DP780高强钢板材温热成形性能的研究

发布时间：2018-05-27 09:14

  本文选题：DP780高强钢 + 成形极限图(FLD)　； 参考：《南昌航空大学》2016年硕士论文

【摘要】：随着汽车工业的快速发展,节能和环保的要求在汽车制造领域越来越明显,同时汽车车身轻量化的概念也日益显著。在汽车制造领域,高强钢板的运用已成为实现汽车车身轻量化和保证汽车强度的主要途径之一。由于高强钢板材强度的提高,高强钢板在冷冲压过程中存在冲压力大、工件易破裂或形状畸变严重等问题;而在热冲压成形过程中则易出现工件的表面容易氧化、表面质量达不到要求和能耗相对过大等问题。温冲压成形技术的提出有望克服热冲压和冷冲压在高强钢板成形方面的局限,同时兼顾它们的一些优点。为此,本文采用试验与微观相结合的方法,开展DP780高强钢板材温热成形性能研究,为深入认识DP780高强钢板的温热成形工艺奠定基础。利用北京航空航天大学研制的BCS-50AR通用板材热成形试验机,在室温、100℃、200℃、300℃、400℃、500℃下对DP780高强钢板材进行成形极限试验,建立不同温度下的成形极限图(FLD)。研究发现,成形温度对DP780高强钢板材成形极限图影响较大,成形极限曲线随变形温度升高而上升,但在300℃时成形极限曲线位置反而比25℃时的还低。在25℃～200℃时成形极限曲线升幅较小,200℃～400℃时升幅明显增加,400℃～500℃时升幅变小。随着变形温度的上升,高强钢板材的塑性有所提高,在400℃时材料的塑性有明显改善,但在300℃时材料发生“蓝脆”。同时研究分析了凸模速度、应力状态对DP780高强钢板成形极限的影响,并基于DP780高强钢板成形极限试验,建立其在不同温度下的成形极限曲线计算模型。通过硬度分析和OM、SEM、TEM等微观分析方法对不同温度下DP780高强钢板变形特征进行了表征。硬度分析表明,DP780高强钢板在温室下成形过程中出现加工硬化现象,随着成形温度升高,成形极限后试样的硬度呈下降趋势,在300℃时出现异常,材料出现“蓝脆”现象,DP780高强钢板变的脆而硬。微观分析表明,随着温度的升高,马氏体的数量逐渐减少,当温度为400℃和500℃时,可以观察到一些黑点组织,这是马氏体组织分解出来的碳化物颗粒;在室温下成形后试样断口上出现细小韧窝,但韧窝不明显,韧窝数量较少,随着温度的升高,韧窝的数量,大小和深度均有显著提升,表明材料的塑性有所提高;而300℃时,断口形貌呈现出解理断裂的形貌。100℃时DP780高强钢中的碳原子在马氏体内发生聚集和偏聚;200℃时马氏体转变为回火马氏体组织;300℃时,马氏体会继续发生分解,同时残余奥氏体完全转变为贝氏体;在400℃～500℃范围内马氏体分解为回火屈氏体组织。室温下塑性变形过程中,位错运动受到晶体间摩擦力的阻碍作用,从而导致大量的位错纠缠和塞积。成形温度升高同时使位错湮灭机制和增殖机制加强,但材料位错湮灭机制起着主导作用,材料位错密度降低。
[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，

本文编号：1941396