Advanced Fe-5Cr-X Alloy

Abstract

A tubular article can be formed from high temperature steam oxidation resistant and high temperature creep resistant alloy steel. The steel can include a chemical composition that include Fe, C, Si, Mn, Ni, Cr, Cu, Ti, Nb, Mo, and N, and optionally other elements. The steel alloy can include 0.06 to 0.15 wt % C, 0.1 to 0.5 wt % Si, 0.2 to 0.6 wt %, 0.05 to 0.4 wt % Ni, 4.5 to 6.0 wt % Cr, 1.0 to 2.0 wt % Cu, 0.04 to 0.08 wt % Ti, 0.01 to 0.06 wt % Nb, 0.45 to 1.2 wt % Mo, and 0.008 to 0.05 wt % N, up to 0.01 wt % of optional element Al, up to 0.01 wt % of optional element Zr, up to 3.0 wt % of optional element Co, up to 0.07 wt % of optional element V, up to 3.0 wt % of optional element W, up to 0.015 wt % of optional element P, up to 0.003 wt % of optional element S, up to 0.1 wt % of optional element Ca, up to 0.1 wt % of optional element Ta, up to 0.1 wt % of optional element Mg, up to 0.1 wt % of optional element Se, up to 0.1 wt % of optional element Te, up to 0.1 wt % of optional element B, up to 0.1 wt % of optional element Bi, and Fe. The steel can include copper precipitates and fine carbides, nitrides, or both. The steel can have a final microstructure comprising tempered martensite, tempered bainite, or a combination thereof. The steel can contain less than 2 vol % residual austenite.

What is claimed is: 
     
         1 . A tubular article formed from high temperature steam oxidation resistant and high temperature creep resistant alloy steel, the chemical composition of which comprises, by weight:
 C of 0.06 to 0.15 wt %;   Si of 0.1 to 0.5 wt %;   Mn of 0.2 to 0.6 wt %;   Ni of 0.05 to 0.4 wt %;   Cr of 4.5 to 6.0 wt %,   Cu of 1.0 to 2.0 wt %;   Ti of 0.04 to 0.08 wt %;   Nb of 0.01 to 0.06 wt %;   Mo of 0.45 to 1.2 wt %;   N of 0.008 to 0.05 wt %;   Al of less than or equal to 0.01 wt %;   Zr of less than or equal to 0.01 wt %;   Co of less than or equal to 3.0 wt %;   V of less than or equal to 0.07 wt %;   W of less than or equal to 3.0 wt %;   P of less than or equal to 0.015 wt %;   S of less than or equal to 0.003 wt %;   and Ca, Ta, Mg, Se, Te, B and Bi in contents of less than or equal to 0.1 wt %;   and a balance comprising Fe and impurities;   
       and wherein the steel comprises: 
       fine carbides, nitrides, or both; and copper precipitates, and wherein the steel has a final microstructure comprising tempered martensite, tempered bainite, or a combination thereof; 
       and wherein the steel contains less than 2 vol % residual austenite. 
     
     
         2 . The tubular article of  claim 1 , wherein the steel contains less than 1 vol % residual austenite. 
     
     
         3 . The tubular article of  claim 1 , wherein less than 4 wt % of the total Cr amount is stable in solid solution at room temperature. 
     
     
         4 . The tubular article of  claim 1 , wherein the steel is comprising maximum 25 percent bainite. 
     
     
         5 . The tubular article of  claim 1 , wherein wt % Ta+wt % Nb<0.1 wt %. 
     
     
         6 . The tubular article of  claim 1 , wherein the copper precipitates have a grain size of less than 40 nm. 
     
     
         7 . The tubular article of  claim 1 , wherein the fine carbides have a mean diameter of less than 200 nm. 
     
     
         8 . The tubular article of  claim 7 , wherein the fine carbides have a size distribution with a mean size of 65 nm or less. 
     
     
         9 . The tubular article of  claim 1 , wherein the steel has a yield strength greater than 450 MPa. 
     
     
         10 . The tubular article of  claim 1 , wherein the steel has a yield strength between 570 MPa and 640 MPa. 
     
     
         11 . The tubular article of  claim 1 , wherein the steel has an ultimate tensile strength greater than 585 MPa at room temperature. 
     
     
         12 . The tubular article of  claim 1 , wherein the steel has a hardness of 200 to 265 Vickers. 
     
     
         13 . The tubular article of  claim 1 , wherein the steel has a creep strength of about 70 MPa for 100,000 h rupture at 600° C. 
     
     
         14 . The tubular article of  claim 1 , wherein the steel has a minimum absorbed energy in Charpy V-notch impact test of 150 J at 0° C. 
     
     
         15 . The tubular article of  claim 1 , wherein the steel consists essentially of:
 C of 0.06 to 0.15 wt %;   Si of 0 to 0.5 wt %;   Mn of 0.2 to 0.6 wt %;   Ni of 0 to 0.4 wt %;   Cr of 4.0 to 6.0 wt %:   Cu of 1.0 to 2.0 wt %;   Ti of 0.04 to 0.08 wt %;   Nb of 0.01 to 0.06 wt %;   Mo of 0.5 to 1.2 wt %;   N of 0.008 to 0.02 wt %;   Al of less than or equal to 0.01 wt %;   Zr of less than or equal to 0.01 wt %;   Co of less than or equal to 2.0 wt %;   V of less than or equal to 0.07 wt %;   W of less than or equal to 2.0 wt %;   P of less than or equal to 0.015 wt %;   S of less than or equal to 0.003 wt %;   and Ca, Ta, Mg, Se, Te, B and Bi in contents of less than or equal to 0.1 wt %; and   a balance comprising Fe and impurities.   
     
