KR20170076912A - High strength steel having low yield ratio method for manufacturing the same - Google Patents

Abstract

One aspect of the present invention is a method of manufacturing a semiconductor device, comprising: 0.02 to 0.11 wt% of carbon; 0.1 to 0.5 wt% of silicon; 1.5 to 2.5 wt% of manganese; 0.01 to 0.06 wt% of aluminum; 0.1 to 0.6 wt% of nickel (Ni), 0.01 to 0.03 wt% of titanium (Ti), 0.005 to 0.08 wt% of niobium (Nb), 0.1 to 0.5 wt% of chromium (Cr) (S): not more than 0.01 wt% (excluding 0 wt%), boron (B): 5 to 30 wt ppm, nitrogen (N): 20 to 70 wt ppm, (Fe), and other unavoidable impurities, such as calcium (Ca): not more than 50 ppm by weight (excluding 0 ppm by weight), tin (Sn): not more than 5 to 50 ppm by weight Type high-strength steel.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high-

BACKGROUND OF THE INVENTION 1. Field of the Invention [0002] The present invention relates to a high-strength steel material having a low resistance and a method of manufacturing the same. More particularly, to a low-yielding high-strength steel having a low yield ratio and a high tensile strength, which can be suitably used as a steel for construction, and a method for producing the same.

Recently, the development of superstructures and high strength steels has been demanded as domestic and overseas buildings, bridges, and other structures are progressing into superstructure and long span. The use of high-strength steel has a high permissible stress, which makes it possible to rationalize and lighten the construction and the bridge structure, making economical construction possible, as well as being able to thin the plate thickness, facilitating machining and welding operations such as cutting and drilling It becomes.

On the other hand, when increasing the strength of the steel, the yield ratio (yield strength / tensile strength), which is the ratio of the tensile strength to the yield strength, often increases. When the yield ratio increases, destruction occurs at the point of plastic deformation (yield point) Since the stress difference up to the starting point is not large, the building absorbs energy by deformation, and there is not a sufficient margin to prevent destruction. Therefore, there is a problem that it is difficult to secure safety when a large external force such as an earthquake acts. Therefore, the structural steel needs to satisfy both high strength and low resistance.

On the other hand, in general, the yield ratio of the steel material is such that the metal structure of the steel is made of a soft phase such as ferrite as a main structure and a hard phase such as bainite or martensite (Hard phase) can be lowered by implementing a suitably dispersed structure.

In order to obtain a structure in which a hard phase is appropriately dispersed in the soft phase-based microstructure described above, Patent Document 1 discloses a method of quenching and tempering in a dual phase region of ferrite and austenite, ) In order to reduce the yield ratio. However, the above method has a problem in that it is inevitable to lower the productivity as well as to increase the manufacturing cost because a heat treatment process is added in addition to the rolling manufacturing process.

Therefore, there is a need to develop a high-strength, high-strength steel having a high strength and a low resistance, and a manufacturing method thereof, while solving problems such as lowering of productivity and increase in manufacturing cost.

Patent Document 1: Japanese Patent Application Laid-Open No. 55-97425

An aspect of the present invention is to provide a low-resistance high-strength steel material and a method of manufacturing the same. And more particularly, to provide a high strength steel having a high strength and a low resistance without a decrease in productivity and a manufacturing cost, and a manufacturing method thereof.

On the other hand, the object of the present invention is not limited to the above description. It will be understood by those of ordinary skill in the art that there is no difficulty in understanding the additional problems of the present invention.

One aspect of the present invention is a method of manufacturing a semiconductor device, comprising: 0.02 to 0.11 wt% of carbon; 0.1 to 0.5 wt% of silicon; 1.5 to 2.5 wt% of manganese; 0.01 to 0.06 wt% of aluminum; 0.1 to 0.6 wt% of nickel (Ni), 0.01 to 0.03 wt% of titanium (Ti), 0.005 to 0.08 wt% of niobium (Nb), 0.1 to 0.5 wt% of chromium (Cr) (S): not more than 0.01 wt% (excluding 0 wt%), boron (B): 5 to 30 wt ppm, nitrogen (N): 20 to 70 wt ppm, (Fe), and other unavoidable impurities, such as calcium (Ca): not more than 50 ppm by weight (excluding 0 ppm by weight), tin (Sn): not more than 5 to 50 ppm by weight Type high-strength steel.

