Hot Deformation Process And Corrosion Resistance Of BFe30-1-1 Copper-Nickel Alloy Tube

Copper-nickel alloys have excellent mechanical properties,welding properties,corrosion resistance and biological pollution resistance.In marine equipment,ocean vessel,deep seabed exploration and petrochemical industry files,B30 copper-nickel alloy tubes are widely used in seawater pipelines,tube sheets,condensers,and heat exchange tubes,etc.With the high requirements for the performance of large-diameter B30 copper-nickel alloy tubes,it puts forward corresponding high requirements for the control of hot working process during production;also,the corrosion resistance in sulfur-containing seawater has attracted more and more attention.In this thesis,we took BFe30-1-1 copper-nickel alloy as the research object and studied the hot deformation behavior and the thermoplastic processing parameters at high temperature.The extrusion process parameters were further optimized by finite element simulation,which can guide the preparation of hot extrusion tubes.Moreover,the corrosion behavior and mechanism of alloy tubes in high sulfur content seawater were also explored.The main research results and contents are as follows:Comprehensively considering the effects of friction and temperature rise on thermal compression test,the high temperature thermal deformation behavior of BFe30-1-1 copper-nickel alloy under the thermal deformation condition of deformation temperature of 750-1000℃and strain rate of 0.01-10 s^-1 was studied.The constitutive equation of BFe30-1-1 copper-nickel alloy characterized by Zener-Hollomon parameters was established,and the average relative error between the calculated value and the experimental value was investigated to be only 3.37%.By analyzing the microstructure of the alloy after deformation,we found that the main deformation mechanism of the alloy in the safety zone in the hot working diagram was dynamic recrystallization,and the dynamic recrystallization softening mechanism and the critical stress equation of recrystallization were also obtained through the analysis.Finally,the optimum deformation process interval of the alloy was obtained,i.e.,deformation temperature of 900-1000℃,and strain rate of 0.04-0.16 s^-1.Aiming at the production demand of large diameter（φ146×8mm）BFe30-1-1copper-nickel alloy tubes,the hot extrusion model of large-diameter BFe30-1-1 copper-nickel alloy in the machining interval determined by the hot working diagram was constructed,and the extrusion processes at different extrusion speeds and radius of bottom die were simulated by finite element method with Deform-3D software.The equivalent stress,temperature rise,and the load of BFe30-1-1 copper-nickel alloy during the extrusion process were analyzed by the finite element simulation.The mechanical property of BFe30-1-1 copper-nickel alloy tubes extruded at 1000℃deformation temperature,40 mm·s^-1 extrusion speed and 15mm die fillet radius was excellent,the recrystallization volume fraction of which reached 80.8%.The yield strength,tensile strength and elongation of extruded BFe30-1-1 copper-nickel alloy tubes were 127.3 MPa,365.6 MPa and 52.1%,respectively.The corrosion behavior and mechanism of BFe30-1-1 copper-nickel alloy in simulated sulfur-contained seawater（3.5 wt.%Na Cl+0.5 wt.%Na₂S）with high sulfur content were studied by immersion experiment,polarization curve test,electrochemical impedance test,X-ray photoelectron spectroscopy and Auger electron spectroscopy.The results showed that the corrosion rate of BFe30-1-1 copper-nickel alloy tubes tended to be flat at 0.05 mm?year^-1 after immersed in sulfur-contained simulated seawater for 120 hours.The corrosion potential of the BFe30-1-1 copper-nickel tubes in sulfur-contained seawater was-1.09--1.01 V_SCE,0.9 V_SCE lower than that in non-sulfur-contained seawater.The product film of target tubes formed in sulfur-contained seawater showed a significant double-layer structure with outer layer of Cu₂S and the inner layer of Fe S and Cu₂O.This study also found that the main failure of BFe30-1-1copper-nickel tubes immersed in sulfur-contained seawater was corrosion cracking,which was due to the Fe distributed along the grain boundary.