JPS5841936B2 - Continuous casting mold for steel - Google Patents

Description

Detailed Description of the Invention The present invention relates to a mold for continuous casting of steel such as low carbon steel, high carbon steel, stainless steel, special steel, etc., and its purpose is to improve various properties such as wear resistance at high temperatures. Our goal is to provide particularly excellent molds for

Conventional continuous casting molds are generally made of copper or copper alloy, which has good thermal conductivity.

However, because the molten steel injected into the continuous casting mold is extremely hot, the molten steel injection surface (hereinafter referred to as the mold base surface) is severely damaged, and the mold reaches the end of its service life in an extremely short period of time. was.

In order to improve this drawback, conventionally, hard chrome plating was applied to the surface of the mold base to improve heat resistance and wear resistance, and vitreous powder was added between the hard chrome plated mold and the molten steel to match the flow of the molten steel. Efforts have been made to prevent direct contact between the mold and molten steel by interposing the metal so that it flows.

Although the above treatment can be expected to extend the life of the mold to some extent, the wear resistance of hard chrome plating still
Due to deterioration of corrosion resistance, etc., the surface of the mold base is exposed due to short-term use and the surface is severely damaged. In addition, copper or copper alloy adheres to and penetrates the slab, often causing embrittlement, resulting in microscopic damage to the resulting slab product. The problem was that cracks (star cracks) occurred.

Also, recently it has been proposed to use nickel as a surface protective layer on the surface of the mold substrate.

For example, in Japanese Patent Publication No. 48-28255, nickel plating is applied to the surface of the copper base of the mold, and a diffusion layer is formed between the nickel plating and the copper by heating it to around 600 to 1000°C in an appropriate non-oxidizing atmosphere. A method for forming is described.

This method is expected to extend the life of the mold due to the strong adhesion between the nickel layer and the surface of the mold base and the heat resistance of nickel.

In this case, the adhesion is improved, but the hardness of the nickel layer is quite low at micro-Vickers hardness HV 250-400, so it lacks wear resistance, but the lifespan is slightly extended compared to the mold with hard chromium plating. It's just that.

Furthermore, when extending the service life by forming an extremely thick plating layer, the thermal conductivity deteriorates.

In addition, in this method, the nickel-copper diffusion layer is 600 to 10
It is formed by heating at a high temperature of about 00° C., but this heating causes the following problems, for example.

That is, during the heat treatment process, the nickel layer may bulge or the mold may become distorted, resulting in a loss of precision in the mold.

Furthermore, in JP-A-48-103031, the mold contains 3 to 1
A mold has been proposed in which nickel containing 3% phosphorus is applied to a thickness of 3 to 300 microns by electroless nickel plating, and then heat treated at 400 DEG C. or less.

This is intended to extend the life of the mold by coating it with a nickel-phosphorus alloy that has excellent heat resistance and hardness.

However, in this case, the hardness of the mold base surface (HV 150~
250) and that of the nickel-phosphorus alloy layer, it is inevitable that the nickel-phosphorus alloy layer will peel off while the mold is in operation, and therefore the life of the mold will not be sufficient.

Regarding the surface protection of the mold, the present inventor aimed to improve the wear resistance of the mold by improving the lubricity between the molten steel and the mold, or more precisely, by improving the lubricity between the vitreous powder and the mold. Various studies were conducted for this purpose.

As a result, a composite plating film containing at least one of graphite and fluorinated graphite dispersed therein and consisting of at least one of nickel and cobalt exhibits excellent performance as a protective layer on the molten steel injection surface of a copper or copper alloy mold. This discovery led to the completion of the present invention.

The composite plating film, which is the surface protective layer of the mold of the present invention, exhibits high wear resistance due to its excellent lubricity during continuous steel casting operations, and also has excellent adhesion to the surface of the mold base.

