JP2003213324A - Method for quenching metallic member - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a quenching method which achieves a prescribed rapid cooling by completing a film boiling process for a short time. <P>SOLUTION: In the quenching method which rapidly cools by dipping a metallic member into liquid, after applying an oxide film forming treatment to at least a part of the metallic member, this member is dipped into the liquid. The oxide film can be formed to the whole body of metallic member or the oxide film can be formed on only a portion, at where the cooling speed is slower than that of the other portion, when the metallic member is quenched. The metallic member may be formed with at least one method of casting, forging, rolling and machining. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a quenching method of quenching a metal member by immersing it in a liquid, and more particularly to a quenching method of a metal member formed by casting, forging, rolling, machining or the like.

[0002]

2. Description of the Related Art Quenching of a metal member is typically performed by quenching for quenching, which is represented by an iron-based material, and quenching for solution treatment, which is represented by an aluminum-based material. Quenching to prevent the formation of unnecessary phases. As the quenching method, quenching by immersing it in a liquid such as water as a quenching medium is the most convenient and widely used.

In such quenching by immersion in a liquid, when a high temperature metal member is immersed in the liquid, vapor generated on the surface of the member forms a film and covers the surface of the member, so that heat transfer from the member to the liquid is hindered. To be done. In the cooling process of cooling from immersion in the liquid to the liquid temperature, especially in the cooling stage where the metal member is still at a high temperature after the immersion, the vapor film is likely to be maintained, so the cooling is slow. When entering the cooling stage at a lower temperature, rapid cooling is performed because the vapor film is destroyed by intense bubble generation due to nucleate boiling and heat transfer is enhanced. When the cooling step at a lower temperature is started, no bubbles are generated, and the convection of the quenching liquid causes slow cooling. As described above, in the liquid immersion quenching, in order from the high temperature region, (I) a slow cooling step by vapor film formation (film boiling step), (II) rapid cooling step by nucleate boiling, and (III) low speed cooling step by convection. 3 stages appear.

FIG. 1 shows a specific example of the quenching and cooling process. That is, when the aluminum alloy test piece shown in FIG. 1 (1) is water-cooled at 85 ° C. in the posture shown in FIG. 2 (2), the above (I) (II) (III) ) Each stage appears.

Here, in particular, the above-mentioned (I) film boiling step has a great influence on the intended rapid cooling. That is, in the high temperature region, the diffusion rate of the component elements is high, so that if the cooling is slow, various component elements will be precipitated in the cooling process, and predetermined quenching cannot be performed.

Japanese Unexamined Patent Publication (Kokai) No. 8-31134 proposes to drop a metal member through a bent inclined path in a quenching tank to give an impact to remove the vapor film and increase the cooling rate.

However, the above conventional method has the following problems. That is, the impact may cause the metal member to be deformed or damaged. Furthermore, since it is not possible to selectively give an impact only to a part having a slow cooling rate depending on the shape of the member, the cooling rate of the entire member cannot be made uniform,
It is impossible to prevent the occurrence of residual strain after quenching.

[0008]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a quenching method capable of realizing a predetermined rapid cooling by finishing a film boiling step in a short time.

[0009]

In order to achieve the above object, a quenching method according to the present invention is a quenching method in which a metal member is rapidly cooled by being immersed in a liquid, and at least a part of the metal member is oxidized. It is characterized in that it is immersed in the above liquid after the film forming treatment.

The oxide film forming treatment in the present invention refers to a treatment for further promoting the formation of an oxide film in addition to the formation of an oxide film inevitably occurring in a manufacturing process at high temperature such as casting and heat treatment. In the present specification, the description that the oxide film is formed according to the present invention means that the above-mentioned oxide film formation treatment is performed to promote the formation of the oxide film.

