OCr13Ni5Mo马氏体不锈钢He/He+CO2双层气流保护TIG焊工艺研究

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	OCr13Ni5Mo马氏体不锈钢He/He+CO2双层气流保护TIG焊工艺研究
	秦名朋
学位类型	硕士
导师	陆善平
	2012
学位授予单位	中国科学院金属研究所
学位授予地点	北京
学位专业	材料工程
关键词	马氏体不锈钢 Tig焊氧含量表面张力对流焊缝形貌 Martensitic Stainless Steel Tig Welding Oxygen Content Surface Tension Convection Weld Shape
摘要	"0Cr13Ni5Mo马氏体不锈钢具有良好的强度、韧性、抗腐蚀性能和焊接性，广泛应用于水轮机转轮、阀体、泵壳、叶轮、电站压力管道、海洋石油和天然气平台以及石化工业上。传统TIG焊工艺焊缝质量好，是0Cr13Ni5Mo马氏体不锈钢最常用的焊接方法之一。然而，传统TIG焊工艺焊缝熔深浅、焊接效率低。为了解决这个问题，人们先后提出了A-TIG焊和混合气体保护TIG焊工艺。但A-TIG焊工艺对活性剂的涂覆量很敏感，焊缝表面容易堆集熔渣，而混合气体保护TIG焊工艺添加活性气体O2或CO2会产生电极氧化烧损的问题。本文以0Cr13Ni5Mo马氏体不锈钢为母材，系统开展了内层为He，外层为He+CO2的He/He+CO2双层气流保护TIG焊工艺研究。该工艺将传统TIG焊焊枪由单层结构改造为双层结构，焊枪内层通纯惰性气体避免电极与外层活性气体直接接触而氧化烧损，焊枪外层添加活性气体向熔池溶解活性元素氧提高焊缝熔深和焊接效率。本文主要研究内容和结论如下： 1. 研究了He/He+CO2双层气流保护TIG焊工艺可行性，分析了CO2增加焊缝熔深的机制。结果表明，双层气流保护TIG焊工艺有效解决了混合气体保护TIG焊工艺电极氧化烧损和传统TIG焊工艺焊缝熔深浅、焊缝效率低的问题。熔池表面张力对流模式的改变是焊缝形貌演变的主要机制。氧是液态铁基合金表面活性元素，在外层保护气中添加CO2可以有效调节熔池氧含量。当熔池氧含量较低时，表面张力温度系数?σ/?T＜0，表面张力引导的对流方向是从熔池中心到熔池周边，有利于熔池阳极斑点热从熔池中心向熔池周边传递，降低焊缝熔深和焊缝深宽比；当熔池氧含量较高时，表面张力温度系数?σ/?T＞0，表面张力引导的对流方向是从熔池周边到熔池中心，有利于熔池阳极斑点热从熔池中心向熔池底部传递，提高焊缝熔深和焊缝深宽比。 2. 研究了焊接工艺参数对焊接电弧、焊缝氧含量和焊缝形貌的影响，确定了熔池表面张力对流由外对流改变为内对流时的临界氧含量。结果表明，改变焊接工艺参数可以有效调节熔池氧含量，进而控制熔池表面张力对流和焊缝形貌；选择合适的焊接工艺参数可以使单道焊焊缝熔深达6～12mm，焊缝深宽比达0.6～1.0，焊接效率为传统TIG焊工艺的2～4倍；熔池表面张力对流由外对流改变为内对流时的临界氧含量在80～120ppm范围。 3. 研究了0Cr13Ni5Mo马氏体不锈钢焊接接头在回火前后的组织和性能。结果表明，焊后焊缝组织为马氏体+少量δ铁素体，不同形态的δ铁素体分布在原奥氏体晶界。焊后在590℃回火可改善焊缝的冲击性能。双层气流保护TIG焊工艺在获得高效率焊接的同时可以获得比MAG焊工艺更好的焊缝冲击性能。双层气流保护TIG焊焊缝碳含量和氧含量都较低，焊缝缺陷少，焊缝冲击功高；MAG焊不仅焊缝碳含量和氧含量都较高，而且焊缝中有较多的夹渣和气孔缺陷，焊缝冲击功低。"
其他摘要	"Because of its superior performance in strength, toughness, corrosion resistance and weldability, 0Cr13Ni5Mo martensitic stainless steel is widely used for hydraulic turbine runners, valve bodies, pump bowls, impellers, high-pressure pipes in power generation, offshore oil and gas, and petrochemical industries. Exhibiting good welds quality, traditional TIG welding process is taken as one of most frequently used welding processes for 0Cr13Ni5Mo martensitic stainless steel. However, the weld depth of traditional TIG welding is low, making welding efficiency also low. In order to overcome this disadvantage, A-TIG and mixed gases TIG welding processes are proposed successively. However, the weld shape of A-TIG welding is sensitive to quantity of activating flux, and slag is easily retained on the weld surface. The limitation of mixed gases TIG welding, if active gas O2 or CO2 is added, lies in electrode oxidation. Using He as inner layer shielding gas and He+CO2 as outer layer shielding gas, He/He+CO2 double shielded TIG welding process was taken to perform on 0Cr13Ni5Mo martensitic stainless steel in this paper. This new TIG welding process changes the traditional welding torch from single layer to double layers. The pure inert gas in inner layer avoids the electrode directly contacting the active gas in outer layer, and being oxidized. Addition of active gas to outer layer provides a surface active element, oxygen, which dissolves in the weld pool to increase weld depth and welding efficiency The main research work