Effects Of Melting Process And Composition On Microstructure And Thermal Conductivity Of High-melting Point Cu-Ni-Nb Alloy

Copper cooling jacket is key cooling equipment applied in blast furance and flashsmelting furance. The copper cooling jacket can not only achieve strengtheningmetallurgy, but also protect furance liner and extend the service life of the furance body.The selection of cooling water jacket material is key to determine the effect of furancewall heat transfer in metallurgical furance. It directly affects metallurgical furance life,productive efficiency and energy consumption. The short process flow and the goodcooling effect is the advantage of copper cooling jacket with an embedded pure coppertube. It gradually became the best choice of the cooling equipment in the world.However, the pure copper tube of Cu/Cu jacket is melt through easily in castingprocess. The NiCu alloy tube of Cu/NiCu jacket has low thermal conductivity. TheCu/Steel jacket has some disadvantages. The mutual solubility between Cu and Fe islow. So it is very difficult to make metallurgical bonding between Cu and steel, whichcause there is a gap between Cu and steel. The thermal conductivity of steel is low. Theembedded pipes of the last two kinds of cast copper water jacket has high meltingpoint. In order to make metallurgical bonding between alloy tube and copper body, thepouring temperature of molten copper must be raised. As a result, molten copperinhales badly and it is difficult to eliminate abscess of casting. Therefor, it is veryimportant to develop the new type alloy with high melting, modrate thermalconductivity, fit the requirement of pouring temperature of pure copper and easy tomake metallurgical bonding between the alloy tube and the copper body. Therefor, it isvery important to develop the new type alloy with high melting, modrate thermalconductivity, fit the requirement of pouring temperature of pure copper and easy tomake metallurgical bonding between the alloy tube and the copper body. In this paper,effects of melting process and alloy composition on mircostructure and thermalconductivity and melting point of Cu-Ni-Nb alloy were studied systematically. Therelations of alloy composition, melting process and micostructure with thermalconductivity and melting point were presented. The main conclusions are as follows.(1) It is hard to dissolve Nb in Cu-Ni alloy by one-step melting process. Themelting point of Ni-Nb intermediate alloy is1183℃at the mess ratio1:1. Nb can bedissolved in Cu-Ni alloy by two-steps melting. The precipitated phase like Ni3Nb,Ni8Nb were generated in martix of Cu-Ni alloy. (2) Under the experiment condition, the matrix of Cu-Ni-Nb alloy is solid solutionof CuNi, which contains precipitated phases with enrichment of Nb element. The grainof alloy become finer as increasing the content of Nb. The grain become coarse asincreasing the content of Ni. The content of precipitated phase increase as increasingthe content of Nb. The content of precipitated phase decrease as increasing the contentof Ni. The dendrite arm space of Cu-30Ni-5Nb is10μm which has the finest grain.The content of precipitated phase peaks in Cu-20Ni-10Nb, the content is16.3%.(3) Ni will be precipitated in the form of Ni-Nb intermetallic compounds such asNi3Nb and Ni8Nb so that the solution of Ni in the matrix decrease. The thermalconductivity of Cu-Ni-Nb alloy increases as increasing the content of Nb. The meltingpoint of that alloy decreases as increasing the content of Nb. With increasing content ofNi, the thermal conductivity decreases and melting point increases.(4) For the same components of copper alloy, the microstructure is determined topreparing method. The grain of alloy is fine and the thermal conductivity is low byelectric arc melting process combine the cooling method of water-cooled coppercrucible. The grain of alloy is coarse and the thermal conductivity is high by inductionmelting process combine the quartz glass tube cooling. The melting process has littleeffect on melting point of alloy. The thermal conductivity of Cu-20Ni-3Nb alloy is43.23W/m·k. The melting point of that alloy is1146.75℃which is prepared by arcmelting process.The thermal conductivity of that alloy prepared by induction meltingprocess is53.73W/m·k，the melting point is1143.74℃.(5) The grain of alloy will become coarse, the content of precipitated phase andthe thermal conductivity will increase by aging treatment. The dendrite arm space ofCu-30Ni-1Nb-1Fe alloy is18μm in as cast condition. In same condition, the thermalconductivity of that alloy is20.94W/m·k and the content of precipitated phase is1.1%.After aging treatment the dendrite arm space is21μm, thermal conducivity is24.30W/m·k and content of precipitated phase is2.4%.(6) With the melting process of arc melting process combine cooling method ofwater-cooled copper crucible, the optimal composition of Cu-Ni-Nb alloy isCu-30Ni-10Nb by comprehensive balance analyzing of orthogonal experiment. Thethermal conductivity of that alloy is36.98W/m·k and the melting point is1153.30℃.