Effect of Tempering Temperature after Thermo-Mechanical Control Process on Microstructure Characteristics and Hydrogen-Induced Ductility Loss in High-Vanadium X80 Pipeline Steel

Abstract

In this study, an optimum tempering temperature after a thermo-mechanical control process (TMCP) was proposed to improve the hydrogen-induced ductility loss of high-vanadium X80 pipeline steel. The results showed that with increasing tempering temperature from 450 to 650 °C, the size and quantity of granular bainite decreased but the spacing of deformed lath ferrite and the fraction of massive ferrite increased. The number of fine vanadium carbides increased as well. However, as the tempering temperature increased to 700 °C, the microstructure of T700 steel completely converted to massive ferrite and the grain size became larger. Additionally, the amount of nanoscale precipitates decreased again, and the mean size of precipitates evidently increased in T700 steel. The steel tempering at 650 °C, containing the most vanadium precipitates with a size less than 20 nm, had the lowest hydrogen diffusion coefficient and the best resistance to hydrogen-induced ductility loss.

Microstructure design strategies to mitigate hydrogen embrittlement in metallic materials

“…The effectiveness of different microstructural approach in enhancing the HE resistance, characterized by (A) the induced improvement of the tensile ductility in the presence of H, and (B) the induced improvement of the H embrittlement index. The data cover a variety of materials (mainly steels) including pure iron, 78 low-alloy martensitic steels, 19,[79][80][81] pipeline steels, 82,83 various advanced highstrength steels (AHSS), [84][85][86][87][88][89][90][91][92][93] maraging steels, 94 various austenitic stainless steels, [95][96][97][98][99] and high entropy alloys (HEAs). 10,11 The literature also covers testing conditions under different H atmospheres including electrochemical and gas pre-charging or in situ charging.…”