JPH08199233A - Production of high strength gauge h steel excellent in surface characteristic - Google Patents

Abstract

PURPOSE: To produce a high strength gauge H steel excellent in corrosion resistance, strength, toughness and surface characteristic by executing a specific acceleration-cooling after a specific hot-rolling and descaling to a cast slab having a specific composition composed of C, Si, Mn, N, Al, Cr, Cu and Fe. CONSTITUTION: The continuously cast slab composed of 0.05-0.15wt.% C, 0.05-0.50% Si, 0.8-2.0% Mn, 0.003-0.015% N, <=0.005% Al, 0.50-1.50% Cr, 0.30-1.00% Cu and if necessary <=1.00% Ni and the balance Fe with inevitable impurities is reheated at 1100-1300 deg.C for 1-<3hr, and the rolling is started. At the initial stage of the rough rolling process, the positions corresponding to the outer side surfaces of flanges are descaled, and the surface layer part of the steel material is water-cooled to (Ar3 -20 deg.C)-(Ar3 -10 deg.C) and finish rolling is executed at 750-1050 deg.C according to needs. Thereafter, immediately, this rolled steel is acceleration-cooled from 700 deg.C to 400 deg.C at 0.5-10.0 deg.C/s average cooling speed.

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 an H-section steel used as a structural member for buildings such as buildings and bridges.

[0002]

2. Description of the Related Art H-shaped steel, which is a typical shaped steel having a flange used for beams and columns due to stricter safety standards for buildings and pursuit of aesthetic appearance, has a higher performance. Is required. For example, when using the H-section steel surface exposed, corrosion resistance and weather resistance are required for beams and columns.
Conventionally, a steel material having high environmental durability, which is free from the occurrence of rust on the surface of the steel material, as represented by stainless H-section steel, has been used. However, since stainless steel requires a large amount of expensive alloying elements such as Cr and Ni, the manufacturing cost is high, and although it is excellent in function, its economical efficiency is problematic. As another method of adding a function of corrosion resistance to a steel material, for example, the invention described in JP-A-54-53627 is disclosed.
After removing the surface scale of the steel material, there is a method of coating with a synthetic resin film, but the descaling step of the steel material in the temperature range of 200 to 300 ° C., the number of steps such as the synthetic resin film coating step, and the like. In general, the process capacity is the lowest in the manufacturing line and the production capacity is lowered by limiting the overall production capacity. is there.

Therefore, although rust is inevitable, stainless steel is often used instead of stainless steel, which is inexpensive and which suppresses the progress of rust and minimizes the amount of corrosion.
The characteristic of this weather resistant steel is that by forming a coating layer other than iron and iron oxide on the surface of the steel material, the progress of oxidation of iron, that is, the generation of rust is suppressed. This coating layer is C
u is most commonly used. The reason is that a Cu concentrated region is formed on the surface only by adding Cu to the steel and heating the material, and this serves as a coating layer to prevent O atoms from entering from the outside. The weathering steel defined by JIS requires Cu to be added in an amount of 0.3% or more.

However, when this steel is manufactured into an H-section steel, a Cu enriched region is formed on the surface during the material heating step, and thereafter, in the rough rolling process with a large amount of deformation, the concentrated region present as a liquid phase in this temperature region. Cu in the chemical region develops so-called “red-heat embrittlement” in which the Cu penetrates into the austenite grain boundaries and becomes brittle, and the frequency of defects increases. Further, since these flaws are inherent in the scale produced on the surface of the steel material in the cooling stage after rolling, it is difficult to detect the flaws by visual inspection after cooling. Therefore, after the product is shipped, defects are first discovered in the scale removal process such as shot blasting,
In some cases, there was a problem in terms of quality control.

From the above-mentioned situation, it is considered that there are two problems regarding the occurrence of this flaw. The first point is how to prevent defects from occurring,
The second point is how to facilitate the detection of defects.

