JP3004155B2 - Manufacturing method of shaped steel with excellent toughness - 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 producing a shaped steel used as a structural member of a building.

[0002]

2. Description of the Related Art H-section steels used for columns and beams are required to have higher strength, higher toughness and lower yield point due to the increase in height of buildings and stricter safety standards. I have. In order to satisfy such required characteristics, conventionally, a heat treatment such as a normalizing process has been performed after the completion of rolling and cooling. The addition of heat treatment causes a significant increase in cost due to a decrease in heat treatment cost and production efficiency, and has a problem in economics. In particular, when a section steel having a flange, for example, an H-section steel is manufactured by continuous hot rolling using a continuous cast slab as a raw material, the toughness of the fillet portion is significantly deteriorated. The reason for this is that in the universal rolling using a continuous cast slab, the central segregation portion of the material is accumulated during rolling, and the impurity elements such as P and S are concentrated at the ferrite grain boundary from the portion where macro segregation does not appear. Because it becomes brittle. As a result, for example, a portion that does not meet the standard such as a rolled steel material for a welding structure (JIS G3106) is generated. In particular, bainite and island-like martensite are generated in the fillet portion, and the toughness is further reduced as compared with general steel. As a result, for example, a portion that does not satisfy the standards such as the JIS standard is generated.

[0003] Regarding measures against the accumulation of segregation,
For example, JP-A-2-46960, JP-A-2-15
As shown in Japanese Patent No. 857 and the like, there is a method of suppressing the generation of macrosegregation at the center during continuous casting in the material manufacturing stage, but since a special rolling reduction device is required for continuous casting equipment, There was a problem in economics such as an increase in manufacturing cost. To solve this problem, it was necessary to develop a new manufacturing method so that high-performance material properties could be obtained as-rolled.

Since high strength and high toughness are well known in the art by the fine graining method using TMCP, it is not possible to perform a large rolling reduction in the shape steel rolling due to restrictions on molding, and thus the grains were not sufficiently fine. Further, in the field of thick steel sheets, techniques for producing high-strength and high-toughness steels utilizing the effect of precipitation of VN, for example, Japanese Patent Publication No. Sho 62-50548 and Japanese Patent Publication No. Sho 62-54862 have been proposed. However, the deoxidation of molten steel in this conventional method focused on lowering the dissolved oxygen and reducing the number of primary deoxidized oxides in the steel. A fine composite oxide showing the effect is not generated,
The grain refinement of the tissue was not enough.

[0005]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention provides a novel manufacturing method which comprehensively covers the processes from steelmaking, rolling and cooling to reducing the fine grain structure as it is rolled. It is intended to provide a rolled section steel excellent in strength and toughness at low cost.

[0006]

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and the feature of the present invention is to perform appropriate deoxidation treatment in the steel making process, to clean the molten steel, and to solve the dissolved oxygen concentration. Controlling the amount of Ti by adjusting the order of addition of Ti among the alloying elements, etc., and dispersing a large number of fine composite oxides in the steel to generate intragranular ferrite and refine the microstructure In the cooling step after the final finish rolling. Further, if necessary, the temperature of the surface layer of the steel material may be adjusted between the passes of the intermediate rolling process by A
_Water cooling to _r3 -20 ° C or lower, _Ar3 -100 ° C or higher, and rolling at least once in the recuperation process to refine the microstructure.

