Under normal forging and annealing conditions, there are different ultra fine carbides (M3C, M23C6, M7Cj, M6C and MC) in high carbon alloy steels when alloy composition design is carried out properly. On the basis of ...Under normal forging and annealing conditions, there are different ultra fine carbides (M3C, M23C6, M7Cj, M6C and MC) in high carbon alloy steels when alloy composition design is carried out properly. On the basis of carbides transformation orderliness, the alloy composition design of the high carbon alloy steels is conducted by phase-equilibrium thermodynamic calculation for Fe-Cr-W-Mo-V-C system. The nucleation and growth of new carbides, dissolution of previous partial carbides in these steels during annealing process, all these lead to ultra-fine distribution of carbides. Due to different crystal structures of carbides and different thermodynamics as well dynamics parameters of the carbides dissolution and precipitation, the range of quenching temperature of these steels is widened, and the good temper-resistance is obtained. The characteristics of heat treatment process and microstructure variance, and the carbides transformation for different temperature are explained by the phase-equilibrium component satisfactorily. Their bend and yield strength, flexibility and toughness all are advanced markedly comparing with that of kindred steels. Results of the applications have proved that the microstructure of ultra-fine carbides in these steels played importance roles in the enhancement of edginess and fatigue crack resistance of the die and knives.展开更多
The structure and hardness of 8CrWMoV steel with multiple types of ultra fine carbides are studied after annealing, quenching and tempering in this paper. The results show that multiple types of carbides M3C, M7C3, M2...The structure and hardness of 8CrWMoV steel with multiple types of ultra fine carbides are studied after annealing, quenching and tempering in this paper. The results show that multiple types of carbides M3C, M7C3, M23C6, M6C and MC were observed in the annealed steel. Nucleation and coalescence of new carbides, partial dissolution of original carbides in γ phase region during annealing at 800～840℃, result in ultra-fine carbides. Average size of the carbides is0.33～0.34μm in the steel annealed at 800～840℃. Because M3C and M23C6 dissolve easily in austenite, the high hardness HRC63～65 can be obtained by quenching at 840～860℃. Un-dissolved carbides M6C and MC (VC) can effectively prevent the coarsening of austenitic grain, and conduce to obtain very fine martensite. The retained austenite can be easy to decompose during tempering at low and middle temperature due to the precipitation of multiple types of carbides and the good tempering-resistance of the steel is obtained. The microstructure and property of the steel after heat treatment can be accurately explained by calculating based on phase equilibrium thermodynamic.Key Words: 8CrWMoV steel, ultra-fine carbide, heat treatment, microstructure,展开更多
This paper deals with the effects of codoped VC/Cr3C2 and sintering temperature on the magnetic and mechanical properties of ultra-fine grained WC-12%Co alloys. Results show that the synergistic action of doped VC/Cr3...This paper deals with the effects of codoped VC/Cr3C2 and sintering temperature on the magnetic and mechanical properties of ultra-fine grained WC-12%Co alloys. Results show that the synergistic action of doped VC/Cr3C2 in optimal proportion enhances both the hardness and transverse rupture strength （TRS） of the alloys, with more homogeneous microstructtLre. When the alloy is sintered at 1430℃ and with 0.5% Cr3C2/0.2% VC, the TRS reaches 3786 MPa, the hardness is 91.7 HRA and the grain size smaller than 0.6 μm. The numerical analyses on grain growth during the sintering process show that both VC precipitating on the WC grain boundary and Cr3C2 dissolving in the Co phase decrease the solid/liquid interfacial energy γ, the process of dissolution and reprecipitation is greatly retarded and the coarsening of WC grains is inhibited.展开更多
The preparation of hydroxyl chromium oxide by hydrogen reduction of disodium chromate and particulate hydroxyl mechanical activation features were studied. Then with self-made hydroxyl chromium as the raw material, a ...The preparation of hydroxyl chromium oxide by hydrogen reduction of disodium chromate and particulate hydroxyl mechanical activation features were studied. Then with self-made hydroxyl chromium as the raw material, a direct reduction and carburization process was used to prepare ultra-fine chromium carbonization. Through SEM and XRD, the high performance mechanical activation, key coefficients, microstructure, hardness and wear-resisting property were investigated. The results reveal that suitable mechanical activation and carbon reducing carbonization temperature, carbonization time, carbon content are beneficial to obtaining ultra-fine chromium carbonization. Typically, when the time of high performance grinding is 5 min, the carbon reducing temperature is 1100 ℃, the carbon reducing time is 1h, the carbon content is 28%, and finally the particle size of chromium carbide powder is 1 μm. Under this condition of preparation of ultra-fine chromium carbide, both the hardness and wear resistance are better than those in the industrialization of chromium carbide coating.展开更多
文摘Under normal forging and annealing conditions, there are different ultra fine carbides (M3C, M23C6, M7Cj, M6C and MC) in high carbon alloy steels when alloy composition design is carried out properly. On the basis of carbides transformation orderliness, the alloy composition design of the high carbon alloy steels is conducted by phase-equilibrium thermodynamic calculation for Fe-Cr-W-Mo-V-C system. The nucleation and growth of new carbides, dissolution of previous partial carbides in these steels during annealing process, all these lead to ultra-fine distribution of carbides. Due to different crystal structures of carbides and different thermodynamics as well dynamics parameters of the carbides dissolution and precipitation, the range of quenching temperature of these steels is widened, and the good temper-resistance is obtained. The characteristics of heat treatment process and microstructure variance, and the carbides transformation for different temperature are explained by the phase-equilibrium component satisfactorily. Their bend and yield strength, flexibility and toughness all are advanced markedly comparing with that of kindred steels. Results of the applications have proved that the microstructure of ultra-fine carbides in these steels played importance roles in the enhancement of edginess and fatigue crack resistance of the die and knives.
