2012 年 52 巻 3 号 p. 464-470
In this work, the martensite treatment consisting of cold deformation by plane strain compression and subsequent annealing was used for producing the nano/ultrafine grained structure in a low carbon steel. The equivalent strain was varied from 0.1 to 2, while the annealing process was carried out in the temperature range of 400–600°C for 0–180 min. The microstructural evolution and mechanical properties of the as-deformed and annealed specimens were investigated. The results showed that in the as-deformed specimens, increase in strain intensified the volume fraction of the martensite cell blocks and consequently the strength. Fully equiaxed nano/ultrafine grained ferrite was developed from the martensite cell blocks during the annealing at warm temperature around 500°C for sufficient time lengths. It was concluded that the final multi-phased microstructure composed of ultrafine ferrite grains, block-tempered martensite, and fine cementite precipitates was responsible for the obtained superior mechanical properties.
