KR101439612B1 - Hot-rolled steel plate having weldability and formability and method for manufacturing thereof - Google Patents

Abstract

An aspect of the present invention is to provide a hot-rolled steel sheet excellent in electrical resistance weldability, easy to perform welding work, and excellent in moldability, and a method for manufacturing the same.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to a hot-rolled steel sheet having excellent weldability and moldability,

The present invention relates to a hot-rolled steel sheet excellent in weldability and moldability and a method for producing the same.

Pipes used in automotive parts are the basic materials used in hydroforming (HF) processes. The hydraulic pressure forming step is one of the molding processes useful for reducing the weight of the vehicle and improving the collision property, and means a method of manufacturing parts by applying a uniform deformation to the pressure of the liquid after mainly manufacturing the pipe.

In order to apply such a hydroforming process, a pipe must first be manufactured. The pipe used in the hydroforming process is usually manufactured by shearing the plate to an appropriate width, molding it into a cylindrical shape, and welding the joint.

At this time, welding is mainly performed by electric resistance welding. Electric resistance welding is widely used as the most general process which is inexpensive and easy to produce. However, when the alloy element such as Mn, Si, Al added to improve the formability of high-strength steel is included, It is known not to have. Researches for improving the weldability to high strength steels have been continuously carried out.

On the other hand, hot-rolled steel sheets are mainly used for parts directly related to the safety of passengers in an emergency such as a vehicle collision. These steel sheets are high-strength steels and may not be suitable for electric resistance welding. Furthermore, merely having a high tensile strength merely lowers competitiveness, and a high elongation for better molding is also required.

For this purpose, there are Multi-Phase Steel Steel, TRIP (Transformation Induced Plasticity) and DP (Dual Phase).

However, in the case of the above-described abnormal texture steel, the martensite-ferrite two-phase structure having an increase in strength as the ratio of martensite increases and an increase in ductility as the ferrite ratio increases increases. If it is too high, the ferrite ratio may be relatively decreased and ductility may be lowered, and since the cooling rate must be increased sharply in order to form martensite at a low temperature, there is a disadvantage that the process load is large during cooling.

Furthermore, a composite structure steel in which strength and ductility are simultaneously improved by forming ferrite, martensite and a mixed phase of bainite and martensite / austenite at normal temperature is a steel grade having improved strength and ductility of a transformed organopolysil There is a problem in that the moldability is disadvantageous. It is important to maintain a certain percentage of ferrite over the composite structure steel. For this purpose, it is important to add Si, Mn, etc. and add a small amount of Nb, Ti, etc. to make fine grains finer. There is a problem that the resistance heat is increased by increasing the electric resistance, or when the input current value is lowered, cold junction occurs. Further, Si, Mn, Al and the like have the problem of deteriorating the integrity of the welded portion by forming oxides during welding.

An aspect of the present invention is to provide a hot-rolled steel sheet excellent in electrical resistance weldability, easy to perform welding work, and excellent in moldability, and a method for manufacturing the same.

One aspect of the present invention is a ferritic stainless steel comprising, by weight%, 0.03 to 0.08% of C, 0.01 to 1.0% of Si, 1.2 to 1.8% of Mn, 0.01 to 0.3% of Al, 0.005 to 0.4% of Cr, 0.001 to 0.05% of P, 0.001 to 0.005% of S, 0.001 to 0.01% of N, and the balance of Fe and other unavoidable impurities. Each of the above-mentioned components satisfies the following formula (1) (EER), elongation FERN (HER) and tensile strength (TS) satisfy the following formula (2).

0.25 [Si] +0.3 [Mn] - 0.1 [Cr] + 0.55 [Al] +0.2 [Mo] -4.23 [Ti] -2.5 [Nb] - 2.9 [V] ≤ 10.8

Equation 2: T-El x HER ≥ 4907 - 4.257 x TS

In the above formula (1), C, Si, Mn, Cr, Al, Mo, Ti, Nb and V represent the contents (weight%) of the respective elements.