[0006] First, regarding the first point of prevention of flaws, liquid C
An important point is how to suppress red heat embrittlement due to u. Conventionally, in order to raise the melting point of Cu, it is effective to add Ni to form a solid solution with Cu and raise the melting point. However, the melting point of Cu is at least 1300 ° C. which is the temperature range in the initial stage of the rough rolling process. It is necessary to increase the temperature to the vicinity, and for this purpose, Ni must be added in an amount of 0.5 to 1.0 times the atomic ratio with Cu, which significantly increases the manufacturing cost. Further, when Cu is not added, red hot embrittlement can be suppressed, but at the same time, since the Cu concentrated region is not formed, the weather resistance function also disappears. In this case, a surface coating layer that substitutes for the Cu concentrated region is required.

Next, regarding the detection of the second flaw, it is an essential condition to suppress the generation of scale that covers the surface. Since the scale is generated by the oxidation reaction of iron in the hot rolling and the subsequent cooling step, it is necessary to reduce the temperature of the surface during rolling and the cooling step as much as possible and complete the cooling in a short time. . However, the temperature control so far during rolling and during the cooling stage after that has been
The MCP method is well known, but this method is for strengthening steel materials,
Although it has been applied to improve the toughness, it has not been applied to improve the surface properties of steel.

[0008]

SUMMARY OF THE INVENTION In order to solve the above problems, the present invention forms a Cr oxide film, which is more susceptible to an oxidation reaction than iron and is passive, on the surface of a steel material during hot rolling and subsequent cooling. However, by coating the steel material with this oxide film, corrosion resistance is secured, and it has a new function of excellent strength, toughness, and surface properties, and the occurrence of bald spots and the like due to red heat embrittlement in Cu-containing steel. It is an object of the present invention to provide a method for manufacturing an H-section steel with reduced heat at low cost.

[0009]

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and its characteristic points are appropriate components, heating temperature before rolling, and control of steel material temperature during rolling and after rolling. As a result, Cr oxide is formed on the surface layer of the steel material to add a function of corrosion resistance, and in addition, the amount of secondary scale that is generated starting from the rolling is controlled by temperature control during and after rolling as much as possible. It suppresses the thickness of the scale on the surface of the steel material to 10 μm or less and smoothes it, and adds excellent surface properties.

The gist of the invention is as described in the following items (1) to (4).

(1) C by weight%: 0.05 to 0.15
%, Si: 0.05 to 0.50%, Mn: 0.8 to 2.
0%, N: 0.003 to 0.015%, Al ≦ 0.00
5%, Cr: 0.50 to 1.50%, Cu: 0.30
Molten steel containing 1.00% and the balance of Fe and unavoidable impurities is cast into a slab by continuous casting.
After reheating to a temperature range of 0 to 1300 ° C. for 1 hour or more and less than 3 hours, rolling is started, and a portion corresponding to the flange outer side surface is descaled at the initial stage of the rough rolling process, and 750 to 105
Finish rolling is completed in the temperature range of 0 ° C., and immediately thereafter, the average cooling rate of the steel material from 700 ° C. to 400 ° C. is set to 0.
A method for producing a high-strength H-section steel having excellent surface properties, which comprises accelerated cooling within a range of 5 ° C / s to 10.0 ° C / s.

(2) C by weight%: 0.05 to 0.15
%, Si: 0.05 to 0.50%, Mn: 0.8 to 2.
0%, N: 0.003 to 0.015%, Al ≦ 0.00
5%, Cr: 0.50 to 1.50%, Cu: 0.30
Molten steel containing 1.00% and the balance of Fe and unavoidable impurities was cast into a slab by continuous casting.
After reheating to a temperature range of 1300 ° C. for 1 hour or more and less than 3 hours, rolling is started, and after descaling the portion corresponding to the flange outer surface at the initial stage of the rough rolling step, the steel material surface layer portion is provided between the passes of the intermediate rolling step. Temperature of Ar ₃ -20 ° C or lower, A
r ₃ −100 ° C. or higher, water-cooled, rolled at least once in the recuperating process, finished rolling in the temperature range of 750 to 1050 ° C., and immediately thereafter from 700 ° C. to 400 ° C.
The average cooling rate of steel up to ℃ 0.5 ℃ / s ~ 10.0
A method for producing a high-strength H-section steel having excellent surface properties, which is accelerated cooling within a range of ° C / s.

