| Grain ultra-refinement is an effective method to improve the strength and hardness of materials without reducing the material plasticity, and has been the research hotspot of metallic materials in the world. Austenitic stainless steel is widely used in chemical engineering, light industry and petroleum field, because it has a variety of excellent properties such as excellent toughness, ductility, high-temperature oxidation resistance and corrosion resistance. It is limited in using on structural parts because of lower intensity. How to obtain the excellent comprehensive properties of austenitic stainless steel is an important task and it has the important value of academic and the project application. Thus, it is important to investigate the fabrication, microstructure and mechanical properties of ultra-fine grained austenitic stainless steel.Microstructure characterization of AISI310 S steels after cold rolling and cryorolling with different reductions were investigated by means of XRD, OM and TEM. The XRD results show that the deformation-induced martensite transformation is not found during cold rolling and cryorolling. After small amount deformation, the main component of deformed microstructure are dislocation multiplication and tangles, meanwhile, a small amount of deformation twins are observed. With the increasing of deformation, a large amount of deformation twins are formed. After 90% deformation, the grains are fractured completely to nanometer level for the interaction between twins and dislocations, deformation and deformation.The hardness and strength of austenitic stainless steel were both increased with the increasing of deformation. They increased rapidly in prophase and slowly in late stage. But the elongation was the opposite. The hardness and strength after cryorolling were much higher than after cold rolling at the same deformation. After 90% deformation, the hardness of austenitic stainless steel after cryorolled was about twice the original sample, the yield strength and tensile strength were respective about 5.1 times and 2.6 times as that of the original sample. The hardness after cold rolled was 1.9 times higher than the original austenitic stainless steel, the yield strength and tensile strength were about 3.9 times and 2.4 times as that of the original sample. The tensile fracture was changed from typical ductile fracture to brittle cleavage fracture.The samples after 90% deformation of cryorolled were annealed at different temperature for different time. When annealed below 700 ℃, deformed structure tend to be recovery, while annealed above 700 ℃, recrystallization occured.With the increase of annealing temperature, the degree of recrystallization was processed fully and completely. When annealed at 800 ℃, with the annealing time increased from 2 min to 60 min, the austenite grain size increased from 300 nm to 700 nm. When annealing at 900 ℃ for 10 min, the grain size was about 750 nm; while temperature increased at 1000 ℃ for 10 min, the austenite grain is nearly homogeneous with an average grain size of 1 ?m.With the annealing temperature increased, the hardness and strength of austenitic stainless steel appeared a decreasing trend at different annealing temperature for 10 min. Microhardness decreased from HV 549(500 ℃) to HV 314(1000 ℃), the tensile strength and yield strength were reduced from 1851 MPa, 1763 MPa(500 ℃) to 1063 MPa, 798 MPa(1000 ℃), respectively. But the elongation was improved from 3.44%(500 ℃) to 39.9%(1000 ℃). The tensile fracture transformed from mixed brittle fracture which is quasi-cleavage-based mixed with a little small and shallow dimples to ductile fracture which has a large number of large and deep nest.Under the experimental condition, the optimum technological of ultra-fine gained austenitic stainless steel fabrication is annealed at 800 ℃ for 10 min after 90% cryorolled reduction. |
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