That is, the present invention is to provide a method of manufacturing a high-quality steel material which is economical, efficiently and excellent in toughness without requiring special equipment. The gist of the present invention is as follows: (1) C: 0.04 to 0.20% by weight;
05-0.50%, Mn: 0.4-2.0%, N: 0.
003 to 0.015%, Al: ≤ 0.005%,
The balance of molten steel consisting of Fe and unavoidable impurities is reduced to 0.003 to 0.01% by weight of dissolved oxygen by preliminary deoxidation.
After adjusting to 5%, the titanium was further deoxidized, and the titanium content was 0.005 to 0.025% by weight, and -0.006 ≦ [Ti% based on the dissolved oxygen [O%] of the molten steel. ] -2
[O%] <= 0.008, cast into a slab by continuous casting, re-heated the slab to a temperature range of 1100 to 1300 ° C, started rolling, and rolled in a temperature range of 750 to 1050 ° C. After the end of the rolling, the cooling rate from 650 to 400 ° C. is cooled in the range of 0.01 ° C./s to 0.30 ° C./s to produce a section steel excellent in toughness characterized by being manufactured. Production method. (2) C: 0.04 to 0.20% by weight, Si: 0.
05-0.50%, Mn: 0.4-2.0%, N: 0.
003 to 0.015%, Al: ≤ 0.005%,
The balance of molten steel consisting of Fe and unavoidable impurities is reduced to 0.003 to 0.01% by weight of dissolved oxygen by preliminary deoxidation.
After adjusting to 5%, the titanium was further deoxidized, and the titanium content was 0.005 to 0.025% by weight, and -0.006 ≦ [Ti% based on the dissolved oxygen [O%] of the molten steel. ] -2
[O%] <= 0.008 Casting is performed by continuous casting on a slab that satisfies the relationship, the slab is reheated to a temperature range of 1100 to 1300 ° C, and rolling is started. The temperature of the section is water-cooled to _Ar3 -20 ° C or lower and _Ar3 -100 ° C or higher, and is rolled at least once in the recuperation process.
Rolling is completed in the temperature range of 0 to 1050 ° C, and after the rolling is completed, the cooling rate to 650 to 400 ° C is set to 0.01 ° C / s.
A method for producing a section steel excellent in toughness, characterized in that the section steel is produced by cooling within a range of 0.30C / s. (3) C: 0.04 to 0.20% by weight, Si: 0.
05-0.50%, Mn: 0.4-2.0%, N: 0.
003 to 0.015%, Al: ≤ 0.005%,
In addition, V ≦ 0.20%, Cr ≦ 0.7%, Nb ≦ 0.0
5%, Ni ≦ 1.0%, Cu ≦ 1.0%, Mo ≦ 0.3
%, And the balance of molten steel consisting of Fe and unavoidable impurities is adjusted to 0.003 to 0.015% by weight of dissolved oxygen by pre-deoxidation treatment. And the titanium content is 0.005% by weight.
0.025% to 0.0025 ≦ [Ti%] − 2 [O%] ≦ 0.00 with respect to the dissolved oxygen [O%] of the molten steel.
8 is cast by continuous casting, and
Rolling is started after reheating to a temperature range of 100 to 1300 ° C, and rolling is ended at a temperature range of 750 to 1050 ° C,
After the end of rolling, the cooling rate to
A method for producing a section steel having excellent toughness, characterized in that it is produced by cooling within a range of 1 ° C / s to 0.30 ° C / s. (4) C: 0.04 to 0.20% by weight, Si: 0.
05-0.50%, Mn: 0.4-2.0%, N: 0.
003 to 0.015%, Al: ≤ 0.005%,
In addition, V ≦ 0.20%, Cr ≦ 0.7%, Nb ≦ 0.0
5%, Ni ≦ 1.0%, Cu ≦ 1.0%, Mo ≦ 0.3
%, And the balance of molten steel containing Fe and inevitable impurities is adjusted to 0.003 to 0.015% by weight of dissolved oxygen by preliminary deoxidation treatment. And the titanium content is 0.005% by weight.
0.025% to 0.0025 ≦ [Ti%] − 2 [O%] ≦ 0.00 with respect to the dissolved oxygen [O%] of the molten steel.
8 is cast by continuous casting, and
Start the rolled after reheating to a temperature range of from 100 to 1,300 ° C., the temperature of the steel surface layer portion between the passes of the intermediate rolling step A _r3 -
20 ° C. or less, and water-cooled to A _r3 -100 ° C. or more, then rolling at least once in its recuperation process, to complete the rolling in a temperature range of from 750 to 1,050 ° C., after completion of rolling 650-40
The cooling rate to 0 ° C is 0.01 ° C / s to 0.30 ° C / s
A method for producing a section steel having excellent toughness, characterized in that the section is produced by cooling within the range described above.

