Structural observations during amorphization of chromium-iron nitride powders by mechanical alloying : T. Fukunaga et al. (Nagoya University, Nagoya, Japan.) J. Japan Soc. Powder and Powder Metallurgy, Vol 38, No 7, 1991, 940–943. (In Japanese.)

Abstract

Cr-alloyed PM steels attract great interest in industry, especially in the automotive industry, because, due to the mechanical requirements for the parts, the parts are often subjected to hardening thermal treatments after sintering.In the present work, a sinter-hardening process was carried out in a single stage for pieces based on PM Astaloy CrA steel using concentrated solar energy. The influence of the sintering cycle and atmosphere used, as well as the content of the alloy, were studied.Among the main results obtained, it has been demonstrated that alloys based on Astaloy CrA have been successfully sintered using solar energy. Almost complete densities have been achieved, but these densities are not achieved by conventional techniques, and much shorter sintering times and temperatures (∼ 15 min of holding time at 1070 ± 10 °C) are required compared to those used in the usual processing techniques. In addition, the use of concentrated solar energy in metal treatment leads to high heating and cooling speeds that have encouraged the sinter-hardening process through the formation of bainitic and martensitic phases, which are characterized by being harder and more resistant than ferritic and pearlitic phases. Homogeneous microstructures have been obtained without the need to apply subsequent heat treatments such as tempering that it uses in the processed by conventional techniques.This research work is also intended to promote the use of concentrated solar energy in metallurgical processes that require high temperatures because it is a cheap, nonpolluting and renewable technology. Additionally, high heating and cooling speeds that often result in an improvement of the final properties of the pieces can be obtained without the need to use any external cooling medium.