KR20230026794A - Steel material having high-strength and high-toughness, and method for manufacturing thereof - Google Patents

Abstract

The present invention relates to a steel material applicable to materials such as hulls, marine structures, construction structures, wind towers, and the like, and more specifically, to a high-strength and high-toughness steel material with excellent low-temperature toughness and a method for manufacturing the same. The high-strength and high-toughness steel material of the present invention comprises 0.08 to 0.13 wt% of carbon (C), 0.2 to 0.6 wt% of silicon (Si), 1.4 to 2.0 wt% of manganese (Mn), 0.01 to 0.06 wt% of aluminum (Sol.Al), 0.02 to 0.06 wt% of niobium (Nb), 0.02 to 0.08 wt% of vanadium (V), 0.02 wt% or less of phosphorus (P), 0.005 wt% or less of sulfur (S), 0.002 to 0.008 wt% of nitrogen (N), and the balance including Fe and other unavoidable impurities, and satisfies the following relations 1 and 2: relation 1 is 1.5(%) <= Si + (0.3×Mn) + (6.6×Nb) + (5.6×V) and relation 2 is 0.15(%) >= C + (0.7×V), wherein each element means a weight content.

Description

High-strength, high-toughness steel and its manufacturing method {STEEL MATERIAL HAVING HIGH-STRENGTH AND HIGH-TOUGHNESS, AND METHOD FOR MANUFACTURING THEREOF}

The present invention relates to a steel material applicable to materials such as hulls, marine structures, construction structures, wind towers, and the like, and more particularly, to a high-strength, high-toughness steel material with excellent low-temperature toughness and a manufacturing method thereof.

Structures such as hulls, offshore structures, construction structures, and wind towers are rapidly becoming larger in order to increase efficiency. For example, transportation efficiency is increased through the enlargement of hulls, and wind power generation, which is rapidly growing as one of the recent renewable energy fields, is being enlarged in wind turbines and towers to improve power generation efficiency.

In order to increase the size of such a structure, high-strength and thick-walled steel materials applied to structure manufacturing are required. Accordingly, many technologies are being developed for high-strength and thick-walled steel materials.

In particular, TMCP (Thermo-Mechanical Control Process) technology, which utilizes controlled rolling and accelerated cooling, reduces the amount of alloy used and utilizes grain size refinement to secure the strength and toughness of steel materials and enable thicker material, thereby achieving high strength and high toughness. It has been widely used in the production of thick materials with

However, since low-temperature rolling and accelerated cooling increase the material variation and residual stress of steel in the TMCP technology, the steel produced by the TMCP technology is inferior in terms of material variation and residual stress compared to normalizing heat treatment steel that secures physical properties through normalizing heat treatment. It is known.

Nevertheless, since the normalized heat treated steel is manufactured through air cooling after reheating and austenitization after normal rolling, it is difficult to refine the grain size compared to TMCP, which is disadvantageous in terms of securing strength and toughness. In particular, as the thickness of the steel material increases, it is more difficult to secure physical properties due to the tendency that the cooling rate decreases during air cooling after austenitization.

In order to solve this problem, Patent Document 1 discloses a steel material having improved low-temperature impact toughness by limiting the content of precipitate forming elements such as Ti, Nb, V, and Mo, and performing a water cooling treatment before normalizing heat treatment. However, in the thick material, the yield strength is low, so there is a limit to its application as a structural steel.

On the other hand, normalizing steel has a disadvantage in that productivity is low and manufacturing cost is high compared to TMCP steel manufactured by an online process, since a heat treatment process must be additionally performed as an offline process after rolling.

Korean Patent Publication No. 10-2019-0065040

One aspect of the present invention is to provide a steel material having high strength and high toughness and a method for manufacturing the same without performing a process such as normalizing heat treatment.

The object of the present invention is not limited to the above. The subject of the present invention will be understood from the entire contents of this specification, and those skilled in the art will have no difficulty in understanding the additional subject of the present invention.

