WO2015099222A1 - Hot-rolled steel plate having excellent welding property and burring property and method for manufacturing same - Google Patents

Abstract

The purpose of an aspect of the present invention is to provide hot-rolled high-burring steel having excellent electric resistance welding property, thereby facilitating welding operations, and a method for manufacturing the same.

Description

Hot rolled steel sheet with excellent weldability and burring property and manufacturing method

The present invention relates to a hot rolled steel sheet excellent in weldability and burring properties and a method of manufacturing the same.

In the automotive industry, the application of high tensile strength steel to automobile bodies has recently been expanded to achieve both weight reduction for reducing CO ₂ emissions and reinforcement of bodies to improve crash safety. High-strength steel is a cost-effective material for realizing these conflicting demands, and its application is expected to increase over time to meet increasingly stringent regulations. In particular, as interest in collision safety increases, its role is increasing.

In general, the higher the material, the worse the formability. The steel material is no exception, and attempts to achieve both high strength and high ductility have been made. Moreover, as a characteristic requested | required of the material used for automobile parts, there are burring processability besides ductility. However, since the burring workability also tends to be lowered with higher strength, the improvement of burring workability also becomes a subject of application of high strength steel sheet to automobile parts. On the other hand, automobile parts are assembled by welding such as spot, arc, plasma, laser, etc., the processed member by press molding. Moreover, in recent years, after joining a steel plate by these welding, it may be press-molded. The strength of the welded part when it is molded or when it is assembled and used as a part is very important from the viewpoint of molding limit and safety. Therefore, in the application of a high strength steel sheet to automobile parts and the like, the strength of the welded part also becomes an important examination subject along with its burring workability.

Patent Literature 1 proposes a technique for improving the elongation flangeability by forming ferrite-bainite structure by using three-stage cooling after cooling to a temperature around 700 ° C. after hot rolling, followed by air cooling for a predetermined time, and then cooling and winding again. . In addition, in Patent Document 2, the ferrite-bainite structure is controlled so that the ferrite ratio is 80% or more, and the ratio of the crystal grains having a short diameter (ds) and a long diameter (dl) of 0.1 is 80% or more. A technique for producing a hot rolled steel sheet having strength of more than 69 kg / cm 2 and excellent in elongation and stretch flangeability is proposed.

However, the above technique mainly uses the alloying components of Si, Mn, Al, Mo, etc. to manufacture the abnormal composite tissue steel of ferrite-bainite, and such alloying components increase resistance by increasing electrical resistance during electrical resistance welding. There is a problem that the heat generation is severe, or cold welding occurs when the operation lowers the input current value. In addition, Si, Mn, Al and the like to form an oxide during welding, there is a problem of reducing the integrity of the weld.

(Patent Document 1) Japanese Unexamined Patent Application Publication No. 6-293910

(Patent Document 2) Korean Patent Publication No. 2003-0055339

One aspect of the present invention is to provide a hot rolled steel sheet excellent in electrical resistance weldability and easy welding work, excellent burring properties and a method of manufacturing the same.

One aspect of the present invention is a weight%, C: 0.03 ~ 0.1%, Si: 0.01 ~ 1.2%, Mn: 1.2 ~ 1.9%, Al: 0.01 ~ 0.08%, Cr: 0.005 ~ 0.8%, Mo: 0.01 ~ 0.12 %, P: 0.01% to 0.05%, S: 0.001% to 0.005%, N: 0.001% to 0.01%, the balance Fe and other unavoidable impurities, and each of the above components satisfy the following Equation 1, and the tensile strength and elongation plan Provided is a hot rolled steel sheet excellent in weldability and burring property of multiplying 48000 or more.

Equation 1: 10.646 + 0.2 [C] + 0.25 [Si] +0.3 [Mn]-0.1 [Cr] + 0.55 [Al] +0.2 [Mo]-4.23 [Ti] -2.5 [Nb]-2.9 [V] ≤ 11.1

However, in Equation 1, C, Si, Mn, Cr, Al, Mo, Ti, Nb, and V represent the content (weight%) of the corresponding element, respectively.

