JP6651306B2 - Continuous casting method - Google Patents

Description

  The present invention relates to a continuous casting method, and more particularly to a continuous casting method for steel capable of reducing the adverse effect of center segregation at the center of a slab.

  When casting a slab or bloom such as a slab by a continuous casting method, so-called center segregation in which components such as sulfur (S) and phosphorus (P) segregate in the center of the slab may occur. The solidification rate during continuous casting decreases as the thickness of the solidified shell increases, and the solidification rate becomes slowest at the center of the slab thickness, so that the solidification structure becomes coarse. Along with this, the problem that center segregation is generated particularly at the center of the slab, which hinders quality improvement, becomes apparent. As a harmful nonmetallic inclusion formed in the center segregation portion, MnS can be mentioned. When a steel sheet is processed, coarse MnS is used as a starting point to cause cracks, thereby reducing the toughness of the steel sheet. In order to prevent this, it is essential to suppress the MnS from becoming coarser and to further reduce the size.

  MnS is formed by crystallization in a liquid phase or precipitation in a solid phase. Therefore, hereinafter, the formation of MnS is collectively referred to as “MnS is crystallized”.

  Conventionally, an extremely thick steel plate has been cast into an ingot, subjected to slab rolling, and then subjected to thick plate rolling. On the other hand, in recent years, it has been attempted to cast an extremely thick steel plate by continuous casting. When continuously casting extremely thick steel plates, it is necessary to make the thickness of the slab extremely thick in order to secure the reduction ratio of hot rolling, and the slab thickness when continuously casting the extremely thick steel plates is over 300 mm. May be. Therefore, the coarsening of the solidification structure at the center of the slab becomes even more remarkable, and the degree of center segregation deteriorates.

  In order to increase the strength of a steel sheet, it is common practice to increase the concentration of Mn in the steel. As described above, Mn reacts with S in molten steel to produce MnS. Since the MnS becomes coarser as the Mn concentration becomes higher, a further countermeasure for center segregation is required in a high Mn steel.

Patent Document 1 discloses that a primary dendrite arm interval λ at a center of a slab thickness direction is used as a reference, based on a dendrite primary arm interval λ ₀ at a center of a slab thickness when casting is performed without reduction. a continuous casting method of a slab, wherein the reduction is performed immediately after the center of the slab in the thickness direction is solidified so that the value λ / λ ₀ of the ratio of λ ₀ is 0.1 to 0.9; And the diameter d ₀ of the precipitate at the center in the thickness direction of the slab when cast without performing reduction, and the value d of the ratio of the diameter d of the precipitate at the center in the thickness direction of the slab to d _0. A continuous casting method of a slab is disclosed in which rolling is performed immediately after the center of the slab in the thickness direction is solidified so that / d ₀ is 0.1 to 0.9.

Patent Document 2 discloses an oxide having a size of 0.01 to 2.0 μm composed of a nitride containing MgO or an Mg-containing oxide as a nucleus by adding Mg and containing or depositing around the oxide. A technique for manufacturing a steel material containing 1.0 × 10 ^{5 to} 1.0 × 10 ⁸ nitride composite particles per 1 mm ² is disclosed.

  However, even if MnS precipitates with MgO or Mg-containing oxides as nuclei, MnS grows in the subsequent temperature-lowering process, and eventually covers the MgO or Mg-containing oxide, so that the effect of miniaturization is lost and MnS becomes coarse. Will be. Therefore, adding Mg alone is not sufficient to increase the strength of the steel sheet by increasing the Mn concentration.

JP-A-2015-6680 JP 2001-335882 A

  An object of the present invention is to provide a continuous casting method that can further reduce adverse effects on quality caused by center segregation at the center of a slab.

