JP2018034189A - Sulfur-added steel continuous casting nozzle block preventing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the block of a continuous casting nozzle without adding Ca to molten steel and raising a molten steel temperature in the continuous casting of sulphur-added steel.SOLUTION: In a sulphur-added steel continuous casting, in which a sulphur-adding source is added, and in which S is adjusted to 0.012 to 0.100 mass %, a sulphur-added steel continuous casting nozzle block preventing method is characterized in that the total amount of an oxygen ingress from a sulphur adding source is suppressed at or lower than 40 ppm.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a method for preventing clogging of a continuous casting nozzle during continuous casting of sulfur-added steel.

  Molten steel refined in a converter or a vacuum processing vessel contains a large amount of oxygen, and this large amount of oxygen contains about 0.015-0.100 mass% of a strong deoxidizing element Al having a strong affinity for oxygen. It is a general technique to add and deoxidize.

However, Al ₂ O ₃ inclusions are produced by Al deoxidation, which are aggregated together to produce coarse alumina clusters. This alumina cluster adheres to the inner wall of the tundish nozzle and immersion nozzle used to inject molten steel from the tundish into the mold, and causes nozzle clogging.

In order to solve such a problem caused by Al deoxidation, a method has been proposed in which Ca is added to molten steel after Al deoxidation to generate a low melting point CaO—Al ₂ O ₃ composite inclusion. For example, Patent Document 1 discloses a method of adding Ca to molten steel and adjusting the Ca concentration / Al concentration of the molten steel to an appropriate range according to the total O concentration as a method for preventing nozzle clogging. However, since metal Ca has a low boiling point, there is a problem that addition to molten steel is difficult and yield is not stable.

  By the way, since sulfur (S) is an element that enhances the machinability of steel, a required amount is often added in the steelmaking process to the molten steel for machine structural steel that is machined into a particularly complicated shape. However, when Ca is added to molten steel containing 0.012 to 0.100% by mass of S, Ca and S react to produce harmful inclusions, CaS, and on the other hand, nozzle clogging is promoted. There is a problem that the steel quality deteriorates.

  With respect to this problem, Patent Document 2 discloses a method for controlling the Ca concentration, S concentration, and O concentration of molten steel within a predetermined range. However, since the predetermined range is an extremely narrow range and the Ca yield is not stable, it is difficult to control the Ca concentration, the S concentration, and the O concentration within the narrow range.

  Patent Document 3 discloses a method in which a lower limit of the molten steel superheat degree is set and the molten steel in the tundish is heated and continuously cast so that the molten steel superheat degree becomes equal to or higher than the lower limit. In this method, since it is necessary to increase the molten steel temperature, there is a problem that the casting speed in continuous casting cannot be increased, and the productivity is significantly reduced.

Japanese Patent Laid-Open No. 03-165952 JP 2002-035894 A Japanese Patent Application Laid-Open No. 07-328753

  In view of the present state of continuous casting technology for sulfur-added steel, the present invention ensures that the continuous casting nozzle is blocked without adding Ca to the molten steel and without increasing the molten steel temperature in continuous casting of sulfur-added steel. It is an object of the present invention to provide a method for preventing clogging of a continuous casting nozzle that solves this problem.

  The present inventors diligently studied a method for solving the above problems. As a result, it has been found that if the amount of intruded oxygen from the sulfur addition source is controlled to a certain value or less, nozzle blockage during continuous casting can be reliably prevented. This point will be described later.

  This invention was made | formed based on the said knowledge, and the summary is as follows.

  (1) In a continuous casting of sulfur-added steel in which a sulfur addition source is added and S is adjusted to 0.012 to 0.100% by mass, the total oxygen intrusion amount from the sulfur addition source is suppressed to 40 ppm or less. To prevent clogging of continuous casting nozzle of sulfur-added steel.

  (2) As the sulfur addition source, a high oxygen concentration sulfur addition source having an oxygen concentration of more than 3% by mass and 20% by mass or less and a low oxygen concentration sulfur addition source having an oxygen concentration of 3% by mass or less are used in combination. The method for preventing clogging of the continuous casting nozzle of sulfur-added steel as described in (1) above.

  (3) The method for preventing clogging of a continuous casting nozzle of sulfur-added steel according to (2), wherein the high oxygen concentration sulfur-added source is sulfide ore.

