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.

Microstructure and corrosion behaviour of gas tungsten arc welds of maraging steel

Superior properties of maraging steels make them suitable for the fabrication of components used for military applications like missile covering, rocket motor casing and ship hulls. Welding is the main process for fabrication of these components, while the maraging steels can be fusion welded using gas tungsten arc welding(GTAW) process. All these fabricated components require longer storage life and a major problem in welds is susceptible to stress corrosion cracking(SCC). The present study is aimed at studying the SCC behaviour of MDN 250(18% Ni) steel and its welds with respect to microstructural changes. In the present study, 5.2 mm thick sheets made of MDN 250 steel in the solution annealed condition was welded using GTAW process. Post-weld heat treatments of direct ageing(480 C for 3 h), solutionizing(815 C for 1 h) followed by ageing and homogenizing(1150 C for 1 h) followed by ageing were carried out. A mixture of martensite and austenite was observed in the microstructure of the fusion zone of solutionized and direct aged welds and only martensite in as-welded condition. Homogenization and ageing treatment have eliminated reverted austenite and elemental segregation. Homogenized welds also exhibited a marginal improvement in the corrosion resistance compared to those in the as-welded, solutionized and aged condition. Constant load SCC test data clearly revealed that the failure time of homogenized weld is much longer compared to other post weld treatments, and the homogenization treatment is recommended to improve the SCC life of GTA welds of MDN 250 Maraging steel.

Microstructure and properties of pure iron/copper composite cladding layers on carbon steel

In the present study, pure iron/copper composite metal cladding was deposited onto carbon steel by tungsten inert gas welding. The study focused on interfacial morphological, microstructural, and mechanical analyses of the composite cladding layers. Iron liquid–solid-phase zones were formed at copper/steel and iron interfaces because of the melting of the steel substrate and iron. Iron concentrated in the copper cladding layer was observed to exhibit belt, globule, and dendrite morphologies. The appearance of iron-rich globules indicated the occurrence of liquid phase separation（LPS） prior to solidification, and iron-rich dendrites crystallized without the occurrence of LPS. The maximum microhardness of the iron/steel interface was lower than that of the copper/steel interface because of the diffusion of elemental carbon. All samples fractured in the cladding layers. Because of a relatively lower strength of the copper layer, a short plateau region appeared when shear movement was from copper to iron.

Alloying OCTG pipes with tungsten

The mechanical and corrosion performance of low alloy steel tubular goods depends on the microstructure obtained as a result of the combination of alloying elements and manufacturing process parameters. The basic design philosophy for the selection of the alloying elements is ruled by the balance between the steel cost and the material performance.Following this approach the alloying sequence for the manufacturing of tubular components in oil country tubular goods(OCTG) application is generally Mn,C,r and Mo,used as substitutional elements in a total added weight concentration around 1%up to 3%.Other elements such as B,Ti,Nb and V are applied as strengthening microalloying elements forming fine precipitates. A lack of experience is found related to the use of Tungsten(W) on OCTG applications,although W is also a substitutional element that belongs to group 6 of the periodic table together with Cr and Mo.On the other hand W is widely added for steel pipes working in high temperature services such as power plant boilers,where creep resistance is needed.It is also applied for tool steels enhancing the hardness,wear resistance and cutting performance. Taken into consideration the similarity between Cr,Mo and W and the applications where W has been proven it was decided to analyze the feasibility of using W as an alternative alloying element for some OCTG applications. Another factor that drives this study is the fact that W could be a cost effective substitute of Mo,depending on the alloy market price. This paper is based on literature review and experimental activity done on laboratory steels in which 0.1%Mo was replaced by 0.2%and 0.4%W.The different findings in regards with manufacturing process considerations, material performance and the possible use of W alloyed steel for OCTG applications are summarized. (1 ) Opposed to the susceptibility shown by low carbon with high Cr-W content,hot cracks are not expected in medium C steels(0.2%-0.3%) with W addition up to 1%. (2) Microporosity-related defects could form if W <<0.4%. (3) An improvement in the oxidation resistance for typical rolling furnace atmospheres in the temperature range 1 200 - 1 340℃was detected if Mo is substituted by W. (4) Theoretically W is one half less efficient in regards with hardenability. (5) No differences were found in the grain size after austenitizing in the temperature range 920 - 1 050℃, independently on Mo and W contents. (6) Tempering resistance was similar to Mo steels and there was no effect on the cementite shape factor,which affects the performance in sour environments. (7) Both pitting and general corrosion resistance are improved by W addition.But W effectiveness in improving pitting resistance is about one half. (8) The use of W as a substitute of Mo has been proven to be feasible and it could be applied for the manufacturing of N80 or L80 OCTG steel grades as per ISO 11960/API 5CT.

