Effect of Laser Welding Process Parameters on Microstructure and Mechanical Properties on Butt Joint of New Hot-Rolled Nano-scale Precipitation-Strengthened Steel

A 4 kW fiber laser was chosen to weld the new hot-rolled nano-scale precipitation-strengthened steel with a thickness of 4.5 mm. The effect of laser power, defocusing distance, and welding speed on the welded joint appearance was examined, and the microstructure and mechanical properties on the typical butt joints were investigated. Results showed that increasing laser welding power may cause faster downward flow of molten metal to produce greater root humping. With the welding speed increasing, the average welding seam （WS） width decreased, and the average WS and heat-affected zone （HAZ） hardness increased. The microstructures of WS, fusion line, and coarse grain heat-affected zone were lath martensite, but the growth direction of the original austenite grain boundaries was significantly different. The microstructures of fine grain heat-affected zone were ferrite and martensite, and the microstructure of mixed grain heat- affected zone contained ferrite, massive M/A island, and a small amount of martensite. The micro-hardness values of WS, HAZ, and base metal （BM） were 358, 302, and 265 HV, respectively. The butt joint fracture at the BM far from the WS and the welded joint tensile strength are observed to follow proportional relationship with hardness.     

Microstructure,Residual Strain and Stress Corrosion Cracking Behavior in 316L Heat-Affected Zone

Austenitic stainless steels are usually chosen to make many components of nuclear power plants(NPPs).However,their microstructure in the heat-affected zone(HAZ)will change during the welding process.Some failures of the weld joints,mainly stress corrosion cracking(SCC),have been found to be located in the HAZ.In this research,the microstructure,micro-hardness,residual strain and SCC behavior at different locations of the 316L HAZ cut from a safeend dissimilar metal weld joint were studied.However,traditional optical microscope observation could not find any microstructural difference between the HAZ and the base metal,higher residual strain and micro-hardness,and higher fraction of random high-angle grain boundaries were found in the HAZ than in the base metal when studied by using electron back-scattering diffraction scanning and micro-hardness test.What’s more,the residual strain,the microhardness and the fraction of random grain boundaries decreased,while the fraction of coincidence site lattice grain boundaries increased with increasing the distance from the fusion boundary in 316L HAZ.Creviced bent beam test was applied to evaluate the SCC susceptibility at different locations of 316L HAZ and base metal.It was found that the HAZ had higher SCC susceptibility than the base metal and SCC resistance increased when increasing the distance from the fusion boundary in 316L HAZ.     

Ti17合金惯性摩擦焊接头力学性能与组织分析

通过室温拉伸、高温拉伸试验以及金相分析对 Ti17 合金惯性摩擦焊接接头的显微组织和力学性能进行了研究.结果表明,采用惯性摩擦焊焊接 Ti17 合金可获得室温及高温性能良好的焊接接头,其焊接接头的室温及高温抗拉强度都不低于母材;Ti17合金母材组织为α+β相,并且β相呈针状均匀分布在α相的基体上;不同焊接工艺参数对 Ti17 合金惯性摩擦焊接头热影响区和焊缝的组织没有影响,其热影响区组织为α+β相,并且β相呈针状均匀分布在α相的基体上,与母材组织相同,焊缝组织为细小的等轴晶.

Abstract：

The microstructures and properties of Ti17 alloy joints welded by inertia friction welding (IFW) were investigated by room-temperature tensile test, high-temperature tensile test and metallographic analyses. The results show that the joint with good performance at room and high temperature for Ti17 alloy can be obtained in IFW. Both the tensile strengths of welded joints at room temperature and at high temperamre are not less than those of the base metal. The microstructure of Ti17 alloy is α+β phase, and the needle β phase is distributing on the α phase. While welding, different welding parameters can not affect the microstructures of the HAZ and the weld seam. The microstructure of HAZ is the same as that of the base metal, and that of the welded seam is fine equiaxed crystal.     

Effect of the heat input on microstructure and properties of submerged arc welded joint of 08Cr19MnNi3Cu2N stainless steel

SAW308L submerged arc welding wire and SJ601A submerged arc welding flux were selected to weld the 12 mm 08Cr19MnNi3Cu2N low nickel and high nitrogen austenitic stainless steel plates with three different welding heat input, and microstructure,tensile properties, microhardness and corrosion properties of the welded joints were studied. The results show that no defects are found in the three groups of welded joints, and the welded joints have better performance.The tensile strength of 08Cr19MnNi3Cu2N stainless steel welded joints with different heat input is slightly lower than that of the base metal,and fracture occurs in the weld zone, and the hardness of the weld zone is lower than that of the base metal. The weld microstructure of stainless steel welded joints with different heat input is composed of austenite + δ ferrite, and ferrite is uniformly distributed in austenite. With the increase of the welding heat input, the ferrite content in the weld zone decrease gradually, the grain size in the thermal affected zone increase gradually, and the impact toughness reduce.     

Texture and mechanical properties of metal inert gas welded 6082-T651 aluminum alloy joints

Metal inert gas(MIG) welding was conducted with 12 mm thick 6082-T651 aluminum alloy plate to investigate the microstructure and mechanical properties of welded joint. The microstructure and element distribution of weld seam were characterized by electron backscattered diffraction(EBSD) and electron probe microanalysis(EPMA). The weld seam has typical cube texture({001}100) characteristics. The closer to the center of weld seam, the weaker the texture feature, the higher the proportion of high-angle grain boundaries. The average tensile strength of joint was 232 MPa which is up to 72% of 6082 aluminum alloy base metal, and the bending angle for the root bend test sample reached 90° without cracks. The lack of strengthening phase and the existence of welding pores and inclusions in the weld seam caused the degradation of mechanical properties of resultant joint. The microhardness increased from the weld center to the base metal,but the overaging zone caused by welding thermal cycle was softening part of the joint, which had lower hardness than the weld seam.     

Effect of upsetting force on microstructure of welds in resistance spot welding of 400 MPa ultra-fine

The ultra-fine grain (UFG) steel is welded by using resistance spot welding technique with or without requirement of upsetting force.Metallographic inspection shows that the grain size of weld nugget is larger than that of the base metal and the microstructure is altered significantly.In addition,contracting defects such as air holes can be found in the nugget center.The experiments show that the defects can be effectively avoided by the technique of adding upsetting force during the nugget cooling and crystallizing processes.In tensile shear tests,the welding joint starts to crack from the inner edge of the corona bond.The results of micro-hardness tests show that the newly born martensite structure dramatically improves the hardness of the joint.Under the interactions between residual stresses and regenerated fine grains,the micro-hardness of the heat-affected zone (HAZ) is lower than that of the nugget,but evidently higher than that of the base metal.     

Research on the properties of laser welded joints of aluminum killed cold rolled steel

Aluminum killed cold rolled steel used for automobiles was welded in this paper by using CO2 laser with wavelength 10.6μm.The experiment shows that high quality of welding can be realized at welding speed of 4500mm/min by optimizing the parameters.The strenth and hardness of laser welded joints for aluminum killed cold rolled steel increased compared to those of the base metal while the formability decreased.Forming limit diagram of joint material indicated that the laser weld seam should avoid the maximum deformation area of automobile parts during the designing period for the position of weld seam.     

Characteristics of 5A90 Aluminum-lithium Alloy by YAG-MIG Hybrid Welding

The characteristics of 5A90 Aluminum-Lithium alloy by YAG laser and MIG arc hybrid welding (Hybrid welding) were studied.Compared with the laser beam welding (LBW),the hybrid welding could not only improve the weld appearance significantly,but also have better engineering compatibility.The obvious microstructure characteristics of joint by the hybrid welding are fine-grained layer near fusion-line and the equiaxed grain in most area of welded seam.The subgrains of the equiaxed grains,located in the weld center,tend to coarse from bottom to top of weld joint.The microhardness of welded seam by the hybrid welding (83.57HV0.2) is lower than that by LBW (95.65HV0.2),but the uniformity of the former is better than that of the latter.The ultimate strength and the elongations after fracture of the joint by the hybrid welding are lower than that by LBW.The tensile fracture always occurs in HAZ or weld centerline,and the fractography presents mixture rupture.Therefore,if the combined mechanical properties of joint by the hybrid welding meet the operation requirements,it should be improved by reasonable artificial aging or heat treatment after welding,and it also should develop a better filler wire matched with the base metal.     

