KR20120066475A - Manufacturing method of austenite stainless steel - Google Patents

Abstract

PURPOSE: A method for manufacturing austenite stainless steel is provided to collect alumina inclusion into slag by reducing the amount of aluminum injected during a refining process and controlling the components and bubbling time of aluminum. CONSTITUTION: A method for manufacturing austenite stainless steel comprises a step of implementing bubbling for 12-16 minutes at an aluminum concentration of 0.03-0.05% during ladle treatment of stainless steel. The austenite stainless steel comprises carbon of 0.08 weight% or less(except 0), silicon of 1.00 weight% or less(except 0), manganese of 2.00 weight% or less(except 0), phosphorus of 0.045 weight% or less(except 0), sulfur of 0.030 weight% or less(except 0), nickel of 9.00-13.00 weight%, chrome of 17.00-19.00 weight%, and iron and inevitable impurities of the remaining amount.

Description

Manufacturing method of austenite stainless steel

The present invention relates to a method for producing austenitic stainless steel, specifically, to the production of austenitic stainless steel that can reduce the surface defects caused by inclusions in the final product by improving the cleanliness of the cast steel by reducing the number of inclusions in the production of stainless steel It is about a method.

The stainless steel is used for heat exchanger or heat-treatment parts by improving the high-temperature strength and high-temperature oxidation resistance with (18Cr-9Ni-0.3Ti) by adding Ni to STS 304 steel with stainless steel and adding Ti, a C stabilizing element. STS 321

The molten iron produced in the blast furnace has high carbon (C) content and contains impurities such as phosphorus (P) and sulfur (S). To make these metals strong, it is necessary to reduce the amount of carbon and remove impurities. This is done in the steelmaking process. The steelmaking process can be divided into three processes: charter preliminary treatment, converter steelmaking and secondary refining.

First, the molten iron preliminary treatment is a process for removing the impurity phosphorus and sulfur contained in the waste water. Second, the converter steelmaking process is the process of burning carbon and removing impurities by blowing high pressure and high purity oxygen after pouring molten iron into the converter. Finally, secondary refining is a process that controls the requirements of the final product internal quality (components, materials, etc.).

In particular, the inclusions that cause surface defects are mainly generated during the refining process during the manufacturing process and the steelmaking process. In order to improve the quality of the thin plate, the inclusions in the steelmaking refining process need to be harmless.

Inclusions are metal oxides in which oxidizing elements are combined with oxygen, and are oxides such as silicon (Si), aluminum (Al), titanium (Ti), and the like, which are mainly introduced in a steelmaking process with a deoxidizer and ferroalloy. In particular, Al ₂ O ₃ and TiO ₂ oxides of aluminum (Al) and titanium (Ti) exist as solids in molten steel as high melting point inclusions, and are the main cause of surface defects in final products. Among them, Al ₂ O ₃ combines with MgO to form inclusions with a spinel structure of Al ₂ MgO _3. The spinel inclusions have a high melting point of more than 2000 ℃ and are hard, so if they exist inside the stainless steel coil, the surface when rolling It causes a flaw, and the thinner the coil, the deeper the surface defect.

As to solve the above problems,

An object of the present invention is to reduce the amount of aluminum introduced during the refining process to control the aluminum alloy (Al) component and bubbling time to ensure that the alumina inclusions are sufficiently collected in the slag to clean the molten steel It is to provide a refining method including the ingredient adjustment process to ensure the.

At the same time, an object of the present invention is to provide a refining method that can fundamentally reduce the amount of alumina inclusions while showing the same refining process efficiency as before.

Austenitic stainless steel manufacturing method according to the present invention is wt%, carbon (C): more than 0 and 0.08 or less, silicon (Si): more than 0 and 1.00 or less, manganese (Mn): more than 0 and 2.00 or less, phosphorus (P): More than 0 and 0.045 or less, sulfur (S): more than 0 and 0.030 or less, nickel (Ni): 9.00 or more and 13.00 or less, chromium (Cr): 17.00 or more and 19.00 or less, and other titanium (Ti) is 5 × carbon (C) The steel grade to which (wt%) or more is added is included, and the following component adjustment process (LT) is included.

