薄板坯连铸连轧过程控制技术的发展、应用及展望

薄板坯连铸连轧面临品种和规格拓展、产品质量提升、生产成本降低及智能化生产等方面的改进以提升产线竞争力。从辊底式隧道加热炉智能燃烧系统、高精度轧制过程控制模型、兼顾全幅宽和多目标的板形综合控制技术3个方面，介绍了薄板坯连铸连轧过程控制关键共性技术的研发进展，并通过数据网关+双系统并行的在线替换模式，实现了新的过程控制技术零停机时间的工业应用。新技术应用后，加热炉实现了全自动烧钢，吨钢煤气消耗下降了19.4%，氧化烧损下降了3.8%，钢坯加热质量大幅度提升；在设备及其他系统不变的情况下，轧线产品质量及轧制稳定性显著提高，薄规格生产能力由2.0 mm扩展至1.2 mm，实现了双流异钢种交叉混合轧制和铁素体轧制，非计划过渡材显著减少，重点计划执行率由20%提高到95%以上，整体提升了薄板坯连铸连轧流程的效益和竞争力。最后，对薄板坯连铸连轧过程控制技术的发展方向进行了展望。     

高效方坯连铸生产工艺技术

连铸连轧是现在正在发展的技术之一,高温连铸坯控制是连铸连轧的基础。根据韶钢炼钢厂方坯连铸机高效工艺技术改进情况和国内外先进企业高效方坯连铸机的技术特点,分析了影响方坯连铸机拉速的各种因素,提出了提升方坯连铸拉速的措施。通过改进,炼钢厂方坯连铸最高拉速从2.8提升至3.5 m/min,满足连铸连轧的需求。对比国内外高速连铸机业绩,找出了提升方坯连铸机拉速的关键控制技术,为高效方坯连铸生产工艺技术奠定了基础。     

五流中间包稳态及非稳态试验

为改善国内某钢厂五流中间包流场,降低非稳态换包过程的负面影响,获得高品质洁净钢,通过水模拟试验进行稳态及非稳态换包过程的研究。试验结果表明,采用方案3的稳流器结构对该中间包稳态浇铸的流场更加有利,该试验条件下的死区体积比例为10.46%;非稳态换包过程的最佳工艺条件为换包液位350 mm、充包流量12 m3/h。     

大方坯连铸轻压下工艺技术开发与应用

连铸轻压下技术为改善铸坯内部质量,减少中心疏松、中心缩孔和中心偏析的重要手段。简述了连铸轻压下冶金技术的基本原理与主要控制参数。介绍了韶关钢铁(SGIS)大方坯连铸轻压下工艺技术开发方法,以及在研究过程中存在的问题和应用的效果。通过大方坯轻压技术的开发, 掌握了轻压下工艺控制方法与要点,以及轻压下工艺参数与铸坯中心疏松、中心偏析的关系。结果表明,大方坯连铸采用轻压下工艺,轴承钢内部质量得到明显的改善,其中轴承钢总压下量达到了12 mm。采用轻压下工艺后,低于1.5级的中心疏松比例提升了18.8%,中心偏析指数由0.877~1.247优化为0.944~1.038。研究结果为韶关钢铁开发高质量、高性能、高附加值的特钢产品提供了重要的技术支撑。     

Prediction of hot tearing susceptibility of direct chill casting of AA6111 alloys via finite element simulations

To predict hot tearing susceptibility (HTS) during solidification and improve the quality of Al alloy castings, constitutive equations for AA6111 alloys were developed using a direct finite element (FE) method. A hot tearing model was established for direct chill (DC) casting of industrial AA6111 alloys via coupling FE model and hot tearing criterion. By applying this model to real manufacture processes, the effects of casting speed, bottom cooling, secondary cooling, and geometric variations on the HTS were revealed. The results show that the HTS of the billet increases as the speed and billet radius increase, while it reduces as the interfacial heat transfer coefficient at the bottom or secondary water-cooling rate increases. This model shows the capabilities of incorporating maximum pore fraction in simulating hot tearing initiation, which will have a significant impact on optimizing casting conditions and chemistry for minimizing HTS and thus controlling the casting quality.     

