微米/亚微米双峰尺度奥氏体组织形成机制

THE FORMATION MECHANISM OF AUSTENITE STRUCTURE WITH MICRO/SUB-MICROMETER BIMODAL GRAIN SIZE DISTRIBUTION

通过冷轧变形结合变形后在820～870℃退火，在316L奥氏体不锈钢中实现了微米（3-5um为主）和亚微米（300-500nm为主）双峰晶粒尺度分布．在奥氏体冷变形过程中，形变孪生与应变诱导马氏体相变都集中发生于大变形阶段，据此推断奥氏体形变孪生是产生应变诱导马氏体的微观机制．在820-870℃范围内退火时，样品的硬度和晶粒尺寸分布几乎保持恒定．通过对退火过程中变形奥氏体和应变诱导马氏体演化驱动力的比较分析，推断奥氏体双峰尺度晶粒尺寸分布的来源是：微米尺度晶粒来自冷变形时未转变的变形奥氏体的再结晶，而亚微米尺度晶粒主要由应变诱导马氏体逆转变而产生．

Nano-crystalline （〈100 nm） and ultrafine grained （100-500 nm） materials have high strength and toughness, but its work hardening ability and uniform elongation decreased relative to the coarse grained material. Through the deformation, phase transformation and recrystallisation combination mode of development of bimodal grain size distribution of ferrite, bainite steel, the elongation rate is greatly improved. These studies are generally in order to improve the mechanical properties of material through change microstructure, but lack of study for the bimodal grain size distribution formation mechanism. This research work by cold rolling with annealing at 820- 870℃℃, in 316L austenitic stainless steel to achieve micro （3-5 um） and sub-micro （300-500 nm） bimodal grain size distribution. In the austenite deformation process, deformation twinning and strain induced martensite transformation occurred in large deformation stage. Accordingly inferred austenite deformation twinning is the micro mechanism of strain induced martensite. Annealing at 820-870 ℃, the hardness of the samples and the grain size distribution remains nearly constant. Through the comparative analysis of induced martensite austenite evolution driving force and strain deformation during annealing, determined the source of bimodal grain size distribution.The micro scale grains came from the recrystallization of deformed austenite in the cold deformation does not change, and sub-micron grain size is mainly composed of strain induced martensite reverse transformation.