Process for local hardening

Abstract

A process for the local hardening of a workpiece by means of local induction hardening includes performing a local perlitization grain transformation on the workpiece after a local inductive diffusion heat treatment and before a local induction hardening on the workpiece.

Claims

1. A process for a local hardening of a workpiece comprising: performing a local inductive diffusion heat treatment on the workpiece; performing a local perlitization grain transformation on the workpiece after the local inductive diffusion heat treatment; and performing a local induction hardening on the workpiece after preforming the local perlitization grain transformation on the workpiece.

2. The process according to claim 1, wherein a ratio of a duration of the local inductive diffusion heat treatment to a duration of the local induction hardening is from 0.3 to 0.8.

3. The process according to claim 2, wherein a ratio of a duration of the local perlitization grain transformation to the duration of the local induction hardening is in a range from 0.8 to 1.2.

4. The process according to claim 3, wherein the local inductive diffusion heat treatment is carried out at a temperature which is the same as or lower than a temperature at which the local induction hardening is carried out.

5. The process according to claim 4, wherein the local perlitization grain transformation is carried out at a temperature which is lower than the temperature at which the local induction hardening is carried out.

6. The process according to claim 3, wherein the local perlitization grain transformation is carried out at a temperature which is lower than a temperature at which the local induction hardening is carried out.

7. The process according to claim 2, wherein the local perlitization grain transformation is carried out at a temperature which is lower than a temperature at which the local induction hardening is carried out.

8. The process according to claim 1, wherein a ratio of a duration of the local perlitization grain transformation to a duration of the local induction hardening is in a range from 0.8 to 1.2.

9. The process according to claim 8, wherein the local inductive diffusion heat treatment is carried out at a temperature which is the same as or lower than a temperature at which the local induction hardening is carried out.

10. The process according to claim 9, wherein the local perlitization grain transformation is carried out at a temperature which is lower than the temperature at which the local induction hardening is carried out.

11. The process according to claim 8, wherein the local perlitization grain transformation is carried out at a temperature which is lower than a temperature at which the local induction hardening is carried out.

12. The process according to claim 1, wherein the local inductive diffusion heat treatment is carried out at a temperature which is the same as or lower than a temperature at which the local induction hardening is carried out.

13. The process according to claim 12, wherein the local perlitization grain transformation is carried out at a temperature which is lower than the temperature at which the local induction hardening is carried out.

14. The process according to claim 1, wherein the local perlitization grain transformation is carried out at a temperature which is lower than a temperature at which the local induction hardening is carried out.

15. The process according to claim 1, wherein the workpiece is a cast iron workpiece.

16. The process according to claim 15, wherein a duration of the local inductive diffusion heat treatment is between 30 percent and 80 percent of a duration of the local induction hardening.

17. The process according to claim 16, wherein a duration of the local perlitization grain transformation is between 80 percent and 120 percent of the duration of the local induction hardening.

18. The process according to claim 17, wherein: the local inductive diffusion heat treatment is carried out at a temperature between 900° C. and 1150° C.; and the local perlitization grain transformation is carried out at a temperature of between 500° C. and 800° C.

19. The process according to claim 18, wherein the local induction hardening is carried out at about 1050° C.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The drawings show:

(2) FIG. 1—a process according to the disclosure for induction hardening,

(3) FIG. 2—a microstructural composition before induction hardening according to a conventional process,

(4) FIG. 3—a microstructural composition before induction hardening according to the process of the disclosure,

(5) FIG. 4—a section through the microstructure of the microstructural composition as per FIG. 2, and

(6) FIG. 5—a section through the microstructure of the microstructural composition as per FIG. 3.

DETAILED DESCRIPTION

(7) FIG. 1 shows a temperature-time graph of a working example of a process according to the disclosure for induction hardening, with this proceeding in three steps A, B, C. These are a local, brief, inductive diffusion heat treatment A, a local grain transformation by perlitization B and finally the local induction hardening C. Here, the process steps are assigned the individual times diffusion heat treatment time t.sub.A, grain transformation time t.sub.B and induction hardening time t.sub.C.

(8) The temperature T.sub.A of the local diffusion heat treatment A is slightly lower than the temperature T.sub.C of the induction hardening in the working example shown. It is about 1050° C. The temperature T.sub.B of the intermediate step of “grain transformation by perlitization” B is about 650° C. in the working example shown. The duration of the diffusion heat treatment t.sub.A is about 40-50% of the duration t.sub.C of the induction hardening in the working example shown. The duration t.sub.B of the grain transformation is approximately equal to the duration t.sub.C of the induction hardening in the working example shown.

(9) FIG. 2 represents a microstructure distribution as is established after the local induction hardening C without the process steps A and B according to the disclosure having taken place, i.e. as is present in the case of conventional induction hardening. The distribution in FIG. 2 is comparatively broad; the microstructure is thus comparatively heterogeneous.

(10) A section of the microstructure shown in FIG. 4 resulting from a conventional process as per FIG. 2 shows this heterogeneity in respect of ferrite and perlite.

(11) FIG. 3 represents the microstructure distribution as is established before the local induction hardening C but after the two process steps A and B according to the disclosure have proceeded. The distribution as shown in FIG. 3 is comparatively narrow, and the microstructure is thus comparatively homogeneous. The hardness distribution after induction hardening C has been carried out will accordingly be homogeneous.

(12) FIG. 5 clearly shows this more homogeneous microstructure after the two process steps A and B according to the disclosure and the local induction hardening C have occurred.

(13) A process for the local hardening of a workpiece, in which a local induction hardening is preceded firstly by a local, brief, in particular inductive, diffusion heat treatment and then a grain transformation, in particular perlitization, so that after the latter step and before the induction hardening a microstructural state is locally homogenized in respect of ferrite/perlite before induction hardening is disclosed.