Carbide precipitates and mechanical properties of medium Mn steel joint with metal inert gas welding

Medium Mn steel was metal inert gas(MIG)welded with NiCrMo-3 and 307Si filler wires.The effect of filler wires on the microstructure and mechanical properties of joint was investigated,and the carbide precipitates were contrastively discussed.The results revealed that the microstructure of weld metal,heat-affected zone and base metal are austenite.Obvious grain coarsening occurred in the heat-affected zone(HAZ),and the maximum grain size grew up to 160 pm.In HAZ,C and Cr segregated at grain boundaries,the carbides was identified as Cr7C3.The dispersive(Nb,Mo)C phase was also found in weld metal with NiCrMo-3 filler wire.All the welded joints failed in HAZ during tensile tests.The tensile strength of welded joint with NiCrMo-3 filler wire was 675 MPa,which is much higher than that with 307Si filler wire.In comparison to base metal,higher microhardness and lower impact toughness were obtained in HAZ for these two welded joints,which was attributed to the precipitation of Cr7C3 phase and grain coarsening.The impact toughness around the fusion line is the worst for these two welded joints.     

Microstructural,compositional and mechanical investigation of Shielded Metal Arc Welding (SMAW) welded superaustenitic UNS N08028 (Alloy 28) stainless steel

Shielded Metal Arc Welding (SMAW) was performed on UNS N08028 (Alloy 28) superaustenitic stainless steel sheets. In the present work, the microstructure and the mechanical properties of base metal (BM), weld metal (WM), and welded joint (WJ) are investigated. Optical micrographs show that the base metal presents austenitic grains, and the weld metal exhibits a fully austenitic dendritic structure, confirming the Schaeffler diagram estimations. Microhardness measurements indicate that the hardness increases in the weld bead due to the rapid cooling and thermal cycle during welding procedure. The measured mechanical properties and the analysis of the fracture profiles show that the two materials are ductile but the ductility is less pronounced in the weld metal. Consistently the yield stress, the plastic strength and the impact toughness are lower than in the base metal. In addition, the BM presents a higher cyclic hardening and plastic strain compared to those of WM. Cyclic stress–strain hysteresis loops show that WM and WJ have almost the same cyclic behavior and especially at high imposed strain levels.     

BT20钛合金激光焊接接头的断裂韧性研究

对BT20钛合金及其激光焊接接头的断裂韧性进行了研究.同时分析了合金及激光焊接接头的硬度分布及显微组织.断裂实验表明,除了一个焊接接头紧凑拉伸(CT)试样是脆性启裂外,其它CT试样均在裂纹延性启裂并缓慢扩展后,发生脆性失稳断裂.母材的断裂韧性明显高于焊接接头,轧制方向对母材断裂韧性的影响不明显.焊接热影响区的断裂韧性介于母材和焊缝金属之间.本研究采用的焊后热处理没有改善焊接接头的断裂韧性,还有进一步恶化的趋势.添加活性剂对焊缝金属的断裂韧性没有明显作用,但对延性裂纹扩展长度有所改善.     

低成本船用EH36高强钢板的研制及其性能

不添加价格昂贵的铌、钒元素,仅在C-Mn钢成分体系上添加钛元素细化晶粒,采用热机械控制工艺研制出低成本的船用EH36高强钢板,并对其力学性能、显微组织等进行了分析。结果表明:该船用EH36高强钢板成本较原来低,其性能满足标准要求,且强度和韧性均有较大的富余量;经人工应变时效后,其低温冲击韧性仍较好;经两种热输入焊接后,其焊接接头的力学性能均满足母材性能的要求,且富余量较大,说明其具有优越的焊接性能。     

Characterization of microstructure,chemical composition,corrosion resistance and toughness of a multipass weld joint of superduplex stainless steel UNS S32750

The superduplex stainless steels have an austeno-ferritic microstructure with an average fraction of each phase of approximately 50%. This duplex microstructure improves simultaneously the mechanical properties and corrosion resistance. Welding of these steels is often a critical operation. In this paper we focus on characterization and analysis of a multipass weld joint of UNS S32750 steel prepared using welding conditions equal to industrial standards. The toughness and corrosion resistance properties of the base metal, root pass welded with gas tungsten arc welding, as well as the filler passes, welded with shielded metal arc welding, were evaluated. The microstructure and chemical composition of the selected areas were also determined and correlated to the corrosion and mechanical properties. The root pass was welded with low nickel filler metal and, as a consequence, presented low austenite content and significant precipitation. This precipitation is reflected in the corrosion and mechanical properties. The filler passes presented an adequate ferrite:austenite proportion but, due to their high oxygen content, the toughness was lower than that of the root pass. Corrosion properties were evaluated by cyclic polarization tests in 3.5% NaCl and H₂SO₄ media.     

