JPH0261553B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION This invention relates generally to metal chemistry and heat treatment of alloys with metals. In particular, the invention relates to a method for chemically and thermally treating steel workpieces to obtain coatings by diffusion precipitation.

The method according to the invention can be used in the field of instrument manufacturing (precision frictional bodies, electrical contacts, terminals, variable resistance wires),
in medicine (for the manufacture of dentures and surgical instruments), in the electrical industry (electrical contacts), in the watch industry (watch cases, bracelets and parts),
To reduce the consumption of precious metals such as gold and platinum, or to use them as an alternative material, in the jewelry industry (for the production of ornaments and tableware) and in the chemical industry (for corrosion prevention or heat-resistant treatment of parts). can be applied to obtain coatings similar to these noble metals in terms of physical and chemical properties.

The method according to the invention can also be used in the production of reflector screens for various applications and for the application of coatings to protect components from corrosion by seawater.

Currently, various techniques (gold plating and palladium plating) are widely used, which generally produce noble metal coatings by electrodeposition. However, electrodeposition methods often do not guarantee reliable coverage on parts with complex shapes. Therefore, the coating obtained by the known method is
It has the inherent disadvantages of poor adhesion to the base metal, non-uniform thickness especially at the corners of the workpiece, low hardness and easy wear. The implementation of these known methods also requires pretreatment of the workpiece surface, such as mechanical cleaning and pickling.

New processing methods have recently come into industrial use to improve the physical and chemical properties of coatings, one of which involves chemical and thermal treatment of metal parts by diffusion deposition.

Diffusion coatings are surface layers characterized by low porosity and high adhesion to the base metal. Diffusion coating methods can produce surface areas of various chemical compositions that guarantee advantageous properties such as high wear resistance, sufficient hardness, resistance to corrosive atmospheres, and high mechanical strength.

Chemical and heat treatment methods for steel workpieces are known in which coatings are formed by diffusion deposition or adsorption of certain substances from melts of low melting point metals onto the base metal. (Soviet inventor's certificate, No. 582329, IPC C23C9/
10).

Sodium is used as the low-melting metal of the melt, whereas platinum is used as the substance forming the coating during the diffusion deposition.

The preferred conditions for diffusion precipitation include a temperature of 630°C.
~670°C, time is 5-6 hours.

Therefore, the above-mentioned method consists in using an easily melting or low melting point metal, into which other metal elements are introduced, and deposited on the base metal to form a diffusion coating.
In this case, isothermal mass transfer processes take place, in which the substances dissolved in the form of metallic elements in the easily meltable metal melt move onto the surface of the workpiece to be coated, are adsorbed and bonded, and this The elements react with the metal of the workpiece by diffusion. As a result, a coating is formed on the base metal consisting of the elements that participate in the diffusion deposition.

However, this method does not allow for a given stoichiometric composition.
It is not possible to produce a coating of uniform thickness.

Also, known chemical and thermal processing methods by diffusion precipitation using noble metals and their substitute imitation metals are disadvantageous due to the high rate of loss of these metals during processing.

The present invention uses modified processing conditions and special deposited materials to produce coatings that imitate gold and noble metals such as platinum in physical and chemical properties, i.e. high resistance to corrosion and The object of the present invention is to provide a chemical and heat treatment method for steel workpieces that can provide a coating with gloss and color.

In a chemical and heat treatment method for forming a coating on a steel workpiece by diffusion depositing a substance from a low melting point metal melt onto the base metal of the steel workpiece, according to the invention, the diffusion deposition method is carried out at a temperature in the range from 720 to 820° C. for a time sufficient to obtain a thick coating, said melt preferably containing sodium or thirium as the low melting metal and in the form of an intermetallic compound. By being precipitated,
The goals of the invention are achieved.

