JPS59223143A - Mold for continuous casting and its production - Google Patents

Abstract

PURPOSE:To obtain a mold for continuous casting having high hardness and excellent wear resistance by providing a chromium plating layer contg. at least carbon on the inside wall surface of the mold of copper or a copper alloy. CONSTITUTION:A chrome plating layer 1 contg. carbon is formed directly on a base body 2 of a casting mold and the effect thereof is improved if a nickel or nickel-base alloy layer 3 is provided on the body 2 and the chrome plating layer 1 contg. carbon is provided thereon. The exfoliation from the underlying layer is prevented if a single layer of an ordinary chrome plating layer 4 or a composite layer of the layer 3 and the layer 4 is provided on the body 2 and the layer 1 is provided thereon. A plating liquid consisting of 55-90% chromium (III) ion and 45-10% chromium (VI) ion 60-140g/l total chromium is used for the compsn. of the mother liquor for plating to be used for the above.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a continuous casting mold having a carbon-containing chromium-plated surface layer having high hardness and excellent wear resistance, and a method for manufacturing the same.

Continuous casting molds are generally made of M or copper alloy, which has good thermal conductivity. The inner surface of the mold base made of copper or copper alloy that comes into contact with the molten steel or slab (hereinafter referred to as the inside surface of the mold base) is coated entirely with a protective film to prevent the base steel or copper alloy from coming into direct contact with the molten steel or slab. is considered essential.

Traditionally, protective surface coatings on continuous casting molds have been applied to (a) prevent molten steel splash from sticking at the beginning of casting, (b) prevent damage during handling, and (c) protect the copper or copper alloy of the substrate or the underlying plating. Chrome-plated products have been widely used to prevent wear.

However, the hardness of the conventional surface chrome plating layer formed using a normal Sargent plating bath decreases significantly at high temperatures, so it wears out early, especially at the bottom of the mold, exposing the base steel or the underlying plating layer. It has the disadvantage of being

Furthermore, since chromium plating obtained using a normal Sargent plating bath contains microcracks, microcracks are likely to develop due to thermal shock caused by contact with high-temperature molten steel. In the vicinity of the severe meniscus, cracks may become so severe that the casting operation must be interrupted. In other words, if a crack develops significantly at the meniscus, the shell of the steel ingot is not yet sufficiently thick near the meniscus, and the surface frictional resistance caused by the crack may impede the smooth development of the shell, or the shell may become thinner. It is also possible that a breakout may occur due to restraint. Further, if the cracks in the surface chromium plating layer develop further, there is a risk that the chrome plating layer will fall off, or that the cracks will reach the lower plating layer and even the lower plating layer will fall off. If such drop-off of the plating layer occurs, the casting operation must be interrupted and the mold replaced.

The present invention can effectively prevent such drawbacks of the conventional continuous casting mold by forming a chromium layer containing carbon on the surface layer, and this chromium layer containing carbon is This was completed based on the knowledge that it is formed by using a chromium oxalate complex.

The mechanism of carbon inclusion in the chromium plating layer has not yet been completely elucidated, but when a chromium oxalate complex is used in the plating mother liquor, minute activity occurs due to the decomposition of carboxyl groups during the plating process. Carbon eutectoids with chromium and is contained in the chromium surface layer. It is thought that the carbon in the plating solution fills the voids of the precipitated chromium molecules, thereby preventing the generation of microcracks.

The carbon-containing chromium plating layer (1) according to the present invention is
As shown in FIG. 1(a), the effect can be sufficiently exhibited by forming the mold directly on the base (2) of the mold, but as shown in FIG. 1(b), ), the effect is increased by providing a nickel or nickel-based alloy layer (3) on top of the nickel or nickel-based alloy layer (3), and providing a carbon-containing chromium plating layer (1) on top of this as a lower layer. Furthermore, as shown in FIGS. 1(C) and (d), the base (
2) A single layer of a normal chromium layer (4) or a composite layer consisting of a nickel or nickel-based alloy layer (3) and a normal chromium layer (4) is provided on top of the carbon-containing layer of the present invention. Providing the chromium plating layer (1) is extremely effective in preventing peeling from the underlying layer.

The thickness of the carbon-containing chromium plating surface according to the present invention is usually 10 to 50 μm, although it depends on the relationship with the underlying layer.
is sufficient.

