Speaker
Description
Ultra high strength steel (UHSS) significantly contribute to lightweight design. However, it is essential that the excellent mechanical properties are maintained after the applied welding process in terms of structural safety such as strength and ductility. This study investigates the microstructural and mechanical properties of MAG welded X-joints of 20mm thick S1100 thermomechanically rolled plates with undermatched 960L-MC filler metal. The welding was carried out fully automated in order to obtain uniform properties of the welds for different heat inputs in PA and PF positions. The mechanical properties of weldments were characterized by a hardness, impact and tensile tests, as well as optical and scanning electron microscopy. Due to different heat inputs and different welding positions, prior austenite grain sizes and orientations have been formed in the weld metal microstructure which are presented and discussed in detail. The microstructures of the fusion zone (FZ) consist of ferrite, while the heat affected zone (HAZ), which was exposed to several thermal cycles, is dominated by bainite and martensite/austenite (M/A) constituents. While in the HAZ at the top layer show untempered martensite of a high hardness, the HAZ of filler and root passes was tempered and gave lower hardness values. Transverse tensile test results did not fulfill base materials strength requirements, thereby all fractures occurred in the weld metal. Although the weld metal microstructure consisted of acicular ferritein PA and PF position, PF weld has lower toughness than PA because of having smaller PAGs.
Keywords: welding position, metal active gas, ultra high strength steel, microstructure, hardness
| Speaker Country | Turkey |
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