【作者】 刘瑞琳；

【导师】 黄勇；

【作者基本信息】 兰州理工大学 ， 材料加工工程， 2012， 硕士

【摘要】 自20世纪90年代以来，A-TIG焊作为活性化焊接技术的代表，引起了人们的广泛关注，它通过在传统的TIG焊前在施焊板材表面上涂敷一层很薄的活性剂后可以使熔深显著增加，但涂敷活性剂的工序既降低了生产效率又不易保证工艺的稳定性，所以使其实际应用的推广受到阻碍。活性TIG焊接法研究表明，对于碳钢、不锈钢等铁系合金而言，O等活性元素可改变焊接熔池表面张力温度系数是活性元素增加焊缝熔深的主要机理。为了充分发挥活性焊的优点，本课题通过改变活性元素的引入方式，提出了一种新的活性焊接方法——气体熔池耦合活性TIG焊（GasPoolCoupledActivatingwelding，简称GPCA-TIG焊），该方法即采用内外两个喷嘴将含有N元素及活性元素O的气体与惰性保护气体分开，内层气体采用惰性气体（Ar或He）起到保护熔池和钨电极的作用；外层气体则为单一的含N元素的气体（N₂）或含活性元素O的气体（O₂或CO₂），或者两者的混合气体（N₂+O₂）。外层气体通过电弧的作用分解出O元素和N元素，并与熔池耦合，以此引入O和N元素，改变熔池金属流动方式，增加熔深，改善焊缝因添加O元素而使得焊缝性能下降的不足。该方法通过改变外层活性气体与熔池的耦合度，可以微量控制熔池中的活性元素O和N元素的引入量，从而达到控制焊缝成形和焊缝质量的目的。本文针对不锈钢GPCA-TIG焊进行了焊枪研制和焊接性研究。试验材料选用SUS304不锈钢作为母材，以氩气作为内层保护气体，对比了传统TIG焊接方法与GPCA-TIG焊接方法的电弧形貌、焊缝表面和截面形貌，结果发现电弧收缩，焊缝深而窄，能将8mm厚不锈钢板不开破口一次性焊透，深宽比为1.06。另外采用GPCA-TIG焊接方法可以有效避免因添加O元素而引起的钨极氧化烧损。分别研究了外层气体与熔池耦合度变化、外层气体配比（N₂+O₂）、内层保护气体流量三个主要因素和其他工艺参数对焊缝熔深的影响。工艺试验结果表明，当外喷嘴上升0mm时，获得的熔深最深，随着外喷嘴相对内喷嘴上升高度的增加也即外层气体与熔池耦合度减小，熔深变浅，因此可以实现控制O元素的引入量从而获得不同的焊缝熔深；随着N₂占外层气体比例（0%-50%）的增加，焊缝熔深先略微下降然后再上升，当N₂所占比例达到60%以上时，焊缝变浅，说明O元素增加焊缝熔深，而N元素则不能，但N元素却能促进O元素的吸收；内层气体的流量过小或过大时，会导致外层气体与熔池的耦合度过大或过小，从而使得熔深随着内层气流量的增加呈现先增大后减小的趋势。通过金相组织观察分析了N、O元素对GPCA-TIG焊缝显微组织的影响。试验结果显示，焊缝组织均由奥氏体和少量的铁素体组成，当外层气体中添加一定比例的N₂后，由于N元素是奥氏体形成元素且具有细化晶粒的作用，相比与外层气体为纯O₂时的焊缝，焊缝组织细化，但随着N₂所占比例的增加，焊缝组织有粗化的趋势。因为随着焊缝中N元素的增加，焊缝中铁素体含量下降，其阻碍一次奥氏体组织长大和细化二次奥氏体组织的作用都将减弱，从而导致焊缝奥氏体组织的粗化。与传统TIG焊后焊缝组织相比，外层气体为纯O₂时焊缝组织晶粒尺寸较小，组织明显细化。通过力学性能测试了GPCA-TIG焊焊缝的室温和-100℃时的冲击韧性以及室温下的抗拉强度，并采用扫描电镜分析了焊缝的拉伸断口形貌。试验结果表明，与母材相比，O元素的添加会使得焊缝的室温和-100℃时的冲击功下降，下降幅度分别为24.79%和24.92%，当往焊缝中引入N元素后，焊缝的冲击功有所上升，但仍然低于母材，当N₂占外层气体50%时，下降幅度分别为6.72%和12.14%。外层气体为纯O₂的抗拉强度为750MPa，与母材相比下降了3.2%，外层气体为O₂+50%N₂的抗拉强度为770MPa，其抗拉强度与母材相当，焊缝均为韧性断裂。另外检测了GPCA-TIG焊缝的腐蚀性能，结果显示焊缝没有出现晶间腐蚀裂纹，达到了国家标准GB/T4334-2008《不锈钢硫酸—硫酸铜腐蚀试验方法》的检测要求；焊缝按照JB4730.2-2005《承压设备无损检测：射线检测》的要求进行了RT（射线检测）100％检测，评片结果为Ⅰ级。与以往的活性TIG焊相比，GPCA-TIG焊接方法不需要涂敷活性剂的工序，不需要精密的气体配比器，焊接时直接通过外层气体引入活性元素O和N元素，显著增加焊缝熔深的同时，改善焊缝的力学性能。该焊接方法减少了热量输入和设备投入，操作更方便，焊接效率高，焊接质量良好，可实现全自动焊接。鉴于以上突出优点，GPCA-TIG焊具有广阔的应用前景。本文的研究将促进该方法的开发和应用，显著提高传统TIG焊的生产效率。更多还原