That is, the gist of the present invention is as follows.
(1) In mass%, C: 0.02 to 1.50%, Si: 0.005 to 0.8%, Mn: 0.05 to 3.0%, P: 0.02% or less, S: 0.001 to 0.02%, N: 0.002 to 0.008%, O: 0.0001 to 0.015%, Ag: 0.0001 to 0.5%, the balance being Fe and inevitable Molten steel consisting of impurities is continuously cast, and the obtained slab is rolled down after the center in the thickness direction of the slab is solidified so that λ / λ ₀ is 0.1 to 0.9. And continuous casting method.
Here, λ is the primary dendrite arm spacing at the center in the thickness direction of the cast slab after reduction, and λ ₀ is the primary dendrite arm spacing at the center in the thickness direction of the slab cast without reduction. It is.
(2) In mass%, C: 0.02 to 1.50%, Si: 0.005 to 0.8%, Mn: 0.05 to 3.0%, P: 0.02% or less, S: 0.001 to 0.02%, N: 0.002 to 0.008%, O: 0.0001 to 0.015%, Ag: 0.0001 to 0.5%, the balance being Fe and inevitable It is characterized in that molten steel consisting of impurities is continuously cast, and reduction is performed at a reduction rate of 5 to 50% when the temperature in the center of the slab in the thickness direction is in the range of solidus temperature to (solidus temperature-400 ° C). And continuous casting method.
(3) Instead of a part of Fe, the molten steel component is represented by mass%, Ti: 0.005 to 0.03%, Cu: 0.05 to 1.5%, Ni: 0.05 to 5.0. %, Cr: 0.02 to 1.0%, Mo: 0.02 to 1.0%, Nb: 0.005 to 0.05%, V: 0.005 to 0.1%, and B: 0. The continuous casting method according to the above (1) or (2), wherein at least one of 0004 to 0.004% is contained.

  ADVANTAGE OF THE INVENTION According to the continuous casting method of the molten metal of this invention, a fine crystalline precipitate can be produced in a continuous cast piece.

  As described above, MnS is an example of a harmful nonmetallic inclusion formed at the center segregation portion of the slab. When a steel sheet is processed, coarse MnS is used as a starting point to cause cracks, thereby reducing the toughness of the steel sheet. In order to prevent this, it is essential to suppress the MnS from becoming coarser and to further reduce the size.

  In the vicinity of the slab solid-liquid interface during continuous casting, particularly for the solidified shell on the casting upper surface side, dendrite solidification proceeds to near the center of thickness. On the casting lower surface side, an equiaxed zone may be formed in the vicinity of the thickness center. Due to solute redistribution in the coagulation process, Mn concentration is low at the core of the dendrite and high at the interdendritic tree, and the Mn concentration greatly differs within the range of dendrites of several tens μm to several mm in size. become. For this reason, even if MnS is not generated at the Mn concentration and S concentration in the molten steel, the Mn concentration increases in the concentrated molten steel portion between the dendrite trees as the solidification progresses, and the MnS exceeds the solubility product of MnS. And MnS crystallizes out. This MnS elongates during rolling of the slab, and reduces the toughness of the steel sheet. In the case of continuously cast slabs, the Mn concentration in the center region of the thickness increases due to segregation, so that MnS is easily crystallized, and together with the low cooling rate, coarse MnS is generated, and the toughness of the steel sheet is greatly reduced. Will be. The decrease in toughness of a steel sheet becomes more remarkable as the steel sheet has higher strength.

  If the size of MnS to be crystallized is small, diffusion during heating in hot rolling performed after casting can be promoted, and harmful crystal precipitates can be reduced or eliminated.

  In Patent Document 1, the MnS crystallized out is deformed flat by applying pressure to the continuously cast slab after solidification is completed and plastically deforming the slab thickness center where the temperature is high and plastic deformation is likely to occur. The diameter of the short diameter portion is reduced, and segregation is reduced by promoting diffusion during a heat treatment in a subsequent step.

  In the present invention, in addition to flattening the MnS shape at the center of the thickness by rolling down the solidified slab as in the invention described in Patent Document 1, crystallization of MnS precipitated between dendrite trees at the end of solidification We considered reducing the size itself.

  As a result, by containing 0.0001 to 0.5% by mass of Ag in the molten steel, the size of MnS crystallized at the center of the slab is larger than that in the case where the other casting conditions are the same and Ag is not contained. Can be miniaturized. By adding Ag which forms a solid solution with Mn constituting the crystal precipitate MnS to 0.0001-0.5% molten steel to produce a continuous cast slab, Mn is obtained during the solidification process of the slab and the subsequent cooling process. It is presumed that the solubility of Mn in the solid solution of Ag and Ag decreases, the amount of Mn that reacts with S to form MnS decreases, the growth of MnS is suppressed, and coarsening can be prevented. Ag has a melting point of 962 ° C. and a boiling point of 2212 ° C., and is easily melted in molten steel at 1600 ° C., which is a steelmaking temperature, hardly evaporates, and a desired effect can be obtained efficiently with high yield. Since the melting point is lower than the steelmaking temperature, the addition position of Ag may be any location in the RH tank, ladle, tundish, or mold.

