Effects of Carbon, Nitrogen and Nickel Content on the Low Temperature Impact Value of High Manganese Austenitic Steel

Abstract

The purpose of this study is to examine the effects of C, N and Ni content on the Charpy impact value and tensile properties at subzero temperatures of high Mn austenitic alloys. The friction stress for Petch equation and load-time curve in Charpy impact test at -196°C have been determined. The effects of C and N on the stacking fault probability and fracture mode have also been examined.
0.2% proof stress and tensile strength are found to increase linearly in proportion to C plus 1.5 times N. Tensile ductilities especially at cryogenic temperature decrease with increasing C and N content. Charpy impact values at the temperature down to -100°C do not change by the addition of C and N, however, those at -150°C and -196°C show decreasing tendency with increasing amount of C and N. Yield and maximum load obtained in the Charpy impact test at -196°C linearly increase with increasing value in C plus 3.3 times N. The fracture mode at -196°C changes from ductile to brittle when the value in C plus 3.3 times N exceeds 1.0.
The improving effect of Ni on the impact value at -196°C can be estimated in terms of stacking fault energy. The embrittling effects of C and N are estimated in terms of stacking fault energy and according to Smallman equation predicting ductile/brittle fracture transition.