CALCULATION OF PHASE-EQUILIBRIA FOR AISI M2 HIGH-SPEED STEEL

Thermo-calc computations have been made for the iron-rich corner of the system Fe-Cr-Mo-W-V-C to obtain phase equilibria for AISI M2 high-speed steel (German designation S-6-5-2). The calculations describe the main transformation temperatures of this steel with good accuracy. The phases which are present during austenitization and their volume fractions are also correctly accounted for. The solidification sequence of the M2 steel, and in particular the occurrence of M2C in the ledeburitic eutectic, can be explained if the segregation of alloying elements and carbon in the interdendritic spaces is taken into account. The secondary hardening precipitates can be described in satisfactory approximation on the basis of local two-phase equilibria between each carbide and the matrix, indicating that their compositions are essentially determined by the nucleation process.