Effect of prestrain on tensile behavior of HS800 steel sheet

Abstract

With the development of advanced high strength steels like HS800 and HS1000, it is imperative to develop an understanding of their tensile properties. The effect of 0%, 5%, 7.5%, and 10% prestrain on the tensile behaviour of HS800 steel sheet was investigated in the current research. The optical micrograph of as received HS800 steels reveals the presence of ferrite grains with polygonal morphology without the presence of pearlite or cementite. Moreover, in higher pre-straining conditions, both polygonal and acicular ferrite phases are observed to coexist with the second phase (martensite/austenite). Tensile tests were performed on base HS800 steel sheets in three different directions (rolling, transverse, and diagonal), and it was found that the strength and ductility in the transverse direction were greater than the rolling and diagonal direction. Tensile strength had a linear relationship with the prestrain condition, whereas ductility had an inverse relationship. XRD analysis was used for phase identification and determination of dislocation density. A scanning electron microscope (SEM) was used to observe the ductile fracture behaviour in tensile specimens. The strain hardening exponent of HS800 steel was determined by comparing tensile data to Hollomon and Ludwik's mathematical equations. To understand the dislocation structure evolution of as received and various prestraining conditions samples, a transmission electron microscope (TEM) study was performed. The prestraining study of the HS800 steel gives a new horizon to high strength materials that can be utilized to design the current and future automobile industries requirements.