S690QL热模拟焊接热影响区组织及韧性研究

Study on Microstructure and Toughness of Thermal Simulation Welding Heat Affected Zone of S690QL Steel

利用热模拟技术研究了焊接热循环对高强钢S690QL焊接热影响区的组织和韧性的影响,重点分析了一次及二次热循环下淬火粗晶区(CGHAZ)组织转变与韧性的关系。结果表明,一次热循环下CGHAZ韧性严重恶化,其值接近S690QL韧性指标下限值,该区随t8/5不同所形成的粗大板条马氏体、富碳淬硬相及上贝氏体组织是致使低温韧性恶化的主导因素,而CGHAZ区段内原奥氏体晶粒大小随峰值温度的梯度变化对该区韧性影响程度较小,不同峰值温度下的二次热循环对原一次CGHAZ的组织及碳化物析出形态有所改变,进而对韧性影响不一。

The effects of welding thermal cycle on the microstructure and toughness of HSLA S690QL welding heat-affected zone were investigated. The relationship between the microstructure of CGHAZ under first and second thermal cycle and toughness was analyzed. The experimental results show that the CGHAZ toughness deteriorates sharply, the value of which is closed to lower limit of toughness requirement of base metal S690QL.The large lath martensite, hardened phase with carbon-rich and upper bainite formed in CGHAZ with different t8/5 are main factors for deteriorating toughness. However, the effect on CGHAZ toughness by difference of prior austenitic grain size in CGHAZ with peak temperature is less. During the second thermal simulation cycle, the changes of microstructure and carbide precipitation morphology in CGHAZ at different peak temperature take various influences on the toughness.