JP2831297B2 - Manufacturing method of stainless steel strip with excellent surface properties - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a twin-drum continuous casting method in which a molten metal is supplied to a pool formed by a pair of cooling drums and cast into a strip. And a method for producing a thin strip by rolling in-line subsequently to a method for producing a thin strip having an excellent surface quality by controlling the depth of a recess formed in the peripheral surface of the cooling drum within a predetermined range. Things.

[0002]

2. Description of the Related Art In a twin-drum continuous casting method, a method for preventing the occurrence of surface cracks in a slab by forming a depression in the peripheral surface of a cooling drum is disclosed in, for example, Japanese Patent Laid-Open No. 1-8334.
0, JP-A-2-224852 and the like.

[0003] When casting is performed in a non-oxidizing gas atmosphere soluble in a molten metal such as N ₂ using such a cooling drum, the occurrence of cracks in the slab can be prevented. When rolling is performed at a rate of 5% to 60%, a scale biting flaw occurs in the thin strip after rolling.

[0004] It is considered that this flaw is caused by the convex transfer portion on the surface of the slab, which is caused by a depression formed in the peripheral surface of the cooling drum, falling down during rolling. Since the flaws have bitten the scale inside, the flaws remain even in a thin product obtained by cold rolling thereafter.

[0005] In addition, if the in-line rolling is not performed after casting, there is no problem because the scale does not bite. In addition, even when performing in-line rolling, it is thought that if the process from casting to rolling is performed completely in a non-oxidizing atmosphere, it is possible to prevent the bite of the scale, but the oxidation of the slab surface is completely prevented at high temperatures. It is not practical to obtain such a non-oxidizing atmosphere.

[0006]

SUMMARY OF THE INVENTION The present invention relates to a method of manufacturing a thin strip by in-line rolling a strip slab cast by twin-drum continuous casting, followed by casting. It is another object of the present invention to provide a thin ribbon having excellent surface properties while preventing the occurrence of scale entrapment flaws generated during rolling.

[0007]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention is to supply a molten metal to a pool formed by a pair of cooling drums, cast the molten metal into a thin strip slab, and subsequently cast the molten metal into a thin strip. In a method of manufacturing a thin strip by rolling a strip slab in-line at a rolling reduction of 5% to 60%, a recess having an average depth of 60 μm or more and a maximum depth of 100 μm or less is formed on the peripheral surface of the cooling drum. Then, the casting is performed in a non-oxidizing gas atmosphere soluble in the molten metal.

Here, the non-oxidizing gas soluble in the molten metal is a non-oxidizing gas (for example, N ₂ ) that is soluble in the molten steel or a non-oxidizing gas that is insoluble and non-oxidizing in the molten steel. It is a mixed gas with a gas (for example, Ar). In the case of a mixed gas, if the molten steel contains at least 20% of a soluble and non-oxidizing gas, it has the same effect as the case of 100% of the soluble and non-oxidizing gas in the molten steel, There is no difference in the effect.

[0009] The depression is formed on the entire peripheral surface of the cooling drum. As a method of processing the dent, there are a photoetching method, a laser processing method, a shot blasting method, and the like.

[0010] The method of measuring the depth of the dent formed in the cooling drum peripheral surface is, for example, to collect a replica from the cooling drum peripheral surface,
The average value and the maximum value are determined based on the replica using a roughness meter.

[0011]

FIG. 1 is a partial sectional side view of a twin-drum continuous casting apparatus used in the present invention. The molten steel is supplied from a ladle via a tundish 1 and a nozzle 3 to a cooling drum 2
The hot water is continuously poured into the pool 4 formed by the a, 2b and the side weirs 8, 8 (the front side is not shown). The molten steel in the pool 4 is cooled by the cooling drum 2 rotating in the direction of the arrow.
The solidification proceeds by cooling by a and b, and a thin strip 6 is obtained at the kissing point 5. The strip slab 6
It is fed by a pinch roll 7 and subsequently rolled by an in-line rolling mill 9 to obtain a thin strip 10. The upper space of the pool 3 is covered with a seal chamber 11,
The inside is sealed with a non-oxidizing gas that is soluble in molten steel.

