高Mnオーステナイト鋼の低温衝撃値におよぼすC, NおよびNiの影響

抄録

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.