古代大马士革钢刀锻打花纹形成机制的理论分析

Theoretic analysis on the mechanism of particular pattern formed on the ancient Damascus steel blades

古代大马士革刀锻打花纹的形成机制是历史上持续数个世纪的热门研究课题.本文简要回顾了乌兹钢、大马士革刀和大马士革花纹的历史背景,着重介绍并分析了当代冶金研究者关于大马士革花纹形成机制的主要观点和争论,并通过现代冶金学热力学和动力学理论模型分析了这些主要观点,包括定量计算钢中S,P,V等元素对Fe-C平衡相图的影响、慢速凝固时S,P等元素的偏析程度、以及V(CN)粒子在奥氏体相区的析出温度以及V在高温退火时扩散动力学等.据此,作者提出了关于古代大马士革刀中花纹形成的新机制,即由于乌兹钢锭中凝固时S,P的枝晶偏析,导致凝固后偏析区形成硫化物或磷化物,尤其是磷的枝晶偏析导致冷却时形成磷化物与渗碳体的共晶体,在后续的加热过程中不能完全固溶,并作为热锻时析出的渗碳体析出核心,从而决定了渗碳体在大马士革刀中的空间分布和最终的大马士革花纹的形成.

What causes the specific pattern on the ancient Damascus steel blades has been a myth for centuries and is still a hot topic for the today＇s metallurgist. Although it has been studied and argued for centuries, the disputes on this topic still remain among the present metallurgists, which are summarized in this paper. Besides, histories of Wootz ingots, Damascus blade and Damascus pattern have been also reviewed respectively in details. With the help of modem metallurgy knowledge, we are now able to quantify all the possibly relevant factors by thermodynamic and kinetic calculations, such as influence of S, P and V elements on the Fe-C phase diagram, the dendritic microsegregation of S and P during a slow solidification, the temperature for precipitation of V（CN） in austenite and the diffusion kinetics of V during high-temperature homogenization. All of those factors have been considered as the possible perquisites for the formation of Damascus pattern. The thermodynamic and kinetics simulations indicate that the sulfide and phosphide, which precipitates at the segregated zone due to the slow solidification, may not be completely dissolved at the high-temperature solution treatment and then might act as the nuclei for the subsequent precipitation of cementite particles during hot hammering. In particular, the P-rich liquid, which is formed due to the segregation during solidification, may transform to eutectic product of phosphide and cementite. This is most likely responsible for the spatial distribution of cementite in Damascus blades and the formation of Damascus pattern.