| Due to the continuous shortage of energy and resources,the steel industry to improve the performance of traditional steel materials,the potential performance requirements,the development of high strength and toughness of steel has become a new direction in the field of steel.Ultrafine-grained materials(submicron and nanocrystalline)have gained significant importance from the scientific and industrial community.Cryorolling technology is a new method of preparing ultra-fine grain sheet metal in recent years in the world.The technology is through the conventional hot-rolled(or cold-rolled)materials for multi-pass rolling in liquid nitrogen under low temperature conditions,suppresses the dynamic recovery during rolling and maintains a high density of dislocations formed during the rolling process,the use of these dislocations to increase the subsequent short annealing process of recrystallization nucleation points,the formation of sub-crystal or ultra-fine crystalline material.Therefore,this topic is austenite grain size,uneven size distribution and low strength and a series of issues for 304 austenitic stainless steel in the conventional room temperature cold-rolled production conditions,the idea of adopting deep cryogenic rolling and short annealing process to realize superfine grain structure is proposed,and the purpose is to improve the strength and toughness of austenitic stainless steel.The main contents of this paper are as follows:(1)Under laboratory conditions,room temperature rolling,cryorolling and short annealing treatment have been conducted on 304 austenite stainless steel samples,and the influence of rolling style,cryorolling reduction rate,annealing temperature and annealing time on austenite stainless steel microstructure has been studied.The experimental results show that austenite content and grain size of austenite increases with the increase of annealing temperature and annealing time,While the annealing temperature on the reverse transformation of the austenite content and grain size is greater than the extent of the annealing time.In the same annealing conditions,comparison of cryogenic rolling and cold rolling at room temperature,stainless steel sample reverse transformation of austenite content of is higher,and the content of austenite increases with the increase of rolling reduction rate,While a sample with reduction rate of 65%annealing above 700?,the equiaxed austenite grains increase and gradually become homogeneous,when the sample with 65%reduction is annealed at 700? for 320s,the average grain size is about 200nm.(2)The mechanical property tests of different cryorolling processes have been conducted on austenite stainless steel samples.The influence of cryorolling process on the strength,elongation rate,product of strength and elongation,fracture morphology of stainless steel has been studied respectively.The experimental results show that the strength of 304 austenite stainless steel samples increases along with annealing temperature and annealing time increasing,while the elongation and strong plastic products are on the rise,when annealing temperature at 700? and above,the strength,elongation and strong plastic products of the stainless steel samples increase with the increasing of the rolling reduction rate,the strong plastic product of samples with cryorolling and annealing are more than 20000MPa%,when the sample with 65%reduction is annealed at 750? for 320s,the elongation and the strong plastic product are about 40.79%and 40475MPa%.The typical plastic fracture morphology of the tensile specimen is gradually increased with the increase of annealing temperature,annealing time and reduction rate after cryogenic rolling and annealing treatment.(3)The Vickers hardness,phase analysis and macroscopic texture analysis of the samples were investigated.The experimental results show that the macro hardness of stainless steel decreases and the degree of deformation induced martensite reversal to austenite increases with the increase of annealing temperature and annealing time,in the same annealing process conditions,the hardness and reverse transformation austenite content is increasing with the increasing of rolling reduction rate,after cryogenic rolling and annealing treatment the hardness value of the sample is above 300HV10,when the sample with 65%reduction is annealed at 750? for 320s,the austenite content is about 65.12%.The orientation density of alpha and gamma alignment lines of stainless steel samples decreased with the increase of the reduction rate,the increase of annealing temperature and the annealing time. |
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