  (4) When adjusting the amount of sulfur of the sulfur-added steel, the high oxygen concentration sulfur addition source is first added to the molten steel, and then the low oxygen concentration sulfur addition source is added (2) Or the prevention method of the blockage | closure of the continuous casting nozzle of sulfur addition steel as described in (3).

  (5) The sulfur-added steel according to any one of the above (1) to (4), wherein the sulfur-added steel contains Al: 0.015 to 0.100% by mass. A method for preventing clogging of a casting nozzle.

  (6) The sulfur-added steel is in mass%, C: 0.07 to 1.20%, Si: 1.00% or less, Mn: 2.50% or less, P: 0.10% or less, N: The method for preventing clogging of a continuous casting nozzle of sulfur-added steel as described in (5) above, containing 0.02% or less, the balance being iron and inevitable impurities.

  (7) The sulfur-added steel further contains one or two kinds of Cu: 2.00% or less and Ni: 2.00% or less in mass% (5) Or the prevention method of the blockage | closure of the continuous casting nozzle of the sulfur addition steel as described in (6).

  (8) The sulfur-added steel further contains one or two kinds of Cr: 2.00% or less and Mo: 2.00% or less in mass% (5). The method for preventing clogging of the continuous casting nozzle of the sulfur-added steel according to any one of to (7).

  (9) The sulfur-added steel further contains one or two kinds of Nb: 0.25% or less and V: 0.25% or less in mass% (5). A method for preventing clogging of a continuous casting nozzle of sulfur-added steel according to any one of to (8).

  (10) The sulfur-added steel further contains one or two kinds of Ti: 0.30% or less and B: 0.005% or less in terms of mass% (5) A method for preventing clogging of a continuous casting nozzle of sulfur-added steel according to any one of to (9).

  (11) When adjusting the amount of sulfur in the sulfur-added steel, the sulfur source is used after the composition adjustment of components other than sulfur is completed in the RH degassing process or after the secondary refining process is completed. The method for preventing clogging of a continuous casting nozzle of sulfur-added steel according to any one of the above (1) to (10), characterized by being added to the molten steel.

  (12) The method for preventing clogging of a continuous casting nozzle of sulfur-added steel according to (11), wherein the sulfur addition source is added in the form of a wire or a plunger.

  According to the present invention, in continuous casting of sulfur-added steel, nozzle clogging can be reliably prevented without adding Ca to the molten steel and without increasing the molten steel temperature.

It is a figure which shows the relationship between the oxygen penetration | invasion total amount from a sulfur addition source, and a nozzle obstruction | occlusion parameter | index.

  The method for preventing clogging of a continuous casting nozzle of sulfur-added steel according to the present invention (hereinafter sometimes referred to as “method for preventing the present invention”) is to add a sulfur addition source and adjust S to 0.012 to 0.100 mass%. In the continuous casting of the sulfur-added steel, the total oxygen intrusion amount from the sulfur addition source is suppressed to 40 ppm or less.

  The sulfur-added steel is characterized by containing Al: 0.015 to 0.100% by mass.

  Hereinafter, a process from the idea to the present invention and a method for preventing the present invention will be described.

  The inventors have various methods for preventing clogging of the continuous casting nozzle without adding Ca to the molten steel and without increasing the molten steel temperature when continuously casting the Al deoxidized sulfur-added steel. A continuous casting test was conducted.

  As a result, in the Al-deoxidized steel not containing Ca and in the sulfur-added steel containing 0.012 to 0.100% S, the occurrence frequency of clogging of the continuous casting nozzle is higher than that in the steel not containing sulfur. It turned out to be.

The inventors further investigated the actual state of the deposits that caused the clogging of the continuous casting nozzle. As a result, it was found that CaS was not detected from the deposit, and the main body of the deposit was Al ₂ O ₃ inclusions.

That is, the nozzle clogging in continuous casting of sulfur-added steel is not caused by CaS, which has been a problem with conventional Ca-added steel, but may be caused by a large amount of Al ₂ O ₃ inclusions produced by the addition of sulfur. found.

  Next, the present inventors conducted a continuous casting test using a sulfur reagent, FeS, or the like instead of the sulfide ore normally used as a sulfur addition source. As a result, it was found that when a highly pure substance such as a sulfur reagent or FeS was used as the sulfur addition source, the frequency of clogging of the continuous casting nozzle was lower than before.

