HIGH-STRENGTH HOT-ROLLED STEEL PLATE WITH EXCELLENT FATIGUE STRENGTH AND ITS MANUFACTURING METHOD Russian patent published in 2014 - IPC C22C38/14 C21D8/02 

FIELD: metallurgy.

SUBSTANCE: invention relates to metallurgy, and namely to production of a high-strength hot-rolled steel plate with excellent fatigue strength. Steel contains the following, wt %: C: 0.08-0.18, Si: less than 0.5, Mn: 0.8-1.8, P: 0.05 or less; S: 0.005 or less; N: 0.008 or less; Al: 0.01-0.1, Ti: 0.01-0.1, Fe and inevitable impurities are the rest, heated to the temperature of 1150-1300°C. Hot steel rolling is performed with rolling end temperature in the range of Ar₃ to (Ar₃+60)°C and with a crimping degree in the last frame of finishing rolling of not less than 25% to obtain a steel plate. The plate is coiled at the temperature of 570-670°C. Microstructure of some part of a surface layer to the depth from surface of up to 100 mcm consists of ferrite as the primary phase and the secondary phase, the fraction of which is 30% or less. Average diameter of ferrite grain is maximum 10 mcm. At least 30% of Ti contained in some part of the surface layer is present in the form of Ti carbide, and average diameter of Ti carbide grain does not exceed 30 nm.

EFFECT: produced steel plates have high fatigue strength and formability.

9 cl, 1 dwg, 3 tbl, 1 ex