【作者】 谭勇；

【导师】 刘常升；

【作者基本信息】 东北大学 ， 材料学， 2012， 博士

【摘要】 随着汽车、家电等行业的快速发展,优质冷轧带钢的需求量逐年提高。成型性能和涂装性能是衡量冷轧板使用性能的重要指标,这均与带钢表面形貌的特征参量有密切关系。其中均匀分布的粗糙度和随机分布的微观凸起形貌,可以减少光学干涉条纹、避免橘皮效应,有利于改善带钢的涂漆光学特性。轧辊在钢铁生产中起着举足轻重的作用,任何一种板材和型材都是由轧辊完成其成形过程而生产出来的。其使用状况不仅影响钢铁生产消耗和生产成本,而且直接影响生产稳定和产品质量。对轧辊表面进行毛化处理是提高其使用性能的最重要方法之一。钢铁材料毛化工艺主要有喷丸毛化工艺、电火花毛化工艺及激光毛化工艺三种。这三种毛化工艺都是使辊面材料脱落或烧损形成尖锐的内凹毛化形貌,生产出来的毛化辊受冷轧辊材质的影响,粗糙度衰减过快,使用寿命低,以及毛化冷轧辊表面形貌中凹坑多于凸起,因而不利于带钢对其表面粗糙度的拷贝。本论文在控制电沉积铬的同时引入表面处理、过渡层和添加剂来强化镀铬毛化过程,籍可控电化学工艺和表面处理来实现表面构型,获得可控的表面形貌、粗糙度和硬度；提高毛化层间的结合强度,降低层脱落风险性；通过添加所含超细颗粒的复合共沉积实现毛化层的强韧化,进一步提高毛化层的耐磨性。结合国内外工艺现状,本论文设计了一种在金属表面进行颗粒复合电化学铬毛化以及脉冲电沉积毛化的实验。实验电源采用脉冲电源以及直流电源,以最终铬毛化层的表面粗糙度Ra为考察对象,采用在金属表面先直流电沉积镍以及颗粒为中间层,再直流电沉积铬,或采用不同参数设置的脉冲电化学毛化。实验得到了具有一定粗糙度且结晶状态为半球状的铬毛化层,同时凸起远多于凹坑,这将有利于实际生产中带钢对于冷轧辊形貌的拷贝,为生产更优质的冷轧产品提供了可能。复合电化学毛化试验结果表明：复合颗粒电化学毛化工艺中,电解液温度对试验的结果影响最大,电解液的pH值对试验结果的影响次之,电流密度对试验结果的影响最小。电流密度为4A/dm2、电解液温度为60℃、电解液的pH值为4.8时,粗糙度结果都比较大,为试验所得的最佳工艺条件。中间层粗糙度主要集中在4～6μm之间,电化学毛化分布均匀,结合力合格。电沉积铬以后表面硬度在1031.8HV,粗糙度主要集中在2～4μm之间,试样在沉积铬后表面具有较好的硬度和比较理想的粗糙度。合适的脉冲工艺实验对粗糙度值Ra有很显著的影响,粗糙度值Ra在0.996～3.788μm内变化,其中脉冲电流密度Jp、关断时间toff及总时间t对于粗糙度值的影响显著。由于占空比γ对粗糙度影响显著,导通时间ton和关断时间toff共同决定占空比γ,因而导通时间ton对粗糙度值的影响也显著；随着总电镀时间t的增长,粗糙度值Ra有一定的增长,但当t大于100min时,Ra变化不大；合适的电镀液温度为50℃。经对脉冲电化学毛化后的试样测试,毛化层与基体间的结合力都合格,镍沉积层作为金属基体和铬沉积层的中间层,起到了很好的过渡作用。不仅使得增加了层之间的结合力,而且降低了铬层的内应力,有效的减少了铬层的表面裂纹。从成分分析可以得出,具有粗糙表面的镀层主要成分是金属铬。这使得毛化层具有很好的硬度和耐磨性。研究证明,在一定的工艺条件下,通过复合颗粒电化学毛化以及脉冲电化学毛化来实现材料表面毛化效果是可行的,该工艺得到的毛化层具有半球状凸起的表面形貌及高的峰值密度。通过脉冲电化学毛化扩散双电层模型的建立,解释电极附近的脉冲扩散层的金属离子的浓度随着脉冲电流的通断而呈现不断地波动,金属离子的运动速度与电流强度相关性大。采用脉冲电化学毛化时,由于脉冲电流具有较高的峰值,可以实现在脉冲扩散层处,具有较大离子浓度,晶粒长大速度较大时,可以获得较大的粗糙度及理想表面形貌。更多还原