Another aspect of the present invention is a ferritic stainless steel comprising, by weight, 0.03 to 0.08% of C, 0.01 to 1.0% of Si, 1.2 to 1.8% of Mn, 0.01 to 0.3% of Al, 0.005 to 0.4% of Cr, 0.001 to 0.005% of S, 0.001 to 0.01% of N, and the balance of Fe and other unavoidable impurities, and each of the above components satisfies the following formula (1): Reheating the steel slab at a temperature of 1200 to 1300 DEG C, hot rolling the reheated steel slab to a finish rolling temperature of 850 to 1000 DEG C to obtain a steel sheet, and heat-treating the hot-rolled steel sheet at a temperature of 500 to 750 DEG C And cooling the steel sheet at a cooling rate of 10 to 100 DEG C / second up to a temperature

0.25 [Si] +0.3 [Mn] - 0.1 [Cr] + 0.55 [Al] +0.2 [Mo] -4.23 [Ti] -2.5 [Nb] - 2.9 [V] ≤ 10.8

In the above formula (1), C, Si, Mn, Cr, Al, Mo, Ti, Nb and V represent the contents (weight%) of the respective elements.

In addition, the solution of the above-mentioned problems does not list all the features of the present invention. The various features of the present invention and the advantages and effects thereof will be more fully understood by reference to the following specific embodiments.

INDUSTRIAL APPLICABILITY According to the present invention, by optimizing the steel component and the hot-rolled structure, it is possible to obtain a hot-rolled steel sheet having excellent formability and improved weldability at the time of electrical resistance welding.

Fig. 1 is a graph showing the values of the product of the elongation and the elongation flangeability of all steels and tensile strength.

The present inventors have conducted research to develop a hot-rolled steel sheet capable of overcoming the problems not solved by the above-described techniques. As a result, it has been found that by controlling steel composition components, microstructure and process conditions, a hot-rolled steel sheet having excellent weldability and moldability can be produced And reached the present invention.

Hereinafter, a hot-rolled steel sheet excellent in weldability and moldability which is one aspect of the present invention will be described in detail.

One aspect of the present invention is a ferritic stainless steel comprising, by weight%, 0.03 to 0.08% of C, 0.01 to 1.0% of Si, 1.2 to 1.8% of Mn, 0.01 to 0.3% of Al, 0.005 to 0.4% of Cr, 0.001 to 0.05% of P, 0.001 to 0.005% of S, 0.001 to 0.01% of N, and the balance of Fe and other unavoidable impurities. Each of the above-mentioned components satisfies the following formula (1) (EER), elongation FERN (HER) and tensile strength (TS) satisfy the following formula (2).

0.25 [Si] +0.3 [Mn] - 0.1 [Cr] + 0.55 [Al] +0.2 [Mo] -4.23 [Ti] -2.5 [Nb] - 2.9 [V] ≤ 10.8

Equation 2: T-El x HER ≥ 4907 - 4.257 x TS

In the above formula (1), C, Si, Mn, Cr, Al, Mo, Ti, Nb and V represent the contents (weight%) of the respective elements.

Carbon (C): 0.03 to 0.08 wt%

C is the most economical and effective element to fortify the river. When the content of carbon is less than 0.03 wt%, the precipitation strengthening effect is low due to a small amount of reaction such as precipitation elements such as Ti, Nb and V. On the other hand, when the content of carbon is more than 0.08% by weight, excessive strength increase, weldability, moldability and toughness are deteriorated. Therefore, the content of C is preferably 0.03 to 0.08% by weight.

Silicon (Si): 0.01 to 1.0 wt%

Si deoxidizes molten steel and has a solid solution strengthening effect, and has the effect of promoting ferrite transformation during cooling after hot rolling as a ferrite stabilizing element. When the content of silicon is less than 0.01% by weight, the effect of stabilizing ferrite is small and it is difficult to make the base structure into a ferrite structure. On the other hand, when the content of silicon exceeds 1.0% by weight, a red color scale due to Si is formed on the surface of the steel sheet during hot rolling, so that the surface quality of the steel sheet becomes very poor, and ductility and weldability also deteriorate. Therefore, the content of the silicon is preferably 0.01 to 1.0% by weight.

