings — Electrodeposited silver and silver alloy coatings for
engineering purposes — Specification and test methods
ISO 8991, Designation system for fasteners
ISO 9227, Corrosion tests in artificial atmospheres — Salt spray tests
ISO 15330, Fasteners — Preloading test for the detection of hydrogen embrittlement — Parallel bearing
surface method
ISO 15726, Metallic and other inorganic coatings — Electrodeposited zinc alloys with nickel, cobalt or iron
ISO 16047, Fasteners — Torque/clamp force testing
ISO 16228, Fasteners — Types of inspection documents
ISO 21968, Non-magnetic metallic coatings on metallic and non-metallic basis materials — Measurement
of coating thickness — Phase-sensitive eddy-current method
ASME B18.6.3, Machine Screws, Tapping Screws, and Metallic Drive Screws (Inch Series)
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 1891-2 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
reference panel
reference material that is to be exposed to check the corrosivity level of the test cabinet used for
fastener testing
4 General characteristics of the coating
4.1 Coating metals or alloys and main purposes
Electroplated coating systems for steel fasteners are primarily applied for corrosion protection and
functional properties, such as torque/clamp force relationship.
In addition, other functional properties or decorative properties can be specified; see Annex A.
ISO 4042:2022(E)
Commonly used electroplated coatings for fasteners are given in Table 1 along with their main
purpose(s). Additional information, such as designation or decorative aspects, can be found in other
relevant ISO standards listed in the last column of Table 1.
Table 1 — Electroplated coatings in accordance with their main purpose(s) and related
ISO standards
Coating metal(s) Main purpose
Nature of the coating ISO standard
Symbol Element
for fasteners
Zn Zinc Metal P/D/F —
ZnNi Zinc-nickel Alloy P/D/F ISO 15726
ZnFe Zinc-iron Alloy P/D/F ISO 15726
a
Cd Cadmium Metal P/F ISO 2082
Ni Nickel Metal D/F ISO 1456
Ni+Cr Nickel+chromium Multi-layer D ISO 1456
Cu+Ni Copper+nickel Multi-layer D ISO 1456
Cu+Ni+Cr Copper+nickel+chromium Multi-layer D ISO 1456
CuZn Brass Alloy D —
CuSn Copper-tin (bronze) Alloy F —
Cu Copper Metal F/D —
Ag Silver Metal F/D ISO 4521
CuAg Copper-silver Alloy F —
Sn Tin Metal F ISO 2093
SnZn Tin-zinc Alloy F/P —
P corrosion protection
F functional properties
D decorative properties (colour, aspect)
a
Cadmium is restricted or prohibited for many applications (remaining cadmium users are predominantly military and
aerospace industries).
4.2 Build-up of basic electroplated coating systems
Figure 1 shows basic electroplated coating systems.
ISO 4042:2022(E)
Key
1 only metal layer(s)
2 metal layer(s) + conversion coating
3 metal layer(s) + conversion coating + additional lubricant
4 metal layer(s) + conversion coating + sealant/top coat
5 metal layer(s) + conversion coating + sealant/top coat + additional lubricant
Figure 1 — Basic electroplated coating systems (schematic)
A conversion coating increases corrosion protection on zinc, zinc alloy and cadmium coatings. It may be
a passivation (chromium VI free) or a chromatation (chromium VI containing). The conversion coating
can also provide better adhesion for additional layer(s) and/or additional colour/paint.
An additional sealant/top coat (with or without integral lubricant) may be chosen to increase corrosion
resistance and/or to achieve other specific properties (e.g. torque/clamp force properties, resistance to
chemicals, mechanical resistance, aspect, colour, thermal stability, increased electrical resistance, UV
radiation resistance). The selection of the nature of a sealant or top coat should be based on the desired
additional properties.
An additional lubricant may be applied to adjust or amend the torque/clamp force relationship.
NOTE Electroplating is also applied on stainless steel fasteners, e.g. for the purpose of lubrication in order to
avoid galling.
4.3 Coating systems and coating processes
The type and geometry of the fastener should be considered when selecting a coating system and the
related coating process (see Annex A) as well as hydrogen embrittlement considerations (see Annex B).
The electroplating process shall be under control, in accordance with a recognized standard and/or a
specification by agreement with the purchaser. Recommendations for supplemental process verification
with regard to internal hydrogen embrittlement are given in 4.5 and B.4.
