钛微合金钢组织变化和析出物控制研究

发布时间：2018-03-23 19:14

  本文选题：钛微合金钢　切入点：动态再结晶　出处：《江苏大学》2016年硕士论文

【摘要】：中国钛资源非常丰富,价格相对便宜,且钛在钢中能产生沉淀强化和细晶强化效果,具有开发出高强韧钢的潜力。本课题参考珠钢钛微合金钢的生产工艺,在普通低碳钢的基础上添加适量的Ti元素,在实验室利用Gleeble-3800热模拟机,结合控制轧制和控制冷却工艺,模拟了不同变形工艺下高温奥氏体再结晶、不同冷却工艺过程中组织的演变和等温过程中碳氮化物在铁素体中的析出行为。另外,借助光学显微镜、显微硬度仪、透射电镜、Matlab等手段,研究分析了不同工艺下钛微合金钢组织的再结晶、演变规律和碳氮化物在铁素体中的析出机理,实验结果表明:(1)钛微合金钢奥氏体化的合理加热温度为1200℃,保温时间为5min,在850~1100℃的温度范围内,以不同的应变速率(0.025~1.0s-1)对试样进行50%单道次压缩变形,结果显示应力-应变曲线呈现两种形式,即动态回复型和动态结晶型。在低温和低应变速率下,应变速率对变形抗力的作用不大,变形温度则对其起决定作用。动态再结晶晶粒随变形程度的增加而明显细化,达到稳态应变后,细化作用减弱。当变形温度为1050℃,应变速率为0.1s-1时,发生完全再结晶后,晶粒尺寸由固溶条件下的99.5um减小到17.4um。(2钛微合金钢的热变形激活能Q=427.85k J mol-1。峰值应力、峰值应变和临界应变与成线性关系,且都随的增大而增大。根据变形程度、变形温度和应变速率对变形抗力的影响作用,回归建立了钛微合金钢的变形抗力模型,通过模型计算结果和实验结果良好吻合。(3无论变形还是未变形条件下,增大冷却速率(V3℃/s),都会出现贝氏体组织,说明钛微合金钢相变过程容易获得贝氏体组织。随着冷速的提高,相变组织由粒状贝氏体向板条贝氏体转变。变形促进贝氏体形核,使贝氏体板条变短,细化贝氏体组织。(4)变形使奥氏体的连续冷却转变曲线向上移动,提高了相变的开始温度并加快了相变的转变速度;变形扩大了先共析铁素体的相变区域并且可以诱发珠光体转变,使得冷速1℃/s时,变形奥氏体的相变组织为先共析铁素体+珠光体而不发生贝氏体转变,但未变形的相变组织为铁素体+少量粒状贝氏体。(5)600℃保温时,碳氮化物析出为平面型相间析出,析出的粒子呈现两种尺寸范围,粒子直径分别为10~20nm的应变诱导析出和5nm左右沉淀析出,在保温5~10min左右时具有最大的形核率。(6)在600℃保温1h后获得最大沉淀效果,贡献值为114MPa,继续保温,沉淀强化效果减弱。
[Abstract]:China is rich in titanium resources and relatively cheap in price, and titanium can produce precipitation strengthening and fine grain strengthening effect in steel, which has the potential to develop high strength and toughness steel. The austenite recrystallization at high temperature under different deformation conditions was simulated by adding appropriate amount of Ti on the basis of common low carbon steel, using Gleeble-3800 thermal simulator in laboratory, combined with controlled rolling and controlled cooling process. The evolution of microstructure in different cooling processes and the precipitation behavior of carbon and nitride in ferrite during isothermal process. In addition, by means of optical microscope, microhardness instrument, transmission electron microscope (TEM) and Matlab, etc. The recrystallization and evolution of microstructure of titanium microalloyed steel under different processes and the mechanism of carbonitride precipitation in ferrite are studied. The experimental results show that the reasonable heating temperature of austenitization of titanium microalloyed steel is 1200 鈩，

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