JPH09272949A - Shape steel having tight scale and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To produce a shape steel with a tight scale having the thickness of a specified value or below and excellent in adhesion on the surface, in a shape steel contg. a specified amt. or above of Si, by incorporating a suitable amt. of Mo, regulating the content of S into a specified level and specifying the conditions of heating, hot rolling, descaling before and after finish rolling, and cooling. SOLUTION: A slab contg., by weight 0.03 to 0.22% C, 0.1 to 035% Si, 0.2 to 0.6% Mn, <0.025% S, 0.003 to 0.09% Al, 0.01 to 0.7% Mo, and the balance Fe is heated at 10000 to 1350 deg.C and is subjected to hot rolling by a rough- intermediate rolling mill. Next it is spayed and bombarded with high pressure water under >=25kg/cm<2> bombarding pressure so as to regulate the number of the bombarding within 5 sec to the same place on the surface of the shape steel to 2 times within 5sec to execute descaling-which is subjected to hot finish rolling at a rolling temp. of 700 to 1000 deg.C at a draft of <=15% by a finish rolling mill, ad the obtd. shape steel is cooled at a rate of 0.5 to 20 deg.C/sec so as to regulate the surface temp. to <=500 deg.C from the finish rolling temp to obtain the shape steel having a tight scale with <=15μm thickness.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention mainly relates to a shaped steel having a tight scale used as a construction material for construction, civil engineering, bridges and the like, and a method for producing the shaped steel.

[0002]

2. Description of the Related Art Shaped steels such as H-shaped steel, I-shaped steel, angled steel and grooved steel which have been conventionally used as building materials for construction, civil engineering, bridges and the like are heated, rough rolled and intermediate rolled. The product is manufactured through a finishing rolling process, a cooling process, and a straightening process.
Generally, in the above hot rolling step and cooling step, scale is generated on the surface of the shaped steel, and if finish rolling is performed in a state where such scale is generated, it may cause deterioration of the quality of the rolled product. Therefore, in general, descaling is often performed before finish rolling. However, scales are also generated in the rolling process by the finish rolling mill and in the cooling process after finish rolling, and a relatively thick scale having a thickness of 30 to 60 μm is generated on the surface of the shaped steel obtained by cooling after the finish rolling. There is.

When a shaped steel having such a relatively thick scale formed on its surface is subjected to, for example, press straightening or roller straightening, when such a relatively thick scale is formed on the shaped steel surface, When the scale is subjected to a bending load during straightening, the scale causes partial peeling, and when left as it is in the atmosphere, red rust occurs, which becomes an obstacle to welding and painting when used as a building material. for that reason,
In the case of shaped steel used for surface coating, it is essential to perform surface cleaning treatment such as shot blasting and brushing after hot rolling and cooling, which has been a factor of increasing manufacturing cost.

To solve such a problem, for example,
In JP-A-1-159348, the surface has a thickness of 10
An H-section steel having a tight scale of μm or less and a method for manufacturing the H-section steel have been proposed. According to the invention of 1 above, in the H-section steel, Al is contained in addition to the general components of C, Si and Mn to prevent surface defects and internal defects, and Cr is contained to improve mechanical properties. , The formation of scale was suppressed, and the oxide of Cr was formed at the interface of the base metal to improve the adhesion of the scale.
It is characterized by being regulated to 01% or less to suppress the generation of FeS during the heat at the interface between the scale and the base metal and prevent the deterioration of the adhesiveness of the scale. The second invention is characterized in that the scale formed on the surface of the H-section steel in the first invention contains 60 to 90% of magnetite (Fe ₃ O ₄ ).
The invention of 3 is for obtaining the H-section steel of the invention of 1 and the invention of 2, wherein the steel slab is heated to 1000 to 1300 ° C. and hot rolled (finish rolling) at 700 to 850 ° C. for H.
The feature is that after the forming of the shaped steel is completed, it is gradually cooled.

However, in the present invention, when Si is more than 0.1%, the produced scale is not a tight scale, and after the finish rolling and cooling, the bending is corrected by the roller straightening machine. In this case, there is a problem that scale peeling occurs under a bending load, and it is hard to say that a shaped steel having tight scale without peeling can be stably manufactured, and there is still room for improvement.

