Effect of niobium and rolling parameters on the mechanical properties and microstructure of dual phase steels

In this study, the effect of hot rolling parameters such as reduction percentage, rolling and coiling temperature on the microstructure and mechanical properties of dual phase (DP) steels with and without niobium was investigated. Melting process was carried out in an induction furnace. The casted products were forged and homogenized before rolling process. Three different reduction percentages (i.e., 15, 30 and 50%), two different rolling temperatures (950 and 850 °C) and two coiling temperatures (550 and 400 °C) were used. The results showed that rolling in dual phase region and coiling at low temperature led to the elongated grains in the rolling direction. Such elongated grains were not observed as coiling temperature increased. At a constant rolling and coiling temperature, increasing the reduction percentage increased the yield and tensile strength and decreased the total elongation. Additionally, specimens containing Nb had greater yield and tensile strength, higher martensite fraction, and lower elongation and ferrite grain size.