Microstructure and Mechanical Properties of Cr-Mn Structural PM Steels

Abstract

The effects of chemical composition, sintering atmosphere and cooling rate on density, microstructure and mechanical properties of Fe-3%Mn-(Cr)-(Mo)-0.3%C PM steels are described. Pre-alloyed Astaloy CrM and Astaloy CrL, ferromanganese and graphite powders were used as the starting materials. After pressing in rigid dies the compacts were sintered at 1120 and 1250 C for 60 minutes atmospheres with different H 2 /N 2 ratios and cooled either at 1.4 Cmin -1 (with the furnace) or 65 Cmin -1 (convective cooling). The convective cooled specimens were subsequently tempered at 200 C for 60 and 240 minutes. All specimens were tested for tensile strength (UTS), elongation (A), offset yield strength (R 0.2 ), TRS, impact toughness and apparent surface hardness (HV 30). After mechanical tests the microstructure of the Fe-Mn-Cr-Mo-C PM steels was studied by optical microscopy. It has been found that by sintering in inexpensive and safe nitrogen-rich atmospheres it is possible to achieve properties similar to those shown by specimens sintered in a hydrogen-rich atmosphere.