"相变-扩散钎焊(T/DB)"新工艺及其接头界面形貌

为减小相变超塑性扩散连接的循环次数,提出了一种新型焊接工艺"相变-液相扩散焊(T/DB)",即在待焊母材间预先放入液相扩散焊用的中间层,然后按传统相变超塑性扩散连接工艺施焊,但要求温度循环的峰值温度须同时大于母材的相变点与中间层的熔点.试验以低碳钢为母材,以镍基非晶箔带(BNi2)为中间层,进行了低碳钢的相变-扩散钎焊(循环3次)与液相扩散焊接(1200℃×3 min)的对比试验.结果表明相变-液相扩散焊所需温度循环次数少,接头无界面空洞,其接合线呈非平面状;而液相扩散焊接头的接合线较平直.分析认为,界面的起伏是母材的适度溶解与超塑性流变共同作用的结果;非平面状界面有利于增大金属-金属接触面积及扩散通道的面积,为获得合格接头做出了相应贡献.     

异种材料的相变超塑性焊接

本文采用热模拟技术,进行了低碳钢与铸铁,低碳钢与不锈钢之间的相变超塑性焊接工艺研究,分析了焊接过程中变型的产生及接头形成机理。     

相变超塑性焊接(TSW)过程的有限元分析

相变超塑性焊接（ＴＳＷ）是一种利用超塑性流动的低应力、大变形的特殊流变规律的新型固相焊接方法。本文在弹粘塑性模型的基础上，建立了相变超塑性焊接过程的力学模型。数值模拟结果表明，对于自由边界的相变超塑性焊接接头，随着膨胀率的增大，边界上的应力将逐渐由压应力向拉应力转化；顶锻压力和循环次数既影响拉应力出现的位置，又影响拉 力数值的大小，这两个参数如何合理配合，成为影响接头质量的关键因素。对Ｑ２３５／Ｑ３５相变超塑性焊接的工艺试验研究表明，接合面中心一定范围内焊合很好，但边界上易于产生张开小口的缺陷，张口出现的位置是由界面应力决定的。     

焊接工艺过程对中厚板埋弧焊应力场影响的数值模拟

通过ANSYS有限元分析软件，采用热-应力直接耦合分析法对低碳钢中厚板埋弧焊焊接温度场与应力场进行了模拟分析，并比较了单面双层焊、正反双面依次焊和正反双面同时焊三种焊接工艺过程对接头焊接残余应力的影响。     

基于试验结果分析角变形形成原因

通过测试低碳钢(Q235)对接接头动态角变形,对其变化过程和特点进行了分析和总结。结果表明:除温度变化引起的体积线性变化对角变形产生影响外,高温相变对自由状态下单层对接接头焊缝以及多层多道焊的首层焊缝角变形变化将产生影响;而多层焊接除首层以外的其他层焊缝,高温相变对角变形变化不产生影响。     

焊接工艺过程对中厚板埋弧焊应力场影响的数值模拟

通过ANSYS有限元分析软件,采用热-应力直接耦合分析法对低碳钢中厚板埋弧焊焊接温度场与应力场进行了模拟分析,并比较了单面双层焊、正反双面依次焊和正反双面同时焊三种焊接工艺过程对接头焊接残余应力的影响。     

低碳钢高温相变对焊接角变形的影响

低碳钢板具有良好的综合力学性能和焊接性能,被广泛地应用在各种焊接结构中,但是对接接头角变形一直是焊接过程中的突出问题.文中通过测试低碳钢对接接头动态角变形,对其变化过程和特点进行了分析和总结.结果表明,除温度变化引起的体积线性变化对角变形产生影响外,700℃以上温度发生的高温相变对自由状态下单层对接接头焊缝以及多层多道焊的首层焊缝角变形变化将产生影响;而多层焊接除首层以外的其它层焊缝,700℃以上温度的相变将对角变形变化不产生影响.     

