JPH0237904A - Die for cross pressing of hot slab - Google Patents

Abstract

PURPOSE:To prolong the life of dies and to reduce the cost of repairing the dies by forming an oxide layer of a specific thickness on the pressing surfaces of the dies. CONSTITUTION:The oxide layer 3 of 20-250mum is formed on the pressing surfaces 2 of the press dies 1 each having a surface 2a parallel with the side faces of a slab S and a surface 2b inclined thereto. The slab S is press-formed by bringing the dies 1 into contact with the high-temp. slab S thereby pressing the slab. The temp. rise of the dies 1 is then suppressed and the exfoliation is prevented, as the oxide layer 3 has a low coefft. of heat transfer, is hard and has wear resistance. The crack of the dies 1 is prevented and the wear resistance thereof is improved. The life of the dies 1 is prolonged and the cost of repairing the dies is reduced.

Description

Detailed Description of the Invention (Field of Industrial Application) This invention relates to a slab width pressing tool used when manufacturing a slab of a predetermined width by width-reducing a hot slab over its entire length by a pressing method. Regarding types.

(Prior Art) In recent years, there has been a wide variety of product sizes of steel sheets requested by customers. If it were possible to easily supply raw material slabs that matched the product size to the rolling process of steel plates of different sizes, it would be possible to simplify the work process and improve yields, so various methods for manufacturing slabs of different widths have been proposed. has been done.

For example, there are a method of changing the width of the mold during continuous casting, a method of width reduction using a vertical rolling mill, a method of width sizing using a press, and the like.

As shown in Fig. 1, the width sizing method using the press described above consists of a surface 2a parallel to the side surface of the slab and a surface 2b inclined.
This is a method of width sizing by moving a pair of molds 1 having pressing surfaces 2 consisting of This method has recently come into widespread use due to its superior sizing ability compared to the width reduction method using vertical rolling mills or vertical rolling mills.

However, in the above-mentioned pressing method, the contact time between the mold and the slab during slab pressing is long, resulting in a significant rise in mold temperature, causing deformation and wear on the pressing surface, which shortens the life of the mold. Furthermore, there is a problem in that productivity decreases due to an increase in the frequency of mold replacement.

Conventionally, the following mold cooling means have been exclusively used to solve the above problems.

(Mold external cooling method in which water is sprinkled on the pressing surface of the mold.This method cools the pressing surface of the mold by sprinkling a large amount of water during pressing of the slab.However, with this cooling method, the edges of the slab are There is a risk that the slab will be overcooled and have an adverse effect on the quality of the slab.In addition to the above-mentioned water spray cooling during pressing, there is also a method of cooling after pressing the previous slab until the next slab arrives. Since the inside of the mold is at a high temperature due to the previous pressing, sufficient cooling cannot be achieved with a short period of water sprinkling.

In addition, in the external cooling method, only the surface of the mold is rapidly cooled and the temperature difference between it and the inside becomes large, and cracks may occur on the pressing surface of the mold due to thermal stress.

(bl Mold internal cooling method by passing water inside the mold This is a method in which a water channel is installed inside the mold and cooling water is passed through it. ,
A device with a large and complicated mechanism is required, which requires a large amount of equipment cost and requires labor for maintenance. Also, since it is internally cooled, there are problems such as low cooling efficiency.

(Problems to be Solved by the Invention) An object of the present invention is to form an oxide layer of an appropriate thickness on the pressing surface of the press die, and to form a slab width press die with wear resistance and crack resistance. Our goal is to provide the following.

(Means for Solving the Problems) The present inventors have conducted various studies in order to extend the life of a width press mold for slabs, and as a result, have obtained the following valuable findings. That is, (a) the contact between the mold and the slab during pressing is metal-to-metal contact, and the slab is plastically deformed to increase the degree of adhesion, resulting in a significant increase in heat transfer coefficient. Therefore, a large amount of the heat retained in the slab is transferred to the mold through the contact surface, and the mold surface temperature rises rapidly.

(b) The temperature is, for example, 0 to 1200°C slab.
．． Even if it is in contact for 5 seconds, the temperature of the mold pressing surface is 400~
Reaching 500'C.

(C) When pressing a slab in full length and width in actual operation, the above (
Since the state b) is repeated 60 to 70 times at intervals of approximately 1 second, the mold surface temperature reaches approximately 800°C, and the internal temperature also becomes quite high.

(d) If the high temperature condition continues for a long period of time, the quality of the mold material changes, the mechanical strength decreases, and deformation and cracks occur.

(e) By forming an oxide having heat resistance and low heat transfer on the surface of the mold, the rise in mold temperature can be suppressed and deformation and cracking can be prevented.

The present invention was made based on the above findings, and includes:
The gist is ``a mold for width pressing of hot slabs, characterized by forming an oxide layer with a thickness of 20 to 250 μm on the pressing surface of the mold, which has a surface parallel to the side surface of the slab and an inclined surface.''
It is in.

(Function) Hereinafter, the slab width press mold of the present invention will be explained in more detail.

In Figure 2, the material is SNCM630 (component C: 0.27%).
, Si: 0.25%, Mn: 0.44%, P: 0.01
3%, S: 0.011%, Cr: 2.98%, Ni: 2
．． 84%; ) is brought into contact with the slab S at a temperature of 1200'C (
This figure shows the temperature change on the mold surface when the mold is pressed. In the bacteria, the A line shows the case of the mold with an oxide layer formed thereon, and the B line shows the case of the mold as it has been machined.

