钐铁合金渗氮动力学实验研究

发布时间：2018-12-13 15:53

【摘要】：自上世纪90年代以来,许多科研工作者对钐铁合金渗氮展开了研究工作,但是目前多数钐铁合金渗氮主要集中在低温固态粉末渗氮方面,其最大的缺点就是氮化时间长,氮化不均匀,氮化效率低。针对低温固态粉末渗氮的缺点,本课题提出了钐铁合金熔体渗氮。本文首先建立了钐铁合金底吹气泡渗氮动力学模型,研究了底吹气泡生成模型:气泡生成的最小压力与外界气压、吹气管半径的关系;气泡的生长模型:外界大气压越大,气泡的生长速率越慢;气泡传质模型:在气泡上浮过程中,气泡的传质速率先增加后减小。最后阐述了气泡上浮至液面后发生聚并破碎的机理。其次进行了钐铁合金熔体渗氮实验。本实验采用了两种渗氮方法,一种是钐铁合金熔体静置渗氮,另一种是钐铁合金熔体底吹氮气泡渗氮。通过钐铁合金熔体静置渗氮实验发现,由于静置渗氮时间长,钐铁合金中的钐挥发严重,又因为熔炼炉腔内存在少量空气,其中的氧与挥发的钐形成氧化钐覆盖在基体表面,进而阻止氮元素向钐铁合金中扩散,因此,静置渗氮并没有达到很好的效果。钐铁合金底吹气泡渗氮熔炼时间短,有效避免了钐的挥发。基体中存在三种相组织,分别是α-Fe相、Sm2Fe17相和富钐相,并且在Sm2Fe17相中发现含有氮元素,其含量最高可以达到0.9%左右。分析认为影响其氮元素的含量没有达到预期Sm2Fe17N3中氮元素的含量有两点原因,一是由于钐铁合金原料中含有碳元素,同为间隙原子的碳也影响了氮原子的渗入;二是渗氮完成后试样基体中仍然有α-Fe相和富钐相,基体并不是均一的Sm2Fe17相。此外,渗氮温度、渗氮时间和渗氮流量的增加均有助于提高钐铁合金中的含氮量。
[Abstract]:Since the 1990s, many researchers have carried out research work on samarium ferroalloy nitriding, but at present most samarium ferroalloy nitriding is mainly concentrated in low temperature solid powder nitriding, its biggest disadvantage is the long nitriding time. The nitridation is uneven and the nitriding efficiency is low. Aiming at the shortcoming of low temperature solid powder nitriding, this paper presents the nitriding of samarium ferroalloy melt. In this paper, the nitriding kinetics model of samarium ferroalloy bottom blowing bubble is established, and the formation model of bottom blowing bubble is studied: the relationship between the minimum pressure of bubble formation and external pressure and the radius of blowing pipe; Bubble growth model: the higher the external atmospheric pressure, the slower the bubble growth rate; the bubble mass transfer model: in the bubble floating process, the bubble mass transfer rate increases first and then decreases. Finally, the mechanism of aggregation and breakup of bubbles after floating to liquid level is described. Secondly, nitriding experiment of samarium ferroalloy melt was carried out. In this experiment, two nitriding methods were used, one was static nitriding of samarium ferroalloy melt, the other was nitriding with bottom blowing nitrogen bubble of samarium ferroalloy melt. Through the static nitriding experiment of samarium ferroalloy melt, it is found that because of the long standing nitriding time, the samarium volatilization in samarium ferroalloy is serious, and because there is a small amount of air in the furnace cavity, the oxygen and the volatile samarium form the oxide samarium to cover the matrix surface. The diffusion of nitrogen elements into samarium ferroalloy was prevented, so the static nitriding did not achieve a good effect. Samarium ferroalloy bottom blowing nitriding melting time is short, effectively avoiding the volatilization of samarium. There are three phases in the matrix, namely 伪-Fe phase, Sm2Fe17 phase and rich phase. It is found that there are nitrogen elements in the Sm2Fe17 phase, the highest content of which is about 0.9%. It is concluded that there are two reasons why the nitrogen content of samarium ferroalloy does not reach the expected content of nitrogen in Sm2Fe17N3. One reason is that the carbon in samarium ferroalloy material also affects the infiltration of nitrogen atoms. Second, there are 伪-Fe phase and rich phase in the matrix after nitriding, and the matrix is not homogeneous Sm2Fe17 phase. In addition, the increase of nitriding temperature, nitriding time and nitriding flow rate can improve the nitrogen content in samarium ferroalloy.
【学位授予单位】：华北理工大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TG156.82

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