In recent years, industrial demands for superior mechanical properties of powder metallurgy steel components with low cost are rapidly growing. Sinter hardening that combines sintering and heat treatment in continuous one step is cost-effective. The cooling rate during the sinter hardening process dominates material microstructures, which finally determine the mechanical properties of the parts. This research establishes a numerical model of the relation between various cooling rates and microstructures in a sinter hardenable material. The evolution of a martensitic phase in the treated microstructure during end quench tests using various cooling media of water, oil, and air is predicted from the cooling rate, which is influenced by cooling conditions, using the finite element method simulations. The effects of the cooling condition on the microstructure of the sinter hardening material are found. The obtained limiting size of the sinter hardening part is helpful to design complicate shaped components.

This research mainly focuses on the development of sinter brazing technology for improving the process related to belt pulley made by sinter hardening. As the machine process of belt pulley takes up more than half of the total manufacturing hours, we propose changing the process to pulley groove brazed and bonded with pulley disc by applying sinter brazing to belt pulley. With the new process, the belt pulley is expected to reduce manufacturing cost to 70% of the original process by applying the sinter brazing technology; and the belt pulley bound by sinter brazing only loses 10% bonding strength compared with the original process.

A CCT diagram for Cr-Mo prealloyed sintered steels suitable for sinter hardening was established by combining dilatometry data, microstructural studies and microhardness measurements of the material. CCT diagrams deepen the understanding of material properties after sinter hardening and support the design of materials on an industrial scale by providing information about required cooling rates for successful sinter hardening of these materials.

In all conventional sintered PM products, the pores present are of two types, primary and secondary. Primary pores forming during compaction and latter during sintering, due to penetration of formed liquid through the matrix grain boundary. Effect of carbon addition on diffusion of Cu in SH737-2Cu system was investigated. After compaction and transient liquid phase sintering at and , samples were characterized for densification, showing rise in sintering density and reduction in swelling on carbon addition. Quantitative microstructural characterization (shape factor and pore size) revealed bimodal distribution for 0% carbon, more rounded pores for 0.9% carbon and higher sintering temperature, and pore coarsening at higher sintering temperature.

Dimensional precision is a critical parameter in net shape processing of ferrous PM components. Sinter-hardening alloys undergo a transformation from austenite to martensite. Martensite formation expands the sintered compact, while tempering hardened steels results in shrinkage. In addition, martensitic regions with high Cu and C contents may contain large amounts of retained austenite. The presence of martensite and retained austenite, in addition to the tempering step, all play a role in the final dimensions of a component. This paper investigates the dimensional and microstructural changes to two sinter-hardening grades through different post-sintering thermal treatments.

The mechanical properties of ferrous powder metallurgy (P/M) materials are directly related to their microstructure. Ferrous P/M materials with sufficient hardenability will develop microstructures containing significant percentages of martensite in the as-sintered condition. Recently, sinter-hardening has developed into a highly cost effective production method through hardened P/M parts without the need for additional heat-treatments. This paper reviews the advances of sinter-hardening as well as some key processing parameters such as sintering temperature, cooling rate, tempering required to produce high quality sinter-hardened components. Specific topics including effect of alloying elements, alloying methods, and the Characterization and observation of microstructure are discussed.