(3) C by weight%: 0.05 to 0.15
%, Si: 0.05 to 0.50%, Mn: 0.8 to 2.
0%, N: 0.003 to 0.015%, Al ≦ 0.00
5%, Cr: 0.50 to 1.50%, Cu: 0.30
Molten steel containing 1.00% and Ni ≦ 1.00%, the balance being Fe and unavoidable impurities, is cast into a slab by continuous casting, and the slab is cast in a temperature range of 1100 to 1300 ° C. for 1 hour or more 3 Rolling is started after reheating for less than a time, the portion corresponding to the flange outer surface is descaled in the initial stage of the rough rolling process, finish rolling is completed in the temperature range of 750 to 1050 ° C, and immediately thereafter, from 700 ° C to 400 ° C. A method for producing a high-strength H-section steel having excellent surface properties, which comprises accelerating and cooling an average cooling rate of the steel material within the range of 0.5 ° C / s to 10.0 ° C / s.

(4) C by weight%: 0.05 to 0.15
%, Si: 0.05 to 0.50%, Mn: 0.8 to 2.
0%, N: 0.003 to 0.015%, Al ≦ 0.00
5%, Cr: 0.50 to 1.50%, Cu: 0.30
Molten steel containing 1.00% and Ni ≦ 1.00%, the balance being Fe and unavoidable impurities, is cast into a slab by continuous casting, and the slab is cast in a temperature range of 1100 to 1300 ° C. for 1 hour or more 3 After reheating for less than a time, rolling is started, and after descaling the portion corresponding to the outer surface of the flange at the initial stage of the rough rolling process, the temperature of the steel surface layer portion is A between the passes of the intermediate rolling process.
r ₃ −20 ° C. or lower, Ar ₃ −100 ° C. or higher, water-cooled, rolled at least once in the recuperating process, 750 to 10
Characteristically, finish rolling is finished in a temperature range of 50 ° C., and immediately thereafter, an average cooling rate of steel products from 700 ° C. to 400 ° C. is accelerated and cooled within a range of 0.5 ° C./s to 10.0 ° C./s. And a method for producing a high-strength H-section steel having excellent surface properties.

[0015]

The operation of the present invention will be described in detail below with reference to examples.

Oxidation (corrosion) of the steel material proceeds mainly by the penetration of oxygen from the outside. The rate of oxygen invasion is determined by the oxygen concentration in the atmosphere, oxygen ions from the surface of the steel material to the inside, or diffusion of metal ions (positive) from the inside to the surface. At this time, if a highly airtight oxide film is formed on the surface layer of the steel material, the penetration of oxygen is hindered and the progress of oxidation is delayed. As an oxide film having high airtightness, a Cr oxide film is typical as applied to stainless steel and the like. In the present invention, the amount of added Cr is 0.5 to 1.5%, which is 1/10 or less of the amount of added Cr in stainless steel. Therefore, although it does not reach the corrosion resistance of stainless steel, it is a structural material. It is characterized by being able to secure the degree of corrosion resistance required for, and being inexpensive. This Cr oxide film is formed in the heating stage before hot rolling, and although the film thickness is reduced by processing in rolling, it remains after rolling and exhibits corrosion resistance.

Next, the reasons for limiting the basic composition range of the H-section steel of 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, and if it is added in excess of 0.15%. Causes significantly lower base metal toughness, weld crack resistance, weld heat affected zone toughness, etc., so the lower limit was made 0.05% and the upper limit was made 0.15%.

Si is necessary for securing the strength of the base metal, pre-deoxidizing molten steel, etc., but if it exceeds 0.50%, high carbon martensite having a hardened structure is formed in the heat affected zone of the weld, and the toughness of the weld joint is improved. Significantly lowers. Further, if it is less than 0.05%, the necessary preliminary deoxidation of molten steel cannot be performed, so that the Si content is set to 0.
It was limited to the range of 05% to 0.50%.

