JPS5929343B2 - Continuous casting mold - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a continuous casting mold, and particularly to a multilayer coated continuous casting mold having a long life.

Conventionally, continuous casting molds have been put into practical use by employing copper or copper alloy as a base and applying chromium plating to the base.

For rapid cooling by water cooling, copper or copper alloy with good thermal conductivity is used, and a base made of soft copper or copper alloy is used to prevent wear due to the descent of the shell layer forming the finished product slab, bloom, etc. This is to prevent the formation of so-called star cracks due to adhesion of copper or copper alloy to the shell layer of the product.

However, chrome plating has low hot hardness and wears out, and the coefficient of thermal expansion is significantly different from that of the base material, so the chrome plating peels off relatively quickly due to thermal shock during casting, exposing the base steel. Therefore, after the chromium coating layer was peeled off, the copper substrate was severely damaged, and star cracks caused by the copper appeared on the product, which required surface preparation and significantly reduced the product yield. .

As a solution to the above drawbacks, nickel-plated molds have been studied and put to practical use.

Nickel had great expectations because its physical properties, such as the coefficient of thermal expansion, are very similar to those of the base steel, but its hardness is extremely low, so in order to obtain a long-life mold, it was necessary to make the plating thicker. However, this requires repairs to restore the surface accuracy between uses, and on the other hand, due to a decrease in the cooling effect, the casting speed must be significantly reduced, both of which require long-term use. It was not favorable.

In order to overcome this drawback, a first layer is added to the surface of the mold substrate.
A plating layer made of one or more of Ni and Co is provided as a layer, an alloy plating layer made of one or more of Ni and Co and one or more of P and B is laminated on the surface, and a plating layer made of one or more of Ni and Co and one or more of P and B is laminated on the surface. A multilayer plating technique in which Cr plating is applied as three layers or an oxide film thereof is formed on the surface of the third layer was disclosed in Japanese Patent Publication No. 52-50733 and Japanese Patent Publication No. 52-50734.

This includes at least one type of Ni or Co with a Vickers hardness of 200 to 300 in the first layer and 23 to 20 in the second layer.
%, a hard alloy layer of 600 or more formed of an alloy consisting of at least one type of B2-15 and the remainder at least one type of Ni and Co, and a Cr plating layer as a third layer. It is a multi-layer coated mold with an oxide layer formed by oxidizing the second alloy plating layer.

With this multilayer mold, the life of a continuous slab caster can be extended by about 6 times compared to a conventional mold with simple Cr plating, and surface defects such as star cracks can be completely prevented.

However, even in this multilayer mold, plumes, billets,
When it was put to practical use as a beam blank, it was found that the second layer melted red hot in the upper part of the mold during use, causing significant local damage.

An object of the present invention is to eliminate the drawbacks of conventional multilayer molds and to provide a continuous casting mold that has a longer life and is more versatile.

The gist of the present invention is as follows.

That is, a base that constitutes a mold made of copper or a copper alloy, a first layer made of nickel or cobalt or a nickel-cobalt alloy that covers the entire inner surface of the base, and 5-phosphorus that further coats only the lower part of the first layer. and a second layer mainly composed of at least one of nickel and cobalt containing at least one of boron, and chromium or nickel further coating the second layer and the top of the first layer.
The continuous casting mold is characterized in that it has a third layer made of cobal oxide.

A multilayer coated continuous casting mold according to the present invention will be described with reference to the accompanying drawings.

FIG. 1 is a partially cut away perspective view of a mold made of Cu or Cu.
It is composed of a base body 1 made of an alloy, and its outer periphery is water-cooled.

FIG. 2 is a sectional view taken along the line ■-■ in FIG.
A first layer 3 made of Ni, Co, or Ni-Co alloy is coated on the inside of the 1st layer 3, and a second layer 4 is coated only on the lower part of the first layer 3, as shown in the second layer coating position 2 shown in FIG. , and further covered with a second layer 4 and a third layer 5 made of Cr on the remaining part of the first layer 3 or an oxide of nickel or cobalt obtained by oxidizing the first layer or the second layer. be.

The second layer 4 is coated directly on the first layer 3 as shown in FIG.
The first layer 3 may be coated on the surface of the first layer 3 as shown in FIG.
A recess may be formed only in the lower part of the recess, and only the recess may be coated with the second layer 4 to make the outer surface flat.

That is, the second layer 4 of the multilayer plating of the continuous casting mold according to the present invention has high hardness at high temperatures, has a dense structure, and has strong resistance to wear.
The first layer 3 is interposed between the second layer 4, which has a significant difference in hardness, and the base 1, and plays a buffering role, as well as significantly improving practical adhesion, thereby explaining its reason for existence. It recognized.

