WO2013081224A1 - Method for manufacturing hot rolled steel sheet having good anti-aging properties and hot rolled steel sheet manufactured using same - Google Patents

Abstract

The object of the present invention is to provide a method for manufacturing a hot rolled steel sheet having confirmed anti-aging properties for restraining processing defects, such as fluting, along with workability and paintability resulting from the optimization of steel components, manufacturing processes, shot blasting conditions, etc., and to provide a hot rolled steel sheet manufactured using same. In order to accomplish said object, the method for manufacturing the hot rolled steel sheet according to the present invention includes shot blasting, with shot balls having a size of 0.10 to 0.40 mm at a blasting spray rate of 40 to 65 m/sec, the surface of a hot rolled steel sheet manufactured by using steel including 0.01 to 0.12% by weight of carbon (C), 0.1 to 0.5% by weight of manganese (Mn), 0.025% by weight or less of phosphor (P) (excluding 0%), 0.02% by weight or less of sulfur (S) (excluding 0%), 0.03 to 0.15% by weight of aluminum (Al), 0.0005 to 0.0020% by weight of boron (B), 0.01 to 0.05% by weight of cobalt (Co), 0.002 to 0.008% by weight of nitrogen (N), and iron (Fe) and inevitable impurities as the remainder.

Description

Method for manufacturing hot rolled steel sheet having excellent aging resistance

The present invention relates to a method for producing a hot rolled steel sheet excellent in aging resistance and a hot rolled steel sheet manufactured thereby, and more particularly, to a method for manufacturing a hot rolled steel sheet for coating having excellent aging resistance and workability by optimizing a steel component and a manufacturing process. It is about.

In order to be used as steel sheets for home appliances and automobiles, excellent aging resistance (flute resistance), processability, paintability, and the like are required.

Fluting refers to a phenomenon in which a processing part is bent at the time of processing, and since fluctuation occurs, it is difficult to maintain the shape of the molding part, so it must be strictly limited in the actual process.

However, in general, the aging phenomenon due to the employment element that causes the fluting phenomenon is practically difficult to be suppressed to achieve high cleanness at the steelmaking stage and to fix these solid elements with titanium (Ti) and niobium (Nb). Carbonitride-forming elements such as) are added and precipitated. The addition of these carbonitride-forming elements is helpful for suppressing processing defects such as fluting, but it is a factor of lowering productivity due to increased steelmaking time for high clarity and increasing production cost by adding expensive alloying elements.

In addition, it is known that in low and medium carbon steels, it is difficult to suppress the bending phenomenon such as fluting. Therefore, when strict shape freezeability and processability are required, such as home appliances and automobiles, there is a demand for the establishment of a method capable of suppressing the bending phenomenon during processing.

On the other hand, in order to improve the shape freezing properties and improve the manufacturing process to increase productivity, not only the fluting prevention by the above-described aging resistance but also various processing characteristics such as elongation flangeability, bending property, and drawing property are required. . In addition, since these structures are exposed to the external environment, work is performed to paint organic materials such as paint on the surface of the steel sheet to improve weather resistance. Therefore, development of plating steel sheet capable of securing paintability in terms of materials is required to secure such characteristics. It is becoming.

For example, Japanese Laid-Open Patent Publication No. 1989-282420 (name of the invention: a manufacturing method of a hot rolled steel sheet for processing and a processing heat treatment method of a hot rolled steel sheet) is a method for producing a steel sheet suitable for a high strength member for automobile or industrial equipment. A method for producing a hot rolled steel sheet excellent in workability and aging is disclosed by adding titanium (Ti), niobium (Nb) and some rare earth elements to a low carbon steel base. However, this method helps to suppress processing defects such as fluting by the addition of carbonitride forming elements, as described above, but increases the production cost by increasing the steelmaking time for high clarity and the addition of expensive alloying elements. There was a problem.

As another example, Korean Patent Laid-Open Publication No. 1996-23130 (name of the invention: a method for manufacturing a high-temperature hot rolled steel sheet having excellent aging resistance) adds a trace amount of zirconium, a carbonitride-forming element, to ultra-low carbon aluminum-kilted steel, A method of improving the aging resistance by hot rolling in the temperature range directly above the Ar ₃ transformation point to coarsen the ferrite grains is disclosed. However, according to this method, it is necessary to add special elements such as zirconium in order to increase the aging, which not only causes deterioration of steelmaking workability and cost increase, but also deteriorates shape freezeability due to low material strength. .

