本文關(guān)鍵詞： 激光填絲焊 核電 異質(zhì)接頭 微觀組織 熱裂紋 力學(xué)性能 耐腐蝕性　出處：《上海交通大學(xué)》2015年博士論文　論文類(lèi)型：學(xué)位論文

【摘要】：在壓水堆核電站設(shè)備中,異種材料之間的焊接是一項(xiàng)復(fù)雜、技術(shù)難度大、質(zhì)量要求高的工程,迄今為止仍是核電加工制造領(lǐng)域的難點(diǎn)。激光焊接技術(shù)是近幾十年來(lái)發(fā)展起來(lái)的一種優(yōu)質(zhì)、高效的新型焊接方法,具有深寬比大、冷卻速度快、熱影響區(qū)窄等特點(diǎn),成為激光加工領(lǐng)域的研究熱點(diǎn)之一。針對(duì)核電一回路Alloy 52M/316L異種金屬關(guān)鍵焊接構(gòu)件,本文提出了采用窄間隙激光填絲焊的方法,探索核電工程中異種金屬激光填絲焊的特點(diǎn)及組織變化規(guī)律,為推廣激光焊接技術(shù)在核電工程的應(yīng)用提供技術(shù)支撐。本文首先開(kāi)展Alloy 52M/316L異種金屬激光填絲焊工藝和焊縫成形的研究,研究表明激光填絲焊Alloy 52M/316L異質(zhì)焊縫具有匙孔形貌特征,兩層焊縫之間有較深的搭接量,揭示了焊縫高度和熔寬隨激光功率、焊接速度和送絲速度等焊接參數(shù)變化的規(guī)律以及焊接側(cè)壁未熔合和氣孔的特征與形成原因。利用光學(xué)顯微鏡(OM)、掃描電鏡(SEM)、透射電鏡(TEM)等分析測(cè)試方法,研究Alloy 52M/316L焊縫區(qū)的微觀組織、成分分布、第二相的析出行為以及異質(zhì)界面結(jié)構(gòu)特征、形成特點(diǎn)和界面區(qū)元素的偏聚行為,對(duì)比研究帶極堆焊(ESW)阻隔層和GTAW阻隔層兩種狀態(tài)下異質(zhì)界面的組織結(jié)構(gòu),結(jié)果表明Alloy 52M/316L焊縫區(qū)靠近熔合線邊界的組織是細(xì)小的胞狀晶,隨著凝固的推進(jìn)胞狀晶轉(zhuǎn)變?yōu)橹鶢顦?shù)枝晶,在焊縫的中心處會(huì)合形成沿焊縫中心對(duì)稱(chēng)生長(zhǎng)的組織形態(tài)；在激光多層焊縫的層間出現(xiàn)了重熔細(xì)晶區(qū),形成了等軸細(xì)晶組織；在焊縫枝晶間主要是由富Nb的析出相和A1203與Ti02聚集一起生長(zhǎng)形成球形復(fù)合氧化物,揭示了Alloy 52M/316L焊縫區(qū)微觀組織和第二相析出的規(guī)律；在ESW52M/WM的界面區(qū)域富Nb的析出相呈鏈狀分布或顆粒狀聚集長(zhǎng)大特征,由于Nb、Si、Cr和Fe等元素在晶界上富集在冷卻凝固階段引起富Nb的第二相析出并聚集、長(zhǎng)大；同時(shí)因GTAW52M與ESW52M微觀組織的差異,在GTAW52M/WM界面上沒(méi)有出現(xiàn)富Nb的碳化物或Laves相；WM/316L界面是由寬度約30-40μm細(xì)小的胞狀晶組成,激光填絲焊縫與316L不銹鋼表現(xiàn)出良好的相容性,體現(xiàn)良好的界面結(jié)合特性；在WM/316L界面附近區(qū)域存在Cr和Mo元素的富集,并詮釋了沿晶界析出呈鏈狀σ相的原因�；贏lloy 52M/316L異質(zhì)接頭熱裂紋產(chǎn)生的位置、特征、化學(xué)成分和斷口分析以及高溫拉伸試驗(yàn)和STF試驗(yàn)的研究,結(jié)果表明富Nb的低熔點(diǎn)共晶相和界面氧化物引起Alloy 52M/316L異質(zhì)焊縫凝固裂紋的重要因素,Alloy 52M/316L異質(zhì)焊縫凝固裂紋的斷口呈凹凸顯著的樹(shù)枝晶狀,表面光滑、無(wú)撕裂棱；基于Alloy 52M/316L焊縫區(qū)凝固裂紋液相回流的分析,推導(dǎo)出裂紋萌生和擴(kuò)展條件下液相回流速度vlx；發(fā)現(xiàn)在液化裂紋處伴隨著富Nb的白色鏈狀析出相,具有晶界低熔點(diǎn)液膜的特征,液化裂紋斷口面的晶粒呈卵石狀,晶粒邊界出現(xiàn)液膜,檢測(cè)表明存在富S和Si的低熔點(diǎn)共晶相,或呈液膜特征的富Nb的析出相附在晶粒表面尖端上；發(fā)現(xiàn)富S的低熔點(diǎn)共晶相和富Nb的析出相是引起Alloy 52M/316L異質(zhì)接頭液化裂紋的冶金因素,并闡明了液膜形成的原因、富Nb的碳化物的組分液化和液膜遷移的裂紋形成機(jī)理；Alloy 52M/316L異質(zhì)接頭的高溫失塑裂紋的走向沿柱狀枝晶發(fā)生開(kāi)裂,其擴(kuò)展方向可能偏離枝晶生長(zhǎng)的方向,高溫失塑裂紋大多起裂于三叉晶界處,而裂紋在晶界上的形成過(guò)程也是孔洞在晶界上形核、長(zhǎng)大和聚合連接的過(guò)程,晶界滑移直接影響晶界上孔洞的形核、長(zhǎng)大與聚合連接,詮釋了Alloy 52M/316L異質(zhì)接頭高溫失塑裂紋形成條件、萌生與擴(kuò)展機(jī)制。通過(guò)力學(xué)性能研究表明Alloy 52M/316L異質(zhì)接頭從Alloy 52M阻隔層經(jīng)過(guò)焊縫到316L不銹鋼的硬度呈下降的趨勢(shì),焊縫區(qū)的平均硬度為180HV；ESW52M/WM界面是沖擊韌性薄弱環(huán)節(jié),在ESW52M/WM界面上不規(guī)則的富Nb的碳化物或脆性的Laves相、氧化夾雜物是導(dǎo)致沖擊韌性降低的主要原因；ESW52M/316L和GTAW52M/316L兩種異質(zhì)接頭的拉伸斷口均呈現(xiàn)出韌性斷裂的特征,但在ESW52M/316L拉伸斷口韌窩處存在大量的析出相,ESW52M/WM界面是整個(gè)焊接接頭的斷裂的薄弱位置；ESW52M/316L異質(zhì)接頭在350℃溫度拉伸的斷裂位置位于316L側(cè),其斷口上存在較多空洞,斷裂機(jī)制是空洞聚集型韌性斷裂。電化學(xué)試驗(yàn)表明,在含Cl-和由Cl-與S2O32-組成的混合介質(zhì)兩種腐蝕溶液體系中,焊縫金屬的極化曲線表現(xiàn)出多次鈍化的特征,腐蝕的形貌呈現(xiàn)差異性,S2O32-促進(jìn)了焊縫金屬的陽(yáng)極溶解,延緩或阻礙其鈍化,促使表面鈍化膜穩(wěn)定性降低作用,揭示了Alloy 52M/316L異質(zhì)焊縫在含C1-和含Cl-與S2O32-的混合介質(zhì)兩種溶液體系中的腐蝕機(jī)制,詮釋了微觀組織、析出相和腐蝕介質(zhì)對(duì)Alloy 52M/316L焊縫金屬腐蝕的影響。