In another aspect of the present invention, there is provided a method of manufacturing a semiconductor device, comprising: 0.02 to 0.11 wt% of carbon; 0.1 to 0.5 wt% of silicon; 1.5 to 2.5 wt% of manganese; 0.1 to 0.6% by weight of nickel (Ni), 0.01 to 0.03% by weight of titanium (Ti), 0.005 to 0.08% by weight of niobium (Nb), 0.1 to 0.5% by weight of chromium (Cr) ): Not more than 0.01 wt% (excluding 0 wt%), sulfur (S): not more than 0.01 wt% (excluding 0 wt%), boron (B) (Ca): not more than 50 ppm by weight (excluding 0 ppm by weight), tin (Sn): not more than 5 to 50 ppm by weight (excluding 0 ppm by weight), the balance of Fe and other unavoidable impurities Heating the slab to 1050 to 1250 캜;

Subjecting the heated slab to rough rolling at 950 to 1150 ° C to obtain a bar;

Hot rolling the bar at a finish rolling temperature of 700 to 950 占 폚 to obtain a hot rolled steel sheet; And

Cooling the hot-rolled steel sheet at a cooling rate of 25 to 50 占 폚 / s to a cooling end temperature not higher than the Bs temperature; Resistant high-strength steel material.

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 can be understood in more detail with reference to the following specific embodiments.

INDUSTRIAL APPLICABILITY According to the present invention, it is possible to provide a high-strength, high-strength steel material with high ultrahigh strength and low frictional resistance without lowering productivity and manufacturing cost, and a manufacturing method thereof.

Hereinafter, preferred embodiments of the present invention will be described. However, the embodiments of the present invention can be modified into various other forms, and the scope of the present invention is not limited to the embodiments described below. Further, the embodiments of the present invention are provided to more fully explain the present invention to those skilled in the art.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will now be described in detail with reference to the appended drawings.

According to an aspect of the present invention, there is provided a high strength steel material having a high resistance to rebound, comprising 0.02 to 0.11 weight% of carbon, 0.1 to 0.5 weight% of silicon, 1.5 to 2.5 weight% of manganese (Mn) : 0.01 to 0.06% by weight of nickel, 0.1 to 0.6% by weight of nickel, 0.01 to 0.03% by weight of titanium, 0.005 to 0.08% by weight of niobium, 0.1 to 0.5% , Phosphorus (P): not more than 0.01 wt% (excluding 0 wt%), S: not more than 0.01 wt% (excluding 0 wt%), boron (B) (Ca): 50 ppm by weight or less (excluding 0 ppm by weight), tin (Sn): 5 to 50 ppm by weight (excluding 0 ppm by weight), remaining iron (Fe) Includes unavoidable impurities.

Carbon (C): 0.02 to 0.11 wt%

C is an important element for forming bainite or martensite and determining the size and fraction of bainite or martensite to be formed.

If the C content is more than 0.11% by weight, the low-temperature toughness is lowered. If the C content is less than 0.02% by weight, the formation of bainite or martensite is inhibited and the strength is lowered. Therefore, the C content is preferably 0.02 to 0.11% by weight.

On the other hand, in the case of a plate used as a steel structure for welding, the upper limit of the C content is more preferably 0.08% by weight for better weldability.

Silicon (Si): 0.1 to 0.5 wt%

Si is used as a deoxidizing agent and is an element for improving strength and toughness.

When the Si content is more than 0.5% by weight, not only the low temperature toughness and weldability are deteriorated but also the scale is formed thick on the surface of the plate material, which may lead to gas cutting property defects and other surface cracks. On the other hand, if the Si content is less than 0.1% by weight, the deoxidation effect may be insufficient. Therefore, the Si content is 0.1 to 0.5% by weight. And more preferably 0.15 to 0.35% by weight.

Manganese (Mn): 1.5 to 2.5 wt%

Since Mn is a useful element for improving the strength by solid solution strengthening, it is necessary to add at least 1.5% by weight. However, if the Mn content exceeds 2.5% by weight, the toughness of the welded portion may be greatly lowered due to an increase in the hardenability. Therefore, the content of Mn is preferably 1.5 to 2.5% by weight.

