Study on role of dynamic recrystallization in fine-structure superplasticity.

为了阐明双相不锈钢（Fe-25%Cr-7%Ni-3%Mo）和高碳钢（Fe-1%C-1.4%Cr）在超塑性流动中的变形机理和动态再结晶作用，研究了超塑性流动过程中的组织变化。主要研究结果如下：在双相不锈钢中，通过热处理获得了由细小铁素体和奥氏体晶粒组成的微双相组织。拉伸变形前的铁素体基体为亚晶，铁素体/铁素体晶界为低角度晶界，不适于晶界滑动。在1273K和ε =1.7x10^<-2>/s条件下，具有这种微双相组织的试样的伸长率超过1700%。变形初期，铁氧体基体发生动态再结晶，铁氧体/铁氧体界面转变为大角度界面。铁素体再结晶后，变形过程中铁素体和奥氏体两相几乎没有位错，表明晶界滑动是该钢超塑性流动的主要方式。结果表明，动态再结晶的作用是在变形初期使组织适合于晶界滑动。在923K温度下，经90%热轧，珠光体转变后的高碳钢获得了带有球化渗碳体颗粒的铁素体晶粒组织。温轧90%后，铁素体晶粒仍以亚晶为主。超塑性变形后，铁素体晶界为大角度晶界。结果表明，在变形过程中，铁素体相发生了动态再结晶，成为晶界滑动的合适组织。

Structural change during superplastic flow has been studied in order to clarify the deformation mechanism and the role of dynamic recrystallization in superplasticity of a duplex stainless steel (Fe-25%Cr-7%Ni-3%Mo) and a high carbon steel (Fe-1%C-1.4%Cr). Main results obtained are as follows.1. A microduplex structure with fine ferrite and austenite grains (about lmum) was obtained in the duplex stainless steel by thermomechamical processing. Ferrite matrix before tensile deformation were subgrains and ferrite/ferrite boundaries were low-angle ones and unsuitable for grain boundary sliding. The specimen with this microduplex structure showed, however, over 1700% elongation at 1273K and epsilon=1.7x10^<-2>/s. In the early stage of deformation, dynamic recrystallization took place in ferrite matrix and ferrite/ferrite boundaries changed to high-angle ones. After the recrystallization of ferrite, dislocations were scarcely observed in both phases of ferrite and austenite during deformation, indicating that grain boundary sliding is the predominant mode of superplastic flow in the present steel. It was concluded that the role of dynamic recrystallization is to make the structure suitable for grain boundary sliding in the early stage of deformation.2. A fine ferrite grain structure with spheroidized cementite particles was obtained in the high carbon steel by warm rolling by 90% at 923K after pearlite transformation. Most of ferrite grains were subgrains even after 90% warm rolling. After superplastic deformation, ferrite grain boundaries were high-angle ones. This result suggests that ferrite phase dynamically recrystallized and became the suitable structure for grain boundary sliding during the deformation.