【摘要】：隨著高強鋼熱沖壓技術(shù)在汽車行業(yè)的廣泛應用,對熱沖壓件提出了更高的要求,例如B柱、車門防撞梁及保險杠等對碰撞安全性能要求比較高的零件來說,僅具有較高的強度,并不能顯著提高碰撞過程的安全性能。為了進一步提高碰撞安全性能,需要一種具有性能梯度分布的沖壓件,通過高強度區(qū)域在碰撞過程中材料的高強度,來保障乘員的安全,并依靠局部的強度相對比較低、塑形比較好的區(qū)域的塑性變形達到吸收碰撞能的目的。高能耗一直是制約熱沖壓成形技術(shù)廣泛應用的一個主要因素,目前廣泛采用的輥底爐坯料加熱方式,存在加熱設備相對體積和能耗相對較大,加熱效率不高等缺點。自阻加熱作為一種新型的板材加熱方式,具有設備體積小、控制方便、加熱速度快且效率高等優(yōu)點,是板材熱成形技術(shù)的理想熱源。本文以高強度22MnB5鋼板為實驗材料,設計開發(fā)了分區(qū)控溫模具及自阻加熱裝置,實現(xiàn)了具有性能梯度U形件的熱沖壓成形,對自阻電加熱方式進行了探索,并對沖壓件的梯度性能進行深入研究。首先,采用平板模試驗方法分析了模具溫度對22MnB5鋼板組織性能的影響規(guī)律。22MnB5鋼板的屈服強度和抗拉強度均隨著模具溫度的逐漸升高而下降,而延伸率逐漸升高的趨勢。模具溫度低于250℃時組織以板條狀馬氏體為主,抗拉強度大于1200MPa,延伸率大于5%,滿足對梯度性能沖壓件的高強區(qū)性能要求。模具溫度高于450℃時組織以鐵素體+珠光體+碳化物為主,抗拉強度大于600MPa,延伸率大于15%,滿足對梯度性能沖壓件的低強度區(qū)力學性能要求。其次,應用分區(qū)控溫的U形件試驗模具裝置,采用數(shù)值模擬與實驗相結(jié)合的研究方法,分析了熱模溫度對過渡區(qū)組織與性能的影響規(guī)律。隨著熱模溫度的升高,高強區(qū)與低強區(qū)的硬度差值逐漸增大,高強區(qū)平均硬度約為500HV,低強度區(qū)的硬度隨模具溫度的上升呈逐漸下降的趨勢,熱模溫度在200℃~500℃之間,硬度在450HV~250HV范圍以內(nèi),過渡區(qū)的寬度約為60mm,位于空氣間隙處且偏向冷模一側(cè),高強度側(cè)微觀組織以馬氏體為主,向低強度區(qū)過渡過程中逐漸出現(xiàn)貝氏體組織,而低強度區(qū)域主要以鐵素體和碳化物為主。自阻電加熱延伸率高于爐加熱,而抗拉強度略有下降,高強區(qū)的組織中馬氏體板條中間存在鐵素體相,而低強度區(qū)域存在更多的碳化物析出相。最后,分析了具有梯度性能管形件軸向壓潰的變形規(guī)律及能量吸收性能。隨著熱模溫度的升高,軸向壓潰所需載荷逐漸降低,壓潰吸收的總能量呈下降趨勢。原始母材及整體冷模淬火件壓潰變形開始于試樣的中部,而具有梯度性能的成形件變形集中在低強度區(qū)。壓潰的主要失效方式為焊點的開裂,強度較高的管形件出現(xiàn)撕裂的現(xiàn)象。
[Abstract]:With the wide application of hot stamping technology of high-strength steel in automobile industry, higher requirements are put forward for hot stamping parts, such as B-column, door anti-collision beam, bumper and other parts with high impact safety performance, which only have higher strength. It can not significantly improve the safety performance of collision process. In order to further improve the safety of collision, a kind of stamping parts with gradient distribution of performance is needed to ensure the safety of the occupants by the high strength of the materials in the high strength area during the impact process, and the relative low strength depends on the local strength. The plastic deformation of the better shape region can absorb the collision energy. High energy consumption has been one of the main factors restricting the wide application of hot stamping forming technology. At present, the widely used heating method of roll furnace billet has some shortcomings, such as the relative volume and energy consumption of heating equipment is relatively large, and the heating efficiency is not high. As a new type of plate heating, autoresistive heating has the advantages of small volume, convenient control, high heating speed and high efficiency. It is an ideal heat source for sheet metal hot forming technology. In this paper, using high strength 22MnB5 steel plate as experimental material, a zonal temperature-control die and a self-resistive heating device are designed and developed. The hot stamping forming of U-shaped parts with performance gradient is realized, and the self-resistive electric heating method is explored. The gradient performance of stamping parts is studied. Firstly, the influence of die temperature on the microstructure and properties of 22MnB5 steel plate was analyzed by plate die test. The yield strength and tensile strength of 22MnB5 steel plate decreased with the increasing of die temperature, but the elongation increased gradually. When the temperature of die is lower than 250 鈩，

本文編號：2334922