As another example, Korean Patent Laid-Open Publication No. 2001-60648 (name of the invention: a method of manufacturing a hot rolled steel sheet having excellent resistance to ageing and uniform stretching) has a weight% of carbon (C): 0.02 to 0.05%, manganese (Mn) : 0.10 to 0.30%, boron (B): 10 to 30 ppm, phosphorus (P): 0.020% or less, sulfur (S): 0.015% or less, aluminum (Al): 0.01 to 0.04%, nitrogen (N): 40 ppm or less After reheating the steel slab composed of residual iron (Fe) and other unavoidable impurities, it is hot rolled to a finish rolling temperature of more than Ar ₃ transformation point to a thickness of 1.4 to 2.3 mm and wound at a temperature of 600 to 700 ° C. And a method in which uniform stretching characteristics can be improved. However, it is difficult to expect high aging resistance because it is not possible to completely prevent aging due to solid elements such as carbon and nitrogen contained in steel only by adding a very small amount of boron and controlling the coiling temperature as in this method. There was this.

As another example, Japanese Laid-Open Patent Publication No. 2008-190008 (name of the invention: a method for manufacturing a hot rolled steel sheet having excellent aging resistance) in weight%, carbon (C): 0.04-0.25%, silicon (Si): 0.001- 0.5%, manganese (Mn): 0.05-1.5%, phosphorus (P): 0.09% or less, sulfur (S): 0.015% or less, aluminum (Al): 0.01-0.08%, nitrogen (N): 0.0005-0.015% And slab of a component consisting of residual iron (Fe) and other unavoidable impurities, hot rolled, cooled to less than 400 ° C. at an average cooling rate of 60 ° C./s or more, and then wound by t / R ≧ 0.0055 (t The method of performing skin pass rolling of 0.1-1.0% of elongation rate using the small diameter roll which satisfy | fills R is a roll diameter) is disclosed. However, since this method lowers the coiling temperature to less than 400 ° C, the low temperature precipitates show a difference in the production behavior due to the nonuniformity of the width direction, causing material variation, thereby deteriorating shape defects, winding defects and post-process workability. there was. In addition, since roll diameters must be controlled in accordance with the thickness of the plate to induce surface operating potential, it is difficult to apply when producing various sizes of materials such as commercial operation lines.

The present invention has been proposed to solve such a conventional problem, by adding cobalt (Co), boron (B) in the steel components and at the same time optimizing the manufacturing process and shot blasting conditions, as well as workability and coating It is an object of the present invention to provide a hot rolled steel sheet and a hot rolled steel sheet manufactured thereby, which can be improved.

Method for producing a hot-rolled steel sheet excellent in aging resistance according to the present invention for achieving the above object, by weight, carbon (C) 0.01 ~ 0.12%, manganese (Mn) 0.1 ~ 0.5%, phosphorus (P) 0.025% Or less (excluding 0%), sulfur (S) 0.02% or less (excluding 0%), aluminum (Al) 0.03 to 0.15%, boron (B) 0.0005 to 0.0020%, cobalt (Co) 0.01 to 0.05%, nitrogen (N ) Shot blasting at the surface of hot rolled steel sheet made of steel containing 0.002 ~ 0.008%, balance iron (Fe) and other unavoidable impurities, 0.10 ~ 0.40mm, blasting speed 40 ~ 65m / sec It consists of.

In addition, it is preferable that the components of the steel satisfy 3.5 ≦ [(B (ppm) × Al (%) × Co (%)) / N (%)] ≦ 18.

In addition, the hot-rolled steel sheet is the finish rolling of the steel made of the composition at 860 ~ 950 ℃, and cooling the finish rolled steel at a cooling rate of 30 ~ 100 ℃ per second, after the cooling at a temperature of 580 ~ 680 ℃ It is desirable to take

In addition, it is preferable that the surface roughness index ratio (Rmax / Ra) is 12 to 23 by the shot blasting.

