Abstract
This study evaluated the influence of plastic deformation during hot strip rolling in the size of TiN precipitates in an industrial Ti microalloyed dual phase steel. TiN is usually used for pinning austenitic grain boundaries during recrystallization and its efficiency depends on factors such as size of the precipitates and Ti precipitated fraction. During the slab reheating process, there occurs a partial dissolution of TiN precipitates that subsequently reprecipitates during the hot rolling process. However, this reprecipitation preferentially takes place at crystalline defects which act as nucleation sites. These sites increase with the amount of applied plastic deformation, resulting in smaller precipitates, due to the partial dissolution of larger particles or due to reprecipitation in the nucleation sites. Results indicate a reduction of about 28 % in the average size of the precipitates for samples extracted from hot bands (with deformation) and, therefore, a significant reduction in austenitic grain size, when compared with samples extracted from slabs (with no deformation).
Highlights
Steels are amongst the most important and useful of engineering materials because of their wide range of mechanical properties and low cost (Puskhareva, 2009)
In order to study the effects of deformation during hot rolling on the precipitation of titanium nitride (TiN), the analysis was done either on an industrial sample or on a sample obtained by simulation, both of them extracted from slabs or hot bands of the same heat at the steel shop
Ti present as TiN was obtained by a methodology that consists in extracting the precipitates of a sample through electrochemical dissolution, obtaining the total precipitation by weight difference and analysis of the Ti in TiN precipitates
Summary
Steels are amongst the most important and useful of engineering materials because of their wide range of mechanical properties and low cost (Puskhareva, 2009). In order to provide a steel-based solution that fulfills the automobile industry’s requirements, a great effort is being made to develop and apply a new class of steel, the so-called advanced high strength steels (AHSS), which combine good formability with high mechanical strength, to reduce the thickness of different parts of the automotive body in white (BIW) without performance losses and ensuring passenger safety (Tsipouridis, 2006). Dual phase (DP) is a class of high strength low alloy steels characterized by a microstructure consisting of martensite and ferrite. This, might be done at the expenses of ductility and elongation Another way to increase strength of such steels is to add dispersoid-forming elements, such as titanium, to the steel melt which would form small precipitates and hinder dislocation movement in ferrite (Saikaly et al, 2001). The objective of this work, was to study the effects of deformation during hot rolling on the precipitation of titanium nitride (TiN) in an industrial Ti microalloyed dual-phase steel, adopting two different soaking times in the reheating furnace
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