Fracture toughness (J1C) of electron beam welded AA2219 alloy

AA2219 (Al–6%Cu) was butt welded in T87 temper (solution heat-treated, cold worked and precipitation hardened) and T6 temper (solution heat-treated and precipitation hardened) using electron beam welding (EBW). Variables studied were base metal temper condition and mode of EBW. Mechanical properties of the weld joint and fracture toughness at fusion zone (FZ) and heat-affected zone (HAZ) were evaluated and compared with those of the base metal. Results showed that EB welds have higher joint efficiency and fracture toughness than that of gas tungsten arc welding (GTAW). Fracture toughness of T6 base metal was found to be higher than its T87 counterpart. When welded, FZ and HAZ in T87 showed higher fracture toughness than that of T6; HAZ was the toughest. Pulsed current (PC) EB weld showed marginal reduction in toughness compared to constant current (CC) weld. Toughness variation is analyzed with the help of tensile test, Charpy impact test and scanning electron microscopy (SEM) and transmission electron microscopy (TEM).     

高温服役对HP40Nb炉管焊接接头组织及性能的影响

以一段服役7年左右的HP40Nb制氢转化炉管为对象,研究了高温服役过程对其焊接接头微观组织及力学性能的影响。观察分析了不同区域显微组织的特征和析出相的形态及分布情况,并测定了各区域的硬度、强度和冲击韧性等性能参数。结果表明:HP40Nb炉管焊接接头的熔敷金属中只有少量碳化物析出,而在母材中有大量的碳化物析出并聚集在奥氏体晶界上形成网链状;接头的抗拉强度只有少量下降,但其延伸率和冲击韧性均发生严重下降。     

Nb、Ti微合金元素对连铸10MnNiCr钢埋弧焊接头组织与韧性的影响

利用金相显微镜、冲击试验等研究了Nb、Ti微合金元素对连铸10MnNiCr钢埋弧焊焊接接头组织与韧性的影响。结果表明,Nb V Ti钢的焊缝和焊接热影响区比Nb V钢的具有更高的冲击韧性。其中Nb元素易促进侧板条铁素体形成,对韧性不利;Ti元素易使焊缝金属产生针状铁素体,并抑制CG HAZ晶粒粗化,对改善埋弧焊接头韧性有显著作用。     

Microstructure and mechanical properties of friction stir welded 18Cr–2Mo ferritic stainless steel thick plate

In this study, microstructure and mechanical properties of a friction stir welded 18Cr–2Mo ferritic stainless steel thick plate were investigated. The 5.4 mm thick plates with excellent properties were welded at a constant rotational speed and a changeable welding speed using a composite tool featuring a chosen volume fraction of cubic boron nitride (cBN) in a W–Re matrix. The high-quality welds were successfully produced with optimised welding parameters, and studied by means of optical microscopy (OM), scanning electron microscopy (SEM), electron back-scattered diffraction (EBSD) and standard hardness and impact toughness testing. The results show that microstructure and mechanical properties of the joints are affected greatly, which is mainly related to the remarkably fine-grained microstructure of equiaxed ferrite that is observed in the friction stir welded joint. Meanwhile, the ratios of low-angle grain boundary in the stir zone regions significantly increase, and the texture turns strong. Compared with the base material, mechanical properties of the joint are maintained in a comparatively high level.     

