JPH0563523B2 - - Google Patents

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a method for correcting heat treatment distortion, and more specifically, for correcting quenching distortion due to deformation and dimensional change accompanying carburizing and quenching treatment of carburized and quenched parts. The present invention relates to a method for correcting heat treatment distortion that can be performed.

[Prior art]

Carburizing and quenching treatment is widely applied to functional parts that require high strength, such as gears and shaft-shaped parts.

However, in carburizing and quenching, quenching distortion (hereinafter simply referred to as quenching distortion) occurs due to deformation and dimensional change of parts based on thermal stress and transformation stress during carburizing and quenching. In post-processing, this often causes problems such as poor functional quality of parts and poor assembly.

Conventionally, as a method for correcting quenching distortion in carburized and quenched parts, an external force is applied to the part in a carburized and quenched state to cause plastic deformation to correct quenching distortion.

Usually, by a method called press tempering, after carburizing and quenching, the material is heated to 150 to 180°C with an external force applied to correct the quenching distortion, and is plastically deformed to correct the quenching distortion.

Methods such as these are being implemented.

However, in the method (2), there is a limit to the amount of plastic deformation for straightening quenching strain, and therefore the straightening effect is insufficient.

In addition, in the method (2), plastic deformation is performed by applying an external force for straightening quenching strain at the above-mentioned temperature, which can cause a diffusion reaction of carbon in the steel. When correcting the inner diameter distortion of a cylindrical part with an outer diameter of 90 mm, an inner diameter of 56 mm, and a length of 30 mm, as shown in Figure 2, in order to obtain a large amount of correction with a small external force, it is necessary to correct it at a high temperature or at a low temperature. It is necessary to carry a load for a long time.

However, when straightening is carried out at a temperature of 200°C or higher, the surface hardness of the carburized parts decreases due to the tempering effect, resulting in functional problems such as insufficient wear resistance.

For this reason, it is necessary to keep the heating temperature below 180℃, and even if press tempering is performed at such a low temperature for a long period of time, a large external force may be required depending on the amount of quenching strain correction required. be.

[Purpose of the invention]

The present invention corrects the quenching distortion caused by the carburizing and quenching treatment of carburized and quenched parts by first adjusting the carburizing and quenching treatment conditions and carrying out the carburizing and quenching treatment, thereby leaving a predetermined amount of residual austenite. After that, the quenching strain is corrected by applying an external force for strain correction during the martensitic transformation process, which is a non-diffusion transformation of carbon in steel. It is an object of the present invention to provide a method for correcting heat treatment distortion, which can correct quenching with extremely low load and in a short time.

[Structure of the invention]

According to the present invention, such an object is to correct heat treatment distortion for correcting quenching distortion due to deformation and dimensional change due to carburizing and quenching treatment of carburized and quenched parts, and to correct heat treatment distortion in which the amount of retained austenite is 20% by volume. A process of carburizing and quenching by adjusting the carburizing and quenching conditions such as the carbon potential of the atmosphere and quenching temperature so that the carbon potential of the atmosphere and quenching temperature are 30%, and correcting the quenching distortion of the carburized and quenched parts as described above. This is achieved by a method for correcting heat treatment distortion, which comprises the steps of performing sub-zero treatment at a temperature that allows residual austenite to transform into martensite while a load is applied.

〔Example〕

Embodiments of the present invention will be described below based on the accompanying drawings.

FIG. 3 is a diagram showing carburizing and quenching conditions in the method for correcting quenching distortion according to the present invention.

In Figure 3, the vertical axis shows the amount of retained austenite generated on the part surface, and the horizontal axis shows the carbon potential of the carburizing atmosphere during quenching. , shows the carbon potential adjustment range of the atmosphere.

That is, the carbon potential is 0.7 to 0.95% based on curve A at a quenching temperature of 950°C, and
At a quenching temperature of 900℃, the carbon potential is increased by 0.7% to 1.0% based on curve B, and the quenching temperature is
At 850°C, the carburizing atmosphere is adjusted so that the carbon potential is 0.7 to 1.05% based on curve C, so that the amount of retained austenite in the carburized and quenched parts is 15 to 40%.