文摘The structure and hardness of 8CrWMoV steel with multiple types of ultra fine carbides are studied after annealing, quenching and tempering in this paper. The results show that multiple types of carbides M3C, M7C3, M23C6, M6C and MC were observed in the annealed steel. Nucleation and coalescence of new carbides, partial dissolution of original carbides in γ phase region during annealing at 800～840℃, result in ultra-fine carbides. Average size of the carbides is0.33～0.34μm in the steel annealed at 800～840℃. Because M3C and M23C6 dissolve easily in austenite, the high hardness HRC63～65 can be obtained by quenching at 840～860℃. Un-dissolved carbides M6C and MC (VC) can effectively prevent the coarsening of austenitic grain, and conduce to obtain very fine martensite. The retained austenite can be easy to decompose during tempering at low and middle temperature due to the precipitation of multiple types of carbides and the good tempering-resistance of the steel is obtained. The microstructure and property of the steel after heat treatment can be accurately explained by calculating based on phase equilibrium thermodynamic.Key Words: 8CrWMoV steel, ultra-fine carbide, heat treatment, microstructure,
基金the National Natural Science Foundation of China (No. 50372043).
文摘This paper deals with the effects of codoped VC/Cr3C2 and sintering temperature on the magnetic and mechanical properties of ultra-fine grained WC-12%Co alloys. Results show that the synergistic action of doped VC/Cr3C2 in optimal proportion enhances both the hardness and transverse rupture strength （TRS） of the alloys, with more homogeneous microstructtLre. When the alloy is sintered at 1430℃ and with 0.5% Cr3C2/0.2% VC, the TRS reaches 3786 MPa, the hardness is 91.7 HRA and the grain size smaller than 0.6 μm. The numerical analyses on grain growth during the sintering process show that both VC precipitating on the WC grain boundary and Cr3C2 dissolving in the Co phase decrease the solid/liquid interfacial energy γ, the process of dissolution and reprecipitation is greatly retarded and the coarsening of WC grains is inhibited.
基金Supported by the National High-tech Research and Development Program of China(863 Program)(No.2012AA062303)National Natural Science Foundation of China(Nos.51764016,U1402271,51504058,51504059)+1 种基金Jiangxi Science and Technology Landing Project(No.KJLD13046)the Doctoral Scientific Research Foundation of Jiangxi University of Science and Technology(No.jxxjbs17045)
文摘The preparation of hydroxyl chromium oxide by hydrogen reduction of disodium chromate and particulate hydroxyl mechanical activation features were studied. Then with self-made hydroxyl chromium as the raw material, a direct reduction and carburization process was used to prepare ultra-fine chromium carbonization. Through SEM and XRD, the high performance mechanical activation, key coefficients, microstructure, hardness and wear-resisting property were investigated. The results reveal that suitable mechanical activation and carbon reducing carbonization temperature, carbonization time, carbon content are beneficial to obtaining ultra-fine chromium carbonization. Typically, when the time of high performance grinding is 5 min, the carbon reducing temperature is 1100 ℃, the carbon reducing time is 1h, the carbon content is 28%, and finally the particle size of chromium carbide powder is 1 μm. Under this condition of preparation of ultra-fine chromium carbide, both the hardness and wear resistance are better than those in the industrialization of chromium carbide coating.
