JPS5841933B2 - 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 hardness, heat resistance and The object of the present invention is to provide a mold particularly excellent in various properties such as wear resistance.

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

However, since the molten steel injected into this continuous casting mold is extremely high temperature, the molten steel injection surface (hereinafter referred to as the mold base surface) is severely damaged, and the mold reaches its lifespan within an extremely short period of time. It had

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 improve the flow of the molten steel. Efforts have been made to prevent direct contact between the mold and molten steel by interposing them so that they flow together.

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 and severely damaged after short-term use, and copper or copper alloy adheres to and penetrates the slab, often causing embrittlement, resulting in slight damage to the resulting slab product. /J4IJre (Star Crack)
The problem was that this 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 the nickel is diffused between the nickel plating and the copper by heating to around 600 to 1000°C in an appropriate non-oxidizing atmosphere. A method of forming the layer 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 chrome plating. It's just being done.

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

Furthermore, in this method, the diffusion layer of nickel na copper has a thickness of 600 to 1
It is formed by heating at a high temperature of about 1,000° 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.

JP-A-48-103031 discloses that the mold contains 3 to 13
It has been proposed that a mold is coated with nickel containing 3% to 300μ of phosphorus by electroless nickel plating and then heat treated at 400°C or less.

The purpose of this is to extend the life of the mold by coating it with a limestone 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 is too large, 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.

The present inventor has developed various methods while keeping in mind the essential conditions for a surface protective layer of a mold, namely, good adhesion to the mold base surface, excellent abrasion resistance, and excellent heat resistance. As a result of research, one or two metal oxides
The present invention has been completed based on the discovery that a composite plating film containing at least one of nickel and cobalt dispersed therein completely satisfies the above-mentioned essential requirements as a protective layer on the molten steel injection surface of a mold made of copper or copper alloy. This is what led to this.

That is, the present invention provides at least one of (1) nickel and cobalt on the molten steel injection surface of copper or copper alloy constituting the mold.
A plating layer consisting of seeds is provided with a thickness of 500 to 3000μ, and further on the plating layer, (1i) a single metal oxide, a composite oxide containing two or more metals, and these oxides. and at least one selected from the above oxides in the form of glass, ceramic, or clay minerals, with a particle size of 30 μm or less, dispersed in an amount of 1 to 40 parts by weight, and at least one of nickel and cobalt. The present invention provides a continuous casting mold for steel, characterized in that a composite plating layer consisting of 99 to 60 parts by weight is provided with a door thickness of 100 to 2000 μm.

The composite plating film, which is the surface protective layer of the mold of the present invention, has excellent heat resistance, extremely high hardness even at high temperatures, and excellent adhesion to the nickel and/or cobalt plating layer provided on the mold base surface. ing.

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

Metal oxides generally have excellent heat resistance and exhibit high hardness even at high temperatures.

Therefore, if these metal oxides can be brought into close contact with the mold surface,
Mold life could be extended.

However, these metal oxides are usually powders or sintered bodies, and do not have any adhesion to the surface of the mold substrate.

For example, even if a coating is applied to the surface of the mold base by plasma spraying, etc., the metal oxide film will peel off and disappear at the same time as molten steel is poured, because the hardness and elongation of the metal oxide and copper are significantly different. .

Furthermore, during the coating operation, the mold base itself is deformed or destroyed by high-temperature plasma or the like.

However, in the mold of the present invention ('!), the above-mentioned remarkable effects can be achieved by combining nickel and/or cobalt selected from a large number of plating metals with metal oxide powder.

In the present invention, nickel and cobalt in the composite plating layer serving as the surface protective layer may be used alone or in combination as an alloy.

The metal oxides dispersed and contained in nickel and/or cobalt are listed in the Periodic Table of Elements (herein, "Iwanami Rikagaku Dictionary" published by Iwanami Shoten, 3rd edition, pp. 1484-14).
Based on the periodic table of short-period elements described on page 85)
Group 1Ia, Group NB, Group MB, Group 1Va, Group 1
Oxide powders of metals belonging to group Vb, group Va, group Via, and group II are used.

The metal oxide may be a single metal oxide, a so-called composite oxide containing two or more metals, or a mixture of two or more of these oxides. It can also be used in the form of various ceramics, clay minerals, etc.

The particle size of the metal oxide powder is preferably 30 μm or less so that it can form a colloid 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 metal oxide relative to nickel and/or cobalt in the composite plating layer can be 99.5 to 5 parts by weight for the former and 0.5 to 95 parts by weight for the latter, but preferably 99 to 95 parts by weight for the former. It is about 1 to 60 parts by weight of the latter to 40 parts by weight, and more preferably about 5 to 40 parts by weight of the latter to 95 to 60 parts by weight of the former.

