Study on decomposition of primary carbonitrides in H13 steel under high temperature
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摘要: 利用光學顯微鏡、掃描電鏡和電子探針研究了H13鋼中初生碳氮化物高溫分解時的形貌、尺寸、成分變化規律.原始初生碳氮化物主要為10~30 μm的長條狀（Vx，Mo1-x）（Cy，N1-y）及少量方形的（Tix，V1-x）（Cy，N1-y）.在1200℃保溫2.5 h后碳氮化物邊緣變為凹凸不平的鋸齒狀，然后形成細小的分解顆粒，10 h后碳氮化物平均長度減小為12.9 μm，主要為（Tix，V1-x）（Cy，N1-y）.當經過1250℃×5 h保溫后87%的碳氮化物發生分解，（Vx，Mo1-x）（Cy，N1-y）溶解消失，碳氮化物長度在20 μm以下，當保溫時間延長到10 h后碳氮化物長度均在10 μm以下，70%為方形并且93%分解形成細小顆粒，未分解的碳氮化物為（Tix，V1-x）（Cy，N1-y）.電子探針分析（Tix，V1-x）（Cy，N1-y）的分解與Fe元素擴散有關，高溫時Fe在（Tix，V1-x）（Cy，N1-y）中含量逐漸增加而Ti、V減少，優先在邊部曲率半徑較小部位或缺陷處分解，形成0.1~1 μm的細小分解顆粒，并由外向內以區域溶解方式使原始碳氮化物逐漸消失.雙亞點陣模型分析兩種碳氮化物的平衡溶解溫度和組成有關，試樣中大部分（Tix，V1-x）（Cy，N1-y）平衡溶解溫度在1200~1246℃之間，與實驗吻合較好.Abstract: Optical microscopy (OM), scanning electron microscopy (SEM), and electron microprobe analysis (EMPA) were used to determine the nature of carbonitrides decomposition in H13 hot work die steel under high temperature, including its morphology, size and composition. Most of the original carbonitrides are long strip (Vx,Mo1-x)(Cy,N1-y) ranging between 10~30 μm with a few square (Tix,V1-x)(Cy,N1-y). The result shows that the edge of the carbonitrides becomes saw-toothed after holding at 1200℃ for 2.5 h, and fine decomposed particles are formed. The average length of carbonitrides, mainly (Tix,V1-x)(Cy,N1-y), is reduced to 12.9 μm as increasing the holding time for 10 h. When the steel is held at 1250℃ for 5 h, about 87% of the carbonitrides disintegrate, especially (Vx,Mo1-x)(Cy,N1-y) dissolving and disappearing, and the carbonitrides size is less than 20 μm. When holding at 1250℃ for 10 h, all the carbonitrides remained are (Tix,V1-x)(Cy,N1-y), of which 70% are square and 93% decompose to fine particles, and can be controlled to size below 10 μm. It is deduced that (Tix,V1-x)(Cy,N1-y) decomposition is related to Fe diffusion by EMPA analysis and that the Fe content in (Tix,V1-x)(Cy,N1-y) gradually enhances while Ti and V contents decline. The carbonitrides reliably decompose at the position of small curvature radius and defect position, forming fine particles of 0.1~1 μm. The original carbonitrides disappear by zone dissolution from outer to inner. The equilibrium temperature of carbonitrides dissolution has a relationship with its constituents based on the two-sublattice model, and dissolution temperature for most (Tix,V1-x)(Cy,N1-y) in sample is between 1200℃ and 1246℃, which fits well with the experimental results.
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