Optimization of gas tungsten arc welding parameters for the dissimilar welding between AISI 304 and AISI 201 stainless steels

This present study applied gas tungsten arc welding in order to join AISI 304 and AISI 201 stainless steels.The objective was to find the optimum welding condition that gave a weld bead in accordance with DIN EN ISO 25817 quality level B, pitting corrosion potential of the weld metal of not less than that of the AISI304 base metal and a ratio of delta-ferrite in austenite matrix of the weld metal of not lower than 3%.Such a ratio is a criterion widely accepted to protect the weld metal from solidification cracking. At the welding current of 75 A and by using pure argon as a shielding gas 0 to 8 vol.% and applying a welding speed in the range of 2-3.5 mm·s^(-1) was found to give a complete weld bead with an increased depthper-width ratio(promote weldability). For welding speed in the range of 3 and 3.5 mm·s^(-1)(promote corrosion resistance). Increasing the welding speed in such a range decreased the amount of delta-ferrite in the austenite matrix, and increased the pitting corrosion potential of the weld metal to be 302 mV_(SCE).This value was still lower than the pitting corrosion potential of the AISI 304 base metal. Mixing nitrogen in argon shielding gas increased the nitrogen content in the weld. The optimum condition was found when using a welding speed of 3 mm· s^(-1) and mixing 1 vol.% of nitrogen in the argon shielding gas(promote weldability and corrosion resistance). Pitted areas after potentiodynamic test were observed in the austenite in which its Cr content was relatively low.

Study on Factors Effecting Weld Pool Geometry of Pulsed Current Micro Plasma Arc Welded AISI 304L Austenitic Stainless Steel Sheets Using Statistical Approach

Pulsed current Micro Plasma Arc Welding is used to joint thin sheets of AISI 304L sheets, which are used in manufacturing of metallic bellows and diaphragms. In this article the effects of pulsing current parameters on weld pool geometry namely front width, back width, front height and back height of pulsed current micro plasma arc welded AISI 304L stainless steel sheets was analyzed. Four factors, five levels, central composite design was used to develop mathematical models, incorporating pulsed current parameters and weld pool geometry. The mathematical models have been developed by Response Surface Method. The adequacy of the models was checked by ANOVA technique. Variation of output responses with input process variables are discussed. By using the developed mathematical models, weld pool geometry parameters can be predicted.

Effect of Pipe Diameter on Electrochemical Behavior of Stainless Steel Type 304 Pipes in Tap Water

We investigated the effects of pipe diameter on the corrosion resistance of stainless steel type 304 pipes using electrochemical measurements. Compared to plate steel, pipes have harder physical properties and tend to be harder and showed greater permeability with decreasing inner diameter. We found that the maximum corrosion current density in the secondary active state, which is the starting point of secondary passivation, appeared in the polarization curve measurement in tap water. Similar to the Vickers hardness and the maximum current density in the secondary active state, the permeability tended to increase as the diameter decreased. This is thought to increase the amount of deformation-induced martensitic and increase corrosion susceptibility. The peak of the secondary active current density was clearly seen as the potential sweep speed was increased. In addition, potential sweep speed dependence was observed in the corrosion susceptibility evaluation of deformation-induced martensite. In comparison with acid treatment, the formation of deformation-induced martensite was considered to occur in the extreme surface layer. The maximum corrosion current density in the secondary active state is expected to be a new susceptibility evaluation method for evaluating the deformation-induced martensitic transformation.

High corrosion resistance 21%Cr-0.4%Cu ferritic stainless steel contributing to resource conservation

With prices for metal resources such as nickel and molybdenum soaring,there is a heightened sense of crisis concerning resource scarcity.While Type304,the most common stainless steel,offers excellent corrosion resistance,its price is affected significantly by the cost of nickel because of its 8%nickel content.The stainless steel that has the same corrosion resistance as that of Type304 and does not contain nickel and molybdenum has been required.JFE Steel Corporation has developed a new 21%Cr-0.4%Cu stainless steel,the world's first ferritic stainless steel,which offers equivalent corrosion resistance to Type304 while containing absolutely no nickel or molybdenum,two rare metals.The newly developed steel contains 21%chromium with the addition of 0.4% copper.The development of the steel is based on a new discovery that the passive films of stainless steels could be strengthened by the synergy effect of high chromium content and copper addition.Copper addition enriches the chromium content in passive films after field exposure.Newly developed 21%Cr-0.4%Cu stainless steel is adopted for many applications as a substitution for Type304,including commercial kitchenware,building materials and industrial machinery.The steel is expected to be a new standard of a ferritic stainless steel as a substitution for Type304.

