Steel for Surface Hardening, Having a High Edge Hardness and Having a Fine Ductile Grain Structure

Abstract

The invention makes a steel available, which, in the case of edge-layer hardening without subsequent relaxation annealing, not only has the potential for developing a hardened edge layer having a great surface hardness, in particular a surface hardness that amounts to more than 820 HV1, but rather also possesses a ductile, fine-grained grain structure and, at the same time, can be easily welded. For this purpose, a steel according to the invention consists of (in weight %) C: 0.10-0.19%, Si: ≤0.15%, Mn: ≤1.0%, P: ≤0.015%, S: ≤0.015%, Cr: 0.2-1.0%, Ni: 0.7-2.0%, Mo: 0.5-1.0%, N: ≤0.015%, Al: 0.010-0.060%, Cu: ≤0.20%, B: ≤0.005%, as well as optionally, in each instance, one or more elements from the group “W, Ti, Nb, V, Ta” in content values in accordance with the following stipulations: W: 0.15-0.65%, Ti: 0.01-0.04%, Nb: 0.015-0.05%, Ta: 0.01-0.04%, V: 0.04-0.12%, and, as the remainder, of iron and unavoidable contaminants.

Claims

1. A steel containing (in weight-%) C: 0.10-0.19%, Si: ≤0.15%, Mn: ≤1.0%, P: ≤0.015%, S: ≤0.015%, Cr: 0.2-1.0%, Ni: 0.7-2.0%, Mo: 0.5-1.0%, N: ≤0.015%, Al: 0.010-0.060%, Cu: ≤0.20%, B: ≤0.005% as well as optionally, in each instance, one or more elements from the group “W, Ti, Nb, V, Ta” in a content in accordance with the following stipulations W: 0.15-0.65%, Ti: 0.01-0.04%, Nb: 0.015-0.05%, Ta: 0.01-0.04%, V: 0.04-0.12%, remainder iron and unavoidable contaminants.

2. The steel according to claim 1, characterized in that its C content amounts to at most 0.13 wt %.

3. The steel according to claim 1, characterized in that its Cr content amounts to at least 0.3 wt %.

4. The steel according to claim 1, characterized in that its Cr content amounts to at most 0.5 wt %.

5. The steel according to claim 1, characterized in that its Ni content amounts to at least 1.5 wt %.

6. The steel according to claim 1, characterized in that its Mo content amounts to at most 0.65 wt %.

7. The steel according to claim 1, characterized in that its W content amounts to at most 0.35 wt %.

8. The steel according to claim 1, characterized in that its Nb content amounts to at most 0.03 wt %.

9. The steel according to claim 1, characterized in that its V content amounts to at least 0.08 wt %.

10. The steel according to claim 1, characterized in that its V content amounts to at most 0.12 wt %.

11. The steel according to claim 1, characterized in that in the case-hardened state, it has a surface hardness of at least 820 HV1 in a carburized edge layer without subsequent relaxation, and has a hardness of at least 550 HV at a hardness penetration depth that corresponds to 0.12% of the diameter of the component, in each instance.

12. The steel according to claim 1, characterized in that in the blank-hardened state, it has a tensile strength of at least 950 MPa.

13. The steel according to claim 1, characterized in that in the blank-hardened state, it achieves a notched bar impact work with an ISO-V notch of more than 90 joules.

14. The steel according to claim 1, characterized in that in the chain test of case-hardened round steel chains according to DIN 22252, it achieves a rupture strength of at least 440 MPa.

15. A use of a steel configured in accordance with claim 1, for producing round steel chains and individual parts.

Description

[0068] In the following, the invention will be explained using an exemplary embodiment.

[0069] To check the properties of a steel according to the invention, hot-rolled rod steel having a circular diameter of 30 mm, in other words a diameter that is representative for chain links or the like, was produced in conventional manner, which had the composition indicated in Table 1, which satisfies the requirements of the invention (information in weight %, remainder iron and unavoidable contaminants):

TABLE-US-00001 TABLE 1 C Si Mn P S Cr 0.12 0.12 0.51 0.008 0.005 0.41 Ni Mo Al N W Cr 1.71 0.52 0.033 0.011 0.030 0.41

[0070] The following properties were found for the rod steel:

[0071] After direct case-hardening at 950° C. with subsequent cooling in oil, a fine-grained grain structure of at least ASTM 6 is present in the rod, in the case-hardened edge layer, having a surface hardness of 840 HV1.

[0072] In the core of the sample, a hardness of 30 HRc is achieved, whereas in a hardness penetration depth of 0.38 mm, a hardness of 560 HV is present.

[0073] The composition of the steel being investigated here thereby guarantees sufficiently great ductility of the material so that subsequent relaxation for adjusting the mechanical properties is not necessary. Thus, notched bar impact work values with an ISO-V notch of 110 to 130 joules are achieved with the rod steel being investigated.

[0074] In this regard, the steel according to the invention reaches a tensile strength of 985 MPa, determined according to DIN EN ISO 17022-3, for the rod being investigated, in the “blank-hardened state” (i.e., hardening at 950° C. with subsequent cooling in oil, no carburization).

[0075] These properties as determined make the steel according to the invention particularly suitable for the production of round steel chains that achieve a rupture strength of more than 440 MPa in a chain test according to DIN 22252.