Effect of process parameters on microstructures and mechanical properties of a nano/ultrafine grained low carbon steel produced by martensite treatment using plane strain compression

Abstract

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. © 2012 ISIJ.