内六角螺钉断裂失效分析  

Analysis of inner hexagon screw fracture failure

作　　者：朱重庆 张先鸣 

机构地区：[1]鹏驰五金制品(广东)有限公司,广东东莞523766 [2]湖南冷水江天宝实业有限公司,湖南冷水江417500

出　　处：《金属制品》2013年第4期60-63,共4页Metal Products

摘　　要：ML40Cr钢12.9级内六角螺钉在装配过程中发生断裂。对断口进行宏观和微观检验分析,结果表明:螺钉表面组织为回火屈氏体及回火索氏体+少量未溶铁素体,表面硬度平均值443.7 HV0.3,断口附近氢质量分数为4.47×10-6,断裂源区及其余外缘均为沿晶断裂形貌,部分晶粒表面出现类似鸡爪纹或发纹特征,表现出氢致延迟断裂的特征,扩展区和终断区主要为沿晶和韧窝的混合断裂形貌。建议采用ML35CrMo或42CrMoA钢制造,改进原材料酸洗工艺;热处理前增加去鳞工序;改善热处理工艺以降低螺钉的抗拉强度和硬度值,增加驱氢工艺,并对该批次螺钉进行48 h氢脆验证试验。ML40Cr steel 12.9 grade inner hexagon screw fractures in assembly process. The fracture is analyzed by macro and micro examination, results show that screw surface structure is tempered troostite and tempered sorbite add little undis solved ferrite, surface hardness average value 443.7 HV0.3, the hydrogen mass fraction near fracture is 4.47 × 10 ^-6 ,frac ture source area and other outer edge is integunular fracture pattern, partial grain surface appears chicken feet grain or grain characteristics, appears the characteristics of hydrogen induced delay cracking, extension section and end section is mainly mixture fracture pattern of integunular and dimple. It is suggested that to produce with MI35CrMo or 42CrMoA steel, to improve wire rod pickling process, to add the process of cutting off scale, to improve heat treatment process to decrease screw tensile strength and hardness value, to add hydrogen elimination process, and to do 48 h hydrogen brittleness remo ving test on the batch screw.

关 键 词：螺钉 氢致延迟断裂 失效分析 回火索氏体 抗拉强度 酸洗 

分 类 号：TG157[金属学及工艺—热处理]