JP3000873B2 - Continuous casting method of steel with excellent toughness in weld heat affected zone - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for continuously casting steel requiring toughness in a heat affected zone such as a line pipe.

[0002]

2. Description of the Related Art In recent years, large heat input of welding has been performed for the purpose of streamlining the welding process. Generally, when welding steel materials, crystal grains of a base material side heat affected zone (hereinafter, referred to as "HAZ zone") are formed. Is known to be coarse and the toughness is reduced. On the other hand, if fine particles such as appropriate oxides and nitrides are dispersed, the structure becomes finer, which is effective in improving the toughness of the HAZ.

Therefore, in a series of patents including Japanese Patent Publication No. 5-17300, the amount of Al in steel is reduced, and fine Ti-based oxides are precipitated and dispersed by adding Ti to change the structure of the HAZ portion. A method for improving toughness by miniaturization has been proposed. In order to further refine the precipitated particles,
No. 7467 proposes a method of controlling the cooling rate during solidification, and Japanese Patent Application Laid-Open No. 4-6243 proposes a method of defining the time from the addition of Ti to the tapping. Also, JP-A-4-27
No. 13 and JP-A-3-177535 further disclose Zr, Y
It is described that the addition of the above is effective for achieving fine and dispersed precipitate particles.

Further, the present applicant has filed a Japanese Patent Application No. 6-77057.
In the description and drawings of the above-mentioned item, when an Al-Mn oxide phase having an atomic ratio of (Al + Mn) of 40% or more and an Al: Mn ratio of 1: 1 to 5: 1 as a constituent element, the HAZ portion Discloses that it is effective in improving the toughness of steel.

[0005] These methods are all excellent methods for refining the microstructure of the HAZ portion and improving the toughness. In particular, when a plate material called a slab is manufactured by a continuous casting method, the casting method is required. In the vicinity of the short side of the slab, the cooling rate is reduced due to the discharge flow from the immersion nozzle, and there is a problem that sufficient fine dispersion cannot be performed near the short side of the slab.

[0006] On the other hand, Japanese Patent Publication No. 5-25580 discloses that oxides dispersed in the vicinity of the short side are made fine by controlling the amount of secondary cooling water on the short side during continuous casting, and the edges of the steel sheet are abutted. Thus, a method for producing a large-diameter steel pipe is described. However, in general, during continuous casting, since the solidification is solidified to a thickness of about 20 mm in the mold, even if the amount of secondary cooling water is controlled thereafter, the effect of sufficiently reducing the oxide cannot be obtained, and the pipe production is not performed. Sometimes the weld gap is 2
There is a problem that there is no effect unless the distance is set to 0 mm or more. Furthermore, when the cooling of only a part of the slab is strengthened in the secondary cooling of the continuous casting, there is a concern that thermal stress is generated and causes a slab surface crack.

On the other hand, in order to control the molten steel discharge flow at the time of continuous casting of steel, a method of devising the shape of the immersion nozzle, a method of installing a magnetic field generator in the continuous casting mold and braking or stirring the molten steel discharge flow. Various methods have been proposed, such as a method of adding, and a method of combining both. For example, Japanese Patent Publication No. 5-55220 specifies the conditions of a magnetic field acting on a molten steel discharge flow, and stabilizes the molten metal surface in a mold and floats bubbles and inclusions. In addition, Japanese Patent Publication 5-275
No. 10 proposes a method in which the shape of the immersion nozzle is devised and braking is further performed by a magnetic field. However,
Each of these flow control methods mainly takes into account the stability of the molten metal surface in the mold and the floating of bubbles and inclusions, but does not take into account the influence on the precipitates.

[0008] As described above, various inventions relating to continuous casting of steel in which fine particles are dispersed have been proposed, but these methods were insufficient to reduce the particles near the short side of the slab. .

