The present study investigated the effect of cold rolling reduction on microstructure and mechanical properties of a 204C2 Cr–Mn austenitic stainless steel which contained 16%Cr, 2%Ni, 9%Mn and 0.083 %C). The 204C2 austenitic stainless steels were cold rolled at multifarious thickness reductions of 10%, 20%, 30%,40% and 50%, which were compared with the solution-treated one. Microstructure of them was investigated by means of optical microscopy, X-ray diffraction technique and scanning electron microscopy. For mechanical properties investigations, hardness and tensile tests were carried out. Results shows that the cold rolling reduction induced the martensitic transformation (γ→α ́) in the structure of the austenitic stainless steel. With the increase of the rolling reduction, the amount of strain-induced martensite increased gradually. Hardness, ultimate tensile strength and yield strength increased with the incremental rolling reduction in 204C2 stainless steels, while the elongation decreased. At the thickness reduction of 50%, the specimen obtained best strength and hardness. Hardness of 204C2 stain steel reached 679HV. Ultimate tensile strength reached 1721 MPa. Yield strength reached 1496 MPa.
In this study, based on the existing 20LH5 austenitic stainless steel for sieve, the influence of different solution treatment parameters on the microstructure and properties were studied. Through the simulation before the experiment, the suitable theoretical solution treatment temperature range for the steel plate is 800 °C~1100 °C according to the empirical formula, and the optimal holding time range is 5 s-15 s. In the optimal temperature range and the best solution treatment time, the gradient was set in the interval and then cooled by water and air after heating. The results show that the grain of the sample steel before pre-treatment (cold rolled then pre-annealed before leaving the factory) is coarser, and the microstructure of the steel plate after solution treatment has obvious refinement tendency and a large number of annealing twins are formed. The softening effect is remarkable. At 800 °C + 15 s + water cooling and 950 °C + 10 s + water cooling, the tensile strength of the two processes are greater than 1000 MPa, the yield strength of the two processes are greater than 440 MPa, and the elongation of the two processes are greater than 46%.The steel sheets obtained by solution treatment under both experimental parameters can achieve good mechanical properties and meet the expected specifications of the products.
The DP1000 cold-rolled dual phase steel, the thickness of which is 1.2 mm, was required to do the tensile test under nine different strain rates from 10-4 s-1 to 1000 s-1. The mechanical properties and morphologies of the steel were obtained and analyzed. According to the C-J model, the plastic deformation characteristics of dual phase steel under different strain rates were studied. By means of transmission electron microscope (TEM), the morphologies of ferrite and martensite in the dynamic were observed. Finally, the constitutive models of quasi-static and high strain rate were established by using the modified Johnson-Cook model. The results reveal that DP1000 dual phase steel has obvious strain rate sensitivity, and it is a relatively pure ferrite and martensite dual phase structure. There are two stage strain hardenging characteristics in DP1000. In the first stage, the strain hardening ability of ferrite is higher, and the second stage is martensite deformation stage, the strain hardening ability is lower. The modified J-C constitutive model has high fitting effect, and the experimental results are matched with the fitting values.
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