Influence of tempering technique on microstructure and properties of 20Cr1Mo1VTiB bolt steel
The mechanical properties of 20Cr1Mo1VTiB bolt steel were tested and characterized by SEM,TEM and EBSD.The microstructures and tensile properties of 20Cr1Mo1VTiB bolt steel tempered at different temperatures and holding times were studied.The results show that the bainite laths in the 20Cr1Mo1VTiB bolt steel merged and grew up after tempering,and the boundary of the laths became fuzzy.With the increase of tempering temperature and tempering time,the extent of the lath merging increased.Compared with 700 ℃× 4h tempering,the bainite lath sizes in the steel tempered at 720 ℃ for 4h and at 700 ℃ for 6h increased by 44.98 nm and 55.93 nm respectively.The main carbides in the steel were VC,TiC and M3C.Their sizes grew with the increase of tempering temperature and tempering time,and the morphologies changed from square to spherical.At the same time,the tensile strength and hardness as well as the elongation and impact toughness at-20℃ of the tested steel decreased and increased respectively.
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