[0008]

The toughness of the steel depends on the alloy components and the crystal grain size. That is, the toughness is improved as the amount of the component that dissolves in the structure is smaller or the ferrite grains in the structure are finer. When a steel section having a flange, for example, an H-section steel is manufactured by universal hot rolling using a continuously cast slab as a raw material, central segregation of the raw material is accumulated in a fillet portion, and the segregated component is significantly concentrated. At the same time, since the fillet portion has a higher rolling temperature than other portions, even when hot rolling is performed, ferrite grains are coarsened more than, for example, a flange portion or a web portion.

[0009] It is known to use the following strengthening mechanism when manufacturing a high-strength section steel. Refinement of ferrite crystal grain size Solid solution strengthening by alloying elements Precipitation strengthening by fine precipitates Among them, solid solution strengthening by alloying elements is the most common, for example, Mn, a typical solid solution strengthening element
Addition significantly increases the hardenability of the steel material and changes the ferrite + pearlite structure to a bainite structure. When a component steel that easily forms a bainite structure is applied to a rolled H-section steel, Mn is segregated, particularly in a fillet portion processed so that the center segregation portion of a continuous cast slab as a material is integrated in a rolling process. It is concentrated as a component, and the bainite and island martensite structure fractions are significantly increased. As a result, the toughness is particularly reduced, cracks are generated in some cases, and UT defects and the like appear.

[0010] The feature of the present invention is that C and N dissolved in a supersaturated solid solution in the structure are gradually cooled in a temperature range of 650 to 400 ° C after rolling to precipitate as stable carbides, thereby forming bainite or island-like martensite. The purpose is to prevent the formation and suppress the decrease in toughness. Next, the reasons for limiting the range of the basic components targeted by the present invention will be described.

First, C is added as an effective component for improving the strength of steel. If it is less than 0.04%, the strength required for structural steel cannot be obtained, and excessive addition exceeding 0.20%. , Significantly lowers the base metal toughness, weld cracking resistance, toughness of the weld heat affected zone, etc., so the lower limit was made 0.04% and the upper limit was made 0.20%. Si is necessary for securing the strength of the base material, preliminary deoxidation of molten steel, etc., but if it exceeds 0.50%, high carbon martensite of a hardened structure is generated in the heat affected zone,
Significantly lowers weld joint toughness. In addition, 0.05%
If it is less than the required value, the necessary pre-deoxidation of molten steel cannot be performed, so the Si content was limited to the range of 0.05% to 0.50%.

Mn is 0.4 to secure the strength and toughness of the base material.
% Or more is necessary, but the upper limit is set to 2.0% within an allowable range of toughness, cracking property and the like of the welded portion. N is an element mixed into steel as an unavoidable impurity, and is an element that lowers the toughness when it is dissolved excessively. Therefore, it is desirable to reduce N as much as possible.
Since the cost for denitrification is high and the manufacturing cost is high, the lower limit is made 0.003%. On the other hand, if it exceeds 0.015%, the base material toughness deteriorates and the steel slab undergoes surface cracking during continuous casting, so the upper limit was made 0.015%.

[0013] Al is a strong deoxidizing element, but 0.00
If the content exceeds 5%, a composite oxide that promotes intragranular ferrite transformation is not formed, resulting in a decrease in toughness.
005% or less. P contained as inevitable impurities,
Although the amount of S is not particularly limited, it should be reduced as much as possible because macrosegregation at the time of solidification causes welding cracks and a decrease in toughness. In the present invention, the amounts of P and S are reduced to target amounts. Only less than 0.02% can be achieved in each case.

The above are the basic components of the steel which is the object of the present invention. However, in order to increase the strength of the base material and improve the toughness, V, C
One, two or more of r, Ni, Nb, Cu, and Mo can be contained. First, V is extremely important as VN for the formation of an intragranular ferrite structure, its grain refinement, and the securing of high-temperature strength. However, if it exceeds 0.20%, precipitates become excessive and the base metal toughness affects the welding heat. Since the toughness deteriorates, the upper limit is limited to 0.20%.

