PRODUCTION OF BUILDING USE THICK FIRE RESISTANT STEEL TUBE HAVING LOW YIELD RATIO

• Main Authors: FUKAI HIDEAKI, NAGAE MORIYASU
• Format: Patent
• Language: English
• Published: 24.06.1997
• Edition: 6
• Subjects: ALLOYS; CHEMISTRY; FERROUS OR NON-FERROUS ALLOYS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUSMETALS OR ALLOYS; MAKING METAL MALLEABLE BY DECARBURISATION, TEMPERING OR OTHERTREATMENTS; METALLURGY; METALLURGY OF IRON; MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; TREATMENT OF ALLOYS OR NON-FERROUS METALS

PROBLEM TO BE SOLVED: To produce a building use thick steel tube capable of attaining high strength and a low yield ratio in each part of the plate thickness and furthermore small in deterioration in strength even at a high temp. by specifying the elemental compsn. and rolling and forming conditions. SOLUTION: As the fundamental component elements of a steel, C, Si, Mn, Mo, V, sol.Al and N are contained. The steel having a prescribed compsn. contg. these elements is subjected to hot rolling at >=30% cumulative draft in the temp. range of lower than the recrystallization temp. to higher than the Ar3 to form a steel plate. After that, it is cooled to lower than the temp. at which transformation is finished at a cooling rate of 5 to 30 deg.C/sec. Next, it is heated to the temp. range of a two phase region of higher than the Ac1 to lower than the Ac3 , and working into a tubular shape is started from the plate edge part from the temp. range of higher than the Ar1 and is finished in the plate center part. After that, cooling is executed at a rate based on a prescribed calculating formula. Then, its microstructure is formed into the one essentially consisting of ferrite + bainite and composed of <=5% insular martensite.