【摘要】：奧氏體耐熱鋼ZG40Cr25Ni20Si2具有良好的高溫力學性能和抗氧化性、耐蝕性及組織穩(wěn)定性,在汽車排氣歧管、渦輪增壓器殼體等零部件上的應用日趨廣泛。然而鑄態(tài)合金中粗大的樹枝晶使其產生嚴重的偏析,即使通過熱處理也無法消除,導致合金性能下降、使用壽命縮短。本文旨在探索單一元素合金化和雙元素合金化對ZG40Cr25Ni20Si2鋼微觀組織及力學性能的作用規(guī)律,揭示合金化處理的強化機制。研究表明:ZG40Cr25Ni20Si2鋼中碳化物數量為8.49%。對其進行單一元素合金化處理后,合金中碳化物的量隨著合金元素含量的增加而增多。同時,Ti、V、Nb的加入可以改善合金中碳化物的形貌以及其在晶界分布的狀態(tài),致使晶間碳化物形態(tài)由最初連續(xù)的網狀分布向細小的斷續(xù)狀分布轉化。ZG40Cr25Ni20Si2鋼的二次枝晶臂間距及一次枝晶直徑分別為13.99μm和174.73μm,其硬度為174HB。當對其進行單一元素合金化處理時,Ti、V、Nb的添加使合金的二次枝晶臂間距及一次枝晶直徑均有不同程度的減小,并且合金的硬度也得到了提升。隨著合金元素Ti、V、Nb添加量的增加,二次枝晶臂間距及一次枝晶直徑先減小后增大,而合金硬度則表現為先增大后減小。當Ti含量為0.15%時,二次枝晶臂間距及一次枝晶直徑分別達到最小值11.15μm及93.05μm,合金硬度達到最大值184HB;在V含量為0.05%時,二次枝晶臂間距及一次枝晶直徑分別達到最小值10.63μm及75.11μm,合金硬度達到最大的186HB;當Nb含量為0.05%時,二次枝晶臂間距及一次枝晶直徑分別達到最小值10.21μm及73.43μm,合金硬度達到最大值198HB。Nb和V在ZG40Cr25Ni20Si2鋼中細化枝晶的能力稍強于Ti,Nb對ZG40Cr25Ni20Si2鋼的強化作用大于Ti和V。經過雙元素合金化處理之后,合金中基體微觀組織顯著細化,碳化物析出量有所增多,合金硬度升高。當復合添加0.05%Ti和0.05%V時,二次枝晶臂間距及一次枝晶直徑分別達到最小值12.07μm及99.36μm,碳化物的量高達14.56%,合金硬度達到195HB;當復合添加0.10%Nb和0.05%V時,合金的二次枝晶臂間距及一次枝晶直徑分別達到最小值10.59μm和86.93μm,合金中碳化物的量達到15.09%,合金硬度達到202HB。并且合金中碳化物的形貌及其在晶界的分布狀態(tài)同樣得到了改善。盡管不同組配的雙元素合金化處理對合金微觀組織的細化作用基本相似,但Nb、V復合合金化對ZG40Cr25Ni20Si2鋼的強化效果明顯優(yōu)于Ti、V復合合金化。此外,經單一元素Ti合金化和雙元素Ti、V合金化處理的合金,基體中存在彌散分布的第二相顆粒,具有第二相強化作用。
[Abstract]:Austenitic heat-resistant steel ZG40Cr25Ni20Si2 has good high temperature mechanical properties, oxidation resistance, corrosion resistance and microstructure stability. It is widely used in automobile exhaust manifold, turbocharger shell and other parts. However, the coarse dendrites in the as-cast alloy cause serious segregation, which can not be eliminated even by heat treatment, which leads to the deterioration of the properties and the shortening of the service life of the as-cast alloys. The purpose of this paper is to explore the effect of single element alloying and double element alloying on microstructure and mechanical properties of ZG40Cr25Ni20Si2 steel, and to reveal the strengthening mechanism of alloying treatment. The results show that the amount of carbides in the 20% ZG40Cr25Ni20Si2 steel is 8.49. After single element alloying, the amount of carbides in the alloy increases with the increase of alloy element content. At the same time, the addition of TiNb can improve the morphology of carbides and the distribution of carbides at grain boundaries. As a result, the morphology of intergranular carbides changed from the initial continuous network distribution to the fine discontinuous distribution. The secondary dendritic arm spacing and primary dendritic diameter of steel ZG40Cr25Ni20Si2 were 13.99 渭 m and 174.73 渭 m, respectively, and the hardness was 174HB. When the alloy was alloyed with single element, the secondary dendritic arm spacing and the primary dendritic diameter of the alloy were decreased to some extent, and the hardness of the alloy was also improved. With the increase of the content of TiNb, the secondary dendritic arm spacing and primary dendritic diameter decrease first and then increase, while the hardness of the alloy increases first and then decreases. When Ti content is 0.15, the secondary dendritic arm spacing and primary dendritic diameter reach the minimum values of 11.15 渭 m and 93.05 渭 m, respectively. The second dendritic arm spacing and the primary dendritic diameter reached the minimum values of 10.63 渭 m and 75.11 渭 m, respectively, and the hardness of the alloy reached the maximum value of 186HB.The NB content was 0.05 渭 m. The secondary dendritic arm spacing and the primary dendrite diameter reached the minimum values of 10.21 渭 m and 73.43 渭 m, respectively. The alloy hardness reached the maximum value 198HB.Nb and V in ZG40Cr25Ni20Si2 steel, the ability to refine the dendrite in ZG40Cr25Ni20Si2 steel was slightly stronger than that of TiG40Cr25Ni20Si2 steel. After double element alloying, the microstructure of the alloy was refined, the amount of carbide precipitated increased and the hardness of the alloy increased. With the addition of 0.05 Ti and 0.05 V, the secondary dendritic arm spacing and primary dendritic diameter reached the minimum values of 12.07 渭 m and 99.36 渭 m, respectively, the amount of carbides reached 14.56 and the hardness of the alloy reached 195HB.When the composite was added 0.10Nb and 0.05V, The secondary dendritic arm spacing and the primary dendritic diameter of the alloy reach the minimum values of 10.59 渭 m and 86.93 渭 m, respectively. The amount of carbide in the alloy reaches 15.09 and the hardness of the alloy reaches 20HB. The morphology and distribution of carbides in the alloy were also improved. Although the effect of different alloying treatments on microstructure refinement is similar, the strengthening effect of NbAV composite alloying on ZG40Cr25Ni20Si2 steel is better than that of TiG40Cr25Ni20Si2 steel. In addition, after Ti alloying and Ti V alloying, the second phase particles are dispersed in the matrix, which has the effect of strengthening the second phase.
【學位授予單位】：西安理工大學
【學位級別】：碩士
【學位授予年份】：2017
【分類號】：TG142.1

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