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利用金相显微镜、扫描电子显微镜及附带EDS系统和透射电子显微镜研究850 MPa级焊缝金属的微观组织,并通过分析焊缝金属凝固和相变过程,研究组织形成机制。发现原δ铁素体柱状晶晶界附近的锰和镍含量高于其心部含量。原δ铁素体柱状晶晶界附近组织由平行板条马氏体组成,板条宽度约为300 nm,原δ铁素体柱状晶心部组织由“交织状”板条马氏体组成,板条宽度约为400 nm。分析认为造成原δ铁素体柱状晶晶界附近和心部组织差异的重要原因是锰和镍的偏析,而焊缝金属良好的冲击韧性是因为存在30%“交织状”马氏体和一定量残余奥氏体。
The microstructure of 850 MPa weld metal was studied by metallographic microscope, scanning electron microscopy, EDS and transmission electron microscopy. The mechanism of microstructure formation was also studied by analyzing the metal solidification and transformation process. It is found that the content of manganese and nickel near the columnar grain boundary of the original δ ferrite is higher than the content of the core. The structure of the original δ-ferrite columnar grain boundaries is composed of parallel lath martensite with a width of about 300 nm. The original δ-ferrite columnar crystal core consists of “interlacing” lath martensite The width of the strips is about 400 nm. It is considered that the important reason for the difference between the grain boundaries of the original δ-ferrite and the core is the segregation of manganese and nickel. The good impact toughness of the weld metal is due to the presence of 30% interlaced martensite And a certain amount of residual austenite.