THICK-WALLED HIGH-STRENGTH HOT-ROLLED STEEL PLATE WITH EXCELLENT LOW-TEMPERATURE IMPACT STRENGTH AND ITS PRODUCTION METHOD Russian patent published in 2013 - IPC C22C38/14 C21D8/02 C21D9/46 

FIELD: metallurgy.

SUBSTANCE: steel which contains the following, wt %, is heated: 0.02-0.08 of C, 0.01-0.50 of Si, 0.5-1.8 of Mn, 0.025 or less of P, 0.005 or less of S, 0.005-0.10 of Al, 0.01-0.10 of Nb, 0.001-0.05 of Ti, the rest is Fe and inevitable impurities, at that content of C, Ti and Nb complies with the ratio (Ti + (Nb / 2)) / C <4. Hot-roll is performed including roughing-down and finish rolling, accelerated cooling at average rate of cooling in the middle of steel plate in the thickness direction equal to 10°C/s or more till temperature of cooling stop is reached, and it is coiled under coiling temperature. Steel microstructure includes ferritic phase being the primary phase and including bainitic ferrite, bainit and their mixed phase and the second phase including pearlite, martensite, austenitic-martensitic component and their mixed phase. Difference ΔD between average size of grain (mcm) of ferritic phase at a distance of 1 mm from the surface of steel plate in the direction of thickness and average size of grain (mcm) of ferritic phase in the middle of steel plate at a distance of 2 mcm or less in the direction of thickness, and difference ΔV between content part (vol %) of the second phase at a distance of 1 mm from the surface of steel plate in the direction of thickness and content part (vol %) of the second phase in the middle of steel plate in the direction of thickness is 2% or less.

EFFECT: providing steel with characteristics of high tensile strength TS in 521 MPa and improved low-temperature impact strength, improved values of DWTT and CTOD.

14 cl, 7 dwg, 12 tbl