  From the above results, the clogging of the continuous casting nozzle is not caused by the high sulfur concentration of the molten steel, but is thought to be caused by the sulfide ore of the sulfur addition source, the present inventors, about the actual state of the sulfide ore, For example, the component composition, crystal phase, and the like of sulfide ore were investigated by chemical analysis, powder X-ray diffraction, and microscopy.

  As a result, it was found that the main component of sulfide ore is pyrite, but it contains carbonates and oxides such as dolomite and quartz. It was found that these impurities (carbonates and oxides such as dolomite and quartz, hereinafter simply referred to as “impurities”) are about 3 to 20% by mass in terms of oxygen concentration.

  Furthermore, the present inventors added a sulfide ore to molten steel in a small-scale laboratory experiment, and investigated fluctuations in the composition of the molten steel. As a result, it has been found that the oxygen concentration, Ca concentration, and / or Mg concentration may increase, and the increase amount is substantially correlated with the impurity concentration of molten steel. That is, as a result of a small-scale laboratory experiment, it was confirmed that impurities in the sulfide ore were dissolved in the molten steel.

  Based on the above knowledge, the cause of the high frequency of nozzle clogging in continuous casting of sulfur-added steel can be estimated as follows.

That is, when the amount of impurities in the sulfide ore used as the sulfur addition source is large and the oxygen concentration of the sulfide ore is high, the oxygen concentration of the molten steel increases, and accordingly, Al ₂ O ₃ inclusions are generated, and during continuous casting, Deposit on the continuous casting nozzle.

Therefore, the present inventors have conceived that if the total amount of oxygen intrusion from the sulfur addition source is reduced to a predetermined value or less, the generation of Al ₂ O ₃ inclusions is suppressed and the clogging of the continuous casting nozzle can be surely prevented. The present invention has been achieved.

  The total amount of oxygen intrusion from the sulfur addition source can be calculated by multiplying the addition amount of the sulfur addition raw material by the oxygen concentration in the raw material and dividing the result by the molten steel amount.

  FIG. 1 shows the relationship between the total amount of oxygen intrusion from the sulfur addition source and the nozzle blockage index. The nozzle blockage index is obtained by indexing the opening degree of the continuous casting nozzle, and is an index defined as follows.

  The ratio of the actual opening of the continuous casting nozzle and the original opening calculated from the molten steel throughput and the molten steel head is used as an index. The larger the nozzle, the more frequently the nozzle clogging occurs. It is as follows.

  From the results shown in FIG. 1, it can be seen that the lower the total amount of oxygen intrusion from the sulfur addition source, the less likely the nozzle clogging occurs. Based on this result, in the prevention method of the present invention, a sulfur addition source is added to the molten steel so that the total oxygen intrusion amount is 40 ppm or less.

  The oxygen concentration of the sulfur addition source can be measured by, for example, an inert gas melting / non-dispersing infrared absorption method.

  Next, a method for reducing the total oxygen intrusion amount from the sulfur addition source will be described. Naturally, it is preferable if the oxygen concentration itself of the sulfur addition source can be lowered, but there is a problem that the raw material cost is greatly increased.

  Therefore, a method of combining a raw material with a somewhat high oxygen concentration and a low raw material was considered. That is, it is a method of adding as much sulfur addition source as possible with a high oxygen concentration and adding a sulfur addition source with a low oxygen concentration when a predetermined S concentration is not reached. By this method, it is possible to minimize the cost of the sulfur addition source while suppressing nozzle blockage.

  A sulfur addition source having an oxygen concentration of 5% by mass or more can be obtained at a relatively low cost. A typical example is sulfide ore. The sulfide ore usually contains oxygen of more than 3% by mass and about 20% by mass or less, and particularly those having an oxygen concentration of 5% by mass or more are relatively easily available.

  On the other hand, FeS, pure sulfur, etc. can be considered as a sulfur addition source having a low oxygen concentration. These sulfur addition sources have been refined industrially to high purity and are high in cost, but the oxygen concentration is extremely low at 3% by mass or less.

  That is, a high oxygen concentration sulfur addition source having an oxygen concentration of more than 3% by mass and 20% by mass or less, preferably 5% by mass or more and 20% by mass or less, and an oxygen concentration of 3% by mass, which are relatively easily available. By using a combination of the following low oxygen concentration sulfur addition sources, it is possible to achieve both nozzle clogging suppression and sulfur addition source cost reduction.

