JP3107695B2 - Method for producing shaped steel having flange with excellent strength, toughness and weldability - 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 Due to the heightening of buildings and stricter safety standards, structural steel with flanges used for columns and beams has been developed.
For example, H-section steel is required to have higher strength, higher toughness, lower yield point, and better weldability. In particular, in the case of an H-section steel having a thick flange, one measure is to add a large amount of alloying elements in order to secure the strength. In this case, however, at the same time, the toughness is reduced and the weldability is deteriorated. In order to ensure high toughness and weldability, a low alloy component is a necessary condition. As a method of satisfying the strength with a low alloy component, an accelerated cooling method (TMCP method) of a steel material after rolling is well known, but in the case of an H-section steel having a thick flange, the steel material temperature immediately after finish rolling is Ar _When cooling from _three or more gamma regions is performed, accelerated cooling until the required strength is ensured increases the structure fraction of the bainite phase or martensite phase and significantly impairs toughness. Further, in the field of thick steel sheets, techniques for producing high-strength and high-toughness steel 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, in this conventional method, the production cost is increased due to the addition of V, and it is difficult to control the N component. On the other hand, in order to secure the strength, toughness, and weldability at the same time, conventionally, a heat treatment such as a normalizing process has been performed after the completion of the rolling and cooling. However, the addition of heat treatment causes a significant increase in cost, such as a decrease in heat treatment cost and production efficiency, and there is a problem in economy.

[0003]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention provides a novel manufacturing method which comprehensively covers the steps from steelmaking, rolling and cooling to strength, toughness and weldability. An object of the present invention is to provide a shaped steel having an excellent flange at low cost.

[0004]

