Pre-treatment process of a surface of a metallic substrate

Abstract

Process for pre-treatment of a surface of a chromium containing corrosion resistant metallic substrate prior to further processing, wherein the metallic substrate is brought into contact with an in-situ generated activating agent, being the thermal decomposition product of a hydrofluoroolefin, the substrate and the activating agent are heated, and optionally the activating agent is partly or entirely removed before further processing.

Claims

1. A process for pre-treatment of a surface of a chromium containing corrosion resistant metallic substrate prior to further processing, wherein a) the metallic substrate is brought into contact with a thermal decomposition product of a hydrofluoroolefin comprising HF, b) the substrate and the thermal decomposition product are heated, c) and optionally the remains of the thermal decomposition product are partly or entirely removed before further processing, wherein the thermal decomposition product is the thermal decomposition product of tetrafluorpropylene, which may have one or two of its fluorine atoms substituted by chlorine atoms.

2. The process according to claim 1, wherein the heating in step b) is achieved by residual heat of the thermal decomposition product.

3. The process according to claim 1, wherein the substrate is selected from the group consisting of a nickel-based alloy and a cobalt-chromium alloy having at least 10% of solved chromium and alloys of these materials as well as mixed material workpieces.

4. The process according to claim 1, wherein the further processing is a coating process or a diffusion treatment.

5. The method of claim 1 wherein the thermal decomposition product is selected from the group consisting of 2,3,3,3-tetrafluoropropene, 1,3,3,3-tetrafluoropropene, 1-chloro-3,3,3-trifluoropropene and mixtures thereof.

6. The method of claim 1 wherein the thermal decomposition product is 2,3,3,3-tetrafluoropropene or 1,3,3,3-tetrafluoropropene.

7. The method of claim 1 wherein the thermal decomposition product is 2,3,3,3-tetrafluoropropene.

8. The process according to claim 1, wherein the substrate is pre-heated prior to contacting with the thermal decomposition product.

9. The process according to claim 8, wherein the substrate is of the form of martensite, austenite, duplex steel, ferrite, and/or a precipitation hardening steel.

10. The process according to claim 8, wherein the substrate is pre-heated prior to contacting with the thermal decomposition product to a temperature of between 150° C. and 250° C.

11. The process according to claim 8, wherein a holding temperature for the activating step/pre-treatment is in the range of about 150° C. to about 500° C.

12. The method of claim 11 wherein the holding temperature is from about 200° C. to below 400° C.

13. The process according to claim 1, wherein the thermal decomposition process comprises the steps of, in that order, Ia) evacuating a decomposition reactor to below 50 kPa atmospheric pressure, then flushing the reactor with inert gas; or Ib) flushing the reactor with inert gas without prior evacuation; II) supplying a hydrofluoroolefin into the decomposition reactor either neat or together with an inert gas; III) raising the temperature in the reactor to a decomposition temperature.

14. The process according to claim 13, wherein the decomposition reactor is an oven or a tube and wherein the decomposition reactor is a made of metal and/or ceramic.

15. The process according to claim 13, wherein the decomposition temperature is between 400 to 1200° C.

16. The process according to claim 13, wherein evacuating the decomposition reactor comprises evacuating the decomposition reactor to 10 kPa or less.

17. The process according to claim 13, wherein the inert gas is selected from the group consisting of noble gas, nitrogen, hydrogen, ammonia, carbon dioxide and mixtures thereof.

18. The method of claim 17 wherein the inert gas is selected from argon, nitrogen and mixtures thereof.

Description

(1) In the enclosed figures the following is illustrated:

(2) FIG. 1 shows a photograph of a border area of an activated and carburized sample made from a steel based on austenite (1.4301) and activated by the process of the present invention.

(3) FIG. 2 shows a photograph of a border area of an activated and nitrocarburized sample made from a steel based on austenite (1.4404) and activated by the process of the present invention.

(4) FIG. 3 is a further photograph of a border area of an activated and nitrocarburized sample made from nickel-based material Inconel 718 (2.4668) and activated by the process of the present invention.

(5) FIG. 4 is a further photograph of a border area of an activated and nitrocarburized sample made from a martensite (1.4057) and activated by the process of the present invention.

(6) FIG. 5 is a representation of an apparatus in which the process of the present invention is conducted (the respective parts are not drawn to scale and only significant parts of the apparatus are shown; e.g. pumps and heating devices are not shown). In FIG. 5 certain parts are represented by the following numbers:

(7) 1 decomposition reactor 2 fluoroolefin storage tank (e.g. gas bottle) 3 inert gas storage tank (e.g. gas bottle) 4 substrate treatment oven 5 metal substrate 6 off-gas cleaning unit (e.g. acid washer based on calcium carbonate) 7 valves 8 pressure relief valve

(8) The present invention will now be explained further by the following non-limiting examples.

EXAMPLES

Example 1

(9) A sample substrate based on austenite (1.4301) was placed in an oven and subsequently, in order to remove oxygen, the oven was evacuated to below 100 Pa (1 mbar) and then flooded with an inert gas (nitrogen). After that the specimen was heated to 200° C. by convection.

(10) In a decomposition reactor (a heatable, metallic heat-resistant tube) attached to the oven 15 vol.-% 2,3,3,3-tetrafluorpropene was cleaved at 850° C. and the decomposition products were introduced into the oven with the aid of 85 vol.-% nitrogen as a carrier gas and circulated for one hour. The amount of 2,3,3,3-tetrafluorpropene and carrier gas introduced into the decomposition reactor was more than twice the volume of the oven space (calculated at 1013 mbar). After one hour the inflow of the activating gas was ceased and the oven space was again evacuated to below 100 Pa (1 mbar).

