Study on sensitization characteristics of TP347H stainless steel welded joints
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摘要:
为明确TP347H不锈钢焊接接头敏化特性，对焊接接头进行不同条件的敏化处理. 结果表明，焊接接头热影响区敏化倾向严重，敏化过程中由于Nb原子在晶界上的结合能高于Cr原子，会先形成了粗大的初级铌碳化合物，后形成细小的二次铌碳化合物. 在700 ℃下保温时，焊接接头热影响区的敏化度呈现先提高后降低的趋势，当温度达到800 ℃及以上时，热处理不再提高接头热影响区的敏化度. 与实际生产线上服役21 000 h的F347H接头热影响区敏化特性对比，证实TP347H焊接接头650 ℃保温100 h即可达到敏化极限，其原因是Nb元素含量为C元素的数倍，大部分C元素与Nb元素结合形成NbC，而晶粒中扩散的C元素已与Cr元素充分结合，造成的敏化程度达到平衡状态.
Abstract:In order to clarify the sensitization characteristics of TP347H stainless steel welded joints, the welded joints were heat treated at different temperatures, and the changes of sensitization degrees at different temperatures were studied. The results showed that an obvious sensitization trend was observed in the heat-affected zone(HAZ) of welded joints. During the sensitization process, because the binding energy of Nb atoms on the grain boundary is higher than that of Cr atoms, coarse primary niobium carbon compounds are formed first, and then fine secondary niobium carbon compounds are formed.When the temperature is kept at 700 ℃, the sensitization degree of the HAZ of the welded joint shows a trend of first increasing and then decreasing. When the temperature reaches 800 ℃ and above, heat treatment no longer increases the sensitization degree of the HAZ of the joint. Comparing with the sensitization characteristics of F347H joints with 21000 h in the actual production line, it is confirmed that the sensitization limit can be reached by holding the welded joints of TP347H at 650 ℃ for 100 h. The reason is that the content of Nb is several times that of C, most of C combines with Nb to form NbC, and the diffusion of C in the grain has been fully combined with Cr. The resulting sensitization reaches an equilibrium state.
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Keywords:
- TP347H stainless steel /
- sensitization /
- welded joint /
- heat treatment /
- corrosion resistance
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图 1 不锈钢管及接头
Figure 1. Stainless steel pipe and welded joint. (a) stainless steel pipe; (b) the metallography of the welded joint
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图 3 不同温度试样腐蚀沟统计归一化数据
Figure 3. Statistical normalized data of the corrosion ditch of the sample at each temperature
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图 4 550 ℃热处理不同保温时间试样热影响区腐蚀形貌
Figure 4. Corrosion morphology of samples at different holding times under 550 ℃ heat treatment. (a) 10 h; (b) 20 h; (c) 50 h; (d) 100 h
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图 5 600 ℃热处理下不同保温时间试样的热影响区腐蚀形貌
Figure 5. Corrosion morphology of samples at different holding times under 600 ℃ heat treatment. (a) 1 h; (b) 4 h; (c) 10 h; (d) 20 h; (e) 50 h; (f) 100 h
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图 6 650 ℃热处理下不同保温时间试样的热影响区腐蚀形貌
Figure 6. Corrosion morphology of samples at different holding times under 650 ℃ heat treatment ℃. (a) 1 h; (b) 4 h; (c) 10 h; (d) 20 h; (e) 50 h; (f) 100 h
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图 7 700 ℃热处理下不同保温时间试样的热影响区腐蚀形貌
Figure 7. Corrosion morphology of samples at different holding times under 700 ℃ heat treatment. (a) 1 h; (b) 4 h; (c) 10 h; (d) 20 h; (e) 50 h; (f) 100 h
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图 8 800 ℃热处理下不同保温时间试样的热影响区腐蚀形貌
Figure 8. Corrosion morphology of samples at different holding times under 800 ℃ heat treatment. (a) 10 h; (b) 20 h; (c) 50 h; (d) 100 h
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图 9 900 ℃和620 ℃热处理试样
Figure 9. Samples at 900 ℃ and 620 ℃ heat treatment. (a) heat treatment at 900 ℃ for 1 h; (b) heat treatment at 900 ℃ for 2 h; (c) heat treatment at 900 ℃ for 5 h; (d) heat treatment at 620 ℃ for 21 000 h
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图 11 TEM选区电子衍射分析
Figure 11. TEM selected area electron diffraction analysis. (a) SAED position ; (b) position b; (c) position c; (d) position d; (e) diffraction patterns corresponding to b; (f) diffraction patterns corresponding to c
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图 12 晶界附近元素分布
Figure 12. Elements distribution around grain boundary. (a) position a; (b) position b; (c) position c
表 1 TP347H不锈钢钢管化学成分(质量分数，%)
Table 1 Chemical composition of TP347H stainless steel pipe
C Si Mn P S Cr Ni Nb Fe 0.061 0.613 1.01 0.018 0.008 17.26 10.13 0.7 余量 
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表 2 焊接工艺及参数
Table 2 Welding method and process parameters
焊道 焊接方法 焊接电流
I/A电弧电压
U/V焊接速度
v/(cm·min−1)1 ~ 2 GTAW 100 ~ 140 8 ~ 14 3 ~ 10 3 ~ 17 SMAW 120 ~ 160 20 ~ 30 4 ~ 12
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表 3 TP347H不锈钢焊接接头热处理工艺
Table 3 Heat treatment process of TP347H stainless steel welded joints
热处理分组 温度T/℃ 保温时间t/h A 550 10 20 50 100 — — — — — B 600 0.5 1 2 4 10 20 50 70 100 C 650 0.5 1 2 4 10 20 50 70 100 D 700 0.5 1 2 4 10 20 50 100 — E 800 10 20 50 100 — — — — — F 900 1 2 5 — — — — — —
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