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, especially for a stored gas inflator pressure vessel, in which the steel tube consists essentially of, by weight: about 0.06% to about 0.18% carbon, about 0.3% to about 1.5% manganese, about 0.05% to about 0.5% silicon, up to about 0.015% sulfur, up to about 0.025% phosphorous, and at least one of the following elements: up to about 0.30% vanadium, upto t about 0.10% aluminum, up to about 0.06% niobium, up to about 1% chromium, up to about 0.70 % nickel, up to about 0.70% molybdenum, up to about 0.35% copper, up to about 0.15% residual elements, and the balance iron and incidental impurities. After a high heating rate of about 100° C. per second; rapidly and fully quenching the steel tubing in a water-based quenching solution at a cooling rate of about 100° C. per second. The steel has a tensile strength of at least about 145 ksi and as high as 220 ksi and exhibits ductile behavior at temperatures as low as −100° 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, and characterized by an austenitic grain size of 7 or finer as measured according to ASTM E-112 Standard resulting from austenitizing said steel tube to a temperature of at least Ac3, at a heating rate of at-least about 100° C. per second for an extremely short heating cycle, 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, and characterized by an austenitic grain size of 7 or finer as measured according to ASTM E-112 Standard resulting from austenitizing said steel tube to a temperature of at least Ac3, at a heating rate of at-least about 100° C. per second for an extremely short heating cycle, 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 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 .- 48 . (canceled) 
   
   
       49 . A low carbon alloy steel tubing for a stored gas inflator pressure vessel, which is a product of the process of subjecting a length of tubing of 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; to a cold-drawing process to obtain desired dimensions; austenitizing by heating the cold-drawn steel tubing in an induction-furnace to a temperature of at least Ac3, at a heating rate of at least about 100° C. per second for an extremely short heating cycle to obtain an austenitic grain size of 7 or finer as measured according to ASTM E-112 standard; 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. 
   
   
       50 . The low carbon alloy steel tube of  claim 49 , 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. 
   
   
       51 . The low carbon alloy steel tube of  claim 49 , 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. 
   
   
       52 . The low carbon alloy steel tube of  claim 49 , wherein the steel tube has a yield strength of at least about 125 ksi. 
   
   
       53 . The low carbon alloy steel tube of  claim 49 , wherein the steel tube has a yield strength of at least about 135 ksi. 
   
   
       54 . The low carbon alloy steel tube of  claim 49 , wherein the steel tube has an elongation at break of at least about 9%. 
   
   
       55 . The low carbon alloy steel tube of  claim 49 , wherein the steel tube has a hardness of no more than about 40 HRC. 
   
   
       56 . The low carbon alloy steel tube of  claim 49 , wherein the steel tube has a hardness of no more than about 37 HRC.