METHOD OF PRODUCING SHIP STEEL PLATE 5NI WITH LOW RESIDUAL MAGNETISM AND EXCELLENT SURFACE QUALITY Russian patent published in 2024 - IPC C21D8/02 C22C38/12 C22C38/08 C22C38/06 C22C38/04 C22C38/02 

FIELD: metallurgy.

SUBSTANCE: invention relates to production of ship steel plate 5Ni, having average residual magnetism at angles of 15 G or less, and surface quality of SA 2.0. Liquid steel is melted containing the following elements, wt.%: C: 0.07–0.10, Si: 0.05–0.20, Mn: 0.60–0.80, Ni: 4.90–5.25, P: 0.007 or less, S: 0.002 or less, Alt: 0.010–0.035, V: 0.010–0.015, Nb: 0.010–0.020, Ca: 0.0005–0.0030, O: 0.0012 or less, N: 0.0040 or less, H: 0.0001 or less, the rest is Fe and unavoidable impurities. A slab is obtained from liquid steel, wherein the degree of overheating of the pouring is controlled in range of 5–25 °C, and the level axial segregation of slab is not higher than level C1.0. After leaving the line, the slab is subjected to slow cooling, wherein the initial slow cooling temperature is not less than 600 °C, and the slow cooling time is not less than 72 hours. After slow cooling, slab surfaces are ground by grinding, wherein the upper and lower surfaces are ground to thickness of 1–2 mm, and then surfaces are coated with paint to prevent air ingress with prevention of oxidation during repeated heating. Performing the slab reheating to 1,170–1,220 °C and adjusting the heating time at 600–900 °C in the range of not less than 0.32 min/mm, note here that when expected temperature in slab thickness reaches surface temperature of slab, temperature is maintained for at least 0.5 hour. After removing the workpiece from the furnace, it is subjected to water treatment under pressure to remove scale and two–stage controlled rolling is performed, including rough rolling and finish rolling. Initial temperature of rough rolling is in range of 1,080–1,150 °C, and percentage of reduction as a result of triple pass through rolls after rough rolling is not less than 15%. Thickness in heated state is not less than 1.8 H, where H is thickness of finished product in form of steel plate. Finishing rolling is high-temperature rolling, wherein the initial rolling temperature is in range of 880–970 °C, the final temperature is not less than 800 °C, and after completion of rolling, the steel plate is air cooled. Quenching is carried out at a temperature of the first hardening of 880±10 °C. After reaching the required temperature in the furnace, holding is performed for 30–100 minutes and water quenching is performed. Second hardening temperature is 760±10 °C. After reaching the required temperature in the furnace, holding is performed for 30–100 minutes and water quenching is performed. Tempering is carried out at temperature of 630±10 °C, after heating area of 1/2 of the thickness of the steel plate, the temperature is maintained for 120–200 min to ensure complete diffusion of carbon in the hardened martensite to obtain a tempering sorbite microstructure.

EFFECT: produced plates have high strength, coefficient of elongation and resistance to impact loads in conditions of ultra-low temperatures of −130 °C.

9 cl, 3 dwg, 4 tbl