Effect of Cold Rolling on Resistance of Ni-Fe Alloys to Hydrogen Cracking

Low carbon 10-19% Ni-Fe alloys become considerably more resistant to hydrogen cracking after severe cold rolling. The observed resistance decreases with increasing carbon content. The improvement is directional, the optimum effect applying to specimens stressed parallel to the rolling direction. Other iron alloys, e.g., 15.1% Co-Fe, martensitic 18-8 stainless steel, 7.5% Mn-Fe, 19.8% Cr-Fe, 0.2% Cu-Fe alloys, in that order, also show a directional improvement conferred by cold rolling. For a cold rolled 19% Ni-Fe alloy of maraging composition, alloyed Co has no effect, but alloyed Mo, Al, or Ti decrease resistance. Pure carbon steels are markedly susceptible to hydrogen cracking indicating that susceptibility of commercial steels is not caused by normal impurities and inclusions. The mechanism of hydrogen cracking is related to microvoids at the interface of precipitate particles and plastically deformed metal which perform as crack nuclei. Cold rolling presumably aligns such nuclei accounting for greater resistance of specimens stressed parallel to the rolling direction.