KR100887109B1 - Method for Manufacturing ??? Stainless Steel Strip with Twin Roll Strip Casting Apparatus - Google Patents

Abstract

The present invention relates to a method for producing a 304 stainless steel sheet from a molten metal by using a twin roll thin plate manufacturing apparatus, wherein the content of O (oxygen) in molten steel in manufacturing a 304 stainless steel sheet using a twin roll thin sheet casting apparatus or The purpose of the present invention is to provide a method for producing a 304 stainless steel sheet which can be stably casted by minimizing the endothermic change caused by the change of molten steel component by appropriately controlling the content of / and Se.

The present invention provides a molten steel of 304 stainless steel between a pair of rolls of a thin roll cast iron casting machine including a pair of rolls positioned opposite to each other with a roll gap, an edge dam provided at both ends of the pair of rolls, and a meniscus shield for sealing the molten steel surface. In the method for producing a thin plate of 304 stainless steel,

304 stainless steel using a sheet caster to control the O (oxygen) content in the molten steel to 150-250ppm or / and the Se content in the molten steel to 15-60ppm so that the difference in roll endothermic density is within 15% The manufacturing method of a thin sheet is made into the summary.

Double Roll Type, Stainless Steel, Absorption, Sheet, Casting, Roll Absorption Density

Description

METHODS FOR MANUFACTURING 316 Stainless Steel Strip with Twin Roll Strip Casting Apparatus}

1 is a schematic view of a conventional twin roll sheet caster

2 is a correlation diagram of surface occupancy for molten steel of a representative surface activation element.

* Explanation of symbols on the main parts of the drawing *

One . . . Nozzle 2. . . Molten steel 3. . . Double roll 5. . . Lamination

6. . . Atmosphere control device 7. . . Ceiling curtain

The present invention relates to a method for producing a 304 stainless steel sheet from a molten metal by using a twin-roll thin caster, and more specifically, to the absorption ability according to the component change of the molten steel during casting by using a certain amount of the surface active element in the molten steel. The present invention relates to a thin plate manufacturing method of 304 stainless steel using a twin-roll thin plate casting machine capable of reducing the change and minimizing the effect of the fine change of molten steel component on the total casting endothermic amount.

The twin-roll type sheet casting machine is an apparatus for manufacturing a thin plate 5 directly through a rotating roll 3, in which the molten steel 2 supplied from the nozzle 1 is water-cooled as shown in FIG. The quality and shape of the (cast) depends heavily on the initial solidification at the surface / roll contact once solidification is initiated.

Therefore, in most twin roll sheet casting machines, it is essential to maintain an inert hot water atmosphere to form a stable solidification interface.

If a large amount of scum or scull is formed on the hot water surface because it is not maintained in an inert atmosphere, it may be mixed in the cast steel, resulting in cast defects and excessive roll repulsion, which may have a major adverse effect on the quality of the cast steel.

In general, the inert gas atmosphere is maintained in a structure that can be sealed in the state that the molten steel supply nozzle (1) is inserted as shown in Figure 1, wherein the inert gas is the gas of the upper or side of the shielding device (6) The method of blowing through the supply part 8 is used.

On the other hand, sealing with a roll can also install the sealing curtain 7 on a roll, and can maintain airtightness.

Argon gas and nitrogen gas are largely used as the inert gas used for such a water surface shield, and when nitrogen content is not a big problem in final casting, it is common to use relatively inexpensive nitrogen.

304 stainless steel can be used as an inert gas because the nitrogen content in the steel is not a big problem.

In particular, 304 stainless steel contains a large amount of Cr element, which has a high affinity for nitrogen, and has high absorbency against nitrogen, and this property plays a role of homogeneous solidification at the interface between molten steel and rolls and promotes solidification. It plays a big role in prevention.

