铌对炼镁还原反应器用奥氏体耐热钢组织及性能的影响

发布时间：2018-05-02 14:41

  本文选题：奥氏体耐热钢 + 铌　； 参考：《郑州大学》2017年硕士论文

【摘要】：目前,全球80%以上的商品原镁是我国通过外热硅热法生产。炼镁还原反应器是硅热法炼镁重要的部件,也是原镁生产最为主要的成本构成之一。目前炼镁还原反应器的主流材质为奥氏体耐热钢,但传统的反应器用奥氏体耐热钢高温性能较差,易产生蠕变失稳及热疲劳开裂破坏,使用寿命较短,大幅增加原镁冶炼成本。因此,开发新型的反应器用奥氏体耐热钢,对降低原镁的冶炼成本,提高企业经济效益具有重要意义。本论文在ZG35Cr26Ni8NRE的基础上添加合金元素铌,重点探究了铌含量对炼镁还原反应器用耐热钢微观组织、常规力学性能、高温抗氧化性能、抗热疲劳性能和高温抗蠕变性能的影响;利用光学显微镜、X射线衍射仪、扫描电子显微镜及其附带的能谱仪探究了Nb元素含量对其组织和性能的影响机理,主要研究结果如下:未添加Nb元素的耐热钢基体组织为奥氏体+第二相,奥氏体晶粒比较粗大,晶界分布大量链状碳化物,晶内分布大量骨骼状碳化物,碳化物类型主要为M23C6型和M7C3型,其中M主要为Cr、Fe和Mn;添加Nb元素后的耐热钢基体组织不变,但奥氏体晶粒明显细化,晶粒细化程度随Nb含量增加而提高,碳化物除M23C6型和M7C3型外,还出现片状的Nb C、Nb N和Nb2CN,这类碳化物的数量随Nb含量的增加逐渐增多,但当铌含量达到1.5%时,组织中各类碳化物出现长大粘连的现象。在1000℃和1200℃条件下,Nb元素的添加对抗氧化性是不利的,随着Nb含量的增加,耐热钢的抗氧化性逐渐下降,并且随着温度升高,抗氧化性能下降越显著。1000℃×150 h高温氧化试验后,未添加Nb元素的耐热钢为完全抗氧化的,添加Nb元素的耐热钢为抗氧化的;1200℃×150 h高温氧化试验后,未添加Nb元素的耐热钢为弱抗氧化的,添加Nb元素的耐热钢为不抗氧化的。在热疲劳上限温度为1200℃条件下,循环150次后,耐热钢的抗热疲劳性能随Nb元素含量的增加呈先提升后降低的趋势,未添加Nb元素的耐热钢热疲劳裂纹最长,为7.321 mm;添加1.0%Nb的耐热钢热疲劳裂纹最短,为5.221 mm。热疲劳试验后,耐热钢组织中M23C6型碳化物长大粗化,而MC型碳化物则弥散细小的分布在基体中。在外加载荷为20 MPa、温度为1000℃的条件下,耐热钢的高温抗蠕变性能随Nb含量增加逐渐降低。加载80 h后,未添加Nb元素的耐热钢延伸率为0.4365%;添加0.5%Nb的耐热钢延伸率为0.4925%;添加1.0%Nb的耐热钢延伸率为4.726%,宏观出现明显伸长但无颈缩;添加1.5%Nb的耐热钢在试验进行34 h后发生断裂,断口呈韧性断裂特征,存在明显颈缩。综合铌对炼镁还原反应器用奥氏体耐热钢组织及性能的影响规律和机理,本文建议在反应器用奥氏体耐热钢中铌元素的添加量不宜超过0.5%。
[Abstract]:At present, more than 80% of the world's primary magnesium is produced by the external thermal silicon thermal process in China. Magnesium reduction reactor is an important part of silicothermic magnesium smelting and one of the most important cost components in magnesium production. At present, the main material of magnesium reduction reactor is austenitic heat-resistant steel, but the high temperature property of austenitic heat-resistant steel used in traditional reactor is poor, and the creep instability and thermal fatigue cracking are easy to be destroyed. The service life is shorter, and the cost of original magnesium smelting is greatly increased. Therefore, the development of a new type of austenitic heat-resistant steel for reactor is of great significance in reducing the smelting cost of raw magnesium and increasing the economic benefit of enterprises. In this paper, the effect of niobium content on microstructure, conventional mechanical properties, high temperature oxidation resistance, thermal fatigue resistance and creep resistance of heat-resistant steel for magnesium reduction reactor was studied based on the addition of niobium on the basis of ZG35Cr26Ni8NRE. The influence mechanism of NB content on microstructure and properties was investigated by means of optical microscope X-ray diffractometer, scanning electron microscope and its accompanying energy spectrometer. The main results are as follows: the microstructure of the heat-resistant steel without NB element is the second phase of austenite, the austenite grain is coarse, a large number of chain-like carbides are distributed at the grain boundary, and a large number of skeletal carbides are distributed in the grain boundaries. The carbides are mainly M23C6 type and M7C3 type, in which M is mainly Cr-Fe and Mn.The matrix microstructure of heat-resistant steel after adding NB element does not change, but the austenite grain is refined obviously, and the grain refinement degree increases with the increase of NB content. In addition to the M23C6 type and M7C3 type, there are also sheets of NB Con NB N and NB 2CN. The amount of these carbides increases with the increase of NB content. However, when the niobium content reaches 1.5%, the adhesion of all kinds of carbides in the tissue is observed. The addition of NB element at 1000 鈩，

本文编号：1834334