WO2018087953A1 - 溶鋼への硫黄添加材及び硫黄添加鋼の製造方法 - Google Patents
溶鋼への硫黄添加材及び硫黄添加鋼の製造方法 Download PDFInfo
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- C21C7/00—Treating molten ferrous alloys, e.g. steel, not covered by groups C21C1/00 - C21C5/00
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Definitions
- the present invention relates to a sulfur additive added to molten steel in order to adjust the components of the molten steel, and a manufacturing method for producing sulfur-added steel using the sulfur additive.
- sulfur (S) is an element that enhances the machinability of steel materials
- the required amount is often added in the steelmaking process, particularly to molten steel for machine structural steel that is machined into a complex shape.
- pure sulfur refined with high purity, iron sulfide produced industrially, pyrite, pyrite, pyrrhotite, etc. obtained by various beneficiation methods are used as the sulfur additive.
- molten steel refined in a converter or vacuum processing vessel contains a large amount of oxygen, and this large amount of oxygen is about 0.015 to 0.100 mass% of deoxidizing element Al having a strong affinity for oxygen. Adding and deoxidizing is a common technique.
- iron sulfide ore when used as is as a sulfur additive to molten steel, impurities (oxides, carbonates, etc.) in the iron sulfide ore become oxygen sources, more alumina clusters are generated, and nozzle clogging occurs more. It becomes easy to do.
- Patent Document 1 discloses decarburization, deoxidation of the molten steel, and addition of the alloy element to the molten steel by a vacuum degassing apparatus.
- the molten steel secondary refining method it has been proposed to add an alloying element during the decarburization treatment of the molten steel and then to perform the deoxidation treatment.
- An object of the present invention is to provide an inexpensive and low-impurity sulfur additive that solves the problem, and to provide a manufacturing method for producing a sulfur-added steel using the sulfur additive. Objective.
- the present inventors have intensively studied a method for solving the above-mentioned problems. As a result, if a sulfide ore having a specific particle size obtained by crushing and sizing is used as a sulfur additive, the yield of sulfur in molten steel can be stabilized. And found that nozzle clogging can be prevented during continuous casting.
- the present invention has been made on the basis of the above findings, and the gist thereof is as follows.
- a sulfur additive used for molten steel characterized by containing 85% by mass or more of iron sulfide ore particles having a particle diameter of 5.0 to 37.5 mm with respect to the total mass% of the sulfur additive.
- the sulfur-added steel is further mass%, Cu: 2.00% or less, Ni: 2.00% or less, Cr: 2.00% or less, Mo: 2.00% or less, Nb: 0.25% or less, V: 0.25% or less, Ti: 0.30% or less, B: 0.005% or less,
- the present invention it is possible to provide a sulfur additive that is inexpensive and has a small amount of impurities, and when the sulfur additive material is added to molten steel, the sulfur yield in the molten steel is stabilized, and It is possible to provide a production method for producing sulfur-added steel that can prevent nozzle clogging during continuous casting.
- the sulfur additive of the present invention used for molten steel (hereinafter sometimes referred to as “the additive of the present invention”) is 85 mass% of iron sulfide ore having a particle size of 5.0 to 37.5 mm with respect to the total mass% of the sulfur additive. % Or more.
- the method for producing sulfur-added steel of the present invention uses the additive of the present invention, Al: 0.015 to 0.100 mass%, and S: 0.00. An aluminum deoxidized sulfur-added steel containing 012 to 0.100 mass% is melted.
- the additive of the present invention after adjusting components other than sulfur in the RH degassing treatment step.
- the present inventors investigated in detail about the composition and characteristics of iron sulfide ore in order to use inexpensive iron sulfide ore as a sulfur additive.
- pyrite was the main component of pyrite, but it was found that pyrite contains carbonates and oxides such as dolomite and quartz. These impurities (carbonates and oxides such as dolomite and quartz, hereinafter simply referred to as “impurities”) are contained in about 3 to 20% by mass in iron sulfide ore when converted to oxygen concentration. I understand.
- the impurities were: (a) the fine particles with a particle size of several millimeters or less in the iron sulfide ore; It was found that they existed as aggregates, and (b) they were not uniformly present in iron sulfide ore but were unevenly distributed. Furthermore, as a result of observing a plurality of iron sulfide ores with different particle sizes in the same manner, it was found that there was a difference in the distribution state of impurities among (c) iron sulfide ore particles.
