冷却速度对铬系铸铁凝固过程中碳化物析出特征的影响

Effect of cooling rate on precipitation characteristics of carbide in high chromium cast iron during solidification

通过改变冷却条件,探讨冷却速度的变化对Cr含量分别为9%、17%的铬系铸铁凝固过程中碳化物形核、长大的热力学驱动力条件及原子扩散移位动力学条件的影响,揭示碳化物类型及尺寸、形貌的变化特征。结果表明：对于Cr含量为9%铸铁,砂型冷却下凝固组织中的碳化物是M3C、M3C7两种类型,呈大块状,尺寸较大;在金属型冷却下碳化物尺寸较砂型有所减小;水冷条件下组织中碳化物的连续性变弱,尺寸明显变小,呈长条状排列。相较于铬含量9%的铸铁,当Cr含量为17%时,砂型冷却下凝固组织中只有M3C7型碳化物,且碳化物尺寸减小,形态呈棒状;在金属型冷却时,碳化物形貌变化程度较Cr含量为9%时从砂型到金属型的变化要小;但在快速水冷下碳化物间距显著变窄,长度尺寸明显变小,分布更加均匀。

The conditions of thermodynamic driving force of nucleation and growth of carbides and the kinetic conditions of atomic diffusion displacement during solidification of chromium cast iron containing 9% Cr and 17% Cr were explored by changing cooling rate,and the type,size and morphology of carbides were described. The results show that when Cr content is 9%,the carbide types are M3 C and M3 C7 with lager size by cooling in sand mould. However,the size of carbides becomes smaller by cooling in metal mould. Additionally,the size is obviously smaller with long strip shape and the continuity becomes weak by water cooling. Compared with 9% chromium content of cast iron,when the Cr content is 17%,there is only M3 C7 with smaller size and rod shape by sand mould cooling. Adopting metal mould cooling,the change degree of carbide morphology is smaller than that of 9% Cr from sand mould to metal mould. However,by water cooling,the distances between carbides become significantly smaller,the length and size are smaller and the distribution is more uniform.