  The present invention reduces the size of MnS crystallized at the center of the slab thickness by adding 0.0001 to 0.5% by mass of Ag in the molten steel as described above, and furthermore, the slab after solidification is completed. By applying large plastic deformation to the center of the slab to flatten the shape of the precipitated MnS. Alternatively, in addition to the addition of Ag, the cast slab after solidification is pressed down to reduce the intervals between dendrites, thereby reducing the space where MnS is deposited and miniaturizing MnS. As a result, it is possible to promote the diffusion of crystal precipitates at the time of heating the slab in the subsequent step, and reduce the influence of segregation on quality.

  First, the reasons for limiting the steel components of the present invention will be described. Unless otherwise specified,% means% by mass.

C: 0.02 to 1.50%
C is an element effective for securing strength and toughness. If the content is less than 0.02%, the above effects cannot be sufficiently obtained. On the other hand, if the content is higher than 1.50%, the toughness of the base material and the HAZ decreases. Therefore, the appropriate range of C is set to 0.02 to 1.50%.

Si: 0.005 to 0.8%
If the content of Si is less than 0.005%, the strength of the base material cannot be secured, so the lower limit is made 0.005%. Further, if it exceeds 0.8%, the weldability decreases, so the upper limit was made 0.8%. For the above reasons, the appropriate range is 0.005 to 0.8%.

Mn: 0.05-3.0%
Mn is an element effective for increasing the strength and ensuring the toughness of the steel sheet. In order to obtain the above effects, the content needs to be 0.05% or more. On the other hand, if the content exceeds 3.0%, toughness is impaired. Therefore, the appropriate range of the Mn content is set to 0.05 to 3.0%. The present invention is particularly suitable when the Mn content is set to 0.5% or more for increasing the strength of the steel sheet. Because the Mn content is high, the concentrated Mn concentration concentrated between dendrite trees in the center of the thickness during solidification of the slab also increases, and the size of MnS to be crystallized also increases, so that the effect of the present invention is particularly remarkable. To appear.

P: 0.02% or less P is an element that deteriorates the ductility, toughness, and workability of the steel sheet, so that its content is limited to 0.02% or less.

S: 0.001 to 0.02%
S has the effect of forming MnS inclusions and promoting the formation of ferrite in crystal grains. If less than 0.001%, there is almost no effect of producing ferrite, so 0.001% was made the lower limit. However, if it exceeds 0.02%, the ductility of the steel sheet is reduced, so the upper limit is made 0.02%. For the above reasons, the appropriate range of the S content is set to 0.001 to 0.02%.

N: 0.002-0.008%
N is an element necessary for reacting with Ti to precipitate TiN. However, if the N content exceeds 0.008% and increases, the toughness of the steel decreases. Therefore, the upper limit of the N content is set to 0.008%. However, since it is impossible to completely remove N from steel industrially, the lower limit of the N content is set to 0.002% in consideration of a range that can be reduced in actual operation.

O: 0.0001 to 0.015%
O is an element necessary for generating an oxide. If the O content is less than 0.0001%, the number of oxides becomes insufficient, so the lower limit of the O content is set to 0.0001%. Further, when the O content exceeds 0.015%, the oxide becomes too large and the toughness of the steel decreases, so the upper limit of the O content is set to 0.015%.

Ag: 0.0001-0.5%
Ag is the most important metal element in the present invention. If the concentration is less than 0.0001%, there is almost no effect of decreasing the solid solubility with a decrease in the temperature of Mn, so the lower limit was made 0.0001%. Moreover, since the solubility of Ag in solid steel is not large, when it exceeds 0.5%, coarse Ag alone precipitates in the cooling process of the slab, or Ag oxide is removed. 0.5% was made the upper limit in order to form and lower the toughness. For the above reasons, the appropriate range of the Ag content is set to 0.0001 to 0.5%.

  The present invention may further contain the following elements as needed.

Ti: 0.005 to 0.03%
Ti is an effective element that mainly precipitates carbonitrides and contributes to improvement of the base metal strength by its precipitation strengthening action. If the Ti content is less than 0.005%, the effect of improving the strength of the base metal by the precipitation strengthening action of carbonitride is not sufficient. On the other hand, if the Ti content exceeds 0.03%, the steel contains It forms coarse precipitates and inclusions, reducing the toughness of the steel. For the above reasons, the appropriate range of the Ti content is set to 0.005 to 0.03%.

