Papers by Author: Li Jun Xin

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Authors: Ya Jie Li, Li Jun Xin, Zhi Yong Wang
Abstract: MS1470 steel is mainly used in the automotive industry, which has high strength, light weight and low cost. However, there always appear grains coarsening, brittle increasing, lower intensity and other issues. To solve this problem, we have analyzed the welding process, the fracture morphology and microstructure etc. The results shown that the microstructure were mainly ferrites and lath martensites. However, grains coarsening in the HAZ were serious, and fracture failure also occurred in the heat affected zone. Meanwhile, MS1470 steel had formed a small amount of pores during rolling process, which also is an important reason for cracks formation.
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Authors: Li Jun Xin, Tao Huang, Zhi Yong Wang
Abstract: In order to implement continuous roll of steel plates, steel plates need to be jointed simply and reliably. CQ steel plates have advantages such as low impurity, composition uniformity, excellent surface quality and good mechanical properties. However, there always has fracture failure of the online welded joint for continuous cool-roll CQ plates. For solving this question, theoretical calculation of weldability, fracture morphology and metallurgical structure were analyzed. The results show that CQ steel plates have good weldability according to the chemical composition, and the microstructure of welding seam are mainly ferrite and a small amount of lath martensite.While grain growth in HAZ is serious, with average grain size 15μm. A lot of impurities and gas cavities in welding seam are the main source of cracks. In addition, stress concentration caused by coarse grain zone in HAZ is one of the reasons for causing cracks. The microhardness was test and the results show that the hardness decrease from weld center to the base metal and there is a minimal value where is softened zone.
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Authors: Li Jun Xin, Zhi Yong Wang
Abstract: In view of the cutting speed reduced and cutting quality became poor because cutting front changes to flat and amount of lag changes to large, light-gas eccentrically cutting method was proposed. Through the experiment and analysis of the results, the conclusion can be obtained that when laser beam is before gas jet, cutting speed can be improved. While offset distance have impacts to cutting result. If the offset distance is too small, it has no difference with light - gas coaxial cutting; if the offset distance is too large, it weakens the gas jet at the cutting surface, which is not conducive to cutting. It can achieve the best results when the offset distance is 0.3mm.The cutting quality with 1.5mm diameter nozzle is better than that of 2mm. Therefore within the allowable range in the offset distance the nozzle aperture should be reduced.
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Authors: Tao Huang, Li Jun Xin, Zhi Yong Wang
Abstract: Welding experiments of DP780 high strength steel plate produced by Baosteel with IPG YLR-6000-ST2 fiber laser have been processed. The influence of welding parameters on welding quality has been investigated. As well as microstructure and mechanical character of welding seam have been analyzed. The results show that the joint appearance of DP780 high strength steel welded with IPG YLR-6000-ST2 fiber laser has good performance and the mechanics property is good without fit-up gap. The microstructure of weld bead is columnar crystals, mainly lath-shaped ferrite, needle-like lower bainite and a small amount of martensite. Heat-affected zone is narrow and the grain grows with little size. The measured micro-hardness values of the sample decrease smoothly from weld center to base metal and there does not have softened zone.
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