Manganese (Mn): 1.2 to 1.8 wt%

Mn, like Si, is an effective element for strengthening the steel. In order to exhibit such an effect in the present invention, it is preferable that it is contained in an amount of 1.2 wt% or more. However, when the content of manganese exceeds 1.8 wt%, the ferrite transformation is excessively delayed and it is difficult to secure a proper fraction of ferrite as a matrix. In addition, there is a problem that the segregation part is greatly developed at the center of the thickness during slab casting in the casting process, thereby deteriorating the weldability of the final product. Therefore, the content of Mn is preferably 1.2 to 1.8 wt%.

Aluminum (Sol.Al): 0.01 to 0.3% by weight,

Al is a component mainly added for deoxidation, and as an element stabilizing ferrite, there is an effect of assisting formation of a ferrite phase on steel during cooling after hot rolling. If the content of aluminum is less than 0.01% by weight, the effect intended by the present invention can not be secured. On the other hand, when the content of aluminum is more than 0.3% by weight, defects tend to occur in the slab during continuous casting, and surface defects occur after hot rolling, resulting in poor surface quality. Therefore, the aluminum content is preferably 0.01 to 0.3% by weight.

Cr (Cr): 0.005 to 0.4 wt%

Cr enhances the solidification of the steel and serves to retard martensite formation by delaying the bainite phase transformation during cooling. In order to secure the intended effect in the present invention, it is preferable that the content is 0.005% by weight or more. On the other hand, when the content of chromium exceeds 0.4% by weight, the ferrite transformation is excessively delayed, and the elongation rate is reduced due to an increase in the fraction of martensite necessary. Therefore, the content of Cr is preferably 0.005-0.4% by weight.

Molybdenum (Mo): 0.01 to 0.2 wt%

Mo is excellent in solid solution strengthening effect, and when added together with Ti forms (TiMo) C and contributes greatly to precipitation strengthening. The precipitate containing Mo has excellent thermal stability and little change in precipitation hardening ability due to temperature change. In order to exhibit such an effect of the present invention, it is preferable to include 0.01 wt% or more. On the other hand, if the content of the molybdenum exceeds 0.2% by weight, the weldability is deteriorated due to an increase in the incombustibility, which is economically disadvantageous. Therefore, the Mo content is preferably 0.01 to 0.2% by weight.

Phosphorus (P): 0.001 to 0.05 wt%

P, like Si, has the effect of strengthening the solution and promoting ferrite transformation. When the phosphorus content is less than 0.001% by weight, the strength of the present invention is insufficient to obtain the desired strength. On the other hand, when the content of phosphorus exceeds 0.05% by weight, ductility is deteriorated due to band organization by microsegregation. Therefore, it is preferable that P is included in an amount of 0.001 to 0.05% by weight.

Nitrogen (N): 0.001 to 0.01 wt%

N is a typical solid solution strengthening element together with C, and coarse precipitates are formed together with Ti, Al and the like. In general, the solid solution strengthening effect of N is better than that of carbon, but the toughness is greatly decreased as the amount of N in the steel is increased. If the content of nitrogen is less than 0.001% by weight, it takes a long time to perform the steelmaking and the productivity is lowered. 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 an amount of 0.001 to 0.01% by weight.

The remainder of the present invention is iron (Fe). However, in the ordinary manufacturing process, impurities which are not intended from the raw material or the surrounding environment may be inevitably incorporated, so that it can not be excluded. These impurities are not specifically mentioned in this specification, as they are known to any person skilled in the art of manufacturing.

However, since sulfur is generally referred to as an impurity, a brief description thereof is as follows.

