【摘要】：模具是制造業(yè)十分重要的工藝裝備,隨著信息化、智能化、高性能制造業(yè)的發(fā)展對(duì)模具的各項(xiàng)性能提出了更高的要求。熱作模具鋼是目前國內(nèi)外模具行業(yè)廣泛應(yīng)用的材料之一,由于其在高溫狀態(tài)下承受強(qiáng)烈的摩擦力和沖擊力,因此對(duì)材料提出了具有較高的韌性,抗熱疲勞性及耐磨性等要求。3Cr2W8V熱作模具鋼是一種用作生產(chǎn)汽車進(jìn)、排氣門的專用模具材料,本文通過采用不同的形變方式(冷壓縮、熱壓縮、冷錘鍛和熱沖擊)對(duì)熱作模具表面進(jìn)行適量變形,以造成表面組織內(nèi)的亞結(jié)構(gòu)等,然后進(jìn)行N-C共滲熱處理,從表層硬度、滲層硬度梯度、試塊尺寸變化、滲層厚度、表面滲層組織及斷口等方面進(jìn)行分析,探討形變軟氮化對(duì)模具鋼3Cr2W8V性能、組織的影響。通過對(duì)失效模具的應(yīng)力、裂紋、組織和硬度等方面進(jìn)行分析,得出模具失效的主要原因,改善模具鋼的組織、性能,確定熱處理工藝及延長模具使用壽命等提供幫助。通過試驗(yàn)研究了不同形變方式及變形量對(duì)試樣尺寸、滲層深度、表層硬度、滲層硬度梯度的影響,結(jié)果表明冷變形在一定的變形范圍(4.87%～10.52%)內(nèi),滲層硬度梯度分布較合理,次表層與基體硬度梯度過渡比較平緩,次表層與基體的結(jié)合力比較理想,滲層表面有較高的硬度值,滲后尺寸變化不大,而且滲層的深度受變形量的影響也不大。熱變形的試樣,所選變形量(0.12%～12.39%)范圍內(nèi),滲層與基體硬度梯度過渡均相對(duì)平緩,硬度分布均比較合理。3Cr2W8V鋼軟氮化后出現(xiàn)白亮層,有網(wǎng)狀或脈狀氮化物的存在。當(dāng)變形量1%時(shí),白亮層寬,存在更加細(xì)小的網(wǎng)狀氮化物。當(dāng)變形量為4.87～10.52%時(shí),白亮層變窄、脈狀氮化物細(xì)長,仍存在網(wǎng)狀氮化物。當(dāng)變形量為13.56-37.5%時(shí),窄的白亮層,少量脈狀氮化物細(xì)短,有網(wǎng)狀氮化物。熱變形試樣隨變形量的增大,白亮薄且連續(xù),脈狀氮化物更短且少,回火馬氏體組織不明顯。未變形試樣的組織中有大量分散的孔洞,冷壓縮的試樣內(nèi)部孔洞集中,而熱變形的試樣孔洞少且均勻,說明熱變形得到白亮層的韌、塑性好。未變形沖擊斷口表現(xiàn)出明顯脆性,冷、熱壓縮變形都比未變形的試樣塑性有所改善,熱變形斷口上有明顯的韌窩出現(xiàn),冷變形斷口上也有,但不如熱變的明顯。
[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.
【學(xué)位授予單位】：山東大學(xué)
【學(xué)位級(jí)別】：碩士
【學(xué)位授予年份】：2017
【分類號(hào)】：TG142.1;TG306

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