JPS63115654A - Method and apparatus for casting metal sheet - Google Patents

Abstract

PURPOSE:To make metallurgical structure fine and to improve the mechanical property by heating or holding to or at the temp. of A3 transformation point or higher after cooling a metal sheet which is continuously cast, to the temp. of A1 transformation point or lower in in-line and repeating the heat-treatment, which again cools to the temp. of A1 transformation point or lower in two times or more. CONSTITUTION:The cast slab 3 formed by casting rolls 1, 1' is drawn by pinch rolls 6 and carried to a cooling device 8 by guide rolls 9, and after cooling to A1 transformation point or lower, it is carried to a heating furnace 7, to heat to the temp. of A3 transformation point or higher. Further, by the cooling device 8 and heating device 7, the cooling and the heating are repeated to the temps. of A1 transformation point or lower and A3 transformation point or higher and at last the cast slab is cooled by the cooling device 8. The cast slab 3 obtd. by such a process, is become to extremely fine metallurgical structure and further by executing the hot rolling in the next process, the mechanical property is improved. And, by executing the cold rolling, the reducing of cold rolling ratio and the annealing by low temp. and the improvement of the quality are obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method and a casting apparatus for manufacturing a thin metal plate with a fine metal structure using a twin-drum continuous casting apparatus.

[Conventional technology]

There are two methods for manufacturing thin metal sheets:

■ A thin plate slab (plate thickness 0.8m to 10m) is obtained using a twin-drum continuous casting machine, then the scale is removed using a scale breaker, and the product is hot-rolled to the specified thickness. How to make it into a product.

■ A thin plate slab (plate thickness α8m to 10mm) is obtained using a twin-drum continuous casting machine, and then the slab is pickled (to remove scale) and cold rolled to the specified product thickness. A method of further annealing the product.

[Problem that the invention seeks to solve]

In the case of the above-mentioned casting technology, the most important point is the properties of the thin plate slab obtained by the drum-type continuous caster, but according to the above-mentioned manufacturing process, the properties of the steel plate that becomes the product as hot-rolled are Even after hot rolling (JLLF product), the metal structure is rough and it is difficult to obtain a commercial quality material. Furthermore, steel sheets that are cold-rolled and annealed products have problems such as the need to increase the cold rolling rate and annealing temperature in order to make them into products.

[Means for solving problems]

Following the conventional 9-ram type continuous casting machine, two or more cooling devices and rolling units are installed in succession alternately, and the thin plate slab (α8m
~10m) is subjected to in-line heat treatment to refine the metal structure.

[For production]

A heat treatment process is repeated two or more times, in which the obtained thin plate slab is cooled to a temperature below the A transformation point and then heated in-line to a temperature above the A3 transformation point. The metal structure is α (ferrite structure)
01 (Austenite structure) Transforms and becomes finer.

〔Example〕

The present invention will be explained in detail based on FIG. FIG. 1 is a longitudinal cross-sectional view of a twin-drum type thin metal sheet casting apparatus embodying the present invention. The apparatus shown in FIG.
Side fixed weir to prevent leakage of molten metal 4 between 2.21 and dandy trough for storing molten metal 4 such as molten steel 5. The main components include a heating device 7 for heating the slab 3 and a cooling device 8.

To explain this apparatus in detail, a water-cooled casting roll 1.1' is installed horizontally and is driven to rotate (in the direction of the arrow) by a drive device (not shown). This water-cooled casting roll 1, 1'
is made of copper, copper alloy, or steel, for example,
It has a built-in water cooling mechanism, and has a fairly large diameter roll in order to obtain a large contact area with the molten metal 4.

In addition, fixed weirs 2, 2' made of refractory material are pressed against both ends of the water-cooled casting rolls 1, 1' to seal the sides. Molten metal 4 is poured into the space formed by the fixed weirs 2 and 2'.

The molten metal is cooled by contacting the surface of the casting roll 1.1',
The resulting solidified shell is integrated into a slab 3.

This slab is pulled out by pinch rolls 6 and guide rolls 9
After being transported to the cooling device 8 and cooled to below the A1 transformation point, it is transported to the heating furnace 7 and heated to a temperature above the A3 transformation point. Furthermore, cooling and heating are repeated by the cooling device 8 and the heating device 7 to temperatures below the 9A□ point and above the A3 point, and finally, the material is cooled by the cooling device fit8.