One aspect of the present invention, in weight%, carbon (C): 0.08 ~ 0.13%, silicon (Si): 0.2 ~ 0.6%, manganese (Mn): 1.4 ~ 2.0%, aluminum (Sol.Al): 0.01 ~ 0.06% Niobium (Nb): 0.02 to 0.06% Vanadium (V): 0.02 to 0.08% Phosphorus (P): 0.02% or less Sulfur (S): 0.005% or less Nitrogen (N): 0.002 to 0.008% , the balance Fe and other unavoidable impurities, and to provide a high-strength, high-toughness steel that satisfies the following relational expressions 1 and 2.

[Relationship 1]

1.5(%) ≤ Si + (0.3×Mn) + (6.6×Nb) + (5.6×V)

[Relationship 2]

0.15(%) ≥ C + (0.7×V)

(In relational expressions 1 and 2, each element means a weight content.)

Another aspect of the present invention, after preparing a steel slab that satisfies the above-described alloy composition and relational expressions 1 and 2, heating in a temperature range of 1050 ~ 1200 ℃; manufacturing a hot-rolled steel sheet by hot-rolling the heated steel slab; and air-cooling the hot-rolled steel sheet, wherein the hot-rolling is terminated in a temperature range of Ac3˜Ac3+30° C.

According to the present invention, it is possible to provide a steel material having a high strength and high toughness suitable for a structural steel while being a thick steel material having a certain thickness or more.

The steel material of the present invention is a structural steel material, and has effects applicable to various fields such as ships, various frames of offshore structures, bridges, infrastructure industries such as construction, and wind towers.

The inventors of the present invention, in providing a thick steel material having a thickness of 50 mm or more suitable as structural steel, studied in depth a method of securing excellent strength and toughness at the same time.

As a result, it was confirmed that it is possible to provide a steel material having intended physical properties by optimizing the process conditions as well as the alloy composition system of the steel material, and came to complete the present invention.

In particular, the present invention is characterized in that a steel material is manufactured by rolling at a normalizing temperature without performing a normalizing heat treatment. Such a normalized rolled steel material has low material deviation and residual stress similar to conventional normalized heat treated steel materials, and high productivity It has the advantage of lowering the manufacturing cost.

These normalized rolled steels are air-cooled after rolling, but the present inventors have found that there is a limit to securing high strength and high toughness due to the slow cooling rate during air-cooling in the case of thick steels.

In particular, the yield strength and low-temperature toughness of normalized rolled steel are affected by the grain size of ferrite, which is the main phase of normalized steel. .

Accordingly, the present inventors, through in-depth research, not only seek to improve strength by sufficiently refining austenite at high temperature to form a fine final structure, but also determine the content relationship between the essential alloy composition and specific elements to ensure high toughness. On the other hand, there is a technical significance in providing a steel material having a microstructure advantageous to securing intended physical properties by controlling manufacturing conditions.

In particular, the present invention has the effect of overcoming the limitations of the existing TMCP technology and normalizing heat treatment technology.

Hereinafter, the present invention will be described in detail.

High-strength, high-toughness steel according to an aspect of the present invention, by weight%, carbon (C): 0.08 ~ 0.13%, silicon (Si): 0.2 ~ 0.6%, manganese (Mn): 1.4 ~ 2.0%, aluminum (Sol. Al): 0.01 to 0.06%, Niobium (Nb): 0.02 to 0.06%, Vanadium (V): 0.02 to 0.08%, Phosphorus (P): 0.02% or less, Sulfur (S): 0.005% or less, Nitrogen (N) : 0.002 to 0.008% may be included.

Hereinafter, the reason for limiting the alloy composition of the steel material provided in the present invention as above will be described in detail.

Meanwhile, in the present invention, unless otherwise specified, the content of each element is based on weight, and the ratio of tissue is based on area.

Carbon (C): 0.08 to 0.13%

Since carbon (C) is an element that directly affects the fraction of the second phase other than the main phase constituting the steel, in the present invention, the content of C is appropriately controlled to secure the second phase at a level favorable to securing physical properties. wanted to

If the content of C is less than 0.08%, the fraction of the second phase is insufficient, making it difficult to secure the strength of the steel. On the other hand, if the content exceeds 0.13%, the fraction of the second phase is excessive, resulting in low-temperature toughness. there is.

Therefore, in the present invention, it is preferable to contain the C at 0.08 to 0.13%. More advantageously, the C may be included in an amount of 0.09% or more and 0.11% or less.