The plating bath used in the present invention is a plating solution prepared by adding stabilizers, surfactants, etc. to an aqueous solution containing a chromium oxalate complex and hexavalent chromium ions as a mother liquor.

The mother liquor can be made by adding and reacting chromic acid aqueous solution with oxalic acid, by adding chromic acid to chromium oxalate aqueous solution, and by dissolving chromium hydroxide in oxalic acid and then electrolyzing it using carbon etc. as an anode. - It can be carried out by a method of producing chromium, etc.

The total amount of chromium in the mother liquor is 70 to 140 f/l (
(as Cr) is preferable. When the total chromium content is less than 7° f/l, the current efficiency decreases and it becomes difficult to control plating conditions to obtain a chromium plating layer with uniform electrodeposition and uniform color tone.

On the other hand, if the total chromium content exceeds 140 f/l,
Although the properties of the plating layer are not affected, the viscosity of the plating solution increases, the electrical conductivity deteriorates, and the bath voltage increases, resulting in an increase in electricity costs.

The amount of octavalent chromium in the mother liquor is preferably 90 to 55% of the total chromium amount. If this amount exceeds 90%,
When the amount of sulfate added is small, the plating layer becomes black.

If it is less than 55%, the plating layer in the low current density portion tends to turn black, cracks occur in the plating layer, and the hardness of the electrodeposited material tends to decrease.

The amount of stabilizer added to the above mother liquor depends on its type,
It may vary slightly depending on the bath usage conditions, etc., but it is 20 to 150
A range of f/l is desirable.

Stabilizers used in the present invention include the following.

(1) Borates such as boric acid and sodium borate.

(11) Sulfuric acid and sulfates such as sodium sulfate, potassium sulfate, ammonium sulfate, etc.

(In) Fluorosilicic acid and fluorosilicate salts such as ammonium fluorosilicide and sodium fluorosilicide.

Gv) Hydrofluoric acid and ammonium fluoride, ammonium hydrogen fluoride, sodium fluoride, potassium fluoride
Hydrofluoric acid salts such as fluoride.

(V) Persulfates and persulfates such as ammonium persulfate and sodium persulfate.

(v[l Sulfamic acid and sulfamate salts such as sodium sulfamate and ammonium sulfamate.

=7- (■1) Others: Sodium sulfide.

Furthermore, the chromium plating bath used in the present invention may contain known additives such as anionic surfactants for purposes such as mist prevention, if necessary.

The method of the present invention is usually carried out as follows.

Note that the degreasing process, the lower plating layer forming process, and the intermediate plating layer forming process can be performed using known processes as they are, and the following description is merely an example, and does not limit or define the present invention in any way. It's not something you do.

iI] After masking the parts of the copper or copper alloy mold other than the inner surface of the mold base with, for example, a vinyl chloride resin paint, the mold is subjected to conventional methods such as alkaline degreasing, electrolytic degreasing, pickling, and water washing.

rll] Formation of Lower Plating Layer A plating layer made of nickel or a nickel-based alloy is formed on the inner surface of the mold base of the mold after the degreasing treatment by a conventional method 8-. Examples of nickel plating baths and their processing conditions are shown in Table 1.

In addition, the plating bath for nickel-based gold and its processing conditions are explained in the second to
It is shown in Table 4. In the same table, examples of nickel-iron, nickel-cobalt, and nickel-tungsten alloys are shown as nickel-based alloys, but nickel-manganese, nickel-chromium, and even chromium plating layers formed with conventional Sargent solution are also used. It can also be used as a lower plating layer when carrying out the present invention.

The thickness of the lower plating layer is usually within a range of about 200 to 5,000 μm.

Table 2 Ni-Fe alloy plating example No. 8 Table N1-Co alloy plating example No. 4 Table NI-W alloy plating example [I11] Formation of chromium plating layer On the lower plating layer obtained as above Then, a chromium plating layer is formed using the chromium plating bath described above.

The operating conditions for chrome plating vary depending on the thickness of the plating, the composition of the plating solution, etc., but are usually pH 1.6 to 2.6 and temperature 4.
0~80°C1 shade aiiw flow density 15~50A/dm2
That's about it.