Mn is 0.8 to secure the strength and toughness of the base material.
% Or more is required, but the upper limit was set to 2.0% within the allowable range of the toughness and crackability of the welded portion.

N is an element mixed in steel as an unavoidable impurity and is an element that reduces toughness if it forms an excessive solid solution, so it is desirable to reduce it as much as possible.
If it is less than 03%, the cost for removing N increases and the manufacturing cost increases, so the lower limit was made 0.003%. On the other hand, if it exceeds 0.015%, the toughness of the base material deteriorates and surface cracks occur in the steel slab during continuous casting, so 0.015% was made the upper limit.

Al is a strong deoxidizing element, but 0.00
If the content exceeds 5%, a large amount of oxide is formed in the steel and the toughness is lowered, so the content is made 0.005% or less.

Cr is effective in adding the function of corrosion resistance and strengthening the base material. It is necessary to add 0.5% or more to form an oxide film for satisfying the corrosion resistance. At the same time Cr
Excessive addition of is harmful from the viewpoint of toughness and curability, so the upper limit was made 1.5%. Further, Cu and Ni are added to the steel material having the function of weather resistance, but the respective component ranges are limited to the following.

Cu is an element effective in strengthening the base material and weather resistance, but it is necessary to add 0.3% or more in order to add the function of weather resistance. In addition, considering the temper embrittlement due to stress relief annealing, weld cracking, hot work cracking, etc., the upper limit was made 1.0%.

Ni is an extremely effective element for enhancing 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%.

The amounts of P and S contained as unavoidable impurities are not particularly limited, but since macro-segregation during solidification causes welding cracks and a decrease in toughness, they should be reduced as much as possible. It is less than 0.02 that the amount of S can be reduced to the target amount.

The molten steel produced by the above production method is produced into a slab by a continuous casting machine, and then reheated to a temperature range of 1100 to 1300 ° C. The reason why the reheating temperature is limited to this temperature range is that the manufacturing of shaped steel by hot working requires heating at 1100 ° C or higher in order to facilitate plastic deformation, and from the performance and economical efficiency of the heating furnace. The upper limit was 1300 ° C. Further, the holding time in the temperature range of 1100 to 1300 ° C is 1 to 3
If the time is limited to less than 1 hour, the oxidation reaction time of Cr is insufficient and a dense Cr oxide film is formed on the surface of the steel slab.
The reaction did not proceed until the coating was completed, and the reaction proceeded sufficiently in 3 hours to form Cr oxide inside the steel slab.
This is because the surface of the steel billet cannot be covered with the oxide.

The heated steel material is rolled and formed by the steps of rough rolling, intermediate rolling and finish rolling.

The descaling of the portion corresponding to the outside of the flange in the initial stage of rough rolling is because Cu in the component system of the present invention is segregated on the surface and becomes liquid in the temperature range of rough rolling. This is because the liquid Cu is removed by descaling. If not removed,
Liquid Cu penetrates into grain boundaries during rolling deformation and causes cracking. The rolling end temperature is set to 750 to 1050 ° C. The toughness is improved as the rolling temperature is low, but it is difficult to process at less than 750 ° C. due to the shaping of the shaped steel, and the processing at more than 1050 ° C. has a coarse grain structure. Is generated and the toughness is reduced.

Further, the temperature of the surface layer portion of the steel material is kept below Ar ₃ -20 ° C. and Ar ₃ -1 between rolling passes in the intermediate rolling process.
Water cooling to 00 ° C. or higher, rolling at least once in the recuperating process, and finishing rolling in the temperature range of 750 to 1050 ° C. are achieved by forming a superfine grain structure in the surface layer part by low temperature rolling and subsequent reheating. In addition to the conventional purpose of re-transforming ferrite to austenite and removing work strain, the surface is forcibly cooled during rolling, so that the heat shrinkage of the scale and base steel generated up to that point. Removal of scale by causing strain due to difference in amount, and oxidation reaction of iron due to low temperature of steel surface (scale formation)
The purpose is to suppress.