[0009]

As described above,
It is well known that fine dispersion of appropriate precipitates in steel is effective in improving the toughness of the HAZ. Also, HA
It is also known that the cooling rate has a large effect on the dispersion of particles that are effective in improving the toughness of the Z portion. However, in the vicinity of the short side during continuous casting, the heat supplied by the discharge flow delays the cooling and solidification of the molten steel and lowers the cooling rate, so that the grain size of the precipitate increases. Therefore, it is difficult to obtain good toughness after welding in the vicinity of the short side of the steel material.

That is, particularly when a plate material called a slab is manufactured by a continuous casting method, the cooling rate in the vicinity of the short side of the slab is reduced due to the molten steel discharge flow from the immersion nozzle, and a sufficient cooling rate is obtained. There is a problem that fine dispersion cannot be performed.

The present invention has been made in view of the above-mentioned conventional problems, and provides a continuous casting method for a steel material capable of obtaining good HAZ toughness even in the vicinity of a short side of a slab. It is intended to be.

[0012]

Means for Solving the Problems In order to achieve the above-mentioned object, the first method of the present invention for continuously casting a steel material having excellent toughness in a weld heat-affected zone is as follows. .25% Si: 0.6% or less Mn: 0.3 to 3.0% P: 0.03% or less S: 0.01% or less O: 0.0010 to 0.0070%
Cr, Mo, and Cu are each 1.5% or less, Ni is 3.0% or less, and Nb and V are each 0.5% or less.
And B contains 0.00005 to 0.002%,
The remainder consists of Fe and unavoidable impurities, and contains dispersed particles containing Ti having a diameter of 0.2 to 20 μm.
In producing a steel material having 4 to 1000 pieces per mm ^2, preliminary deoxidation is performed by adding Si and Mn in advance, and after controlling the dissolved oxygen concentration to 20 to 100 ppm and Al to 0.01% or less, Ti is added. Added in the range of 0.005 to 0.05%,
The continuous casting is performed while applying braking to the molten steel discharge flow supplied from the immersion nozzle to the continuous casting mold.

Further, the second continuous casting method for steel having excellent toughness in the heat-affected zone of the present invention is as follows: C: 0.01 to 0.25% Si: 0.6% or less Mn: 0 0.3 to 3.0% P: 0.03% or less S: 0.01% or less O: 0.0010 to 0.0070%
Cr, Mo, and Cu are each 1.5% or less, Ni is 3.0% or less, and Nb and V are each 0.5% or less.
And B contains 0.00005 to 0.002%,
The balance consists of Fe and unavoidable impurities, and contains Ti-containing particles having a diameter of 0.2 to 20 μm.
In addition to the presence of 4 to 1000 particles per mm ^2, the oxide phase constituting the dispersed particles has a metal element atomic ratio of (Al + Mn) of 40% or more and an Al: Mn ratio of 1: 1 to 5:
In producing a steel material containing an Al-Mn oxide phase having a feature of 1 as a component, preliminary deoxidation is performed by adding Si and Mn in advance, and a dissolved oxygen concentration of 20 to 100 ppm,
After controlling Al to 0.0001 to 0.0050%, Ti is added in the range of 0.005 to 0.030%, and braking is added to the molten steel discharge flow supplied from the immersion nozzle to the continuous casting mold. It is decided to perform continuous casting.

[0014]

The reason for completing the continuous casting method for steel material of the present invention will be described below. In recent years, large heat input during welding has been promoted in the field of thick plate materials and the like. At this time, it is important to ensure sufficient strength and toughness of the welded portion and the HAZ at the time of welding. On the other hand, a process of rolling a cast slab into a plate and then welding a short side thereof is often performed at the time of manufacturing a large-diameter steel pipe or a structural material. Assuming such a process, it is important to ensure performance near the short side. In such a process,
When the short side is welded, the HAZ portion corresponds to at most 20 from the short side of the original slab, even when considering the groove at the time of welding.
mm. In other words, 2 mm from the short side of the original slab
It is important how to secure the performance of the portion within about 0 mm.

Generally, steel materials for such uses are manufactured by continuous casting. In the continuous casting process, the thickness of a slab is solidified to about 20 mm in a water-cooled copper mold. Therefore, in order to improve the performance of the welded portion in the vicinity of the short side, it is necessary to take a measure or the like to obtain good performance in the portion solidified in the mold.

