Tempering of 3Cr–0·5Mo sintered steel: influence on mechanical properties

Abstract

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 650uC 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 650uC for 30 min resulted in a significant increase of impact energy (17 J), while the hardness remained the same. Tempering at 400uC for 2 h led to temper embrittlement and hence the lowest impact properties.

Microstructural Investigation and Impact Strength of Sinter-Hardened PM Steels: Influence of Ni Content and Tempering Temperature

“…As PM steels are often alloyed with high C content to increase apparent hardness, a post-sintering tempering treatment is necessary to restore their mechanical properties [20][21][22][23][24]. The specific tempering temperature is crucial and can be related to several factors, including C content, targeted mechanical properties (e.g., tensile, fatigue, impact or tribological resistance) and hardness.…”

“…Chagnon and Gagnè [22] evaluated the effect of tempering temperature on the tensile properties, apparent hardness, impact energy and microstructure of two PM materials tempered for 60 min at temperatures ranging from 150 • C to 600 • C. They observed a reduction in apparent hardness, due to the formation of cementite, for samples tempered in the range of 200-400 • C. In the as-sintered condition, the low ultimate tensile strength (UTS) values were related to the brittleness of untempered martensite, while the highest yield strength (YS) was measured after tempering at 300 • C, and resulted from the complete transformation of retained austenite into bainite. More recently, Hatami et al [23] sought to improve the low toughness of a pre-alloyed 3Cr-0.5Mo PM steel using tempering treatments performed at 200 • C, 400 • C, 550 • C and 650 • C for different times. The best combination of hardness, toughness and tensile strength was found for a tempering route of 200 • C for 1 h, while the highest elongation and impact strength were obtained after tempering at 650 • C for 30 min.…”

Euromat 2011: powder synthesis and processing for controlled microstructure

“…The other papers report the use of MA to develop special materials such as aluminium base composites3 and steels with nanostructured features 4. Two contributions focus on the development and optimisation of low alloyed steels, one using the master alloy approach5 and the second employing heat treatments 6. Finally, there is space to consider additive technologies such as selective laser melting, in this case for titanium base materials,7 and metal injection moulding,8 through a review of materials that present difficulties in the context of manufacturing by this technology (i.e.…”