Steel with high toughness used as a constructional steel e.g. for rods, profiles and thin and thick plates

摘要

A steel with high toughness has a structure in which the prior-austenite grain boundary has peaks and troughs of specified spacing and amplitude. A steel with high toughness and strength has a structure in which = 70% of the total prior-austenite grain boundary length has peaks and troughs with a spacing of }5 mu m and an amplitude of = 200 nm. Independent claims are also included for the following: (i) a tough tempered martensitic steel with a structure in which carbides are present along }80% of the total length of the prior-austenite grain boundary; (ii) production of the steel by deformation in the austenitic state with = 30% of the total area reduction in the region below the austenite recrystallization temperature and then cooling without recrystallization or diffusion-dependent phase transformation; and (iii) production of the tough tempered martensitic steel by carrying out the above deformation, cooling to form martensite, heating to 300-500 deg C at = 100 deg C/sec, holding for 10-30 sec. and then rapidly cooling. Preferred Features: The steel with high toughness and strength has the composition (by wt.) 0.10-0.80% C, }0.80% Si, 0.30-3.0% Mn, balance Fe and impurities, while the tough tempered martensitic steel has the composition (by wt.) 0.20-0.80% C, 0.80-3.0% Mn, balance Fe and impurities.