HOT DUCTILITY OF 304HC STAINLESS STEEL AND THE MODEL OF RESISTANCE TO DEFORMATION

The ductility map of 304HC stainless was determined by using the Gleeble-1500 dynamic thermal-mechanical simulator. The effect of Cu on the hot ductility of 304HC stainless steel was analyzed and the mathematical model of resistance to deformation was established. The microstructure, inclusion and fracture surface were studied by using the method of micro structure analysis, scanning, energy spectrum and electron microscope. The results show that Cu has effect on the hot ductility, and the hot ductility of 304HC stainless steel decrease with the increase of content of Cu. The deformation temperature also has much effect on the hot ductility, the suitable deformation temperature are 1100-1200℃. The reason of it is that the Cu rich chemical compounds were precipitated from austenite phase during cooling. The Cu rich chemical compounds are brittle substance such as Cu2S, Cu2O and ε-Cu etc.

Extrusion process of 304L H-shaped stainless steel used in passive residual heat removal heat exchanger

304L H-shaped stainless steel is used as the support frame of the passive residual heat removal heat exchanger(PRHR HX) in a nuclear fission reactor. The extrusion process is adopted to manufacture the 304L H-shaped stainless steel. Finite element method simulation is herein used to analyze metal flow characteristics, optimize the extrusion die, and predict the extrusion force at different temperatures and speeds. A Φ400-mm container and Φ388-mm forging billet are selected, and the 304L H-shaped stainless steel is successfully manufactured using a Germany SMS 60 MN horizontal extruder. The mechanical properties and microstructure of the manufactured 304L H-shaped stainless steel meet the requirements of the PRHR HX, and the surfaces of the product pass the dye penetration test. The H-shaped stainless steels are used in Haiyang nuclear power plant in Shandong Province.

Effect of current intensity on radiological properties of joined 304L stainless steels for photon interaction

Radiological properties, such as the linear attenuation coefficient(μ), mass attenuation coefficient(μ/ρ), half-value layer(HVL), tenth-value layer(TVL), mean free path(MFP), and effective atomic number(Z_(eff)), of 304 L stainless steels have been investigated with respect to photon interactions to determine the influence of current intensity at different gamma-ray energies.^(137)Cs and ^(60)Co radioactive point sources were used to irradiate 304 L stainless steels joined at 45–70-A weld currents for the transmission of the gamma rays at photon energies of661.0, 1173.2, and 1332.5 ke V. The μ, μ/ρ, HVL, TVL,MFP, and Z_(eff) of the steels were measured at the mentioned energies, and theoretical values for pure 304 L stainless steel were calculated for comparison. The minimum differences(%) in Z_(eff) between pure steel and steel joined at a weld current of 60 A were observed for relevant photon energies; the minimum difference between the theoretical value for pure 304 L and the experimental value for joined steel was 4.76%, and that between the experimental value for pure 304 L and the experimental value for joined steel was 2.60% at 1332.5 ke V. Moreover, the MFPs of the joined steels were compared with that of pure 304 L, and steel joined at 60 A, which had the minimum MFP, was compared with some radiation-shielding concretes in terms of MFP at the same gamma-ray energies.