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. Adjustment, change of the order of addition of Ti among alloying elements, etc., control the amount of Ti added, disperse a large number of fine composite oxides in steel to generate intragranular ferrite, and then accelerate cooling To prevent an increase in the structure fraction of the bainite phase or the martensite phase, form a fine-grained ferrite structure, and secure strength and toughness. Further, if necessary, the temperature of the surface layer portion of the steel material between the passes of the intermediate rolling step is Ar ₃ −20 ° C. or less, water-cooled to Ar ₃ −100 ° C. or more, and rolled at least once in the recuperation process,
Further, the microstructure is refined, and particularly in an H-section steel, the toughness of a fillet portion at a high temperature rolling and a low cooling rate is improved. That is, the present invention is to provide a method for producing a high-quality steel material which is economical, efficiently and excellent in toughness without requiring special equipment. The gist of the present invention is the following (1) to
It is as described in (4). (1) In mass%, C: 0.05 to 0.15%, Si:
0.05-0.50%, Mn: 0.8-2.0%,
N: The molten steel containing 0.003 to 0.012%, the balance being Fe and unavoidable impurities is adjusted to 0.003 to 0.015% by mass of dissolved oxygen by preliminary deoxidation treatment, and then titanium is removed. The titanium content is 0.005 to 0.025% by mass and the dissolved oxygen [O
%], -0.006 ≦ [Ti%] − 2 [O%] ≦
After casting the slab which satisfies the relationship of 0.008 by continuous casting, re-heating the slab to a temperature range of 1100 to 1300 ° C. and then starting rolling, one of the following (a) and (b) A method for producing a shaped steel having a flange excellent in strength, toughness and weldability, which is characterized by undergoing a production process. (A) The intermediate rolling is completed in a temperature range of 750 to 1050 ° C., and the surface of the steel material is Ar ₃ −20 ° C. or less before finish rolling,
After finishing cooling to a temperature range of Ar ₁ or more, finish rolling is performed,
Then, the steel is immediately cooled at an average cooling rate of 700 ° C. to 400 ° C. within the range of 0.5 ° C./s to 3.0 ° C./s. (B) After finishing the intermediate rolling and the finish rolling in the temperature range of 750 to 1050 ° C., the surface of the steel material is Ar ₃ −20 ° C.
Thereafter, after cooling to a temperature range of Ar ₁ or more, immediately
The average cooling rate of steel from 0 ° C to 400 ° C is 0.5 ° C /
Accelerated cooling is performed within the range of s to 3.0 ° C./s. (2) In mass%, C: 0.05 to 0.15%, Si:
0.05-0.50%, Mn: 0.8-2.0%,
N: The molten steel containing 0.003 to 0.012%, the balance being Fe and unavoidable impurities is adjusted to 0.003 to 0.015% by mass of dissolved oxygen by preliminary deoxidation treatment, and then titanium is removed. The titanium content is 0.005 to 0.025% by mass and the dissolved oxygen [O
%], -0.006 ≦ [Ti%] − 2 [O%] ≦
The slab which satisfies 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. ₃ -20 ° C. or less, and water-cooled in Ar ₃ -100 ° C. or more,
After rolling at least once in the recuperation process, a shaped steel having a flange excellent in strength, toughness and weldability characterized by passing through one of the following manufacturing processes (a) and (b): Production method. (A) The intermediate rolling is completed in a temperature range of 750 to 1050 ° C., and the surface of the steel material is Ar ₃ −20 ° C. or less before finish rolling,
After finishing cooling to a temperature range of Ar ₁ or more, finish rolling is performed,
Then, the steel is immediately cooled at an average cooling rate of 700 ° C. to 400 ° C. within the range of 0.5 ° C./s to 3.0 ° C./s. (B) After finishing the intermediate rolling and the finish rolling in the temperature range of 750 to 1050 ° C., the surface of the steel material is Ar ₃ −20 ° C.
Thereafter, after cooling to a temperature range of Ar ₁ or more, immediately
The average cooling rate of steel from 0 ° C to 400 ° C is 0.5 ° C /
Accelerated cooling is performed within the range of s to 3.0 ° C./s. (3) In mass%, C: 0.05 to 0.15%, Si:
0.05-0.50%, Mn: 0.8-2.0%,
N: 0.003 to 0.012%, plus V ≦
0.20%, Cr ≦ 0.7%, Nb ≦ 0.05%, Ni
≦ 1.0%, Cu ≦ 1.0%, Mo ≦ 0.3%, the molten steel containing one or more of the remaining Fe and unavoidable impurities is dissolved by preliminary deoxidation to reduce dissolved oxygen by mass%.
After adjusting to 0.003 to 0.015% with titanium, the titanium is further deoxidized, and the titanium content is 0.005 to 0.02% by mass.
5% and -0.0% with respect to the dissolved oxygen [O%] of the molten steel.
Continuous casting is performed on a slab satisfying the relationship of 0.6 ≦ [Ti%] − 2 [O%] ≦ 0.008.
A shape having a flange excellent in strength, toughness and weldability, characterized in that after rolling is started after reheating to a temperature range of 00 ° C., any one of the following manufacturing processes (a) and (b) is performed. Steel production method. (A) The intermediate rolling is completed in a temperature range of 750 to 1050 ° C., and the surface of the steel material is Ar ₃ −20 ° C. or less before finish rolling,
After finishing cooling to a temperature range of Ar ₁ or more, finish rolling is performed,
Then, the steel is immediately cooled at an average cooling rate of 700 ° C. to 400 ° C. within the range of 0.5 ° C./s to 3.0 ° C./s. (B) After finishing the intermediate rolling and the finish rolling in the temperature range of 750 to 1050 ° C., the surface of the steel material is Ar ₃ −20 ° C.
Thereafter, after cooling to a temperature range of Ar ₁ or more, immediately
The average cooling rate of steel from 0 ° C to 400 ° C is 0.5 ° C /
Accelerated cooling is performed within the range of s to 3.0 ° C./s. (4) In mass%, C: 0.05 to 0.15%, Si:
0.05-0.50%, Mn: 0.8-2.0%,
N: 0.003 to 0.012%, plus V ≦
0.20%, Cr ≦ 0.7%, Nb ≦ 0.05%, Ni
≦ 1.0%, Cu ≦ 1.0%, Mo ≦ 0.3%, the molten steel containing one or more of the remaining Fe and unavoidable impurities is dissolved by preliminary deoxidation to reduce dissolved oxygen by mass%.
After adjusting to 0.003 to 0.015% with titanium, the titanium is further deoxidized, and the titanium content is 0.005 to 0.02% by mass.
5% and -0.0% with respect to the dissolved oxygen [O%] of the molten steel.
Continuous casting is performed on a slab satisfying the relationship of 0.6 ≦ [Ti%] − 2 [O%] ≦ 0.008.
Rolling was started after reheating to a temperature range of 00 ° C., and the temperature of the surface layer of the steel material was reduced to Ar ₃ −20 ° C. or less between passes of the intermediate rolling step,
Ar ₃ −100 ° C. or higher, and at least one rolling in the reheating process, and then undergoing any one of the following manufacturing steps (a) and (b): strength, toughness, and welding For producing shaped steel having a flange with excellent heat resistance. (A) The intermediate rolling is completed in a temperature range of 750 to 1050 ° C., and the surface of the steel material is Ar ₃ −20 ° C. or less before finish rolling,
After finishing cooling to a temperature range of Ar ₁ or more, finish rolling is performed,
Then, the steel is immediately cooled at an average cooling rate of 700 ° C. to 400 ° C. within the range of 0.5 ° C./s to 3.0 ° C./s. (B) After finishing the intermediate rolling and the finish rolling in the temperature range of 750 to 1050 ° C., the surface of the steel material is Ar ₃ −20 ° C.
Thereafter, after cooling to a temperature range of Ar ₁ or more, immediately
The average cooling rate of steel from 0 ° C to 400 ° C is 0.5 ° C /
Accelerated cooling is performed within the range of s to 3.0 ° C./s.

