珠光体形核-长大理论的更新

The renewal of nucleation-growth theory of pearlite

现有的珠光体转变知识存在错误,因此,纠正错误、更新知识具有理论意义和应用价值.综合近年来的新成果,并且依据电子显微镜观察,进一步阐述了共析分解的新机制,对于"相间沉淀"机理做了新的解释,重申了珠光体的新概念.认为:珠光体是共析铁素体和共析渗碳体(或碳化物)构成的整合组织,不是机械化合物.珠光体的形核-长大是以界面扩散为主进行的相变.过冷奥氏体在一定过冷度下,将出现贫碳区和富碳区的涨落.加上随机出现的结构涨落、能量涨落,非线性的因果正反馈相互作用,在贫碳区建构铁素体核坯的同时,在富碳区也建构渗碳体(或碳化物)的核坯,共同组成珠光体的晶核(F+Fe3C).铁素体和渗碳体两相是共析共生,协同长大,不存在领先相."相间沉淀"是珠光体转变的一个特例,应用共析分解的新理论解释了"相间沉淀"机理.

It has practical value and theoretical significance to correct and renovate the knowledge of pearllte transformation. This article integated the new production in recent years, further expounded the new mechanism of eutectoid reaction, made the new explanation for the mechanism of the interphase precipitation and reiterated the new definiens of pearlite as follows： the pearlite is integration structure consisting of the ferrites（F） and the eutectoid cementites （Fe3C） or carbides, which is not the mechanical compound. The interphase diffusion predominates in the nucleation-growth of pearlite. Under the definite supercooling degree, the subcooling austenite will appear fluctuating in the poor-carbon areas and the rich-carbon areas. With the randomly appeared structure fluctuation and energy fluctuation, the non-linear cause and effect, and positive feedback interacting,the nucleus of cementites or carbides form in the rich-carbon areas at the same time the nucleus of ferrite are con- structed in the poor-carbon areas, building up the crystal nucleus （F ＋ Fe3 C） of pearlite together. The two-phase of ferrite and cementites is eutectoid and symbiosis,whose growth is synergistic without any one of them taking the lead. The interphase precipitation is one special case of pearlite transformation, so the new theory was used to explain the mechanism of interphase precipitation.