Aluminum (Al): 0.01 to 0.06 wt%

Al is an element capable of deoxidizing molten steel at low cost and stabilizing ferrite. When the Al content is less than 0.01% by weight, the above-mentioned effect is insufficient. On the other hand, when the Al content exceeds 0.06% by weight, nozzle clogging may occur during continuous casting. Therefore, the Al content is preferably 0.01 to 0.06% by weight.

Nickel (Ni): 0.1 to 0.6 wt%

Ni is an element capable of simultaneously improving the strength and toughness of a base material. In order to sufficiently exhibit the above-described effects in the present invention, it is preferable to add 0.1 wt% or more. However, since Ni is an expensive element, the addition of an amount exceeding 0.6% by weight may reduce the economical efficiency and deteriorate the weldability. Therefore, the Ni content is preferably 0.1 to 0.6%.

Titanium (Ti): 0.01 to 0.03 wt%

Since Ti improves the low-temperature toughness by suppressing the growth of crystal grains during reheating, it is preferable to add Ti by 0.01 wt% or more. However, when the Ti content is more than 0.03% by weight, problems such as clogging of the performance nozzle and reduction in low temperature toughness due to centering can occur. Therefore, the Ti content is preferably 0.01 to 0.03% by weight.

Niobium (Nb): 0.005 to 0.08 wt%

Nb is an important element in the production of TMCP steel and precipitates in the form of NbC or NbCN, which greatly improves the strength of the base material and the weld. In addition, Nb dissolved at the time of reheating at a high temperature suppresses recrystallization of austenite and transformation of ferrite or bainite, thereby exhibiting an effect of making the structure finer. Further, in the present invention, not only bainite is formed at a low cooling rate when the slab is cooled after rough rolling, but also promotes the formation of martensite even at low speed cooling by increasing the stability of austenite even after cooling after final rolling Also.

In order to sufficiently obtain the above-mentioned effect, it is preferable that the Nb content is 0.005 wt% or more. However, if the Nb content exceeds 0.08 wt%, a brittle crack may appear at the edge of the steel. Therefore, the Nb content is preferably 0.005 to 0.08% by weight.

Cr (Cr): 0.1 to 0.5 wt%

Cr is an element added to secure the strength, which also serves to increase the hardenability. In order to sufficiently obtain the above-mentioned effect, it is necessary to add it by 0.1% or more. However, when the Cr content exceeds 0.5%, the hardness of the welded portion can be excessively increased and the toughness can be inhibited. Therefore, the Cr content is preferably 0.1 to 0.5%.

Phosphorus (P): not more than 0.01% by weight

P is an element favoring strength improvement and corrosion resistance, but it is advantageous to keep the impact toughness as low as possible, and it is preferable to set the upper limit to 0.01 wt%.

Sulfur (S): not more than 0.01% by weight

Since S is an element that significantly inhibits impact toughness by forming MnS or the like, it is advantageous to keep it as low as possible, and the upper limit is preferably 0.01 wt%.

Boron (B): 5 to 30 ppm by weight

B is a very low cost additive element and exhibits a strong curing ability and is a beneficial element contributing greatly to the formation of bainite even in the cooling after the rough rolling and at the low cooling rate.

Since the strength can be greatly improved by only adding a small amount, it is possible to add 5 ppm by weight or more. However, when the B content is more than 30 ppm by weight, Fe ₂₃ (CB) ₆ is formed and the hardenability is lowered, and the low temperature toughness can be largely lowered. Therefore, the B content is preferably 5 to 30 ppm by weight

Nitrogen (N): 20 to 70 ppm by weight

N is preferably controlled to be 70 ppm by weight or less because N increases the strength while greatly reduces toughness. However, since controlling the N content to less than 20 ppm by weight increases the steelmaking load, the lower limit of the N content is preferably 20 ppm by weight.

Calcium (Ca): 60 ppm by weight or less (excluding 0)

Ca is mainly used as an element for suppressing non-metallic inclusions of MnS and improving low-temperature toughness. However, excessive Ca addition reacts with oxygen contained in the steel to produce CaO, which is a nonmetallic inclusion. Therefore, the upper limit of the Ca content is preferably 60 ppm by weight.