On the other hand, recently, for example, in the case of a structural steel having a high Si content and a high strength, which is used as a building material or a bridge material requiring fire resistance, the adhesion of the scale is increased, and the pretreatment cost before coating is increased. Although there has been a demand for reduction, it is difficult to meet this demand either by the conventional shaped steel made of general steel or the shaped steel of the invention disclosed in Japanese Patent Application Laid-Open No. 1-159348.

[0007]

DISCLOSURE OF THE INVENTION The present invention is a shaped steel made of a high strength steel having a Si content of 0.1% or more, and does not peel off even if the material is finish-rolled and then straightened after cooling and has good adhesion. It is intended to provide a shaped steel having a tight scale in which the tight scale is allowed to remain inexpensively and stably, and a manufacturing method thereof.

[0008]

That is, the present invention is, as the first invention, in% by weight, C: 0.03 to 0.22%,
Si: 0.1-0.5%, Mn: 0.2-1.6
%, S: <0.025%, Al: 0.00
3% to 0.09%, Mo: 0.01 to 0.7%, with the balance being Fe and unavoidable impurities, and having a tight scale with a thickness of 15 μm or less on the surface. The second aspect of the present invention is a shaped steel having a tight scale, wherein C: 0.03 to 0.22 in% by weight.
%, Si: 0.1 to 0.5%, Mn: 0.2 to
1.6%, S: <0.025%, Al:
0.003% to 0.09%, Mo: 0.01 to 0.7
%, With the balance being Fe and unavoidable impurities, the steel slab is heated to 1000 to 1350 ° C. in a heating furnace, hot-rolled by a rough rolling mill and an intermediate rolling mill, and subjected to high pressure before the finish rolling mill. At a collision pressure of 25 kg / cm ² or more, water is jetted and collided so that the number of collisions with the same location on the surface of the shaped steel is 5 or more times within 5 seconds, and descaling is conducted to the finishing rolling mill. At a rolling temperature of 700 to 1000 ° C. and a rolling reduction of 15% or less, the surface temperature of the obtained shaped steel is reduced to 500 ° C. or less at a cooling rate of 0.5 to 20 ° C./sec from the finish rolling temperature. After cooling, the thickness of this shaped steel surface is 1
A method for manufacturing a shaped steel, characterized in that a tight scale of 5 μm or less is generated.

In the present invention, in a high-strength shaped steel containing 0.1% or more of Si, an appropriate amount of Mo is added, and S
The thickness of the surface is 15 μm or less, for example, by limiting the content of 0.025% to a level of 0.025%, and adjusting heating, hot rolling, descaling before finish rolling, and cooling conditions after descaling to appropriate conditions. It is possible to stably and inexpensively provide a shaped steel in which a scale having good adhesion and having no peeling even when subjected to bending correction is generated.

The present inventors have found that the conventional Si content is less than 0.
In the case of a shaped steel made of general steel of 1% or less, for example, the above-mentioned Japanese Unexamined Patent Publication No.
Like the shaped steel of the invention disclosed in JP-A-159348, even if a component such as Cr is contained to form a scale excellent in adhesion to the base iron, the Si content is 0.1% or more. In the case of the shaped steel of (1), there is a problem that it is difficult to make a tight scale due to scale peeling after bending correction by a roller straightening machine, so that the Si content is 0.1
%, The manufacturing conditions for forming a tight scale with excellent adhesion to the base steel were investigated.

As a result, in terms of composition, Mo is contained in an appropriate amount under the condition that the Si content is 0.1% or more.
By controlling the S content to 0.025% or less, and satisfying the descaling conditions before finish rolling in addition to the heating, rolling and cooling conditions, the thickness is 15 μm even when straightened by a straightening machine. It was found that a shaped steel can be obtained in which a tight scale that does not peel even if it is relatively thick remains stable.

FIG. 1 shows the relationship between the thickness of the adhesive scale in the composition of the shaped steel of the present invention and the residual rate of the adhesive scale after the tensile test. The adhesive scale has a thickness of 15 μm or less. Even in the case, the residual rate of the adhesive scale was 90%, which shows that the residual rate of the adhesive scale is high. Here, the tensile test is for imparting a strain equivalent to the strain generated by, for example, bending correction in a roller straightening machine, and the residual ratio of the adhesion scale here is 10
It is represented by the ratio of the area without scale peeling to the total area when a tensile strain of 10% is applied.