Another aspect of the present invention is a method for producing a hot rolled steel sheet having excellent weldability and burring property, in weight%, C: 0.03 to 0.1%, Si: 0.01 to 1.2%, Mn: 1.2 to 1.9%, Al: 0.01 to 0.08% , Cr: 0.005 to 0.8%, Mo: 0.01 to 0.12%, P: 0.01 to 0.05%, S: 0.001 to 0.005%, N: 0.001 to 0.01%, balance Fe and other unavoidable impurities Preparing a steel slab satisfying Equation 1 below, reheating the steel slab at 1200 to 1300 ° C., and hot rolling the reheated steel slab to a finish rolling temperature of 850 to 1000 ° C. to obtain a steel sheet. The first step of cooling the hot rolled steel sheet at a cooling rate of 10 ~ 100 ℃ / second to a temperature of 500 ~ 750 ℃, air cooling the cooled steel sheet for 4 to 10 seconds and the air-cooled steel sheet 300 ~ Secondary cooling at a cooling rate of 10-100 ° C./sec to a temperature of 500 ° C .;

Equation 1: 10.646 + 0.2 [C] + 0.25 [Si] +0.3 [Mn]-0.1 [Cr] + 0.55 [Al] +0.2 [Mo]-4.23 [Ti] -2.5 [Nb]-2.9 [V] ≤ 11.1

However, in Equation 1, C, Si, Mn, Cr, Al, Mo, Ti, Nb, and V represent the content (weight%) of the corresponding element, respectively.

In addition, the solution of the said subject does not enumerate all the characteristics of this invention. Various features of the present invention and the advantages and effects thereof may be understood in more detail with reference to the following specific embodiments.

According to the present invention, by optimizing the steel component and the hot rolled structure, the product of tensile strength and extension flange is 48000 or more, and the integrity of the welded portion is improved during welding, thereby ensuring a hot rolled steel sheet excellent in weldability and burring property.

FIG. 1 is a graph showing a value obtained by substituting the product of the tensile strength (TS) and the elongation flange property (HER) of all the steels of the examples and the formula (1).

The present inventors have conducted research to develop a hot rolled steel sheet capable of overcoming the problems that the above-described technologies have not solved. As a result, the hot rolled steel sheet having excellent weldability and burring property can be produced by controlling the composition, microstructure, and processing conditions of the steel. The present invention was confirmed.

Hereinafter, a hot rolled steel sheet excellent in weldability and burring property as one side of the present invention will be described in detail.

One aspect of the present invention is a weight%, C: 0.03 ~ 0.1%, Si: 0.01 ~ 1.2%, Mn: 1.2 ~ 1.9%, Al: 0.01 ~ 0.08%, Cr: 0.005 ~ 0.8%, Mo: 0.01 ~ 0.12 %, P: 0.01% to 0.05%, S: 0.001% to 0.005%, N: 0.001% to 0.01%, the balance Fe and other unavoidable impurities, and each of the above components satisfy the following Equation 1, and the tensile strength and elongation plan Provides hot-rolled steel sheet with excellent weldability and burring property of multiplying 48000 or more.

Equation 1: 10.646 + 0.2 [C] + 0.25 [Si] +0.3 [Mn]-0.1 [Cr] + 0.55 [Al] +0.2 [Mo]-4.23 [Ti] -2.5 [Nb]-2.9 [V] ≤ 11.1

However, in Equation 1, C, Si, Mn, Cr, Al, Mo, Ti, Nb, and V represent the content (weight%) of the corresponding element, respectively.

Carbon (C): 0.03-0.1 weight%

C is the most economical and effective element for strengthening steel. As the amount of carbon added increases, the martensite fraction of the ferritic-martensitic composite steel increases and the tensile strength increases. If the carbon content is less than 0.03% by weight, it is not easy to form martensite phase during cooling after hot rolling. On the other hand, when the carbon content exceeds 0.1% by weight, there is a problem in that excessive strength increase and weldability, formability and toughness are reduced. Therefore, the content of C is preferably contained in 0.03 ~ 0.1% by weight.

