Effects of TiC on the microstructure and formation of acicular ferrite in ferritic stainless steel

The formation mechanism of acicular ferrite and its microstructural characteristics in 430 ferrite stainless steel with TiC additions were studied by theory and experiment.Using an"edge?to?edge matching"model,a 5.25 mismatch between TiC(FCC structure)and ferritic stainless steel(BCC structure)was identified,which met the mismatch requirement for the heterogeneous nucleation of 430 ferritic stainless steel.TiC was found to be an effective nucleation site for the formation of acicular ferrite in a smelting experiment,as analyzed by metallographic examination,Image-Pro Plus 6.0 analysis software,and SEM–EDS.Furthermore,small inclusions in the size of 2–4?m increased the probability of acicular ferrite nucleation,and the secondary acicular ferrite would grow sympathetically from the initial acicular ferrite to produce multi-dimensional acicular ferrites.Moreover,the addition of Ti C can increase the average microstrain and dislocation density of 430 ferrite stainless steel,as calculated by Williamson-Hall(WH)method,which could play some role in strengthening the dislocation.

Numerical investigation on melting characteristics of scrap with heat and mass transfers in molten steel

Herein,a numerical simulation with simultaneous heat and mass transfers is carried out to investigate the scrap melting characteristics in molten steel after model verification by published experimental data.The numerical results show that the scrap melting stages consist of the frozen shell formation stage,the frozen shell remelting stage and the parent scrap melting stage.The heat transfer coefficient and the carbon mass transfer coefficient between the scrap and the molten steel are,respectively,in the range of 4209-6249 W m^(-2) K^(-1) and 6.4×10^(-5) m s^(-1).Meanwhile,the effects of process parameters on scrap melting time were studied.An increase in the scrap preheating temperature(T_(scrap)),the molten steel temperature(T_(steel))and the carbon content of molten steel(C_(steel)),and a decrease in the scrap thickness dscrap,can reduce the frozen shell existence time,as well as the scrap melting time.On this basis,a quantitative relationship between the aforementioned process parameters and the scrap melting time is obtained to predict the formation of frozen shell(W),which provides process guidance for shortening the scrap melting time.The quantitative relationship is expressed as:lnΨ=311.32-2.34ln(T_(scrap))-39.99ln(T_(steel))-0.08ln(d_(scrap))-0.57ln(C_(steel)).