STEEL SHEET FOR SHIELDING MAGNETIC FIELD AND METHOD FOR MANUFACTURING SAME
The present invention relates to a steel sheet for shielding a magnetic field, which is used for a medical magnetic resonance imaging (MRI) room wall body and the like, and a method for manufacturing the same.
1 . A steel sheet for shielding magnetic field, comprising:
by weight %, 0.02% or less of carbon (C), 0.001% to 0.05% of silicon (Si), 0.01% to 0.2% of manganese (Mn), 0.001% or 0.05% of aluminum (Al), 0.005% or less niobium (Nb), 0.07% or less of titanium (Ti), 0.01% or less of nitrogen (N), 0.015% or less of phosphorus (P), 0.005% or less of sulfur (S), and a remainder of iron (Fe) and inevitable impurities,
wherein a microstructure has ferrite as main structure, wherein the ferrite has an average grain size of 100 μm or greater.
2 . The steel sheet for shielding magnetic field of claim 1 , wherein the steel sheet has a maximum size of a precipitate existing at a boundary of or within the ferrite grain is 100 nm or less.
3 . The steel sheet for shielding magnetic field of claim 1 , wherein the steel sheet has a magnetic flux density of 1 T (Tesla) or higher under a magnetic field intensity of 300 A/m.
4 . The steel sheet for shielding magnetic field of claim 1 , wherein steel sheet has yield strength of 190 MPa or less, tensile strength of 220 MPa to 300 MPa, elongation of 40% or more, and a yield ratio of 0.8 or less.
5 . A method for manufacturing a steel sheet for shielding magnetic field, comprising:
reheating a steel slab comprising by weight %, 0.02% or less of carbon (C), 0.001% to 0.05% of silicon (Si), 0.01% to 0.2% of manganese (Mn), 0.001% or 0.05% of aluminum (Al), 0.005% or less niobium (Nb), 0.07% or less of titanium (Ti), 0.01% or less of nitrogen (N), 0.015% or less of phosphorus (P), 0.005% or less of sulfur (S), and a remainder of iron (Fe) and inevitable impurities at a temperature of Ac3 to 1250° C.;
hot rolling the reheated slab and finish hot rolling at a temperature of Ar3 or higher to obtain a steel sheet; and
air cooling the steel sheet to room temperature.
6 . The method for manufacturing a steel sheet for shielding magnetic field of claim 5 , further comprising normalizing heat treatment of maintaining at a temperature of Ar3 or higher for at least (1.3t+30) minutes, and then, of furnace cooling or air cooling.
7 . The method for manufacturing a steel sheet for shielding magnetic field of claim 6 , further comprising stress relief annealing of heat treating at a temperature of 800° C. to 900° C. for at least (1.3t+30) minutes after the normalizing heat treatment, and then, of furnace cooling.
8 . The method for manufacturing a steel sheet for shielding magnetic field of claim 5 , wherein, during the hot rolling, rough rolling is performed at a temperature of Tnr to 1250° C. before finish hot rolling.