镁对H13热作模具钢组织及夹杂物的影响

发布时间：2018-10-05 13:51

【摘要】：目前,我国的普钢生产无论是规模还是质量,都达到了一个较高的水平。但是在具有高附加值的模具钢领域,与国外相比还存在很大差距,其中很重要的原因就是模具钢中夹杂物以及碳化物的问题。国产的模具钢存在碳化物和夹杂物分布不均、颗粒粗大等缺点,严重影响了模具的性能。基于这些原因,本文提出了钢中加入镁改善钢质量的新思路,即向钢中加入镁,观察镁对碳化物的影响规律,同时也观察了镁对夹杂物的影响规律。本文以最常用的H13热作模具钢为研究对象,采用中频炉冶炼含镁H13钢。实验过程中分别向钢中加入0、0.001%、0.0025%、0.004%以及0.0055%的镁,研究了不同镁含量对钢中碳化物以及夹杂物的影响,同时分别从动力学和热力学角度分析了镁细化碳化物的条件,以及镁对夹杂物改性的原理,并得到了如下结论。(1)向钢中加入镁,研究镁对钢中碳化物的影响,结果发现:钢中加入微量的镁元素之后,能够打断组织中的网状碳化物,改善碳化物的形状以及其在钢中的分布,使其均匀细小的分布在组织中。镁细化H13钢中的碳化物有一个含量范围,在这个范围内随着镁含量的增加,碳化物的细化程度就越高,但是当达到一定程度之后随着镁含量的加入,其对碳化物细化效果变差,直至最后细化效果消失。镁含量的加入量为0.004%时,其对碳化物的细化效果最佳。(2)通过对镁细碳化物的动力学和热力学分析表明:在钢凝固冷却的过程中,镁元素向晶界处的偏聚倾向较大,偏聚程度也较高,当镁元素的偏聚到晶界处之后,析出的碳化物以镁为形核核心形成碳化物晶体。(3)通过探究镁对钢中主要合金元素的偏析以及致密度的影响,研究发现:钢中加入镁改善C、Cr、Mo、V元素偏析以及组织的致密度存在一个最佳范围,在这个范围内随着钢中镁含量的增加,对元素偏析的改善效果越好,超过最佳值,对元素偏析的改善效果降低,钢中镁含量的加入量为0.004%时,镁对钢中元素偏析和组织致密度的改善效果最好,此时各元素的统计偏析度均达到最小,统计均匀度达到最大,组织致密度最高。(4)通过探究镁对钢中夹杂物的影响,研究发现:镁能够改变钢中夹杂物的尺寸和分布。一定范围内随着钢中镁含量的增加,对夹杂物的改善效果就越好,继续增加钢中镁的加入量,对钢中夹杂物的改善效果变差。此外,钢中加入镁之后能够对钢中的夹杂物改性。经过镁处理后,钢中出现MgO?Al2O3夹杂,且镁与硫的结合能力强于锰与硫的结合能力,钢中加入镁之后会优先与钢中的硫结合,抑制MnS的形成,从而使得钢中的MnS夹杂转变成MgS夹杂。
[Abstract]:At present, the general steel production in China has reached a high level both in scale and quality. However, in the field of die steel with high added value, there is still a big gap compared with foreign countries, and the most important reason is the inclusion and carbides in die steel. The domestic die steel has the disadvantages of uneven distribution of carbides and inclusions and coarse particles, which seriously affects the properties of dies. For these reasons, a new way to improve the quality of steel by adding magnesium to steel is put forward in this paper, that is, adding magnesium to steel, observing the effect of magnesium on carbides, and observing the influence of magnesium on inclusions at the same time. In this paper, the Mg-bearing H13 steel is smelted in medium frequency furnace with the most commonly used hot work die steel H13 as the research object. In the course of the experiment, the effect of different magnesium content on carbides and inclusions in steel was studied by adding 0.004% and 0.0055% magnesium respectively to the steel, and the conditions of magnesium refining carbides were analyzed from the point of view of kinetics and thermodynamics, respectively. And the principle of magnesium modification of inclusions, and the following conclusions are obtained. (1) the effect of magnesium on carbides in steel is studied by adding magnesium. The results show that the addition of a small amount of magnesium in steel can break the network carbide in the microstructure. The shape of carbides and their distribution in steel are improved so that they are evenly distributed in the microstructure. There is a content range of carbides in magnesium refining H13 steel. In this range, with the increase of magnesium content, the refining degree of carbides is higher, but with the addition of magnesium content, the refining effect of carbides becomes worse. Until the final refinement effect disappeared. When the content of magnesium is 0.004, the effect of refining the carbides is the best. (2) the kinetic and thermodynamic analysis of magnesium fine carbides shows that during solidification and cooling of steels, magnesium tends to segregate to grain boundaries. The degree of segregation is also high. When magnesium is segregated to the grain boundary, the precipitated carbides form carbide crystals with magnesium as the core of nucleation. (3) the effect of magnesium on the segregation and density of the main alloying elements in the steel is investigated. It is found that there is an optimum range for the improvement of segregation and the density of microstructure by adding magnesium to the steel. With the increase of magnesium content in the steel, the better the effect of improving the segregation is, which exceeds the optimum value. When the content of magnesium in steel is 0.004, the effect of magnesium on element segregation and microstructure density in steel is the best, and the statistical segregation degree of each element is the smallest, and the statistical uniformity is the largest, when the content of magnesium in steel is 0.004%, the effect of improving the segregation of elements is decreased, and the content of magnesium in steel is 0.004. The microstructure density is the highest. (4) by exploring the influence of magnesium on inclusions in steel, it is found that magnesium can change the size and distribution of inclusions in steel. With the increase of magnesium content in steel in a certain range, the better the effect of inclusion is, the more magnesium is added in steel, the worse the improvement effect of inclusion in steel becomes. In addition, the addition of magnesium into the steel can modify the inclusions in the steel. After magnesium treatment, MgO? appears in steel Al2O3 inclusion, and the binding ability of mg and sulfur is stronger than that of manganese and sulfur. Adding magnesium to steel will preferentially bind to sulfur in steel, inhibit the formation of MnS, and make the inclusion of MnS in steel transform into MgS inclusion.
【学位授予单位】：安徽工业大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TG142.1

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