Studies On The Correlation Of Cold-rolled Hardness And Strength Of Austenitic Stainless Steel Sheets With The Cold Rolling Deformation

With the rapid development of the automobile, home appliances and petroleum chemical engineering, austenitic stainless steel is one of important nonmagnetic high alloy steels which has extensive applications with high toughness, large plasticity and excellent corrosion resistance. Austenitic stainless steel is a kind of recycling materials with excellent durability. Its performance is excellent. Austenitic stainless steel is widely used to manufacture many kinds of automobile body. The cold-rolled steel sheets’surface quality, appearance, and size precision are better than those of hot-rolled sheets. The thickness of rolled sheet could be0.18mm. Strain-induced martensitic transformation is the main reason with the resultant work hardening in the austenitic stainless steel. The final hardness of cold rolled stainless steel sheets should be controlled in actual production. The plasticity and subsequent processing ability should be good enough to avoid the cold work hardening. The high hardness and strength will affect the use of next working procedure. It will reduce the scrap rate and the energy consumption. In this studies, the schematic design and lots of experimental researchs on austenitic stainless steel sheet’s cold rolling are carried out. The relationship between the hardness and strength of301and304stainless steels subjected to cold rolling is analyzed. The evolution of the microstructures and contents of martensite caused by strain-induced martensitic transformation are studied. The mathematical relationship between the tensile strength and the hardness of cold rolling is determined.The innovation of the present studies lies in a new method to study the hardness change of cold rolling stainless steel sheets. This method is to get its hardness with the change rule of deformation through the tensile strength of parent stainless steels. The mathematical relationship between the tensile strength and hardness during cold rolling is determined. The cold-rolled hardness of the corresponding strain can be obtained through the tensile strength. In practical production, this method can not only achieve the purpose of controlling cold-rolled hardness, but also cut costs and improve efficiency. This rule can be extended to other kinds of production practice.It is found that the work hardening rate of301austenitic is faster than that of304stainless steel through experimental studies. On the contrary, the plasticity of304stainless steels is better than that of301stainless steels. But both trends of hardness-cold rolling deformation and hardness-tensile deformation are consistent. They all conform to the rule in current studies. The formation of a’-martensite caused by strain-induced martensitic transformation during cold rolling and tension increases. At the same time, γ phase is reduced. Along with the increase of deformation, a’-martensite content is increasing, during which, y phase is changed into a’-martensite gradually. Strain-induced martensitic transformation is the main reason which caused cold-rolled work hardening. The forming of a’-martensite is mainly attribuated wattle martensite.The cold-rolling leads to strain-induced martensitic transformation in the austenitic stainless steels. With the deformation, more shear zones form within grains. The volume fraction of a’-martensite induced by cold deformation increases. The higher degree of work hardening is, the greater the work hardening rate is. It is attrib wattle martensite observed using transmission electron microscopy. It is found that the shear zones and the delivery of shear bands in the austenitic matrix appeared by fine structure observation. The a’-martensite induced by strain-induced martensitic transformation is full of high-density dislocations. Intersections of shear bands in metastable austenites have been shown to be effective sites for strain-induced martensitic nucleation. Martensitic embryos are more possible to generate at intersections of shear bands.The mechanical properties of the301and304austenitic stainless steels are improved distinctly through cold rolling. After20%cold rolling, the Vickers hardness is2.2times higher than that of the primary one, the yielding strength are greatly increased to about895MPa, which is nearly2.4times higher than that of the primary one. After40%cold rolling, the Vickers hardness is2.2times higher than that of the primary one, the yielding strength and tensile strength are greatly increased to about880MPa and1312MPa, respectively, which are nearly4.2times and1.8times higher than those of the primary one. It is found that the ratio of the average tensile strength in MPa to the average Vickers hardness in different percentages of cold rolling was constant and approximately equal to three. Cold deformation is a suitable strengthening method for301and304stainless steels.