【摘要】：目前,我國的普鋼生產無論是規(guī)模還是質量,都達到了一個較高的水平。但是在具有高附加值的模具鋼領域,與國外相比還存在很大差距,其中很重要的原因就是模具鋼中夾雜物以及碳化物的問題。國產的模具鋼存在碳化物和夾雜物分布不均、顆粒粗大等缺點,嚴重影響了模具的性能。基于這些原因,本文提出了鋼中加入鎂改善鋼質量的新思路,即向鋼中加入鎂,觀察鎂對碳化物的影響規(guī)律,同時也觀察了鎂對夾雜物的影響規(guī)律。本文以最常用的H13熱作模具鋼為研究對象,采用中頻爐冶煉含鎂H13鋼。實驗過程中分別向鋼中加入0、0.001%、0.0025%、0.004%以及0.0055%的鎂,研究了不同鎂含量對鋼中碳化物以及夾雜物的影響,同時分別從動力學和熱力學角度分析了鎂細化碳化物的條件,以及鎂對夾雜物改性的原理,并得到了如下結論。(1)向鋼中加入鎂,研究鎂對鋼中碳化物的影響,結果發(fā)現(xiàn):鋼中加入微量的鎂元素之后,能夠打斷組織中的網(wǎng)狀碳化物,改善碳化物的形狀以及其在鋼中的分布,使其均勻細小的分布在組織中。鎂細化H13鋼中的碳化物有一個含量范圍,在這個范圍內隨著鎂含量的增加,碳化物的細化程度就越高,但是當達到一定程度之后隨著鎂含量的加入,其對碳化物細化效果變差,直至最后細化效果消失。鎂含量的加入量為0.004%時,其對碳化物的細化效果最佳。(2)通過對鎂細碳化物的動力學和熱力學分析表明:在鋼凝固冷卻的過程中,鎂元素向晶界處的偏聚傾向較大,偏聚程度也較高,當鎂元素的偏聚到晶界處之后,析出的碳化物以鎂為形核核心形成碳化物晶體。(3)通過探究鎂對鋼中主要合金元素的偏析以及致密度的影響,研究發(fā)現(xiàn):鋼中加入鎂改善C、Cr、Mo、V元素偏析以及組織的致密度存在一個最佳范圍,在這個范圍內隨著鋼中鎂含量的增加,對元素偏析的改善效果越好,超過最佳值,對元素偏析的改善效果降低,鋼中鎂含量的加入量為0.004%時,鎂對鋼中元素偏析和組織致密度的改善效果最好,此時各元素的統(tǒng)計偏析度均達到最小,統(tǒng)計均勻度達到最大,組織致密度最高。(4)通過探究鎂對鋼中夾雜物的影響,研究發(fā)現(xiàn):鎂能夠改變鋼中夾雜物的尺寸和分布。一定范圍內隨著鋼中鎂含量的增加,對夾雜物的改善效果就越好,繼續(xù)增加鋼中鎂的加入量,對鋼中夾雜物的改善效果變差。此外,鋼中加入鎂之后能夠對鋼中的夾雜物改性。經過鎂處理后,鋼中出現(xiàn)MgO?Al2O3夾雜,且鎂與硫的結合能力強于錳與硫的結合能力,鋼中加入鎂之后會優(yōu)先與鋼中的硫結合,抑制MnS的形成,從而使得鋼中的MnS夾雜轉變成MgS夾雜。
[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.
【學位授予單位】：安徽工業(yè)大學
【學位級別】：碩士
【學位授予年份】：2017
【分類號】：TG142.1

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