Effect of hydrogen charging intensities and times on hydrogen embrittlement of Q&P980 steel

Abstract

Q&P steel has good development prospects because of its excellent mechanical properties, but with the improvement in strength grade, hydrogen-induced delayed fracture (HIDF) is almost inevitable. In this paper, slow strain rate tensile tests and deep-drawn cup tests of Q&P980 steel under different hydrogen charging strengths and times were carried out, and the microstructure and fracture morphology were analysed by SEM. The results show that the plastic loss of Q&P980 steel was more obvious with increasing hydrogen charging intensity and hydrogen charging time, and a good elongation of 6.63% is still retained under the hydrogen content of 2.134 ppm. The deep-drawn cup samples were placed in acidic distilled water and alkaline and acidic solutions, and only a deep-drawn ratio of 1.9 showed HIDF in the three solutions. Specifically, 12 cracks were observed after soaking in HCl solution for two days. The main reason is that the martensite, austenite island and ferrite phase interface of Q&P980 steel increase stress during deformation and with the transformation-induced plasticity (TRIP) effect, resulting in hydrogen segregation at the phase interface and crack initiation leading to HIDF.

Keywords

• Q&P steel
• slow strain rate tensile
• deep-drawn cup test
• hydrogen-induced delayed fracture
• TRIP effect