Silicon (Si): 0.2 to 0.6%

Silicon (Si) is an element that contributes to deoxidation of steel and is an element that is advantageous for strength improvement. If the content of Si is less than 0.2%, it is difficult to secure yield strength, whereas if the content exceeds 0.6%, there is a problem in that low-temperature toughness and weldability of steel materials are reduced.

Therefore, in the present invention, the Si may be included in an amount of 0.2 to 0.6%, and more advantageously, it may be included in an amount of 0.3% or more and 0.55% or less.

Manganese (Mn): 1.4 to 2.0%

Manganese (Mn) is an element that improves strength through solid solution strengthening and contributes to refinement of the grain size of ferrite by lowering the austenite-ferrite transformation temperature. If the content of Mn is less than 1.4%, the above effect cannot be sufficiently obtained, making it difficult to secure strength and toughness of the steel. On the other hand, if the content exceeds 2.0%, there is a concern that the internal quality of the steel may be deteriorated by causing segregation in the center.

Therefore, in the present invention, the Mn may be included in an amount of 1.4 to 2.0%, more advantageously in an amount of 1.5% or more, and even more advantageously in an amount of 1.55% or more.

Aluminum (Sol.Al): 0.01 to 0.06%

Aluminum (Sol.Al) is an element that contributes to the deoxidation of steel, and it is advantageous to include it at 0.01% or more in order to sufficiently obtain its effect. However, if the content exceeds 0.06%, fine Al nitride is formed during the continuous casting process, which may deteriorate the surface quality of the steel.

Therefore, in the present invention, the Al may include 0.01 to 0.06%.

Niobium (Nb): 0.02 to 0.06%

Niobium (Nb) forms fine Nb carbonitride in steel, induces austenite refinement during a rolling process, and is an effective element for refining the final microstructure. In order to sufficiently obtain the above-described effect, it is advantageous to add Nb at an amount of 0.02% or more, but when the content exceeds 0.06%, the effect of refining the austenite grain size is saturated and the surface quality may be deteriorated during the continuous casting process.

Therefore, in the present invention, the Nb may be included in 0.02 to 0.06%, more advantageously, 0.03% or more and 0.55% or less.

Meanwhile, in the present invention, it is revealed that the rolling process is a normalizing rolling process.

Vanadium (V): 0.02 to 0.08%

Vanadium (V) is an element that is dissolved in the austenite state and precipitates as V carbonitride in the ferrite state during the cooling process to cause precipitation strengthening. If the content of V is less than 0.02%, the effect of precipitation strengthening cannot be obtained sufficiently. On the other hand, if the content exceeds 0.08%, precipitation strengthening becomes excessive, and rather, there is a problem of inhibiting low-temperature toughness.

Therefore, in the present invention, the V may include 0.02 to 0.08%, and more advantageously may include 0.03% or more and 0.07% or less.

Phosphorus (P): 0.02% or less

Phosphorus (P) is an impurity element that is inevitably incorporated into steel, and it is advantageous to lower its content as much as possible because it inhibits the impact toughness of steel. However, in order to reduce the content of P to a minimum, the load in the steelmaking process increases and the cost of steelmaking increases, so the upper limit of P may be limited to 0.02%.

Sulfur (S): 0.005% or less

Sulfur (S) is an impurity element that is inevitably incorporated into steel, and it is advantageous to lower its content as much as possible because it inhibits the impact toughness of steel. Similar to P, in order to reduce the content of S to a minimum, the load on the steelmaking process increases and the cost of steelmaking increases, so the upper limit of S can be limited to 0.005%.

Nitrogen (N): 0.002 to 0.008%

Since nitrogen (N) is an essential element for forming Nb and V carbonitrides in steel, it is preferably contained in an amount of 0.002% or more. However, if the content is excessively high, there is a risk of impairing the surface quality of the steel cast piece, so it may be included in 0.008% or less in consideration of this.

The steel material of the present invention may further include one or more of copper (Cu), nickel (Ni), and molybdenum (Mo) in addition to the above-described alloy composition, and these elements can more advantageously secure the physical properties of the steel material. can

Copper (Cu): 0.5% or less

Copper (Cu) is an element that contributes to the improvement of strength of steel through solid solution strengthening and less deterioration of impact toughness.

