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.

Deformation Behavior and Formability of Gradient Nano-grained AISI 304 Stainless Steel Processed by Ultrasonic Impact Treatment

The deformation behavior and formability of gradient nano-grained（GNG） AISI 304 stainless steel in uniaxial and biaxial states were investigated by means of tensile test and small punch test（SPT）. The GNG top layer was fabricated on coarse grains（CG） AISI 304 by ultrasonic impact treatment. The results showed that the CG substrate could effectively suppress the strain localization of NC in GNG layer, and an approximate linear relationship existed between the thickness of substrate（h） and uniform true strain before necking（ε_（unif））. Grain growth of NC was observed at the stress state with high Stress triaxiality T, which led to better ductility of GNG/CG 304 in SPT, as well as similar true strain after the onset of necking（ε_（neck）） compared with coarse 304 in tensile test. Ei-values of GNG/CG 304 with different structures were nearly the same at different punch speeds, and good formability of GNG/CG 304 was demonstrated. However, punch speed and microstructure needed to be optimized to avoid much lost of membrane strain region in biaxial stress state.

1-Hydroxyethylidene-1,1-diphosphonic Acid (HEDP) as a Corrosion Inhibitor of AISI 304 Stainless Steel in a Medium Containing Chloride and Sulfide Ions in the Presence of Different Metallic Cations

The novelty of this paper is the analysis in a medium containing sulfide ion due to the generation of this ion in petroleum industries, in the refining stage (the sulfide ion is also present on the produced water). The performance of 1-hydroxyethylidene-1,1-diphosphonic acid inhibitor (HEDP) was investigated by potentiodynamic polarization, electrochemical impedance spectroscopy, and weight loss measurements in a dissolution of AISI 304 stainless steel immersed in a solution containing chloride and sulfide ions. The protection of the stainless was increased with the addition of divalent cations (Ca2+, Zn2+, and Mg2+). Potentiodynamic polarization studies have shown that the inhibitor alone has anodic protection, but the addition of Ca2+ (10 mg·L-1) favors the cathodic protection, and the addition of Zn2+ (20 mg·L-1) and Mg2+ (10 mg·L-1) mixed-type is observed. Electrochemical impedance spectroscopy was performed at three distinct potentials: -0.3 [V vs. SCE], Ecorr [V vs. SCE], and 0.1 [V vs. SCE]. This revealed that calcium is responsible for favoring the formation of the film and the other elements (zinc and magnesium) favor the stabilization of the protective film. Scanning electron microscopy analysis revealed that the addition of cations provided the adsorption of HEDP on the metal surface. Weight loss results showed that the presence of zinc in a solution containing HEDP favored greater inhibitor efficiency (Zn2+ ηm = 85.2% and for Mg2+ ηm = 70.4%).

表面机械研磨诱导AISI 304不锈钢表层纳米化 Ⅰ.组织与性能

采用表面机械研磨处理(SMAT)在AISI 304不锈钢上制备出纳米结构表层,研究纳米化行为及其对硬度的影响。结果表明:经过SMAT后,样品表面形成了厚度约为30μm的纳米晶层,显微组织由平均晶粒尺寸约为10nm的单一马氏体相演变为尺寸稍大的双相组织;在距表面30—300μm的范围内,显微组织由以亚微米级的奥氏体多系孪晶为主逐渐演变为单系孪晶,表面纳米化是晶粒碎化与纳米尺度新相形成共同作用的结果,与心部相比,表面硬度显著提高。

表面机械研磨诱导AISI 304不锈钢表层纳米化 Ⅱ.晶粒细化机理

采用表面机械研磨处理(SMAT)在AISI 304不锈钢上制备出纳米结构表层,用透射电镜(TEM)研究组织演变过程,晶粒细化机理可归纳如下:位错在{111}面上滑移并相互交割形成网格结构;单系孪晶形成并逐渐过渡到多系孪晶;多系孪晶相互交割使晶粒尺寸不断减小,并在孪晶交叉处形成了马氏体相;孪晶系增多与孪晶重复交割强度加大使得细化晶粒的尺寸进一步减小;最终在大应变量、高应变速率和多方向重复载荷的作用下,形成等轴状、取向呈随机分布的马氏体相纳米晶组织。

