JPS5841935B2 - 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 its lifespan in an extremely short period of time. Ta.

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 100°C in an appropriate non-oxidizing atmosphere. A method for examining the formation of

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 HV250-400, so it lacks wear resistance, but the lifespan is slightly extended compared to the mold with hard chrome plating. Not too much.

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

Also, in this method, the nickel-copper diffusion layer has a density of 600 to 100
It is formed by heating at a high temperature of about 0° 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 No. 48-103031, 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 400C 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 (HV150-2
50) 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 glassy powder and the mold. Various studies were conducted.

As a result, a composite plating film consisting of at least one of nickel and cobalt with a low content of molybdenum sulfide and sulfur dispersed therein exhibits excellent performance as a protective layer on the molten steel injection surface of copper or copper alloy molds. This 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 glassy powder is interposed between the 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 sulfur and molybdenum sulfide exhibit excellent lubricity at room temperature, but it is completely difficult to predict whether they can exhibit the same lubricity at high temperatures. A major technical issue was how to form the coating layer on the surface of the mold.

However, in the mold of the present invention, by combining nickel and/or cobalt selected from a large number of metals for plating with at least one of sulfur and molybdenum sulfide, the above-mentioned remarkable effects can be achieved very easily. It will be achieved.

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

The sulfur and molybdenum sulfide 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 ttm 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 sulfur and/or molybdenum sulfide relative to nickel and/or cobalt in the composite plating layer is between 99 and 99% for the former.
The latter is preferably about 1 to 40 parts by weight relative to 60 parts by weight.

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 bottle is less than 5 μm, the surface protection effect will not be sufficiently exhibited, and if it exceeds 3000 μm, the film surface tends to become uneven.

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, caustic soda 20 to 2001/11 and soda carbonate 0 to 150.
? /L Sodium orthosilicate O~100 ? /l: and a degreasing bath containing 0.5 to 30z/l of surfactant (pH 10 to
Temperature: 20-80'
This is done by immersing it at about C for about 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/dmj, temperature about 30-70℃, time 1-
Electrolytic degreasing is performed for about 30 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 sulfur and/or molybdenum sulfide fine powder is suspended.

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

In order to uniformly disperse sulfur and/or molybdenum sulfide fine powder into the nickel and/or cobalt plating layer,
How these fine powders are suspended in the plating bath is extremely important.

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

Q East When using a surfactant: Cationic surfactant o, 5? /l~10f/A and normal nail polishing 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
0-601/l, cationic surfactant 0.5-1M'/
7 and fine powder 50-300? By performing electroplating in a plating bath containing 1.0 to 2.0% of nickel under the conditions of pH 1.0 to 2.01, temperature of 50 to 60°C, and cathode current of 5 to 15 A/dm, nickel of 80 to 80% is deposited on the molten steel injection surface of the mold. A composite plating layer containing 90% 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, the surface of the copper casting base is first pretreated in accordance with a conventional method, and then a plating film consisting of at least one of nickel and cobalt is formed by a conventional method, and then sulfur and sulfide are further coated by the above-mentioned method. By forming a composite plating film consisting of one or more molybdenum 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 problems.

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 first layer made of nickel and/or cobalt has a thickness of about 500 to 3000μ, and the second layer made of sulfur and/or molybdenum sulfide and nickel and/or cobalt has a thickness of 100 to 2000μ. It is preferable to set it as approximately.

In addition, in the present invention, by further forming a chrome 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 may be sufficient as long as it can prevent the adhesion of molten steel sparks (although not particularly limited, generally O1)
~10 μm is sufficient.

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

Example 1 The parts other than the molten steel forming surface of the base of a continuous casting mold for steel sheets made of pure copper (short side width 300% x height 700%, long side width 1300% x height 700%) were coated with polyvinyl chloride paint. Masking and caustic soda 50'? It is degreased by immersing it in an aqueous solution consisting of 25 g/l of sodium carbonate, 25 g/l of soda carbonate, and 51 g/l of an anionic surfactant at 50° C. for 40 minutes.

