JP7617451B2 - Steel - Google Patents

Description

The present invention relates to steel materials.

It is generally known that refining the metal structure is an effective way to improve the material properties required of steel. In this regard, in the past, in order to refine the metal structure, for example, the end temperature when hot rolling steel, more specifically when finish rolling, was controlled to suppress the recrystallization of austenite grains, and the driving force of ferrite transformation was increased due to such suppression of recrystallization, resulting in the generation of more new crystals. (See, for example, Patent Documents 1 to 4)

Patent Document 1 teaches that by adding B in addition to Nb, the recrystallization temperature of austenite increases by 50°C or more, hardenability improves significantly, and the strength/toughness balance is improved significantly compared to the value expected from a system of Nb and B alone. Patent Documents 2 and 3 state that Nb is an element that is effective in refining austenite grains at high temperatures because it increases the recrystallization temperature. Patent Document 4 states that a small amount of Nb suppresses the recrystallization of austenite and contributes to refining the metal structure.

Japanese Unexamined Patent Publication No. 58-077528 Japanese Unexamined Patent Publication No. 63-235430 Japanese Patent Application Publication No. 63-235431 JP 2004-269924 A

Niobium (Nb) is known to be an effective element for suppressing recrystallization, but it also contributes to improving hardenability and precipitation strengthening. Therefore, if the Nb content is increased to obtain a higher recrystallization suppression effect, the strength of the resulting steel may become too high, and the toughness may decrease accordingly. Therefore, in this technical field, there is a need for steel containing elements other than Nb that have a recrystallization suppression effect similar to or greater than that of Nb, depending on the application in which the steel is used and the characteristics required for that application.

The present invention has been made in consideration of the above-mentioned circumstances, and its object is to provide a steel material having an improved recrystallization inhibition effect or improved inhibition of recrystallization through a novel configuration.

In order to achieve the above object, the inventors have investigated elements that can suppress or delay the recrystallization of austenite grains. As a result, the inventors have discovered that by increasing the amount of a specific element dissolved in steel, it is possible to suppress or delay recrystallization and shift the temperature at which recrystallization begins (hereinafter also simply referred to as the "recrystallization start temperature") to a higher temperature, thereby completing the present invention.

