Wrinkling is a type of surface defect that easily occurs when the strain of
ferritic stainless steel is large in the forming process. It occurs in the rolling direction of the strip and appears as a narrow convex strip, that is, a surface corrugation.
Reducing wrinkles by controlling the production process:
(1) Reduce the columnar crystal billet, an increase of equiaxed. Methods are: ① Electromagnetic stirring can promote the columnar crystal to the equiaxed crystal transformation. ② In the process of metal solidification or metal solidification before the application of impulse current to the metal melt, pulse current and due to the interaction of the pulse generated by the magnetic field, so that the solidified metal by strong electromagnetic force and impact force and vibration Dendrites crystallized first break up, forming more crystalline core, so that the solidified tissue has been refined. ③ Control the composition of the front solid-liquid interface coagulation, the larger the better the cooling area. Appropriate amount of water, reducing the solid phase, liquid steel temperature gradient; solidification after the grain is still growing, especially above 900 ℃, the grain grows quickly. Therefore, the late solidification, should be properly accelerated cooling rate, slow down grain growth.
(2) Select the appropriate slab heating temperature, low finishing temperature and high annealing temperature. Almost all the disadvantages of ferritic stainless steels are related to the carbon and nitrogen in the steels. With the increase of carbon and nitrogen content, the impact toughness of ferritic stainless steel decreased and the brittle transition temperature increased obviously, especially when the content of chromium in steel was more than 15% ~ 18%. The notch sensitivity of steel cooling. The speed effect and size effect also increased significantly with the increase of carbon and nitrogen in steel. With the increase of CN content, the intergranular corrosion sensitivity of ferritic stainless steel increased, and the corrosion resistance of ferritic stainless steel to carbon and nitrogen was general. Pitting corrosion, crevice corrosion and stress corrosion are also harmful. The oxygen content in steel also has a similar effect. With the increase of oxygen content, the brittle transition temperature of ferritic stainless steel increases.It shows that smelting low-carbon, nitrogen and ultra-low carbon, high-purity nitrogen ferritic stainless steel production and development trend.
