JPH06248416A - Modifying method by mixed gas penetration - Google Patents

Abstract

PURPOSE:To provide the modifying method by mixed gas penetration which prevents the deterioration and variation in modification by penetration occurring in the nonuniformity of treating temp., is good in thermal efficiency, suffices with the smaller amt. of the costly gases to be used, is inexpensive, provides stable wear-, heat- and corrosion resistant surface characteristics in a short period of time and can freely adjust the surface characteristics. CONSTITUTION:A metallic base material is inserted into a modifying surface by penetration and gaseous N2 is injected into this furnace. The temp. of the furnace is increased from room temp. to 200 to 550 deg.C in 10 to 230 minutes. A mixture composed of ammonia, N2 and CO2 or independent gases is heated up near to the temp. in the furnace 1 and are then injected into the furnace. The base material is held at 350 to 590 deg.C for 10 to 1800 minutes in the gaseous mixture composed of the ammonia, N2 and CO2. The CO2, concn. of the gaseous mixture is then increased and the gaseous mixture is discharged after holding for 10 to 900 minutes. The base material is cooled while the N. is further circulated and thereafter, the gases are removed at room temp. to 300 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 improving a metal surface by gas composite permeation.

[0002]

2. Description of the Related Art Conventionally, as a method of modifying the metal surface of machine parts, tools, jigs, dies, etc., the elements of the modifying medium such as carburizing, nitriding, sulfurizing, and boriding penetrate and diffuse into the metal surface layer. There have been proposed many methods of modifying the surface by nitriding the metal base material. For example, as a method of nitriding the metal base material, as disclosed in Japanese Patent Publication No. 3-12140, the metal base material is inserted into a permeation reforming furnace and removed at room temperature. After the vaporization, N ₂ gas is injected into the furnace, and the temperature is 300 to 450 from room temperature.
The temperature is raised to 20 ° C. in 20 to 230 minutes, then heated to 400 to 580 ° C. in a mixed gas of N ₂ and ammonia for 10 to 90 minutes, and then 10 minutes in a mixed gas of ammonia, N ₂ and CO _2. Gas mixture in which the temperature is kept at 400 to 580 ° C. for 240 minutes, then the CO ₂ concentration of the air-fuel mixture is raised and the N ₂ concentration is lowered, and held for 10 to 120 minutes, and further cooled while circulating N _2. Penetration modification methods are known.

Further, in a nitriding method of steel in which the surface of steel is preheated in a furnace at a high temperature and in a nitriding gas atmosphere, and then hardened, vacuum heating is performed at least once during the preheating step, and the nitriding gas is converted into ammonia gas. Gas, oxygen gas, and nitrogen gas are used as a three-component gas, the content rate of ammonia gas in the nitriding gas is in the range of 40 to 60% by volume, and the content rate of oxygen gas in the nitriding gas is 0.2 to 3 By performing vacuum heat treatment during preheating within the range of volume%, a trace amount of impure gas components remaining in the furnace are vaporized and cleaned to remove stains etc. on the surface of the steel and make the steel suitable for nitriding. A method of activation is proposed in JP-A-62-270761.

Among the factors of the permeation modification effect, the treatment temperature has a great influence. However, in these conventional methods, when a mixed gas of ammonia, N ₂ , CO _2, etc. is introduced, the room temperature gas is introduced all at once into the furnace at several hundred degrees, so that the permeation reformed metal surface part and the atmosphere in the furnace are introduced. A large temperature gradient is caused in the furnace, resulting in non-uniform temperature in the furnace, which causes deterioration and dispersion of the permeation reforming.

[0005]

The object of the present invention is to prevent deterioration and variation in permeation reforming due to non-uniformity of treatment temperature, to improve thermal efficiency, and to use less expensive gas.
It is an object of the present invention to provide a gas composite permeation reforming method that is inexpensive and can obtain stable surface properties of abrasion resistance, heat resistance, and corrosion resistance in a short time, and that the surface properties can be freely adjusted.