In order to improve the toughness of the HAZ portion, it is effective to finely disperse an appropriate oxide or nitride, and the composition and morphology of the finely dispersed particles are important as described above. . FIG. 1 schematically shows the flow of molten steel inside a slab in continuous casting, but usually, in continuous casting of plate slab,
The molten steel flow (hereinafter referred to as “discharge jet”) 2 ′ discharged from the discharge port 1 a of the immersion nozzle 1 having two discharge ports 1 a on the left and right sides of the lower end is a solidified shell 2 a on the short side of the slab.
It is well known to collide with. Since the temperature of the discharge jet 2 ′ is higher than the temperature of the molten steel 2 in the mold 3, the cooling rate decreases near the short side due to the heat supplied by the discharge jet 2 ′. The formation and growth of precipitates are correlated with the cooling rate,
Under the condition where the cooling rate is low, the precipitates are enlarged and the toughness of the HAZ is deteriorated. Therefore, even when a steel material in which precipitates are finely dispersed in steel is manufactured by continuous casting for the purpose of improving the toughness of the HAZ portion, etc., the cooling rate becomes slow in the vicinity of the short side. And it is difficult to obtain good performance. Incidentally, reference numeral 4 in FIG. 1 denotes a mold powder.

In order to promote cooling near the short side in the mold, the shape of the immersion nozzle and the shape of the discharge port are reduced in order to reduce the amount of heat supplied by reducing the discharge jet colliding near the short side. However, in general, these changes are not suitable because they have adverse effects such as fluctuation of the molten metal level in the mold, harmful bubbles in the steel, and difficulty in floating and separating inclusions.

On the other hand, suppressing the flow velocity of the discharge jet can be realized by installing a magnetic field generator in the continuous casting mold and applying a braking force without any adverse effect. The jet jet to the short side can also be suppressed by a method of adding agitation to the molten steel by a magnetic field generator, but it is better to apply braking from the viewpoint of reducing the flow rate of the molten steel and reducing the amount of heat supplied to the short side. More effective.

That is, when a steel type is manufactured by continuous casting to improve the welding performance by dispersing fine particles such as oxides in the steel, the discharge jet supplied into the mold is braked. Is extremely effective in improving the welding performance near the short side. It should be noted that, as described above, the braking of the discharge jet supplied into the mold has been conventionally performed. However, an example in which the dispersion is applied to reduce the dispersed particles in the vicinity of the short side in the slab is used. There is no.

On the other hand, in a steel type in which the performance is improved by dispersing the particles, the performance can be improved by controlling the form of the dispersed particles. For example, Al-killed steel, which is commonly used, forms oxides of Al in the steel, but Al-oxides are very agglomerated in the steel and cannot be finely dispersed. It is impossible to improve the toughness by finely dispersing it in.

On the other hand, the fact that Ti oxide is suitable as finely dispersed particles is disclosed in, for example, Japanese Patent Application Laid-Open No. 61-238940.
As described in the issue. That is, during continuous casting of a steel material in which Ti oxides are finely dispersed in steel, if braking is applied to the discharge jet supplied into the mold, a steel material having excellent welding performance can be obtained. Based on this finding, the inventor has completed the invention of claim 1.

That is, in order to finely disperse the Ti oxide in the steel and secure the toughness in the HAZ, it is important to define the composition of the steel material. Therefore, in the first aspect of the present invention, Al has a higher affinity for O than Ti, so that Al is reduced to 0.01% or less. For O, Ti
Is an element necessary for forming oxides of the steel. On the other hand, if present in excess, the cleanliness of the molten steel is reduced and coarse inclusions are formed, which adversely affects the performance of the steel material.
It was specified as 0 to 0.0070%. Since Ti is an element necessary for forming an oxide of Ti, 0.00
The lower limit is 5%, and if present in excess, TiC is formed to harden the steel material and lower the toughness.
And The reason for limiting other components will be described later.

