Nucleation, growth and maturation analysis of MnS during solidification in axle steel ingots

Abstract

To reduce the non-compliance rate of magnetic particle detection of axles caused by large-size MnS inclusions, the formation, growth, and maturation of MnS in ingot of axle steel were calculated and analyzed based on the second phase precipitation theory and the numerical simulation of ingot solidification. The calculation results show that both the core size of the MnS nucleus and the size increase during the maturation process are in the nanometer. The growth of MnS throughout the solidification process determines the diameter of MnS particles after solidification. The theoretical calculation results show that in the riser, center, and bottom of the vertical center-line of the ingot, the corresponding MnS grew to a size of 156.35,107.37 and 94.96 μm, respectively, which is twice the size of MnS in continuous casting slab and consistent with the practice. The slow solidification process of the ingot is the direct cause of easy MnS growth, which is significantly different from the continuous casting process. Under the existing process conditions, in order to control the MnS size in axle steel ingot, it is critical to reduce the S content of the molten steel and control the S segregation. In order to control the MnS inclusions in the finished product of the axle not exceeding 1.5 grades, it is necessary to reduce w([S]) of the molten steel to below 0.004 3%.