KR20130059538A - Method for manufacturing formable hot-rolled steel having excellent surface quality and the hot-rolled steel by the same method - Google Patents

Abstract

PURPOSE: A manufacturing method of a hot-rolled steel sheet with excellent surface characteristics and bending resistance is provided to apply a shot blasting process spraying short balls with a size of 0.1-0.4 mm to the surface of the hot-rolled steel sheet at 4-65 m/s. CONSTITUTION: A manufacturing method of a hot-rolled steel sheet with excellent surface characteristics and bending resistance is short-blasted by spraying short balls with a size of 0.1-0.4 mm to the surface of the hot-rolled steel sheet. The hot-rolled steel sheet is made of steel composed of 0.01-0.10 wt.% of C, 0.05-0.3 wt.% of Mn, 0.001-0.020 wt.% of P, 0.020 wt.% or less of S(not including O wt.%), 0.04-0.12 wt.% of Al, 0.001-0.004 wt.% of N, 0.05-0.25 wt.% Sn, and the rest of Fe and other inevitable impurities. The steel is rolled at 860-950 degrees, and then is cooled at 30-100°C/s. The cooled steel is wound at 550-700 degrees. [Reference numerals] (a) Normal ferrite rib; (b) Transformed ferrite rib

Description

Processed hot rolled steel with excellent bending resistance and surface characteristics and manufacturing method {METHOD FOR MANUFACTURING FORMABLE HOT-ROLLED STEEL HAVING EXCELLENT SURFACE

The present invention relates to a method for manufacturing a hot rolled steel sheet for processing having excellent bending resistance and surface characteristics, and a hot rolled steel sheet manufactured by the same. More specifically, a low to medium carbon base having excellent bending resistance and surface characteristics by optimizing a steel component and a manufacturing process. It relates to a method for producing a hot rolled steel sheet and a hot rolled steel sheet produced thereby.

In steel sheets used in household appliances and automobiles, it is necessary to prevent occurrence of machining defects due to aging. Conventionally, materials such as ultra low carbon steel to which carbonitride-forming elements excellent in endurance have been added have been used for suppressing aging processing defects.

In particular, in automobiles, it is necessary to prevent the steel sheet from being oxidized by the external atmosphere condition, and it is also necessary to prevent organic substances such as paint As the coating process is carried out on the surface, the surface property management is becoming a very important factor.

The bending property is also referred to as fluting. Fluting means a phenomenon in which a machined portion is bent into a diamond shape when machining. When fluting is generated, it is difficult to maintain the shape of the formed portion. Should be limited.

However, in general, it is difficult to substantially limit the aging phenomenon due to the solid element which is a cause of the fluting phenomenon. As a result, it is difficult to carry out a high purification treatment in the steelmaking process step or a carbonitride formation such as titanium (Ti), niobium Adding elements, and fixing the hiring elements.

However, the addition of these carbonitride-forming elements contributes to the suppression of machining defects such as fluting, but it also reduces the productivity by increasing the steelmaking process steps for high-cleanliness and increases the manufacturing cost by adding expensive alloying elements There are disadvantages.

In addition, it is known that it is extremely difficult to suppress fluting in the low-carbon carbon steel fundamentally. In the case where rigidity and machinability such as home appliances and automobiles are required, establishment of a plan for suppressing the fluting phenomenon is urgently required .

On the other hand, various processing characteristics such as elongation flangeability, bending property and drawing ability are required not only to prevent flutting caused by the above-mentioned endurance, but also to improve the shape dynamics of the final product and improve the production process and improve the productivity. In addition, since these structures are exposed to the external environment, the surface coating of the steel sheet is performed in order to improve the weatherability. Therefore, in order to secure such processing characteristics, development of a steel sheet for plating,

Japanese Patent Laid-Open No. 1989-282420 discloses "a method for manufacturing a hot-rolled steel sheet for processing and a heat-treating method for a hot-rolled steel sheet ".

This is a method for producing a steel sheet suitable for a high strength member for automobiles or industrial equipment, which comprises adding a titanium (Ti), niobium (Ni) and a rare earth element to an ultra low carbon steel base to produce a hot- And a method for manufacturing the same.