[0006]

In order to solve the above-mentioned problems, a gas composite permeation reforming method of the present invention inserts a metal base material into a permeation reforming furnace and injects N ₂ gas into the furnace. Then, the temperature is raised from room temperature to 200 to 550 ° C. in 10 to 230 minutes, and the temperature of a mixture of ammonia, N ₂ and CO ₂ or a single gas is raised to a temperature close to the temperature in the furnace and then injected into the furnace,
Then, in a mixed gas of ammonia, N ₂ and CO ₂ , 10
Hold at 350 to 590 ° C. for up to 1800 minutes, then increase the CO ₂ concentration of the air-fuel mixture and hold for 10 to 900 minutes, further cool while circulating N ₂ , and then degas at room temperature to 300 ° C. It is characterized by

Ammonia, N ₂ and C injected into the furnace
A preheater equipped with a heating filter is used for mixing O ₂ or heating a single gas, and the material of the heating filter is
It is made of stainless steel, graphite, ceramic, or various coatings thereof, and is provided with triangular, polygonal, circular, elliptical, etc. holes.

In the mixed gas, H ₂ ,
One or more kinds of Ar, ENDO, EXO, etc. can be added, and the above-mentioned continuous heating, holding in a mixed gas, and further heating / holding can be carried out in multiple stages to achieve better results.

On the other hand, during the temperature rising and the temperature holding in the mixed gas, the vacuum heating is performed twice or more by the pressure reduction of 10 ^-2 to 8 × 10 ^-1 mb, and the mixed gas or the single gas is specified twice or more. By maintaining the decompression for a time higher than the decompression for a period of time, it is possible to further improve the cleaning, activation, permeability, surface smoothness, and homogeneity of the metal due to the prevention of cavitation of the metal. You can

[0010]

According to the gas composite permeation reforming method of the present invention, since heating is carried out in a gas atmosphere, the thermal efficiency is good, the heating time is short, and the type and ratio of the mixed gas in the atmosphere while the temperature is maintained are adjusted. As a result, the thickness and properties of the surface compound layer can be freely adjusted and blended.

When a gas such as ammonia, N ₂ or CO ₂ is introduced into the furnace, the introduced gas is heated to a temperature close to the furnace temperature and then introduced into the furnace so that the metal surface or the furnace In the atmosphere, the treatment temperature, which has a large influence among the factors of the permeation reforming effect, is made uniform, and deterioration and variation of the permeation reforming are prevented.

As a result, the characteristics of permeation reforming can be greatly increased by simply adjusting the temperature and controlling the temperature of each gas.

The atmosphere and process gas are usually CO ₂ , C
Since impure gases such as O, H ₂ O, O ₂ and oils and fats are contained, it is difficult to create an optimum permeation reforming atmosphere in the furnace according to the vacuum decompression infiltration method. It takes a long time to replace the gas, which makes it difficult to apply the metal surface hardness, depth, and surface texture to be modified.However, in addition to performing vacuum heating during preheating, surface modification By performing vacuuming and depressurizing during the quality treatment, the modified surface is activated by vaporization and cleaning, and contaminants and destabilized impure trace gas components are removed, greatly improving the purity and accuracy of gas mixing. As a result, the deterioration of the metal surface can be prevented and the accuracy can be improved.