Tin (Sn): 5 to 50 ppm by weight

Sn is a useful element for securing corrosion resistance.

It is preferable to add 5 ppm or more from the viewpoint of ensuring corrosion resistance. However, when the Sn content exceeds 50 ppm by weight, defects such as swollen or popping scale may occur on the surface of the steel material rather than the contribution to the improvement of corrosion resistance. Further, Sn can increase the strength of the steel but deteriorates the elongation and low-temperature impact toughness, so that the upper limit is preferably 50 ppm 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.

The steel having the advantageous steel composition of the present invention can obtain a sufficient effect even if it contains the alloying element in the above-mentioned content range. However, the steel having 0.1 to 0.5 wt% of copper (Cu) and 0.15 to 0.3 mol of molybdenum (V): 0.005 to 0.3% by weight, it is possible to further improve properties such as strength, toughness, toughness of weld heat affected zone, weldability and the like.

Copper (Cu): 0.1 to 0.5 wt%

Cu is an element capable of minimizing the toughness of the base material and simultaneously increasing its strength. In order to sufficiently obtain the above-mentioned effect, it is preferable to add 0.1 wt% or more. However, when the Cu content exceeds 0.5% by weight, the product surface quality can be greatly deteriorated. Therefore, the Cu content is preferably 0.1 to 0.5 wt%.

Molybdenum (Mo): 0.15 to 0.3 wt%

Since Mo has a large effect of improving the hardenability by only adding a small amount of Mo, it is required to add 0.15% by weight or more of Mo because it can greatly improve the strength. However, when Mo is added in an amount exceeding 0.3% by weight, . ≪ / RTI > Therefore, the Mo content is preferably 0.15 to 0.3% by weight.

Vanadium (V): 0.005-0.3 wt%

V has a low temperature to be employed as compared with other fine alloys and has an effect of preventing precipitation of the welded heat affected portion and lowering of the strength. In order to sufficiently obtain the above-mentioned effect, it is preferable to add 0.005 wt% or more. However, if the V content is more than 0.3% by weight, the toughness may be lowered. Therefore, the V content is preferably 0.005 to 0.3% by weight.

In addition, the microstructure of the steel material of the present invention may include bainitic ferrite and granular bainite as main phases, and may include M-A (malleous martensite) as a secondary phase.

Since bainitic ferrite contains many high-hardness grain boundaries in the mouth while maintaining the initial austenite grain boundaries, it is useful for improving strength and impact toughness due to grain refinement effect.

Granular bainite retains the initial austenite grains as bainitic ferrite, but there is a secondary phase such as MA in the grain or grain boundary. Since there is no high-rigid intrinsic system in the mouth, the impact toughness is somewhat disadvantageous, but the strength is somewhat increased by the presence of a large amount of low-rigidity grain boundaries such as the grain potential.

By including bainitic ferrite and granular bainite as the main phase, it is possible to secure a low resistance and a high strength.

At this time, the bainitic ferrite is 80 to 95%, the granular bainite is 5 to 20%, and the M-A is 3% or less (including 0%) in an area fraction.

When the area fraction of the bainitic ferrite is less than 80%, it is difficult to secure a high tensile strength. When the area fraction exceeds 95%, the yield ratio increases.

When the area fraction of granular bainite is less than 5%, not only the tensile strength but also the yield strength are increased, so that a low yield ratio can not be secured. When the area fraction is more than 20%, the coarse initial austenite grains can not be effectively refined, Strength can become dull.

The secondary phase, such as MA, is preferably a microstructure useful for low resistivity implementation and preferably has an area fraction of less than 3%. When the area fraction of MA is more than 3%, the yield ratio may decrease, but it may act as a crack initiation point for external stress relatively, which is disadvantageous in securing a high tensile strength.

On the other hand, the steel according to the present invention may have a PImax (111) / PImax (100) of 1.0 or more and 1.8 or less. (111) is a pole intensity (PImax.) Of a (111) crystal plane obtained by a method such as X-ray diffraction or electron backscattering diffraction, and the PImax (100) It is strength.

