Mold electromagnetic stirring effect the quality of bearing steel casting
Because of the electromagnetic stirring (M - EMS) make the rotary motion of liquid steel in mold core, improve the heat transfer rate inside the mold, also have some other beneficial effects. (1) liquid core sports uniform liquid steel temperature, reduce the temperature gradient, is conducive to eliminate overheat, to improve the uniformity of the shell solidification;(2) close to the movement of liquid on the solid phase interface, make the solidification front of a large number of unstable dendritic crystal were transferred into the molten steel, part of the remelting, part of the formation of the growth of the isometric core slab of isometric zone expanded, improve osteoporosis and center segregation;(3) the electromagnetic force can enhance the class of shares, mould will be high temperature steel flow to the upper part, make the meniscus surface of initial solidified shell shortened, so that the vibration mark becomes shallow;To high stocks have mould inside the top of the "hot" conditions, also conducive to the protection slag melting and lubrication, prevent the surface crack;(4) stirring can also keep in the surface area of the slag and the large inclusions to clean up, to the protection slag, to obtain a clean surface.Electromagnetic stirrer in the current low frequency magnetic field penetration depth is big, high frequency penetration depth is shallow, stirring intensity increase with the increase of coil current.Only when low superheat casting, the use of mixing is good effect, or it will be hard to expand slab internal isometric zone, center segregation improvement effect is poor.Foreign studies show that electromagnetic stirring at the end of the solidification direction, two-way than one-way more conducive to the improvement of center carbon segregation.Validation tests also illustrates this point.The M - EMS, billet shell is evener, moreover, reduce slag quantity in the surface layer is helpful to the shell growth.Because of the slag have adiabatic effect, will hinder the growth of the shell.The S - EMS, the maximum value of carbon segregation, from 1.68 to 1.38.The F - EMS, can interrupt bridge, near the center of the well supply due to liquid steel needed for the solidification shrinkage.
