JP2000144235A - Heat treatment for strengthening surface of metallic formed product - Google Patents

Abstract

PROBLEM TO BE SOLVED: To easily execute the strengthening of the surface of a metallic formed product with jetting shots. SOLUTION: The shots having 20-200 μm size and the same or higher hardness as the formed product hardness are jetted at >=50 m/sec jetting speed by using low temp. compressed gas. The temp. near the surface is raised to A3 transformation point or higher to a ferrous metallic formed product and to recrystallizing temp. or higher to non-ferrous metallic formed product, and also, instantially cooled to room temp. or with the low temp. compressed gas. The low temp. compressed gas is desirable to be <=0 deg.C.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for heat treating a surface of a metal product, and more particularly, to a method for rapidly heating the surface of a metal product by impact of a shot and rapidly cooling the surface to a room temperature or lower by a low-temperature compressed gas. Accordingly, the present invention relates to a heat treatment method for strengthening the surface of a workpiece.

[0002] In this specification, "normal temperature" is synonymous with "room temperature", and "low temperature" is the same as "normal temperature".
Refers to the following temperatures.

[0003]

2. Description of the Related Art As a method for locally heat-treating the surface of a metal product, shot peening is performed on the surface of iron and an iron-based alloy (hereinafter referred to as "iron-based metal") as disclosed in Japanese Patent No. 1594305. A method of instantaneously heating the surface of a metal product by the impact of a shot and obtaining an improvement in fatigue strength and the like by a self-quenching action to room temperature has already been performed.

In addition to the above-described treatment by shot peening, there are laser quenching, electron beam quenching and the like as a method of performing surface treatment on metal products.

[0005] Among these, laser quenching involves irradiating the surface of a metal product made of steel with a laser beam having a high energy density and quenching and hardening by a self-cooling effect. Heating by a laser is super rapid, and quenching is self-cooling. Therefore, the surface of the irradiated portion can be quenched and hardened in a short time.

[0006] Electron beam quenching is a method in which an electron beam is scanned on a surface of a metal product in a vacuum and heated, and then self-cooling quenching is performed. How to

[0007]

As described above, it is possible to carry out a surface strengthening treatment of a metal product by various methods, but it is difficult to perform laser quenching or electron beam quenching which requires irradiation of a laser beam or an electron beam. Therefore, complicated and expensive means for generating a laser or an electron beam are required.Especially, in the case of electron beam quenching, a vacuum is required for the irradiation of the electron beam. Requires significant capital investment.

For example, when the above-mentioned surface hardening by shot peening or the effect of quenching by a laser beam or an electron beam is obtained, a desired processing strengthening can be obtained with a normal iron-based metal. In metal products made of low non-ferrous metals and their alloys (hereinafter referred to as "non-ferrous metals"), the effect of quenching by a laser beam or an electron beam cannot be sufficiently obtained as compared with general ferrous metal products. There are cases.

That is, in the case of a non-ferrous metal having a low recrystallization temperature, even if the shot-peened portion is cooled to room temperature after the shot peening, it does not rapidly cool, and is obtained from the ferrous metal. It was found that it was not possible to obtain a fine structure and high density.

After the quenching, a sub-zero treatment is further performed to cool the quenching to a temperature lower than the room temperature. By this sub-zero treatment, austenite which still remains in a state cooled to room temperature is transformed into martensite, thereby improving hardness and preventing aging deformation, aging deformation and the like.

However, such sub-zero treatment is to cool steel once quenched to room temperature or lower using a coolant or the like. Such treatment is performed by laser beam, electron beam irradiation or the like. It must be performed separately from the quenching step. Therefore, when performing the process, it is necessary to separately provide one step for the sub-zero process, which complicates the operation and increases the cost for the process.

An object of the present invention is to solve the above-mentioned drawbacks in the prior art, and is intended to improve the surface quality of a metal product during a surface strengthening heat treatment by shot peening which can be performed by relatively simple equipment. Metal products that can be suitably subjected to surface strengthening to impart effects such as improvement in hardness, aging deformation, and prevention of aging deformation even for non-ferrous metals having a low recrystallization temperature by rapidly cooling to below normal temperature. An object of the present invention is to provide a surface strengthening heat treatment method.

[0013]

Means for Solving the Problems In order to achieve the above object, the surface treatment heat treatment method of the present invention is characterized in that a low-temperature compressed gas of 20 to 200 μm having a hardness equal to or higher than the hardness of a metal product is formed on the surface of a metal product. used jet velocity 50 m / sec or more, or injected in injection pressure 0.2Mpa or more, the temperature in the vicinity of the surface, or more a ₃ transformation point for ferrous metallic product,
Non-ferrous metal products are characterized in that they are raised to a temperature higher than the recrystallization temperature and are rapidly cooled to a room temperature or lower by the low-temperature compressed gas instantaneously.