AISI 304不锈钢表面Fe_3Si型硅化物渗层的制备及渗硅机理

以n(NaCl):n(KCl):n(NaF)=2:2:1碱金属卤化物混合体系做载体,采用不同摩尔比的Na2SiF6和Si粉作渗硅剂,在800℃下利用熔融盐法分别对AISI 304不锈钢进行渗硅处理。采用X射线衍射仪(XRD)分析渗硅层的物相组成,用附带能量色散谱仪(EDS)附件的扫描电子显微镜(SEM)研究渗层截面的形貌和成分,分析熔盐法渗硅层的形成机理。结果表明:融盐中SiF62-的浓度决定渗层中Si元素的含量,由于SiO2在融盐体系中的溶解,融盐中SiF62-得到补充,渗层中Si元素的含量进一步提高。

AISI304奥氏体不锈钢阳极渗氮层的组织与摩擦磨损性能

为避免传统直流离子渗氮存在的表面打弧和边缘效应等弊端,采用活性屏阳极渗氮法对AISI 304奥氏体不锈钢进行表面处理。将样品放置于阳极电位,在440~520℃范围内,渗氮处理8 h。分析了渗氮层的微观组织结构与形貌,并考察了渗氮前后的摩擦磨损性能。结果表明:在低温440℃下,在表面制备了高硬度的S相强化层。XRD与TEM表明S相为面心立方结构,且无Cr N相析出。高温520℃渗氮表面硬度值(1100 HV0.1)是基体的5倍,但Cr N相明显析出。在干摩擦条件下,渗氮处理后的摩擦系数在0.8左右,相对渗氮前降低约0.2,特别是磨损率只有渗氮前的十分之一量级。磨损机制从原始基体的严重粘着转变为轻微的氧化和磨粒磨损。

AISI304不锈钢表面硅化物渗层的制备与抗氧化性能

采用ω(NaCl)∶ω(KCl)∶ω(NaF)=2∶2∶1(摩尔比,下同)的中性熔融盐作为载体,ω(Na2SiF6)∶ω(Si)=8∶2粉末做为渗硅剂,800℃下渗硅10 h可实现在AISI 304不锈钢表面形成厚度约500μm的富含Cr、Ni合金元素的Fe3Si型硅化物渗层。采用X射线衍射仪(XRD)分析了渗硅层的物相组成,用附带能量色散谱仪(EDS)附件的扫描电子显微镜(SEM)研究了渗层截面的形貌和成分。结果表明,渗层以Fe3Si相为主,Cr在渗层中含量低于其在304不锈钢基体中含量,而Fe和Ni在基体和渗层中的含量大致相当。Fe3Si型硅化物渗层在800℃和900℃下的氧化动力学均遵从二次抛物线规律。AISI 304不锈钢渗硅层在800℃下的抗氧化性能略优于不锈钢基体,而在900℃下AISI 304不锈钢发生灾难性破坏,硅化物渗层表现出比其在800℃下更为好的抗氧化性能。900℃下Cr和Si元素发生上坡扩散最终在渗硅层表面形成富含SiO2和Cr3O4的复合氧化膜是其优异抗氧化性能的原因。

AISI304不锈钢表面Fe_3Si型硅化物渗层制备及其力学性能

采用NaCl∶KCl∶NaF=2∶2∶1(摩尔比)的中性熔融盐作为载体,Na2SiF6∶Si=8∶2粉末作为渗硅剂,以SiO2为助渗剂,800℃下渗硅5h可实现在AISI 304不锈钢表面形成厚约600μm的富含Cr、Ni合金元素的Fe3Si型硅化物渗层。采用万能材料试验机进行了轴向拉伸试验,并对应力-应变曲线进行了分析。结果表明,硅化物渗层为脆性断裂,基体部分为塑性断裂;AISI 304不锈钢渗硅后的名义屈服应力有明显提高。

