钎焊焊缝的枝晶间显微疏松导致的应力集中与微裂纹效应以及近焊缝区母材晶粒长大是导管早期疲劳开裂的主要原因。
The results show that the crack initiates at the outer surface of the weld comer and propagates into the steel base material with a high cycle fatigue mode.
结果表明：在焊缝区域内存在着局部未熔区以及铸造疏松组织和二次裂纹等缺陷，这是导致试样低应力断裂的根本原因。
The results show that the partial unmelted region, casting defect structure and secondary crack form in the welding seam, which result in the low stress breakage of the samples.
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