It is preferable that the low-temperature compressed gas has a temperature of room temperature or lower, preferably 0 ° C. or lower.

As the low-temperature compressed gas, various gases such as argon and nitrogen can be used. Preferably, a vaporized gas of nitrogen, more preferably, liquid nitrogen is used.

When nitrogen is used as the low-temperature compressed gas, the metal product may contain a nitrogen-reactive component.

Further, as the shot, metal or ceramic or a mixture thereof is preferably used, and more preferably, a spherical shot is used.

Here, the shots include not only metal and synthetic resin but also fine particles and fine particles used for any grinding or surface cleaning. Grid). In this specification, shot peening is a general term for a means for injecting a solid-gas two-phase flow of a shot of a metal or the like and a gas,
Including so-called blast or sand blast.

The average particle diameter is represented by the average of the average diameter of the largest particle and the average diameter of the 30th particle from the largest particle.

For example, a fine powder having an average particle diameter of 80 μm has an average diameter of the largest particle of 171 μm or less, an average diameter of the 30th particle from the largest particle is 120 μm or less, and an average of the average diameter of 87.5 to 73.5 μm. (JISR6001).

The operation of the present invention will be briefly described as follows. By blasting, when a shot is sprayed on the surface of the metal product at a high injection speed, the speed change before and after the shot hits the surface of the metal product,
Considering the law of energy invariance, heat energy is generated. Since this energy conversion is performed only at the deformed portion where the shot collides, the temperature near the surface of the metal product locally rises.

Since the temperature rise is proportional to the speed of the shot before the collision, if the shot injection speed is increased,
The temperature of the surface of the shot and the metal product can be raised to a higher temperature. As an example, a shot of 20 to 200 μm having a hardness equal to or higher than the base material of a metal product is taken for 50 m.
/ sec or more ejection velocity, or by spraying the above injection pressure 0.2 Mpa, with the iron-based metal or more A ₃ transformation point, in the non-ferrous metals of the metallic product to above the recrystallization temperature The surface temperature can be locally increased instantaneously.

On the other hand, since the low-temperature compressed gas for injecting the shot is at room temperature or lower, preferably 0 ° C. or lower, the metal heated to a high temperature above the A ₃ transformation point or above the recrystallization temperature by injection of the shot is used. wherein the cold compressed gas is blown with shots on the surface of the finished product, the local surface of the blown metallic product of this cold compression gas, to temperatures higher than a ₃ transformation point or above or recrystallization temperature by collision with the shot From the heated state, the metal product is rapidly cooled to a temperature equal to or lower than room temperature, the structure of the surface of the metal product is suitably fine, and the mechanical strength can be improved, and aging deformation and aging deformation can be suitably prevented. That is, in the present invention, because of the low temperature, the metal is hardly deformed, and the slip of the grain boundary is hardly generated. Therefore, the impact energy is not absorbed and the heat becomes high, and as a result, the rapid heating / cooling action is obtained, and the structure of It is considered that miniaturization and high density are achieved.

[0024]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, embodiments of the present invention will be described below with reference to the accompanying drawings.

According to the method of the present invention, a shot is injected with a low-temperature compressed gas by a blasting device to impinge on the surface of a metal product, and the shot is accelerated using a known air-type blasting device. Can be.

Various types of pneumatic blasting devices can be used. For example, compressed air is supplied into a tank in which shots are charged, and shots conveyed by the compressed air are separately given. A direct-pressure blasting device that blasts from a blast gun on the air flow of compressed air, a gravity-type blasting device that blasts shots dropped from the shot tank by gravity onto the compressed air, and a negative pressure generated by the injection of compressed air Various blasting devices such as a siphon blasting device that suctions a shot by pressure and sprays the shot with compressed air can be used.

In the present invention, the gas for accelerating the shot in the blast device uses a low-temperature compressed gas instead of the compressed air. As the low-temperature compressed gas, air and other gases passed through a refrigerant, dry ice, liquid nitrogen, gas obtained by vaporizing liquid helium, and the like, and a low-temperature gas at room temperature or lower, preferably 0 ° C. or lower Various gases can be used. In the present embodiment, nitrogen gas which can be obtained inexpensively by removing oxygen from liquefied air, in particular, a vaporized gas of liquid nitrogen which can easily obtain a low-temperature gas of 0 ° C. or less by vaporization is used. I have.

In this embodiment, an example in which a direct pressure type and a gravity type are used among the air type blasting devices will be described, and the description of other types will be omitted.

[Embodiment 1] A direct-pressure blast apparatus 30 shown in FIG. 1 is provided with a nozzle 32 for ejecting abrasives such as shots in a cabinet 31 having an entrance 35 through which a workpiece W is put in and out. A hopper 38 is provided at a lower portion of the hopper 31, and a lowermost end of the hopper 38 communicates via a conduit 43 with an upper side surface of a collection tank 33 installed separately and adjacent to the cabinet 31.

