【作者】 王洁；

【导师】 刘允中；

【作者基本信息】 华南理工大学 ， 材料加工工程， 2010， 硕士

【摘要】 高合金工具钢具有高强、高韧、耐磨的优点,在工模具制造中应用广泛,但是由于合金化程度高,传统的制备工艺复杂,生产流程较长。利用机械合金化和放电等离子烧结技术制备的新型高合金工具钢,具有高硬度和高的致密度,晶粒细小,组织均匀,无碳化物偏聚。具有良好的综合力学性能,应用前景良好。本文首先研究了机械合金化制备HGSF01高合金工具钢粉末,利用X射线衍射(XRD)、扫描电子显微镜(SEM),DSC分析等手段分析了球磨后粉末的特征。采用不同的球磨时间和球料比进行了HGSF01高合金工具钢的球磨实验,球磨时间分别为40h、60h和80h,球料比分别为7.5:1、10:1和15:1。结果表明:混合元素粉末经球磨后得到了细小的粉末颗粒,粉末中有新的合金相生成,主要是(Fe,Cr)3C型碳化物,实现了机械合金化。球磨后的高合金工具钢粉末固相线温度为1161℃,确定烧结温度范围为1100℃左右。制备HGSF01高合金工具钢粉末的合理球料比和球磨时间分别为10:1和60h。本文还研究了HGSF01高合金工具钢粉末的放电等离子烧结(SPS)工艺,对HGSF01高合金工具钢粉末的放电等离子烧结进行5因素3水平正交试验。结果表明:在烧结过程中,烧结温度和保温时间对致密度影响最大。正交实验最优工艺参数为:球磨时间为40h,球料比为7.5:1,烧结温度为1100℃,升温速率为100℃/min,保温时间为10min。本文还对烧结后的试样进行了球化退火预处理和1100℃氮气淬火+560℃双重回火的最终热处理。利用光学显微镜和扫描电子显微镜观察了热处理前后烧结试样的显微组织,利用阿基米德排水法、洛氏硬度计、CMT5105微机控制电子万能试验机和M-2000型摩擦磨损试验机等手段分析了热处理前后烧结试样的相对密度、洛氏硬度、抗弯强度和摩擦磨损性能。结果表明:SPS烧结试样晶粒细小,晶粒尺寸在5μm左右,碳化物颗粒细小,弥散分布在基体上。同时,试样中存在少量的孔洞,但是孔洞直径一般不超过1μm。热处理前试样硬度达到HRC62,最终热处理后硬度为HRC61。热处理前后试样最高抗弯强度均达到1500MPa左右。通过对比摩擦磨损后试样的磨痕宽度发现,烧结态试样比电渣重熔态试样具有更好的耐磨性,热处理态试样比烧结态试样具有更好的耐磨性。往HGSF01高合金工具钢中添加WC颗粒制备成复合材料后,其抗弯强度和耐磨性能显著提高。更多还原

【Abstract】 High-alloying tool steels are widely used in the industrial production of tools and dies due to their high strength,good ductility and excellent wear resistance. However,the conventional processes are very complex with long production runs because of the high alloying contents. A new kind of high-alloying tool steel was prepared by mechanical alloying and spark plasma sintering,obtaining high hardness and relative density,fine grain size and uniform microstructures without carbide segregation.In this work,HGSF01 high-alloying tool steel powders were prepared by mechanical alloying,and the characteristics of ball-milling powders were analyzed by means of SEM,XRD and DSC. The experiments for preparation of HGSF01 high-alloying tool steel powders with different ball milling time and weight ratio of balls to powders were performed. The ball milling time was 40h,60h and 80h and the weight ratio of balls to powders was 7.5:1,10:1 and 15:1. The results show that the powders have been alloyed by ball-milling,after ball-milling a new phase (Fe,Cr)3C carbide appears in the small powder particles. The sintering temperature is selected as about 1100℃because the solidus temperature of the ball-milled high-alloying tool steel powders is 1085℃. A reasonable ball milling time and weight ratio of balls to powders for the preparation of HGSF01 high-alloying tool steel were 10:1 and 60h.The spark plasma sintering technology for the prepared HGSF01 of high-alloying tool steel powder was also investigated. The orthogonal experiments with 5 factors and 3 levels were studied for preparation of HGSF01 high-alloying tool steel powders by spark plasma sintering. The results show that the sintering temperature and holding time have the greatest effect on relative density of the samples in the sintering process. The best reasonable sintering parameters was that: milling time for 40h,weight ratio of balls to powders for 7.5:1,sintering temperature for 1100℃,heating rate for 100℃/min and holding time for 10min.Annealing pretreatment was taken and nitrogen quenching at 1100℃as well as double tempering at 560℃were taken as the final heat treatment for the sintered samples. The microstructure of the sintered samples before and after the heat treatment was observed by optical microscope and scanning electron microscopy. The relative density,Rockwell hardness,bending strength and friction and wear properties of the sample before and after the heat treatment was analyzed by Archimedes’ principle,Rockwell hardness tester,and CMT5105 computer controlled electronic universal testing machine and the M-2000 friction and wear tester,respectively. The results show that the properties of the sintered sample obtained by SPS are as follows. Fine grains with a mean grain size of 5μm and very small carbide segregation uniform disperse in the matrix; a small number of holes exist in the sample with the diameter not more than 1μm. Before heat treatment the hardness is HRC 62,while after the final heat treatment the hardness change to HRC 61. The maximum bending strength of samples both before and after treatment is about 1500 MPa. Moreover,the wear resistance of the sintered samples is better than that of the ESR samples,and a better wear resistance of the samples after heat treatment is obtained by compared the wear scar width of sample after friction and wear. The bending strength and wear resistance of HGSF01 high-alloy tool steel is improved evidently by WC particles reinforced.更多还原