Low Yield Ratio Dual Phase Steel Linepipe with Superior Strain Aging Resistance

Abstract

A steel composition and method from making a dual phase steel therefrom. The dual phase steel may have carbon of about 0.05% by weight to about 0.12 wt %; niobium of about 0.005 wt % to about 0.03 wt %; titanium of about 0.005 wt % to about 0.02 wt %; nitrogen of about 0.001 wt % to about 0.01 wt %; silicon of about 0.01 wt % to about 0.5 wt %; manganese of about 0.5 wt % to about 2.0 wt %; and a total of molybdenum, chromium, vanadium and copper less than about 0.15 wt %. The steel may have a first phase consisting of ferrite and a second phase having one or more of carbide, pearlite, martensite, lower bainite, granular bainite, upper bainite, and degenerate upper bainite. A solute carbon content in the first phase may be about 0.01 wt % or less.

1 . A dual phase steel, comprising:
 carbon in an amount of about 0.05% by weight to about 0.12 wt %;   niobium in an amount of about 0.005 wt % to about 0.03 wt %;   titanium in an amount of about 0.005 wt % to about 0.02 wt %;   nitrogen in an amount of about 0.001 wt % to about 0.01 wt %;   manganese in an amount of about 0.5 wt % to about 2.0 wt %;   silicon in an amount of about 0.01 wt % to about 0.5 wt %   a total of molybdenum, chromium, vanadium and copper is less than about 0.15 wt %;   a first phase consisting of ferrite;   a second phase comprising one or more constituents selected from the group consisting of carbide, pearlite, martensite, lower bainite, granular bainite, upper bainite, and degenerate upper bainite; and   a solute carbon content in the first phase of about 0.01 wt % or less.   
   
   
       2 . The dual phase steel of  claim 1 , wherein the second phase comprises pearlite. 
   
   
       3 . The dual phase steel of  claim 1 , wherein nickel is present in an amount of less than about 1.0 wt %. 
   
   
       4 . The dual phase steel of  claim 1 , wherein boron is present in an amount less than about 0.02 wt %. 
   
   
       5 . The dual phase steel of  claim 1 , wherein the steel has a Pcm of less than about 0.22. 
   
   
       6 . The dual phase steel of  claim 1 , wherein the steel has a tensile strength of at least 500 MPa. 
   
   
       7 . The dual phase steel of  claim 1 , wherein the steel has a tensile strength of at least 520 MPa. 
   
   
       8 . The dual phase steel of  claim 1 , wherein the steel has a minimum uniform elongation of at least 8%. 
   
   
       9 . The dual phase steel of  claim 1 , wherein the steel has a minimum uniform elongation of at least 10%. 
   
   
       10 . The dual phase steel of  claim 1 , wherein the steel has a yield ratio of less than 0.90. 
   
   
       11 . The dual phase steel of  claim 1 , wherein the steel has a yield ratio of less than 0.85. 
   
   
       12 . A method for preparing a dual phase steel, comprising:
 heating a steel slab to a reheating temperature from about 1,000° C. to about 1,250° C.;   reducing the steel slab to form a plate in at least one hot rolling pass at a first temperature;   reducing the plate in at least one hot rolling pass at a second temperature;   cooling the plate to a first cooling temperature sufficient to transform an austenite to a ferrite; and   reducing cluster forming atoms within the ferrite;   wherein the heating of the steel slab at the reheating temperature provides a steel slab consisting essentially of an austenite phase;   wherein the first temperature is sufficient to recrystallize the austenite phase;   wherein the austenite phase does not recrystallize at the second temperature; and   wherein the second temperature is below the first temperature.   
   
   
       13 . The method of  claim 12 , wherein the cluster forming atoms comprise carbon. 
   
   
       14 . The method of  claim 12 , wherein the cluster forming atoms comprise nitrogen. 
   
   
       15 . The method of  claim 12 , wherein the cluster forming atoms comprise carbon and nitrogen. 
   
   
       16 . The method of  claim 12 , wherein reducing cluster forming atoms within the ferrite comprises quenching the cooled plate at a rate of at least 10° C. per second to a second cooling temperature. 
   
   
       17 . The method of  claim 12 , wherein the first cooling temperature is from about 650° C. to about 750° C. 
   
   
       18 . The method of  claim 12 , wherein the first cooling temperature is from about 660° C. to about 750° C. 
   
   
       19 . The method of  claim 12 , wherein the first cooling temperature is from about 670° C. to 740° C. 
   
   
       20 . The method of  claim 12 , wherein the first cooling temperature is about 730° C. 
   
   
       21 . The method of  claim 16 , wherein the second cooling temperature is from about 400° C. to about 700° C. 
   
   
       22 . The method of  claim 16 , wherein the second cooling temperature is from about 450° C. to about 650° C. 
   
   
       23 . The method of  claim 16 , wherein the second cooling temperature is from about 500° C. to about 600° C. 
   
   
       24 . The method of  claim 16 , wherein the second cooling temperature is about 560° C. 
   
   
       25 . The method of  claim 12 , wherein the rolled plate comprises of from about 10% by volume to about 90% by volume of the ferrite. 
   
