304不锈钢中夹杂物的控制

发布时间：2018-05-23 18:50

本文选题：304不锈钢 + 夹杂物　；参考：《北京科技大学》2017年博士论文

【摘要】：非金属夹杂物对不锈钢的强度、硬度、疲劳和表面质量等影响很大。同时,夹杂物还可能引起很多不锈钢产品的缺陷。夹杂物的控制已经成为不锈钢生产关键任务之一。一些高端304不锈钢产品被应用于手机壳和手表链的生产,因此对不锈钢对产品的表面质量具有很高的要求。目前我国自主生产的高端304不锈钢产品很难满足用户的需求,夹杂物引起的产品缺陷是最主要原因之一。因此,关于304不锈钢中的夹杂物控制的基础研究对我国企业实现高端304不锈钢的自主生产具有重大意义。本课题首先通过文献调研和产品调研等方法,确定了304不锈钢夹杂物的控制目标。研究发现夹杂物中MgO-Al2O3和Al2O3含量很高会引起304不锈钢产品的缺陷,某一样品的分析结果表明不锈钢现场冶炼过程夹杂物中Al2O3含量逐渐升高。确定304不锈钢中夹杂物的控制目标为：减少夹杂物中的Al2O3含量,将钢中夹杂物成分控制在Al2O3-SiO2-CaO系和Al2O3-SiO2-MnO系夹杂物相图的低熔点区域。其次,研究了精炼过程精炼渣成分对304不锈钢中夹杂物的影响。研究发现低碱度精炼渣有利于降低304不锈钢夹杂物中Al2O3含量；初始渣中的Al2O3含量增加,夹杂物中Al2O3含量明显增加；初始精炼渣中MgO增大对夹杂物中Al2O3含量影响不大,但有利于减小耐材的侵蚀。结合实验结果,应用FactSage热力学计算软件建立了渣-钢-夹杂物平衡反应热力学模型,通过模型研究了不同精炼渣成分对钢液成分、脱硫、夹杂物成分、夹杂物熔点、耐火材料侵蚀等的影响。最后确定精炼渣碱度小十1.75、MgO含量为10%-15%且不含Al2O3的精炼渣有利于降低304不锈钢夹杂物中Al2O3含量。再次,研究了精确钙处理的控制对304不锈钢中夹杂物改性的可行性,建立了304不锈钢中夹杂物的精确钙处理模型,可实现根据304不锈钢中不同钢液成分对最优喂钙线量进行精确计算。同时,通过现场实验验证了钙处理变性夹杂物的效果,从而实现304不锈钢中夹杂物钙处理改性的精确控制。接着,研究了中间包二次氧化对304不锈钢中夹杂物的影响。研究发现在硅锰脱氧304不锈钢发生二次氧化后,钢中吸氧区域的[Al]和[Ca]元素迅速被氧化并且降低到极低的含量。钢中过量的氧会氧化钢中含量较高的[Mn],瞬态生成大量的MnO含量很高的1-2μm的小尺寸夹杂物。从开浇到稳定浇铸过程中,夹杂物中瞬态生成的MnO含量逐渐减小并降低至正常水平。热力学计算结果表明：硅锰脱氧304不锈钢二次氧化会引起夹杂物中MnO含量上升,铝脱氧的304不锈钢二次氧化会引起夹杂物中Al2O3含量上升。然后,研究了热处理对304不锈钢中夹杂物的影响。研究发现在1373 K下的氩气保护气氛的热处理过程中,304不锈钢夹杂物的演变机理为：在热处理之前,钢中的夹杂物主要为球形液态MnO-SiO2夹杂物。热处理过程中,钢中的[Cr]元素逐渐向钢/MnO-SiO2夹杂物界面传质,随后[Cr]还原MnO-SiO2夹杂物中的SiO2和MnO,在MnO-SiO2夹杂物表面生成MnO·Cr2O3尖晶石夹杂物,同时生成的[Si]和[Mn]从反应界面传质回钢中。最终,MnO-SiO2夹杂物被完全变性为纯MnO·Cr2O3尖晶石夹杂物。将热处理温度从1273 K增加至1473 K可以有效地加快夹杂物的转变速率。此外,建立了一个热处理过程夹杂物转变动力学模型,可以有效预测不同温度下的热处理过程中夹杂物的转变率。本文通过304不锈钢的工艺的调研、试样产品的检测、精炼过程渣改性和钙处理改性、连铸过程二次氧化影响、热处理对夹杂物的影响等研究,确定了304不锈钢中冶炼过程各类夹杂物的生成机理和影响因素。可根据304不锈钢的不同用途和不同的夹杂物控制需求,确定最优的冶炼工艺,实现对304不锈钢的各类夹杂物的控制。
[Abstract]:Non-metallic inclusions have great influence on the strength, hardness, fatigue and surface quality of stainless steel. At the same time, inclusions may also cause defects in many stainless steel products. Inclusion control has become one of the key tasks of stainless steel production. Some high-end 304 stainless steel products are used in the production of cell phone shells and watch chains. The steel has a high requirement for the surface quality of the products. At present, the high-end 304 stainless steel products produced by our country are difficult to meet the needs of the users. The product defects caused by inclusions are one of the main reasons. Therefore, the basic research about the inclusion control in 304 stainless steel is the independent production of the high end 304 stainless steel in our country. It is of great significance to determine the control target of 304 stainless steel inclusions by means of literature investigation and product investigation. It is found that the high content of MgO-Al2O3 and Al2O3 in inclusions will cause defects of 304 stainless steel products. The analysis results of a sample show that the content of Al2O3 in the inclusions of stainless steel in the process of smelting process is the same. The control goal of inclusion in 304 stainless steel is to be determined: to reduce the Al2O3 content in the inclusions, to control the inclusions in the steel in the low melting point area of the Al2O3-SiO2-CaO and Al2O3-SiO2-MnO inclusions. Secondly, the influence of the refining slag composition on the inclusions in the 304 stainless steel is studied. The refining slag can reduce the content of Al2O3 in the inclusions of 304 stainless steel, the content of Al2O3 in the initial slag increases, the content of Al2O3 in the inclusion increases obviously, and the increase of MgO in the initial refining slag has little effect on the Al2O3 content in the inclusions, but it is beneficial to reduce the corrosion of the refractory. The slag is used to establish the slag by the thermodynamic calculation software of FactSage. - the influence of the composition