KR100899706B1 - Method for Producing Austenitic Stainless Steel Sheet Using Strip Caster - Google Patents

Abstract

The present invention relates to a twin roll thin plate manufacturing apparatus for producing a thin sheet directly from a molten metal, and more particularly, to a manufacturing method for effectively reducing delta ferrite remaining in an austenitic stainless steel sheet produced by a twin roll thin sheet apparatus.

In the present invention, in order to increase the decomposition effect of delta ferrite in the annealing pickling process, a cold rolling process was added before the annealing pickling. Cold rolling prior to passing through the annealing pickling process not only accumulates the strain energy, but also increases the surface area of the delta ferrite, thereby increasing the rate of decomposition during delta ferrite annealing and reducing the delta ferrite.

Twin Roll, Casting Machine, Stainless Steel, Delta Ferrite, Cold Rolled

Description

Manufacturing method of austenitic stainless steel sheet using sheet casting machine {Method for Producing Austenitic Stainless Steel Sheet Using Strip Caster}

The present invention relates to a method for producing a thin plate directly from the molten metal using a twin roll thin caster, and more particularly to the production of an austenitic stainless steel sheet that can effectively reduce the amount of residual delta ferrite using a twin roll thin caster It is about a method.

In the twin roll type sheet casting method, as shown in Fig. 1, a strip of 2.0 to 4.0mm thickness is produced directly from the molten metal by casting. As compared with the slab casting method, the hot rolling and the reheating of the slab are omitted. This is a process that can reduce.

When austenitic stainless steels are manufactured by sheet casting, residual delta ferrite may cause product quality problems. When the austenitic stainless steel sheet is manufactured by the conventional slab casting method, the slab is reheated and hot-rolled again at a high temperature, so that the delta ferrite existing in the slab casting structure is decomposed to a large extent, thereby eliminating a problem in the quality of the final product.

The austenitic stainless steel sheet produced by the sheet casting method shows a duplex structure containing 2-6% of delta ferrite at room temperature because it is a cast structure such as slab or welded structure by the conventional casting method. Deltaferrite remaining in the cast sheet becomes a serious problem because delta ferrite cannot be decomposed by reheating or hot rolling. Deltaferrite not only deteriorates high temperature processability, corrosion resistance, etc. but also has a disadvantage of limiting the use of the final product because it is magnetic, so it is desirable to remove it from the final product where possible.

As a method of reducing the residual delta ferrite of the austenitic stainless steel manufactured by the conventional sheet casting machine, the winding temperature of the cast steel produced by the sheet casting machine in the Republic of Korea Patent Publication No. 2002-0016266 for 1 hour After maintaining the above to precipitate the carbide and then heat treatment at a high temperature of 1000 degrees or more, a two-stage heat treatment technique for increasing the decomposition rate of delta ferrite by precipitation of carbide has been proposed.

However, in the case of the prior art, it is difficult to complicate the process because the two-step heat treatment to maintain at least one hour at a constant temperature after the winding and heat treatment again at a high temperature, there is a difficulty in complicated process, when a long heat treatment at 600 degrees-800 degrees There is a disadvantage in that the error rate is reduced by the formation of an oxide scale.

The present invention has been made to solve the above problems, by adding a cold rolling process before the annealing pickling process using a sheet caster to increase the decomposition rate of delta ferrite in the annealing pickling process to significantly reduce the residual delta ferrite It is an object of the present invention to provide a method for manufacturing an austenitic stainless steel sheet.

The configuration of the present invention comprises the steps of casting an austenitic stainless steel into a cast using a twin roll sheet caster, rolling the cast in a hot rolling machine to obtain a thin sheet, and edges of the thin sheet to remove edge defects. Trimming, cold rolling the edge trimmed thin plate, and annealing and pickling the cold rolled thin plate.

In the casting step of the cast steel, cast using a meniscus shield and the oxygen concentration inside the meniscus shield is less than 0.1%, the solidification rate by the casting roll is 100 ℃ / sec or more to austenitic stainless steel sheet Can be manufactured.

The hot rolling step may be a reduction ratio of 20 to 40%, the cold rolling step is to reduce the content of delta ferrite by increasing the decomposition rate of delta ferrite during annealing pickling treatment to 20 ~ 40% You can.

Delta ferrite adversely affects the quality of the product, such as causing magnetism or reducing corrosion resistance. In the present invention, by adding a cold rolling process before the conventional annealing pickling process to increase the decomposition rate of the delta ferrite in the subsequent annealing pickling process it can significantly reduce the residual delta ferrite can contribute to the improvement of product quality.

1 shows a method of manufacturing an austenitic stainless steel sheet using a twin roll sheet caster.

Casting method using a twin roll sheet caster is a new process that can be produced by casting the cast slab of 2-6 mm thickness directly from the molten metal, so that the hot rolling in the slab casting method.