Silicon (Si): 0.01 ~ 1.2 wt%

Si deoxidizes molten steel and has a solid solution strengthening effect. As a ferrite stabilizing element, it has an effect of promoting ferrite transformation during cooling after hot rolling, and is an effective element for increasing the ferrite fraction constituting the matrix of ferritic martensite composite steel. When the content of the silicon is less than 0.01% by weight, the ferrite stabilization effect is small, making it difficult to make the matrix into a ferrite structure. On the other hand, when the silicon content exceeds 1.2% by weight, red scales formed by Si are formed on the surface of the steel sheet during hot rolling, so that the surface quality of the steel sheet is not very bad, and the ductility and weldability are also reduced. Therefore, the content of the silicon is preferably contained in 0.01 to 1.2% by weight.

Manganese (Mn): 1.2-1.9 wt%

Mn, like Si, is an effective element to solidify steel and increases the hardenability of steel to facilitate the formation of bainite phase during cooling after hot rolling. In order to exhibit such an effect in the present invention, it is preferable that 1.2 wt% or more is included. However, if the content of the manganese exceeds 1.9% by weight excessively delay the ferrite transformation is difficult to secure the appropriate fraction of the ferrite known matrix. In addition, there is a problem in that the segregation part in the thickness center during the slab casting in the playing process greatly develops, which impairs the weldability of the final product. Therefore, the content of Mn is preferably contained in 1.2 to 1.9% by weight.

Aluminum (Sol.Al): 0.01 to 0.08% by weight,

Al is a component mainly added for deoxidation, and is a ferrite stabilizing element, and has an effect of helping to form a ferrite phase in steel during cooling after hot rolling. When the content of aluminum is less than 0.01% by weight, it is impossible to secure the effect intended for the present invention. On the other hand, when the content of aluminum exceeds 0.08% by weight, defects such as corner cracks are easily generated in the slab during continuous casting, and surface defects occur after hot rolling, thereby deteriorating surface quality. Therefore, the content of aluminum is preferably contained in 0.01 to 0.08% by weight.

Chromium (Cr): 0.005 to 0.8 wt%

Cr hardens the steel and assists bainite formation by retarding ferrite phase transformation during cooling. In order to secure the effect to be intended in the present invention, it is preferable to include 0.005% by weight or more. On the other hand, when the content of chromium exceeds 0.8% by weight, the ferrite transformation is excessively delayed and the elongation is reduced due to the increase of martensite fraction more than necessary. Therefore, the content of Cr is preferably contained in 0.005 ~ 0.8% by weight.

Molybdenum (Mo): 0.01 ~ 0.12% by weight

Mo has the effect of increasing the hardenability of the steel to facilitate the formation of bainite structure. In order to exhibit such an effect of the present invention, it is preferable that 0.01 wt% or more is included. On the other hand, when the content of molybdenum exceeds 0.12% by weight, the weldability is deteriorated due to excessive increase in hardenability, which is also economically disadvantageous. Therefore, the content of Mo is preferably contained in 0.01 to 0.12% by weight.

Phosphorus (P): 0.01% to 0.05% by weight

P, like Si, has the effect of strengthening solid solution and promoting ferrite transformation. If the content of phosphorus is less than 0.01% by weight is insufficient to obtain the strength to be secured by the present invention. On the other hand, when the content of phosphorus exceeds 0.05% by weight, ductility is lowered due to band organization by micro segregation. Therefore, the P is preferably contained in 0.01 to 0.05% by weight.

Nitrogen (N): 0.001-0.01 wt%

N is a representative solid solution strengthening element with C, and forms coarse precipitate with Ti, Al, and the like. In general, the solid solution strengthening effect of N is better than carbon, but the problem of toughness is greatly reduced as the amount of N in the steel increases. When the content of nitrogen is less than 0.001% by weight, the steelmaking industry takes a lot of time, resulting in decreased productivity. On the other hand, when the nitrogen content exceeds 0.01% by weight, the risk of brittleness is greatly increased. Therefore, the nitrogen is preferably contained in 0.001 to 0.01 wt%.

The remaining component of the present invention is iron (Fe). However, in the conventional manufacturing process, impurities which are not intended from the raw material or the surrounding environment may be inevitably mixed, and thus cannot be excluded. Since these impurities are known to those skilled in the art, all of them are not specifically mentioned in the present specification.

However, since sulfur is a commonly mentioned impurity, a brief description thereof is as follows.

