Influence of sintering parameters on the mechanical performance of PM steels pre-alloyed with chromium

Powder grades pre-alloyed with 1.5-3 wt% chromium are suitable for PM steel components in high performance applications. These materials can be successfully sintered at the conventional temperature 1120 degrees C, although well-monitored sintering atmospheres with low oxygen partial pressures (< 10(-17)-10(-18) atm) are required to avoid oxidation. Mechanical properties of the Cr-alloyed PM grades are enhanced by a higher sintering temperature in the range 1120-1250 degrees C, due to positive effects from pore rounding, increased density and more effective oxide reduction. A material consisting of Astaloy CrM, which is pre-alloyed with 3 wt% Cr and 0.5 wt% Mo, and 0.6 wt% graphite obtains an ultimate tensile strength of 1470 MPa combined with an impact strength of 31 J at density 7.1 g/cm(3), after sintering at 1250 degrees C followed by cooling at 2.5 degrees C/s and tempering.