The thickness of the surface chromium plating layer according to the present invention may vary depending on the type of steel to be cast, casting speed, mold dimensions, etc., but is usually within a range of about 10 to 50 μm.

By removing the masking paint from the mold on which the surface chromium plating layer has been formed, the desired product can be obtained.

Examples of continuous casting molds having a carbon-containing surface chromium plating layer formed by the method of the present invention and comparative examples of continuous casting molds having a surface chromium plating layer formed by a conventional Sargent bath are shown below. Let us clarify the characteristics of the invention.

Example 1 As shown in FIG. 2, a lower layer (3) of nickel plating was provided on a copper substrate (2), and a carbon-containing chromium plating layer (1) of the present invention was formed thereon. This is an example of comparison with the law.

Short side of silver-containing deoxidized copper continuous casting mold (width 250mm)
The following surface treatment was applied to the molten steel injection surface (with a height of 800 mm).

(1) Pretreatment 2 After masking the parts of the mold other than the molten copper injection surface with vinyl chloride resin paint, caustic soda 5
0 f/l, 25 f/l of soda carbonate, and 5 f/l of an anionic surfactant at 50°C for 40 minutes to degrease.

After washing with water, add 80 f/l of caustic soda, 150 f/l of sodium orthosilicate and 10 f/l of anionic surfactant.
Electrolytic degreasing is carried out for 2 minutes under conditions 16- of 10 A/dm and 60° C. including l. After washing the mold with water, store it at room temperature.
% sulfuric acid aqueous solution for 10 minutes.

(11) Formation of nickel plating B (3): Wash the activated mold with water and apply nickel sulfamate 400.
f/(1, nickel chloride 10 f/l, boric acid 25
immersed in a bath containing 0 Vl of f/L sodium laurate, and the bath temperature was 50-55°C, pH 8,
5 to 4.5, under the condition of cathode current density 2A/dm 6
Electrolytic plating was performed for 5 hours, the surface was mechanically shaped, and 10
A nickel plating layer (3) with a thickness of 0.00 μm is formed.

(+tlj Formation of the chromium layer (1) of the present invention: After degreasing the surface of the nickel plating layer (3) whose surface precision has been obtained by machining using an organic solvent and an alkaline degreaser, the above-mentioned alkaline electrolytic degreasing is further performed. .

After the above pretreatment, the mold was washed with water and placed in a bath containing 200 f/l of chromic acid, 650 f/l of oxalic acid, 100 f/l of ammonium sulfate, 12 f/12 sodium hydroxide, 4 f/l of anionic surfactant. Soak, bath temperature 65°
Electrolytic plating was performed for 1 hour and 80 minutes at C, pH 2.0, and cathode current density of 25 A/dm to form a chromium plating layer (1) of the present invention having a thickness of 15 μm.

Comparative Example 1 The same mold as in Example 1 was pretreated with 1000
A nickel plating layer with a thickness of μm is formed.

After pretreatment, chrome plating is performed using a bath called a normal Sargent bath. That is, chromic anhydride 2
50 f/l, sulfuric acid 2.5 f/l, bath temperature 40-50°C, cathode current density 20 A/dm.
Electrolytic plating was performed for 1 hour to form a 20 μm chromium plating layer.

EXAMPLE The short sides of the molds of Example 1 and Comparative Example 1 were assembled so as to face the slab molds of the same set, and 202 charges of 150 tons of molten steel were continuously cast.

After that, when it was dismantled and investigated, as shown in Figure 5, in Comparative Example 1, a crack (A) occurred in the meniscus part, and the wear-and-disappearance part ()-1 of the chromium layer exceeded 1/2 of the total height. The exposure of the copper substrate (B) had also expanded and reached its serviceable limit.

On the other hand, in Example 1, there were no cracks as shown in FIG.
However, the exposure of the copper substrate (B) was extremely small, and the condition was such that it could be used continuously.

Example 2 As shown in FIG. 8, a nickel-iron alloy plating layer (3) was provided on a copper substrate (2), and a carbon-containing chromium plating layer (1) of the present invention was provided thereon. This is an example of a similar comparison.

