KR101665781B1 - METHOD FOR MANUFACTURING Ti-CONTAINING STAINLESS STEEL - Google Patents

Abstract

The present invention relates to a method for manufacturing stainless steel, and a method for manufacturing titanium (Ti) -containing stainless steel which can reduce nitrogen clogging and surface defects of a slab by preventing nitrogen pickup and high melting point inclusion production .
According to an aspect of the present invention, there is provided a method of manufacturing a stainless steel comprising: a molten steel refining step of refining titanium (Ti) -containing stainless steel in a refining furnace; And a ladle treatment (LT) step of raising refined molten steel into ladles and performing deoxidation and component adjustment of molten steel in the ladle, the method comprising the steps of: before refining the molten steel into the ladle After charging the ladle with calcium carbonate (CaCO ₃ ), the refined molten steel is poured into the ladle; After the addition of Al in the deacidification step in the ladle treatment (LT) step, Ca is firstly introduced; A method for producing titanium (Ti) -containing stainless steel is provided in which a part of Ti is firstly charged in the component adjusting step of the ladle processing (LT) step, a remaining part of Ti is charged secondly, and then Ca is charged secondarily .
According to the present invention, high-Ti-containing stainless steel having excellent quality can be produced without nozzle clogging.

Description

METHOD FOR MANUFACTURING Ti-CONTAINING STAINLESS STEEL [0002]

The present invention relates to a method of manufacturing stainless steel, and more particularly, to a method of manufacturing stainless steel containing titanium (Ti).

In the manufacturing process of stainless steel (STS), molten metal produced by melting in electric arc furnace (EAF), that is, electric furnace molten metal, is introduced into the loading ladle, the loading ladle is tilted and floated on top of the molten metal Remove some of the slag.

Thereafter, the remaining molten slag is removed from the discharge site, and the furnace is put into a refining furnace (Argon Oxygen Decarburization (AOD)), followed by decarburization and deoxidization, and then transferred to a main shaft and cast.

Atmospheric exposure due to the process characteristics of moving the molten steel and slag together from the AOD to the main feedstock causes reoxidation and nitrogen pickup (Pick u).

Also, the AOD slag is clouded and non-metallic inclusions are generated in the molten steel.

This reoxidation and nitrogen pick-up and inclusions create an environment that facilitates the formation of oxides and nitrides in the molten steel.

Particularly, in the case of Ti-containing stainless steel, TiN (Titanium nitride) or TiO _x Surface cracks and nozzle clogging may occur due to excessive formation of titanium oxide.

There are two main ways to remove nitrogen in molten steel during the steelmaking process in the production of stainless steel. In the refining furnace process (AOD) using the dilution decarburization method, CO (g) gas and Tuyere In the ladle vacuum treatment system applying the vacuum decarburization method (VOD), the CO (g) gas generated during the decarburization reaction and the Ar (g) gas introduced from the bottom of the ladle g to remove nitrogen. Particularly, under this vacuum treatment, the denitrification effect is very large as the nitrogen partial pressure in the atmosphere is lowered.

However, as can be seen from FIG. 1, since the high-chromium-containing steel such as stainless steel has a very high nitrogen solubility in molten steel, even if nitrogen is removed from AOD and VOD, ladle treatment (LT) Quot; LT "), it is inevitable that the nitrogen solubility increases due to adsorption during operation. Especially, when stainless steel is exposed to nitrogen which occupies about 70% of the atmosphere at the time of refining, a large amount of nitrogen pickup becomes inevitable.

In the refining furnace that has been developed so far, there is a technique of preventing the adsorption of precious metals. After the oxygen refining is completed in the refining furnace, the steel is laden with a large amount of oxygen remaining in the molten steel, There is a method of preventing permeation of the atmosphere by forming a film on the molten steel surface.

Another method is to generate CO ₂ (g) gas by using dolomite (CaCO ₃ , MgCO ₃ ) input and to prevent the adsorption by applying pressure on the surface of molten steel to be.

There is a problem that the reduction and desulfurization are required to be performed in the LT process, which is the next step of the refining furnace, and additional facilities and processing steps are required.

