STEEL ALLOY

Abstract

A steel alloy providing from 0.05 to 0.25 wt. % carbon, from 10 to 14 wt. % chromium, from 1.5 to 4 wt. % molybdenum, from 0.3 to 1.2 wt. % vanadium, from 0.3 to 3 wt. % nickel, from 6 to 11 wt. % cobalt from 0.05 to 0.4 wt. % silicon, from 0.1 to 1 wt. % manganese, from 0.02 to 0.06 wt. % niobium, optionally one or more of the following elements from 0 to 2.5 wt. % copper from 0 to 0.1 wt. % aluminum, from 0 to 250 ppm nitrogen, from 0 to 30 ppm boron, and the balance iron, together with any unavoidable impurities, wherein the alloy has a Ni.sub.eq of greater than 11.5, the Ni.sub.eq being defined by the formula Ni.sub.eq=Ni+Co+(0.5Mn)+(30C), in wt. %.

Claims

1. A steel alloy comprising: from 0.05 to 0.25 wt. % carbon, from 10 to 14 wt. % chromium, from 1.5 to 4 wt. % molybdenum, from 0.3 to 1.2 wt. % vanadium, from 0.3 to 3 wt. % nickel, from 6 to 11 wt. % cobalt from 0.05 to 0.4 wt. % silicon, from 0.1 to 1 wt. % manganese, from 0.02 to 0.06 wt. % niobium, optionally one or more of the following elements from 0 to 2.5 wt. % copper from 0 to 0.1 wt. % aluminum, from 0 to 250 ppm nitrogen, from 0 to 30 ppm boron, and the balance iron, together with any unavoidable impurities, wherein the alloy has a Ni.sub.eq of greater than 11.5, the Ni.sub.eq being defined by the formula Ni.sub.eq=Ni+Co+(0.5Mn)+(30C), in wt. %.

2. The steel alloy of claim 1, wherein the Ni.sub.eq is from 11.6 to 17, preferably from 11.7 to 16, more preferably from 12 to 15.

3. The steel alloy of claim 1, comprising from greater than 0.1 wt. % carbon to 0.25 wt. % carbon, preferably from 0.11 to 0.2 wt. % carbon, more preferably from 0.12 to 0.19 wt. % carbon, even more preferably from 0.13 to 0.18 wt. % carbon.

4. The steel alloy of claim 1, comprising from 0.05 to 0.09 wt. % carbon, preferably from 0.06 to 0.08 wt. % carbon.

5. The steel alloy of claim 1, comprising from 10.5 to 13 wt. % chromium, preferably from 10.7 to 12.8 wt. % chromium, more preferably from 11 to 12.5 wt. % chromium.

6. The steel alloy of claim 1 comprising: from 2 to 3.9 wt. % molybdenum, preferably from 2.5 to 3.8 wt. % molybdenum, more preferably from 2.7 to 3.7 wt. % molybdenum; and/or from 0.35 to 1.1 wt. % vanadium, preferably from 0.35 to 1 wt. % vanadium, more preferably from 0.4 to 0.7 wt. % vanadium; and/or from 0.3 to 1.9 wt. % nickel, preferably from 0.4 to 1.8 wt. % nickel; and/or from 7 to 10 wt. % cobalt, preferably from 7.5 to 9.5 wt. % cobalt, more preferably from 8.1 to 9.3 wt. % cobalt; and/or from 0.05 to 0.3 wt. % silicon, preferably from 0.15 to 0.25 wt. % silicon; and/or from 0.13 to 0.7 wt. % manganese, preferably from 0.14 to 0.6 wt. % manganese, more preferably from 0.15 to 0.19 wt. % manganese; and/or from 0.025 to 0.055 wt. % niobium, preferably from 0.03 to 0.05 wt. % niobium.

7. A bearing component formed from the steel alloy of claim 1, preferably wherein the bearing component is at least one of a rolling element, an inner ring, and an outer ring.