of different refining slag on the composition of molten steel, desulphurization, inclusion composition, inclusion melting point and corrosion resistance of refractory material. Finally, it is determined that the alkalinity of the refining slag is ten 1.75, the content of MgO is 10%-15% and the refining slag without Al2O3 is beneficial to the reduction of Al2O3 in the inclusions of 304 stainless steel. Again, the feasibility of controlling the inclusion of inclusions in 304 stainless steel by the control of precise calcium treatment was studied. A precise calcium treatment model for inclusion in 304 stainless steel was established. The exact calculation of the optimal calcium feeding line was achieved according to the composition of different steel liquid in 304 stainless steel. In order to achieve the accurate control of the calcium treatment modification in 304 stainless steel, the effect of the two oxidation of the tundish on the inclusions in 304 stainless steel was studied. The study found that after two oxidation of the 304 stainless steel, the [Al] and [Ca] elements in the oxygen absorption region of the steel were rapidly oxidized and reduced to a very low content. Excessive oxygen in the medium will oxidize the high content of [Mn] in the steel and produce a large number of small size inclusions with a large number of MnO content of 1-2 m. The transient MnO content in the inclusions gradually decreases and decreases to the normal level from the open cast to the stable casting process. The thermodynamic calculation shows that the two oxidation of silicon manganese deoxidization 304 stainless steel will cause the process. The content of MnO in the inclusions increases and the two oxidation of 304 stainless steel with aluminum deoxidization causes the increase of Al2O3 content in the inclusions. Then, the effect of heat treatment on inclusions in 304 stainless steel is studied. It is found that the evolution mechanism of the 304 stainless steel inclusion in the argon gas protection atmosphere under 1373 K is that before heat treatment, the steel is in the steel. The inclusions are mainly spherical liquid MnO-SiO2 inclusions. During the process of heat treatment, the [Cr] elements in the steel gradually transfer to the interface of the steel /MnO-SiO2 inclusions, then [Cr] reduction of SiO2 and MnO in the MnO-SiO2 inclusions and the formation of MnO Cr2O3 spinel inclusions on the surface of the inclusions on MnO-SiO2, and the [Si] and [Mn] from the reaction interface from the reaction interface are mass transfer back to the steel. Finally, MnO-SiO2 inclusions are completely denatured into pure MnO Cr2O3 spinel inclusions. The increase of heat treatment temperature from 1273 K to 1473 K can effectively speed up the transition rate of inclusions. In addition, a kinetic model of inclusion transition in heat treatment process is established, which can effectively predict inclusions in the heat treatment process at different temperatures. In this paper, through the investigation of the technology of 304 stainless steel, the testing of the sample products, the modification of the slag in the refining process, the modification of the calcium treatment, the influence of the two oxidation of the continuous casting process and the influence of the heat treatment on the inclusions, the formation mechanism and influence factors of all kinds of inclusions in the smelting process of 304 stainless steel are determined. It can be based on the difference of the 304 stainless steel. Use and different control requirements of inclusions, determine the best smelting process, and achieve the control of all kinds of inclusions in 304 stainless steel.
【学位授予单位】：北京科技大学
【学位级别】：博士
【学位授予年份】：2017
【分类号】：TF764.1

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