The third layer 5, chromium or oxide film layer, is a layer to prevent molten steel splash from sticking in the initial stage of casting.

Molten steel is usually supplied from the top of the mold through a type of conduit such as an immersion nozzle, is water-cooled from the four peripheries of the back of the mold, and gradually solidifies, and then solidifies around the molten steel from the middle to the bottom of the mold, that is, in the area in contact with the inner surface of the mold. A shell is formed, and the thickness of the shell gradually increases inwardly as it is pulled downward from the lower end of the mold.

Depending on the type of mold, some are pulled vertically downwards from the mold, others are bent horizontally as soon as they leave the mold, and others are curved so that when they leave the mold, they are already angled from vertical to horizontal. Although the load on the inner surface of the mold is different, it is the shell that undergoes severe wear, and the upper part of the mold, where the shell is formed, is hot but comes into contact with the wall surface. The molten steel still has fluidity, so severe wear does not occur.

Therefore, the second layer, which is mainly expected to have the function of resisting wear, can be installed over the entire surface, but it is required from the middle to the bottom of the mold for shell formation. It is not necessarily required in the upper part, and its absence will not reduce the overall life of the mold.

However, as we conducted many continuous castings using multilayer plating molds and continued to research their improvement, it became clear that the presence of the second layer on top often caused warping, which was inconvenient.

That is, thermal damage to the second layer at the top of the mold,
This is particularly the case where melting damage, which is a dense collection of fine irregularities, occurs in areas that are exposed to high temperatures.

To explain in more detail how such damage occurs,
Molten steel is poured from the top of the mold through a type of conduit, such as a submerged nozzle.

In the case of the type in which the molten steel leaves the conduit and falls vertically, that is, the type in which it blows out downward,
However, impurities in the molten steel, which are not related to the above-mentioned thermal damage, are not pushed out to the upper surface by the convection circulation of the molten steel, but instead enter the product as they are.

Therefore, a type of conduit that blows out from the lower end of the conduit below horizontally in two directions of 180 degrees, four directions of 90 degrees, and sometimes six directions of 60 degrees is sometimes used.

If the blowing direction is close to and directly facing the inner wall of the mold, that is, if the molten steel is operated in a state where it collides with the wall, the wall directly facing the blowout will be water-cooled from the back side. Even though it is still there, the temperature is extremely high.

On the other hand, alloys of Ni or Co, Ni-Co and P or B have lower melting points than metals containing only Ni or Co.
As shown in the N1-P alloy equilibrium diagram in the figure, N15
The melting point of P (Pl 1%) is 880°C, and even if the alloy has a P content of 8 to 9%, if the temperature rises to 1000°C, it will be in the danger zone of melting.

By cooling from the back side, the inside temperature of the mold is generally 800°C.
Although not higher than this, there is of course a danger that the temperature will approach the melting temperature as long as the steel is in contact with high-temperature molten steel.

In fact, as mentioned above, when molten steel was blown out horizontally and applied to the adjacent wall surface, a second layer of dense uneven surfaces was observed on the inner wall surface of the mold in a small portion directly facing the spout.

If such damage occurs, it can cause molten steel to stick in that area, cause surface scratches on the product, and other defects.
In some cases, friction may occur in the flow, or it may become caught and cause a breakout accident, so it is safer to avoid and omit the second layer at the height of the molten steel blowout area. be.

Therefore, the preferred upper limit for installing the second layer is above the middle point where the shell is formed and below the height where the spout is installed and the molten steel is sprayed onto the front surface. It is within the range of 200 to 500 mm when viewed from the top of the copper or copper alloy material.

The present invention provides a second layer in the area below the upper limit of the second layer, and does not plate the second layer in the area above the upper limit, so that it can sufficiently withstand high-temperature abrasion, and can also withstand ultra-high temperatures. An improved continuous casting mold that does not cause thermal damage can be provided.

Example 1 The short side (width 200 mm x height 700 mm) of a continuous casting mold for slabs made of pure copper with a cross section of 200 mm x 1800 mm, the part outside the molten steel molding chamfer was masked with polyvinyl chloride paint and hydroxylated. Sodium 509//l,
Carbon bed sodium 259/L anionic surfactant 5f
! It was degreased by immersing it in an aqueous solution consisting of /l at 50°C for 40 minutes.

