Precipitation Behavior Of MnS Inclusion In The Steel

Nowadays, the iron and steel materials play important roles in our national defense and economic construction. To meet the demand of the rapid development of economic construction, the performance requirement for the iron and steel materials is more and more strict. However, there are plenty of inclusions in steel, which can greatly affect the quality of steel products and limit the application of steel product. Therefore, some effective measures should be taken to reduce inclusions in the steel and promote the performance of steel products after having a deep insight into the formation and morphology of inclusions,In the present paper, the manganese sulphide inclusion in steel has been studied numerically by Fortran source codes with the thermodynamic software Thermo-Calc. The lever rule and Scheil model have been employed to calculate the liquidus temperature, the solidus temperature and the precipitation temperature of manganese sulphide inclusion, And the key factors to affect precipitation temperature of manganese sulphide inclusion is also discussed. Moreover, the morphology and number of MnS inclusion in the case of different carbon contents have been investigated by experiments. The research results are shown as follows:(1) Besides the elements Mn and S, the elements C and Si are the key factors to affect the liquidus temperature, the solidus temperature and the MnS precipitation temperature. On the base of the lever rule, with the increasing C content from0.13%to0.6%, the solidus temperature ranges from1463℃to1381℃, and the MnS precipitation temperature ranges from1465℃to1393℃. In the case of20Mn steel, with the increasing Si content from0.05%to0.45%, the solidus temperature ranges from1459℃to1449℃, and the MnS precipitation temperature ranges from1462℃to1452℃. On the base of Scheil model, with the increasing C content from0.13%to0.6%, the MnS precipitation temperature ranges from1426℃to1336℃.(2) The melting point of manganese steel and the MnS precipitation temperature decreases with the increase of the carbon and silicon contents.(3) The difference between the MnS precipitation temperature and the solidus temperature increases with the increasing carbon content.(4) The MnS precipitation temperature with oxygen in the steel is higher than that without oxygen in the steel.(5)With the increasing carbon content, the ratio of the spherical manganese sulphide in the manganese steel decreases, and the variation ranges from47.6%to0%. But the ratio of the massive manganese sulphide in the manganese steel increases, and the variation ranges from52.4%to100%.(6) With the increase of carbon content, the area of the manganese sulphide inclusion deceases.