MANUFACTURING METHOD FOR TENSILE STRENGTH OF 58KGF/MILLIMETER SQUARE GRADE STEEL WITH IMPROVED HIGH TEMPERATURE STRENGTH PROPERTIES FOR BEING USED AS CONSTRUCTION MATERIAL

摘要

PURPOSE: A manufacturing method for a refractory steel having a tensile strength of 58kg/mm square grade, with an improved properties at high temperature being used as a construction material is provided which satisfies a certain level of properties at room temperature and high temperature, even when the cooling rate is lower than 16C/sec, and makes possible to produce a refractory steel in economical and practical manner. CONSTITUTION: A method comprises: heating a steel slab to the range of 1150-1300C, wherein the steel slab is comprised of C: 0.05-0.15wt.%, Si: 0.55wt.% or less, Mn: 1.0wt.% or less, Cr: 0.70wt.% or less, Mo: 0.3-0.9wt.%, P: 0.03wt% or less, S: 0.025wt.% or less, Sol. Al: 0.01-0.06wt%, and Fe and other unintentionally included impurities: balance, and optionally is comprised of Nb: 0.01-0.06wt.% or V: 0.03-0.10wt.% and the combination thereof by addition; completing a rolling process at 700-790C, that is 2-phase zone of Austensite/Ferrite; doing water cooling by carrying out accelerated cooling at a rate of 8C/second to the temperature range of 500-650C and; then processing air cooling. By applying an accelerated cooling process in low rate, it is possible to enlarge the practicability of steel in economical way, as well as improve the room temperature and high temperature properties. Thus produced refractory steel of high strength-high toughness has a tensile strength of 58kg/mm square grade particularly, a yield strength of 6kgf/millimeter square or more at room temperature and of 9kgf/millimeter square or more at 600C and may be beneficially used in construction industry.