On the microstructure formation in chromium steels rapidly cooled from the semi-solid state

Semi-solid metal forming requires precise knowledge concerning the microstructural parameters in the mushy state. For many light metals, the liquid and solid fraction and the size, shape and contiguity of the solid phase can be evaluated easily in the “quenched from the freezing range” condition. For iron-based alloys, however, determining them is more difficult or even impossible because steels may undergo different phase-transformations during cooling. Due to the high processing temperatures, diffusion during quenching is also of more importance. Here we describe the phase formation during rapid cooling from the semi-solid state of two different steel grades, tool steel X210CrW12 and bearing steel 100Cr6. For both of these steels the microstructure in the as-quenched state does not directly reflect the condition in the semi-solid state, and thus no metallographic evaluation of the microstructural parameters is possible. It is also shown here that the microstructure of semi-solid processed steels is completely different from that of the conventionally treated species.