[0015] Ni is a very effective element for increasing the toughness of the base material, but the addition of more than 1.0% increases the alloy cost and is not economical, so the upper limit was made 1.0%. Cr improves the hardenability and is effective for strengthening the base material and strengthening at high temperatures. However, an excessive addition exceeding 0.7% is harmful from the viewpoint of toughness and curability, so the upper limit is set to 0.7%.

Although Nb is effective for toughening the base material,
An excessive addition exceeding 0.05% is detrimental from the viewpoint of toughness and curability, so the upper limit was made 0.05%. Cu is an element effective for strengthening the base material and weather resistance, but the upper limit is set to 1.0% in consideration of temper brittleness due to stress relief annealing, welding cracks, hot working cracks, and the like. Mo is an element effective for strengthening the base material and weather resistance, but the upper limit is set to 0.3% in consideration of welding cracks.

Preliminary deoxidation treatment of the molten steel and control of the dissolved oxygen to 0.003 to 0.015% by weight are performed to purify the molten steel at the same time as dispersing fine oxides in the slab. Because it is extremely important. If the [O] concentration after the preliminary deoxidation is less than 0.003%, the composite oxide of the intragranular ferrite nucleus which promotes the intragranular ferrite transformation decreases, and the grain cannot be refined, so that the toughness cannot be improved. on the other hand,
If the content exceeds 0.015%, the oxide becomes coarse and becomes a starting point of brittle fracture even if other conditions are satisfied, and the toughness is reduced. For the above reasons, the [O] concentration after preliminary deoxidation was limited to 0.003 to 0.015%.

The preliminary deoxidizing treatment is performed by vacuum degassing and Al,
Deoxidation was performed using one or more of Si, Zr, Ca, and Mg deoxidation. The reason is that vacuum degassing directly removes oxygen in molten steel as gas and CO gas, and removes Al, S
This is because oxide-based inclusions generated by strong deoxidation such as i, Zr, Ca, and Mg float and are easily removed, and are extremely effective in cleaning molten steel.

Ti forms a Ti-based oxide as a deoxidizer, promotes the formation of intragranular ferrite during rolling, and precipitates fine TiN to promote austenite grain refinement and the formation of intragranular ferrite. The effect of improving the toughness of the base material and the welded portion is less than 0.005%. However, if the content is less than 0.005%, the Ti content in the oxide becomes insufficient, and the effect as intragranular ferrite generation nuclei decreases. Exceeding excess Ti
Generates TiC, causes precipitation hardening, and significantly lowers the toughness of the weld heat affected zone, so the content is limited to 0.005 to 0.025%.

Further, the Ti content [Ti%] of the molten steel is defined as −0.006 ≦ [Ti%] − with respect to the dissolved oxygen [O%] of the molten steel.
2 [O%] ≦ 0.008% is limited to satisfy the relation that if Ti is excessive in weight [O] concentration relative to the [O] concentration, Ti is ineffective as an intragranular ferrite formation nucleus. _{Since a} large amount of ₂ O is generated and the structure cannot be refined, the toughness is reduced. If the content of Ti is too small relative to the [O] concentration by weight, the amount of composite oxides serving as intragranular ferrite nuclei is significantly reduced. This is because the structure cannot be refined and the toughness decreases. The reason why the order of addition of Ti is last is to facilitate the control of the amount and composition of Ti oxide when it is added in the initial stage of steelmaking.

After the molten steel produced by the above-described production method is produced into a slab by a continuous casting machine, it is reheated to a temperature range of 1100 to 1300 ° C. The reason for limiting the reheating temperature to this temperature range is that the production of shaped steel by hot working requires heating at 1100 ° C. or higher to facilitate plastic deformation, and also from the performance and economy of the heating furnace. The upper limit was 1300 ° C. The heated steel material is roll-formed in each of the steps of rough rolling, intermediate rolling and finish rolling. Rolling end temperature 750-1050
The reason why the temperature is set to 0 ° C is that the lower the temperature, the more the toughness is improved.
Processing at a temperature exceeding 0 ° C. is because a coarse-grained structure is formed and toughness is reduced.