On the other hand, the hot-rolled steel sheet excellent in aging resistance prepared according to the present invention, by weight%, carbon (C) 0.01 ~ 0.12%, manganese (Mn) 0.1 ~ 0.5%, phosphorus (P) 0.025% or less, sulfur (S) 0.02% or less, aluminum (Al) 0.03 to 0.15%, boron (B) 0.0005 to 0.0020%, cobalt (Co) 0.01 to 0.05%, nitrogen (N) 0.002 to 0.008%, balance iron (Fe) and other unavoidable impurities It is made of steel containing and the surface roughness index ratio (Rmax / Ra) is 12-23 by shot blasting process.

In addition, the steel component preferably satisfies 3.5 ≦ [(B (ppm) × Al (%) × Co (%)) / N (%)] ≦ 18.

In addition, the modified ferrite structure generated by the shot blasting process occupies 3 to 10% in the thickness direction of the hot rolled steel sheet.

According to the method of manufacturing the hot rolled steel sheet of the present invention configured as described above, through the appropriate component control and optimization of the manufacturing process to secure the aging resistance and improve the workability and paintability to produce high value-added steel sheet used in home appliances, automobiles, etc. To help. In addition, it has excellent descaling properties, which can increase the efficiency of pickling operations and at the same time prevent environmental pollution and shorten processes.

1 is a hot-rolled steel sheet tissue photograph 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, the technical configuration of the present invention will be described in more detail.

As described above, the hot-rolled steel sheet of the present invention is a high value-added hot-rolled steel sheet that can be used for home appliances and automobiles by satisfying aging resistance, processability and paintability at the same time, and completed the present invention. The steel component according to the invention is preferably controlled as follows.

Carbon (C) is an element added for improving the strength of the steel sheet, the tensile and yield strength increases as the content is increased, but the excessive limit is limited to 0.12% because the workability of the material is lowered. On the other hand, if the carbon content is less than 0.01%, as well as additional operating time is required for decarburization during steelmaking, there is a problem that it is difficult to secure a stable material because a sudden change in the material occurs. Therefore, the content of carbon is limited to 0.01 to 0.12% and preferably managed at 0.02 to 0.08%.

Manganese (Mn) is an element widely used as a solid solution strengthening element and is an important element for increasing the strength of steel and improving hot workability, but is an element that inhibits the ductility and workability of a material due to MnS formation. If the content of manganese is small, the workability is improved but it is difficult to secure the strength. Therefore, 0.1% or more must be added to secure the target strength. On the other hand, if the manganese is added excessively, the upper limit is limited to 0.5% because it causes economic deterioration and central segregation caused by the addition of a large amount of alloying elements.

Phosphorus (P) is an element that improves the strength and corrosion resistance of steel, and it is preferable to add a large amount in order to secure these properties, but since it is an element causing central segregation during casting, a large amount of phosphorus deteriorates workability. The content is limited to 0.025% or less (excluding 0%), and preferably controlled to 0.005 to 0.015%.

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

Aluminum (Al) is generally an element added for molten steel deoxidation, but the lower limit is limited to 0.03% because it combines with solid solution in steel to improve the aging characteristics. Not only does it cause a problem, but also deteriorates the workability, so the upper limit is limited to 0.15% and the management range is limited to 0.03 ~ 0.15%.

 Boron (B) is an element that combines with solid solution element in steel to improve the aging property and improves the strength of the material by addition of a small amount as a hardenability enhancing element. Addition is required. However, if the content exceeds 0.0020%, not only the material deterioration and grain boundary cracking during play, but also the problem of roughening the surface of the hot-rolled steel sheet is limited to 0.0005 ~ 0.0020%.

 Cobalt (Co) is an element that promotes the formation of precipitates in steel, and should be added at least 0.01% in order to obtain such an effect. However, when cobalt is added in excess of 0.05%, the range is limited to 0.01 to 0.05% because the cobalt acts as an increase factor of manufacturing cost due to the addition of a large amount of expensive alloying elements rather than a contribution to precipitation promotion.

