Studies on solidification, aging and forgeability of modified stainless steels

The present study is concerned with a comparative evaluation of three Fe–Cr–Ni steels with different compositions. These are: (1) Fe–0.2C–18.2Mn–18.5Cr–0.83Si–0.7Mo–0.15Ni–0.6N; (2) Fe–0.16C–18.5Mn–18.4Cr–0.33Si–1.7Mo–0.09Ni; (3) Fe–0.07C–1.08Mn–21.6Cr–0.63Si–0.14Mo–9.63Ni. Four types of studies were conducted on each of these steels for their characterization, viz.: (a) solidification behavior by cooling curve analysis; (b) non-isothermal phase transformation through dilatometric study; (c) isothermal phase transformations at 500, 650 and 800°C; (d) forgeability studies at 1050±50 and 800±50°C. Depending on the chemistry, the melting point of the steels vary. Steel 1 is the highest melting point alloy (1530±10°C). Steel 2 melts at 1510±10°C and Steel 3 has the lowest melting point of 1430±10°C. Dilatometric study reveals that at slow cooling condition (10°C/min) Steel 2 undergoes major phase transformations at two different ranges of temperatures, i.e., at 1070–1040 and 600–550°C. This type of transformation was not observed in the other two steels. Steel 3 softens during holding at 1150°C. Steel 1 is insensitive to aging treatment at 500 and 650°C but undergoes pearlitic transformation on aging at 800°C. Similarly, Steel 2 is sensitive at 650 and 800°C. But Steel 3 shows little aging response at any of the temperatures. Steels 1 and 2 are forgeable at 1050±50 and 800±50°C, respectively. The forgeability of Steel 3 is poor compared to that of the other two steels and fails with opening up of large cracks. It may be concluded that Steel 1 shows better properties compared to other two compositions of steel