The present inventor has completed the present invention by finding that when immersion quenching is performed with an oxide film formed on the surface of a metal member, film boiling ends in a short time and the cooling rate increases.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION In the quenching method of the present invention,
When the difference in cooling rate between the parts can be substantially ignored, the cooling rate can be increased over the entire member by forming an oxide film on the entire metal member. For example, even if the shape of the metal member is simple, or even if the shape is somewhat complicated and the cooling rate differs depending on the part, there is a substantial difference in the quenching effect (quenching hardness, achievement of solution treatment, etc.) depending on the part. In this case, the residual strain can be ignored.

On the other hand, when the difference in cooling rate depending on the site cannot be substantially ignored, the cooling of the specific site is performed by forming the oxide film only on the specific site where the cooling rate during quenching is slower than other sites. The cooling speed of the entire member can be made uniform by increasing the speed. For example, this corresponds to a case where the shape of the metal member is complicated, or a case where the difference in the quenching effect due to the site cannot be ignored due to the difference in the cooling rate depending on the site even if the shape is not so complicated.

The quenching method of the present invention can be applied to metal members formed by any of casting, forging, rolling, machining and the like.

[0015]

EXAMPLE A quenching experiment was performed by forming an oxide film according to the present invention using a water jacket mini model made of an aluminum alloy (JIS AC4CH) whose schematic shape and dimensions are shown in FIG.

(1) Measurement of Quenching and Cooling Curve The above mini model was produced by applying an oxidizing agent to a sand mold under the following conditions and performing casting.

Oxidizing agent application conditions: A 10 wt% potassium nitrate aqueous solution was applied at an application amount of 50 mg / cm ² to the site corresponding to the sand type mini model port portion (sand type core).

Casting conditions: The above aluminum alloy was heated to a temperature of 7
It was melted at 50 ° C and cast in the sand mold at a casting temperature of 720 ° C.

In the cast mini model, an oxide film having a thickness of 440 μm is formed on the port P where the oxidizing agent is applied to the sand mold, and the oxide film thickness of the portion where the oxidizing agent is not applied to the sand mold is 190 μm. Met.

Using a mini model cast under the same conditions as above, heat treatment was performed under the following conditions.

Heat treatment conditions (T6 treatment): Solution heat: 530 ° C. × 3 hours Quenching: 80 ° C. Water cooling aging 170 ° C. × 3 hours During the solution quenching, temperature measurement was performed on the inside and outside surfaces of the port in FIG. Was done. As a comparative example, heat treatment and temperature measurement were performed under the same conditions as above for a mini model produced under the same conditions except that the sand mold was not coated with the oxidizing agent. The temperature measurement result is shown in FIG.

First, FIG. 3 (1) shows a temperature measurement result at the time of solution hardening for a mini model cast without applying an oxidizing agent to a sand core as a comparative example. It can be seen that the cooling curve shifts to the long side and the cooling rate is slow.

On the other hand, FIG. 3 (2) shows the temperature measurement results during solution hardening of a mini model cast by applying an oxidizer to a sand core as an example of the present invention. It can be seen that the cooling curves match well with the surface. This is because the film boiling step (I) shown in FIG. 1 was shortened especially at the port portion.

(2) Measurement of Quenching Residual Strain Next, a water jacket mini model cast under the same conditions as in (1) above except that the amount of the oxidizer applied to the sand core was set to 25 mg / cm ² Heat treatment was performed under the same conditions as 1), and the residual strain of the port portion P was measured. In this case, the oxide film thickness of the port portion was 250 μm.

As a comparative example, the residual strain of the port portion was similarly measured for a mini model cast without applying an oxidizing agent. In this case, the oxide film thickness of the port portion was 190 μm.

In any case, the measurement points were four points M1 to M4 in the port P as shown in FIG. The residual strain was measured as the strain released when the port portion was cut out from the mini model after heat treatment. The measurement results are shown in FIG.

As shown in the figure, in each of the measurement points M1 to M4, the example of the present invention in which the oxidation promoting treatment was performed with the oxidizing agent to form the oxide film having a thickness of 250 μm was performed without performing the oxidation promoting treatment with the oxidizing agent. Film thickness is 190 μm
It can be seen that the residual strain is significantly reduced compared to the comparative example.