Sulfur (S): 0.001 to 0.005%

The sulfur is inevitably contained as an impurity, which is combined with Mn or the like to form a nonmetallic inclusion, thereby significantly reducing the toughness of the steel. Therefore, the content of the sulfur is preferably suppressed as much as possible. The theoretical sulfur content is advantageous to be limited to 0 wt%, but it is inevitably contained in the manufacturing process inevitably. Therefore, it is important to manage the upper limit, and in the present invention, the upper limit of the sulfur content is preferably limited to 0.005 wt%.

In addition, the steel of the present invention can further improve the effect of the present invention when one or more elements selected from the group consisting of niobium (Nb), titanium (Ti) and vanadium (V) are additionally added. More preferably 0.001 to 0.25 wt% of the total of one or more elements selected from the above group.

Ti exists as TiN in the steel and has an effect of inhibiting the growth of the crystal grains in the heating process for hot rolling. Also, it is a useful component to improve the strength of steel by forming TiC precipitate by reacting with nitrogen and remaining Ti solved in steel and bonding with carbon.

Nb and V form carbides in the steel, which are effective in grain refinement and form fine precipitates to improve strength and toughness of steel. C and N which increase the electrical resistivity are stabilized, so that the phenomenon of local flame generation is alleviated during electric resistance welding, and the softening of the welded portion is also suppressed.

In order to improve the weldability, it is preferable that C, Si, Mn, Cr, Al, Mo, Ti, Nb and V satisfies the following formula (1) The electrical resistivity at high temperature is increased and the weldability is remarkably lowered. The lower limit is not particularly limited, but the lower limit may be limited to 10.0 in consideration of stretch flangeability and elongation. There is a problem that the strength or the elongation rate is drastically lowered.

0.25 [Si] +0.3 [Mn] - 0.1 [Cr] + 0.55 [Al] +0.2 [Mo] -4.23 [Ti] -2.5 [Nb] - 2.9 [V] ≤ 10.8

In the above formula (1), C, Si, Mn, Cr, Al, Mo, Ti, Nb and V represent the contents (weight%) of the respective elements.

Further, it is preferable that the fracture elongation, stretch flangeability and tensile strength satisfy the following formula (2). By satisfying the following expression (2), there is an excellent balance between the strength-to-strength elongation flange and elongation.

Equation 2: T-El x HER ≥ 4907 - 4.257 x TS

It is preferable that the hot-rolled steel sheet includes a ferrite single-phase structure. By including such a microstructure, both the elongation and the stretch flangeability are excellent. In order to provide a preferred hot-rolled steel sheet intended by the present invention, it is preferable to include only a ferrite single-phase structure, but it may inevitably include a second phase. At this time, it is preferable that the second phase contains less than 5% by area fraction. When the fraction of the second phase is 5% or more, the elongation or elongation flangeability is weakened.

Hereinafter, a method for producing a hot-rolled steel sheet excellent in weldability and moldability will be described in detail.

Another aspect of the present invention is a ferritic stainless steel comprising, by weight, 0.03 to 0.08% of C, 0.01 to 1.0% of Si, 1.2 to 1.8% of Mn, 0.01 to 0.3% of Al, 0.005 to 0.4% of Cr, 0.001 to 0.005% of S, 0.001 to 0.01% of N, and the balance of Fe and other unavoidable impurities, and each of the above components satisfies the following formula (1): Reheating the steel slab at a temperature of 1200 to 1300 DEG C, hot rolling the reheated steel slab to a finish rolling temperature of 850 to 1000 DEG C to obtain a steel sheet, and heat-treating the hot-rolled steel sheet at a temperature of 500 to 750 DEG C And cooling the steel sheet at a cooling rate of 10 to 100 占 폚 / second up to the temperature.

0.25 [Si] +0.3 [Mn] - 0.1 [Cr] + 0.55 [Al] +0.2 [Mo] -4.23 [Ti] -2.5 [Nb] - 2.9 [V] ≤ 10.8

In the above formula (1), C, Si, Mn, Cr, Al, Mo, Ti, Nb and V represent the contents (weight%) of the respective elements.