[0005]

Hereinafter, the operation of the present invention will be described in detail based on embodiments. The toughness of the steel depends on the alloy components and the crystal grain size. That is, the toughness improves 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.

[0006] 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. In addition, precipitation strengthening by fine precipitates also reduces toughness. Therefore, only the refinement of the ferrite crystal grain size can increase the strength while securing the toughness.

According to the weldability evaluation formula (hereinafter abbreviated as WES formula) defined by the Japan Welding Society, the weldability is as shown below. The weldability increases with the increase of alloying elements such as C and Mn. Is impaired. In order to ensure good weldability, it is necessary that the WES equation is at least 0.40 or less. The features of the present invention, for example, during the production of the H-section steel having a thick flange by hot rolling, after air cooling before or after finish rolling to make a part of ferrite appear, accelerated cooling, bainite phase, The object is to prevent a rise in the structure fraction of the ferrite phase, to provide a fine-grained ferrite structure, and to satisfy all of the strength, toughness, and weldability.

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 0.05%, the strength required for structural steel cannot be obtained.
Excessive addition of more than 5% results in base metal toughness, weld cracking resistance,
The lower limit was set to 0.05% and the upper limit was set to 0.15% because the toughness of the heat-affected zone of the weld was significantly reduced.

[0009] Si is necessary for securing the strength of the base material, pre-deoxidizing the molten steel, etc. If it exceeds 0.50%, high carbon martensite of a hardened structure is generated in the heat affected zone of the weld, and the toughness of the weld joint is reduced. Significantly lowers. If the content is less than 0.05%, the necessary pre-deoxidation of molten steel cannot be performed.
It was limited to the range of 05% to 0.50%. Mn needs to be added in an amount of 0.8% or more to ensure the strength and toughness of the base material, but the upper limit is set to 2.0% within an acceptable range of the toughness, cracking, and the like of the welded portion.

[0010] N is an element that is mixed into steel as an unavoidable impurity, and is an element that reduces toughness when it is dissolved excessively. Therefore, it is desirable to reduce N as much as possible.
If it is less than 03%, the cost for denitrification will be high and the production cost will be high, so the lower limit was 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%.

Although the amounts of P and S contained as inevitable impurities are not particularly limited, they should be reduced as much as possible because macrosegregation at the time of solidification causes welding cracks and a decrease in toughness. , And S can be reduced to the target amounts by less than 0.02%, respectively.

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

[0013] 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%.

Nb is effective for toughening the base material,
An excessive addition exceeding 0.05% is harmful from the viewpoint of toughness and hardenability, 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, but the upper limit is set to 0.3% in consideration of welding cracks, hot working cracks and the like.

The reason why the molten iron is preliminarily deoxidized and the dissolved oxygen is controlled to 0.003 to 0.015% by weight is to purify the molten iron at the same time as dispersing fine oxides in the slab. Because it is extremely important. If the [O] concentration after the pre-deoxidation is less than 0.003%, the amount of 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,
When 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,
The deoxidation was performed by 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,
This is because oxide-based inclusions generated by strong deoxidation such as i, Zr, Ca, and Mg easily float and are easily removed, and are extremely effective in cleaning molten steel.