From this figure, it can be seen that 0 after the mold 1 starts contacting the slab S.
．． The temperature after 5 seconds is 45% for a mold with a machined surface.
In contrast, in the case of a mold with an oxide layer formed by surface treatment, the temperature is approximately 350°C, and the temperature in the case of an oxide mold is more than 100°C lower. I understand.

The heat transfer coefficient at this time is 8400 Kcal/m2h'c in the case of a machined surface mold, but 3500 Kcal/m''h'c in the case of an oxide mold. It was found that the reduction was approximately 2.4 times.

SNCM630 or the like is used as the width press mold material. When an oxide layer is formed on the pressing surface of a mold made of such a material, the oxide itself is hard, has high mechanical strength, and has extremely low thermal conductivity.
As shown in FIG. 3, the oxide 3 enters the pressing surface 2 and serves as an anchor effect, and is firmly fixed to the pressing surface of the mold.

Further, it is important that the oxide layer has an appropriate thickness. As shown in Figure 4, the thickness of the oxide layer is 20 μm.
If the thickness is less than 250 .mu.I, the insulation effect will be poor, and if it exceeds 250 .mu.I, it may peel off due to mechanical impact. Therefore, in the present invention, the thickness of the oxide layer is limited to 20 to 250 .mu.I.

The test results shown in FIG. 4 above were obtained by a test using the apparatus shown in FIG.

That is, the result is that an oxide layer 5 is formed on the surface of the slab-equivalent material S1, which has been previously heated to 1200°C by the induction coil 4.
The temperature of the test piece 6 formed thereon was pressed against it by a hydraulic cylinder 7, and the temperature of the test piece at that time was measured with a thermocouple installed inside the test piece 6.

Further, the following method is used to form an oxide layer on the pressing surface of the mold.

For example, there is a method in which a mold is carried into an air atmosphere furnace or a steam atmosphere furnace, held at a temperature of 900° C. for 2 to 5 hours, and then cooled to room temperature in the furnace.

(Example) Hereinafter, the mold of the present invention will be further explained based on Examples. The shape is as shown in Figure 1, and the material is SNCM630.
The mold was heated to 800-900°C in a steam atmosphere furnace for 4 days.
After holding for a period of time, the furnace was cooled and an average thickness of 80 mm was formed on the pressing surface of the mold.
An oxide layer containing FeO as a main component was formed using a μ customization.

Using this mold, a width of 1000 mm was cast by continuous casting.
~1600mm, thickness 250~270mm, length 6~
10m, 500 slabs with a temperature of 1100-1200°C
', was pressed with a width reduction amount of 100 to 3501Il11, and the temperature change of the pressing surface of the mold and the damage state of the pressing surface were examined.

Further, in order to clarify the effect of the mold of the present invention, a 5001 mm slab was pressed across the width under the same conditions using a mold whose pressing surface had been machined.

FIG. 5 shows temperature changes on the pressing surface of both the present invention and the conventional mold. In the figure, line a shown as a solid line shows the case when the mold of the present invention is used, and line b shown as a dotted line shows the case when the mold with a machined pressing surface is used.

In addition, the section marked ■ in the figure shows the temperature change when the slab with the first grain is pressed, and the section marked ■ indicates the case where there are two holes. The 5th wood and onwards were omitted. Further, C in the figure indicates a section where external cooling was performed by water sprinkling on the pressing surface of the mold while the next slab was being transported after the previous slab had been pressed.

From Figure 5, conventional! ! ! In the case of a mold with a machined surface, the temperature of the pressing surface of the mold rises to a maximum of 600°C, but the temperature rise of the mold in which an oxide layer is formed on the pressing surface of the present invention is about 500°C. C, and the mold according to the present invention is 10
It's about 0°C lower.

Next, we examined the pressing surface of the mold after pressing 500 slabs, and found that in the case of the mold of the present invention, there was almost no cracking or wear on the pressing surface (and no peeling of the oxide layer was observed). On the other hand, in the case of conventional molds with machined surfaces, wear occurred and many cracks occurred on the entire pressing surface.

(Effects of the Invention) As explained above, the mold of the present invention has extremely excellent wear resistance and cracking resistance, so the life of the mold can be significantly extended, improving width press efficiency and maintaining maintenance. The effects are significant, such as labor saving and reduction of mold repair costs.

[Brief explanation of the drawing]

Fig. 1 is a schematic plan view showing a state in which a slab is pressed by a press die, and Fig. 2 is a diagram showing a state in which the mold surface temperature of the present invention and a conventional mold increases due to contact with a slab. , Figure 3 is an enlarged cross-sectional view of the oxide layer formed on the pressing surface of the mold, and Figure 4 shows the relationship between the thickness of the oxide layer formed on the pressing surface of the mold and the mold surface temperature. Figure 5 is a diagram showing the elapsed press time and the temperature change of the mold pressing surface, and Figure 6 is a diagram for investigating the relationship between the oxide layer thickness and mold surface temperature shown in Figure 4. This is a schematic diagram of the test equipment used. 1 is a mold, 2 is a pressing surface, 3 and 5 are oxide layers, 4 is an induction coil, 6 is a test piece, 7 is a blood pressure cylinder, and S and Sl are slabs. Se/ Figure ↓ ↓ Ke? Zukan+, Tokiguchi (Li/Shi) Nuisuzu Otsutejizu Luxury St4-'Jh Ginen (Iki)

Claims (1)

[Claims] A mold for width pressing of a hot slab, characterized in that an oxide layer with a thickness of 20 to 250 μm is formed on a mold pressing surface having a surface parallel to the side surface of the slab and a surface inclined.