Further, a recovery tank 33 is provided above, and a tank 51 for shot pressure feeding is provided below the recovery tank 33 via a dump valve 52, and the lower end of the tank 51 is connected via a shot adjuster 53. The pipe 54 communicates with the nozzle 32 provided in the cabinet 31.

In the recovery tank 33, as a shot, S after carburizing, quenching and tempering, which is the base material of the gear as the workpiece W,
A shot of a high-speed steel having an Hv900 higher than the hardness of the CM steel and having an average shot diameter of 0.1 mm (# 150) is introduced.

When a gear as the workpiece W is inserted into the cabinet through the entrance 35 and a foot switch or a micro switch (not shown) is operated, the electromagnetic valve is operated, the dump valve 52 in the tank 51 is raised, and the collection tank 33 is moved. And the communication with the tank 51 is cut off. At the same time, a low-temperature compressed gas, in this embodiment, nitrogen is fed into the tank 51 from a supply source of a low-temperature compressed gas (not shown). The shot in the tank 51 and the compressed gas pressed by the compressed gas enter the lower abrasive controller 53 of the tank 51, and the low-temperature compressed gas and the shot are appropriately adjusted by the abrasive controller 53. The mixed gas enters the pipe 54 and is injected from the nozzle 32 at an injection pressure of 0.39 Mpa, a compressed gas temperature of 0 ° C., and an injection distance of 20.
At 0 mm, it is sprayed onto the surface of the gear that is the workpiece W.

After injecting shots in three directions for 60 seconds from each direction for one gear, when the switch is returned to the original position, the low-temperature compressed gas in the tank 51 escapes into the recovery tank 33, The pressure in the tank 51 becomes atmospheric pressure. Immediately before that, if the dump valve 52 is pushed down, the ejection of the shot stops immediately. At the same time, the collection tank 33
Shots accumulated at the bottom of the collection tank 33 fall into the tank 51 at a stretch from the gap between the tank and the dump valve 52.

The abrasive 36 and the dust 37 generated at this time are transferred to the lower hopper 3 of the cabinet 31.
8, the ascending airflow generated in the conduit 43, the ascending airflow is sent to the collection tank 33, and the abrasive 36 is collected. The dust 37 in the collection tank 33
The dust is guided from the upper end of the collection tank 33 to the dust collector 34 via the pipe 42 by the airflow inside the dust collector 34.
, And clean gas is discharged from an exhaust fan 39 provided above the dust collector 34.

The processing conditions of the above-described direct-pressure blast device are as follows. It should be noted that, in the present invention, nitrogen (0 ° C.) was used as the injection gas, whereas in Comparative Example 1, air at room temperature (28 ° C.) was used, and other processing conditions were common. And

[0036]

[Table 1] Processing conditions

Table 2 shows the results of comparison of the surface internal residual stress and the surface hardness of the metal product of the present invention processed under the above conditions and the metal product of Comparative Example 1.

[0038]

[Table 2] Comparison results

As described above, when a gear made of SCM steel after carburizing, quenching, and tempering was subjected to surface processing by the method of the present invention, the surface portion was compared with the gear processed under the conditions of Comparative Example 1. Is 200Mp at internal residual compressive stress
a) It was confirmed that the surface hardness was improved by 200 Hv.

Therefore, the rapid cooling using nitrogen at 0 ° C. as the low-temperature compressed gas contributes to the improvement of the residual compressive stress inside the surface of the metal product, and thus to the improvement of the peening effect on the fatigue strength and the improvement of the surface hardness. it is obvious.

[Embodiment 2] In this embodiment, an example in which a gravity type blast device is used as an example of a shot acceleration device will be described. In addition, the gravity type blast device 30 is for injecting the shot dropped by gravity from the shot tank onto the compressed air as described above, and in the present embodiment, the shot is collected in the collection tank 33 which is the shot tank. ♯
400 (40 μm), alumina and silica beads having a hardness of about 1000 Hv are charged, and a shot dropped by gravity from the recovery tank 33 is introduced into the nozzle 32 through the conduit 41. It is configured so that it can be joined with a conduit 44 communicating with a supply source, and can be accelerated by being loaded on a low-temperature compressed gas introduced through the conduit 44 (see FIG. 2).

The point that nitrogen at 0 ° C. is used as the cooling compressed gas introduced into the blast device 30 and that the device includes a dust collector 34 having an exhaust fan 39 and a cabinet 31 are as described above. This is the same as the direct pressure type blast device in the first embodiment.

A piston made of an aluminum alloy was subjected to the surface treatment of the present invention by the above-described gravity type blast apparatus. The processing conditions are as shown in Table 3 below.