Ti forms a Ti-based oxide as a deoxidizing material, promotes the formation of intragranular ferrite during rolling, and precipitates fine TiN, thereby promoting the reduction of austenite 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 is reduced. Exceeding excess Ti
Generates TiC, causes precipitation hardening, and significantly reduces the toughness of the heat affected zone by welding, so the content is limited to 0.005 to 0.025%.

Further, the Ti content [Ti%] of the molten steel is set to -0.006 ≦ [Ti%]-based on 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 grain 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 time is 750-1050
The reason why the temperature was set to 0 ° C is that the lower the temperature, the better the toughness is, but the processing at less than 750 ° C is difficult due to the shaping of the shaped steel.
This is because processing at a temperature exceeding 0 ° C. generates a coarse-grained structure and lowers toughness.

Further, the temperature of the steel surface layer portion between rolling passes in the intermediate rolling step Ar ₃ -20 ° C. or less, Ar ₃ -1
Water cooling to at least 00 ° C., rolling at least once in the recuperation process, and terminating the rolling at a temperature in the range of 750 to 1050 ° C. are performed by low-temperature rolling so that the surface layer has an ultrafine-grained structure. Thereby, the ferrite is transformed again to austenite to remove working strain. Due to 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 completion of the intermediate rolling and before or after finish rolling, the surface temperature is allowed to cool to Ar ₃ -20 ° C. or lower and Ar ₁ or higher because the ferrite transformation proceeds to a thickness of about 20 mm from the surface. This is because the formation of a ferrite suppresses the formation of a bainite phase or a martensite phase. When the cooling is stopped in a temperature range higher than this temperature range and accelerated cooling is performed, the structure fraction of the bainite phase or the martensite phase is significantly increased, and the toughness is reduced.
Further, if the temperature is allowed to cool to a temperature lower than this temperature range, the effect of ferrite fine graining by accelerated cooling is not seen, and the strength is reduced. The cooling to the above-mentioned optimum temperature range may be performed before or after finish rolling. The reason is that the amount of reduction in the finish rolling is small, and the material variation due to the presence or absence of the finish rolling can be ignored.

The steel material that has been allowed to cool before finish rolling is
The steel that has been cooled after finish rolling is immediately subjected to accelerated cooling.
The average cooling rate from 700 ° C to 400 ° C is 0.5 ° C /
The reason why the cooling is performed within the range of s to 3.0 ° C./s is that when accelerated cooling is performed at a higher cooling rate than this cooling rate range, the structural fraction of the bainite phase or the martensite phase increases, and the toughness increases. Decrease. In addition, even if accelerated cooling is performed at a cooling rate lower than this cooling rate range, the effect of ferrite grain refinement by accelerated cooling is not observed, and strength is reduced. Therefore, the above-described range of the cooling rate is set as the optimum cooling rate range.

[0023]

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 rough-rolled by the rough rolling mill 2, subsequently, the first intermediate rolling mill 3 and the second intermediate rolling mill 4 form the steel until it becomes an H-shaped steel having a predetermined size. Do.
In this case, among the rolling passes of the second intermediate rolling mill 4 as required, the temperature of the steel surface layer portion Ar ₃ -20 ° C. or less, Ar ₃
Water cooling to -100 ° C or higher, and at least 1
Rolling more than once and finishing the intermediate rolling in a temperature range of 750 to 1050 ° C. After that, before the finish rolling by the finish rolling mill 5, the predetermined temperature range, that is, the steel material surface is Ar ₃ -20 at an arbitrary position between the second intermediate rolling mill 4 and the finish rolling mill 5.
℃ below, it is allowed to cool to Ar ₁ or more temperature region. afterwards,
After the finish rolling, a predetermined cooling rate, that is, a cooling rate from 700 ° C. to 400 ° C. by 0.5 is accelerated by a water-cooled accelerated cooling device 6 for steel material installed downstream of the finishing mill 5.
Accelerated cooling is performed so that the temperature can be maintained in the range of ° C / s to 3.0 ° C / s. After cooling, it is allowed to cool on the cooling floor 7 until it is corrected in the next step.