Therefore, in a normal usage method in which a glassy powder is interposed between a mold and molten steel so as to flow in accordance with the flow of the molten steel, the life of the mold is dramatically increased compared to known molds.

It is generally known that graphite and fluorinated graphite exhibit excellent lubricity at room temperature, but it is completely difficult to predict whether they can exhibit the same excellent lubricity at high temperatures. However, a major technical problem was how to form the coating layer on the surface of the mold.

However, in the mold of the present invention, the above-mentioned remarkable effect can be extremely easily achieved by combining nickel and/or cobalt selected from a large number of plating metals with at least one of graphite and fluorinated graphite. It will be achieved.

In the present invention, nickel and cobalt may be used alone or in combination as an alloy.

The graphite and fluorinated graphite powders dispersed and contained in nickel and/or cobalt may be used alone or in combination.

The particle size of the powder is preferably 30 μm or less so that a uniform colloid can be formed in the plating bath.

However, it is desirable that the particle size does not exceed the thickness of the composite plating film.

The amount of graphite and/or graphite fluoride relative to nickel and/or cobalt in the composite plating layer is preferably about 99 to 60 parts by weight for the former and 1 to 40 parts by weight for the latter.

The thickness of the composite plating film for surface protection in the present invention is:
Usually 5 to 3000 μm, more preferably 30 to 2
000 μm.

If the thickness is less than 5 μm, the surface protection effect will not be sufficiently exhibited, and if it exceeds 3000 μm, the tendency for the film surface to become non-uniform increases.

In order to form a composite plating film in the present invention, first, the surface of the mold substrate is pretreated.

That is, the parts of the copper or copper alloy mold other than the molten steel injection surface are masked with a suitable coating material such as vinyl chloride resin paint, and then degreasing, acid treatment, washing with water, etc. are performed in sequence according to conventional methods.

Examples of the series of treatments include alkaline degreasing→water washing→electrolytic degreasing→water washing→acid treatment→water washing.

In this series of treatments, alkaline degreasing is carried out using, for example, 20 to 200 f//l of caustic soda and O to 150 f//l of soda carbonate.
? /l, sodium orthosilicate O~100 f/l and surfactant 0.5~30 f/l
Temperature 20-80
This is done by immersing the sample at a temperature of approximately 5 to 60 minutes.

After washing the mold with water, in the same bath as above, the cathode current density was 1 to 1.
About 30A/dm, temperature about 30-70℃, time 1-3
Electrolytic degreasing is performed for approximately 0 minutes.

After further washing the mold with water, it is activated by immersing it in an approximately 5-50% aqueous solution of hydrochloric acid, sulfuric acid, etc. at room temperature for approximately 1-10 minutes.

The pretreated mold is subjected to electroplating or electroless plating in a nickel and/or cobalt plating bath in which graphite and/or fluorinated graphite fine powder is suspended.

The plating bath may be a normal nickel and/or cobalt plating bath in which fine powder of graphite and/or graphite fluoride is suspended.

In order to uniformly disperse graphite and/or fluorinated graphite fine powder into the nickel and/or cobalt plating layer, it is extremely important how to suspend these fine powders in the plating bath.

For this purpose, suspension stabilization with a surfactant and/or gentle mechanical stirring is performed to the extent that the fine powder can be suspended in the mustard.

When using a surfactant, use a cationic surfactant of o, 5? /li~xo? /l and a normal plating bath (0
,001~0.01? It is preferable to use the amount in a larger amount than the amount (approximately 1/l).

Examples of mechanical stirring methods include air blowing and rotary stirring using a screw.

The conditions during plating may be substantially the same as those for normal nickel and/or cobalt plating.

For example, nickel sulfate 200-300 g/l, boric acid 1
0~6o? /l, cationic surfactant 0.5-1 (1/l)
pH 1.0-2.0°, temperature 50-60°C, and cathode current 5 in a plating bath containing 50-300 V/l of fine powder and
By electroplating under conditions of ~15 A/d rtl, nickel 80~9 is deposited on the molten steel injection surface of the mold.
A composite plating layer containing 0% and 20 to 10% of the above-mentioned fine powder is obtained.

