Superaustenitic stainless steel and method of making and use thereof

1. A superaustenitic stainless steel comprising, in weight %:

0.15 to 0.9% C;

0.2 to 1.3% Si;

0 to 0.45% Mn;

32.5 to 37.5% Cr;

13.5 to 17.5% Ni;

3.2 to 5.5% Mo;

0 to 2% Nb;

0 to 0.5% B;

0 to 2% Zr; and

30 to 51% Fe.

2. The superaustenitic stainless steel of claim 1 , consisting essentially of 0.5 to 0.9% C, 0.2 to 0.5% Si, 0.2 to 0.4% Mn, 33.0 to 35.0% Cr, 15.5 to 17.5% Ni, 4.0 to 4.5% Mo, 0.7 to 0.9% Nb, 0.07 to 0.13% B, 0 to 0.05% Zr and 40 to 46% Fe.

3. The superaustenitic stainless steel 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, Ta, Ti, V, W, Y and Zn with a total content of incidental impurities of 1.5 weight % or less.

4. The superaustenitic stainless steel of claim 1 , having a microstructure with an austenitic matrix free of primary carbides, ferrite and/or martensite, the microstructure having strengthening phases distributed along interdendritic regions or intergranular regions.

5. The superaustenitic stainless steel of claim 1 , having a microstructure with intergranular or dendritic regions comprising an austenitic matrix; and interdendritic regions comprising eutectic reaction phases.

6. The superaustenitic stainless steel of claim 5 , wherein the austenitic matrix is rich in Cr; the eutectic reaction phases are rich in Ni; and/or the austenitic matrix contains precipitates of niobium carbide and/or niobium carbonitride.

7. The superaustenitic stainless steel of claim 1 , wherein C is 0.5 to 0.9%.

8. A valve seat insert comprising in weight %:

0.15 to 0.9% C;

0.2 to 1.3% Si;

0 to 0.45% Mn;

32.5 to 37.5% Cr;

13.5 to 17.5% Ni;

3.2 to 5.5% Mo;

0 to 2% Nb;

0 to 0.5% B;

0 to 2% Zr; and

30 to 51% Fe.

9. The valve seat insert of claim 8 , consisting essentially of 0.5 to 0.9% C, 0.2 to 0.5% Si, 0.2 to 0.4% Mn, 33.0 to 35.0% Cr, 15.5 to 17.5% Ni, 4.0 to 4.5% Mo, 0.7 to 0.9% Nb, 0.07 to 0.13% B, 0 to 0.05% Zr and 40 to 46% Fe.

10. The valve seat insert of claim 8 , wherein the insert is a casting.

11. The valve seat insert of claim 8 , wherein the insert has a hardness from about 35 to about 45 Rockwell C, a compressive yield strength from about 80 ksi to about 100 ksi at about room temperature; and/or a compressive yield strength from about 60 ksi to about 80 ksi at 1000° F.

12. The valve seat insert of claim 8 , wherein the insert has an ultimate tensile rupture strength from about 50 ksi to about 70 ksi at about room temperature; and/or an ultimate tensile rupture strength from about 40 ksi to about 60 ksi at about 1000° F.

13. The valve seat insert of claim 8 , wherein the insert exhibits a dimensional stability of less than about 0.3×10 −3 inches per inch of insert outside diameter (O.D.) after heating for about 20 hours at about 1200° F.; and wherein the weight % Mn is present in an amount effective to produce a microstructure free of σ-iron-chromium tetragonal precipitates, martensite phases and/or ferrite phases after heating the insert to about 20 hours at about 1200° F.

14. The valve seat insert of claim 8 , wherein:

(a) the insert exhibits an HV10 Vickers hardness from about 420 HV10 at about room temperature to about 335 HV10 at about 1000° F.; or

(b) the insert exhibits a decrease in hardness of 25% or less when heated from about room temperature to about 1000° F.

15. A method of manufacturing an internal combustion engine comprising inserting the valve seat insert of claim 8 in a cylinder head of the internal combustion engine.

16. The method of claim 15 , wherein the engine is a diesel or natural gas engine.

17. A method of operating an internal combustion engine comprising closing a valve against the valve seat insert of claim 8 to close a cylinder of the internal combustion engine and igniting fuel in the cylinder to operate the internal combustion engine.

18. The method of claim 17 , wherein the valve:

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

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

19. The valve seat of claim 8 , wherein C is 0.5 to 0.9%.

20. A method of making a superaustenitic stainless steel, comprising in weight %:

0.15 to 0.9% C;

0.2 to 1.3% Si;

0 to 0.45% Mn;

32.5 to 37.5% Cr;

13.5 to 17.5% Ni;

3.2 to 5.5% Mo;

0 to 2% Nb;

0 to 0.5% B;

0 to 2% Zr; and

30 to 51% Fe;

wherein:

(a) the superaustenitic stainless steel is cast into a shaped component from a melt at a temperature from about 2800° F. to about 3000° F.; or

(b) a powder of the superaustenitic stainless steel 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.

21. The method of claim 20 , wherein the shaped component is a valve seat insert and the superaustenitic stainless steel consists essentially of 0.5 to 0.9% C, 0.2 to 0.5% Si, 0.2 to 0.4% Mn, 33.0 to 35.0% Cr, 15.5 to 17.5% Ni, 4.0 to 4.5% Mo, 0.7 to 0.9% Nb, 0.07 to 0.13% B, 0 to 0.05% Zr and 40 to 46% Fe.

22. The method of claim 20 , further comprising precipitation hardening by heat treating the shaped component at a temperature from about 900° F. to about 1700° F. for about 2 hours to about 15 hours; and the heat treating is performed in an inert, oxidizing, or reducing atmosphere, or in a vacuum such that a hardness of the shaped component after heat treating is greater than a hardness of the shaped component before heat treating.