1997 年 37 巻 4 号 p. 412-418
Low alloy Cr and CrMo steels have been studied to determine their susceptibility to hydrogen embrittlement. The steels were quenched at a constant cooling rate of 30 K s-1 and tempered at 673 and 973 K. Hydrogen charging of steels was carried out in 0.5 M H2SO4 solution without and with addition of propargylic alcohol as corrosion inhibitor. In spite 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 highly sensitive to hydrogen embrittlement. The steels tempered at 973 K showed significantly higher resistance to hydrogen embrittlement. In spite of higher strength, the CrMo steel showed higher resistance to hydrogen embrittlement than the Cr steel. The fracture of steels was initiated at the second phase particles followed by transgranular fracture from iron carbide or iron-manganese sulphide inclusions. Since the inclusion distributions are similar in both steels, the enhanced resistance of CrMo steel to hydrogen embrittlement is due to finer prior austenite grain and presence of Mo2C in the ferrite matrix. With the addition of propargylic alcohol in 0.5 M H2SO4 solution the resistance of steels to hydrogen embrittlement was increased and fracture surface showed mostly dimple fracture.
