Ti微合金中厚钢板析出行为研究及组织性能控制
发布时间：2018-10-12 06:50
【摘要】：Ti微合金钢的微观组织和力学性能与钢中各类含Ti第二相颗粒析出行为密切相关。热轧后连续冷却过程中相变铁素体中形成的相间析出碳化物在强化铁素体基体方面起关键作用。回火过程中纳米碳化物的析出行为及碳化物的变化特征,显著影响实验钢的力学性能。淬火、回火处理以及两相区变形在改变实验钢微观组织形态的同时显著影响了碳化物的析出特征,从而影响实验钢的力学性能。铁素体中均匀分布的纳米碳化物析出可以显著提高实验钢强度,为此研究了Ti微合金钢轧后连续冷却过程中含Ti析出相的析出行为及析出特征。结果表明,连续冷却过程中形成的大量含Ti碳化物主要在铁素体中以相间沉淀形式析出,析出相的形成与冷却速率和Ti含量密切相关。而添加Mo元素推迟并促进了铁素体中纳米碳化物析出,使沉淀强化作用更显著。为了探究回火工艺对相间析出与过饱和析出的影响,研究了不同温度、不同时间条件下Ti微合金钢中纳米碳化物的析出行为和析出特征。结果表明,回火后屈服强度变化与回火过程中纳米碳化物的析出、长大和粗化行为有关,在高温长时间等温过程中这种含Mo的纳米碳化物具有较好的热稳定性,且相间析出颗粒较过饱和析出颗粒具有更优越的抗粗化能力,析出强化作用更明显。淬火、回火处理通过改变微观组织形态显著改善了钢的低温韧性,但也同时对热轧钢板中形成的纳米碳化物颗粒产生影响。韧性改善主要得益于板条贝氏体组织的形成；而淬火、回火过程虽然弱化了热轧态形成纳米碳化物的强化作用但却使这些碳化物充分保留下来并促进了过饱和碳化物析出。为了充分发挥细晶强化与沉淀强化的综合作用,研究了终轧温度对微观组织演变及碳化物析出行为的影响。第二阶段变形延续至两相区时,不仅能够细化晶粒,而且能生成由等轴晶粒及亚晶粒组成的混合组织。随变形温度降低,组织细化明显,因此提高了钢的低温韧性。降低变形温度抑制了相间析出形成,但应变累积促进了低温铁素体中过饱和碳化物析出,在一定程度上发挥了析出强化效应。
[Abstract]:The microstructure and mechanical properties of Ti microalloyed steel are closely related to the precipitation behavior of the second phase particles containing Ti. The precipitation of carbides from phase change ferrite during continuous cooling after hot rolling plays a key role in strengthening ferrite matrix. The precipitation behavior of nano-carbides and the changing characteristics of carbides during tempering have a significant effect on the mechanical properties of experimental steels. Quenching, tempering and deformation in the two-phase region have a significant effect on the precipitation of carbides while changing the microstructure of the experimental steels, thus affecting the mechanical properties of the experimental steels. The precipitation of nano-carbide in ferrite can improve the strength of experimental steel significantly. The precipitation behavior and characteristics of precipitated phase containing Ti in Ti microalloyed steel during continuous cooling after rolling are studied. The results show that a large number of Ti carbides formed during continuous cooling are precipitated in ferrite in the form of interphase precipitation. The formation of precipitates is closely related to the cooling rate and the content of Ti. The addition of Mo element delayed and promoted the precipitation of nano-carbides in ferrite, which made the precipitation strengthening more obvious. In order to investigate the effect of tempering process on the precipitation between phases and supersaturation, the precipitation behavior and precipitation characteristics of nano-carbides in Ti microalloyed steel at different temperatures and different time were studied. The results show that the change of yield strength after tempering is related to the precipitation, growth and coarsening behavior of nano-carbides during tempering, and the nano-carbides containing Mo have better thermal stability during high temperature and long time isothermal process. The interphase precipitated particles have better anti-coarsening ability than supersaturated precipitated particles, and the precipitation strengthening effect is more obvious. Quenching and tempering significantly improved the toughness of steel at low temperature by changing the microstructure, but also affected the formation of nano-carbides in hot rolled steel. The toughness improvement is mainly due to the formation of the lath bainite structure, while the hardening and tempering process weakens the strengthening effect of the hot rolled nano-carbides, but it makes these carbides fully retain and promote the precipitation of supersaturated carbides. In order to give full play to the comprehensive effect of fine grain strengthening and precipitation strengthening, the effect of finishing rolling temperature on microstructure evolution and carbide precipitation behavior was studied. When the second stage deformation continues to the two-phase region, it can not only refine the grain, but also produce the mixed microstructure composed of equiaxed grain and sub-grain. With the decrease of deformation temperature, the microstructure is refined obviously, so the low temperature toughness of the steel is improved. Lowering the deformation temperature inhibits the formation of interphase precipitation, but the accumulation of strain promotes the precipitation of supersaturated carbides in ferrite at low temperature, thus exerting the precipitation strengthening effect to some extent.