Next, after washing with water, add 3 o's of caustic soda. /l, sodium orthosilicate 150? /l, surfactant 10? p consisting of /l:
Cathode current density 10A/dl in aqueous solution of H4, 60°C
Electrolytically degrease 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 30i/l
, nickel chloride 70? /l, saccharin 1? A bottle of sulfur powder with an average particle size of 7 μm was added to an electrolytic nickel basic composition plating solution consisting of 30°/l of sulfur powder. /l of the plating solution was stirred with air to suspend the sulfur, and the cathode current density was 5A/dm.
, the mold was plated at a temperature of 55°C for 20 hours, and N
Composite plating film of 83% i-17% sulfur (1050μ
Perform m).

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

The surface hardness of the mold thus obtained was micro-Vickers hardness HV850, and the usable heat-resistant temperature was 1160° C. By using this mold, product slabs with a charge of 450 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 430P/11 hydrochloric acid 10cc/7
．． Boric acid 20? In a composite plating bath, 20Of/A of molybdenum sulfide fine powder with an average particle size of 10 μm was mixed in a Co plating solution consisting of 1/L, and a cationic surfactant of 21/L was added, while stirring with a screw. pH1.60
℃, IOA/dm'' for 20 hours, and a composite plating film of 85% Co and 15% molybdenum sulfide was applied to a thickness of 1050 μm.

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

The surface hardness of the mold thus obtained was MicroVickers HV890, the usable heat resistance temperature was 1200°C, and by using this mold, product slabs with a charge of 440 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 4oo?
/l and boric acid 40f? Sulfur 250 with an average particle size of 5 μm in a Co-Ni plating solution consisting of /J? /l and 150 f/l of molybdenum sulfide were suspended at 55°C, pH 4, and cathode current density 5 A/d r.
The mold was plated for 22 hours under the conditions of RL.
40%-C.

A composite plating of 35%-15% sulfur-10% molybdenum sulfide is applied to a thickness of 1100 μm.

The surface hardness of the mold obtained after washing, drying, and paint removal was HV950, and the usable heat-resistant temperature was 1350°C, and 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% 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 an orthosilicate saw f120? /l, caustic sorter 50 f/l, soda carbonate 3o? /73 and sodium alkylbenzenesulfonate 5? 55 in an aqueous solution containing /l
Degrease by soaking at ℃ for 20 minutes.

After washing with water, the mold is electrolytically degreased for 5 minutes at a current density of 10 A/d m' in a bath with a suitable composition, using the mold as a cathode.

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.

Then, after washing with water, nickel sulfamino acid 500 g/l,
Boric acid 20? The mold was immersed in a nickel plating bath (pH approximately 5.01, liquid temperature 50°C) containing 15 fl/l (nickel chloride and nickel chloride) and plated at a current density of i2A/dm for 50 hours, resulting in a nickel plating of 1000 μm. Form a layer.

Immediately after washing with water, apply nickel chloride 300? /l, boric acid 2
0? /l, aliphatic amine cationic surfactant 3?
/l and fine sulfur powder with an average particle size of 5μm) 200f/l
The mold was immersed in a composite plating bath (pH approximately 1.01, liquid temperature 60°C) containing 900 μm of 85% Ni-15 sulfur and plated at a current density of IOA/dm for 30 hours.
% composite plating layer is formed.

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

Claims (1)

[Scope of Claims] 1. 1 to 40 parts by weight of at least one of sulfur and molybdenum sulfide 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 dispersed. 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 type is provided with a thickness of 5 to 3,000,11,772. 2. On the molten steel injection surface of the copper or copper alloy constituting the mold, (
1) 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) 1 to 40 parts by weight of at least one of sulfur and molybdenum sulfide with a particle size of 30 μm or less and at least one of nickel and cobalt 99~
Composite plating layer consisting of 60 parts by weight, 100 to 2000 parts by weight
Continuous casting mold for steel, characterized by having the thickness of a μ door.