固态相变对P91钢激光对接接头残余应力的影响

基于SYSWELD软件,模拟了P91钢激光对接焊时的温度场和焊接残余应力,并探讨了固态相变产生的体积膨胀、屈服强度变化和相变塑性对焊接残余应力的影响. 数值模拟结果表明,体积膨胀和屈服强度变化对焊接残余应力的大小与分布有显著的影响; 相变塑性在相变过程中有"应力松弛"效应,对焊缝和热影响区的纵向和横向残余应力的值有一定程度的影响. 对比数值模拟结果与试验结果可知,采用文中建立的有限元模型计算得到的残余应力与中子法测量得到的结果基本吻合,在考虑相变塑性的情况下,计算结果与实测值吻合更好.     

异种金属电容储能冲击焊规范参数优化及接头连接机理分析

以小截面低碳钢－紫铜焊接对偶为例,利用正交实验方法研究了电容储能焊规范参数对接头质量的影响规律,为规范参数的合理选择提供了科学依据,同时对低碳钢－澳氏体不锈钢、低碳钢－紫铜、镍－钨三种对接接头的连接机理进行了分析,为进一步扩大这一焊接方法的应用奠定了良好基础。     

铝合金与钢的搅拌摩擦焊焊缝成形及接头性能

用搅拌摩擦焊方法焊接了异种材料铝合金与低碳钢,分析了接头的截面形貌及力学性能.结果表明,当焊接工艺参数合适时,可以获得表面成形良好、无变形的铝合金与钢的对接接头和搭接接头.对于对接接头,金相分析表明,在焊缝横截面,低碳钢与铝合金呈较好的混合状态,在平行焊缝表面的平面内,两种材料呈交叠分布.力学性能试验表明,焊核内局部区域具有较高的显微硬度,可能是形成了钢与铝的金属间化合物,拉伸试样断裂在焊核区边缘偏低碳钢一侧.对于搭接接头,接合面处的钢呈形似"钳子"或弯钩状的分布,钢铆进了铝合金焊缝中,两种材料能有效地达到塑性结合,接头的抗剪切性能较好.     

焊接CGHAZ相变超塑性及对疲劳寿命的影响

采用热模拟方法，对ＥＨ３６ＭＯＤ钢焊接热影响区粗晶区（ＣＧＨＡＺ）的相变超塑性及其对疲劳寿命的影响进行了研究，研究结果证明；（１）采用热作用与拘束位移的方法，在模拟ＣＧＨＡＺ中确实在存着相变超塑性现象；（２）该超塑性应变值为１．０％时，其ＣＧＨＡＺ疲劳寿命比无相变超塑性的提高了１９％（３）微观分析表明，前者Ｍ－Ａ组元的形态为长条状与块状的混合体，其分布为铁素体（Ｆ）基体包围Ｍ－Ａ组元和Ｍ－Ａ组元包     

Design concept and material demand characteristics of rail

In order to improve fatigue strength in welded joints, low transformation-temperature welding wire has been developed in which residual tensile stress can be reduced. In application of the low transformation-temperature welding wire, the prevention of cold cracking without preheating in high strength steel welded joints is expected and examined from the control of residual tensile stress. However, it is expected that residual stress distribution in a welded joint can be suggested by numerical analysis, because the residual stress cannot be measured simply and non-distractively.

In this report, martensite transformation behaviour such as Ms point, transformation expansion, and so on is measured firstly by the Formaster test.

And temperature dependence of several mechanical properties was measured in full-austenite and full-martensite microstructures, and temperature dependence of mechanical properties was estimated in dual phase microstructure of austenite and martensite.

By these data, numerical analysis was carried out and martensite transformation behaviour was compared with measured and calculated results in a rigid model test. From the comparison, it was suggested that transformation superplasticity had to be considered in numerical analysis.

Next, the increase of Ms point due to transformation induced plasticity was guessed from the comparison with measured data by laser speckle measurement and calculated data under transformation superplasticity consideration.

From the all results, it was found that the measured transformation behavior and residual stress had good agreement with the calculated results under transformation superplasticity and transformation induced plasticity considerations.     