[0014]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram of an apparatus used in the gas composite permeation reforming method of the present invention. In FIG. 1, the permeation reforming furnace 1 uses a vacuum tank, and is connected to a vacuum pump 2 via conduits 4 and 4 and valves 5 and 5. The permeation reforming furnace 1 is equipped with an external heating type retort or the like for purifying the atmosphere, preventing oxidation, and keeping the moisture and oxygen concentrations low at all times. Cylinder A, B, C, D, ammonia as each protective gas is _{E, N 2, CO 2,} H 2, Ar, ENDO, EX
O or the like is enclosed in the permeation reforming furnace 1 manually or automatically via the conduits 4 and 4, the valves 5 and 5 and the preheater 3 depending on the reaction stage, and only N ₂ gas or N ₂ gas is supplied. ₂ Gas is mixed with other gas and injected into the furnace. This gas is selected according to the material, size and shape of the metal base material and the properties of the reforming layer. The preheater 3, for example, arranges a mesh-shaped metal on the inner cross section of the introduction pipe and heats the mesh-shaped metal. As a heating source, for example, if a high frequency heating method in which heating is performed by an induction current by a high frequency generator and a coil is adopted, the configuration of the device is simple and inexpensive, and the efficiency is high. Further, in the case of automatic operation, the permeation reforming furnace 1 is provided with a temperature detecting means and a control section for moving the preheater 3 based on a detection signal of the temperature detecting means.

Further, a blower is provided in the furnace 1 so as to efficiently and uniformly circulate the atmosphere, and for example, N ₂ is injected from the cylinder B and circulated and cooled to improve the quality and efficiency. Can be achieved.

The relationship between temperature and time is 0.5 to 1
The temperature is linearly raised from 350 ° C. to 590 ° C. in 0 hours and kept at 350 ° C. to 590 ° C. for several hours as it is, while the vacuum heating is performed twice or more and the mixed gas or the single gas is heated twice or more for a predetermined time. A decompression of a pressure higher than the decompression of 10 ^-2 to 8 x 10 ^-1 mb is performed, and then degassing is performed,
₂ Cool rapidly or slowly.

The procedure of the present invention will be described with reference to the relationship between the thermal cycle during processing and the pressure cycle in the permeation reforming furnace shown in FIG. 7 as a typical example.

(1) Insert the metal base material into the furnace.

(2) 2 to 12 Nm ³ / hr (total amount 2 to 22)
N m ³ ) N ₂ is injected, and then 200 to 5 from room temperature.
The temperature is raised to 50 ° C. in 10 to 230 minutes.

(3) In the process of raising the temperature to 200 to 550 ° C., the exhaust pressure reduction treatment of 10 ⁻² to 8 × 10 ⁻¹ mb is performed twice.

[0021] (4) in advance of ammonia was heated to ^{200~500 ℃ 1~8N m 3 / hr,} N 2 1~8N m 3 / hr, C
A mixture of O ₂ 0.1 to ₂ Nm ³ / hr is supplied into the furnace, and the mixture is kept at 400 to 590 ° C. for 10 to 1200 minutes. (Total amount: Ammonia _{2 to} 16 N m ³ , N ₂ 2 to
In _{^{16N m 3, CO 2 0.1N m}} 3 ~3N m 3) (5) 350~590 during the holding period of ° C., 10 ^-2
Exhaust depressurization treatment of 8 × 10 ⁻¹ mb is performed twice.

(6) The CO ₂ concentration is increased and maintained for 10 to 900 minutes. The gas supply amount in that case is as follows. N _{2 1 to} 6 N m ³ / hr, ammonia 1 to 4 N m ³
/ Hr, CO ₂ 0.1 to ₂ N m ³ / hr (7) In the CO ₂ concentration rising holding period, 10 ^-2 to
The exhaust pressure reduction process of 8 × 10 ⁻¹ mb is performed twice.

(8) After the CO ₂ concentration rising holding period, deaeration is performed.

(9) 2 to 12 Nm ³ / hr N at room temperature
₂ is circulated in the furnace for displacement cooling tempering.

(10) The holding pressure during the holding period of 350 to 590 ° C., the CO ₂ concentration rising holding period and the replacement cooling adjustment period is not higher than atmospheric pressure, and 10 ⁻² to 8 × 10 ⁻¹ m
b or above.

(11) Degas from room temperature to 300 ° C.