The sound absorption performance of the highly porous silica ceramics prepared using freeze casting method

Highly porous silica ceramics with unidirectional pores were prepared using the freeze casting method. By adjusting the solid content and freezing temperature, the porosity of the ceramics was tailored in the range of 78.20%-84.59% and pore size in the range of 8.4-71.4 μm, respectively. Sound absorption properties of porous silica ceramics was studied and the effect of structural factors was systematically investigated. The results showed that higher porosity and smaller pores of the porous ceramics favored the sound absorption in the entire sound wave frequency. By backing the sample with small pore size porous ceramics, the sound absorption property was enhanced, particularly in the low and medium frequency range, thus the sound absorption peak shifted towards lower frequency. The presence of air gap in the back would also favor sound absorption in low and medium frequency range. The as-fabricated porous silica ceramics owed excellent sound absorption properties due to their unidirectional pores and low flow resistances.     

Pressureless ultrafast sintering of near-net-shaped superhard isotropic B4C/rGO composites with Ti-Al additives

Superhard composites of B₄C reinforced with randomly-oriented reduced graphene oxide (rGO) nanoplatelets are manufactured by a near-net-shape fabrication route based on three successive steps. Firstly, aqueous colloidal processing is used for the environmentally-friendly preparation of a semi-concentrated multi-component slurry (B₄C as main component, Ti-Al as sintering additive, and rGO as toughening reinforcement), whose suitability for wet shaping is demonstrated by rheological measurements. Secondly, slip casting is used to produce robust green parts with shapes on demand and microstructures free of macro- and micro-defects. And thirdly, pressureless spark-plasma sintering (PSPS) is used for the ultrafast and energy-efficient densification of the green parts with shape retention. Measurements of shrinkage and hardness, as well as the microstructural observations, are used to identify suitable PSPS temperatures leading to obtaining isotropic B₄C/rGO composites that are superhard and almost twice as tough as the monolithic B₄C ceramics.     

油气润滑对AZ80镁合金铸坯表面质量和组织的影响

本文以自主设计的镁合金油气润滑铸造装置制备了直径154mm的AZ80镁合金铸坯,系统研究油气润滑对AZ80镁合金铸坯表面质量和凝固组织的影响,并对其机理进行了探讨。采用结果表明:采用油气润滑铸造时,氩气和润滑油在石墨环内表面形成了一层油气混合膜,改变了熔体和结晶器的接触方式和热交换状态,从而制备出高品质的AZ80镁合金铸坯。随着气体压力的增加,铸坯表面粗大的偏析瘤和皮下偏析层得到抑制,凝固组织得到了明显细化。当气体压力增加到0.4 MPa时,铸坯皮下偏析层厚度从1252μm降至628μm,铸坯R/2、心部晶粒尺寸和二次枝晶间距显著减小。随着凝固组织的细化,Al、Zn和Mn元素的宏观偏析得到了改善。     

应用PMO提高连铸坯生产拉速及成分均匀性

为了实现电炉厂提产增效的目标,研究了脉冲磁致振荡(PMO)在提高铸坯生产拉速中的应用潜能。结果表明,优化PMO处理参数可以适应生产拉速提高的要求,并改善铸坯的中心偏析和宏观偏析。当连铸拉速提至1.05 m/min,PMO脉冲频率为1.16K_f Hz,峰值电压为1.00K_iV处理参数(K_f和K_i分别为仪器的放电频率和电压峰值)时, 铸坯横断面碳偏析指数可控制在1±0.05内;当连铸拉速提至1.15 m/min,PMO脉冲频率为1.28K_fHz,峰值电压为1.00K_iV处理参数时,铸坯横断面碳偏析指数可控制在1±0.07内。试验证明,在高拉速条件下通过保证单位时间内对钢液施加的脉冲能量可以使连铸坯质量得到有效改善。     

ZL104铝合金连杆半固态挤压铸造工艺实验研究

研究了传统液态挤压铸造与半固态挤压铸造成形ZL104铝合金连杆的充填状态、微观组织及力学性能。结果表明:传统液态挤压铸造成形连杆充填饱满,但其抗拉强度及伸长率低于半固态挤压铸造成形连杆。对于半固态挤压铸造成形,浇注温度高于565℃时,铸件充填性能良好;平均晶粒尺寸及形状因子随浇注温度的升高而逐渐增大;连杆抗拉强度及伸长率先增加后减小。挤压压力高于25MPa时,铸件均充填饱满;挤压压力升高,平均晶粒尺寸不断减小且形状因子不断增大,连杆机械性能不断提高。模具预热温度升高,平均晶粒尺寸和形状因子不断增大,连杆机械性能逐渐提高。但当模具预热温度超过300℃时,平均晶粒尺寸进一步增大而其形状因子减小,导致连杆的机械性能下降。