Effect of Spheroidizing Annealing on the Carbide Precipitation Behavior of Cr-Mo-V-W Hot Work Die Steels

The effect of the spheroidizing annealing on the carbide precipitation behavior of Cr-Mo-V-W die steels (SR19^®) was systematically investigated. Thermodynamic simulation was applied for the optimization of the new spheroidizing annealing process. Microstructure was revealed by SEM and TEM. The small size precipitations (average diameter < 200 nm) obtained by quenching–tempering–holding (QTH) annealing process reached 67.27%, which is 7.22% higher than that by traditional continuous cooling holding annealing of 60.05%. It testified that the newly proposed QTH annealing process effectively improved the uniformity of precipitations as well as reduced the detrimental fresh martensite. It was determined by STEM-EDS that the larger (average diameter 200-400 nm) spherical particles were mostly Cr-rich M₂₃C₆ carbides, whereas the smaller (average diameter 50-200 nm) spherical particles were mostly Mo-W-rich M₆C carbides.