EN ISO 4042:2018

SLOVENSKI STANDARD
01-december-2018
1DGRPHãþD
SIST EN ISO 4042:2001
Mehanski vezni elementi - Sistemi galvanskih prevlek veznih elementov (ISO
4042:2018)
Fasteners - Electroplated coating systems (ISO 4042:2018)
Verbindungselemente - Galvanisch aufgebrachte Überzugsysteme (ISO 4042:2018)
Fixations - Systèmes de revêtements électrolytiques (ISO 4042:2018)
Ta slovenski standard je istoveten z: EN ISO 4042:2018
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
September 2018
EUROPÄISCHE NORM
ICS 21.060.01 Supersedes EN ISO 4042:1999
English Version
Fasteners - Electroplated coating systems (ISO 4042:2018)
Fixations - Systèmes de revêtements électrolytiques Verbindungselemente - Galvanisch aufgebrachte
(ISO 4042:2018) Überzugsysteme (ISO 4042:2018)
This European Standard was approved by CEN on 4 July 2018.

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, Former Yugoslav Republic of Macedonia, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania,
Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, 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
© 2018 CEN All rights of exploitation in any form and by any means reserved Ref. No. EN ISO 4042:2018 E
worldwide for CEN national Members.

Contents Page
European foreword . 3

European foreword
This document (EN ISO 4042:2018) 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 March 2019, and conflicting national standards shall
be withdrawn at the latest by March 2019.
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 4042:1999.
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, Former Yugoslav Republic of Macedonia,
France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta,
Netherlands, Norway, Poland, Portugal, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland,
Turkey and the United Kingdom.
Endorsement notice
The text of ISO 4042:2018 has been approved by CEN as EN ISO 4042:2018 without any modification.
INTERNATIONAL ISO
STANDARD 4042
Third edition
2018-08
Fasteners — Electroplated coating
systems
Fixations — Systèmes de revêtements électrolytiques
Reference number
ISO 4042:2018(E)
©
ISO 2018
ISO 4042:2018(E)
© ISO 2018
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.
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Phone: +41 22 749 01 11
Fax: +41 22 749 09 47
Email: copyright@iso.org
Website: www.iso.org
Published in Switzerland
ii © ISO 2018 – All rights reserved

ISO 4042:2018(E)
Contents Page
Foreword .v
Introduction .vii
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 2
4 General characteristics of the coating . 3
4.1 Coating metals or alloys and main purposes . 3
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 below 360 HV . 5
4.4.3 Fasteners with hardness equal to and 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 Baking and test requirements for case-hardened and tempered screws . 7
4.4.7 Work-hardened fasteners . 8
4.4.8 Fasteners with bainitic structure . 8
4.5 Baking . 8
5 Corrosion protection and testing . 8
5.1 General . 8
5.2 Neutral salt spray test (NSS) for zinc based coating systems . 9
5.3 Sulfur dioxide test (Kesternich test) .10
5.4 Bulk handling, automatic processes such as feeding and/or sorting, storage and
transport . .11
6 Dimensional requirements and testing .11
6.1 General .11
6.2 Fasteners with ISO metric thread .11
6.2.1 Coating thickness .11
6.2.2 Gaugeability and assemblability .12
6.3 Other fasteners .12
6.4 Test methods for thickness determination .13
7 Mechanical and physical properties and testing .15
7.1 General .15
7.2 Appearance .15
7.3 Corrosion resistance related to temperature .15
7.4 Torque/clamp force relationship .15
7.5 Determination of hexavalent chromium .15
8 Applicability of tests .15
8.1 General .15
8.2 Tests mandatory for each lot .15
8.3 Tests for in-process control.16
8.4 Tests to be performed when specified by the purchaser .16
9 Designation system .16
9.1 General .16
9.2 Designation of electroplated coating systems for the order .17
9.3 Examples of designation of hexavalent chromium free electroplated coating
systems for fasteners .18
9.4 Designation of fasteners with electroplated coating systems for labelling .19
10 Ordering requirements for electroplating .19
ISO 4042:2018(E)
11 Storage conditions .20
Annex A (informative) Design aspects and assembly of coated fasteners .21
Annex B (informative) Hydrogen embrittlement consideration .29
Annex C (informative) Corrosion protection related to zinc coatings with chromate
conversion coatings .33
Annex D (informative) Coating thickness and thread clearance for ISO metric screw threads .34
Annex E (informative) Coating systems tested in accordance with ISO 9227, NSS —
Evaluation of cabinet corrosivity for the neutral salt spray test .42
Annex F (informative) Obsolete designation codes for electroplated coating systems on
fasteners according to ISO 4042:1999 .51
Bibliography .54
iv © ISO 2018 – All rights reserved