The component adjusting process LT performs bubbling for 12 to 16 minutes while the steel-clad aluminum (Al) concentration is 0.03 to 0.05%.

In addition, the aluminum (Al) is added in the component adjustment step (LT) to control the concentration of the aluminum (Al) to 0.03 to 0.05%.

It may also further comprise a refining process (AOD). The refining process (AOD) is carried out before the ingredient adjusting process. At this time, in the refining step (AOD), at the end of the step, the residual aluminum concentration is controlled to be within the concentration range of the mild steel (Al).

It may also further comprise a vacuum decarburization process (VOD). Vacuum decarburization (VOD) is performed prior to the component adjustment process. At this time, the residual aluminum concentration at the end of the process is controlled to be within the concentration range of the mild steel (Al).

In addition, the target steel grade is wt%, it may contain chromium 18 and nickel 9, Ti (0.3%) may be added. (18Cr-9Ni-0.3Ti)

According to the present invention, by reducing the amount of aluminum introduced during the refining process and increasing the bubbling time, it was possible to reduce the incidence of defects caused by the alumina inclusions without affecting the refining process.

1 is a conceptual diagram showing a process in which the inclusions 50 in the molten steel 100 float and are dissolved into and removed from the slag 200.

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.

Steelmaking process according to this embodiment is made through the refining process (AOD, Argon Oxygen Decarburization)-ingredient adjustment process (LT, Ladle Treatment)-continuous casting process (C / C, Continuous Casting), or vacuum decarburization (refining step) VOD, Vaccum Oxygen Decarburizatin) process may be further included.

In the refining process (AOD), desulfurization and deoxidation are performed through decarburization and slag production. That is, in the refining process (AOD), argon (Ar) and oxygen mixed gas or nitrogen and oxygen mixed gas are blown into the molten metal. When oxygen is supplied into molten steel, decarburization proceeds as chromium (Cr) is oxidized first.

Vacuum decarburization (VOD) is a vacuum decarburization of high chrome molten steel. Vacuum decarburization in vacuum decarburization generally uses molten steel preliminarily decarburized in a previous step. In the vacuum decarburization process, argon is injected into the vacuum container by argon (Ar) gas through a porous plug installed at the bottom of the ladle, and oxygen is blown from the lance installed at the top while stirring molten steel to perform decarburization. The productivity is lower than that of the refining process (AOD), but is suitable for the production of ultra low carbon (C) and nitrogen (N) steels of high chromium ferrite type.

The VOD process according to the present embodiment may be divided into a total of three stages of an oxygen blowing decarburizer (VOD), a fine decarburizer (VCD) and a deoxidizer (VD, reduced desulfurizer).

In the oxygen blowing decarburizer, degassing and denitrification is carried out by reducing the vacuum to below 5 mbar while blowing argon (Ar) gas from the bottom of the ladle as a decarburizer. In the vacuum decarburizer, oxygen blowing is stopped, and only a large amount of argon (Ar) gas is blown from the bottom to promote fine decarburization reaction according to the reaction of oxygen and carbon blown into the molten steel. In the deoxidation step, it is controlled in a low vacuum state compared to the vacuum state in the decarburization step and the fine decarburization step, and the deoxidizer is added. Next, for degassing, (Cr ₂ O ₃ ) in the slag is reduced, recovered, and deoxidized and desulfurized.

After the ingredient adjustment process (LT, Ladle Treatment) is adjusted by stirring after deoxidation. The component adjustment process is the final process for hitting components and temperatures in molten steel. That is, when argon (Ar) and / or nitrogen (N ₂ ) is blown into the rising pipe in the composition adjustment process, bubbles are formed in the rising pipe and rise up, and the molten steel is moved toward the down pipe due to the potential energy difference. It comes down and circulates. As the molten steel circulates, degassing is carried out to the scattering and foam layers with the bursting of argon (Ar) and nitrogen (N₂) bubbles in the ladle.