     
         16 . The tubular article of  claim 1 , wherein the alloy steel consists essentially of:
 C of 0.06 to 0.15 wt %;   Si of 0 to 0.5 wt %;   Mn of 0.2 to 0.6 wt %;   Ni of 0 to 0.4 wt %;   Cr of 4.0 to 6.0 wt %;   Cu of 1.0 to 2.0 wt %;   Ti of 0.04 to 0.08 wt %;   Nb of 0.01 to 0.06 wt %;   Mo of 0.5 to 1.2 wt %;   N of 0.008 to 0.02 wt %;   Al of less than or equal to 0.01 wt %;   Zr of less than or equal to 0.01 wt %;   Co of less than or equal to 2.0 wt %;   V of less than or equal to 0.07 wt %;   W of less than or equal to 2.0 wt %;   P of less than or equal to 0.015 wt %;   Ta of less than or equal to 0.1 wt %;   S of less than or equal to 0.005 wt %;   Se of less than or equal to 0.005 wt %; and   a balance comprising Fe and impurities.   
     
     
         17 . The tubular article of  claim 1 , wherein the steel has a final microstructure consisting essentially of martensite, bainite, or a combination thereof. 
     
     
         18 . The tubular article of  claim 1 , wherein the fine carbides comprise fine titanium carbides. 
     
     
         19 . The tubular article of  claim 1 , wherein the fine carbides comprise fine niobium carbides. 
     
     
         20 . The tubular article of  claim 1 , wherein the tubular article has a wall thickness between 2 mm and 30 mm. 
     
     
         21 . The tubular article of  claim 1 , wherein the outer diameter of between 20 mm and 624 mm. 
     
     
         22 . A method of forming a tubular article, the method comprising:
 providing an ingot or continuous casting of an alloy steel by combining the following added elements:
 C of 0.06 to 0.15 wt %; 
 Si of 0 to 0.5 wt %; 
 Mn of 0.2 to 0.6 wt %; 
 Ni of 0 to 0.4 wt %; 
 Cr of 4.0 to 6.0 wt %, 
 Cu of 1.0 to 2.0 wt %; 
 Ti of 0.04 to 0.08 wt %; 
 Nb of 0.01 to 0.06 wt %; 
 Mo of 0.5 to 1.2 wt %; 
 N of 0.008 to 0.02 wt %; 
 Al of less than or equal to 0.01 wt %; 
 Zr of less than or equal to 0.01 wt %; 
 Co of less than or equal to 2 wt %; 
 V of less than or equal to 0.07 wt %; 
 W of less than or equal to 2 wt %; 
 P of less than or equal to 0.015 wt %; 
 Ta of less than or equal to 0.1 wt %; 
 S of less than or equal to 0.005 wt %; 
 Se of less than or equal to 0.005 wt %; 
 Ca of less than or equal to 0.1 wt %; 
 Mg of less than or equal to 0.1 wt %; 
 Se of less than or equal to 0.1 wt %; 
 Te of less than or equal to 0.1 wt %; 
 B of less than or equal to 0.1 wt %; 
 Bi of less than or equal to 0.1 wt %; and 
 a balance comprising Fe and impurities; 
   forming the alloy steel into a raw tubular article;   sizing the raw tubular article to yield a sized raw tubular article;   cooling the sized raw tubular article to ambient temperature;   normalizing the sized raw tubular article to yield a normalized tubular article having a microstructure comprising:   martensite, bainite, or a combination thereof; and   less than 20 vol % austenite; and   tempering the normalized tubular article to yield a tempered tubular article comprising:   alpha ferrite matrix, fine carbides and nitrides; and less than 2 vol % austenite.   
     
     
         23 . The method of  claim 22 , wherein normalizing the sized raw tubular article comprises:
 heating the sized raw tubular article to yield a heated sized raw tubular article having a microstructure consisting essentially of austenite; and   cooling the heated sized raw tubular article to ambient temperature to yield the normalized tubular article.   
     
     
         24 . The method of  claim 23 , wherein heating the sized raw tubular article comprises heating the sized raw tubular article to a temperature in a range between 1040° C. and 1080° C. for at least 20 minutes. 
     
     
         25 . The method of  claim 24 , further comprising heating the sized raw tubular article at a rate between 15° C./min and 25° C./min. 
     
     
         26 . The method of  claim 23 , wherein cooling the heated sized raw tubular article comprises cooling in still air. 
     
     
         27 . The method of  claim 23 , wherein the wall thickness of the sized raw tubular article is between 2 mm and 15 mm, and the average cooling rate of the heated sized raw tubular article between 800° C. and 500° C. exceeds 1° C./s. 
     
     
         28 . The method of  claim 23 , wherein the wall thickness of the sized raw tubular article is about 20 mm, and the average cooling rate of the heated sized raw tubular article between 800° C. and 500° C. is about 0.8° C./s. 
     
     
         29 . The method of  claim 23 , wherein the wall thickness of the sized raw tubular article is between 21 and 30 mm, and the average cooling rate of the heated sized raw tubular article between 800° C. and 500° C. is between 0.4° C./s and 0.7° C./s. 
     
     
         30 . The method of  claim 22 , wherein tempering the normalized tubular article comprises heating the normalized tubular article to a temperature between 700° C. and 780° C. for at least 20 minutes, thereby decomposing the retained austenite to yield ferrite and carbides. 
     
     
         31 . The method of  claim 30 , further comprising straightening the treated tubular article. 
     
     
         32 . The tubular article of  claim 1 , wherein the chemical composition is free of at least one of Al, Zr, Co, V, W, Ca, Ta, Mg, Se, Te, B, or Bi.