After finishing rolling, the average cooling rate of the steel material from 700 ° C. to 400 ° C. is 0.5 ° C./s to 10.0 ° C. /
Accelerated cooling within the range of s is not only for improving strength and toughness as a fine-grained ferrite-pearlite structure, as conventionally used, but also for accelerating cooling of the steel surface, This is because it does not give a margin for scale generation.

The average cooling rate is 0.5 ° C./s to 10.
The cooling is performed within the range of 0 ° C./s, and the reason for producing is that accelerated cooling at a cooling rate higher than this cooling rate range increases the structure fraction of the bainite phase and martensite phase, resulting in lower toughness. Material deterioration appears. Further, even if accelerated cooling is performed at a cooling rate lower than this cooling rate range, the effect of lowering the temperature of the surface is no longer observed, and the scale is formed thick. Therefore, the range of the cooling rate described above is set as the optimum cooling rate range.

The scale thickness is not particularly limited,
To obtain a smooth surface texture even after the scale is peeled off, 10
μm or less is desirable.

[0034]

[Example] A prototype shaped steel was melted in a converter, adjusted in composition, and cast into a 240 mm to 300 mm thick ingot by continuous casting.
Heated in the heating furnace 1 having the layout shown in FIG.
After rough rolling in, the first intermediate rolling mill 3 and the second intermediate rolling mill 4 continue to form H-shaped steel having a predetermined size. At this time, if necessary, the temperature of the steel material surface layer portion is set to Ar ₃ −20 ° C. or lower between rolling passes in the second intermediate rolling mill 4, A
It is water-cooled to r ₃ −100 ° C. or higher, rolled at least once in the recuperating process, and finished the intermediate rolling in the temperature range of 750 to 1050 ° C. Then, after finishing rolling, a predetermined cooling rate, that is, 700 ° C. to 40 ° C., is set by a water-cooled accelerated cooling device 6 for steel material installed on the downstream side of the finishing rolling mill 5.
Accelerated cooling is performed so that the cooling rate up to 0 ° C can be ensured within the range of 0.5 ° C / s to 3.0 ° C / s. After cooling, the cooling floor 7 is allowed to cool until the correction of the next step.

The mechanical characteristics are shown in FIG. 2 from the 1/4 width (1 / 4B) of the total length (B) of the flange shaft at the center (1 / 2t ₁ ) of the plate thickness t ₁ of the flange 9 of the H-section steel 8. A test piece was collected and determined. The characteristics of this portion were obtained because the flange 1 / 4B portion shows the average mechanical characteristics of the base metal, so that the mechanical test characteristics of the H-section steel can be represented at this portion.

Further, the evaluation of the surface texture in the present invention was judged by the scale thickness. That is, if the scale thickness of the product is 10 μm or less, it is considered that the surface properties are excellent, and it is indicated by a circle in Table 2 described later.

Regarding corrosion resistance, JIS Z 2381
The outdoor exposure test method was carried out in accordance with the general direct exposure test, and the rust generated during one month was peeled by applying tensile strain, and the rust was compared with that before the exposure.
That is, the amount of rust after exposure is 5% less than that before exposure.
If it is not more than twice, it is considered that the corrosion resistance is excellent, and it is shown by a circle in Table 2 described later.

Further, among the steels excellent in corrosion resistance, if the amount of rust generated after 3 months is less than twice as much as that after 1 month, it is considered that the weather resistance is also excellent, and Table 2 described later. Is indicated by ⊚.

Table 1 shows the chemical composition values of the trial steels, and Table 2
Shows mechanical test characteristics for rolling and cooling conditions. In addition,
The heating temperature is 1280 ° C or 1300 ° C.
Generally, it is well known that reduction of heating temperature improves mechanical properties, and it is estimated that high temperature heating condition shows the lowest value of mechanical properties, and this value can represent the property at heating temperature lower than that. This is because it was determined. In addition, in the composition range shown in Table 1, the Ar ₃ point is between 860 ° C. and 800 ° C.

