中碳低合金耐磨钢的材料研究与应用

发布时间：2018-05-11 12:19

本文选题：低合金耐磨钢 + 微合金化　；参考：《中国科学技术大学》2016年博士论文

【摘要】：为了提高生产效率和降低制造成本,铁矿粉生产线关键装备及其工作部件不断大型化。其中,耐磨衬板是铁矿粉生产线关键装备——磨机的核心工作部件,其使用寿命直接影响整条铁矿粉生产线的运行效率和制造成本。然而,目前国内尚未形成超大型磨机的自主选材规范,致使我国超大型铁矿粉生产线项目的主要关键设备完全依赖进口,造成项目成本和进度受制于人。为了达到预期设计使用寿命,大型耐磨部件选材在具有较高硬度和强度的同时,应当具有优异的韧性和塑性以及良好的淬透性。因此,如何获得良好的强韧性匹配以及淬透性,进一步提高耐磨钢的耐磨性能,一直是研究者非常关注的课题。本文通过Ti、B和RE多元微合金化处理,设计了一系列新型中碳低合金耐磨钢,分析了Ti、B和RE对微观组织演变的影响,系统研究了在凝固和热处理过程中含Ti析出相和稀土夹杂物的类型、尺寸和分布,及其对组织和力学性能的影响,探讨了实验钢的磨损机理以及Ti和RE微合金化、力学性能与耐磨性能之间的关系。在此基础上,结合生产实际,实现了自主设计中碳低合金钢耐磨衬板铸件的批量化生产,为我国低合金耐磨钢的材料开发积累了宝贵经验,同时也为高品质耐磨部件的应用奠定了坚实的理论基础。本文的主要研究内容包括：(1)结合热力学计算和实验研究,提出了Ti、B和RE多元微合金化思想：通过微量B提高淬透性；加入适量Ti与钢中N结合,确保B对淬透性的作用,并且形成TiN析出相,细化组织;加入适量RE(La、Ce),净化钢液、改善夹杂、细化晶粒。由此,设计了新型中碳低合金耐磨钢合金体系。(2)采用热膨胀仪测定了实验钢的连续冷却转变(CCT)曲线,分析了Ti、B和RE多元微合金化对淬透性的影响。结果表明,实验钢中,单独加入B元素时,B易与钢中N结合,形成BN,严重削弱对淬透性的作用；并且,过量的B将促进M23(C,B)6型碳化物沿晶界析出,反而降低钢的淬透性。在此基础上,加入适量的Ti元素,能够有效固N,形成TiN析出相,抑制BN的产生,有利于发挥B显著提高淬透性的作用。然而,实验钢中加入RE元素,主要与钢液中O、S结合形成RE203和RE202S稀土夹杂物,对钢的淬透性基本没有影响。(3)通过固液两相区保温凝固和连续冷却凝固实验,研究了实验钢中TiN和稀土夹杂物的析出行为及其对凝固组织的影响。研究结果表明,等温凝固和水淬冷却后,实验钢中的TiN和稀土夹杂物主要分布于凝固组织的粗大枝晶间、枝晶前沿和最后凝固的等轴晶晶界处,少量分布于凝固组织的粗大枝晶和等轴晶内。低倍组织对比表明,加入Ti和RE元素,能够显著提高等轴晶比率,细化凝固组织。(4)系统研究了热处理后实验钢中含Ti析出相和稀土杂物的析出特征,并探讨了Ti、RE含量对晶粒尺寸和力学性能的影响。结果表明,随着Ti含量增加,实验钢中含Ti析出相颗粒尺寸增大、析出含量增多,析出相类别逐渐转变为微米级的Ti(C,N)和纳米级的(Ti,Mo)(C,N),具有明显的弥散强化、细晶强化和韧塑性改善作用。当Ti含量为0.021%时,实验钢综合力学性能最佳;随着Ti含量进一步增加,含Ti析出相在凝固初期形核并快速长大,导致析出相的颗粒尺寸和析出量明显升高,严重降低钢的冲击韧性。单独加入适量RE元素时,RE元素与钢液中的O、S结合,生成绝大部分小于1μm的RE2O3和RE202S稀士夹杂物,有效起到净化钢液和变质夹杂的作用,可以小幅提高钢的冲击韧性；但是,当RE元素与Ti元素复合微合金化时,稀土夹杂物极易作为钢中TiN的有效形核核心,促使TiN与其形成尺寸较大的微米级复合类型析出相,造成冲击韧性降低。(5)利用MLD-10型动载磨料磨损实验机,探讨了实验钢在冲击磨料磨损条件下的磨损机理,以及Ti和RE微合金化、力学性能与耐磨性能之间的关系。实验结果显示,在冲击磨料磨损条件下,实验钢磨损表面,除少量的显微切削磨损外,主要以塑性变形导致疲劳剥落磨损为主。在B微合金化基础上,实验钢中分别单独加入适量的Ti和RE元素,能够提高综合力学性能,从而一定程度提升耐磨性能。但是,将RE元素加入Ti和B微合金化的实验钢中,形成的粗大TiN-稀土夹杂物颗粒,在磨损过程中破碎,造成基体开裂,明显降低钢的耐磨性能。(6)在上述材料研究基础上,结合实际工况,制定了大型耐磨衬板选材成分规范、性能指标和全流程生产工艺。并且,采用电弧炉(EAF)-精炼炉(LF)-真空处理(VOD)冶炼技术,通过控制Ti、B和RE加入顺序,实现了自主设计中碳低合金钢耐磨衬板铸件的批量化生产,并且已经基本替代进口。使用结果显示,自主研制的大型耐磨衬板服役寿命达到75天,现有进口服役寿命为65天,提高15.4%。
[Abstract]:In order to improve the production efficiency and reduce the manufacturing cost, the key equipment and its working parts of the iron ore production line are continuously large. Among them, the wear-resistant lining plate is the key equipment of the iron ore powder production line, the core working part of the mill. Its service life directly affects the operation efficiency and manufacturing cost of the whole iron ore production line. However, at present, the domestic iron ore powder production line has a direct effect on the operation efficiency and manufacturing cost. The independent material selection criterion of the super large mill has not been formed. The main key equipment of the super large iron ore production line project in our country depends entirely on the import, resulting in the cost and progress of the project. In order to achieve the expected design life, the material of large wear-resistant parts should have excellent toughness while having high hardness and strength. Therefore, how to obtain good strength and toughness matching and hardenability and further improve the wear resistance of wear resistant steel has always been a subject of great concern for researchers. In this paper, a series of new medium carbon low alloy wear resistant steels have been