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.

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搅拌区细晶组织的显微硬度及抗拉强度相比于铸态母材有所提高，而伸长率显著提高。

The microhardness and tensile strength of stir zone increase compared with the base material, and the elongation increases significantly due to its fine and uniform microstructure of the specimen.

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