In the present invention, the thickness of the nickel and/or cobalt plating layer is preferably about 500 to 3000 μm, and the thickness of the surface protective composite plating film is preferably about 100 to 2000 μm.

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

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 sequentially performed according to conventional methods.

An example of such a series of treatments is alkaline degreasing - water washing - electrolytic degreasing - water washing = acid treatment - water washing.

In this series of treatments, alkaline degreasing is performed using, for example, a caustic powder of 20 to 200? /l, carbonate 0-150
11/l.

Orthosilicate 0-100? A masked mold is placed in a degreasing bath (about pH 10 to 14) containing 0.5 to 30 g/l of surfactant and 0.5 to 30 g/l of surfactant at a temperature of 20 to 80°C.
This is done by soaking for about 60 minutes.

After washing the mold with water, in the same bath as above, the cathode current density was 1 to 1.
About 30A/di', 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.

After completing the pretreatment, a plating film made of at least one of nickel and cobalt is formed on the mold by a conventional method.
Electroplating or electroless plating is carried out in a copper and/or cobalt plating bath in which fine metal oxide powder is suspended.

The plating bath may be a normal nickel and/or cobalt plating bath in which fine metal oxide powder is suspended.

In order to uniformly disperse the metal oxide fine powder in the nickel and/or cobalt plating layer, it is extremely important how the metal oxide fine powder is suspended in the plating bath.

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

When using a surfactant, use a cationic surfactant of 0.5y/l to 1o? /l and a normal plating bath (0,
001 to 0.01 g/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
0-60g/11 cationic surfactant 0.5-10f/
J and metal oxide fine powder 50-300 f/l! By performing electroplating in a plating bath containing nickel at a pH of 1.0 to 2.0, a temperature of 50 to 60°C, and a cathode current of 5 to 15 A/di, nickel of 80 to 9
A composite plating layer of 0% and 20-10% metal oxide 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.

According to the present invention, a plating film made of at least one of nickel and cobalt is formed by a conventional method, and then one or more metal oxides and at least one of nickel and cobalt are further added by the method described above. By forming a composite plating film consisting of the following, it is possible to form a plating layer with a large thickness, excellent smoothness, and excellent adhesion to the base copper plate without any defects.

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

In addition, in the present invention, by further forming a chrome plating layer on the composite plating layer, adhesion of molten steel sparks at the initial stage of pouring can be completely prevented without impairing the effect of the composite plating layer. The mold life can be further increased.

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
It may be about 10 μm.

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

Example 1 Mold for continuous casting of copper alloy steel sheets containing 1% silver (short side width 30
0% x height 700%, long side width 1100'! ? x height 70
After masking the parts of the molten steel injection surface other than the injection surface of the molten steel base (0%) with vinyl chloride resin paint, the mold was coated with 120'if/l of sodium orthosilicate, 50 g/l of caustic soda, 3of/l of soda carbonate, and alkylbenzene. Sodium sulfonate? /l for 20 minutes at 55°C to degrease.

After washing with water, the mold was used as a cathode for 1 hour in a bath of the same composition.
Electrolytic degreasing is carried out for 5 minutes at a current density of 0 A/drrl:.

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 500f/J,
Boric acid 20? /l and nickel chloride x 5fl/l in a nickel plating bath (pH approximately 5.0, liquid temperature 50°C) -
The mold was immersed in No. 1 and plated for 50 hours at a current density of 24 A/dm to form a nickel plating layer of 1000μ door.

Immediately after washing with water, nickel chloride 300f/J, boric acid 20
fl/l, aliphatic amine cationic surfactant and A1□03 fine powder with an average particle size of 5μ 200? The mold was immersed in a composite plating bath (pH approximately 1.0, liquid temperature 60°C) containing 900 μm of Ni85%-A120315% at a current density of 10 A/dm for 30 hours.
A composite plating layer is formed.

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

Examples 2 to 6 According to Example 1, copper molds of the present invention having a first layer (nickel and/or cobalt plating layer) and a second layer (composite plating layer) were obtained.

Table 1 below shows the performance of each mold.

Claims (1)

[Claims] 1. 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 (11th coast - single metal oxide, composite oxide containing two or more metals) Contains 1 to 40 parts by weight of at least one selected from the above oxides in the form of a single substance, a mixture of these oxides, and a glass, ceramic, or clay mineral with a particle size of 30 μm or less, and 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 nickel and cobalt is provided with a door thickness of 100 to 2000 μm.