Microstructure and mechanical properties of wrought magnesium alloy AZ31B welded by laser-TIG hybrid

The laser-TIG hybrid welding was mainly used to weld the wrought magnesium alloy AZ31B. The tech-nical characteristics of laser-TIG hybrid welding process was investigated and the interactional mechanism between laser and arc was discussed, at the same time the microstructure and mechanical properties of the wrought magnesi-um alloy AZ31B using laser-TIG hybrid welding were analyzed by optical microscope, EPMA, SEM, tensile ma-chine, hardness machine. The experimental results show that the presence of laser beam boosts up the stability of the arc during high speed welding and augments the penetration of weld； the crystal grains of magnesium alloy weld are fine without porosity and cracks in the best welding criterion and the microstructure of HAZ does not become coarse obviously. The elements profile analysis reveals that Mg content in the weld is lower than that of the base metal, but Al content is higher slightly. Under this experimental condition, the wrought magnesium alloy AZ31B joint can be achieved using laser-TIG hybrid process and the tensile strength of the joint is equivalent to that of the base metal.     

Quantitative research on the heat affected zone of weave bead welding for Invaralloy

Quantitative research on the heat affected zone( HAZ) of weave bead welding( WBW) joint for Invar alloy is carried out in this paper. Based on the morphology and related data analysis of the weld seam,the width difference of each layer and the forming mechanism are analyzed. Results show that the bottom layer( Layer 1) has the widest HAZ and the smallest fluctuation,which reaches 1 200 μm. HAZ width of layer 2 to 5 is relatively narrower which is basically below 600μm,while the amplitude fluctuation is greater. The main reason lies in the welding path. The long straight welding without weave causes the base metal near the groove fully melts which causes by the long straight welding without weave,while welding with weave leads to the uneven and inadequate melting of metal near groove.     

X80管线钢及其接头的低温韧性和显微组织

分别利用示波冲击韧性试验、硬度试验和光学显微镜、透射电镜研究了X80管线钢及其焊管接头的力学性能和显微组织。试验结果表明，X80钢及其焊管接头具有良好的韧性，其中焊缝的韧性最高，焊接热影响区粗晶区因受焊接热效应引起晶粒粗化和形成脆性组织，故韧性最低。试验钢由针状铁素体和少量块状铁素体组成，焊缝为典型的针状铁素体组织，焊接热影响区粗晶区以粒状贝氏体为主。焊接热影响区熔合线附近的硬度值最高，越远离熔合线硬度值越低，并逐渐接近母材的硬度值。     

ST14钢激光拼焊板焊缝组织及成形性能分析

对1.5mm和0.8mm两种规格的ST14钢等厚激光拼焊板焊缝部位进行杯突试验,比较焊缝与母材杯突值;再对由这两种规格组合拼焊的不等厚激光拼焊板进行单向拉伸试验,检验拼焊板经拉伸后的断裂部位;分析焊缝区组织及其硬度变化,研究激光焊接参数变化对ST14钢拼焊板成形性能的影响.结果表明,焊缝深冲性能低于母材,焊缝杯突值受焊接速度影响,随焊接速度增加而增加;激光焊缝抗拉强度高于母材;对于1.5 mm拼焊板,提高焊接速度,加快焊缝冷却,有利于生成细小的针状铁素体,可提高激光拼焊板的成形性能;而0.8 mm板焊缝生成晶粒细小的粒状贝氏体组织,可使焊缝区材料成形性能接近母材;焊缝及其热影响区的硬度高于母材硬度.     

不等厚高强钢激光拼焊板焊缝组织及胀形性能分析

采用激光焊接方法,针对1.8mm厚的SAPH440与2.2mm厚的DP600高强钢实施激光拼焊.测试了不等厚拼焊板焊接接头的金相组织以及显微硬度,然后通过杯突试验对所得到的不等厚高强钢拼焊板的胀形性进行了研究,进一步与母材的胀形性相比较.结果表明,焊缝的金相组织为针状铁素体和板条马氏体,焊缝两侧硬度分布不同,焊缝处的硬度要高于母材.拼焊板的杯突值低于任何一侧母材的杯突值,焊缝的位置对不等厚拼焊板的胀形性有一定的影响,薄板所占比例越大拼焊板的胀形性越好,在胀形成形过程中焊缝向厚板侧移动.     

