KR20150075337A - Method for manufacturing ferritic stainless steel having excellent ridging property and abrasive property - Google Patents
Method for manufacturing ferritic stainless steel having excellent ridging property and abrasive property Download PDFInfo
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- KR20150075337A KR20150075337A KR1020130163395A KR20130163395A KR20150075337A KR 20150075337 A KR20150075337 A KR 20150075337A KR 1020130163395 A KR1020130163395 A KR 1020130163395A KR 20130163395 A KR20130163395 A KR 20130163395A KR 20150075337 A KR20150075337 A KR 20150075337A
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- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21C—PROCESSING OF PIG-IRON, e.g. REFINING, MANUFACTURE OF WROUGHT-IRON OR STEEL; TREATMENT IN MOLTEN STATE OF FERROUS ALLOYS
- C21C7/00—Treating molten ferrous alloys, e.g. steel, not covered by groups C21C1/00 - C21C5/00
Abstract
Disclosed is a ferritic stainless steel casting slab excellent in lubrication property and abrasive property. According to an aspect of the present invention, there is provided a method of manufacturing stainless steel, comprising: a refining step of deoxidizing molten steel by injecting a deoxidizing agent into stainless steel; A component adjusting step for refined molten steel; And a continuous casting step, wherein the composition of the oxides present in the molten steel in the refining step is controlled so as to satisfy the following relational equations (1) and (2), and the component adjusting step for the refined molten steel (Ca) of 0.6 to 1.7 kG / ton-steel in a molten steel at a high temperature of atmospheric pressure.
[Relation 1]
% (TiO 2 ) +% (CaO) +% (Al 2 O 3 ) +% (MgO)? 85%
[Relation 2]
(CaTiO 3) / (MgAl 2 TiO 6) ≥ 1.7
Description
The present invention relates to a method for producing ferritic stainless steels, and more particularly to a method for producing ferritic stainless steels having excellent ridging properties and abrasive properties.
Generally, in the production of ferritic stainless steels, a cast steel having an equiaxed structure ratio of not more than 40% has a band structure in the hot-rolled coil, which causes deep drawing of the cold-rolled steel sheet ) Or in the forming process, the surface of the coil is likely to be parallel to the cold rolling direction called "ridging" or "roping" and to have thin irregularities.
In order to prevent such ridging defects, cold rolled steel and hot rolled steel have been used in the past. However, the production cost of ferritic stainless steel is increased and productivity is lowered.
Recently, low-temperature casting methods, a method of adding iron or steel, a method of adding rare earth elements, and an electro-magnetic stirrer have been used as techniques for improving the equiaxedelement ratio of ferritic stainless steels.
For example, Patent Document 1 discloses that Al-Ti-based composite inclusions having a size of 0.3 to 0.5 탆 act as an equiaxed nucleation seed. In
However, in these patent documents, the equiaxed crystal generating mechanism has not been clearly defined, and there is a possibility that many deviations may occur depending on working conditions and surrounding conditions.
On the other hand, when Ti is added to ferritic stainless steel, it is known that when TiN precipitated in molten steel is used as ferrite solidification nuclei, the coagulated structure is likely to be equilibrated and purified. In order to improve the equilibrium constant, sufficient Ti addition is required .
However, since excessive Ti addition causes a problem such as nozzle clogging and surface flaws, it is not preferable to simply increase the equiaxed durability of the solidified structure by Ti addition.
One of the biggest problems in the manufacture of Ti-added stainless steel is nozzle clogging, which is mainly due to the generation of a large amount of Ti-based oxides having good wetting properties. The resulting Ti-based oxides easily migrate to the nozzle wall due to eddy currents generated by the turbulent flow and adhere and grow by sintering. The grown oxide clusters have a good wettability with the molten steel, so that the molten steel easily flows into the clusters, which causes nozzle clogging as the growth of the nozzle deposits rapidly increases.
Various methods such as prevention of re-oxidation, slag control, injection of argon (Ar) gas, and change of nozzle material have been suggested as measures for preventing the clogging of the nozzle, but there is no technique related to the equilibrium constant rate.