However, as described above, this method is effective for suppressing machining defects such as fluting by addition of carbonitride-forming elements, but it is difficult to reduce the productivity and to add expensive alloying elements by increasing the steelmaking process time for high- Thereby raising the cost of production.

Korean Unexamined Patent Publication No. 1996-23130 discloses a method for producing a hot rolled steel sheet having high aging resistance.

A small amount of zirconium, which is a carbonitride-forming element, is added to the ultra-low carbon aluminum-kilted steel, and Ar ₃ By hot rolling in the temperature range directly above the transformation point to coarsen the ferrite grains. It relates to a method of improving the aging resistance.

However, according to this method, it is necessary to add a special element such as zirconium in order to increase the aging, steelmaking workability is deteriorated, the cost is increased, and the shape freezeability deteriorates as the material strength is lowered. have.

Japanese Patent Laid-Open No. 2008-190008 discloses a "method for producing a hot-rolled steel sheet excellent in endurance."

(P), 0.09% or less of sulfur (P), 0.015% or less of sulfur (S), 0.015% or less of aluminum (Si) (Al) and 0.0005 to 0.015% nitrogen (N), and the remainder is formed by hot-rolling the slab composed of the iron (Fe) and other unavoidable impurities at an average cooling rate of 60 DEG C / , And then subjected to skin pass rolling at an elongation of 0.1 to 1.0% using a small-diameter roll satisfying t / R? 0.0055 (t is the sheet thickness and R is the roll diameter).

However, since this method lowers the coiling temperature to less than 400 ° C, the generation of the low-temperature precipitates differs due to the non-uniformity of the widthwise temperature, and by causing the material deviation, the shape defects, . Further, since the roll diameter is controlled individually according to the thickness of the plate for inducing the surface movable potential, it is difficult to apply it to production of various sizes of materials such as a commercial operation line.

It should be understood that the foregoing description of the background art is merely for the purpose of promoting an understanding of the background of the present invention and is not to be construed as adhering to the prior art already known to those skilled in the art.

Japanese Laid-Open Patent Application No. 1989-282420 Korean Patent Publication No. 1996-23130 Japanese Patent Laid-Open No. 2008-190008

The present invention has been proposed in order to solve such a conventional problem, by adding tin (Sn) in the steel component in the low-low carbon steel, while optimizing the cooling conditions and shot blasting conditions and the like, while ensuring the paintability of the steel sheet, It is an object of the present invention to provide a method for manufacturing a hot rolled steel sheet having excellent bending resistance and surface characteristics capable of suppressing processing defects such as pull rooting, and a hot rolled steel sheet manufactured thereby.

Process for producing a hot-rolled steel sheet for processing excellent in bending resistance and surface properties according to the present invention for achieving this object, by weight, carbon (C): 0.01 ~ 0.10%, manganese (Mn): 0.05 ~ 0.3%, phosphorus (P): 0.001 ~ 0.020%, Sulfur (S): 0.020% or less (excluding 0%), Aluminum (Al): 0.04 ~ 0.12%, Nitrogen (N): 0.001 ~ 0.004%, Tin (Sn): 0.05 ~ 0.25%, the rest is shot blasted by spraying a 0.1 ~ 0.4mm shotball at a speed of 4. ~ 65 m / s on the surface of hot-rolled steel sheet made of steel containing iron (Fe) and other unavoidable impurities It is done.

The steel made of the composition is finish rolled at 860 ~ 950 ℃, the finish rolled steel is cooled at a cooling rate of 30 ~ 100 ℃ / s, the cooled steel is characterized in that wound at 550 ~ 700 ℃ .

The surface roughness index ratio (R _max / R _a ) is 20 to 30 by the shot blasting.