The above results show that when the conditions of the present invention are satisfied, if the thickness of the adhesive scale is adjusted to 15 μm or less, even if the straightening of the adhesive scale is carried out, for example, the adhesive scale is slightly peeled. It means that the adhesive scale having a thickness of 15 μm or less can be stably left. In addition, it was also found that when descaling by high-pressure water injection is performed before finish rolling in this type of component steel, the residual rate of the adhesion scale differs depending on the collision pressure and the number of collisions. .

FIG. 2 shows the adhesion scale residual rate after the tensile test when a test piece of a steel material obtained by finish rolling after descaling by the injection of high-pressure water and the collision pressure by the injected high-pressure water. It shows the relationship of the number of collisions. As shown in Fig. 2, high-pressure water has a collision pressure of 25 kg.
/ Cm ² or more, the number of collisions to the same place on the steel surface,
When sprayed and collided under the condition of twice a second, the adhesive scale residual rate becomes 90% or more, and the scale residual rate gradually increases until the impact force of high pressure water reaches the level of 50 kg / cm ^2. To do.

On the other hand, the high-pressure water has a collision pressure of 25
kg / cm ² , the number of collisions is 1 for the same location on the steel surface
When injected and collided under the condition of once per second, the adhesion scale residual rate reaches 60% level, and the adhesion scale residual rate gradually increases until the collision pressure of high-pressure water reaches the 50 kg / cm ² level. Then, the collision pressure rises to 80% level, but compared to the case where the number of collisions is twice per second, the collision pressure is 25%.
In the region of kg / cm ² or more, it is shown that the purpose is achieved only up to the 60-80% level. The present inventors have conceived the present invention based on these findings, and have completed the present invention by repeating various experiments.

[0016]

BEST MODE FOR CARRYING OUT THE INVENTION As described above, the first invention of the present invention is such that, in the component composition, Mo is contained in an appropriate amount and S is contained under the condition that the Si content is 0.1% or more. Is a shaped steel having a tight scale with a thickness of 15 μm or less, which has excellent adhesion to the base steel and is obtained at a low content of 0.025%, and has excellent weldability and paintability, and can be obtained at low cost. And is obtained by the second invention described later.

The composition of the shaped steel of the first invention of the present invention is as follows. (1) The content of C is 0.03 to 0.22%. C needs 0.03% or more to secure the strength,
If it exceeds 0.22%, the weldability is deteriorated.

(2) The Si content is 0.1 to 0.5%. Si is required to be 0.1% or more for deoxidation and securing strength. This Si forms ferrite at the interface between the base metal and the scale by oxidation during heating, and promotes the adhesion between the scale and the base iron, but if it exceeds 0.5%, the thickness of the contact portion with the base iron increases. Too much. Since this scale is not easily plastically deformed, cracks and scale peeling of the scale become noticeable by roller straightening and press straightening.

(3) Mn content is 0.2 to 1.6%
And Mn is essential to secure strength and toughness. In addition, sulfide MnS is generated by a hot reaction of FeS + Mn → MnS + Fe to suppress generation of harmful FeS on the surface of the steel material and in the steel. Therefore, 0.2
% Is required. If it exceeds 1.6%, not only the weldability is deteriorated but also the machinability is deteriorated, which is not preferable. It is contained at a normal level in order to improve deoxidation, desulfurization and hardenability.

(4) The content of Al is 0.003 to 0.
Restrict to 09%. Al has a great effect as a deoxidizing agent in the refining process, and is required to be 0.003% or more in order to prevent surface defects and internal defects of the cast slab. If it exceeds 0.09%, Al ₂ O ₃ -based inclusions and clusters frequently occur and the internal quality deteriorates.

(5) The Mo content is 0.01 to 0.7.
%. Mo improves temper embrittlement, promotes the formation of irregularities at the interface between the base steel and the scale, and enhances the wedge-like action (anchor effect) of the scale entering the interface of the base steel.
0.01% in order to promote the adhesion between base steel and scale
The above is necessary. This Mo is expensive, and if it exceeds 0.7%, the increase in the effect is improved to some extent, but it is not preferable because the manufacturing cost becomes large.

(6) The S content is restricted to 0.025% or less. S produces FeS at the interface between scale and base steel,
0.025%, which hinders scale adhesion.
If it exceeds, the inhibition of scale adhesion becomes significant.

