Low carbon alloy steel tube having ultra high strength and excellent toughness at low temperature and method of manufacturing the same

Abstract

A low carbon alloy steel tube and a method of manufacturing the same, in which the steel tube consists essentially of, by weight: about 0.06% to about 0.18% carbon; about 0.5% to about 1.5% manganese; about 0.1% to about 0.5% silicon; up to about 0.015% sulfur; up to about 0.025% phosphorous; up to about 0.50% nickel; about 0.1% to about 1.0% chromium; about 0.1% to about 1.0% molybdenum; about 0.01% to about 0.10% vanadium; about 0.01% to about 0.10% titanium; about 0.05% to about 0.35% copper; about 0.010% to about 0.050% aluminum; up to about 0.05% niobium; up to about 0.15% residual elements; and the balance iron and incidental impurities. The steel has a tensile strength of at least about 145 ksi and exhibits ductile behavior at temperatures as low as −60° C.

1 . A low carbon alloy steel tube consisting essentially of, by weight: about 0.06% to about 0.18% carbon; about 0.5% to about 1.5% manganese; about 0.1% to about 0.5% silicon; up to about 0.015% sulfur; up to about 0.025% phosphorous; up to about 0.50% nickel; about 0.1% to about 1.0% chromium; about 0.1% to about 1.0% molybdenum; about 0.01% to about 0.10% vanadium; about 0.01% to about 0.10% titanium; about 0.05% to about 0.35% copper; about 0.010% to about 0.050% aluminum; up to about 0.05% niobium; up to about 0.15% residual elements; and the balance iron and incidental impurities, wherein the steel tube has a tensile strength of at least about 145 ksi and has a ductile-to-brittle transition temperature below −60° C.  
     
     
         2 . The low carbon alloy steel tube of  claim 1 , wherein the steel tube consists essentially of, by weight: about 0.07% to about 0.12% carbon; about 1.00% to about 1.40% manganese; about 0.15% to about 0.35% silicon; up to about 0.010% sulfur; up to about 0.015% phosphorous; up to about 0.20% nickel; about 0.55% to about 0.80% chromium; about 0.30% to about 0.50% molybdenum; about 0.01% to about 0.07% vanadium; about 0.01% to about 0.05% titanium; about 0.15% to about 0.30% copper; about 0.010% to about 0.050% aluminum; up to about 0.05% niobium; up to about 0.15% residual elements; and the balance iron and incidental impurities.  
     
     
         3 . The low carbon alloy steel tube of  claim 1 , wherein the steel tube consists essentially of, by weight: about 0.08% to about 0.11% carbon; about 1.03% to about 1.18% manganese; about 0.15% to about 0.35% silicon; up to about 0.003% sulfur; up to about 0.012% phosphorous; up to about 0.10% nickel; about 0.63% to about 0.73% chromium; about 0.40% to about 0.45% molybdenum; about 0.03% to about 0.05% vanadium; about 0.025% to about 0.035% titanium; about 0.15% to about 0.30% copper; about 0.010% to about 0.050% aluminum; up to about 0.05% niobium; up to about 0.15% residual elements; and the balance iron and incidental impurities.  
     
     
         4 . The low carbon alloy steel tube of  claim 1 , wherein the steel tube has a yield strength of at least about 125 ksi.  
     
     
         5 . The low carbon alloy steel tube of  claim 1 , wherein the steel tube has a yield strength of at least about 135 ksi.  
     
     
         6 . The low carbon alloy steel tube of  claim 1 , wherein the steel tube has an elongation at break of at least about 9%.  
     
     
         7 . The low carbon alloy steel tube of  claim 1 , wherein the steel tube has a hardness of no more than about 40 HRC.  
     
     
         8 . The low carbon alloy steel tube of  claim 1 , wherein the steel tube has a hardness of no more than about 37 HRC.  
     
     
         9 . The low carbon alloy steel tube of  claim 1 , wherein the steel tube has a carbon equivalent of less than about 0.63%, the carbon equivalent being determined according to the formula:  
           Ceq =% C+% Mn/6+(% Cr+% Mo+% V)/5+(% Ni+% Cu)/15.  
     
     
         10 . The low carbon alloy steel tube of  claim 9 , wherein the steel tube has a carbon equivalent of less than about 0.60%.  
     
     
         11 . The low carbon alloy steel tube of  claim 9 , wherein the steel tube has a carbon equivalent of less than about 0.56%.  
     
