發(fā)布時間：2018-01-24 04:01

  本文關鍵詞： 有序相 低密度高強度鋼 第一性原理 電子結構 力學性能　出處：《昆明理工大學》2017年碩士論文　論文類型：學位論文

【摘要】：低密度高強度鋼具有低密度、耐腐蝕、高強韌性等較好的綜合性能,該鋼在汽車、軍工、化工等領域具有巨大的潛力,同時在汽車輕量化和安全性上也具有廣泛應用的前景。低密度高強度鋼中的有序相相主要為B2型的(Fe,Mn)Al和DO_3型的(Fe,Mn)3Al,然而這些有序相在低密度高強度鋼中含量較少,且在一定條件下才會生成。由于目前關于有序相的研究比較少,因此本論文通過理論計算與實驗相結合的方法,計算了 Fe-Al金屬間化合物與Fe-Mn-Al合金的穩(wěn)定性、電子結構、力學性質和德拜溫度等,研究了 Fe-Al化合物的組織與力學性能,同時對Fe-Mn-Al-C鋼的組織與力學性能進行了進一步研究。這些研究可以為低密度高強高塑性特種鋼鐵新材料的工業(yè)化提供理論基礎與數(shù)據(jù)支持。本論文主要獲得了以下研究結果:這些Fe-Al化合物、DO_3型Fe-Mn-Al合金和B2型Fe-Mn-Al合金的結合能和形成焓均為負值,表明它們具有熱力學穩(wěn)定性;通過力學穩(wěn)定性判定條件表明這些合金具有結構穩(wěn)定性。計算了這些化合物的體模量、剪切模量、楊氏模量、硬度及泊松比,研究表明:DO_3型Fe-Mn-Al合金具有較好的塑性和較低的強度,B2型Fe-Mn-Al合金的有較差的塑性和較高的強度。同時還研究了這些化合物的力學各向異性,發(fā)現(xiàn)它們都有較強的楊氏模量各向異性。通過對這些化合物的電子結構與德拜溫度的研究,發(fā)現(xiàn)這些化合物的化學鍵主要是金屬鍵和共價鍵的作用,同時也有反鍵作用。通過實驗合成了 Fe_3Al和FeAl化合物,研究了它們的組織和與學性能,表明FeAl合金具有較高的硬度和強度,而具有較差的塑性;Fe_3Al合金具有較低的硬度和強度,但有較好的塑性。最后,還研究了 Fe-Mn-Al-C鋼的組織與力學性能,研究表明該實驗鋼為雙相鋼,以奧氏體和鐵素體為基體。通過XRD物相分析,發(fā)現(xiàn)在組織中存在B2和DO_3的有序相,即使經(jīng)過較高溫度的固溶處理,B2和DO_3有序相依然能夠穩(wěn)定存在。隨著固溶溫度的升高,該鋼中有序相含量越來越低。通過室溫拉伸力學性能的研究,表明隨著固溶溫度的升高材料的抗拉強度降低,而延伸率增大。因此,可以推測有序相能夠提高鋼的強度而降低鋼的塑韌性。
[Abstract]:Low density high strength steel has good comprehensive properties, such as low density, corrosion resistance, high strength and toughness. It has great potential in automobile, military industry, chemical industry and so on. The ordered phase in low density and high strength steel is mainly composed of B _ 2 type Fe _ 2O _ MnAl and DO_3 type Fe _ (Fe). However, these ordered phases are less in low density and high strength steel, and can only be formed under certain conditions. Therefore, the stability, electronic structure, mechanical properties and Debye temperature of Fe-Al intermetallic compound and Fe-Mn-Al alloy were calculated by the method of theoretical calculation and experiment. The microstructure and mechanical properties of Fe-Al compounds were studied. At the same time, the microstructure and mechanical properties of Fe-Mn-Al-C steel have been further studied. These studies can provide theoretical basis and data support for industrialization of new special steel materials of low density, high strength and high plasticity. The main results of this thesis are as follows:. These Fe-Al compounds. The binding energy and formation enthalpy of DO_3 type Fe-Mn-Al alloy and B2 type Fe-Mn-Al alloy are both negative, which indicates that they have thermodynamic stability. The structural stability of these alloys was determined by mechanical stability. The bulk modulus, shear modulus, Young's modulus, hardness and Poisson's ratio of these compounds were calculated. The results show that the Fe-Mn-Al alloy has good plasticity and low strength. The b2-type Fe-Mn-Al alloy has poor plasticity and high strength. The mechanical anisotropy of these compounds has also been studied. It is found that they all have strong Young's modulus anisotropy. By studying the electronic structure and Debye temperature of these compounds, it is found that the chemical bonds of these compounds are mainly metal bonds and covalent bonds. Fe_3Al and FeAl compounds were synthesized by experiments and their microstructure and mechanical properties were studied. The results show that FeAl alloy has high hardness and strength. But with poor plasticity; Fe_3Al alloy has lower hardness and strength, but better plasticity. Finally, the microstructure and mechanical properties of Fe-Mn-Al-C steel are studied. The results show that the experimental steel is a dual phase steel. Using austenite and ferrite as the matrix, the ordered phase of B2 and DO_3 was found in the microstructure by XRD phase analysis, even after solution treatment at a higher temperature. The ordered phase of B2 and DO_3 can still exist stably. With the increase of solution temperature, the content of ordered phase in the steel becomes lower and lower. The tensile mechanical properties of the steel at room temperature have been studied. The results show that the tensile strength decreases and the elongation increases with the increase of the solution temperature. Therefore, it can be inferred that the ordered phase can increase the strength of the steel and decrease the ductility of the steel.
【學位授予單位】：昆明理工大學
【學位級別】：碩士
【學位授予年份】：2017
【分類號】：TG142.1

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