Effect of Tempering Temperature on Sintered Properties of Sinter Hardened PM Steels

Abstract

The development of low alloy steel powders specifically designed for sinter hardening applications enables components to reach high sintered strength and apparent hardness in sintering furnaces equipped with either conventional or rapid cooling units. By adjusting the mix formulation, the sintered properties can be tailored to optimise both strength and apparent hardness. As untempered martensite is a fragile structure, sinter hardened parts are generally given a tempering treatment to restore strength and improve toughness. However, this treatment also affects the apparent hardness of PM parts. A study was carried out to evaluate the effect of tempering temperature on mechanical properties of sinter hardened steels containing 2% copper and either 0·65 or 0·80% carbon. Testpieces were pressed to 6·8 g cm⁻³ and sintered at 1120°C in a production furnace equipped with a conventional cooling unit. Three tempering temperatures, 150, 175, and 205°C, were selected for the test programme. A reduction in apparent hardness of about 10HRC (85 HV) was observed after tempering at 150°C but tensile properties were significantly increased, particularly at high carbon concentration. PM/0788