Iron-chromium alloy with improved compressive yield strength and method of making and use thereof

1. A chromium-iron alloy comprising in weight %:

1 to 3% C;

1 to 3% Si;

up to 3% Ni;

25 to 35% Cr;

1.5 to 3% Mo;

up to 2% W;

2.0 to 4.0% Nb;

up to 3.0% V;

up to 3.0% Ta;

up to 1.2% B;

up to 1% Mn;

43 to 64% Fe; and

comprising a ferrite-carbide matrix with spherical and/or polyhedron-shaped particles distributed throughout the ferrite-carbide matrix.

2. The chromium-iron alloy of claim 1 comprising in weight %:

1.5 to 2.3% C;

1.6 to 2.3% Si;

0.2 to 2.2% Ni;

27 to 34% Cr;

1.7 to 2.5% Mo;

0.04 to 2% W;

2.2 to 3.6% Nb;

up to 1% V;

up to 1.0% Ta;

up to 0.7% B;

0.1 to 0.6% Mn;

43 to 64% Fe.

3. The chromium-iron alloy of claim 1 , further comprising incidental impurities of one or more of Al, As, Bi, Cu, Ca, Ce, Co, Hf, Mg, N, P, Pb, S, Sn, Ti, Y and Zn with a total content of incidental impurities of 1.5 weight % or less.

4. The chromium-iron alloy of claim 1 , wherein the ferrite-carbide matrix comprises a primary carbide phase having an acicular microstructure and a ferrite phase having a semi-acicular microstructure; and the spherical and/or polyhedron-shaped particles are metal carbides, metal nitrides and/or metal carbonitrides dispersed along phase boundaries of the primary carbide phase and the ferrite phase.

5. The chromium-iron alloy of claim 4 , wherein the primary carbide phase is chromium-rich and molybdenum-rich; the ferrite phase is chromium-rich; and the phase boundaries of the primary carbide phase and the ferrite phase are boron-rich.

6. A valve seat insert made essentially of the chromium-iron alloy of claim 1 .

7. The valve seat insert of claim 6 , wherein the insert is a casting.

8. A method of manufacturing the valve seat insert of claim 6 , comprising machining a piece of the chromium-iron alloy.

9. A method of manufacturing an internal combustion engine comprising inserting the valve seat insert of claim 6 in a cylinder head of the internal combustion engine.

10. The method of claim 9 , wherein the engine is a diesel or natural gas engine.

11. A method of operating an internal combustion engine comprising closing a valve against the valve seat insert of claim 6 to close a cylinder of the internal combustion engine and igniting fuel in the cylinder to operate the internal combustion engine.

12. The method of claim 11 , wherein the valve:

(i) is a high-chromium iron-based alloy or a high-temperature, nickel-based superalloy; or

(ii) the valve is hard-faced with a high temperature, wear-resistant alloy strengthened by carbides.

13. A chromium-iron alloy comprising in weight %:

1 to 3% C;

1 to 3% Si;

up to 3% Ni;

25 to 35% Cr;

1.5 to 3% Mo;

up to 2% W;

2.0 to 4.0% Nb;

up to 3.0% V;

up to 3.0% Ta;

up to 1.2% B;

up to 1% Mn;

43 to 64% Fe;

wherein the chromium-iron alloy has an as-cast bulk hardness from 40 to 56 Rockwell C; a hot hardness (HV10) from 450 to 500 at 75° F., from 280 to 300 at 1000° F., from 55 to 70 at 1600° F.; a compressive yield strength from 90 to 220 KSi at 75° F., from 70 to 130 at 1000° F.; a linear thermal expansion coefficient from 8×10 −6 to 12×10 −6 /° C.

14. A valve seat insert made of a chromium-iron alloy comprising in weight %:

1 to 3% C;

1 to 3% Si;

up to 3% Ni;

25 to 35% Cr;

1.5 to 3% Mo;

up to 2% W;

2.0 to 4.0% Nb;

up to 3.0% V;

up to 3.0% Ta;

up to 1.2% B;

up to 1% Mn;

43 to 64% Fe;

wherein the insert exhibits a dimensional stability of less than 0.3×10 −3 inch per inch of insert outside diameter (O.D.) after heating for 20 hours at 1200° F.

15. A method of making a chromium-iron alloy comprising in weight %:

1 to 3% C;

1 to 3% Si;

up to 3% Ni;

25 to 35% Cr;

1.5 to 3% Mo;

up to 2% W;

2.0 to 4.0% Nb;

up to 3.0% V;

up to 3.0% Ta;

up to 1.2% B;

up to 1% Mn;

43 to 64% Fe;

wherein:

(a) the chromium-iron alloy is cast into a shaped component from a melt at a temperature from about 2700° F. to about 3000° F.; or

(b) a powder of the chromium-iron alloy is pressed into a shaped component and sintered at a temperature from about 1950° F. to about 2300° F. in a reducing atmosphere, wherein the reducing atmosphere is hydrogen or a mixture of dissociated ammonia and nitrogen.

16. The method of claim 15 , further comprising a high temperature tempering heat treatment at about 1325° F. for about 5 hours.