冷却速度对高硅球墨铸铁组织和性能的影响

Effect of Cooling Rate on Microstructure and Properties of High-Silicon Ductile Iron

采用消失模铸造工艺制得不同壁厚梯度的高硅球铁试样,用以研究不同冷却速度对其组织和性能的影响,使用光学显微镜和扫描电镜观察高硅球铁试样的微观组织,利用万能拉伸试验机和数显布氏硬度仪测量其力学性能。结果表明:随着冷却速度的增加,高硅球墨铸铁试样的基体组织为全铁素体,球状石墨尺寸逐渐减小,铁素体晶粒尺寸逐渐减小,晶粒细化;硅元素在铁素体晶界处的偏析现象越来越明显,铁素体基体的晶格常数逐渐减小,铁素体的晶格畸变程度增大。硅含量4.59%的高硅球墨铸铁试样在壁厚12 mm处,球状石墨的平均尺寸约为20.4μm,铁素体晶粒平均尺寸约为31.9μm,抗拉强度约为683 MPa,伸长率为19%;在壁厚42 mm处,球状石墨平均尺寸约为29.2μm,铁素体晶粒平均尺寸约为54.9μm,抗拉强度约为666 MPa,伸长率为15%。冷却速度的增加使高硅球墨铸铁的强度和硬度逐渐增加,力学性能得到提升。

High silicon ductile iron samples with different wall thickness gradients were prepared by EPC process to study the effects of different cooling rates on their microstructure and properties.The microstructure of the specimens was observed by optical microscopy and scanning electron microscopy,and the mechanical properties were measured by universal tensile testing machine and digital Brinell hardness tester.The results showed that with the increase of the cooling rate,the matrix microstructure of the high silicon ductile iron was full ferrite,the size of spheroidal graphite and ferrite grains were gradually reduced,and the grain size was refined;the segregation of silicon element at ferrite grain boundaries was more and more obvious,the lattice constant of ferrite matrix was gradually reduced,and the degree of ferrite lattice distortion was increased.The average size of the spheroidal graphite was about 20.4μm,the average size of the ferrite grain was about 31.9μm,the tensile strength was 683 MPa,and the elongation was 19% at the wall thickness of 12 mm of the high silicon ductile iron sample with 4.59% silicon;At the wall thickness of 42 mm,the average size of the spheroidal graphite was about 29.2μm,the average size of the ferrite grain was about 54.9μm,the tensile strength was 666 MPa,and the elongation was 15%.With the increase of the cooling rate,the strength and hardness of the high silicon ductile iron increased gradually,and the mechanical properties were improved.