Electro-deposition tangsten coating on low activation steel substrates from Na_2WO_4-ZnO-WO_3 melt salt

Tungsten coating is considered as a promising alternative material for plasma facing materials(PFC) in future fusion devices.The electro-deposition of tungsten in Na_2WO_4-ZnO-WO_3 melt at 1173 K on low activation steel substrates was studied in this work.Adherent and smooth tungsten films were deposited under various pulsed current conditions.The crystal structure and microstructure of tungsten deposits were characterized by XRD,SEM and EDX techniques.The results show that pulsed current density and duty cycle have a significant influence on tungsten nucleation and electro-crystallization phenomena.Uniform and smooth tungsten coating with high purity and high adherence is obtained on low active steel substrates as cathodic current density ranges from 35 to 25 mA·cm_(-2).

Effect of shielding gas on microstructure and properties of GTAW joints of 2205 duplex stainless steel

2205 duplex stainless steels （ DSSs） are welded in gas tungsten arc welding （GTAW） with the addition of N2 to argon, and the desirable microstructure and properties of the joints are obtained by altering the nitrogen percentage in the shielding gas mixture. The mechanical properties of joints are tested with tensile and microhardness machine, and the joint micrustructure is analyzed with scanning electron microscope （SEM） and optical microscope （ OM ） , and detrimental phase precipitate is investigated with X-ray diffraction （XRD）, respectively. Finally, the corrosion behaviour of joint is also evaluated. Results show that the favorable joint strength and corrosion resistance can be obtained with appropriate shielding gas mixture in GTA W. No detrimental phase precipitates in the weldment, and the joint tensile fracture obviously presents the characteristic of ductile fracture.

Mechanical and corrosion properties of 445J2 ultra pure ferritic stainless steel joint

The microstracture, mechanical and corrosion resistance properties of 445J2 ultra pure ferritic stainless steel thin plate joints conducted by the pulsed current gas tungsten arc welding （PCGTAW） were discussed in this paper. In order to avoid weld defects, the appropriate welding process was adjusted. The joints were subjected to optical microscopy, transverse static tensile, plastic deformation, intergranular corrosion and electrochemistry corrosion tests. The results indicated that the weld zone （WZ） is characterized with columnar grains and equiaxed grains and the heat-affected zone （HAZ） shows coarse ferrite grains due to the rapid solidification of thin plate welding. The PCGTAW joint exhibited acceptable mechanical properties and equivalent corrosion resistance properties as the base metal.

石墨烯纳米流体微量润滑磨削钨钢的加工性能评价

钨钢因其优异的性能在各种领域中得到广泛应用,但钨钢具有硬度高、难加工等特点,导致磨削时工件表面质量差。为解决这一现状,对钨钢进行了纳米流体微量润滑磨削试验,采用石墨烯纳米流体微量润滑、浇注式和干式3种不同条件对钨钢进行磨削试验,提出了一种正多边形磨削轨迹的组合试验方法,比较磨削速度、进给速度、磨削深度对磨削力、工件表面质量的影响。研究发现,在磨削参数相同的条件下,纳米流体微量润滑下的磨削力最小,浇注式次之,干式最大。在磨削速度v=15 m/s时,与干式和浇注式相比,纳米流体微量润滑条件下的法向磨削力Fn分别降低约25.13%和4.52%,切向磨削力Ft分别降低约28.97%和9.92%,石墨烯纳米流体微量润滑在改善钨钢磨削方面具有显著作用。

A Fuzzy Logic Approach to Predict Tensile Strength in TIG Mild Steel Welds

Welding defects influence the desired properties of welded joints giving fabrication experts a common problem of not being able to produce weld structures with optimal strength and quality. In this study, the fuzzy logic system was employed to predict welding tensile strength. 30 sets of welding experiments were conducted and tensile strength data was collected which were converted from crisp variables into fuzzy sets. The result showed that the fuzzy logic tool is a highly effective tool for predicting tensile strength present in TIG mild steel weld having a coefficient of determination value of 99%.

