【摘要】：當今汽車節(jié)能減排和提高安全性能問題日益突出，強度級別在1500MPa以上的熱成形用鋼已經在減輕車身重量和提高汽車安全性能方面表現(xiàn)出巨大的優(yōu)勢，其在未來汽車車身零件中的應用潛力也毋庸置疑。為了研究和開發(fā)新一代具有自主知識產權的高性能超高強度熱成形用鋼，滿足國內市場的需求，本文設計了四種不同碳含量的熱成形用鋼新鋼種，，對設計的熱成形用鋼進行基礎性研究工作，為開發(fā)新型具有自主知識產權的熱成形用鋼提供必要的基礎數(shù)據和設計原則。 本文采用熱膨脹法和熱分析法對四種熱成形用鋼實驗鋼連續(xù)冷卻轉變規(guī)律進行了分析研究，得到了四種實驗鋼的CCT曲線，觀察了不同冷卻速率下轉變的微觀組織。研究結果表明：增加碳含量，能夠有效的提高熱成形用鋼的奧氏體穩(wěn)定性，鐵素體析出溫度、珠光體轉變溫度、貝氏體轉變溫度和馬氏體轉變溫度下降；同時增加碳含量提高了熱成形用鋼的淬透性，CCT曲線向右下方移動。對于碳含量為0.35%的熱成形用鋼，當以20°C/s的冷卻速率冷卻到室溫，就可獲得100%馬氏體組織。此外，碳含量的增加還可以提高熱成形用鋼冷卻轉變后組織的顯微硬度。 最后本文研究了四種實驗鋼的力學性能，研究結果發(fā)現(xiàn)：碳含量較低的兩種實驗鋼經淬火后得到100%馬氏體組織的抗拉強度低于1500MPa；而碳含量較高的兩種實驗鋼100%馬氏體組織的試樣拉伸時出現(xiàn)脆性斷裂。針對這兩種碳含量較高的實驗鋼，我們采用馬氏體、貝氏體或馬氏體、貝氏體、少量鐵素體的復合組織來代替100%馬氏體組織，從而使得試樣在淬火后擁有高強度和一定的塑性。
[Abstract]:Nowadays, the problems of energy saving and emission reduction and improving safety performance of automobile are becoming more and more prominent. Hot forming steel with strength grade above 1500MPa has shown great advantages in reducing body weight and improving vehicle safety performance. Its application potential in the future car body parts is beyond doubt. In order to study and develop a new generation of high performance ultra-high strength hot forming steels with independent intellectual property rights to meet the needs of the domestic market, four new types of hot forming steels with different carbon content are designed in this paper. The basic research work of hot forming steel is carried out in order to provide the necessary basic data and design principles for the development of new hot forming steel with independent intellectual property rights. In this paper, the continuous cooling transformation of four experimental steels for hot forming was studied by means of thermal expansion method and thermal analysis method. The CCT curves of four experimental steels were obtained, and the microstructure of the transformation at different cooling rates was observed. The results show that the austenite stability, ferrite precipitation temperature, pearlite transformation temperature, bainite transformation temperature and martensite transformation temperature of hot forming steel can be improved effectively by increasing carbon content. At the same time, the hardenability of hot forming steel was improved by increasing carbon content, and the CCT curve moved to the lower right. For hot forming steel with 0.35% carbon content, 100% martensite structure can be obtained when cooling rate is 20 擄C / s to room temperature. In addition, the increase of carbon content can also improve the microstructure microhardness of hot forming steel after cooling transformation. Finally, the mechanical properties of four kinds of experimental steels are studied. The results show that the tensile strength of 100% martensite microstructure of two experimental steels with low carbon content is less than 1500 MPA after quenching. The brittle fracture occurred in the specimens of 100% martensite microstructure of two experimental steels with higher carbon content. For these two kinds of experimental steels with high carbon content, the composite structure of martensite, bainite or martensite, bainite, and a small amount of ferrite is used to replace the 100% martensite structure, which makes the specimen have high strength and certain plasticity after quenching.
【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】：2013
【分類號】：TG142.1

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