In the latter method, the dissociation reaction as shown in the following formula (1) occurs, and the generation of CO ₂ (g) gas causes absorption of N ₂ (g) from the atmosphere due to CO ₂ To prevent the nitrogen pick-up. However, the dissociation reaction as shown in the following formula (2) occurs to increase the Mg potential in the molten steel. In particular, Ti-containing stainless steel to the steel producing city, Ti deployment.Whoa Ti silsuyul secure, due to the Al deoxidization is not enough in, LT process for the addition of Ti and then Al deoxidation, Ti is added in the dissolved oxygen high state, TiO _x is created, and, is dissolved in Mg, Ti, Al with the high state to the equation (3) - (7) to the reaction, such as a high-melting-point inclusions of TiOx, CaTiO _3, Al ₂ O ₃ and MgAl ₂ O ₄ (Spinel) occurs And nozzle clogging as shown in FIG. 2 occurs.

CaCO ₃ MgCO ₃ → CaO + MgO + ₂ CO ₂ (g). . . (One)

MgO - > Mg + O. . . (2)

2 Al + 3 O ? Al ₂ O ₃ (s). . . (3)

Mg + 2 Al + 4 O - > MgAl ₂ O ₄ (s). . . (4)

2 Ti + 3 O - > Ti ₂ O ₃ (s). . . (5)

_{Ti + 2 O → TiO 2 (} s). . . (6)

Ca + Ti + 3 O → CaTiO 3 (s). . . (7)

An aspect of the present invention is to provide a method of manufacturing stainless steel containing titanium (Ti) capable of reducing nozzle clogging and surface defects of a slab by preventing nitrogen pickup and the formation of high melting point inclusions.

According to an aspect of the present invention, there is provided a method of manufacturing a stainless steel comprising: a molten steel refining step of refining titanium (Ti) -containing stainless steel in a refining furnace; And a ladle processing (LT) step of introducing refined molten steel into the ladle and performing deoxidation and component adjustment of molten steel in the ladle, the method comprising the steps of:

The limestone before tapping the molten steel in the ladle refining (Calcium Carbonate; CaCO ₃₎ was charged into the ladle, and tapping the molten steel refined in the ladle;

After the addition of Al in the deacidification step in the ladle treatment (LT) step, Ca is firstly introduced; A method for producing titanium (Ti) -containing stainless steel is provided in which a part of Ti is firstly charged in the component adjusting step of the ladle processing (LT) step, a remaining part of Ti is charged secondly, and then Ca is charged secondarily .

According to the present invention, the production of TiN (s) and the formation of high melting point inclusions (TiO _x , Al ₂ O ₃ , MgAl ₂ O ₄ Etc.) can be suppressed, and as a result, high-Ti-containing stainless steel having excellent quality can be produced without nozzle clogging (Nozzle Clogging).

FIG. 1 is a graph showing the solubility of nitrogen according to the content of Cr in molten steel by the partial pressure of nitrogen.
FIG. 2 is a photograph showing the inside of an immersion nozzle in which clogging of an immersion nozzle occurs when manufacturing a Ti-containing stainless steel according to a conventional method.
Fig. 3 is a view showing changes in inclusion composition in a conventional Ti-containing stainless steel manufacturing process.
Fig. 4 is a graph showing changes in inclusion composition in the Ti-containing stainless steel producing process of the present invention.
FIG. 5 is a state diagram of CaO-MgO-Al ₂ O ₃ at 1500 ° C. showing the phase relationship of the inclusion composition obtained through the present invention and the conventional method.
FIG. 6 is a photograph showing the inside of the immersion nozzle after finishing three trials in the manufacturing process of the Ti-containing stainless steel according to the present invention.

Hereinafter, the present invention will be described in detail.

A method of manufacturing a Ti-containing stainless steel according to an aspect of the present invention includes: a molten steel refining step of refining titanium (Ti) -containing stainless steel in a refining furnace; And a ladle treatment (LT) step of raising refined molten steel into ladles and performing deoxidation and component adjustment of molten steel in the ladle, and a method of producing titanium (Ti) containing stainless steel.

A method of manufacturing a Ti-containing stainless steel according to an aspect of the present invention comprises the steps of: preparing a Ti-containing stainless steel by passing through an electric furnace process (EAF) - refining process (AOD) - ladle process (LT) process - tundish process - continuous casting process Can be more preferably applied to the production method.