The pole strength of the crystal face is determined by the final microstructure of the steel according to one aspect of the present invention. When the bainitic ferrite and granular bainite are used as the main phase, the value of PImax (111) increases as the fraction of bainitic ferrite increases, while the value of PImax. (100) increases as the fraction of granular bainite increases. . According to one aspect of the present invention, the final microstructure of the steel is capable of producing a high strength steel having a high area fraction of bainitic ferrite than granular bainite and having a PImax (111) / PImax (100) of less than 1.8 . When the ratio of PImax. (111) / PImax. (100) is more than 1.8, the resistance ratio can not be satisfied, so that the upper limit is preferably 1.8 or less. More preferable PImax (111) / PImax (100) is 1.6 or less.

When the ratio of PImax. (111) / PImax. (100) is less than 1.0, the fraction of granular bainite increases to more than 20%, which makes it difficult to secure high strength. Therefore, the lower limit value of PImax. (111) / PImax. (100) is preferably 1.0 or more, and more preferably 1.2 or more.

Further, the steel material according to the present invention can have a yield ratio of 0.85 or less, a tensile strength of 800 MPa or more, and can be suitably used as a steel material for construction.

Further, the thickness of the steel material according to the present invention may be 60 mm or less.

Since the steel material according to the present invention can secure a high strength and low resistance, the plate thickness can be reduced to 60 mm or less, which facilitates machining and welding work such as cutting and drilling. Therefore, the thickness of the steel material is preferably 60 mm or less. More preferably not more than 40 mm, even more preferably not more than 30 mm.

The lower limit is not particularly limited, but it may be more than 15 mm for use as a steel for constructional construction.

Hereinafter, a method for manufacturing a high-strength steel material having a low-resistance type, which is another aspect of the present invention, will be described in detail.

According to another aspect of the present invention, there is provided a method of manufacturing a high-strength steel material having a low resistance, comprising the steps of: heating a slab having the above-described alloy composition at 1050 to 1250 占 폚; Subjecting the heated slab to rough rolling at 950 to 1150 ° C to obtain a bar; Hot rolling the bar at a finish rolling temperature of 700 to 950 占 폚 to obtain a hot rolled steel sheet; And cooling the hot-rolled steel sheet to a cooling end temperature not higher than a Bs temperature at a cooling rate of 25 to 50 ° C / s; .

Slab heating step

The slab having the above-described alloy composition is heated to 1050 to 1250 占 폚.

Rough rolling  step

The heated slab is rough-rolled at 950 to 1050 ° C to obtain a bar.

If the rough rolling temperature is lower than 950 ° C, the austenite may be deformed in a state in which recrystallization does not occur. In this case, when the temperature exceeds 1050 ° C, recrystallization occurs, There is a fear that the particles become coarse.

Hot rolling step

The hot rolled steel sheet is obtained by hot rolling the bar at a finishing rolling temperature of 700 to 950 占 폚.

If the finishing rolling temperature is lower than 700 캜, the temperature of the plate material is low, and a load may be generated in the rolling mill, which may result in failure of rolling to the final thickness, and if it exceeds 950 캜, recrystallization may occur during rolling.

At this time, the reduction ratio of the hot rolling may be 50 to 80%.

If the finish rolling reduction ratio is less than 50%, there is a risk of equipment accidents due to an increase in the load acting on the material during rolling. If the finish rolling reduction ratio exceeds 80%, the rolling pass number increases, There is a fear that it will not be able to do.

Cooling step

The hot-rolled steel sheet is cooled at a cooling rate of 25 to 50 DEG C / s to a cooling termination temperature below the Bs temperature.

When the hot-rolled steel sheet is cooled at a temperature exceeding the Bs temperature, the bainitic ferrite and the granulobenite are not sufficiently transformed into phase, and the strength can not be secured. The cooling rate is physically limited depending on the thickness of the plate, but it is difficult to satisfy the tensile strength of 800 MPa or more as soft ferrite is generated at a cooling rate of less than 25 ° C / s. In addition, at a cooling rate exceeding 50 ° C / s, the probability of producing martensite, which is a low temperature transformation structure, increases, so that not only the tensile strength but also the yield strength is increased, and it is difficult to satisfy the yield ratio of 0.85 or less.

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 slabs satisfying the composition shown in Table 1 were heated to 1160 DEG C and subjected to rough rolling at 1000 DEG C, followed by hot rolling and cooling in accordance with the production conditions shown in Table 2 below to obtain a steel material. The yield strength, tensile strength, yield ratio and microstructure of the steel were measured and are shown in Table 3 below.