4.4 Internal hydrogen embrittlement
4.4.1 General
The three following conditions shall be concurrently present for fasteners to generate a risk of Internal
Hydrogen Embrittlement (IHE), see also Annex B:
— high tensile strength or high hardness, including case-hardening;
— tensile stress, including residual tensile stress;
— atomic hydrogen absorbed by the steel.
ISO 4042:2022(E)
The susceptibility to IHE increases with increasing hardness of the fastener. Appropriate measures for
prevention of IHE for quenched and tempered fasteners depending on hardness are specified in Table 2.
Table 2 and 4.4.2 to 4.4.4 provide the general guidelines for measures related to IHE as a function of
hardness.
The general guidelines of Table 2 are translated in 4.4.5 and 4.4.6 into normative requirements
applicable specifically to each type of fasteners in relation to its property class (see Tables 3 to 5) or its
core hardness (see Tables 6 and 7). These specific normative requirements are based on both hardness
and the degree of tensile stress experienced by each type of fasteners by its design and function.
Table 2 — Measures related to IHE for quenched and tempered fasteners
a
with regard to hardness
360 HV 390 HV
A B C
No supplemental process verification Supplemental process verification Supplemental process verification
or product testing and/or product testing and/or product testing
with regard to IHE with regard to IHE with regard to IHE
AND OR AND
Baking
No baking necessary Baking (baking temperature and duration
shall be specified)
At the discretion of the
— —
fastener manufacturer
See 4.4.2 See 4.4.3 and B.6 See 4.4.4 and B.6
a
For fasteners work hardened to high hardness, see 4.4.7 and B.5.
4.4.2 Fasteners with hardness up to 360 HV
When electroplating quenched and tempered fasteners with specified maximum hardness up to 360 HV
(A in Tables 2, 3, 4 and 5), no supplemental process verification with regard to IHE and no baking are
necessary.
4.4.3 Fasteners with hardness above 360 HV and up to 390 HV
When electroplating quenched and tempered fasteners with specified maximum hardness above
360 HV and up to and including 390 HV (B in Tables 2, 3 and 5), at the choice of the fastener manufacturer
baking is not required provided supplemental process verification and/or product testing with regard
to IHE have been performed.
For fasteners in this specified hardness range, electroplating does not pose a risk of IHE. In case of a
failure in a product test, it cannot be assumed that baking the parts would have prevented such failure:
the metallurgical and physical conditions of the fastener material should be investigated for non-
conformances. For more information, see B.2 and B.4.
4.4.4 Fasteners with hardness above 390 HV
When electroplating quenched and tempered fasteners with specified maximum hardness above
390 HV (C in Tables 2 and 3), baking is required; see B.4 for minimum recommended baking temperature
and duration.
The following exemptions apply:
— for fasteners which are not specified to be under tensile stress by design or standard (e.g. set screws
in accordance with ISO 898-5), baking is not required (see B.2);
ISO 4042:2022(E)
— induction hardened ends (e.g. for thread forming screws) shall not be considered for determining
measures related to IHE in relation to Table 2, because they are normally not subjected to tensile
stress provided that the end protrudes through the mating thread;
— alkaline zinc-nickel electroplatings with nickel content of 12 % to 16 % present a lower risk of IHE
(see B.3), therefore it is possible to avoid baking; the decision to not carry out baking shall be based
on testing (see B.6) and be agreed between the supplier and the purchaser.
NOTE 1 Alkaline zinc-nickel electroplating processes with typical nickel content of 12 % to 16 % are also
known as “low hydrogen embrittlement” processes (LHE) in the aerospace industry, see B.3.
NOTE 2 For acid zinc-nickel electroplatings, studies have shown similar benefits as for alkaline zinc-nickel
electroplatings, however more data are necessary to confirm baking avoidance.
4.4.5 Fasteners in accordance with ISO 898-1, ISO 898-2 and ISO 898-3
For fasteners in accordance with ISO 898-1, ISO 898-2 and ISO 898-3, Tables 3, 4 and 5 apply.