In the present invention, instead of dolomite, calcium carbonate (CaCO ₃ ) is charged into the ladle before AOD liquefaction to generate CO ₂ (g) gas to prevent adsorption, and Mg potential is removed to form a high melting point inclusion spinel MgAl ₂ O ₄ ) and to improve the deoxidation performance of the conventional deoxidation method, it is necessary to control the order of introduction of Al, Ca and Ti to be introduced in the LT step, ) Is injected before Ti is injected to deoxidize the molten steel to thereby reduce excess dissolved oxygen to secure the Ti real water rate and to prevent surface defects and occurrence of nozzle clogging by inclusion modification through Ca-splitting input (Ca second injection) Ti-containing stainless steel having excellent quality can be produced.

In the present invention, in order to prevent nitrogen pick-up at the time of entering the molten steel in the refining furnace, CO ₂ (g) is charged by charging calcium carbonate (CaCO ₃ ) instead of dolomite (CaCO ₃ .MgCO ₃ ) Thereby reducing the Mg potential in the molten steel and suppressing the nitrogen pickup.

As described above, calcium carbonate (CaCO ₃ ) is charged into the ladle before the molten steel is poured into the ladle in the refining furnace, and then the molten steel is poured into the ladle to perform deoxidation and component adjustment (LT process).

In the LT process, AOD slag is completely discharged and then CaO and Al ₂ O ₃ Containing slag, for example, Lafarge Slag.

The amount of the calcium carbonate (CaCO ₃ ) to be loaded is preferably limited to 50 to 300 kg per 100 ton of molten steel. When 300 kg or more is charged, CaCO ₃ released with dissolution reacts with the raffia slag, There is a possibility of causing a problem. More preferably, the amount of the limestone to be charged is 100 to 300 kg per 100 ton of molten steel, and more preferably, the amount of the limestone to be charged is 150 to 250 kg per 100 ton of molten steel.

The time for loading the limestone (CaCO ₃ ) into the ladle is not particularly limited as long as the ladle is introduced into the ladle in the refining furnace.

Typically, ladders are pre-heated to, for example, 1200 ° C prior to taking molten steel, in which case limestone is likely to decompose.

Therefore, it is preferable that the limestone (CaCO ₃ ) is charged into the ladle 1 to 2 minutes before the ladle.

Further, in the present invention, a new deoxidation method is applied in the LT process to prevent Ti clogging and to prevent the generation of TiO _x , CaTiO ₃ , Al ₂ O ₃ and MgAl ₂ O ₄ , which are high-melting inclusions, Can be improved.

In the present invention, the order of introduction of Al, Ca and Ti is changed from Al to Ca (primary) to Ti (primary) to Ti Ti (secondary) to Ca (secondary).

That is, in the present invention, a part of Ti is firstly introduced in the deacidification step of the ladle treatment (LT) step and then the Ca is introduced first and the component adjustment step of the ladle treatment (LT) a in the rest of the Ti 2 car, then a by charging the Ca 2 drive, by reducing the surplus dissolved oxygen, at the same time to ensure the Ti silsuyul, high-melting point inclusions produced during the steel making process through the inclusion modified with Ca divided input TiO _x , CaTiO ₃ , Al ₂ O ₃ , MgAl ₂ O _4, and the like.

In the present invention, it is preferable to set the appropriate amounts of Al, Ti, and Ca as the target amounts of Al, Ti, and Ca, respectively, before the Al injection, Ti, and Ca are separately added.

The amount of Al charged in the deoxidation step in the LT step is preferably set so that the Al content in the molten steel is 0.05 to 0.2 wt%.

It is preferable that the amount of Ti input after the deoxidation step of the LT process is first charged so as to be 80 wt% or less of the target content of Ti contained in the stainless steel molten steel, and the remaining amount is charged secondarily, more preferably, To 80%, and secondly, 20 to 50%.

The amount of Ca charged in the LT process may be changed according to the type of steel, but the amount of Ca is preferably set so that the Ca content in the molten steel is 10 to 50 ppm.

When Ca is added, it is preferable that 70% or less of the total amount is charged in the first step, and the remainder is charged in the second step, more preferably 40 to 70% is charged in the first step, %.