Further, the present inventors have energetically studied the fine particle morphology for improving the toughness in the HAZ. And, in the process, when Al-Mn oxide is dispersed in the steel, (Al + Mn) is 40% or more in atomic ratio and A
It was found that when the l: Mn ratio had a characteristic of 1: 1 to 5: 1, the toughness in the HAZ portion was extremely high, and was disclosed in the specification and drawings of Japanese Patent Application No. 6-77057. . In order to generate this Al-Mn oxide, it is important to control a small amount of Al in the steel. O, Al is used so that Mn in the oxide is not replaced by Al or Ti having a stronger affinity for oxygen. ,
It is necessary to control the balance of the Ti content so that the oxygen content is higher than the Al content and the Ti content. The present inventors completed the invention of claim 2 based on this finding, and set the Al content to 0.0001 to 0.0050% and the Ti content to 0.00
It was specified as 5 to 0.030%.

Furthermore, the present inventors have to control the morphology of the oxides in the molten steel during the smelting process in order to finely disperse these Ti oxides and Al-Mn oxides in the steel. I knew it was important. If Ti oxide or Al-Mn oxide is generated during smelting, the particles are enlarged and good performance cannot be obtained. Further, the Al-Mn oxide is unstable and changes its form to Al ₂ O ₃ or the like.
That is, it is important that these oxides are formed as secondary deoxidation products that crystallize during the cooling and solidification processes. Therefore, in the first and second aspects of the present invention, preliminary deoxidation is performed by adding Si and Mn in advance, and the dissolved oxygen concentration is adjusted to 20 to 100.
ppm, and the amount of Al is as defined in claim 1 for the reasons described above.
In this case, the content is 0.01% or less.
After controlling to ~ 0.0050%, Ti is added.

According to experiments by the present inventors, the diameter of particles contributing to the improvement of performance is about 0.2 to 20 μm, and the number of particles is 4 to 10 per 1 mm ² of steel material cross section.
Since good results are obtained when there are 00 pieces,
The first and second aspects of the present invention limit this range.

Next, the reasons for limiting the content of other elements in the first and second aspects of the present invention will be described. C is
Since it is an element necessary for securing the strength of the base material and the HAZ portion, and about 0.01% is required to obtain these effects when Nb or V is added, the lower limit is set. However, an excessive amount adversely affects toughness, so the upper limit was made 0.25%.

Si is an element contained in steel at the time of preliminary deoxidation, but if added excessively, it promotes the formation of acicular martensite in the HAZ, so the upper limit was made 0.6%. Mn is an element necessary for ensuring the strength of the base material and the HAZ portion, and is preferably contained in an oxide.
The lower limit was 3%. However, if added in excess, the toughness in the HAZ portion is reduced, so the upper limit was 3.0%.

P is an impurity inevitably contained in steel and is an element that segregates at the grain boundary and causes cracking. Therefore, the upper limit is set to 0.03%. S is also an impurity unavoidably contained in steel, and if present in excess, causes welding cracks, so the upper limit was made 0.01%. Regarding O, the steel material produced by the method of the present invention naturally has a lower limit in order to secure toughness by finely dispersing oxides, and it is necessary to contain O by 0.0010% or more.
However, if the content exceeds 0.0070%, the amount of oxides becomes excessive and the cleanliness of the steel decreases, and the performance deteriorates.

Cr, Mo, Cu, Ni, Nb and V are elements which can obtain good strength and toughness by adding one or more of these, but when any of them is added in excess, Deteriorates the toughness of the HAZ, so Cr, Mo, Cu
Are 1.5% or less, Ni is 3.0% or less, and Nb and V are 0.5% or less, respectively. Since these elements do not affect the dispersion of the fine particles, they are appropriately added in accordance with the requirements on the material properties.

