Influence of Carbon Content and Deformation Temperature on Ultra-Grain Refinement of Plain Carbon Steels by Means of Torsion Test

The effect of carbon content and deformation temperature on ultra-grain refinement of two plain carbon steels was studied. The steels samples were severely deformed by means of warm torsion tests. For both steels, the final microstructure consisted of ultrafine ferrite grains and small dispersed cementite particles depend on the test temperature. Increase in carbon content led to a decrease in the average ferrite grain size due to the presence of a higher volume fraction of cementite particles. Increasing in deformation temperature led to an increase in ferrite grain size. In addition, a critical strain for ultra grain refinement was reached for both steels. This critical deformation represents a minimum accumulated equivalent strain beyond which further significant grain size refinement is not more achievable. The higher the C content, the smaller this critical deformation was.