Chemical activation of self-passivating metals

1. A method for treating a workpiece made from a self-passivating metal and having a Beilby layer comprising:

nitrocarburizing the workpiece, wherein the nitrocarburizing consists of

exposing the workpiece to vapors produced by heating a reagent having a guanidine [HNC(NH 2 ) 2 ] moiety and complexed with HCl for a time period of 1 to 5 minutes.

2. The method of claim 1 , further comprising:

maintaining a reaction vessel containing the workpiece at a temperature of 700°° C. or less during the exposing; and

wherein exposing the workpiece to the vapors forms a treated surface layer in the workpiece, the treated surface layer having a carbon concentration of 5 to 15 atomic % and being substantially free of coarse carbide or coarse nitride precipitates.

3. The method of claim 2 , wherein:

the treated surface layer comprises fine carbide precipitates; and

nitrogen in the treated surface layer is present primarily as at least one of interstitial nitrogen and fine nitride precipitates.

4. The method of claim 3 , wherein:

the fine carbide precipitates do not substantially degrade corrosion resistance provided by a surface passivation layer in the workpiece; and

the surface passivation layer includes chromium oxide.

5. The method of claim 1 wherein at least one of:

exposing the workpiece to the vapors further comprises maintaining a reaction vessel containing the workpiece at a temperature of 700° C. or less during the exposing; and

the reagent includes at least one of Dimethylbiguanide HCI, Guanidine HCI, Biguanide HCI, and Melamine HCl-.

6. The method of claim 1 wherein exposing the workpiece to the vapors further comprises forming a case-hardened layer that is less than 30 μm thick and comprises:

an outer sublayer that is rich in interstitial nitrogen; and

an inner sublayer that is rich in interstitial carbon.

7. The method of claim 6 , wherein the case-hardened layer is less than 20 μm thick.

8. The method of claim 1 , wherein the reagent includes at least one of an oxygen-free nitrogen halide salt and a non-polymeric N/C/H compound.

9. The method of claim 1 , wherein exposing the workpiece to the vapors occurs with the workpiece in a reaction vessel at a distance of 8 inches (20 cm) or more from the reagent.

10. The method of claim 1 , wherein exposing the workpiece to the vapors comprises:

applying a heating protocol that ramps from a lower temperature to a higher temperature during the exposing to enhance decomposition of the reagent and/or surface harden the workpiece.

11. The method of claim 10 , wherein the lower temperature is approximately 450° C. or greater and the higher temperature is approximately 550° C. or less.

12. The method of claim 10 , wherein applying the heating protocol comprises pulsing from the lower temperature to the higher temperature.

13. The method of claim 10 , wherein the heating protocol is as follows:

maintain a temperature of substantially 500° C. for approximately 15 minutes;

ramp the temperature from approximately 500° C. to approximately 480° C.;

maintain a temperature of 480° C. for approximately 15 minutes;

ramp the temperature from approximately 480° C. to approximately 470° C.; and

maintain a temperature of 470° C. for approximately 30 minutes.

14. A workpiece made according the method of claim 1 .

15. A method for treating a workpiece made from a self-passivating metal and having a Beilby layer comprising:

exposing the workpiece to the vapors produced by heating a reagent having a guanidine [HNC(NH 2 ) 2 ] moiety and complexed with HCl to activate the workpiece for low temperature interstitial surface hardening; and

applying a heating protocol during the exposing that ramps from a lower to a higher temperature during the exposing to enhance decomposition of the reagent and/or surface harden the workpiece, wherein the heating protocol is as follows:

maintain a temperature of substantially 470° C. for approximately 30 minutes;

ramp the temperature from approximately 470° C. to approximately 480° C.;

maintain a temperature of 480° C. for approximately 15 minutes;

ramp the temperature from approximately 480° C. to approximately 500° C.; and

maintain a temperature of 500° C. for approximately 15 minutes.

16. A method for producing a case-hardened at least one component in continuous conveyer belt production comprising:

purging an atmosphere of the continuous conveyor belt with gas;

while maintaining the atmosphere at a temperature of 700° C. or less:

placing the at least one component on the continuous conveyor belt, with each of the at least one component comprising a self-passivating metal and having a Beilby layer;

nitrocarburizing the at least one component, wherein the nitrocarburizing consists of

exposing the at least one component to vapors produced by heating a reagent having a guanidine [HNC(NH 2 ) 2 ] moiety and complexed with HCl for a period of 1 to 5 minutes, whereby the at least one component is activated and surfaced hardened from exposure to the vapors.

17. The method of claim 16 , wherein the at least one component comprises a plurality of components.

18. A component made according to the method of claim 16 .