Low strain high ductility alloy

Abstract

The present invention relates to alloys used to prepare a low strain steel pipes for use in chemical engineering applications. In particular, the invention relates to low carbon high strength steel alloys and pipes made from such alloys which have low strain but high ductility at elevated temperatures. Such pipes are typically used in chemical plants for transporting reactants and products, as the inlet manifolds in plants for producing hydrogen and methanol. They may be used in plant such as steam reformer furnaces which include inlet manifolds that need to possess good creep resistance (low strain) as well as having good thermo-mechanical fatigue resistance (high ductility).

1 . A steel consisting of:
 from 20.0 to 40.0 atomic % nickel,   from 20.0 to 40.0 atomic % chromium,   from 1.0 to 3.0 atomic % silicon,   from 0.2 to 1.0 atomic % carbon,   from 0.01 to 1.0 atomic % nitrogen, from 0.30 to 0.90 atomic % niobium,   from 0.5 to 3.0 atomic % manganese, and   from 0.01 to 0.90 atomic % of one or more second carbide forming elements selected from: titanium, hafnium, zirconium, vanadium, tungsten, or molybdenum,   wherein:
 (a) a total amount of niobium and the one or more second carbide forming elements is from 0.50 to 0.91 atomic %; 
 (b) a total amount of carbon plus nitrogen is in the range of 0.2 to 1.2 atomic %; 
 (c) an amount (nitrogen/carbon) is in the range 0.60 to 0.90, and 
 (d) an amount [nitrogen/(the one or more second carbide forming elements plus niobium)] is in the range 0.2 to 1.1; 
   with the balance of the composition being iron and incidental impurities.   
     
     
         2 . A steel consisting of:
 from 20.0 to 40.0 atomic % nickel,   from 20.0 to 40.0 atomic % chromium,   from 1.0 to 3.0 atomic % silicon,   from 0.2 to 1.0 atomic % carbon,   from 0.01 to 1.0 atomic % nitrogen,   from 0.50 to 0.91 atomic % niobium, and   from 0.5 to 3.0 atomic % manganese, and   wherein:
 (a) a total amount of carbon plus nitrogen is in the range of 0.2 to 1.2 atomic %; 
 (b) an amount (nitrogen/carbon) is in the range 0.60 to 0.90, and 
 (c) an amount (nitrogen/niobium) is in the range 0.2 to 1.1; 
   with the balance of the composition being iron and incidental impurities.   
     
     
         3 . A steel as claimed in  claim 1 , wherein titanium is present in the range of from 0.01 to 0.20 atomic %. 
     
     
         4 . A steel as claimed in  claim 1 , wherein carbon is present in the range of from 0.4 to 0.7 atomic %. 
     
     
         5 . A steel as claimed in  claim 1 , wherein nitrogen is present in an amount in the range of from 0.30 to 0.60 atomic %. 
     
     
         6 . A steel as claimed in  claim 1 , wherein the amount (nitrogen/carbon) is in the range of from 0.70 to 0.80 atomic %. 
     
     
         7 . A steel as claimed in  claim 1 , wherein nickel is present in the range of from 25.0 to 35.0 atomic %. 
     
     
         8 . A steel as claimed in  claim 7 , wherein nickel is present in an amount from 30.0 to 33.0 atomic %. 
     
     
         9 . A steel as claimed in  claim 1 , wherein chromium is present in the range of from 20.0 to 30.0 atomic %. 
     
     
         10 . A steel as claimed in  claim 8 , wherein chromium is present in an amount from 22.5 to 27.5 atomic %. 
     
     
         11 . A steel pipe made from an alloy according to  claim 1 . 
     
     
         12 . A steel pipe as claimed in  claim 11 , wherein the time to rupture is at least 215 hrs when tested at 1050° C. with 30 MPa Stress. 
     
     
         13 . A steel pipe as claimed in  claim 11 , wherein the time to rupture is at least 210 hrs when tested at 1000° C. with 40 MPa Stress. 
     
     
         14 . A steel as claimed in  claim 2 , wherein carbon is present in the range of from 0.4 to 0.7 atomic %. 
     
     
         15 . A steel as claimed in  claim 2 , wherein nitrogen is present in an amount in the range of from 0.30 to 0.60 atomic %. 
     
     
         16 . A steel as claimed in  claim 2 , wherein the amount (nitrogen/carbon) is in the range of from 0.70 to 0.80 atomic %. 
     
     
         17 . A steel as claimed in  claim 2 , wherein nickel is present in the range of from 25.0 to 35.0 atomic %. 
     
     
         18 . A steel as claimed in  claim 17 , wherein nickel is present in an amount from 30.0 to 33.0 atomic %. 
     
     
         19 . A steel as claimed in  claim 2 , wherein chromium is present in the range of from 20.0 to 30.0 atomic %. 
     
     
         20 . A steel as claimed in  claim 18 , wherein chromium is present in an amount from 22.5 to 27.5 atomic %.