617B alloy is a Ni-Cr-Co-Mo superalloy based on solid solution strengthening based on Inconel617 alloy. Al and Ti are added to the alloy to form a small amount of γ ‘phase (4% ~ 5 %) Precipitation strengthening, there is a small amount of M6C phase and Ni2 (Cr, Mo) phase in the aging alloy. Due to the excellent high temperature durability and high temperature oxidation resistance of the alloy, it has been used as an advanced ultra-supercritical thermal power plant at 700 ℃ Candidate materials for boiler superheaters, reheaters, headers and main steam piping. The research on this alloy mainly focuses on the high-temperature microstructure stability, steam oxidation and corrosion resistance, etc., and there are few studies on cold working and heat treatment. Researchers study the effects of cold rolling and annealing processes on the microstructure and mechanical properties of alloy pipes through experiments and theoretical calculations.
The experimental material is a 617B alloy smelted in a vacuum induction furnace and an atmosphere protection electroslag remelting double process. The ingot is made into an extruded billet after homogenization, forging and machining, and the tube is extruded on a 6000t horizontal extruder The billet is cold rolled into tubes according to the deformation of 9% to 58%. Cut the metallographic samples and mechanical test samples on the cold-rolled pipe, and perform annealing treatment at different temperatures and times in the box-type heat treatment furnace, the annealing temperature is 1080 ～ 1200 ℃, the annealing time is 5 ～ 90min, cooling The method is water cooling.
After grinding and polishing the heat-treated sample, electrolysis is carried out with 10% oxalic acid solution, the voltage is 5V, and the microstructure of the alloy is observed and analyzed by the LEICA-DMR optical microscope, and according to GB / T6394-2002 “Metal average grain size measurement method 》 A straight line intercept method is used to calculate the average grain size. The tensile test of the standard tensile samples before and after heat treatment is performed on the Z150 / SN5A electronic material testing machine. The results showed that:
- (1) With the increase of the amount of cold deformation, the grains are elongated along the direction of the maximum main deformation, forming a strip-shaped deformation zone; the tensile strength and yield strength of the alloy increase at room temperature, and the elongation decreases; the amount of deformation reaches 9 %, The plasticity of the pipe is very sensitive to deformation hardening.
- (2) With the increase of annealing temperature, the grains of the alloy gradually grow, and when the annealing temperature is above 1160 ℃, the grain growth rate is significantly increased; the activation of cold-deformed alloy grain growth under different deformation amounts The energy Q is much larger than the self-diffusion activation energy of pure Ni. The Q value increases first and then decreases as the amount of deformation increases.
- (3) When the annealing temperature is increased from 1080 ℃ to 1160 ℃, as the temperature increases, the tensile strength and yield strength of the 617B alloy pipe decrease, and the plasticity increases; continue to increase the temperature, the alloy strength and plasticity change little.
- (4) As the annealing temperature increases, the value of the alloy grain growth index η increases first and then decreases. At 1080 ℃, the value of η is between 0.1 and 0.2. When the temperature rises to 1120 to 1160 ℃, the value of η suddenly increases to between 0.5 and 0.6. At 1200 ℃, the value of η decreases to 0.3 to 0.4.