[Abstract]:In the nuclear power plant equipment in PWR, welding between dissimilar materials is a complex, difficult, high quality requirements of the project, so far is still difficult to manufacture nuclear power. Laser welding technology is developed in recent years, a new type of high quality, high efficient welding method, has deep and wide ratio, cooling speed, narrow heat affected zone etc, become a hot research topic in the field of laser processing. Aiming at the nuclear power plant Alloy 52M/316L dissimilar metal welding key components, this paper proposes a method using narrow gap laser welding with filler wire, to explore the characteristics and microstructure of dissimilar metal laser welding in nuclear power engineering technology, provide technical support for the promotion of nuclear power engineering application in laser welding. This research was first carried out Alloy 52M/316L dissimilar metal wire filling laser welding process and weld formation, research shows that laser wire filling Alloy 52M/316L has heterogeneous welding weld keyhole morphology, there is overlap between the two deep layer weld, reveals the weld height and weld width with laser power, welding speed and wire feeding speed of welding parameters and welding characteristics and forming reasons of the side wall without fusion and porosity. By using optical microscopy (OM), scanning electron microscopy (SEM), transmission electron microscopy (TEM) analysis method, the distribution of Alloy 52M/316L on microstructure, weld composition, precipitation behavior of second phase and the interface structure characteristics, formation characteristics and segregation of elements of the interface of strip cladding (ESW) structure barrier the interface layer and GTAW barrier layer under two conditions, the results show that the Alloy 52M/316L weld zone near the fusion line boundary organization is cellularcrystal small, with the advance of the solidification of cellular crystal into the dendrite in the weld. At the junction of center formation along the weld center symmetrical structure; in the laser multilayer welding layer between the fine grain zone remelting, formation of equiaxed grains in the weld microstructure; dendrite is mainly composed of A1203 and Ti02 Nb rich precipitates together to form spherical composite oxide growth, revealing the microstructure Alloy 52M/316L weld zone and the precipitation of the second phase of the law; in the interface region of the precipitation of ESW52M/WM rich Nb phase of chainlike distribution or granular aggregation and growth characteristics, due to Nb, Si, Cr and Fe enrichment at the grain boundary in the cooling stage caused by the precipitation of the second phase Nb rich and aggregation, also because of differences in GTAW52M growth; ESW52M and the microstructure of the interface in the GTAW52M/WM no Nb rich carbide or Laves; WM/316L interface is composed of width of columnar crystal is about 30-40 m small, wire filling laser weld and 316L stainless steel Exhibit good biocompatibility, represents good interfacial characteristics; in the area around the WM/316L interface enrichment of Cr and Mo elements, and the interpretation of the cause is precipitated along grain boundary phase characteristics of Alloy 52M/316L chain. A heterogeneous joint hot crack position, based on the analysis and research of fracture and high temperature tensile test and STF the test results show that the chemical, Nb rich and low melting point eutectic phase and interfacial oxide an important factor in causing Alloy 52M/316L heterogeneity of weld solidification crack, fracture of Alloy 52M/316L heterogeneity of weld solidification crack is of concave convex significant dendritic