块状组织细化对贝氏体钢断裂行为的影响

 中碳贝氏体钢由亚微米贝氏体铁素体板条和残余奥氏体组成,对韧性起主要作用的为残余奥氏体,通过细化块状组织能显著提高贝氏体钢的韧性。为了探究块状组织细化对断裂行为的影响,采用两步贝氏体等温工艺对中碳(碳质量分数为0.3%)贝氏体钢中块状组织进行细化,对拉伸和冲击性能及其裂纹扩展行为变化进行了研究。利用光学、扫描电子(SEM)、透射电子(TEM)显微镜、X射线衍射(XRD)等对试验钢的显微组织类型和尺寸、拉伸和冲击性能及断口形貌进行表征和分析。结果表明,与一步贝氏体工艺相比,两步贝氏体工艺中新形成的贝氏体铁素体分割细化块状马氏体+残余奥氏体,随着真应变的增加,加工硬化的效果更好;断裂形式为韧性断裂,且韧窝的数量、深度更优于一步贝氏体转变,塑韧性更佳。

Effect of refinement of bulk structure on fracture behavior of bainitic steel

The medium carbon bainitic steel consists of sub-micro structured bainitic-ferrite and retained austenite. The retained austenite plays a leading role for the toughness,it can significantly increase the toughness of bainitic steel by refining the size of blocky structure. In order to explore the effect of block structure refinement on mechanical properties and fracture behavior,the two-step bainite isothermal process was used to study the refinement of the bulk structure,mechanical properties,tensile and impact crack behavior of medium carbon (0.3%) bainitic steel. Optical,scanning electron (SEM),transmission electron (TEM) microscope,X-ray diffraction (XRD),etc. were used to characterize and analyze the type and size of microstructure,tensile and impact properties,and fracture morphology of the test steel. The results show that compared with the one-step bainite process,the newly formed bainite ferrite in the two-step bainite process divides and refines the bulk martensite+retained austenite,and the work hardens with the increase of true strain. The effect of the rate is better;the fracture form is ductile fracture,and the number and depth of the dimples are better than one-step bainite transformation,and the plastic toughness is better.