Cu: 0.05-1.5%
Cu is an element that, when contained, has an effect of improving hardenability and strengthening precipitation. However, if the Cu content is less than 0.05%, there is no quenching improvement effect and no precipitation strengthening effect. On the other hand, when the Cu content exceeds 1.5%, the hot workability of steel decreases. For the reasons described above, the range of the Cu content when Cu is contained is set to 0.05 to 1.5%.

Ni: 0.05 to 5.0%
Ni is an element having an effect of improving the toughness of the base material when contained. However, if the Ni content is less than 0.05%, there is no effect of improving the toughness of the base material. On the other hand, when the Ni content is higher than 5.0%, the hardenability becomes excessive, which adversely affects the toughness of the steel. Therefore, the range of the Ni content when Ni is contained is set to 0.05 to 5.0%.

Cr: 0.02 to 1.0%
Cr is an element that, when contained, exhibits an effect of improving hardenability and improving base material strength by precipitation strengthening. However, if the Cr content is less than 0.02%, there is no quenching property improving effect and no precipitation strengthening effect. On the other hand, when the Cr content exceeds 1.0%, the toughness and weldability of steel tend to deteriorate. Therefore, the range of the Cr content when Cr is contained is set to 0.02 to 1.0%.

Mo: 0.02 to 1.0%
Mo is an element that, when contained, exerts an effective action for improving hardenability and strength. However, if the Mo content is less than 0.02%, the effect of improving hardenability and the effect of improving strength are not clear. On the other hand, when the Mo content exceeds 1.0%, the toughness and ductility of the steel and the weldability deteriorate. Therefore, the range of the Mo content when Mo is contained is set to 0.02 to 1.0%.

Nb: 0.005 to 0.05%
Nb is an element having a function of improving the strength of steel by generating carbides and nitrides when contained. However, when the Nb content is less than 0.005%, the effect of improving the strength of steel due to generation of carbides and nitrides is not clear. On the other hand, when the Nb content is higher than 0.05%, coarse carbides and nitrides are formed in the steel, so that the toughness is reduced. For the above reasons, the range of the Nb content when Nb is contained is set to 0.005 to 0.05%.

V: 0.005 to 0.1%
V is an element that has an effect of increasing the strength of steel by generating carbides and nitrides when contained. However, when the V content is less than 0.005%, the effect of improving the strength of steel by the generation of carbides and nitrides is not clear. On the other hand, when the V content is higher than 0.1%, the toughness of the steel is reduced. For the above reasons, the range of the V content when V is contained is set to 0.005 to 0.1%.

B: 0.0004-0.004%
When B is contained, it has the effect of increasing the quenchability, and also producing BN, thereby reducing the content of solid solution N and improving the toughness of HAZ. However, if the B content is less than 0.0004%, the effect of increasing hardenability and the effect of improving the toughness of HAZ are not clear. However, when the B content is higher than 0.004%, coarse borides precipitate in the steel, thereby deteriorating the toughness of the steel. For the reasons described above, the range of the B content when B is contained is set to 0.0004 to 0.004%.

  Next, the continuous casting method of the present invention will be described.

The molten steel having the above-described components is continuously cast into a slab, and the slab is reduced after the thickness direction of the slab solidifies. With respect to the rolling position and the rolling reduction, the primary dendrite arm spacing λ ₀ at the center of the slab in the thickness direction of the slab is used as a reference, based on the dendrite primary arm spacing λ ₀ at the center of the slab in the case of casting without rolling. By performing the reduction so that the value λ / λ ₀ of the ratio of λ ₀ and λ ₀ becomes 0.1 to 0.9, the shape of MnS is sufficiently flattened, and the diffusion of MnS is reduced by a heat treatment in a later step. Can be promoted.

