In Situ Study Of The Factors Influencing The Solidification Process Of High Titanium Wear Resistant Steel

At present,the wear-resistant steel plate used for manufacturing coal mining equipment in China is relatively single and not reasonably differentiated,which leads to the situation that the same wear-resistant steel plate has a large difference in life in different coal mining working conditions,causing huge economic losses.The application of high titanium wear-resistant steel has a broad prospect,but a large number of frequent surface quality defects seriously restrict the production of cast billets,significantly reduce the production efficiency of continuous casting machines,and seriously restrict the expansion of China in the field of high titanium wear-resistant steel technology.The prevalence and multiplicity of surface cracks on cast billets can lead to steel leakage accidents and affect the smooth production of continuous casting machines.Not much research has be en done on the precipitation mechanism during the solidification of this high-titanium wear-resistant steel,so in-situ observation of the solidification process of high-titanium wear-resistant steel was carried out.By preparing the wear-resistant steel with 0.3-0.7%Ti element content in the laboratory,the possibility of precipitation of titanium-containing precipitates Ti N and Ti C in the liquid and solid phases and their growth kinetic conditions were firstly discussed by theoretical calculations in a wide range of chemical composition changes and cooling rates,and some measures that could control the precipitation of coarse Ti N were proposed.Then,the high-temperature laser confocal in-situ study of the high-titanium wear-resistant steels'high-temperature tissue evolution was carried out from the steel solidification tissue evolution,and the in fluence of the solidification tissue evolution behavior of high-titanium wear-resistant steels at different cooling rates,different chemical compositions an d different pouring temperatures was investigated.The main findings of the paper can be summarized as follows:(1)The solidification process of high-Ti wear-resistant steels with Ti N and Ti C in the liquid-solid phase precipitation possibility and the precipitation growth kinetic conditions were investigated by theoretical calc ulations.The thermodynamics based on the real-time equilibrium partition coefficients found that the solid phase rates in the paste zone corresponding to the precipitation of Ti N and Ti C in the liquid phase were 0.53 and 0.66,respectively.Increasing w₀[Ti]and w₀[N]would significantly increase the starting temperature of Ti N precipitation in the liquid phase;while incre asing w₀[C]would lead to a decrease in the temperature of Ti N precipitation in the liquid phase,but a decrease in the solid phase rate f _S.(2)In-situ observation shows that the growth of?-phase at low cooling rate is mainly influenced by the temperature and diffusion rate of solute elements,and increasing the cooling rate will intensify the enrichment of solute elements at the L/?interface front and increase the solute concentration gradient between the L/?interface front and the remaining liquid phase.The rapid increase in solute element concentration of local deviations at high cooling rates and the inhomogeneous solute distribution in the liquid phase are the main reasons for the changes in morphology and migration behavior at the L/?interface.The adjustment of the composition of the titanium content did not change the mechanism of the solidification phase transition generation in the high-titanium wear-resistant steel.In the moderate content range,the higher the titanium content the smaller the driving force and initial rate of L+???occurring;moreover,increasing the titanium content leads to a decrease in?-phase generation,prompting a decrease in the volume shrinkage produced by L??,???.In the scope of this paper,the change of pouring temperature does not change the mechanism of solidification phase change generation of high titanium wear-resistant steel,and it can be considered that the pouring temperature has basically no effect on the solidification process of high titanium wear resistant steel.