Therefore, there is an advantage that the manufacturing cost is reduced compared to the slab playing method, and because the presence of non-equilibrium due to rapid solidification, the quality of the cast steel is also excellent due to the finer grain size or inclusions. The cooling rate of the casting roll should be at least 100 ° C / sec to produce a cast of excellent strength by the refinement of the particle size and the inclusions.

In order to produce a crack-free good slab 8, a meniscus shield 5 capable of completely covering the molten surface and supplying gas, as shown in FIG. 1, should be used. At this time, the atmosphere gas may be argon or nitrogen, and in order to prevent oxidation of the molten metal, the atmosphere gas should be sufficiently supplied to manage the oxygen concentration at 0.1% or less.

The cast slab 8 is hot rolled by a hot rolling mill 12 at a reduction ratio of 20 to 40%, cooled by water and manufactured as a winding coil 11. The reason for limiting the reduction rate to 20-40% is that if the reduction ratio is less than 20%, sufficient surface area cannot be secured during the annealing process, and if the reduction ratio is more than 40%, surface defects may occur due to hot rolling. to be.

In the present invention, in order to increase the decomposition effect of delta ferrite in the annealing pickling process, a cold rolling process is added before annealing pickling as in the third degree. Cold rolling prior to passing through the annealing pickling process not only accumulates the strain energy, but also increases the surface area of the delta ferrite, thereby reducing the delta ferrite by increasing the decomposition rate during the delta ferrite annealing heat treatment.

The reason for limiting the cold rolling reduction rate to 20-40% is that when the cold rolling reduction rate is less than 20%, the strain energy is not sufficient, and the delta ferrite reduction is not enough, and the delta ferrite reduction effect is almost over 40%. It is not increased because the accumulation of strain energy is saturated and no longer increases the rate of delta ferrite decomposition.

Cold rolled coils contain 2 to 6% of delta ferrite. The post-treatment process after sheet casting is trimmed to remove defects such as cracks at the edges, removal of oxidized scale and decomposition of delta ferrite. To pass through the annealing pickling process.

Hereinafter, the present invention will be described in detail by way of examples.

The austenitic stainless steel was dissolved in the composition shown in Table 1 below, and the thin plate was continuously cast using a thin plate player. The solidification rate during casting was 100 ^o C / sec or more, and the distance between resin twins was 3.0-5.0 microns. The oxygen concentration in the meniscus shield 5 was 0.1% or less. After casting, the sheet was rolled by a hot rolling mill 12 at a 30% reduction ratio to obtain a thin cast specimen.

C Si Mn P S Cr Ni Mo Ti Cu Nb N 0.053 0.33 1.06 0.026 0.005 18.18 8.17 0.15 0 0.34 0.005 0.049

The initial delta ferrite content of the prepared specimen was 2.02%. Thereafter, the thin sheet casting specimens were cold rolled to 10%, 20%, 30%, 40%, 50%, and 60%, respectively, and then annealed for 15 seconds at 1150 ° C. 4 shows the amount of change of delta ferrite in a graph.

In the case of annealing without cold rolling, the annealing heat treatment decreased to 1.4%, and further decreased with cold rolling. In the graph, when the cold rolling reduction is less than 20%, the strain energy is not sufficiently accumulated, and the delta ferrite reduction is not sufficient, and the delta ferrite reduction effect is hardly increased at 40% or more, which means that the accumulation of strain energy is saturated. This will no longer increase the rate of delta ferrite degradation.

1 is a detailed view of a general sheet casting machine.

Figure 2 is a schematic configuration diagram of a post-treatment process in the conventional sheet casting.

3 is a schematic configuration diagram of a post-treatment process during thin plate casting according to the present invention.

4 is a delta ferrite decomposition graph according to cold reduction rate.

< Description of the reference numerals for the main parts of the drawings>

1. Casting Roll 2. Ladle

3. Tundish 4. Immersion Nozzle

5. Meniscus Shield 6. Brush Roll

7. Edge dam 8. Cast

9. Pinch Roll 10. Water Cooling System

11. Coiling coil 12. Hot rolling machine

Claims (4)

Casting the austenitic stainless steel into slabs using a twin roll sheet caster; Rolling the cast steel at a reduction ratio of 20 to 40% in a hot rolling mill to obtain a thin plate; Edge trimming the thin plate to remove an edge defect; Cold rolling the edge trimmed thin plate at a reduction ratio of 20 to 40%; And Annealing and pickling the cold rolled cold rolled sheet; Method for producing an austenitic stainless steel sheet using a thin plate casting machine, characterized in that made to reduce the residual delta ferrite content. The method of claim 1, wherein the casting of the cast is cast using a meniscus shield, the oxygen concentration in the meniscus shield is less than 0.1%, the solidification rate by the casting roll is characterized in that more than 100 ℃ / sec Method for producing austenitic stainless steel sheet using a thin plate casting machine. delete delete

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