Then, washed with water, sodium hydroxide 30 g/71, sodium orthosilicate 150 g #, surfactant 10EI/1
Cathode current density 10 A/d in a pH 4 aqueous solution consisting of 3
n12. Electrolytic degreasing was carried out at 60°C for 2 minutes.

After washing with water, it was 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, sulfamino acid nickel 6009/l.

In an aqueous solution consisting of nickel chloride 1og/11 and boric acid 30g/12, pH 4.0, bath temperature 50°C, 1.5A/d.
Ni plating was applied as the first layer for 70 hours.
000 μm thick.

Next, after inspecting the flatness of the finished surface and performing repair work if necessary, 350 mm from the top of the Ni-plated surface.
The upper part of the line lowered by 1 mm is covered with adhesive cloth-filled vinyl tape, the exposed lower half is subjected to degreasing and electrolytic degreasing, and then nickel sulfate 1809/13, boric acid 309/11. p in an aqueous solution consisting of 50 &/l phosphoric acid
H1,7, bath temperature 50°C1 current density 4 A/dm2
After plating for 9 hours under 0 conditions, the second layer of N1-P alloy
A thickness of 0 μm was applied.

At this time, the current density was lowered and the upper edge of the plated portion of the second layer was rounded so as not to form a sharp step.

Remove the vinyl tape covering the upper half of the water-washed area, and apply chromic anhydride 2509/11 and sulfuric acid 2.
In an aqueous solution consisting of 5 g/l, bath temperature 45°C, 10 A/dm
2 for 1 hour and 13 μm of Cr plating as the third layer.
was applied.

In the end, on the short side of this object, the first layer Ni1O is 00 μm thick, and the bottom layer is 100 μm thick.
For /2, the second layer was plated with Ni--P2O with a thickness of 0 μm, and the entire third layer was plated with Cr with a thickness of 13 μm.

The slab mold thus obtained was used as a result of use 2.
A slab of 0.00 mm x 1800 mm could be manufactured with high quality without exposing the open substrate Cu of 720 charges.

Example 2 Cu with a cross section of 300 mm x 400 internal dimensions and a height of 700 wtt
- On the inner surface of the blooming mold made of A9 alloy, the first layer was coated with 200 μm of Ni in the same manner as in Example 1, the second layer was coated with N1-P of 60 μm on the lower half below 350 u from the top, and the third layer was further applied on the entire surface. Cr was applied to a thickness of 20 μm.

When using the plume mold coated with multilayer plating in this way, 580 charges of steel blooms with a cross section of 300 mm x 400 mm were manufactured, and the product was able to be manufactured with extremely high quality without exposing the Cu surface of the base.

As is clear from the above examples, the present invention provides a multi-layer coated continuous casting mold in which a second layer containing at least one of nickel and cobalt as a main component and containing at least one of phosphorus and boron is used. Only the lower part of the mold is coated, and on top of that, a third layer of chromium, nickel, or cobalt oxide is applied.
Since the layer was coated, the following effects could be achieved.

(b) The second layer, which is easily susceptible to local thermal damage due to the red-hot steel introduced into the mold, is the upper part of the mold, and the second layer is mainly composed of at least one of Ni and Cr, which contains at least one of P and B. , so the risk of breakout has been completely eliminated.

(b) The present invention greatly extends the life of conventional multilayer coated molds, eliminates short-term exposure of the copper or copper alloy of the mold base, and eliminates star cracks on the surface of the product.

The effects of Gl ((2) and (2) make it possible to stabilize the quality of the finished product, and eliminate the need for surface care of the finished product, improving yield and productivity.

[Brief explanation of drawings]

FIG. 1 is a partially cutaway perspective view showing an example of a continuous casting mold;
2 is a sectional view taken along the line ■-■ in FIG. 1, showing an embodiment of the present invention, FIG. 3 is a sectional view showing another embodiment of the invention similar to FIG. 2, and FIG. N to explain the function of the second layer of the invention
FIG. 1 is an equilibrium state diagram of a 1-P alloy. DESCRIPTION OF SYMBOLS 1... Base body, 2... Covering position of second layer, 3... First layer, 4... Second layer, 5...
...Third layer.

Claims (1)

[Claims] 1. A base that constitutes a mold made of copper or copper alloy,
A first layer made of nickel or cobalt or a nickel-cobalt alloy that covers the entire inner surface of the substrate, and at least nickel and cobalt containing at least one of phosphorus and boron that further coats only the lower part of the first layer. 1
A continuous layer characterized by comprising a second layer mainly composed of seeds, and a third layer made of chromium, nickel, or cobalt oxide, further covering the second layer and the top of the first layer. Casting mold.