- the present inventors have conceived that “the amount of impurities contained may vary depending on the particle size of the iron sulfide ore”.
- the amount of impurities for each particle size was measured by ordinary chemical analysis or X-ray diffraction method.
- FIG. 1 as an example, the particle size (mm) of iron sulfide ore after pulverizing and sieving in three stages, three types of practical brands A, B, and C having different production areas, The relationship with the oxygen concentration (mass%) in the iron sulfide ore for every particle is shown.
- the oxygen concentration of the pyrite was measured by an inert gas melting-infrared absorption method, which is a kind of chemical analysis.
- the relationship between the particle size and the oxygen concentration shows almost the same behavior even when the production areas are different, and the particle size is in the range of 5.0 to 37.5 mm, more preferably 9.
- the oxygen concentration was low in the range of 5 to 31.5 mm. Further, as shown in FIG.
- the particle size of the iron sulfide ore is in the range of 5.0 to 37.5 mm, the oxygen concentration is small (the oxygen concentration is 10% by mass or less), and the particle size is 9.5 to 31. It can be seen that the oxygen concentration is even smaller in the range of 0.5 mm (oxygen concentration of 9% by mass or less). In this respect, similar results were obtained for the three brands A, B, and C. From this result, even if each brand is blended and subjected to the same analysis, the grain size is in the range of 5.0 to 37.5 mm, more preferably the grain size is 9.5 to 31. In the range of 5 mm, the oxygen concentration is expected to be low.
- the iron sulfide ore produced from the mine inevitably contains impurities such as carbonates and oxides, but its particle size is as small as several millimeters or less. And the hardness of these impurities is greatly different from pyrite, which is the main component of pyrite.
- iron sulfide ore is used by crushing the ore with a crusher or the like so that it can be easily handled.
- iron sulfide ore particles having a particle size of 5.0 to 37.5 mm preferably iron sulfide ore particles having a particle size of 9.5 to 31.5 mm are used as sulfur additives to be added to molten steel. I decided to use it.
- the sulphite ore ore is crushed and the sulphide ore with a particle size of 5.0 to 37.5 mm is used by sieving, but the particle size is in the range of 5.0 to 37.5 mm without being crushed.
- the sulfide ore in is used as it is. Particles having a particle size exceeding 37.5 mm as a result of sieving may be crushed again so that the particle size is in the range of 5.0 to 37.5 mm.
- iron sulfide ore particles having a particle size of 9.5 to 31.5 mm are used.
- the sulfur additive to be added to the molten steel is composed of iron sulfide ore particles having a particle size of 5.0 to 37.5 mm, preferably iron sulfide ore particles having a particle size of 9.5 to 31.5 mm. What contains above is used.
- the iron sulfide ore particles having a particle size of 5.0 to 37.5 mm in the sulfur additive is less than 85% by mass, it is difficult to accurately adjust the amount of sulfur in the molten steel within a required range.
- the amount of iron sulfide ore particles having a particle size of 5.0 to 37.5 mm is 85% by mass or more with respect to the total amount of sulfur additive. Preferably it is 90 mass% or more.
- the particle size of the iron sulfide ore particles is measured by sieving the iron sulfide ore by a method specified in JIS Z 8815 (ISO2591-1). Grains of iron sulfide ore passing through a test sieve mesh with a nominal aperture of 37.5 mm specified in JIS Z 8801-1 (ISO 3310-1) and remaining on the test sieve mesh with a nominal aperture of 5.0 mm Use iron sulfide ore particles with a diameter of 5.0 to 37.5 mm.
- the inventors added iron sulfide ore particles to the molten steel and investigated the fluctuation of the oxygen concentration in the molten steel.
- An increase in oxygen concentration was observed after the addition of the iron sulfide ore.
- the amount of change was small with the addition of the iron sulfide ore particles having a particle size of 5.0 to 37.5 mm, and the particle size was 9.5 to 31. It was confirmed that the addition of iron sulfide ore particles in the range of 0.5 mm was smaller.
- the Al source is preferably added to the molten steel as early as possible after the primary smelting, and then the molten steel is stirred to float and separate the Al 2 O 3 inclusions.
