Investigation of the effects of sinter hardening process on microstructures and mechanical properties of prealloyed metal powders

In this study, the effect of sinter-hardening process on Astaloy Mo (Fe prealloyed with 1,5 wt.% Mo) based powder metallurgical steels was investigated. In accordance with this purpose, 3 different powder mixes were studied. These are as follows: diffusion alloyed Distaloy DH (Astaloy Mo-2 wt.% Cu) with 0,6 wt.% C, Astaloy Mo with 2 wt.% Cu and 0,6 wt.% C, and Astaloy Mo with 1 wt.% Cu and 0,6 wt.% C powder mixes. The powder mixes were pressed under 600 MPa and were sintered at 1120°C under endogas atmosphere for 25 minutes in an industrial belt sintering furnaces. After the sintering process, 0,5°C/s, 1,5°C/s, 2°C/s and 3°C/s cooling rates were applied to the samples. Subsequent to production phase, sample preparation process was carried out to sinter-hardened samples. Thereafter, microstructures of the samples were analyzed under the optical and scanning electron microscopes. Three-point bending tests, tensile tests and microhardness tests were performed in order to determine the mechanical properties. The findings obtained in consequence of experimental studies were discussed and concluded. Due to this study, the effects of Cu amounts, cooling rates and prealloying methods on microstructure and mechanical properties of mentioned powders were examined. Experimental studies have shown that increasing cooling rate led to transformation of bainite to martensite and thereby an increase in the hardness values of the sinter-hardened samples. Besides, it was determined that Distaloy DH specimens have better mechanical propersties owing to having less porous structure and smaller pores in comparison to Astaloy Mo specimens.