By performing the exhaust gas depressurization process twice during the temperature raising process, the metal base material and the inside of the permeation reforming furnace are vacuum-heated, and the oil and water adhering to the surface of the metal base material are vaporized, and the metal base material is vaporized. The surface of the material is cleaned and exhausted to the outside of the permeation reforming furnace to improve the atmospheric purity.

When introducing a gas such as ammonia, N ₂ or CO ₂ , the temperature of the introduced gas is heated to a temperature close to the furnace temperature and then introduced into the furnace so that the metal surface portion or the atmosphere in the furnace is Among the factors of the permeation modification effect, the treatment temperature, which has a large effect, is made uniform, and deterioration and variation of the permeation modification are prevented.

CO ₂ , H ₂ O and O ₂ generated during the nitriding reaction try to form a porous portion in the nitride layer by the oxidation reaction, but by nitriding under a pressure lower than atmospheric pressure, oxygen is generated. The partial pressure becomes low, the oxidation reaction is suppressed, and the generation of the porous portion is suppressed.

Further, during this time, the exhaust pressure reduction process is performed twice to reclean the dirt that could not be removed during the temperature rise process, and at the same time, to generate C during the nitriding reaction.
Since impure gases such as O ₂ , H ₂ O and O ₂ are also discharged,
Atmosphere purity is improved.

Although it may take several hours to replace the gas in the conventional method with the atmosphere depending on the nature of the gas flow, the present invention has made it possible to significantly reduce the operating time. In addition, consumption gas and electricity bills were saved.

Further, according to the present invention, the cooling characteristic can be improved. Cooling with a gas depends on the pressure and flow rate of the cooling gas. Therefore, by utilizing the jet in the region of 3 bar from atmospheric pressure, cooling is improved, which contributes to shortening the time and refining the base material and the surface layer. Therefore, the solid solution of the element diffusion layer is promoted / completed.

Next, there is an excellent glittering property. T in the base material
In materials containing active metals such as i, W, Mo and V, embrittlement due to gas absorption and oxidation due to affinity with O ₂ proceed,
It is effective in preventing these.

According to the present invention, the surface roughness can be improved. The main purpose of this kind of surface modification is deeply correlated with the surface roughness, and the degree of this is an important factor for evaluation.

This effect is remarkably exhibited in die steel, high-speed steel, etc., which are the mainstream in this treatment, and the experimental value shows that the roughness (Rmax) is improved by about 2 to 4 times.

The above-mentioned permeation reforming furnace is provided with an automated system using various sensors and microprocessors, so that quality stabilization and labor saving can be further thoroughly implemented.

The metal base material is placed in a basket,
The basket is inserted into the permeation reforming furnace, and the dimensions of the basket are, for example, length x length x width 1150 mm x 650 mm x 71
It is 0 mm.

According to the gas composite permeation reforming method of the present invention, the element causes a chemical reaction on the surface of the metal, and the produced element diffuses into the metal to form a hard and tough surface layer portion.

A tough compound is formed in the surface layer portion, and fine granular and acicular precipitates are formed in the diffusion layer, showing effective properties.

The characteristics obtained by this reforming method are as follows.

(1) Reduction of hardness / depth variation The metal surface obtained by the present reforming method exhibits high hot strength retention. FIG. 2 represents the decrease in hardness with depth from the surface. These variations are reduced by preheating, vacuum decompression effect and the like.

(2) Improvement of wear resistance FIG. 3 is an example showing a comparison of SKD61 with other permeation modification methods. The horizontal axis shows the friction time and the vertical axis shows the amount of wear. In the figure, the solid line shows the product subjected to the treatment of the present invention, the dotted line shows the product without treatment, and the alternate long and short dash line shows the product subjected to the modification method described in Japanese Patent Publication No. 3-12140. According to the invention,
The amount of wear resistance is greatly improved as shown in the figure. Further, since the penetration depth is also large, the total wear amount shows a larger value.

