Optimization Of Preparing Process And Microstructure Precise Control Of Iron Nickel Base Corrosion Resistant Alloy 028 For Oil Country Tubular Goods

With the development of national economy, the demand for oil, natural gas increased year by year, lots of oil country tubular goods are used in the process of oil and gas exploration. The corrosion resistant alloy 028 is widely used in petroleum, natural gas and other fields for its excellent corrosion resistance. However, because in the process of preparation of tubular goods, such problems as the precipitated phases appeared, uneven grain size, which influence the using performance of the alloy pipes, especially corrosion resistance, short process to improve the finished product rate is also urgent issue to consider. Therefore, the relevance of process and microstructural control of alloy 028 tubular goods preparation is systematically studied, explore the law of the microstructure evolution of tubular goods preparation, the deformation behavior of alloy, for the optimization of process improve the comprehensive performance of tubes and economic competitiveness has important significance in theory and engineering application.This paper systematically studied ingot and the influence of the homogenizing degree to hot deformation behavior of ingot, obtained ingot directly forging feasible but greater risk of cracking, the flow stress of ingot after 1170℃ /10h partial homogenization is less than that of after 1200℃/30h completely homogenized, and the volume fraction of dynamic recrystallization was greater than the latter. So alloy 028 ingot may be 1170℃/10h partial homogenization process, which can reduce economic costs, but also reduce deformation resistance, increase recrystallization degree, studies have shown that the process has the kind of economic rationality. At the same time, combined with the actual producing process, clearly precipitated phase a phase mainly affect the tubes performance, the formula Cr2.4Mo0.5Fe7Ni0.1, precipitation peak temperature of 900℃, after this temperature, a large number of a phase precipitates dissolve completely without making the grain size quickly grew of the solid solution system is 1160℃/2h.Through systematically thermal physical simulation, obtained hot deformation flow stress curves of alloy 028, established the constitutive equations of alloy 028, analyzed the impact of hot deformation parameters on dynamic recrystallization microstructures and built dynamic recrystallization diagram alloy and hot processing maps. On the basis of hot deformation behavior in alloy 028, combined with the analysis of different areas of hot processing maps, obtained the security zone in hot processing map of the strain 0.844, for the deformation temperature of 1120～1160℃, the strain rate of 0.1～1s-1, the strain 0.163 and 0.357 when the hot processing security zone are deformation temperature 1120～1156℃, strain rate of 0.1～6s-1 and deformation temperature 1120～1180℃, strain rate of 0.1～3s-1 respectively.On this basis, established the dynamic recrystallization and grain growth of microstructural control model, and by using the software Deform-2D, compared and analyzed hot compression sample experimental and simulation results, verified the correctness of the microstructural model and calculation method. The model can realize hot extrusion process parameters to accurately predict the tubes microstructures. And then put forward the best hot extrusion process ranges that meet the requirements of equipment tonnage(35MN) and microstructure(55μm): billet preheating temperature of 1160℃～1180℃, extrusion speed is 170-200mm/s, extrusion ratio is 9.8-12, the coefficient of friction is 0.02-0.09.Further to systematically research on cold rolling and intermediate annealing treatment of the pierced billet after solution treatment, established work hardening model of alloy 028 in the process of cold rolling, has been met the requirements of mechanical properties in oil tubes cold rolling reduction of 23% to 45%. Constructed annealing recrystallization grain growth model, obtained precipitates evolution law during the annealing process, revealing the influence of cold rolling and annealing process for texture and grain boundary characteristics. Comprehensive precipitates back to dissolve and grain size uniformity and texture and grain boundary characteristics and other factors, puts forward the optimum annealing process is 1160℃/3min when cold rolling reduction of 30%.In conclusion, results of this study can improve and optimize the economic and production processes alloy 028 tubes to provide guidance, and to realize accurate control of tubes microstructure and the improvement of mechanical properties have important value for engineering application.