The functions of such a device are as follows: (1) The thin plate slab obtained by the drum type continuous thin plate casting device is
Cool to a temperature below the L transformation, and then in-line A again.
Heat treatment to a temperature of 3 transformation points or higher is repeated two or more times.

(2) Thereafter, it is cooled to a predetermined temperature and sent to the next process (winding process or continuous rolling process).

The present invention aims to refine the metal structure, but this refinement of the metal (ordinary steel) structure is due to α (ferrite structure).
This is carried out using 44-γ (austenite structure) transformation.

When ordinary steel is gradually heated from room temperature, it reaches a boiling point (723℃).
α → r transformation starts at point A3, and everything becomes r. The particle size of r depends on temperature and time, and increases as the temperature increases and the time increases. Here, the heating temperature is only slightly higher than the t-A3 point, so it is in the state of being cast from molten metal (as
The grain size of the cast slab is smaller than that of the cast piece.

Next, when it is cooled down to below the A3 point, α
A nucleus is generated and metamorphosis occurs).It ends at point A□, and everything becomes α.

Therefore, the crystals (α) of the slab are refined by the above heat treatment. (The smaller the grain size of r, the more grain boundaries there are and the more α nuclei are generated.) In addition, the reasons for repeating the α → γ transformation two or more times are as follows:
This is because the crystal grains are not sufficiently refined in the second process.

The present invention refines the metal structure by the above means, thereby improving the quality (material quality) of the steel plate that becomes the product after hot rolling and cold rolling and annealing in the manufacturing process of the steel plate that becomes the product after cold rolling and annealing. The purpose is to reduce the rolling reduction and the annealing temperature, and the reason for this is as follows.

<Regarding the steel plate that becomes a product after hot rolling> The hot rolling temperature is usually 1000 to 1200°C, and this temperature range is the area where γ recrystallizes. When rolled at this temperature, nucleation occurs at the prior γ grain boundaries at the r position and recrystallization occurs. The size of the recrystallized γ grains depends on the size of the prior γ grains. tb, the finer the prior γ grains, the finer the recrystallized r grains.

When it is then cooled to below the A3 transformation point, γ transforms into α, but at this time, α nuclei are mainly generated from the γ grain boundaries, so the size of the α grains depends on the size of the γ grains. .

Therefore, the refinement of the old r grains leads to the refinement of the α grains, and according to the present invention, the refinement of the crystal grains (α) is more remarkable than in the conventional method. In addition, in the method of the present invention, since the prior γ grains are refined, cracks do not occur even when rolled at a lower temperature than conventional methods.
Rolling in 'C) is possible, and rolling in this region deforms the γ grains and generates deformation bands within the r grains. When cooled in this state, α nuclei are generated in the deformation bands generated at the γ grain boundaries and within the r grains, and the α grains become significantly finer.

<Regarding the steel plate that becomes the product after cold rolling and annealing> The slab is elongated by α by cold rolling, and another subgrain boundary is generated within one crystal grain.

When the cold-rolled material is annealed, α nuclei are generated at grain boundaries and subgrain boundaries, and α recrystallizes.

The recrystallization temperature of α decreases as the strain energy accumulated in α increases (the higher the rolling ratio, the smaller the crystal grains). Therefore, by refining the structure (α structure) of the slab through heat treatment in advance, the number of grain boundaries and subgrain boundaries is increased, and the strain energy during cold rolling is increased. It is also possible to reduce the annealing temperature.

As described in detail above, the present invention is characterized in that the slab 3 formed by the casting rolls 1, 1' is heated at 9A by a cooling device and a heating device.
Cooling to a temperature below the engineering transformation point and heating to a temperature above the A3 transformation point, preferably 20-50°C higher than the A3 point, are repeated two or more times, and after cooling the steel plate, it is transported to the next process.

The slab 3 obtained by this process has a very fine metal structure, and it is believed that the next process of hot rolling will improve its mechanical properties. By rolling, it is possible to reduce the cold rolling rate, reduce the annealing temperature, and improve the quality of the material.

Next, a specific example will be described: The dimensions and various conditions of the component parts when steel is cast are as follows. The number of repetitions from point A to point A3 is 2.
It was times.