By using molten sodium or thium,
There is no need to pre-treat the workpiece surface by pickling. This is because the metal melt has high wetting power and fluidity, which makes it difficult to remove surface oxides and clean workpieces and parts with complex shapes and internal cavities and grooves. This is because it can be done. The use of such a molten metal bath also makes a subsequent mechanical cleaning treatment of the workpiece surface unnecessary.
This is because melt residues that have entered the slits and cracks of the workpiece are removed by washing the workpiece under water. Furthermore, the amount of loss of the substance used for depositing the coating by diffusion is low. This is because this type of material dissolves only in small amounts in the sodium or thium melt, whereas chemical and heat treatment methods limit the amount of material dissolved in the melt to the workpiece being coated. This is because the process proceeds in a pattern that is substantially equal to the amount deposited on the surface.

As the substance to be deposited, a stoichiometric intermetallic compound having predetermined physicochemical properties, for example a compound imitating the properties of noble metals, is introduced into the melt. This makes it possible to obtain coatings consisting of compounds introduced into the melt, ie coatings of a defined composition. This is because the dissolution, migration, and precipitation of compound elements in the melt occur in stoichiometric proportions corresponding to the composition of the introduced compound, and as a result, the composition of the resulting coating layer changes with respect to its thickness. It shows a tendency to be uniform over the entire area.

This processing is carried out at temperatures in the range 720-820°C. Such temperature conditions give rise to all the basic physical and chemical methods necessary for carrying out chemical and thermal treatments. In particular, the requirements imposed by the sufficiently active dissolution of the various intermetallic compounds into the melt, the diffusive transfer of the elements precipitated from the melt into the base metal of the workpiece, and the desired conditions of use of the workpiece. This results in the formation of a coating having a thickness sufficient to meet the requirements. The thickness of the coating depends on the diffusion deposition time, which is determined by the physical and chemical parameters of the process.

When carrying out this process, the amount of intermetallic compound introduced into the melt is preferably determined by the following formula:

G ₁ =0.03G ₂ +S・δ・γ Where, G ₁ = Weight of intermetallic compound, g, G ₂ = Weight of low melting point metal, g, S = Surface area of workpiece, cm ² , δ = Coating layer required thickness, cm, γ=density of the intermetallic compound, g/cm Imitate platinum in ^three colors to obtain a coating with sufficient corrosion resistance, high temperature oxidation resistance and high mechanical properties (hardness and abrasion resistance). For this purpose, heat the mixture at 720-780°C for 6-8 hours in a melt bath containing thirium and a nickel-aluminum intermetallic compound.
It is desirable to carry out the diffusion precipitation at a temperature of .

In order to obtain a gold imitation coating, 780 to
Preferably, the diffusion precipitation is carried out at a temperature of 820°C.

Molten sodium also provides all the conditions necessary to obtain a coating with the required properties. (sufficient solubility of the compound, adsorption of the compound elements on the base metal of the steel workpiece, phase junction: intermetallic compound of palladium and indium - absence of steel elution in sodium - steel).

Preferred process parameters of temperatures of 780 DEG-820 DEG C. and deposition times of 6-8 hours ensure adsorption of coatings with useful thicknesses for a wide range of applications.

In the following, the invention will be explained in more detail with respect to its preferred embodiments.

The workpiece to be coated is placed in a reaction vessel such as an ampoule made of an inert material (a material that does not dissolve in the molten metal used to deposit the coating). Thereafter, in a neutral gas atmosphere such as argon gas, the ampoule is filled with a low melting point alkali metal melt such as sodium or thium and the substance in the form of an intermetallic compound to be deposited on the base metal.

The ampoule is then sealed by welding or seam filling in argon gas and placed in a furnace such as a Matsufuru electric furnace for diffusion deposition at temperatures between 720 and 280°C for the time necessary to obtain the desired coating thickness. Processing was carried out.