Characterization of Passive Films Formed on As-received and Sensitized AISI 304 Stainless Steel

The current research of corrosion resistance of stainless steels mainly focuses on characterization of the passive films by point defect mode and mixed-conduction model. The corrosion resistance of the passive films formed on asreceived and sensitized AISI304 stainless steel in borate bu er solution were evaluated in this paper. The degree of sensitization and corrosion resistance of AISI304 stainless steels was evaluated by double loop electrochemical potentiodynamic reactivation and electrochemical impedance spectroscopy. The passive films formed on the stainless steels were studied by XPS technique. It was found that as-received specimen had higher pitting corrosion potential and corrosion resistance than sensitized one. The Mott-Schottky results showed that sensitized stainless steel had more defects in the passive film than as-received one. The compositions of the passive films were mainly Cr and Fe oxides according to XPS results.

EFFECT OF COPPER ON THE HOT PLASTICITY OF 304HC STAINLESS STEEL

The plasticity map of 304HC stainless steel was determined by using tensile and compressive test. The effect of Cu on the hot plasticity of 304HC stainless steel was analyzed. The microstructure, inclusion and fracture surface were studied by using the method of optical microscopy, SEM, EDS and EPMA. The results showed that Cu has effect on the hot plasticity and the hot plasticity of 304HC stainless steel decrease with the increase of Cu content. The deformation temperature also has much effect on the hot plasticity, the suitable deformation temperature are 1100-1200℃. The reason is that the brittle compounds were precipitated from austenite during cooling. These brittle compounds are Cu2S, Cu2O and PbCI etc.

Investigation of the Grain Growth Evolution in the AISI 304H Austenitic Stainless Steel

The austenitic stainless steels usually present an excellent combination of corrosion resistance and mechanical properties such as ductility in the annealed condition and high yield strength after cold deformation. Solution annealing in the AISI 304H is recommended before deformation process in order to improve ductility. However, long annealing during solution annealing can cause GG （grain growth） or AGG （abnormal grain growth） in the AISI 304H. In these cases, ductility is strongly decreased. Therefore, GG or AGG must be avoided during solution annealing. In this article, grain growth during solution annealing of the AISI 304H samples was determined. Samples of the AISI 304H were annealed at 1,100 ℃ for solution-annealing times varying from 15 min to 180 min. The results show that AGG took place for samples annealed at 1,100 ℃ for 30 min. In this condition, grain size reached 70 ± 10 μm. After annealing solution at 1,100 ℃ for 180 min, grain size reached 120 ~ 20 μm. In summary, the results shown that solution annealing at 1,100 ℃ even for relatively short annealing promotes the prompt increase of the grain size.

Temperature and stress fields in electron beam welded Ti-15-3 alloy to 304 stainless steel joint with copper interlayer sheet

Electron beam welding of Ti-15-3 alloy to 304 stainless steel （STS） using a copper filler metal was carried out. The temperature fields and stress distributions in the Ti/Fe and Ti/Cu/Fe joint during the welding process were numerically simulated and experimentally measured. The results show that the rotated parabola body heat source is fit for the simulation of the electron beam welding. The temperature distribution is asymmetric along the weld center and the temperature in the titanium alloy plate is higher than that in the 304 STS plate. The thermal stress also appears to be in asymmetric distribution. The residual tensile stress mainly exists in the weld at the 304 STS side. The copper filler metal decreases the peak temperature and temperature grade in the joint as well as the residual stress. The longitudinal and lateral residual tensile strengths reduce by 66 MPa and 31 MPa, respectively. From the temperature and residual stress, it is concluded that copper is a good filler metal candidate for the electron beam welding of Ti-15-3 titanium alloy to 304 stainless steel.

Electron beam welding of 304 stainless steel to QCr0.8 copper alloy with copper filler wire

Electron beam welding （EBW） of 304 stainless steel to QCr0.8 copper alloy with copper filler wire was carried out. Orthogonal experiment was performed to investigate the effects of process parameters on the tensile strength of the joints, and the process parameters were optimized. The optimum process parameters are as follows：beam current of 30 mA, welding speed of 100 mm/min, wire feed rate of 1 m/min and beam offset of-0.3 mm. The microstructures of the optimum joint were studied. The results indicate that the weld is mainly composed of dendriticαphase with little globularεphase, and copper inhomogeneity only occurs at the top of the fusion zone. In addition, a melted region without mixing exists near the weld junction of copper side. This region with a coarser grain size is the weakest section of the joints. It is found that the microhardness of the weld decreases with the increase of the copper content in solid solution. The highest tensile strength of the joint is 276 MPa.

