Effect of Strain Rate on Hot Ductility Behavior of a High Nitrogen Cr-Mn Austenitic Steel

18Mn18Cr0.6N steel specimens were tensile tested between 1173 K and 1473 K (900 degrees C and 1200 degrees C) at 9 strain rates ranging from 0.001 to 10 s(-1). The tensile strained microstructures were analyzed through electron backscatter diffraction analysis. The strain rate was found to affect hot ductility by influencing the strain distribution, the extent of dynamic recrystallization and the resulting grain size, and dynamic recovery. The crack nucleation sites were primarily located at grain boundaries and were not influenced by the strain rate. At 1473 K (1200 degrees C), a higher strain rate was beneficial for grain refinement and preventing hot cracking; however, dynamic recovery appreciably occurred at 0.001 s(-1) and induced transgranular crack propagation. At 1373 K (1100 degrees C), a high extent of dynamic recrystallization and fine new grains at medium strain rates led to good hot ductility. The strain gradient from the interior of the grain to the grain boundary increased with decreasing strain rate at 1173 K and 1273 K (900 degrees C and 1000 degrees C), which promoted hot cracking. Grain boundary sliding accompanied grain rotation and did not contribute to hot cracking. (C) The Minerals, Metals & Materials Society and ASM International 2015