The proportion of intermetallic compounds that should be present in the melt is determined by:

G ₁ =0.03G ₂ +S・δ・γ Where, G ₁ = Weight of intermetallic compound, g, G ₂ = Weight of low melting point metal, g, S = Surface area of workpiece, cm ² , δ = Coating layer Required thickness, cm, γ=density of the intermetallic compound, g/cm ³ .

The first term in the above equation takes into account the amount of compound required to saturate the molten sodium or thiium, and for a wide range of compounds this corresponds to 0.03G ₂ . That is, the saturation concentration is guaranteed at a value close to 3% by mass.

The second term of the equation considers the amount of compound required to form the required thickness of the coating layer and is determined by the dimensions of the workpiece being coated, the thickness of the coating layer and the density of the compound. That is, this second term determines the general relationship between geometrical methods and the mass of a substance via its density.

The ampoule is held at a temperature that causes diffusional deposition and then, after cooling, the ampoule is opened and the coated workpiece is withdrawn from the ampoule and washed under running water.

To obtain a coating that imitates platinum with respect to color and physico-chemical properties, it is possible to obtain a coating that imitates platinum in terms of color properties and physico-chemical properties, for 6 to 8 hours at a temperature of 720 to 780° C. in a molten metal composition containing lithium and a nickel-aluminum intermetallic compound.
Perform diffusion deposition on the workpiece. The amount of compound is determined by the equation above.

To obtain a gold-imitating coating with respect to color and physico-chemical properties, it is possible to obtain a coating consisting of molten sodium and palladium-indium intermetallic compound at a temperature of 780-820° C. for 6-8 hours. Perform diffusion precipitation.

A few examples of the best mode of carrying out the invention are described below.

Example 1 A tea spoon made of steel having the following composition (% by mass) was placed in an ampoule. C=0.08, Mn=1~2,
Cr=17-19, Ni=9-11, Ti=0.7, Fe=residue.
A sample of the intermetallic compound also containing a mixture of palladium and indium in a ratio of 56:44 by weight was placed in an ampoule and the ampoule was then filled with molten sodium.

The amount of intermetallic compound G ₁ =5.17 g was determined from the above equation. Here, G ₂ = 150g, S = 37cm ² , δ = 0.0018cm, γ = 10g/cm ³ .

After sealing the ampoule in argon gas, place it in a Matsufuru electric furnace and place it in a
The temperature was maintained at ℃ for 6 hours. Thereafter, the ampoule was opened, the workpiece was taken out, and washed under running water.

As a result of this chemical and heat treatment, a coating similar to gold in corrosion resistance and luster was formed on the workpiece, with a microhardness of 18 mKm, 2100-2400 MPa, and a gold-pink color.

A 100 hour test in acidic and alkaline media showed no corrosion of the surface of the coating.

Example 2 Unlike Example 1, the following composition (mass%): C=
The ampoule containing the workpiece in the form of a steel ring of 0.24-0.32; Fe=residue was subjected to a heat treatment at a temperature of 800° C. for 7 hours.

of intermetallic compounds (palladium and indium)
The starting data for determining the value of G ₁ =1.16g are determined from the above equation. Here, G ₂ = 30g, S = 9.4cm ² , δ = 0.0025cm, γ = 10g/cm ³ .

As a result of chemical and heat treatment, it imitates gold in corrosion resistance and luster, with a thickness of 25mKm,
A coating layer with a microhardness of 1850-2025 MPa and a gold-pink color was formed on the steel ring.
The corrosion resistance was substantially equivalent to the coating obtained according to Example 1.

Example 3 The following composition (mass%): C = 0.07 to 0.13; Fe = residual steel watch case and palladium-indium intermetallic compound samples of 56% and 44% by mass, respectively, were placed in an ampoule. The ampoule was then filled with dissolved sodium.

The amount of intermetallic compounds was determined by the equation above. In this case, G ₂ = 70 g, S = 28 cm ² , δ = 0.0035 cm, γ = 10 g/cm ³ , so that G ₁ = 3.08 g.

