钨铝合金化的改进型乙烯裂解炉管1150℃条件下的模拟渗碳行为研究

Study on simulated carburizing behavior of modified ethylene cracking furnace tube alloyed by tungsten and aluminum under 1150℃

为探究钨铝合金化的改进型乙烯裂解炉管27Cr44Ni5W3Al+MA在1150℃条件下的渗碳损伤情况,采用粒径1.5~3 mm的固体渗碳剂,针对27Cr44Ni5W3Al+MA炉管开展1150℃条件下50,100,150,200 h的固体渗碳试验。采用C-S分析仪和OM,SEM,EDS,XRD及维氏硬度计等对渗碳前后炉管进行成分、组织及性能分析,研究炉管渗碳行为。结果表明:从铸态至渗碳200 h时,炉管内壁1 mm范围内平均碳浓度由约0.5%增长至饱和碳浓度2.2%左右;渗碳时间由50 h增至200 h,炉管内壁渗碳层厚度由800μm增至2860μm,渗碳层由内向外依次为严重渗碳区、中度渗碳区及轻微渗碳区,其宽度分别由400μm增至1920μm、100μm增至140μm、300μm增至800μm。从铸态至渗碳200 h,碳化物平均宽度由2.0μm增至3.5~13.0μm,面积分数由5.6%增至13.6%~34.9%;原始铸态复相碳化物外部的小块状M_(23) C_(6)逐渐粗化呈链块状,然后转变为岛块状M_(7)C_(3)及岛块中间的颗粒状WC,内部片层状M_(7)C_(3)部分转变为小块状M_(23) C_(6),并与外部M_(23) C_(6)聚集连接后转变为M_(7)C_(3),剩余部分片层状M_(7)C_(3)逐渐粗化聚集成块状M_(7)C_(3)。原始铸态炉管硬度值约为304.0HV10,渗碳200 h后,由距内壁4 mm处至1 mm处,硬度值由386.7HV10增至504.0HV10。本文还就27Cr44Ni5W3Al+MA合金炉管的渗碳行为和渗碳过程中碳化物演变机理进行了讨论。

In order to investigate the carburizing damage of 27Cr44Ni5W3Al+MA modified ethylene cracking furnace tube alloyed by tungsten and aluminum under 1150℃,the solid carburizing tests were carried out at 1150℃for 50 h,100 h,150 h and 200 h by using solid carburizing agent with particle size of 1.5~3 mm for the tube.C-S analyzer,OM,SEM,EDS,XRD and Vickers hardness tester were used to analyze the composition,microstructure and properties of the furnace tube before and after carburizing to study the carburizing behavior of the furnace tube.The results show that the average carbon concentration within 1 mm of the inner wall of the furnace tube increases from about 0.5%to about 2.2%from the as-cast state to 200 h of carburizing.When the carburizing time increases from 50 h to 200 h,the thickness of carburized layer on inner wall of the furnace tube increases from 800μm to 2860μm.The carburized layer from inside to outside is followed by severely carburized zone,moderately carburized zone and mildly carburized zone,and its width increases from 400μm to 1920μm,100μm to 140μm and 300μm to 800μm,respectively.From the as-cast state to 200 h of carburizing,the average width of carbide increases from 2.0μm to 3.5~13.0μm,and the area fraction of carbide increases from 5.6%to 13.6%~34.9%.The small block of M_(23) C_(6) outside the original as-cast complex carbide gradually coarsens to chain block,and then transforms to island block of M_(7)C_(3) and granular WC in the middle of the island block.The inner lamellar M_(7)C_(3) partially transforms to small block of M_(23) C_(6),and then transforms to M_(7)C_(3) after aggregation and connection with external M_(23) C_(6).The remaining lamellar M_(7)C_(3) gradually coarsens and aggregates to massive M_(7)C_(3).The hardness value of the original as-cast tube is about 304.0HV10.After 200 h of carburizing,the hardness value increases from 386.7HV10 to 504.0HV10 from 4 mm to 1 mm from the inner wall.The carburizing behavior of the 27Cr44Ni5W3Al+MA furnace tube and the mechanism of carbide evolution during carburizing were also discussed.