Hot-rolled steel sheet for processing excellent in bending resistance and surface properties according to the present invention for achieving this object, in weight%, carbon (C): 0.01 ~ 0.10%, manganese (Mn): 0.05 ~ 0.3%, phosphorus (P ): 0.001 ~ 0.020%, sulfur (S): 0.020% or less (excluding 0%), aluminum (Al): 0.04 ~ 0.12%, nitrogen (N): 0.001 ~ 0.004%, tin (Sn): 0.05 ~ 0.25% , The remainder is made of steel containing iron (Fe) and other unavoidable impurities, characterized in that the surface roughness index ratio (R _max / R _a ) is formed by 20 ~ 30 by shot blasting treatment.

Deformed ferrite structure generated by the shot blasting process is characterized in that occupying 3 to 10% in the thickness direction of the hot-rolled steel sheet.

The present invention has the advantage of being able to manufacture a high value-added hot rolled steel sheet that can be used for home appliances and automobiles by satisfying the surface characteristics such as bending resistance, workability as well as paintability due to the above technical configuration.

1 is a tissue photograph of the soft-rolled steel sheet according to the present invention,
2 is a characteristic evaluation graph according to the surface roughness index ratio of the hot-rolled steel sheet according to the present invention.

Hereinafter, with reference to the accompanying drawings will be described a hot rolled steel sheet for processing and excellent manufacturing method excellent in bending resistance and surface properties according to an embodiment of the present invention.

The hot rolled steel sheet for processing having excellent bending resistance and surface properties of the present invention satisfies surface characteristics such as bending resistance and workability as well as paintability at the same time and studies and experiments on high value-added hot rolled steel sheet that can be used for home appliances and automobiles. The steel component of the present invention is limited as follows.

Carbon (C) is an element added to improve the strength of the steel sheet and its content is limited to 0.01% to 0.10%.

As the carbon (C) content increases, the tensile and yield strengths increase, but when the content is excessively added in excess of 0.10%, the workability of the material decreases and the bending resistance also decreases.

In addition, if the content is less than 0.01%, additional operation time is required for decarburization during steelmaking, and it is difficult to secure stable materials such as target strength.

Manganese (Mn) is an element that enhances the strength of the steel and improves the hot workability as a solid solution strengthening element, whereas MnS is an element that inhibits the ductility and workability of the material by forming MnS.

If the content of manganese is small, the workability is improved, but it is difficult to secure the strength. Therefore, it is necessary to add 0.05% or more to secure the target strength. On the other hand, excessive addition of manganese not only causes economic deterioration and central segregation, but also deteriorates weldability, so the upper limit is limited to 0.3%.

Phosphorus (P) is an element that serves to improve the strength and corrosion resistance of steel, and it is preferable to add a large amount in order to secure these characteristics. The content is limited to 0.02% or less. On the other hand, if the content of phosphorus is less than 0.001% it is difficult to secure the strength and corrosion resistance is managed to more than 0.001%.

Sulfur (S) combines with manganese (Mn) in the steel to form non-metallic inclusions that serve as a starting point for corrosion, as well as acting as a factor of red brittleness, it is desirable to reduce the content as much as possible. Therefore, the content of sulfur is limited to 0.02% or less (exclusive of 0%), preferably 0.01% or less.

Aluminum (Al) is generally an element added for deoxidation of molten steel, but it has a function of improving the aging characteristics by combining with solid solution elements in steel. Therefore, the lower limit thereof is limited to 0.04%. Not only cause surface defects but also reduce workability. Therefore, the upper limit is preferably 0.12%.

Nitrogen (N) exists in solid solution in steel and is useful for reinforcing the material, but since it is the main element causing aging phenomenon, it is necessary to manage it to a certain amount or less to secure workability. The upper limit thereof is limited to 0.004%. In addition, if it is less than 0.001%, sufficient rigidity cannot be obtained and the site for precipitate formation will decrease, so the lower limit is limited to 0.001%.

Tin (Sn) is an element that exists in solid solution inside the steel to improve high temperature properties and corrosion resistance.

That is, it is heated and oxidized by heat treatment to form an Sn-based oxide such as Sn ₂ O ₃ on the surface of the steel sheet, thereby suppressing the formation of an alloy layer on the surface of the steel sheet, thereby improving the corrosion resistance and discoloration resistance at high temperatures.

