Method for enhancing the self-feeding ability of a heavy section casting blank

Abstract

The present invention relates to the field of casting blank manufacturing, in particular to a method for enhancing the self-feeding ability of a heavy section casting blank, which can solve the problems of poor centre quality, surface crack and high rejection rate of the heavy section casting blanks in the prior art. By controlling the outer cooling conditions of different solidification stages of the casting blank, the present invention quickly solidifies and crusts the outer surface of the casting blank to increase the strength and prevent surface crack at first, and then performs thermal insulation on the casting blank surface such that large area of the core forms the mushy region such that the solidified layer of the casting blank surface is maintained at a relatively high temperature to facilitate realization of the plastic deformation, thus realizing synchronous solidification and solid movement in the subsequent solidification and shrinkage processes of the casting blank, fulfilling the aim of radial self-feeding of the high-temperature deformable metal, eliminating the inner shrinkage voids and surface crack, and obviously eliminating the inner shrinkage of the casting blank. The present invention is applicable to the heavy section metal castings, in particular to the round and square heavy section casting blanks which have a large height-diameter ratio and cannot eliminate the axis shrinkage pipe through the feeder head.

1 . A method for enhancing the self-feeding ability of a heavy section casting blank, wherein: after metal pouring, immediately force-cooling the casting blank surface to quickly solidify and crust the casting blank surface;
 then, performing thermal insulation on the casting blank surface with a thermal insulation material or a heat cover for reducing the intensity of heat exchange between the casting blank surface and the environment;   raising the temperature of the casting blank surface by latent heat in the casting blank core and reducing the radial temperature gradient of the blank to enable the casting blank core to form a large mushy region synchronously and promote the synchronous solidification of the casting blank core;   when the casting blank core is solidified synchronously, the casting blank surface is still in a high temperature state, enhancing the self-feeding ability by the action of the tensile stress generated by solidification and shrinkage of the core;   after the casting blank core is completely solidified, de-molding at a high temperature, and then performing slow cooling or high-temperature annealing.   
     
     
         2 . The method for enhancing the self-feeding ability of a heavy section casting blank according to  claim 1 , wherein, after pouring the liquid metal, immediately forced-cooling the outer surface of a casting blank by means of water cooling, direct water spraying, fog spraying or blowing; when the temperature of the outer surface of the casting blank is reduced to 800˜1000° C. and the thickness of the solidified layer reaches 5-30% of the thickness or diameter of the blank section, stopping forced-cooling the outer surface. 
     
     
         3 . The method for enhancing the self-feeding ability of a heavy section casting blank according to  claim 1 , wherein, when the thickness of the solidified layer reaches 50-300 mm, forced-cooling of the outer surface of the casting blank is stopped. 
     
     
         4 . The method for enhancing the self-feeding ability of a heavy section casting blank according to  claim 1 , wherein, controlling the cooling conditions of the outer surface of the casting blank to keep the outer surface of the casting blank at a temperature of 200˜400° C. below solidus, so the solidified layer of the outer surface of the casting blank stays in the plastic deformation region with a low deformation resistance. 
     
     
         5 . The method for enhancing the self-feeding ability of a heavy section casting blank according to  claim 1 , wherein, when the liquid metal of the core is solidified synchronously, solidification and shrinkage generate a radial tensile stress which is acted on the high-temperature solidified layer of the outer surface, so the solidified metal generates plastic deformation and plastically moves from the outer surface to the casting blank centre, thus realizing radial self-feeding of the casting blank. 
     
     
         6 . The method for enhancing the self-feeding ability of a heavy section casting blank according to  claim 1 , wherein, for high-temperature de-molding, the de-molding temperature required by the casting blank is bigger than 800° C. 
     
     
         7 . The method for enhancing the self-feeding ability of a heavy section casting blank according to  claim 6 , wherein the de-molding temperature required by the casting blank is preferably 850-1,200° C. 
     
     
         8 . The method for enhancing the self-feeding ability of a heavy section casting blank according to  claim 1 , wherein the slow cooling is performed after the casting blank is de-molded at a high temperature, and the cooling speed is smaller than 50° C./h. 
     
     
         9 . The method for enhancing the self-feeding ability of a heavy section casting blank according to  claim 8 , wherein the cooling speed is preferably 10-30° C./h. 
     
     
         10 . The method for enhancing the self-feeding ability of a heavy section casting blank according to  claim 1 , wherein after the casting blank is de-molded, the high-temperature annealing temperature is bigger than 800° C., and the annealing cooling speed is smaller than 50° C/h. 
     
     
         11 . The method for enhancing the self-feeding ability of a heavy section casting blank according to  claim 10 , wherein the annealing cooling speed is preferably 10-40° C./h. 
     
     
         12 . The method for enhancing the self-feeding ability of a heavy section casting blank according to  claim 1 , wherein the method is applicable to square or rectangular continuous casting blanks with a thickness of over 400 mm, round continuous casting blanks with a diameter of over 500 mm, and molded wide and thick slabs (special slabs) with a thickness of over 600 mm. 
     
     
         13 . The method for enhancing the self-feeding ability of a heavy section casting blank according to  claim 2 , wherein, when the thickness of the solidified layer reaches 50-300 mm, forced-cooling of the outer surface of the casting blank is stopped. 
     
     
         14 . The method for enhancing the self-feeding ability of a heavy section casting blank according to  claim 1 , wherein after the casting blank is de-molded, the high-temperature annealing temperature is 850° C.-1100° C. and the annealing cooling speed is smaller than 50° C./h. 
     
     
         15 . The method for enhancing the self-feeding ability of a heavy section casting blank according to  claim 14 , wherein the annealing cooling speed is preferably 10-40° C./h.