Therefore, the addition of Cu may be limited to 0.5% or less.

Nickel (Ni): 1.0% or less

Nickel (Ni) is an element that has a solid solution strengthening effect and is effective in suppressing glowing brittleness caused by Cu when added in combination with Cu. However, excessive addition of Ni may impair low-temperature toughness.

Therefore, the addition of Ni may be limited to 1.0% or less.

Molybdenum (Mo): 0.3% or less

Molybdenum (Mo) is advantageous for improving strength, but may inhibit toughness, and since molybdenum (Mo) is an expensive element, its content may be limited to 0.3% or less.

The remaining component of the present invention is iron (Fe). However, since unintended impurities from raw materials or the surrounding environment may inevitably be mixed in a normal manufacturing process, this cannot be excluded. Since these impurities are known to anyone skilled in the ordinary manufacturing process, not all of them are specifically mentioned in this specification.

The steel material of the present invention satisfying the above-described alloy composition preferably satisfies the following relational expressions 1 and 2 in relation to the content of specific elements.

[Relationship 1]

1.5(%) ≤ Si + (0.3×Mn) + (6.6×Nb) + (5.6×V)

[Relationship 2]

0.15(%) ≥ C + (0.7×V)

(In relational expressions 1 and 2, each element means a weight content.)

Si, Mn, Nb, and V of the relational expression 1 are elements that affect the yield strength of the steel, and C and V of the relational expression 2 are elements that affect the impact toughness of the steel.

In the present invention, the content relationship between the elements that affect the yield strength within the proposed content range of each element is controlled by Relational Equation 1, and the content relationship between elements affecting impact toughness is controlled by Relational Equation 2. toughness can be obtained.

That is, even if the content of Si, Mn, Nb, and V of the steel of the present invention satisfies the limited range, it is difficult to achieve the yield strength when it deviate from the above relational expression 1, and the relationship between the C and V contents of the steel material meets the above relational expression 2 If it deviates, it becomes difficult to secure impact toughness.

Therefore, it is preferable that the steel material of the present invention satisfies the relational expressions 1 and 2 together with the alloy composition described above.

The steel material of the present invention that satisfies the above-described alloy composition and component relational expressions (relational expressions 1 and 2) may have a microstructure composed of ferrite and the second phase.

The steel includes ferrite as a main phase, and may include at least one of pearlite, bainite, and M-A structure as the second phase. In the present invention, ferrite means polygonal ferrite.

The second phase is preferably included in an area fraction of 5 to 15%. If the fraction of the second phase is less than 5%, the strength of the steel cannot be sufficiently secured, whereas if the fraction exceeds 15%, there is a concern that toughness may be inferior. Of the second phase, pearlite and bainite are included in the present invention if at least one structure is within the suggested fraction range.

However, the M-A structure in the second phase is a mixed structure of martensite and austenite, and it is preferable that the fraction does not exceed 1%. That is, when the fraction of the M-A structure exceeds 1%, it becomes difficult to secure the toughness and strength of the steel.

In the present invention, in order to secure desired strength and toughness, it is preferable to control the grain size of the ferrite, and in the present invention, it is preferable that the average grain size of the ferrite is 18 μm or less.

When the average grain size of the ferrite exceeds 18 μm, excellent strength and toughness cannot be secured at the same time. Here, it should be noted that the average grain size can be expressed based on the equivalent circle diameter.

The steel material of the present invention having the above-described alloy component system and microstructure may have high strength and high toughness with a yield strength of 400 MPa or more, a tensile strength of 500 MPa or more, and an impact toughness of 100 J or more at -40 ° C.

It is revealed that the steel material of the present invention is a thick steel material having a thickness of 50 to 100 mm.

Hereinafter, a method for manufacturing a high-strength, high-toughness steel material according to another aspect of the present invention will be described in detail.

Briefly, after preparing a steel slab that satisfies the alloy composition and component relational expression proposed in the present invention, it can be manufactured through a process of [heating - rolling - air cooling]. In particular, the present invention has technical significance in that a rolling process is performed in a normalizing heat treatment area as a rolling process without performing a separate heat treatment after completing the rolling process as described above.

Each process condition is explained in detail below.

