Tempering of 3Cr–0.5Mo sintered steel: influence on mechanical properties

Prealloyed 3Cr–0.5Mo steel powder (FL-5305) is considered as an outstanding sinter hardenable grade. Although the FL-5305 powder, at conventional sintering conditions, renders excellent tensile strength, yield stress and hardness, it suffers from low toughness. In this study, with the aim of increasing toughness without a considerable loss of hardness, different tempering treatments have been evaluated. To this end, tempering treatments have been performed at 200, 400, 550 and 650°C for different times. The influence of tempering on hardness, tensile properties as well as impact energy has been investigated. As compared to the hardness (20 HRC) and impact energy (14 J) of a conventionally sintered material, sinter hardening plus tempering at 650°C for 30 min resulted in a significant increase of impact energy (17 J), while the hardness remained the same. Tempering at 400°C for 2 h led to temper embrittlement and hence the lowest impact properties