Assembly component

Abstract

The present invention relates to an assembly component of an alloy based on iron, nickel and/or cobalt containing at least 10% (w/w) chromium, the assembly component having an annular shape with an inner surface and an outer surface and a thickness between the inner surface and the outer surface in the range of 0.1 mm to 5 mm, the alloy having a content of nitrogen in solid solution providing a microhardness in the range of 250 HV.sub.0.05 to 370 HV.sub.0.05 at a depth from the surface in the range of 0 μm to 100 μm. The invention also relates to an assembly with the assembly component.

Claims

1. An assembly component for providing a gas tight seal, the assembly component being of an austenitic alloy based on iron, nickel, and/or cobalt and containing at least 10% (w/w) chromium, the assembly component having an annular shape with an inner surface and an outer surface and a thickness between the inner surface and the outer surface in the range of 0.1 mm to 5 mm, the austenitic alloy having a content of nitrogen in solid solution providing a microhardness in the range of 250 HV.sub.0.05 to 370 HV.sub.0.05 at a depth from the surface in the range of 0 μm to 100 μm.

2. The assembly component according to claim 1, wherein the microhardness is in the range of 280 HV.sub.0.05 to 320 HV.sub.0.05 at a depth from the surface in the range of 0 μm to 100 μm.

3. The assembly component according to claim 1, wherein the assembly component has an average microhardness in the range of 280 HV.sub.0.05 to 320 HV.sub.0.05 over the thickness of the assembly component as calculated from at least 5 microhardness measurements, where the at least 5 microhardness measurements deviate up to 15% from the average microhardness.

4. The assembly component according to claim 1, wherein the nitrogen content is in the range of 0.1% (w/w) to 0.8% (w/w) at a depth from the surface in the range of 0 μm to 100 μm.

5. The assembly component according to claim 3, wherein the nitrogen content is in the range of 0.1% (w/w) to 0.8% (w/w) over the thickness of the assembly component.

6. The assembly component according to claim 5, wherein the nitrogen content deviates by up to 10% from the average nitrogen content over the thickness of the assembly component.

7. The assembly component according to claim 1, wherein the outer diameter of the annular shape is in the range of 3 mm to 50 mm.

8. The assembly component according to claim 1, wherein the annular shape has an axial length in the range of 2 mm to 500 mm.

9. The assembly component according to claim 1, wherein the assembly component has frustoconical annular shape defining a narrow end and a wide end.

10. The assembly component according to claim 1, wherein the assembly component is free from nitride compounds.

11. The assembly component according to claim 1, wherein the austenitic alloy is an austenitic stainless steel.

12. An assembly of the assembly component according to claim 1, an inner tubular member having a peripheral surface and an outer tubular member having an interior surface, wherein the assembly component is positioned between the inner tubular member and the outer tubular member so that the inner surface of the assembly component abuts the peripheral surface of the inner tubular member and the outer surface of the assembly component abuts the interior surface of the outer tubular member.

13. The assembly according to claim 12, wherein the assembly component has been subjected to cold deformation after positioning between the inner tubular member and the outer tubular member.

14. The assembly according to claim 12, wherein the inner tubular member comprises an external helical thread and the outer tubular member comprises an internal helical thread complementary to the external helical thread.

15. The assembly according to claim 12, wherein the outer tubular member comprises an external helical thread and the assembly further comprises a connector having an internal helical thread complementary to the external helical thread.

16. A kit of parts comprising an outer tubular member, one or more assembly components according to claim 1, and a connector.

17. The kit of parts according to claim 16, wherein the outer tubular member has an external helical thread, and that the connector has an internal helical thread complementary to the external helical thread of the outer tubular member.

18. The kit of parts according to claim 17, wherein the outer tubular member and the connector have an outer circumferential shape facilitating rotation of the outer tubular member and the connector.