B is usually an effective element for improving the strength of the base material, but has an adverse effect on the toughness of the HAZ.
However, in the case of the steel in which the oxide is dispersed as in the present invention, the addition of a small amount can improve the toughness of the HAZ. For this purpose, an appropriate addition amount is 0.00005 to 0.5.
Although it is 0004%, if the purpose is to secure the strength of the base material in addition, 0.0004 to 0.002% is appropriate.

Although the method of the present invention focuses on improving the performance in the vicinity of the short side, the other portions do not originally suffer from a phenomenon that delays the cooling rate such as collision of the discharge jet. . Therefore, good performance can be originally secured in portions other than the vicinity of the short side, and there is no problem in performing welding. Also, the method of the present invention has no effect on the performance of other parts.

It is not preferable to change the shape of the immersion nozzle in order to control the discharge jet, as described above, because it has adverse effects. However, a greater effect can be obtained if the shape of the immersion nozzle is changed within a range that does not involve such adverse effects and used together with the method of the present invention.

In order to improve the cooling rate near the short side, a method of promoting heat removal to the mold side may be considered. Therefore, a greater effect can be obtained by using a method such as making the shape of the mold non-linear so as to cope with the solidification shrinkage of the slab in order to promote heat removal to the mold side in combination with the method of the present invention.

Various proposals have also been made regarding the size, shape, and other conditions of the magnetic field generator to be installed. Obviously the conditions are suitable. However, when the magnetic field strength is extremely improved, the flow of molten steel in the mold is excessively suppressed, and the temperature of the meniscus portion is lowered, which is not preferable.

As is apparent from the above description, in the method of the present invention, it is important to reduce the supply of heat to the short side, and the condition is such that the discharge velocity colliding with the short side is large and the casting speed is high. Shows greater effect. Specifically, the slab production amount, that is, the amount of molten steel supplied from the immersion nozzle is 3To
The method of the present invention shows a sufficient effect under conditions exceeding n / min, and is more preferable under conditions exceeding 5 Ton / min.
For the same reason, it goes without saying that the lower the degree of superheat ΔT of molten steel during continuous casting, the smaller the amount of heat supplied to the short side, the finer the particles, and the better the performance.

[0036]

EXAMPLES The effects of the continuous casting method for steel materials of the present invention will be described below based on examples and comparative examples. After smelting molten steel of a predetermined component by a converter process, continuous casting was performed. The obtained slab was rolled into a thick plate having a thickness of 35 mm, and the short sides were butt-welded and subjected to a performance test.

For continuous casting, a curved continuous casting machine with a machine length of 23 m and three-point correction was used. The slab is 300mm x 1800
mm. The degree of superheat of molten steel in the tundish was set to a substantially constant condition of 25 to 30 ° C. in order to minimize influences other than operating factors. Immersion nozzle is 2
A hole having an outlet angle of 20 ° downward was used, and a static magnetic field was applied so as to suppress the discharge jet. The magnetic field strength was changed in two steps of 0.2T and 0.4T in the central magnetic field strength. Since the strength of the discharge jet colliding with the short side is considered to change depending on the discharge flow rate, the discharge flow rate was variously changed by changing the continuous casting speed and the slab size.

The obtained cast slab was evaluated by examining fine particles dispersed in the vicinity of the short side in the rolled steel material. The shape, number, and size of the dispersed particles were examined with an optical microscope and a scanning electron microscope. The object of the investigation was 0.2 to 20 μm which affects the performance.

Further, in some examples, welding was actually performed, and the performance of the welded portion was examined. 100kJ / cm for welding
Was carried out under the conditions corresponding to the heat input. The obtained weld was processed to prepare a 2 mm V notch Charpy impact test piece. The performance was evaluated based on the absorbed energy when the test was performed at −50 ° C. and the ductile / brittle fracture transition temperature when the test was performed at various temperatures.

[Preliminary Test] Table 1 shows that the other conditions during continuous casting were made substantially equal, and the fine dispersion in steel was changed by changing the composition of the steel material when the conditions were changed only with or without braking on the discharge jet. Approximately 15m from the short side when variously changing the morphology of particles
It shows the result of investigating the number and size of finely dispersed particles dispersed at the position of m. As is clear from Table 1,
Comparing under the condition of particles of the same morphology [No1a and No1b, No2a
And No2b, No3a and No3b ] , regardless of the form, the size of the dispersed particles is reduced by braking the molten steel,
The number of variances is also increasing.

