【作者】 赵峰；

【导师】 马幼平；

【作者基本信息】 西安建筑科技大学 ， 钢铁冶金， 2007， 硕士

【摘要】 本文通过改变化学成分和工艺条件研究了高铬白口铸铁凝固过程中碳化物形核长大的热力学与动力学条件变化及其对随后碳化物生长形态的影响，以期揭示高铬白口铸铁凝固过程中碳化物的形成机制和形态控制机理，为获得良好力学性能的新型高铬白口铸铁奠定理论基础。研究结果表明：化学成分对碳化物形态有重要影响：硅对碳化物形态的影响具有二重性：一方面硅增加碳的活性，促进碳的扩散，硅量的增加，使得初生碳化物易于粗大化；另一方面，硅与碳之间的排斥作用，导致碳原子在微区富集，使共晶碳化物的形核率增加，同时随着凝固的进行，共晶碳化物四周区域温度的降低以及硅含量的增加，碳、铬元素扩散到碳化物的生长界面受到限制，相应阻碍了碳化物的生长，从而细化了共晶碳化物；钒钛微合金化不仅能增加异质形核核心，而且熔液中溶解的钛还能抑制碳的扩散，阻碍碳化物的长大，使碳化物细化、球化，对力学性能改善有利；当铬(碳)量一定时，随着碳(铬)量的增加，碳化物数量增加，硬度增加而冲击韧性降低，特别是碳量的增加更能使碳化物形态和性能恶化。在过共晶高铬白口铸铁凝固过程中，通过改变其熔炼和冷却条件的方式来改变碳化物的形核和生长机制，可达到改善其形态的目的：当过热为1600℃时，实现了熔液净化，促进热力学过冷，使碳化物细化；当冷速较大时，碳化物形核率增加，且Fe、C、Cr等原子难以扩散到碳化物生长界面，从而抑制其长大，同时整体组织更为均匀。变质处理可有效的改善凝固过程中碳化物的生长形态。加铝镁合金复合变质，能促使碳化物生长界面形成富镁吸附薄膜，该薄膜的形成能有效的阻碍熔体中的Fe、C、Cr等原子的向碳化物生长界面扩散，从而抑制碳化物的长大，使碳化物细小、圆整且弥散分布，使其硬度HRC高达61时冲击韧性α_k提高到14.6J／cm~2。更多还原

【Abstract】 By means of altering chemical compositions and technology effects of nucleating and growing thermodynamic and kinetic conditions on morphology and distribution of carbides in high chromium white cast irons have been studied, expecting to discover the freezing mechanism and morphological characteristics of carbides, aiming to establish the theory foundations for the high chromium white cast irons with better mechanical performance. The results have been shown that:Chemical compositions have significant effects on the carbide morphology. The effects of silicon on carbides morphology have duality: on the one hand, silicon enhances the activity of carbon and accelerate its diffusion. Thus, the primary carbides morphology deteriorates with the increase of the silicon content; on the other hand, the carbon atoms enrich in micro-zone due to the exclusion between silicon and carbon atoms, which causes the increase of the nucleation rate of eutectic carbides. However, with the temperature reduction and the increase of silicon amount around eutectic carbides, the diffusion of carbon and silicon to the growing interface of carbides is restricted, and the growth of carbides is hindered correspondingly, thereby refining eutectic carbides; vanadium and titanium Micro-alloying can increase the heterogeneous nucleation cores, and the solvent titanium holds down the carbon diffusion, thereby hindering the growth of carbides, which is favorable to mechanical properties. When the amount of chromium (carbon) keeps constant, as the amount of carbon (chromium) increases, the amount of carbides increases whereas the impact toughness decreases, especially the increase of carbon amount.During the solidification of hypereutectic high chromium white irons, the nucleation and growth mechanism of carbides are changed by varying the melting and cooling conditions, aiming to improve its morphology. The superheating to 1600℃ can purify the molten metal and promote thermodynamic supercooling, leading to the refinement of carbides; When the cooling rate become larger, the nucleation rate increases, however, it is difficult for Fe, C and Cr atoms to diffuse to the growing interface of carbides, thereby restraining the growth of carbides and at the same time the whole microstructure becomes more uniform.Modification can effectively improve the carbide morphology of hypereutectic high chromium cast irons. The addition of magnesium and aluminum compound modification can promote to form a rich magnesium adsorbed film at the carbides growing interface. The film can effectively prevent the Fe, C and Cr atoms diffusing to the interface, which restrains the growth of carbides, and the carbides become fine, spheroidized and dispersed. The macrohardness can reach HRC 61 and α_k increases to 14.6 J/cm~2.更多还原