Cr25Ni35Nb and Cr35Ni45Nb alloys are usually used in the ethylene cracking furnaces. However, premature failure of furnace tubes often occurs ahead of design life due to elevated temperature exposure conditions （1050...Cr25Ni35Nb and Cr35Ni45Nb alloys are usually used in the ethylene cracking furnaces. However, premature failure of furnace tubes often occurs ahead of design life due to elevated temperature exposure conditions （1050-1100 ℃） and aggressive service environment. Effects of exposure temperature and time on microstructure and mechanical properties of Cr25Ni35Nb and Cr35Ni45Nb steel at aging temperature （1200 ℃） with various exposure time were simulated different service times at 1050 ℃. Change of mechanical properties at room temperature and elevated temperature （900 ℃） of the aged Cr25Ni35Nb and Cr35Ni45Nb steel were investigated. Under exposure at 1200 ℃, ultimate tensile and yield strength, elongation of Cr35Ni45Nb steel increase initially and then decrease, however, strength and ductility of Cr25Ni35Nb steel decrease with aging time increasing. Large amount of fine secondary carbide particles precipitated and dispersed in matrix of Cr35Ni45Nb steel, which increased strength and ductility for dispersion strengthening. However, the effect of the dispersion strengthening is weakened by needle-like secondary carbides. Strength and ductility decreased with fine secondary carbide particles growing. For Cr25Ni35Nb steel, few fine secondary carbide particles precipitated and dispersed in the matrix, and needle-like secondary carbides generated in the matrix, which causes strength and ductility decreased with aging time increasing.展开更多
Through the mass balance and thermal balance calculation for a typical OxyCup （or OxiCup） furnace process featuring a capacity of 380 kt/a of steel plant residuMs, the material flow and thermal flow diagrams were fi...Through the mass balance and thermal balance calculation for a typical OxyCup （or OxiCup） furnace process featuring a capacity of 380 kt/a of steel plant residuMs, the material flow and thermal flow diagrams were firstly obtained. Then, the performance of the main fuel in the OxyCup process, i.e. coke and carbon dust, was ana lyzed, and the results indicated that coke was mainly used as the stock column skeleton for the furnace and exothermal agent with a weak reduction ability; whereas carbon dust was mixed in the C-brick to reduce the iron oxide. In addition, the comparison between OxyCup process and traditional blast furnace process indicated that the reduction and melting processes in the OxyCup process were relatively isolated, while in the traditional blast furnace process, they were mixed with each other in the high temperature zone. Moreover, oxidizing atmosphere is necessary in part of the OxyCup furnaces to ensure the complete combustion of part of the coke, while only reducing atmosphere is al lowed in traditional blast furnaces. Finally, it was confirmed that oxygen enrichment can make a remarkable increase of the energy income and high temperature blast makes oMy a small contribution to energy income as the energy from the combustion of carbon takes up nearly 90% of the total income.展开更多
Continuous furnaces are widely used in the heat treatment of mass-produced parts. However, the heating up process of parts in continuous furnace is still decided by experience. In this paper the heat transfer in the c...Continuous furnaces are widely used in the heat treatment of mass-produced parts. However, the heating up process of parts in continuous furnace is still decided by experience. In this paper the heat transfer in the continuous furnace is formulated firstly. The heat balance in each zone is discussed and equations are given. Coupled with the model for heat transfer between workpieces and furnace and the heat transfer in the workload as well presented in the former developed CHT-6/ for batch furnaces, a program CHT- for continuous furnaces was developed. The model deals with two typical movements of parts: continuous or step by step. The moving speed of parts and load pattern can be optimized based on the calculated temperature distributions and curves, especially, the fastest heated and slowest-heated temperature-distance profiles. A case study is carried out for the heat treatment of a kind of hook-shaped part. The calculated results are analyzed and in good agreement with the measured ones.展开更多
基金supported by the National Natural Science Foundation of China(No.50775107)National High Technical Research and Development Program of China (No.2007AA04Z407)Innovation Program for Graduate Students in Nanjing University of Technology (No.BSCX200816)
文摘Cr25Ni35Nb and Cr35Ni45Nb alloys are usually used in the ethylene cracking furnaces. However, premature failure of furnace tubes often occurs ahead of design life due to elevated temperature exposure conditions （1050-1100 ℃） and aggressive service environment. Effects of exposure temperature and time on microstructure and mechanical properties of Cr25Ni35Nb and Cr35Ni45Nb steel at aging temperature （1200 ℃） with various exposure time were simulated different service times at 1050 ℃. Change of mechanical properties at room temperature and elevated temperature （900 ℃） of the aged Cr25Ni35Nb and Cr35Ni45Nb steel were investigated. Under exposure at 1200 ℃, ultimate tensile and yield strength, elongation of Cr35Ni45Nb steel increase initially and then decrease, however, strength and ductility of Cr25Ni35Nb steel decrease with aging time increasing. Large amount of fine secondary carbide particles precipitated and dispersed in matrix of Cr35Ni45Nb steel, which increased strength and ductility for dispersion strengthening. However, the effect of the dispersion strengthening is weakened by needle-like secondary carbides. Strength and ductility decreased with fine secondary carbide particles growing. For Cr25Ni35Nb steel, few fine secondary carbide particles precipitated and dispersed in the matrix, and needle-like secondary carbides generated in the matrix, which causes strength and ductility decreased with aging time increasing.
基金Sponsored by National Natural Science Foundation of China(51174023)5th Special Funding of Postdoctoral Science Foundation of China(2012T50045)
文摘Through the mass balance and thermal balance calculation for a typical OxyCup （or OxiCup） furnace process featuring a capacity of 380 kt/a of steel plant residuMs, the material flow and thermal flow diagrams were firstly obtained. Then, the performance of the main fuel in the OxyCup process, i.e. coke and carbon dust, was ana lyzed, and the results indicated that coke was mainly used as the stock column skeleton for the furnace and exothermal agent with a weak reduction ability; whereas carbon dust was mixed in the C-brick to reduce the iron oxide. In addition, the comparison between OxyCup process and traditional blast furnace process indicated that the reduction and melting processes in the OxyCup process were relatively isolated, while in the traditional blast furnace process, they were mixed with each other in the high temperature zone. Moreover, oxidizing atmosphere is necessary in part of the OxyCup furnaces to ensure the complete combustion of part of the coke, while only reducing atmosphere is al lowed in traditional blast furnaces. Finally, it was confirmed that oxygen enrichment can make a remarkable increase of the energy income and high temperature blast makes oMy a small contribution to energy income as the energy from the combustion of carbon takes up nearly 90% of the total income.
文摘Continuous furnaces are widely used in the heat treatment of mass-produced parts. However, the heating up process of parts in continuous furnace is still decided by experience. In this paper the heat transfer in the continuous furnace is formulated firstly. The heat balance in each zone is discussed and equations are given. Coupled with the model for heat transfer between workpieces and furnace and the heat transfer in the workload as well presented in the former developed CHT-6/ for batch furnaces, a program CHT- for continuous furnaces was developed. The model deals with two typical movements of parts: continuous or step by step. The moving speed of parts and load pattern can be optimized based on the calculated temperature distributions and curves, especially, the fastest heated and slowest-heated temperature-distance profiles. A case study is carried out for the heat treatment of a kind of hook-shaped part. The calculated results are analyzed and in good agreement with the measured ones.
