低合金鋼の水素誘起き裂進展加速とき裂の開口状態について

抄録

Crack propagation rate of SCM440H low alloy steel under long term varying load is enhanced by absorbed hydrogen. Substantial acceleration of crack propagation rate up to 100 times was observed. Macroscopic approach to examine the role of hydrogen on the acceleration was investigated by changing loading condition and charging condition. (1) The predominant fracture mode of hydrogen charged material showing acceleration was quasi cleavage. The application of stress prior to hydrogen charge prevented the quasi cleavage cracking in the following hydrogen-charged condition. This suggests that hydrogen restrained blunting of crack tip, which resulted in relatively higher stress state in hydrogen charged material. The higher stress state caused quasi cleavage and acceleration of crack propagation. (2) The crack opening displacement (COD) was measured on hydrogen charged material and uncharged material. COD was smaller in hydrogen charged material. The stress for the onset of non-linear deformation in stress-COD relation was higher in hydrogen charged material. These examinations suggested that the mechanistic role of hydrogen is to prevent the blunting of crack tip and bring about higher stress field near the crack tip.