ISO 4042:2018(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: www .iso .org/iso/foreword .html.
This document was prepared by Technical Committee ISO/TC 2, Fasteners, Subcommittee SC 14, Surface
coatings.
This third edition cancels and replaces the second edition (ISO 4042:1999), which has been technically
revised. The main changes compared to the previous edition are as follows:
— application to all fasteners, including self-tapping and thread forming screws, washers, rivets,
clips, etc.;
— focus on coatings designed for corrosion protection of fasteners;
— application to electroplated coating systems with or without additional layers (conversion coating,
sealant, top coat, lubricant);
— specification of minimum corrosion resistance (white corrosion and red rust);
— inclusion of up-to-date knowledge about hydrogen embrittlement and prevention measures;
— definitions specified in ISO 1891-2;
— concerning corrosion tests, inclusion of sulfur dioxide test (Kesternich) and calibration of neutral
salt spray test;
— inclusion of gaugeability and assemblability requirements;
— for thickness determination, addition of adequate test methods and deletion of the batch average
thickness;
— new designation system for all coating systems;
— specification for mechanical and physical properties and related test methods;
— information about design aspects and assembly of coated fasteners;
ISO 4042:2018(E)
— information for coating thickness and thread clearance for ISO metric screw threads;
— information about evaluation of cabinet corrosivity for the neutral salt spray test.
vi © ISO 2018 – All rights reserved

ISO 4042:2018(E)
Introduction
This document 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.
INTERNATIONAL STANDARD ISO 4042:2018(E)
Fasteners — Electroplated coating systems
1 Scope
This document specifies requirements for electroplated coatings and coating systems on steel
fasteners. 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 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.
This document applies to bolts, screws, studs and nuts with ISO metric thread, to fasteners with non-
ISO metric thread, and to non-threaded fasteners such as washers, pins, clips and rivets.
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.
NOTE Other International Standards specify differing electroplating processes. For electroplating of
fasteners, the requirements of this document apply, unless otherwise agreed.
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 2081, Metallic and other inorganic coatings — Electroplated coatings of zinc with supplementary
treatments on iron or steel
ISO 2082, Metallic and other inorganic coatings — Electroplated coatings of cadmium with supplementary
treatments on iron or steel
ISO 4042:2018(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 3231, Paints and varnishes — Determination of resistance to humid atmospheres containing sulfur dioxide
ISO 3497, Metallic coatings — Measurement of coating thickness — X-ray spectrometric methods
ISO 3613:2010, 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 6988, Metallic and other non organic coatings — Sulfur dioxide test with general condensation of
moisture
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 19598, Metallic coatings — Electroplated coatings of zinc and zinc alloys on iron or steel with
supplementary Cr(VI)-free treatment
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 terminological databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https: //www .iso .org/obp
— IEC Electropedia: available at http: //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
2 © ISO 2018 – All rights reserved

ISO 4042:2018(E)
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.
Table 1 shows commonly used electroplated coatings in relation with their main purposes and
references to related ISO standards, which give additional general information not covered by this
document, e.g. for designation. Some of the International Standards listed in Table 1 specify differing
electroplating processes. For the purpose of fasteners, the requirements of this document apply.
Table 1 — Electroplated coatings in accordance with their main purposes and related
ISO standards
Main purpose of
Coating metal(s) Nature the coating for ISO standard
fasteners
Symbol Element
Zn Zinc Metal P/D/F ISO 2081, ISO 19598
ZnNi Zinc-nickel Alloy P/D/F ISO 15726, ISO 19598
ZnFe Zinc-iron Alloy P/D/F ISO 15726, ISO 19598
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 Metal 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 4042:2018(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 alloys 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 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 desired
additional properties.
An additional lubricant may be applied to adjust or amend the torque/clamp force relationship.
4.3 Coating systems and coating processes
The type and geometry of the fasteners 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 customer.
4.4 Internal hydrogen embrittlement
4.4.1 General
If the three following conditions are concurrently present for fasteners:
— with high tensile strength or hardness or which have been case-hardened and tempered or cold
worked to high hardness,
— which are under tensile stress, and
— which have absorbed hydrogen,
there is a risk of Internal Hydrogen Embrittlement (IHE).
The susceptibility to IHE increases with increasing hardness of the fastener material. Appropriate
measures for prevention of IHE for quenched and tempered fasteners depending on hardness are
4 © ISO 2018 – All rights reserved

