Heat treatment method of pin for endless track

摘要

The present invention relates to a method for heat treatment of a columnar work. In order to provide the method for heat treatment of a columnar work being able to attain a high productivity, a reduction of cost, and an improvement of quality, as compared with the prior art, the method for heat treatment of a columnar work of the present invention includes a quench-hardening step (S1) and a tempering step (S2) being carried out after the quench-hardening step (S1), the quench-hardening step (S1) includes a first quench-hardening step (S11) and a second quench-hardening step (S12) being carried out after the first quench-hardening step (S11), the entire region of the columnar work (3) from an outer circumferential surface (31f) to a core thereof (32), or a partial region thereof, is heated up to a temperature not lower than a transformation temperature Ac3, and then, the work is quench-hardened.

主权项

1. A heat treatment method of a pin for an endless track, in which a heat treatment of the pin for an endless track made of a medium-carbon alloy steel is carried out, the method comprising:
a quench-hardening step and a tempering step being carried out after the quench-hardening step; the quench-hardening step includes a first quench-hardening step and a second quench-hardening step being carried out after the first quench-hardening step; the first quench-hardening step is a quench-hardening step in which a partial region in the radius inwardly direction from an outer circumferential surface side of the pin is heated to a temperature not lower than a transformation temperature Ac3, the first quench-hardening step is not a quench-hardening step in which an entire region in the radius inwardly direction from an outer circumferential surface side of the section of the pin is heated to a temperature not lower than a transformation temperature Ac3, and a dimension of the partial region in the radial inwardly direction thereof, which region is heated in the first quench-hardening step, is not less than ⅓ of the radius of the pin and is not more than ¾ of the radius of the pin; the second quench-hardening step is a quench-hardening step in which the outer circumferential surface region of the pin carried out by the quench-hardening in the first quench-hardening step is merely heated by an induction heating to a temperature not lower than the transformation temperature Ac3, in the second quench-hardening step, a depth of the outer circumferential surface region is not less than 1/10 of a radius of the pin for an endless track, and not more than ½ of the radius of the pin for an endless track; the tempering step is a step for low-temperature tempering to the pin carried out by the quench-hardening in the quench-hardening step; and that in a hardness distribution in a cross section of the pin, hardness undergoes a decrease at a first position, corresponding to a location less than ½ of the distance from the outer circumferential surface toward a center of a core in the radial direction of the pin, in the radius inwardly direction from an outer circumferential surface side, and a further decrease at a second position corresponding to ½ of the distance from the outer circumferential surface toward the center of the core in the radial direction of the pin, so as to increase a strength against the maximum shearing stress, a compressive residual stress and a strength for bending load in the pin, wherein the second position is disposed between the first position and the center of the core.