Next, the timing for adding the sulfur addition source to the molten steel will be described. If the sulfur addition source is added to the molten steel immediately before continuous casting of the molten steel, the floating separation of the Al ₂ O ₃ inclusions generated by the oxygen in the sulfur addition source, that is, the oxygen in the sulfide ore impurities is difficult to proceed. Nozzle blockage tends to occur during casting. Thus, since the oxygen concentration of molten steel has a great influence on nozzle clogging, caution is required when adding a sulfur addition source.

  Here, the specific addition method of a sulfur addition source is demonstrated.

  The component composition of the molten steel that is primarily refined in a converter or electric furnace is adjusted. If necessary, secondary refining is performed with an RH degassing refining device, a ladle heating refining device, a simple molten steel processing facility, or the like. Deoxidation with Al is performed after primary refining or during secondary refining. When deoxidation is performed after primary refining, an Al source may be added at the time of steel removal from the ladle. When deoxidation is performed during secondary refining, if the ladle slag at the position where the Al source is added is removed, the yield of Al becomes stable.

Al is preferably added to the molten steel as early as possible, and then the molten steel is agitated to float and separate the Al ₂ O ₃ inclusions.

  As described above, after the Al deoxidation is performed, the sulfur addition source is added at the end of the secondary refining or after the secondary refining. During the secondary refining, a sulfur addition source may be added, or after the secondary refining, a sulfur addition source may be added using a wire or the like.

In addition, when a sulfur addition source is added before the secondary refining or the first half of the secondary refining, desulfurization proceeds due to reaction with the ladle slag, and the sulfur concentration may not be controlled within a required range. For this reason, the sulfur addition source is added to the molten steel at the end of the secondary refining or after the secondary refining. In this case, the floating separation of the _{Al 2} O ₃ inclusions generated from the oxygen in the sulfur addition source is difficult to proceed. During continuous casting, nozzle clogging is likely to occur.

Therefore, when combining a high oxygen concentration sulfur addition source and a low oxygen concentration sulfur addition source, the high oxygen concentration sulfur addition source is added first, and the floating separation of the generated Al ₂ O ₃ inclusions can be advanced as much as possible. preferable. Thereafter, a low oxygen concentration sulfur addition source is added, but no problem arises because Al ₂ O ₃ inclusions are not generated.

The molten steel thus prepared is continuously cast according to a conventional method to obtain a slab. During continuous casting, keep oxygen sources from entering the molten steel as much as possible. This is because when an oxygen source is mixed in the molten steel, Al ₂ O ₃ inclusions that cause nozzle clogging are generated, and thus the formation of Al ₂ O ₃ inclusions is prevented.

  The continuous casting nozzle used at the time of continuous casting may be made of an inexpensive alumina graphite material, but it is also possible to use a hardly adherent one containing CaO.

  In the prevention method of the present invention, the sulfur-added steel continuously cast by adding a sulfur addition source contains S: 0.012 to 0.100% by mass, preferably Al: 0.015 to 0.100% by mass. Including steel.

  Hereinafter, the reason for limitation of the component composition of the sulfur-added steel (hereinafter also referred to as “the present invention-added steel”) continuously cast by the present invention prevention method will be described. Hereinafter,% is mass%.

S: 0.012-0.100%
S is an element necessary for ensuring the machinability of steel, and is an element that affects the occurrence of nozzle clogging during continuous casting. If S is less than 0.012%, the addition amount of the sulfur addition source is small, and nozzle clogging does not occur, but the required machinability cannot be secured, so S is made 0.012% or more. Preferably it is 0.015% or more.

  On the other hand, if S exceeds 0.100%, Ca in the ladle slag reacts with S in the molten steel to generate CaS, and during continuous casting, nozzle clogging occurs, so S is 0.100% or less. And Preferably it is 0.075% or less.

Al: 0.015-0.100%
Al is an element that reacts with O in molten steel to produce Al ₂ O ₃ and deoxidizes the molten steel. When Al is less than 0.015%, the deoxidation effect is not sufficiently exhibited, so Al is made 0.015% or more. Preferably it is 0.025% or more.

