Experimental Study on Fracture Toughness of Weld Joint of Pipeline Steel

摘要

本文针对X70管线钢焊接接头测定焊缝中心金属、热影响区和熔合线附近粗晶区的低温(-10℃)断裂韧性.试件取样、制备和试验方法服从标准BS7448:part1和BS7448:part2.按照标准采用两种三点弯曲试样:全壁厚试样测定焊缝中心和热影响区断裂韧性,表面缺口试样测定靠近熔合线热影响粗金区的断裂韧性.试验后根据标准对表面缺口试件裂纹尖端处进行金相分析,判定试验有效性.试验结果数据显示,焊接接头不同区域CTOD值差异明显,其中熔合线区域CTOD值明显小于其它区域,可以判断该区域是焊接接头启裂薄弱环节.文中还探讨了试验方法可为工程类似试验提供参考.%In this paper,three-point bending specimens made of X70 pipeline steel are conducted to measure the fracture toughness CTOD(δ) of three zones of weld joint: center metal of the weld,heat affected zone(HAZ) and grain coarsened HAZ(CGHAZ) under the temperature of -10℃.According to BS7448,there are two kinds of specimens prepared for the test: through-thickness specimen for center metal of the weld and HAZ,while surface notched specimen for CGHAZ.It is found that the fracture toughness of CGHAZ is much less than that of the other zones,which is due to the size of metallurgical structure shown in metallography,with a conclusion that CGHAZ near the fusion line is weakness of weld joint for fatigue cracking,providing a reference for the engineering design.The study also pay attention to test methods to improve the efficiency and accuracy of the similar test.