Analysis of microstructural changes in fiber laser welded galvanized DP980 and HSLA steels
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Date
2014-09-02
Authors
Zhang, Jianqi
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Abstract
The rapid thermal cycle involved in fiber laser welding (FLW) generates welds with narrow heat affected zones (HAZs) that contain large microstructural gradients, which make it very difficult to properly elucidate microstructural changes that occur during welding in the HAZ and fusion zone (FZ). Evaluation of the microstructural changes is, nonetheless, vital in order to understand and predict how FLW affects the mechanical properties of welded materials. Dual phase (DP) steels, which are designed to obtain soft ferrite and hard martensite, have gained increasing popularity in structural applications. In this research, the microstructural changes that occur in narrow HAZ and FZ are systematically studied by using a Gleeble thermo-mechanical simulation system and transmission electron microscopy (TEM). It is found that significant microstructural changes occur in the FZ and HAZ, which could result in dramatic changes in the mechanical properties of welded materials. An indication of this is the observation that the microhardness values in the FZ and adjacent HAZ are notably disparate from that in the base metal (BM). Further, cracks were observed in the zinc coating on the HAZs of both HSLA and DP980 steels, which may also have effect on mechanical performance of the welded materials.
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Keywords
microstructure, steel