* Nitrogen (N) exists in solid solution in steel and is useful for reinforcing the material, but it is the main element that causes aging phenomenon, so it is necessary to manage below a certain amount in order to secure workability, and the upper limit is limited to 0.008%. In addition, if less than 0.002% is not obtained sufficient stiffness and the site for precipitate formation is reduced, the lower limit is limited to 0.002%, the management range is limited to 0.002 ~ 0.008%.

In order to properly manage the fractions of precipitates and solid solution, and to obtain better processing characteristics, the content ratio between alloy elements is 3.5 ≤ [(B (ppm) × Al (%) × Co (%)) / N (%)) ≤ 18. It is desirable to maintain. When [(B (ppm) × Al (%) × Co (%)) / N (%)] is less than 3.5, it was difficult to secure high aging resistance and processability due to the expression of solid elements, whereas [( When B (ppm) × Al (%) Co (%)) / N (%)] is greater than 18, it is possible to secure workability, but it acted as a cause of some surface defects and productivity decrease due to excessive addition elements. . In this regard, the content ratio between the alloying elements is preferably managed by 3.5 ≦ [(B (ppm) × Al (%) × Co (%)) / N (%)] ≦ 18.

Hereinafter, a method for manufacturing a hot rolled steel sheet 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 to 0.12%, manganese (Mn) 0.1 to 0.5%, phosphorus (P) 0.025% or less (excluding 0%), sulfur (S) 0.02% or less (excluding 0%), Steel containing 0.03 to 0.15% of aluminum (Al), 0.0005 to 0.0020% of boron (B), 0.01 to 0.05% of cobalt (Co), 0.002 to 0.008% of nitrogen (N), residual iron (Fe) and other unavoidable impurities. The hot rolled steel sheet is manufactured according to a conventional hot rolling process, and shot blasting is performed on the surface of the hot rolled steel sheet at a size of 0.10 to 0.40 mm of shot balls and a spraying speed of 40 to 65 m / sec.

The shot blasting process is one of the most characteristic technical configurations of the present invention for securing aging resistance, and a modified ferrite lip (Ferrite) having significantly increased dislocation density, among them, by introducing an appropriate compressive stress on the surface of a hot rolled steel sheet. By producing new grains, it is possible to reduce the sticking of dislocations due to the solid solution element, which is the main cause of the aging phenomenon, thereby improving the aging resistance.

In order to achieve such an effect, it is preferable to control the size of the shot ball used for shot blasting to 0.10 to 0.40 mm. If the size of the shot ball is less than 0.10mm, the mechanical peeling effect of the surface layer is small, so that it is difficult to obtain an adequate residual stress effect.If the size of the shot ball exceeds 0.40mm, the maximum roughness of the surface rises rapidly, This is because it acts as a factor of crack generation.

On the other hand, the injection speed of the shot blasting is preferably controlled to 40 ~ 65m / sec. If the injection speed is less than 40m / sec, the impact pressure of the shot ball acting on the surface layer is low, it is difficult to secure the desired aging resistance, 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 non-uniform processing beyond.

In order to secure the mechanical properties according to the present invention, it is preferable to control the surface roughness index ratio (Rmax / Ra) of the hot rolled steel sheet after the shot blasting process to be 12 to 23. Here, Rmax means the maximum height in the surface roughness curve of the hot-rolled steel sheet, Ra means the average surface roughness of the center line. When the surface roughness index ratio is less than 12, as the ratio of roughness acid and bone is not secured, not only the adsorption of organic matters is lowered, but also the residual stress distribution in the thickness direction of the material is insufficient, making it difficult to secure aging resistance. On the other hand, when the surface roughness index ratio exceeds 23, processing cracks begin to occur while reaching saturation in terms of securing adsorptivity, so that the management range is preferably 12 to 23.

(A) of FIG. 1 shows a ferrite grain in a steady state with a low dislocation density, and FIG. 1 (b) shows a strain having a network structure with a high density of dislocations in which dislocations are integrated by a shot blasting process according to the present invention. Shows ferrite lip. Deformed ferrite structure produced by shot blasting is preferably controlled to occupy 3 to 10% in the thickness direction of the hot-rolled steel sheet in order to ensure appropriate age resistance. If the deformed ferrite structure is less than 3% in the thickness direction, the target aging resistance cannot be secured due to the lack of organizational properties that can sufficiently fix solid elements in the steel. If it exceeds, it acts as a hardening factor of the material in the processing and post-treatment process to act as a factor to deteriorate the workability, it is preferable to make the management range 3 to 10%.