   
       26 . The method of  claim 12 , wherein the rolled plate comprises of from about 10% by volume to about 90% by volume of a second phase. 
   
   
       27 . The method of  claim 26 , wherein the second phase comprises one or more constituents selected from the group consisting of carbide, pearlite, martensite, lower bainite, granular bainite, upper bainite, and degenerate upper bainite. 
   
   
       28 . The method of  claim 16 , further comprising cooling the steel plate to ambient temperature after quenching to the second cooling temperature. 
   
   
       29 . The method of  claim 12 , further comprising forming the cooled plate into a linepipe using an UOE technique. 
   
   
       30 . The method of  claim 29 , further comprising applying a coating for corrosion resistance to at least a portion of the linepipe. 
   
   
       31 . The method of  claim 30 , wherein the coating comprises at least one fusion bonded epoxy compound. 
   
   
       32 . A method for preparing a dual phase steel, comprising:
 heating a steel slab to about 1,000° C. to about 1,250° C. to provide a steel slab consisting essentially of an austenite phase;   reducing the steel slab to form a plate in at least one hot rolling pass at a temperature sufficient to recrystallize the austenite phase to produce a fine grained austenite phase;   reducing the plate in at least one hot rolling pass at a temperature below a temperature where austenite does not recrystallize;   cooling the plate to a first temperature sufficient to transform an austenite to a ferrite;   quenching the plate at a rate of at least 10° C. per second (18° F./sec) to a second temperature; and   cooling the plate at a rate sufficient to reduce solute carbon in the ferrite.   
   
   
       33 . The method of  claim 32 , wherein the second temperature is sufficient to diffuse the carbon from the ferrite to a second phase. 
   
   
       34 . The method of  claim 32 , wherein the second temperature is sufficient to precipitate out the carbon in the ferrite into one or more carbides. 
   
   
       35 . The method of  claim 33 , wherein the second phase comprises one or more constituents selected from the group consisting of carbide, pearlite, martensite, lower bainite, granular bainite, upper bainite, and degenerate upper bainite. 
   
   
       36 . The method of  claim 32 , further comprising forming the cooled plate into a linepipe using an UOE technique. 
   
   
       37 . The method of  claim 32 , wherein the first temperature is from about 650° C. to about 750° C. 
   
   
       38 . The method of  claim 32 , wherein the first temperature is from about 670° C. to about 740° C. 
   
   
       39 . The method of  claim 32 , wherein the second temperature is from about 400° C. to about 700° C. 
   
   
       40 . The method of  claim 32 , wherein the second temperature is from about 450° C. to about 650° C. 
   
   
       41 . The method of  claim 32 , wherein the second temperature is from about 500° C. to about 600° C. 
   
   
       42 . The method of  claim 32 , wherein the second temperature is about 560° C. 
   
   
       43 . The method of  claim 32 , further comprising:
 forming a linepipe from the plate;   heating the linepipe to a temperature between about 180° C. and 300° C.; and   applying at least one coating to at least a portion of the linepipe.   
   
   
       44 . The method of  claim 43 , wherein the at least one coating comprises one or more fusion bonded epoxy compounds. 
   
   
       45 . A dual phase steel, comprising:
 carbon in an amount of about 0.05% by weight to about 0.12 wt %;   niobium in an amount of about 0.005 wt % to about 0.03 wt %;   titanium in an amount of about 0.005 wt % to about 0.02 wt %;   nitrogen in an amount of about 0.001 wt % to about 0.01 wt %;   manganese in an amount of about 0.5 wt % to about 2.0 wt %;   silicon in an amount of about 0.01 wt % to about 0.5 wt %   a total of molybdenum, chromium, vanadium and copper is less than about 0.10 wt %;   a first phase consisting of ferrite;   a second phase comprising one or more constituents selected from the group consisting of carbide, pearlite, martensite, lower bainite, granular bainite, upper bainite, and degenerate upper bainite; and   a solute carbon content in the first phase of about 0.01 wt % or less.   
   
   
       46 . The dual phase steel of  claim 45 , wherein nickel is present in an amount of less than about 1.0 wt %. 
   
   
       47 . The dual phase steel of  claim 45 , wherein boron is present in an amount less than about 0.02 wt %. 
   
   
       48 . The dual phase steel of  claim 45 , wherein the steel has a Pcm of less than about 0.22. 
   
   
       49 . The dual phase steel of  claim 45 , wherein the steel has a tensile strength of at least 500 MPa. 
   
   
       50 . The dual phase steel of  claim 45 , wherein the steel has a tensile strength of at least 520 MPa. 
   
   
       51 . The dual phase steel of  claim 45 , wherein the steel has a minimum uniform elongation of at least 8%. 
   
   
       52 . The dual phase steel of  claim 45 , wherein the steel has a minimum uniform elongation of at least 10%. 
   
   
       53 . The dual phase steel of  claim 45 , wherein the steel has a yield ratio of less than 0.90. 
   
   
       54 . The dual phase steel of  claim 45 , wherein the steel has a yield ratio of less than 0.85. 
   
   
       55 . The dual phase steel of  claim 45  wherein the second phase comprises pearlite.