EH36厚壁海上风电用钢及其焊接热影响区的断裂韧性研究

Fracture Toughness of Thick-wall EH36 Offshore Wind Power Steel and Heat-affected Zone

目的开发大壁厚抗断裂、耐不同线能量焊接EH36海上风电用钢,满足深水海上风电平台的服役需求。方法试制了80 mm厚的EH36海上风电用钢,研究了不同温度下EH36的断裂韧性变化规律,并进行了7 kJ/cm和50 kJ/cm线能量的焊接试验。通过裂纹尖端张开位移(CTOD)试验,评估母材及焊接CGHAZ的断裂韧性。使用光学显微镜和电子显微镜对其微观组织及其CTOD试样断口形貌进行表征和分析。结果EH36的断裂韧性在−10~−30℃区间内保持较高的值,−40℃为该材料的韧脆转变温度,此时断裂模式从韧性断裂转变为脆性断裂,但其临界CTOD平均值仍高于标准要求。此外,7 kJ/cm热输入的CGHAZ临界CTOD平均值为0.658 mm,其微观组织主要由针状铁素体组成,50 kJ/cm热输入的CGHAZ临界CTOD平均值为0.468 mm,其微观组织主要由针状铁素体和粒状贝氏体组成。在电镜下观察到CGHAZ内含有大量由Ti的氧化物组成的高熔点夹杂物,大量针状铁素体在其周围形核并生长,可有效提升CGHAZ的断裂韧性。结论所开发的EH36厚壁海上风电用钢具有优越的抗断裂性能和焊接性能。

The work aims to develop thick-wall EH36 offshore wind power steel with fracture resistance and high heat input resistance,so as to meet the service needs of deep-water offshore wind power platforms.The 80 mm thick EH36 steel for offshore wind power was trial produced,and the change rule of fracture toughness of EH36 at different temperature was investigated,and welding tests with line energy of 7 kJ/cm and 50 kJ/cm were carried out.The fracture toughness of the base metal and the welded coarse grain heat affected zone(CGHAZ)was evaluated by crack tip opening displacement(CTOD)test.The microstructure and the fracture morphology of its CTOD specimens were characterized and analyzed by optical microscopy and electron microscopy.The fracture toughness of EH36 maintained a high value in the interval from−10℃to−30℃.−40℃was the tough-brittle transition temperature of this material,when the fracture mode changed from ductile fracture to brittle fracture,but the average value of its critical CTOD was still higher than the standard requirement.In addition,the average value of critical CTOD of CGHAZ with 7 kJ/cm heat input was 0.658 mm,and its microstructure mainly consisted of acicular ferrite.The average value of critical CTOD of CGHAZ with 50 kJ/cm heat input was 0.468 mm,and its microstructure mainly consisted of acicular ferrite and granular bainite.It was observed that CGHAZ contained a large number of high-melting inclusions composed of Ti oxides,and a large number of acicular ferrites nucleated and grew around it,which could effectively improve the fracture toughness of CGHAZ.The results of this study show that the developed thick-wall EH36 offshore wind power steel has superior fracture resistance and welding performance.