本文選題：DP780高強鋼 + 成形極限圖(FLD)��； 參考：《南昌航空大學》2016年碩士論文

【摘要】：隨著汽車工業(yè)的快速發(fā)展,節(jié)能和環(huán)保的要求在汽車制造領(lǐng)域越來越明顯,同時汽車車身輕量化的概念也日益顯著。在汽車制造領(lǐng)域,高強鋼板的運用已成為實現(xiàn)汽車車身輕量化和保證汽車強度的主要途徑之一。由于高強鋼板材強度的提高,高強鋼板在冷沖壓過程中存在沖壓力大、工件易破裂或形狀畸變嚴重等問題;而在熱沖壓成形過程中則易出現(xiàn)工件的表面容易氧化、表面質(zhì)量達不到要求和能耗相對過大等問題。溫沖壓成形技術(shù)的提出有望克服熱沖壓和冷沖壓在高強鋼板成形方面的局限,同時兼顧它們的一些優(yōu)點。為此,本文采用試驗與微觀相結(jié)合的方法,開展DP780高強鋼板材溫熱成形性能研究,為深入認識DP780高強鋼板的溫熱成形工藝奠定基礎(chǔ)。利用北京航空航天大學研制的BCS-50AR通用板材熱成形試驗機,在室溫、100℃、200℃、300℃、400℃、500℃下對DP780高強鋼板材進行成形極限試驗,建立不同溫度下的成形極限圖(FLD)。研究發(fā)現(xiàn),成形溫度對DP780高強鋼板材成形極限圖影響較大,成形極限曲線隨變形溫度升高而上升,但在300℃時成形極限曲線位置反而比25℃時的還低。在25℃～200℃時成形極限曲線升幅較小,200℃～400℃時升幅明顯增加,400℃～500℃時升幅變小。隨著變形溫度的上升,高強鋼板材的塑性有所提高,在400℃時材料的塑性有明顯改善,但在300℃時材料發(fā)生“藍脆”。同時研究分析了凸模速度、應(yīng)力狀態(tài)對DP780高強鋼板成形極限的影響,并基于DP780高強鋼板成形極限試驗,建立其在不同溫度下的成形極限曲線計算模型。通過硬度分析和OM、SEM、TEM等微觀分析方法對不同溫度下DP780高強鋼板變形特征進行了表征。硬度分析表明,DP780高強鋼板在溫室下成形過程中出現(xiàn)加工硬化現(xiàn)象,隨著成形溫度升高,成形極限后試樣的硬度呈下降趨勢,在300℃時出現(xiàn)異常,材料出現(xiàn)“藍脆”現(xiàn)象,DP780高強鋼板變的脆而硬。微觀分析表明,隨著溫度的升高,馬氏體的數(shù)量逐漸減少,當溫度為400℃和500℃時,可以觀察到一些黑點組織,這是馬氏體組織分解出來的碳化物顆粒;在室溫下成形后試樣斷口上出現(xiàn)細小韌窩,但韌窩不明顯,韌窩數(shù)量較少,隨著溫度的升高,韌窩的數(shù)量,大小和深度均有顯著提升,表明材料的塑性有所提高;而300℃時,斷口形貌呈現(xiàn)出解理斷裂的形貌。100℃時DP780高強鋼中的碳原子在馬氏體內(nèi)發(fā)生聚集和偏聚;200℃時馬氏體轉(zhuǎn)變?yōu)榛鼗瘃R氏體組織;300℃時,馬氏體會繼續(xù)發(fā)生分解,同時殘余奧氏體完全轉(zhuǎn)變?yōu)樨愂象w;在400℃～500℃范圍內(nèi)馬氏體分解為回火屈氏體組織。室溫下塑性變形過程中,位錯運動受到晶體間摩擦力的阻礙作用,從而導致大量的位錯糾纏和塞積。成形溫度升高同時使位錯湮滅機制和增殖機制加強,但材料位錯湮滅機制起著主導作用,材料位錯密度降低。
[Abstract]:With the rapid development of automobile industry, the requirements of energy saving and environmental protection are becoming more and more obvious in the field of automobile manufacturing, and the concept of lightweight automobile body is becoming more and more obvious. In the field of automobile manufacturing, the application of high strength steel plate has become one of the main ways to realize the lightweight and ensure the strength of automobile body. Due to the increase of strength of high strength steel sheet, the high strength steel sheet has some problems such as high punching pressure and serious shape distortion, while the surface of the workpiece is easy to be oxidized during hot stamping. The surface quality is not up to the requirement and the energy consumption is too large. The development of warm stamping technology is expected to overcome the limitation of hot stamping and cold stamping in high strength steel sheet forming, and at the same time give consideration to their advantages. Therefore, in this paper, the research on the warm forming properties of DP780 high strength steel sheet is carried out by means of the combination of test and microcosmic, which lays a foundation for further understanding the warm forming process of DP780 high strength steel sheet. In this paper, the forming limit test of BCS-50AR high strength steel sheet was carried out at room temperature 100 鈩，

本文編號：1941396