【作者】 胡明谦；

【导师】 沈峰满；

【作者基本信息】 东北大学 ， 钢铁冶金， 2010， 博士

【摘要】 随着我国国民经济的发展,各行业对钢材的需求越来越大,对钢材质量的要求也越来越高。连续铸钢是钢材生产流程中的重要环节,控制连铸钢坯质量,对提高最终产品质量具有重要的意义。本钢炼钢厂从1993年开始实施大规模设备改造,通过技术与装备的革新,产品种类逐年增加,质量逐步提高。然而,与国际、国内先进企业相比,在产品成份、性能、外形、尺寸精度等方面尚存在一定差距。本研究以本钢现有工艺条件为基础,围绕提高汽车板和高强钢铸坯质量,包括铸坯成分控制、内部质量控制、表面质量控制等展开一系列研究。主要内容如下：(1)铸坯高温塑性是与铸坯质量有关的重要参数。本研究选取本钢主要钢种(SPHC、DC01、A36-2、S235-JR、CRA2、DC53D+Z、BG420CL、Q235B)的连铸板坯,在Gleebe-2000型热模拟试验机进行700℃、750℃、800℃、900℃、1000℃、1100℃、1200℃、1300℃高温拉伸实验,测定各温度条件下的真应力-应变曲线,并确定其临界应变,掌握各钢种高温塑性特点。对所选择的中、低、超低碳钢和微合金钢钢种进行高温塑性模拟研究,测定其高温面塑率、零强度温度及脆化温度区间,分析并提出了适宜的板坯出结晶器及矫直温度,各钢种的合理拉坯速度,为优化工艺参数提供了理论依据。(2)连铸坯缺陷中约80%为铸坯裂纹。铸坯出现裂纹,既影响连铸机生产率,又影响产品质量,增加生产成本。论文分析了本钢高强钢铸坯产生裂纹的成因和特点,提出应严格控制钢中S质量分数、根据钢种选取过热度、调整拉坯速度和拉矫压力等措施,并进行了试验验证,提出钢水w[s]应控制<0.020%,w[Mn]/w[S]≥20,钢水过热度在30℃左右,拉速不超过1.2m/min;高于此拉速时,对过热度、二冷水分配进行调整；连续弯曲连续矫直,控制铸坯矫直温度≥900℃；在确保坯壳生成良好的前提下,相应减少一冷强度；合理匹配各区配水比例。根据试验结果,对车轮用钢(BG420CL)的连铸工艺参数进行了优化。兼顾本钢生产实际和铸坯质量要求,优选拉坯速度为1.0m/min;确定结晶器和二冷水适宜配水比例；通过添加稀土,夹杂物球化率提高到87.21%以上,铸坯质量显著提高,达到生产要求。(3)连续铸钢铸坯表面的实物质量水平,直接关系到后序产品的成材率。本钢连铸机自投产以来,铸坯表面裂纹缺陷一直困扰着铸机生产。论文采用六西格玛方法,对连铸过程中各参数进行分析,提出铸坯表面裂纹主要与钢种成份、结晶器振动及水量配比、二次冷却区、铸机辊子状态等因素有关,其实质是结晶器内部诱发形成,在二次冷却区扩展的过程；通过调整结晶器振幅、冷却水量、改变二冷配水模型、控制钢水中的N、S元素,有效控制了铸坯表面裂纹的发生,改善了铸坯质量。(4)对本钢现有技术装备和生产技术水平进行分析,确定了高级汽车板坯生产的工艺技术流程,制定了包括铁水预处理、炼钢、钢包处理、精炼、连铸、铸坯清理等各个工序的质量控制指标,为生产出合格的高级汽车用板连铸坯打下基础。(5)要获得高延展性、高r值以及优良表面性能的高级汽车板坯,要求钢中含碳、氮、氧量尽可能低,钢材铸坯侧面和角部振痕尽可能少。论文应用六西格玛管理方法对影响连铸过程的增碳因素进行分析,确定了影响增碳的主要因素为钢包砖衬、开浇渣种类、保护渣种类；在生产中采取了使用无碳砖衬钢包、无碳开浇渣、低碳结晶器保护渣等措施,铸坯增碳量显著降低,超低碳钢连铸工序增碳量小于0.0003%。论文分析了影响连铸过程的增氮因素,采取了改善密封圈密封、改进中包渣密封效果、改进中间包氩气密封等措施,增氮控制平均水平达到2.8×10-6,合格率达到90.7%,效果明显,经济效益显著。通过本文的研究,本钢炼钢厂高强钢和高级汽车板用钢的连铸工艺进一步完善,其中高强钢铸坯内部缺陷和表面缺陷显著减少,高级汽车板成分达到国内先进钢厂的水平,铸坯质量显著提高,为企业了创造可观的经济效益。更多还原