ISO 4042:2018(E)
specified in Table 2. For fasteners in accordance with ISO 898-1, ISO 898-2 and ISO 898-3, Tables 3, 4
and 5 apply.
Table 2 — Measures related to IHE for quenched and tempered fasteners with regard to
hardness
360 HV 390 HV
A B C
No supplemental process veri- Supplemental process verifica-
Supplemental process verification and/or
fication or product testing with tion and/or product tests with
product testing with regard to IHE
regard to IHE regard to IHE
OR
AND AND
No baking necessary Baking Baking
(at the choice of the fastener manufacturer) (baking temperature and dura-
tion shall be specified)
See 4.4.2 See 4.4.3 and B.6 See 4.4.4 and B.6
4.4.2 Fasteners with hardness below 360 HV
When electroplating fasteners with specified maximum hardness below 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 equal to and above 360 HV and up to 390 HV
When electroplating fasteners with specified maximum hardness equal to and above 360 HV and up to
and including 390 HV (B in Tables 2, 3, 4 and 5), baking is not required provided supplemental process
verification and/or product testing with regard to IHE have been performed. However, the purchaser is
free to require baking generally.
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.4.
4.4.4 Fasteners with hardness above 390 HV
When electroplating fasteners with specified maximum hardness above 390 HV (C in Tables 2, 3 and 5),
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),
— 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.
For alkaline zinc-nickel electroplatings (and nickel content from 12 % to 16 %), it is possible to avoid
baking because of low risk of IHE (see B.3). The decision not to carry out baking shall be based on
testing (see B.6) and be agreed between the supplier and the purchaser.
NOTE For acid zinc-nickel electroplatings, studies have shown similar benefits as for alkaline zinc-nickel
electroplating, however more data is necessary with regard to baking avoidance.
ISO 4042:2018(E)
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
Bolts, screws, studs in ac-
≤ 9.8 10.9 12.9 and 12.9
cordance with ISO 898-1
A B C
No supplemental process Supplemental process ver- Supplemental process ver-
verification or product ification and/or product ification and/or product
testing with regard to IHE testing with regard to IHE testing with regard to IHE
Measures related to IHE
AND OR AND
a
No baking necessary Baking Baking
Baking temperature and
At the choice of the fasten-
— duration shall be specified
er manufacturer
(see also B.4)
See 4.4.2 See 4.4.3 and B.6 See 4.4.4 and B.6
a
For alkaline zinc-nickel electroplatings (and nickel content from 12 % to 16 %), the decision not to carry out baking
shall be based on testing (see B.6) and be agreed between the supplier and the purchaser.
Table 4 — Measures related to IHE for nuts in accordance with ISO 898-2
Property class
≤ 12
Nuts in accordance with
Nuts with specified maximum Nuts with specified maximum
ISO 898-2
a
hardness < 360 HV hardness ≥ 360 HV
A B
No supplemental process verification Supplemental process verification
with regard to IHE
AND
Measures related to IHE
OR
No baking necessary
Baking
At the choice of the fastener
—
manufacturer
See 4.4.2 See 4.4.3
a
Only:
—  for regular nuts (style 1) with fine pitch thread, property class 10, and
—  for high nuts (style 2) with fine pitch thread, property class 12, and diameters above 16 mm.
6 © ISO 2018 – All rights reserved

