Microstructural Evolution of Semi-Solid Type 304 Stainless Steel Deformed Severely by ECAP

Thixoforming or semi-solid metal forming offers many advantages in comparison with casting and conventional forging. However, due to the high-melting temperature and related difficulties, there is relatively a few experimental data on the semi-solid processing of steels. Therefore, this study is subjected to study the microstructure evolution during partial remelting of 304 stainless steel which is priorely deformed in solid state by equal channel angular pressing (ECAP) at room temperature. ECAP is a promising technique to induce a great homogeneous strain in bulk metals known as a new method for strain induced melt activation (SIMA) process for preparing thixoforming ingot. Simultaneously, the effect of number of passes during ECAP was also discussed in terms of the microstructure change. The results showed that the microstructure was well refined with formation of fine twins and partial martensite along with many fine equiaxed grains which in turn lead to fine and spheroidal semi-solid slurry. It can be confirmed that ECAP followed by reheating was an effective method to produce semi-solid ingot for thixoforming.