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采用焊接热模拟技术、金相分析及透射电镜研究了X70管线钢在役焊接粗晶区及其经受不同峰值温度二次焊接热循环作用后热影响区各区的金相组织和精细结构.结果表明,在役焊接粗晶区的金相组织主要是板条束贝氏体和粒状贝氏体,经历不同峰值温度的二次热循环后,组织类型没有发生变化,但各种组织的形态、大小、数量以及原奥氏体晶粒大小有些差异.热影响区各区的主要形貌都是铁素体板条和分布在板条之间或板条基体上的M-A组元.在役焊接粗晶区M-A组元形态以条状为主,经历二次热循环后,再热临界粗晶区的M-A组元有所细化.再热临界粗晶区存在下贝氏体组织,且具有典型的“中脊”形貌.
The microstructure and fine structure of X70 pipeline steel in-service welded coarse-grained zone and its heat-affected zone subjected to secondary heat cycle with different peak temperatures were studied by means of welding thermal simulation, metallographic analysis and transmission electron microscopy. In the in-service welding, the microstructure of the coarse-grained zone is mainly lath bainite and granular bainite. After the second thermal cycle with different peak temperatures, the type of the structure does not change, but the morphology, size , The number of the original austenite grain size and some differences.The main morphology of the various regions of the heat-affected zone are ferrite laths and distributed in the slab or slab matrix MA group components in the welding of coarse grained area The morphology of MA is dominated by the stripe, and the MA elements in the reheat critical coarse grain region are refined after the second thermal cycle.The lower reheat critical coarse grain region exists in the lower bainite and has the typical “Ridge ” topography.