Table 3 — Measures related to IHE for fasteners in accordance with ISO 898-1
Property class < 10.9 10.9 12.9/12.9
A B C
No supplemental process Supplemental process Supplemental process
verification or product verification and/or product verification and/or product
testing with regard to IHE testing with regard to IHE testing with regard to IHE
Measures related
AND OR AND
to IHE
a, b
No baking necessary Baking Baking
At the choice of the fastener
— —
manufacturer
See 4.4.2 See 4.4.3 and B.6 See 4.4.4 and B.6
a
For alkaline zinc-nickel electroplatings with nickel content of 12 % to 16 %, the decision to not carry out baking shall
be based on testing (see B.6) and be agreed between the supplier and the purchaser.
b
For baking temperature and duration, see B.4.
Table 4 — Measures related to IHE for nuts in accordance with ISO 898-2
Property class ≤ 12
A
No supplemental process verification
or product testing with regard to IHE
Measures related to IHE
AND
a, b
No baking necessary
See 4.4.2
a
Investigations have shown that tensile stress in critical areas of nuts (including nuts with flange) is
always lower than tensile stress in the thread of the mating bolts, screws or studs with corresponding
property class (see measures related to IHE in Table 3); nuts in accordance with ISO 898-2 (all property
classes) always have a hardness less than 390 HV, therefore baking is not necessary.
b
For all-metal prevailing torque nuts of property classes 10 and 12, supplemental process
verification or baking is required, at the choice of the manufacturer.
ISO 4042:2022(E)
Table 5 — Measures related to IHE for flat washers in accordance with ISO 898-3
Property class ≤ 300HV 380HV
A B
No supplemental process verification Supplemental process
or product testing verification and/or product
with regard to IHE testing with regard to IHE
AND OR
Measures related to IHE
a b
No baking necessary Baking
At the choice of the
—
fastener manufacturer
See 4.4.2 See 4.4.3
a
When flat washers of property class 300HV are to be used in special applications (e.g. enlarged or slotted holes) where
bending stress may be present, baking may be necessary and shall be required by the purchaser at the time of the order. For
baking temperature and duration, see B.4.
b
When flat washers of property class 380HV are to be used in special applications (e.g. enlarged or slotted holes) where
bending stress may be present, baking is necessary and shall be required by the purchaser at the time of the order. For
baking temperature and duration, see B.4.
4.4.6 Case-hardened fasteners
Fasteners where the surface is intentionally case-hardened to fulfil specific function(s) include:
— tapping screws (see ISO 2702),
— thread-forming screws for metallic materials,
— self-drilling screws (see e.g. ISO 10666),
— screws for soft materials (e.g. plastic, wood).
Measures related to IHE for case-hardened screws are based on core hardness, which has the most
significant effect on IHE susceptibility (see B.3).
Case-hardened screws are grouped into two different categories, a) and b).
a) Case hardened screws not designed for high clamp force
This category includes tapping screws and self-drilling screws with thread according to ISO 1478,
screws for soft materials, etc.
As these screws are typically not designed for high clamp force, the risk of IHE is significantly reduced.
Measures related to IHE for this category are specified in Table 6.
NOTE Non-threaded case-hardened fasteners not subjected to tensile stress by design (such as pins or
washers) do not need special measures related to IHE, unless specifically agreed between the purchaser and the
manufacturer for a particular application.
b) Case hardened and tempered screws intended to be preloaded
This category includes case-hardened and tempered screws that form ISO metric mating threads
according to ISO 965-1 and other case-hardened and tempered thread-forming or self-drilling screws
intended to be preloaded.
Measures related to IHE for this category are specified in Table 7.
ISO 4042:2022(E)
Table 6 — Measures related to IHE for case-hardened screws
typically not designed for high clamp force
Core
≤ 360 HV > 360 HV and ≤ 390 HV > 390 HV
hardness
Supplemental process Supplemental process Supplemental process
verification with regard to IHE verification with regard to IHE verification with regard to IHE
OR AND AND
a
Product testing Baking
Measures
related to IHE
OR Product testing AND
and/or baking
Product testing for each
Baking
b
manufacturing lot
At the choice of the fastener manufacturer —
a
For baking temperature and duration, see B.4.
b
For alkaline zinc-nickel electroplatings with nickel content of 12 % to 16 %, product testing shall be considered as part
of in-process control (not mandatory for each manufacturing lot).
