高温时H13钢中初生碳氮化物的分解研究

Study on decomposition of primary carbonitrides in H13 steel under high temperature

利用光学显微镜、扫描电镜和电子探针研究了H13钢中初生碳氮化物高温分解时的形貌、尺寸、成分变化规律.原始初生碳氮化物主要为10~30μm的长条状(V_x,Mo_(1-x))(C_y,N_(1-y))及少量方形的(Ti_x,V_(1-x))(C_y,N_(1-y)).在1200℃保温2.5 h后碳氮化物边缘变为凹凸不平的锯齿状,然后形成细小的分解颗粒,10 h后碳氮化物平均长度减小为12.9μm,主要为(Ti_x,V_(1-x))(C_y,N_(1-y)).当经过1250℃×5 h保温后87%的碳氮化物发生分解,(V_x,Mo_(1-x))(C_y,N_(1-y))溶解消失,碳氮化物长度在20μm以下,当保温时间延长到10 h后碳氮化物长度均在10μm以下,70%为方形并且93%分解形成细小颗粒,未分解的碳氮化物为(Ti_x,V_(1-x))(C_y,N_(1-y)).电子探针分析(Ti_x,V_(1-x))(C_y,N_(1-y))的分解与Fe元素扩散有关,高温时Fe在(Ti_x,V_(1-x))(C_y,N_(1-y))中含量逐渐增加而Ti、V减少,优先在边部曲率半径较小部位或缺陷处分解,形成0.1~1μm的细小分解颗粒,并由外向内以区域溶解方式使原始碳氮化物逐渐消失.双亚点阵模型分析两种碳氮化物的平衡溶解温度和组成有关,试样中大部分(Ti_x,V_(1-x))(C_y,N_(1-y))平衡溶解温度在1200~1246℃之间,与实验吻合较好.

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 at1250 ℃ 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. Theoriginal 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.