Comparison of microstructure and properties between joints of FSW and TIG 316L austenitic stainless steel

FSW and TIG were conducted on 316L stainless steel.Variation during microstructure and properties in joints obtained by different welding methods was studied.The results show that the effect of severe mechanical stirring and intense plastic deformation creat a fine recrystallized grain in the welding joint during FSW.As for TIG,the temperature of welding joint exceeds the melting point of welded material itself.The entire welding process belongs to the solidification of a small molten pool;and the microstructure of the joint takes on a typical casting structure.When the welding parameters were selected appropriately,the average ultimate tensile strength of FSW joints can reach 493 MPa,which is 83.6%of base metal;the average elongation is 52.1%of base metal.The average ultimate tensile strength of TIG joints is 475 MPa, which is 80.5%of base metal;the average elongation is 40.8%of base metal.The tensile test of FSW joints is superior to the TIG joints.The microhardness of FSW joint compared to base metal and TIG joint having a significant improvement,which arel95.5 HV,159.7 HV and 160.7 HV,respectively;grain refinement strengthening plays an important role in enhancing the microhardness.The electrochemical corrosion tests show that the joint of FSW 316L austenitic stainless steel has a good corrosion resistance.

Welding of nickel free high nitrogen stainless steel: Microstructure and mechanical properties

High nitrogen stainless steel(HNS) is a nickel free austenitic stainless steel that is used as a structural component in defence applications for manufacturing battle tanks as a replacement of the existing armour grade steel owing to its low cost, excellent mechanical properties and better corrosion resistance.Conventional fusion welding causes problems like nitrogen desorption, solidification cracking in weld zone, liquation cracking in heat affected zone, nitrogen induced porosity and poor mechanical properties.The above problems can be overcome by proper selection and procedure of joining process. In the present work, an attempt has been made to correlate the microstructural changes with mechanical properties of fusion and solid state welds of high nitrogen steel. Shielded metal arc welding(SMAW), gas tungsten arc welding(GTAW), electron beam welding(EBW) and friction stir welding(FSW) processes were used in the present work. Optical microscopy, scanning electron microscopy and electron backscatter diffraction were used to characterize microstructural changes. Hardness, tensile and bend tests were performed to evaluate the mechanical properties of welds. The results of the present investigation established that fully austenitic dendritic structure was found in welds of SMAW. Reverted austenite pools in the martensite matrix in weld zone and unmixed zones near the fusion boundary were observed in GTA welds. Discontinuous ferrite network in austenite matrix was observed in electron beam welds.Fine recrystallized austenite grain structure was observed in the nugget zone of friction stir welds.Improved mechanical properties are obtained in friction stir welds when compared to fusion welds. This is attributed to the refined microstructure consisting of equiaxed and homogenous austenite grains.

超级双相不锈钢S32750深熔TIG焊接工艺研究

为提高薄壁、大直径压力容器产品的焊接效率,研究了5 mm厚超级双相不锈钢S32750的深熔非熔化极惰性气体保护电弧焊(TIG)焊接工艺。通过焊接试验和工艺评定确定了S32750的焊接工艺参数,对焊接接头进行了力学性能试验和腐蚀试验。试验结果表明,对厚度5 mm的S32750不开坡口进行焊接,深熔TIG焊接可实现一次熔透,并获得质量可靠的焊接接头,可大幅提高薄壁、大直径超级双相不锈钢压力容器的生产效率。

一种考虑球体变形的钨球侵彻低碳钢深度计算模型

为了研究钨球在高速撞击下的变形行为对侵彻效果的影响,对钨球侵彻半无限低碳钢靶进行试验研究,得到<1600 m/s冲击速度下钨球变形特征和靶板侵彻深度随冲击速度的变化规律。在此基础上构建钨球侵彻塑性变形模型。将钨球变形模型和球形空腔膨胀阻力模型相结合,建立钨球变形侵彻深度计算模型。对比不同撞击速度下钨球变形侵彻模型、刚性侵彻模型的计算结果。对比结果表明,变形侵彻模型能够更加准确地计算钨球对半无限靶的侵彻深度,计算结果与试验相比最大误差20%(正误差15%,负误差5%),精度较刚性侵彻模型提升42.86%。

00Cr13Ni5Mo不锈钢四钨极耦合电弧双丝增材制造工艺

为解决现有基于GTA热源增材制造工艺存在的熔覆效率较低、焊接效率较低的突出问题,该文提出一种四钨极耦合电弧双丝增材制造工艺,并通过控制变量的试验方法研究熔覆电流、行走速度与送丝速度对单层单道沉积层成形质量的影响。结果表明,熔池面积的波动与电弧压力是四钨极热源单道沉积层出现单道沉积层不连续、咬边等缺陷的主要原因,在保证成形质量的前提下,四钨极热源最大行走速度为400 mm/min、最大送丝速度为12 m/min、熔覆效率为6.24 kg/h,沉积件微观组织由回火索氏体、逆变奥氏体及碳化物组成,沉积件冲击吸收能量达到208 J,为MAG热源的2.5倍。综上所述,四钨极耦合电弧双丝增材制造工艺可以在保证优良冲击性能的前提下显著解决GTA热源增材制造工艺存在的熔覆效率较低、焊接效率较低的问题。