【Abstract】 With the rapid development of the auto appliance industry and electrical household appliances industry, the quantity demand of the high quality of cold rolled sheet is increasing with each passing year. The operational performances, molding and painting, are the most important targets for cold rolling plate. The operational performances are closely connected with the characteristic parameters of steel strip surface topography. The uniform distribution of the roughness and the irregular distribution of the morphology can reduce optical interference fringes and avoid the orange peel effect to improve the optical properties of the coated strip.Roller plays a critical role in iron and steel industry. Any kind of plates and profiles are produced roll forming process. The service condition of the roller affects not only the steel consumption in the process of production and the production cost, but also the stability of production and product quality. Now the manufacturing quality and level of the roller is becoming the vital signs for national metallurgy technology.There are three textured technologies in common industry use, Shot Blast Texturing (SBT)、 Electrical Discharge Texturing (EDT) and Laser Beam Texturing (LBT). All of the three textured technologies can make roller surface materials fall off or overfire to form aculeate and concave surface. The roughness of the manufactured texturing rollers attenuated rapidly inducing lower using life because of the effect of cold roller’s material. If the amounts of the concaves on the surface of cold roller are higher than that of heaves, it makes against for steel strip to copy the roughness of the roller.In this thesis, the surface treatment, central layer and additive agents were induced the controlled chromium deposition to achieve the surface conFig.uration and to obtain the controlled surface morphology, roughness and hardness. Through the controlled process, the bonding strength of the substrate and central layer, the chromium layer and the central layer can be improved to reduce the risk of the electroplating sloughing.In this thesis, a series of chromium plating experiments were designed to perform the particle-doped and pulse chromium electroplating texture experiments on steel. Pulse power source and DC electrical source were used in these experiments. For the particle-doped chromium electroplating texture experiments, the Al2O3and the WC particle-doped nickel electroplating were prepared as the central layer, followed the top chromium coating was obtained by DC electroplating. For the pulse chromium electroplating texture experiments, the nickel electroplating was prepared as the central layer and followed top chromium layer was obtained by pulse electroplating with different parameters. The certain extent of roughness and hemispherical crystal coatings, which there were more bulging on the surface, were obtained by both the methods mentioned above. This kind of morphology can be beneficial for copying the surface topography of cold rolls.From the results of particle-doped electroplating experiments, it was shown that the temperature of the electroplating bath was the greatest impact factor, the pH value of the electroplating bath was the second greatest impact factor and the current density had less effecting in all effecting parameters. To obtain the highest roughness of the central layer, the optimal technological conditions were as following:temperature50℃, current density5A/dm2, and pH4.8. The surface roughness of the central electroplating layer was in the range of2-5μm. When deposited by chromium coating, the hardness of the coatings was about1031.8HV, and the roughness of the coatings was in the range of2-4μm. The coatings deposited on steel sheet showed better roughness and rigidity.From the results of pulse electroplating experiments, it was shown that the pulse technological parameters affected the roughness (Ra) very distinctly from0.966to3.788. The three parameters, which consisted of pulse current density Jp, turn-off time toff and electroplating time t, were the evident facters to affect the roughness. The duty cycle y, which was determined by turn-on time ton and turn-off time toff, also affected the roughness. With the increasing of electroplating time, the roughness increased to a certain degree until the electroplating time reached to100min. The appropriate temperature of the electroplating bath was about50℃.The tests of pulse texturing showed that the binding force between the coating and the substrate are qualified. The nickel electroplating layer, which was as the intermediate layer between the metal substrate and chromium deposition, showed a well role transition. This intermediate layer can not only increase the binding force between the coatings, but also can reduce the internal stress of the chromium electroplating to lessen the surface cracks of the chromium deposition. From the analysis of compositions, it was shown that the main component chromium can obtain better hardness and wear resistance.The experiments showed that texturing on the surface of steel sheet was feasible under certain conditions by particle-doped and pulse electroplating. The textural coatings showed hemispherical crystals and high peak density.The model of pulse electroplating diffusion double electric layer was established. The concentration metal ions located in the pulse diffusion layers near the electrode presented undulate constantly with the switching of pulse current. The movement velocity of metal ions was critical relatively with the current intensity. When using pulse electroplating, the larger concentration of metal ions in the diffusion layer can be obtained on account of higher peak value of pulse current. The larger roughness and perfect surface morphology can be obtained when the growing-up velocity of grains was greater.更多还原