Chromium-Alloyed PM Steels with Excellent Fatigue Properties Obtained by Different Process Routes
EURO PM2003, in Valencia, Spain. Author: Ola Bergman. Chromium is an attractive alloying element in steels due to its positive effect on the hardenability, its low cost and environmental benefits. These advantages are utilised in two recently developed pre-alloyed water-atomised PM grades. Astaloy CrL, which contains 1.5% Cr and 0.2% Mo, and Astaloy CrM, which contains 3% Cr and 0.5% Mo, are suitable for high-performance applications. This paper is focused on the fatigue properties of these materials. The bending fatigue limits at sintered density 7.1 g/cm³ are 261 MPa for Astaloy CrL + 0.8% graphite and 287 MPa for Astaloy CrM + 0.45% graphite after conventional sintering at 1120 ºC. High temperature sintering followed by rapid cooling increase the fatigue limits of the materials by 20-30% to 320 MPa and 372 MPa respectively. Moreover, Astaloy CrM + 0.45% graphite obtains a very high fatigue limit of 527 MPa at sintered density 7.3 g/cm³ after high temperature sintering and vacuum-carburising.