Description

BRIEF DESCRIPTION OF THE FIGURES

(1) In the following the invention will be explained in greater detail with the aid of an example and with reference to the schematic drawings, in which

(2) FIG. 1 shows a cross-section of an assembly of the invention;

(3) FIGS. 2A and 2B show an exploded view of an assembly of the invention;

(4) FIGS. 3A and 3B show an assembly of the invention;

(5) FIG. 4 shows a cross-section of an assembly component of the invention;

(6) FIG. 5 shows a microhardness profile of an assembly component of the invention;

(7) FIG. 6 shows a microhardness profile of an assembly component of the invention;

(8) FIG. 7 shows a microhardness profile of an assembly component of the invention.

DETAILED DESCRIPTION OF THE INVENTION

(9) The present invention relates to an assembly component and to a method of producing the assembly component, and when the term “component” is used in this document it may refer to the assembly component of the invention or to the component treated in the method of the invention. Any embodiment of the assembly component may be produced in the method of the invention. In another aspect the invention relates to an assembly involving an assembly component of the invention. Any assembly component of the invention may be included in the assembly of the invention, but the assembly may also include components not of the invention. In yet a further aspect the present invention relates to a kit of parts comprising the assembly component.

(10) The component is of an alloy based on iron, nickel and/or cobalt containing at least 10% (w/w) chromium, e.g. an iron based alloy with 10.5% (w/w) chromium or more, and the chromium content provides that an oxide layer will form on the surface of the component. The oxide layer provides corrosion resistance and an alloy based on iron, nickel and/or cobalt containing at least 10% chromium may also be referred to as a passive alloy. By the term “passive” in connection with alloys or metals is thus to be understood an alloy, which has a protective oxide layer. A passive alloy can be both self-passivating or be passivated as a consequence of a process to which the alloy is subjected. Belonging to the group of self-passivating alloys are those, which have a strong affinity to oxygen (e.g. Cr, Ti, V), including alloys containing such alloying elements, e.g. stainless steel which essentially is an iron based alloy containing at least 10.5% (w/w) Cr. It is also contemplated that the component may be of an alloy containing at least 10% (w/w) vanadium or at least 10% (w/w) titanium or 10% (w/w) of any combination of chromium, vanadium and titanium.

(11) Unless otherwise noted a percentage in relation to a metal element or a non-metallic element in an alloy, is by weight and is denoted % (w/w). When the assembly component of the invention has a microhardness deviating with up to 15% from the average hardness the assembly component has a uniform nitrogen content over the thickness of assembly component and the percentage, % (w/w) is by the total weight of material. However, when percentage, expressed as % (w/w), is stated for the hardened layer the percentage is based on the weight of the hardened layer. In general, a content of nitrogen in the alloy will be measured relative to the immediate surroundings of the measurement, and this measurement thus represents the nitrogen content of the hardened layer. Unless otherwise noted a composition of a mixture of gasses is on an atomic basis and may be provided as a percentage or in ppm (parts per million). With respect to compositions of alloys or gasses unavoidable impurities may also be present, even if this is not specifically mentioned.

(12) In terms of the invention an “alloying element” may refer to a metallic element or a non-metallic element in the alloy. In particular, alloys of relevance in the method of the invention comprise an element, e.g. a metallic element, that may form nitrides and/or carbides with present nitrogen and carbon, respectively. The method of the invention advantageously provides a hardened layer on an assembly component, e.g. a nitrogen saturated component, free from nitrides and carbides of alloying elements. It is however also contemplated in the invention that an alloy may comprise only a single metallic element capable of forming nitrides and/or carbides. An alloy may also comprise other elements, such as semi-metallic elements, inter-metallic elements, or non-metallic elements. Alloying elements capable of forming nitrides and/or carbides may typically be metallic elements providing corrosion resistance to the alloy due to formation of a passive oxide layer with the alloying element. The terms “nitride” and “carbide” as used in the context of the invention refer to nitrides and carbides formed between alloying elements and nitrogen and carbon, respectively. An exemplary nitride is chromium nitride, CrN or Cr.sub.2N although terms “nitride” and “carbide” are not limited to nitrides and carbides with chromium.

(13) By the term “sensitisation” is to be understood that nitrogen or carbon have formed nitrides and carbides, respectively, by reaction with one or more alloying elements otherwise utilised to form the protective oxide layer on the surface, as for example chromium in stainless steel. When sensitisation occurs, the free content of the alloying element, such as chromium, in solid solution is lowered to a level, which is no longer sufficient to maintain a complete protective oxide layer, which means that the corrosion characteristics are deteriorated.

