不同热处理条件下U75V重轨钢的组织及断裂韧性研究

Microstructure and Fracture Toughness of U75V Heavy Rail Steel Under Different Heat Treatment Conditions

以U75V重轨钢为研究对象,采用万能试验机、应变仪、扫描电镜等测定和分析其在线轧态和在线热处理态条件下的微观组织、断口形貌及三点弯曲断裂韧性,揭示其微观组织对断裂韧性的影响规律,为研究珠光体重轨钢热处理工艺提供参考。结果表明:U75V重轨钢热处理态和轧态的表面应变变化规律相似,但热处理态U75V重轨钢从弹性变形到塑性变形比轧态滞后;热处理态和轧态U75V重轨钢的断裂韧性K_(IC)值分别为45.122、42.048 MPa•m^(1/2),热处理态的断裂韧性比轧态高;轧态U75V重轨钢断口为解理断裂,而热处理U75V重轨钢为准解理断裂;轧态和热处理态U75V重轨钢的珠光体片层间距分别为272.2、148.4 nm,热处理态U75V重轨钢的珠光体片层细密,存在显著的珠光体团簇,不利于裂纹的扩展,使得热处理态U75V重轨钢断裂韧性高于轧态。

U75V heavy rail steel was studied as the research object,and the microscopic structure,fracture morphology and three-point bending fracture toughness under the conditions of rolling and heat treatment were analyzed by the universal testing machine,strain gauge,OM,and SEM.The influence of microstructure on fracture toughness was revealed,providing reference for studying the heat treatment process of pearlescent heavy rail steel.The results show that the surface strain changes of U75V heavy rail steel in the heat treated and rolled states are similar,but the elastic deformation to plastic deformation of U75V heavy rail steel in the heat treated state lags behind that in the rolled state.The fracture toughness K_(IC) values of heat treated and rolled U75V heavy rail steel are 45.122 MPa•m^(1/2) and 42.048 MPa•m^(1/2) respectively,and the fracture toughness in the heat treated state is higher than that in the rolled state.The fracture surface of the rolled U75V heavy rail steel is cleavage fracture,while the heat treated U75V heavy rail steel is quasi cleavage fracture.The interlayer spacing of pearlite in the rolled and heat treated U75V heavy rail steel is 272.2 and 148.4 nm,respectively.The pearlite layer in the heat treated U75V heavy rail steel is fine and there are significant pearlite clusters,which is not conducive to crack propagation,making the fracture toughness of the heat treated U75V heavy rail steel higher than that of the rolled state.