By reducing the slab in the thickness direction center temperature within the range of the solidus temperature to (solidus temperature-400 ° C) at a reduction rate of 5 to 50%, the dendrite primary arm interval λ and the λ The value λ / λ ₀ of the ratio of ₀ can be set to 0.1 to 0.9. By starting the reduction at a temperature at the center of the slab in the thickness direction lower than the solidus temperature, the slab after solidification can be reduced. Further, by starting the reduction at a temperature in the center of the slab in the thickness direction at a temperature higher than (solidus temperature −400 ° C.), the slab thickness center is higher in temperature than the surface layer side. When the rolling is performed, the central portion of the thickness is particularly subjected to plastic deformation due to the rolling, and the interval between the primary arms of the dendrite can be sufficiently reduced. Further, by setting the rolling reduction to 5% or more, the rolling reduction effect is exhibited, and the interval between the primary arms of the dendrite can be sufficiently reduced. Since the effect is saturated even if the rolling reduction is too high, the upper limit of the rolling reduction is set to 50%. The rolling reduction (%) can be calculated as (thickness of slab before rolling-thickness of slab after rolling) / thickness of slab before rolling × 100.

Here, a method of calculating the center temperature in the slab thickness direction in the casting longitudinal direction during continuous casting will be described. Using a slab heat transfer simulation program, perform solidification analysis in advance taking into account the concentration of solute elements by microsegregation, find the relationship between the temperature at the center of the slab thickness and the solid fraction, and measure it even during operation The relationship between the surface temperature of the slab and the solid fraction at the center of the slab thickness can be determined. In this calculation, the position of the solidified portion where the solid phase ratio becomes 1.0 is calculated, and the transition of the slab thickness direction center temperature in the casting longitudinal direction after the solidification is completed by performing heat transfer simulation. Can be. Here, the surface temperature of the slab during casting was actually measured, the solidification analysis was performed by a computer by substituting the actually measured surface temperature of the slab, and the center temperature of each part in the casting longitudinal direction was calculated. Here, the density ρ was defined as ρ = 7.27 + 0.25 × solid fraction (g / cm ³ ). (Iron and Steel, vol. 94 (2008), p. 507: Hideo Mizukami, Akihiro Yamanaka)

In a converter, molten steel having the component contents shown in Table 1 was smelted and continuously cast by a vertical bending type slab continuous casting apparatus. The components in the molten steel, including Ag, were added to the molten steel in the ladle.
In continuous casting, the molten steel temperature target in the tundish was 1550 ° C., the mold size was 1600 mm in width × 250 mm in thickness, and the casting speed was 0.5 to 1.5 m / min. The rolling roll diameter for reducing after the center in the thickness direction of the slab was solidified was 800 mm in diameter. The rolling position by the rolling roll was a rolling start position where the temperature at the center of the thickness of the slab became the temperature shown in Table 2 in relation to the solidus temperature. The slab thickness after rolling was 140 mm, 170 mm, or 235 mm. The rolling reductions are 44%, 32%, and 6%, respectively.

First, the effect of the continuous casting method of the present invention was evaluated based on the dendrite primary arm spacing at the center of the slab thickness. Based on the dendrite primary arm spacing λ ₀ at the center in the thickness direction of the slab of Comparative Example 1 in Table 2 cast without addition of Ag and without reduction, the center of the slab in the thickness direction of each example was used. Table 2 shows the evaluation results using the value λ / λ ₀ of the ratio between the dendrite primary arm spacing λ and the above λ ₀ in Table 2 as an evaluation index. A small equiaxed zone was formed on the side that was the lower side of the thickness at the time of casting from the center of the thickness of the slab, but the surface that was the upper side of the thickness during casting included dendrite solidification including the center of the thickness. As a result, the primary dendrite arm interval could be measured.

  Second, the effect of the continuous casting method of the present invention was evaluated by evaluating the size (short diameter) of the crystalline precipitate MnS at the center of the thickness of the cast slab. A sample for measuring inclusions was collected from the center of the thickness at the center of the slab width. A sample having a size of ± 25 mm from the center of the thickness and 50 mm in the casting direction was sampled, and a 50 mm × 50 mm surface was analyzed. The analytical surface of the sample was polished and finished using emery paper and an abrasive (diamond grains of 6 μm and 1 μm in diameter) in this order.

  The crystal precipitate was analyzed at a magnification of 1000 times using SEM-EDAX. In the present invention, the central portion of the slab thickness is mainly subjected to plastic deformation by the reduction after the solidification is completed, and the MnS crystal precipitates are also flattened with the plastic deformation of the slab. Therefore, the minor axis of the crystal precipitate MnS having a minor axis size of 1 μm or more was measured. The minor axis of the crystalline precipitate MnS of each example was evaluated using the average minor axis of Comparative Example 1 in Table 2 cast without addition of Ag and without reduction as a reference value of 1.0. The ratio is shown in Table 2 below.