Sulfur (S): 0.001-0.005%

The sulfur is inevitably contained as an impurity, and combines with Mn to form a non-metallic inclusion and thus greatly reduces the elongation flangeability of the steel. The theoretical sulfur content is advantageously limited to 0% by weight, but inevitably contained in the manufacturing process. Therefore, it is important to manage the upper limit, the upper limit of the sulfur content in the present invention is preferably limited to 0.01% by weight.

In addition, the steel of the present invention may further improve the effect of the present invention when additionally adding one or more elements selected from the group consisting of niobium (Nb), titanium (Ti) and vanadium (V) described below. More preferably, the total content of one or more elements selected from the group is 0.001 to 0.15% by weight.

Ti is present in the steel as TiN, thereby suppressing the growth of grains during heating for hot rolling. In addition, Ti remaining after reacting with nitrogen is dissolved in the steel and bonded with carbon to form TiC precipitates, which is a useful component for improving the strength of steel.

Nb and V form carbides in the steel, which are effective for grain refinement, and fine precipitates are formed to improve the strength and toughness of the steel. It stabilizes the solid solution elements such as C and N, which increase the electrical resistivity, thereby mitigating the phenomenon of local spark generation during electric resistance welding, and also suppressing softening of the weld.

In addition, in order to improve weldability, C, Si, Mn, Cr, Al, Mo, Ti, Nb, and V preferably satisfy Equation 1 below. The electrical resistivity at high temperatures is high, and the weldability is significantly lowered. The lower limit need not be particularly limited, but the lower limit may be limited to 10.5 in consideration of elongation flangeability and elongation. If it is added below, there is a problem that the strength or elongation is inferior rapidly.

Equation 1: 10.646 + 0.2 [C] + 0.25 [Si] +0.3 [Mn]-0.1 [Cr] + 0.55 [Al] +0.2 [Mo]-4.23 [Ti] -2.5 [Nb]-2.9 [V] ≤ 11.1

However, in Equation 1, C, Si, Mn, Cr, Al, Mo, Ti, Nb, and V represent the content (weight%) of the corresponding element, respectively.

In addition, it is preferable that the hot rolled high burring steel has a product of tensile strength and extension flange property of 48000 or more.

In addition, the hot rolled steel sheet preferably comprises a microstructure including a bainite phase in the ferrite structure. By including such a microstructure, it is possible to suppress the formation of coarse carbides and to prevent destruction at the interface during plastic deformation. In addition, the bainite phase fraction in the ferrite structure is more preferably contained 5 to 20%. If the included bainite phase fraction is less than 5%, the present invention does not secure the strength to be secured, whereas if it exceeds 20%, the elongation is inferior.

Hereinafter, a method of manufacturing a hot rolled steel sheet excellent in weldability and burring property as another aspect of the present invention will be described in detail.

Another aspect of the present invention is a method for producing a hot rolled steel sheet having excellent weldability and burring property, in weight%, C: 0.03 to 0.1%, Si: 0.01 to 1.2%, Mn: 1.2 to 1.9%, Al: 0.01 to 0.08% , Cr: 0.005 to 0.8%, Mo: 0.01 to 0.12%, P: 0.01 to 0.05%, S: 0.001 to 0.005%, N: 0.001 to 0.01%, balance Fe and other unavoidable impurities Preparing a steel slab satisfying Equation 1 below, reheating the steel slab at 1200 to 1300 ° C., and hot rolling the reheated steel slab to a finish rolling temperature of 850 to 1000 ° C. to obtain a steel sheet. The first step of cooling the hot rolled steel sheet at a cooling rate of 10 ~ 100 ℃ / second to a temperature of 500 ~ 750 ℃, air cooling the cooled steel sheet for 4 to 10 seconds and the air-cooled steel sheet 300 ~ Secondary cooling at a cooling rate of 10-100 ° C./sec to a temperature of 500 ° C .;

Equation 1: 10.646 + 0.2 [C] + 0.25 [Si] +0.3 [Mn]-0.1 [Cr] + 0.55 [Al] +0.2 [Mo]-4.23 [Ti] -2.5 [Nb]-2.9 [V] ≤ 11.1

However, in Equation 1, C, Si, Mn, Cr, Al, Mo, Ti, Nb, and V represent the content (weight%) of the corresponding element, respectively.

