Effect Of Nucleation Stirred By Vibration On Solidification Of Ferritic Stainless Steel

Wrinkle is prone to a serious defect along the rolling direction in the molding process of ferritic stainless steels. Refinement of solidification structure is of vital for reduction in wrinkles defect. In order to obtain higher rate of equiaxed grains in the process of solidification, in recent years a new isometric inspire forming technology-the technology of nucleation in liquid metal excited by vibration was put forward. The nucleation in liquid metal excited by vibration technology was more concentrated in research on ammonium chloride solution and low melting point metal. The research content mainly involved the following three aspects, namely, nucleation behavior on the surface of the crystal nucleus generator, peeling behavior of the grains, melting behavior of grain in the superheated melt. There is a key problem needed to be solved that how to avoid the formation of the solidified shell in the superheated melt under the cooling effect of the crystal nucleus transmitter. It is necessary to further clarify the factors affecting the nucleation of the nucleation generator, the main source of stripping grain and the stripping mechanism under vibration condition.Based on the nucleation in liquid metal excited by vibration technology, nucleation process of Cr17 ferrite stainless steel with various pouring temperature,cooling intensity,vibration frequency and amplitude was considered. The mechanical models of dendrite fracture under vibration condition had been developed by mechanical analysis of grain nucleation primary phase on a chilling generator.The results indicated that the nucleation in liquid metal excited by vibration technology can promote grains refinement, especially refinement of columnar crystal.Vibration frequency had greatest effect on grain refinement, and pouring temperature and cooling intensity had minimal, which compared with amplitude. It is found that the force along the crystal growth direction of dendrites led to shear fracture, and the force perpendicular to the growth direction of dendrites led to bending fracture. The mechanical models indicated that the factors acting on the dendrites fracture include vibration frequency, amplitude and undercooling, in which the influence of vibration frequency is the largest. Vibration frequency had significant effects on the degree of grain refinement, amplitude on the range of grain refinement, and the intensity of cooling on the growth of the columnar crystal.