Reheat step

It is preferable to reheat the slab satisfying the above-mentioned component system at 1200 to 1300 占 폚. If the reheating temperature is lower than 1200 ° C, precipitates are not sufficiently reused, and precipitates such as NbC and TiC are reduced in the process after hot rolling. On the other hand, if the temperature exceeds 1300 DEG C, the strength is lowered due to abnormal grain growth of the austenite grains. Therefore, the reheating temperature of the slab is preferably limited to 1200 to 1300 占 폚.

Hot rolling step

As described above, the hot-rolled slab can be subjected to hot rolling. At this time, the finish rolling is preferably performed at 850 to 1000 캜. If the hot finish rolling temperature is lower than 850 占 폚, the rolling load greatly increases. On the other hand, when the hot finish rolling temperature exceeds 1000 캜, the structure of the steel sheet becomes coarse, the steel becomes weak, the scale becomes thick, and the surface quality deteriorates such as a high-temperature rolling-ability scale defect. Therefore, the hot finish rolling is preferably limited to 850 to 1000 ° C.

Cooling step

It is preferable to cool the hot-rolled steel sheet as described above. Further, it is preferable to cool the hot-rolled steel sheet at a cooling rate of 10 to 100 ° C / second until the temperature reaches 500 to 750 ° C from the finish hot-rolling temperature of the hot-rolled steel sheet. When the temperature at which the cooling is terminated is less than 500 DEG C, the microstructure of the steel mainly contains bainite, so that the microstructure to be secured by the present invention can not be secured. On the other hand, when the temperature exceeds 750 ° C, coarse ferrite and pearlite structure are formed to reduce the strength of the steel. If the cooling rate is less than 10 ° C / second, coarsening of the ferrite grains occurs and the precipitates become coarse, making it difficult to ensure the strength to be secured by the present invention. On the other hand, if it exceeds 100 ° C / second, the low-temperature ferrite fraction increases and the elongation rate decreases.

And after the cooling step, winding the steel sheet to facilitate storage and movement of the cooled steel sheet.

The steel sheet produced by the above-mentioned method is naturally cooled, pickled, and then the scale of the surface layer is removed and the steel sheet is additionally provided, whereby the pickled steel sheet can be produced.

Further, after the pickling steel sheet is reheated to 450 to 480 캜, a step of passing the hot-dip galvanizing bath is further included, whereby a hot-dip galvanized steel sheet can be produced.

Hereinafter, the present invention will be described more specifically by way of examples. It should be noted, however, that the following examples are intended to illustrate the invention in more detail and not to limit the scope of the invention. The scope of the present invention is determined by the matters set forth in the claims and the matters reasonably inferred therefrom.

(Example)

The steel slabs satisfying the component systems described in Table 1 were heated to 1250 占 폚 and hot-finished at a temperature (FDT) shown in Table 2 below. Thereafter, cooling was carried out at a cooling rate of 40 DEG C / sec up to the coiling temperature (CT) described in Table 2, and the coiling was carried out at the temperature listed in Table 2 below.

The yield strength (YS), the tensile strength (TS), the fracture elongation (T-El) and the stretch flangeability (HER) of the final hot-rolled steel sheet obtained by completing the winding process are shown in Table 2 below.

