Investigation on microstructure and properties of U71Mn steel joints by Flash-Friction hybrid welding
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摘要:
闪光对焊在焊接钢轨时易在焊缝中心产生氧化夹杂缺陷以及软化层，严重降低了接头力学性能，针对上述问题，开发了闪光-摩擦复合焊， 并基于不同的顶锻距离对U71Mn钢进行了焊接工艺研究.结果表明，焊接接头成形良好，接头组织主要分为母材(base material， BM)、热影响区(heat-affected zone， HAZ)、热力影响区(thermo-mechanically affected zone， TMAZ)以及焊核区(weld zone， WZ)，其中，在焊接热输入以及摩擦顶锻的作用下，TMAZ及WZ晶粒发生细化，同时，在线性摩擦的作用下，WZ未出现明显的高铁素体含量的软化层组织.接头显微硬度呈M形分布，最高硬度位于TMAZ，接头抗拉强度随顶锻距离的增加呈先上升后下降趋势，最高抗拉强度约为900.3 MPa，达到母材的89.1%，其断裂形式为准解理断裂.
Abstract:Flash butt welding, when applied to rail welding, is prone to the formation of oxidized inclusion defects and softening layers at the weld, significantly impairing the mechanical properties of the joints. To address these issues, this study proposed a novel flash-friction hybrid welding(F-FHW) method and explored the welding process for U71Mn steel based on varying upsetting distances. The results revealed that the welded joint was well formed and the joint structure was mainly divided into base material (BM), thermo-mechanically affected zone (TMAZ), heat-affected zone (HAZ) and weld zone (WZ). Notably, the grains in the TMAZ and WZ were refined under the combined influence of welding heat input and friction upsetting. Additionally, under the action of linear friction, the softening layer with elevated ferrite did not appear in the WZ. The microhardness of the joints displayed an M-shaped distribution, with the highest hardness located at TMAZ. The tensile strength of the joint initially increased and then decreased as the upsetting distance extended. The maximum tensile strength of the joints was approximately 900.3 MPa, achieving 89.1% of the BM, and its fracture form is quasi-cleavage fracture.
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Keywords:
- flash-friction hybrid welding /
- U71Mn steel /
- microstructures /
- mechanical property
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图 2 不同顶锻距离F-FHW的焊缝成形
Figure 2. Weld formation in F-FHW with different upset distances. (a) 3 mm; (b) 6 mm; (c) 9 mm
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图 3 不同顶锻距离接头宏观形貌(mm)
Figure 3. Macroscopic-morphology of joints with different upset distances. (a) 3 mm; (b) 6 mm; (c) 9 mm
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图 4 顶锻距离为6 mm接头不同区域微观组织形貌
Figure 4. Microstructural morphology of joints in different regions with an upset distance of 6 mm. (a) BM; (b) HAZ; (c) TMAZ; (d) WZ
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图 5 SEM形貌及EDS结果
Figure 5. SEM morphology and EDS results. (a) SEM morphology and measurement location; (b) EDS line scan results
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图 6 接头不同区域晶粒形态
Figure 6. Grain morphologies of the F-FHW joints in rarious zones. (a) BM; (b) TMAZ; (c) WZ
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图 7 接头不同区域晶粒尺寸分布
Figure 7. Grain size distribution in different areas of the F-FHW joint. (a) BM; (b) TMAZ; (c) WZ
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图 8 振动速度为5 mm/s，顶锻时间为25 s，不同顶锻距离下的接头显微硬度分布
Figure 8. Microhardness distribution of the joint at different upsetting distances (vibration speed 5 mm/s, upsetting time 25 s)
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图 9 振动速度为5 mm/s，顶锻时间为25 s，不同顶锻距离下的接头抗拉强度及断后伸长率
Figure 9. Tensile strength of the joint at different upsetting distances (vibration speed 5 mm/s, upsetting time 25 s)
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图 10 接头断裂位置及不同顶锻量的断口形貌
Figure 10. Fracture location and morphology of F-FHW joints. (a) Joint fracture location; (b) Upset distance of 3 mm; (c) Upset distance of 6 mm; (d) Upset distance of 9 mm
表 1 U71Mn化学成分(质量分数，%)
Table 1 Chemical compositions of U71Mn
C Si Mn S P V Fe 0.65 0.25 1.2 0.03 0.03 0.03 余量 
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表 2 EDS点扫描区域元素比例(%)
Table 2 EDS point scanning area element ratio
元素 C Si O Mn Fe A 3.76 0.65 2.8 0.66 92.13 B 3.94 0.82 1.49 0.99 92.76 C 3.09 0.67 2.64 0.80 92.79 D 2.99 0.65 0.96 0.75 94.65
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