In order to obtain such an effect, it is preferable to add 0.05% or more. However, if the content exceeds 0.25%, the disadvantages of higher manufacturing cost and lower rolling property act more than the contribution to improving corrosion resistance or discoloration resistance. Is limited to 0.05 ~ 0.25%.

Hereinafter, a method of manufacturing a hot rolled steel sheet for processing having excellent bending resistance and surface properties according to the present invention using the component controlled steel as described above will be described in detail.

First, in weight percent, carbon (C) 0.01-0.10%, manganese (Mn) 0.05-0.3%, phosphorus (P) 0.001-0.020%, sulfur (S) 0.020% or less (excluding 0%), aluminum (Al) A steel sheet containing 0.04 to 0.12%, nitrogen (N) 0.001 to 0.004%, tin (Sn) 0.05 to 0.25%, residual iron (Fe) and other unavoidable impurities is produced according to a conventional hot rolling process, and Shot blasting is performed on the surface of hot-rolled steel sheet by spraying shot balls of size 0.1 ~ 0.4mm at a speed of 40 ~ 65m / sec.

This shot blasting process is one of the most characteristic technical features of the present invention for securing the bending resistance (aging resistance), by introducing an appropriate compressive stress on the surface of the hot-rolled steel sheet, the dislocation density, especially the movable dislocation density is greatly increased. It is a process to create a new ferrite grain. In other words, the shot blasting process improves the aging resistance by reducing the seizure of dislocations due to the solid solution element, which is the main cause of the aging phenomenon.

In order to achieve this effect, it is preferable to control the size of the shotball used for shot blasting to 0.10 to 0.40 mm.

If the size of the shotball is less than 0.10mm, the mechanical peeling effect of the surface layer is small, so that it is difficult to obtain an appropriate dislocation density increasing effect.If the size of the shotball exceeds 0.40mm, the maximum roughness of the surface rises rapidly and cracks occur during processing. Because it acts as a factor.

On the other hand, the injection speed of the shot blasting is preferably controlled to 40 to 65 m / sec.

If the injection speed is less than 40m / sec, the impact pressure of the shotball acting on the surface layer is low, it is difficult to secure the desired aging resistance, and if it exceeds 65m / sec, the depth of the surface hardened layer is 10% in the thickness direction of the material This is because it causes the uneven processing over.

In order to secure the mechanical properties of the present invention, it is preferable to control the surface roughness index ratio (R _max / R _a ) of the hot rolled steel sheet after the shot blasting process to 20 to 30.

Here, R _max means the maximum point height in the surface roughness curve of the hot-rolled steel sheet, R _a means the center line average surface roughness.

Increasing the surface roughness ratio increases the density of the working potential as the fixation potential in the steel sheet surface layer leaves the Cottrell atmosphere with carbon and nitrogen dissolved in the steel.

If the surface roughness index ratio is less than 20, the appropriate ratio of rough acid and bone is not secured, and thus, the adsorption property of organic matters is lowered, and the density distribution of the working potential for fixing solid solution is insufficient, thus making it difficult to secure aging resistance. On the other hand, if the surface roughness index ratio exceeds 30, the density of the movable potential reaches saturation, but since the tip cracking occurs during processing, it is preferable to set the management range to 20 to 30.

FIG. 1 (a) shows a steady state ferrite grains having a low dislocation density. FIG. 1 (b) shows a transformed structure having a dislocation structure having a high potential density by the short blasting process according to the present invention. Show ferrite lips.

It is preferable that the deformed ferrite structure produced by shot blasting is controlled to occupy 3 to 10% in the thickness direction of the hot-rolled steel sheet so as to ensure proper endurance.

If the strain ferrite structure is less than 3% in the thickness direction, it can not secure the desired antioxidant property because it does not show a structural characteristic capable of sufficiently fixing the solid element in the steel, and the strain ferrite structure is 10% If it exceeds the above range, it acts as a factor of hardening of the material in the processing and post-processing, which causes deterioration of the workability. Therefore, the management range is preferably 3 to 10%.