As described above, if the shot blasting process of a predetermined condition is applied to the surface of the steel sheet produced through the usual 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 above composition components 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./sec, 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 / sec or more, it acts as a factor of the occurrence of material deviation due to the widthwise cooling unevenness, so the range of the cooling rate is preferably managed at 30 to 100 ° C / sec.

Finally, the hot rolled steel sheet is preferably wound at a temperature of 580 ~ 680 ℃ 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 other hand, when the coiling temperature exceeds 680 ° C, a problem arises in that the workability and corrosion resistance are degraded as the structure of the final product forms a coarse cementite phase, so that the range of the coiling temperature is controlled at 550 to 680 ° C. desirable.

In order to find out the technical effect of the method for producing a hot rolled steel sheet excellent in aging resistance according to the present invention described above was performed as follows.

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

Table 1

Steel grade	Chemical composition (wt%)									Inter-element ratio
	C	Mn	P	S	Al	B	Co	N	Ti
Inventive Steel 1	0.044	0.22	0.010	0.007	0.089	0.0015	0.030	0.004	-	10.01
Inventive Steel 2	0.056	0.23	0.011	0.009	0.096	0.0012	0.041	0.004	-	11.81
Comparative Steel 1	0.007	0.19	0.015	0.008	0.041	-	-	0.006	-	0.00
Comparative Steel 2	0.002	0.22	0.008	0.009	0.035	-	-	0.003	0.043	0.00
Comparative Steel 3	0.064	1.30	0.010	0.002	0.031	-	0.042	0.006	-	0.00
Comparative Steel 4	0.154	0.26	0.009	0.004	0.052	0.0031	0.091	0.006	-	24.45
Comparative Steel 5	0.041	0.45	0.080	0.025	0.042	0.0002	0.071	0.004	-	1.49
Comparative Steel 6	0.031	1.89	0.043	0.003	0.034	-	-	0.006	0.027	0.00

※ Component ratio between elements: (B (ppm) × Al (%) × Co (%)) / N (%)]

TABLE 2

division	Steel grade used	Reheating Temperature (℃)	Finishing temperature (℃)	Cooling rate (℃ / s)	Winding temperature (℃)	Short Ball Size (mm)	Blasting speed (m / sec)
Inventive Example 1	Inventive Steel 1	1250	890	50	600	0.25	50
Inventive Example 2		1250	890	70	650	0.32	60
Inventive Example 3		1250	890	90	600	0.32	50
Inventive Example 4	Inventive Steel 2	1250	910	90	600	0.19	50
Inventive Example 5		1250	910	90	650	0.27	60
Inventive Example 6	Inventive Steel 1	1250	750	50	600	0.25	50
Inventive Example 7		1250	890	15	600	0.32	50
Inventive Example 8	Inventive Steel 2	1250	890	40	400	0.31	20
Comparative Example 1	Inventive Steel 1	1250	910	90	650	0.91	90
Comparative Example 2	Comparative Steel 1	1250	910	50	650	0.16	50
Comparative Example 3	Comparative Steel 2	1250	910	50	650	0.25	60
Comparative Example 4	Comparative Steel 3	1250	890	50	650	0.25	60
Comparative Example 5	Comparative Steel 4	1250	890	50	650	0.16	50
Comparative Example 6	Comparative Steel 5	1250	890	50	650	0.25	60
Comparative Example 7	Comparative Steel 6	1250	890	50	650	0.25	60

