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#012 Hydrogen Embrittlement - Baking Process - 4

Category : Hydrogen embrittlement
September18, 2009

(8) Standards regarding the baking process

(1) ISO standards

In ISO standards, hydrogen embrittlement relief of electro-galvanized steel is provisioned as follows.

Following heat treatment processes must be applied to certain steel alloys in order to reduce part breakage risks due to hydrogen embrittlement, if requested by customers. Additionally, conventional zinc electro-plating should not be applied to steel alloys with tensile strength higher than 1500N/mm2 (or hardness shown in note 1). For steel alloys with tensile strength higher than 1000N/mm2, it should be noted that proper heat treatment processes are required in order to reduce the hydrogen embrittlement breakage risks.
(Note 1: Hardness HRC45, HV440, HB415)

a. Stress relief before plating

Stress relieving heat treatments are necessary for parts made with steel alloys with tensile strength higher than 1000N/mm2 (or hardness shown in note 2) that have been: extensively cold worked, annealed, ground, or subjected to severe machining. (Note 2: Hardness HRC30, HV295, HB280)

b. Heat treatment processes after plating

Post-plating heat treating is necessary for parts that are expected to receive stress and/or static loadings, and for parts that are produced by severe cold working processes. (Table 1) below shows the guideline for heat treating conditions. For parts produced from case-hardened alloys that may be negatively affected by the heat treating guideline, processes with lower temperature at longer durations are required.

(Table 1) Guideline for heat treating steel alloy parts after plating
Tensile strength
Cross section thickness
Process time at 190-210 deg.C
1000〜115012 or less2 or more
12〜254 or more
25 or more8 or more
1150〜140012 or less4 or more
12〜2512 or more
25〜4024 or more, apply the process within 16 hours of plating.
40 or moreTo be derived by experimentations.

(2) JIS standards

The JIS standards also defines post-plating heat treatment references as shown in Table 2 below.

(Table 2) Heat treating guideline for stress relieving
Tensile strength of steel alloy (Mpa)Temp. (deg.C)Process time (h)
Before platingAfter plating
Up to 1000---
1051〜1450190-22018 or more
1451〜1800190-2201818 or more
Over 1800190-2202424 or more