Study On Work Hardening Behavior Of Steady And Metastable Austenitic Stainless Steels

Austenitic stainless steel has the characteristics of high plastic toughness,strong corrosion resistance and good cold forming performance at room temperature,so some austenitic stainless steel is used in high-end electronic products.Due to the special chemical composition of austenitic stainless steel,some products will undergo deformation induced martensitic transformation during cold working,which will change the permeability and mechanical properties of stainless steels materials.If the permeability exceeds a certain limit,it will also cause shielding effect on signal transmission.In view of the above problems,this paper takes the austenitic stainless steel for special communication products as the research object.For the SUS304 and the optimized composition SUS316 L austenitic stainless steel hot-rolled solid solution pickling coil produced through a large-scale industrial production of a domestic stainless steel company,they are carried out cold rolling deformation test,the work hardening behavior of two kinds of steel during cold rolling and the influence mechanism of cold working on the permeability and mechanical properties of strip products were studied,and then guide the production process of raw materials.The specific research results are as follows:The microstructure evolution of SUS304 austenitic stainless steel during cold rolling at room temperature was studied by means of metallographic microscope,X-ray diffractometer,scanning electron microscopy(EBSD),transmission electron microscopy,etc.The results show that the microstructure change of 304 austenitic stainless steel can be divided into three stages: stage I: in the early stage of deformation(reduction rate < 10%),a few austenitic grains form shear bands through the application of stress and the stacking dislocation energy,and shear bands provide nucleation position for martensite during the phase transformation;stage II: As the reduction rate increases gradually(10% < reduction rate < 23%),non-diffusive deformation induces martensite transformation in 304 austenitic stainless steel,and there are two phase transformation ways: ??????and ????;stage III: When the reduction rate of cold rolling further increases(reduction rate > 23%),???? phase transformation occurs mainly.Compared with SUS304 stainless steel,SUS316 L austenitic stainless steel increases the content of Ni,Mn and N,enlarges austenitic phase region,improves austenitic stability,and does not undergo martensite transformation.The influence mechanism of cold rolling reduction rate on permeability of two kinds of steel was explored by using Ferromaster Premeability Meter and ferrite measuring instrument.During cold rolling of SUS304 austenitic stainless steel,deformation induced martensitc transformation occurs.The transformation product ?? martensite is ferromagnetic phase.With the increase of cold rolling reduction rate,the transformation of ?? martensite increases,and the permeability increases.Due to the special chemical composition and production process of 316 L austenitic stainless steel,martensitic transformation did not occur during cold rolling deformation,and the permeability remained below 1.01 basically,without obvious change.The mechanical properties of the two steels during cold rolling were studied by tensile test and Vickers hardness test.It is found that with the increasing reduction rate of cold rolling,the tensile strength and yield strength of SUS304 and 316 L austenitic stainless steel continue to increase,and the hardness is also increasing.At the same time,the plasticity is keeps falling.The microstructure evolution and performance changes of the two steel grades during cold rolling deformation were analyzed: the stability of 316 L austenitic stainless steel is significantly higher than that of SUS304 austenitic stainless steel,so the microstructure evolution and performance changes during cold rolling deformation are also different.Therefore,the properties and uses of the two steel types are also different.With the increase of cold rolling reduction rate,ferromagnetic ?? martensite is also continuously generated inside SUS304 austenitic stainless steel,resulting in continuous increase of magnetic permeability,which interferes with the signal transmission of electronic products.SUS304 austenitic stainless steel with a reduction rate of 5% to10% can meet the end user's needs for logo parts for electronic products.For 316 L austenitic stainless steel,due to the composition and process,no martensite transformation occurs during the cold rolling deformation,the magnetic permeability is basically kept below 1.01,and the 316 L between 5% ? 20% reduction ratio austenitic stainless steel can meet the needs of end users for electronic products housings and other precision parts.