TABLE 3

division	Surface Roughness Index Ratio	Yield point extension phenomenon	Yield strength (kgf / mm 2 )	Elongation (%)	Paintability	Machinability	Anti-aging
Inventive Example 1	14.6	Not Occurred	23.8	40.5	Good	Good	Good
Inventive Example 2	19.1	Not Occurred	22.4	42.2	Good	Good	Good
Inventive Example 3	17.8	Not Occurred	26.9	43.1	Good	Good	Good
Inventive Example 4	13.7	Not Occurred	24.2	41.5	Good	Good	Good
Inventive Example 5	15.9	Not Occurred	23.1	43.5	Good	Good	Good
Inventive Example 6	12.9	Not Occurred	32.6	29.8	Good	usually	Good
Inventive Example 7	8.9	Not Occurred	26.1	41.1	Good	usually	Good
Inventive Example 8	7.8	Occur	29.5	36.8	Good	usually	Good
Comparative Example 1	28.4	Not Occurred	27.4	30.7	Bad	Bad	Good
Comparative Example 2	12.8	Occur	33.1	38.6	Good	Bad	Bad
Comparative Example 3	16.7	Not Occurred	20.8	44.1	Bad	Good	Bad
Comparative Example 4	8.1	Occur	42.4	24.6	Bad	Bad	Bad
Comparative Example 5	4.6	Occur	43.6	20.5	Bad	Bad	Bad
Comparative Example 6	9.2	Occur	31.8	30.6	Bad	Bad	Bad
Comparative Example 7	14.8	Not Occurred	44.7	24.9	Good	Bad	Bad

In Table 3, the paintability was excellent in both the coating adhesion and the surface properties among the evaluation items of the coating material, and the case in which only one of the two properties was excellent was shown as the case where the two properties were not good.

The workability was measured by crack length for bending test specimens and divided into five stages as shown in [Table 4] below. One stage was good, two to three stages were normal, and four to five stages were marked as defective.

Table 4

step	Specific criteria
Stage 1	No cracks in the bending part
2 steps	No cracking at the bending part, but the surface of the machining part is rough
3 steps	The number of microcracks on the spot occurred 1 to 3
4 steps	4 or more microcrack on point or sum of total crack length within 10mm
5 steps	A crack occurs and the length of the total crack sum is 10 mm or more.

The aging resistance was classified according to the degree of surface bending after steel sheet processing, and by dividing the bending index that expresses this into five stages, the first stage, which is relatively insignificant, is good. And, it was determined that the four to five 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.

Inventive Examples 1 to 5 satisfy all of the steel component control, hot rolling process and shot blasting process conditions according to the present invention. Yield point stretching did not occur in all the invention examples, and the surface roughness index ratio (Rmax / Ra) was also within 12 to 23, satisfies the management range and no bending occurred during processing, thereby ensuring excellent aging resistance. . Moreover, no cracking occurred during bending, resulting in high processability and paintability, thereby making it possible to manufacture excellent hot rolled steel sheets and original plates for plating.

Inventive Examples 6 to 8 satisfy the conditions of the steel component control (invention steel 1, invention steel 2) and shot blasting process conditions according to the present invention, but do not satisfy the hot rolling process. In more detail, Inventive Example 6 performs the finish rolling temperature at 750 ° C. lower than the control range, Inventive Example 7 performs the cooling rate in the ROT process at 15 ° C./s lower than the control range, and Inventive Example 8 It is a case where winding temperature is performed at 400 degreeC lower than a control range. Inventive Examples 6 to 8 exhibited some yield point stretching but still showed good aging resistance. Although the workability was slightly lowered due to grain blending, solid element precipitation, material variation, etc., it satisfies the high quality requirements and is still good. Because of its paintability, it could be used as a high value-added steel sheet for home appliances and automobiles.

Comparative Example 1 is a case where the steel component control (invention steel 1) and the hot rolling process conditions according to the present invention are satisfied, but the short blasting conditions are not satisfied. More specifically, in the case of shot blasting conditions, the shot ball is used to be 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 yield point stretching phenomenon does not occur, which is good in terms of aging resistance, but due to the increase in surface roughness and the increase in the internal hardening layer, both workability and paintability are deteriorated, which is not suitable for use as a hot rolled steel sheet requiring high quality.

Comparative Examples 2 to 7 are cases in which steel grades (comparative steels 1 to 6) that satisfy the hot rolling process conditions and the shot blasting conditions according to the present invention but do not satisfy the steel component conditions are used. In most cases, it was difficult to suppress the yield point stretching phenomenon, and thus the aging resistance was lowered, and the processing and coating properties according to the present invention could not be satisfied due to the occurrence of bending during processing.