     
         12 . The low carbon alloy steel tube of  claim 1 , wherein the steel tube has a maximum microinclusion content of 2 or less—thin series—, and level 1 or less—heavy series—, measured in accordance with ASTM E45 Standard-Worst Field Method (Method A).  
     
     
         13 . The low carbon alloy steel tube of  claim 1 , wherein the steel tube has a maximum microinclusion content measured in accordance with ASTM E45 Standard-Worst Field Method (Method A), as follows:  
       
         
           
                 
                 
                 
               
                     
                 
                     
                 
                   Inclusion Type 
                   Thin 
                   Heavy 
                 
                     
                 
                     
                 
                 
                 
                 
               
                   A 
                   0.5 
                   0 
                 
                   B 
                   1.5 
                   1.0 
                 
                   C 
                   0 
                   0 
                 
                   D 
                   1.5 
                   0.5 
                 
                     
                 
                     
                 
             
                
                
                
                
               
               
                
               
            
             
                
                
                
                
                
                
               
            
           
         
       
     
     
         14 . The low carbon alloy steel tube of  claim 13 , wherein oversize inclusion content with 30 μm or less in size is obtained.  
     
     
         15 . The low carbon alloy steel tube of  claim 14 , wherein the total oxygen content is limited to 20 ppm.  
     
     
         16 . The low carbon alloy steel tube of  claim 1 , wherein the tube has a seamless configuration.  
     
     
         17 . A stored gas inflator pressure vessel comprising the low carbon alloy steel tube of  claim 1 .  
     
     
         18 . An automotive airbag inflator comprising the low carbon alloy steel tube of  claim 1 .  
     
     
         19 . A low carbon alloy steel tube consisting essentially of, by weight: about 0.08% to about 0.11% carbon; about 1.03% to about 1.18% manganese; about 0.15% to about 0.35% silicon; up to about 0.003% sulfur; up to about 0.012% phosphorous; up to about 0.10% nickel; about 0.63% to about 0.73% chromium; about 0.40% to about 0.45% molybdenum; about 0.03% to about 0.05% vanadium; about 0.025% to about 0.035% titanium; about 0.15% to about 0.30% copper; about 0.010% to about 0.050% aluminum; up to about 0.05% niobium; up to about 0.15% residual elements; and the balance iron and incidental impurities, wherein the steel tube has a yield strength of at least about 135 ksi, a tensile strength of at least about 145 ksi, an elongation at break of of at least about 9%, a hardness of no more than about 37 HRC, and has a ductile-to-brittle transition temperature below −60° C.  
     
     
         20 . The low carbon alloy steel tube of  claim 19 , wherein the tube has a seamless configuration.  
     
     
         21 . A stored gas inflator pressure vessel comprising the low carbon alloy steel tube of  claim 19 .  
     
     
         22 . An automotive airbag inflator comprising the low carbon alloy steel tube of  claim 19 .  
     
     
         23 . A method of manufacturing a length of steel tubing for a stored gas inflator pressure vessel, comprising the following steps: 
 producing a length of tubing from a steel material consisting essentially of, by weight: about 0.06% to about 0.18% carbon, about 0.5% to about 1.5% manganese, about 0.1% to about 0.5% silicon, up to about 0.015% sulfur, up to about 0.025% phosphorous, up to about 0.50% nickel, about 0.1% to about 1.0% chromium, about 0.1% to about 1.0% molybdenum, about 0.01% to about 0.10% vanadium, about 0.01% to about 0.10% titanium, about 0.05% to about 0.35% copper, about 0.010% to about 0.050% aluminum, up to about 0.05% niobium, up to about 0.15% residual elements, and the balance iron and incidental impurities;    subjecting the steel tubing to a cold-drawing process to obtain desired dimensions;    austenizing by heating the cold-drawn steel tubing in an induction-type austenizing furnace to a temperature of at least Ac3, at a heating rate of at feast about 100° C. per second;    after the heating step, quenching the steel tubing in a quenching fluid until the tubing reaches approximately ambient temperature, at a cooling rate of at least about 100° C. per second; and    after the quenching step, tempering the steel tubing for about 2-30 minutes at a temperature below Ac1.    
     
