Effect Of Annealing Technology On Microstructure And Properties Of Cold-Rolled High-Strength Low Carbon Steel

Cold rolled low carbon high-strength steel has the advantages of good surface quality and high dimensional accuracy,and is widely used in household appliances,automobiles,construction and other industries.In the production of cold rolled sheet,annealing heat treatment after cold deformation is an important process,which directly affects the final microstructure and properties of the product.In this paper,the effects of annealing temperature,holding time,cold rolling reduction rate and microalloying element Ti on microstructure and mechanical properties of the cold rolled low carbon high-strength steel were studied by means of recrystallization annealing process.And scanning electron microscopy,transmission electron microscopy,energy dispersive spectrometer,microhardness tester,tensile testing machine and other testing equipment and analytical means were used in the research.The research results provide a theoretical reference for the development of cold rolled sheet.The results show that: The recrystallization activation energy of the experimental steel is about 73.7 kJ/mol after cold rolling with 66% reduction.when annealed at 600 oC,the microstructure stayed at the recovery stage and almost no recrystallization occurred.After annealing at 625 oC for 5min,the recrystallization was basically completed,and a large number of cementite and TiC particles were precipitated and dispersed in the microstructure,and the cementite particles would gather and coarsen along the grain boundary of ferrite with the increase of temperature or the prolongation of holding time.After annealing at 625 oC for 10 min,the recrystallization was completed and the grains grew up.The microstructure was equiaxed ferrite + cementite particles,and the grain size was about 5.01 um.When annealed at 650 oC?675 oC or 700 oC for 10 min,the ferrite grains grew further.In addition,the yield strength and tensile strength decreased and the elongation increased with the increase of annealing temperature and the prolongation of holding time.The excellent comprehensive mechanical properties could be obtained by the annealing at 625 oC for 5 min.After recrystallization annealing,the microstructure of cold rolled sheets with reduction rate of 32.5% and 66% was both ferrite + cementite.But the microstructure of cold rolled sheet with reduction rate of 32.5% was not uniform enough and some ferrite grains were larger.And the recrystallization softening curves showed that the recrystallization temperatures were 680 oC and 600-625 oC respectively when annealed for 10 minutes.The recrystallization temperatures could be reduced by increasing the deformation degree.With the increase of annealing temperature or the prolongation of holding time,the mechanical properties of annealed plates with 32.5% and 66% reduction rates changed in the same way.