In other words, when argon is used as a shielding gas for 304 stainless steel, argon existing in the gas layer between molten steel and the roll expands between shells / rolls as the solidification progresses, thereby slowing the solidification, and thus a slight defect on the roll surface is observed. Even if present, the shell thickness of the cast iron is locally reduced, which prevents the strain from occurring when the cast is solidified, which is more likely to cause cast defects than when nitrogen is used as the atmospheric gas.

Therefore, as in US Pat. No. 5,033,595, using a gas having a reactivity with molten steel ensures uniform solidification of the cast steel and at the same time, irregularities are applied to the surface of the roll to effectively disperse thermal stress generated during solidification, thereby eliminating defects. Fabrication of cast steel is widely used in twin roll sheet casting method.

However, when casting molten steel having a hygroscopicity through a nitrogen atmosphere, there was a problem that a large number of castings having a large change in the solidification ability of the rolls occurred.

In other words, in the double roll type sheet casting method, unlike the continuous casting process using the mold flux, which is a heat transfer delay material between the mold and the molten steel, the molten steel is in direct contact with the roll, so the solidification speed is high, and thus there is a factor that affects the solidification pattern. The effect is so large that it is incomparable with continuous casting, and when the same casting thickness is cast even though there is no change of casting variables, the roll speed is quite different.

The change in the solidification ability of the roll, that is, the change in the casting result, is due to the change in endothermic amount due to the change in the molten steel component.

This large change in casting results has a significant impact on the initial roll crown amount applied for the desired shape of the sheet and the uniformity of the solidification performance in the roll width direction, which can cause many obstacles in the production of reproducible quality cast steel.

Moreover, during continuous casting, the rapid change in the solidification capacity at the time of ladle exchange is not only required for the rapid correction of the casting speed for the target thickness, but also the change in the cooling conditions of the casting in the discharge. In operation, there is a high possibility of lowering the reliability of the process itself and impairing the operation stability, which may cause more problems.

In the present invention, in producing a 304 stainless steel sheet using a twin-roll sheet caster, by appropriately controlling the content of O (oxygen) or / and Se content in the molten steel by minimizing the endothermic change due to the change in molten steel stable casting It is an object of the present invention to provide a method for producing a 304 stainless steel sheet as possible.

EMBODIMENT OF THE INVENTION Hereinafter, this invention is demonstrated.

The present invention provides a molten steel of 304 stainless steel between a pair of rolls of a thin roll cast iron casting machine including a pair of rolls positioned opposite to each other with a roll gap, an edge dam provided at both ends of the pair of rolls, and a meniscus shield for sealing the molten steel surface. In the method for producing a thin plate of 304 stainless steel,                     

By controlling the content of O (oxygen) in the molten steel to 150-250ppm or / and the content of Se in the molten steel to 15-60ppm of the difference between the maximum value and the minimum value compared to the average value of the roll endothermic density (unit area and calories per unit time) The present invention relates to a method for producing a 304 stainless steel sheet using a twin roll sheet caster such that the percentage is within 15%.

EMBODIMENT OF THE INVENTION Hereinafter, this invention is demonstrated in detail.

The present invention relates to a method for producing a thin plate of steel having molten steel, the steel which is preferably applied to the present invention is 304 stainless steel, the composition is by weight% C: 0.08% or less, Si: 1.0% or less, Mn: 2.0% or less, P: 0.045% or less, S: 0.03% or less, Cr: 18.0-20.0%, and Ni: 8.0-10.50%.

Factors affecting the absorption when molten steel is absorbable include the elements related to the nitrogen balance concentration in molten steel and the components related to the absorption of molten steel surface at the interface between the molten steel and the roll.

That is, for good absorption, it is preferable that the concentration of nitrogen in the molten steel is low and the concentration difference with the atmospheric nitrogen is large, and the absorption at the contact interface should not be disturbed.

In order for nitrogen to dissolve in molten steel, the following three processes are required in order.

