(1180)A new method of optimization and inclusions control during a ladle treatment process of rail and rail wheel steels

摘要

Nonmetallic inclusions, which are present in a metal matrix in a significant amount, are known to be main sites of fatigue and tensile crack nucleation in the rail and rail wheel steels. The procedure of steel cleanliness control during the ladle treatment of steel by using a combination of a fractional gas analysis method and calculations was developed. It was shown that the new method allowed us to find the sources of origin of harmful oxide inclusions during the ladle treatment process, to predict their influence on the steel quality, and to adjust the technology. It was shown that the method can be successfully used for optimization of a ladle treatment process for different steel grades. The prospects of using barium contained master alloys for the deoxidation and modification of carbon steels are considered. The oxygen solubility is thermodynamically calculated in carbon steel melts for various deoxidizers, and the results of laboratory and industrial experiments on the deoxidation and modification of railroad rail and wheel steels are discussed. Using SEM and EPMA that average oxide inclusions size decreases substantially, we detected barium in inclusions smaller than 10 μm in size, which indicates a high degree of removal of coarse inclusions from a melt. Industrial experiments show that the use of barium bearing master alloys for the deoxidation and modification of wheel steel under mass production conditions leads to a decrease in the nonmetallic inclusion contamination of a metal, grain refinement, and an increase in mechanical properties of steel. The grain refinement of a metal induced by barium bearing master alloys was assumed to be related to the formation of a disperse phase along grain boundaries; this phase prevents the growth of primary austenite grains during heat treatment of the metal.