Hydrogen Embrittlement Resistance of High Strength 9260 Bar Steel Heat Treated by Quenching and Partitioning

The influence of microstructure on hydrogen embrittlement of high strength steels for fastener applications is explored in this study. Space limiting applications in areas such as the automotive or agricultural industries provide a need for fasteners to have higher strengths than is typically allowed, though hydrogen embrittlement susceptibility typically increases with strength. Using a 9260 steel alloy, the influence of retained austenite presence, stability, and volume fraction in a martensitic matrix is evaluated with microstructures generated via quenching and partitioning. X-ray diffraction and scanning electron microscopy are used to assess the influence of retained austenite stability and volume fraction in the matrix with different quenching parameters. Initial quench temperatures are from 160 ºC up to 220 ºC and a constant partitioning temperature of 290 ºC is employed for all quenched and partitioned conditions. The target hardness for all testing conditions is 52-54 HRC. Slow strain rate tensile and incremental step load tensile testing is conducted with cathodic hydrogen pre-charging on circumferentially notched tensile specimens to evaluate hydrogen embrittlement susceptibility of these various microstructures.