Particularly, in order to commercialize the oxide utilization technology for improving the equilibrium constant, it is required to develop a technique that simultaneously minimizes adherence of the effective oxides to the nozzle wall surface and maximizes the equiaxed rate of the casting.
An aspect of the present invention is to provide a method of maximizing the equiaxed rate of stainless steel while minimizing the adherence of the active oxides to the wall surface of the immersion nozzle.
According to an aspect of the present invention, there is provided a method of manufacturing stainless steel, comprising: a refining step of deoxidizing molten steel by injecting a deoxidizing agent into stainless steel; A component adjusting step for refined molten steel; And a continuous casting step, wherein the composition of the oxides present in the molten steel in the refining step is controlled so as to satisfy the following relational equations (1) and (2), and the component adjusting step for the refined molten steel (Ca) of 0.6 to 1.7 kG / ton-steel in a molten steel at a temperature of 200 ° C or higher. The present invention also provides a method for producing ferritic stainless steels excellent in ridging and abrasion properties.
[Relation 1]
% (TiO 2 ) +% (CaO) +% (Al 2 O 3 ) +% (MgO)? 85%
[Relation 2]
(CaTiO 3) / (MgAl 2 TiO 6) ≥ 1.7
In addition, the solution of the above-mentioned problems does not list all the features of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS The various features and advantages and effects of the present invention will become more fully understood with reference to the following specific embodiments.
According to the present invention, it is possible to provide a ferritic stainless steel excellent in ridging property and abrasive property by securing an equiaxed constant of 65% or more of the stainless steel casting.
In addition, there is an advantage that stable operation can be performed by significantly reducing the thickness of the effective oxide attached to the immersion nozzle.
BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a photograph of ferrite based stainless steels cast steel of the invention material and comparative material.
Fig. 2 is a graph showing the size and number of TiN in the cast steel of the inventive material and the comparative material.
Fig. 3 shows the results of identifying the kinds of spherical oxides in the TiN precipitates of the inventive material and the comparative material by EMPA.
Fig. 4 shows the compositions of the oxides of the molten steel in the refining step of the inventive material and the comparative material, and the results are shown in the Al2O3-TiO2-CaO ternary phase diagram.
5 is a photograph showing a section of the immersion nozzle.
6 is a photograph of a deposit attached to the immersion nozzle by a scanning electron microscope.
7 shows the composition of the nozzle attachment in a ternary phase diagram.
8 shows the rate of change of the opening rate according to the degree of superheat.
FIG. 9 shows a region where the weight ratio (Al / Ti) of Al and Ti and the equiaxed constant ratio according to the superheat degree are 70% or more in the component adjustment step.
10 is a graph showing the TiN size distribution in the cast steel when the weight ratio of Al and Ti and the superheating degree during casting are different in the component adjusting step.
Fig. 11 shows the results obtained by measuring the equiaxed constant rate of the cast steel cast continuously casting according to the casting condition and the thickness of the adhered material of the immersion nozzle.
The inventors of the present invention have conducted intensive studies to suppress the clogging of the nozzle due to Ti addition while adding Ti in order to improve the equiaxed constant ratio in manufacturing ferritic stainless steels. As a result, it has been found that oxide- And controlling the content of calcium (Ca) introduced into molten steel, it is confirmed that the object of the present invention can be achieved when the melting point of these oxides is lowered. It came to the following.
Since the equiaxed crystal of the ferritic stainless steels produced in the casting process affects not only the rolling process but also the product in the subsequent process, clarifying the equiaxed crystal generation mechanism in the steelmaking and continuous casting processes in order to improve the equiaxed crystal ratio of the ferritic stainless steels More important than anything else.
When comparing the inventive material and the comparative material of Fig. 1, it can be seen that only about 50% of the cast steel is formed with equiaxed crystals, and in the case of the inventive material, equiaxed crystals are uniformly formed throughout the cast steel. In this way, we have been able to identify the equilibrium generation mechanism and to improve the equilibrium on the basis of the difference in the casting structure.
