【摘要】：低合金高強(qiáng)鋼由于具有強(qiáng)度高、塑韌性及焊接性良好等特點(diǎn),廣泛應(yīng)用于汽車、鐵路車輛、橋梁等行業(yè)。低合金高強(qiáng)鋼在焊接的過程中容易生成大而集中的焊接殘余應(yīng)力,會(huì)使焊接構(gòu)件產(chǎn)生應(yīng)力腐蝕開裂,甚至脆性斷裂,嚴(yán)重降低抗疲勞性能,大大縮減構(gòu)件的服役壽命。工程上通常采用機(jī)械法和熱處理法來減小或消除焊接殘余應(yīng)力,這樣就會(huì)增加額外的生產(chǎn)成本。低溫相變材料可降低馬氏體的相變溫度,目的是在低溫區(qū)產(chǎn)生馬氏體相變膨脹抵消焊接冷卻過程所產(chǎn)生的熱收縮,起到降低殘余應(yīng)力的作用。該方法不需進(jìn)行焊前預(yù)熱與焊后熱處理,可有效降低焊接殘余應(yīng)力,不僅降低了生產(chǎn)成本,還提高了焊接構(gòu)件的抗疲勞性能。本文分析了合金元素降低馬氏體轉(zhuǎn)變溫度(Ms點(diǎn))的作用,并與舍弗勒相圖相結(jié)合,研制出了一種低溫相變(LTT)焊絲,用于解決高強(qiáng)鋼焊后殘余應(yīng)力集中的問題。以低合金高強(qiáng)鋼Q690D為母材,LTT焊絲和普通ER110S-G焊絲作為焊縫填充材料,并利用活性氣體保護(hù)焊(MAG)對其進(jìn)行了焊接試驗(yàn)。分別使用光學(xué)顯微鏡(OM)、掃描電子顯微鏡(SEM)、X射線衍射儀(XRD)等分析測試技術(shù)對接頭的顯微組織進(jìn)行了分析,結(jié)果顯示LTT接頭焊縫區(qū)的組織主要由馬氏體和少量殘余奧氏體組成,ER110S-G接頭焊縫區(qū)的組織主要由鐵素體和少量粒狀貝氏體組成,LTT接頭焊縫區(qū)與母材區(qū)存在元素的擴(kuò)散現(xiàn)象,Cr、Ni元素變化趨勢明顯。對焊接接頭的力學(xué)性能進(jìn)行了測試,結(jié)果顯示LTT接頭焊縫金屬處的顯微硬度高于ER110S-G接頭,LTT接頭的抗拉強(qiáng)度也高于ER110S-G接頭,但LTT接頭的沖擊韌性不如ER110S-G接頭。使用Geleeble3500熱模擬試驗(yàn)機(jī)測量了焊縫熔敷金屬應(yīng)變隨溫度的變化曲線。LTT接頭焊縫金屬的馬氏體相變開始溫度約為212℃,相變結(jié)束溫度約為50℃,由相變引起的膨脹量為0.48%,遠(yuǎn)遠(yuǎn)超過母材(0.15%)及ER110S-G接頭(0.18%)組織的相變膨脹量。利用X射線衍射法對接頭的殘余應(yīng)力進(jìn)行測量,結(jié)果顯示,ER110S-G接頭焊縫中心處的殘余拉應(yīng)力值為175.5 MPa,LTT接頭焊縫中心處殘余壓應(yīng)力為-257.6 MPa,表明低溫相變焊絲能夠在焊縫處產(chǎn)生有利于改善接頭性能的殘余壓應(yīng)力。使用LTT低溫相變焊絲作為焊縫填充材料時(shí)焊接試板的角變形弧度為0.0375rad,使用ER110S-G焊絲作為焊縫填充材料時(shí)焊接試板的角變形弧度為0.0625rad,可知LTT接頭的角變形量僅為ER110S-G接頭角變形量的60%,主要原因是殘余應(yīng)力狀態(tài)發(fā)生了改變。
[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，

本文編號：2253324