Thick-walled high-toughness high-strength steel plate and method for manufacturing the same

Abstract

A thick-walled, high-toughness, high-strength steel plate manufactured from steel having a particular composition and casted under conditions where the cooling rate of a surface during solidification is 1° C./s or less. The surface of the steel plate has a toughness (vE-40) of 70 J or more, and the steel plate has a thickness of 100 mm or more.

1 . A thick-walled, high-toughness, high-strength steel plate having a thickness of 100 mm or more, comprising, on a mass percent basis,
 C: 0.08% to 0.20%,   Si: 0.40% or less,   Mn: 0.5% to 5.0%,   P: 0.010% or less,   S: 0.0050% or less,   Cr: 3.0% or less,   Ni: 0.1% to 5.0%,   Al: 0.010% to 0.080%,   N: 0.0070% or less, and   O: 0.0025% or less,   wherein the following formulae (1) and (2) being satisfied, a remainder being Fe and incidental impurities:
   Ceq IIW =C+Mn/6+(Cu+Ni)/15+(Cr+Mo+V)/5≧0.65  (1);
 
   (C L −C)/C L ×100≧30  (2);
 
 wherein C L  is defined by the following formula:
   C L =0.2−(−0.1×(0.2−Si)−0.03×(1.1−Mn)−0.12×(0.2−Cu)−0.11×(3−Ni)+0.025×(1.2−Cr)+0.1×(0.5−Mo)+0.2×(0.04−V)−0.05×(0.06−Al))  (3);
 
 
 wherein element symbols in the formulae denote the respective alloy component contents (% by mass), and in the absence of an element the element symbol is denoted by 0; 
   and a surface of the steel plate having a toughness (vE-40) of 70 J or more.   
     
     
         2 . The thick-walled, high-toughness, high-strength steel plate according to  claim 1 , further comprising, on a mass percent basis, at least one of:
 Cu: 0.50% or less,   Mo: 1.50% or less,   V: 0.400% or less,   Nb: 0.100% or less, and   Ti: 0.005% to 0.020%.   
     
     
         3 . The thick-walled, high-toughness, high-strength steel plate according to  claim 1 , further comprising, on a mass percent basis, at least one of:
 Mg: 0.0001% to 0.0050%,   Ta: 0.01% to 0.20%,   Zr: 0.005% to 0.1%,   Y: 0.001% to 0.01%,   B: 0.0030% or less,   Ca: 0.0005% to 0.0050%, and   REM: 0.0005% to 0.0100%.   
     
     
         4 . The thick-walled, high-toughness, high-strength steel plate according to  claim 1 , wherein the steel plate has a yield strength of 620 MPa or more. 
     
     
         5 . The thick-walled, high-toughness, high-strength steel plate according to  claim 1 , wherein a reduction of area in a thickness direction at half the thickness of the plate is 40% or more. 
     
     
         6 . A method for manufacturing the thick-walled, high-toughness, high-strength steel plate according to  claim 1 , comprising:
 heating steel to 1200° C. to 1350° C.,   hot-forging the steel at a cumulative rolling reduction of 25% or more,   heating the steel to a temperature in the range of from an Ac3 temperature to 1200° C.,   hot-rolling the steel at a cumulative rolling reduction of 40% or more,   leaving the steel to cool,   reheating the steel to a temperature in the range of from the Ac3 temperature to 1050° C.,   rapidly cooling the steel from the Ac3 temperature or more to a lower temperature selected from 350° C. or less and an Ar3 temperature or less, and   tempering the steel at a temperature in the range of from 450° C. to 700° C.   
     
     
         7 . A method for manufacturing the thick-walled, high-toughness, high-strength steel plate according to  claim 1 , comprising:
 heating steel to 1200° C. to 1350° C.,   hot-forging the steel at a cumulative rolling reduction of 25% or more,   heating the steel to a temperature in the range of from an Ac3 temperature to 1200° C.,   hot-rolling the steel at a cumulative rolling reduction of 40% or more,   rapidly cooling the steel from the Ar3 temperature or more to a lower temperature selected from 350° C. or less and an Ar3 temperature or less, and   tempering the steel at a temperature in the range of from 450° C. to 700° C.   
     
     
         8 . A method for manufacturing the thick-walled, high-toughness, high-strength steel plate according to  claim 1 , comprising:
 heating steel to 1200° C. to 1350° C.,   slabbing the steel at a cumulative rolling reduction of 40% or more,   heating the steel to a temperature in the range of from an Ac3 temperature to 1200° C.,   hot-rolling the steel at a cumulative rolling reduction of 40% or more, leaving the steel to cool,   reheating the steel to a temperature in the range of from the Ac3 temperature to 1050° C.,   rapidly cooling the steel from the Ac3 temperature or more to a lower temperature selected from 350° C. or less and an Ar3 temperature or less, and   tempering the steel at a temperature in the range of from 450° C. to 700° C.   
     
