Effect of Quenching Temperature on Microstructure and Hydrogen-Induced Cracking Susceptibility in S355 Steel

S355 steels are widely used in various applications. However, they may be affected by hydrogen, which can induce hydrogen-induced cracking (HIC). The effects of the quenching temperature (T_wq) on the microstructure variation and HIC susceptibility of S355 steel was investigated by microstructural characterization, hydrogen permeation (HP) test, slow strain rate tensile (SSRT) test, hydrogen microprint technique (HMT) test, and hydrogen-charged cracking test. The results indicate that the microstructure of the treated specimens consisted of predominantly lath martensite (LM) and small amounts of lath bainite (LB) for the T_wq of 950 °C and 1000 °C, while the microstructure of the treated specimens mainly consisted of LM for the T_wq of 1050 °C and 1100 °C. The results indicate that as the T_wq increased, the sample treated at 950 °C exhibited a minimum hydrogen embrittlement index (I_z), while the sample treated at 1050 °C exhibited the maximum I_z. The hydrogen diffusion coefficient was relatively low, while the hydrogen concentration and trap density were relatively high for the T_wq of 1050 °C. The lath interfaces in martensite were effective hydrogen traps with high hydrogen-trapping efficiency. Hydrogen-induced cracks were significantly affected by hydrogen trapping at martensitic lath interfaces, exhibiting a basically transgranular fracture.