After the mold on which the plating layer has been formed is washed with water and dried, the masking coating material is removed, thus obtaining the mold of the present invention.

Note that depending on the type of steel to be cast, it may be necessary to increase the thickness of the plating film because it is used under more severe conditions.

However, if the thickness of the composite plating film becomes too large, problems arise such as a slight decrease in the smoothness of the film surface and a decrease in adhesion due to the difference in hardness with the base copper plate.

In such a case, first pre-treat the surface of the copper mold substrate in accordance with a conventional method, then form a plating film containing a small amount of nickel and cobalt (or both), and then coat graphite on top of it by the method described above. By forming a composite plating film consisting of at least Class I fluorinated graphite and at least one of nickel and cobalt, a plating layer that is thick, has excellent smoothness, and has excellent adhesion to the base copper plate. It has been found that it can be formed without any problem.

A mold with such a double plating layer can withstand harsher working conditions than a mold with a single plating layer.

When forming a double plating layer, the second layer made of nickel and/or cobalt has a thickness of about 500 to 3000 μm, and the second layer made of graphite and/or fluorinated graphite and nickel and/or cobalt has a thickness of about 100 to 3000 μm. It is preferable to set it to about 2000 μm.

In the present invention, by further forming a chromium plating layer on the composite plating layer, it is possible to completely prevent the adhesion of molten steel sparks at the initial stage of pouring, and to further increase the life of the mold.

Formation of the chrome plating layer can be easily carried out by a conventional electroplating method.

The thickness of the chromium plating layer is not particularly limited as long as it can prevent the adhesion of molten steel sparks, but is generally 0.1
A ~10μ door is sufficient.

The features of the present invention will be further clarified by examples below.

Example 1 The parts other than the molten steel molding surface of the base of a pure copper steel plate continuous casting mold (short side width 300% x height 700%, long side width 1300% x height 700%) were coated with polyvinyl chloride paint. Masking and caustic soda 50f/11 carbonated soda 25
? /73. It is degreased by immersing it in an aqueous solution containing 5 y/l of anionic surfactant at 50° C. for 40 minutes.

After washing with water, add 30% caustic soda. /l, orthosilicate 150? /l, p consisting of surfactant lO1/l
Electrolytic degreasing is performed in an aqueous solution of H4 at a cathode current density of 10 A/di at 60° C. for 2 minutes.

After washing with water, it is activated by immersing it in a 5% sulfuric acid aqueous solution at room temperature for 10 minutes.

The above steps are referred to as pretreatment.

After washing with water, nickel sulfate 300? /l, boric acid 30 f?
/l, nickel chloride 70f//l, saccharin 1? /l
The average particle size is 7 in the electrolytic nickel basic composition plating solution consisting of
μm graphite powder 300 f? A plating solution containing 53% Ni and 17% graphite was plated on a mold at a cathode current density of 5 A/d ms and a temperature of 55°C for 20 hours while suspending the graphite powder. Apply a composite plating film (1050 μm).

After washing with water and drying, remove the masked polyvinyl chloride paint.

The surface hardness of the mold thus obtained is micro Vickers hardness HV 850, and the usable heat resistance temperature is 1160°C.
By using this mold, 450 charge product slabs were produced without fail.

Example 2 Mold for continuous casting of steel sheets made of copper alloy containing 0.5% silver (short side width 300% x height 700%, long side width 1100
% x height 700%) is pretreated in the same manner as in Example 1.

