Method of producing a cold temperature high toughness structural steel tubing

Abstract

An apparatus ( 10 ) includes a low-carbon steel tube ( 24 ). The low-carbon steel tube ( 24 ) yields plastically more than about 5% before fracturing at temperatures down to about −40° C. when stress is applied to the low-carbon steel tube sufficient to cause the low carbon steel tube to so yield.

Having described the invention, the following is claimed:  
     
         1 . An apparatus comprising a low-carbon steel tube, said low-carbon steel tube yielding plastically more than about 5% before fracturing at temperatures down to about −40° C. when stress sufficient to cause said low-carbon steel tube to so yield is applied to said low-carbon steel tube.  
     
     
         2 . The apparatus of  claim 1  wherein said low-carbon steel tube is formed from a low-carbon steel consists essentially of, by weight, about 0.07% to about 0.12% carbon, about 0.70% to about 1.60% manganese, up to about 0.020% phosphorous, up to about 0.015% sulfur, about 0.06% to about 0.35% silicon, about 0.25% to about 1.20% chromium, up to about 0.65% nickel, about 0.20% to about 0.70% molybdenum, up to about 0.35% copper, about 0.02% to about 0.06% aluminum, up to about 0.05% vanadium, up to about 0.25% residual elements, and the balance iron.  
     
     
         3 . The apparatus of  claim 1 , wherein said low-carbon steel tube has a tensile strength of at least about 130,000 psi, a yield strength of at least about 104,000 psi, and an elongation at break of at least about 14%.  
     
     
         4 . The apparatus of  claim 1 , wherein said low-carbon steel tube is formed from a low-carbon steel that consists essentially of, by weight, about 0.07% to about 0.12% carbon, about 0.70% to about 1.60% manganese, up to about 0.020% phosphorous, up to about 0.015% sulfur, about 0.06% to about 0.35% silicon, about 0.25% to about 1.20% chromium, up to about 0.65% nickel, about 0.20% to about 0.70% molybdenum, up to about 0.35% copper, about 0.02% to about 0.06% aluminum, up to about 0.05% vanadium, up to about 0.19% residual elements, and the balance iron and has a tensile strength of at least about 130,000 psi, a yield strength of at least about 104,000 psi, and an elongation at break of at least about 14%.  
     
     
         5 . A method comprising the steps of: 
 casting a billet of low-carbon steel, said billet of low-carbon steel having a first diameter and consists essentially of, by weight, about 0.07% to about 0.12% carbon, about 0.70% to about 1.60% manganese, up to about 0.020% phosphorous, up to about 0.015% sulfur, about 0.06% to about 0.35% silicon, about 0.25% to about 1.20% chromium, up to about 0.65% nickel, about 0.20% to about 0.70% molybdenum, up to about 0.35% copper, about 0.02% to about 0.06% aluminum, up to about 0.05% vanadium, up to about 0.25% residual elements, and the balance iron;    reducing the diameter of said billet of low-carbon steel by hot-rolling said billet,    forming a tube having an annular wall by piercing said billet;    reducing the thickness of said annular wall to a first thickness by cold drawing said tube,    heat treating said tube after said cold drawing to form a low-carbon steel tube that yields plastically more than about 5% before fracturing at temperatures down to about −40° C. when stress sufficient to cause said low carbon steel tube to so yield is applied to said low-carbon steel tube.    
     
     
         6 . The method of  claim 5 , wherein the step of heat treating comprises heating said tube to a temperature of at least about 900° C., cooling said tube to room temperature, and tempering said tube to a temperature of at least about 500° C.  
     
     
         7 . The method of  claim 6 , wherein the step of heat treating comprises induction heating said tube to a temperature of about 900° C. and cooling said tube to room temperature.