冷轧AISI 304不锈钢微观组织及力学性能的变化

采用金相显微镜、铁素体测量仪、硬度计及力学分析等手段,研究了AISI 304不锈钢的微观组织和力学性能在冷轧过程中的演变规律.试验结果表明:冷轧变形可使AISI 304不锈钢产生形变诱发马氏体相变,试样中金属晶粒沿着轧制方向被拉扁拉长;在冷轧压下量较小时,仅有少量的奥氏体相转变为马氏体相,并且马氏体组织以板条状出现;冷轧压下量较大时,金属晶粒逐渐被拉长为纤维状;随着冷轧压下量的增大,马氏体体积分数、硬度和抗拉强度均随之增大,但延伸率逐步下降.

等离子体源渗氮AISI 304不锈钢在3.5%NaCl溶液中钝化膜的稳定性

采用等离子体源渗氮技术对AISI 304奥氏体不锈钢进行表面渗氮处理.利用X射线衍射(XRD)、扫描电子显微镜(SEM)和电子探针显微分析(EPMA)技术,并结合电化学交流阻抗(EIS)测试技术和Zsimp Win软件拟合技术研究改性前后AISI 304奥氏体不锈钢的表面组成结构及在3.5%NaCl溶液中钝化膜的稳定性.研究结果表明,等离子体源渗氮AISI 304奥氏体不锈钢表面形成了氮浓度峰值为23.0%、厚度约为17μm的相改性层.改性前后AISI 304不锈钢在3.5%NaCl溶液中浸泡不同时间形成的钝化膜电极过程的等效电路为R(QR);浸泡时间为10 h时,与AISI 304不锈钢相比,γN改性层的钝化膜电阻R_p从3.615×10~4Ω·cm^2增加至3.765×105Ω·cm^2,增大了1个数量级,具有更好的耐点蚀性能.随着浸泡时间增加至48 h,γN相改性层的钝化膜电阻始终高于AISI 304不锈钢1个数量级,保持在105Ω量级,具有良好的稳定性.

AISI 304不锈钢的车削加工

针对AISI 304奥氏体不锈钢的特点,分析了AISI 304不锈钢材料的物理性能和切削加工性能,从刀具材料、切削用量和冷却液的选择等方面研究了AISI 304不锈钢车削加工的影响因素,通过合理选择和优化相关参数等方法有效解决了AISI 304不锈钢的加工难题,获得了较好的车削加工效果,提高了生产效率。

AISI 304不锈钢铣削加工刀具磨损实验研究

AISI 304不锈钢具有低导热性和高韧性等特性,切削加工性较差。研究采用复合涂层硬质合金铣刀,对AISI 304不锈钢进行了端铣实验研究,考察后刀面磨损情况。实验表明,进给率对磨损的影响大于切削速度。针对刀具后刀面磨损,给出了相对较好的切削条件组合。

AISI304钢埋弧焊工艺的研究

本文对AISI 3 0 4钢薄板的埋弧焊工艺进行了试验研究。并对焊材性能进行了工艺试验 ,在对试验结果分析的基础上确定了最佳焊接工艺参数。焊接接头的各项力学性能实验结果完全满足图纸要求。通过采取先进的焊接工艺装备 。

AISI304表面Fe_3Si型过渡金属硅化物渗层结构缺陷初探

利用NaCl∶KCl∶NaF=2∶2∶1(摩尔比)的碱金属卤化物混合体系为载体,Na2SiF6∶Si=8∶2粉末为渗硅剂,SiO2为助渗剂,800℃下渗硅5 h可实现在AISI 304不锈钢表面形成Fe3Si型硅化物渗层.采用万能材料试验机进行轴向拉伸试验,用附带能量色散谱仪的扫描电子显微镜进行断面分析.结果表明,渗层中的大空洞为包盐孔洞.

