JPS63255355A - Modifying method by mixed gas penetration - Google Patents

Abstract

PURPOSE:To efficiently modify the surface of a metallic base material by mixed gas penetration at a low cost by putting the base material in a furnace, introducing a gas such as NH3, N2, CO2, H2, Ar, ENDO or EXO into the furnace, heating the base material and circulating gaseous N2. CONSTITUTION:A metallic base material is put in a penetration modifying furnace and the furnace is evacuated and kept at a prescribed degree of vacuum. A gas such as NH3, N2, CO2, H2, Ar, ENDO or EXO or a mixture of such gases is introduced into the furnace and the internal temp. of the furnace is raised from room temp. to continuously heat the base material. The heated base material is held, a mixture of such gases is further fed into the furnace and the base material is held while feeding. Gaseous N2 is then circulated in the furnace to carry out substitution, cooling and refining. The surface of the base material is modified by mixed gas penetration and stable surface properties such as wear, heat and corrosion resistances are obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a method for modifying a metal surface by gas mixture permeation.

[Conventional technology] Methods for modifying the metal surface of machine parts, tools, jigs, molds, etc. can be roughly divided into carburizing, nitriding, sulfurizing, and boronizing, which penetrate elements of a number of 11 media into the metal surface layer. - There are two methods: methods that modify the surface by diffusion, and methods that modify the surface layer by physically and chemically reacting with surface hardening, plating, chemical treatment JIp, overlay, etc. The latter requires complex and advanced technology, is expensive, has limited base materials, and has many difficulties in work and quality control.

The former osmotic modification method is divided into two types depending on the modification medium as follows.

That is, there are two methods: one uses liquid/solid as the reforming medium, and the other uses gas.

[Problems to be Solved by the Invention] Conventional methods that use liquids, solids, and gases as reforming media have the following problems.

(1) For example, a salt bath reforming method is currently widely used in which a mixed salt of NaCN and NaCN0 is used as a charging salt, melted in an external heating furnace, and reformed at a predetermined temperature for a predetermined period of time. However, salts are highly toxic and pose a pollution problem, which calls for social responsibility, requiring a large amount of money for pollution prevention equipment, and at the current state of technology, no perfect prevention method has yet been established.

(2) Modification methods such as carburization have the problem of high modification temperatures (damaging the base material and wasting heating energy. In this method, it is usually necessary to maintain the temperature at a high temperature of 900°C or higher for several hours. First, the base material hardens and requires heat treatment after modification, which causes deformation and dimensional changes in the product and requires a large number of man-hours.On the other hand, the surface hardness is low.

(3) For example, a reforming method using nitrogen gas permeation has a problem in that the reforming time is long. After the initial air replacement in the furnace, the cycle of heating - holding - heating - long-term holding - cooling in the furnace takes more than 100 hours, and even short ones take more than 30 hours. , the thermal energy is large, and a large amount of gas is used, resulting in a large operating cost.
It also takes a long time to deliver. This is due to the nature of the gas, which requires two hours to penetrate into the metal.

, (4) For example, in the salt bath modification method described above, the surface modified layer is limited to a compound layer, so the thickness of the surface modified layer is
? ItI is less than 1/100111 m at h, and there is a problem that the layer thickness cannot be adjusted and managed, and it cannot withstand high pressure loads in terms of usage.

(5) There is a problem that some shapes of the base material to be surface modified exist that cannot be modified.

For example, in a modification method using ion nitriding, the treated product is heated as ions jump.

Since ions travel in a straight line, there are areas where surface modification cannot be performed in the shadow areas where ions cannot travel. That is, it is extremely difficult to form a uniform layer on a narrow vortex, the inner surface of a fine hole, the bottom surface, the inner surface of a long object, etc. Also, what about the shape? J2 Uniform layer formation on coarse objects 2 Simultaneous processing cannot be expected when the difference in surface area or mass is large. Furthermore, rapid cooling using water or oil cooling is not possible.

