Creep resistant, precipitation-dispersion-strengthened, martensitic stainless steel and method thereof
AssigneeRobert F. Buck
InventorRobert F. Buck
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Abstract
An iron-based, corrosion-resistant, precipitation strengthened, martensitic steel essentially free of delta ferrite for use at high temperatures has a nominal composition of 0.05-0.1 C, 8-12 Cr, 1-5 Co, 0.5-2.0 Ni, 0.41-1.0 Mo, 0.1-0.5 Ti, and the balance iron. This steel is different from other corrosion-resistant martensitic steels because its microstructure consists of a uniform dispersion of fine particles, which are very closely spaced, and which do not coarsen at high temperatures. Thus at high temperatures this steel combines the excellent creep strength of dispersion-strengthened steels, with the ease of fabricability afforded by precipitation hardenable steels.
Claims21
An iron based alloy having good corrosion resistance and high strength at elevated temperatures consisting essentially of 0.05-0.15% carbon, 2-15% chromium, 0.1-10.0% cobalt, 0.1-4.0% nickel, 0.1-2.0% molybdenum, 0.1-0.75% titanium, less than 0.1% boron, less than 0.02% nitrogen, and the remainder essentially iron plus impurities in which alloy is heat treated to be a face centered cubic structure at temperatures above about 900.degree. C. and body centered cubic structure on cooling.
An iron base alloy having good corrosion/oxidation resistance and high strength at elevated temperatures consisting essentially of 0.05-0.15% C, 7.5-14.5% Cr less than 5% Ni, 5.0%-14.5% Cr+Ni, less than 10% Co, more than 1% Co+Ni, less than 5% Cu, less than 5% Mn, less than 2.6% Mo, less than 1.5% Si, W+Si+Mo<4%, less than 0.75% Ti, less than 2% Zr, less than 4% Ta, less than 4% Hf;
- Ti, Zr, Ta, Hf present such that
- 0.135<1.17Ti+0.6Zr+0.31Ta+0.31Hf<1.0,
- less than 1% Nb, less than 2% V, less than 0.02% N and N-0.5Al<0.015, less than 0.1% Al, B, Ce, Mg, Sc, Y, La, and Be, less than 0.1% total and less than 0.02% of each of S, P, Sn, Sb, O, and the balance essentially iron in which the structure contains less than 40% delta ferrite, and the Ac1 temperature is between 500.degree. C. and 820.degree. C.
A method for producing an iron base alloy having good corrosion/oxidation resistance and high strength at elevated temperatures comprising the steps of:
- a) preparing a transformable austenitic iron base alloy which alloy is a face centered cubic structure at temperatures above about 900.degree. C. and body centered cubic structure on cooling the alloy consisting essentially of less than 15% Cr, less than 0.2% C, less than 0.1% N, less than 2% Si, less than 4% Mo, less than 4% W, less than 5% Ni, less than 5% Mn, less than 5% Cu, less than 10% Co, less than 4% V, and 0.1<1.17Ti+0.6Nb+0.6Zr+0.31Ta+0.31Hf<1.0;
- b) solution heat treating the alloy at a temperature higher than 1100.degree. C., so that the alloy has a structure at said solutionizing temperature which is greater than 60% austenite;
- and
- c) cooling the alloy in such a way as to result in one of a martensitic, bainitic and ferritic microstructure with an Ac1 temperature greater than 500.degree. C., that contains a fine dispersion of MX precipitates (where M=Zr, V, Ti, Ta, Hf, Nb;
- and X=C, N), in which the alloy has an MX number density of at least 500 atomic number pairs per million.
An iron based alloy having good corrosion/oxidation resistance and high strength at elevated temperatures comprising less than 15% Cr, less than 0.2% C, less than 0.1% N, less than 2% Si, less than 4% Mo, less than 4% Si, less than 5% Ni, less than 5% Mn, less than 5% Cu, less than 10% Co, less than 4% V, at least one of Ti, Nb, Zr, Ta, and Hf in an amount so that
- 0.1<1.17Ti+0.6Nb+0.6Zr+0.31Ta+0.31Hf<1.0;
- and the balance iron, the alloy containing a fine dispersion of MX precipitates (where M=Zr, V, Ti, Ta, Hf, Nb;
- and X=C, N), in which the alloy has an MX number density of at least 500 atomic number pairs per million.
Dependencies are inferred from the claim text.