After washing with water, cobalt chloride 430 f/l, hydrochloric acid 1OCC/l
l, boric acid 20...? Fine powder of graphite fluoride with an average particle size of 10\μm is placed in a Co plating solution consisting of 200 μm/l of Co plating solution. /l
: Mix and then add cationic surfactant 2? /l in a composite plating bath, the pH was adjusted with screw stirring.
The mold was plated under the conditions of 1.60°C and IOA/dm'' for 20 hours, and a composite plating film of 1050 μm of C085% and fluorinated graphite 15% was applied.

Next, it is washed with water and dried to remove the masked polyvinyl chloride paint.

The surface hardness of the mold thus obtained was Micro Vickers HV 890, and the usable heat resistant temperature was 1200°C.
By using this mold, 440 charge product slabs could be produced without fail.

Example 3 A mold similar to Example 1 was used and pretreated in the same manner as in Example 1, followed by washing with water.

Cobal chloride) 300? /l, nickel sulfate 400
? /l and boric acid 40? 250 t/73 of graphite with an average particle size of 5 μm and 150 g/l of fluorinated graphite were suspended in a Co-Ni plating solution consisting of 5 μm/l with air stirring at 55° C., pH 4, and cathode current density of 5 A/l. drr?
The mold was plated for 22 hours under the conditions of Ni40
%-35% Co-15% graphite-10% fluorinated graphite composite plating is applied to the 1100μ door.

The surface hardness of the mold obtained after washing with water, drying, and paint removal was 950, and the usable heat-resistant temperature was 1350°C. By using this mold, product slabs with a charge of 540 could be produced without fail.

Example 4 Mold for continuous casting of copper alloy steel plate containing 1% silver (short side width 30
0 demon x height 700%, long side width 1100% x height 700%
) was masked in the same manner as in Example 1, and then the mold was coated with 12 o? of sodium orthosilicate. /l, caustic powder 50? 5/l in an aqueous solution containing 30 ff/l of soda carbonate and 51/l of sodium alkylbenzenesulfonate.
Degrease by soaking at 5°C for 20 minutes.

After washing with water, the mold was used as a cathode in a bath of the same composition as I
Electrolytic degreasing is carried out for 5 minutes at a current density of OA/di''.

After washing with water, the mold is immersed in a 5% aqueous sulfuric acid solution for 2 minutes at room temperature to activate the surface.

After washing with water, sulfamino acid nickel 500? /l
, boric acid 2o? /l and nickel chloride 151? The mold was immersed in a nickel plating bath (pH approximately 5.0, liquid temperature 50°C) containing 2A/drI? Plating was carried out for 50 hours at a current density of 1,000 μm to form a nickel plating layer of 1000 μm.

Immediately after washing with water, apply nickel chloride 300? /l, boric acid 2
0? /l, aliphatic amine cationic surfactant 31/
Fine graphite powder with an average particle size of 5μ and a door size of 200? The mold was immersed in a composite plating bath (pH approximately 1.0, liquid temperature 60°C) containing 900 μm of 85% Ni-15% graphite at a current density of IOA/di for 30 hours. Form a plating layer.

By using the mold of this example, a 570 charge stainless steel slab was produced without any trouble.

Claims (1)

[Scope of Claims] 1. 1 to 40 parts by weight of at least one of graphite and fluorinated graphite with a grain size of 30 μm or less are dispersed on the molten steel injection surface of copper or copper alloy constituting the mold, and nickel and cobalt are A continuous casting mold for steel, characterized in that a composite plating layer consisting of 99 to 60 parts by weight of at least one of the following is provided in a thickness of 5 to 3000 μm. 2. On the molten steel injection surface of the copper or copper alloy constituting the mold, (
i) A plating layer consisting of at least one of nickel and cobalt is provided with a thickness of 500 to 3000 μm, and further on the plating layer (11) a small amount of graphite with a particle size of 30 μm or less and graphite fluoride (both 1 to 40 μm of each type) 1. A continuous casting mold for steel, characterized in that a composite plating layer containing 99 to 60 parts by weight of at least one of nickel and cobalt is provided with a thickness of 100 to 2000 μm.