(6) There is a problem that the base material is limited. Among the base materials, there are many metals such as A1 and A1 alloys in which a predetermined modified layer cannot be obtained. Compounds like Cr and MO (nitriding)
A material containing substance-forming elements is an essential requirement.

(7) There is a problem of deterioration of surface roughness. In particular, the salt bath modification method causes surface deterioration and reduces surface roughness.

(8) There is a problem in that the base material expands and contracts due to the thermal effects of processing, resulting in dimensional deviations. In addition, some of them are defective due to an increase in size due to the thickness of the layer deposited on the surface layer.

The purpose of the present invention is to solve the problems of the surface modification methods described above, and to provide a special gas complex permeation modification method that is inexpensive, highly efficient, and can provide stable wear-resistant, heat-resistant, and corrosion-resistant surface properties. It's about doing.

[Means for Solving the Problems] In order to solve the above problems, the present invention includes inserting a metal base material into a permeation reforming furnace, evacuating air, and maintaining the inside of the furnace in a vacuum.
Ammonia, N, Co2. H2゜Ar, ENDO,
A mixture of EXO and other gases or a plurality of gases is injected into the furnace, heated from room temperature, then continuously heated in a mixed gas selected from the above gases, and then a mixture selected from the above gases. This is a gas composite permeation reforming method in which the reactor is held in a gas, and in that state, a mixed gas selected from the gases is supplied while N2 gas is circulated in the furnace. Furthermore, by appropriately selecting quenching, slow cooling, etc. after treatment, refining and efficiency can be achieved.

Note that the continuous heating, holding in a mixed gas, and further heating and holding can be performed in multiple stages to achieve better results.

[Example] Embodiments of the present invention will be described below based on 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, a osmotic reforming furnace 1 uses a vacuum tank and is connected to a vacuum pump 2 via pipes and pulp (not shown). The interior of the permeation reforming furnace 1 is equipped with an external heating retort and the like to purify the atmosphere, prevent oxidation, and keep moisture and oxygen concentrations low at all times.

Cylinder A, [3, C, D, and E contain ammonia, N, CO, H, and Δr as protective gases, respectively.

ENDO, EXO, etc. are sealed, and after evacuating the inside of the permeation reforming furnace 1, each gas is manually or automatically mixed singly or in combination through pipes and valves (not shown). Inject into. This gas is selected depending on the material, dimensions and shape of the metal base material, and the properties of the modified layer. In addition, a blower is provided in Class 1 to circulate the atmosphere uniformly with high efficiency. For example, N2 is injected from cylinder B to avoid circulation and cool it, thereby achieving thermal refining and efficiency.

In addition, the relationship between temperature and hour is 400℃ for 0.5 to 10 hours.
The temperature is raised linearly from °C to 700 °C, maintained as it is for several hours, and then cooled slowly or slowly.

The procedure of the present invention is shown below using a typical example.

(1) Insert the metal base material into the furnace and vent the air. The degree of vacuum in the furnace is 800 to 10-6 mbar.

(2) 2~12NIIl/hr (total ff12~22N
m3) of N2 is injected, and then from room temperature to 300~4
Raise the temperature to 50°C in 20-230 minutes.

(3) 1 to 8 NILl/hr nitrogen and 1 to 8 Nm3/hr
400 for 10-90 minutes in a mixed gas of hr ammonia.
Drop continuous heating to ~650°C.

(Total ffi2N21~6Nm3.Ammonia 1~6NI
l13) (4) Ammonia 1-8 NIl/hr, N21-8N
It is maintained at 400-650° C. for 10-240 minutes in a mixture of 1-2 N m /hr and CO2. (Total amount: ammonia 2-16Nffi, N22-16
NIll.

CO20,1NI! 1-3Nm3) (5) Increase the CO2 concentration for another 10-120 minutes and
It is held to reduce the temperature by 211 degrees. In that case, the gas supply amount is as follows.

N21~6N m3/hr, ammonia 1~4N m
3/hr, Co20. 1~2N m3/hr
(6) Replace N2 of 2-12NIIl and U cold uI
m' Circulate for R.

