钛微合金钢的组织演变规律和控轧控冷工艺研究

发布时间：2018-07-03 14:05

  本文选题：钛微合金钢 + 静态再结晶　； 参考：《江苏大学》2017年硕士论文

【摘要】：中国钛资源丰富,价格优势明显,而且钛的析出物在钢中有明显的细化晶粒和沉淀强化作用,采用Ti微合金化技术是开发高强钢的有效途径。本文从生产现场取铸坯样(主要成分为0.051%C-0.96%Mn-0.104%Ti),在实验室采用物理热模拟方法,研究钛微合金钢的静态再结晶和相变规律,在此基础上,分析了TMCP工艺对其组织和性能的影响,得到以下主要结论:(1)同样道次间隔时间内,不同实验参数下的再结晶软化率表明:高温、大变形量将促进静态再结晶的发生,而应变速率和原始奥氏体晶粒尺寸对静态再结晶的影响相对较小;变形温度在980℃以上,变形量超过30%时,当道次间隔时间小于1s时,以静态回复为主并伴有少量再结晶,1s到10s之内,静态再结晶软化率迅速升高,超过30s之后,再结晶软化率上升缓慢。(2)在950℃变形之后,道次间隔时间为1s时,形变诱导TiC粒子析出量较少,随着道次间隔时间延长至100s时,TiC粒子数量显著增加,这些析出粒子沿位错线随机分布,对位错产生强烈的钉扎作用,将会明显抑制静态再结晶发生。(3)随着冷却速率的增加,相变开始温度和结束温度都呈现下降趋势,晶粒尺寸逐渐细化;当冷速为20℃/s时,动态相变的温度区间为513.4~717.8℃;变形使CCT曲线向上移动,提高钛微合金钢的相变温度,促进铁素体相变,加快相变转变速率,细化贝氏体晶粒。(4)由于实验钢含碳量较低,静态CCT曲线上不存在珠光体转变区间,当冷却速率5℃/s时,先共析铁素体相变受到抑制,组织以粒状贝氏体为主。当冷却速率1℃/s时,动态CCT曲线上存在珠光体转变区间,当冷却速率10℃/s时,先共析铁素体相变受到抑制,组织以粒状贝氏体为主。随着冷速进一步提升,粒状贝氏体向板条贝氏体转变。(5)对比不同压缩变形和冷却工艺下的室温组织强度。在1050℃和900℃先后进行30%的变形,并在600℃保温60min和直接采用空冷的实验钢DW和DA,其强度值分别为636.0MPa和514.4MPa,组织为先共析铁素体和粒状贝氏体;在1050℃进行50%变形,保温和空冷下的实验钢SW和SA,其强度值分别为537.9MPa和482.6MPa,组织为先共析铁素体和粒状贝氏体,伴有少量针状铁素体。实验钢DW的屈服强度值最高,其强化方式为细晶强化和沉淀强化。压缩变形后的冷却工艺对实验钢屈服强度提升幅度最大。(6)分析表明:600℃处于钛微合金钢的相变温度区间,在该温度下保温,TiC粒子会发生相间析出,尺寸为纳米级,能够钉扎位错,发挥显著的沉淀强化作用,而直接进行空冷,由于冷却速率大,会抑制TiC的析出。对纳米碳化物相间析出的研究是发开钛微合金钢的关键。
[Abstract]:China is rich in titanium resources and has obvious price advantages, and titanium precipitates have obvious effect on grain refinement and precipitation strengthening in steel. The use of Ti microalloying technology is an effective way to develop high strength steel. In this paper, the static recrystallization and phase transformation of titanium microalloyed steel were studied by physical thermal simulation method, and the effect of TMCP process on the microstructure and properties of the steel was analyzed based on the sample of casting billet (0.051C-0.96Mn-0.104Ti) taken from the production site, and the physical thermal simulation method was used to study the effect of TMCP process on the microstructure and properties of titanium microalloyed steel. The main conclusions are as follows: (1) in the same interval, the recrystallization softening rate under different experimental parameters shows that high temperature and large amount of deformation will promote the occurrence of static recrystallization. However, the effect of strain rate and original austenite grain size on static recrystallization is relatively small, and when the deformation temperature is above 980 鈩，

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