Tempered Martensitic Ni-Cr-Mo-V Steel: Microstructure Characterization and Mechanical Behavior
摘要
Manufacturing advanced high strength steels with tailored microstructure is necessary for attaining balanced strength-ductility-toughness in the automobile industries. In this research paper, an advanced high strength martensitic Ni-Cr-Mo-V steel was subjected to various tempering treatments. Different evolutions such as ferrite formation, stress relief/recovery, and precipitation would take place during tempering of martensitic structure. An increase in the hardness and strength was documented by tempering at 300 and 550 °C for 3 h. Nano-sized precipitates were responsible for this matter at 300 °C. Complex carbides along with boosted solid solution hardening in the ferritic matrix were the main reasons for this issue at 550 °C. Tempering at 300 °C for 3 h resulted in achieving the highest strength-ductility balance (19.0 ± 0.4 GPa%). Developed steels showed different failure behavior in the tensile and Charpy impact tests. Tempering at 300 °C for 3 h made maximum tensile toughness (183.0 ± 6.0 J/cm3). Charpy impact toughness was not greatly changed by tempering at 300 °C for 1 h (88 ± 3 J) and 3 h (90 ± 3 J) and also, 550 °C for 1 h (90 ± 6 J). However, an extraordinary improvement in the Charpy impact toughness (181 ± 4 J) was obtained once tempering was done at 550 °C for 3 h. The adverse phenomena of tempered martensite embrittlement and temper embrittlement were not seen in the tempered martensitic Ni-Cr-Mo-V steel. Lastly, failure mechanisms were considered based on the principles of fracture mechanics.