(14) In the method of the invention the component is treated at a dissolution temperature of at least 1000° C. A temperature of at least 1000° C. may also be referred to as a temperature above the solubility temperature for carbide and/or nitride. By the term “solubility temperature for carbide and/or nitride” is to be understood the temperature at which nitrides/carbides are not stable, and where already formed nitrides/carbides are dissolved. In general, alloys comprising metallic alloying elements capable of forming nitrides and/or carbides will have a temperature interval in which nitrides and/or carbides may form when nitrogen and carbon, respectively, are present. Thus, above this temperature, nitrides and carbides will not form, and already formed nitrides/carbides are dissolved. When nitrides or carbides exist, i.e. sensitisation has occurred, these carbides can generally only be removed by exposing the sensitised metal to a temperature above the austenisation temperature. Furthermore, such alloys have a temperature below the temperature interval, where nitrides and carbides will not form, although nitrides or carbides already formed in an alloy cannot be removed at the low temperature.

(15) The dissolution temperature may also correspond to the austenisation temperature of the alloy of the component. The “austenisation temperature” is typically the temperature used when heat treating an alloy in order to dissolve carbides, and “austenisation temperature” may thus correspond to the “solubility temperature for carbide”. At the austenisation temperature the alloy is in the austenitic phase. The temperature at which a steel alloy changes phase from ferrite to austenite is typically at a somewhat lower temperature than the austenisation temperature.

(16) By the term “cold deformation” (also named “cold working”) is to be understood a plastic deformation induced in the material by external forces at a temperature below the recrystallisation temperature of the material. Cold deformation may be provided by any shape change, such as forging, extrusion, shaping, drawing, pressing, or rolling, or by a combination of these processes. In the context of the invention the hardness is generally the HV.sub.0.05 as measured according to the DIN EN ISO 6507 standard. If not otherwise mentioned the unit “HV” thus refers to this standard. The hardness may be recorded for a cross-section and it may be noted with respect to the depth of the measurement. A hardness recorded in a cross-section is, in the context of the invention, referred to as a “microhardness”. In general, a microhardness measurement requires about 5 μm of material so that multiple microhardness measurements are possible for a material having a thickness of 100 μm. In an embodiment of the invention at least 5 microhardness measurements are recorded in order to determine an average microhardness and deviations from the average microhardness. When at least 5 microhardness measurements are recorded these should be recorded over the thickness of relevance for the average microhardness of interest. For example, the at least 5 microhardness measurements could include a measurement near the centre of the material, 1 microhardness measurement near each surface of the material and 2 microhardness measurements between the centre and the surface of the material. For determining an average microhardness and the deviation from the average microhardness 5 measurements are considered sufficient but more measurements may be included as desired. Measurement of microhardness typically has an uncertainty of about ±10% so that microhardness measurements providing a deviation of up to 10% from the average hardness is considered to represent a uniform material. However, a microhardness measurement may represent an outlier that should not be included in the determination of the average microhardness and should not be considered for the deviation from the average microhardness. The skilled person will know how to identify an outlier.

(17) In the context of the invention the “depth” is the distance from the surface. When the hardness is recorded at a cross-section the measurement is considered to represent a homogeneous sample with respect to the direction of the pressure applied. Alternatively, the hardness may be obtained from measurements at the surface, and the measurement may thus represent an average of several different values of hardness, i.e. at different depths. In the context of the invention a hardness measurement recorded in a cross-section at a depth of about 1 μm is considered to provide the actual hardness of the surface of the material. However, as an effect of the fact that nitrogen may be dissolved from the surface to have a deviation over the thickness of up to 15% the hardness may be generally uniform over the cross-section of the assembly component, including the surface hardness.