- the present invention is added to the Al deoxidized molten steel at the end of the secondary refining after adjusting the composition of the molten steel A material (85% by mass or more of iron sulfide ore having a particle size of 5.0 to 37.5 mm) is added.
- a material 85% by mass or more of iron sulfide ore having a particle size of 5.0 to 37.5 mm
- desulfurization proceeds due to reaction with ladle slag, and the sulfur concentration of the resulting sulfur-added steel may not be controlled within the required range. There is.
- the molten steel thus prepared is continuously cast according to a conventional method to obtain a slab. Make sure that the oxygen source does not enter the molten steel during continuous casting. This is because when an oxygen source is mixed into the molten steel, Al 2 O 3 inclusions are generated, and thus Al 2 O 3 inclusions are prevented from being generated.
- the immersion nozzle used at the time of continuous casting may be an inexpensive alumina graphite material, it is also possible to use a nozzle with poor adhesion containing CaO.
- the production method of the present invention is suitable for melting sulfur-added steel containing S: 0.012 to 0.100% by mass.
- the sulfur-added steel obtained by the production method of the present invention contains Al: 0.015 to 0.100% by mass after Al deoxidation.
- S 0.012 to 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 the amount of S is less than 0.012%, the amount of sulfur additive added is small and nozzle clogging does not occur, but the required machinability cannot be ensured, so the amount of S is 0.012% or more. . Preferably it is 0.015% or more.
- the amount of S exceeds 0.100%, Ca in the ladle slag and sulfur in the molten steel react to generate CaS, and during continuous casting, nozzle clogging occurs, so the amount of S is 0.100. % Or less. Preferably it is 0.075% or less.
- Al 0.015 to 0.100%
- Al is an element used to react with O in molten steel to produce Al 2 O 3 and deoxidize the molten steel. If the Al content is less than 0.015%, the deoxidation effect is not sufficiently exhibited, so the Al content is 0.015% or more. Preferably it is 0.025% or more. On the other hand, if the Al content exceeds 0.100%, a large amount of Al 2 O 3 inclusions are generated and nozzle clogging occurs frequently during continuous casting, so the Al content is set to 0.100% or less. Preferably it is 0.070% or less.
- the additive steel according to the present invention basically contains S: 0.012 to 0.100%, and further needs to contain Al: 0.015 to 0.100%.
- the composition is not particularly limited, but C: 0.07 to 1.20%, Si: more than 0 and 1.00% or less, in order to more effectively express the effect of improving the machinability by adding sulfur.
- Mn is more than 0 and is controlled to 2.50% or less
- P is more than 0 and is 0.10% or less
- N is more than 0 and is 0.02% or less. This will be described below.
- C 0.07 to 1.20%
- C is an element necessary for ensuring the strength of steel and the hardenability of welds. If the C content is less than 0.07%, it becomes difficult to ensure the strength required for the steel for machine structural use, so the C content is 0.07% or more. More preferably, it is 0.10% or more. On the other hand, if the C content exceeds 1.20%, the toughness decreases, so the C content is 1.20% or less. More preferably, it is 1.00% or less.
- Si more than 0, 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 the Si content is 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 more than 0 and not more than 2.50% Mn is an element that improves the hardenability of steel and contributes to the improvement of strength. If the amount of Mn exceeds 2.50%, the weldability of the steel decreases, so Mn is 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 more than 0, 0.10% or less
- P is an element that segregates and inhibits toughness. If the P content exceeds 0.10%, the toughness is remarkably reduced, so the P content is 0.10% or less. More preferably, it is 0.05% or less.
- the lower limit is not particularly limited, but if the amount of P 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, 0.010% or more is more preferable.
- N more than 0, 0.02% or less N is an element that contributes to improving the strength of steel by solid solution strengthening. If the amount of N exceeds 0.02%, the amount of solid solution N increases, the strength increases, and the toughness decreases, so the amount of N is 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 added steel according to the present invention further has (a) Cu: 2.00 or less and / or Ni: 2.00% or less, (b) Cr: 2.00% or less, and / or for improving the characteristics. Or Mo: 2.00% or less, (c) Nb: 0.25% or less, and / or V: 0.25% or less, and (d) Ti: 0.30% or less, and / or B: You may contain 1 or 2 or more of 0.005% or less of element groups.