The ampoule containing the contents was kept in a Matsufuru furnace for 8 hours at a temperature of 820°C.

The resulting chemical reaction is processed by heat treatment.
A coating layer with a thickness of 35 mKm and a microhardness of 1800-2100 MPa was obtained. The color and corrosion resistance of this coating is similar to that described for Example 1.

Example 4 The following composition (mass%): C = 0.24 to 0.32; Fe = steel tea leaves having a residue and a nickel-aluminum intermetallic compound sample (G ₁ = 3.35 g) were placed in an ampoule, The ampoule was then filled with molten lithium. The amount of intermetallic compound G ₁ is determined by the above formula. Here, G ₂ = 82g, S = 37cm ² , δ = 0.004cm, γ = 6g/cm ³ .

After sealing the ampoule under argon gas, the ampoule was kept in the oven for 6 hours at a temperature of 720°C.
Thereafter, the ampoule was opened and the steel was taken out and washed with running water.

The result of this chemical and heat treatment is similar to platinum in corrosion resistance and luster, with a thickness of 40mKm and a thickness of 4100~
A coating layer with a microhardness of 4200 MPa was formed. The color of the coating thus obtained was light gray, but its resistance to acidic and alkaline corrosive media is comparable to chrome-nickel steel.

Example 5 The following composition (mass%): C=0.07-0.13, Fe=
A steel watch case with residue and a nickel-aluminum intermetallic sample (G ₁ =2.9 g) were placed in an ampoule, which was then filled with molten lithium. The amount of G ₁ was determined from the above equation. Here, _G2 =40g, S= ^28cm2 , δ=0.010cm, γ=6g/ ^cm3 .

The ampoule is held at a temperature of 750°C for 7 hours.

As a result of chemical and heat treatment, it approximates platinum in corrosion resistance and luster, with a thickness of 130mKm, approximately 4500 ~
A coating layer with a microhardness of between 4800 MPa was formed. The corrosion resistance and color of the coating thus obtained are similar to that produced by the method described in Example 4.

Example 6 This treatment was carried out substantially as described for Example 5, with the difference that a nickel-aluminum intermetallic compound in an amount of G ₁ =3.38 g, determined from the same equation as above, was used. It has been used.

_G2 =40g, S= ^28cm2 , δ=0.013cm, γ=6g/ ^cm3 .

The ampoule was heat treated at a temperature of 780°C for 8 hours.

Similar to platinum in corrosion resistance and luster, 130mKm
A coating with a thickness of 4500-4800 MPa and a microhardness of 4500-4800 MPa was formed on the base metal of the workpiece. Its color and corrosion resistance were substantially equivalent to the coating described for Example 4.

Claims (1)

[Claims] 1. A steel workpiece in which a coating is formed by diffusing and precipitating a substance in the form of an intermetallic compound onto a base metal from a melt of a low melting point metal such as sodium or lithium. A chemical and thermal treatment method characterized in that the diffusion deposition is carried out at a temperature of 720 to 820° C. for a period of time necessary to obtain a coating layer of the required thickness. 2 The amount of intermetallic compound in the melt is determined from the following formula, G ₁ = 0.03G ₂ + S・δ・γ where, G ₁ = weight of intermetallic compound, g, G ₂ = low melting point metal weight of the intermetallic compound, g, S=surface area of the workpiece, cm ² , δ=required thickness of the coating layer, cm, γ=density of the intermetallic compound, g/cm ³ Method according to Section 1. 3 Diffusion precipitation occurs in a melt containing lithium and a nickel-aluminum intermetallic compound.
Process according to claim 1 or 2, characterized in that it is carried out at a temperature of 720-780° C. for 6-8 hours. 4. The diffusion precipitation is carried out in a melt containing sodium and palladium-indium intermetallic compound for 6 to 8 hours at a temperature of 780 to 820°C. Or the method according to paragraph 2.