In this study, the phenomenon of hydrogen-induced delayed fracture of two cold-rolled DP980 steels with different chemical compositions was studied. The results show that the microstructure of both steels is… Click to show full abstract
In this study, the phenomenon of hydrogen-induced delayed fracture of two cold-rolled DP980 steels with different chemical compositions was studied. The results show that the microstructure of both steels is composed of ferrite matrix, martensite-austenite islands and small amount of bainite. DP980-1 having higher contents of C and Si exhibits higher tensile strength, lower yield strength and higher elongation in comparison with DP980-2 having lower contents of C and Si. According to the results of slow strain rate tensile tests, the tensile strength of DP980-1 after hydrogen charging is reduced by 20.8%, while it is just 5.4% for DP980-2. Moreover, very fine dimples can still be observed in the fracture surface of DP980-2 after hydrogen charging, which indicates a good ductile. The main reasons leading to the better delayed fracture resistance of DP980-2 are the lower volume fraction of martensite-austenite islands, lower content of diffusible hydrogen and the grain refinement effects.
               
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