[0044]

[Table 3] Processing conditions

Table 4 shows the results of comparison between the residual internal compressive stress and the hardness of the surface of the piston processed by the method of the present invention and the aluminum alloy piston processed under the conditions of Comparative Example 2.

[0046]

[Table 4] Comparison results

As described above, as shown in Table 4, in the piston made of the aluminum alloy, the internal residual stress on the surface was 110 Mp.
a, It was confirmed that the surface hardness was improved by 100 Hv or more. Therefore, it was confirmed that the method of the present invention is effective not only for ferrous metals but also for non-ferrous metals such as aluminum alloys.

Example 3 The results of the surface processing by the method of the present invention on a connecting rod made of a 6Al 4V titanium alloy are shown below.

In this embodiment, a direct pressure blasting device similar to that of the first embodiment is used.
A shot of 900 Hv, high-speed steel was replaced with nitrogen (0
° C) at an injection pressure of 0.39 Mpa for about 3 minutes. Table 5 shows the processing conditions.

[0050]

[Table 5] Processing conditions

Table 6 shows the results of comparing the internal residual stress and the surface hardness of the connecting lot of the 6Al 4V titanium alloy of the present invention processed under the above-described processing conditions with the surface of the connecting lot processed under the conditions of Comparative Example 3.

[0052]

[Table 6] Comparison results

As shown in Table 6, the connecting lot processed by the method of the present invention showed an improvement of 110 Mpa in internal residual stress on the surface and 100 Hv in surface hardness as compared with that of Comparative Example 3. Therefore, it is clear that the method of the present invention can be suitably used for non-ferrous metals such as titanium alloys.

As described in Examples 1 to 3, when nitrogen is used as the low-temperature compressed gas,
When the metal product contains a nitrogen-reactive component such as Ti, V, Al, or Cr, it is considered that the surface of the metal product has undergone micronitridation. That is, a shot is injected using low-temperature compressed nitrogen, and the shot collides with the surface of the metal product, so that the surface temperature of the metal product increases to the diffusion and penetration temperature of nitrogen. It is considered that the above-mentioned nitrogen reaction component and nitrogen, which is a low-temperature compressed gas, are simultaneously activated and reacted to perform nitriding.

Therefore, by injecting a shot with a low-temperature compressed gas of nitrogen into a metal product containing a nitrogen reaction component, it is possible to expect an effect of surface strengthening such as improvement of surface hardening by fine nitriding of the metal product. .

[0056]

According to the configuration of the present invention described above, according to the method of the present invention, by using a low-temperature compressed gas at the time of shot injection, rapid heating due to the impact of the shot on the surface of the metal product, The surface of the metal product can be suitably strengthened by quenching by blowing a low-temperature compressed gas at room temperature or lower onto the metal product surface, and not only a metal product having a ferrous metal as a base material but also a non-ferrous metal having a low remelting temperature. The strengthening treatment by shot peening was able to be suitably performed also on metal products having a base metal as a base material.

When nitrogen is used as the low-temperature compressed air for accelerating the shot, and when the metal product is made of a base material containing a nitrogen reactive component, the chemical generated by heat generated when the shot collides with the surface of the metal product is used. Due to the change, nitrogen was diffused and permeated into the surface of the metal product to obtain the effect of micronitridation, and the surface of the metal product could be suitably strengthened.

[Brief description of the drawings]

FIG. 1 is a schematic diagram of a direct pressure blast device.

FIG. 2 is a schematic view of a gravity type blast apparatus.

[Explanation of symbols]

 REFERENCE SIGNS LIST 30 blast device 31 cabinet 32 nozzle 33 recovery tank 34 dust collector 36 shot 38 hopper 39 exhaust fan 41 conduit 42 pipe 43 conduit 44 conduit 51 shot pumping tank 52 dump valve 53 shot adjuster 54 pipe

Claims (5)

[Claims] 1. A shot of 20 to 200 μm having a hardness equal to or higher than the hardness of a metal product on a surface of a metal product using a low-temperature compressed gas at a spray speed of 50 m / sec or more, or a spray pressure of 0.1 μm.
Injected above 2Mpa, the temperature in the vicinity of the surface than A ₃ transformation point for ferrous metallic product, the non-ferrous metallic product with increase above the recrystallization temperature, quenched instantaneously higher than room temperature by the cold compressed gas A method for heat-treating a surface of a metal product, comprising the steps of: 2. The method according to claim 1, wherein the low-temperature compressed gas has a temperature of 0 ° C. or lower. 3. The low-temperature compressed gas is nitrogen.
Or the method for heat treating a surface of a metal product according to 2 above. 4. The method according to claim 3, wherein the metal product contains a nitrogen reactive component. 5. The shot according to claim 1, wherein the shot is metal, ceramic, or a mixture thereof.
The method for heat treating a surface of a metal product according to any one of the preceding claims.