【作者】 吴平生；

【导师】 董闯； 郝胜智；

【作者基本信息】 大连理工大学 ， 材料物理与化学， 2008， 硕士

【摘要】 本文利用“Nadezhda-2”型强流脉冲电子束装置处理模具钢SKD11,分析强流脉冲电子束处理产生的表面形貌和微观组织变化及其对材料表面性能的影响,以提高其使用寿命。研究表明,模具钢SKD11富集（Cr,Fe）₇C₃型碳化物,它与材料基体的热物理性能存在显著差异,强流脉冲电子束处理会引发碳化物的熔体喷发,这是处理该材料时形成表面熔坑的主要原因。经强流脉冲电子束不同工艺参数处理,样品表面的熔坑分布呈现以下规律:在相同加速电压下,熔坑面密度随脉冲处理次数的增加而减少,而熔坑平均尺寸呈现先随脉冲次数增加到最大值而后减小的趋势;对于相同处理次数时,使用高加速电压的样品表面形成的熔坑面密度较低,而且要比低电压更快的进入到平稳阶段。表面粗糙度呈现随脉冲次数增加而降低的现象。在强流脉冲电子束处理时,SKD11样品表层碳化物经过熔坑喷发和液相溶解扩散等过程,原始形态各异、颗粒粗大、分布不均匀的碳化物会变得圆润、细小、分布均匀;表面的Cr、C元素成分均匀化。此外,基体铁素体组织被瞬时加热到奥氏体温度以上,在极快速冷却时,高温态的奥氏体组织会保留到常温状态,并且冷却时碳化物固溶于奥氏体中,形成高奥氏体含量的重熔组织;随着脉冲次数的增加,铁素体和碳化物含量不断降低,而奥氏体的含量逐步增加;经15次脉冲轰击后,奥氏体的含量达到最大,铁素体完全转化成奥氏体;使用更多脉冲次数处理时,由于多脉冲的热量累积导致热影响区的温度与表层相差不大,使表层冷却速度减慢,铁素体得以再次析出,而奥氏体含量也会相应地降低。表面形貌和微观组织变化使得材料表面性能呈现以下变化:处理样品表面硬度较原始样品有所降低,且随着脉冲次数的增加先降低再回升;而耐磨性和耐腐蚀性能将随着脉冲次数的增加先增加后降低;性能变化趋势的极值均对应于强流脉冲电子束轰击15次的样品。更多还原

【Abstract】 In this study,one kind of mold steel,SKD1 lwas treated by High Current Pulsed Electron Beam（HCPEB） with different treating regimes on a ’Nedazhda-2’ type equipment.The main task of this work is to investigate the fundamental regularities of surface morphology and microstructure evolutions induced by HCEPB treatment and their effect on the surface property and service performance of SK.D11 mold steel.Under the HCPEB treatment,the difference of thermal physical properties between Cr-rich carbide（Cr,Fe）₇C₃ located in subsurface and material matrix will cause the eruption of carbide melt droplet and leave the typical crater forms on the modified surface.The distribution of craters on the treated samples exhibits the following regularity:for the same accelerating voltage,the area density of craters decreases with the increasing number of pulses;while the crater size increases to its maximum,then decreases with the increasing number of pulses.As for the same pulses,the higher voltage gives fewer craters and entered the stable stage earlier than the case of lower.The surface roughness decreases with the increasing number of pulses.The carbide in the initial sample is large sized and irregular shaped.It exhibits an inhomogeneous distribution.When treated by HCPEB,the carbide in the surface layer could be erupted and dissolved.The carbide in the treated sample become refined,spherical and exhibits a homogeneous distribution.The distribution of Cr and C becomes homogeneous after HCPEB treatment.Ferrite is transformed to austenite instantly in the fast heating process during HCPEB irradiation.During the fast cooling process,the austenite is suppressed until room temperature and carbide is included in the austenite.Remelted layer with high volume austenite is formed.The content of ferrite and carbide decreases with the increasing number of pulses.Contrarily,the content of austenite increase gradually.After 15 pulses treatment, ferrite has already transformed to austenite and the content of austenite gets its maximum. The decomposition of austenite would occur again when using too many numbers of pulses because the accumulation of heat in the matrix would lead to the decrease of cooling rate,as a result the process of transformation from austenite to ferrite could not be suppressed.Because of the surface morphology and microstructure evolution after HCPEB treatment, the surface properties exhibit the following evolution.The microhardness values measured on the treated surface are all smaller than initial sample;it would decrease with the increasing number of pulses firstly,and then decrease.Wear and corrosion resistance would increase firstly and then decrease with the increasing number of pulses;the HCEPB treated sample at 15 pulses treatment exhibits the extremum of the resistance values.更多还原