Further, the pole strengths of the (100) and (110) crystal faces of the steel material were measured and the values of PImax. (111) / PImax. (100) were shown in Table 3 below.

Yield strength and tensile strength were measured using universal tensile testing machine.

The microstructures were observed by optical microscopy after steel abrasion after chemical polishing.

The pole strength and texture intensity were measured via an X-ray diffractometer and an electron backscattering diffractometer

In the following Table 1, the unit of each element content is% by weight.

Steel grade C Si Mn P S Al Cr Ni Ti Nb B N Ca Sn Inventive Steel A 0.045 0.17 2.12 0.007 0.002 0.029 0.32 0.40 0.018 0.04 0.0016 0.0037 0.0010 0.0008 Invention steel B 0.052 0.15 2.48 0.008 0.001 0.026 0.30 0.15 0.016 0.04 0.0015 0.0035 0.0007 0.0042 Inventive Steel C 0.065 0.16 1.75 0.011 0.001 0.030 0.29 0.29 0.019 0.04 0.0014 0.0029 0.0012 0.0021 Inventive Steel D 0.054 0.25 2.29 0.007 0.002 0.030 0.31 0.50 0.011 0.03 0.0013 0.0042 0.0005 0.0034 Comparative Steel E 0.045 0.11 1.91 0.005 0.003 0.006 0.04 1.52 0.008 0.01 0.0001 0.0040 0.0011 0.0004 Comparative Steel F 0.049 0.15 2.85 0.009 0.002 0.029 0.28 0.41 0.018 0.03 0.0015 0.0040 0.0014 0.0003

Steel grade division Hot finish rolling Cooling Bs temperature
(° C) Temperature
(° C) Reduction rate
(%) Cooling rate
(° C / s) Termination temperature
(° C) Inventive Steel A Inventory 1 844 75 46.6 523 589 Inventory 2 860 70 41.1 537 Inventory 3 892 60 40.6 492 Invention steel B Honorable 4 873 70 41.2 536 565 Inventory 5 890 60 37.7 506 Inventory 6 901 60 26.2 441 Inventive Steel C Honorable 7 899 60 25.8 451 623 Honors 8 890 60 26.3 447 Proposition 9 859 70 41.4 528 Inventive Steel D Comparative Example 1 852 75 51.4 534 568 Comparative Example 2 863 75 57.7 507 Comparative Example 3 904 45 6.4 182 Comparative Steel E Comparative Example 4 870 72 34.1 350 574 Comparative Example 5 871 66 24.1 356 Comparative Example 6 869 52 20.2 357 Comparative Steel F Comparative Example 7 864 78 48.5 505 526 Comparative Example 8 877 65 31.4 502 Comparative Example 9 835 55 20.4 496

Steel grade division Central microstructure Yield strength
(MPa) The tensile strength
(MPa) Yield ratio PImax (111) / PImax (100) BF GB M.A. Inventive Steel A Inventory 1 86 12 2 677 843 0.80 1.14 Inventory 2 89 10 One 703 872 0.81 1.25 Inventory 3 91 8 One 717 909 0.79 1.50 Invention steel B Honorable 4 87 10 3 697 866 0.80 1.16 Inventory 5 92 6 2 736 898 0.82 1.64 Inventory 6 88 11 One 707 871 0.81 1.27 Inventive Steel C Honorable 7 92 7 One 761 919 0.83 1.52 Honors 8 93 7 0 786 926 0.85 1.71 Proposition 9 83 15 2 686 860 0.80 1.10 Inventive Steel D Comparative Example 1 97 3 0 797 931 0.86 1.98 Comparative Example 2 98 2 0 893 981 0.91 1.96 Comparative Example 3 71 24 5 613 780 0.79 0.87 Comparative Steel E Comparative Example 4 AF: 72, B: 28, 562 694 0.81 1.08 Comparative Example 5 AF: 79, B: 21, 530 643 0.82 1.05 Comparative Example 6 AF: 74, B: 26, 504 612 0.82 1.07 Comparative Steel F Comparative Example 7 BF: 97, GB: 3
MA: 0 876 984 0.89 1.97 Comparative Example 8 BF: 72, GB: 24
MA: 4 725 841 0.86 0.85 Comparative Example 9 BF: 66, GB: 31
MA: 3 660 776 0.85 0.82

In Table 3, BF: bainitic ferrite, GB: granular bainite, MA: amorphous martensite, AF: ascicular ferrite, and B: bainite.