1) Atmosphere gas diffuses to the molten steel surface

2) Chemical reaction on molten steel surface

3) Nitrogen atoms diffuse from the surface into the molten steel

1) does not act as a rate-velocity step because the atmosphere near the hot water surface is nitrogen, and 3) proceeds only after nitrogen has adhered to the molten steel surface, and internal diffusion is closely related to the nitrogen equilibrium concentration in the molten steel. In the end, the absorption is primarily dependent on the chemical reaction in which atmospheric nitrogen melts to the molten steel surface, and is represented by the following formula (1).

dN ₂ / dt = kA (1-f) (PN ₂ -PN ₂ ^e )

Where k is the rate of constant of pure iron, A is the contact area, f is the share of the molten steel surface of a specific element, 1-f is the effective area ratio of nitrogen contact, PN ₂ ^{e is the} equilibrium nitrogen pressure,

PN ₂ : nitrogen pressure)

In other words, the most significant influence on the absorption is the effective area ratio of the molten steel surface, and the aspect of the absorption depends on the magnitude of the effective area ratio.

Elements such as oxygen, S, Se, etc. are active at least on the molten steel surface, and as a result, when these components are large, the proportion of the molten steel surface increases with the increase of the components as shown in FIG. 2, resulting in a reaction area between nitrogen and molten steel. Will be greatly reduced.

In other words, oxygen, S, Se, and the like can be cited as important elements that affect the absorption when a certain amount of nitrogen is present in the molten steel.

In the present invention, it is preferable to control the content of oxygen in the molten steel to 150-250ppm and / or to control the content of Se in the molten steel to 15-60ppm so that the percentage of the difference between the maximum value and the minimum value relative to the average value of the roll endothermic density is within 15%. Do.

Oxygen, S, and Se are typical molten steel surface activation elements, and if the content of these activation elements is large, these elements are distributed on the molten steel surface to prevent the nitrogen gas present in the atmosphere from being absorbed into the molten steel interface.

Therefore, when the content of oxygen and S in the molten steel is small, the absorption of the atmospheric gas into the molten steel does not interfere, and in this case, the difference between the concentration of the atmospheric gas and the nitrogen gas in the molten steel has a great influence on the absorption.

On the contrary, when the content of oxygen and S in the molten steel is large, the absorption of the atmospheric gas into the molten steel is greatly prevented, and the difference between the concentration of the atmospheric gas and the nitrogen gas in the molten steel can exhibit only a secondary effect.

Therefore, in order to keep the adsorption capacity affecting the solidification during casting within a certain range, nitrogen, oxygen and S components in the molten steel must be in a certain range.

However, it is very difficult to manage all the contents of these components in the molten steel within a certain range, and it is not desirable to increase the cost of the steelmaking process, such as lengthening the refining time of the steelmaking process and strengthening the selection criteria of the scrap used as a solvent. The side is likely to emerge.

Therefore, it is preferable to select a relatively easy adjustment of the content of these elements to ensure reproducible absorption within a certain range through the adjustment of the components.

In the present invention, in order to reduce the change in the cooling capacity during casting by adjusting the components related to the absorption, the oxygen content in the molten steel, the oxygen component in the nitrogen and the S component in the molten steel to increase the content As a result, the change in the roll cooling ability due to the variation of the nitrogen or S component in the molten steel component is considerably insensitive, thereby enabling stable and reproducible casting.

The reason why oxygen was selected as the adjustment component among the nitrogen, oxygen, and S components in the molten steel is as follows.

First of all, when adjusting the nitrogen component, it is necessary to increase the nitrogen component in the molten steel. If the nitrogen component is increased, the change in absorption ability due to the change in the oxygen and S components may decrease, but the nitrogen is released as a gas through the solidification process of the molten steel. It is highly undesirable to increase the nitrogen content for the purpose of reducing the coagulation capacity fluctuation because there is a high possibility of adversely affecting the quality of the cast by generating pores in the cast.

In the present invention, the nitrogen content can be in any range as long as it is usually contained, but is preferably limited to 600 ppm or less.