小模数齿轮接触式钨钢测针微球头夹具设计

对小模数齿轮常利用接触式微球头测针进行精密测量,由于其体积较小、表面形貌复杂,对加工的测针微球头直径、圆度等精度有很高的要求。首先简要分析了利用钨钢制作小模数齿轮接触式测针的优点,并利用垂直激光束进行了微球头加工试验,根据试验结果及出现的问题设计了加工钨钢测针微球头的专用定位夹具;其次利用紧固弹簧的弹性势能实现对加工针件的夹持与放松,并搭建X/Y滚珠丝杠定位平台,实现了夹持与定位相结合;最后在加工平面引入半球形磁铁与调速马达,从而进一步提高了所加工微球头的精度与圆度。

焊接热输入量和保护气体成分对S32205双相不锈钢低温冲击韧性的影响

采用等离子弧焊(PAW)+钨极惰性气体保护焊(GTAW)对2205双相不锈钢进行焊接,研究了在GTAW焊接过程中,热输入量和保护气体这两个要素对材料焊接部位低温冲击韧性的影响,并通过金相和SEM等对微观组织结构进行分析研究。结果表明,采用GTAW焊接时,热输入量会影响晶粒组织中铁素体/奥氏体相比例和奥氏体形态,当热输入量为1.76 kJ/cm时,焊接部位的低温冲击性能(-46℃)最佳;在保护气体中添加N_(2),会影响奥氏体和铁素体比例以及氮化物(CrN/Cr_(2)N)析出相在铁素体中的析出数量,并且导致微气孔形成,当N_(2)添加量为1%左右时,焊接部位的低温冲击性能最佳。

扩散焊接钨/钢接头残余应力的数值模拟

采用有限元法分析钨/钢扩散焊接头残余应力,并探讨添加钒/镍和钒/铜复合中间层对钨/钢扩散焊接头残余应力分布的影响。结果表明:钨/钢扩散焊接头存在较大的残余应力,靠近中间层附近的钨处存在极大的径向压应力,而靠近中间层附近的钢处和整个中间层区域均存在较大径向拉应力;钨/钢直接扩散焊接头的残余应力极大,钨/钒/镍/钢扩散焊接头的残余应力有所降低,钨/钒/铜/钢扩散焊接头残余应力最小;接头力学性能及断裂特征验证了有限元计算结果的准确性。

钒/镍复合中间层扩散焊接钨与钢的界面结构及力学性能

通过添加钒/镍复合中间层,在1 050℃/10 MPa/1 h的工艺条件下,对钨/钢异种材料进行真空扩散焊接.采用扫描电镜(SEM)、能谱仪(EDS)、电子探针(EPMA)、纳米压痕、X射线衍射对接头的微观组织、元素分布及显微硬度进行分析和测试;对焊接接头的拉伸性能进行测试,并对拉伸断口的形貌特征,元素分布及物相组成进行分析.结果表明,采用钒/镍复合层可实现钨与钢的可靠焊接;钨/钢焊接接头界面区由钨-钒固溶体层、未反应的钒层、钒-镍界面层、未反应的镍层、镍-铁固溶体层五部分组成,其中钒-镍界面层结构为碳化钒层/钒-镍金属间化合物和碳化钒混合层/钒-镍金属间化合物层;钒/镍界面由于硬脆碳化物与金属间化合物的产生,具有最高的显微硬度,硬度高达9.7 GPa;接头强度达164 MPa,断裂点位于含脆性相碳化钒及钒-镍金属间化合物的钒/镍界面.

基于镍基微晶钎料的钨/钢真空焊接接头的组织及性能

采用镍基微晶箔带作为钎料,在1150℃、30 min的工艺条件下研究直接钎焊和添加Ni-Cu合金中间层两种工艺焊接钨和钢的特性。采用扫描电镜(SEM)、电子探针(EPMA)和纳米压痕分别对接头的显微组织、元素分布及显微硬度进行分析,测试接头的拉伸强度并分析断口形貌和物相组成。结果表明:添加Ni-Cu合金中间层的钎焊接头的拉伸强度(300 MPa)远高于直接钎焊的焊接接头的拉伸强度。两种钎焊接头的断裂均发生在残余应力集中的靠近钨/钎料界面的钨基体内,为典型的脆性断裂方式。接头界面硬度分析表明,固溶强化效应及脆性化合物的生成,使靠近钨侧的钨/钎料扩散区域的显微硬度得到显著增加。