The mechanical properties of the H-section steel 8 shown in FIG.
Thickness t of J9_TwoCenter (1 / 2t _Two) At full flange width
Take a test piece from 1/4 width (1 / 4B) of length (B)
I asked. The characteristics of this location were determined by the flange
Since the 1 / 4B section shows the average mechanical properties of the base material,
Because it was possible to represent the mechanical test characteristics of H-section steel
is there.

Tables 1 and 2 show the chemical composition values of the prototype steel.
Table 3 shows mechanical test characteristics for rolling and cooling conditions.
You. The reason why the heating temperature is set to 1280 ° C. is generally
It is well known that reducing the heating temperature improves the mechanical properties
It is estimated that high-temperature heating conditions show the lowest value of mechanical properties
This value can represent the characteristics at the lower heating temperature.
This is because it was determined to be. Tables 1 and 2
Ar in the minute range _ThreeThe point is between 860 ° C and 800 ° C
Between, Ar₁Since the point is between 700 ° C and 650 ° C,
Ar cooling stop temperature₁Ar points_ThreePoint -20 ℃ or less
To at least 700 ° C and 780 ° C
There is a need.

[0026]

[Table 1]

[0027]

[Table 2]

[0028]

[Table 3]

As shown in Table 3, steels 1 to 6 according to the present invention
Is the target base metal strength at the flange 1 / 4B portion, which is a portion representative of the base material (the above-mentioned JISG3106, SM490)
And the target value of the Charpy impact absorbed energy at 0 ° C. (JISG3106, SM490C) and 45 (J)
The above is fully satisfied. On the other hand, in Comparative Steel No. 7, T
Components other than i and O, cooling stop temperature, 700 ° C to 400
Although the cooling rate up to ° C. conforms to the conditions in the present invention, the concentration balance between Ti and O is [Ti%]-2 [O].
Is 0.0090, which is the condition in the present invention, -0.00
Since the intensity deviates from the range of 6 or more and 0.008 or less, the intensity is lower than the target value. In the steel 8, the cooling stop temperature and the cooling rate up to 400 ° C. are within the range of the production conditions in the present invention, but the Mn concentration is 2.04%,
The target value of the Charpy impact absorption energy at 0 ° C. is not satisfied. In steel 9, although the components, the cooling rate from 700 ° C. to 400 ° C., both satisfy the production conditions of the present invention, the cooling stop temperature is 610 ° C., and since the temperature is lower than the Ar ₁ point, the strength is the target. Below the value. In steel 10, the components
The cooling rate from 700 ° C. to 400 ° C. after cooling both satisfies the production conditions of the present invention, but the cooling stop temperature is 86 ° C.
At 0 ° C., the Ar temperature is ₃ ° C. or higher, −20 ° C., and the Charpy impact absorption energy at 0 ° C. is extremely low and is lower than the target value.
In steel 11, both the components and the cooling stop temperature satisfy the manufacturing conditions in the present invention, but the cooling rate from 700 ° C. to 400 ° C. is 0.4 ° C./s, and the lower limit of the cooling rate in the present invention is 0.5. Since the temperature is lower than ° C./s, the intensity is lower than the target value. Although the steel 12 satisfies the production conditions in the present invention in terms of both the composition and the cooling stop temperature,
Cooling rate from 3.2 ° C to 400 ° C is 3.2 ° C / s,
Because the cooling rate in the present invention exceeds the upper limit of 3.0 ° C./s, the Charpy impact absorption energy at 0 ° C. is low,
The target value is not satisfied.

Regarding the weldability, if the WES formula is 0.40 or less, excellent weldability can be ensured. Steels 1 to 6 satisfy the conditions, so that good weldability is obtained. You can judge that you have. That is, when all the requirements of the present invention are satisfied, the production by hot rolling of a thick-walled flange H-section steel excellent in base material strength, toughness, and weldability as in steels 1 to 6 shown in Table 3 is performed. Will be possible. 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 I-section steel, angle steel, channel steel, and unequal thickness angle steel. Of course, you can.