It can be seen that Inventive Examples 1 to 9 satisfying the alloy composition and the manufacturing conditions of the present invention can secure a tensile strength of not less than 0.85 and a tensile strength of not less than 800 MPa.

On the other hand, in Comparative Examples 1 to 3, the alloy composition of the present invention was satisfied, but the manufacturing conditions were not satisfied and it was confirmed that the resistance ratio could not be secured or the tensile strength was increased.

In Comparative Examples 4, 7 and 8, the production conditions of the present invention were satisfied, but the alloy composition was not satisfied and it was confirmed that the resistance ratio could not be secured.

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 (10)

(Al): 0.01 to 0.06 wt.%, Nickel (Ni): 0.1 wt.%, Carbon (C): 0.02 to 0.11 wt.%, Silicon (Si): 0.1 to 0.5 wt.%, Manganese 0.005 to 0.08% by weight of niobium (Nb), 0.1 to 0.5% by weight of chromium (Cr), 0.01% by weight or less of phosphorus (P) S: not more than 0.01 wt%, boron (B): 5 to 30 wt ppm, nitrogen (N): 20 to 70 wt ppm, calcium (Ca) 5 to 50 ppm by weight, the balance of Fe (Fe) and other unavoidable impurities.
The method according to claim 1,
Wherein the steel material further comprises at least one of copper (Cu): 0.1 to 0.5 wt%, molybdenum (Mo): 0.15 to 0.3 wt%, and vanadium (V): 0.005 to 0.3 wt% High strength steel.
The method according to claim 1,
Characterized in that the microstructure of the steel contains bainitic ferrite and granular bainite as a main phase and MA as a secondary phase.
The method of claim 3,
Characterized in that the bainitic ferrite is 80 to 95%, the granular bainite is 5 to 20%, and the MA is 3% or less (including 0%) in an area fraction.
The method according to claim 1,
(111) / PImax (100) which is the pole intensity (PImax.) Ratio of the (100) and (111) crystal faces of the steel is 1.0 or more and 1.8 or less.
(111) is the pole intensity at the (111) crystal face, and PImax (100) is the pole intensity at the (100) crystal face.
The method according to claim 1,
Wherein the steel has a yield ratio of 0.85 or less and a tensile strength of 800 MPa or more.
The method according to claim 1,
Wherein the thickness of the steel material is 60 mm or less.
(Al): 0.01 to 0.06 wt.%, Nickel (Ni): 0.1 wt.%, Carbon (C): 0.02 to 0.11 wt.%, Silicon (Si): 0.1 to 0.5 wt.%, Manganese 0.005 to 0.08% by weight of niobium (Nb), 0.1 to 0.5% by weight of chromium (Cr), 0.01% by weight or less of phosphorus (P) S: not more than 0.01 wt%, boron (B): 5 to 30 wt ppm, nitrogen (N): 20 to 70 wt ppm, calcium (Ca) Heating the slab containing 5 to 50 wt. Ppm or less, remaining iron (Fe), and other unavoidable impurities to 1050 to 1250 캜;
Subjecting the heated slab to rough rolling at 950 to 1050 ° C to obtain a bar;
Hot rolling the bar at a finish rolling temperature of 700 to 950 占 폚 to obtain a hot rolled steel sheet; And
Cooling the hot-rolled steel sheet at a cooling rate of 25 to 50 占 폚 / s to a cooling end temperature not higher than the Bs temperature; Resistant high-strength steel material.
9. The method of claim 8,
Wherein the slab further comprises at least one of copper (Cu) in an amount of 0.1 to 0.5 wt%, molybdenum (Mo) in an amount of 0.15 to 0.3 wt%, and vanadium (V) in an amount of 0.005 to 0.3 wt% Method of manufacturing high strength steels.
9. The method of claim 8,
Wherein the hot rolling is carried out at a reduction ratio of 50 to 80%.