That is, in order to remove the inclusions in the component adjustment process LT, an inert gas such as argon (Ar) and nitrogen (N ₂ ) is blown in the lower part of the ladle to stir molten steel to promote the inclusion of the inclusions. 1 is a conceptual diagram showing a process in which the inclusions 50 in the molten steel 100 float and are dissolved into and removed from the slag 200. Removal of the inclusions in the molten steel consists of the following three steps.

First, the inclusion 50 rises and moves to the surface of the molten steel 100. (S1) Next, the molten steel 100 moves to the slag 200 through the interface 10 (S2), and finally the slag ( 200) (S3).

On the other hand, the component analysis and statistical analysis of the defect material was found to have a high incidence of defects due to the alumina inclusions in addition to the Ti oxide inclusions. In addition, through the analysis of the effect of defect occurrence by operating conditions, it was found that the aluminum concentration in the deoxidation process was closely related to the alumina defect of the intermediate or final product.

<Test Process and Results>

In the following, the following test was carried out. The steel grade for this test was STS 321 steel. STS 321 steel is a steel grade containing (18Cr-9Ni-0.3Ti) by adding nickel (Ni) component to STS 304 steel and adding titanium (Ti) as a carbon (C) stabilizing element. Specifically, STS 321 steel is in weight percent, carbon (C): more than 0 and 0.08 or less, silicon (Si): more than 0 and 1.00 or less, manganese (Mn): more than 0 and 2.00 or less, phosphorus (P): more than 0 and 0.045 or less, Sulfur (S): more than 0 and 0.030 or less, nickel (Ni): 9.00 or more and 13.00 or less, chromium (Cr): 17.00 or more and 19.00 or less, and other titanium (Ti) is 5 × carbon (C) (wt%) or more It is steel grade to add. STS 321 steel is mainly used in heat exchanger or heat treatment furnace parts to improve high temperature strength and high temperature oxidation resistance.

Meanwhile, the operating conditions were changed as follows to reduce the alumina inclusions while maintaining the composition adjustment function of the existing ingredient adjustment process.

[Table 1]

In the case of the embodiment according to the present invention, as shown in Table 1 above, the test was carried out with the concentration of aluminum steel as 0.03 to 0.05%, and the bubbling time after the aluminum (Al) was adjusted from 12 minutes to 16 minutes. Proceeded.

On the other hand, the concentration of the calcined aluminum can be controlled by the following method. In the component adjustment step (LT), aluminum (Al) is added to control the concentration of aluminum (Al) to 0.03 to 0.05%, or used as a deoxidizer in a deoxidation step such as refining process (AOD) or vacuum decarburization process (VOD). There is a method of controlling the concentration of aluminum (Al) within the above-mentioned range by adjusting the amount of aluminum (Al).

As a comparative example, the case where the concentration of the calcined aluminum (Al) was 0.05 to 0.098% and the bubbling time after the addition of aluminum was set from 8 minutes to 12 minutes. In this case, the test was performed by dividing the comparative example into three groups as shown in Table 2 below for the reliability of each element.

In Comparative Example 1, the steel aluminum concentration was 0.05 to 0.09%, and the test was performed with the bubbling time after 8 minutes to 12 minutes after the addition of aluminum. That is, in Comparative Example 1, the test was carried out with the steel aluminum concentration and the amount of bubbling time after the aluminum input not in the range of the present invention.

In Comparative Example 2, the aluminum steel concentration was 0.03 to 0.05%, and the test was performed with the bubbling time from 8 minutes to 12 minutes after the addition of aluminum. That is, in Comparative Example 2, the steel aluminum concentration was set to the same conditions as the present invention, and the test was conducted with only the bubbling time after the aluminum injection being in the range not the scope of the present invention.

In Comparative Example 3, the steel aluminum concentration was 0.05 to 0.09%, and the test was conducted with the bubbling time after 12 minutes to 16 minutes after the addition of aluminum. That is, in Comparative Example 3, only the bubbling time after the addition of aluminum was tested under the same conditions as the range of the present invention.