(3) Relationship between coating amount of oxidizer and residual strain after quenching The coating amount of the oxidizer on the sand mold core was variously changed within the range of 0 to 50 mg / cm ² , and after heat treatment as in (2) above. Was measured for residual strain. FIG. 5 shows the results of measurements performed under the same conditions and with the number of repetitions n = 8.

As shown in the figure, according to the present invention, when a small amount of oxidizer is applied, the residual strain at the port portion decreases, and the residual strain monotonically decreases as the amount of oxidizer applied increases. However, if the coating amount exceeds 60 mg / cm ² , casting defects may occur, so the coating amount is preferably 60 mg / cm ² or less. Although it is not possible to clearly determine the lower limit of the coating amount from the results shown in the figure, since the residual strain reducing effect is already clearly recognized at the minimum coating amount of 10 mg / cm ² used in this example, the lower limit of the coating amount is set. It is estimated to be about 5 mg / cm ² .

In this embodiment, the oxidizing agent is applied to the sand mold, but as another method, it is also possible to mold the oxide film forming target portion with mixed sand in which the oxidizing agent is mixed with the foundry sand. In that case, it is appropriate that the mixing amount of the potassium nitrate powder as the oxidizing agent is 3 wt% or more and less than 20 wt% of the mixed sand. If the mixing amount of the oxidizing agent is too small, the effect of forming an oxide film cannot be obtained, and if the mixing amount is too large, the moldability may be deteriorated and a casting defect may be caused.

In this embodiment, the sand mold was used for casting, but the present invention can also be applied to metal mold casting. In that case, for example, potassium nitrate powder as an oxidizing agent can be dissolved in a release agent so as to be 20 wt% or less and applied to a mold.

[0032]

According to the present invention, by quenching after forming an oxide film on a metal member, the film boiling step is completed in a short time and a predetermined rapid cooling can be realized.

Further, by forming the oxide film only on the portion where the quenching cooling rate becomes slow and then quenching,
The quenching cooling rate can be made uniform over the entire metal member, and the quenching residual strain can be reduced or eliminated.

[Brief description of drawings]

FIG. 1 shows a specific example of quenching by water cooling,
(1) A plan view showing a test piece shape, (b) a side view, (2) a cross-sectional view showing a quenching posture, and (3) a graph showing a quenching cooling curve.

FIG. 2 is (1) a plan view and (2) a cross-sectional view showing a schematic shape and dimensions of a water jacket mini model used in a quenching experiment according to the present invention.

FIG. 3 shows quenching and cooling curves of the inside and the outside of the port of the mini model for (1) a comparative example not using an oxidant and (2) an example of the present invention in which the formation of an oxide film was promoted by the oxidant. It is a graph shown.

FIG. 4 is a graph showing comparative results of quenching residual strain measurement for a comparative example not using an oxidizing agent and an example of the present invention in which formation of an oxide film was promoted by the oxidizing agent.

FIG. 5 is a graph showing a relationship between an applied amount of an oxidant for forming an oxide film and a residual strain after quenching according to the present invention.

─────────────────────────────────────────────────── ─── Continued Front Page (51) Int.Cl. ⁷ Identification Code FI Theme Coat (Reference) C23C 8/04 C23C 8/04 8/10 8/10 8/80 8/80

Claims (4)

[Claims] 1. A quenching method of quenching a metal member by immersing it in a liquid, characterized in that at least a part of the metal member is subjected to an oxide film forming treatment and then immersed in the liquid. Hardening method for metal parts. 2. The method according to claim 1, wherein the oxide film is formed on the entire surface of the metal member. 3. The method according to claim 1, wherein the oxide film is formed only on a portion where the cooling rate during quenching of the metal member is slower than other portions. 4. The method according to claim 1, wherein the oxide film is formed by casting the metal member using a mold coated or mixed with an oxidizing agent.