Characteristics of Laser Beam and Friction Stir Welded AISI 409M Ferritic Stainless Steel Joints

This article presents the comparative evaluation of microstructural features and mechanical properties of friction stir welded (solid-state) and laser beam welded (high energy density fusion welding) AISI 409M grade ferritic stainless steel joints. Optical microscopy, microhardness testing, transverse tensile, and impact tests were performed. The coarse ferrite grains in the base material were changed to fine grains consisting duplex structure of ferrite and martensite due to the rapid cooling rate and high strain induced by severe plastic deformation caused by frictional stirring. On the other hand, columnar dendritic grain structure was observed in fusion zone of laser beam welded joints. Tensile testing indicates overmatching of the weld metal relative to the base metal irrespective of the welding processes used. The LBW joint exhibited superior impact toughness compared to the FSW joint.     

Use of DL-EPR Test to Assess Sensitization Resistance of AISI 409M Grade Ferritic Stainless Steel Joints

The susceptibility of 409M grade ferritic stainless steels to sensitization due to welding was investigated. Joints were fabricated by gas tungsten arc welding, friction stir welding, laser beam welding, and electron beam welding processes. Double loop electrochemical potentiokinetic reactivation test was carried out for determining the degree of sensitization of welded joints. The experimental result reveals that, the friction stir welded joint is less prone to sensitization, when compared to the other joints.     

409L铁素体不锈钢的高温拉伸行为和形变组织研究

利用金相显微镜、X射线衍射仪、EPMA、拉伸试验机研究铸态409L铁素体不锈钢在高温下的力学性能和变形组织特征.结果表明,随着温度的升高,409L不锈钢的强度在300～800℃迅速下降,800～1150℃下降变缓;伸长率在1000℃时达到最大,为131.44%;断面收缩率在800℃时最大,为97.71%.409L不锈钢的再结晶温度在950℃左右.通过XRD鉴定表明,409L不锈钢中主要组成物相为铁素体、Fe-Cr系合金和游离Cr元素.EPMA结果显示,409L不锈钢中含有的黑色点状第二相颗粒主要是Ti(C、N),此种粒子可提高钢铁材料的综合性能.     

409不锈钢在消声器冷凝液中的腐蚀行为

运用氧化-冷凝液蒸发循环方法模拟汽车消声器内腐蚀环境,研究了409不锈钢在两种冷凝液中的腐蚀行为,并分析了Cl-对冷凝液腐蚀的作用.结果表明,经250℃氧化后409不锈钢在冷凝液中表现出良好的钝态腐蚀性能,但无论冷凝液中是否存在Cl-,钝化膜在氧化和腐蚀的循环作用下均会被破坏而形成局部腐蚀坑.Cl-存在时,蚀坑内不易形成保护性氧化膜,形成的蚀坑更深.     

Corrosion Behavior of Metal Active Gas Welded Joints of a High-Strength Steel for Automotive Application

In this work, the corrosion behavior of metal active gas-welded joints of a high-strength steel with tensile yield strength of 900 MPa was investigated. The welded joints were obtained using two different heat inputs. The corrosion behavior has been studied in a 3.5 wt.% NaCl aqueous solution using electrochemical impedance spectroscopy and potentiodynamic polarization tests. Optical microscopy images, scanning electron microscopy and transmission electron microscopy with energy-dispersive x-ray revealed different microstructural features in the heat-affected zone (HAZ) and the weld metal (WM). Before and after the corrosion process, the sample was evaluated by confocal laser scanning microscopy to measure the depth difference between HAZ and WM. The results showed that the heat input did not play an important role on corrosion behavior of HSLA steel. The anodic and cathodic areas of the welded joints could be associated with depth differences. The HAZ was found to be the anodic area, while the WM was cathodic with respect to the HAZ. The corrosion behavior was related to the amount and orientation nature of carbides in the HAZ. The microstructure of the HAZ consisted of martensite and bainite, whereas acicular ferrite was observed in the weld metal.     

Effect of Welding Consumables on Fatigue Performance of Shielded Metal Arc Welded High Strength, Q&T Steel Joints

Quenched and Tempered (Q&T) steels are widely used in the construction of military vehicles due to their high strength-to-weight ratio and high hardness. These steels are prone to hydrogen-induced cracking in the heat affected zone (HAZ) after welding. The use of austenitic stainless steel consumables to weld the above steel was the only remedy because of higher solubility for hydrogen in austenitic phase. Recent studies proved that high nickel steel and low hydrogen ferritic steel consumables can be used to weld Q&T steels, which can give very low hydrogen levels in the weld deposits. In this investigation an attempt has been made to study the effect of welding consumables on high cycle fatigue properties of high strength, Q&T steel joints. Three different consumables namely (i) austenitic stainless steel, (ii) low hydrogen ferritic steel, and (iii) high nickel steel have been used to fabricate the joints by shielded metal arc (SMAW) welding process. The joints fabricated using low hydrogen ferritic steel electrodes showed superior fatigue properties than other joints.     