The steel materials that have achieved the above objectives are as follows:
(1) In mass%,
C: 0.001-1.000%,
Si: 0.01-3.00%,
Mn: 0.10 to 4.50%,
P: 0.300% or less,
S: 0.0300% or less,
Al: 0.001-5.000%,
N: 0.2000% or less,
O: 0.0100% or less,
at least one X element selected from the group consisting of Pr: 0 to 0.8000%, Sm: 0 to 0.8000%, Eu: 0 to 0.8000%, Gd: 0 to 0.8000%, Tb: 0 to 0.8000%, Dy: 0 to 0.8000%, Ho: 0 to 0.8000%, Er: 0 to 0.8000%, Tm: 0 to 0.8000%, Yb: 0 to 0.8000%, Lu: 0 to 0.8000%, and Sc: 0 to 0.8000%,
Nb: 0 to 3.000%,
Ti: 0 to 0.500%,
Ta: 0-0.500%,
V: 0-1.00%,
Cu: 0-3.00%,
Ni: 0 to 60.00%,
Cr: 0-30.00%,
Mo: 0-5.00%,
W: 0-2.00%,
B: 0 to 0.0200%,
Co: 0-3.00%,
Be: 0 to 0.050%,
Ag: 0-0.500%,
Zr: 0 to 0.5000%,
Hf: 0-0.5000%,
Ca: 0-0.0500%,
Mg: 0 to 0.0500%,
At least one of La, Ce, Nd, Pm, and Y: 0 to 0.5000% in total,
Sn: 0-0.300%,
Sb: 0 to 0.300%,
Te: 0 to 0.100%,
Se: 0 to 0.100%,
As: 0 to 0.050%,
Bi: 0-0.500%,
Pb: 0 to 0.500%, and the balance: Fe and impurities;
A steel material having a chemical composition that satisfies the following formula 1.
0.40[Pr]+0.37[Sm]+0.37[Eu]+0.36[Gd]+0.35[Tb]+0.34[Dy]+0.34[Ho]+0. 33[Er]+0.33[Tm]+0.32[Yb]+0.32[Lu]+1.24[Sc]-2.33[O]-3.99[N]-1.74[S] ≧ 0.0003 ... Formula 1
Here, [Pr], [Sm], [Eu], [Gd], [Tb], [Dy], [Ho], [Er], [Tm], [Yb], [Lu], [Sc], [O], [N], and [S] are the contents [mass %] of each element, and are 0 when the element is not contained.
(2) The chemical composition is, in mass%,
Nb: 0.003 to 3.000%,
Ti: 0.005-0.500%,
Ta: 0.001 to 0.500%,
V: 0.001-1.00%,
Cu: 0.001 to 3.00%,
Ni: 0.001 to 60.00%,
Cr: 0.001 to 30.00%,
Mo: 0.001 to 5.00%,
W: 0.001-2.00%,
B: 0.0001 to 0.0200%,
Co: 0.001-3.00%,
Be: 0.0003-0.050%,
Ag: 0.001-0.500%,
Zr: 0.0001 to 0.5000%,
Hf: 0.0001-0.5000%,
Ca: 0.0001-0.0500%,
Mg: 0.0001-0.0500%,
At least one of La, Ce, Nd, Pm, and Y: 0.0001 to 0.5000% in total,
Sn: 0.001-0.300%,
Sb: 0.001 to 0.300%,
Te: 0.001 to 0.100%,
Se: 0.001-0.100%,
As: 0.001 to 0.050%,
Bi: 0.001 to 0.500%, and Pb: 0.001 to 0.500%
The steel material according to the above (1), comprising one or more of the following:

According to the present invention, it is possible to provide a steel material having an improved recrystallization inhibition effect or improved inhibition of recrystallization.

1 is a graph showing test conditions for a compression processing test in an example. This is a graph showing a method for determining the softening rate, excerpted from "State of Nb in the Early Stage of Recovery and Recrystallization of Hot-Worked Austenitic Structure of Steel" by Naoki Maruyama et al., Journal of the Japan Institute of Metals, Vol. 60, No. 11 (1996), pp. 1051-1057.

<Steel>
The steel material according to the embodiment of the present invention has, in mass%,
C: 0.001-1.000%,
Si: 0.01-3.00%,
Mn: 0.10 to 4.50%,
P: 0.300% or less,
S: 0.0300% or less,
Al: 0.001-5.000%,
N: 0.2000% or less,
O: 0.0100% or less,
at least one X element selected from the group consisting of Pr: 0 to 0.8000%, Sm: 0 to 0.8000%, Eu: 0 to 0.8000%, Gd: 0 to 0.8000%, Tb: 0 to 0.8000%, Dy: 0 to 0.8000%, Ho: 0 to 0.8000%, Er: 0 to 0.8000%, Tm: 0 to 0.8000%, Yb: 0 to 0.8000%, Lu: 0 to 0.8000%, and Sc: 0 to 0.8000%,
Nb: 0 to 3.000%,
Ti: 0 to 0.500%,
Ta: 0-0.500%,
V: 0-1.00%,
Cu: 0 to 3.00%,
Ni: 0 to 60.00%,
Cr: 0-30.00%,
Mo: 0-5.00%,
W: 0-2.00%,
B: 0-0.0200%,
Co: 0-3.00%,
Be: 0 to 0.050%,
Ag: 0-0.500%,
Zr: 0 to 0.5000%,
Hf: 0-0.5000%,
Ca: 0-0.0500%,
Mg: 0 to 0.0500%,
At least one of La, Ce, Nd, Pm, and Y: 0 to 0.5000% in total,
Sn: 0-0.300%,
Sb: 0 to 0.300%,
Te: 0 to 0.100%,
Se: 0-0.100%,
As: 0 to 0.050%,
Bi: 0-0.500%,
Pb: 0 to 0.500%, and the balance: Fe and impurities;
It is characterized by having a chemical composition that satisfies the following formula 1.
0.40[Pr]+0.37[Sm]+0.37[Eu]+0.36[Gd]+0.35[Tb]+0.34[Dy]+0.34[Ho]+0. 33[Er]+0.33[Tm]+0.32[Yb]+0.32[Lu]+1.24[Sc]-2.33[O]-3.99[N]-1.74[S] ≧ 0.0003 ...Formula 1
Here, [Pr], [Sm], [Eu], [Gd], [Tb], [Dy], [Ho], [Er], [Tm], [Yb], [Lu], [Sc], [O], [N], and [S] are the contents [mass %] of each element, and are 0 when the element is not contained.