Table 7 — Measures related to IHE for case-hardened and tempered screws
intended to be preloaded
Core
≤ 360 HV > 360 HV and ≤ 390 HV > 390 HV
hardness
Supplemental process Supplemental process Supplemental process
verification with regard to IHE verification with regard to IHE verification with regard to IHE
OR AND AND
a a
Product testing Baking Baking
Measures
OR AND
related to IHE
Baking Product testing for each

b
manufacturing lot
At the choice of the fastener Product testing solely at the
—
manufacturer manufacturer’s choice
a
For baking temperature and duration, see B.4.
b
For alkaline zinc-nickel electroplatings with nickel content of 12 % to 16 %, product testing shall be considered as part
of in-process control (not mandatory for each manufacturing lot).
When product testing with regard to IHE is performed on case-hardened screws, it shall be in
accordance with ISO 15330 or ASME B18.6.3; see also B.6.
4.4.7 Work hardened fasteners and fasteners with threads rolled after heat treatment
For fasteners not intended to be quenched and tempered that are work hardened to high hardness
resulting in high residual stress, stress relief prior to electroplating may be necessary. See B.5.
For fasteners with threads rolled after heat treatment (i.e. after quenching and tempering), the
measures in Table 3 for fasteners in accordance with ISO 898-1 shall apply without modification, as a
local increase of surface hardness by work hardening combined with residual compressive stress have
no negative impact on susceptibility to IHE.
ISO 4042:2022(E)
4.4.8 Fasteners with bainitic structure
Fasteners with bainitic structure are not addressed in 4.4. A written agreement between the supplier
and the purchaser with regard to IHE is necessary.
4.5 Baking
When baking is performed, baking conditions including temperature and duration shall be based on
fastener material properties, electroplating process, and coating material. See B.4 for more detailed
guideline/recommendations.
Baking is usually performed before application of a conversion coating and/or before application of an
additional sealant/top coat. In case of passivation (with or without sealant) and depending on baking
temperature, baking in the passivated and/or sealed condition may be suitable provided corrosion
resistance is not impaired.
NOTE With proper care, many steel fasteners are electroplated without baking by correlating process
conditions and coating material to the susceptibility of the fastener material to hydrogen embrittlement, and
by applying adequate process control procedures. DIN 50969-2 and ASTM F1940 are recognized methods
for process control to evaluate the risk of IHE. These or other similar test methods are used as the basis for
determining if baking is required.
However, prevention of the risk of IHE does not only depend on baking (see 4.4 and Annex B).
5 Corrosion protection and testing
5.1 General
The corrosion protection of an electroplated coating system depends to a considerable extent on the
thickness of the metal layer(s). Conversion coatings and/or sealants and/or top coats on zinc, zinc-iron,
zinc-nickel and cadmium coatings provide protection against coating metal corrosion (formation of
white corrosion), thus providing additional protection against basis metal corrosion.
Metallic coatings such as zinc, zinc alloys and cadmium are less electropositive than the steel basis
metal, which is the condition to provide cathodic protection. In contrast, metals more electropositive
than the steel basis metal (e.g. nickel, copper, silver) cannot provide cathodic protection, which can
intensify corrosion of the fastener if the coating is damaged or pitted.
The frequency and duration of wetting and service temperatures, contact with corrosive chemicals,
and contact with other metals and materials (galvanic corrosion/contact corrosion), can influence the
protective performance of coatings.
Corrosion resistance is a product characteristic that can be reduced as a consequence of the following
factors:
— physical damage to the coating from handling and transportation, and
— oxidation of the coating or reaction with the environment during transportation and storage.
Before selecting a coating system, all functions and conditions of the assembly should be considered
and not just the fastener; see Annex A. An appropriate choice for a given application should be made
between the purchaser and the fastener supplier and/or the coater and/or the chemical supplier.
Corrosion resistance in accelerated corrosion tests (e.g. neutral salt spray test, sulfur dioxide test)
cannot be directly related to corrosion protection behaviour in service environments. However,
accelerated tests are commonly used to evaluate the corrosion resistance of the coating system.
ISO 4042:2022(E)
5.2 Neutral salt spray test (NSS) for zinc-based coating systems
The neutral salt spray test (NSS) in accordance with ISO 9227 is used to evaluate the corrosion
resistance of the coating system.
When evaluation of the cabinet corrosivity is requested, it should be performed in accordance with
Annex E.
The NSS test in accordance with ISO 9227 shall be used to monitor the consistency of the process by
quantifying corrosion resistance on sample
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