Investigation On Cold Deformation Behavior Of GH3625 Superalloy Tubes

GH3625 superalloy tube by hot-extrusion process was prepared.The cold deformation behavior,static recrystallization behavior,deformation induced ? phase precipitation behavior of GH3625 superalloy hot-extruded tube was studied.And GH3625 superalloy seamless pipe through short process preparation process was developed.The influence of cold deformation and heat treatment on microstructure and properties of the GH3625 alloy was studied through room-temperature compression test,mathematical model fitting,optical microscopy,Rockwell hardness and other means.And cold deformation constitutive equation of GH3625 alloy tubes was established.The results show that GH3625 alloy hardening law basically follows Hollomon equation,especially the cold deformation was the main factor of affecting work hardening.With the increasing of cold deformation extend,grain deformation degree raised,deformation uniformity of the grains gradually improved and average grain size decreased.With the increase of heat treatment temperature,the average grain size of the alloy first decreased and then climbed up.When the temperature was at the ranges of 1100~1250 ?,grain growth activation energy reached at 180.46 k J/mol.Hardness declined during the process of heat treatment temperature increased,and its values and the average grain size of the alloy kept in line with Hall-Patch relation.Microstructure evolution rule during intermediate annealing of cold deformed GH3625 superalloy tubes was studied.And the equation of static recrystallization kinetics and recrystallization grain growth was established.The results show that with the increase of cold deformation degrees,the uniformity of the alloy microstructure gradually got improved and the hardness value significantly was increased during the 0~50 % cold deformation extent especially.The relationship between volume fraction of GH3625 superalloy tube recrystallization and holding time can be described by the JMAK equation.The GH3625 superalloy tube activation energy values calculated through experimental dates decreases range from 344.26 to 287.12 k J/mol,with the increase of cold deformation degrees.As the temperature rise,recrystallization completion time shortened from 30.57 min to 12.69 min.The annealing temperature and cold deformation degrees had significant influence on the velocity of recrystallization.At 1120 ? annealing temperature,grains of cold deformation occur completely recrystallized,with the cold deformation degrees increasing,grain sizes of fully recrystallized decreases.Finally,the static recrystallization kinetics curve of GH3625 superalloy tube was worked out,which could be a provide theoretical basis of GH3625 superalloy tube intermediate annealing treatment and grain refining.The microstructure of GH3625 superalloy tubes made in 1120 ?/15 min/AC can achieve refined and homogeneous full recrystallization grains in suitable intermediate annealing process.The predicted outcomes were generated from grain growth model coincided with the experimental results well.The effect of cold deformation on the law and kinetics of ? phase precipitation was investigated.The results show that ? phase first precipitates at the deformation twin and grain boundaries as well as deformation bands,and then precipitates in the grains.The amount of ? phase at the deformation bands increases with the increase of cold deformation.The morphologies of ? phase change gradually from needles to spheroids or rodlike with increasing cold deformation.With the extend of aging time,the average size of ? phase increases,and the average size of ? phase grows according to LSW theory.At 800?,the relationship between the precipitation content of ? phase and aging time follows Avrami equation.As cold deformation increases,the content of ? phase increases as well,the time index n decreases,whereas the ? phase precipitation rate increases.Cold deformation promotes the precipitation of ? phase.The solute drags Nb in soild solution and pinning of ? phase inhibits the grain growth during aging process of cold deformed GH3625 superalloy hot-extruded tube.The hardness of the alloy increases with the extension of the holding time,? = 35 %,and ??50 %,no obvious change occurs.In order to obtain GH3625 alloy seamless pipe,the GH3625 alloy seamless pipe with ?28×5.5 mm was developed through short process hot extrusion forming and cold rolling process.And to GH3625 alloy seamless pipe the microstructure and mechanical properties to conduct a comprehensive evaluation.The results show that hollow tube has been successfully extruded the GH3625 alloy tube with ?43×9.5 mm under the condition of fixed extrusion speed of 50 mm/s,preheating temperature of 1150 ? and extrusion ration of 7.4.The alloy tube is composed of a small amount of deformation twin and a large number of equiaxed crystal mixed crystal structure,the average grain size is about 8.6,and the tensile strength at room temperature and elongation at break are 771 MPa and 52.33%,respectively,and have good cold working performance and mechanical properties.The performance of GH3625 alloy seamless pipe after cold rolling and annealing is in accordance with ASTM-B163-04 international standard.