【Abstract】 Since the1990s, A-TIG welding as activeness representatives of welding technology, has been attracted widespread attention, which uses small amounts of flux on the surface of welding plates before welding progress. It can obtain excellent welding line and significantly improve the welding efficiency compared with TIG wedling. However, its practical application promotion was hampered, because the coating process would reduce the production efficiency and not easy to ensure the stability of the process through manual coating process.As active TIG welding method research shows, the main mechanism which the weld penetration can be significantly increased for the iron series of alloy such as carbon steel, stainless steel by adding O element, is that active elements can change the welding pool surface tension temperature coefficient. In order to give full play to the advantages of active welding method, this topic through changing the way of importing active element, puts forward a new activity welding method—Gas Pool Coupled Activating welding. The method contains two layers of gas, the inner layer gas is pure inert gas(Ar or He) which would protect the welding pool and tungsten electrode; and the outer layer gas is single pure active gas(O2or CO2) or including N elements of gas(N2),or oxygen and nitrogen gas mixture (O2+N2). Oxygen or nitrogen element which is ionized through the role of the arc couples with molten pool at the surrounding of low temperature area. The function of the oxygen element is changing the Marangoni convection to obtain deep and narrow weld depth, and the performance of the weld can be improved through nitrogen element for its features of high strength and excellent toughness. This method through changing coupling of degree between outer gas and molten pool, can trace control the introduced quantity of O and N elements, and thus achieve purpose for controlling the appearance of weld and improving the quality of weld seam.This paper is mainly for GPCA-TIG welding method of developing a special welding torch and welding property. This article adopts SUS304stainless steel for welding based metal, as to the inner argon protection gas, contrast the arc welding appearance, welding surface and cross-section morphology between using the GPCA-TIG welding method and the traditional TIG welding. The results revealed the arc contracts, the penetration is deep and narrow and the depth-to-width ratio reaches1.06, in this standard the8mm thick stainless steel plate can be weld fully at one time without making a groove. In addition, the GPCA-TIG welding method can avoid the oxidation of tungsten electrode in weld process.The effects of the coupling between outer gas and welding pool, the ratio of outer gas (N2+O2), the flow of inner protection gas, and other process parameters on weld depth were researched respectively. Test results show that along with the increase of the higher level of the outer nozzle which is the coupling of degree between with the outer gas and molten pool decrease, the depth of molten become shallow. When the high level is0mm rise, the depth of molten is the deepest. So this method can control the introduction of the content of O element, and then obtain different depth of the weld penetration. With N2ratio of outer gas (0-50%) increase, the weld penetration first slightly decreased and then rise. When the proportion of N2reached above60%, the weld depth of molten became shallow. That is to say, the weld depth of molten can be increased by O element rather than N element, but N element can promote the absorption of O element. The flow of lining gas is too small or too big, can lead to the coupling between the outer gas and weld pool is too large or too small, so along with the flow of inner gas increase, the weld depth first increase and then decreases.Through the microscope, the elements of N and O were analyzed on the influence of the microstructure about GPCA-TIG welding. The results showed, weld microstructure were austenite and a small amount of ferrite composition; when outer gas added to certain proportion of N2, the weld structure was finer than outer gas as pure O2, because N element is one of austenitic form elements and has the function of fine grains. However with the increase of the proportion of N2, the weld seam organization had become thick, because the content of the ferrite decreased along with the increasing N elements of weld, which block the first austenitic organization grow up and refined the second austenite the function of the organization will abate, leading to weld austenitic coarsening of the organization. Compared to the traditional TIG welding seam organization, the grain size of weld microstructure which adopted GPCA-TIG welding method with pure O2of outer gas was smaller, the organization was refined.And the impact toughness at the room temperature and-100℃and tensile properties of GPCA-TIG welding bead were proofed by mechanical properties test. The welding line tensile fracture morphology were analysised by the scanning electron microscopy (SEM). The results showed that, whether room temperature or-100℃the impact energy was lower rather than base metal when the weld line added O element, they declined to24.79%and24.92%respectively. But when the N element was introduced into the weld, the impact energy increased, and still less than the base metal. When the N2accounted50%for outer gas, it declined to6.72%and12.14%respectively. The tensile strength is750MPa with the outer gas is pure O2, compared with base metal it had fallen by3.2%. And the tensile strength is770MPa with the N2account50%in the outer gas, quite with base metal. Weld was ductile fracture.In addition, the corrosion performance of the GPCA-TIG welding joints were tested, the result shows all the welding joints did not appear intergranular corrosion weld crack, up to the detection requirements of the national standard GB/T4334-2008"the test method about stainless steel quid of sulfuric acid—copper sulfate ". And welds according to JB4730.2-2005"of the pressure equipment nondestructive testing:the X-ray testing requirements of the" the RT (X-ray testing)100%inspection, evaluation for I level of results.Contrasted to the previous active TIG welding, this method does not need to coat with the working procedure of surfactant and precision of gas ratio, active element oxygen and nitrogen element were directly introduced by the outer gas while welding. It can significantly increase the weld penetration and improve the mechanical properties of welding seam. And for a single arc welding, the heat input and equipment investment are reduced. The welding operation is more convenient. It also has the features of high welding efficiency, stable process, strong practice, at last it can realize the automatic production. In view of the above outstanding advantages, GPCA-TIG welding has wide application prospects. This study will promote the development and application of this method, which can improve the efficiency of the traditional TIG welding.更多还原