B2模具钢激光熔覆层微观组织与疲劳性能的研究

发布时间：2018-03-19 01:22

  本文选题：B2模具钢　切入点：激光熔覆层　出处：《吉林大学》2015年硕士论文　论文类型：学位论文

【摘要】：冲压模具在使用过程因承受交变载荷作用而发生腐蚀、磨损、疲劳和断裂等各种形式的失效。本文针对冲压模具使用过程中的失效问题，特别是模具刃角部位的性能与模具整体寿命不匹配的问题，采用激光熔覆的方法，对冲压模具失效表面进行修复。试验在B2模具钢基体制备了Ni60A熔覆层和Ni60A+WC熔覆层，研究了熔覆层的组织与性能，分析了工艺参数和熔覆合金成分对熔覆层组织与性能的影响。 熔覆试件由熔覆层、热影响区和基体三部分组成。Ni60A熔覆层组织由底部胞状晶和上部树枝晶组成，胞状晶为γ-(Fe,Ni)相，树枝晶为Cr2Ni3，，树枝晶间分布着M23C6和CrB等强化相。熔覆层显微硬度在570~580HV之间，基体显微硬度在400~420HV之间。熔覆层表面的磨痕犁沟窄且浅，凹坑数量较少，耐磨性能优于基体。加载载荷F=15KN，循环次数N=2×104时，熔覆层气孔处产生裂纹源；N=3×104时，熔覆层在硬质相处产生裂纹源；N=4×104时，熔覆层与基体熔合线处产生裂纹源；N=5×104时，熔覆层在γ相内部产生疲劳裂纹。 试验研究了工艺参数对Ni60A熔覆层组织和性能的影响。结果表明，随脉冲电流增大，熔覆层底部胞状晶变得均匀致密，脉冲电流大于80A时，基体与熔覆层之间形成亮白色的条带状区域；随脉宽值增加，熔覆层上部树枝晶形态变得粗大；频率的变化对熔覆层的组织没有显著影响。熔覆层显微硬度随脉冲电流增大而降低，由熔覆层到基体的变化趋势随脉宽增加而变得显著，随频率的改变变化不明显。熔覆层稀释率随脉冲电流、频率和脉宽的增加而增大。 试验研究了WC含量对Ni60A+WC熔覆层组织和性能的影响。ω(WC)=10wt%时，WC大部分熔解在熔覆层中，促进了Cr23C6、Cr4Ni15W和Cr3Ni2Si等强化相的形成；ω(WC)=20wt%时，熔覆层上部树枝晶消失，形成块状晶，组织更为细化；ω(WC)=30wt%时，熔覆层的组织为富W块状共晶，其间含有未熔解的WC和部分W、Cr的碳化物和硼化物。Ni60A+WC熔覆层显微硬度随WC含量增加而增大，最高为1520HV，明显高于Ni60A熔覆层。Ni60A+WC熔覆层的耐磨性因WC颗粒的加入得以改善，磨痕表面犁沟较Ni60A熔覆层窄且浅，凹坑数量也较少。WC含量为35%时，Ni60A+WC熔覆层磨痕表面有大块硬质相颗粒脱落。承受F=15KN，N=5×104的交变载荷时，Ni60A+WC熔覆层以剥离裂纹的形式从基体表面脱落。ω(WC)≤15wt%时，熔覆层剥落的厚度较小，疲劳性能较好；ω(WC)≥20wt%时，熔覆层剥落的厚度随WC含量的增加而增加；ω(WC)≥30wt%时，熔覆层全部从基体脱落。
[Abstract]:In the process of using stamping die, corrosion, wear, fatigue and fracture occur due to the action of alternating load. Especially, the failure surface of stamping die was repaired by laser cladding, the Ni60A cladding layer and Ni60A WC cladding layer were prepared on B2 die steel substrate. The microstructure and properties of the cladding were studied, and the effects of process parameters and alloy composition on the microstructure and properties of the cladding were analyzed. The cladding specimen consists of a cladding layer, a heat-affected zone and a matrix. The microstructure of the cladding layer is composed of cellular crystal at the bottom and dendrite in the upper part, and the cellular crystal is 纬 -fen Fe Ni) phase. The microhardness of the cladding layer is between 570,580HV and 400-420HV. The surface of the cladding layer is narrow and shallow, and the number of pits is relatively small, and the microhardness of the cladding layer is Cr _ 2Ni _ 3, and M23C6 and CrB are distributed among the dendrites, and the microhardness of the cladding layer is between 570,580HV and 400-420HV. The wear resistance of the cladding is better than that of the matrix. When the loading load is F _ (15) KN, the cycle number is N ~ (2 脳 10 ~ 4), the crack source is 3 脳 10 ~ 4 at the porosity of the cladding layer, the crack source N _ (4 脳 10 ~ 4) is produced in the cladding layer when the crack source is N4 脳 10 ~ 4, the crack source is N _ (5) 脳 10 ~ 4 at the fusion line between the cladding layer and the matrix. Fatigue cracks occur in the 纬 phase of the cladding layer. The effect of process parameters on the microstructure and properties of Ni60A cladding coating was studied. The results show that the cellular crystal at the bottom of the cladding layer becomes uniform and compact with the increase of pulse current, and the pulse current is greater than 80A. A bright white stripe region was formed between the substrate and the cladding layer, and the dendritic morphology of the upper cladding became coarse with the increase of the pulse width. The change of frequency has no significant effect on the microstructure of the cladding layer. The microhardness of the cladding layer decreases with the increase of pulse current, and the change trend from the cladding layer to the substrate becomes obvious with the increase of pulse width. The dilution rate of cladding layer increases with the increase of pulse current, frequency and pulse width. The effect of WC content on the microstructure and properties of Ni60A WC cladding coating was studied. When the content of WC was 10 wt%, most of WC was melted in the cladding layer, which promoted the formation of strengthening phases such as Cr23C6C6Cr4Ni15W and Cr3Ni2Si. The microhardness of the cladding layer increases with the increase of WC content, the microstructure of the cladding layer is W-rich bulk eutectic, and the microhardness of WC and boride. Ni60A WC cladding coating increases with the increase of WC content, while the microstructure of the coating is more fine, and the microhardness of the cladding coating increases with the increase of WC content, and the microhardness of the cladding coating increases with the increase of WC content. The wear resistance of WC cladding layer is obviously higher than that of Ni60A cladding coating. The wear resistance of WC cladding coating is improved because of the addition of WC particles, and the ploughing groove on the surface of wear mark is narrower and shallower than that of Ni60A cladding coating. The number of pits is also less .WC content is 35% and Ni60A WC cladding layer has large hard phase particles falling off on the surface of wear mark. The Ni60A WC cladding layer shedding from the substrate surface in the form of peeling crack when the FN 15KN NU 5 脳 10 4 AC cladding layer is subjected to the alternating load. 蠅 WC鈮

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