Investigation of metallurgical and mechanical properties of 21st century nickel-based superalloy 686 by electron beam welding technique

Electron Beam Welding (EBW) was performed on the highly corrosion resistance superalloy 686. The present research work investigates the metallurgical and mechanical properties of the weld joint fabricated by Electron Beam Welding technique, and the results are compared with the base metal. Optical and Scanning Electron Microscope (SEM) analysis were carried out to study the structural properties of the weld joint. The fine equiaxed dendritic structure was revealed in the Center Fusion Zone (CFZ). The columnar dendrite was noticed in the Transition Fusion Zone (TFZ). Energy-dispersive X-ray spectroscopy (EDS) analysis results show that segregation of Mo and W were noticed in the sub-grain boundary. X-ray diffraction analysis (XRD) confirmed the presence of Mo and W rich phases in the weldment. Tensile testing was carried out to evaluate the strength and ductility of the weld joint. The result revealed that the weld strength was equal to the base metal strength. The presence of Mo and W-rich intermetallic phase reduced the ductility and toughness of the weld joint compared to base metal. Bend test confirmed the defect-free weld joint that was achieved in the Electron Beam Welding technique. The corrosion rate of base metal and EBW weldment are calculated in the synthetic seawater environment with the help of Potentiodynamic polarization experiment, and corrosion rate is measured with Tafel’s interpolation technique. The corrosion test result shows that the resistance of EBW weldment is lesser than base metal corrosion resistance because of the microsegregation of alloying elements in the interdendritic region.     

热输入对Q1100钢焊接接头低温韧性及耐蚀性能的影响

采用10 kJ/cm和15 kJ/cm两种焊接热输入对Q1100超高强钢进行熔化极气体保护焊,研究焊接接头的组织性能及局部腐蚀行为。结果表明：两种热输入焊接接头的焊缝组织主要为针状铁素体和少量的粒状贝氏体,粗晶区组织均为板条贝氏体,细晶区组织均为板条贝氏体和粒状贝氏体,临界相变区组织为多边形铁素体、马奥岛和碳化物的混合组织。两种热输入焊接接头中电荷转移电阻均为母材>热影响区>焊缝区,母材耐蚀性最好,热影响区次之,焊缝区耐蚀性最差。在腐蚀过程中,焊缝区作为阳极最先被腐蚀,当腐蚀一定时间后,腐蚀位置发生改变,阳极腐蚀区域转移到母材区,而焊缝区作为阴极得到保护。热输入为10 kJ/cm时,焊接接头具有更好的低温韧性和耐蚀性,其焊缝和热影响区-40℃冲击功分别为46.5 J和30.2 J。     

Characterization of mechanical properties,fatigue-crack propagation,and residual stresses in a microalloyed pipeline-steel friction-stir weld

The influence of the friction-stir welding process on microstructure and mechanical properties of API 5L X80 skelp was investigated. Friction-stir welds were produced using welding parameters optimized to promote weld toughness. The solid-state welding process produced microstructures that significantly varied from those observed in the base metal, namely the redistribution and resizing of Martensite–Austenite constituent in the heat-affected zone and stir zone regions of the welds. Mechanical properties of the welds and base metal were evaluated with uniaxial tension testing and microhardness testing revealing overmatching welds and a hard zone within the weld stir zone. Residual stresses were determined in several directions with respect to the joint revealing that stress in the longitudinal direction is highest, yet well below material yield strength. Fatigue-crack propagation behavior was characterized in the different weld regions and base metal by testing with the compact tension specimen configuration showing that welds have impeded fatigue-crack growth compared to the base metal mostly due to welding-induced residual stress fields interacting with the crack.     

Effect of Post-weld Heat Treatment on Microstructure and Fracture Toughness of 30CrMnSiNi2A Steel Welded Joints

The electron beam local post-weld heat treatment (EBLPWHT) is a rather new method that provides the advantages of high precision, flexibility and efficiency, energy saving and higher productivity. This paper studies the effect of two post-weld heat treatment processes on the microstructure, mechanical properties and fracture toughness of an electron beam welded joints in 30CrMnSiNi2A steel. EBLPWHT, in a vacuum chamber, immediately after welding and a traditional furnace whole post-weld heat treatment (FWPWHT) were compared. The experimental results show that, after EBLPWHT treatment, the main microstructure of weld was changed from coarse acicular martensite into lath rnartensite, HAZ was changed from lath martensite, bainite into lower bainite, and base metal was changed from ferrite and pearlite into upper bainite and residual austenite. The microstructures of different zones of joints in FWPWHT condition were tempered sorbite. The properties of welded joints can be improved by the EBLPWHT in some extent, and especially largely for the fracture toughness of welded joints. However the value of fracture toughness of base metal is comparatively low, so appropriate heat treatment parameters should be explored in the future.     

