含Nb-Ti低碳钢的析出与细晶强化效应研究

采用控轧控冷(TMCP)工艺制备的0.013%Nb-0.013%Ti钢和C-Mn钢性能对比显示,添加微量Nb-Ti明显提高了钢的强度和冲击韧性,原因是微量Nb-Ti细化了铁素体晶粒并得到更高体积分数的弥散分布(Nb,Ti)(C,N)析出颗粒。用Hall-Petch晶粒尺寸强化和Ashby-Orowan弥散强化模型计算铁素体晶粒尺寸、析出颗粒尺寸和体积分数等微观组织变量对强度的量化贡献,结果表明,Nb-Ti钢的主要强化机理为细晶强化和弥散强化,而降低韧脆转变温度的主要机理是晶粒细化和微合金碳氮化物析出降低了钢中的自由氮含量。

Study on Precipitation and Fine Grain Strengthening Effects of Low Carbon Steel with Nb-Ti

The properties of the steal with adding 0.013%Nb and 0.013%Ti produced by thermo-mechanical control process （TMCP） is compared with that of the steel with adding C-Mn produced by TMCP, and the comparing results show that the strength and impact toughness of the steel with trace elements of Nb and Ti have obviously improved, which result from refining ferrite grains and obtaining dispersed （Nb ,T i）（C, N）preclpitation particles with higher volume fraction by addition of trace elements of Nb-Ti. Such microstructure variables as grain sizes of the ferrite, sizes of precipitated grains and volume fractions which contribute to the quantization of strengthen- ing are calculated by Hall-Petch model for strengthening the size of a grain and Ashby-Orowan model for strengthening the dispersion. The calculating results show that the main strengthening mechanisms for the steel with Nb-Ti are due to the functions of the fine grain strengthening and dispersion strengthening, while the main mechanism for lowering the ductile-brittle transition tem- perature is due to the reduction of free nitrogen in steel by grain refinement and precipitation of micro-alloying carbonitrides.