On the other hand, when Al exceeds 0.100%, a large amount of Al ₂ O ₃ inclusions are generated and nozzle clogging occurs frequently during continuous casting, so Al is made 0.100% or less. Preferably it is 0.070% or less.

  The steel according to the present invention basically contains S: 0.012 to 0.100%, more preferably Al: 0.015 to 0.100%. Although there is no particular limitation on the composition, C: 0.07 to 1.20%, Si: 1.00% or less, Mn: 2. If the effect of improving the machinability by adding sulfur is to be expressed more effectively. It is preferable to control to 50% or less, P: 0.10% or less, and N: 0.02% or less. This will be described below.

C: 0.07-1.20%,
C is an element necessary for ensuring the strength of steel and the hardenability of welds. If C is less than 0.07%, it becomes difficult to ensure the strength required for steel for machine structural use, so C is preferably 0.07% or more. More preferably, it is 0.10% or more. On the other hand, if C exceeds 1.20%, the toughness decreases, so C is preferably 1.20% or less. More preferably, it is 1.00% or less.

Si: 1.00% or less Si is an element that contributes to improving the strength of steel by solid solution strengthening. If the Si content exceeds 1.00%, the toughness decreases, so Si is preferably 1.00% or less. More preferably, it is 0.70% or less. The lower limit is not particularly limited, but is preferably 0.01% or more in order to sufficiently obtain the effect of adding Si. More preferably, it is 0.10% or more.

Mn: 2.50% or less Mn is an element that improves the hardenability of steel and contributes to the improvement of strength. If Mn exceeds 2.50%, the weldability of the steel decreases, so Mn is preferably 2.50% or less. More preferably, it is 2.00% or less. The lower limit is not particularly limited, but 0.30% or more is preferable in order to sufficiently obtain the effect of adding Mn. More preferably, it is 0.50% or more.

P: 0.10% or less P is an element that segregates and inhibits toughness. If P exceeds 0.10%, the toughness is remarkably lowered, so P is preferably 0.10% or less. More preferably, it is 0.05% or less. The lower limit is not particularly limited, but if P is reduced to less than 0.001%, the production cost increases significantly, so 0.001% is a practical lower limit on practical steel. In terms of manufacturing cost, 0.010% or more is more preferable.

N: 0.02% or less N is an element that contributes to improving the strength of steel by solid solution strengthening. If N exceeds 0.02%, the amount of solid solution N increases, the strength increases, and the toughness decreases, so N is preferably 0.02% or less. More preferably, it is 0.015% or less. The lower limit is not particularly limited, but if N is reduced to less than 0.001%, the manufacturing cost increases significantly, so 0.001% is a practical lower limit on practical steel. In terms of manufacturing cost, 0.002% or more is more preferable.

  The steel according to the present invention is further improved in properties by (a) Cu: 2.00 or less and Ni: 2.00% or less, or (b) Cr: 2.00% or less, And Mo: 2.00% or less, 1 or 2 types, (c) Nb: 0.25% or less, and V: 0.25% or less, or (d) Ti: One or more of one or two element groups of 0.30% or less and B: 0.005% or less may be contained.

(A) Group element Cu: 2.00% or less Ni: 2.00% or less Both Cu and Ni are elements that contribute to improving the strength of steel.

  If Cu exceeds 2.00%, the strength increases excessively and the toughness decreases, so Cu is preferably 2.00% or less. More preferably, it is 1.60% or less. Although a minimum is not specifically limited, In order to fully acquire the addition effect of Cu, 0.10% or more is preferable. More preferably, it is 0.20% or more.

  If Ni exceeds 2.00%, the strength increases excessively and the toughness decreases, as with Cu, so Ni is preferably 2.00% or less. More preferably, it is 1.60% or less. Although a minimum is not specifically limited, In order to fully acquire the addition effect of Ni, 0.10% or more is preferable. More preferably, it is 0.30% or more.

(B) Group element Cr: 2.00% or less Mo: 2.00% or less Both Cr and Mo are elements contributing to the improvement of the strength of steel.

  If Cr exceeds 2.00%, the strength increases excessively and the toughness decreases, so Cr is preferably 2.00% or less. More preferably, it is 1.60% or less. The lower limit is not particularly limited, but 0.15% or more is preferable in order to sufficiently obtain the effect of adding Cr. More preferably, it is 0.25% or more.