[0041]

[Table 1]

[Test 1] Table 2 shows Examples [No5a to No8a] and Comparative Examples [No5b to No9b] corresponding to Claim 1 of the present invention. The evaluation was performed based on the results of experiments on the average particle size and number of oxides dispersed in the steel and the performance of the actual joint. In the example, Cr, Mo, Cu, Ni, Nb, V, and B were appropriately added to the steel material in order to secure strength and toughness. However, the effect of the present invention was examined between steel materials having almost the same composition.

[0043]

[Table 2] Note) Among the smelting conditions, ○ indicates that the smelting was performed under the specified conditions, c indicates that the Al content was 0.012%, which was out of the specified conditions, and d indicates the Ti content. Dissolved at 0.015%
This indicates that oxygen was melted out of the specified conditions.

No5a and No6a having the same particle morphology and production conditions
When comparing No5b with No5b, No5
In the case of a and No6a, the particles are clearly smaller and the number is larger than that of No5b without braking. It can also be seen that the fineness is further increased by increasing the magnetic field strength of the braking. In addition, the investigation results of the absorbed energy and the transition temperature have a good correlation with the size and the number of particles, and higher performance can be obtained when fine particles are dispersed. Furthermore, as a result of calculating the cooling rate from the dendrite secondary arm interval, it was confirmed that the cooling rate was promoted by 20% or more by applying the magnetic field braking, and it was revealed that the mechanism described in the present invention was correct. .

No. 7a and No. 6b show the results under the condition that the discharge flow rate was reduced to 4.3 ton / min. Further, including these results, the relationship between the discharge flow rate of the molten steel and the average particle diameter under various braking conditions under the condition where the oxide of Ti is dispersed in the steel material is shown in FIG. It is considered that as the discharge flow rate is reduced, the collision of the discharge jet with the short side is weakened, so that the heat supply to the short side is small and the delay of the cooling rate is also small. This figure 2
From the results shown in the above, the method of braking the discharge flow rate of molten steel of the present invention shows a great effect when the discharge flow rate is as high as 3 ton / min or more, and is more preferably applied under the condition of 5 ton / min or more. You can see that.

Nos. 8a and 7b show the results when the oxides dispersed in the steel material were changed to Al-Ti-O by adjusting the components. Even if the form of the oxide is changed, when the discharge jet is braked, the particles are obviously finer and the number increases, and higher performance is obtained in terms of the absorbed energy and the transition temperature.

No. 8b shows the result in the case where Al was increased to obtain Al killed steel. In this case, the particles in the steel were mainly cluster-like alumina, and the particle diameter was large, and good performance was not obtained. In the case of No9b, the dissolved oxygen was 1
When about 50 ppm of Ti was present, Ti was excessively added at an early stage to precipitate an oxide of Ti as a primary deoxidation product. At this time, the precipitate particle size was enlarged, and good performance could not be obtained.

[Test 2] Table 3 shows examples [No9a, No10a] and comparative examples [No10b to No12b] corresponding to claim 2 of the present invention.
]. A test was conducted under the conditions where the composition of the dispersed particles was changed so as to obtain better toughness. In the dispersed particles
In order to reduce the Ti and control the morphology so that Al and Mn coexist, the components were adjusted so that the Ti in the molten steel was less than 0.01%. As a result, a significant performance improvement is obtained A
Particles mainly composed of l and Mn could be dispersed in steel. The morphology of the particles is Al and Mn in the metal components contained in the particles.
Is expressed as an atomic fraction.

[0049]

[Table 3] Note) The unit of dispersed particle form is at%.

