缩松对铁素体球墨铸铁QT400-18L力学性能和断裂机理的影响  

Effect of Shrinkage Porosity on Mechanical Properties and Fracture Characteristics of Ferritic Ductile Iron EN-GJS-400-18-LT

作　　者：王泽华[1] 梅婉 蔡有伟 周泽华[1] 赵伟华[1] 张欣[1] WANG Ze-hua;MEI Wan;CAI You-wei;ZHOU Ze-hua;ZHAO Wei-hua;ZHANG Xin(College of Mechanics and Materials,Hohai University,Nanjing 211100,Jiangsu,China)

机构地区：[1]河海大学力学与材料学院,江苏南京211100

出　　处：《铸造》2021年第8期906-914,共9页Foundry

基　　金：中央高校基本科研业务费项目(2013B200205011)。

摘　　要：制作了不同程度缩松缺陷的QT400-18L球墨铸铁试样,研究了缩松对铁素体球墨铸铁力学性能和断裂机理的影响。结果表明:QT400-18L的抗拉强度R_(m)随缩松孔面积率r_(p)的增加呈线性下降,可表示为R_(m)=358-352r_(p)(MPa);QT400-18L的断后伸长率随着缩松的出现而急剧下降,且缩松分布越集中,断后伸长率越小;QT400-18L的疲劳寿命随缩松的增加而急剧下降,在σ_(max)=150MPa、r=0的轴向循环载荷作用下,其疲劳寿命N与缩松孔面积率r_(p)可表示为N=5.79×10^(3)r_(p)^(-1.4),缩松孔面积率r_(p)和缩松孔尺寸越大,疲劳寿命越短。缩松对QT400-18L的断裂机理影响不大,不规则石墨颗粒和缩松的锐角都有可能成为裂纹源,所以球墨铸铁疲劳源众多,疲劳断口形貌复杂。A number of test pieces with different levels of shrinkage porosity were cut from an EN-GJS-400-18-LT spheroidal graphite casting.The tensile test and the fatigue test were performed to investigate the impact of shrinkage porosity on their mechanical properties and fracture characteristics.The results show that the tensile strength decreased linearly with the increase of the pore area ratio(r_(p))of shrinkage porosity,and the relationship could be expressed by a fitting formula,R_(m)=358-352r_(p)(MPa).The tensile elongation decreased sharply with the increase of the shrinkage porosity due to the non-uniform plastic deformation.The bigger the pore area ratio(r_(p))and the smaller the area of the shrinkage porosity,the lower the tensile elongation will be.The fatigue life also dramatically declined with the increase of the pore area ratio(r_(p)).Under a cyclying tensile stress of 0 and 150 MPa,the fatigue life of the sample could be expressed by a fitting formula,N=5.79×10^(3)r_(p)-1.4.Besides the pore area ratio(r_(p)),the bigger the size of the pore of the shrinkage porosity,the lower the fatigue life will be.The fracture characteristics had no much difference no matter with shrinkage porosity or not.Not only the shrinkage porosity,but also the irregular graphite particles,all the sharp corner of them may become the initiation sites of the fatigue cracks.The fatigue fracture of spheroidal graphite cast iron is very complex.There are many initiation sites of the fatigue cracks.Cracks propagating from different initiation sites result in the failure of the test pieces.

关 键 词：铁素体球墨铸铁 QT400-18L 缩松缺陷 力学性能 疲劳性能 断裂机理 

分 类 号：TG143.5[一般工业技术—材料科学与工程]