The heated steel material is roll-formed in each of the steps of rough rolling, intermediate rolling and finish rolling. The reason why the rolling end temperature is set to 750 to 1050 ° C. is that although the toughness is improved as the rolling is performed at a lower temperature, it is difficult to work at a temperature lower than 750 ° C. due to the shaping of the shaped steel. Is generated to lower the toughness. In addition, the temperature of the surface layer of the steel material during the rolling pass in the intermediate rolling process is _Ar3-20 ° C.
Hereinafter, water cooled to A _r3 -100 ° C. or more, then rolling at least once in its recuperation process, is to terminate the rolling at a temperature range of 750 to 1,050 ° C., the surface layer portion and ultrafine grain tissue at low temperature rolling The purpose is to re-transform the ferrite into austenite by the subsequent reheating to remove the processing strain. By the combination of the water cooling, the rolling pass, and the recuperation, the surface layer of the steel material has an ultrafine grained ferrite + pearlite structure without distortion, and the toughness is improved.

After hot rolling, the average cooling rate in the temperature range from 650 to 400 ° C. was set to 0.01 to 0.30 ° C./s because supersaturated solid solution is formed in the fillet portion to reduce toughness. , N are gradually cooled and tempered in a cooling process to precipitate carbides and nitrides, thereby improving toughness . In order to sufficiently precipitate carbides and nitrides,
Rather than relying on natural cooling such as air cooling, proper cooling
It is necessary to control the cooling by selecting the speed, but 0.01
If the temperature is lower than ℃ / s, the carbide and nitride are sufficiently advanced,
Although the toughness is sufficiently improved, the cooling rate is too slow and hinders the production efficiency. Therefore, the lower limit is set to 0.01 ° C./s. On the other hand , if it exceeds 0.30 ° C./s, carbides and nitrides are formed. The upper limit was set to 0.30 ° C./s because the effect was insufficient and the effect of improving toughness was small.

Hereinafter, the present invention will be described based on examples.

[0025]

EXAMPLE A prototype steel was melted from a converter, the components were adjusted, and then cast into a slab of 240 to 300 mm thick by continuous casting.
After being heated in the heating furnace 1 having the layout shown in FIG. 1 and coarsely rolled by the rough rolling mill 2, subsequently, the first intermediate rolling mill 3, the second intermediate rolling mill 4, and the finishing mill 5 form an H-shaped steel having a predetermined size. Forming is performed until The cooling rate after the rolling is adjusted by cooling the steel material on the cooling floor 6 or the off-line 7 or by cooling while covering the steel material with a cooling cover to reduce the cooling rate between 650 to 400 ° C to 0.01 to 400 ° C. 0.30
Adjust to ° C / s.

The mechanical properties of the H-shaped steel 8 shown in FIG.
Thickness t of J9_TwoCenter (1 / 2t _Two) At full flange width
（Width (１ ／ B), １ ／ width (１ ／) of length (B)
B) and at the center of the web 10, the web height
A test piece was sampled from 1/2 part (1 / 2H) and determined. What
The characteristics of these locations were determined by using the flange 1/4
B part and web 1 / 2H part are flange part and web part respectively
Shows the average mechanical properties of
These three points correspond to the lowest fillet part.
In some places, the mechanical test characteristics of H-section steel can be represented.
It is.

Table 1 shows the chemical component values of the prototype steel, and Table 2
Indicates mechanical test characteristics for rolling and cooling conditions. In addition,
It is well known that the heating temperature is adjusted to 1280 ° C., in general, it is well known that the reduction of the heating temperature improves the mechanical properties, and it is estimated that the high-temperature heating condition shows the lowest value of the mechanical properties. This is because it has been determined that the characteristics at the following heating temperatures can be represented.

