一种中碳高强韧合金钢的组织与力学性能

Microstructure and mechanical properties of a medium carbon alloy steel with high strength and toughness

中碳高强度钢可以用作高强度钢材分切刀片,其力学性能对于刀片的使用寿命等有重要的影响。设计了一种高强韧性中碳合金钢,测得了其特性参数,利用Thermal-Calc软件计算了其相图。采用光学显微镜、扫描电镜、洛氏硬度计和拉伸及冲击试验等研究了不同热处理工艺对试验钢的组织、力学性能和断口形貌的影响。结果表明:在H13钢的基础上添加3.5~4.0 mass%Ni和2.0 mass%Mo元素可以进一步提高其强韧性。试验钢淬火后的组织为板条马氏体及少量未溶MC型碳化物和残留奥氏体;试验钢存在回火二次硬化现象,520℃回火时硬度达到峰值,产生二次硬化的主要原因是回火时析出弥散细小与基体共格的MC、M2C型碳化物,以及棒状M_(7)C_(3)型碳化物;500℃以下回火,试验钢的拉伸和冲击断口形貌主要是解理+准解理,随着回火温度进一步升高,准解理断裂比例增加,解理断裂比例减少,600℃回火开始出现韧窝,韧性随之改善。试验钢的最佳热处理工艺为900℃×2 h+730℃×4 h球化退火+1025℃油淬+520℃两次回火,经最佳工艺热处理后其硬度为58.8 HRC、抗拉强度为1955.4 MPa、夏氏冲击韧性为3.2 J/cm^(2)。

Medium carbon high-strength steel can be used as high-strength steel cutting tools,and its mechanical properties have an important effect on the service life of the tools.A kind of medium carbon alloy steel with high strength and toughness was designed,its characteristic parameters were measured,and its phase diagram was calculated using Thermal-Calc software.The effects of different heat treatment processes on microstructure,mechanical properties and fracture morphology of the experimental steel were studied by means of optical microscope,scanning electron microscopy,Rockwell hardness tester and tensile and impact tests.The results show that adding 3.5-4.0 mass%Ni and 2.0 mass%Mo elements to H13 steel can further improve its strength and toughness.After quenching,the microstructure of the experimental steel is composed of lath martensite,a small amount of undissolved MC type carbides and retained austenite.There is a phenomenon of tempering secondary hardening in the experimental steel,and the hardness reaches its peak value when tempered at 520℃.The main reason for secondary hardening is the precipitation of dispersed fine MC and M2C type carbides that are coherent with the matrix during tempering,as well as rod-shaped M_(7)C_(3) type carbides.When tempered below 500℃,the tensile and impact fracture surface morphology of the experimental steel is mainly composed of cleavage+quasi-cleavage.As the tempering temperature further increases,the proportion of quasi-cleavage fracture increases,while the proportion of cleavage fracture decreases.After tempering at 600℃,ductile dimples appear and toughness improves accordingly.The optimal heat treatment process for the experimental steel is 900℃×2 h+730℃×4 h spheroidizing annealing+1025℃oil quenching+520℃tempering for twice,and after the optimal heattreatment process,its hardness is 58.8 HRC,tensile strength is 1955.4 MPa,and Charpy impact toughness is 3.2 J/cm^(2).