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对比研究了电磁感应及传统箱式炉2种不同回火加热方式对1000 MPa级别高强度低合金钢淬火后组织中碳化物的尺寸、形貌、分布及其对力学性能的影响.结果表明,实验钢淬火后组织包括下贝氏体及板条马氏体.2种加热方式回火后,对于下贝氏体组织,随着回火温度由400℃升高至550℃,碳化物由针状向短棒状转变.其中,经550℃传统加热回火后,贝氏体内部碳化物长轴尺寸约为200 nm,而经该温度电磁感应加热回火后其长轴尺寸约为60 nm.对于板条马氏体组织,经传统加热回火后,碳化物主要沿着板条边界连串析出;电磁感应加热回火后,马氏体板条中析出的碳化物在板条内部及边界均匀弥散分布.经550℃传统方式回火后,马氏体中的碳化物尺寸约为200 nm,而电磁感应回火的碳化物尺寸均小于100 nm.经过不同加热方式回火后,实验钢的硬度差别不显著,随着回火温度升高,2种加热方式回火试样冲击功均升高,但感应加热回火后冲击功升高更为显著,实验钢经550℃电磁感应加热回火后-20℃冲击功达到133 J,是传统加热回火工艺的4.5倍,实现了1000 MPa级高强度低合金钢良好的强韧化组合.

By comparing induction tempering with conventional tempering,the effect of induction reheating tempering on carbide precipitation behavior and toughness of a 1000 MPa grade high strength low alloy steel was investigated.Microstructures of the steel in different heat treatment stages were characterized using SEM and TEM (with EDS),mechanical properties inclusive of Vickers hardness and toughness were tested.The results showed that microstructure of quenched samples consisted of lath martensite and lower bainite,needle like carbides were observed in lower bainitic lath.With tempering temperature increasing from 400 ℃ to 550 ℃,the shape of carbides located within the bainitic lath gradually changed from needle like to short rod like type.Carbides were fine and well distributed using induction tempering.When the tempering temperature was 550 ℃,the long axis length of short rod like carbides located within the bainitic lath by conventional reheating tempering was 200 nm,whereas the long axis length of short rod like carbides located within the bainitic lath by induction reheating tempering was about 60 nm.When tempering by conventional reheating,carbides mainly precipitated along martensite lath boundaries,while carbides were more dispersed in the matrix lath by induction reheating,the size of these dispersed carbides was less than 100 nm when tempering temperature was 550 ℃.As a result,a superior of mechanical properties with 344 HV and Charpy impact energy of 133 J at-20 ℃ was obtained with induction reheating tempering at 550 ℃.