Although the above is a case of one-stage processing, multi-stage processing such as two-stage or three-stage processing can also be performed. This makes it easy to select gas-intermittent mixing and temperature/time, and performs effective surface modification through optimal and efficient combinations, making it possible to perform single-phase or mixed-phase (e.g. γ'-Fe4
N, ε-Fe2-3N) is obtained. For example, as a two-stage treatment, the temperature is linearly raised to 500°C over 0.5 to 10 hours, held for a predetermined time, then raised to 550°C, held for a predetermined time, and then cooled and slowly cooled.

Utilizing a vacuum system has several advantages. First is the improvement of atmosphere purity. In the conventional method, initial air evacuation is insufficient, so atmospheric purity cannot be obtained, resulting in poor air quality. Although it is often not possible to obtain a modified layer of 11 J, this problem can be solved by adjusting the degree of vacuum.

Next, the conventional method of popular replacement with gas can take several hours depending on the properties of the gas flow, but the present invention has made it possible to significantly shorten the operating time. Additionally, gas consumption was reduced.

Furthermore, compared to other heating furnaces, this osmotic reforming furnace has less heat storage m and radiant heat ω in the furnace body, so that the gastric elimination rate of the furnace temperature is faster. Table 1 shows Fj? in vacuum. -During the drying process, the indicated temperature of the furnace and sample diameter x length 15mmφ x 100m
5' until the center of m reaches a constant temperature? This shows an example of the relationship between W times.

As shown in this figure, efficiency can be improved.

Table 1 Note that in the conventional method, after treatment, the base material must be moved to a separation facility and heated and cooled, but in the method of the present invention, cooling and other refining can be performed as is in the latter half of the treatment. Quality can be improved and processing time can be shortened. In particular, the effect of post-processing cooling conditions on the fatigue strength of the material is large; in low-alloy steel, slow cooling produces a single grain of γ' (Fo4N) phase.
(Fe16N2) etc., resulting in a decrease in fatigue strength.

Furthermore, according to the present invention, cooling characteristics can be improved. Cooling with gas depends on the pressure and flow rate of the cooling gas. For this purpose, jet flow in the range of 3 bar from atmospheric pressure is used to improve cooling, reduce time, and reduce the thickness of the base material and surface layer.
Contributes to quality. Therefore, solid solution formation of the element diffusion layer is promoted and completed.

Next, there is the excellent brightness. Ti in the base material.

In materials containing active metals such as W, Mo, and V, embrittlement due to gas absorption and oxidation due to affinity with 02 progress, so this is effective in preventing these.

Note that according to the present invention, surface roughness can be improved. The main purpose of this type of surface modification is closely related to surface roughness. The degree of this is an essential factor in evaluation.

In die steels, high-speed steels, etc., which are the mainstream in this treatment, this effect is remarkable, and according to experimental values, R■aX) has been improved by a factor of 2 to 4.

The above-mentioned osmotic reforming furnace is equipped with an automation system that uses various sensors and microprocessors, making it possible to further ensure quality stabilization.

The metal base material is placed in a basket, and the basket is inserted into the permeation reforming furnace. The dimensions of the basket are, for example, length x length x width 1100 mm x 650 ms x 650 mm.
It is.

According to the gas composite permeation reforming method of the present invention, the elements cause a chemical reaction on the surface of the metal, and the generated elements diffuse into the metal.
Forms a hard and tough surface layer.

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

The properties obtained by this modification method are as follows.

(1) Improved hot strength The surface obtained by the present modification method exhibits high hot strength. Figure 2 shows an example, where the horizontal axis shows temperature and
Hardness (Vickers) is taken on the vertical axis. In the figure, the solid line and the two-dot chain line represent the results obtained by the one-stage treatment and the multi-stage treatment of the present invention, respectively, and the dotted line represents the results obtained by another osmotic modification method. In particular, SNCM shows a significant decrease in hardness as the temperature increases, as shown in the figure.

