【作者】 孙华平；

【导师】 倪红卫；

【作者基本信息】 武汉科技大学 ， 钢铁冶金， 2008， 硕士

【摘要】 冷镦钢是一种生产互换性较高标准件的钢种,对连铸坯质量要求很高,铸坯表面缺陷和内部缺陷都容易引起后序加工时开裂或无法成型。本文针对武钢一炼钢厂生产的SWRM8方坯存在表面振痕和凹陷缺陷的问题,通过建立连铸方坯传热数学模型和保护渣道动态压力模型,分析了凹陷和振痕的形成过程及各工艺参数对凹陷和振痕形成的影响,提出了改善缺陷的措施。模拟计算分析表明:(1)在方坯连铸过程中,铸坯表面温度分布从边角部到中心先是急剧增加,然后趋于稳定。距铸坯边部20～40mm的地方出现表面温度的最高点,此区域坯壳凝固生长减慢,坯壳变薄,是整个横断面的薄弱区域。坯壳收缩不均导致的拉伸力和钢水静压力的共同作用,在该区域产生应力集中,凹陷开始形成。在二冷及空冷区,铸坯温度呈“波浪型”变化,温度的剧烈变化导致强的热应力,与钢水静压力、摩擦力和其它应力共同作用,使形成的凹陷发展扩大并可能导致裂纹等其他缺陷。(2)结晶器振动过程中,保护渣道压力呈周期性变化,进入负滑脱期时,渣道入口处开始受正压力作用,当产生的正压力大于钢水静压力时,初始凝固坯壳开始被推离结晶器壁,正压越大,负滑脱时间越长,初始凝固坯壳被压的越弯,振痕就越深。根据模拟分析结果,提出解决SWRM8方坯凹陷与振痕缺陷的措施如下:控制碳含量在0.08%以下,过热度稳定在30℃左右,拉速稳定在1.6m/min,采用中等冷却强度冷却,增大振动频率,减小振幅,建议使用h=3Vc,f=-10Vc+190高频小振幅的振动模式。更多还原

【Abstract】 Cold forging steel is used for producing higher standardized parts and components with interchangeability, which have high demands for the quality of billet.The surface and internal defects of billet can easily lead to a crack in the following processing or become hard to forming. This paper aims at resolving the existing surface defects of the oscillation marks and the depression in the SWRM8 billet produced by the NO.1 Steel-making Plant of WISCO. Analysis on forming and influencing factor of processing parameters for oscillation marks and depression has been done, through building mathematical heat transfer model and mould flux channel dynamic pressure model of the billet. At last, the article proposes the improvement defects measures.Simulation and analysis show: (1)The billet surface temperature distribution from the corner to the centre is rapidly increasing at first, and then stabilize in the process of billet casting. The highest temperature point occurs in the billet side area between 20 to 40mm distances, where the billet shell grow slowly, become thinner, So it is the weak area of the entire cross-section. The shrinkage force and the static pressure of molten concentrate both make the depression form. In the second-cooling area, the curve of billet temperature looks like wave. The strong thermal stress and the others stress all together makes the depression expand, that could engender crack or other flaws. (2)The mould flux channel pressure measures presents periodic change in the process of mould oscillation. When oscillation enters the negative strip time, the flux channel starts to be under the positive pressure. When the positive pressure is stronger than the static pressure of liquid steel, the initial solidification shell is pushed out of the mould wall. The oscillation mark becomes deeper with the increasing positive pressure and negative strip time that cause initial solidification shell being curved much.According to the simulation results, some suggestions have been proposed in order to solve the oscillation marks and the depression in the SWRM8 billet as follows: Controling the carbon content of molten steel below 0.08%, the superheat in about 30℃, the pulling speed at 1.6m/min, adopting medium cooling intensity, increasing the frequency of oscillation, reducing the amplitude of oscillation, and using the high frequency and small amplitude oscillating mode as h=3Vc,f=-10Vc+190.更多还原