As described above, by applying a shot blasting process of a predetermined condition to the surface of the steel sheet produced through a conventional hot rolling process, it is possible to produce a hot rolled steel sheet excellent in aging resistance and processing characteristics. Furthermore, by optimizing the hot rolling process, a hot rolled steel sheet having better aging resistance, processability, and paintability can be manufactured. Hereinafter, the optimized hot rolling process will be described in detail.

First, the hot rolled steel sheet according to the present invention is preferably finish-rolled steel made of the composition component at 860 ~ 950 ℃.

If the finish rolling temperature is less than 860 ° C, as the hot rolling is finished in the low temperature region, the crystal grains rapidly progress, resulting in deterioration of the rollability and workability.

On the other hand, when the finish rolling temperature is higher than 950 ° C, uniform hot rolling is not performed throughout the thickness, so that grain refinement is insufficient, resulting in a drop in impact toughness due to grain coarsening, and thus the finish rolling temperature range is 860. It is preferable to manage at -950 degreeC.

In addition, the hot-rolled steel sheet is preferably cooled to the finish-rolled steel at a cooling rate of 30 ~ 100 ℃ per second in a run-out (ROT, Run-out-table).

If the cooling rate in the ROT is less than 30 ° C / s, relatively coarse grains are formed by dynamic grain growth, which causes a decrease in strength and workability.

On the other hand, when the cooling rate is 100 ° C / s or more, it acts as a factor of material variation caused by the widthwise cooling unevenness, so the range of the cooling rate is preferably managed at 30 to 100 ° C / s.

Finally, the hot rolled steel sheet is preferably wound at a temperature of 550 ~ 700 ℃ after cooling in the ROT step.

If the coiling temperature is lower than 550 ° C, the formation behavior of low-temperature precipitates is different due to the width-wise temperature unevenness during cooling and holding, thereby causing material variation, which adversely affects workability.

On the contrary, when the coiling temperature exceeds 700 ° C., as the structure of the final product becomes coarse, problems of workability and corrosion resistance decrease, so the range of the coiling temperature is preferably managed at 550 to 700 ° C.

In order to investigate the technical effect of the method of manufacturing hot rolled steel sheet having excellent anti-aging properties according to the present invention, the following experiment was conducted.

First, the respective steels (three invention steels and three comparative steels) having the composition shown in [Table 1] below were prepared and reheated in a heating furnace at 1250 ° C. for 2 hours, followed by the hot rolling conditions disclosed in [Table 2]. Hot rolling was performed accordingly.

Steel grade Chemical composition (% by weight) C Mn P S Al N Sn Inventive Steel 1 0.022 0.20 0.008 0.006 0.068 0.0020 0.18 Invention river 2 0.039 0.16 0.011 0.010 0.081 0.0029 0.21 Invention steel 3 0.055 0.25 0.010 0.008 0.058 0.0026 0.09 Comparative River 1 0.002 0.21 0.007 0.009 0.046 0.0031 - Comparative River 2 0.041 0.13 0.011 0.003 0.039 0.0065 0.02 Comparative Steel 3 0.114 1.91 0.015 0.008 0.066 0.0031 0.68

division
Used steel grade
Reheating
Temperature (℃)
Wrap-up
Temperature (℃)
Cooling rate
(° C / s)
Coiling temperature
(℃)
Short Ball Size
(mm)
Blasting
Speed (m / s) Inventory 1
Inventive Steel 1 1250 890 40 600 0.25 50 Inventory 2 1250 890 70 650 0.32 60 Inventory 3 1250 890 90 600 0.32 50 Honorable 4 Inventive Steel 2
1250 910 70 600 0.19 50 Inventory 5 1250 910 70 650 0.27 60 Inventory 6 Invention steel 3 1250 890 70 600 0.31 50 Honorable 7 Inventive Steel 1
1250 750 70 600 0.25 50 Honors 8 1250 890 15 600 0.32 50 Proposition 9 Invention river 2 1250 890 70 400 0.31 50 Comparative Example 1 Inventive Steel 1 1250 910 60 650 0.91 90 Comparative Example 2 Comparative River 1 1250 910 60 650 0.16 50 Comparative Example 3 Comparative River 2 1250 910 60 650 0.25 60 Comparative Example 4 Comparative Steel 3 1250 890 60 650 0.25 60

In addition, the physical properties and mechanical properties of the prepared steels were measured and shown in [Table 3].