高强度桥梁钢焊接接头疲劳裂纹扩展速率的研究

利用高频疲劳试验机对高强度桥梁钢的母材、热影响区和焊缝的疲劳裂纹扩展速率进行了测定,并结合疲劳扩展断口分析各部位疲劳裂纹扩展快慢的原因。结果表明,高强度桥梁钢焊接接头中焊缝裂纹扩展速率最低,抗疲劳裂纹扩展能力最高;母材疲劳裂纹扩展速率最高,抗疲劳裂纹扩展能力最差;热影响区介于二者之间。焊缝的疲劳断裂模式是以穿晶断裂为主,母材是以沿Z字形路径扩展的沿晶断裂为主,热影响区则介于两者之间。     

Prediction of Grain Growth Behavior in HAZ During Gas Tungsten Arc Welding of 304 Stainless Steel

In this study, the thermal cycles and the grain structure in the weld heat-affected zone (HAZ) are predicted. At the first stage, a combined heat transfer and fluid flow model is employed to assess the temperature fields during and after welding of 304 stainless steel and then, the evolution of grain structure is conducted using the predicted temperature distribution and an analytical model of grain growth. The grain sizes of the CGHAZ (coarse grain heat affected zone) achieved from the model are basically in agreement with those obtained from experimental measurement under different heat inputs in the range of 0.33-1.07 MJ/m. Both the experimental data and the calculated results show that the average grain size near the fusion plane is about two to four times larger than the average grain size in the base plate depending on the applied heat input.     

Tensile and Impact Toughness Properties of Gas Tungsten Arc Welded and Friction Stir Welded Interstitial Free Steel Joints

Welded regions of interstitial free (IF) steel grades in the vicinity of weld center exhibits larger grains because of the prevailing thermal conditions during weld metal solidification. This often causes inferior weld mechanical properties. In the present study, tensile properties, charpy impact toughness, microhardness, microstructure, lowest hardness distribution profile, and fracture surface morphology of the gas tungsten arc welded (GTAW) and friction stir welded joints were evaluated, and the results are compared. From this investigation, it is found that friction stir welded joint of IF steel showed superior tensile and impact properties compared with GTAW joint, and this is mainly due to the formation of very fine, equiaxed microstructure in the weld zone.     

16Mn钢埋弧焊接头疲劳裂纹扩展速率的研究

对16Mn钢双面埋弧焊CT试样的焊缝、热影响区、母材及垂直焊缝方向的疲劳裂纹扩展速率进行了研究。结果表明,焊接接头的不同部位疲劳裂纹扩展速率不同,平均应力、焊接残余应力、金相组织对疲劳裂纹的扩展速率都有一定的影响。     

Computational Modeling of Microstructural-Evolution in AISI 1005 Steel During Gas Metal Arc Butt Welding

A fully coupled (two-way), transient, thermal-mechanical finite-element procedure is developed to model conventional gas metal arc welding (GMAW) butt-joining process. Two-way thermal-mechanical coupling is achieved by making the mechanical material model of the workpiece and the weld temperature-dependent and by allowing the potential work of plastic deformation resulting from large thermal gradients to be dissipated in the form of heat. To account for the heat losses from the weld into the surroundings, heat transfer effects associated with natural convection and radiation to the environment and thermal-heat conduction to the adjacent workpiece material are considered. The procedure is next combined with the basic physical-metallurgy concepts and principles and applied to a prototypical (plain) low-carbon steel (AISI 1005) to predict the distribution of various crystalline phases within the as-welded material microstructure in different fusion zone and heat-affected zone locations, under given GMAW-process parameters. The results obtained are compared with available open-literature experimental data to provide validation/verification for the proposed GMAW modeling effort.     

Sensitization Behavior of Type 409 Ferritic Stainless Steel: Confronting DL-EPR Test and Practice W of ASTM A763

Stainless steels employed for manufacturing automotive exhaust systems must withstand severe thermal cycles, corrosive environment due to urea decomposition, and welding operations. AISI 409 ferritic stainless steel can be considered a low-cost alternative for this application. However, depending on the manufacturing conditions during welding cycles, this material can be sensitized due to the precipitation of chromium carbides at grain boundaries. In this work, the intergranular corrosion resistances of the AISI 409 ferritic stainless steel were evaluated after annealing at 300, 500, and 700 °C for 2, 4, and 6 h. Solution-annealed samples were also tested for comparison purposes. Two methodologies were used to assess the sensitization behavior of the 409 stainless steel samples: the first one was based on the ASTM A763 (practice W), while the second one was based on the double-loop electrochemical potentiodynamic reactivation test. It was possible to identify that the annealing treatment performed at 500 °C was more critical to the occurrence of intergranular corrosion.     

TA15钛合金潜弧焊焊接接头疲劳损伤研究

本文对TA15钛合金潜弧焊焊接接头性能进行了研究,结果表明,TA15钛合金潜弧焊焊缝晶粒粗大,热影响区晶粒尺寸过渡明显,焊缝与热影响区界限不明显.焊接件的疲劳试验结果表明,潜弧焊焊接接头的疲劳性能较母材有较大的下降,距焊缝中心线距离为6mm～14mm的焊接区域是焊接接头的薄弱部位,疲劳裂纹大多萌生于此区域.     