The steel making method in the above embodiment is premised on the production in a converter, but employs an electric furnace in which the pre-deoxidation treatment is more easily performed, or a step of combining them with an auxiliary melting furnace. Then, the dissolved oxygen of the present invention may be adjusted. In addition, the recuperation process between the rolling passes is performed during the pass from the start to the end of the reverse rolling or the continuous rolling, but the recuperation may be forcibly performed by the rapid heating means.

[0032]

According to the present invention, it is possible to manufacture a thick flange H-section steel having excellent base material strength, toughness, and weldability by hot rolling, 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 ... Steel cooling device 7 ... Cooling floor 8 ... H-shaped steel 9 ... Flange 10 ... Web 11 ... Fillet part

──────────────────────────────────────────────────の Continuing on the front page (72) Inventor Kazuhiko Eda 1 Chikuko Hachimancho, Sakai City, Osaka Prefecture Nippon Steel Corporation Sakai Works (72) Inventor Noriaki Onodera 1 Chikuko Hachimancho Sakai City, Osaka New Nippon Steel Corporation Sakai Works (56) References JP-A-5-263182 (JP, A) JP-A-4-157117 (JP, A) JP-A-2-163341 (JP, A) JP 6-122922 (JP, A) JP-A-7-76725 (JP, A) JP-A-6-100924 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) C21D 8/00 -8/10

Claims (4)