The present inventor has conducted various studies on the relationship between the surface properties of the strip slabs, strips, and cold rolled sheet products manufactured as described above and the depressions of the cooling drum. for surface cracks prevention of the slab is cooled drum and to form a gas gap between the solidified shell, thereby slow cooling <br/> retirement the solidified shell, to form a convex transcription by depressions in the cast slab surface As a result, it has been found that it is necessary to start solidification from the peripheral portion of the convex transfer and to make the solidification uniform in the slab width direction.

On the other hand, in order to prevent the scale biting flaws of the strips after in-line rolling and the sheet product after cold rolling, the scale biting flaws are high in the convex transfer portion of the convex transfer portion, that is, cooled. Since the pits are preferentially generated from the portions corresponding to the deep dents among the dents formed on the drum peripheral surface, it has been found that the convex transfer height needs to be low, that is, the dent depth needs to be small.

In order to obtain the effect of formation of formation and convex transcription of said gas gap, when the stainless steel, with indentations greater than the average depth 60 [mu] m, soluble in and under a non-oxidizing gas atmosphere molten steel Casting is required. Average depth 60
The insufficient gas gap in recess below [mu] m, cracks are the lack of slow cooling <br/> retirement effect. Further, when the casting atmosphere is a gas insoluble in molten steel, no convex transfer is formed on the slab surface, and the solidification starting point of starting solidification from the periphery of the convex transfer cannot be controlled. It cannot be completely prevented. Further, when the casting atmosphere is an oxidizing gas, the surface of molten steel is oxidized and the oxide is involved and becomes a base point of cracks, so that cracks cannot be completely prevented.

[0015] In order to reduce the above-mentioned convex transfer height and prevent scale biting flaws on the in-rolled slab and the product surface after cold rolling, in the case of stainless steel, the maximum depth of the depression is 100 µm. It must be:

Here, the diameter of the depression is 100 μm.
It is preferably about m to 3000 μm. If the diameter is too small, the formation of the convex transfer becomes unstable, and if the diameter is too large, the interval between the solidification start points at which coagulation starts from the periphery of the convex transfer becomes too wide, and the control of the solidification start point becomes unstable. In either case, cracks are likely to occur.

Further, the area ratio of the depression is 25% to 7%.
About 5% is preferable. If the area ratio is small, the number of depressions is small, the gas gap to be formed is insufficient, and the cooling effect is insufficient, and cracks are likely to occur. On the other hand, if the area ratio is too large, most of the cooling drum becomes a depression, which is not practical in terms of stable processing of the depression and durability of the cooling drum surface after the processing.

In the case of forming a dent on the surface of the cooling drum, it is difficult to make all the pit depths exactly the same, and the pit depth after the processing has a certain variation. Therefore, a hollow within the variation range that satisfies the above conditions is processed into the surface of the cooling drum, cast in a non-oxidizing gas atmosphere soluble in the molten metal, and then rolled in-line to produce a thin strip. By doing so, it becomes possible to prevent both cracking and scale biting flaws.

[0019]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A twin-drum continuous casting apparatus shown in FIG.
A strip slab having a thickness of 3.5 mm was cast, rolling was performed in-line following the casting, and a thin strip having a thickness of 2.7 mm was produced after rolling. .5mm SUS30
Four sheet products were produced.

When manufacturing the above cast slab, a depression was formed on the peripheral surface of a cooling drum having a width of 800 mm and a diameter of 1200 mm under the conditions shown in Table 1. In this example, the processing of the depression was performed by shot blast processing.

[Table 1]

The casting atmosphere in this embodiment used N ₂ as a non-oxidizing gas soluble in molten steel, and used Ar as a non-oxidizing gas insoluble in molten steel.

FIGS. 2 and 3 show typical depth distributions of depressions. FIG. 2 and FIG.
12 and 13 are examples. The surface qualities of the ribbon and the product were as follows.