There is no particular limitation on the Ca addition method, but it is preferable that the effect of the nitrogen pickup effect is minimized by, for example, introducing a Ca-Si lump.

In the case of using the metal Ca or Ca-Si wire in the above-mentioned Ca injection method, splashing due to long-time wire injection is formed and at the same time, the bath surface is exposed to the atmosphere, .

For example, when a Ca-Si lump is charged, the first charge amount is preferably set to 150 kg or less per 100 ton of molten steel, and the second charge amount is preferably set to 100 kg or less per 100 ton of molten steel. More preferably, The amount of tea is set at 120kg or less per 100 tons of molten steel, and the amount of secondary injection is set at 80kg or less per 100 tons of molten steel.

Meanwhile, the stainless steel produced according to one aspect of the present invention is a steel containing Ti, preferably 0.05 to 1.5% of Ti (Titanium), 10 to 20% of Cr (Chrome), Ni Nickel): 0-14%, the balance Fe and other unavoidable impurities.

Hereinafter, the present invention will be described more specifically by way of examples.

It should be noted, however, that the following examples are intended to illustrate the invention in more detail and not to limit the scope of the invention. Since the scope of the present invention is determined by the matters described in the claims and the matters reasonably deduced therefrom.

( Example )

(Conventional method) or limestone (Calcium Carbonate; CaCO ₃ ) (according to the present invention) under the conditions shown in Table 1 before refining the refined molten steel in the ladle and refining the refined molten steel with titanium (Ti) The refined molten steel was poured into a ladle, subjected to deoxidation treatment under the conditions shown in Table 1, and the components were adjusted to prepare molten steel shown in Table 2 below.

In the case of the method of the present invention, the charging method of Al, Ca and Ti in the LT process is as follows: Al → Ca (primary) → Ti (primary) → Ti (secondary) → Ca (secondary) , And in the case of the conventional method, the method of injecting Al → Ti → Ca was employed.

The molten steel subjected to deoxidation and composition adjustment as described above was produced as a cast through a tundish process and a continuous casting process.

The nitrogen content in the refined molten steel and the nitrogen content in the molten steel in the tundish process were measured and the respective nitrogen contents and their differences were determined and are shown in Table 2 below.

The surface defects of the cast steel were observed and the results are shown in Table 2 below.

The inclusion composition changes in the Ti-containing stainless steel manufacturing process were observed. The results are shown in Fig. 3 for the conventional method and in Fig. 4 for the method of the present invention. Fig. 5 shows changes in inclusions in a Ti-containing stainless steel manufacturing process.

Further, according to the present invention, the inside of the immersion nozzle after the completion of the triple performance in the manufacturing process of the Ti-containing stainless steel was observed, and the results are shown in FIG.

division Produce
Way Loading process before lecture (Kg) of Al, Ca and Ti per 100 tons of molten steel in the LT process, Charge Amount of charge per 100 tons of molten steel (kg) Al
Ca
(Primary) Ti
(Primary) Ti
(Secondary) Ca
(Secondary) One Conventional
Way Dolomite 200 350 0 340 85 108 2 200 350 0 340 85 120 3
The present invention method Limestone 150 350 80 340 85 80 4 180 350 80 322 80 80 5 200 350 80 338 81 80 6 175 350 80 325 82 80 7 220 350 80 325 75 80 8 185 350 80 342 72 80 9 200 350 80 334 70 80 10 190 350 80 341 75 80

division Produce
Way Cr
(weight%) Ni (% by weight) Ti (% by weight) N (AOD)
[ppm] N (tundish) [ppm] ΔN
(ppm) Average Nitrogen Pickup Amount (ppm) Tundish temperature (℃) TiN precipitation temperature
(° C) Surface defect order rate (%) One Conventional
Way 17.25 9.18 0.342 54 102 48 51
1505 1517 100 2 17.31 9.19 0.301 45 98 53 1501 1505 100 3 example
foot
persons
method


