High Strength Steel Plate for Nuclear Reactor Containment Vessel and Method of Manufacturing the Same

Abstract

There is provided a high strength steel plate including, by weight: 0.03% to 0.20% C, 0.15% to 0.55% Si, 0.9% to 1.5% Mn, 0.001% to 0.05% Al, 0.030% or less P, 0.030% or less S, 0.30% or less Cr, 0.2% or less Mo, 0.6% or less Ni, 0.07% or less V, 0.04% or less Nb, 5 ppm to 50 ppm Ca, 0.005% to 0.025% Ti, 0.0020% to 0.0060% N, 0.0005% to 0.0020% B, the balance of F and unavoidable impurities. The steel plate may be formed of tempered martensite, and conditions for cooling and recrystallization controlled rolling are optimized so as to control an average grain size of a microstructure and an aspect ratio of structure grains. Accordingly, a superior high-strength steel plate that can be used for an atomic plant, for example, an atomic plant rated at IOOOMW or more by having a tensile strength of at least 650 MPa and an impact toughness of at least 200 J at −5O ° C., and a method of manufacturing the same can be provided.

1 . A high strength steel plate comprising, by weight: 0.03% to 0.20% C, 0.15% to 0.55% Si, 0.9% to 1.5% Mn, 0.001% to 0.05% Al, 0.030% or less P, 0.030% or less S, 0.30% or less Cr, 0.2% or less Mo, 0.6% or less Ni, 0.07% or less V, 0.04% or less Nb, 5 ppm to 50 ppm Ca, 0.005% to 0.025% Ti, 0.0020% to 0.0060% N, 0.0005% to 0.0020% B, the balance of F and unavoidable impurities,
 wherein relations of Cu+Ni+Cr+Mo≦1.5%, Cr+Mo≦0.4%, V+Nb≦0.1%, and Ca/S≦1.0 are satisfied.   
     
     
         2 . The high strength steel plate of  claim 1 , wherein the steel plate has a microstructure including a martensite structure. 
     
     
         3 . The high strength steel plate of  claim 2 , wherein the microstructure has a grain aspect ratio (longer axis/shorter axis) ranging from 1.1 to 2.5. 
     
     
         4 . The high strength steel plate of  claim 1 , wherein the steel plate has a tensile strength of at least 650 MPa, and an impact toughness of at least 200 J (charpy impact energy) at −50° C. 
     
     
         5 . A method of manufacturing a high strength steel plate, the method comprising:
 reheating a steel slab at 1050° C. to 1250° C., the steel slab comprising, by weight: 0.03% to 0.20% C, 0.15% to 0.55% Si, 0.9% to 1.5% Mn, 0.001% to 0.05% Al, 0.030% or less P, 0.030% or less S, 0.30% or less Cr, 0.2% or less Mo, 0.6% or less Ni, 0.07% or less V, 0.04% or less Nb, 5 ppm to 50 ppm Ca, 0.005% to 0.025% Ti, 0.0020% to 0.0060% N, 0.0005% to 0.0020% B, the balance of F and unavoidable impurities, wherein relations of Cu+Ni+Cr+Mo≦1.5%, Cr+Mo≦0.4%, V+Nb≦0.1%, and Ca/S≦1.0 are satisfied;   controlled-rolling the reheated steel slab in a recrystallization region at Tnr° C. to Tnr+100° C.;   performing an austenization thermal treatment on the rolled steel plate at 870° C. to 950° C. for a duration of 1.3*t+(10 to 30 minutes) and then rapidly cooling the steel plate; and   tempering the cooled steel plate at 650° C. to 700° C.   
     
     
         6 . The method of  claim 5 , wherein the controlled-rolling of the reheated steel slab is performed with a rolling reduction of at least 10% for each rolling pass and with a cumulative rolling reduction ranging from 50% to 90%. 
     
     
         7 . The method of  claim 5 , wherein, in the controlled-rolling of the reheated steel slab, a grain aspect ratio (longer axis/shorter axis) of a microstructure is controlled to a range of 1.1 to 2.5. 
     
     
         8 . The method of  claim 5 , wherein the tempering of the cooled steel slab is performed for a duration of 1.9*t+(10 to 30 minutes). 
     
     
         9 . The high strength steel plate of  claim 2 , wherein the steel plate has a tensile strength of at least 650 MPa, and an impact toughness of at least 200 J (charpy impact energy) at −50° C. 
     
     
         10 . The high strength steel plate of  claim 3 , wherein the steel plate has a tensile strength of at least 650 MPa, and an impact toughness of at least 200 J (charpy impact energy) at −50° C. 
     
     
         11 . The method of  claim 6 , wherein, in the controlled-rolling of the reheated steel slab, a grain aspect ratio (longer axis/shorter axis) of a microstructure is controlled to a range of 1.1 to 2.5.