The second invention is a method for manufacturing a shaped steel characterized by the first invention, and in this manufacturing method, as conditions for finally leaving a scale having a thickness of 15 μm or less on the surface of the shaped steel. , Heating and hot rolling conditions of the billet of the above component composition, descaling conditions before finish rolling,
The cooling conditions after this descaling are specified as follows.

(1) The heating temperature of the steel slab in the heating furnace is 10
The temperature is set to 00 to 1350 ° C. This heating temperature is an important requirement for smooth hot rolling and generation of tight scale in the surface layer. Below 1000 ° C, the rolling load becomes excessive and the rolling mill burden increases, and the universal rolling mill is If it is used, the shape will be insufficiently filled, and it will be difficult to stably secure a desired rolled shape. Moreover, the formation of a scale having excellent adhesion to the base steel becomes insufficient. Above 1350,
In addition to the cost increase due to an increase in heat intensity, the yield decrease due to excessive generation of scale becomes noticeable and the descaling load increases.

(2) Finish rolling temperature is 700 to 1000
° C. In the final rolling, the final shape accuracy is ensured by light-load rolling, but if the temperature is less than 700 ° C., the rolling load becomes excessive, the load on the rolling mill increases, and it becomes difficult to ensure the desired accuracy of the rolling shape. Above 1000 ° C, in addition to the cost increase due to the increase of the heat consumption per unit in finish rolling, the yield decreases due to the excessive generation of scale, and
This is not preferable because the descaling load increases.

(3) The reduction ratio of finish rolling is 15% or less. In finish rolling, the scale at the interface between the base steel and the scale is eroded into the surface of the base steel to improve the adhesion of the scale to the base steel, but if the reduction ratio exceeds 15%, the load on the rolling mill becomes large and the dimensional accuracy is improved. It is not preferable because it worsens.

(4) Descaling before finish rolling This descaling removes fragile scales other than the scale closely adhered to the steel at the interface between the steel and the scale produced in the hot rolling stage before finish rolling. The thickness of the adhered scale is reduced to 15 μm or less, and the scale peeling is suppressed thereafter.

The collision pressure at the time of descaling is 25 to
It is preferable that the number of collisions is 70 kg / cm ² , and the number of collisions is two or more times within 5 seconds with respect to the same place on the surface of the shaped steel. When a gap of 5 seconds or more is opened between the first collision and the second collision, a new scale is generated in the meantime, and the propagation of the second collision force for eliminating the initial weak scale is hindered, The descaling effect due to the second collision will fade. In this case, the peeling rate of the fragile scale is about 70%
This weakness scale remains insufficiently removed.

If the collision pressure is less than 25 kg / cm ² , the descaling effect is insufficient, and if it exceeds 70 kg / cm ² ,
Since the descaling cost burden becomes excessive with respect to the increase in the descaling effect, it is hard to say that it is very preferable. The descaling effect is not sufficient if the number of collisions is only once within 5 seconds with respect to the same place on the section steel surface. However, when the number of collisions is increased to 6 times or more within 5 seconds, the facility cost and the maintenance cost become excessive. Therefore, the number of collisions is set in consideration of the descaling effect and the cost burden. The above-mentioned collision pressure can be applied by high-pressure water jetting or electrical, hitting with a mechanical hammer, etc., but it is advantageous to give it by high-pressure water jetting that can be obtained at low cost and can simultaneously peel and remove the scale. is there.

The collision pressure P obtained by injecting high-pressure water is
For example, it can be obtained by using a collision force estimation formula derived by the momentum conservation law and the mass conservation law (continuity equation). It is also possible to obtain the value by actually measuring with a load cell or the like and substituting the operating condition satisfying this. P = {ρ ^0.5 * C ₃ * / (2 * 2 ^0.5 * tan α * tan β)} * P ₀ ^0.5 * Q * H ^-2 * sin ² γ ... ... (1) P: Collision pressure (kg / cm ² ) ρ: Fluid density (kg / m ³ ) C ₃ : C ₃ = C ₁ * C ₂ = 0.9 C ₁ : Pressure in the nozzle Velocity coefficient due to loss (0.95 <C ₁ <1.0) C ₂ : Jet deceleration coefficient due to air resistance (0.90 <C ₂ <1.0) α: Spread angle in jet width direction (degrees) → ( (See Fig. 3-a) β: Spread angle in the jet thickness direction (degrees) → (See Fig. 3-b) γ: Nozzle orientation angle (°) → (See Fig. 3-c) P ₀ : Header pressure (kgf / cm) ² ) Q: Liquid flow rate of the nozzle (liter / min) H: Distance between the tip of the nozzle and the surface of the material to be descaled (mm) where C ₃ = 0.9 and β is considered to be about 1 degree Then It is equal to or less than the as. P = 30.4 * P ₀ ^0.5 * Q * sin ² γ / (H ⁻² tan α) (2) The collision force P can also be obtained by actually measuring with a load cell or the like.

