JPS5825535B2 - 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 wear resistance at high temperatures. The object of the present invention is to provide a mold that is particularly excellent in various properties such as properties.

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

However, since the molten metal injected into the 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 limit 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 abrasion resistance, and vitreous powder was added between the hard chrome plated mold and the melt to match the flow of the melt. Efforts have been made to prevent direct contact between the mold and the melt by interposing the melt so that it flows.

Although the above treatment can be expected to extend the life of the mold to some extent, the surface of the mold base will be exposed and severely damaged after short-term use due to the deterioration of the wear resistance and contact resistance of the hard chrome plating. At the same time, copper or copper alloy adheres to and penetrates the slab, often causing embrittlement, resulting in the problem of microcracks (star cracks) occurring in the resulting slab product.

Furthermore, it has recently been proposed to use nickel as a surface protective layer on the surface of a 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 since the hardness of the nickel layer is quite low at micro-Vickers hardness Hv250-400, it lacks wear resistance and the lifespan is only slightly extended compared to the mold with hard chrome plating. do not have.

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 μm by electroless nickel plating, and then heat treated at 400° 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 (HV150-2
5o) 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 (therefore, the life of the mold will not be sufficient). do not have.

The present inventor has developed various methods while keeping in mind the essential requirements for a surface protective layer of a mold, namely, good adhesion to the surface of the mold base, excellent wear resistance, and excellent heat resistance. As a result of our research, we found that a composite plating film consisting of at least one of nickel and cobalt and containing one or more metal silicides dispersed therein can be used as a protective layer on the molten steel injection surface of copper or copper alloy molds. We have discovered that the above essential requirements are completely satisfied, and have completed the present invention.

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 surface of the mold substrate.

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.

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

Therefore, if these metal silicides could be brought into close contact with the surface of the mold, the life of the mold could be extended.

However, these metal silicides 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, the metal silicide film will peel off and disappear at the same time as molten steel is poured, because the hardness and elongation of metal silicide and copper are significantly different. Probably.

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 are achieved by combining nickel and/or cobalt selected from a large number of plating metals with metal silicide powder.

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

Metal silicides dispersed and contained in nickel and/or cobalt are those listed in the periodic table of elements (in this specification, "Iwanami Rikagaku Dictionary" published by Iwanami Shoten, 3rd edition, p. 1484 -
A silicide powder of a metal belonging to Group 1 Va, Group Va, or Group Vla of the periodic table of short-period elements described on page 1485 is used, and specifically, TtSt2+
ZrSi2. V2Si, TaSi2. CrSi2,
MoSi2°WS 12 etc. are exemplified.

These metal silicides may be used alone or in combination of two or more.

The particle size of the metal silicide 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 metal silicide 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 agent 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 performed using, for example, caustic soda at 20 to 200 Vt.

A mold masked in a degreasing bath (about pH 10 to 14) containing 0 to 100 tons of sodium carbonate/orthosilicate and 0.5 to 30 g/l of surfactant is heated to a temperature of 20 to 80°C. This is done by soaking 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.
30A/dm" 8 degrees, temperature 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 aqueous solution of about 5 to 50% strength, such as hydrochloric acid or sulfuric acid, at room temperature for about 1 to 10 minutes.

The pretreated mold is subjected to electroplating or electroless plating in a nickel and/or cobalt plating solution in which fine metal silicide powder is suspended.

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

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

For this purpose, suspension stabilization with a surfactant and/or gentle mechanical stirring to the extent that the metal silicide fine powder can be suspended with the mustard must be carried out.

When using a surfactant, use a cationic surfactant at a rate of 0.5'i/l to 10? / degree and normal plating bath (
It is preferable to use a larger amount than 0,001 to 0.01 'if/.

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? /l, boric acid 10-60 1/11 cationic surfactant 0.5-10
In a plating bath containing 50 to 300 t/l of metal silicide fine powder, pH 1.0 to 2.0 and temperature 50 to 60.
By performing electroplating under the conditions of .degree. C. and a cathode current of 5 to 15 A/dm@2, a composite plating layer of nickel of 80 to 90 parts and metal silicide of 20 to 10 parts is obtained on the molten steel injection surface of the mold.

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 capacitance difference with the base copper plate.

In such a case, the surface of the copper mold substrate 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 a metal silicide is further coated on top of the plated film made of at least one of nickel and cobalt. By forming a composite plating film consisting of one or more of the following and at least one of nickel and cobalt, a plating layer that is thick, has excellent smoothness, and has excellent adhesion to the copper base plate can be obtained. 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, it is preferable that the first layer made of nickel and/or cobalt has a thickness of about 500 to 3000 μm, and the second layer made of metal silicide and nickel and/or cobalt has a thickness of about 100 to 2000 μm. .