(57) [Claims] 1. C: 0.05 to 0.15 by mass%
%, Si: 0.05 to 0.50%, Mn: 0.8 to 2.0%, N: 0.003 to 0.012%, and the molten steel consisting of the balance Fe and inevitable impurities is Dissolved oxygen by deoxidation treatment is 0.00% by mass.
After adjusting the content to 3 to 0.015%, the titanium is further deoxidized. The titanium content is 0.005 to 0.025% in mass%, and -0.006 with respect to the dissolved oxygen [O%] of the molten steel. ≤ [T
i%]-2 [O%] ≦ 0.008, cast continuously by casting, and after reheating the cast piece to a temperature range of 1100 ° C. to 1300 ° C., start rolling. a),
A method for producing a shaped steel having a flange excellent in strength, toughness and weldability, which is characterized by passing through any one of the production steps (b). (A) The intermediate rolling is completed in a temperature range of 750 to 1050 ° C., and the surface of the steel material is Ar ₃ −20 ° C. or less before finish rolling,
After finishing cooling to a temperature range of Ar ₁ or more, finish rolling is performed,
Then, the steel is immediately cooled at an average cooling rate of 700 ° C. to 400 ° C. within the range of 0.5 ° C./s to 3.0 ° C./s. (B) After finishing the intermediate rolling and the finish rolling in the temperature range of 750 to 1050 ° C., the surface of the steel material is Ar ₃ −20 ° C.
Thereafter, after cooling to a temperature range of Ar ₁ or more, immediately
The average cooling rate of steel from 0 ° C to 400 ° C is 0.5 ° C /
Accelerated cooling is performed within the range of s to 3.0 ° C./s. 2. C: 0.05 to 0.15 by mass%
%, Si: 0.05 to 0.50%, Mn: 0.8 to 2.0%, N: 0.003 to 0.012%, and the molten steel consisting of the balance Fe and inevitable impurities is Dissolved oxygen by deoxidation treatment is 0.00% by mass.
After adjusting the content to 3 to 0.015%, the titanium is further deoxidized. The titanium content is 0.005 to 0.025% in mass%, and -0.006 with respect to the dissolved oxygen [O%] of the molten steel. ≤ [T
i%]-2 [O%] ≤ 0.008, which is cast by continuous casting, and after reheating the slab to a temperature range of 1100 to 1300 ° C, rolling is started. the temperature of the steel surface layer portion Ar ₃ -20 ° C. or less between the passes, Ar ₃ -1
Excellent in strength, toughness and weldability, characterized in that it is water-cooled to a temperature of at least 00 ° C., rolled at least once in the recuperation process, and then subjected to one of the following manufacturing steps (a) and (b): Of manufacturing a shaped steel having a bent flange. (A) The intermediate rolling is completed in a temperature range of 750 to 1050 ° C., and the surface of the steel material is Ar ₃ −20 ° C. or less before finish rolling,
After finishing cooling to a temperature range of Ar ₁ or more, finish rolling is performed,
Then, the steel is immediately cooled at an average cooling rate of 700 ° C. to 400 ° C. within the range of 0.5 ° C./s to 3.0 ° C./s. (B) After finishing the intermediate rolling and the finish rolling in the temperature range of 750 to 1050 ° C., the surface of the steel material is Ar ₃ −20 ° C.
Thereafter, after cooling to a temperature range of Ar ₁ or more, immediately
The average cooling rate of steel from 0 ° C to 400 ° C is 0.5 ° C /
Accelerated cooling is performed within the range of s to 3.0 ° C./s. 3. C: 0.05 to 0.15 by mass%
%, Si: 0.05 to 0.50%, Mn: 0.8 to 2.0%, N: 0.003 to 0.012%, and in addition, V ≦ 0.20%, Cr ≦ 0.7%, N
b ≦ 0.05%, Ni ≦ 1.0%, Cu ≦ 1.0%, M
After the molten steel containing one or more kinds of o ≦ 0.3%, the balance being Fe and inevitable impurities, the dissolved oxygen is adjusted to 0.003 to 0.015% by mass% by preliminary deoxidation treatment, Titanium is further deoxidized, the titanium content is 0.005 to 0.025% by mass, and the dissolved oxygen [O
%], -0.006 ≦ [Ti%] − 2 [O%] ≦
After casting the slab which satisfies the relationship of 0.008 by continuous casting, re-heating the slab to a temperature range of 1100 to 1300 ° C. and then starting rolling, one of the following (a) and (b) A method for producing a shaped steel having a flange excellent in strength, toughness and weldability, which is characterized by undergoing a production process. (A) The intermediate rolling is completed in a temperature range of 750 to 1050 ° C., and the surface of the steel material is Ar ₃ −20 ° C. or less before finish rolling,
After finishing cooling to a temperature range of Ar ₁ or more, finish rolling is performed,
Then, the steel is immediately cooled at an average cooling rate of 700 ° C. to 400 ° C. within the range of 0.5 ° C./s to 3.0 ° C./s. (B) After finishing the intermediate rolling and the finish rolling in the temperature range of 750 to 1050 ° C., the surface of the steel material is Ar ₃ −20 ° C.
Thereafter, after cooling to a temperature range of Ar ₁ or more, immediately
The average cooling rate of steel from 0 ° C to 400 ° C is 0.5 ° C /
Accelerated cooling is performed within the range of s to 3.0 ° C./s. 4. C: 0.05 to 0.15 by mass%
%, Si: 0.05 to 0.50%, Mn: 0.8 to 2.0%, N: 0.003 to 0.012%, and in addition, V ≦ 0.20%, Cr ≦ 0.7%, N
b ≦ 0.05%, Ni ≦ 1.0%, Cu ≦ 1.0%, M
After the molten steel containing one or more kinds of o ≦ 0.3%, the balance being Fe and inevitable impurities, the dissolved oxygen is adjusted to 0.003 to 0.015% by mass% by preliminary deoxidation treatment, Titanium is further deoxidized, the titanium content is 0.005 to 0.025% by mass, and the dissolved oxygen [O
%], -0.006 ≦ [Ti%] − 2 [O%] ≦
The slab which satisfies 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. ₃ -20 ° C. or less, and water-cooled in Ar ₃ -100 ° C. or more,
After rolling at least once in the recuperation process, a shaped steel having a flange excellent in strength, toughness and weldability characterized by passing through one of the following manufacturing processes (a) and (b): Production method. (A) The intermediate rolling is completed in a temperature range of 750 to 1050 ° C., and the surface of the steel material is Ar ₃ −20 ° C. or less before finish rolling,
After finishing cooling to a temperature range of Ar ₁ or more, finish rolling is performed,
Then, the steel is immediately cooled at an average cooling rate of 700 ° C. to 400 ° C. within the range of 0.5 ° C./s to 3.0 ° C./s. (B) After finishing the intermediate rolling and the finish rolling in the temperature range of 750 to 1050 ° C., the surface of the steel material is Ar ₃ −20 ° C.
Thereafter, after cooling to a temperature range of Ar ₁ or more, immediately
The average cooling rate of steel from 0 ° C to 400 ° C is 0.5 ° C /
Accelerated cooling is performed within the range of s to 3.0 ° C./s.