Study of welding ultra‐fine grained ferrite steel by CO2 laser

Ultra‐fine grained ferrite steels have higher strength and better toughness than the normal ferrite steels because of their micrometer or sub‐micrometer sized grains. In this paper the ultra‐fine grained steel SS400 is welded by CO₂ laser. The shape of weld, cooling rate of HAZ, width of HAZ, microstructures and mechanical properties of the joint are discussed. Experimental results indicate that laser beam welding can produce weld with a large ratio of depth to width. The cooling rate of HAZ of laser beam welding is fast, the growth of prior austenite grains of HAZ is limited, and the width of weld and HAZ is narrow. The microstructures of weld metal and coarse‐grained HAZ of laser beam welding mainly consist of B_L + M (small amount). With proper laser power and welding speed, good comprehensive mechanical properties can be acquired. The toughness of weld metal and coarse‐grained HAZ are higher than that of base metal. There is no softened zone after laser beam welding. The tensile strength of a welded joint is higher than that of base metal. The welded joint has good bending ductility.     

Gas Tungsten Arc Welding of 316L Austenitic Stainless Steel with UNS S32205 Duplex Stainless Steel

In the present work, dissimilar welding between UNS S32205 duplex stainless steel (DSS) and 316L austenitic stainless steel (ASS) was performed by using gas tungsten arc welding and ER2209 filler at two different heat inputs (0.52 and 0.98 kJ/mm). Microstructures were characterized using reflected light optical microscope and scanning electron microscope. Micro-hardness and tensile properties were measured across the weld for both the heat inputs. The microstructure of the welded region was primarily austenitic (for both heat inputs) with Widmanstätten morphology. The grain size of the heat affected zone on DSS side was very large (~200 µm) for the high heat input sample with the presence of partially transformed austenite and acicular austenite. The precipitation of intermetallic phases and carbides was not observed for both the heat inputs. The proportion of ferrite in the weld metal (as measured by feritscope) was higher for the high heat input sample than the low heat input sample. During the tensile test, fracture occurred in 316L ASS base metal (because of its lower strength) in ductile manner. For high heat input welds, the impact tested sample showed the presence of fine spherical precipitates rich in Cr, Mn and Fe in the fracture surface of weld metal.     

1800 MPa热成形钢与CR340LA低合金高强钢激光焊接性能

采用光纤激光焊接设备对1800 MPa级热成形钢与CR340LA低合金高强钢进行对接激光拼焊,研究了不同激光焊接功率和焊接速度下焊接接头的组织演变规律及热冲压成形性能,并对焊接接头的力学性能和硬度进行了分析。结果表明,3种焊接工艺下激光拼焊原板综合力学性能相差较小,由焊接接头造成的伸长率和抗拉强度的损失均在母材的28.3%和9.1%以内。激光焊接后焊缝区均为粗大、高硬度的马氏体结构;两侧热影响区组织主要为铁素体和马氏体,接头未出现明显的软化区。激光拼焊原板拉伸试样均断裂于CR340LA母材区,距离焊缝12 mm左右,且存在焊缝隆起现象。选取焊接功率和焊接速率分别为4000 W和0.18 m·s?1的焊接试样在高温下进行热冲压成形检测,未出现焊缝开裂,热成形后拼焊板具有良好性能,满足汽车激光拼焊板使用要求,拉伸结果表明,试样断裂位置与未热冲压成形前一致,均位于CR340LA母材区,拉伸过程中,焊缝向高强度母材侧偏移,在弱强度母材侧产生应力集中并缩颈断裂。      

Evaluation of Microstructure and Mechanical Properties of Laser Beam Welded AISI 409M Grade Ferritic Stainless Steel

 The microstructure analysis and mechanical properties evaluation of laser beam welded AISI 409M ferritic stainless steel joints are investigated. Single pass autogeneous welds free of volumetric defects were produced at a welding speed of 3000 mm/min. The joints were subjected to optical microscope, scanning electron fractographe, microhardness, transverse and longitudinal tensile, bend and charpy impact toughness testing. The coarse ferrite grains in the base metal were changed into dendritic grains as a result of rapid solidification of laser beam welds. Tensile testing indicates overmatching of the weld metal is relative to the base metal. The joints also exhibited acceptable impact toughness and bend strength properties.     