17.234 9.161 0.305 42 89 47 30 or less





1512 1500 0 4 17.205 9.185 0.302 45 87 42 1500 1498 4 5 17.524 9.167 0.301 47 81 34 1512 1490 0 6 17.318 9.161 0.334 39 62 23 1503 1480 0 7 17.420 9.136 0.322 58 80 22 1505 1495 4 8 17.321 9.209 0.339 68 79 11 1500 1498 0 9 17.392 9.247 0.331 46 92 46 1515 1506 0 10 17.395 9.152 0.302 56 69 13 1503 1481 0

As shown in Table 2, in the case of carrying out the charging of limestone (CaCO ₃ ) and the deoxidation of the LT process in the production of the Ti-containing stainless steel according to the present invention, the nitrogen pickup is reduced to 30 ppm or less And the calculated TiN precipitation temperature is controlled to be lower than the temperature of the tundish molten steel.

Therefore, it is possible to effectively suppress TiN (Titanium nitride) generation, inhibit precipitation of MgAl ₂ O ₄ (spinel) in the tundish through inclusion modification, prevent nozzle clogging, It can be confirmed that the out-of-order ratio due to defects can be improved up to 100%.

As shown in FIG. 3, according to the conventional method (Al? Ti? Ca), it can be confirmed that the inclusions are precipitated in spinel (MgAl ₂ O ₄ ) which is a high melting point inclusion in low-temperature operation. In the case of the LT operation, the spinel (MgAl ₂ O ₄ ) product, which is a high melting point inclusion, accounts for a maximum of 95% of the total inclusions in the tundish operation, thereby causing nozzle clogging, It causes.

On the other hand, when the method of the present invention is applied, generation of MgAl ₂ O ₄ (spinel), which is a high melting point inclusion in the Ti-containing steel, can be suppressed. That is, as shown in FIG. 4, Al, Ca and Ti are injected in the order of Al → Ca (primary) → Ti (primary) → Ti (secondary) → Ca (secondary) , It is confirmed that the inclusions are liquefied by the CaO-Al ₂ O ₃ system which is a low-melting inclusion from LT to tundish.

As shown in FIG. 5, the composition of the conventional Ti-added stainless steel was found to be the main phase in the tundish after Spinel (MgAl ₂ O ₄ ) phase precipitates in the inclusions from the LT arrival to the tundish operation, In the case of applying the method of the present invention, inclusion composition changes in or near the liquid slag region during LT arrival to tundish to suppress precipitation of spinel (MgAl ₂ O ₄ ) which is a high melting point inclusion . As a result, as shown in FIG. 6, no nozzle clogging occurs and operation can be performed up to three consecutive years.

Claims (8)

A molten steel refining step of refining titanium (Ti) -containing stainless steel in a refining furnace; And a ladle processing (LT) step of introducing refined molten steel into the ladle and performing deoxidation and component adjustment of molten steel in the ladle, the method comprising the steps of:
The limestone before tapping the molten steel in the ladle refining (Calcium Carbonate; CaCO ₃₎ was charged into the ladle, and tapping the molten steel refined in the ladle;
After the addition of Al in the deacidification step in the ladle treatment (LT) step, Ca is firstly introduced; And
In the ladle processing (LT) step, a part of Ti is firstly introduced and a remaining part of Ti is added in a second step. Then, Ca is added in a second step, and Ca is added in an amount of 40 to 70% (Ti) is added in a first order and 30 to 60% is introduced in a second order.
The method according to claim 1,
Wherein the amount of the calcium carbonate (CaCO ₃ ) is 50 to 300 kg per 100 ton of molten steel.
The method according to claim 1,
Wherein the limestone (CaCO ₃ ) is charged into the ladle one to two minutes before excavation.
The method according to claim 1,
Wherein the amount of Al charged in the deoxidation step is set so that the Al content in the molten steel is 0.05 to 0.2 wt%.
The method according to claim 1,
Wherein the Ti addition is carried out in such a manner that the Ti addition is carried out in such a manner that the Ti content becomes 80% by weight or less of the target Ti content in the stainless steel and the remainder is added in the second order.
The method according to claim 1,
Wherein the amount of Ca added in the LT step is set so that the Ca content in the molten steel is 10 to 50 ppm.
delete The method according to claim 6,
Wherein the Ca is introduced by a Ca-Si lump. ≪ RTI ID = 0.0 > 15. < / RTI >

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