Reheating stage

It is preferable to reheat the slab which satisfies the above-mentioned component system at 1200-1300 degreeC. When the reheating temperature is less than 1200 ° C, the precipitates are not sufficiently reused, so that precipitates such as NbC and TiC are reduced in the process after hot rolling. On the other hand, when it exceeds 1300 degreeC, intensity | strength falls by abnormal grain growth of austenite grains. Therefore, it is preferable to limit the reheating temperature of the slab to 1200 to 1300 ° C.

Hot rolling stage

Hot rolling may be performed on the slab reheated as described above. At this time, it is preferable to perform finish rolling at 850-1000 degreeC. If the hot finish rolling temperature is less than 850 ℃ rolling load is greatly increased. On the other hand, when the hot finishing rolling temperature exceeds 1000 ° C., the structure of the steel sheet becomes coarse and the steel becomes brittle, the scale becomes thick, and surface quality deterioration such as hot rolling scale defect occurs. Therefore, the hot finish rolling is preferably limited to 850 ~ 1000 ℃.

1st cooling stage

It is preferable to primary-cool the hot rolled steel sheet as described above. In addition, it is preferable to primary cool until it reaches 500-750 degreeC from the said finishing hot rolling temperature of the said hot rolled sheet steel. When the temperature at which the primary cooling is terminated is less than 500 ° C., most of the microstructures in the steel have bainite, and thus the microstructures of the present invention cannot be secured. On the other hand, when the temperature exceeds 750 ° C., coarse ferrite and pearlite structures are formed to reduce the strength of the steel. In addition, it is preferable to perform primary cooling at a cooling rate of 10 to 100 ° C / sec. If it is less than 10 ° C / second coarsening of the ferrite grains occurs and the precipitate is also coarse to secure the strength to be obtained by the present invention, if the temperature exceeds 100 ° C / second the shape of the hot rolled sheet is poor .

Air cooling stage

It is preferable to air-cool the steel plate cooled as mentioned above. Preferably, the cooled steel sheet is subjected to air cooling for 4 to 10 seconds. In the case of performing air cooling for less than 4 seconds, there is a problem in that ductility is greatly deteriorated due to insufficient formation of ferrite structure. On the other hand, if air cooling is performed for more than 10 seconds, the ferrite fraction is increased to decrease the martensite fraction, thereby failing to secure the strength and elongation to be secured by the present invention.

2nd cooling stage

It is preferable to secondary-cool the steel plate cooled by air as mentioned above. In addition, it is preferable to perform secondary cooling at a cooling rate of 10 ~ 100 ℃ / sec until reaching 300 ~ 500 ℃ from the temperature of the air-cooled steel sheet. If the temperature at which the secondary cooling is terminated is less than 300 ° C, the martensite phase is formed and the extension flange is inferior. On the other hand, when it exceeds 500 degreeC, extension flange property is inferior by formation of coarse carbide. In addition, it is preferable to perform primary cooling at a cooling rate of 10 to 100 ° C / sec. If it is less than 10 ° C / second coarse carbide is formed there is a problem to secure the stretch flange to be secured by the present invention, if it exceeds 100 ° C / second there is a problem that the formation of the hot rolled sheet is poor.

After the cooling step may further comprise the step of winding to facilitate storage and movement of the cooled steel sheet.

The pickled steel sheet may be manufactured by further including the step of removing the surface layer portion scale and oiling the steel sheet prepared by the above method after natural cooling.

In addition, after reheating the pickling steel sheet to 450 ~ 480 ℃, by further comprising the step of passing through a hot dip galvanizing bath, it is possible to manufacture a hot dip galvanized steel sheet.

Hereinafter, the present invention will be described in more detail with reference to Examples. However, it is necessary to note that the following examples are only for illustrating the present invention in more detail, and are not intended to limit the scope of the present invention. This is because the scope of the present invention is determined by the matters described in the claims and the matters reasonably inferred therefrom.

(Example)

The steel slab satisfying the component system shown in Table 1 below was heated to 1250 ° C. and hot-rolled at the temperature shown in Table 2 below. Thereafter, primary cooling at a cooling rate of 70 ° C./sec to a temperature of 680 ° C., air cooling for 6 seconds, and secondary cooling at a cooling rate of 70 ° C./sec to a temperature of 450 ° C., followed by the temperatures shown in Table 2 below Wound up in.