  If Mo exceeds 2.00%, the strength increases excessively and the toughness decreases as in Cr, so Mo is preferably 2.00% or less. More preferably, it is 1.60% or less. Although a minimum is not specifically limited, In order to fully acquire the addition effect of Mo, 0.02% or more is preferable. More preferably, it is 0.10% or more.

(C) Group element Nb: 0.25% or less V: 0.25% or less Nb and V both form carbonitrides and contribute to improvement in strength and toughness by the pinning effect of carbonitrides. Element.

  If Nb exceeds 0.25%, carbonitrides become coarse and the toughness decreases, so Nb is preferably 0.25% or less. More preferably, it is 0.20% or less. The lower limit is not particularly limited, but 0.01% or more is preferable in order to sufficiently obtain the effect of adding Nb. More preferably, it is 0.02% or more.

  If V exceeds 0.25%, the carbonitrides become coarse and the HAZ toughness decreases like Nb. Therefore, V is preferably 0.25% or less. More preferably, it is 0.20% or less. The lower limit is not particularly limited, but 0.01% or more is preferable in order to sufficiently obtain the effect of adding V. More preferably, it is 0.10% or more.

(D) Group element Ti: 0.30% or less B: 0.005% or less Ti is an element that combines with N to form nitrides to refine crystal grains and contribute to improvement of toughness. If Ti exceeds 0.30%, the machinability deteriorates, so Ti is preferably 0.30% or less. More preferably, it is 0.25% or less. The lower limit is not particularly limited, but 0.01% or more is preferable in order to sufficiently obtain the effect of adding Ti. More preferably, it is 0.02% or more.

  B is an element that suppresses the formation of grain boundary ferrite and contributes to the improvement of toughness. If B exceeds 0.005%, BN precipitates at the austenite grain boundaries and the toughness decreases, so B is preferably 0.005% or less. More preferably, it is 0.003% or less. The lower limit is not particularly limited, but 0.0005% or more is preferable in order to sufficiently obtain the effect of adding B. More preferably, it is 0.0010% or more.

  Next, examples of the present invention will be described. The conditions in the examples are one example of conditions used for confirming the feasibility and effects of the present invention, and the present invention is based on this one example of conditions. It is not limited. The present invention can adopt various conditions as long as the object of the present invention is achieved without departing from the gist of the present invention.

(Example)
When the molten steel primarily refined in a converter having a capacity of 300 tons was put into a ladle, Al metal was added and Al deoxidation was performed.

  Table 1 shows the composition of the molten steels of the inventive examples and comparative examples.

  After Al deoxidation, the temperature was adjusted with a ladle heating-type refining device, and then degassing treatment and component adjustment were performed using an RH-type degassing refining device, and the inclusions were removed by stirring the molten steel. After degassing treatment and component adjustment, sulfur was added by adding sulfur addition sources having different oxygen concentrations to the molten steel. After the addition of the sulfur addition source, stirring was performed for a uniform mixing time or longer to promote the removal of inclusions.

  The uniform mixing time is the time required for the added alloy element to asymptotically fall within a predetermined range near the final value, and is a time correlated with the stirring force. The uniform mixing time can be obtained by a tracer experiment, and using a relational expression with a known stirring power density (for example, Shigeo Asai, Tetsuo Okamoto, Kosei, Whip, Iron and Steel 68, 426). Can be estimated.

  The molten sulfur-added steel was continuously cast. Continuous casting was carried out with a continuous caster of Bloom 6 strand having a cross-sectional size of 220 mm × 220 mm.

  The superheat degree (the value obtained by subtracting the liquidus temperature of the steel having this composition from the temperature of the molten steel) in the tundish during continuous casting was 10 to 60 ° C. The throughput of molten steel (amount of cast molten steel per unit time) was 0.3 to 0.6 t / min.

  Table 2 shows the total oxygen intrusion amount from the sulfur addition source, the oxygen concentration of the high oxygen concentration sulfur addition source and the low oxygen concentration sulfur addition source, and the oxygen intrusion amount from each sulfur addition source in the invention examples and comparative examples. , Nozzle blockage index, and nozzle blockage results.

