THE INVESTIGATION OF THE UNINTERRUPTEDLY-CASTED BILLETS OF SMALL CROSS-SECTION WITH THE SHAPE DEFECT «RHOMBOIDITY» DEFORMATION PROCESS IN BOX PASSES

Abstract

The purpose of the present investigation is technological capability evaluation of obtaining of high quality semifinished rolled products from uninterruptedly-casted billets with great value of the «rhomboidity» and «diagonal cracks» without reaching the surface of billet. Design/methodology/approach. The finite element method is used as a method of investigation. The mathematical model realization is executed using the software DEFORM 3D. The validation of the finite element model is executed according to the actual data of metal forming of uninterruptedly-casted billets with cross-section 135×135 mm in breakdown mill of linear medium-section mill with diameter of forming rolls 500 – 600 mm according to the acting strain-rate and temperature technological regulations. Billets with different value of the initial «rhomboidity» (Δd) were rolled in the course of the experimental-industrial rolling. During the execution of calculated investigation with the help of the developed mathematical model, two variants of the deformation schemes were examined. The first variant is based on the well-known scheme of rolling on the flat body of forming rolls. The difference consists in the fact that instead of rolling on the flat body, rolls were used with box passes. The function of box passes consists in prevention the loss of billet stability (dumping) at the expense of fixation (clamping) only in the corners of the pass (the corners between the base of a groove and outlet of pass) and limitation absence of the transverse flow of metal. According to the second variant, the mathematical simulation of uninterruptedly-casted billets rolling process is executed according to the operating roll pass design of breakdown mill. The realization of calculated experiment, which provides for different variants of billet rolling with value of the «rhomboidity» 20 mm in box pass with billet rotation along the longitudinal axis with limited rotation possibility and without it, is executed. The mathematical simulation for non-stationary thermal conditions of billet is executed. Rheological curves and thermophysical properties of steel (%C = 0,42…0,50; %Mn= 0,17…0,37; %Si= 0,50…0,80; %Cr<0,25) are accepted in accordance with reference data. Dimensions of the «diagonal cracks» are accepted on the basis of an average statistical data of the template cross-section analysis, obtained from the billets of current production, casted in the conditions of high-speed continuous casting machine. Findings. The character of metal forming in the course of uninterruptedly-casted billet rolling with great value of the «rhomboidity» and «diagonal cracks» is determined. The technological regimes of rolling, providing a guaranteed roll bite, obtaining required shape of semi-finished rolled products and minimization or partial welding of the «diagonal cracks» without reaching the surface of feed is defined. Value. Results of this paper have perspective of practical application, provided improvement of production technology of rolled section steel of uninterruptedly-casted metal, on linear rolling mills and on modern continuous rolling mills.