  The cast slab was rolled and subjected to a Charpy test in order to evaluate the effect of the refinement of the crystal precipitate at the center of the slab thickness. A sample for measuring toughness was prepared by subjecting a continuous cast slab produced under the above conditions to heat treatment at 1250 ° C. for 90 minutes, followed by controlled rolling / controlled cooling, quenching / tempering, and direct quenching / tempering. A steel plate having a thickness of 50 mm was manufactured by any one of the above manufacturing methods. The shape of the sample was a prism having a length of 10 mm, a width of 10 mm, and a length of 50 mm. The thickness direction of the steel sheet was defined as the longitudinal direction of the sample, the center of the thickness of the steel sheet was defined as the longitudinal center of the sample, and the center was defined as the notch position. A Charpy test was performed after performing a reproduction HAZ heat treatment using this sample.

  The reproduction HAZ heat treatment was performed in an Ar gas atmosphere using a high-frequency induction heating device to heat an area having a width of 10 mm at the center in the longitudinal direction of the sample. The heating was performed from room temperature to 1450 ° C. for 30 seconds, and after maintaining for 60 seconds, the heating unit was rapidly cooled using He gas.

  The Charpy test was evaluated by the energy absorbed at 0 ° C. The toughness index of each example was calculated with the absorbed energy of Comparative Example 1 of Table 2 cast without addition of Ag and without rolling down as a reference value of 1.0, and is shown in Table 2.

Comparative Example 1 is a comparative example without Ag addition and no reduction after solidification, and λ / λ ₀ , crystal precipitate diameter ratio, and toughness index are all 1.0.

In Comparative Example 2, although Ag was added, the reduction after solidification was not performed, and λ / λ ₀ was 1.0. The effect of the addition of Ag was effective in improving the crystal precipitate diameter ratio, but was sufficient. However, the effect of improving the toughness index was not sufficient.

In Comparative Example 3, the reduction after solidification was performed without adding Ag, and although the effect of improving λ / λ ₀ was observed, the effect of improving the crystal precipitate diameter ratio was not sufficient, and the effect of improving the toughness index was also sufficient. Was not.

In each of Inventive Examples 1 to 9, Ag is contained in the molten steel within the scope of the present invention, and the reduction after solidification is performed under the appropriate conditions of the present invention, and an improvement effect of λ / λ ₀ is seen. At the same time, the crystal precipitate refinement effect due to the inclusion of Ag is synergistic, the crystal precipitate diameter ratio can be as good as 0.63 or less, and the toughness index can be as large as 2.3 or more. did it.

Claims (3)

In mass%, C: 0.02 to 1.50%, Si: 0.005 to 0.8%, Mn: 0.05 to 3.0%, P: 0.02% or less, S: 0.001 0.02%, N: 0.002 to 0.008%, O: 0.0001 to 0.015%, Ag: 0.0001 to 0.5%, the balance being Fe and unavoidable impurities Continuous casting of molten steel, and rolling the obtained slab after solidifying the center in the thickness direction of the slab so that λ / λ ₀ is 0.1 to 0.9. Casting method.
Here, λ is the primary dendrite arm spacing at the center in the thickness direction of the cast slab after reduction, and λ ₀ is the primary dendrite arm spacing at the center in the thickness direction of the slab cast without reduction. It is.   In mass%, C: 0.02 to 1.50%, Si: 0.005 to 0.8%, Mn: 0.05 to 3.0%, P: 0.02% or less, S: 0.001 0.02%, N: 0.002 to 0.008%, O: 0.0001 to 0.015%, Ag: 0.0001 to 0.5%, the balance being Fe and unavoidable impurities Continuous casting wherein molten steel is continuously cast, and the reduction is performed at a reduction rate of 5 to 50% when the temperature in the center of the slab in the thickness direction is in the range of solidus temperature to (solidus temperature-400 ° C). Casting method.   The molten steel component is 0.005 to 0.03% of Ti, 0.05 to 1.5% of Cu, 0.05 to 5.0% of Ni, Cr of 0.05 to 5.0% by mass instead of a part of Fe. : 0.02 to 1.0%, Mo: 0.02 to 1.0%, Nb: 0.005 to 0.05%, V: 0.005 to 0.1%, and B: 0.0004 to 0 The continuous casting method according to claim 1 or 2, wherein the method comprises one or more of 0.004%.