High-strength, low-alloy steel for seamless pipes with outstanding weldability and corrosion resistance

Abstract

A high-strength steel and a high-strength, weldable steel pipe. The invention relates to a high-strength steel and to a high-strength, weldable steel pipe. The high-strength, low-alloy steel for seamless steel pipes with outstanding weldability and resistance to stress corrosion cracking with a minimum yield strength of 620 MPa and a tensile strength of at least 690 MPa is characterized by the composition indicated in claim 1.

1 .- 8 . (canceled) 
     
     
         9 . A high-strength, low-alloy steel for seamless steel pipes with excellent weldability and resistance against stress corrosion cracking and with a minimum yield strength of 620 MPa and a tensile strength of at least 690 MPa, comprising in mass-%:
 0.030-0.12% C,   0.020-0.050% Al,   max. 0.40% Si,   1.30-2.00% Mn,   max. 0.015% P,   max. 0.005% S,   0.20-0.60% Ni,   0.10-0.40% Cu,   0.20-0.60% Mo,   0.02-0.10% V,   0.02-0.06% Nb,   max. 0.0100% N, and   remainder iron with melt-related impurities, wherein a ratio Cu/Ni has a value of <1.   
     
     
         10 . The steel of  claim 9 , further comprising Ti, wherein a sum of Ti+Nb+V concentrations has a value from =0.04% to =0.15%. 
     
     
         11 . The steel of  claim 10 , wherein the Ti concentration is less than or equal to 0.02%. 
     
     
         12 . The steel of  claim 9 , comprising in mass-%
 0.080-0.11% C   0.020-0.050% Al,   0.25-0.35% Si,   1.65-1.90% Mn,   max. 0.015% P,   max. 0.005% S,   0.45-0.55% Ni,   0.15-0.20% Cu,   0.35-0.55% Mo,   0.04-0.06% V,   0.04-0.05% Nb,   max. 0.006% N.   
     
     
         13 . The steel of  claim 9 , wherein the steel has a minimum yield strength of 690 MPa and a tensile strength of at least 760 MPa. 
     
     
         14 . A high-strength, weldable seamless steel pipe, produced by hot-rolling followed by tempering, with excellent weldability and resistance against stress corrosion cracking and with a minimum yield strength of 620 MPa and a tensile strength of at least 690 MPa, comprising a steel having the following alloy composition in mass-%:
 0.030-0.12% C,   0.020-0.050% Al,   max. 0.40% Si,   1.30-2.00% Mn,   max. 0.015% P,   max. 0.005% S,   0.20-0.60% Ni,   0.10-0.40% Cu,   0.20-0.60% Mo,   0.02-0.10% V,   0.02-0.06% Nb,   max. 0.0100% N, and   remainder iron with melt-related impurities, wherein a ratio Ni/Cu has a value of =1.   
     
     
         15 . The steel pipe of  claim 14 , wherein the steel further comprises Ti, and wherein a sum of Ti+Nb+V concentrations has a value <0.15. 
     
     
         16 . The steel pipe of  claim 14 , wherein the steel has a titanium concentration of less than or equal to 0.020%. 
     
     
         17 . The steel pipe of  claim 14 , wherein the steel has the following alloy composition in mass-%:
 0.080-0.11% C   0.020-0.050% Al,   0.25-0.35% Si,   1.65-1.90% Mn,   max. 0.015% P,   max. 0.005% S,   0.45-0.55% Ni,   0.15-0.20% Cu,   0.35-0.55% Mo,   0.04-0.06% V,   0.04-0.05% Nb,   max. 0.006% N.   
     
     
         18 . The steel pipe of  claim 14 , wherein the steel has a minimum yield strength of 690 MPa and a tensile strength of at least 760 MPa.