形变软氮化对模具钢3Cr2W8V性能、组织影响的研究

发布时间：2018-12-23 18:46

【摘要】：模具是制造业十分重要的工艺装备,随着信息化、智能化、高性能制造业的发展对模具的各项性能提出了更高的要求。热作模具钢是目前国内外模具行业广泛应用的材料之一,由于其在高温状态下承受强烈的摩擦力和冲击力,因此对材料提出了具有较高的韧性,抗热疲劳性及耐磨性等要求。3Cr2W8V热作模具钢是一种用作生产汽车进、排气门的专用模具材料,本文通过采用不同的形变方式(冷压缩、热压缩、冷锤锻和热冲击)对热作模具表面进行适量变形,以造成表面组织内的亚结构等,然后进行N-C共渗热处理,从表层硬度、渗层硬度梯度、试块尺寸变化、渗层厚度、表面渗层组织及断口等方面进行分析,探讨形变软氮化对模具钢3Cr2W8V性能、组织的影响。通过对失效模具的应力、裂纹、组织和硬度等方面进行分析,得出模具失效的主要原因,改善模具钢的组织、性能,确定热处理工艺及延长模具使用寿命等提供帮助。通过试验研究了不同形变方式及变形量对试样尺寸、渗层深度、表层硬度、渗层硬度梯度的影响,结果表明冷变形在一定的变形范围(4.87%～10.52%)内,渗层硬度梯度分布较合理,次表层与基体硬度梯度过渡比较平缓,次表层与基体的结合力比较理想,渗层表面有较高的硬度值,渗后尺寸变化不大,而且渗层的深度受变形量的影响也不大。热变形的试样,所选变形量(0.12%～12.39%)范围内,渗层与基体硬度梯度过渡均相对平缓,硬度分布均比较合理。3Cr2W8V钢软氮化后出现白亮层,有网状或脉状氮化物的存在。当变形量1%时,白亮层宽,存在更加细小的网状氮化物。当变形量为4.87～10.52%时,白亮层变窄、脉状氮化物细长,仍存在网状氮化物。当变形量为13.56-37.5%时,窄的白亮层,少量脉状氮化物细短,有网状氮化物。热变形试样随变形量的增大,白亮薄且连续,脉状氮化物更短且少,回火马氏体组织不明显。未变形试样的组织中有大量分散的孔洞,冷压缩的试样内部孔洞集中,而热变形的试样孔洞少且均匀,说明热变形得到白亮层的韧、塑性好。未变形冲击断口表现出明显脆性,冷、热压缩变形都比未变形的试样塑性有所改善,热变形断口上有明显的韧窝出现,冷变形断口上也有,但不如热变的明显。
[Abstract]:Mould is a very important process equipment in manufacturing industry. With the development of information, intelligence and high performance manufacturing industry, higher requirements are put forward for the properties of die and mould. Hot work die steel is one of the widely used materials in die industry at home and abroad. Because of its strong friction and impact force at high temperature, it has high toughness to the material. Thermal fatigue resistance and wear resistance. 3Cr2W8V hot work die steel is a kind of special die material used to produce automobile intake and exhaust valves. In this paper, different deformation methods (cold compression, hot compression, etc.) are used to produce automobile inlet and exhaust valves. Cold hammer forging and thermal shock) deform the surface of hot working die in order to cause substructure of surface structure, then carry on N-C co-permeation heat treatment, from surface hardness, hardness gradient of infiltration layer, change of sample size, thickness of infiltration layer, etc. The effect of deformation soft nitridation on 3Cr2W8V properties and microstructure of die steel was discussed by analyzing the microstructure and microstructure of surface infiltrating layer. By analyzing the stress, crack, microstructure and hardness of the failure mould, the main causes of die failure are obtained, the structure and properties of die steel are improved, the heat treatment process is determined and the service life of die is extended. The effects of different deformation modes and amount of deformation on specimen size, depth of infiltration layer, surface hardness and hardness gradient of infiltrating layer are studied. The results show that cold deformation is within a certain deformation range (4.87% or 10.52%). The distribution of hardness gradient is more reasonable, the transition of hardness gradient between subsurface layer and matrix is relatively smooth, the adhesion between subsurface layer and matrix is relatively ideal, the surface of infiltrating layer has higher hardness value, and the size of infiltrating layer does not change much after infiltration. Moreover, the depth of seepage layer is not affected by the amount of deformation. In the range of 0.12% (12.39%) of hot deformation, the transition of hardness gradient between infiltrating layer and matrix is relatively smooth, and hardness distribution is reasonable. White bright layer appears after soft nitriding of 3Cr2W8V steel. The presence of reticular or veined nitrides. When the deformation is 1, the white layer is wide and the nitride is smaller. When the deformation ranges from 4.87 to 10.52, the white layer becomes narrower, the vein-like nitride is slender, and the reticular nitride still exists. When the amount of deformation is 13.56-37.5%, the narrow white bright layer, a small amount of veined nitride is thin and short, and there is a network of nitride. With the increase of the amount of deformation, the hot deformation specimen is white thin and continuous, the vein-like nitride is shorter and less, and the tempering martensite structure is not obvious. There are a large number of dispersed pores in the microstructure of the undeformed specimen, and the pores in the cold compressed specimen are concentrated, while the pores in the hot deformation sample are less and uniform, which indicates that the white layer is toughened and the plasticity is good. The undeformed impact fracture shows obvious brittleness, cold and hot compression deformation is better than the undeformed specimen's plasticity, there are obvious dimples on the hot deformation fracture surface and cold deformation fracture surface, but it is not as obvious as the thermal deformation fracture surface.
【学位授予单位】：山东大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TG142.1;TG306

【相似文献】