Microstructure analysis of additive manufacturing produced RAFM steel laser welding joint
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摘要: 局部工件采用增材制造技术成型再焊接完成装配是未来精密加工较为可行的方案之一. 采用激光焊对4种不同粒径粉末增材制造得到的低活化铁素体/马氏体钢板（reduced activation ferritic/martensitic steel，RAFM钢）进行焊接，分析激光焊接头显微组织演变特征.结果表明，粉末粒径小于25 µm的增材RAFM钢的道间未熔合缺陷在焊缝区得到修复，而热影响区与母材未熔合缺陷无法改善；粉末粒径为15 ~ 53，45 ~ 105 µm以及大于100 µm的增材RAFM钢的气孔缺陷在焊接过程中无法消除，焊缝区与母材皆有分布，后者的气孔数量和大小明显大于前两者；4种接头焊缝区微观组织皆为粗大的板条状马氏体，柱状晶生长至中心线相交，无等轴晶出现. 由增材制造工艺特点导致热影响区与母材区出现偏析带.近焊缝淬火区峰值温度较高，为细小的马氏体组织；远焊缝回火区产生二次回火的珠光体组织，且伴随部分晶粒长大.Abstract: It’s one of the more feasible solutions for precision machining in the future that a mount of the workpieces produced by the additive manufacturing technology are connected by welding. Reduced activation ferrite/martensitic (RAFM) steel plates produced with four different particle sizes powder (0 ~ 25, 15 ~ 53, 45 ~ 105, > 100 μm) additive manufacturing are connected by laser welding technology. The microscopic microstructure evolution characteristics of laser welding joints were characterized. The results show that the unfused defects of additive manufacturing RAFM steel with powder particle size less than 25 μm are repaired in the weld area, while the unfused defects of the heat-affected zone and the base metal area cannot be improved. The defects in the welding of other steel plates are mainly pores, which are both distributed in the weld area and the base material area. And the number of steel welding pores with powder particle size exceeds 100 μm is much greater than other two welds. The microscopic structure of the weld area of the four joints is a coarse slatted martensite, and the columnar crystals grow from the edge of the pool to intersect the centerline. The characteristics of the additive manufacturing process lead to precipitation zone in heat affected area and base metal zone. The peak temperature of the quenched zone near the weld is higher, which is fine martensite structure. The tempering area far away from the weld is composed of secondary tempered pearlite structure, and therein grains partially get coarsened.
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Keywords:
- laser additive manufacturing /
- RAFM steel /
- laser welding /
- lack of fusion
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图 2 不同粒径粉末增材制造RAFM钢激光焊后表面形貌
Figure 2. Surface morphology of RAFM steel with different particle size powder by additive manufacturing after laser welding. (a) c1 weld upper surface; (b) c1 weld bottom surface; (c) c2 weld upper surface; (d) c2 weld bottom surface; (e) c3 weld upper surface; (f) c3 weld bottom surface; (g) c4 weld upper surface; (h) c4 weld bottom surface
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图 3 不同粒径粉末增材 + 热处理RAFM钢母材
Figure 3. Base metal of RAFM steel with different particle size powder by additive manufacturing + heat treatment. (a) b1 base metal; (b) b2 base metal; (c) b3 base metal: (d) b4 base metal
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图 4 不同粒径粉末增材 + 热处理RAFM钢的激光焊接头
Figure 4. Laser welding joints of RAFM steel with different particle size powder by additive manufacturing + heat treatment. (a) c1 joint; (b) c2 joint; (c) c3 joint; (d) c4 joint
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图 6 c3接头的微观组织
Figure 6. Microstructure of c3 joint. (a) weld center zone; (b) quenching zone; (c) tempering zone; (d) base metal
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图 7 c3接头不同区域的SEM图
Figure 7. SEM images of different regions in c3 joint. (a) weld zone; (b) quenching zone; (c) tempering zone; (d) base metal
表 1 RAFM钢化学成分(质量分数，%)
Table 1 Chemical compositions of RAFM steel
材料 C Cr Ta V W Si Mn Fe RAFM粉末 0.092 8.9 0.14 0.20 1.5 0.05 0.49 余量 增材RAFM钢 3.3 8.9 — 0.3 1.3 — — 余量 
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表 2 激光焊工艺参数
Table 2 Parameters of laser welding
激光功率
P/kW焊接速度
v/(m·min−1)离焦量
f/mm气体流量
Q/(L·min−1)6.1 1.3 + 10 1.5
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