     
         9 . A method for manufacturing the thick-walled, high-toughness, high-strength steel plate according to  claim 1 , comprising:
 heating steel to 1200° C. to 1350° C.,   slabbing the steel at a cumulative rolling reduction of 40% or more,   heating the steel to a temperature in the range of from an Ac3 temperature to 1200° C.,   hot-rolling the steel at a cumulative rolling reduction of 40% or more,   rapidly cooling the steel from the Ar3 temperature or more to a lower temperature selected from 350° C. or less and an Ar3 temperature or less, and   tempering the steel at a temperature in the range of from 450° C. to 700° C.   
     
     
         10 . The thick-walled, high-toughness, high-strength steel plate according to  claim 2 , further comprising, on a mass percent basis, at least one of:
 Mg: 0.0001% to 0.0050%,   Ta: 0.01% to 0.20%,   Zr: 0.005% to 0.1%,   Y: 0.001% to 0.01%,   B: 0.0030% or less,   Ca: 0.0005% to 0.0050%, and   REM: 0.0005% to 0.0100%.   
     
     
         11 . The thick-walled, high-toughness, high-strength steel plate according to  claim 2 , wherein the steel plate has a yield strength of 620 MPa or more. 
     
     
         12 . The thick-walled, high-toughness, high-strength steel plate according to  claim 3 , wherein the steel plate has a yield strength of 620 MPa or more. 
     
     
         13 . The thick-walled, high-toughness, high-strength steel plate according to  claim 2 , wherein a reduction of area in a thickness direction at half the thickness of the plate is 40% or more. 
     
     
         14 . The thick-walled, high-toughness, high-strength steel plate according to  claim 3 , wherein a reduction of area in a thickness direction at half the thickness of the plate is 40% or more. 
     
     
         15 . The thick-walled, high-toughness, high-strength steel plate according to  claim 4 , wherein a reduction of area in a thickness direction at half the thickness of the plate is 40% or more. 
     
     
         16 . A method for manufacturing the thick-walled, high-toughness, high-strength steel plate according to  claim 2 , comprising:
 heating steel to 1200° C. to 1350° C.,   hot-forging the steel at a cumulative rolling reduction of 25% or more,   heating the steel to a temperature in the range of from an Ac3 temperature to 1200° C.,   hot-rolling the steel at a cumulative rolling reduction of 40% or more,   leaving the steel to cool,   reheating the steel to a temperature in the range of from the Ac3 temperature to 1050° C.,   rapidly cooling the steel from the Ac3 temperature or more to a lower temperature selected from 350° C. or less and an Ar3 temperature or less, and   tempering the steel at a temperature in the range of from 450° C. to 700° C.   
     
     
         17 . A method for manufacturing the thick-walled, high-toughness, high-strength steel plate according to  claim 2 , comprising:
 heating steel to 1200° C. to 1350° C.,   hot-forging the steel at a cumulative rolling reduction of 25% or more,   heating the steel to a temperature in the range of from an Ac3 temperature to 1200° C.,   hot-rolling the steel at a cumulative rolling reduction of 40% or more,   rapidly cooling the steel from the Ar3 temperature or more to a lower temperature selected from 350° C. or less and an Ar3 temperature or less, and   tempering the steel at a temperature in the range of from 450° C. to 700° C.   
     
     
         18 . A method for manufacturing the thick-walled, high-toughness, high-strength steel plate according to  claim 2 , comprising:
 heating steel to 1200° C. to 1350° C.,   slabbing the steel at a cumulative rolling reduction of 40% or more,   heating the steel to a temperature in the range of from an Ac3 temperature to 1200° C.,   hot-rolling the steel at a cumulative rolling reduction of 40% or more, leaving the steel to cool,   reheating the steel to a temperature in the range of from the Ac3 temperature to 1050° C.,   rapidly cooling the steel from the Ac3 temperature or more to a lower temperature selected from 350° C. or less and an Ar3 temperature or less, and   tempering the steel at a temperature in the range of from 450° C. to 700° C.   
     
     
         19 . A method for manufacturing the thick-walled, high-toughness, high-strength steel plate according to  claim 2 , comprising:
 heating steel to 1200° C. to 1350° C.,   slabbing the steel at a cumulative rolling reduction of 40% or more,   heating the steel to a temperature in the range of from an Ac3 temperature to 1200° C.,   hot-rolling the steel at a cumulative rolling reduction of 40% or more,   rapidly cooling the steel from the Ar3 temperature or more to a lower temperature selected from 350° C. or less and an Ar3 temperature or less, and   tempering the steel at a temperature in the range of from 450° C. to 700° C.   
     
     
         20 . A method for manufacturing the thick-walled, high-toughness, high-strength steel plate according to  claim 3 , comprising:
 heating steel to 1200° C. to 1350° C.,   hot-forging the steel at a cumulative rolling reduction of 25% or more,   heating the steel to a temperature in the range of from an Ac3 temperature to 1200° C.,   hot-rolling the steel at a cumulative rolling reduction of 40% or more,   leaving the steel to cool,   reheating the steel to a temperature in the range of from the Ac3 temperature to 1050° C.,   rapidly cooling the steel from the Ac3 temperature or more to a lower temperature selected from 350° C. or less and an Ar3 temperature or less, and   tempering the steel at a temperature in the range of from 450° C. to 700° C.