不同硫化物形态中碳非调质43MnS钢连杆的组织与性能

Microstructure and properties of connecting rods made of medium carbon non-quenched and tempered forging steel 43MnS with different sulfide morphologies

利用光学显微镜、扫描电镜、拉伸试验机及硬度计,对比研究了硫化物变性处理后(1号)、变形处理前(2号)43MnS非调质钢连杆毛坯不同部位的硫化物形貌、微观组织及力学性能特征。结果表明,1号连杆中的硫化物分布较为均匀,绝大部分呈纺锤状;在连杆锻造变形过程中硫化物略有所伸长,硫化物平均长宽比为3.5~3.9。2号连杆中的硫化物分布均匀性较差,多呈长条状,在锻造变形过程中硫化物易伸长变形,部分发生断裂,硫化物平均长宽比为5.5~7.0。1号连杆的强度和硬度略高于2号连杆,两者拉伸试样断裂机制均为韧窝塑性断裂,在粗大的韧窝底部往往存在硫化物夹杂。主要受连杆不同部位锻造变形量及冷却速度差异等影响,连杆毛坯按照大头、小头及工字筋部位的顺序,组织逐渐细化,铁素体和晶内铁素体的含量及硬度均逐渐增加。

Sulfide morphologies,microstructural characteristics and mechanical properties of different parts of connecting rods made of commercial medium carbon non-quenched and tempered steel 43MnS with sulfide-modification(No.1)and without sulfide-modification(No.2)were studied by using optical microscopy,scanning electron microscopy,tensile testing machine and hardness tester.The results show that the sulfides in No.1 steel connecting rod are distributed relatively uniform and most sulfides exhibit a spindle shape,which are slightly elongated during forging deformation process and have an average aspect ratio(the ratio of length to width of sulfide)of 3.5-3.9.The sulfides in No.2 steel connecting rod are elongated and partially fractured during forging,thus poorly distributed and exhibit a highly elongated shape with a average aspect ratio of 5.5-7.0.The strength and hardness of No.1 steel connecting rod are higher than that of No.2.The fracture mechanism of both kinds of specimens is plastic fracture of dimples,and sulfide inclusions often exist at the bottom of large size dimples.Mainly caused by the forging deformation difference and the cooling rate difference at different parts of the connecting rod,according to the order of the big-end,small-end and shank of the connecting rod,the microstructure is gradually refined,and the content and hardness of both the ferrite and intragranular ferrite are gradually increased.