Tensile Properties of Q690-QT High Strength Steel Welded Sections with Different Heat Input Energy During Welding
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摘要: Q690-QT高强钢具有轻质高强等优点,应用于钢结构建筑中,可显著减轻结构自重、降低成本。过去20年里,大量Q690-QT高强钢焊接材料及构件的力学性能试验结果表明,如果焊接控制不当,会导致高强钢微观结构出现变化,出现焊接截面的屈服强度、抗拉强度和延性显著下降的现象。上述试验更多地是进行焊接后接头表现的性能特点描述,未能系统采用试验或理论分析不同焊接工艺的参数对高强钢焊接接头力学性能的影响,也未能形成可避免高强钢焊接强度折减的焊接工艺参数,难以为高强钢材料在建筑和桥梁等工程的实际应用提供技术支撑。在此背景下,以焊接热输入为控制变量,利用惰性气体保护焊(GMAW)和埋弧自动焊(SAW)的机器人自动焊接系统,设计并制作了12个不同热输入(1.0、1.5、2.0、5.0 kJ/mm) Q690-QT高强钢焊接接头试件、3个Q690-QT高强钢金属母材试件及3个焊接材料试件进行标准拉伸试验。通过分析引伸计和高精度连续摄像方式采集的试件过程应力、应变数据,探究不同焊接参数对高强钢焊接接头强度折减的影响,为实际工程Q690-QT高强钢材料焊接强度控制提出相应的工程建议。结果表明:不同焊接热输入的Q690-QT高强钢焊接接头试件,在竖向拉力的作用下,其断裂位置均位于热影响区(HAZ)内,未受焊接冷热循环影响的金属母材部分和焊接材料部分均未出现明显损伤现象。分析应变引伸计和高速摄像机采集的应力、应变数据可知,相较于Q690-QT高强钢母材试件,当焊接热输入由1.0、1.5、2.0 kJ/mm至5.0 kJ/mm变化,不同Q690-QT焊接接头试件的屈服强度和抗拉强度由基本不变变化为10%折减,最后出现30%左右屈服强度折减现象。母材与焊接接头试件的伸长率测试数据对比结果表明,随着焊接热输入升高,钢材焊接延性折减程度增高。通过对实际工程中焊接热输入进行监测,可较为准确地预测不同Q690-QT高强钢焊接接头强度,将焊接热输入控制为1.0 kJ/mm和1.5 kJ/mm,可实现高强钢焊接接头的等强连接。Abstract: High strength steel with yield strengths at 690 MPa has been widely used in primary structural members of steel structures because of their strength-to-self-weight ratios. Over the past two decades, there were a number of experimental investigations into mechanical properties as well as structural behaviour of high strength Q690-QT steel welded sections. It is evident now that, these welded sections will suffer from a significant reduction in their mechanical properties, i. e. both yield and tensile strengths as well as ductility, due to change in microstructures if welding is not properly controlled. These experimental investigations focus on describing the structural behaviour of welded sections, and the mechanism of the influence of different welding process parameters on the mechanical properties of high-strength steel welded connections has not been studied. Moreover, the improved welding technology that could avoid the strength reduction of welded high-strength steel could not be proposed. These studied are difficult to provide theoretical evidence for the practical engineering of high-strength steel materials in buildings and bridges. Therefore, a series of carefully planned and executed standard tensile tests were carried out to investigate and quantify effects of various line heat input energy onto the mechanical properties of the Q690-QT steel welded sections. A total of 12 standard tensile tests on cylindrical coupons of welded sections, 3 standard tensile tests on cylindrical coupons of base plate, 3 standard tensile tests on cylindrical coupons of welded metal were conducted, and full range deformation characteristics of these coupons were obtained through use of strain gauges and measurements on high resolution digital images. Both welding methods, namely, GMAW and SAW, were employed to prepare full penetration butt-welded section with various line heat input energy (1. 0, 1. 5, 2. 0, 5. 0 kJ/ mm). It should be noted that GMAW was performed with a robotic welding system while SAW was performed with an automated welding machine to attain high quality welding consistently. After comparison the tested data, the design suggestions for controlling the welded Q690-QT high-strength steel material strength in practical engineering will be proposed. The results show that almost all coupons of the welded sections tested in the present study, fracture occurred within the heat affected zones (HAZ) of the welded sections without any failure in neither the weld metal nor the base plates. For welded sections prepared with a line heat input energy equal to 1.0 or 1.5 kJ/ mm, there were almost no reduction in the mechanical properties of the welded sections. However, for these welded sections prepared with a line heat input energy equal to 2.0 kJ/ mm, only 90% of the yield and the tensile strengths of the base plates was attained. As for these welded sections prepared with a line heat input energy equal to 5.0 kJ/ mm, only 70% of the yield strength of the base plates was attained. Compared with the elongation tested data of base plates and welded sections, the ductility reduction of welded sections is more significant with the increase of heat input energy. Consequently, the effects of welding onto mechanical properties of the Q690 - QT steel welded sections have been successfully quantified, and the information is readily adopted in assessing their mechanical behavior according to various line heat input energy employed during welding. In practical engineering, the equal strength connection of high-strength steel materials could be achieved by setting the heat input energy as 1.0 or 1.5 kJ/mm.
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Key words:
- high strength steel /
- welded sections /
- heat input energy /
- strength reduction /
- ductility reduction
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