The Research Of Si-Mn Hot Rolled Dual Phase Steel In FTSR

According to the designing steel grades of low Si-Mn containing Nb,Ti, this paper carry out an experiment on hot-rolled dual phase steel in the condition of laboratory by the method of continuous and two steps cooling modes, through the controlling technological parameters, obtained the hot strip fine grain dual phase steel which have martensitic structure evenly distributed in the fine ferritic matrix, besides lower yield ratio and the tensile strength 550MPa, the influence of technological parameters on the microstructures and mechanical properties of the dual phase steel have been discussed, and the influence of technological parameters on the separation of the Nb,Ti, carbonitriding compounds have also been discussed. All of the above works provide theory foundation for the industrial production.The main research work and achievements are as follow:1.In-order to realize low cost hot-rolled dual phase steel, by the method of low C, containing Si-Mn, low content of Nb,Ti, a method of the production of hot rolled dual phase steel suitable for FTSR has been designed. In this method the hot strip dual phase steel with the content of Nb 0.02%, Ti 0.013% and having the tensile strength grade of 550MPa, up to good microstructures, better property can be obtained.2.Through Using the MMS-200 test machine, the experiment of the continuous cooling transformation of austenite in the condition of no-deformation and different deformation have been carried out, and the static and the dynamic CCT curves have been drawn, which provide theory foundation for the hot rolled of the dual phase and the controlled cooling technology.3.The method of continuous and two step cooling modes are adopted respectively, and the rolling experiment of the two kinds of steel are carried out in the laboratory, and the fine microstructures of the obtained typical samples are observed and analyzed respectively.4.The in situ tensile testing on the typical samples after hot rolling has been carried out in the SEM, and the crack inititation and expansion of dual phase steel has been studied.5.On the basis of hot-rolling experiment in lab, the industrial experiment in the BX STEEL FTSR has been carried out, it is obtained the ferrite and the martensite dual phase microstructures and the hot-rolled dual phase steel which have the yield strength over 450MPa, ultimate tensile strength over 700MPa, elong over 24%, and good mechanical properties.Through analyzing the influence of technological parameters on the microstructures and mechnical properties, it is obtained the better technological parameters of the hot rolled dual phase steel which have the low content of Si, Mn and containing Nb, Ti, and among all of the above factors, the finishing temperature and coiling temperature are especially important.