Mechanical Properties of Thick Plates After Welding of Q690 High Strength Steel
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摘要: 对50、70 mm厚的高强度Q690钢板及其对接焊接件在拉伸条件下的机械性能进行了全面研究,共进行了40次拉伸试验。首先,针对母材在钢板厚度范围内的3个不同层上提取了18个圆形截面比例试样。对所有这些试样进行了拉伸试验,以获得其机械性能,并研究了它们在不同板厚上的变化。其次,在这些厚钢板之间采用不同热输入能量的埋弧焊制备焊接件。此外,还对焊接部分的典型热影响区进行了微观结构检查。对总共22个矩形截面标准试样进行了拉伸试验,以获得其机械性能,并评估和比较了这些试样的全方位变形特性,特别是其抗拉强度和断裂伸长率,以评价热输入对厚板焊接件力学性能的影响。在拉伸试验过程中,使用数字图像相关技术(DIC)观测并记录试件表面在拉伸状态下的真实应变,进一步研究热影响区对焊接件力学性能的影响。通过针对母材的试验发现,从50 mm厚Q690钢板的各层中取出的试件,其力学性能只有可忽略不计的差别,可以认定沿板厚方向,50 mm板各层之间的力学性能是均一的。而70 mm板中层取出的试件,其屈服强度与抗拉强度相较于上、下两层中的试件,各有7%与6%的折减,而断后延伸率则相差不大。对于焊接件的试验表明,相对于16 mm Q690板,焊接热输入对50、70 mm厚板的力学性能影响更小:对16 mm板焊接件热输入由1.0 kJ/mm增大至2.0 kJ/mm时,焊接件强度折减由0%增大至8%;而对于50 mm板焊接件热输入由2.4 kJ/mm增大至5.0 kJ/mm时,焊接件强度折减保持在4%左右;而对于70 mm板焊接件热输入由2.4 kJ/mm增大至5.0 kJ/mm时,焊接件强度折减保持在1%以内。可以看到对于厚板焊接件,热输入的增大引起的焊接件强度折减的波动更小,因而在厚板焊接时,可以使用更大的热输入以提高焊接效率。同时,提供了有关这些建筑用高强度钢板及其对焊部分机械性能的重要试验证据。试验证明,只要按照既定的焊接规范对焊接过程进行适当控制,这些对焊部分的机械性能几乎不会降低,甚至不降低。因此,这些厚的高强度Q690钢之间的全强度对焊型材在实践中很容易实现,与通常采用的Q355钢类似。Abstract: A comprehensive investigation into the mechanical properties of 50 and 70 mm thick plates of Q690 high strength steel and their butt-welded sections under tension was presented in this paper, and a total of 40 tensile tests were conducted. Firstly, a total of 18 proportional coupons with circular cross-sections were extracted at three different layers within the plate thicknesses. Tensile tests on all of these coupons were carried out to obtain their mechanical properties, and their variations across the plate thicknesses were also examined. Secondly, submerged arc welding was adopted to prepare butt-welded sections between these thick steel plates with various heat input energy. Micrograpic examinations on typical heat-affected zones of the welded sections were also performed. Standard tensile tests on a total of 22 proportional coupons with rectangular cross-sections were carried out to obtain their mechanical properties, and the full range deformation characteristics of these coupons were assessed and compared, in particular, their tensile strengths and elongations at fracture. Based on the tests on the base metal, it was found that there was only a negligible difference in the mechanical properties of the coupons from different layers of the Q690 50 mm thick steel plate, and it can be concluded that the mechanical properties of the 50 mm plate are homogeneous along the thickness direction. The yield strength and tensile strength of the coupons from the middle layer of the 70 mm plate, compared with the specimens in the upper and lower layers, possess a 7% and 6% reduction, while no reduction of elongation after fracture is found. The tests of welded sections show that, compared with these 16 mm thick plates, the influence of heat input energy on the mechanical properties of these 50 and 70 mm thick plates is small: with the increase of heat input energy from 1.0 to 2.0 kJ/ mm, the reduction of the tensile strength of coupons from 16 mm thick welded sections increased from 0% to 8%; While for the 50 and 70 mm plates, with the increase of heat input energy from 2.4 to 5.0 kJ/ mm, the reductions of tensile strengths maintained to be 4% and 1%. It is obvious that for the thick plate, the effect of increasing heat input energy on the reduction of the mechanical properties is smaller. Therefore, a larger heat input energy is allowed to improve the welding efficiency.
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Key words:
- high strength steel /
- welding /
- mechanical properties after welding
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