[Heating of steel slabs]

In the present invention, it is preferable to go through a process of heating and homogenizing the steel slab prior to performing the rolling process, and at this time, the heating process may be performed in a temperature range of 1050 to 1200 ° C.

If the heating temperature of the steel slab is less than 1050 ° C., the number of rolling passes greatly increases due to a rapid increase in the rolling load during subsequent rolling, which may result in a significant drop in industrial productivity. On the other hand, when the heating temperature exceeds 1200 ° C., the grain size of the initial austenite before rolling becomes coarse, and as a result, it is impossible to achieve grain size refinement of the final microstructure.

Therefore, heating of the steel slab can be performed in a temperature range of 1050 to 1200 ° C. At this time, the heating time is not particularly limited, but usually the heating process can be performed for 1 minute or more per 1 mm of steel cast thickness.

[Rolling process]

A hot-rolled steel sheet may be manufactured by hot-rolling the steel slab heated according to the above.

In the present invention, the hot rolling process is performed in the temperature range where the normalizing heat treatment is performed, and specifically, it is preferable to terminate the hot rolling in the temperature range of Ac3 ~ Ac3 + 30 ℃.

If the hot rolling end temperature is less than Ac3, it is not possible to secure the properties of the rolled steel material equal to or higher than that of the normalized heat treated steel material. getting harder to get

The Ac3 temperature can be obtained by the following equation, wherein each element means a weight content.

Ac3 = 937 - 437C + 56Si - 20Mn + 198Al - 27Ni - 19Nb + 125V

[air cooling]

Cooling may be performed on the hot-rolled steel sheet obtained by completing the rolling process according to the above, and at this time, it is preferable to perform air cooling in order to realize the effect of normalizing heat treatment. The air cooling may be performed to room temperature.

By performing air cooling after completing the rolling process according to the present invention, there is an effect of obtaining a steel material having excellent strength and toughness without performing a subsequent heat treatment process.

More specifically, as the intended microstructure is formed, the steel material of the present invention can be excellently secured in both strength and toughness characteristics for an ultra-thick steel having a thickness of 50 to 100 mm.

Hereinafter, the present invention will be described in more detail through examples. However, it should be noted 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 molten steel having the alloy components shown in Table 1 was continuously cast to produce a cast steel having a thickness of 300 mm. Thereafter, each cast piece was subjected to [heating-hot rolling] under the conditions shown in Table 2 below, and then air-cooled to room temperature to manufacture a steel material.

In order to analyze the microstructure of each steel material manufactured, specimens were taken at the point of 1/4t (where t means thickness (mm)) in the thickness direction of each steel material. Thereafter, the specimen was polished and etched with Nital and Lepera corrosion solutions, and then the ferrite grain size and the fraction of the second phase (perlite, bainite, M-A structure, etc.) were measured, and the results were as follows. Table 3 shows.

In addition, after processing the specimen so that the length of the tensile specimen is perpendicular to the rolling direction at the point of 1/4t in the thickness direction of each steel material, a tensile test was performed at room temperature to measure the yield strength and tensile strength. In addition, after processing the specimen so that the length of the tensile specimen is parallel to the rolling direction at the point of 1/4t in the thickness direction of each steel material, an impact test was performed at -40 ° C to evaluate low-temperature toughness. Each result is shown in Table 3.