However, even if the amount of retained austenite is within this range, if the retained austenite is small, the quenching strain correction effect will be relatively small, and if the retained austenite is too large, the strength of the part will be reduced, or the retained austenite will be reduced. Since it is stabilized and does not completely transform into martensite, the quenching strain correction effect tends to reach a plateau.

From the above, in order to fully exhibit the effect of correcting quenching distortion, it is desirable to adjust the carbon potential of the carburizing atmosphere and the quenching temperature so that the amount of retained austenite is 20 to 30%.

FIG. 4 schematically shows a device for correcting quenching distortion.

The part 1 having quenching distortion that requires straightening is carburized and quenched under the above-mentioned carburizing and quenching treatment conditions, and is mounted on a fixing jig 3 disposed in a quenching strain straightening treatment tank 2. 4, the necessary load P is applied by a method such as hydraulic pressure, and at the same time, a coolant 7 consisting of liquid nitrogen or a mixture of alcohol and dry ice is injected from the coolant inlet 5 to immerse the part 1,
After holding the temperature of part 1 for a time of -80 to -100°C and discharging the coolant 7 from the coolant discharge port 6, the load P is removed and the part 1 is taken out to complete the correction of quenching distortion. It is something to do.

FIG. 5 is a diagram showing the quenching distortion correction effect by the method of the present invention.

In this figure, the vertical axis is a constant load from the direction of the arrow on a ring-shaped part shown in Figure 1, which has been carburized and quenched by adjusting the carburizing and quenching conditions so that the amount of retained austenite is 20 to 30%. The ratio of the amount of quenching distortion correction to the load is shown, and the horizontal axis shows the load application time (coolant immersion time).

As is clear from FIG. 5, compared to the conventional method for correcting heat treatment distortion shown in FIG.
Moreover, it can be done effectively.

[Function and effect of the invention]

As is clear from the above, according to the method for correcting heat treatment distortion according to the present invention, the quenching distortion caused by the carburizing and quenching treatment of carburized and quenched parts can be corrected by first adjusting the carburizing and quenching treatment conditions. Strain straightening method consists of leaving a predetermined amount of retained austenite remaining through charcoal quenching, and then applying an external force to straighten the quenching strain during the martensitic transformation process, which is a non-diffusion transformation of carbon in steel. It has the advantage that quenching distortion can be corrected with a significantly lower load and in a shorter time than in the conventional method.

[Brief explanation of the drawing]

Fig. 1 is a cross-sectional view of a ring-shaped test piece used for evaluating the quenching strain correction effect by the method of the present invention, Fig. 2 is a graph showing the quenching strain correction effect by the conventional press tempering method, and Fig. 3 is a graph showing the quenching strain correction effect by the conventional press tempering method. , a graph showing the relationship between the carbon potential of the atmosphere and the amount of retained austenite in carburizing and quenching treatment, FIG. 4 is a schematic diagram of a quenching strain correction device according to the method of the present invention, and FIG. It is a graph showing the correction effect. 1... Parts, 2... Quenching distortion straightening treatment tank, 3...
Fixing jig, 4...Jig, 5...Cooling medium inlet, 6
...Cooling medium outlet, 7...Cooling medium, P...Load,
A, B, C...curve.

Claims (1)

[Scope of Claims] 1. A heat treatment distortion correction method for correcting quenching distortion due to deformation and dimensional change accompanying carburizing and quenching treatment of carburized and quenched parts, wherein the amount of retained austenite is 20 to 30% in volume ratio. The process involves adjusting the carburizing and quenching conditions such as the carbon potential of the atmosphere and the quenching temperature, and applying a load to correct the quenching distortion of the carburized and quenched parts as described above. A method for correcting heat treatment distortion, comprising: performing sub-zero treatment under load at a temperature that allows retained austenite to transform into martensite.