Coupling Effect Of Vibration And Heterogeneous Nucleation On Solidification Microstructure Of Ferritic Stainless Steel

Comparing with austenitic stainless steel,ferritic stainless steel has an obvious price advantage,and its cold-rolled products can be widely used in interior decoration,household electrical appliances and kitchen equipment.However,the coarse columnar crystals are easy to grow during the solidification of continuous casting,the textures with low deformability may be generated in the subsequent rolling process and then cause the formation of wrinkling and crack defects on the surface of the rolled products.Increasing the ratio of equiaxed grains in the solidification microstructure of casting is an effective method to decrease the surface defects.The methods to promote equiaxed crystal nucleation include the application of physical field,casting process controlling,chemical methods,and temperature field controlling,the effects of the above latter three methods are limited in the solidification process of high-melting ferritic stainless steel.At present,exerting mechanical vibration and adding nucleation agent can be used to control solidification microstructure of ferritic stainless steel,but the coupling effects of mechanical vibration and heterogeneous nucleation have not been reported so far.It is necessary to study the coupling effects of the two methods on the solidification microstructure of ferritic stainless steel.In this paper,Cr17 ferritic stainless steel was selected and three different treatment methods,such as mechanical vibration,adding Ti N heterogeneous nucleating agent,and the coupling of the both,were used to control the solidification process.The effects of experimental conditions on the solidification microstructure,mechanical properties and fracture morphology were studied,and their mechanisms were also discussed.The results show that it is effective for the three treatment methods to increase the ratio of fine equiaxed grains in the solidification microstructure,and the effect of the coupling treatment is the most significant.After the coupling treatment at a vibration frequency of 800 Hz,the average grain size of the sample decrease to 109?m,and the distribution density of equiaxed crystal grains increase from 8.9/mm~2 to 104.7/mm~2.The application of vibration can not only eject the TiN particles into the melt,but also promote the detachment of the primary crystal grains on the chilling generator surface.Moreover,the growing dendrites can be broken to form fine equiaxed grains in the melt which stirred by mechanical vibration.Three different treatment methods are helpful to improve the mechanical properties of the samples.After coupling treatment,the tensile strength of the specimen increase from 410.7 MPa(the original as-cast condition)to 828.1 MPa,the yield strength increase from 227.6 MPa to 359.4 MPa,and the elongation increase from 2.5%to4.16%.