THE SUSCEPTIBILITY TO THE HYDROGEN EMBRITTLEMENT OF LOW-ALLOY CR AND CRMO STEELS

Low alloy Or and CrMo steels have been studied to determine their susc eptibility to hydrogen embrittlement. The steels were quenched at a co nstant cooling rate of 30 Ks(-1) and tempered at 673 and 973 K. Hydrog en charging of steels was carried out in 0.5 M H2SO4 solution without and with addition of propargylic alcohol as corrosion inhibitor. In sp ite of the current density of 2-3 mA cm(-2) and the applied load of 40 % yield strength was found that the steels tempered at 673 K were high ly sensitive to hydrogen embrittlement. The steels tempered at 973 K s howed significantly higher resistance to hydrogen embrittlement. In sp ite of higher strength, the CrMo steel showed higher resistance to hyd rogen embrittlement than the Or steel. The fracture of steels was init iated at the second phase particles followed by transgranular fracture from iron carbide or iron-manganese sulphide inclusions. Since the in clusion distributions are similar in both steels, the enhanced resista nce of CrMo steel to hydrogen embrittlement is due to finer prior aust enite grain and presence of Mo2C in the ferrite matrix. With the addit ion of propargylic alcohol in 0.5 M H2SO4 solution the resistance of s teels to hydrogen embrittlement was increased and fracture surface sho wed mostly dimple fracture.