Dilution control in hardfacing severe service components

1. A method for forming a wear- and corrosion-resistant coating on an industrial component comprising:

a) applying a cobalt-based dilution buffer layer having a thickness between about 0.005 and about 0.03 inch directly onto an iron-based substrate by slurry coating of a cobalt-based alloy powder followed by sintering to fuse the powder together and to the substrate, wherein the cobalt-based dilution buffer layer is a cobalt-based alloy;

b) applying by welding a cobalt-based build-up layer over the cobalt-based dilution buffer layer to integrate the build-up layer and the dilution buffer layer into an integral cobalt-based wear- and corrosion-resistant layer, wherein the cobalt-based build-up layer is a cobalt-based alloy and is an outer surface layer; and

c) cooling the component to room temperature.

2. The method of claim 1 wherein the cobalt-based wear- and corrosion-resistant layer after said cooling has an average level of iron dilution from the iron-based substrate into the cobalt-based wear- and corrosion-resistant layer of less than 5 wt % iron at a level spaced 0.06 inch from the substrate surface.

3. The method of claim 1 wherein the sintering is carried out at a temperature above a solidus temperature but below a liquidus temperature of the cobalt-based alloy being sintered and the temperature of the substrate during sintering is maintained below a solidus temperature of the substrate.

4. The method of claim 1 wherein any heat-affected zone and/or fusion zone at an interface between the substrate and the dilution buffer layer has a thickness of less than 0.005 inch.

5. The method of claim 1 wherein the cobalt-based build-up layer is applied by welding directly over the cobalt-based dilution buffer layer.

6. The method of claim 5 wherein the sintering is carried out at a temperature above a solidus temperature but below a liquidus temperature of the cobalt-based alloy being sintered and the temperature of the substrate during sintering is maintained below a solidus temperature of the substrate.

7. The method of claim 5 wherein any heat-affected zone and/or fusion zone at an interface between the substrate and the dilution buffer layer has a thickness of less than 0.005 inch.

8. A method for forming a wear- and corrosion-resistant coating on an industrial valve component comprising:

a) applying a cobalt-based dilution buffer layer having a thickness between about 0.005 and about 0.03 inch directly onto to an iron-based valve component body substrate selected from the group consisting of a valve body, a ball of a ball-and-ring valve assembly, a seat of a ball-and-ring valve assembly, a gate valve component body, a V-ball valve component body, a wedge valve component body, wedge valve guides, and a valve seat body, said applying comprising slurry coating of a cobalt-based alloy powder followed by sintering to fuse the powder together and to the substrate, wherein the cobalt-based dilution buffer layer is a cobalt-based alloy;

b) applying by welding a cobalt-based build-up layer over the cobalt-based dilution buffer layer to integrate the build-up layer and the dilution buffer layer into an integral cobalt-based wear- and corrosion-resistant layer, wherein the cobalt-based build-up layer is a cobalt-based alloy and is an outer surface layer; and

c) cooling the component to room temperature.

9. The method of claim 8 wherein the cobalt-based wear- and corrosion-resistant layer after said cooling has an average level of iron dilution from the iron-based substrate into the cobalt-based wear- and corrosion-resistant layer of less than 5 wt % iron at a level spaced 0.06 inch from the substrate surface.

10. The method of claim 9 wherein the build-up layer has a thickness between about 0.05 and about 0.8 inch.

11. The method of claim 8 wherein the build-up layer has a thickness between about 0.05 and about 0.8 inch.

12. The method of claim 11 wherein the cobalt-based wear- and corrosion-resistant layer after said cooling has an average level of iron dilution from the iron-based substrate into the cobalt-based wear- and corrosion-resistant layer of between 2 and 5 wt % iron at a level spaced 0.06 inch from the substrate surface.

13. The method of claim 11 wherein the cobalt-based wear- and corrosion-resistant layer after said cooling has an average level of iron dilution from the iron-based substrate into the cobalt-based wear- and corrosion-resistant layer of between 3 and 4 wt % iron at a level spaced 0.06 inch from the substrate surface.

14. The method of claim 8 wherein the welding partially melts the dilution buffer layer.

15. The method of claim 8 wherein the welding is by a welding technique which includes establishment of an arc between an electrode and the substrate as a counter-electrode.

16. The method of claim 8 wherein the welding is plasma transferred arc welding.

17. The method of claim 8 wherein the cobalt-based powder comprises between 40 and 70 wt % Co, between 25 and 35 wt % Cr, between 2 and 7 wt % W, up to about 1.5 wt % Si, and between 0.5 and 1.5 wt % C.

18. The method of claim 17 wherein the cobalt-based powder further comprises between 0.05 and 0.5% B.

19. The method of claim 17 wherein the build-up layer comprises between 40 and 70 wt % Co, between 25 and 35 wt % Cr, between 2 and 7 wt % W, up to about 1.5 wt % Si, and between 0.5 and 1.5 wt % C.

20. The method of claim 8 wherein the build-up layer comprises between 40 and 70 wt % Co, between 25 and 35 wt % Cr, between 2 and 7 wt % W, up to about 1.5 wt % Si, and between 0.5 and 1.5 wt % C.

21. The method of claim 8 wherein the cobalt-based build-up layer is applied by welding directly over the cobalt-based dilution buffer layer.

22. The method of claim 21 wherein the sintering is carried out at a temperature above a solidus temperature but below a liquidus temperature of the cobalt-based alloy being sintered and the temperature of the substrate during sintering is maintained below a solidus temperature of the substrate.

23. The method of claim 21 wherein any heat-affected zone and/or fusion zone at an interface between the substrate and the dilution buffer layer has a thickness of less than 0.005 inch.

24. The method of claim 8 wherein the sintering is carried out at a temperature above a solidus temperature but below a liquidus temperature of the cobalt-based alloy being sintered and the temperature of the substrate during sintering is maintained below a solidus temperature of the substrate.

25. The method of claim 8 wherein any heat-affected zone and/or fusion zone at an interface between the substrate and the dilution buffer layer has a thickness of less than 0.005 inch.