【Abstract】 With the development of the national economy, the requirement for the steel output has become more and the demands for the steel quality become higher. Due to the quality of slab will effect on the quality of final product greatly, the process controlling to continuous casting slab is very important for steel manufacture.The steelmaking branch of Benxi Steel has made great efforts to renewal and improves production equipment since 1993; its product category and product quality has increased greatly. However, compared with the foreign and some of domestic factories, the composition of product, performance, shape and dimensional accuracy still have certain shortcomings. In order to improve the quality of automobile sheet and high strength steel slab in Benxi Steel, this study is carried out based on the existing process condition. The main contents are as follows:(1) The main steel grades for continuous casting slab in Benxi Steel were selected such as SPHC, DC01, A36-2, S235-JR, CRA2, DC53D+Z, BG420CL, Q235. Their hot ductility was measured using Gleebe-2000 Hot Simulation Test, because hot ductility is a very important parameter to continuous casting slab. The stretch test were carried at temperature of 700℃,750℃,800℃,900℃,1000℃,1100℃,1200℃, 1300℃, and the actual stress-strain at top of temperature, and the critical strain of selected steel were obtained.The selected steel, include carbon steel, low carbon steel, ultra low carbon steel and microalloy steel, was studied with hot ductility simulation test. The experimental parameters were determined and analyzed, and then the appropriate slab mould and the temperature straightening, as well as the withdrawal speed which suited for the steel above were put forward.(2) In all of casting slab shortcomings, the proportion of the slab cracks is about 80%. Casting slab cracks not only affect the productivity of continuous casting machine, but also affect the product quality and increase the production costs. This study analyzed the characteristics of slab cracks and the relevant factors, proposed measures for reducing the slab and conducted a production test, the results show that: the content of element S in steel should be controlled less than 0.020%, w[Mn]/w[S]≥20, superheat should be about 30℃, the pulling speed should not more than 1.2m/min. The superheat and secondary cooling water allocation should be adjusted when casting speed exceeds the speed limit. Casting slab straightening temperature should be controlled more than 900℃. According to the results, the continuous casting process parameters for wheels steel (BG420CL) were optimized:the casting speed was selected at 1.0m/min and the cooling water volume of mould and secondary section were determined, and the suitable surface temperature for high strength steel slab was obtained. The ratio of spheroidal inclusions has raise to 87.21% after RE added.(3) The surface quality of slab is directly related to the quality of the follow-up products. The slab surface crack has existed since the device been put into operation. In this research work, the parameters that may influence quality of casting slab were analyzed by the six sigma management method, such as the chemical composition, mould vibration, mass area ratio, secondary cooling zone and continuous casting roller. Then the relevant measures to solve the problem were put forward in practice. The result shows the slab surface crack was effectively controlled through adjustment of the mould amplitude, the water quantity, the content controlling to w[N] and w[S]. The quality of slab was improved greatly.(4) In order to produce qualified automobile steel sheet, the existing production technique level and equipment condition of Benxi Steel was analysised and discussed in detail. Then, the technological process for advanced automobile sheet was be proposed, the quality standard and main parameters of each process were made.(5) In order to produce advanced automobile slab with high ductility, high r and excellent surface properties, the content of C, N, O in steel should be as low as possible. The factor that may influence on carbon pick up during continuous casting process of ultra low carbon steel, such as ladle brick, front powder, tundish powder is analyzed by the six sigma management method. The results show that the ladle brick, starter flux, covering slag are the most influence factors on the carbon pick up. According to the results, the carbon-free brick ladle, carbon-free starter flux and carbon-free powder were applied and produced an obvious result; the carbon increment of the ultra low-carbon steel was lower than 0.0003%.The factor that influenced on nitrogen pick up also been analyzed, the corresponding technical measures, such as improving the seal of seal ring and the seal of slag of tundish, were applied in practice. The average nitrogen increment is reduced to 2.8 X 10’6; The qualified ratio reached 90.7%.更多还原