Application of reduction of area-temperature diagrams to the prediction of surface crack formation in continuous casting of steel

Abstract

A method is proposed for the prediction of surface crack formation in continuous casting, based on reduction of area (RA) functions measured by the tensile test. From the RA values a critical strain is deduced which is then compared with the strain developed in the surface of the strand. The latter is computed with a thermo-mechanical model. There is the fundamental difference in the tensile test and in continuous casting that in the first the deformation is carried out under conditions of constant temperature (D and strain rate whereas in the second, temperature and strain rate are transients. For the application of the RA(7~) function to the transient conditions a procedure is used that is known from the computation of continuous transformation diagrams from isothermal transformation diagrams (Scheil procedure) and from the computation of fatigue strength of machine parts. That is the strain developed in the strand surface during a time increment is weighted by division through the critical strain for rupture at the conditions existing during the time increment, and the weighted strains are then added up. Rupture occurs when the sum, or integral, attains a certain value. The method is applied to the prediction of transverse cracks on the slab surface of aluminum deoxidized carbon steel. © 2009 ISIJ.