Yield strength (YS), tensile strength (TS), elongation at break (T-El), and elongated flange property (Hole Expanding Ratio, HER) of the final hot-rolled steel sheet obtained by completing the winding process were shown in Table 2 below.

In addition, the bainite fraction in the ferrite structure was observed at 500 magnification using an optical microscope after etching the final hot rolled steel sheet, and then fractionated with an image analyzer.

In addition, the weldability of the final hot rolled steel sheet is also shown in Table 2 below. The weldability was measured by the uniaxial tensile test method after welding under the conditions shown in Table 3. At this time, the weldability was evaluated as being poor when the welded part was broken.

Table 1

division	C	Si	Mn	Cr	Al	P	S	N	Ti	Mo	Nb	V
Comparative Example 1	0.05	0.6	1.5	0	0.03	0.01	0.003	0.004	0	0.01	0.05	0
Comparative Example 2	0.06	0.5	1.6	0	0.1	0.01	0.003	0.004	0	0.01	0.02	0.02
Comparative Example 3	0.06	0.8	1.8	0	0.03	0.01	0.003	0.004	0.04	0.01	0	0
Comparative Example 4	0.06	1.2	1.6	0	0.03	0.01	0.003	0.004	0.02	0.01	0.05	0
Comparative Example 5	0.07	One	1.6	0	0.03	0.01	0.003	0.004	0.04	0.01	0	0.025
Comparative Example 6	0.07	0.8	1.8	0	0.03	0.01	0.003	0.004	0.02	0.01	0.02	0.03
Comparative Example 7	0.08	1.2	1.6	0	0.1	0.01	0.003	0.004	0.04	0.01	0.03	0
Comparative Example 8	0.08	1.5	1.8	0	0.03	0.01	0.003	0.004	0.06	0.04	0.025	0
Comparative Example 9	0.1	One	1.8	0.3	0.03	0.01	0.003	0.004	0.06	0.01	0.05	0.02
Inventive Example 1	0.08	0.05	1.5	0	0.03	0.01	0.003	0.005	0	0.01	0.05	0
Inventive Example 2	0.07	0.7	1.4	0.1	0.03	0.01	0.003	0.005	0.03	0.04	0.03	0
Inventive Example 3	0.04	1.1	1.7	0.7	0.03	0.01	0.003	0.005	0.06	0.01	0.03	0
Inventive Example 4	0.07	0.8	1.8	0.4	0.03	0.01	0.003	0.005	0.08	0.1	0.03	0.02
Inventive Example 5	0.08	0.6	1.8	0.4	0.03	0.01	0.003	0.004	0.03	0.01	0.02	0.03
Inventive Example 6	0.09	0.8	1.6	0.2	0.03	0.01	0.003	0.004	0.04	0.04	0.02	0.02

TABLE 2

division	FDT (℃)	CT (℃)	Equation 1	YS (MPa)	TS (MPa)	T-El (%)	HER (%)	TSxHER	Bainite fraction (%)	Weldability
Comparative Example 1	886	461	11.150	420	420	29	91	44317	7	X
Comparative Example 2	893	452	11.212	504	573	27	87	49851	9	X
Comparative Example 3	899	455	11.247	522	634	25	80	50720	8	X
Comparative Example 4	902	460	11.247	577	710	54	65	46150	9	X
Comparative Example 5	903	453	11.167	543	656	53	56	36736	10	X
Comparative Example 6	905	443	11.197	605	722	50	50	36100	11	X
Comparative Example 7	907	434	11.255	697	785	18	52	40820	8	X
Comparative Example 8	912	441	11.285	743	833	17	58	48314	10	X
Comparative Example 9	922	438	11.008	905	1011	14	35	35385	13	X
Inventive Example 1	892	440	11.018	548	636	25	89	56604	10	O
Inventive Example 2	887	443	11.068	537	622	26	79	49138	9	O
Inventive Example 3	882	467	11.059	736	862	21	62	53444	10	O
Inventive Example 4	891	445	10.925	866	1006	15	50	50300	14	O
Inventive Example 5	895	436	11.067	774	932	15	54	50328	12	O
Inventive Example 6	893	432	11.071	793	966	14	50	48300	13	O

TABLE 3

Welding condition	Initial clearance (mm)	Final clearance (mm)	Upset length (mm)	Welding time (sec)	Upset time (seconds)	Upset Current (%)	Upset pressure (kgf / ㎠)
	13	13	2.0	4	0.5	60	60

As shown in Table 2, Inventive Examples 1 to 6 satisfy the component range and manufacturing conditions proposed by the present invention, it is possible to secure a hot rolled steel sheet having a high value of the product of tensile strength and elongated flange property and excellent weldability. You can check it.