Increasing the S component in the molten steel to reduce the change in cooling capacity due to the variation of other elements is not preferable because the MnS increases with increasing S component, which acts as a grain boundary fragility and causes cast defects.

In the present invention, any of the ranges can be used as long as the content of S is usually contained, but it is preferably limited to 80 ppm or less.

In the case of large amounts of oxygen in molten steel, the amount of inclusions in the continuous casting leads to an increase in the amount of inclusions, which degrades the quality of the cast steel.

However, in the double roll type sheet casting method, since the solidification time of the cast is completed within a short time of less than 1 second, the solidification pattern is fundamentally different from that of continuous casting in which the solidification time is relatively small, and the residence time of inclusions is also considerably shorter. Has characteristics.

Therefore, unlike the continuous casting process in which the inclusion time is long and small inclusions have a high possibility of converting into large inclusions that cause defects of slabs through agglomeration, the twin roll type sheet casting method allows time for small inclusions to aggregate into large inclusions. Since the size of the inclusions remaining in the cast steel becomes small since there is no.

Therefore, even if the oxygen concentration contained in molten steel is slightly higher, the internal quality of the as-cast thin plate produced is hardly affected, and there is no significant effect even in the post-treatment process such as cold rolling.

In the present invention, as described above, by controlling the content of Se in the molten steel to 15-60ppm so that the percentage of the difference between the maximum value and the minimum value relative to the average value of the roll endothermic density is less than 15%, the variation of nitrogen or S component in the molten steel component As a result, the change in the roll cooling ability is considerably insensitive, thereby allowing stable and reproducible casting.

Hereinafter, the present invention will be described in more detail with reference to Examples.

(Example 1)

In a large twin roll sheet metal casting machine having roll diameters and widths of 1250 mm and 1300 mm, respectively, casting was made of 304 stainless steel molten steel having the composition shown in Table 1 to prepare a thin plate, and the endothermic density of the roll was measured, and the results are shown in Table 1 below. Shown in

At this time, the molten steel height was 450 mm, and the casting thickness was 3.4 mm.                     

Casting number Composition (wt%) Roll endothermic density (Mw / m ² ) nitrogen Oxygen S Cr Ni Se A 0.0320 0.0041 0.0031 18.41 8.30 - 6.8 B 0.0143 0.0045 0.0035 18.23 8.51 - 6.1 C 0.0316 0.0051 0.0025 18.34 8.25 - 6.4 D 0.0388 0.0044 0.0041 18.43 8.46 - 6.5 E 0.0321 0.0056 0.0013 18.40 8.44 - 7.5 F 0.0345 0.0062 0.0044 18.14 8.21 - 6.3 G 0.0334 0.0041 0.0017 18.39 8.11 - 7.3 H 0.0256 0.0045 0.0014 18.19 8.31 - 8.0 I 0.0390 0.0055 0.0040 18.24 8.25 - 6.2 J 0.0460 0.0050 0.0058 18.61 8.18 - 5.7

As shown in Table 1, when the oxygen or Se content is not controlled according to the present invention, it can be seen that the roll endothermic density difference is large.

(Example 2)

As shown in Table 2, except that the molten steel composition of the 304 stainless steel was changed, casting was carried out in the same manner as in Example 1 to prepare a thin plate, the endothermic density of the roll was measured, and the results are shown in Table 2 below.

Casting number Composition (wt%) Roll endothermic density (Mw / m ² ) nitrogen Oxygen S Cr Ni Se A 0.0401 0.0188 0.0026 18.33 8.21 - 6.7 B 0.0324 0.0176 0.0031 18.41 8.33 - 6.6 C 0.0344 0.0199 0.0034 18.51 8.21 - 6.8 D 0.0291 0.0210 0.0033 18.27 8.35 - 6.9 E 0.0356 0.0202 0.0048 18.42 8.40 - 6.4 F 0.0342 0.0208 0.0029 18.42 8.44 - 6.5 G 0.0394 0.0188 0.0021 18.31 8.49 - 6.4 H 0.0320 0.0195 0.0043 18.27 8.23 - 6.4 I 0.0411 0.0189 0.0034 18.49 8.18 - 6.3 J 0.0430 0.0178 0.0051 18.55 8.32 - 6.4

As shown in Table 2, by controlling the oxygen content in the molten steel according to the present invention it can be seen that the roll endothermic density difference is small.                     

