| abstract |
In order to obtain a semi-finished product, the method uses 0.10% ≤ C ≤ 0.35%, 0.8% ≤ Si ≤ 2.0%, 1.8% ≤ Mn ≤ 2.5%, P ≤ 0.1%, 0% ≤ S ≤ 0.4%, 0% ≤ Al ≤ 1.0%, N ≤ 0.015%, 0% ≤ Mo ≤ 0.4%, 0.02% ≤ Nb ≤ 0.08%, 0.02% ≤ Ti ≤ 0.05%, 0.001% ≤ B ≤ 0.005%, 0.5% ≤ Cr ≤ 1.8%, 0 Casting a steel having a composition comprising% ≦ V ≦ 0.5%, 0% ≦ Ni ≦ 0.5%, hot rolling the semifinished product at a hot rolling initiation temperature higher than 1000 ° C., and obtaining a hot rolled steel part Cooling the product through air to room temperature, wherein the hot rolled steel part comprises 70% to 90% bainite, 5% to 25% M / A compounds and up to 25% martensite It has a microstructure consisting of, the bainite and the M / A compounds contain residual austenite such that the total content of residual austenite in the steel is 5% to 25% And, the carbon content of the retained austenite is 0.8% to 1.5%. |