[0040]

[Table 1]

[0041]

[Table 2]

As shown in Table 2, steels 1 to 6 according to the present invention
Indicates the target base metal strength (JIS G 3106, SM49 mentioned above) at the flange 1 / 4B part which is a part representing the base metal.
0) and the target value of Charpy impact absorbed energy at 0 ° C. (said JIS G 3106, SM490C) 4
Sufficiently satisfies 5 (J) or more. Among them, in the intermediate rolling process, the temperature of the surface layer of the steel material is set to Ar ₃ −20 ° C. or less, Ar ₃ −
Steels 4, 5 and 6 which have been water-cooled to 100 ° C. or higher and rolled at least once in the recuperative process have a smaller scale thickness than steels 1, 2 and 3 which are not water-cooled similarly.

On the other hand, in Comparative Steel 7, the components other than Mn and Cr and the manufacturing conditions satisfied the present invention, but the Mn content was 2.11%, which exceeded the upper limit, so the tensile strength exceeded the target value and was excessive. However, the corrosion resistance is poor because the coating of the steel surface with the Cr oxide film is insufficient. In Steel 8,
Although the components other than Mn and the manufacturing conditions satisfy the present invention, the Mn content is 0.65% and is below the lower limit, and the tensile strength is less than the target value.

Further, in the steels 9 and 10, the Cr contents are 0.27% and 0.46%, respectively, which are below the lower limit value of the present invention, so that the coating of the steel surface with the Cr oxide film is insufficient. Therefore, it is inferior in corrosion resistance.

Although the composition of each of the steels 11, 12, 13, 14, and 15 has been changed within the range of the present invention, the manufacturing method thereof has the following inadequate points. , Does not meet the required characteristics. Ie steel 1
In No. 1, the cooling rate after rolling was 0.4 ° C./s, which was below the lower limit of the present invention, so the scale thickness exceeded 10 μm and smooth surface properties could not be obtained. Steel 12 is 11 at the heating stage
Since the holding time in the temperature range of 00 to 1300 ° C is insufficient, the coating of the steel material surface with the Cr oxide film is insufficient.
Steel 13 has a cooling rate after completion of rolling and 1 at the heating stage.
Since the holding time in the temperature range of 100 to 1300 ° C. is less than the range of the present invention, the scale thickness exceeds 10 μm and a smooth surface property cannot be obtained, and the coating of the steel material surface with the Cr oxide film is insufficient. is there. Further, with Steel 14, the cooling rate after rolling is 0.4 ° C./s, which is below the lower limit of the present invention, so the scale thickness exceeds 10 μm and smooth surface properties cannot be obtained. Since descaling was not performed, a bald defect was generated on the outer surface of the flange. With respect to the steels 15 and 16 as well, since descaling was not performed in the rough rolling stage, a dent defect was generated on the outer surface of the flange.

[0046]

EFFECTS OF THE INVENTION According to the present invention, corrosion resistance is secured by coating a Cr oxide film on the surface of a steel material by an oxidation reaction in the hot rolling and the subsequent cooling process, and the strength, toughness and smoothness of the surface are novel. It has various functions and contains C
u-shaped steel can be manufactured at low cost with less occurrence of bald spots, burn marks, etc. due to red hot embrittlement in u steel, and can improve the reliability of buildings, ensure safety, improve economic efficiency, etc. The effect is extremely remarkable.

[Brief description of drawings]

FIG. 1 is a schematic diagram illustrating an example of a device arrangement row for implementing the present invention.

