Adding
rare earths into permeating agent has an obvious catalytic effect on vanadizing on steel surface, and the vanadizing
rate can increase by about 30%～40%. The case depth ( x ) of the samples which has undergone different periods of
vanadizing time at 950 ℃ was measured. These depth values ( x ) and its corresponded time ( t ) were substituded into the experience formula, x n=Kt (ln x=(1/n) ln K+(1/n) ln t ), and were processed by mono linear regression. It is found that x and t have the relationship of x 2=Kt . Addition of rare earth can promote reaction of the permeating agent, and therefore increase vanadium potential of the agent. Rare earths, as a strong reductant, makes the oxide on the steel surface reduce, and thus activates the steel surface. Permeating of rare earths into steel and the VC layer increase the crystal fault density, and, together with its excellent chemical activation, makes carbon atoms diffuse easily. These functions of rare earth can decrease the
diffusion activation energy of the carbon atoms, and therefore has catalytic effect on permeation.