【作者】 周玉成；

【导师】 李远睿；

【作者基本信息】 重庆大学 ， 材料科学与工程， 2009， 硕士

【摘要】 高能激光在工业上的应用逐渐增加,激光表面热处理技术的发展是个很重要的原因。利用高能激光束扫描金属材料表面,金属表面薄层吸收激光辐射能量而迅速升温,很快便达到奥氏体温度区域,随着激光束离开金属表面,材料表面的热量依靠金属本身的热传导迅速向内部传递,以自激冷却的方式使金属表层达到极大的冷却速度,从而获得马氏体组织,这便是激光表面淬火工艺过程。激光表面淬火工艺最重要的特点是加热及冷却的速度极快,利于淬火层的晶粒显著细化,强化金属表层,使金属表面具有高的耐磨性能。淬火硬化层的硬度、有效硬化层深度、形貌及搭接区等的组织综合质量高是激光表面淬火欲达到的重要目的。然而激光表面淬火工艺的影响因素很多,导致实际操作中控制淬火质量的难度较大,激光热处理工艺的重复性及可移植性较差,从而制约了激光表面淬火技术在工业上的应用。为了强化激光加工技术的优势,促进其在工业上的应用,重要的是需要更好地认识和理解激光与材料相互作用的物理过程以及各工艺参数的影响,在此基础上确定激光淬火的主要工艺参数并对主要工艺参数结合设备进行试验和优化,再选择适当的方法对优化的相关激光淬火优化参数进行精确控制,从而实现良好的工业应用。本文使用3kWCO2激光器对优质碳素结构钢(20钢和45钢)以及Cr12MoV冷作模具钢进行激光表面淬火处理的工艺试验,研究了主要工艺参数(如激光功率、扫描速度以及搭接率等)对淬火质量(SEM形貌、金相组织、硬度及硬化层深度等)的影响作用。在实验的基础上,对表面淬火质量的影响因素进行分析研究,探求生产条件下工艺参数的选取方法,实现淬火工艺参数的优化。得到能够指导生产实践的有价值的工艺参数及控制质量的方法,促进激光表面淬火技术在结构钢和冷作模具钢的表面强化方向上的实际应用。经过对前述三种钢的单道扫描淬火工艺试验与分析,确定出了最佳工艺参数后,再以此参数进行多道扫描搭接试验,分析测定相关技术指标后得到各自的合理搭接率。通过以上工作,在重庆光机所的3kWCO2激光淬火设备上得出相关材料的最佳淬火工艺参数为:45钢优化参数为激光功率1350W,扫描速度1200mm/min,搭接率为20%;20钢的工艺参数应该在45钢优化参数进行基础上进行小的调整,使搭接率低于20%,或者稍降激光功率;Cr12MoV钢的激光功率为1500 W,搭接率不超过10%,亦可以采用无搭接的扫描方式。更多还原

【Abstract】 High-energy lasers are increasing being used in the industry for laser surface heat treatment to modify metal surface structures through intense heating followed by self-cooling. In laser quenching, a thin layer of the substrate is rapidly heated well into the austenitizing temperature range by laser heating and is cooled subsequently at a very fast rate, due to self-quenching by the conduction of heat into the bulk body, to produce a martensitic structure.Rapid heating and cooling are the key characteristics of laser quenching that enable the formation of a novel microstructure and thereby improve the hardness and the wear resistance. To achieve high wear resistance, the combination of the hardness, case depth, profile and microstructure of the quenched zone is important. Because there is so many factors influencing the laser surface hardening process that make it very hard to control the quality during the performance. This industrial application is limited by the poor repeatability and transportability of laser machining process.In order to enhance the potential for such laser machining process, it is essential to get better understanding of the physical process associated with the laser material interaction and the effect of various operating parameters on the performance, and then optimization the mostly important parameters and find the effective method to exactly control related parameters.This paper operate laser surface hardening experiment using 3kW CO2 continuous wave laser, the experiment materials are premium carbon steels (20#,45#) and Cr12MoV steel, The effect of process parameters (such as laser power, travel speed , overlapping ratio etc) on quenching quality (profile, microstructure, case depth and hardness etc) was examined. Base on experiment result, analysis the most influencing parameter on surface hardening quality, choose the suitable process parameter and then optimize the laser quenching process. These valuable process parameters meeting the experimental conditions and the method of controlling quality can be used in productive practice, it will promote the industrial application of laser surface hardening process on steel surface hardening specially die steel.We obtain the optimum parameters of laser surface hardening process by laser surface quenching experiments of single track quenching and multiple tracks quenching based on laser processing system of ChongQing Institute of Optics and Mechanics: for 45 steel laser power is 1350w, traverse speed is 1200 mm/min and overlapping ratio is 20%; for 20 steel, laser power is near to 1350w, it need lower overlapping ratio comparing to 45 steel; for Cr12MoVsteel, laser power is 1500 w and overlapping ratio is lower than 15%.更多还原