Numerical Investigation On Thermo-mechanical Behavior Of Mold And Strand In Beam Blank Continuous Casting

As an economic section material, H-beam with its obvious mechanical andfunctional properties has been used in many fields of national economy developmentsince its first appearence. Beam blank is the idealist strand for H-beam production.Rolling H-beam by beam blank has some significant advantages, such as low energyconsumption, less process, high finished product rate and low cost. During beam blankcontinuous casting, there are many surface and inner defects in the strand which can notbe satisfied with the developing requirment of continuous casting technology innowadays. Therefore, studying on the thermo-mechanical behavior of mold and strandand researching on the key factors which shorten the mold service life and cause thedefects during beam blank continuous casting have great significance to the economyand science.Thermo-mechanical behavior of beam blank mold during continuous casting is oneof the key factors for the mold service life and product quality. In this paperthermo-elastic-plastic creep finite element models of beam blank molds were firstlyestablished, and the numerical method for the simulation of the cyclic process ofheating, casting and cooling were carried out. The user defined subroutines in ABAQUSwere developed to define the nonlinear material constitutive relationship and boundaryconditions. The distributions of temperature, distortion, and stress across the hot facesas well as the fatigue life of the two molds, the large hole mold and the small hole mold,were numerically simulated, based on which the influences of mold grinding thicknessand cooling water flow were discussed. The results show, there is a notable differencebetween molds with different water slot designs. The distributions of temperature anddistortion of the small hole mold are more uniform than those of the large hole mold,and the peak temperature of the former mold is smaller than that of the later mold.Increasing mold grinding thickness or cooling water flow is benifical for mold toachieve lower peak temperature and uniform temperature and distortion. An improvedwater slot design was proposed and it is superior to those molds by numerical analysis.It is also important for studying the solidification and distortion of strand duringmold to improve casting process and product quality. For simulating the solidificationand distortion of strand during mold, a method for the application of ferrostatic pressureon the front of solidification was proposed. By means of ABAQUS user defined subrountine UEL, a kind of ferrostatic pressure element shares the same nodes with thestrand element which was used to simulate the ferrostatic pressure on the front ofsolidification, was obtained. By means of GAPCON, the heat transfer between thestrand and mold was carried out. A transient thermo-elastic-plasitc finite element modelwas developed, and the influence of solutes microsegregation on material propertieswas taken into account. The distributions of gap between the strand and mold, strandand mold temperature, strand distortion and stress of two molds were obtained. Theresults show, gap is a key factor for the strand solidification, which must be controlled.The taper should be increased to reduce the gap in the flange tip, owing to the large gapand thin shell thickness.It is known that the surface temperature of the strand must be carefully controlledin the process because it is a key factor in inducing defects, such as internal and surfacecracks. Therefore, a three dimensional simulation method of moving heat tranferconditions was presented to calculate the solidification process of strand. The userdefined subroutines DFLUX and FLIM in ABAQUS were developed to apply thecomplex heat transfer boundary conditions. Based on the method, the temperaturedistribution of the strand was numerically investigated under original and improvedcooling schemes. The results show, the original cooling scheme could not meet themetallurgical principles of beam blank continuous casting. By the numerical simulationthat the uniformity of transverse surface temperature on cross-sections of the beamblank was improved, and better product quality was obtained after the improved coolingscheme was employed in the steel plant.