In each of No. 9a and No. 10a in Table 3, the number and size of the dispersed particles are almost the same as those of Al-Ti-O shown in Table 2, but the performance is remarkably improved. Also, when the ejection jet is braked, the precipitates are clearly finer, the number is increased, and the performance is improved. Even when braking is applied, the form of precipitates (Al + Mn) is 40%
In the case of No11b that does not satisfy the above conditions or No12b where the Al: Mn ratio does not satisfy the condition of 1: 1 to 5: 1, no good performance is obtained.

[0051]

As described above, in the method for continuously casting steel according to the present invention, in producing a steel specified to have a predetermined component content and the like, preliminary deoxidation is performed by adding Si and Mn in advance. After controlling the concentration of dissolved oxygen and the amount of Al within a predetermined range,
Since Ti is added in a predetermined range and continuous casting is performed while applying braking to the discharge flow from the immersion nozzle, cooling and solidification of molten steel is slowed by heat supplied by the discharge flow rate near the short side during continuous casting. Since the cooling rate does not decrease without decreasing, the grain size of the precipitates can be reduced, and good toughness after welding can be obtained in the vicinity of the short side of the steel material.

[Brief description of the drawings]

FIG. 1 is a diagram schematically showing the flow of molten steel in a mold during normal continuous casting.

FIG. 2 is a diagram showing the relationship between molten steel discharge flow rate and average particle diameter under various braking conditions under the condition that particles dispersed in a steel material are Ti—O.

[Explanation of symbols]

 1 immersion nozzle 2 molten steel 3 mold

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-4-279248 (JP, A) JP-A-47-31827 (JP, A) JP-A-2-220735 (JP, A) 27510 (JP, B2) JP 5-55220 (JP, B2) (58) Fields investigated (Int. Cl. ⁷ , DB name) B22D 11/00 B22D 11/10 350 B22D 11/10 370 C21C 7 / 06 C22C 38/00 301

Claims (2)

(57) [Claims] 1. In weight%, C: 0.01 to 0.25% Si: 0.6% or less Mn: 0.3 to 3.0% P: 0.03% or less S: 0.01% or less O: contains 0.0010 to 0.0070%, and
Cr, Mo, and Cu are each 1.5% or less, Ni is 3.0% or less, and Nb and V are each 0.5% or less.
And B contains 0.00005 to 0.002%,
The remainder consists of Fe and unavoidable impurities, and contains dispersed particles containing Ti having a diameter of 0.2 to 20 μm.
In producing steel having 4 to 1000 pieces per mm ^2, preliminary deoxidation is performed by adding Si and Mn in advance, and after controlling the dissolved oxygen concentration to 20 to 100 ppm and Al to 0.01% or less,
Is added in the range of 0.005 to 0.05%, and the molten steel discharge flow supplied from the immersion nozzle to the continuous casting mold is subjected to continuous casting while applying braking to the weld heat affected zone toughness. Excellent steel continuous casting method. 2. In% by weight, C: 0.01 to 0.25% Si: 0.6% or less Mn: 0.3 to 3.0% P: 0.03% or less S: 0.01% or less O: contains 0.0010 to 0.0070%, and
Cr, Mo, and Cu are each 1.5% or less, Ni is 3.0% or less, and Nb and V are each 0.5% or less.
And B contains 0.00005 to 0.002%,
The remainder consists of Fe and unavoidable impurities, and contains dispersed particles containing Ti having a diameter of 0.2 to 20 μm.
In addition to the presence of 4 to 1000 particles per mm ^2, the oxide phase constituting the dispersed particles has a metal element atomic ratio of (Al + Mn) of 40% or more and an Al: Mn ratio of 1: 1 to 5:
In producing a steel material containing an Al-Mn oxide phase as a constituent element having a characteristic of 1, pre-deoxidation is performed by adding Si and Mn in advance, the dissolved oxygen concentration is 20 to 100 ppm, and Al is 0.0001. ~ 0.0050%
After adding Ti, it is added in the range of 0.005 to 0.030%, and the continuous casting is performed while adding a braking force to the molten steel discharge flow supplied from the immersion nozzle to the continuous casting mold. A continuous casting method for steel with excellent toughness in the weld heat affected zone.