No. In the case of 1, the convex transfer was obtained by casting in an N ₂ gas atmosphere, but the average depth of the pits was insufficient, so that cracks occurred and the maximum depth of the pits was large. Later, a scale biting flaw also occurred, and the surface quality was poor.

No. Case 2: Since the maximum depth of the depression satisfies the condition, no scale entrapment flaw was generated after in-line rolling, and a convex transfer was obtained by casting in an N ₂ gas atmosphere. Was insufficient in average depth, cracking occurred and surface quality was poor.

No. Cases 3 and 4: The average depth of the depressions satisfies the conditions, and the convex transfer was obtained by casting in an N ₂ gas atmosphere. No cracking occurred, but the maximum depth of the depressions was large. After the in-line rolling, a scale biting flaw occurred, and the surface quality was poor.

No. 5,6,7,8,9: Since casting was performed in an Ar gas atmosphere, no scale flaw was generated, but no convex transfer was obtained, and cracks were generated irrespective of the depression depth.
Surface quality was poor.

No. In the case of 10, the maximum depth of the depression satisfies the condition, so that no scale flaw is generated. However, since the casting is performed in the air atmosphere, cracks due to the entrapment of oxides generated on the surface of the pool remain. Occurred and the surface quality was poor.

No. Cases 11 and 12: The average depth of the depression satisfies the condition, and the convex transfer was obtained by casting in an N ₂ gas atmosphere. Since they were satisfied, there was no scale biting flaw after in-line rolling, and the surface quality was good.

No. In the case of 13, the average depth of the depression satisfies the condition, the convex transfer was obtained by casting in an atmosphere of 20% N ₂ + 80% Ar gas, no crack was generated, and the maximum depth of the depression was obtained. Satisfying the conditions, no scale biting flaws occurred after in-line rolling, and the surface quality was good.

The presence or absence of convex transfer in Table 1 was determined by visual observation after pickling the slab of the part where in-line rolling was not performed. Further, cracks and scale entrapment flaws were visually observed after the obtained thin strip was pickled and then again visually determined after cold rolling.

[0031]

According to the present invention, a stainless steel strip having a thickness close to the thickness of a continuously cast product is rolled in-line and then cold-rolled to produce a thin product. Since the largest surface defect, that is, surface cracks, is prevented, and the scale biting flaws remaining after in-line rolling and cold rolling are also prevented at the same time, the industrial effect is extremely large.

[Brief description of the drawings]

FIG. 1 is a partially sectional side view showing a twin-drum continuous casting apparatus for carrying out the present invention.

FIG. 2 is a diagram illustrating an example of a pit depth distribution processed on a cooling drum. (Example No. 2)

FIG. 3 is a diagram showing an example of a pit depth distribution processed on the cooling drum of the present invention. (Example Nos. 12, 13)

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Tundish 2a, 2b ... Cooling drum 3 ... Nozzle 4 ... Pool part 5 ... Kissing point 6 ... Strip slab (before in-line rolling) 7 ... Pinch roll 8 ... Side weir (The front side is not shown) 9 ... In-line rolling mill 10 ... Thin strip (after in-line rolling) 11 ... Seal chamber

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-3-77747 (JP, A) JP-A-3-71902 (JP, A) JP-A-2-224852 (JP, A) JP-A 64-64 83340 (JP, A) (58) Field surveyed (Int. Cl. ⁶ , DB name) B22D 11/04 B22D 11/06 B22D 11/10 B22D 11/12

Claims (1)

(57) [Claims] 1. A stainless steel melt is supplied to a pool formed by a pair of cooling drums and cast into a thin slab, and subsequently, the thin slab is reduced in-line by 5% to 6%.
In a method of manufacturing a ribbon by performing 0% rolling,
A stainless steel having an excellent surface property, wherein a recess having an average depth of 60 μm or more and a maximum depth of 100 μm or less is formed in the peripheral surface of the cooling drum and cast in a non-oxidizing gas atmosphere soluble in a molten metal. A method of manufacturing a ribbon.