In the present invention, the collision pressure P at the time of high-pressure water injection / collision on the surface of the shaped steel is determined as described above, and the collision pressure P is set to 25 kg / cm ² or more, and the same on the surface of the shaped steel. The number of collisions with a place within 5 seconds is set to be two or more.

Regarding the number of collisions of the high-pressure water, generally, when the shaped steel is in a running state, a. b A rotary injection nozzle is provided. When the shaped steel is in a stationary state: a) High-pressure water is intermittently injected (including strength / weakness switching injection) using mechanical and electrical means. In such a method, it can be controlled by the arrangement conditions of the injection nozzles and the line speed, but the line speed is often fixed within a certain range depending on the rolling conditions. Therefore, depending on the line speed, the number of collisions is 5 seconds in advance. Arrangement conditions of the ejection nozzles are set so that the number of injection nozzles is two or more.

(5) Cooling after finish rolling In the temperature range of finish rolling temperature to 500 ° C., 0.5 to
Cool at a cooling rate of 20 ° C./sec. After this finish rolling 5
In the temperature range up to 00 ° C, when the cooling rate is higher than 20 ° C / sec, in the shaped steels having different thicknesses in cross section, the thermal stress force increases, so that the shaped steel is deformed in a wave shape and the shape is impaired. At the same time, scale peeling occurs on the surface during deformation, which is not preferable. Further, at a cooling rate of less than 0.5 ° C./sec, the scale grows and the thickness thereof exceeds 15 μm because the time to 500 ° C. becomes long, which is not preferable. The cooling after cooling to 500 ° C. may be natural cooling because the growth of scale is so small that it can be ignored.
By satisfying the above conditions, a tight scale having a thickness of 15 μm or less, which is excellent in adhesion to the base steel,
A shaped steel having excellent mechanical properties, weldability and paintability can be manufactured inexpensively and stably.

Shaped steel for carrying out the present invention (here, H
The hot-rolling equipment (example) of shaped steel is generally configured as shown in FIG. In FIG. 4, 1 is a billet, and 1 is a heating furnace 2.
After being heated in the temperature range of 000 to 1350 ° C., the rough rolling mill 3, the intermediate universal rolling mill 4 and the edger rolling mill 5 are used.
(The paired rolling mills 4 and 5 are hereinafter referred to as "intermediate rolling mill 5t".
Is abbreviated) to form an H-shaped steel 1s having an intermediate shape, and a finish universal rolling machine (hereinafter abbreviated as “finishing rolling machine”) 7 finish-rolls it into an H-shaped steel 1p.
In the present invention, between the intermediate rolling mill 5t and the finishing rolling mill 7, high-pressure water 9 is applied to the surface of the H-section steel 1s by the high-pressure water injection device (descaling device) 6 at a collision pressure of 25 kg / cm ² or more. After the descaling by jetting and collision so that the number of collisions is two or more within 5 seconds, the finish rolling mill 7
Lead to.

With this finish rolling mill, 700 to 1000 ° C.
After performing hot finish rolling with a rolling reduction of 15% or less in the temperature range of 1 to form H-section steel 1s into 1p, the cooling device 8 cools the finish rolling temperature at a cooling rate of 0.5 to 20 ° C./sec.
Cool to below ° C. After cooling, a sawing machine (not shown) measures the length to a predetermined length and guides it to a straightening machine (not shown) to correct the bend and commercialize it as H-section steel.

Here, it is arranged in front of the finish rolling mill 7,
The injection holes of the injection nozzle 6n of the high-pressure water injection device 6 are arranged toward the surface of the H-section steel 1s immediately before being inserted into the finish rolling mill 7. The jet nozzle 6n has a plurality of slit-shaped jet holes ha, hb arranged conceptually, for example, as shown in FIG. 5 (a) or 5 (b) on the high-pressure water jetting surface. .