Gas tungsten arc welding of CP-copper to 304 stainless steel using different filler materials

The dissimilar joining of CP-copper to 304 stainless steel was performed by gas tungsten arc welding process using different filler materials. The results indicated the formation of defect free joint by using copper filler material. But, the presence of some defects like solidification crack and lack of fusion caused decreasing tensile strength of other joints. In the optimum conditions, the tensile strength of the joint was 96% of the weaker material. Also, this joint was bent till to 180° without any macroscopic defects like separation, tearing or fracture. It was concluded that copper is a new and good candidate for gas tungsten arc welding of copper to 304 stainless steel.

不锈钢表面Al/Cu涂层制备与第一性原理计算

为了研究Al/Cu涂层中金属间化合物的生成顺序和形成机理,在304不锈钢基体表面制备了Al/Cu涂层。对试样进行热处理使得Al/Cu涂层原位反应生成金属间化合物,随后测试了涂层的高温抗氧化性能。采用第一性原理计算Al-Cu金属间化合物的焓、熵、吉布斯自由能和热容等数据。将热力学和扩散动力学相结合,提出有效生成自由能模型来预测化合物在Al/Cu界面的生成顺序。结果表明:Al/Cu涂层中首先形成Al_(2)Cu相,在Al/Cu界面处出现了AlCu相,加热时间增加至20 h后出现了富Cu的Al_(4)Cu_(9)相。由第一性原理计算得出,Al-Cu金属间化合物的形成顺序为Al_(2)Cu→AlCu→Al_(4)Cu_(9),与实验结果一致。此外,氧化实验结果表明,涂层具有良好高温抗氧化性能。

二溴海因与三氯异氰尿酸消毒剂对不同航材表面细菌的消杀性能研究

针对航天员在执行远距离复杂环境的地外天体作业后导致舱内携带微生物风险增加的问题,围绕不同航材表面微生物的消杀试剂、消杀方法及消杀效果开展研究。选择杀菌效果强、持续时间长以及对环境和人体友好的含氯消毒剂三氯异氰尿酸和含溴消毒剂二溴海因,以3种典型空间微生物风险菌(大肠杆菌、金黄色葡萄糖球菌和芽孢杆菌)作为实验对象,研究了单一消毒剂及其复合浓度配比对舱内常见的3种材料(304不锈钢、PP塑料和PVC板)表面的微生物消杀效果。结果表明:表面喷洒单一消毒剂对3种材料表面细菌的杀灭率可达99.9999%以上,而表面喷洒复合浓度配比的消毒剂消杀效果要优于单一组分,杀灭率均大于99.99999%,且大大降低了消毒剂的使用量。

Electrochemical Synthesis of Phenol-aniline Copolymerization Coating on 304 Stainless Steel Anodes and Coating Microstructure Analysis

Electrochemical copolymerization of phenol and aniline was achieved on 304 stainless steel anodes in neutral water solution with an electrolyte of Na2SO4O4. Compared with pit corrosion potential of different copolymer coatings, the best solution composition was 0.09 mol/L phenol and 0.01 mol/L aniline. Through infrared spectrum analysis, polyaniline structure was proved in phenol-aniline copolymer, as well as more side chains. Scanning electron microscope was used to analyze microstructure of copolymer coating, taking advantage of part solubility of phenol-aniline eopolymer in tetrahydrofuran, the bifurcate network structure was observed. The copolymer coating microstructure was summarized, compared with the performance of polyphenol coatings, the reasons of corrosion resistance enhancement with the addition of aniline in electropolymerization reaction was assumed as well.

