Process Route Influence on Performance of PM Steels Pre-Alloyed with Chromium
PM²TEC 2004, in Chicago, USA. Authors: Sigurd Berg, Barbara Maroli. Increased demand on high strength PM applications and cost reduction from the automotive industry has lead to introduction of chromium as an alloying element mainly due to its low cost and high hardenability. A common process for pre-alloyed material with 3% chromium has been sinter-hardening using normal sintering temperatures. Further increase in mechanical properties is achieved utilizing high sintering temperature or heat treatment operations like vacuum case hardening. In this paper the influence of process conditions on the static and dynamic properties of materials pre-alloyed with chromium are presented and explained through their microstructure. After high temperature sintering with a carbon content of 0.7% a fatigue strength of 445 MPa (65 ksi) is obtained. Combining high temperature sintering with rapid cooling yield strength up to 1250 MPa (181 ksi) is obtained at 0.45% C. If high temperature sintering is followed by vacuum carburizing fatigue strength of 527 MPa (76 ksi) is achieved.