Characterization on strength and toughness of welded joint for Q550 steel

Q550 high strength steel was welded using gas shielded arc welding and three different welding wires without pre- or post-heat treatments. The paper investigates the influence of welding wire on the microstructure, tensile strength and impact toughness of Q550 steel weld joints. Results showed that the microstructure of the weld metal of joints produced using ER50-6 wire was a mixture of acicular ferrite and grain boundary ferrite including pro-eutectoid ferrite and ferrite side plate. Acicular ferrite was mainly obtained in the weld metal of the joints produced using MK·G60-1 wire. Pro-eutectoid ferrite was present along the boundary of prior austenite. Crack initiation occurred easily at pro-eutectoid ferrite when the joint was subjected to tensile. Tensile strength and impact toughness were promoted with increasing acicular ferrite. Tensile strength of the joint fabricated using MK·G60-1 wire was close to that of base metal. And tensile samples fractured at location of the fusion zone, which had lower toughness and thus became the weak region in the joint. Impact absorbing energy was the highest in the heat affected zone. Fibrous region in fracture surfaces of impact specimens was characterized as transgranular fracture with the mechanism of micro-void coalescence. Acicular ferrite microstructure region corresponded to relatively large dimples while boundary ferrite microstructure corresponded to small dimples.     

Enhancement of mechanical properties and failure mechanism of electron beam welded 300M ultrahigh strength steel joints

In this study, four post-weld heat treatment (PWHT) schedules were selected to enhance the mechanical properties of electron beam welded 300M ultrahigh strength steel joints. The microstructure, mechanical properties and fractography of specimens under the four post-weld heat treatment (PWHT) conditions were investigated and also compared with the base metal (BM) specimens treated by conventional quenching and tempering (QT). Results of macro and microstructures indicate that all of the four PWHT procedures did not eliminate the coarse columnar dendritic grains in weld metal (WM). Whereas, the morphology of the weld centerline and the boundaries of the columnar dendritic grains in WM of weld joint specimens subjected to the PWHT procedure of normalizing at 970 °C for 1 h followed by conventional quenching and tempering (W-N2QT) are indistinct. The width of martensite lath in WM of W-N2QT is narrower than that of specimens subjected to other PWHT procedures. Experimental results indicate that the ductility and toughness of conventional quenched and tempered joints are very low compared with the BM specimens treated by conventional QT. However, the strength and impact toughness of the W-N2QT specimens are superior to those of the BM specimen treated by conventional QT, and the ductility is only slightly inferior to that of the latter.     

Effects of heat treatment process and niobium addition on the microstructure and mechanical properties of low carbon steel weld metal

The mechanical properties and microstructure were evaluated and analyzed by optical microscopy (OM) and transmission electron microscopy (TEM) for micro-alloy carbon steel weld metal with and without Nb addition, respectively, under different heat treatment processes including stress relief annealing, normalizing, and no treatment after welding. The strength and elongation of the weld metal without treatment after welding were improved with the addition of Nb element, and the impact toughness was not affected obviously with the Nb addition. After stress relief annealing, the strength decreased for the Nb-free weld metal, while the elongation and impact toughness increased. However, for the Nb-bearing weld metal, stress relief annealing improved the strength of the weld metal significantly, and deteriorated the elongation and impact toughness. In the case of normalizing treatment to the weld metal, it was shown that with the increase of the holding time at the normalizing temperature of 920 °C, for both the weld metals with and without Nb addition, the microstructure of the columnar grain zone (CGZ) was transformed from one of columnar grain into one of equiaxed grain. The grain size of the equiaxed grain zone (EGZ) increased initially, then remained almost unchanged with the prolonging of the holding time. The mechanical properties of the weld metal with and without Nb addition showed no obvious change with the increasing holding time. With the increase of the normalizing temperature, the strength of the Nb-bearing weld metal increased, while the elongation and impact toughness decreased significantly. OM and TEM analysis found that the fine NbC particles were precipitated at the normalizing temperature of 920 °C, which refined the grains of the weld metal and increased the impact toughness. With the increase of the normalizing temperature, the content of widmanstatten ferrite (WF) in the Nb-bearing weld metal increased, whereas the quantity of the NbC particles decreased, which improved the strength and lowered the impact toughness.     