     
         24 . The method of  claim 23 , wherein the steel tubing produced consists essentially of, by weight: about 0.07% to about 0.12% carbon, about 1.00% to about 1.40% manganese, about 0.15% to about 0.35% silicon, up to about 0.010% sulfur, up to about 0.015% phosphorous, up to about 0.20% nickel, about 0.55% to about 0.80% chromium, about 0.30% to about 0.50% molybdenum, about 0.01% to about 0.07% vanadium, about 0.01% to about 0.05% titanium, about 0.15% to about 0.30% copper, about 0.010% to about 0.050% aluminum, up to about 0.05% niobium, up to about 0.15% residual elements, and the balance iron and incidental impurities.  
     
     
         25 . The method of  claim 23 , wherein the steel tubing produced consists essentially of, by weight: about 0.08% to about 0.11% carbon, about 1.03% to about 1.18% manganese, about 0.15% to about 0.35% silicon, up to about 0.003% sulfur, up to about 0.012% phosphorous, up to about 0.10% nickel, about 0.63% to about 0.73% chromium, about 0.40% to about 0.45% molybdenum, about 0.03% to about 0.05% vanadium, about 0.025% to about 0.035% titanium, about 0.15% to about 0.30% copper, about 0.010% to about 0.050% aluminum, up to about 0.05% niobium, up to about 0.15% residual elements, and the balance iron and incidental impurities.  
     
     
         26 . The method of  claim 23 , wherein the finished steel tubing has a yield strength of at least about 125 ksi.  
     
     
         27 . The method of  claim 23 , wherein the finished steel tubing has a yield strength of at least about 135 ksi.  
     
     
         28 . The method of  claim 23 , wherein the finished steel tubing has a tensile strength of at least about 145 ksi.  
     
     
         29 . The method of  claim 23 , wherein the finished steel tubing has an elongation at break of at least about 9%.  
     
     
         30 . The method of  claim 23 , wherein the finished steel tubing has a hardness of no more than about 40 HRC.  
     
     
         31 . The method of  claim 23 , wherein the finished steel tubing has a hardness of no more than about 37 HRC.  
     
     
         32 . The method of  claim 23 , wherein the finished steel tubing has a ductile-to-brittle transition temperature below 60° C.  
     
     
         33 . The method of  claim 23 , wherein in the austenizing heating step, the steel tubing is heated to a temperature between about 920-1050° C.  
     
     
         34 . The method of  claim 33 , wherein in the austenizing heating step, the steel tubing is heated at a rate of at least about 200° C. per second.  
     
     
         35 . The method of  claim 23 , wherein in the quenching step, the steel tubing is cooled at a rate of at least about 200° C. per second.  
     
     
         36 . The method of  claim 23 , wherein in the tempering step, the steel tubing is tempered at a temperature between about 400-600° C.  
     
     
         37 . The method of  claim 36 , wherein in the tempering step, the steel tubing is tempered for about 4-20 minutes.  
     
     
         38 . The method of  claim 23 , further comprising a finishing step wherein the tempered steel tubing is pickled, phosphated, and oiled.  
     
     
         39 . A method of manufacturing a length of steel tubing for a stored gas inflator pressure vessel, comprising the following steps: 
 producing a length of tubing from a steel material consisting essentially of, by weight: about 0.08% to about 0.11% carbon, about 1.03% to about 1.18% manganese, about 0.15% to about 0.35% silicon, up to about 0.003% sulfur, up to about 0.012% phosphorous, up to about 0.10% nickel, about 0.63% to about 0.73% chromium, about 0.40% to about 0.45% molybdenum, about 0.03% to about 0.05% vanadium, about 0.025% to about 0.035% titanium, about 0.15% to about 0.30% copper, about 0.010% to about 0.050% aluminum, up to about 0.05% niobium, up to about 0.15% residual elements, and the balance iron and incidental impurities;    subjecting the steel tubing to a cold-drawing process to obtain desired dimensions;    austenizing by heating the cold-drawn steel tubing in an induction-type austenizing firnace to a temperature between about 920-1050° C., at a heating rate of at least about 200° C. per second;    after the heating step, quenching the steel tubing in a water-based quenching solution until the tubing reaches approximately ambient temperature, at a cooling rate of at least about 200° C. per second; and    after the quenching step, tempering the steel tubing for about 4-20 minutes at a temperature between about 450-550° C.,    a finishing step wherein the tempered steel tubing is pickled, phosphated, and oiled,    wherein the finished steel tubing has a yield strength of at least about 135 ksi, a tensile strength of at least about 145 ksi, an elongation at break of at least about 9%, a hardness of no more than about 37 HRC, a ductile-to-brittle transition temperature below −60° C. and a good surface appearance.