shape, smooth surface, no tear edge; Alloy 52M/316L analysis of solidification cracks in weld metal based liquid phase reflux. Derived from the crack initiation and propagation under the condition of liquid reflux rate vlx; found in liquation crack is accompanied by a white chain Nb rich precipitates, the grain boundary has a low melting point liquid The characteristics of crack fracture surface liquefaction grains are oval shaped, grain boundary appeared film, testing showed the presence of S rich and Si low melting point eutectic phase, precipitation or a feature rich Nb film attached on the grain surface on the tip; found that the precipitation of S rich and low melting point eutectic phase and Nb rich phase is caused by Alloy 52M/316L heterogeneous joint metallurgical factors liquation crack, and illustrates the reason of liquid film formation, crack formation mechanism of Nb rich carbide components of liquefied and liquid film migration; high temperature Alloy 52M/316L heterogeneous joint loss to plastic crack along the columnar dendrite fracture, the propagation direction may deviate from the direction of dendrite growth. High temperature plastic crack initiation in the loss of most of the triple junctions and crack formation at the grain boundary is void in grain boundary nucleation, growth and coalescence of the connection process, grain boundary sliding directly affect the grain boundary void nucleation, growth The polymerization and interpretation of the Alloy connection, 52M/316L joints ductility dip crack formation conditions, initiation and propagation mechanism. Through the study of mechanical properties showed that the Alloy 52M/316L connector from the Alloy 52M heterogeneous barrier layer of 316L stainless steel after weld hardness decreased, the average hardness of the weld zone is 180HV; the ESW52M/WM interface is the weak link of impact toughness. Irregular interface in the ESW52M/WM rich Nb carbides or brittle Laves phase, oxide inclusion is the main cause of the fracture toughness decrease; ESW52M/316L and GTAW52M/316L two kinds of joints showed the characteristics of ductile fracture, but ESW52M/316L tensile dimples were found a large number of precipitates, the ESW52M/WM interface is weak the position of welded joint fracture; ESW52M/316L joints at the fracture location to the temperature of 350 DEG C stretching in the 316L side, the fracture There are many holes, fracture mechanism is void coalescence fracture. The electrochemical test showed that in the mixed medium containing Cl- and composed of Cl- and S2O32- two kinds of etching solution, the polarization curve of weld metal characterized by multiple passivation, corrosion morphology difference, S2O32- promoted the anodic dissolution of weld metal that delay or prevent the passivation, prompted the passivating film on the surface of reduced stability, revealing the corrosion mechanism of Alloy 52M/316L in heterogeneous weld mixed medium containing C1- and Cl- and S2O32- two in the solution system, the interpretation of the microstructure, effects of precipitated phases and corrosion medium on Alloy 52M/316L weld metal corrosion.

【學(xué)位授予單位】：上海交通大學(xué)
【學(xué)位級(jí)別】：博士
【學(xué)位授予年份】：2015
【分類(lèi)號(hào)】：TM623.91;TG456.7

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