Carbide precipitation and hydrogen embrittlement susceptibility of a 960 MPa grade ultra-high strength steel

Abstract

ABSTRACT Carbide precipitation and hydrogen embrittlement susceptibility of a 960 MPa grade ultra-high strength low carbon low alloy steel processed by quenching and tempering (Q-T) via different reheating routes (conventional air furnace and high frequency induction) were investigated. After tempering at 600°C via both methods, carbides precipitated along the prior austenite grain boundaries and within the matrix lath. It was observed that dispersed carbides in induction tempered (Q&IT) sample were finer and more spheroidized than those in conventional tempered (Q&CT) sample, resulting in superior mechanical properties of strength, ductility and hydrogen embrittlement susceptibility resistance of Q&IT sample. Moreover, slow strain rate tests (SSRT) revealed that RFS (reduction of the fracture stress) was decreased from 0.16 for CT sample to 0.07 for IT sample. Fractography after SSRT indicated that CT sample exhibited a fracture surface with a few small dimples, whereas, IT sample presented a fracture surface with many large dimples.