Heat transfer during Nd: Yag pulsed laser welding and its effect on solidification structure of austenitic stainless steels

Theoretical and experimental investigations were carried out to determine the effect of process parameters on weld metal microstructures of austenitic stainless steels during pulsed laser welding. Laser welds made on four austenitic stainless steels at different power levels and scanning speeds were considered. A transient heat transfer model that takes into account fluid flow in the weld pool was employed to simulate thermal cycles and cooling rates experienced by the material under various welding conditions. The weld metal thermal cycles and cooling rates are related to features of the solidification structure. For the conditions investigated, the observed fusion zone structure ranged from duplex austenite (γ)+ferrite (δ) to fully austenitic or fully ferritic. Unlike welding with a continuous wave laser, pulsed laser welding results in thermal cycling from multiple melting and solidification cycles in the fusion zone, causing significant post-solidification solid-state transformation to occur. There was microstructural evidence of significant recrystallization in the fusion zone structure that can be explained on the basis of the thermal cycles. The present investigation clearly demonstrated the potential of the computational model to provide detailed information regarding the heat transfer conditions experienced during welding.     

Laser Welding of Ultra-Fine Grained Steel SS400

Steeliswidelyusedbecauseofitsgoodcompre hensive properties ,plentyofresourceandlowerprice .Thestrengthandtoughnessaretwoimpor tantpropertiesofsteels ,andpeoplemakeeffortstoincreasetheirvalues .Addingalloyingelementandcontrollingmicrostructurearetwobasicwaystoac complishtheaim .Therefinedmicrostructureob tainedbyprocessingtechniqueenablesthestrengthandtoughnessofsteeltobeincreasedwithoutaddingalloyingelementandtheratioofperformance costtobeincreased .Theultra finegrainedsteelshavefer ritegrains…     

Effect of Laser Beam Welding on Microstructure and Mechanical Properties of Commercially Pure Titanium

Laser beam welding of commercially pure titanium sheets were carried out at different operating conditions. Laser powers of 2.0 and 2.5 kW, beam diameters of 0.18 and 0.36 mm and welding speeds of 4–8 m/min were used. The microstructure and mechanical properties of the welded samples were investigated in the present study. It was observed that the grain size of the welded samples increased with increasing laser power while it decreased with increasing welding speed and beam diameter. The sample welded at 2.5 kW laser power with 4 m/min welding speed and 0.36 mm beam diameter had comparable tensile properties with the base metal.     

Deep Drawing of Friction Stir Welded Thin Sheet Aluminium Steel Tailored Hybrids

Friction stir welding undergoes a steep evolution in industrial applications since the invention in the early 1990s. Especially for aluminium alloys in sheet thicknesses over 2 mm a lot of applications are established, whereas a lack in knowledge about friction stir welding of thin sheets with sheet thickness less than 2 mm exists. This article deals with friction stir welding of thin sheet aluminium steel tailored hybrids and their formability. These investigations tend to close the gap of availability of friction stir welded blanks in the range of 1 mm sheet thickness and to offer new applications of this joining technology. For production of aluminium steel tailored hybrids AA5182 with a thickness of 1.2 mm and DC04 in 1.0 mm are used, the joining partners are friction stir welded in a lap joint. Different tool geometries and process parameters are performed to achieve the highest strength and elongation at fracture of the tailored hybrids. The influence of the stirring on the arrangement and distribution of both materials in the welding zone and its microstructure is analysed using light optical and scanning electron microscopy. In addition to tensile tests planar microhardness measurements help to detect the local changes of the mechanical properties in the characteristic zones of the weld seam. Tailored hybrids, which were friction stir welded with the best welding parameters in accordance to the mechanical properties of the weld seams, were used for deep drawing tests of friction stir welded thin sheet aluminium steel tailored hybrids. The maximum drawing ratio of these tailored hybrids coincides with the one of the parent material of AA5182.     

低碳相变诱发塑性钢的综合性能

对抗拉强度600 MPa级的低碳相变诱发塑性钢(TRIP钢)进行了拉伸、成形、高速冲击拉伸和激光焊接试验.对焊接前后的综合性能进行了对比,并对其金相组织、显微硬度进行了观察和测试分析.与原始板材相比,激光焊接后,低碳TRIP钢的强度和硬度增加,而伸长率略有下降;焊接热影响区的硬化较明显,但均未发现明显的焊接裂纹及其它缺陷,表明其焊接性能良好.发现低碳TRIP钢成形性能、抗凹陷性能、激光焊接性能良好.     

