500MPa级超低碳Nb-Ti微合金钢板梯度结构制备及其低温韧性

Preparation of gradient structure of 500 MPa ultra-low carbon Nb-Ti microalloyed steel plate and its low temperature toughness

采用超快冷返温轧制工艺制备了一种500 MPa级超低碳Nb-Ti微合金梯度结构钢板。利用全自动相变仪、微观硬度计、电子万能试验机、光学显微镜、扫描电镜(SEM)、电子背散射衍射(EBSD)等研究了梯度结构钢板组织演变规律及力学性能,并在-80~20℃下对钢板表层和心部进行了低温冲击试验。结果表明:钢板呈现出表层超细晶铁素体组织到心部粗晶铁素体组织的晶粒尺寸梯度变化。由于细晶强化的作用,钢板表层强度得到提升,屈服强度较心部增加41 MPa;表层的断后伸长率为35%,要高于心部的31%。表层晶粒细化和心部大量大角度晶界的存在使得钢板具有优异的低温韧性,-80℃下表层和心部的冲击吸收能量分别可以达到106和90 J。

A 500 MPa grade ultra-low carbon Nb-Ti microalloyed gradient structural steel plate was prepared by ultra-fast cooling return temperature rolling process.Microstructure evolution and mechanical properties of gradient structural steel plate were studied by means of automatic phase change instrument,microhardness tester,electronic universal testing machine,optical microscope,scanning electron microscopy(SEM)and electron backscatter diffraction(EBSD)technique.The low temperature impact test was carried out on the surface and center of the steel plate at -80℃-20℃.The results show that the steel plate presents a gradient change of grain size from ultra-fine grained ferrite in the surface to coarse grained ferrite in the center.Due to the effect of fine grain strengthening,the surface strength of the steel plate is improved,and the yield strength is 41 MPa higher than that of the center.The elongation of the surface layer is 35%,which is higher than 31% of the center.The surface grain refinement and the existence of a large number of large-angle grain boundaries in the center make the steel plate have excellent low-temperature toughness,and the impact absorbed energy of the surface and the center can reach 106 J and 90 J respectively at -80℃.