回火温度对高强韧厚壁管组织和性能的影响

Effect of tempering temperature on microstrcuture and properties of high strength thick-walled tube

将中低碳合金钢经渗碳处理后在不同温度下回火,分析实验钢显微组织、碳化物形态、尺寸和分布特征,研究回火温度对实验钢显微组织和力学性能的影响。结果表明：实验钢经200~300℃低温回火后,心部为条束状的贝氏体与粒状贝氏体交织分布,且随回火温度的升高,实验钢中碳化物的形态由长条状或椭球状转变为颗粒状,分布也更为均匀、弥散,铁素体基体被残留奥氏体薄膜分割获得更为细小的亚结构;由渗层表面至心部的维氏硬度梯度随回火温度的增加而逐渐平缓,强度和洛氏硬度随回火温度的升高而降低,冲击性能随回火温度的升高而升高;经过250℃回火后,实验钢的亚结构主要由宽度为0.2~0.4μm、长度为0.7~1.2μm的贝氏体亚片条构成,细小、弥散分布的颗粒状碳化物明显改变了诱发裂纹萌生的临界断裂应力,在保证其抗拉强度达到1182 MPa的同时,冲击吸收能量也达到了157 J。

Influence of tempering temperature on microstructure and mechanical properties of high strength thick-walled tube after carburizing treatment was studied. The microstructure,carbide morphology,size and distribution characteristics of the tested steel were analyzed. The results show that the central microstructure of the steel is striped bainite and granular bainite after tempering at 200-300 ℃,and with the increasing of tempering temperature,the morphology of carbides in the steel changes from long strip or ellipsoid to granular,and its distribution is more uniform and dispersedly,the ferrite matrix is separated by residual austenite thin film to obtain a smaller substructure.The Vickers hardness gradient from the surface of the carburized layer to the center of the steel gradually decreases with the increasing of tempering temperature. The strength and Rockwell hardness of the steel decrease and the impact property increases with the increasing of tempering temperature. After tempering at 250 ℃,the substructure of the tested steel is mainly composed of bainite sub-strips with a width of 0. 2-0. 4 μm and a length of 0. 7-1. 2 μm,the fine and dispersed granular carbides obviously change the critical fracture stress which induces crack initiation,and the tensile strength and impact absorbed energy of the tested steel are 1182 MPa and 157 J,respectively.