40CrNiMoA钢同质焊条焊接接头组织和性能研究

分析了焊接电流70A、80A、90A对40CrNiMoA钢焊缝接头组织和力学性能的影响。随着焊接电流的增大,焊缝外观质量较好。随着焊接电流的增大,熔池区温度升高,奥氏体晶粒尺寸增大,导致马氏体组织粗大。焊缝的显微组织为马氏体及少量残余奥氏体。焊缝的硬度远高于母材的硬度,且波动较大。热影响区的硬度从母材向沿焊缝方向逐渐升高。焊接接头纵向应力在焊缝中心为压应力,向外压应力减小。焊接颜色区边界处纵向应力为拉应力,且该点拉应力最大。焊接接头横向应力在焊缝中心为拉应力,向外逐渐增大,焊接颜色区边界处变横向拉应力达到最大。焊接电流和热输入增大,降低了材料的韧性,组织中铁素体增多及焊接残余应力是诱发脆性断裂的原因。焊接电流80A是40CrNiMoA同质焊条平板对接焊接工艺的最佳的焊接电流。     

Effect of Heat Input on Macro,Micro and Tensile Properties of Flux Cored Arc Welded Ferritic Stainless Steel Joints

This paper discusses the influence of Flux Cored Arc Welding Process parameters such as welding current, travel speed, voltage on bead profile, metallurgical and mechanical properties of welds of 2 mm thick 409M ferritic stainless steel sheets. The study reveals that, grain coarsening, volume fraction of martensite, hardness of heat affected zone and % of delta ferrite in ER 309 weld metal increases with increase in heat input. However, the results show that variation of heat input does not make any significant effect on tensile strength of the joint. Hence, welding parameters that provide uniform bead profile for the weld are recommended for fabrication.     

Metallurgical and Mechanical Characterization of Laser Spot Welded Low Carbon Steel Sheets

This paper aims at investigating metallurgical and mechanical characterization of low carbon steel laser spot welds. Microstructural examinations, microhardness tests and quasi‐static tensile‐shear tests were preformed. Mechanical properties of the welds were described in terms of peak load and failure mode. The effects of laser spot welding parameters including pulse frequency, laser energy, welding speed, pulse width and welded circle diameter, on low carbon steel laser spot weld performance were studied using the Taguchi design of experiment method. It was found that the effective laser pulse energy is the controlling factor in the determination of mechanical strength of laser spot welds.     

热输入对DP600激光焊组织和力学性能的影响

摘要：为了研究DP600钢的焊接性能,采用5种不同的激光焊接工艺进行焊接试验。结果表明,焊接接头表面成形质量良好,随着热输入的增加,上下熔宽逐渐增大;熔融区均为板条状马氏体组织,当热输入高于33J/mm时热影响区组织为马氏体、铁素体和少量的回火马氏体;当热输入低于33J/mm时,热影响区组织为马氏体和铁素体。在低热输入条件下,回火时间很短,马氏体未发生分解;在高的热输入条件下,回火时间较长,马氏体分解显著,热影响区中出现M3C型碳化物,碳化物形貌以球状和片状为主。从熔融区到母材,显微硬度值逐渐降低;焊接接头静态拉伸失效位置均在母材,拉伸断口为韧性断口,DP600钢激光焊接接头不存在软化现象。     

超低碳微合金X100管线钢CO2焊焊接接头的组织和性能

 采用CO2焊接方法焊接X100管线钢,分析了不同焊接工艺下焊接接头组织和性能的变化特征。随着焊接热输入的增加,焊接接头的屈服强度和抗拉强度降低,焊缝和热影响区处的冲击吸收功呈现先增大后减小的变化趋势,而焊缝组织均以针状铁素体（AF）为主。焊接热输入为1.17 kJ/mm时,粗晶区的显微组织主要是贝氏体铁素体（BF）,强韧匹配性最为优异;当热输入增加至1.91 kJ/mm时,粗晶区的组织除了BF外,还出现了粒状贝氏体（GB）,强韧水平明显降低。综合考虑,可将1.17 kJ/mm作为X100管线钢CO2焊接时的最佳热输入。     

双相不锈钢与微合金钢异金属焊接接头的组织及性能

采用ER2209焊丝对双相不锈钢SAF2205与微合金管线钢X65进行熔化极气体保护焊接,获得了具有良好力学性能的异种钢焊接接头.焊接接头不同区域显微组织观察和成分分析表明,微合金钢与不锈钢焊缝间存在异金属熔合区和第二类边界线,熔合区存在Ni、Cr的浓度梯度分布,且硬度高于两侧的焊缝和母材.通过宏观拉伸、缺口拉伸和低温冲击实验测试了焊接接头的力学性能,并获得了接头不同部位在1mol·L^-1 NaCl溶液中的极化曲线.拉伸试样断裂发生于强度相对较低的微合金钢母材.焊缝金属的缺口拉伸强度和冲击韧性均略低于双相不锈钢母材,但腐蚀电位略高于母材.微合金钢热影响区与母材力学性能相当,腐蚀电位略高于母材.     