- Cu and Ni are elements that contribute to improving the strength of steel. If the Cu content exceeds 2.00%, the strength increases excessively and the toughness decreases, so the Cu content 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.
- the Ni content 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.
- the Mo amount 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.
- 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 the Nb content exceeds 0.25%, the carbonitrides become coarse and the toughness decreases, so the Nb content 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.
- the V content 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.
- Ti is an element that combines with N to form a nitride to refine crystal grains and contribute to improvement of toughness. If the Ti content exceeds 0.30%, the machinability deteriorates, so the Ti content 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 intergranular ferrite and contributes to the improvement of toughness. If the B content exceeds 0.005%, BN precipitates at the austenite grain boundaries and the toughness decreases, so the B content 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.
- the conditions in the examples are one example of conditions adopted for confirming the feasibility and effects of the present invention, and the present invention is an example of this one condition. It is not limited to.
- 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 1 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.
- Example 1 brand A sulfide ore particles shown in FIG. 1 were used as the sulfur additive.
- Table 1 shows the component composition of the molten steel after adding the sulfur additive during continuous casting of the inventive sulfur-added steel.
- T.Al represents the total amount of Al.
- the temperature was adjusted with a ladle heating type refining device, then degassing treatment and component adjustment were performed using the RH type degassing refining device, and the inclusion was removed by stirring the molten steel.
- degassing treatment and component adjustment a sulfur additive containing iron sulfide ore with different particle sizes was added to the molten steel. After the addition of the sulfur additive, the inclusions were removed by stirring over a uniform mixing time.
- the superheat degree 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. Throughput was adjusted by the opening of the sliding nozzle.
- Table 2 shows the mass% of iron sulfide ore having a particle size of 5.0 to 37.5 mm, the mass% of iron sulfide ore having a particle size of less than 5.0 mm, the mass% of iron ore having a particle size of more than 37.5 mm, the nozzle clogging index, The nozzle blockage results are shown respectively.
- “No.” in Table 2 corresponds to “No.” in Table 1.
- the nozzle clogging index is an index obtained by indexing the opening degree of the sliding nozzle and is defined as follows.
- the “theoretical opening” is the opening of the sliding nozzle necessary for obtaining a predetermined throughput in a state where the immersion nozzle and / or the sliding nozzle is not melted or blocked.
- the “actual opening degree” is an opening degree actually indicated by the gauge of the injection system at the time of casting.
- the nozzle clogging results are the results of evaluation of the nozzle clogging index in three stages.
- a nozzle clogging index of 1 or less is ⁇ (good), 1 is 3 or less is ⁇ (not good), and 3 is more than x (bad). .
- the ratio of the iron sulfide ore particles having a particle diameter of 5.0 to 37.5 mm in the sulfur additive is 85% by mass or more, the nozzle clogging index is 1 or less, Continuous casting was possible without clogging.
- the ratio of the iron sulfide ore particles having a particle size of 5.0 to 37.5 mm in the sulfur additive was less than 85% by mass, and nozzle clogging occurred frequently during continuous casting.
- Example 2 the sulfur-added steel was continuously cast in the same manner as in Example 1 except that brand B and brand C sulfide iron ore particles shown in FIG. 1 were used as the sulfur additive.
- Table 3 shows the composition of the molten steel after addition of the sulfur additive during continuous casting of the inventive sulfur-added steel.
- T.Al represents the total amount of Al.
- Table 4 shows the mass% of iron sulfide ore having a particle size of 5.0 to 37.5 mm, the mass% of iron ore sulfide having a particle size of less than 5.0 mm, the mass% of iron sulfide ore having a particle size of more than 37.5 mm, the nozzle clogging index, The nozzle blockage results are shown respectively.
- “No.” in Table 4 corresponds to “No.” in Table 3.
- sulfur addition that stabilizes the yield of sulfur in molten steel and prevents the occurrence of nozzle clogging during continuous casting is inexpensive and has a small amount of impurities. Material can be provided. Therefore, the present invention has high applicability in the steel industry.