Furthermore, in Comparative Example 2, in which the component ratio between elements [(B (ppm) × Al (%) × Co (%)) / N (%)] is 0.00 and does not include Ti, a carbonitride-forming element, Not only is it difficult to secure workability due to generation, but also has a low strength, resulting in a problem of deterioration in shape freezing property during processing. On the other hand, Comparative Example 3 including Ti, a carbonitride-forming element, having a component ratio between elements ((B (ppm) × Al (%) × Co (%)) / N (%)) is 0.00 and can be secured. Even if the manufacturing process and shot blasting conditions according to the invention were applied, the target age resistance and paintability could not be secured.

Finally, Figure 2 is a graph measuring the change in the aging resistance (expressed as fluting index) and the workability (expressed as the crack generation sensitivity during processing) according to the surface roughness index ratio using the invention steel 1. In order to satisfy the target aging resistance and workability, 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 12 to 23, the fluting index and cracking sensitivity are excellent. On the other hand, in the region lower than the above control range, there is a problem that the bending effect occurs when the fluting index is 2 or more, and in the region above the above control range, the aging resistance indicates the saturation value while the processing crack occurs. I could confirm it.

Claims (9)

1. By weight, carbon (C) 0.01 to 0.12%, manganese (Mn) 0.1 to 0.5%, phosphorus (P) 0.025% or less (excluding 0%), sulfur (S) 0.02% or less (excluding 0%), aluminum ( Al) 0.03 to 0.15%, boron (B) 0.0005 to 0.0020%, cobalt (Co) 0.01 to 0.05%, nitrogen (N) 0.002 to 0.008%, balance iron (Fe) and other unavoidable impurities The method of manufacturing hot rolled steel sheet having excellent aging resistance, characterized in that the shot blasting on the surface of the hot-rolled steel sheet 0.10 ~ 0.40mm, the blasting rate of 40 ~ 65m / sec.
2. The method according to claim 1,

   The steel component is 3.5 ≤ [(B (ppm) × Al (%) × Co (%)) / N (%)]] ≤ 18 to produce a hot rolled steel sheet having excellent aging resistance, characterized in that.
3. The method according to claim 1 or 2,

   The hot rolled steel sheet is a method of producing a hot rolled steel sheet excellent in aging resistance, characterized in that the finish rolling of the steel made of the composition at 860 ~ 950 ℃.
4. The method according to claim 3,

   The hot rolled steel sheet is a method of producing a hot rolled steel sheet having excellent age resistance, characterized in that for cooling the finish-rolled steel at a cooling rate of 30 ~ 100 ℃ per second.
5. The method according to claim 4,

   The hot rolled steel sheet is a method of producing a hot rolled steel sheet excellent in aging resistance, characterized in that the winding after the cooling at a temperature of 580 ~ 680 ℃.
6. The method according to claim 1,

   Surface roughness ratio (Rmax / Ra) of 12 to 23 by the shot blasting method of producing a hot rolled steel sheet excellent in aging resistance.
7. By weight%, carbon (C) 0.01 to 0.12%, manganese (Mn) 0.1 to 0.5%, phosphorus (P) 0.025% or less, sulfur (S) 0.02% or less, aluminum (Al) 0.03 to 0.15%, boron (B ) 0.0005 to 0.0020%, cobalt (Co) 0.01 to 0.05%, nitrogen (N) 0.002 to 0.008%, balance Fe and other unavoidable impurities, and is made of shot blasting surface roughness index ratio (Rmax / Hot rolled steel sheet having excellent aging resistance, characterized in that Ra) is 12 to 23.
8. The method according to claim 7,

   Hot-rolled steel sheet having excellent aging resistance, characterized in that the component of the steel satisfies 3.5 ≤ [(B (ppm) × Al (%) × Co (%)) / N (%)] ≤ 18.
9. The method according to claim 7,

   Hot-rolled steel sheet having excellent age resistance, characterized in that the deformation of the ferrite structure produced by the shot blasting occupies 3 to 10% in the thickness direction of the hot-rolled steel sheet.

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