FIG. 2 is a diagram showing the cross-sectional shape of the H-section steel, showing the name of each part and the sampling position of the 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 material cooling device 7 ... Cooling floor 8 ... H-shaped steel 9 ... Flange

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI technical display location C22C 38/42

Claims (4)

[Claims] 1. By weight%, C: 0.05 to 0.15%, Si: 0.05 to 0.50%, Mn: 0.8 to 2.0%, N: 0.003 to 0.015. %, Al ≦ 0.005%, Cr: 0.50 to 1.50%, Cu: 0.30 to 1.00%, with the balance Fe and unavoidable impurities, and cast into a cast piece by continuous casting. And then re-heating the slab to a temperature range of 1100 to 1300 ° C. for 1 hour or more and less than 3 hours, and then starting rolling, and descaling the portion corresponding to the outer side surface of the flange at the initial stage of the rough rolling step. Finish rolling in the temperature range of 1050 ° C,
Immediately thereafter, accelerated cooling of the steel material from 700 ° C. to 400 ° C. within the range of 0.5 ° C./s to 10.0 ° C./s is accelerated and the high strength H with excellent surface properties is characterized.
Shaped steel manufacturing method. 2. C: 0.05 to 0.15% by weight, Si: 0.05 to 0.50%, Mn: 0.8 to 2.0%, N: 0.003 to 0.015 %, Al ≦ 0.005%, Cr: 0.50 to 1.50%, Cu: 0.30 to 1.00%, with the balance Fe and unavoidable impurities, and cast into a slab by continuous casting. Cast,
The slab is placed in a temperature range of 1100 to 1300 ° C for 1 hour or more 3
Rolling is started after reheating for less than time, and after descaling the portion corresponding to the flange outer surface at the initial stage of the rough rolling process, the temperature of the steel surface layer is set to Ar ₃ between passes in the intermediate rolling process.
Water cooling to −20 ° C. or lower and Ar ₃ −100 ° C. or higher, and rolling at least once in the recuperation process, 750 to 1050
Finish rolling in the temperature range of ℃, and immediately after 7
The average cooling rate of steel from 00 ℃ to 400 ℃ is 0.5
A method for producing a high-strength H-section steel having excellent surface properties, which comprises performing accelerated cooling within a range of ° C / s to 10.0 ° C / s. 3. C: 0.05 to 0.15% by weight%, Si: 0.05 to 0.50%, Mn: 0.8 to 2.0%, N: 0.003 to 0.015 %, Al ≤ 0.005%, Cr: 0.50 to 1.50%, Cu: 0.30 to 1.00%, Ni ≤ 1.00%, with the balance being Fe and inevitable impurities Is cast into a slab by continuous casting, and the slab is
After reheating to a temperature range of 100 to 1300 ° C. for 1 hour or more and less than 3 hours, rolling is started, and the portion corresponding to the flange outer surface is descaled in the rough rolling initial step, and 750 to 1
Finish rolling is performed in the temperature range of 050 ° C., and immediately thereafter, the average cooling rate of the steel material from 700 ° C. to 400 ° C. is set to 0.
A method for producing a high-strength H-section steel having excellent surface properties, which comprises performing accelerated cooling within a range of 5 ° C / s to 10.0 ° C / s. 4. C: 0.05 to 0.15% by weight, Si: 0.05 to 0.50%, Mn: 0.8 to 2.0%, N: 0.003 to 0.015. %, Al ≤ 0.005%, Cr: 0.50 to 1.50%, Cu: 0.30 to 1.00%, Ni ≤ 1.00%, with the balance being Fe and inevitable impurities Is cast into a slab by continuous casting, and the slab is
After reheating to a temperature range of 100 to 1300 ° C. for 1 hour or more and less than 3 hours, rolling is started, and after descaling the portion corresponding to the flange outer surface at the initial stage of the rough rolling step, the steel material surface layer between the passes of the intermediate rolling step. Parts are water-cooled to Ar ₃ -20 ° C or lower and Ar ₃ -100 ° C or higher, rolled at least once in the recuperating process, finish rolling in the temperature range of 750 to 1050 ° C, and immediately thereafter 700. The average cooling rate of the steel material from ℃ to 400 ℃ is 0.5 ℃ / s ~ 1
A method for producing a high-strength H-section steel with excellent surface properties, which comprises accelerating cooling within a range of 0.0 ° C / s.