A plurality of the jet nozzles 6n are used, and conceptually, as shown in FIG. 6 (a), high pressure water is jetted and made to collide with the entire surface of the flange f of the H-section steel 1s and the web w. Is arranged as. In this case, this injection nozzle 6
n may be further divided, or as shown in FIG. 6B, a plurality of rows may be arranged in the traveling direction of the H-section steel 1s, for example, two rows of 6n row and 6n1 row. In addition, the injection nozzle 6n
May be arranged in a plurality of rows in the width direction of the H-section steel 1s.

The number of collisions with the high-pressure water 9 can be set by the arrangement condition of the injection holes ha and hb of the injection nozzle 6n and the line speed condition. The high-pressure water 9 jetted from the jet nozzle 6n is obtained by filtering industrial water with a filtering device (not shown), and is usually at room temperature. The high-pressure water 9 is supplied from the supply source 10 to the high-pressure water injection device 6 via the high-pressure pump 11, and is injected from the injection holes ha and hb of the injection nozzle 6n onto the surface of the H-section steel 1s immediately before being inserted into the finish rolling mill 7. Is jetted. This injection nozzle can adjust the distance h with respect to the surface position of the H-shaped steel 1s.

The present invention is characterized by controlling (or setting) the collision pressure and the number of collisions by the high-pressure water 9 injected from the injection nozzle 6n of the high-pressure water injection device 6 within a predetermined range. Therefore, the output control device 1 of the high-pressure pump 11 that controls the supply of the high-pressure water 9 that influences the collision pressure.
2 and a position control device 13 for the injection nozzle 6n, and an arithmetic device 14 for arithmetically controlling these control devices. Here, the collision force of the high-pressure water 9 is set to 25 kg / cm ² or more in advance. The supply conditions of the high-pressure water 9 and the injection nozzle 6n
The height, angle, etc. are set. Further, the number of collisions is influenced by the line speed, so here, in consideration of the line speed in advance, high-pressure water is injected and collided twice or more within 5 seconds at the same place on the surface of the shaped steel. As described above, the arrangement conditions of the injection holes ha and hb of the injection nozzle 6n are set.

The present invention is also characterized in that the cooling conditions of the H-section steel 1p after finish rolling are controlled (set). For that purpose, a cooling device 8 is arranged at the subsequent stage of the finish rolling mill 7, and is connected to a computing device 14 via a cooling control device 15 to set preset cooling conditions, a line speed meter 16, and an exit side of the finishing rolling mill. Based on the measurement information from the thermometer 17 and the cooling device outlet side thermometer 18, the cooling water supply condition from the cooling water supply device 19 is arithmetically controlled via the calculator 14, and the H-section steel 1p after finish rolling is calculated. Is cooled under predetermined conditions.

The collision pressure and the number of collisions of the high-pressure water at the time of descaling, and the cooling conditions after finish rolling may be initialized according to the rolling target and rolling conditions, or rolling conditions (rolling temperature, rolling reduction, On-line control may be performed according to changes in the rolling speed and the like. In addition, in the present invention, the temperature of the heating furnace, the finish rolling temperature, and the rolling reduction are also constituent factors, but the mechanism for controlling these is general, and therefore the description thereof is omitted here.

The present invention can be carried out by using the hot-rolling equipment (example) for shaped steel configured as described above. The shaped steel obtained by the present invention has good adhesion between the base steel and the scale, and the scale does not peel even if strain of 10% level, such as straightening and bending with a straightening machine, is applied. There is little concern that red rust will occur, and there is no concern of impairing weldability and paintability.

The present invention is not limited to the above embodiment. For example, the target is not limited to H-section steel, but various types of section steel (channel steel, I-section steel, chevron steel, C-section steel, etc.), bar steel (rail, bar steel, etc.), flat steel, etc. The type of rolling mill, the type of high-pressure water jet device, the structure, the arrangement, the number of arrangements, the control mechanism, the control conditions, etc. are changed according to the rolling target, process arrangement, rolling conditions, etc. It is something.

[0044]

EXAMPLE A hot rolling equipment for H-section steel equipped with a high-pressure water injection device 6 and a cooling device 8 as shown in FIGS.
Under the conditions satisfying the conditions specified in the second invention of the present invention,
Heating and hot rolling are performed, and the surface temperature before final finishing rolling is in the temperature range of 700 to 1000 ° C. In the temperature range of 700 to 1000 ° C., descaling is performed by controlling the impact force and the number of collisions using a descaling device by high-pressure water injection. Finished rolling and cooling under conditions satisfying the conditions specified in the second aspect of the invention result in a thickness of 1
An H-section steel for general structure having a scale of 5 μm or less (component composition is shown in Table 1) was manufactured.

