Based on the experiments of laser welded ultra-high strength steel with thickness of 1.8 mm,the effects of the welding speed on microstructure and microhardness of the weld seam were studied.The results showed that microstructures of the weld seam are the lathy martensites.The picric acid solution was used to display the boundary of the prior austenite grain,and the grain exhibits the columnar crystals.With the increase of the welding speed,the grain sizes of the prior austenite decrease and the fine cellular dendrites in the center of the weld seam change into the equiaxed grains.The microhardness of the weld seam increases with the welding speed.%研究了厚度为1.8mm的超高强度钢板的激光焊接性能,分析了焊接速度对焊缝微观组织和显微硬度的影响。试验结果表明,超高强度钢焊缝组织为板条马氏体。采用苦味酸溶液显示原奥氏体晶界,发现原奥氏体呈现柱状晶的晶体形态。随着焊接速度的增加,原奥氏体晶粒尺寸变小,焊缝中心由细小的胞状树枝晶变为等轴晶。焊缝硬度随着焊接速度的增加而增大。
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