Materials Science & Engineering

Biography

Biography: Abdullah Qaban

Abstract

Control rolled steels are characterized by their excellent mechanical properties and are employed in many tough engineering applications. However, the cost factor and the unavailability of the control rolling facilities in most of the small steel plants make it necessary for researchers to explore alternative options. Hot rolling is cheaper than control rolling but the mechanical properties are poor giving inferior impact resistance and often lower strengths. The mechanical behaviour of hot rolled steels are affected significantly by their chemical compositions, thus understanding the role of alloying elements in steel and specifying their optimum quantity in the composition may give competitive steels which can replace the control rolled steels. In many cases, the improvement of strength is at the expense of impact behaviour and vice versa, and the key factor in balancing both properties is the chemical composition. Currently, many researchers have focused on Al as an addition to play a major role in improving both strength and impact behaviour. The work presented in this paper examines the effect of low and high Al content on microstructure and mechanical properties of hot rolled steel. The influence of control rolling has also been examined. In addition, the work will explore any additional benefits that can be achieved by the addition of Nb to the chemical composition. Previous works have found that a high Al addition to steels is beneficial to both strength and impact behaviour. In the current paper, high and normal low Al containing steel were examined to determinethe influence this higher Al addition has on the mechanical behaviour. Two rolling conditions were studied, hot rolled and control rolled. Nb was also added to the high Al containing steel to enable higher strengths more typical to that pertaining to control rolled steels. For the steels, a high N content was chosen so as to increase AlN precipitation and hopefully gain more grain refinement. It was found that high Al steel gave the best impact behaviour with an ITT of -90°C. This gave the lowest LYS of 290 MPa. The improvement of impact behaviour can be attributed to AlN precipitation and refinement of both grain boundary carbides and ferrite grain size. The present work shows that the addition of Nb to the high Al containing steels is very beneficial to strength giving a LYS of 385 MPa close to that given by someof the control rolled steels. However, poor impact behaviour was obtained and has an ITT of only 10oC. The improvement of strength is due to grain refinement and precipitation hardening by Nb while the deterioration of impact behaviour might is due to the martensite and bainite formation.