In addition, in the present invention, by further forming a chrome plating layer on the composite plating layer, the effect of the composite plating layer is not impaired in any way (adhesion of molten steel sparks at the initial stage of pouring is completely prevented). , 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
~10 μm is sufficient.

The features of the present invention will be further clarified with the following examples.

Example 1 The outside of the molten steel molding chamfer of the base of a mold for continuous casting of steel plates made of pure copper (short side width 300 mm x height 700 mvt, long side width 1300 mm x height 700 mm) was masked with polyvinyl chloride paint. and caustic soda 50f/1. Carbonated soda 25? /l of anionic surfactant and 51/l of anionic surfactant for 40 minutes at 50°C to degrease.

Then, after washing with water, cylindrical soda 30 Y/l, orthosilicate sodium 1505'/11 surfactant 10? p consisting of /l
Cathode current density 10 A/dm2.60 in aqueous solution of H4
Electrolytically degrease for 2 minutes at ℃.

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 300ff/l, boric acid 30g/
1. Nickel chloride 701? /l, saccharin 1 f/l
Electrolytic nickel base composition plating solution consisting of an average particle size of 9μ
A plating solution containing 300 g/l of Ti5I2 powder was mixed with air, and while TiSi2 was suspended, the mold was plated at a cathode current density of 5 A/dm2, a temperature of 55°C, and a temperature of 55°C for 20 hours. A composite plating film (1050 μm) of 17% TiSi3 is applied.

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

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 plate made of copper alloy containing 0.5% silver (short side width 300 mm x height 700 mm, long side, Fuku 11
A substrate measuring 0.00 mm x 700 mm in height was pretreated in the same manner as in Example 1.

After washing with water, 430 L of cobalt chloride? /l, 10 c of hydrochloric acid
c/l, boric acid 2OL? V2Si fine powder with an average particle size of 10 μm is placed in a Co plating solution consisting of 200 μm/L of Co plating solution. In a composite plating bath containing 21/l of cationic surfactant and 21/l of cationic surfactant, pH 1,
The mold is plated under the conditions of 60° C. and IOA/dm2.20 hours, and a composite plating film of Co85 and V2Si15 is applied to a thickness of 1050 μm.

Next, wash with water and dry to remove the masking vinyl 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 400
? / and boric acid 40L? C o−N i consisting of /l
CrSi250 fi/with an average particle size of 6 μm in the plating solution
and WS i2150 Y/l were suspended at 55°C, pH 4, and cathode current density 5 A/d with air stirring.
The mold was plated for 22 hours under the condition of Ni
Section 40-Co35-CrSi15%-WS i 21
Apply 1100 μm of 0% composite plating.

The surface hardness of the mold obtained after washing with water, drying, and paint removal was HV960, and the usable heat-resistant temperature was 1350°C, and by using this mold, we were able to produce a product slab with a charge of 540.

Example 4 Mold for continuous casting of copper alloy steel plate containing 1% silver (short side width 30
After masking the substrate (0 mm x height 700 mm, long side width 1100 mm - height 700 mm) in the same manner as in Example 1, the mold was molded with Orun silicate soda 120 Y/1.
1 Caustic soda 509/l, carbonated soda! It is degreased by immersing it in an aqueous solution containing 30 V/l and 5'if/l of sodium alkylbenzenesulfonate at 55°C for 20 minutes.

After washing with water, the mold was used as a cathode for 1 hour in a mold of the same composition.
Electrolytic degreasing for 5 minutes at a current density of 0 A/dm2.

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

After washing with water, nickel sulfamate 500? /1
1 boric acid 2Of/7 and nickel chloride 15? The mold is immersed in a nickel plating bath (pH approximately 5.0, liquid temperature 50° C.) containing 1000 μm of nickel plating at a current density of 2 A/dm 2 for 50 hours to form a nickel plating layer of 1000 μm.

Immediately after washing with water, apply nickel chloride 300? /l, boric acid 2
0 V/, l, aliphatic amine cationic surfactant 81
/ and MoSi 2195 fV with an average particle size of 6 μm
The mold was immersed in a composite plating bath (pH approx. 1.0, bath temperature 60°C) containing 300 ml of plating solution at a cathodic current density of 10 A/dm2.
After time plating treatment, 900 μm Ni86%-M
A composite plating layer of 214% oSi is formed.

By using the mold of this example, a 670 charge stainless steel slab was produced without any problems.

Claims (1)

[Scope of Claims] 1. One or more metal silicides with a grain size of 30 μm or less are added to the molten injection surface of the copper or copper alloy constituting the mold.
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 5 to 3000 μm. 2. On the molten 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 (1i) one or more metal silicides with a particle size of 301 kn or less are provided on the plating layer at a thickness of 1 to 40 μm. 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.