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 after the welding under the conditions shown in Table 3, and the strength of the welded portion of the steel sheet was measured. At this time, it was evaluated that the weldability was improved when the welded portion was broken.

division C Si Mn Cr Al P S N Ti Mo Nb V Comparative Example 1 0.02 0.01 1.6 0.01 0.03 0.01 0.003 0.004 0.03 0.05 0.03 0 Comparative Example 2 0.03 0.5 1.2 0.1 0.03 0.01 0.003 0.004 0.05 0.1 0.01 0 Comparative Example 3 0.04 0.1 1.6 0.01 0.1 0.01 0.003 0.004 0.08 0.1 0 0 Comparative Example 4 0.05 0.2 1.4 0.01 0.1 0.01 0.003 0.004 0.06 0.05 0.05 0 Comparative Example 5 0.07 0.3 1.5 0.4 0.1 0.01 0.003 0.004 0.08 0.18 0 0.025 Comparative Example 6 0.09 0.2 1.5 0.1 0.03 0.01 0.003 0.004 0.18 0.12 0 0.03 Comparative Example 7 0.1 0.05 1.8 0.01 0.2 0.01 0.003 0.004 0.08 0.06 0.03 0 Comparative Example 8 0.05 0.05 1.5 0.01 0.2 0.01 0.003 0.004 0.15 0.05 0.025 0 Comparative Example 9 0.06 0.05 1.8 0.3 0.03 0.01 0.003 0.004 0.12 0.01 0.015 0.02 Comparative Example 10 0.065 0.5 1.6 0.01 0.03 0.01 0.003 0.004 0.2 0.2 0.03 0.02 Inventory 1 0.03 0.05 1.2 0.01 0.03 0.003 0.003 0.005 0.08 0.04 0 0 Inventory 2 0.04 0.15 1.2 0.01 0.03 0.01 0.003 0.004 0.1 0.01 0.02 0 Inventory 3 0.04 0.15 1.2 0.01 0.03 0.01 0.003 0.004 0.1 0.01 0.02 0 Honorable 4 0.06 0.05 1.4 0.1 0.1 0.01 0.003 0.004 0.15 0.05 0 0.03 Inventory 5 0.055 0.05 1.4 0.01 0.03 0.01 0.003 0.004 0.11 0.11 0.015 0.045 Inventory 6 0.045 0.4 1.3 0.01 0.03 0.01 0.003 0.004 0.1 0.09 0.02 0.03 Honorable 7 0.06 0.05 1.5 0.3 0.03 0.01 0.003 0.004 0.15 0.15 0.02 0.06 Honors 8 0.06 0.5 1.5 0.01 0.03 0.01 0.003 0.004 0.15 0.12 0.01 0.04

Psalter FDT
(° C) CT
(° C) Equation 1 YS
(MPa) TS
(MPa) T-El
(%) HER
(%) At the beginning of Equation 2 Later in Equation 2 Second phase
Phase fraction
(%) Weldability Comparative Example 1 870 623 10.956 466 497 25 91 2275 2790 2 X Comparative Example 2 882 631 10.927 560 621 27 100 2700 2262 3 X Comparative Example 3 875 618 10.895 487 615 28 96 2688 2288 6 X Comparative Example 4 878 635 10.811 594 664 24 66 1584 2079 4 X Comparative Example 5 868 615 10.825 753 803 20 56 1120 1487 3 X Comparative Example 6 905 652 10.346 896 964 17 38 646 802 2 ○ Comparative Example 7 907 643 10.926 588 740 18 65 1170 1755 7 X Comparative Example 8 912 628 10.541 763 801 18 65 1170 1496 3 ○ Comparative Example 9 910 615 10.596 807 845 15 38 570 1308 3 ○ Comparative Example 10 922 622 10.341 965 1016 14 32 448 580 3 ○ Inventory 1 902 638 10.710 568 621 27 101 2727 2262 2 ○ Inventory 2 908 642 10.596 567 619 26 96 2496 2271 3 ○ Inventory 3 912 646 10.596 618 693 25 89 2225 1956 2 ○ Honorable 4 906 639 10.424 725 793 24 82 1968 1530 3 ○ Inventory 5 916 642 10.494 774 832 22 81 1782 1364 3 ○ Inventory 6 925 646 10.619 774 830 21 69 1449 1372 3 ○ Honorable 7 917 638 10.279 925 1008 17 55 935 614 2 ○ Honors 8 905 642 10.497 899 1000 16 58 928 649 2 ○

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

As shown in Table 2, it can be confirmed that Inventive Examples 1 to 8 satisfy the composition range and manufacturing conditions proposed by the present invention, and thus can secure a hot-rolled steel sheet having excellent formability and weldability.

