Microstructure and mechanical properties of powder metallurgy sinter hardening steels with low Cr content

Sinter hardening is an established cost-effective process to produce high strength powder metallurgy parts by controlling the cooling speed to affect the sintered microstructure (martensite content) to improve the final performance. A newly developed pre-alloy sinter hardening steels with low Cr content (Astaloy^TM CrA) was introduced in this paper, the mechanical properties and microstructure under the different sintering temperature and cooling rate were investigated, and the common powder metallurgy sinter hardening material (Distaloy^® DH) was referenced for the comparison. In the results, under the pressing density of 7.0 g·cm⁻³ at the same carbon level, the Astaloy^TM CrA added with 2% nickel (mass fraction) has the highest hardenability which can obtain the highest martensite content and the macro hardness compared to the other materials. Astaloy^TM CrA sintered at 1250 ℃ and followed with the cooling rate of 3 ℃·s⁻¹ can achieve the hardness of HRC 38, which can obtain the optimum strength and toughness by sintered at the same temperature and followed with the lower cooling rate of 1 ℃·s⁻¹.