(2) Improved wear resistance Figure 3 is an example showing a comparison of 5KD61 with other osmotic modification methods, where the horizontal axis shows the friction time and the vertical axis shows the amount of wear. In the figure, the solid line and the two-dot chain line indicate the one-stage treatment and the two-stage treatment of the present invention, respectively, and the dotted line indicates the one subjected to another osmotic modification method. According to the present invention, the wear resistance is greatly improved as shown in the figure. Furthermore, since the penetration depth is large, the total wear amount is even larger.

(3) Reducing wear resistance According to the present invention, powder wear resistance performance is significantly improved.

This can also be explained by the fact that the present invention improves the wear coefficient from 0.3 to 0.4 in the case of non-penetration to 0.1 to 0.2. This prevents temperature rises during use and significantly improves product accuracy and lifespan.

FIG. 4 shows an example of 5KD61, with the horizontal axis representing the test load and the vertical axis representing the temperature rise. In the figure, the solid line and the two-dot chain line indicate the one-stage treatment and the two-stage treatment of the present invention, respectively, and the dotted line indicates the one subjected to another osmotic modification method.

(4) Improvement in R-force strength The present invention can be applied uniformly to products with complex shapes such as grooves. Elements dissolved in the matrix improve fatigue strength α under repeated stress, bending stress, and rotational bending stress. Figure 5 shows 5KD
61, in which the horizontal axis represents processing time and the vertical axis represents fatigue strength. In the figure, the solid line and the two-dot chain line indicate the one-stage processing and the two-stage processing of the present invention, respectively. The present invention exhibits a significant improvement in fatigue strength.

(5) Improvement in creep strength Figure 6 shows the creep of 815C, SN0M3.5KD61 by non-permeable product (shown by dotted line), one-stage treatment (shown by solid line), and two-stage treatment (shown by two-dot chain line) of the present invention. This figure shows a comparison of strength, and according to the present invention, a significant improvement in creep strength can be seen in any steel type.

(6) Improvement in corrosion resistance and other significant improvements compared to throughput. The improvement has been proven in various corrosion tests such as salt water tests, acid tests, and ammonia tests.

(7) Improvement of surface roughness As mentioned above, the surface roughness (Rmax) was improved.

[Effects of the invention] Above)! As mentioned above, according to the present invention, the surface layer of the base material is modified, hot strength and wear resistance are improved, wear resistance is reduced, and fatigue strength, creep strength, and corrosion resistance are improved. It also has the excellent effect of improving surface roughness, and is of great industrial value.

[Brief explanation of drawings]

Figure 1 is a block diagram of an apparatus using the gas composite permeation reforming method of the present invention, Figure 2 is a diagram showing changes in hardness with respect to temperature for the present invention and the conventional method, and Figure 3 is for the present invention and the conventional method. Figure 4 shows the change in wear n1 with respect to wear time for the conventional method. Figure 4 is a diagram showing the change in temperature with respect to the test load for the present invention and the conventional method. Figure 5 shows the processing time for the present invention and the conventional method. FIG. 6 is a diagram showing a comparison of creep strength between the present invention and the conventional method. 1... Osmotic reforming furnace, 2... Vacuum pump.

Claims (2)

[Claims] (1) Insert the metal base material into the osmotic reforming furnace, evacuate the furnace and maintain the inside of the furnace in vacuum, and then add gases such as ammonia, N_2, CO_2, H_2, Ar, ENDO, EXO, etc. singly or in combination. The mixture is injected into a furnace, heated from room temperature, then continuously heated in a mixed gas selected from the above gases, further held in a mixed gas selected from the above gases, and further maintained in that state. A gas mixture permeation reforming method characterized in that a mixed gas selected from the above gases is supplied and held, and mainly N_2 gas is circulated in the furnace. (2) The gas composite permeation reforming method according to claim 1, wherein the continuous heating, holding in a mixed gas, and further heating and holding are performed in multiple stages.