On the other hand, it can be seen that Comparative Examples 1 to 5 and 7 do not satisfy the formula (1) and weldability is improved. Further, in Comparative Examples 4 to 10, the weldability is good but the formula (2) is not satisfied, and it can be confirmed that the balance between elongation, stretch flangeability and tensile strength is improved.

That is, as shown in FIG. 1, when the values of the fracture elongation, the stretch flangeability and the tensile strength of all the steels in the inventive and comparative examples are plotted in the graph, It can be seen that the effect can be exerted.

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 in the appended claims. It will be possible.

Claims (7)

The steel sheet according to any one of claims 1 to 3, wherein the steel sheet contains 0.03 to 0.08% of C, 0.01 to 1.0% of Si, 1.2 to 1.8% of Mn, 0.01 to 0.3% of Al, 0.005 to 0.4% of Cr, 0.01 to 0.2% 0.001 to 0.005% of S, 0.001 to 0.01% of N, and the balance of Fe and other unavoidable impurities. Each of the components satisfies the following formula (1), and the fracture elongation (T-El) (HER) and tensile strength (TS) satisfy the following formula (2).
0.25 [Si] +0.3 [Mn] - 0.1 [Cr] + 0.55 [Al] +0.2 [Mo] -4.23 [Ti] -2.5 [Nb] - 2.9 [V] ≤ 10.8
Equation 2: T-El x HER ≥ 4907 - 4.257 x TS
(Wherein C, Si, Mn, Cr, Al, Mo, Ti, Nb and V are the contents (weight%
The method according to claim 1,
And 0.001 to 0.25% in total of at least one selected from the group consisting of Nb, Ti and V. The hot-rolled steel sheet has excellent weldability and moldability.
The method according to claim 1,
Wherein the microstructure of the hot-rolled steel sheet is ferritic and has excellent weldability and moldability.
The steel sheet according to any one of claims 1 to 3, wherein the steel sheet contains 0.03 to 0.08% of C, 0.01 to 1.0% of Si, 1.2 to 1.8% of Mn, 0.01 to 0.3% of Al, 0.005 to 0.4% of Cr, 0.01 to 0.2% 0.05 to 0.05%, S: 0.001 to 0.005%, N: 0.001 to 0.01%, balance Fe and other unavoidable impurities, and each of the components satisfies the following formula (1).
Reheating the steel slab at 1200-1300 占 폚;
Hot-rolling the reheated steel slab to a finish rolling temperature of 850 to 1000 占 폚 to obtain a steel sheet; And
And cooling the hot-rolled steel sheet to a temperature of 500 to 700 占 폚 at a cooling rate of 10 to 100 占 폚 / sec.
0.25 [Si] +0.3 [Mn] - 0.1 [Cr] + 0.55 [Al] +0.2 [Mo] -4.23 [Ti] -2.5 [Nb] - 2.9 [V] ≤ 10.8
(Wherein C, Si, Mn, Cr, Al, Mo, Ti, Nb and V are the contents (weight%
5. The method of claim 4,
And further comprising 0.001 to 0.25% of at least one selected from the group consisting of Nb, Ti and V, wherein the weldability and formability are excellent.
5. The method of claim 4,
A method for producing a hot-rolled steel sheet excellent in weldability and moldability, wherein a fracture elongation (T-El), a stretch flangeability (HER) and a tensile strength (TS) of the hot-rolled steel sheet satisfy the following formula (2).

Equation 2: T-El x HER ≥ 4907 - 4.257 x TS
5. The method of claim 4,
Further comprising a step of reheating the steel sheet at 450 to 480 占 폚 after the pickling treatment and performing hot dip galvanizing, thereby producing a hot-rolled steel sheet having excellent weldability and moldability.

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