TWIP钢激光拼焊板的力学性能及微观组织分析

为评价TWIP钢的焊接性能,对1.2 mm厚的Fe-Mn-C系TWIP钢进行了激光拼焊实验,用线扫描分析了锰元素的分布,对拼焊板进行了拉伸试验,用扫描电镜观察了拉伸断口形貌,采用背散射电子分析技术分析了拉伸前后的组织变化及孪晶形成,测试了维氏硬度的分布曲线.实验结果表明:焊缝区未发生Mn元素的挥发,室温下为显著的柱状枝晶铸态组织;断裂发生在存在气孔等微小缺陷的焊缝区,拼焊板强度与母材接近,韧性显著降低;拉伸过程中有大量的形变孪晶形成,拉伸前后均为全奥氏体组织.     

U75V轨道钢线性摩擦焊工艺研究

目的 提高及改善目前轨道连接与修复的质量。方法 采用线性摩擦焊（LFW）的方法,对高碳轨道钢（U71Mn）在不同参数下进行了焊接试验,并对其微观组织和力学性能进行了表征。结果 焊接参数对接头质量起着决定性的作用。根据焊后接头的微观组织差异,可将其分为4个部分：焊缝中心区（WCZ）、热力影响区（TMAZ）、热影响区（HAZ）和母材（BM）。BM为珠光体和上贝氏体的混合组织,TMAZ由珠光体和少量马氏体组成。在WCZ中,由于受到的热力耦合作用的增强和更高的冷却速率,该区域马氏体含量进一步增加。在拉伸试验中,所有试样均在WCZ处发生断裂,接头的最大抗拉强度达到BM强度的86.6%。此外,WCZ中存在大量马氏体,在增加焊缝显微硬度的同时也降低了焊缝的冲击韧性。结论 采用LFW的方法可以得到焊接质量优良的轨道钢接头。     

Effect of laser beam welding on fracture toughness of a Ti-6.5Al-2Zr-1Mo-1V alloy sheet

Investigation of fracture toughness on Ti-6.5Al-2Zr-1Mo-1V alloy thin sheet and its laser-welded joints has been carried out. In the test compact tension (CT) specimens and single specimen technology were used. In addition, hardness distribution and microstructure of the welded joints were examined. Fracture test indicates that brittle unstable fracture occurs after slow crack propagation for all the specimens, except that one heat affected zone (HAZ) specimen is brittle crack initiation. It is found that rolling directions have no obvious effect on fracture toughness of base metal. Moreover, fracture toughness of weld metal is obviously decreased in comparison with base metal whatever in as-welded condition or in stress relief condition. Post-weld heat treatment (PWHT) leads to fracture toughness of the welds further decreasing. Fractography observation shows that the fracture mode is predominantly dimpled in base metal. However, there exists intergranular fracture in the weld metal. Thus, the transition of fracture mode from both base metal and HAZ to weld metal may lead to dramatic decrease in fracture toughness. Microstructure examination reveals that the microstructure of weld metal consists of large grains with fine acicular structure. The formation of fine α acicular structure is due to rapid cooling during laser welding. After PWHT, the acicular structure is coarsened.     

药芯焊丝Mo含量对低合金钢焊缝金属性能影响

通过在金红石型药芯焊丝中加入不同含量的金属Mo,研究了Mo对熔敷金属组织及力学性能的影响。研究表明,药芯焊丝中的Mo基本全部过渡到焊缝中;添加微量Mo时,焊缝金属强度显著提升,同时冲击韧性恶化严重;进一步增加Mo含量,焊缝金属强化效果不明显,而冲击性能继续下降。组织分析发现,增加焊丝中的Mo含量,首先会降低奥氏体转变温度,增加基体中的碳化物析出相;继续增加Mo时,碳化物含量减少,但M-A组元含量增加,导致韧性持续下降。