[Table 2]

Table 2 shows the conditions and the result data of each test group. The resulting data is the result of testing the other process under the same conditions and operating with each condition only in the component adjustment process. In this case, the numerical value of the result data is an average value of data obtained by producing a plurality of test products under the corresponding conditions. The test results are as follows.

In the case of Comparative Example 1, the main inclusion composition is Al ₂ O ₃ which is alumina. In the case where other processes were carried out under the same conditions and operated only under the conditions according to Comparative Example 1 only in the component adjustment process, the surface defect occurrence rate of the resultant was 6.6%, which was a high level.

In the case of Comparative Example 2, the main inclusion composition was Ti ₂ O _3, and as a result of operating under the conditions according to Comparative Example 2, the surface defect occurrence rate of the resultant was 8.9%, which was further increased compared to Comparative Example 1. That is, in the result of Comparative Example 1, in order to reduce Al ₂ O ₃ defects simply to reduce the amount of aluminum input, Ti-Oxide defects were increased, and the maximum inclusion size was increased rather relatively, resulting in an increase in surface defect incidence. You get a result.

In the case of Comparative Example 3, the inclusion composition is Al ₂ O ₃ which is alumina. As a result of operating under the conditions according to Comparative Example 3, the surface defect occurrence rate of the resultant was reduced to 4.5%. In other words, the incidence of inclusions was reduced by increasing the time of separation of the inclusions.

On the other hand, in the case of the embodiment, the inclusion composition was present in both alumina Al ₂ O ₃ and Ti-Oxide-like Ti ₂ O ₃ . As a result of operating under the conditions according to the examples, the surface defect occurrence rate of the resultant was reduced to 2.1%. This is a numerical value of the defect occurrence rate decreased to less than one third of Comparative Example 1, and is a numerical value reduced to less than half as compared with Comparative Example 3. In addition, the maximum inclusion size of the resultant according to the embodiment was shown to be reduced to less than a quarter compared to Comparative Example 1, and shows a value reduced to less than one fifth compared to Comparative Example 2.

Although the amount of Ti-Oxide inclusions was slightly increased in comparison with Comparative Example 1, the incidence of alumina inclusions was minimized, and the incidence of surface defects rapidly decreased while the maximum inclusion size was reduced to less than one quarter. Could get

Although the preferred embodiments of the present invention have been described above, the technical idea of the present invention is not limited to the above-described preferred embodiments, and the refining, LT process, and the like in the scope not departing from the technical idea of the present invention specified in the claims. It can be implemented as a facility.

Claims (5)

In wt%, carbon (C): more than 0 and 0.08 or less, silicon (Si): more than 0 and 1.00 or less, manganese (Mn): more than 0 and 2.00 or less, phosphorus (P): more than 0 and 0.045 or less, sulfur (S): 0 In a method for producing austenitic stainless steel containing more than 0.030 or less, nickel (Ni): 9.00 or more and 13.00 or less, chromium (Cr): 17.00 or more and 19.00 or less and Fe and other inevitable impurities,
The stainless steel includes titanium (Ti) in an amount of 5 wt.% Or more, but the carbon steel (C) is more than 12 × 16 minutes in a state in which the concentration of aluminum steel (Al) is 0.03 to 0.05% in the component adjusting process (LT) of the stainless steel. A process for producing austenite stainless steel that performs bubbling for a minute.
The method of claim 1,
Austenitic stainless steel manufacturing method for controlling the concentration of the aluminum (Al) by further adding aluminum (Al) in the component adjustment step (LT).
The method of claim 1,
A method of manufacturing austenite stainless steel, which is performed before the component adjusting step, and includes a refining step (AOD) for controlling the residual aluminum concentration within the concentration range of the aluminum steel (Al) at the end of the step.
The method of claim 1,
A method of manufacturing austenite stainless steel, which is performed before the component adjusting step, and includes a vacuum decarburization process (VOD) at the end of the process to control the residual aluminum concentration within the concentration range of the small steel aluminum (Al).
The method of claim 1,
The target steel grade is wt%, and includes chromium (Cr): 18, nickel (Ni): 9, and titanium (Ti): 0.3.

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