纳米贝氏体的热力学分析及强韧化研究

Thermodynamic analysis and strength-toughness research of nanobainite

针对目前高碳高硅低温贝氏体(纳米结构贝氏体)相变速度缓慢的现状,采用贝氏体相变热力学理论分析主要合金元素对低温贝氏体相变驱动力的影响,设计了新型纳米结构贝氏体钢成分0.83C-2.44Si-0.43Mn-0.73Al.利用膨胀仪研究该成分贝氏体钢在不同温度下的相变整体动力学,综合使用扫描电子显微镜、X射线衍射、电子背散射衍射等方法研究热处理工艺对实验钢组织和力学性能的影响.结果表明,350℃等温转变贝氏体的抗拉强度为1401 MPa,延伸率为42.21%,强塑积可达59136 MPa·%,在室温拉伸过程中发生明显的相变诱导塑性效应;230℃等温转变组织中贝氏体铁素体片层厚度小于100 nm,抗拉强度达2169 MPa.

In view of slow phase transformation rate in high-carbon,silicon-rich and low-alloy bainite steel（ nanostructured bainite steel）,the effects of alloy elements on the overall kinetics of low temperature bainite phase transformation were analyzed by using the thermodynamic theory of bainite phase transformation,and a composition of 0. 83C-2. 44Si-0. 43Mn-0. 73Al（ mass fraction,%）was designed to develop a novel nanostructured bainitic steel. The overall phase transformation kinetics of this new designed nanobainitic steel at different temperatures were investigated by dilatometry. The effects of heat treatment parameters on the microstructure and mechanical properties were analyzed by scanning electron microscopy,X-ray diffraction and electron backscatter diffraction. It is found that the nanobainitic steel,which exhibited excellent mechanical properties with an ultimate tensile strength of 1401 MPa,a total elongation rate of 42. 21% and a strength and ductility product of 59136 MPa·%,can be obtained by austempering at 350 ℃. In addition,transformation-induced plasticity（ TRIP） effect appears during tensile testing at room temperature. When austempered at 230 ℃,the nanobainitic steel has a finer microstructure with the thickness of bainite ferrite laths less than 100 nm,and its tensile strength can reach up to 2169 MPa.