[0028]

[Table 1]

[0029]

[Table 2]

As shown in Table 2, steels 1 to 6 according to the present invention
Is the target base metal strength (JIS G3106) at the flange 1 / 4B portion, web 1 / 2H portion, and flange 1 / 2B, and the Charpy impact absorption energy value at 0 ° C of 120 (J).
At the same time, the Charpy impact absorption energy values at 0 ° C. of the flange Ｂ B portion and the web ウ ェ ブ H portion at 0 ° C. satisfying the above conditions do not cause a large difference, so that there is no problem. On the other hand, the steel 7 of the comparative steel is 650 to 400 after the end of the rolling.
Although the average cooling rate between ° C is 0.32 ° C / s, the base metal strength satisfies the standard, but the Charpy impact absorption energy value at 0 ° C at the flange 1 / 2B corresponding to the fillet portion is 100 (J). The following shows that the Charpy impact absorption energy of the flange 1 / 2B portion is lower than that of the steel of the present invention, and at the same time, the Charpy impact absorption energy at 0 ° C. of the flange 1 / 4B portion and the web 1 / 2H portion for the same steel material. The value is significantly lower than the value. The steel 8 has a flange plate thickness of 24 mm and a size 11 mm thinner than the flange plate thickness of the steel 7 of 35 mm, and has an average cooling rate of 1.51 ° C./s between 650 ° C. and 400 ° C. after the completion of rolling.
B, the Charpy impact absorption energy value at 0 ° C. is the same as in the case of steel 7;
And Charpy impact absorption energy value at 0 ° C. is 102
(J), the Charpy impact absorption energy of the flange 1 / 2B portion is lower than that of the steel of the present invention, and at the same time, the Charpy impact of the flange 1 / 4B portion and the web 1 / 2H portion at 0 ° C. for the same steel material. The value is significantly lower than the absorbed energy value. Further, in steel 9, the flange plate thickness is as thick as 60 mm, and the average cooling rate between 650 and 400 ° C. after rolling is 0.31 ° C./s.
The decrease in toughness in No. 2 becomes even more remarkable.

That is, when all the requirements of the present invention are satisfied, the steel sheet has sufficient strength even in a fillet portion which hardly satisfies the mechanical test characteristics of the rolled section steel, as shown in steels 1 to 6 shown in Table 2. In addition, it becomes possible to produce a rolled steel section having UT characteristics. The rolled section steel to which the present invention is applied is applicable not only to the above-mentioned H-section steel, but also to section steels having flanges such as 1-section steel, angle steel, channel steel, and unequal thickness angle steel. Of course, you can.

[0032]

Industrial Applicability According to the present invention, it is possible to efficiently manufacture a shaped steel having excellent material properties even in a low toughness fillet portion, thereby improving the reliability of a large building, ensuring safety, and economical efficiency. The industrial effects such as improvement of the quality are extremely remarkable.

[Brief description of the drawings]

FIG. 1 is an explanatory schematic view of an example of a device arrangement row for implementing the method of the present invention.

FIG. 2 is a view showing a cross-sectional shape of an H-section steel, showing names of respective parts and a sampling position of a mechanical test piece.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Heating furnace 2 ... Rough rolling mill 3 ... 1st intermediate rolling mill 4 ... 2nd intermediate rolling mill 5 ... Finishing rolling mill 6 ... Cooling floor 7 ... Offline 8 ... H-shaped steel 9 ... Flange 10 ... Web

Continuation of the front page (72) Inventor Masafumi Shibata 1, Sakai, Hachiman-cho, Sakai-shi, Osaka Nippon Steel Corporation Sakai Works (56) References JP-A-4-83821 (JP, A) JP-A-3 -249149 (JP, A) JP-A-64-57901 (JP, A) JP-A-7-76724 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) G21D 8/00 G21D 9/00

Claims (4)