Abstract
Description
質量%で、
C:0.07~1.20%、
Si:0超、1.00%以下、
Mn:0超、2.50%以下、
N:0超、0.02%以下
S:0.012~0.100%、
Al:0.015~0.100、
P:0.10%以下に制限し、残部が鉄及び不可避的不純物からなる硫黄添加鋼を溶製することを特徴とする硫黄添加鋼の製造方法。
Cu:2.00%以下、
Ni:2.00%以下、
Cr:2.00%以下、
Mo:2.00%以下、
Nb:0.25%以下、
V:0.25%以下、
Ti:0.30%以下、
B:0.005%以下、
から選ばれる1種又は2種以上の元素
を含有することを特徴とする前記(3)に記載の硫黄添加鋼の製造方法。
また、図1より、硫化鉄鉱の粒径が、5.0~37.5mmの範囲で、含有酸素濃度が少なく(酸素濃度で10質量%以下)、また、粒径が、9.5~31.5mmの範囲で酸素濃度がさらに少ない(酸素濃度9質量%以下)ことが解る。この点においても、3種類の銘柄A、B、C共に同様の結果が得られた。この結果から、各銘柄をブレンドして同様の分析を行っても、単一銘柄の場合と同様に粒度が5.0~37.5mmの範囲で、より好ましくは粒度が9.5~31.5mmの範囲で、酸素濃度が低位となると見込まれる。
Sは、鋼の切削加工性の確保に必要な元素であり、また、連続鋳造時のノズル閉塞の発生に影響を及ぼす元素である。S量が0.012%未満であると、硫黄添加材の添加量が少なくて済み、ノズル閉塞は発生しないが、所要の切削加工性を確保できないので、S量は0.012%以上とする。好ましくは0.015%以上である。
Alは、溶鋼中のOと反応してAl2O3を生成し、溶鋼を脱酸するのに用いる元素である。Al量が0.015%未満であると、脱酸効果が十分に発現しないので、Al量は0.015%以上とする。好ましくは0.025%以上である。一方、Al量が0.100%を超えると、Al2O3介在物が大量に生成し、連続鋳造時に、ノズル閉塞が頻発するので、Al量は0.100%以下とする。好ましくは0.070%以下である。
Cは、鋼の強度や溶接部の焼入れ性の確保に必要な元素である。C量が0.07%未満であると、機械構造用鋼に必要な強度を確保することが難しくなるので、C量は0.07%以上である。より好ましくは0.10%以上である。一方、C量が1.20%を超えると、靭性が低下するので、C量は1.20%以下である。より好ましくは1.00%以下である。
Siは、固溶強化で、鋼の強度の向上に寄与する元素である。Si量が1.00%を超えると、靱性が低下するので、Si量は1.00%以下である。より好ましくは0.70%以下である。下限は特に限定しないが、Siの添加効果を十分に得るには、0.01%以上が好ましい。より好ましくは0.10%以上である。
Mnは、鋼の焼入れ性を高め、強度の向上に寄与する元素である。Mn量が2.50%を超えると、鋼の溶接性が低下するので、Mnは2.50%以下である。より好ましくは2.00%以下である。下限は特に限定しないが、Mnの添加効果を十分に得るには、0.30%以上が好ましい。より好ましくは0.50%以上である。
Pは、偏析して、靭性を阻害する元素である。P量が0.10%を超えると、靭性が著しく低下するので、P量は0.10%以下である。より好ましくは0.05%以下である。下限は特に限定しないが、P量を0.001%未満に低減すると、製造コストが大幅に上昇するので、実用鋼上、0.001%が実質的な下限である。製造コストの点で、0.010%以上がより好ましい。
Nは、固溶強化で、鋼の強度の向上に寄与する元素である。N量が0.02%を超えると、固溶N量が増大して、強度が上昇し、靱性が低下するので、N量は0.02%以下である。より好ましくは0.015%以下である。下限は特に限定しないが、Nを0.001%未満に低減すると、製造コストが大幅に上昇するので、実用鋼上、0.001%が実質的な下限である。製造コストの点で、0.002%以上がより好ましい。
Cu:2.00以下
Ni:2.00%以下