In Table 3, corrosion resistance after saline spray test with 5% NaCl for 240 hours was determined to be less than 0.05 g / cm ^{2, and} worse than that. The paintability was good when the coating adhesiveness and surface characteristics were excellent among the evaluation items of the coating material, and when only one of the two characteristics was excellent, the case where both characteristics were not good was indicated as defective.

Workability was measured by crack length for the bending test specimen (divided into 5 steps, as shown in Table 4 below), 1 step is good, 2 to 3 steps are normal, 4 to 5 steps are marked as bad.

The bending resistance was classified according to the degree of surface bending after steel sheet processing, and the bending index representing this was divided into five stages, and the first stage, which is relatively insignificant in bending, was good. And, it was determined that the 4 to 5 stages that the bending occurred to the extent that the naked eye can be observed as bad.

According to the above criteria, the experimental results disclosed in Table 3 above are summarized as follows.

division
Surface roughness
Exponent ratio yield point
Extension phenomenon
Elongation (%)
Corrosion resistance
Paintability
Processability
Bending property Inventory 1 21.4 Not occurring 40.1 Good Good Good Good Inventory 2 22.9 Not occurring 39.8 Good Good Good Good Inventory 3 26.2 Not occurring 39.4 Good Good Good Good Honorable 4 23.1 Not occurring 40.8 Good Good Good Good Inventory 5 27.1 Not occurring 39.4 Good Good Good Good Inventory 6 25.6 Not occurring 41.1 Good Good Good Good Honorable 7 26.1 Not occurring 32.4 Good Good usually Good Honors 8 22.9 Not occurring 34.9 Good Good usually Good Proposition 9 21.7 Occur 21.9 Good Good usually Good Comparative Example 1 31.2 Not occurring 17.6 Bad Bad Bad usually Comparative Example 2 36.4 Not occurring 43.4 Bad Bad Bad Good Comparative Example 3 13.9 Occur 27.9 Bad usually Bad Bad Comparative Example 4 16.9 Occur 14.8 Good Good Bad Bad

step Specific criteria Stage 1 No cracks in the bending process area Step 2 Cracks do not occur in the bending portion, but the surface of the portion to be processed is rough Step 3 The number of microcracks on the surface is about 1 to 3 Step 4 If the number of microscopic cracks on the surface is 4 or more or the sum of the total crack length is within 10 mm Step 5 Cracks occur, and the total length of the cracks is 10 mm or more

Inventive Examples 1 to 6 are cases in which both the steel component control, hot rolling process and shot blasting process conditions according to the present invention are satisfied.

In all the invention examples, no yield point stretching occurred, and the surface roughness index ratio (Rmax / Ra) was also within 20 to 30, satisfies the management range and no bending occurred during processing, thereby ensuring excellent aging resistance. . In addition, since no cracking occurs during bending, it exhibits high workability and paintability, thereby making it possible to manufacture excellent hot rolled steel sheets and original plates for plating.

Examples 7 to 9 are cases in which the steel component control (invention steel 1, invention steel 2) and shot blasting process conditions according to the present invention were satisfied, but the hot rolling process was not satisfied.

In more detail, Example 7 performs the finish rolling temperature at 750 ° C. lower than the control range, and Example 8 performs the cooling rate in the ROT process at 15 ° C./s lower than the control range. It is a case where winding temperature is performed at 400 degreeC lower than a control range.

In Examples 7 to 9, some yield point elongation phenomena occurred but still exhibited good endurance. Although the processability was slightly lowered due to crystal grain precipitation, precipitation of solid elements and material variations, it satisfied the high quality requirements, It can be used as a high value added steel sheet for household appliances and automobiles because it has paintability.

Comparative Example 1 satisfied the steel component control (Inventive Steel 1) and hot rolling process conditions according to the present invention, but did not satisfy the shot blasting condition.