(18) A cross-section of an assembly of the invention is depicted in FIG. 1, and an exploded view of the assembly is shown in FIG. 2. FIG. 1 and FIG. 2 show the assembly component 1, which has a frustoconical shape, between an outer tubular member 2 having a first external helical thread 21 and a second external helical thread 22, and an inner tubular member 3; the end 31 of the inner tubular member 3 is shown in FIG. 1. The inner tubular member 3 is a straight cylindrical tube. The assembly further has a connector 4 having an internal helical thread (not shown), which is complementary to the first external helical thread 21 of the outer tubular member 2. Thus, the outer tubular member 2 is a “male connector”, and the connector 4 is a “female connector”. In FIG. 1 the assembly is assembled but in FIG. 2 the assembly is not assembled. In FIG. 2A the components of the assembly are not assembled but in FIG. 2B the components are partly assembled. Thus, in FIG. 2B the assembly component 1 is mounted on the inner tubular member 3 to allow the peripheral surface of the inner tubular member 3 to abut the inner surface of the assembly component 1. The assembly in FIG. 1 further has a back ferrule 11, which is also an assembly component of the invention.

(19) Thus, the assembly is assembled by pushing the outer tubular member 2 and the connector 4 towards each other to bring them into contact and rotating the outer tubular member 2 and the connector 4 in opposite directions with respect to each other. For example, the outer tubular member 2 may be fixed and the connector 4 rotated, or vice versa, or both the outer tubular member 2 and the connector 4 may be rotated but in opposite rotational directions. Upon assembly the first external helical thread 21 of the outer tubular member 2 will be screwed into the internal helical thread of the connector 4 thereby subjecting the assembly component 1 to cold deformation and providing a gas tight seal. The external helical thread 22 of the outer tubular member 2 may then be joined with a further tubular member (not shown) with an assembly component and a connector having an internal helical thread complementary to the second external helical thread 22 of the outer tubular member 2. Both the outer tubular member 2 and the connector 4 have a hexagonal outer circumferential shapes 23,41, which may be rotated using a standard wrench.

(20) Parts of an assembly of the invention with a back ferrule 11 are illustrated in FIG. 3. Thus, FIG. 3A shows the assembly component 1 and the back ferrule 11, the inner tubular member 3 and the connector 4. FIG. 3B shows, in a perspective view, the assembly component 1 and the back ferrule 11, the outer tubular member 2 and the connector 4. It is to be understood that the assembly of the invention comprises the parts not shown in FIG. 3 as appropriate.

EXAMPLES

Example 1

(21) An annular component of AISI 316 stainless steel having a thickness between the inner surface and the outer surface of 1.50 mm was provided. The annular component was heated to 1150° C. and subjected to an atmosphere of N.sub.2 with a partial pressure of 0.5 bar at a dissolution temperature of 1050° C. The duration was 4 hours. The annular component was quenched in argon at 5 bar to ambient temperature to provide the assembly component.

(22) The cross-section of the treated assembly component was exposed and the microhardness profile was determined. A photo of a cross-section of the assembly component is shown in FIG. 4. FIG. 4 shows how the material of the assembly component is completely austenised and free of any nitrides or crystal structures. The microhardness profile is shown in FIG. 5, which shows a that the hardened layer extended to a depth above 100 μm, at which point the microhardness was about 260 HV.sub.0.05. The assembly component had a core microhardness of about 190 HV.sub.0.05.

Example 2

(23) The process of Example 1 was modified by increasing the duration to 6 hours. Thereby nitrogen was inserted to a greater depth as shown in FIG. 6 where a hardened layer of 300 μm is evident, since at the depth of 300 μm the microhardness was about 250 HV.sub.0.05. By increasing the duration to 8 hours sufficient nitrogen was also dissolved though the thickness of the assembly component to increase the core microhardness to about 240 HV.sub.0.05. This core microhardness corresponds to a nitrogen content of approximately 0.4% (w/w).

Example 3

(24) An annular component of AISI 316 stainless steel having a thickness between the inner surface and the outer surface of 1.50 mm was provided, and the process of Example 1 was repeated but with a duration of 8 hours in order to saturate the assembly component with nitrogen over its thickness. The partial pressure of N.sub.2 was 1.1 bar, which provided a microhardness of 310±30 HV.sub.0.05 corresponding to a nitrogen content of about 0.8% (w/w) in the assembly component. The hardness profile is depicted in FIG. 7.