喷射成形含铌M3型高速钢组织性能优化与应用研究

发布时间：2018-03-03 13:30

  本文选题：喷射成形　切入点：高速钢　出处：《北京科技大学》2016年博士论文　论文类型：学位论文

【摘要】：M3型高速钢具有高硬度、高耐磨性、良好的强韧性,被广泛应用于刀具和冷作模具,其制备方法主要有传统铸造及粉末冶金。传统铸造冷速慢,形成的组织中含有大量网状共晶碳化物,直接影响其产品性能的提升。粉末冶金冷速快,生产的高速钢组织性能优良,但其复杂的制备工艺及过高的生产成本限制了其产品应用范围。此外,合金设计也是改善组织性能的重要途径,采用强碳化物形成元素提高耐磨性并结合快速凝固技术改善强韧性是高速钢的主要研发趋势。基于课题组开展的结合铌合金化与喷射成形技术制备M3型高速钢的相关研究,本文主要对喷射成形高速钢组织性能调控机理及应用展开相关研究,获得主要结论如下：通过研究关键工艺参数对沉积坯质量的影响规律,确定了喷射成形M3型高速钢的制备工艺：过热度160-180℃,雾化压力0.45-0.5MPa,气液比0.7-0.75。利用Gleeble热模拟研究了喷射成形M3型高速钢的热变形行为,建立了实验钢的本构方程、动态再结晶动力学方程、热加工图,确定出致密化处理工艺为：变形温度1050-1150℃,变形速率0.001-0.1 s-1,锻造比6.25。并最终制定了适合刀具应用的强韧化热处理工艺：淬火1200℃,回火560℃。发现喷射成形M3型高速钢沉积态的组织具有等轴晶及微观孔隙两个特征,其平均晶粒尺寸约为45μm,且晶界上分布着以钒为主的块状MC及以钼、钨为主的片层状M2C。热变形借助动态再结晶及机械破碎等机制使晶粒尺寸细化至10μm,并将片层状M2C分解破碎成均匀细小的颗粒状M6C与MC。回火二次硬化主要由二次M2C和MC碳化物析出所致,其中M2C呈针状,长约5-10nm,厚度约2nm。MC呈颗粒状,约3-5nm。铌能有效细化沉积态M2C共晶片层尺寸,并通过减少M2C中钨、钒、钼等强碳化物形成元素的含量降低其热稳定性,从而促进M2C分解,使含铌钢热变形后可获得更均匀细小的M6C,淬火时更易溶入基体提高过饱和度,从而提高二次硬化能力。同时,铌也提高了沉积态中一次MC的数量及其所含钨、钼元素的含量,并代替部分钒进入MC中,使含铌钢中MC硬度和稳定性提高,耐磨性增强。此两方面的作用是含铌钢刀具寿命提升的主要原因。总结而言,本文研究所得喷射成形高速钢制备、致密化及强韧化三个工艺与组织调控及铌合金化作用两个机理可为喷射成形含铌M3型高速钢在刀具上的应用提供工艺及理论支持。
[Abstract]:M3 high speed steel has high hardness, high wear resistance, good strength and toughness. It is widely used in cutting tools and cold working dies. The main preparation methods are traditional casting and powder metallurgy. The resulting microstructure contains a large number of reticular eutectic carbides, which directly affects the improvement of the properties of the products. However, its complex preparation process and high production cost limit its application scope. In addition, alloy design is also an important way to improve microstructure and properties. It is the main research trend of high speed steel to improve wear resistance by means of strong carbide forming element and to improve strength and toughness by combining rapid solidification technology. Based on the related research on the preparation of M3 type high speed steel by combining niobium alloying and spray forming technology carried out by our research group. In this paper, the control mechanism and application of microstructure and properties of spray forming high speed steel are studied. The main conclusions are as follows: the influence of key process parameters on the quality of deposition billet is studied. The preparation process of spray formed M3 high speed steel was determined: superheat 160-180 鈩，

本文编号：1561230