river Alloy composition (% by weight) relationship
formula 1 relationship
formula 2 C Si Mn P S Al Nb V N At least one of Cu, Ni, and Mo A 0.084 0.38 1.64 0.012 0.004 0.032 0.052 0.071 0.0032 - 1.613 0.134 B 0.092 0.51 1.79 0.009 0.002 0.047 0.033 0.043 0.0050 - 1.506 0.122 C 0.108 0.57 1.58 0.013 0.003 0.025 0.028 0.051 0.0052 - 1.514 0.144 D 0.127 0.42 1.95 0.010 0.002 0.035 0.058 0.022 0.0047 - 1.511 0.142 E 0.084 0.34 1.66 0.008 0.003 0.053 0.049 0.063 0.0033 Cu 0.17
Ni 0.31 1.514 0.128 F 0.095 0.45 1.95 0.014 0.003 0.017 0.027 0.067 0.0039 - 1.588 0.142 G 0.088 0.49 1.69 0.012 0.002 0.034 0.033 0.053 0.0051 Mo 0.18 1.512 0.125 H 0.070 0.53 1.41 0.011 0.004 0.054 0.059 0.031 0.0043 - 1.516 0.092 I 0.134 0.51 1.91 0.009 0.004 0.032 0.051 0.021 0.0032 - 1.537 0.149 J 0.115 0.68 1.44 0.008 0.002 0.017 0.023 0.046 0.0028 - 1.521 0.147 K 0.091 0.48 1.86 0.011 0.003 0.036 0.011 0.072 0.0045 - 1.514 0.141 L 0.106 0.59 1.84 0.011 0.003 0.037 0.046 0.012 0.0031 - 1.513 0.114 M 0.085 0.36 1.69 0.012 0.002 0.044 0.030 0.089 0.0035 - 1.563 0.147 N 0.094 0.57 1.44 0.011 0.003 0.035 0.045 0.031 0.0043 - 1.473 0.116 O 0.113 0.41 1.48 0.007 0.004 0.021 0.052 0.063 0.0038 - 1.550 0.157

river thickness
(mm) Ac3
(℃) Ac3+30
(℃) heating
(℃) End of rolling temperature
(℃) division A 100 903 933 1156 907 Invention example 1 B 80 904 934 1128 911 Invention example 2 C 100 901 931 1146 922 Inventive example 3 D 100 875 905 1182 891 Inventive Example 4 E 80 895 925 1141 905 Inventive Example 5 F 100 893 923 1076 910 Inventive Example 6 G 80 905 935 1147 915 Inventive Example 7 H 100 921 951 1157 922 Comparative Example 1 I 80 877 907 1170 885 Comparative Example 2 J 90 905 935 1141 918 Comparative Example 3 K 100 903 933 1146 922 Comparative Example 4 L 90 895 925 1169 904 Comparative Example 5 M 100 905 935 1163 926 Comparative Example 6 N 100 909 939 1152 923 Comparative Example 7 O 100 892 922 1160 899 Comparative Example 8 C 90 901 931 1243 921 Comparative Example 9 C 100 901 931 1138 947 Comparative Example 10

division microstructure mechanical properties ferrite
Particle size (㎛) phase 2
(area%) MA organization
(area%) yield strength
(MPa) tensile strength
(MPa) impact toughness
(J, -40℃) Invention Example 1 14.4 5.7 0.7 423 515 123 Invention example 2 13.9 8.5 0.3 419 533 146 Inventive example 3 17.6 11.1 0.4 405 537 125 Inventive example 4 17.4 14.6 0 413 591 105 Inventive Example 5 14.5 5.2 0.7 417 504 129 Inventive example 6 14.7 7.1 0.8 419 544 113 Inventive Example 7 16.0 6.9 0.6 414 521 138 Comparative Example 1 14.4 4.4 0.1 405 491 178 Comparative Example 2 16.1 16.3 0 412 602 85 Comparative Example 3 17.7 10.8 1.2 407 551 97 Comparative Example 4 19.1 7.8 0.5 389 524 117 Comparative Example 5 16.9 9.3 0 397 530 152 Comparative Example 6 17.4 5.9 1.6 405 504 74 Comparative Example 7 16.6 7.1 0.2 390 526 150 Comparative Example 8 15.5 11.4 1.3 408 527 86 Comparative Example 9 20.8 11.6 0.5 397 533 59 Comparative Example 10 19.7 10.7 0.6 388 527 92 The second phase of the microstructure is represented by the sum of the fractions of the pearlite, bainite, and MA phases.
In all cases, the structure other than the second phase is ferrite.

As shown in Tables 1 to 3, Inventive Examples 1 to 7 satisfying the alloy composition system and manufacturing conditions proposed in the present invention secured the target level of yield strength and tensile strength, and had excellent low-temperature toughness.

On the other hand, Comparative Example 1, in which the C content was insufficient, had low strength due to an insufficient fraction of the second phase, and Comparative Example 2, in which the C content was excessive, showed poor low-temperature toughness due to an excessively high fraction of the second phase.

Comparative Example 3 was a case in which the Si content was excessive, and the fraction of the M-A structure was increased, resulting in inferior low-temperature toughness.