冷轧不锈钢-碳钢复合板弯曲裂纹的分析

通过“爆炸+轧制”法生产的0.80～1.20mm的304不锈钢碳钢(Q235A,08Al)304不锈钢复合板的厚度比例为1∶10∶1,该板在建筑门窗幕墙和日用炊具领域有广泛应用前景。冷弯试样产生裂纹的分析结果表明,基板含碳量高的Q235A钢(0.16%C)比基板含碳量低的08Al钢(0.06%C)出现裂纹的几率大,并且钢中夹杂物、钢的晶粒度和热处理工艺均影响冷轧复合板的弯曲性能。通过选择08Al钢为基层板,控制1050℃热处理工艺,使晶粒度级别≤8级,可明显改善冷轧复合钢板的弯曲性能。

Influence of flash trap profiles on joint properties of friction welded CP-Ti tube to 304L stainless steel tube plate using external tool

Titanium tube and stainless steel tube plate were welded by an innovative friction welding of tube to tube plate using an external tool (FWTPET). Copper was used as an interlayer for joining the dissimilar materials and also to minimize the effect of intermetallics formed at the joint interface. The process parameters that govern FWTPET process are plunge rate, rotational speed, plunge depth, axial load and flash trap profile. Among them, the flash trap profile of the tube has a significant influence on the joint integrity. Various flash trap profiles like vertical slots, holes, zig-zag holes, and petals were made on the titanium tube welded to the stainless steel tube plate. Macroscopic and microscopic studies reveal defect-free joints. The presence of copper interlayer and intermetallics was evident from X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) studies. The microhardness survey was presented across and along the interface. A novel test procedure called “plunge shear test” was developed to evaluate the joint properties of the welded joints. The highest shear fracture load of 31.58 kN was observed on the sample having petals as flash trap profile. The sheared surfaces were further characterized using SEM for fractography.

热电厂波纹管开裂原因分析

对某电厂使用几百小时而破损的3层不锈钢波纹管,进行了宏观、金相、断口形貌及腐蚀产物的分析.结果表明,波纹管破裂从内层开始,逐渐引发中间层和外层开裂;开裂是由于内层水蒸气结露,水蒸气中的氯化物浓缩而导致穿晶型应力腐蚀开裂;应力来自工作应力和冷加工残余应力.管壁上除环向裂纹,还有轴向裂纹。

Effects of Laser Shock Processing on Mechanical Properties of Laser Welded ANSI 304 Stainless Steel Joint

With the rapid development of engineering component with integration,high-speed and multi-parameter,traditional techniques haven＇t met practical needs in extreme service environment.Laser welding,a new welding technology,has been widely used.However,it would generate the drop of mechanical properties for laser welded joint due to its thermal effect.Laser shock processing（LSP） is one of the most effective methods to improve the mechanical properties of laser welded ANSI 304 stainless steel joint.In this paper,the effects of LSP on the mechanical properties of laser welded ANSI 304 stainless steel joint have been investigated.The welded joint on the front of the tensile samples is treated by LSP impacts,and the overlapping rate of the laser spot is 50%.The tensile test of the laser welded joint with and without LSP impacts is carried out,and the fracture morphology of the tensile samples is analyzed by scanning electron microscope（SEM）.Compared with the yield strength of 11.70 kN,the tensile strength of 37.66 kN,the yield-to-tensile strength ratio of 0.310 7,the elongation of 25.20%,the area reduction of 32.68% and the elastic modulus of 13 063.876 MPa,the corresponding values after LSP impacts are 14.25 kN,38.74 kN,0.367 8,26.58%,42.29% and 14 754.394 MPa,respectively.Through LSP impacts,the increasing ratio of the yield strength and tensile strength are 121.79% and 102.87%,respectively;the elongation and area reduction are improved by 5.48% and 29.38%,respectively.By comparing with coarse fracture surface of the welded joint,the delamination splitting with some cracks in the sharp corner of the welded joint and asymmetric dimples,LSP can cause brighter fracture surface,and finer and more uniform dimples.Finally,the schematic illustration of dimple formation with LSP is clearly described.The proposed research ensures that the LSP technology can clearly improve the yield strength,tensile strength,yield-to-tensile strength ratio,elongation,area reduction and elastic modulus of the welded joint.The enhancement mechanism of LSP on laser welded ANSI 304 stainless steel joint is mainly due to the fact that the refined and uniform dimples effectively delay the fracture of laser welded joints.