【作者】 罗高强；

【导师】 唐萍；

【作者基本信息】 重庆大学 ， 冶金工程， 2007， 硕士

【摘要】 常规板坯连铸技术经过几十年的发展,已日渐成熟,高速化、高效化成为当今板坯连铸技术发展的目标。由于低拉速常规稳态浇注相对容易控制,铸坯质量能够得到保证,但高拉速非稳态条件的产品质量还存在很多问题。因此,针对高拉速和非稳态条件铸坯质量的研究具有重要意义。结晶器作为连铸机的心脏,对连铸表面质量的控制起着至关重要的作用。本文以梅钢2#板坯连铸机为研究对象,针对结晶器非稳态和高拉速下存在的铸坯质量问题,进行了现场调研,获取了铸机基本参数及相关浇注条件的控制标准。在取了大量铸坯样离线进行低倍硫印检测之后,对铸坯表面及皮下取金相样进行显微观察,统计单位面积夹杂物含量。为进一步评估铸坯质量水平,对其全氧量进行了分析。此外,本文针对梅钢2#铸机建立了结晶器内的钢液流动的数学模型。在对模型进行验证的基础上,对不同断面、拉速、水口插入深度下的钢液流动形态,结晶器内气泡与液渣层分布及偏流状态下的流动行为进行了模拟,为铸坯质量的控制提供理论及实践依据。铸坯质量研究表明,梅钢铸坯质量整体处于中等水平,表现出来的缺陷主要是夹杂和气孔。其中,夹杂物多为50μm以下的球状Al2O3或者铝酸盐,而气孔则主要是由吹氩导致,多分布于铸坯窄面。开浇、浇注末期、拉速变化等非稳态过程对铸坯质量影响很大,换大包、换浸入式水口等对铸坯质量的影响相对较小。非稳态夹杂物含量是稳态条件的2~6倍,全氧量比稳态条件铸坯高三分之一。头尾坯质量都差于正常坯,夹杂物含量比正常坯高26%以上,但越接近正常坯,质量越好。根据评估结果,尾坯倒数第二块坯可不用降级处理。数值模拟显示,拉速为1.8m/min时,常规断面窄面附近较大面积无液渣分布,在1300mm×210mm断面条件下,结晶器液面流速达到0.34m/s,须采用电磁制动或降低拉速来控制液面流速。当拉速达到1.2m/min时,结晶器窄面液渣很薄,此时需要采取电磁制动等措施以保证必要的液渣层厚度。偏流易导致液面流动不对称,从而形成漩涡,并导致卷渣。小粒径气泡、50μm及以下脱落的结瘤物和夹杂物,其跟随性好,容易随流股到达结晶器窄面和下部形成缺陷。更多还原

【Abstract】 After several decades’ development, the conventional slab continuous casting technology has been sophisticated gradually. High casting speed and high efficiency become the goal. Due to the easier control in low casting speed, the slab quality can meet the requirement. However, high casting speed and unsteady casting easily lead to product quality problems. Therefore, it’s significant to research the slab quality on high casting speed and unsteady conditions.As the heart of a caster, continuous casting mold plays a crucial role in slab surface quality control. No.2 caster of Meishan Steel was regarded as the research object in the paper. And the industrial investigation was executed to handle the slab quality on unsteady and high casting speed conditions. It also obtained the basic caster parameter and control criterion of the related casting processing. After an amount of slab samples were detected off line by sulfur print and macroscopic examination, small samples were taken from the slab surface, and the quantity of inclusions per unit area ware counted. In order to evaluate the quality of slab, the total oxygen(T[O]) content was measured. Furthermore, this paper constructed the mathematic model,which would be used to simulate the liquid steel flow in mold of Meishan Steel No.2 caster. Based on the model, this paper simulated the flow behavior of liquid steel, including in different section, casting speed, SEN depth, distribution of bubbles and molten slag layer, and the bias flow etc. It would provide a theoretical and practical foundation for the slab quality control.The slab quality study shows that, as a whole, the slab quality at Meishan Steel is placed at a mid-level. The main defects are inclusions and pinholes. The most of inclusions are indigenous Al2O3 and aluminate, and the pinholes caused by argon injection mostly distribute in narrow face. Several unsteady conditions, such as casting start, end and casting speed variation, affect the slab quality greatly, and the influence of laddle exchange ,SEN change, SEN clogging is relative low. The content of inclusion on unsteady conditions is 2-6 times of that on steady conditions. And the T[O] on unsteady conditions is 1.33 times of that on steady ones. Otherwise, the quality of beginning and tail slab is worse than normal ones. The former inclusion content is 26% higher than the latter. Based on the evaluation, the last second slab needn’t to be degrade.Numerical simulation shows, when casting speed is 1.8m/min, normal section, near narrow face, there is not flux layer in a large area. And in section 1300mm×210mm, the flow rate in surface level reaches 0.34m/s. So, it should control the surface flow rate by EMBr or decrease casting speed. when casting speed is 1.2m/min, molten slag layer is thin in narrow face, and need to be improved by EMBr. Bias flow is easy to generate asymmetry flow and vortices. What’s worse, it will induce slag entrapment. The fine bubbles, desquamation clogging and inclusions easily follow the stream and reach the narrow face and bottom of mold. It’s easy to induce defects.更多还原