(11) After that the oven was flooded with nitrogen as inert gas until 95 kPa (950 mbar) were reached and the sample was heated to 480° C. by convection.

(12) The sample was then gassed with a mixture of 98 vol.-% H.sub.2 and 2 vol.-% C.sub.2H.sub.2 for 20 hours at a temperature of 480° C.

(13) After cooling to room temperature under inert atmosphere (nitrogen) the sample was colored black. The surface hardness according to Vickers (DIN EN ISO 6507) of the sample was measured to be 1.023 HV0.025 and the carburizing layer thickness in the microsection to be 25 μm (the hardness of the substrate before treatment was 205 HV0.025).

(14) The resulting sample was photographed and is shown in FIG. 1, from which it is obvious that a very even, hardened layer on the outside of the material was formed.

Example 2

(15) A sample substrate based on austenite (1.4404) was placed in an oven and subsequently, in order to remove oxygen, the oven was evacuated to below 100 Pa (1 mbar) and then flooded with an inert gas (argon). After that the specimen was heated to 300° C. by convection.

(16) In a decomposition reactor (a heatable, metallic heat-resistant tube) attached to the oven 10 vol-% 2,3,3,3-tetrafluorpropene was cleaved at 900° C. and the decomposition products were introduced into the oven with the aid of 90 vol.-% nitrogen as a carrier gas and circulated for 30 minutes. The amount of 2,3,3,3-tetrafluorpropene and inert gas introduced into the decomposition reactor was more than four times the volume of the oven space (calculated at 1013 mbar). After 30 minutes the inflow of the activating gas was ceased and the oven space was again evacuated to below 100 Pa (1 mbar).

(17) After that the oven was flooded with nitrogen as inert gas until 95 kPa (950 mbar) were reached and the sample was heated to 400° C.

(18) The sample was then gassed with a mixture of 75 vol.-% NH.sub.3, 20 vol.-% H.sub.2 and 5 vol.-% C.sub.2H.sub.2 for 18 hours at a temperature of 400° C.

(19) After cooling to room temperature under inert atmosphere (nitrogen) the sample was colored grey. The surface hardness according to Vickers of the sample was measured to be 1150 HV0.025 and the nitrocarburizing layer thickness in the microsection to be 11 μm (the hardness of the substrate before treatment was 215 HV0.025).

(20) The resulting sample was photographed and is shown in FIG. 2, from which it is obvious that an even, hardened layer on the outside of the material was formed.

Example 3

(21) A sample substrate based on Inconel 718 (2.4668) was placed in an oven and subsequently, in order to remove oxygen, the oven was evacuated to below 100 Pa (1 mbar) and then flooded with an inert gas (argon). After that the specimen was heated to 300° C. by convection at 85 kPa (850 mbar).

(22) In a decomposition reactor (a heatable, metallic heat-resistant tube) attached to the oven 5 vol.-% 2,3,3,3-tetrafluorpropene was cleaved at 950° C. and the decomposition products were introduced into the oven with the aid of 95 vol.-% argon as a carrier gas and circulated for 2 hours. The amount of 2,3,3,3-tetrafluorpropene and carrier gas introduced into the decomposition reactor was more than five times the volume of the oven space (calculated at 1013 mbar). After 2 hours the inflow of the activating gas was ceased and the oven space was again evacuated to below 100 Pa (1 mbar).

(23) After that the oven was flooded with argon as inert gas until 95 kPa (950 mbar) were reached and the sample was heated to 480° C.

(24) The sample was then gassed with a mixture of 80 vol.-% NH.sub.3, 18 vol.-% H.sub.2 and 2 vol.-% C.sub.2H.sub.2 for 36 hours at a temperature of 480° C.

(25) After cooling to room temperature under inert atmosphere (argon) the surface hardness according to Vickers of the sample was measured to be 1070 HV0.025 and the nitrocarburizing layer thickness in the microsection to be 26 μm (the hardness of the substrate before treatment was 362 HV0.025).

(26) The resulting sample was photographed and is shown in FIG. 3, from which it is obvious that a very even, hardened layer on the outside of the material was formed.

Example 4

(27) A sample substrate based on martensite (1.4057) was placed in an oven and subsequently, in order to remove oxygen, the oven was evacuated to below 100 Pa (1 mbar) and then flooded with an inert gas (nitrogen). After that the specimen was heated to 200° C. by convection at 85 kPa (850 mbar).

(28) In a decomposition reactor (a heatable, metallic heat-resistant tube) attached to the oven 20 vol.-% 2,3,3,3-tetrafluorpropene was cleaved at 950° C. and the decomposition products were introduced into the oven with the aid of 80 vol.-% n argon as a carrier gas and circulated for 45 minutes. The amount of 2,3,3,3-tetrafluorpropene and carrier gas introduced into the decomposition reactor was more than twice the volume of the oven space (calculated at 1013 mbar). After 45 minutes the inflow of the activating gas was ceased and the oven space was again evacuated to below 100 Pa (1 mbar).

(29) After that the oven was flooded with nitrogen as inert gas until 95 kPa (950 mbar) were reached and the sample was heated to 395° C.

(30) The sample was then gassed with a mixture of 95 vol.-% NH.sub.3, and 5 vol.-% CO.sub.2 for 24 hours at a temperature of 395° C.

(31) After cooling to room temperature under inert atmosphere (nitrogen) the sample was colored grey. The surface hardness according to Vickers of the sample was measured to be 975 HV0.025 and the nitrocarburizing layer thickness in the microsection to be 17 μm (the hardness of the substrate before treatment vas 401 HV0.025).

(32) The resulting sample was photographed and is shown in FIG. 4, from which it is obvious that a very even, hardened layer on the outside of the material was formed.