爆炸冲击诱发AISI304不锈钢表面硬化层结构及性能

利用爆炸冲击硬化方法,对AISI304不锈钢板进行表面硬化处理,制备了一定厚度的硬化层;利用X射线衍射仪、光学显微镜、透射电子显微镜,对横截面微观组织及表层物相组成进行表征,分析爆炸冲击对表层组织转变及显微硬度、耐磨性能的影响.结果表明:AISI304不锈钢板爆炸硬化后表层耐磨性提高50%,显微硬度提高1倍,显微硬度沿着厚度方向呈梯度变化;硬化层中形成了取向接近随机分布、晶粒尺寸为20-30nm范围的奥氏体和马氏体混合纳米晶;横截面奥氏体晶粒沿厚度方向从表层纳米晶过渡至基体原始晶粒;爆炸加载过程中表面产生应变诱发马氏体相变,在奥氏体晶粒内形成大量变形带及交叉.

AISI304不锈钢铣削加工性能实验分析

利用硬质合金铣刀,对奥氏体不锈钢AISI 304进行铣削加工实验研究。讨论切削速度和进给率的变化对刀具寿命的影响。实验结果表明,刀具寿命随切削速度的增加而降低,随进给率的增加而增加。以生产率最高和刀具寿命最长为目标,给出单刃铣刀铣削加工的最佳切削参数。

AISI 304不锈钢车削加工切削速度对加工性能影响的实验研究

利用硬质合金刀具,对奥氏体不锈钢AISI 304进行了车削加工实验研究.讨论了车削速度对切屑形态、刀具磨损及工件表面粗糙度的影响.试验结果表明,随着切削速度的增大,切削热对切屑形态的影响降低,刀具后刀面磨损及工件表面粗糙度均减小.给出了不同切削速度下的切屑形态以及切削速度与刀具磨损、切削速度与表面粗糙度的关系曲线.

AISI 304钢-铌异种金属激光焊温度场及残余应力研究

采用SYSWELD软件,对AISI 304钢–铌异种金属激光焊接过程进行动态模拟,在研究了AISI 304钢–铌异种金属激光焊接接头温度场的基础上,分析了焊后薄板的残余应力分布。结果表明:异种金属焊接温度场呈不对称分布,铌侧高温区域比不锈钢侧要宽;沿焊接方向上,无论是横向残余应力还是纵向残余应力,焊缝中部区域都存在最大残余拉应力;而垂直于焊缝方向上,横向残余应力和纵向残余应力在焊缝及焊缝附近区域应力梯度都比较大,分布形态都呈“M”状,纵向残余应力在焊缝区表现为残余拉应力,而横向残余应力在焊缝中心处出现了压应力。

Development of processing windows for diffusion bonding of Ti-6Al-4V titanium alloy and 304 stainless steel with silver as intermediate layer

As titanium alloy is chemically reactive,it is very difficult to join by conventional welding techniques.Titanium alloys can easily pick up nitrogen and oxygen from the atmosphere.In the fusion welding method,brittle intermetallic compounds are formed when joining titanium alloy and stainless steel,which decrease the mechanical behavior of the couples.Hence,for joining of titanium alloy,diffusion bonding is recommended.This work dealt with the measurement of feasible process parameters for diffusion bonding of Ti-6Al-4V and AISI 304 stainless steel with silver as an intermediate layer.The quality of the bonds was confirmed by the lap shear test and microstructural analysis.With the experimental results obtained,diffusion bonding windows were constructed and this will act as reference maps to identify the process parameters for obtaining defect free bond.Bonding was successful in the temperature range of 750-800 °C.Maximum lap shear strength was achieved under a bonding pressure of 5 MPa and holding time of 90 min.