Investigations Into the Influence of Weld Zone on Formability of Fiber Laser-Welded Advanced High Strength Steel

In this study, two different dual phase steel grades DP980 and DP600, and IFHS steel sheets were laser welded by a 2-kW fiber laser. The weld quality of these three different LWBs was assessed with the help of microstructure, micro-hardness and transverse tensile tests. Tensile testing of longitudinal and miniature samples was performed to evaluate the mechanical properties of the weld zone. Formability of parent materials and LWBs were assessed in bi-axial stretch forming condition by Erichsen cupping test. To validate the weld zone properties, 3-D finite element models of Erichsen cupping test of LWBs was developed, and the failures in the deformed cups were predicted using two theoretical forming limit diagrams. It was observed that hardness of the fusion zone and HAZ in laser welded DP600 and IFHS steels was more compared to the respective parent metal. However, 29% reduction in hardness was observed at the outer HAZ of DP980 steel weldments due to tempering of martensite. Reduction of formability was observed for all the LWBs with two distinct failure patterns, and the maximum reduction in formability was observed in the case of DP980 LWBs. The presence of the soft zone is detrimental in forming of welded DP steels.     

焊接工艺对TP304钢焊缝金属组织及性能的影响

针对TP304不锈钢,采用三种不同的焊接工艺方法,选取合适的焊接工艺参数,成功制备三组完整的焊接接头.通过X荧光化学成分分析、显微组织观察和显微硬度试验研究了不同焊接方法对TP304不锈钢焊缝金属组织和性能的影响.结果表明,不同焊接方法下焊缝合金成分有所差异,且分布不均;各焊层显微组织形态和晶粒大小差异较大;整个接头的硬度值分布并不均匀,焊缝高于热影响区,热影响区高于母材.三种焊接方法相比,TIG-MAG焊缝的硬度值最大,TIG-SMAW的最小.对于薄板不锈钢焊接,TIG-MAG组合焊法优选.     

400MPa级超细晶粒钢的焊接

对超细晶粒钢在焊接热循环作用下晶粒长大和组织、性能变化的规律进行了研究。400MPa级钢由于不存在第Ⅱ相粒子对晶粒长大的钉扎作用,晶粒长大趋势明显,焊接热输入越大,长大程度越严重。无论是焊接热模拟试件还是焊接接头硬度测试均表明HAZ不存在软化问题,接头拉伸试验断在远离热影响区的母材上。HAZ粗晶区有较多的侧板条铁素体,但制品冲击功未显示热影响区的冲机韧性低于母材,尽管试件断口分析说明粗晶区的韧性低于母材。     

非调质HB400级高强度耐磨钢板焊接接头组织与性能

利用手工电弧焊研究了非调质HB400耐磨板的焊接接头的组织和力学性能,结果表明,焊缝组织主要为块状铁素体和少量珠光体,热影响区组织为新型贝氏体组织,熔合区结合良好,晶粒比较细小,非调质HB400耐磨板焊接接头具有良好的强韧性。     

铝合金5A02不等厚板的CO_2激光填粉拼焊

在填加粉末的条件下,采用CO2激光器焊接铝合金5A02不等厚板,研究焊接参数对焊缝成形的影响;利用金相显微镜、扫描电镜、拉伸试验机分别研究了激光拼焊板焊接接头的力学性能、断口形貌及微观组织特点。结果表明,填加粉末可使5A02不等厚薄板的激光焊接过程的稳定性显著提高,在比较宽的参数范围内,可以得到成形良好的焊缝;拼焊板的横向拉伸试样均断裂于薄板热影响区,拉伸性能与母材中变形能力较好的板料所占比例有关,该比例越大则拼焊板具有较大的延伸率,变形能力越强;拼焊板的焊缝组织极为细小,在熔合线附近开始向焊缝中心生长的是树枝状晶,在焊缝中心是等轴晶。