designed by Ti, B and RE microalloying. The microstructure of Ti, B and RE is analyzed. The type, size and distribution of Ti precipitates and rare earth inclusions in the process of solidification and heat treatment are systematically studied. The wear mechanism of the experimental steel and the relationship between Ti and RE microalloying and the relationship between mechanical properties and wear resistance are discussed. At the same time, the mass production of carbon low alloy steel wear-resistant lining castings in the independent design has been realized. It has accumulated valuable experience for the development of low alloy wear resistant steel materials in China, and laid a solid theoretical foundation for the application of high quality and wear-resistant components. The main contents of this paper include: (1) combined with thermodynamic calculation and experimental research, the paper puts forward the research of the paper. Ti, B and RE microalloying thought: improving hardenability by trace B, adding appropriate Ti and N in steel to ensure B to hardenability, forming TiN precipitate phase, refining microstructure, adding a proper amount of RE (La, Ce), purifying molten steel, improving inclusion and refining grain. By this, a new medium carbon low alloy wear resistant steel alloy system was designed. (2) adoption of a new medium carbon alloy system. (2) The continuous cooling transition (CCT) curve of experimental steel was measured by a thermal expaner. The effect of Ti, B and RE Microalloying on the hardenability was analyzed. The results showed that when B element was added to the experimental steel, B was easily combined with N in steel to form BN, which seriously weakened the effect of hardenability, and the excess B would precipitate the precipitation of M23 (C, B) 6 carbides along the grain boundary. Instead of reducing the hardenability of steel, on this basis, adding a proper amount of Ti elements can effectively fix N, form TiN precipitation phase and inhibit the production of BN, which is beneficial to play a significant role in improving the hardenability of B. However, the addition of RE elements in the experimental steel is mainly combined with O and S in molten steel to form RE203 and RE202S rare earth inclusions, and has no effect on the hardenability of steel. (3) the precipitation behavior of TiN and rare-earth inclusions in the experimental steel and its effect on the solidification structure of the experimental steel were studied by the experiments of thermal insulation solidification and continuous cooling solidification in the solid-liquid two phase region. The results showed that after the isothermal solidification and water quenching, the TiN and the rare earth inclusions in the experimental steel were mainly distributed in the coarse interdendritic interdendrites of the solidified structure and before the dendrites. Along with the finally solidified equiaxed grain boundaries, a small amount is distributed in the coarse dendrites and equiaxed grains of the solidified tissue. The comparison of the low fold microstructure shows that the ratio of the equiaxed grain and the solidification structure can be greatly improved by adding Ti and RE elements. (4) the precipitation characteristics of the precipitated phase and the rare earth