8. The bearing component of claim 7, wherein a surface of the bearing component has been case hardened, preferably by carburizing, nitriding and/or carbonitriding.

9. A bearing comprising a bearing component according to claim 7, preferably wherein the bearing component is an inner and/or outer ring and the bearing comprises rolling elements made of a ceramic material.

10. A process for the manufacture of a bearing component, the process comprising: providing a steel alloy as defined in claim 1; (ii) forming a bearing component from the steel alloy; and (iii) case hardening the component.

Description

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

[0100] The invention will now be described further, by way of examples, with reference to a number of non-limiting embodiments of steel alloys according to the invention, with reference to a suitable heat treatment for the steel alloys; and with reference to the accompanying drawings, in which:

[0101] FIG. 1 shows plots of Nieq against Creq for a number of steel alloys according to the present invention and a number of steel alloys according to reference examples.

[0102] FIG. 2 shows results of thermodynamic modelling for a steel with a high -ferrite content.

[0103] FIG. 3 shows results of thermodynamic modelling for a steel with a low -ferrite content.

[0104] Examples

[0105] A number of steel alloys were prepared having the compositions listed in

TABLE-US-00001 TABLE 1 Steel C Si Mn Cr Mo Ni V Nb Co Ni.sub.eq P675* 0.07 0.40 0.65 13.0 1.8 2.6 0.6 5.4 10.4 A* 0.076 0.18 0.47 12.42 2.0 0.53 0.6 0.032 7.2 10.3 B2* 0.069 0.16 0.47 12.05 2.5 1.04 0.5 0.030 7.23 10.6 B3* 0.054 0.16 0.47 11.19 3.46 1.02 0.51 0.033 7.18 10.1 B4* 0.050 0.15 0.47 12.37 2.49 1.83 0.51 0.033 6.51 10.1 B5 0.09 0.18 0.18 11.3 3.5 1.8 0.5 0.05 8.8 13.4 C2 0.054 0.17 0.51 13.4 2.74 1.54 0.53 0.032 8.16 11.6 C4* 0.040 0.16 0.47 11.31 3.48 0.54 0.51 0.033 8.47 10.4 D2* 0.050 0.21 0.68 11.45 1.82 0.56 1.01 0.034 8.06 10.5 C5 0.16 0.17 0.23 11.3 3.44 0.43 0.33 0.04 9.2 14.5 C6 0.11 0.16 0.16 11.2 3.6 0.41 0.55 0.04 9.1 12.6

[0106] Table 1The chemical compositions of a number of steel alloys according to the invention and a number of reference example alloys*. All quantities are in wt. %. The balance is iron, together with any unavoidable impurities.

DETAILED DESCRIPTION OF THE INVENTION

[0107] The -ferrite contents of the steel alloys were determined by optical microscopy, using techniques known in the art. The steel alloys according to the invention had -ferrite contents of less than 3 vol. %, whereas some of the steel alloys according to the reference examples had -ferrite contents in excess of 9 vol. %. In addition, the -ferrite contents of alloys containing greater than 0.1 wt. % carbon are always low.

[0108] Plots of Nieq against Creq are shown in FIG. 1. Below Nieq values of about 11.5 the -ferrite contents can be either high or low, whereas above Nieqq values of about 11.5 the -ferrite contents are always low.

[0109] Thermodynamic modelling of the compositions shows the effect of alloying on the size of the -ferrite phase field and the proximity of the composition to this phase field. FIG. 2 is a graph for a steel with a high -ferrite content. It can be seen that the dashed vertical line representing the steel composition actually goes through the grey shaded -ferrite phase field. FIG. 3 is a graph for a steel with a low -ferrite content and it is clear that the dashed vertical line representing this steel composition is further away from the shaded -ferrite phase field.

[0110] The steel alloys according to the invention underwent carburizing, rehardening and tempering (secondary hardening). The surface hardness of the steel alloys was found to be between HV 820 and HV850, i.e. higher than the values of HV 750 or HV 780 for standard carburized Pyrowear 675.