316L/X65双金属复合管焊接接头组织与性能

 采用钨极氩弧焊和手工电弧焊焊接316L/X65双金属复合管。利用光学显微镜、能谱仪、扫描电镜、力学性能测试及电化学测试等分析手段研究了复合管焊接接头的微观结构、化学成分、力学性能及电化学腐蚀性能。结果表明,过渡层焊缝的化学成分受到稀释较小,过渡层熔合线附近出现了元素迁移,不锈钢层焊缝与母材的化学成分基本一致;扩散层为类马氏体＋残留奥氏体,过渡层和不锈钢层焊缝均为奥氏体＋少量铁素体;在试验参数下,焊接接头各项力学性能优良、无缺陷;覆层焊缝与母材的电化学腐蚀性能相差极小。     

High-Speed Friction Stir Welding of AA7075-T6 Sheet: Microstructure,Mechanical Properties,Micro-texture,and Thermal History

Friction stir welding (FSW) is a cost-effective and high-quality joining process for aluminum alloys (especially heat-treatable alloys) that is historically operated at lower joining speeds (up to hundreds of millimeters per minute). In this study, we present a microstructural analysis of friction stir welded AA7075-T6 blanks with high welding speeds up to 3 M/min. Textures, microstructures, mechanical properties, and weld quality are analyzed using TEM, EBSD, metallographic imaging, and Vickers hardness. The higher welding speed results in narrower, stronger heat-affected zones (HAZs) and also higher hardness in the nugget zones. The material flow direction in the nugget zone is found to be leaning towards the welding direction as the welding speed increases. Results are coupled with welding parameters and thermal history to aid in the understanding of the complex material flow and texture gradients within the welds in an effort to optimize welding parameters for high-speed processing.     

Grain structures in gas tungsten-arc welds of austenitic stainless steels with ferrite primary phase

The grain structures were investigated in full penetration gas tungsten-arc (GTA) welds in sheets of 304 and 321 austenitic stainless steels for a range of welding conditions. In type 321 steel welds, fine equiaxed ferrite dendrites were observed in the ferrite phase. The equiaxed structure was ascribed to heterogeneous nucleation of ferrite on Ti-rich cuboidal inclusions present in this steel, since these inclusions were observed at the origin of equiaxed dendrites. In type 304 welds, the ferrite grains were columnar, except in less complete penetration specimens, where a few coarse equiaxed dendrites appeared to originate from the weld surface. The secondary austenitic grain structure was columnar in both steels. In type 304 steel, the columnar austenitic grain structure did not necessarily correspond to the primary ferrite grains. In type 321 steel, the secondary austenite was columnar despite the equiaxed structure of the primary ferrite. Factors which affect the columnar-to-equiaxed transition (CET) are discussed. The failure to form equiaxed austenitic grains in type 321 steel is ascribed to austenite growing across the space between ferrite grains instead of renucleating on the primary equiaxed ferrite.     

Friction Stir Welding of HSLA-65 Steel: Part II. The Influence of Weld Speed and Tool Material on the Residual Stress Distribution and Tool Wear

A set of single pass full penetration friction stir bead-on-plate and butt welds in HSLA-65 steel were produced using a range of traverse speeds (50 to 500?mm/min) and two tool materials (W-Re and PCBN). Part I described the influence of process and tool parameters on the microstructure in the weld region. This article focuses on the influence of these parameters on residual stress, but the presence of retained austenite evident in the diffraction pattern and X-ray tomographic investigations of tool material depositions are also discussed. The residual stress measurements were made using white beam synchrotron X-ray diffraction (SXRD). The residual stresses are affected by the traverse speed as well as the weld tool material. While the peak residual stress at the tool shoulders remained largely unchanged (approximately equal to the nominal yield stress (450?MPa)) irrespective of weld speed or tool type, for the W-Re welds, the width of the tensile section of the residual stress profile decreased with increasing traverse speed (thus decreasing line energy). The effect of increasing traverse speed on the width of the tensile zone was much less pronounced for the PCBN tool material.