CuとNiは、いずれも、鋼の強度の向上に寄与する元素である。Cu量が2.00%を超えると、強度が上昇しすぎて、靱性が低下するので、Cu量は2.00%以下が好ましい。より好ましくは1.60%以下である。下限は特に限定しないが、Cuの添加効果を十分に得るには、0.10%以上が好ましい。より好ましくは0.20%以上である。
Cr:2.00%以下
Mo:2.00%以下
CrとMoは、いずれも、鋼の強度の向上に寄与する元素である。Cr量が2.00%を超えると、強度が上昇しすぎて、靱性が低下するので、Cr量は、2.00%以下が好ましい。より好ましくは1.60%以下である。下限は特に限定しないが、Crの添加効果を十分に得るには、0.15%以上が好ましい。より好ましくは0.25%以上である。
Nb:0.25%以下
V:0.25%以下
NbとVは、いずれも、炭窒化物を形成し、炭窒化物のピン止め効果により、強度や靭性の向上に寄与する元素である。Nb量が0.25%を超えると、炭窒化物が粗大化し、靱性が低下するので、Nb量は0.25%以下が好ましい。より好ましくは0.20%以下である。下限は特に限定しないが、Nbの添加効果を十分に得るには、0.01%以上が好ましい。より好ましくは0.02%以上である。
Ti:0.30%以下
B:0.005%以下
Tiは、Nと結合して窒化物を形成して結晶粒を微細化し、靭性の向上に寄与する元素である。Ti量が0.30%を超えると、切削加工性が低下するので、Ti量は0.30%以下が好ましい。より好ましくは0.25%以下である。下限は特に限定しないが、Tiの添加効果を十分に得るには、0.01%以上が好ましい。より好ましくは0.02%以上である。
容量300トンの転炉で一次精錬した溶鋼を取鍋に出鋼する際、金属Alを添加してAl脱酸を実施した。実施例1では、硫黄添加材として図1に示す銘柄Aの硫化鉄鉱粒子を用いた。
ここで、「理論開度」とは、浸漬ノズル及び/又はスライディングノズルが溶損も閉塞もしていない状態において、所定のスループットを出すために必要なスライディングノズルの開度のことである。また、「実際の開度」とは鋳造時に注入系のゲージが実際に示す開度である。浸漬ノズル及び/又はスライディングノズルにアルミナクラスター等が付着して、閉塞が進行すると同じ流量を出すのに、スライディングノズルの開度が大きくなる。したがって、ノズル閉塞指数が大きいほど、ノズル閉塞が頻発することを意味し、目標は1以下である。
また、ノズル閉塞の状況を定常鋳造期のノズル開度に対する変化でも評価した。
表2中の「ノズル開度の変化」の項目の記号「+」は、ノズル開度の増加、即ち、ノズル閉塞傾向であることを示し、「-」は、ノズル開度の減少、即ち、ノズル閉塞減少傾向又はノズル開度が安定であることを表す。
実施例2では、硫黄添加材として、図1に示す銘柄B、銘柄Cの硫化鉄鉱粒子を用いた以外は、実施例1と同様の操作で硫黄添加鋼の連続鋳造を行った。
Claims (4)
- 硫黄添加材の全質量%に対し、粒径5.0~37.5mmの硫化鉄鉱粒子を85質量%以上含むことを特徴とする溶鋼に用いる硫黄添加材。
- 前記粒径が9.5~31.5mmであることを特徴とする請求項1に記載の溶鋼への硫黄添加材。
- Al脱酸された溶鋼に請求項1又は2に記載の硫黄添加材を添加する硫黄添加工程を含み、
質量%で、
C:0.07~1.20%、
Si:0超、1.00%以下、
Mn:0超、2.50%以下、
N:0超、0.02%以下
S:0.012~0.100%、
Al:0.015~0.100を含有し、
P:0.10%以下に制限し、残部が鉄及び不可避的不純物からなる硫黄添加鋼を溶製することを特徴とする硫黄添加鋼の製造方法。 - 前記硫黄添加鋼が、さらに、質量%で、
Cu:2.00%以下、
Ni:2.00%以下、
Cr:2.00%以下、
Mo:2.00%以下、
Nb:0.25%以下、
V:0.25%以下、
Ti:0.30%以下、
B:0.005%以下、
から選ばれる1種又は2種以上の元素
を含有することを特徴とする請求項3に記載の硫黄添加鋼の製造方法。
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