Low alloy steel

Abstract

A low alloy steel, containing, by mass percent, C: 0.01 to 0.15%, Si: 3% or less, Mn: 3% or less, B: 0.005 to 0.050%, and Al: 0.08% or less, and the balance being Fe and impurities, wherein in the impurities, N: 0.01% or less, P: 0.05% or less, S: 0.03% or less, and O: 0.03% or less. In the alloy steel, a HAZ has excellent resistance to embrittlement attributable to hydrogen such as stress corrosion cracking in wet hydrogen sulfide environments.

1 . A low alloy steel, containing, by mass percent,
 C: 0.01 to 0.15%, Si: 3% or less,   Mn: 3% or less,   B: 0.005 to 0.050%, and   Al: 0.08% or less, and   the balance being Fe and impurities,   wherein in the impurities,   N: 0.01% or less,   P: 0.05% or less,   S: 0.03% or less, and   O: 0.03% or less.   
     
     
         2 . The low alloy steel according to  claim 1 , wherein the low alloy steel contains, by mass percent, of one or more elements selected from Cr, Mo, Ni and Cu: 1.5% or less in total in lieu of a part of Fe. 
     
     
         3 . The low alloy steel according to  claim 1 , wherein the low alloy steel contains, by mass percent, of one or more elements selected from Ti, V and Nb: 0.2% or less in total in lieu of a part of Fe. 
     
     
         4 . The low alloy steel according to  claim 1 , wherein the low alloy steel contains, by mass percent, of Ca and/or Mg: 0.05% or less in total in lieu of a part of Fe. 
     
     
         5 . The low alloy steel according to  claim 1 , wherein the content of B satisfies Formula (1):
   0.005× Hv/ 300+0.0023≦ B   (1)
   where, “Hv” in the formula means the maximum value of Vickers hardness of HAZ, and “B” means the content of B (mass %).   
     
     
         6 . The low alloy steel according to  claim 2 , wherein the low alloy steel contains, by mass percent, of one or more elements selected from Ti, V and Nb: 0.2% or less in total in lieu of a part of Fe. 
     
     
         7 . The low alloy steel according to  claim 2 , wherein the low alloy steel contains, by mass percent, of Ca and/or Mg: 0.05% or less in total in lieu of a part of Fe. 
     
     
         8 . The low alloy steel according to  claim 3 , wherein the low alloy steel contains, by mass percent, of Ca and/or Mg: 0.05% or less in total in lieu of a part of Fe. 
     
     
         9 . The low alloy steel according to  claim 6 , wherein the low alloy steel contains, by mass percent, of Ca and/or Mg: 0.05% or less in total in lieu of a part of Fe. 
     
     
         10 . The low alloy steel according to  claim 2 , wherein the content of B satisfies Formula (1):
   0.005× Hv/ 300+0.0023≦ B   (1)
   where, “Hv” in the formula means the maximum value of Vickers hardness of HAZ, and “B” means the content of B (mass %).   
     
     
         11 . The low alloy steel according to  claim 3 , wherein the content of B satisfies Formula (1):
   0.005× Hv/ 300+0.0023≦ B   (1)
   where, “Hv” in the formula means the maximum value of Vickers hardness of HAZ, and “B” means the content of B (mass %).   
     
     
         12 . The low alloy steel according to  claim 4 , wherein the content of B satisfies Formula (1):
   0.005× Hv/ 300+0.0023≦ B   (1)
   where, “Hv” in the formula means the maximum value of Vickers hardness of HAZ, and “B” means the content of B (mass %).   
     
     
         13 . The low alloy steel according to  claim 6 , wherein the content of B satisfies Formula (1):
   0.005× Hv/ 300+0.0023≦ B   (1)
   where, “Hv” in the formula means the maximum value of Vickers hardness of HAZ, and “B” means the content of B (mass %).   
     
     
         14 . The low alloy steel according to  claim 7 , wherein the content of B satisfies Formula (1):
   0.005× Hv/ 300+0.0023≦ B   (1)
   where, “Hv” in the formula means the maximum value of Vickers hardness of HAZ, and “B” means the content of B (mass %).   
     
     
         15 . The low alloy steel according to  claim 8 , wherein the content of B satisfies Formula (1):
   0.005× Hv/ 300+0.0023≦ B   (1)
   where, “Hv” in the formula means the maximum value of Vickers hardness of HAZ, and “B” means the content of B (mass %).   
     
     
         16 . The low alloy steel according to  claim 9 , wherein the content of B satisfies Formula (1):
   0.005× Hv/ 300+0.0023≦ B   (1)
   where, “Hv” in the formula means the maximum value of Vickers hardness of HAZ, and “B” means the content of B (mass %).