SLIDING ELEMENT, IN PARTICULAR PISTON RING, AND METHOD FOR PRODUCING SAME

Abstract

A sliding element, in particular a piston ring, includes a base material of martensitic or austenitic stainless steel having a chromium content of at least 6.0% by mass and a nitrided layer having a surface hardness of up to 950 HV1. A method of producing such a sliding layer is also provided.

Claims

1. A sliding element, comprising: a base material of martensitic or austenitic stainless steel having a chromium content of at least 6.0% by mass, preferably at least 11% by mass, particularly preferably at least 17% by mass, and a nitrided layer having a surface hardness of up to 950 HV1, preferably at least 700 HV1 and/or up to 900 HV1.

2. The sliding element according to claim 1, including a wear-resistant layer selected from a PVD layer or electroplated layer, particularly preferably a DLC layer, as the outermost layer on at least part of the surface of the sliding element.

3. The sliding element according to claim 2, wherein the sliding element is a piston ring and the wear-resistant layer is applied a DLC layer to one or both of the outer circumferential surface and a flank of the piston ring.

4. The sliding element according to claim 1, wherein the nitrided layer constitutes the outermost layer on at least part of the surface of the sliding element and is applied to one or more of the outer circumferential surface and the flank of a piston ring.

5. The sliding element according to claim 1 one of, wherein the nitrided layer has a nitriding hardness depth Nht 700 HV0.1, measured according to ISO6621-2, section 4.2.15, of between 20 and 100 .Math.m.

6. The sliding element according to claim 1 one of, wherein the wear-resistant layer has a thickness of at least 3 .Math.m.

7. The sliding element according to claim 1 one of wherein the nitrided layer consists exclusively of a single-zone nitrided layer with continuous hardness decrease from the outer surface into the base material which is free of nitrides.

8. The sliding element according to claim 1 one of, wherein the base material has a uniform, fine-grained tempered structure without carbide accumulations and a maximum carbide grain size of 50 .Math.m.

9. A method for producing a sliding element, comprising providing a base material of martensitic or austenitic stainless steel having a chromium content of at least 6.0% by mass, and nitriding the base material at a nitriding temperature of between at least 600° C. and 700° C.

10. The method for producing a sliding element according to claim 9, wherein the base material is subjected to a cleaning treatment prior to nitriding.

11. The method for producing a sliding element according to claim 9, wherein prior to nitriding, the base material is heated in a gas nitriding facility to a pretreatment temperature of between 450° C. and 550° C. with the addition of nitrogen gas.

12. The method for producing a sliding element according to claim 9, wherein the base material is subjected to a single- or multi-stage etching treatment prior to nitriding, with ammonia as well as etchants, in solid or liquid form, being added.

13. The method for producing a sliding element according to claim 9, wherein nitriding is carried out with the addition of ammonia.

14. The method for producing a sliding element according to claim 9, wherein during heating to the nitriding temperature, at least one holding phase is provided during which the base material is held at a temperature lower than the nitriding temperature.

15. The method for producing a sliding element according to claim 9, wherein during nitriding, the solubility limit for nitrogen in the base material is exceeded.

16. The sliding element of claim 1, wherein the chromium content is at least 11% by mass.

17. The sliding element of claim 1,wherein the chromium content is at least 17% by mass.

18. The sliding element of claim 1, wherein the hardness is at least 700 HV1.

19. The sliding element of claim 1, wherein the hardness is greater than 700 HV1 and less than 900 HV1.

20. The sliding element of claim 2, wherein the wear resistant layer comprises a DLC layer.

21. The sliding element of claim 6, wherein the thickness is at least 10 .Math.m.

22. The method of claim 9, wherein the nitriding temperature is at most 650° C.

23. The method of claim 13, wherein at least one of nitrogen and hydrogen are added during nitriding.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0033] In the following, the basic idea of the invention will be explained in more detail by way of example with reference to the drawings in which

[0034] FIG. 1 shows a comparison of the surface hardnesses of a conventionally nitrided piston ring (Var. 1) and a piston ring nitrided according to the invention (Var. 2), measured according to HV1 and HV0.5;

[0035] FIG. 2 shows a comparison of the piston ring-specific fatigue strength of the conventionally nitrided piston ring (Var. 1) and the piston ring nitrided according to the invention (Var. 2); and

[0036] FIG. 3 shows a comparison of the metallographic transverse microsections of the conventionally nitrided piston ring (Var. 1) and the piston ring nitrided according to the invention (Var. 2), wherein both piston rings were additionally provided with a PVD wear-resistant layer.

DETAILED DESCRIPTION

[0037] The expected connection between the surface hardness of the nitrided layer and the fatigue strength of accordingly nitrided piston rings is proven by the results shown in FIGS. 1 and 2: On the one hand, the method leads to significantly reduced surface hardnesses of the nitrided layer (cf. FIG. 1). This reduced surface hardness in turn leads to a significantly increased fatigue strength, as shown by FIG. 2. The piston ring-specific fatigue strength was derived in the measurement method forming the basis for FIG. 2 by determining the mean stress and the stress amplitude for fatigue strength-typical load cycles 10.sup.7. The growing of the iron and chromium nitride precipitates preferred according to the invention is further manifested in an enhanced etchability of the nitrided layer with 1% alcoholic nitric acid solution in the metallographic transverse microsection, as shown in FIG. 3.

[0038] The following additional embodiment example again illustrates the effect of nitriding according to the invention on hardness: The surface hardnesses according to Table 1 were measured on the nitrided layer of a sliding element nitrided according to standard methods. In contrast, the surface hardnesses according to Table 2 were measured on the nitrided layer of a sliding element nitrided according to the method of the invention. As can be clearly seen by comparing the two tables, the method according to the invention leads to significantly reduced surface hardnesses.

TABLE-US-00001 HV1 HV 0.5 HV 0.3 HV 0.2 HV 0.1 HV 0.05 1 1150 1207 1192 1268 1275 1416 2 1172 1194 1281 1257 1307 1246 3 1159 1183 1167 1246 1359 1339 4 1155 1156 1200 1214 1275 1246 5 1120 1131 1272 1192 1345 1339 ∅ 1151 1175 1222 1233 1339 1317

TABLE-US-00002 HVI HV 0.5 HV 0.3 HV 0.2 HV 0.1 HV 0.05 1 765 885 932 899 971 986 2 789 841 832 994 962 1246 3 760 849 909 934 1039 956 4 799 855 921 1002 950 956 5 784 765 938 979 1016 1339 ∅ 779 863 918 962 992 994