N对低碳V-Ti钢焊接热影响区晶内铁素体和强韧性调控研究

发布时间：2018-06-18 10:20

  本文选题：V-N-Ti钢 + 大线能量焊接　； 参考：《燕山大学》2016年博士论文

【摘要】：V元素作为重要的合金元素之一,通过与N元素的配合使用能够显著提高材料的强度和韧性,然而V和N元素对焊接粗晶热影响区(Coarse grain heat affected zone(CGHAZ))的组织和韧性的影响一直存在争议。本文借助Gleeble-3800热模拟试验机、扫描电镜(SEM)和透射电镜(TEM)等分析技术,结合力学性能测试,系统研究了N对低碳V-Ti钢CGHAZ的IGF组织和强韧性的调控作用。研究了N含量对低碳V-Ti钢CGHAZ连续冷却转变行为的影响。结果表明,首先,增N后试验钢CGHAZ相变开始温度升高。其次,增N降低了临界t8/5时间tc1和tc2,,减小了贝氏体区域的大小;第三,增N改变了不同t8/5时间下CGHAZ的组织类型,促进了多边形铁素体和针状铁素体的形成。最后,与N钢相比,增N显著降低了CGHAZ的硬度。研究了N含量对低碳V-Ti钢CGHAZ组织和韧性的影响。结果表明,试验钢CGHAZ的50%FATT是有效晶粒尺寸、固溶N和析出强化综合作用的结果。当试验钢的N含量从44 ppm增加到94 ppm,有效晶粒尺寸(晶粒取向差角≥15o)细化,CGHAZ的50%FATT降低;N含量继续增加,试验钢CGHAZ中固溶N、析出强化对韧性的降低作用增加使CGHAZ的50%FATT降低。当N含量为94 ppm时,试验钢CGHAZ获得了最佳的强韧性匹配。研究了焊接热输入对低碳V-Ti钢CGHAZ的组织和韧性的影响。结果表明,试验钢的模拟CGHAZ的屈服强度随着焊接热输入的增加而降低。由于增N促进了TiN粒子的析出,有效细化了原始奥氏体晶粒尺寸和有效晶粒尺寸,导致91N钢模拟CGHAZ的50%FATT随着有效晶粒尺寸的减小而降低,且显著高于32钢。原始奥氏体晶粒和有效晶粒尺寸的细化可以降低固溶N对韧性的损害作用。与32钢相比,91N钢的CGHAZ能够获得良好的强韧性匹配。研究了N对低碳V-Ti钢焊接热循环过程中析出粒子的影响。结果表明,对于低N钢的目次析出粒子的类型为富Ti的(Ti,V)(C,N)粒子,经过焊接热循环后发生粗化,从而导致奥氏体晶粒的粗化。对于增N钢,母材的析出粒子类型为富Ti的(Ti,V)(C,N)、富V的(V,Ti)(C,N)粒子和V(C,N)。在焊接热循环过程中,富V的(V,Ti)(C,N)粒子和V(C,N)发生完全的溶解,而富Ti的(Ti,V)(C,N)部分溶解。焊接峰值温度和焊接冷却过程中尺寸小于50 nm的富Ti的(Ti,V)(C,N)粒子能够有效的钉扎奥氏体晶界,从而细化奥氏体晶粒。N含量从44 ppm增加到190 ppm降低了基体中固溶Ti元素的含量,使富Ti的(Ti,V)(C,N)粒子的粗化速率降低,最终细化了富Ti的(Ti,V)(CN)粒子尺寸。研究了(Ti,V)(C,N)析出粒子促进CGHAZ晶内铁素体(IGF)形成机理。焊接冷却过程中,未溶解的富Ti粒子可以作为富V粒子的形核质点,并且使富Ti的(Ti,V)(C,N)粒子达到临界形核尺寸。富V粒子的形成提高了富Ti的(Ti,V)(C,N)复合析出粒子促进铁素体形核的能力,其作为形核质点促进了晶内铁素体的形成,且复合析出相和晶内铁素体之间的取向关系为B-N关系,导致铁素体相变开始温度升高。
[Abstract]:As one of the most important alloy elements, the V element can significantly improve the strength and toughness of the material through the use of N element. However, the effect of V and N elements on the microstructure and toughness of coarse grain heat affected zonezonium (CGHAZ) in the coarse heat affected zone (HAZ) has always been controversial. By means of Gleeble-3800 thermal simulation test machine, scanning electron microscope (SEM) and transmission electron microscope (TEM), combined with mechanical properties test, the effect of N on the structure and strength of CGHAZ of low carbon V-Ti steel was studied systematically. The effect of N content on the continuous cooling transition behavior of low carbon V-Ti steel CGHAZ was studied. The results show that, firstly, the initial temperature of CGHAZ phase transition increases after N addition. Secondly, the increase of N decreases the critical t8 / 5 tc1 and Tc2N, and decreases the size of the bainite region. Thirdly, the increase of N changes the structure types of CGHAZ at different t8 / 5 times, and promotes the formation of polygonal ferrite and acicular ferrite. Finally, compared with N steel, the hardness of CGHAZ was significantly decreased by increasing N. The effect of N content on the microstructure and toughness of low carbon V-Ti steel CGHAZ was studied. The results show that the 50TT of CGHAZ is the result of effective grain size, solid solution N and precipitation strengthening. When the N content of the test steel increased from 44 ppm to 94 ppm, the effective grain size (grain orientation difference angle 鈮，

本文编号：2035143