连铸起步段液芯压下薄板坯的热-力行为分析

Thermomechanical Analysis on Continuous Casting Thin Slab With Liquid Core Reduction at Start-Up Stage

基于ALE算法和三维热弹黏塑性本构方程并考虑湍流的影响,模拟了连铸起步段低碳钢带液芯压下薄板坯的凝固行为、应力应变分布及变形情况。研究表明,薄板坯连铸液芯压下过程中对板坯的压缩作用主要由板坯中未凝固的部分(液芯部分)来承担,板坯凝固坯壳部分在板坯厚度方向的尺寸变化不大。连铸液芯压下过程中板坯不同位置处的应力不同,板坯在经过液芯压下辊前后,应力发生了较大的变化。在板坯近角部区域应力最大,窄面区域所承受的应力比宽面区域大。连铸液芯压下过程中板坯的等效应变与液芯压下量有关,液芯压下量越大,等效应变值越大,而且应变最大值出现在窄面,且随着时间而发生变化,在起步段的某一时刻(13.5s)应变达到最大值,此时更易接近板坯的临界等效应变,从而诱发裂纹等缺陷。研究证实了对带液芯压下薄板坯连铸起步段开展瞬态数值分析的必要性。

The transient temperature field, stress-strain field and deformation have been simulated at the start-up phase for a low-carbon steel thin slab with liquid core reduction by using three-dimensional thermo-elastic-viscoplastic constitutive equations, utilizing ALE algorithm to realize the grids movement and expansion and considering the turbulent fluid flow. It is shown that the compression role during liquid core reduction is withstood by the un-solidi- lied part, i.e. liquid core and the solidified shell thickness has no obvious change. Moreover, the stress distribution is different from different locations of a thin slab during liquid core reduction and stress will vary largely before and after the slab going through the liquid core reduction rolls. Near the corner of a thin slab, the stress is larger and the stress at the narrow face is larger than that of wide surface. The larger the liquid core reduction is, the larger the ef- fective strain is during the liquid core reduction in a steel continuous casting. The maximum strain is located at the narrow surface which will vary with the time. At a certain time （13.5 s） for a start-up period the effective strain will attain the maximum value, approaching the critical effective strain and easily inducing the crack defect, which can prove the necessity to carry out the transient simulation at a start-up stage for a steel continuous casting.