汽车球墨铸铁制动钳不同壁厚处的组织与性能研究

Study on Structure and Property of Ductile Iron AutomobileBrake Pliers at Different Wall Thicknesses

了解汽车制动钳球墨铸铁件不同壁厚处的组织与性能规律,有利于改善产品质量及稳定性。以QT500-7和QT550-6的制动钳为对象,通过分析其不同部位的组织与性能,研究铸件壁厚对球墨铸铁石墨、基体组织、硬度的影响。结果表明:制动钳由部位A至C,壁厚依次增大,其石墨球化率变化不大,石墨颗粒数先增多后减少,石墨平均直径先减小后增大,珠光体含量和布氏硬度先下降后上升,珠光体片间距变化趋势则与Si元素微区含量的变化趋势接近一致。A部位壁厚小于B部位,但由于凝固过程温度场分布不同,A部位温度要高于B部位,故A部位石墨颗粒数反而较少、石墨平均直径反而较大。较厚部位C和冷却较慢的部位A比B部位的珠光体含量反而多,是受稳定珠光体的元素如Mn偏析影响的结果,并且冷却速度越慢偏析越严重。铸件不同壁厚处的组织与性能的差异本质上是冷却速度和微区成分综合影响的结果。

Understanding the structure and property of different wall thickness of automobile brake clamp ductile iron casting is conducive to improving the product quality and stability.With the brake clamp of QT 500-7 and QT 550-6,the influence of casting wall thickness on ductile iron graphite,the structure of the matrix and the hardness was studied.The results show that the brake clamp from part A to C,as the wall thickness increases in turn,the graphite spherical rate change is not big,The number of graphite particles increasesfirst and then decreases,the average diameter of graphitefirst decreases and then increases,the pearlite content and Brinell hardnessfirst decreased and then increased,pearlite sheet spacing change trend with Si element micro content change trend close to consistent.The wall thickness of A is smaller than that of B,but due to the different temperaturefield distribution in the solidification process,the temperaturefield of A is higher than that of B,so the number of graphite particles in A is smaller and the average diameter of graphite is larger.Thickness site C and slower cooling site A are more abundant than pearlite in site B because of the influence of stable pearlite elements such as Mn segregation,and the slower the cooling rate,the worse the segregation.The difference in the structure and property of the different wall thickness of the casting is essentially the result of the combined influence of the cooling speed and the microzone composition.