FIG. 2 is a graph showing the analysis of the size and number of TiN in the cast steel when the equilibrium constant is 0% and 100%. Referring to FIG. 2, it can be seen that the size and number of TiN affects the formation of isotropic crystals, and in particular, TiN having a size of 4 to 8 μm has a favorable effect on the isotropic crystal formation.
As a result of observation of the TiN in the cast slab by an electron microscope, it was observed that spherical oxides in TiN were observed in the case of the inventive material. When the spherical oxide was closely observed through an electron microscope, two kinds of materials As shown in Fig. The kinds of the two kinds of materials were identified using EMPA, and the results are shown in FIG. The brightly visible oxide is composed of CaO-TiO2 system, and the black oxide exists in Al2O3-MgOTiO2 system. On the other hand, in the case of conventional materials, spherical oxides exist in TiN, but most of the oxides are Al2O3-MgOTiO2. From the above results, it was confirmed that CaO-TiO2 system is advantageous as equiaxed or TiN nucleation sites.
In order to study the relationship between the composition of the oxides present in the molten steel and the ratio of the equiaxed crystals in the refining step, it has been found that the molten steel in the refining step in the case where the high- As a result, the present inventors have found that the composition of the oxide of the molten steel in the refining step should satisfy the following
[Relation 1]
% (TiO 2 ) +% (CaO) +% (Al 2 O 3 ) +% (MgO)? 85%
[Relation 2]
(CaTiO 3) / (MgAl 2 TiO 6) ≥ 1.7
On the other hand, FIG. 5 is a photograph of a cross section of the immersion nozzle observed after molten steel having the compositions of oxides of the refining step steels satisfying the
FIG. 6 is a photograph of a deposit attached to the immersion nozzle by a scanning electron microscope. It can be seen that the composition of the deposit is formed of a composite layer including an oxide layer composed of CaOTiO.sub.2, MgOAl.sub.2 O.sub.3, and a ground layer. That is, the effective oxide produced by controlling the composition of the oxide of the molten steel in the refining step to satisfy the
7 shows the composition of the nozzle attachment in a ternary phase diagram. As can be seen from Fig. 7, the composition of the nozzle attachment is CaOTiO2, and the crystallization temperature range is considerably high at 1700 ~ 1800 ℃. Such an oxide having a high melting point has high high-temperature strength once formed, so that it is not easy to remove it. As a method for suppressing adhesion or growth of the oxide on the immersion nozzle, there is a method of maintaining the molten steel temperature at or above the softening temperature of the oxide by increasing the degree of superheat, or a method of controlling the composition of the oxide to decrease the melting point, There is a way to lower it. As shown in FIG. 7, the present inventors selected a method of lowering the melting point of oxides by lowering the amount of Ca added in the component adjusting step. More specifically, the inventors of the present invention controlled the Ca input amount in the component adjusting step to 0.6 to 1.7 kg / ton-steel The inclusions having a melting point of 1700 to 1800 ° C were lowered to 1500 to 1600 ° C. As a result, the equiaxed rate of the casting was 65% or more, and the problem of nozzle clogging could be solved.
On the other hand, the inventors of the present invention have found that the composition of the oxide of the molten steel in the refining step is controlled to satisfy the
FIG. 8 shows the rate of change of the opening rate according to the degree of superheat after casting under the above-mentioned Ca addition condition. Generally, the opening rate for stable casting is 65 ~ 80%. It is known that stable operation is possible when the rate of change of opening rate is 0.1% / m or less when the ferrite-based stainless steels are set to three ferrite have. In the case of the present invention, it has been found that the superheating degree of the molten steel for controlling the rate of change of the opening rate by the length of the slab to 0.1% / m or less is 40 to 60 ° C.
