论文总字数：24026字

摘 要

近些年来，奥氏体不锈钢在工业及生活中的应用越来越广泛，而提高奥氏体不锈钢的焊接效率则成为客观需求。活性焊接方法是一种能够增大焊接熔深，改善焊缝成形，提高焊接生产效率的的焊接技术。早期主要应用在活性剂TIG焊中，经过发展A-TIG焊已经成熟，在碳钢、不锈钢、钛合金等材料的焊接中有成功的应用。目前对活性焊增加熔深机理的主要观点为“电弧收缩”和“表面张力温度梯度改变”理论，它们分别从活性元素影响焊接电弧行为和焊接熔池内部流动对焊接熔深增加进行解释。

A-TIG焊需要在焊前手工涂敷活性剂，不利于焊接自动化，而且焊剂涂敷量不易均匀，会造成焊接参数的波动。为了解决这一问题，陆善平等人开发了双层气流保护TIG焊工艺。内层的高纯度惰性气体He/Ar可以避免电极与外层的活性气体O₂/CO₂直接接触，焊接过程中参数稳定性大大提高。而外层加入的O₂/CO₂可以提供表现活性元素氧，溶解于焊接熔池中，增加焊缝熔深并提高焊接效率。

新型活性等离子弧焊以双层气流保护TIG焊为基础，加入等离子体，既增强了电弧的穿透力，提高了焊缝的深宽比，也保护钨极不受活性气体氧化，提高了焊接过程的稳定性，便于焊接的高效化、自动化。本课题使用新型活性等离子弧焊焊机，研究等离子的使用对焊缝形状及焊接效率的影响。在使用等离子的情况下，改变保护气体中氧气的含量，研究氧气含量对焊缝形状的影响。试验结果表明，新型活性等离子弧焊可以显著提高焊接效率，并且可以改善焊缝成形，是一种非常具有开发和应用价值的焊接技术。

关键词：双层气流保护TIG焊；等离子体；氧气添加量；焊缝形状；焊接效率

ABSTRACT

In recent years, the application of austenitic stainless steel in industry and society has become more and more popular, and highly efficient welding of austenitic stainless steel is required. The active welding method is one kind of welding technology which can increase the welding penetration, improve the welding formation the welding efficiency. The active agent was first investigated in TIG welding, and now the development of A-TIG welding has been mature.it is successful employed in the welding of carbon steel, stainless steel, titanium alloy and other kinds of materials. The main viewpoints of the mechanism of deep penetration include the arc contraction theory and the marangoni convection change theory, which explaining that the reactive elements affect the welding arc behavior and change internal flow direction of the welding pool respectively.

Before the A-TIG welding, a layer of active flux must be smeared on the surface of the workpiece manually, which is not conducive to automatic welding. When the amount of active flux is not evenly distributed, the fusion zone profile could become worse. To overcome this problem, Lu shanping proposed a double-shielded TIG wielding process. He/Ar is used as inner shielding gas, which can protect the electrode from the oxidation, so the stability of parameters in welding process is greatly improved. O₂/CO₂ in outer shielding gas can provide active elements to the welding pool, so bead penetration can be increased.

Active plasma arc welding process is designed based on double-shielded TIG welding process. With the plasma, it has more concentrated heat input and can achieve a deeper bead penetration than double-shielded TIG welding process. This new process also has advantages of prohibiting the tungsten electrode from the oxidation of active gas and improving the stability of welding process. In this paper, a new type of active plasma arc welding machine is used to study the effect of the use of plasma on the weld shape and welding efficiency. In the case of using plasma, how the oxygen content in the outer shielding gas would influence the weld shape is also studied. The experimental results show that the new active plasma arc welding can significantly improve the welding efficiency the welding formation. Sincerely, it is a kind of welding technology with great advantages and application value.

Key words: double-shielded TIG welding; plasma; oxygen addition; weld shape; welding efficiency

目 录

摘 要 I

ABSTRACT II

第一章 绪论 1

1.1 奥氏体不锈钢简介及分类 1

1.1.1 简介 1

1.1.2 分类及牌号 1

1.2 奥氏体不锈钢的焊接性 4

1.2.1 奥氏体不锈钢焊接接头的耐蚀性 4

1.2.2 σ相脆化 8

1.2.3 低温脆化 9

1.2.4 焊接变形 10

1.3 等离子弧焊发展背景 11

1.4 活性物质熔深增加机理的研究 12

1.4.1 “阳极斑点收缩”理论 13

1.4.2 “电弧收缩”理论 13

1.4.3 “表面张力温度梯度改变”理论 14

1.5 本课题研究的目的及内容 15

第二章 活性焊接方法 17

2.1 A-TIG焊 17

2.1.1 活性剂TIG焊 17

2.1.2 混合气体TIG焊 17

2.2 AA-TIG焊 18

2.2.1 电弧辅助AA-TIG焊 18

2.2.2 双层气流保护AA-TIG焊 19

2.3 新型等离子弧焊 20

第三章 等离子体对焊接效率的影响 22

3.1 实验方法 22

3.2 实验结果 22

3.3 本章小结 25

第四章 氧气添加量对焊接效率的影响 26

4.1 实验方法 26

4.2 实验结果 26

4.2.1 保护气体为Ar 26

4.2.2 保护气体为He 28

4.3 本章小结 30

第五章 总结 32

参考文献 33

致 谢 36

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