(1) Water-cooled cast roll Made of steel with internal water cooling, roll diameter 2000
The slab size is 3+u+t×1200+a width with mmφ and roll width of 1200 nm, and the roll rotation speed (casting speed) at this time is about 5Qm1mil.

(2) The heating furnace is composed of a refractory material, an electric heater or a gas heater, etc., and the heating temperature is 900 to 950°C. In addition, the installation location is 650-700℃ (below A1 transformation).
The heating time is 1 to 2 minutes.

(3) The cooling system consists of multiple gas or water injection nozzles (capable of mixed cooling of gas and water), the nozzles are arranged in two places in the vertical direction, and the cooling rate of the slab is increased in the vertical direction. Cool at approximately 0°C/sec.

(4) The composition of the molten metal is C: 20 when it is made into a product as hot rolled.
%, Si: 0.20 St MrL: 0.4
The remaining percentage is free from impurities and Fg, and for steel sheets subjected to cold rolling, C: 0.03%, s=:
0.05 To, MFL: α22, the remainder is free from impurities and Fg, tanditsu self-melting temperature is 15
The temperature is 60°C to 1570°C.

(5) Hot rolling The hot rolling rate is 25 degrees and the hot rolling temperature is 1100'C.
, 950°C.

(6) Cold rolling rate The cold rolling rate is 15 inches to 85%.

(Force annealing temperature The annealing temperature is 700°C to 900°C.

Figure 2 shows the yield points of the hot-rolled steel sheet manufactured under the above conditions and the hot-rolled copper sheet manufactured by the conventional process, and the seven values of the cold-rolled steel sheet manufactured under the above conditions and the cold-rolled steel sheet manufactured by the conventional process. (The index is used to express the hardness. The higher the value, the better the hardness is.) and the cold rolling rate.
Furthermore, FIG. 4 shows the relationship between T value and annealing temperature. As a result, the hot-rolled steel sheets manufactured by the process of the present invention have improved mechanical properties compared to steel sheets manufactured by the conventional process due to the fine metal structure before hot rolling. The manufactured cold rolled steel sheet had a fine metal structure before cold rolling, which made it possible to lower the cold rolling rate and annealing temperature compared to conventional processes. Furthermore, we were able to improve the quality of the material.

〔Effect of the invention〕

By repeating the heat treatment of cooling the cast thin metal sheet to below the A□ transformation point and then heating it again to above the A3 transformation point twice or more, and then cooling it, a thin sheet slab with a refined metal structure is produced. The mechanical properties can be improved by hot rolling in the next step.

Furthermore, it is possible to reduce the cold rolling rate and annealing temperature in the cold rolling process and annealing process, and to improve the material quality.

[Brief explanation of the drawing]

FIG. 1 is a longitudinal sectional view of a thin metal plate casting apparatus embodying the present invention. FIG. 2 is a diagram showing the yield points of hot rolled steel sheets manufactured by the process of the present invention and the conventional process. Third
Figures 4 and 4 show the relationship between the 7 values, cold rolling ratio (Figure 3), and annealing temperature (Figure 4) of cold rolled steel sheets manufactured by the process of the present invention and the conventional process. . 1.1'...Water-cooled casting roll 3...Thin slab 6...Pinch roll 7...Heating device 8...Cooling device Sub-agent Patent attorney Shige Okamoto Father of 2 people Figure 2

Claims (2)

[Claims] (1) A method of casting thin metal sheets using two water-cooled casting rolls arranged horizontally with an interval corresponding to the thickness of the thin metal sheet to be cast and rotating in opposite directions. A_1 After cooling to a temperature below the transformation point,
Heating or heating and holding at a temperature of A_3 transformation point or higher again,
A method for casting a thin metal sheet, characterized in that the heat treatment of cooling again to a temperature below the A_1 transformation point is repeated two or more times in-line. (2) In a continuous casting machine that has two water-cooled casting rolls arranged horizontally with an interval corresponding to the thickness of the thin metal sheet to be cast and rotating in opposite directions, the cast thin metal sheet is heated to below the A_1 transformation point. A thin metal sheet casting apparatus characterized in that two or more cooling devices for cooling and two or more heating devices for heating above A_3 transformation point are provided alternately and consecutively.