ISO 4042:2018(E)
Table 5 — Measures related to IHE for flat washers in accordance with ISO 898-3
Property class
Flat washers in accord-
≤ 200HV 300HV 380HV
ance with ISO 898-3
A B C
No supplemental process Supplemental process veri- Supplemental process veri-
verification fication with regard to IHE fication with regard to IHE
Measures related to IHE
AND OR AND
a
No baking necessary Baking Baking
Baking temperature and
At the choice of the
— duration shall be specified
fastener manufacturer
(see also B.4)
See 4.4.2 See 4.4.3 See 4.4.4
a
For alkaline zinc-nickel electroplatings (and nickel content from 12 % to 16 %), the decision not to carry out baking
shall be based on testing (see B.6) and be agreed between the supplier and the purchaser.
4.4.6 Baking and test requirements for case-hardened and tempered screws
Case-hardened and tempered fasteners include self-tapping screws (see ISO 2702), thread-forming
screws for metallic materials, self-drilling screws (see ISO 10666) and screws for soft materials (e.g.
plastic, wood). The surface of these screws is usually intentionally hardened to fulfil their specific
functions.
The susceptibility to IHE of case-hardened and tempered screws depends not only on core hardness;
see B.3.
Requirements for case-hardened and tempered fasteners (except for self-tapping screws and screws for
soft materials) are specified in Table 6.
Requirements for self-tapping screws and screws for soft materials are specified in Table 7.
Testing with regard to IHE for case-hardened and tempered screws with core hardness above 370 HV
(C in Table 6) and for self-tapping screws above 390 HV (C in Table 7) shall be performed in accordance
with ISO 15330 or ASME B18.6.3.
Table 6 — Measures related to IHE for case-hardened and tempered screws
(except self-tapping screws and screws for soft materials)
Core hardness
≤ 370 HV > 370 HV
B C
Supplemental process verification with
regard to IHE
Supplemental process verification with
AND
regard to IHE
Measures related to IHE Baking
AND
AND
Product testing and/or baking
Product testing for each manufactur-
a
ing lot
At the choice of the fastener Baking temperature and duration shall
manufacturer be specified (see also B.4)
a
For alkaline zinc-nickel electroplatings (and nickel content from 12 % to 16 %), product testing shall be considered as
part of in-process control (not mandatory for each manufacturing lot).
ISO 4042:2018(E)
Table 7 — Measures related to IHE for self-tapping screws and screws for soft materials
Core hardness
≤ 390 HV > 390 HV
B C
Supplemental process verification with
regard to IHE
Supplemental process verification with
AND
regard to IHE
Measures related to IHE Baking
AND
AND
Product testing and/or baking
Product testing for each manufactur-
a
ing lot
At the choice of the fastener Baking temperature and duration shall
manufacturer be specified (see also B.4)
a
For alkaline zinc-nickel electroplatings (and nickel content from 12 % to 16 %), product testing shall be considered as
part of in-process control (not mandatory for each manufacturing lot).
4.4.7 Work-hardened fasteners
For fasteners work-hardened to high hardness resulting in residual stresses and not intended to be
quenched and tempered, see B.5.
Table 3 for fasteners with ISO metric thread shall apply regardless of thread rolling before or after
heat treatment: a local increase of surface hardness by work-hardening has no negative impact on
susceptibility to IHE.
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/advice.
Baking is usually performed before application of a conversion coating and/or before application of an
additional sealant/top coat. In case of passivations (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. Methods according to DIN 50969-2 or ASTM F1940 are recognized
investigation methods for process control to minimize the risk of IHE. These or other similar test methods can be
used as the basis for specifying baking requirements in a controlled process.
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/top coats on zinc, zinc-iron, zinc-
8 © ISO 2018 – All rights reserved

ISO 4042:2018(E)
nickel and cadmium coatings provide protection against coating metal corrosion (formation of white
corrosion), thus providing additional protection against basis metal corrosion.
Coatings of 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 considered to be a product characteristic that can be altered 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.
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 fasteners taken periodically from the electroplating
process (i.e. in-process control). For these reasons, the NSS test shall be carried out on sample fasteners
in the “as-coated” condition.
The “as-coated” condition is defined as the condition after completion of all steps of coating (including
application of any sealant, top coat or lubrication) without the occurrence of deterioration from the
factors listed in 5.4, i.e. before any sorting, packaging, assembling, transportation or storage.
NOTE 1 Customers or end-users often wish to separately use the NSS test as a reference to evaluate corrosion
resistance as a “performance characteristic” and/or for supplier monitoring. In such cases, corrosion resistance
is evaluated on sample fasteners in the “as-received” condition, i.e. after the occurrence of deterioration from
sorting, packaging, assembling, transportation and/or storage; in these cases, it is not appropriate to use the
minimum neutral salt spray test duration in Table 8. Rather, the values in Table 8 serve as a starting basis to
evaluate corrosion resistance in the as-received condition, taking into account factors that cause deterioration of
the corrosion resistance. See 5.4.
The neutral salt spray test duration specified in Table 8 for coating systems with Cr(VI)-free passivation
shall apply for fasteners alone, tested no sooner than 24 h after coating and in the “as-coated” condition.
For neutral salt spray test duration of zinc coating systems with chromate conversion coatings, see
Annex C.
Contact points of the fastener with a holding fixture, if any, shall not be considered in the evaluation of
the corrosion test.
Fasteners with a captive washer have areas between the mating fastener and the washer with less
coating thickness due to intrinsic electrochemical deposition behaviour; this is similar for fasteners
ISO 4042:2018(E)
with blind holes. Both result in reduced corrosion resistance in these areas during the corrosion test
and should not be cause for rejection. In service, these areas are not normally exposed to environmental
corrosion.
NOTE 2 For fasteners intended to be subjected to a high level of plastic deformation after coating (crimping,
riveting, etc.), corrosion resistance is reduced in the deformed area.
Table 8 — Corrosion resistance for commonly used zinc and zinc alloy coating systems
Minimum neutral salt spray test duration for
a
barrel coating
hours
Zinc based coating system Code No basis metal corrosion
(red rust)
No coating
(see Table 11)
metal corrosion
Coating thickness
(white corrosion)
5 µm 8 µm 12 µm
b
Zn, transparent passivated Zn//An/T0 8 48 72 96
b
Zn, iridescent passivated Zn//Cn/
...