On the other hand, Comparative Examples 1, 4, 5, 6 and 7 do not satisfy the equation (1) can be confirmed that the weldability is inferior.

In addition, Comparative Examples 2, 3 and 8, although the value of the product of tensile strength and extension flange property satisfied the value of the range proposed by the present invention, it does not satisfy the equation 1, it can be confirmed that the weldability is inferior.

Claims (7)

1. By weight%, C: 0.03 to 0.1%, Si: 0.01 to 1.2%, Mn: 1.2 to 1.9%, Al: 0.01 to 0.08%, Cr: 0.005 to 0.8%, Mo: 0.01 to 0.12%, P: 0.01 to 0.05%, S: 0.001% to 0.005%, N: 0.001% to 0.01%, balance Fe and other unavoidable impurities, each of the above components satisfy the following Equation 1, and the weldability of which the product of tensile strength and extension flange property is 48000 or more. And hot rolled steel sheet having excellent burring property.

   Equation 1: 10.646 + 0.2 [C] + 0.25 [Si] +0.3 [Mn]-0.1 [Cr] + 0.55 [Al] +0.2 [Mo]-4.23 [Ti] -2.5 [Nb]-2.9 [V] ≤ 11.1

   (However, in the above Equation 1, C, Si, Mn, Cr, Al, Mo, Ti, Nb and V are the content (weight%) of the corresponding element, respectively)
2. The method of claim 1,

   Hot-rolled steel sheet excellent in weldability and burring properties, including 0.001 to 0.15% by weight of at least one selected from Nb, Ti, and V in total.
3. The method of claim 1,

   Hot-rolled steel sheet having excellent weldability and burring property having a microstructure containing 5-20% of bainite phase fraction in a ferrite structure.
4. By weight%, C: 0.03 to 0.1%, Si: 0.01 to 1.2%, Mn: 1.2 to 1.9%, Al: 0.01 to 0.08%, Cr: 0.005 to 0.8%, Mo: 0.01 to 0.12%, P: 0.01 to Preparing a steel slab containing 0.05%, S: 0.001% to 0.005%, N: 0.001% to 0.01%, residual Fe and other unavoidable impurities, wherein each of the components satisfies Equation 1 below;

   Reheating the steel slab at 1200-1300 ° C .;

   Hot rolling the reheated steel slab to a finish rolling temperature of 850 to 1000 ° C. to obtain a steel sheet;

   Primary cooling the hot rolled steel sheet at a cooling rate of 10 to 100 ° C./sec to a temperature of 500 to 750 ° C .;

   Air cooling the cooled steel sheet for 4 to 10 seconds; And

   The method of manufacturing a hot rolled steel sheet having excellent weldability and burring property comprising the step of second cooling the air-cooled steel sheet to a temperature of 300 ~ 500 ℃ at a cooling rate of 10 ~ 100 ℃ / sec.

   Equation 1: 10.646 + 0.2 [C] + 0.25 [Si] +0.3 [Mn]-0.1 [Cr] + 0.55 [Al] +0.2 [Mo]-4.23 [Ti] -2.5 [Nb]-2.9 [V] ≤ 11.1

   (However, in the above Equation 1, C, Si, Mn, Cr, Al, Mo, Ti, Nb and V are the content (weight%) of the corresponding element, respectively)
5. The method of claim 4, wherein

   The slab is a method of manufacturing a hot-rolled steel sheet having excellent weldability and burring properties further comprises 0.001 to 0.15% by weight of one or more weights selected from Nb, Ti and V.
6. The method of claim 4, wherein

   The method of manufacturing a hot rolled steel sheet having excellent weldability and burring property, further comprising the step of pickling the steel sheet after natural cooling.
7. The method of claim 6,

   Re-heating at 450 ~ 480 ° C after the pickling and hot-dip galvanizing method further comprising the step of performing hot dip galvanizing.

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