低温相变填充焊丝对Q690D低合金高强钢组织及性能的影响
发布时间：2018-10-05 12:08
【摘要】：低合金高强钢由于具有强度高、塑韧性及焊接性良好等特点,广泛应用于汽车、铁路车辆、桥梁等行业。低合金高强钢在焊接的过程中容易生成大而集中的焊接残余应力,会使焊接构件产生应力腐蚀开裂,甚至脆性断裂,严重降低抗疲劳性能,大大缩减构件的服役寿命。工程上通常采用机械法和热处理法来减小或消除焊接残余应力,这样就会增加额外的生产成本。低温相变材料可降低马氏体的相变温度,目的是在低温区产生马氏体相变膨胀抵消焊接冷却过程所产生的热收缩,起到降低残余应力的作用。该方法不需进行焊前预热与焊后热处理,可有效降低焊接残余应力,不仅降低了生产成本,还提高了焊接构件的抗疲劳性能。本文分析了合金元素降低马氏体转变温度(Ms点)的作用,并与舍弗勒相图相结合,研制出了一种低温相变(LTT)焊丝,用于解决高强钢焊后残余应力集中的问题。以低合金高强钢Q690D为母材,LTT焊丝和普通ER110S-G焊丝作为焊缝填充材料,并利用活性气体保护焊(MAG)对其进行了焊接试验。分别使用光学显微镜(OM)、扫描电子显微镜(SEM)、X射线衍射仪(XRD)等分析测试技术对接头的显微组织进行了分析,结果显示LTT接头焊缝区的组织主要由马氏体和少量残余奥氏体组成,ER110S-G接头焊缝区的组织主要由铁素体和少量粒状贝氏体组成,LTT接头焊缝区与母材区存在元素的扩散现象,Cr、Ni元素变化趋势明显。对焊接接头的力学性能进行了测试,结果显示LTT接头焊缝金属处的显微硬度高于ER110S-G接头,LTT接头的抗拉强度也高于ER110S-G接头,但LTT接头的冲击韧性不如ER110S-G接头。使用Geleeble3500热模拟试验机测量了焊缝熔敷金属应变随温度的变化曲线。LTT接头焊缝金属的马氏体相变开始温度约为212℃,相变结束温度约为50℃,由相变引起的膨胀量为0.48%,远远超过母材(0.15%)及ER110S-G接头(0.18%)组织的相变膨胀量。利用X射线衍射法对接头的残余应力进行测量,结果显示,ER110S-G接头焊缝中心处的残余拉应力值为175.5 MPa,LTT接头焊缝中心处残余压应力为-257.6 MPa,表明低温相变焊丝能够在焊缝处产生有利于改善接头性能的残余压应力。使用LTT低温相变焊丝作为焊缝填充材料时焊接试板的角变形弧度为0.0375rad,使用ER110S-G焊丝作为焊缝填充材料时焊接试板的角变形弧度为0.0625rad,可知LTT接头的角变形量仅为ER110S-G接头角变形量的60%,主要原因是残余应力状态发生了改变。
[Abstract]:Low alloy high strength steel is widely used in automobile, railway vehicle, bridge and so on because of its high strength, toughness and weldability. It is easy to produce large and concentrated residual stress in the welding process of low alloy high strength steel, which will cause stress corrosion cracking, even brittle fracture of welded members, seriously reduce the fatigue resistance and greatly reduce the service life of the components. Mechanical and heat treatment methods are usually used in engineering to reduce or eliminate welding residual stress, which increases the production cost. The transformation temperature of martensite can be reduced by low temperature phase change material. The purpose is to produce martensite transformation expansion in low temperature region to counteract the thermal shrinkage caused by welding cooling process and to reduce the residual stress. This method does not need pre-welding preheating and post-welding heat treatment, which can effectively reduce the welding residual stress, not only reduce the production cost, but also improve the fatigue resistance of welded components. In this paper, the effect of alloying elements on the reduction of martensite transformation temperature (Ms) is analyzed, and a low temperature phase change (LTT) welding wire is developed by combining with Schaeffler diagram, which is used to solve the problem of residual stress concentration in high strength steel after welding. The low alloy high strength steel Q690D was used as the base material and the ordinary ER110S-G wire as the weld filling material. The welding tests were carried out by using active gas shielded (MAG). The microstructure of the joint was analyzed by means of optical microscope, (OM), scanning electron microscope, (SEM) X ray diffractometer, (XRD), etc. The results show that the microstructure of the weld zone of LTT joint mainly consists of martensite and a small amount of retained austenite. The microstructure of the weld zone of ER110S-G joint is mainly composed of ferrite and a little granular bainite. The variation trend of Cr-Ni element is obvious. The mechanical properties of the welded joints were tested. The results showed that the microhardness of LTT joints was higher than that of ER110S-G joints and that of ER110S-G joints, but the impact toughness of LTT joints was not as good as that of ER110S-G joints. The variation curve of strain with temperature of weld deposited metal was measured by Geleeble3500 thermal simulator. The martensitic transformation temperature of weld metal in LTT joint was about 212 鈩，
本文编号：2253324
[Abstract]:Low alloy high strength steel is widely used in automobile, railway vehicle, bridge and so on because of its high strength, toughness and weldability. It is easy to produce large and concentrated residual stress in the welding process of low alloy high strength steel, which will cause stress corrosion cracking, even brittle fracture of welded members, seriously reduce the fatigue resistance and greatly reduce the service life of the components. Mechanical and heat treatment methods are usually used in engineering to reduce or eliminate welding residual stress, which increases the production cost. The transformation temperature of martensite can be reduced by low temperature phase change material. The purpose is to produce martensite transformation expansion in low temperature region to counteract the thermal shrinkage caused by welding cooling process and to reduce the residual stress. This method does not need pre-welding preheating and post-welding heat treatment, which can effectively reduce the welding residual stress, not only reduce the production cost, but also improve the fatigue resistance of welded components. In this paper, the effect of alloying elements on the reduction of martensite transformation temperature (Ms) is analyzed, and a low temperature phase change (LTT) welding wire is developed by combining with Schaeffler diagram, which is used to solve the problem of residual stress concentration in high strength steel after welding. The low alloy high strength steel Q690D was used as the base material and the ordinary ER110S-G wire as the weld filling material. The welding tests were carried out by using active gas shielded (MAG). The microstructure of the joint was analyzed by means of optical microscope, (OM), scanning electron microscope, (SEM) X ray diffractometer, (XRD), etc. The results show that the microstructure of the weld zone of LTT joint mainly consists of martensite and a small amount of retained austenite. The microstructure of the weld zone of ER110S-G joint is mainly composed of ferrite and a little granular bainite. The variation trend of Cr-Ni element is obvious. The mechanical properties of the welded joints were tested. The results showed that the microhardness of LTT joints was higher than that of ER110S-G joints and that of ER110S-G joints, but the impact toughness of LTT joints was not as good as that of ER110S-G joints. The variation curve of strain with temperature of weld deposited metal was measured by Geleeble3500 thermal simulator. The martensitic transformation temperature of weld metal in LTT joint was about 212 鈩，
本文编号：2253324
本文链接：https://www.wllwen.com/kejilunwen/jiagonggongyi/2253324.html