In Comparative Example 4, the yield strength was inferior due to the coarse ferrite grain size due to the insufficient Nb content.

In Comparative Example 5, the yield strength was inferior due to insufficient V carbonitride due to insufficient V content affecting yield strength, and in Comparative Example 6, in which the V content was excessive, the M-A structure increased and the low-temperature toughness was inferior.

On the other hand, Comparative Example 7, in which the content of each element satisfies the suggested range, but the value of Relational Expression 1 was unsatisfactory, had inferior yield strength, and Comparative Example 8, in which the value of Relational Expression 2 was unsatisfactory, showed poor low-temperature toughness. In particular, Si and Mn constituting relational expression 1 show a solid solution strengthening effect, Nb has a particle size refinement effect, and V has a precipitation strengthening effect. did

In addition, the alloy component system satisfies the present invention, but Comparative Examples 9 and 10, in which the manufacturing conditions deviate from the present invention, showed poor strength and toughness due to coarse ferrite grain size.

Claims (10)

By weight, carbon (C): 0.08-0.13%, silicon (Si): 0.2-0.6%, manganese (Mn): 1.4-2.0%, aluminum (Sol.Al): 0.01-0.06%, niobium (Nb) : 0.02~0.06%, Vanadium(V): 0.02~0.08%, Phosphorus(P): 0.02% or less, Sulfur(S): 0.005% or less, Nitrogen(N): 0.002~0.008%, balance Fe and other unavoidable impurities Including, high-strength high-toughness steel that satisfies the following relations 1 and 2.

[Relationship 1]
1.5(%) ≤ Si + (0.3×Mn) + (6.6×Nb) + (5.6×V)
[Relationship 2]
0.15(%) ≥ C + (0.7×V)
(In relational expressions 1 and 2, each element means a weight content.)
According to claim 1,
The steel material is copper (Cu): 0.5% or less, nickel (Ni): 1.0% or less and molybdenum (Mo): high-strength, high-toughness steel further comprising one or more of 0.3% or less.
According to claim 1,
The steel is composed of ferrite and a second phase as a microstructure,
The second phase is a high-strength, high-toughness steel material containing at least one of pearlite, bainite, and MA structure in an area fraction of 5 to 15%.
According to claim 3,
The ferrite is a high-strength, high-toughness steel having an average grain size of 18 μm or less.
According to claim 3,
The MA structure is a high-strength, high-toughness steel material comprising an area fraction of 1% or less.
According to claim 1,
The steel is a high-strength, high-toughness steel having a yield strength of 400 MPa or more, a tensile strength of 500 MPa or more, and an impact toughness of 100 J or more at -40 ° C.
According to claim 1,
The steel is a high-strength, high-toughness steel having a thickness of 50 to 100 mm.
By weight, carbon (C): 0.08-0.13%, silicon (Si): 0.2-0.6%, manganese (Mn): 1.4-2.0%, aluminum (Sol.Al): 0.01-0.06%, niobium (Nb) : 0.02~0.06%, Vanadium(V): 0.02~0.08%, Phosphorus(P): 0.02% or less, Sulfur(S): 0.005% or less, Nitrogen(N): 0.002~0.008%, balance Fe and other unavoidable impurities Including, after preparing a steel slab that satisfies the following relational expressions 1 and 2, heating in a temperature range of 1050 ~ 1200 ℃;
manufacturing a hot-rolled steel sheet by hot-rolling the heated steel slab; and
Including the step of air-cooling the hot-rolled steel sheet,
The hot rolling is a method for producing a high-strength, high-toughness steel material, characterized in that terminated in the temperature range of Ac3 ~ Ac3 + 30 ℃.

[Relationship 1]
1.5(%) ≤ Si + (0.3×Mn) + (6.6×Nb) + (5.6×V)
[Relationship 2]
0.15(%) ≥ C + (0.7×V)
(In relational expressions 1 and 2, each element means a weight content.)
According to claim 8,
The steel slab is copper (Cu): 0.5% or less, nickel (Ni): 1.0% or less and molybdenum (Mo): a method for producing a high-strength, high-toughness steel material further comprising one or more of 0.3% or less.
According to claim 8,
The steel is a method for producing a high-strength, high-toughness steel having a thickness of 50 to 100 mm.