This is because the oxygen content is large and the surface active agent acts as a surface activator when oxygen is absorbed in the molten steel of the atmospheric nitrogen significantly inhibits the endothermic amount, but it is possible to secure a stable casting not affected by the fluctuations in the molten steel component.

(Example 3)

As shown in Table 3, except that the molten steel composition of the 304 stainless steel was changed by casting in the same manner as in Example 1 to prepare a thin plate, the endothermic density of the roll was measured, and the results are shown in Table 3 below.

Casting number Composition (wt%) Roll endothermic density (Mw / m ² ) nitrogen Oxygen S Cr Ni Se A 0.0451 0.0045 0.0016 18.13 8.29 0.0017 6.5 B 0.0374 0.0055 0.0025 18.54 8.31 0.0021 6.3 C 0.0305 0.0057 0.0027 18.44 8.39 0.0020 6.4 D 0.0391 0.0061 0.0031 18.31 8.29 0.0022 6.3 E 0.0288 0.0041 0.0035 18.45 8.21 0.0022 6.2 F 0.0311 0.0034 0.0039 18.22 8.18 0.0019 6.6 G 0.0334 0.0053 0.0051 18.28 8.38 0.0017 6.2 H 0.0345 0.0052 0.0024 18.33 8.33 0.0018 6.2 I 0.0409 0.0049 0.0037 18.31 8.25 0.0019 6.4 J 0.0290 0.0061 0.0043 18.30 8.29 0.0020 6.5

As shown in Table 3, by controlling the Se content in the molten steel according to the present invention it can be seen that the roll endothermic density difference is small.

As described above, the present invention is to stably cast by using a twin roll type sheet casting apparatus by minimizing the endothermic change due to the change of molten steel by appropriately controlling the content of O (oxygen) in the molten steel or / and Se content It is effective to provide a method for producing a 304 stainless steel sheet.

Claims (4)

304 stainless steel is supplied by supplying the molten steel of 304 stainless steel between the twin rolls which are positioned against each other with a roll gap, the edge dams installed at both ends of the twin rolls, and the twin rolls of the twin roll sheet casting machine including a meniscus shield that blocks and seals the molten steel surface. In the method of manufacturing a thin plate, Double-roll type, characterized in that the percentage of the difference between the maximum value and the minimum value compared to the average value of the roll endothermic density (unit area and calories per unit time) by controlling the content of O (oxygen) in the molten steel to 150-250ppm Method for manufacturing 304 stainless steel sheet using sheet casting machine The method for producing a 304 stainless steel sheet using a twin roll thin plate casting machine according to claim 1, wherein the content of N in the molten steel is 600 ppm or less, and the content of S in the molten steel is 80 ppm or less. 304 stainless steel is supplied by supplying the molten steel of 304 stainless steel between the twin rolls which are positioned against each other with a roll gap, the edge dams installed at both ends of the twin rolls, and the twin rolls of the twin roll sheet casting machine including a meniscus shield that blocks and seals the molten steel surface. In the method of manufacturing a thin plate, By controlling the content of O (oxygen) in the molten steel to 150-250ppm and the content of Se in the molten steel to 15-60ppm, the percentage of the difference between the maximum value and the minimum value compared to the average value of the roll endothermic density (unit area and calories per unit time) Method for producing 304 stainless steel sheet using a twin roll sheet caster, characterized in that less than 15% 4. The method for producing a 304 stainless steel sheet using a twin roll thin plate casting machine according to claim 3, wherein the content of N in the molten steel is 600 ppm or less, and the content of S in the molten steel is 80 ppm or less.

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