and results of this paper are as follows: 1. The feasibility of He/He+CO2 double shielded TIG welding process is studied, and mechanisms of CO2 increasing weld depth are discussed. The results show that this new TIG welding process can successfully solve the problem of electrode oxidation under mixed gases TIG welding, and the problem of low weld depth and welding efficiency under traditional TIG welding. The change of surface tension convection mode is the main mechanism in affecting weld shape. Oxygen is one of liquid ferrous-based alloy surface active elements, the quantity of which in the weld pool can be effectively adjusted by addition of CO2 to outer layer shielding gas. When oxygen content in the weld pool is low, temperature coefficient of surface tension ?σ/?T is negative, and surface tension induces outward convection from the center to edge of weld pool, leading to heat flux easily transferred to the edge of weld pool to form low weld depth and weld depth/width ratio. When oxygen content in the weld pool is high, temperature coefficient of surface tension ?σ/?T is positive, and surface tension induces inward convection from the edge to center of weld pool, leading to heat flux easily transferred to the bottom of weld pool to form high weld depth and weld depth/width ratio. 2. The effects of welding parameters on arc, weld oxygen content, and weld shape are investigated, and the critical oxygen content is proposed when surface tension convection changs from outward to inward. The results indicate that adjusting welding parameters can effectively control weld oxygen content, further controlling surface tension convection and weld shape. With suitable welding parameters, the weld depth in a single pass and weld depth/width ratio can arrive at 6～12mm and 0.6～1.0 respectively. Double shielded TIG welding is 2～4 times welding efficiency of traditional TIG welding. The critical oxygen content of surface tension convection changing from outward to inward is in the range of 80～120ppm. 3. The microstructure and mechanical properties of welded joints of 0Cr13Ni5Mo martensitic stainless steel are analyzed before and after tempering. The results suggest that the microstructure of the weld metal is composed of martensite and little δ ferrite, and different shapes of δ ferrite distribute in original austenite grain boundaries. The impact property of weld tempered at 590℃ is improved. Double shielded TIG welding can not only obtain high welding efficiency, but also gain better weld impact property than that of MAG welding. Under double shielded TIG welding, both the weld carbon and oxygen content are low, and weld defects is little, which leads to high weld impact energy. On the contrary, under double shielded TIG welding, both weld the carbon and oxygen content are high, and weld defects, such as slag and void, are serious, which leads to low weld impact energy."
文献类型	学位论文
条目标识符	http://ir.imr.ac.cn/handle/321006/64550
专题	中国科学院金属研究所
推荐引用方式 GB/T 7714	秦名朋. OCr13Ni5Mo马氏体不锈钢He/He+CO2双层气流保护TIG焊工艺研究[D]. 北京. 中国科学院金属研究所,2012.