Solidification Structures of Fe–Cr–Ni–Mo–N Super-austenitic Stainless Steel Processed by Twin-roll Strip Casting and Ingot Casting and Their Segregation Evolution Behaviors

Abstract

Fe–Cr–Ni–Mo–N super-austenitic stainless steels were processed by using twin-roll strip casting and ingot casting, and their solidification structures and segregation behaviors were comparatively studied. The results show that serious center macro-segregation and massive eutectics were detected in ingot, with the amount of eutectics being increased from surface to center. By contrast, macro-segregation and eutectics were inhibited in cast strip (CS) due to its rapid cooling rate during the solidification process. In order to obtain optimum hot workability, homogenization treatments were carried out in the temperature range from 1050 to 1200°C for different time from 30 to 480 min in CS and ingot. The results show that the homogenized temperature of CS should be higher than 1100°C to avoid the formation of precipitates, and the optimum homogenization process was 1150–1200°C for 30 min. For the ingot homogenized at 1200°C, eutectics gradually dissolved into the matrix with increasing the homogenization time, and after 4 hours, they completely dissolved. Ingot could be homogenized after more than 8 hours of homogenization, indicating that CS has intrinsic advantages in homogenization. Finally, mechanical property and pitting corrosion resistance of 1 mm-thick cold-rolled bands, fabricated from CS and ingot, were tested and compared. The results show that the overall performance of cold-rolled bands of CS was superior to that of ingot.