H13模具半导体激光强化与修复的研究

发布时间：2018-10-15 17:44

【摘要】：H13热作模具钢（国际牌号40CrMoV5，国内牌号4Cr5MoSiV1）是目前应用最广泛的热作模具钢之一，被广泛应用于铝、铜、镁及其合金的热挤压模、热锻模和铝、镁及其合金的压铸模等。由于模具的工作环境恶劣、成本高，对其进行强化与修复存在实际意义。激光淬火技术是现有各种激光表面处理技术中研究和应用最多的方法之一，具有变形小、硬度高等优点。激光熔覆技术是近年来发展比较迅速的一种表面改性技术，在激光作用下，基材表面形成良好冶金结合的熔覆层，从而改善或修复零部件，，延长其使用寿命。本文采用FL-DLS21-Dlight4kW半导体激光器对H13模具钢表面进行激光淬火强化和Ni基粉末激光熔覆修复。通过X-射线衍射仪（XRD）、光学显微镜（OM）和扫描电镜（SEM）等手段分析硬化层和熔覆层组织结构、物相组成，解释组织形态的形成机理及物相分布区域；采用HVS-1000A数显维氏硬度计对硬化层和熔覆层进行显微硬度测量；利用MG-2000型摩擦磨损试验机对基体、硬化层和熔覆层的耐磨性进行测试，并分析耐磨机理。同时本文还分析了熔覆层的裂纹和气孔的形成机理，并给出改进方法。组织分析表明，激光淬火后组织由表及里分为硬化区、热影响区和基体，硬化区主要由针状马氏体和少量残余奥氏体组成。激光熔覆后组织由表及里依次是熔覆区、结合区、热影响区和基体，组织形状依次为等轴晶、树枝晶、胞状晶和平面晶，Ni/SiC-Y2O3熔覆层由γ-(Ni,Fe)、Ni31Si12、M23C6、Ni3B组成， Y元素可能以Cr2Si2Y形式存在，同时还存在FeNi3化合物。硬化层与熔覆层硬度都得到明显提高。优化后的激光淬火硬化层最大硬度达到达到792.1Hv0.2，较基体提高58.4%，搭接区硬度较非搭接区有所下降，是由后续激光的回火作用导致。添加1.0wt.%Y2O3得到的激光熔覆层硬度最高，达867.4Hv0.2，较基体硬度提升73.5%。摩擦磨损实验表明，各试样磨损初期均表现为氧化磨损，H13基体主要表现为粘着磨损，激光淬火后硬化层与基体相比相对磨损性达到2.5，磨损机理表现为磨粒磨损。Ni/SiC-1.0wt.%Y2O3熔覆层耐磨性较基体提高1倍多，磨损机理以磨粒磨损和粘着磨损为主。裂纹形成的主要形式有：基体与结合区的界面产生的弥散裂纹；熔覆层顶部萌生的粗大裂纹；碳化物颗粒上的裂纹。气孔主要产生的原因：熔覆过程中熔池内的反应生成气体；粉末潮湿高温下产生气体。改善裂纹的主要方法：减少残余内应力；不使开裂的倾向性成为现实。改善气孔的主要方法：改进工艺参数与熔覆粉末配方；熔覆前对粉末进行预热。
[Abstract]:H13 hot work die steel (international grade 40CrMoV5, domestic grade 4Cr5MoSiV1) is one of the most widely used hot work die steels at present. It is widely used in hot extrusion dies of aluminum, copper, magnesium and its alloys, hot forging dies and die casting dies of aluminum, magnesium and its alloys. Because of the bad working environment and high cost, it has practical significance to strengthen and repair the mould. Laser quenching is one of the most studied and applied methods of laser surface treatment, which has the advantages of small deformation and high hardness. Laser cladding is a kind of surface modification technology which has been developed rapidly in recent years. Under the action of laser, a good metallurgical cladding layer is formed on the substrate surface, which can improve or repair parts and prolong their service life. In this paper, the surface of H13 die steel is strengthened by laser quenching with FL-DLS21-Dlight4kW semiconductor laser and repaired by laser cladding of Ni based powder. By means of X-ray diffractometer (XRD),) optical microscope (OM) and scanning electron microscopy (SEM), the microstructure and phase composition of hardened and cladding layers were analyzed, and the formation mechanism and phase distribution region of microstructure were explained. The microhardness of hardened layer and cladding layer was measured by HVS-1000A digital display Vickers hardness tester, the wear resistance of substrate, hardened layer and cladding layer was tested by MG-2000 friction and wear tester, and the wear resistance mechanism was analyzed. At the same time, the formation mechanism of cracks and pores in the cladding is analyzed, and the improvement method is given. The microstructure analysis shows that the microstructure can be divided into hardening zone, heat affected zone and matrix from outside to inside after laser quenching. The hardening zone is mainly composed of acicular martensite and a small amount of residual austenite. After laser cladding, the microstructure was in turn cladding zone, binding zone, heat affected zone and matrix. The microstructure shape was equiaxed crystal, dendrite, cellular crystal and plane crystal in turn. The Ni/SiC-Y2O3 cladding layer consisted of 纬-(Ni,Fe), Ni31Si12,M23C6,Ni3B, and Y element might exist in the form of Cr2Si2Y. There are also FeNi3 compounds. The hardness of hardened layer and cladding layer are improved obviously. The maximum hardness of the hardened layer after laser quenching is 792.1 Hv0.2, which is 58.4% higher than that of the matrix, and the hardness of the lap zone is lower than that of the non-lap zone, which is caused by the subsequent laser tempering. The hardness of laser cladding coating obtained by adding 1.0wt.%Y2O3 is the highest, reaching 867.4Hv0.2, which is 73.555% higher than that of matrix. The results of friction and wear experiments show that all the specimens exhibit oxidation wear at the beginning of wear, while the H13 matrix mainly exhibits adhesive wear. The relative wear resistance of the hardened layer after laser quenching is 2.5, and the wear mechanism is abrasive wear. The wear resistance of the Ni/SiC-1.0wt.%Y2O3 cladding layer is more than twice that of the substrate. The wear mechanism of the Ni/SiC-1.0wt.%Y2O3 cladding layer is mainly abrasive wear and adhesive wear. The main forms of crack formation are: dispersion crack at the interface between matrix and bonding zone; coarse crack at the top of the cladding layer; crack on carbide particle. The main reasons for the formation of porosity are the reaction gas in the melting pool during cladding, and the gas produced in the powder under moist and high temperature. The main ways to improve the crack are to reduce the residual internal stress and not to make the crack tendency come true. The main methods to improve the porosity are to improve the technological parameters and the formula of cladding powder, and preheat the powder before cladding.
【学位授予单位】：吉林大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TG174.4

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