The long side of the chromium-containing copper continuous casting mold (width 2400m)
m, height 904 mm) was machined on the molten steel injection surface.
After completing the same pretreatment as in Example 1, the mold was activated, washed with water, and mixed with nickel sulfamate 8009/L iron sulfamate 8 f/L boric acid 25 f/L sodium citrate 10 f/L sodium lauryl sulfate 0.
01 f/l, bath temperature 40-45℃, P
Electrolysis was performed for 80 hours under the conditions of H8.5~4.5 and a cathode current density of 2.5 A/dm to form a nickel-iron alloy plating with a thickness of approximately 1800 μm.
A tapered shape is machined so that the lower end of 0 μm becomes 1500 μm. Thereafter, in the same manner as in Example 1, the mold with the activated nickel-iron alloy plating surface was washed with water, and the chromic acid 2
50 f/L oxalic acid 700 f/L boric acid so y
/L ammonium sulfate 1501/L, surfactant 8f
/l, bath temperature 50-55°C, P)
11.8 to 2.0, electrolytic plating was performed for 2 hours and 80 minutes at a cathode current density of 25 A/dm to form a chromium plating layer of the present invention having a thickness of 25 μm.

19- Comparative Example 2 After forming a nickel-iron plating layer on the long sides of the mold in the same manner as in Example 2, a 80 μm plated layer was formed using a normal Sargent bath.
A chromium plating layer of m was formed.

EXAMPLE Using the long sides of the molds obtained in Example 2 and Comparative Example 2, steel was cast at a casting speed of 1.5 m/min.

In the case of the long side of the mold in Example 2, 846 charges (1
50) (N/Charge) could be cast without any problems, the surface of the slab was good, and the mold could continue to be used.

On the other hand, in the case of the long side of the mold in Comparative Example 2, at the time of 298 charges, there was little copper exposure at the bottom and it was usable, but there were severe cracks in the upper meniscus, and the overall use was at its limit. had reached.

Furthermore, as an embodiment of the present invention, as shown in FIG.
The carbon-containing chromium of the present invention is applied to a so-called two-stage coating mold in which a nickel alloy layer, such as a nickel-tan 20-gesten layer (3), is electrodeposited only on the lower layer, and a conventional chromium plating layer (4) is provided on top of it. By providing the plating layer, the same effects as in the first example and the second example were also confirmed.

[Brief explanation of drawings]

1 to 4 are diagrams showing embodiments of the present invention,
FIG. 1 shows its general aspect, and FIGS. 2 to 4 show the
Embodiments based on Examples are shown, and FIG. 6, right, and FIG. 6 are diagrams showing test results of a mold according to the present invention and a conventional mold, respectively. (1)...carbon-containing chromium plating layer, (2)...substrate, (3)...nickel or nickel-based alloy layer, (4
)...Normal chromium layer, (A)...Crack, (B), (B)...Exposure of copper substrate, (H), (t()...Abrasion-disappeared portion of chromium layer. (more than that), -11, heh, -7, -1 -Kiichi klY 1
i'7;'1 ヱ、'N2 Figure 3 Section 4 Figure 2 2 2 No. 51"ZJ No. 6 227-

Claims (1)

[Claims] ■ A mold for continuous casting, characterized in that a chromium plating layer containing carbon is provided on at least the inner wall surface of the mold. (2) The continuous casting mold according to item 1, wherein the inner wall surface of the mold has a nickel or nickel-based alloy layer. (2) The continuous casting mold according to item 1, wherein the inner wall surface of the mold has a chromium layer. (2) The continuous casting mold according to item 1, wherein the inner wall of the mold has a nickel or nickel-based alloy layer and a chromium layer on a copper or copper alloy substrate. ■ The chromium plating mother liquor composition on the inner wall surface of the mold is 60 to 140 g/A' (as Cr) of total chromium, of which 8 valent chromium ions (mainly composed of chromium oxalate complexes) are 55 to 140 g/A' (as Cr).
A method for producing a continuous casting mold, characterized in that plating is performed using a mother liquor plating solution containing 90% hexavalent chromium ions and 45 to 10% hexavalent chromium ions. ■ The plating solution contains one or more stabilizers from the group of boric acid, sulfuric acid, silicofluoric acid, hydrofluoric acid, persulfuric acid, sulfamic acid, salts of these acids, and sodium sulfide at 20 to 150 f/ 1. The method for manufacturing a continuous casting mold according to item 5, characterized in that it contains: