KR100992317B1 - High Yield Ratio Hot Rolled Steel Sheet and Hot Rolled Pickled Steel Sheet with Excellent Descalability and Manufacturing Method Thereof - Google Patents

Abstract

In the present invention, by weight%, C: 0.04 to 0.13%, Mn: 0.4 to 1.3%, Si: 0.3% or less, P: 0.03% or less, S: 0.01% or less, sol.Al: 0.005 to 0.10%, N: Hot rolled steel sheet and the hot rolled steel sheet comprising at least one of 0.002 ~ 0.008%, Sb: 0.005 ~ 0.04% and Ti: 0.01 ~ 0.06%, Nb: 0.01 ~ 0.06%, V: 0.01 ~ 0.1% It provides a hot-rolled steel sheet, characterized in that the pickling treatment with a 10-20% HCl aqueous solution maintained at a temperature of 50 ~ 100 ℃. In this case, a relationship of 0.01 ≤ {[Ti] + [Nb] + [V]} ≤ 0.15 may be established between Ti, Nb, and V, and may be wound in a temperature range that is effective for improving surface quality during manufacturing of the steel sheet. Taking steps.

According to the present invention, it is possible to economically and efficiently provide a hot rolled steel sheet, a hot-rolled steel sheet, and a manufacturing method thereof having excellent mechanical properties and excellent surface quality.

Hot Rolled Steel Sheet, Hot Calculated Steel Sheet, Surface Scale, Sb, High Yield Ratio

Description

High Yield Ratio Hot Rolled Steel Sheet and Hot Rolled Pickled Steel Sheet with Excellent Descalability and Manufacturing Method Thereof}

The present invention relates to a method for manufacturing a high strength hot rolled steel sheet and pickled steel sheet having a yield ratio of 0.8 or more, which is mainly used for automobile wheels, rims, frames, and other automotive parts, and more particularly, yielding a yield strength of 270 to 600 MPa. The present invention relates to a method of producing a high yield ratio hot rolled steel sheet and a hot-rolled steel sheet having a ratio of 0.8 or more and exhibiting a scale peeling characteristic much better than that of a conventional high strength steel.

Recently, steel sheets for automobiles require a higher level of strength in order to reduce the weight of automobile molded articles, and also require steel sheets having a beautiful surface with uniform surface roughness. In general, however, solid solution strengthening elements such as Mn, P, and Si or precipitation strengthening elements such as Nb, Ti, and V are added to increase the strength of the steel sheet. However, excessive increase of alloying elements causes load of equipment during manufacturing, which can lead to plate breakage or shape defects during hot rolling, and high-alloy can cause various oxides to be formed non-uniformly on the surface layer. It is difficult to carry out, the pickling characteristics are deteriorated and the surface roughness deviation can be deepened.

In order to satisfy these requirements, the technology of conventionally controlling the surface temperature of steel slabs to which a certain amount of Si and Mn is added to facilitate the removal of scales related to Si, and to secure the surface quality, the surface of Si by a certain amount or more Technology to secure the quality, technology to secure the surface quality by adding Sn, Ti and B, technology to secure the surface quality by controlling the content of Cu and P has been shown.

However, all the components utilized by the above-mentioned prior arts may affect the mechanical properties of the steel sheet in addition to the surface quality, so that the surface quality and the mechanical properties may be simultaneously affected by the hot rolling operation conditions. Controlling techniques can bring about changes in metamorphosis. Therefore, it is necessary to control the cooling-related processes in the manufacture of the steel sheet, so difficulties in the production process are expected. In addition, the above-described conventional techniques all utilize expensive elements, and thus can be said to be economically inefficient.

The present invention is to solve the problems of the prior art described above by adding Sb to suppress the formation of oxides on the surface and the surface of the steel during hot rolling and to improve the peeling characteristics of the iron oxide film, The present invention provides a high yield ratio hot rolled steel sheet, a hot-rolled steel sheet, and a method of manufacturing the same, having a high-strength property and a yield ratio of 0.8 or more and exhibiting a scale peeling property much better than that of a conventional high-strength steel.

In order to achieve this object, the present invention provides a weight%, C: 0.04 to 0.13%, Mn: 0.4 to 1.3%, Si: 0.3% or less, P: 0.03% or less, S: 0.01% or less, sol.Al: 0.005 ~ 0.10%, N: 0.002 ~ 0.008%, Sb: 0.005 ~ 0.04% and Ti: 0.01 ~ 0.06%, Nb: 0.01 ~ 0.06%, V: 0.01 ~ 0.1% Steel sheet and the hot rolled steel sheet provides a hot-rolled steel sheet, characterized in that the pickling treatment with a 10-20% HCl aqueous solution maintained at a temperature of 50 ~ 100 ℃. In this case, a relationship of 0.01 ≦ {[Ti] + [Nb] + [V]} ≦ 0.15 may be established between the Ti, Nb, and V.

Furthermore, the present invention is in weight%, C: 0.04 to 0.13%, Mn: 0.4 to 1.3%, Si: 0.3% or less, P: 0.03% or less, S: 0.01% or less, sol.Al: 0.005 to 0.10%, 1200 to 1300 ° C for steel slabs containing at least one of N: 0.002 to 0.008%, Sb: 0.005 to 0.04%, Ti: 0.01 to 0.06%, Nb: 0.01 to 0.06%, V: 0.01 to 0.1% Reheating step of reheating, Ar ₃ +30 ~ Ar ₃ + 100 ℃ manufacturing method of the hot rolled steel sheet and the manufacturing method comprising a finish rolling step of finishing rolling at + 100 ℃ and winding step at 500 ~ 650 ℃ It provides a method for producing a hot-rolled steel sheet further comprising a pickling step of pickling treatment with an aqueous HCl solution maintained at a temperature of 50 ~ 100 ℃.

(Where Ar ₃ = 910-310 * C-80 * Mn-20 * Cu-15 * Cr-55 * Ni-80 * Mo-0.35 * (thick-8))

In the method of manufacturing the hot rolled steel sheet and the method of manufacturing the hot-rolled fine steel sheet, a relation of 0.01 ≦ {[Ti] + [Nb] + [V]} ≤ 0.15 may be established between Ti, Nb, and V. HCl aqueous solution used in the steel sheet manufacturing method may have a concentration of 10 to 20%.

According to the present invention, it is possible to economically and efficiently provide a hot rolled steel sheet, a hot-rolled steel sheet, and a manufacturing method thereof having excellent mechanical properties having a yield ratio of 0.8 or more and a yield ratio of 0.8 or more and having a strength of yield strength of 270 to 600 MPa. .

Hot rolled steel sheet of the present invention by weight% C: 0.04 ~ 0.13%, Mn: 0.4 ~ 1.3%, Si: 0.3% or less, P: 0.03% or less, S: 0.01% or less, sol.Al: 0.005 ~ 0.10%, It contains one or more of N: 0.002 ~ 0.008%, Sb: 0.005 ~ 0.04%, Ti: 0.01 ~ 0.06%, Nb: 0.01 ~ 0.06%, V: 0.01 ~ 0.1% and is composed of the remaining Fe and other unavoidable impurities . At this time, the sum of the weight percent of the alloying elements added to the steel is characterized by satisfying the following formula.

[Equation 1]

0.01 ≤ {[ Ti ] + [ Nb ] + [V]} ≤ 0.15

Hereinafter, the component system of the present invention will be described in detail (hereinafter by weight).

C: 0.04-0.13%

C is the most economical and effective element for reinforcing steel. If the content is less than 0.04%, other alloying elements should be added in order to secure the same strength, and if it exceeds 0.13%, weldability, formability and toughness will be reduced. There is a problem. Therefore, the content of C is limited to 0.04 to 0.13%.

Si: 0.3% or less

Si is effective for deoxidizing molten steel and exerting a solid solution effect. If the content exceeds 0.3%, the red scale by Si is formed on the surface of the steel sheet during hot rolling. Since there is a problem, the content is limited to 0.3% or less.

Mn: 0.4-1.3%

Mn acts as an effective element to solidify the steel. If the Mn content is less than 0.4%, the solid solution strengthening effect of the addition is insignificant, whereas if it exceeds 1.3%, the segregation part is greatly developed at the center of thickness during slab casting in the steelmaking process, and there is a problem that the weldability of the final product is damaged. Therefore, the content of Mn is limited to 0.4 ~ 1.3%.

P: 0.03% or less

P is an impurity present in the steel. When the content exceeds 0.03%, P is combined with Mn to form a non-metallic inclusion, thereby greatly reducing the toughness and strength of the steel. Therefore, P is limited to 0.03% or less.

S: 0.010% or less

S is an impurity present in the steel. When the content exceeds 0.010%, S is combined with Mn to form a non-metallic inclusion, and thus, the toughness and strength of the steel are greatly reduced. Therefore, the content is limited to 0.010% or less.

Sol.Al: 0.005 ~ 0.10%

Sol.Al is a component added for deoxidation. If the content is less than 0.005%, the deoxidation effect is insufficient, whereas if it exceeds 0.10%, the effect is saturated, resulting in an increase in manufacturing cost. The content is limited to 0.005 to 0.10%.

N: 0.002-0.008%

The content of N is due to the content of Ti. In general, N is dissolved in steel and precipitated to increase the strength of the steel, which is superior to carbon. On the other hand, however, the toughness decreases significantly as the amount of nitrogen in the steel increases. Therefore, in the present invention, by containing an appropriate amount of nitrogen in the steel, it forms a TiN and serves to suppress grain growth during the reheating process. If the content of N is less than 0.002%, TiN formation may be insufficient and manufacturing costs may increase during steelmaking. On the other hand, if the content of N exceeds 0.008%, toughness may be greatly reduced, leading to poor workability. Therefore, the content is limited to 0.0020 to 0.0080%.

Sb: 0.005-0.04%

Sb is an important element in the present invention, the 0.005 ~ 0.04% is added. If Sb is less than 0.005%, the concentration of Sb in the surface layer is insufficient, so that it is difficult to effectively suppress the formation of oxides, and it is difficult to contribute to the easy removal of the already formed iron oxide film. On the other hand, if the content of Sb exceeds 0.04%, Sb is excessively concentrated in the surface layer, thereby deteriorating the surface properties, bringing about the material change of the steel, the ductility is lowered and the hole expanding ability (HER, Hole Expanding Ratio) is lowered. Therefore, the content is limited to 0.005 to 0.04%.

In the present invention, it is preferable to add at least one element selected from Ti, Nb and V to the above composition.

Ti: 0.01 ~ 0.06%

Ti is an effective component for refining grains, and is present as TiN in steel, 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 greatly improving the strength of the steel. When the content of Ti is less than 0.01%, the austenite grain growth inhibition effect and the strength increase effect by TiC formation cannot be obtained. On the other hand, when the content of Ti exceeds 0.06%, the steel sheet is welded to the melting point when the steel pipe is manufactured, thereby rapidly melting. Since TiN is re-used and the toughness of the weld heat affected zone is deteriorated, it is preferable to limit the content to 0.01 to 0.06%.

Nb: 0.01 ~ 0.06%

Nb is not only effective for refining grains, but is also an effective component for greatly improving the strength of steel. If the content of Nb is less than 0.01%, it is difficult to obtain the effect of addition, while if it exceeds 0.06%, the austenite microcrystallization temperature is excessively high due to excessive precipitation of Nb carbonitride, thereby increasing material anisotropy. Therefore, the content of Nb is limited to 0.01 ~ 0.06%.

V: 0.01 ~ 0.1%

V is not only an effective element for solidifying steel, but also an element that can form carbide to increase the precipitation strengthening effect. However, if the amount is less than 0.01%, the above effects due to the addition cannot be obtained. If the amount exceeds 0.1%, the weldability is deteriorated and it is economically disadvantageous. Therefore, the content of V is limited to 0.01 ~ 0.1%.

Relationship between Ti, Nb and V: 0.01 ≤ {[Ti] + [Nb] + [V]} ≤ 0.15

The sum of the weight percentages of the alloying elements added in the steel should be added so as to satisfy the following formula 0.01? {[Ti] + [Nb] + [V]}? 0.15. This can promote the formation of Ti, Nb, V-based carbonitride which is unevenly precipitated during hot rolling when excessive alloying elements are added in steel, and deformation resistance variation occurs due to deformation organic precipitation during hot rolling, resulting in poor shape and equipment. Bring a load of In addition, the formation of nonuniform precipitates leads to nonuniformity of oxide formation in the surface layer. Therefore, the addition amount of the alloying element is limited by the above formula.

Hereinafter, the manufacturing process of the present invention will be described in detail by dividing step by step.

In the present invention, a process of reheating, hot rolling and winding the steel slab having the above-described composition is performed, wherein the yield strength of the hot rolled coil is determined by the microstructures and precipitates generated during hot rolling and various oxides formed on the surface layer. Considering the high dependence on the silver temperature, the target yield strength of the hot rolled coil can be obtained by controlling the temperature at which the hot rolling of the slab is finished, and the hot rolled steel having excellent scale peeling characteristics of the hot rolled coil and the hot rolled steel having a beautiful surface Pickling steel sheet can be obtained.

Reheating Temperature: 1200 ~ 1300 ℃

The steel slab of the composition mentioned above is reheated at the temperature of 1200-1300 degreeC. If the reheating temperature is less than 1200 ℃, precipitates are not sufficiently reused, and precipitates such as NbC and TiC are reduced in the process after hot rolling. On the other hand, when the reheating temperature is higher than 1300 ℃, the strength may decrease due to abnormal grain growth of austenite grains. Therefore, the reheating temperature of the present invention is limited to 1200 to 1300 ° C.

Finish rolling temperature: Ar ₃ + 30 ~ Ar3 + 100 ℃

Reheated steel slabs are rolled by rough and finish rolling. At this time, the finish rolling is finished in the temperature range higher than Ar ₃ +30 ℃ and lower than Ar3 + 100 ℃ based on the transformation temperature (Ar ₃ ) calculated by the equation (1). The yield strength of the hot rolled coil is determined by the microstructures and precipitates formed during hot rolling, and since the various oxides formed on the surface layer have a large dependence on the hot rolling temperature, the uniform yield strength and surface oxide are limited by limiting the hot rolling temperature range. To get

[Equation 2]

Ar ₃ = 910-310 * C-80 * Mn-20 * Cu-15 * Cr-55 * Ni-80 * Mo-0.35 * (thick-8)

(However, thick is the thickness of the rolled plate after hot rolling (mm))

Coiling temperature: 500 ~ 650 ℃

The rolled steel sheet is wound at a temperature of 500 to 650 ° C. At this time, if the winding temperature is less than 500 ℃ precipitates do not form crazy, the low temperature structure bainite transformation occurs to increase the strength, but the ductility is lowered, whereas if it exceeds 650 ℃ microstructure is formed of coarse ferrite and pearlite Precipitates are coarsened and formed non-uniformly, so that the strength is decreased, and a non-uniform oxide layer is formed, thereby degrading scale peeling characteristics.

The present invention provides a hot-rolled steel sheet and a method for manufacturing the hot-rolled steel sheet prepared by the above method, further comprising the step of pickling using a 10-20% HCl aqueous solution maintained at a temperature of 50 ~ 100 ℃. The aqueous HCl solution was experimentally found to have the best pickling efficiency at a concentration of 50 to 100 ° C. and 10 to 20%. In the present invention, pickling treatment is performed using these conditions.

Hereinafter, the present invention will be described in more detail with reference to Examples. However, this embodiment is only for illustrating the present invention in more detail, the present invention is not limited by the description of these embodiments.

(Example 1)

Table 1 shows the slabs having the component composition of the present invention and the slabs of the comparative material in Table 1.

division [C] [Mn] [Si] [P] [S] [Nb] [Ti] [V] [Sb] Comparative material 1 0.038 0.48 0.03 0.012 0.003 0.01 0 0 0 Comparative material 2 0.042 0.52 0.04 0.014 0.004 0.003 0 0 0.03 Invention 1 0.051 0.68 0.045 0.014 0.004 0.015 0 0 0.01 Comparative material 3 0.048 0.67 0.03 0.01 0.004 0.018 0 0 0.08 Invention Material 2 0.057 0.82 0.04 0.014 0.004 0.015 0 0 0.02 Invention 3 0.062 0.8 0.028 0.01 0.005 0.02 0 0 0.1 Comparative material 4 0.068 0.77 0.035 0.012 0.003 0.027 0 0 0.06 Comparative material 5 0.071 0.78 0.04 0.01 0.004 0.043 0 0.02 0 Invention 4 0.069 0.81 0.038 0.014 0.003 0.045 0 0.02 0.02 Comparative Material 6 0.07 0.78 0.04 0.014 0.004 0.045 0 0.02 0.08 Comparative material 7 0.071 0.82 0.042 0.013 0.003 0.025 0 0.04 0.08 Invention 5 0.073 1.18 0.039 0.014 0.004 0.06 0.02 0.035 0.02 Comparative Material 8 0.077 1.22 0.04 0.012 0.004 0.049 0.02 0.035 0 Invention Material 6 0.072 1.2 0.041 0.01 0.004 0.06 0.02 0.06 0.08 Invention Material 7 0.069 1.24 0.04 0.014 0.003 0.058 0.04 0.04 0.02 Comparative material 9 0.07 1.19 0.033 0.01 0.004 0.06 0.06 0.04 0.04 Comparative Material 10 0.072 1.17 0.043 0.013 0.004 0.045 0.04 0.04 0.06 Comparative Material 11 0.081 1.21 0.04 0.016 0.004 0.06 0.04 0.04 0.08 Comparative Material 12 0.071 1.2 0.04 0.013 0.005 0.06 0.04 0.04 0.1 Invention Material 8 0.078 1.21 0.03 0.014 0.004 0.058 0.04 0.04 0.02 Invention Material 9 0.051 0.68 0.045 0.014 0.004 0.015 0 0 0.01 Invention Material 10 0.049 0.71 0.05 0.013 0.003 0.02 0 0 0.04 Invention Material 11 0.057 0.82 0.04 0.014 0.004 0.015 0 0 0.02 Invention Material 12 0.069 0.78 0.04 0.014 0.004 0.025 0 0 0.02 Invention Material 13 0.069 0.8 0.04 0.014 0.004 0.035 0 0 0.02 Invention Material 14 0.069 0.81 0.038 0.014 0.003 0.045 0 0.02 0.02 Invention Material 15 0.072 0.83 0.04 0.015 0.004 0.047 0 0.02 0.04 Invention 16 0.066 0.79 0.041 0.011 0.004 0.046 0 0.06 0.04 Invention Material 17 0.073 1.18 0.039 0.014 0.004 0.06 0.02 0.035 0.02 Invention Material 18 0.069 1.24 0.04 0.014 0.003 0.058 0.04 0.04 0.02 Invention 19 0.078 1.21 0.03 0.014 0.004 0.058 0.04 0.04 0.02

(Unit is weight%)

Steel sheet was prepared by varying the operating conditions as shown in Table 2 for each Example shown in Table 1. For reference, Comparative Tables 3, 5, 8, 11, 13, 18, and 19 in Table 2 are component systems satisfying the scope of the present invention.

division {[Nb] + [Ti] + [V]} (%) Ar ₃
(℃) Ar ₃ +30
(℃) Ar ₃ +100
(℃) FDT
(℃) CT
(℃) Comparative Steel 1 0.01 860.52 890.52 960.52 910 600 Comparative Steel 2 0.003 856.08 886.08 956.08 895 550 Comparative Steel 3 0.015 840.49 870.49 940.49 890 700 Comparative Steel 4 0.018 842.22 872.22 942.22 890 550 Comparative Steel 5 0.015 827.43 857.43 927.43 880 700 Inventive Steel 1 0.02 827.48 857.48 927.48 905 500 Comparative Steel 6 0.027 828.02 858.02 928.02 890 650 Comparative Steel 7 0.063 826.29 856.29 926.29 880 550 Comparative Steel 8 0.065 824.51 854.51 924.51 840 600 Comparative Steel 9 0.065 826.6 856.6 926.6 885 600 Comparative Steel 10 0.065 823.09 853.09 923.09 900 600 Comparative Steel 11 0.115 793.67 823.67 893.67 875 750 Comparative Steel 12 0.104 789.23 819.23 889.23 885 600 Inventive Steel 2 0.14 792.38 822.38 892.38 870 650 Comparative Steel 13 0.138 790.11 820.11 890.11 910 600 Comparative Steel 14 0.16 793.8 823.8 893.8 870 550 Comparative Steel 15 0.125 794.78 824.78 894.78 880 600 Comparative Steel 16 0.14 788.79 818.79 888.79 870 650 Comparative Steel 17 0.14 792.69 822.69 892.69 865 650 Comparative Steel 18 0.138 789.72 819.72 889.72 860 700 Inventive Steel 3 0.015 840.49 870.49 940.49 890 600 Inventive Steel 4 0.02 838.71 868.71 938.71 887 650 Inventive Steel 5 0.015 827.43 857.43 927.43 880 650 Inventive Steel 6 0.025 826.91 856.91 926.91 875 600 Comparative Steel 19 0.035 825.31 855.31 925.31 890 450 Inventive Steel 7 0.065 824.51 854.51 924.51 900 550 Inventive Steel 8 0.067 821.98 851.98 921.98 890 600 Inventive Steel 9 0.106 827.04 857.04 927.04 880 650 Inventive Steel 10 0.115 793.67 823.67 893.67 875 550 Inventive Steel 11 0.138 790.11 820.11 890.11 865 600 Inventive Steel 12 0.138 789.72 819.72 889.72 860 600

Experimental results based on the component system of Table 1 and the manufacturing conditions of Table 2 are shown in Table 3 below the mechanical properties of each steel sheet and the results of the surface area residual scale after pickling.

division YS (MPa) TS (MPa) TS / YS T-El. (%) YSxT-El. HER (%) Remaining Scale (%) Comparative Steel 1 308 380 0.81 38.3 11796.4 93.2 6.2 Comparative Steel 2 285 370 0.77 36 10260 96.7 1.8 Comparative Steel 3 330 400 0.82 38.7 12771 72.4 4.2 Comparative Steel 4 380 460 0.83 36.1 13718 55.7 6.3 Comparative Steel 5 378 465 0.81 37.5 14175 75.3 2.2 Inventive Steel 1 420 480 0.87 36 15120 75.1 1.6 Comparative Steel 6 420 480 0.87 35 14700 65.5 3.3 Comparative Steel 7 460 520 0.88 32 14720 70.4 3.1 Comparative Steel 8 485 500 0.97 26 12610 67.2 3.7 Comparative Steel 9 520 620 0.84 29 15080 50.4 5.4 Comparative Steel 10 510 615 0.83 30 15300 50.8 4.1 Comparative Steel 11 534 627 0.85 29 15486 50.1 2.8 Comparative Steel 12 556 634 0.88 27 15012 58.2 4.3 Inventive Steel 2 560 635 0.88 26 14560 45.6 4.4 Comparative Steel 13 575 648 0.88 22 12650 50.5 1.3 Comparative Steel 14 578 655 0.88 21 12138 45.3 2.9 Comparative Steel 15 570 645 0.88 23 13110 45.5 5.2 Comparative Steel 16 565 640 0.88 23 12995 40.1 6.3 Comparative Steel 17 570 635 0.90 23 13110 41.9 6.2 Comparative Steel 18 550 630 0.87 25 13750 40.6 3.8 Inventive Steel 3 345 400 0.86 37.5 12937.5 89.8 0.5 Inventive Steel 4 350 410 0.85 37 12950 80.6 1.1 Inventive Steel 5 400 450 0.89 36.6 14640 75.8 0.3 Inventive Steel 6 410 470 0.87 36 14760 72.2 0.2 Comparative Steel 19 440 565 0.78 33 14520 70.3 0.5 Inventive Steel 7 475 530 0.90 31 14725 68.5 0.4 Inventive Steel 8 510 590 0.86 30 15300 65.4 0.2 Inventive Steel 9 490 575 0.85 28 13720 55.6 1.0 Inventive Steel 10 557 650 0.86 27 15039 55.8 0.7 Inventive Steel 11 563 660 0.85 25 14075 54.4 0.8 Inventive Steel 12 563 665 0.85 23 12949 45.4 1.1

In Table 3, YS represents yield strength, TS represents tensile strength, and T-El. Represents elongation. In addition, HER is the hole expanding ability of the hole expanding ratio up to the diameter of the hole when the crack began to occur when the punched hole of 10mm diameter is expanded (Hole Expanding Ratio = {(D ₀ -D _f ) x100} / D ₀ ). The remaining scale means the area fraction of the scale remaining unremoved per unit area of the surface part after pickling for 60 seconds in a 15% HCl aqueous solution maintained at a temperature of 80 ° C. of the hot rolled sheet.

Referring to the results of this embodiment, all the steels out of the Sb content range proposed in the present invention remain on the surface after pickling excessively, which is ① the surface layer when added in excess of the Sb content range proposed in the present invention The distribution of Sb is very high. Particularly, segregation occurs at grain boundaries, causing uneven peeling of the oxide during hot rolling or uneven pickling, which may cause defects. It is believed that this is due to the lack of the effective effect of Sb.

On the other hand, when looking at the invention steels added Sb to the content range proposed in the present invention, Sb is mainly present between the oxide formed on the surface of the steel sheet and the steel sheet matrix structure can effectively act to remove the oxide and remove pickling, It can be seen that the surface quality is excellent. Furthermore, it can be seen that the yield strength of 270 ~ 600MPa while maintaining the excellent mechanical properties having a yield ratio of 0.8 or more.

On the other hand, even when Sb is added in an appropriate amount of the proposed content range, if the coiling temperature of the hot rolled steel sheet is too high after hot rolling, the amount of Sb diffuses smoothly at high temperature and the amount of concentration on the surface increases more than necessary, resulting in uneven surface area. It can be seen from the results of Table 2 and Table 3 that the oxide formation and non-uniform pickling is performed, the surface quality is deteriorated, and the HER value is decreased due to the formation of coarse carbide and coarsening of the pearlite structure. In addition, even when the coiling temperature is too low, the bainite transformation fraction in the microstructure is too high to increase the strength, but elongation is reduced, so it is unreasonable to use it as a steel sheet for automobiles.

(Example 2)

The winding temperature and Sb content range required to obtain the steel of the present invention from the results of Example 1 are shown in Figs. 1, 2, and 3, "○", "△" and "x" mean the relative degree of the characteristic and mean "good", "normal" and "bad", respectively.

1 is a comparative comparison results of the hole expansion capacity (HER, Hole Expanding Ratio) according to the winding temperature and the Sb content of the steel satisfying the component range proposed in the present invention, Figure 2 is a steel satisfying the component range proposed in the present invention The comparison results of the elongation according to the change in the coiling temperature and the Sb content, and FIG. 3 compares the scale peeling characteristics representing the coiling temperature of the steel satisfying the component range proposed in the present invention and the remaining scale ratio according to the Sb content.

In addition, based on the results shown in FIGS. 1 to 3, each characteristic is shown in FIG. 4 to obtain a good common range. Steel having a winding temperature and Sb content satisfying the range shown in Figure 4 is expected to be excellent in its utility as well as the physical properties as well as the surface quality.

1 is a graph showing the hole expansion capacity change according to the coiling temperature and the Sb content.

2 is a graph showing the change in elongation according to the coiling temperature and the Sb content.

Figure 3 is a graph showing the change in scale peeling characteristics according to the coiling temperature and Sb content.

4. Graph showing the area between the coiling temperature and the content of Sb in accordance with the present invention

Claims (9)

In weight%, C: 0.04 to 0.13%, Mn: 0.4 to 1.3%, Si: 0.3% or less (excluding 0), P: 0.03% or less (excluding 0), S: 0.01% or less (excluding 0) , sol.Al: 0.005 ~ 0.10%, N: 0.002 ~ 0.008%, Sb: 0.005 ~ 0.04% and Ti: 0.01 ~ 0.06%, Nb: 0.01 ~ 0.06%, V: 0.01 ~ 0.1% Hot rolled steel sheet characterized in that the yield ratio is 0.8 or more. The hot rolled steel sheet according to claim 1, wherein a relationship of 0.01? {[Ti] + [Nb] + [V]}? 0.15 is established between the Ti, Nb, and V. In weight%, C: 0.04 to 0.13%, Mn: 0.4 to 1.3%, Si: 0.3% or less (excluding 0), P: 0.03% or less (excluding 0), S: 0.01% or less (excluding 0) , sol.Al: 0.005 ~ 0.10%, N: 0.002 ~ 0.008%, Sb: 0.005 ~ 0.04% and Ti: 0.01 ~ 0.06%, Nb: 0.01 ~ 0.06%, V: 0.01 ~ 0.1% , Hot-rolled steel sheet, characterized in that the pickling treatment with 10-20% HCl aqueous solution maintained at a temperature of 50 ~ 100 ℃, yield ratio is 0.8 or more. The hot-rolled steel sheet according to claim 3, wherein a relation of 0.01? {[Ti] + [Nb] + [V]}? 0.15 is established between the Ti, Nb, and V. By weight%, C: 0.04 to 0.13%, Mn: 0.4 to 1.3%, Si: 0.3% or less (excluding 0), P: 0.03% or less, S: 0.01% or less, sol.Al: 0.005 to 0.10%, For steel slabs containing at least one of N: 0.002 to 0.008%, Sb: 0.005 to 0.04% and Ti: 0.01 to 0.06%, Nb: 0.01 to 0.06%, V: 0.01 to 0.1%, Reheating step to reheat to 1200 ~ 1300 ℃; Ar ₃ + 30 ~ finish rolling step of rolling, finishing Ar ₃ + 100 ℃; And Winding step of winding at 500 ~ 650 ° C; The method of manufacturing a hot rolled steel sheet comprising a hot rolled steel sheet having a yield ratio of 0.8 or more. However, Ar ₃ = 910-310 * C-80 * Mn-20 * Cu-15 * Cr-55 * Ni-80 * Mo-0.35 * (thick-8) The method of manufacturing a hot rolled steel sheet according to claim 5, wherein a relation of 0.01? {[Ti] + [Nb] + [V]}? 0.15 is established between the Ti, Nb, and V. By weight%, C: 0.04 to 0.13%, Mn: 0.4 to 1.3%, Si: 0.3% or less (excluding 0), P: 0.03% or less, S: 0.01% or less, sol.Al: 0.005 to 0.10%, For steel slabs containing at least one of N: 0.002 to 0.008%, Sb: 0.005 to 0.04% and Ti: 0.01 to 0.06%, Nb: 0.01 to 0.06%, V: 0.01 to 0.1%, Reheating step to reheat to 1200 ~ 1300 ℃; Ar ₃ + 30 ~ finish rolling step of rolling, finishing Ar ₃ + 100 ℃; Winding step of winding at 500 ~ 650 ° C; And Pickling step of pickling treatment with aqueous HCl solution maintained at a temperature of 50 ~ 100 ℃; The method of manufacturing a hot-rolled steel sheet comprising a hot-rolled steel sheet having a yield ratio of 0.8 or more. However, Ar ₃ = 910-310 * C-80 * Mn-20 * Cu-15 * Cr-55 * Ni-80 * Mo-0.35 * (thick-8) The method for manufacturing a hot-rolled steel sheet according to claim 7, wherein a relationship of 0.01? {[Ti] + [Nb] + [V]}? 0.15 is established between the Ti, Nb, and V. 8. The method of claim 7, wherein the concentration of the HCl aqueous solution is 10-20%.

Images