Heavy-wall steel plate having 450mpa-grade tensile strength and excellent resistance to hydrogen induced cracking and method for manufacturing same

Abstract

The present disclosure relates to a heavy-wall steel plate having 450 MPa-grade tensile strength and excellent resistance to hydrogen induced cracking, and a method for manufacturing the same. The heavy-wall steel plate includes, by weight, carbon (C): 0.03% to 0.06%, silicon (Si): 0.2% to 0.4%, manganese (Mn): 1.0% to 1.6%, phosphorus (P): 0.03% or less, sulfur (S): 0.003% or less, aluminum (Al): 0.06% or less, nitrogen (N): 0.01% or less, copper (Cu): 0.05% to 0.4%, nickel (Ni): 0.05% to 0.5%, calcium (Ca): 0.0005% to 0.003%, a balance of iron (Fe), and other unavoidable impurities, wherein a thickness of the heavy-wall steel plate is 40 mm or more.

1 . A heavy-wall steel plate having excellent resistance to hydrogen induced cracking, comprising, by weight, carbon (C): 0.03% to 0.06%, silicon (Si): 0.2% to 0.4%, manganese (Mn): 1.0% to 1.6%, phosphorus (P): 0.03% or less, sulfur (S): 0.003% or less, aluminum (Al): 0.06% or less, nitrogen (N): 0.01% or less, copper (Cu): 0.05% to 0.4%, nickel (Ni): 0.05% to 0.5%, calcium (Ca): 0.0005% to 0.003%, a balance of iron (Fe), and other unavoidable impurities,
 wherein a thickness of the heavy-wall steel plate is 40 mm or more, and   tensile strength of the heavy-wall steel plate is 450 MPa or more.   
     
     
         2 . The heavy-wall steel plate according to  claim 1 , further comprising niobium (Nb): 0.005% to 0.05% and titanium (Ti): 0.005% to 0.03%. 
     
     
         3 . The heavy-wall steel plate according to  claim 1 , wherein the heavy-wall steel plate is a microstructure having a composite structure of ferrite and pearlite, and an area fraction of the pearlite is less than 10%. 
     
     
         4 . The heavy-wall steel plate according to  claim 1 , wherein the heavy-wall steel plate further comprises Al—Ca-based inclusions, and a minimum distance between Al—Ca-based inclusions having a diameter of 2 μm or more is 100 μm or more in a rolling direction. 
     
     
         5 . The heavy-wall steel plate according to  claim 1 , wherein a hydrogen induced cracking sensitivity of the heavy-wall steel plate has a crack length ratio (CLR) of 1% or less. 
     
     
         6 . A method for manufacturing a heavy-wall steel plate having 450 MPa-grade tensile strength and excellent resistance to hydrogen induced cracking, comprising:
 preparing a slab having a composition comprising, by weight, carbon (C): 0.03% to 0.06%, silicon (Si): 0.2% to 0.4%, manganese (Mn): 1.0% to 1.6%, phosphorus (P): 0.03% or less, sulfur (S): 0.003% or less, aluminum (Al): 0.06% or less, nitrogen (N): 0.01% or less, copper (Cu): 0.05% to 0.4%, nickel (Ni): 0.05% to 0.5%, calcium (Ca): 0.0005% to 0.003%, a balance of iron (Fe), and other unavoidable impurities;   heating the slab to 1100° C. to 1300° C.;   hot-rolling the heated slab such that the total rolling reduction thickness is less than 200 mm at a finish rolling temperature of 900° C. or higher, so as to prepare a hot-rolled steel plate; and   subjecting the hot-rolled steel plate to a normalizing heat treatment at a temperature of 1000° C. to 1100° C.   
     
     
         7 . The method according to  claim 6 , wherein the heavy-wall steel plate is a microstructure having a composite structure of ferrite and pearlite, and an area fraction of the pearlite is less than 10%. 
     
     
         8 . The method according to  claim 6 , wherein the heavy-wall steel plate further comprises Al—Ca-based inclusions, and a minimum distance between Al—Ca-based inclusions having a diameter of 2 μm or more is 100 μm or more in a rolling direction.