喷丸处理对304不锈钢焊接接头氯化钠应力腐蚀开裂的影响

对304不锈钢氩弧焊焊接接头表面作了喷丸处理,并在金相显微镜与扫描电镜下对处理后材料表面的微观组织进行了观察,用X射线应力衍射仪测试了喷丸处理后试样的残余应力分布,并进行了NaC1水溶液应力腐蚀试验.结果表明,304不锈钢焊缝在NaCl溶液中具有明显的应力腐蚀开裂敏感性,喷丸处理能够很好地提高焊接构件抗应力腐蚀开裂能力;应力腐蚀裂纹断口表现为脆性断裂,各区的应力腐蚀裂纹属于穿晶型裂纹.     

Cr-Mn-Si-Ni高强度钢疲劳裂纹的萌生行为

通过扫描电镜原位疲劳试验,研究Cr-Mn-Si-Ni高强度钢疲劳裂纹的萌生行为,观察并记录从滑移带自然萌生的小裂纹和其发展到宏观裂纹的过程。研究结果表明：在低周疲劳情况下,不是所有萌生的裂纹都会持续扩展,大部分微裂纹在疲劳早期即已萌生,但是裂纹发展很慢,导致失效的裂纹快速扩展在疲劳晚期发生,微裂纹长度与循环数之间也有一定的关系。     

409型不锈钢在冷凝液中的缝隙腐蚀行为

运用冷凝液循环蒸发方法模拟汽车消声器内部腐蚀环境,对比研究了在有/无缝隙条件下409型不锈钢在冷凝液中的腐蚀行为。结果表明:与无缝隙试样相比,有缝隙试样在循环试验过程中表现出相对较低的自腐蚀电位;20次循环试验后,腐蚀阻力较低,腐蚀深度较大;缝隙导致不锈钢局部腐蚀速率约增大2.4倍,这主要是由缝隙内部在蒸发过程中更容易保持电解液腐蚀环境、并不断酸化导致的。     

低碳多元高强结构钢焊接接头疲劳强度试验及分析

对低碳多元高强结构钢焊接接头在应力比r=0．12下，采用单点试验法和小样子升降法相结合的试验方法，进行了拉．拉疲劳强度试验。对焊接接头型式对疲劳寿命的影响进行了数理统计分析，并对疲劳断口进行了扫描电镜观察。试验结果和分析表明：对接接头的疲劳极限σ0.12=230MPa；角接接头的疲劳极限σ0.12=130MPa；得到了两种接头型式的S-N曲线和P-S-N曲线方程。在应力水平250MPa、可靠度95％条件下，对接接头的中值疲劳寿命是角接接头中值疲劳寿命的6～18倍。疲劳断口分析认为，焊缝的焊趾和裂纹是影响高强钢疲劳强度的主要原因。     

基于磁记忆机理的焊缝疲劳累积损伤特征

通过20号钢焊接平板试件的拉-拉疲劳试验,研究了在单周期和多周期循环载荷下焊缝疲劳累积损伤的磁记忆信号特征。结果表明,由于试件内部初始状态下各处应力分布不均匀,焊缝原始磁信号表现为起伏较大;随着循环周次的增加,试件内部应力集中重新分布,信号趋于稳定;在周期累积循环试验中,磁记忆信号随着循环周次的增加出现螺旋上升的趋势,呈现出磁弹性效应变化特征;通过建立磁记忆信号与损伤度函数的模型,可根据磁记忆信号的变化准确判断裂纹扩展趋势,用于焊缝剩余寿命的预测。     

Oxidation Kinetics of AISI 441 Ferritic Stainless Steel at High Temperatures in CO2 Atmosphere

Ferritic stainless steels used as interconnectors in SOFC stacks are subjected to air and fuel atmospheres at 800 °C. The use of hydrogen as fuel gas may be substituted by fermentative biogas consisting of mainly CO₂ and CH₄. In this gas mixture, carbon dioxide leads to steel oxidation whereas methane induces carburization. The objective of this study was to investigate the oxidation kinetics of the AISI 441 ferritic stainless steel under pure CO₂ in order to understand oxidation mechanisms. The results show that the kinetic behaviour is linear at low temperatures (800–900 °C) and initially linear then parabolic at higher temperatures (925–1,000 °C). Oxide scale consisted of major Cr₂O₃-rich oxide, topped with MnCr₂O₄ and a dispersion of TiO₂. The chromium-rich oxide was analysed by using the photoelectrochemical method. It exhibits N-type semi-conductor. Oxidation kinetics is modelled by the mixed surface and oxide-diffusion limited steps.     

TCS不锈钢与Q450NQR1高强耐候钢焊接接头性能比较

通过对TCS不锈钢与Q450NQR1高强耐候钢的焊接接头性能进行对比分析,得出TCS不锈钢的焊接性能要差于Q450NQR1高强耐候钢。TCS不锈钢的焊接生产工艺要求要更严格,以保证焊接质量。