Microstructural characteristics in friction stir welded aluminium alloys

In order to elucidate distortion and residual stress generated by welding of high strength steel (HT780) by laser beam, a series of experiments and analyses were carried out. The angular distortion generated by bead-on-plate welding was V-shaped and its magnitude was about 2 mm. The longitudinal bending distortion was extremely small. On the surface of the plate, the residual stress component in the welding direction was tensile and it was smaller than the yield stress in the weld metal. The residual stress was almost zero outside the weld metal. The phase transformation range in the cooling stage and the temperature dependency of mechanical properties were obtained. The mechanical properties in the phase transformation range in the cooling stage could not be specified due to transformation expansion. Therefore, they were idealized by considering transformation expansion and transformation superplasticity. The validity of the idealized mechanical properties was verified by simulating the experiment by the thermal elastic–plastic analysis. It was elucidated that the welding out-of-plane distortion and tensile residual stress were largely controlled by phase transformation in the cooling stage, although the bead width of laser beam welding was extremely narrow.     

轴承钢GCr15的恒温相变超塑性

研究了ＧＣｒ１５钢在Ａｃ１相变点附近的恒温超塑性特性与变形温度的关系。结果表明，与一些材料一样，该钢也存在恒温相变超塑性现象。当初始应变速率为２．５×１０＾－４ｓ＾－１时，经预调质处理的ＧＣｒ１５钢试样，在７４８℃进行超塑性拉伸试验获得最大延伸率达８００％，流动应力为２４ＭＰａ。与已有的同类研究结果相比，其延伸率提高了２００％以上。     

激光淬火后40Cr与Cr12MoV固态焊接的工艺研究

利用对40Cr钢与Cr12MoV钢分别进行表面激光淬火预处理后进行固态焊接试验,探讨了焊接工艺参数（焊接温度、焊接时间、应变速率、保温过程等因素）对焊接质量的影响。焊接温度过低,拉伸强度不高,但焊接温度太高材料抗氧化性下降,同时对提高生产率、节能降耗产生不利影响。焊接时间过长,晶粒长大,接头强度降低。表面激光淬火使表层组织显著细化,超塑性机制得到充分发挥。试验结果表明：预压应力为56．6MPa,加热温度为800℃,焊接时间为5min,保温时间为10min可达到高质量的固相焊接。     

纯铝中间层厚度对铝/钢点焊接头性能的影响

采用纯铝作为中间层对铝合金与低碳钢进行了电阻点焊,分析中间夹层厚度对界面反应层厚度和接头抗拉强度的影响。在钢/中间夹层界面观察到有界面反应层生成,其主要由靠近钢侧的Fe2Al5和靠近中间夹层铝侧的FeAl3两种金属间化合物组成。与不加中间夹层相比,利用纯铝作为中间夹层点焊的铝合金与低碳钢的接头具有较薄的界面反应层和较高的接合强度。随着中间夹层厚度的增加,界面反应层厚度逐渐减小,而接头抗拉强度则呈增大趋势。结果表明,采用纯铝作为中间夹层点焊铝合金与钢具有一定的有效性。     

Electrical-thermal interaction simulation for resistance spot welding nugget process of mild steel and stainless steel

A three-dimensional finite difference electrical-thermal model for resistance spot welding nugget process of mild steel and stainless steel is introduced. A simulation method of the interaction of electrical and thermal factors is presented. Meanwhile, calculation method of contact resistance and treatment method of heater structure is provided. The influence of the temperature dependent material properties and various cooling boundary conditions on welding process was also taken intoaccount in the model. A method for improving the mild steel and stainless steel joint was analyzed in numerical simulation process. Experimental verification shows that the model prediction agrees well with the practice. The model provides a usefultheoretic tool for the analysis of the process of resistance spot welding of mild steel and stainless steel.     

铸铁冷焊的氧化铁系低碳钢焊条的研制

针对采用低碳铜焊条在冷焊铸铁时极易出现白口屡、抗裂性差的问题,本文利用氧化铁皮和石墨,研制了铸铁冷焊用氧化铁系低碳钢焊条,在半熔化区和焊缝区降低了白口层和裂纹的发生.