More specifically, in the case of shot blasting conditions, the shot ball is 0.91 mm larger than the management range and the shot blasting speed is also performed at 90 m / sec larger than the management range. In this case, the elongation at yield point does not occur, which is good in terms of durability, but the paintability and workability are also lowered due to an increase in surface roughness and an increase in internal hardening layer, which is unsuitable for use as a hot-rolled steel sheet requiring high quality.

Comparative Examples 2 to 4 are cases in which hot steel process conditions and shot blasting conditions according to the present invention are used, but steel grades (comparative steels 1 to 3) that do not satisfy the steel component conditions are used. In most cases, it is difficult to inhibit the draw point stretching phenomenon, so that the endurance property is lowered and the processing and coating properties according to the present invention can not be satisfied due to the occurrence of the bending phenomenon at the time of processing.

In addition, in the case of Comparative Examples 2 and 3 having a low Sn content, the target corrosion resistance could not be obtained because the surface properties could not be secured. In Comparative Example 4, where the Sn content was too high, cracks at the tip end during rolling were not obtained. It also showed a problem that rolling workability is significantly reduced, such as occurs.

Lastly, FIG. 2 is a graph measuring changes in aging resistance (expressed as fluting index) and workability (expressed as cracking sensitivity during processing) according to the surface roughness index ratio using Inventive Steel 1. FIG.

In order to satisfy the desired endurance and processability, it is preferable to manage the fluting index to 2 or less and the crack generation sensitivity to 0.5 or less.

When the control range of the surface roughness index ratio according to the present invention is adjusted to 20 to 30, the fluting index and the crack generation sensitivity show excellent behavior. On the other hand, in the area lower than the upper management range, both the fluting index and the workability index exceed the reference value, and there is a problem that the bending phenomenon and the working crack occur. In the region above the upper management range, the anti- It is possible to confirm the problem that processing cracks occur.

While the present invention has been particularly shown and described with reference to specific embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the following claims It will be apparent to those of ordinary skill in the art.

Claims (5)

By weight%, carbon (C): 0.01 to 0.10%, manganese (Mn): 0.05 to 0.3%, phosphorus (P): 0.001 to 0.020%, sulfur (S): 0.020% or less (excluding 0%), aluminum ( Al): 0.04 to 0.12%, Nitrogen (N): 0.001 to 0.004%, Tin (Sn): 0.05 to 0.25%, the remainder on the surface of hot-rolled steel sheet made of steel containing iron (Fe) and other unavoidable impurities, A method for manufacturing hot rolled steel sheet having excellent bending resistance and surface characteristics, characterized by spraying a shot ball having a size of 0.1 to 0.4 mm at a speed of 4. to 65 m / s.
The method according to claim 1,
The steel having the above composition is finishing rolled at 860 to 950 캜,
The finish rolled steel is cooled at a cooling rate of 30 ~ 100 ℃ / s,
The cooled steel is wound at 550 ~ 700 ℃, characterized in that the excellent bending resistance and surface properties manufacturing method for hot rolled steel sheet.
The method according to claim 1,
The surface roughness index ratio (R _max / R _a ) by 20 to 30 by the shot blasting, characterized in that the excellent bending resistance and surface characteristics manufacturing method for hot rolled steel sheet for processing.
By weight%, carbon (C): 0.01 to 0.10%, manganese (Mn): 0.05 to 0.3%, phosphorus (P): 0.001 to 0.020%, sulfur (S): 0.020% or less (excluding 0%), aluminum ( Al): 0.04 to 0.12%, Nitrogen (N): 0.001 to 0.004%, Tin (Sn): 0.05 to 0.25%, the remainder is made of steel containing iron (Fe) and other unavoidable impurities, Surface roughness index ratio (R _max / R _a ) by 20 to 30, characterized in that the hot-rolled steel sheet for processing excellent in bending resistance and surface properties.
The method of claim 4,
The deformed ferrite structure produced by the shot blasting process occupies 3 to 10% in the thickness direction of the hot rolled steel sheet, hot-rolled steel sheet for processing excellent in bending resistance and surface properties.

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