A test piece prepared by cutting the web portion and the flange portion of the H-section steel into a piece having a width of 40 mm and a length of 300 mm was subjected to a tensile test to evaluate the adhesion of the scale. The execution conditions and evaluation results of this example are shown in Table 2 in comparison with the case of the comparative example outside the scope of the present invention.

[0046]

[Table 1]

[0047]

[Table 2]

As shown in Table 2, examples (No. 1, No. 1, No. 1, No. 1, No. 1, No. 1, No. 1, No. 1, No. 1, No. 1, No. 1, No. 1, No. 1, No. 1, No. 1, No. 2, No. 1, No. 2, No. 2, and No. 2, No. 1) in which the component composition, descaling conditions (collision pressure, number of collisions), finish rolling temperature and reduction ratio conditions, and cooling conditions are within the scope of the present invention. 2, 3, 4, 5, 18, 19, 20, 21,
22, 23, 24, 25, 26), the scale thicknesses are all 15 μm or less, and the scale adhesion after the tensile test shows that the scale remains in an area ratio of 90 μm.
% Or more, which was quite satisfactory.

On the other hand, a comparative example in which the descaling conditions, finish rolling temperature and reduction conditions, and cooling conditions are within the scope of the present invention, but the Mo content is less than the lower limit of the present invention in the component composition ( In Comparative Example (No. 6) in which the Si content exceeds the upper limit of the present invention and the Mo content is less than the lower limit of the present invention, the scale thickness is 15 μm or less, but the scale after the tensile test is Regarding the adhesiveness, it cannot be said that the area ratio in which the scale remains is less than 90%, which is not sufficiently satisfactory.

The composition, the number of collisions among the descaling conditions, the finishing rolling temperature and the reduction ratio condition, and the cooling condition are within the scope of the present invention, but the collision pressure among the descaling conditions is less than the lower limit of the present invention. Comparative Example (No. 8, 9,
10, 11, 12), the scale thickness is 15
In some cases, the scale adhesion after the tensile test exceeded 90 μm and the area ratio in which the scale remained was less than 90% and less than 75%, which was not satisfactory.

The component composition, the collision pressure among the descaling conditions, the finishing rolling temperature and the reduction ratio condition, and the cooling condition are within the scope of the present invention, but the number of collisions among the descaling conditions is the lower limit of the present invention. Less than, Comparative Example (No. 1
3, 14, 15, 16, 17), the scale thickness exceeds 15 μm, and the scale adhesion after the tensile test shows that the scale remaining area ratio is 7%.
It was unsatisfactory at 5% or less.

[0052]

EFFECTS OF THE INVENTION In the present invention, in terms of composition, the content of Si is 0.1 to 0.1 in the composition of general shaped steel.
In the 0.5% region, Mo is contained in an amount of 0.01 to 0.7% and the S content is. A tight scale with a thickness of 15 μm or less and excellent adhesion to the base steel can be obtained by controlling the content to be 025% or less, and appropriately adjusting the heating, hot rolling, descaling after finish rolling, and cooling conditions. Thus, it is possible to inexpensively and stably manufacture shaped steel having excellent mechanical properties, weldability, and paintability.

[Brief description of drawings]

FIG. 1 is a conceptual explanatory view showing the relationship between the thickness of an adhesion scale formed on the surface of a steel material and the residual rate of the scale after a tensile test.

FIG. 2 is a conceptual explanatory view showing the relationship between the collision pressure and the number of collisions due to the injection of high-pressure water, and the scale residual rate of the steel material surface after the tensile test.

FIG. 3 is a conceptual explanatory view showing a height h and angles α, β, γ of a high-pressure water jet nozzle for obtaining a collision force by jetting high-pressure water.

FIG. 4 is a side view conceptual diagram showing an arrangement example of a hot-rolling equipment for shaped steels embodying the present invention.

5 is a plan conceptual explanatory diagram showing an example of the arrangement of injection holes on the injection surface of the injection nozzle of the high-pressure water injection device (descaling device) used in FIG.

