Thermal and mechanical behavior of copper molds during thin-slab casting (II): Mold crack formation

Abstract

The formation of cracks in a funnel mold of thin-slab casting is investigated using metallographic studies and mathematical models. In Part II of this two-part article on thin-slab casting molds, short longitudinal cracks near the meniscus region of a thin-slab funnel mold are studied metallurgically. X-ray analyses revealed the formation of Cu-Zn brass on the copper matrix at high temperature where the crack initiated. Heat-transfer and thermal-elastic-viscoplastic stress models described in Part I are applied to investigate the temperature and stress fields associated with the cracks. Large cyclic inelastic strains were found in the funnel transition region just below the meniscus due to the slightly higher temperature at that location. The cracks then appear to have propagated by thermal fatigue caused by major level fluctuations at transitions. The stress and strain predictions suggest cycles to failure for molds for various hot-face temperatures. I. BACKGROUNDis fully closed. Won et al., [2] using a two-dimensional (2-D) coupled thermo-elasto-plastic finite-element model of con-JOONG KIL PARK, Graduate Student, and INDIRA V.Most previous research has focused on conventional cast-SAMARASEKERA, Professor, are with the Department of Metals and ing, which has relatively lower mold temperatures due to

Modeling of the continuous casting of steel—past, present, and future

“…Building on the early work of Brimacombe [37] , 3-D finite-element models of thermal distortion can now be extended to predict crack formation, including creep and plastic strain accumulated over many fatigue cycles [38][39][40] . An important application is the study of surface cracks in the copper plates near the meniscus of thin slab casting molds.…”

“…For example, Fig. 28 [40] shows short longitudinal cracks on the surface of a thin slab funnel mold, which formed beneath cracks in the protective Cr coating layer. This exposed the copper to Zn residuals in the steel that penetrated to form brass.…”

“…Figure 29 [40] shows the temperature and distorted shape of a thin slab mold during operation, from a finiteelement simulation developed to investigate this problem. To accurately model the thermal distortion, it is important to include the backing plate and water box, which adds rigidity to lessen the bending of the copper plates.…”

Heat Transfer in Funnel-mould Casting: Effect of Plate Thickness

“…Heat transfer in funnel moulds has been investigated in only a few previous studies, examining heat flux profiles, 1) mould distortion and cracking, [1][2][3] phenomena in the steel/flux interface, [4][5][6] and fluid flow coupled with solidification heat transfer. 7) Heat flux tends to be higher in thin-slab casting than in conventional billet or slab casting, which is attributed to the higher casting speeds.…”

Optimization design of wide face water slots for medium-thick slab casting mold

“…In order to assess the role of various process parameters impacting mold life, O'Connor and Dantzig developed a finite-element model to calculate the thermo-mechanical state in the mold and casting slab [4] . Thomas and Park et al applied a threedimensional finite-element model to predict temperature, thermal distortion, thermal stress and hot face cracks in a funnel shaped mold for casting thin-slab [1,[5][6][7] . Santillana et al applied a one-dimensional finite-element model to modify the 3D model, and predict temperatures for copper plates with different thicknesses [8,9] .…”