(3) Reduction of abrasion resistance According to the present invention, the powder abrasion resistance performance is remarkably improved.
This can also be explained by the fact that, when the wear coefficient is impervious, the value of 0.3 to 0.4 is improved to 0.1 to 0.2 by the present invention. As a result, the temperature rise during use was stopped, and significant improvements were made in product accuracy and life. Figure 4 shows SKD
61 shows an example, where the horizontal axis represents the test load and the vertical axis represents the temperature rise. In the figure, the solid line shows the product subjected to the treatment of the present invention, the dotted line shows the product without treatment, and the alternate long and short dash line shows the product subjected to the permeation modification method described in Japanese Patent Publication No. 3-12140.

(4) Improvement of Fatigue Strength The present invention can be applied uniformly to a product having a complicated shape such as a groove. The element dissolved in the matrix improves the fatigue strength under cyclic stress, bending stress and rotational bending stress. Figure 5 shows SKD6
1 is an example, in which the processing time is plotted on the horizontal axis and the fatigue strength is plotted on the vertical axis. In the figure, the solid line shows the product subjected to the treatment of the present invention, and the alternate long and short dash line shows the product subjected to the permeation modification method described in Japanese Patent Publication No. 3-12140. The present invention is
This shows a remarkable improvement effect on fatigue strength.

(5) Improvement of creep strength FIG. 6 shows S15C, SNCM3 and SKD61 non-penetrating products (shown by dotted lines) and products processed by the permeation reforming method described in Japanese Patent Publication No. 3-12140 (shown by dashed lines). 4) and the treatment of the present invention (shown by the solid line) are compared, and according to the present invention, a remarkable improvement in creep strength is observed in any steel grade.

(6) Improvement of corrosion resistance There is a significant improvement over other treated products. Improvements have been proved in various corrosion tests such as salt water test, acid test, and ammonia test.

(7) Improvement of surface roughness The surface roughness (Rmax) was improved as described above.

[Brief description of drawings]

FIG. 1 is a block diagram of an apparatus used in the gas composite permeation reforming method of the present invention.

FIG. 2 is a diagram showing changes in hardness with depth for the present invention and a conventional method.

FIG. 3 is a diagram showing changes in wear amount with wear time for the present invention and a conventional method.

FIG. 4 is a diagram showing changes in the rising temperature with respect to a test load for the present invention and the conventional method.

FIG. 5 is a graph showing changes in fatigue strength with respect to processing time for the present invention and a conventional method.

FIG. 6 is a diagram showing a comparison of creep strength between the present invention and a conventional method.

FIG. 7 is a diagram showing a heat cycle and a pressure cycle according to an embodiment of the present invention.

[Explanation of symbols]

 1 Infiltration reforming furnace 2 Vacuum pump 3 Preheater 4 Pipeline 5 Valve

Claims (2)

[Claims] 1. A metal base material is inserted into a permeation reforming furnace, and N ₂
Gas is injected into the furnace and the temperature is raised from room temperature to 200 to 550 ° C.
The temperature was raised at 230 minutes, ammonia, is injected into the furnace the temperature of the mixture or a single gas N ₂ and CO ₂ after raising to a temperature near the furnace, and then ammonia, N ₂
And in a mixed gas of CO ₂ for 10 to 1800 minutes and 350 to
Holding at 590 ° C., then raising the CO ₂ concentration of the mixture and holding for 10 to 900 minutes, then degassing, further cooling while circulating N ₂ , and then degassing at room temperature to 300 ° C. A gas composite permeation reforming method characterized by: 2. During the temperature rising and the temperature holding in the mixed gas, the vacuum heating is performed twice or more by the reduced pressure of 10 ⁻² to 8 × 10 ⁻¹ mb and the mixed gas or the single gas is specified twice or more. The gas composite permeation reforming method according to claim 1, wherein the holding is performed by reducing the pressure for a time higher than the pressure reducing.