The harder the steel, the less hydrogen it takes to crack it. ASTM F1941 makes baking mandatory where the specified hardness is over 39 HRC. Alloy socket head cap screws (ASTM A574) are 39 to 44 HRC up to 1/2 in. and 37 to 44 HRC above, so plating them calls for the bake; their standard black oxide finish needs no embrittlement testing. B7 studs and 2H nuts, at 35 HRC maximum, are below that line, so baking is not mandatory for them under F1941.
Baking reduces the risk; it cannot fully remove it. ASTM F1941 does not recommend electroplating case-hardened fasteners or fasteners harder than 39 HRC at all.
Read the full hydrogen embrittlement testing page →
model dataScrews drawn as ASTM A574 1/2 in. socket head cap screws to ASME B18.3 proportions, with an unthreaded length under 2D, so ASTM F606 Table 7 calls for the 4° wedge. Hardness and minimum tensile strength from ASTM A574 Table 1; bake temperature and times from ASTM F1941 Table 4, and the 4-hour limit from ASTM B633; the sustained-load test and its pass criteria from ASTM F606; process-control tests ASTM F1940 and F519. Hydrogen atoms are drawn hugely enlarged in a magnified cut-away and the zinc layer is exaggerated; the oven reading, the hours counters and the retightening ratio are for illustration.
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