On the other hand, the superheat degree is closely related to the equilibrium constant, and it is generally known that the higher the superheat degree, the lower the equilibrium constant. Generally, the superheating degree of ferritic stainless steel during casting is in the range of about 30 to 50 ° C. However, in order to prevent clogging of the nozzle in the present invention, additional research is required Respectively.
FIG. 9 shows a region where the weight ratio (Al / Ti) of Al and Ti and the equiaxed constant ratio according to the superheat degree are 70% or more in the component adjustment step. As can be seen from FIG. 9, the weight ratio (Al / Ti) should be 0.15 or less in order to maintain an equilibrium constant of 70% or more, and the equiaxed rate 70% can be ensured as the weight ratio (Al / Ti) It is confirmed that the range of the superheating degree is wide. This is because as the weight ratio (Al / Ti) is lowered, the number of effective oxides is increased, and at the same time, the melting point of the effective oxide is slightly increased, so that sufficient equiaxed nuclei remain in the condition of high superheat, It is judged to be active.
That is, the conditions for securing an equiaxed rate of 70% or more and preventing clogging of the immersion nozzle proposed in the present invention are shown by the following relational expressions (3) and (4).
[Relation 3]
(Al / Ti)? 0.15
[Relation 4]
40 ° C ≤ molten steel superheat ≤ 67.5-150 * (Al / Ti)
(In the above
10 is a graph showing the TiN size distribution in the cast steel when the weight ratio of Al and Ti and the superheating degree during casting are different in the component adjusting step. As described above, the size of effective TiN favorable to the production of equiaxed crystals is 4 to 8 탆. When a certain number or more of such effective TiNs exist, a high equiaxed rate can be secured. Can be predicted. As can be seen from FIG. 10, when the superheating degree of Al / Ti and the molten steel satisfy the
On the other hand, FIG. 11 shows the results of comparing the average values by measuring the equiaxed constant rate of the casting continuously cast according to the casting condition and the thickness of the adhered material of the immersion nozzle. The comparative material of Fig. 11 is a casting under the conditions satisfying the
The ferritic stainless steel produced by the present invention contains 0.02% or less of C, 0.5% or less of Si, 15 to 30% of Cr, 0.1 to 0.4% of Ti, 0.01% or less of S, % Or less, the balance Fe and unavoidable impurities.
Claims (4)
In the refining step, the oxides present in the molten steel are controlled so as to satisfy the following relational equations (1) and (2), and 0.6 to 1.7 kG / ton-steel Ca is introduced into the molten steel in the component adjusting step for the refined molten steel Wherein the ferrite-based stainless steel is excellent in ridging property and abrasive property.
[Relation 1]
% (TiO 2 ) +% (CaO) +% (Al 2 O 3 ) +% (MgO)? 85%
[Relation 2]
(CaTiO 3) / (MgAl 2 TiO 6) ≥ 1.7
And the Ti content is controlled to satisfy the following relational expression (3) in the component adjusting step, the ferrite-based stainless steel having excellent ridging property and abrasive property.
[Relation 3]
(Al / Ti)? 0.15
(Wherein (Al / Ti) means the weight ratio of Al and Ti in the component adjusting step)
And the superheating degree of molten steel in the continuous casting step is controlled so as to satisfy the following relational expression (4).
[Relation 4]
40 ≤ superheating degree of molten steel (° C) ≤ 67.5-150 * (Al / Ti)
(Wherein (Al / Ti) means the weight ratio of Al and Ti in the component adjusting step)
The stainless steel according to claim 1, wherein the stainless steel contains 0.02% or less of C, 0.5% or less of Si, 15 to 30% of Cr, 0.1 to 0.4% of Ti, 0.01% or less of S and 0.015% or less of N, A method for producing a ferritic stainless steel excellent in ridging and abrasion including impurities.
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Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN112029961A (en) * | 2020-09-10 | 2020-12-04 | 东北大学 | Aluminum deoxidation method for nitrogen-containing super stainless steel |
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Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN112029961A (en) * | 2020-09-10 | 2020-12-04 | 东北大学 | Aluminum deoxidation method for nitrogen-containing super stainless steel |
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