【学位授予单位】：北京科技大学
【学位级别】：博士
【学位授予年份】：2015
【分类号】：TG142.1
本文编号：2265182
[Abstract]:The microstructure and mechanical properties of Ti microalloyed steel are closely related to the precipitation behavior of the second phase particles containing Ti. The precipitation of carbides from phase change ferrite during continuous cooling after hot rolling plays a key role in strengthening ferrite matrix. The precipitation behavior of nano-carbides and the changing characteristics of carbides during tempering have a significant effect on the mechanical properties of experimental steels. Quenching, tempering and deformation in the two-phase region have a significant effect on the precipitation of carbides while changing the microstructure of the experimental steels, thus affecting the mechanical properties of the experimental steels. The precipitation of nano-carbide in ferrite can improve the strength of experimental steel significantly. The precipitation behavior and characteristics of precipitated phase containing Ti in Ti microalloyed steel during continuous cooling after rolling are studied. The results show that a large number of Ti carbides formed during continuous cooling are precipitated in ferrite in the form of interphase precipitation. The formation of precipitates is closely related to the cooling rate and the content of Ti. The addition of Mo element delayed and promoted the precipitation of nano-carbides in ferrite, which made the precipitation strengthening more obvious. In order to investigate the effect of tempering process on the precipitation between phases and supersaturation, the precipitation behavior and precipitation characteristics of nano-carbides in Ti microalloyed steel at different temperatures and different time were studied. The results show that the change of yield strength after tempering is related to the precipitation, growth and coarsening behavior of nano-carbides during tempering, and the nano-carbides containing Mo have better thermal stability during high temperature and long time isothermal process. The interphase precipitated particles have better anti-coarsening ability than supersaturated precipitated particles, and the precipitation strengthening effect is more obvious. Quenching and tempering significantly improved the toughness of steel at low temperature by changing the microstructure, but also affected the formation of nano-carbides in hot rolled steel. The toughness improvement is mainly due to the formation of the lath bainite structure, while the hardening and tempering process weakens the strengthening effect of the hot rolled nano-carbides, but it makes these carbides fully retain and promote the precipitation of supersaturated carbides. In order to give full play to the comprehensive effect of fine grain strengthening and precipitation strengthening, the effect of finishing rolling temperature on microstructure evolution and carbide precipitation behavior was studied. When the second stage deformation continues to the two-phase region, it can not only refine the grain, but also produce the mixed microstructure composed of equiaxed grain and sub-grain. With the decrease of deformation temperature, the microstructure is refined obviously, so the low temperature toughness of the steel is improved. Lowering the deformation temperature inhibits the formation of interphase precipitation, but the accumulation of strain promotes the precipitation of supersaturated carbides in ferrite at low temperature, thus exerting the precipitation strengthening effect to some extent.
【学位授予单位】：北京科技大学
【学位级别】：博士
【学位授予年份】：2015
【分类号】：TG142.1
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