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采用光学显微镜、扫描电子显微镜和透射电子显微镜对热轧态和回火态AH80DB低碳贝氏体钢的显微组织、马氏体/奥氏体(M/A)岛、第二相的析出行为以及晶界取向差、有效晶粒尺寸进行研究,揭示回火后低碳贝氏体钢冲击韧性得到改善的原因.结果表明:两种试样的组织均由板条状贝氏体、粒状贝氏体和针状铁素体组成,其中回火态试样中针状铁素体组织较多.热轧态钢中存在较大尺寸M/A岛且呈方向性分布,大角度晶界比例占17.33%,有效晶粒尺寸为3.57μm;而回火态钢中M/A岛的尺寸较小,大角度晶界比例增加3.43%,有效晶粒尺寸减小0.56μm.热轧态钢中析出相主要是(Nb,Ti)C,尺寸在50~150 nm之间,回火态试样中析出较多细小的球状(Nb,Ti)C析出相,尺寸在10 nm左右.
Microstructure, martensite / austenite (M / A) island and precipitation of the second phase of AH80DB low carbon bainitic steel were studied by optical microscope, scanning electron microscope and transmission electron microscope Behavior and the grain boundary orientation difference and effective grain size were studied to reveal the reasons for the improvement of the impact toughness of low carbon bainitic steels after tempering.The results showed that the microstructure of the two samples were composed of lath bainite, Bainite and acicular ferrite, of which the microstructure of acicular ferrite is more in the tempered samples.The larger size M / A islands are present in the hot-rolled steel and have a directional distribution with large-angle grain boundaries Accounting for 17.33%, the effective grain size of 3.57μm; tempered steel M / A island smaller size, high-angle grain boundaries increased 3.43%, the effective grain size decreases 0.56μm hot-rolled steel (Nb, Ti) C, the size of which is between 50 and 150 nm, the precipitation of more and more small spherical (Nb, Ti) C precipitates in the tempered samples is about 10 nm in size.