(57) [Claims] C .: 0.04 to 0.20%, Si: 0.05 to 0.50%, Mn: 0.4 to 2.0%, N: 0.003 to 0.015 by weight%. %, Al ≦ 0.005%, with the balance being 0.003% by weight of dissolved oxygen by pre-deoxidation of molten steel consisting of Fe and unavoidable impurities.
After adjusting to 0.015%, titanium is further deoxidized, and the titanium content is 0.005 to 0.025% by weight, and -0.006 ≦ [with respect to the dissolved oxygen [O%] of the molten steel. Ti
%]-2 [O%] ≦ 0.008, cast by continuous casting, re-heated the slab to a temperature range of 1100 to 1300 ° C., and started rolling. Rolling is terminated in the temperature range, and after rolling is completed, 650 to 400
A method for producing a section steel excellent in toughness, characterized in that the steel is produced by cooling at a cooling rate to 0.01 ° C./s to 0.30 ° C./s. 2. In% by weight, C: 0.04 to 0.20%, Si: 0.05 to 0.50%, Mn: 0.4 to 2.0%, N: 0.003 to 0.015 %, Al ≦ 0.005%, with the balance being 0.003% by weight of dissolved oxygen by pre-deoxidation of molten steel consisting of Fe and unavoidable impurities.
After adjusting to 0.015%, titanium is further deoxidized, and the titanium content is 0.005 to 0.025% by weight, and -0.006 ≦ [with respect to the dissolved oxygen [O%] of the molten steel. Ti
%]-2 [O%] ≦ 0.008, cast by continuous casting, re-heated the slab to a temperature range of 1100 ° C. to 1300 ° C., and started rolling. The temperature of the surface layer of the steel material is _Ar3 -20 ° C or less, and _Ar3 -100 ° C
Water-cooling as above, rolling at least once in the recuperation process, terminating the rolling in a temperature range of 750 to 1050 ° C,
After the end of rolling, the cooling rate to
A method for producing a section steel having excellent toughness, characterized in that it is produced by cooling within a range of 1 ° C / s to 0.30 ° C / s. 3. In% by weight, C: 0.04 to 0.20%, Si: 0.05 to 0.50%, Mn: 0.4 to 2.0%, N: 0.003 to 0.015 %, Al ≦ 0.005%, V ≦ 0.20%, Cr ≦ 0.7%, Nb
≦ 0.05%, Ni ≦ 1.0%, Cu ≦ 1.0%, Mo
≦ 0.3%, the balance being F
e, and the molten steel consisting of unavoidable impurities is adjusted to 0.003 to 0.015% by weight of dissolved oxygen by pre-deoxidation treatment, and is further deoxidized with titanium, and the titanium content is 0.005 to 0.005% by weight. 0.025% and dissolved oxygen [O
%], -0.006 ≦ [Ti%] − 2 [O%] ≦
The slab that satisfies the relationship of 0.008 is cast by continuous casting, the slab is reheated to a temperature range of 1100 to 1300 ° C, rolling is started, and rolling is completed in a temperature range of 750 to 1050 ° C. After completion, cool down to 650-400 ° C
A method for producing a section steel having excellent toughness, characterized by being produced by cooling within a range of 0.01 ° C./s to 0.30 ° C./s. 4. In% by weight, C: 0.04 to 0.20%, Si: 0.05 to 0.50%, Mn: 0.4 to 2.0%, N: 0.003 to 0.015 %, Al ≦ 0.005%, V ≦ 0.20%, Cr ≦ 0.7%, Nb
≦ 0.05%, Ni ≦ 1.0%, Cu ≦ 1.0%, Mo
≦ 0.3%, the balance being F
e, and the molten steel consisting of unavoidable impurities is adjusted to 0.003 to 0.015% by weight of dissolved oxygen by pre-deoxidation treatment, and is further deoxidized with titanium, and the titanium content is 0.005 to 0.005% by weight. 0.025% and dissolved oxygen [O
%], -0.006 ≦ [Ti%] − 2 [O%] ≦
A slab satisfying the relationship of 0.008 is cast by continuous casting, the slab is reheated to a temperature range of 1100 to 1300 ° C., and rolling is started. Water cooling to _r3 -20 ° C or less, _Ar3 -100 ° C or more, and rolling at least once in the recuperation process, 750 to 105
Rolling is completed in a temperature range of 0 ° C.
The cooling rate from 0.01 to 400 ° C is 0.01 ° C / s to 0.30.
A method for producing a section steel having excellent toughness, characterized by being produced by cooling within a range of ° C / s.