1990 年 30 巻 8 号 p. 639-645
The effects of cold rolling on strength and toughness at 4 K were investigated for a high manganese steel, 32Mn-7Cr steel. The yield strength at 4 K was 1118 MPa for the unrolled material and was increased to 1379 and 1786 MPa for the 20 and 40% cold-rolled materials, respectively. However, the elongation and the reduction of area were decreased with an increase in reduction ratio. Especially, the elongation was significantly decreased. The Charpy absorbed energy and the fracture toughness were also decreased markedly. The decrease in toughness by cold rolling was due to the formation of subcrack and "flat brittle facet" in the fracture surface. The subcrack was caused by intergranular fracture, and the flat brittle facet is believed to be produced mainly by intergranular fracture and partly by twin cracking.