6A is a front conceptual explanatory view showing an arrangement example (for H-shaped steel) of the high-pressure water injection nozzle used in FIG. 4, and FIG. 6B is a plan conceptual explanatory view of FIG.

[Explanation of symbols]

1 billet 1s H-shaped steel with intermediate shape 1p H-shaped steel 2 Heating furnace 3 Rough rolling mill, 4 Intermediate universal rolling mill 5 Edger rolling mill 5t Intermediate rolling mill (paired intermediate universal rolling mill and edger rolling mill) 6 High-pressure water injection device (descaling device) 6n, 6n1 injection nozzles ha, hb injection holes 7 finishing rolling mill 8 cooling device 9 high-pressure water 10 water supply source 11 high-pressure pump 12 output control device 13 injection nozzle control device 14 arithmetic unit 15 cooling Control device 16 Line speed meter 17 Finishing mill output side thermometer 18 Cooling device output side thermometer

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[Procedure amendment]

[Submission date] June 28, 1996

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0030

[Correction method] Change

[Correction contents]

The collision pressure P obtained by injecting high-pressure water is
For example, it can be obtained by using a collision force estimation formula derived by the momentum conservation law and the mass conservation law (continuity equation). It is also possible to obtain the value by actually measuring with a load cell or the like and substituting the operating condition satisfying this. P = {ρ ^0.5 * C ₃ / (2 * 2 ^0.5 * tan α * tan β)} * P ₀ ^0.5 * Q * H ⁻² * sin ² γ ... (1) P: Impact pressure (kg / cm ² ) ρ: Fluid density (kg / m ³ ) C ₃ : C ₃ = C ₁ * C ₂ = 0.9 C ₁ : Pressure loss in the nozzle Velocity coefficient (0.95 <C ₁ <1.0) C ₂ : jet deceleration coefficient due to air resistance (0.90 <C ₂ <1.0) α: jet width direction spreading angle (degrees) → (Fig. 3-a) β: Spread angle in jet thickness direction (degree) → (see Fig. 3-b) γ: Nozzle orientation angle (deg) → (see Fig. 3-c) P ₀ : Header pressure (kgf / cm ² ) Q: Liquid flow rate of the nozzle (liter / min) H: Distance between the tip of the nozzle and the surface of the material to be descaled (mm) where C ₃ = 0.9 and β is considered to be about 1 degree. , P Is as follows. P = 30.4 * P ₀ ^0.5 * Q * sin ² γ / (H ⁻² tan α) (2) The collision force P can also be obtained by actually measuring with a load cell or the like.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI Technical display location C21D 9/00 102 9352-4K C21D 9/00 102Z 9352-4K 102B C22C 38/12 C22C 38/12 (72) Inventor Koichi Yamamoto 1 Tsukiko Yawatacho, Sakai City, Osaka Prefecture Nippon Steel Works Sakai Works Co., Ltd.

Claims (2)

[Claims] 1. By weight%, C: 0.03-0.22%, Si: 0.1-0.5%, Mn: 0.2-1.6%, S: <0.025%, Al: 0.003 to 0.09%, Mo: 0.01 to 0.7%, the balance being Fe and unavoidable impurities, and having a tight scale with a thickness of 15 μm or less on the surface. Shaped steel with a characteristic tight scale. 2. By weight%, C: 0.03-0.22%, Si: 0.1-0.5%, Mn: 0.2-1.6%, S: <0.025%, A steel slab containing Al: 0.003 to 0.09%, Mo: 0.01 to 0.7% and the balance of Fe and unavoidable impurities was heated to 1000 to 1350 ° C. in a heating furnace, Hot rolling with a rolling mill or an intermediate rolling mill, and before the finishing rolling mill, the high-pressure water has a collision pressure of 25 kg / cm ² or more, and the number of collisions with the same location on the surface of the shaped steel within 5 seconds is 2 or more times. So that it may be injected and collided to be descaled and guided to a finishing rolling mill, where hot finishing rolling with a rolling temperature of 700 to 1000 ° C and a rolling reduction of 15% or less is performed, and the surface temperature of the obtained shaped steel Is cooled from the finish rolling temperature to 500 ° C. or less at a cooling rate of 0.5 to 20 ° C./sec to obtain a thickness on the surface. Is 15μ
A method for producing a shaped steel, characterized in that a tight scale of m or less is generated.