Effect of Preheating Temperature on Surface Cracking of High Nitrogen CrMn Austenitic Stainless Steel

18Mn18Cr0.5N steel specimens were preheated at the temperatures from 1100 to 1250°C for 5 min, and then cooled to 950°C and compressed. The cracking behaviors were investigated using optical microscopy and scanning electron microscopy. The results showed that the hot workability of 18Mn18Cr0.5N steel gradually decreased with increasing preheating temperature between 1100 and 1200°C, and quickly deteriorated up to 1250°C. Above 1200°C, delta ferrite particles appeared in 18Mn18Cr0.5N steel, promoted cavity coalescence on grain boundary, and accelerated surface crack formation during the hot working process.