EFFECTS OF Ti AND Mn CONTENTS ON THE PRECIPITATE CHARACTERISTICS AND STRENGTHENING MECHANISM IN Ti MICROALLOYED STEELSPRODUCED BY CSP

Abstract

As an advanced manufacturing technology to produce hot rolled strips,compact strip production(CSP) process was developed at the end of the last century and has been widely applied due to its high efficiency and low cost.Compared with the traditional technology,the advantages of CSP technology benefit from the refinement of austenitic grains and precipitation strengthening in the steels.This is because cooling rate is higher during the solidification of slab and the direct charging slab temperature is also higher in the CSP process,resulting in much higher solute contents in the solid solution before hot rolling than expected by the experiences from traditional steel production. Therefore,the Ti microalloyed steels produced by the CSP process exhibit good performance and have drawn much attention to Ti precipitate behavior and strengthening mechanism.However,the influence of alloying element Mn on the Ti microalloyed steels produced by CSP.especially the synergistic effect of Mn and Ti,was rarely reported.Therefore,in this work the microstructure and precipitate characteristics of two Ti microalloyed steels with different Ti and Mn contents produced by the CSP process were studied by electron backscatter diffraction(EBSD) technology and high resolution transmission electron microscope(HRTEM).The results show that the steel with higher Ti and Mn contents has a higher fraction of small-angle grain boundaries.Furthermore,the weight fraction of TiC precipitates with particle size smaller than 10 nm increases significantly,from 7.6%in the lower Ti and Mn steel to 26.1%in the higher Ti and Mn steel.However,the amount of Fe_3C precipitates decreases markedly. In addition,the strengthening mechanism analysis of the two tested steels shows that grain refinement strengthening and dislocation strengthening make great contribution to the yield strength,while the precipitation strengthening is the primary reason for the difference in the strength between two tested steels.