Effects of introductions of oxygen and nitrogen elements on impact toughness of gas pool coupled activating TIG weld metal
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摘要: 通过外层气体引入O和N元素，气体熔池耦合活性TIG焊(gas pool coupled activating TIG welding)可以实现深熔深、高质量和连续焊接. 为了研究清楚O和N元素引入对焊缝冲击韧性的影响规律和机理，针对SUS304不锈钢分别测试了外层气体为O2，N2和O2 + N2时的焊缝低温冲击韧性，并从焊缝组织成分、析出物种类及形态以及晶粒取向等方面分析了其影响机理. 结果表明，外层气体引入对GPCA-TIG焊焊缝低温冲击韧性影响较大，单独引入O2时将明显降低，单独引入N2时降低较少，而同时引入O2和N2将增加焊缝金属低温冲击韧性. O和N元素同时引入增强GPCA-TIG焊缝金属低温冲击韧性的机理主要在于：焊缝组织较细，金属中的O和N元素含量和所形成的非金属夹杂物的增加程度和铁素体数量的下降程度都较少，却增加了奥氏体晶粒大角度晶界数量以及铁素体晶粒与奥氏体晶粒之间位向关系的匹配性，从而使得裂纹不易扩展，韧性增强.
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关键词:
- 不锈钢 /
- O元素 /
- N元素 /
- 气体熔池耦合活性TIG焊 /
- 冲击韧性
Abstract: Through introducing oxygen and nitrogen elements from the outer gas of gas pool coupled activating TIG(GPCA-TIG) welding, deep penetration, high quantity and continuous welding are accessible. In order to obtain the dependence and mechanism of weld metal impact toughness on the introduced oxygen and nitrogen elements, GPCA-TIG welding for stainless steel SUS304 with the outer gases oxygen, nitrogen and nitrogen-oxygen gas mixture respectively were performed to gauge low temperature impact toughness of the weld metal. Then, a series of testing experiments including weld microstructure and chemical composition, nonmetallic inclusion and grain orientation were conducted. The results reveal that, the introduction of oxygen makes the low temperature impact toughness of weld metal decease obviously, nitrogen decease a little, while the low temperature impact toughness of weld metal can be increased a little conversely when oxygen and nitrogen are synchronously introduced. The main mechanism is proven that the synchronous introduction of oxygen and nitrogen elements leads to fine grain of weld microstructure, less increases of the contents of oxygen and nitrogen elements and the nonmetallic inclusions, much decrease of ferrite number in weld metal. Meanwhile, the high angle grain boundary number in austenite crystal and the matching property of grain orientations between ferrite and austenite are improved. All of these result in difficult cracking propagation and higher toughness. -
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图 2 TIG焊和GPCA-TIG焊焊缝微观组织
Figure 2. Weld microstructures of TIG welding and GPCA-TIG welding. (a) TIG welding; (b) GPCA-TIG welding (O2); (c) GPCA-TIG welding (N2); (d) GPCA-TIG welding (O2 + N2)
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图 3 焊缝金属中的非金属夹杂物
Figure 3. Nonmetallic inclusions in the weld metal. (a) granular carbide; (b) network carbide; (c) blocky carbide; (d) lath carbide; (e) granular oxide; (f) blocky nitride
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图 4 TIG焊和GPCA-TIG焊焊缝金属fcc晶粒取向差
Figure 4. FCC grain misorientation angles in weld metal of TIG welding and GPCA-TIG welding. (a) TIG welding; (b) GPCA-TIG welding (O2); (c) GPCA-TIG welding (N2); (d) GPCA-TIG welding (O2 + N2)
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图 5 TIG焊和GPCA-TIG焊的焊缝晶粒ODF图
Figure 5. Orientation distribution functions of TIG weld metal and GPCA-TIG weld metal grains. (a) TIG welding; (b) GPCA-TIG welding (O2); (c) GPCA-TIG welding (N2); (d) GPCA-TIG welding (O2 + N2)
表 1 外层气体和耦合度对焊缝金属−40 ℃低温冲击吸收能量的影响
Table 1 Effects of outer gas and coupling degree on low temperature impact toughness of the weld metal at −40 ℃
金属 耦合度h 外层气体 冲击吸收能量 Akv/J TIG焊焊缝 — — 36.67 GPCA-TIG焊焊缝 + 2 O2 31.33 N2 34.33 N2 + O2 40.00 
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表 2 焊缝组织晶粒度
Table 2 Grain size grades of weld metals
TIG焊 GPCA-TIG焊
(O2)GPCA-TIG焊
(N2)GPCA-TIG焊
(O2 + N2)6.715 7.030 7.273 7.314
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表 3 外层气体对焊缝中主要元素含量的影响(质量分数，%)
Table 3 Effects of outer gas on the main element contents in the weld metal
焊接方法 Fe Cr Ni N O TIG焊 69.3 17.8 7.5 0.039 0.001 7 GPCA-TIG焊(O2) 73.1 16.8 6.95 0.057 0.010 0 GPCA-TIG焊(N2) 70.5 17.2 7.2 0.072 0.004 5 GPCA-TIG焊(O2 + N2) 70.0 17.1 7.2 0.056 0.005 8
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表 4 外层气体对焊缝铁素体数(FN)的影响
Table 4 Effect of outer gas on the ferrite number (FN) in the weld metal
TIG焊 GPCA-TIG焊
(O2)GPCA-TIG焊
(N2)GPCA-TIG焊
(O2 + N2)6.85 6.48 6.05 6.73
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表 5 外层气体对fcc晶界角分布的影响
Table 5 Effect of outer gas on distribution of fcc grain boundary angle θ
晶界角 TIG焊 GPCA-TIG焊 (O2) GPCA-TIG焊 (N2) GPCA-TIG焊 (O2 + N2) ＞15° 81% 73% 74% 83% ＜15° 19% 27% 26% 17%
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