  The oxygen concentration of the sulfur addition source is an actual measurement value, and the oxygen intrusion amount is a value calculated from the oxygen concentration and the addition amount. The thing without description of the oxygen concentration and oxygen penetration | invasion amount of a low oxygen concentration sulfur addition source means having used only one kind of sulfur addition source.

  As described above, the nozzle blockage index is obtained by indexing the opening degree of the continuous casting nozzle and is defined as follows. The ratio of the actual opening of the continuous casting nozzle and the original opening calculated from the molten steel throughput and the molten steel head is used as an index. The larger the nozzle, the more frequently the nozzle clogging occurs. It is as follows.

  The nozzle clogging results are the results of a three-stage evaluation of the nozzle clogging index, where the nozzle clogging index 1 or less is marked with ◎, the value exceeding 1 and 3 or less is Δ, and the value exceeding 3 is marked with ×.

  In each of Invention Examples 1 to 50, the total oxygen intrusion amount from the sulfur addition source was 40 ppm or less, the nozzle clogging index was 1 or less, and continuous casting could be performed without occurrence of nozzle clogging.

  In Comparative Examples 51 to 65, the total oxygen intrusion amount from the sulfur addition source exceeded 40 ppm, and nozzle clogging occurred during continuous casting.

  As described above, according to the present invention, in continuous casting of sulfur-added steel, nozzle clogging can be reliably prevented without adding Ca to the molten steel and without increasing the molten steel temperature. Therefore, the present invention has high applicability in the steel industry.

Claims (12)

  In the continuous casting of sulfur-added steel in which S is adjusted to 0.012 to 0.100 mass% by adding a sulfur addition source, the sulfur addition is characterized by suppressing the total amount of oxygen intrusion from the sulfur addition source to 40 ppm or less. A method for preventing clogging of a continuous casting nozzle for steel.   A high oxygen concentration sulfur addition source having an oxygen concentration of more than 3% by mass and 20% by mass or less and a low oxygen concentration sulfur addition source having an oxygen concentration of 3% by mass or less are used in combination as the sulfur addition source. Item 2. A method for preventing clogging of a continuous casting nozzle of sulfur-added steel according to item 1.   The method for preventing clogging of a continuous casting nozzle of sulfur-added steel according to claim 2, wherein the high oxygen concentration sulfur addition source is sulfide ore.   4. When adjusting the amount of sulfur in the sulfur-added steel, the high oxygen concentration sulfur addition source is first added to the molten steel, and thereafter the low oxygen concentration sulfur addition source is added. To prevent clogging of continuous casting nozzle of sulfur-added steel.   The said sulfur addition steel is mass% and contains Al: 0.015-0.100%, The obstruction | occlusion of the continuous casting nozzle of the sulfur addition steel of any one of Claims 1-4 characterized by the above-mentioned. Prevention method.   The sulfur-added steel is in mass%, C: 0.07 to 1.20%, Si: 1.00% or less, Mn: 2.50% or less, P: 0.10% or less, N: 0.02 The method for preventing clogging of a continuous casting nozzle of sulfur-added steel according to claim 5, wherein the remaining portion comprises iron and inevitable impurities.   The sulfur-added steel further contains one or two kinds of Cu: 2.00% or less and Ni: 2.00% or less in mass%. To prevent clogging of continuous casting nozzle of sulfur-added steel.   The sulfur-added steel further contains one or two kinds of Cr: 2.00% or less and Mo: 2.00% or less in mass%. A method for preventing clogging of a continuous casting nozzle of sulfur-added steel according to claim 1.   The sulfur-added steel further contains one or two of Nb: 0.25% or less and V: 0.25% or less in mass%. A method for preventing clogging of a continuous casting nozzle of sulfur-added steel according to claim 1.   The sulfur-added steel further contains one or two kinds of Ti: 0.30% or less and B: 0.005% or less in mass%. A method for preventing clogging of a continuous casting nozzle of sulfur-added steel according to claim 1.   When adjusting the amount of sulfur in the sulfur-added steel, the sulfur addition source is the molten steel after the composition adjustment of components other than sulfur is completed in the RH degassing process or after the secondary refining process is completed. The method for preventing clogging of a continuous casting nozzle of sulfur-added steel according to any one of claims 1 to 10, wherein the addition is performed.   12. The method for preventing clogging of a continuous casting nozzle of sulfur-added steel according to claim 11, wherein the sulfur addition source is added in the form of a wire or a plunger.

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