impurities in the experimental steel after heat treatment were systematically studied, and Ti, R was discussed. The effect of E content on grain size and mechanical properties showed that, with the increase of Ti content, the particle size of the precipitated phase in the experimental steel increased, the precipitation content increased, the precipitate category gradually changed into micron grade Ti (C, N) and nanoscale (Ti, Mo) (C, N), with obvious dispersion strengthening, fine grain strengthening and ductile plasticity improvement. When Ti content was obtained. At 0.021%, the comprehensive mechanical properties of the experimental steel are the best. As the content of Ti is further increased, the precipitate containing Ti is nucleated at the initial stage and grows rapidly, resulting in a significant increase in the size and precipitation of the precipitated phase, which seriously reduces the impact toughness of the steel. When a proper amount of RE elements is added to the steel, the RE element is combined with O and S in the molten steel. The RE2O3 and RE202S dilute inclusions at 1 m can effectively purify the molten steel and the metamorphic inclusion, and improve the impact toughness of the steel. However, when the RE element and the Ti element are microalloyed with the Ti element, the rare earth inclusions are very easy to be used as the effective core of the TiN in the steel, prompting the TiN and its formation of a larger size and micron grade. The impact toughness is reduced. (5) the wear mechanism of the experimental steel under the impact abrasive wear condition, and the relationship between the microalloying of Ti and RE, the mechanical properties and the wear resistance are discussed by using the MLD-10 dynamic abrasive wear test machine. The experimental results show that the wear surface of the experimental steel in the condition of impact abrasive wear, with the exception of a small amount of display, is shown. On the basis of B microalloying, a proper amount of Ti and RE elements are added separately to the experimental steel on the basis of microalloying, which can improve the comprehensive mechanical properties and improve the wear resistance to a certain extent. However, the RE element is added to the experimental steel of Ti and B microalloying, and the coarse TiN- is formed. The debris particles are broken during the wear process, which causes the matrix cracking and obviously reduces the wear resistance of the steel. (6) on the basis of the research on the above materials, the material material specification, performance index and the whole process production process of the large wear-resistant lining board are formulated on the basis of the above materials, and the EAF refining furnace (LF) vacuum treatment (VOD) smelting technique is adopted. By controlling the order of Ti, B and RE, the mass production of the carbon low alloy steel wear-resistant lining castings in the independent design has been realized, and it has basically replaced the import. The results show that the service life of the self developed large wear-resistant liner has reached 75 days, and the existing import service life is 65 days and 15.4%. is improved.

【学位授予单位】：中国科学技术大学
【学位级别】：博士
【学位授予年份】：2016
【分类号】：TG142.72

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