预热及保温对严寒环境X80钢管道全自动外焊焊缝组织与性能的影响

研究了-30 ℃严寒环境下采用不同预热及保温措施进行电弧焊接的X80钢，观察了不同焊接条件下接头各区域的显微组织特点，通过硬度测试、拉伸试验、低温冲击试验对接头的力学性能进行了表征。研究结果表明：严寒环境下焊接得到的X80钢焊缝以柱状晶为主，填充区主要由针状铁素体、先共析铁素体及少量魏氏组织组成，随着预热及保温温度升高，魏氏组织的尺寸和数量都有所减小;接头硬度的极大值与极小值分别出现在热影响区的粗晶区与不完全重结晶区，随着预热及保温温度的升高，接头的整体硬度降低，焊缝区域的低温冲击韧性增强，而抗拉强度先提高后降低;预热及保温是接头在严寒环境下获得具有良好综合性能的有效措施，预热及保温温度为100 ℃时接头性能最优。

Effects of Preheating and Heat Preservation on Microstructure and Properties of Fully Automatic External Welding Seams of X80 Steel Pipes in Severe Cold Environment

X80 pipeline steel arc welded was studied with different preheating and heat preservation measures in -30 ℃ severe cold environment. The microstructure characteristics of each region of the joints were observed under different welding conditions. The mechanics properties of the joints were characterized by hardness tests, tensile tests and low temperature impact tests. The results show that the welding seams of X80 steel welded are mainly columnar crystal in severe cold environment, and the filling areas are mainly composed of acicular ferrite, proeutectoid ferrite and a small amount of Widmanstatten structure. With the increasing of preheating and holding temperature, the size and quantity of Widmanstatten structure decrease. The maximum and minimum values of joint hardness appear in the coarse-grained areas and the incomplete recrystallization areas respectively. With the increasing of preheating and holding temperature, the overall hardness of the joints decreases, the low-temperature impact toughness of the weld areas increases, and the tensile strength increases first and then decreases. Preheating and heat preservation are effective measures to obtain joints with good comprehensive performance in severe cold environment. The joint performance is the best when preheating and holding temperature is as 100 ℃.