关键词: 高锰钢, 固溶处理, 低温冲击韧性, 机械孪晶, (Cr, Mn)₂₃C₆型碳化物

Abstract: Effect of solution treatment temperature on microstructure and mechanical properties of a high manganese steel for LNG storage tanks was studied by means of OM, SEM, EBSD, EPMA, TEM and tensile, impact and hardness tests. The results show that compared with the hot-rolled steel plates, there is no significantly change in microstructure and properties of the steel after solution treatment at 500 ℃. When the solution treatment temperature is 600-800 ℃, the austenite grain size is 10-15 μm, and a large amount of carbides precipitate at the austenite grain boundaries, so that the yield strength decreases from 400 MPa to 379 MPa, while the tensile strength remains almost unchanged (879-880 MPa), meanwhile, the impact absorbed energy at -196 ℃ is poor, which is only about 50 J. When the solution treatment temperature rises to 900-1000 ℃, the yield strength and tensile strength decrease sharply, and the impact absorbed energy at -196 ℃ increases. When the solution treatment temperature is 600-800 ℃, the (Cr, Mn)₂₃C₆ carbides precipitated along the grain boundaries significantly reduce the bonding force of austenite grain boundaries, lower the impact crack formation energy and crack propagation energy, and thus seriously deteriorate the low-temperature impact toughness of the steel. When the solution treatment temperature rises to 1000 ℃, the impact absorbed energy at -196 ℃ is 180 J, the carbides at the grain boundaries completely dissolve back, the grains grow, and a large number of mechanical twins are generated under impact loads, even activating the secondary twin system, effectively suppressing the nucleation and propagation of cracks, which is the main reason for the excellent low-temperature toughness of the steel the impact abserbed energy at -196 ℃ is 180 J.

Key words: high manganese steel, solution treatment, low-temperature impact toughness, mechanical twin, (Cr, Mn)₂₃C₆ type carbide