STEEL EXCELLENT IN BRITTLE CRACK PROPAGATION STOPPING CHARACTERISTICS AND RUPTURE CHARACTERISTICS IN SHEET THICKNESS AND ITS PRODUCTION METHOD

• Main Authors: KOSEKI TOSHIHIKO, SHIRAHATA HIROYUKI, INOUE TAKEHIRO, OTANI JUN
• Format: Patent
• Language: English
• Published: 23.01.2002
• Edition: 7
• 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 provide steel improved in arrest performance while securing rupture characteristics in the sheet thickness direction by performing the modification of the structure at least in the surface layer of the steel and to provide its production method. SOLUTION: In this steel excellent in brittle crack propagation stopping characteristics and rupture characteristics in the sheet thickness direction, as to steel having prescribed components, in a region of at least >=5% of the sheet thickness from the surface layer, a texture colony with the average minor axis grain size of 2 to 5 μm containing equi-axed ferritic grains with the average grain size of <=3 μm in >=20% by area ratio and further consisting essentially of elongated ferritic grains is present, and also, the (100) face intensity ratio is controlled to 1.5 to 4.0. In its production method, a slab heated at Ac3 to 1,200 deg.C is cooled at a cooling rate of >=2 deg.C/s till the temperature of the surface layer region of at least >=5% of the slab thickness in the central direction of the slab thickness from the surface reaches <=Ar3, and after that, in a process in which the surface layer region is recuperated, rolling in which the cumulative draft in the temperature region of Ac1 to Ac1+70 deg.C is controlled to 30 to 70%.