白口铁热处理时共晶碳化物的溶解与粒状化

本文研究了白口铸铁热处理过程中共晶碳化物的溶解规律及形貌变化机制。结果表明,由于加热时基体内二次碳化物析出,因此使高温保温时共晶与二次碳化物的溶解共存。二次碳化物由于尺寸小及合金元素含量低从而溶解快。其溶解极限为:F_s=K′C_(t(∞))-C_(t(0))]F_(a(0))/1/4Ω-K·C_(t(∞)]。二次碳化物的析出量大于该溶解极限,将有利于共晶碳化物团聚化及粒状化过程的进行。溶解过程中;共晶碳化物网的破碎主要是通过网状连接中生长缝隙的扩大、“缩颈”部位的溶断以及表面孔洞的扩大而进行。破碎后的共晶碳化物继续保温时,由于表面自由能的作用而最终粒状化。

DISSOLUTION AND GRANULATION OF EUTECTIC CARBIDE DURING HEAT TREATMENT OF WHITE CAST IRON

The dissolution mechanism and morphology changes of eu-tectic carbide in white cast iron during heat treatment were studied. It was found that during high temperature holding, the dissolution of eutectic carbide and the secondary carbide which was separated from the matrix during heating up occured simultaneously, but the latter was dissolved more rapidly because of its smaller size and lower content of alloy elements. There existed a dissolution limit of the secondary carbide which was derived asIf the amount of secondary carbide separated exceeded its dissolution limit, the process of agglomeration and granulation of the eutectic carbide would be more favourable. The break-up of the eutectic carbide network occured by the enlargement of fissures in the network, the fragmentation at the necking portions, and the enlargement of the holes on the surface of the carbide. All these places were thermodynamically favourable sites for dissolution. When high temperature holding continued, the fragmented eutecdc carbide was eventually granulated in order to decrease the interfacial free energy.