As mentioned above, in order to suppress the recrystallization of austenite grains, it is necessary to end the finish rolling at a low temperature. However, in this case, it may be necessary to wait until the steel material has cooled to an appropriate temperature before starting the finish rolling, which may result in a decrease in productivity. In particular, when the product is a relatively thick steel material used in applications such as building materials, it may take a considerable amount of time to sufficiently lower the temperature to the center of the steel material before the finish rolling, and in such cases the decrease in productivity is particularly noticeable. For this reason, in order to manufacture steel material without impairing productivity, it is generally desirable to end the hot rolling at a higher temperature, but on the other hand, suppressing recrystallization is required to refine the metal structure.

Therefore, in order to improve productivity while refining the metal structure, it is necessary to expand the non-recrystallization temperature range, specifically, to raise the temperature at which recrystallization of austenite grains begins. To explain in more detail, when steel is hot-rolled, the crystals in the steel are crushed by the hot rolling, and the arrangement of Fe atoms that was arranged in an orderly manner in the crystals is disturbed, resulting in many discontinuous structures called deformation bands, and many step-like irregularities (ledges) are also generated at the grain boundaries. However, if the rolling temperature is high at this time, the Fe atoms will move on their own to eliminate the deformation bands and ledges, and will try to return from a disordered, unstable state to a stable crystal in which the Fe atoms are neatly arranged. This is a phenomenon called recrystallization. On the other hand, if the rolling temperature is low (for example, less than about 800°C), the Fe atoms cannot move, so the hot rolling ends with ledges and deformation bands remaining at many places on the grain boundaries and within the grains.

During the cooling process after hot rolling, the metal structure transforms from austenite to ferrite, but this transformation generally occurs at places where the arrangement of Fe atoms in austenite is disturbed. Therefore, when austenite recrystallizes during hot rolling, the only places where the arrangement of Fe atoms is disturbed are the grain boundaries, so new ferrite crystals can only be generated from the grain boundaries of austenite. On the other hand, when hot rolling is performed at a low temperature of, for example, less than about 800°C, it is possible to generate many new ferrite crystals from ledges and deformation bands that exist in many places in austenite. Steel materials with austenite metal structure and steel materials with martensite metal structure do not transform into ferrite, but by suppressing recrystallization, the strain accumulated in the austenite grains during the hot rolling process increases, and the crystal grains become finer. Thus, although hot rolling at a low temperature, more specifically finish rolling at a low temperature, is very effective in refining the metal structure, it is required to finish the hot rolling at a higher temperature from the viewpoint of productivity as described above. Therefore, in order to improve productivity while refining the metal structure, it is preferable to increase the recrystallization start temperature.

Therefore, the present inventors have investigated elements that can suppress or delay the recrystallization of austenite grains. As a result, the present inventors have found that by setting the amount of specific elements dissolved in steel, namely, Pr, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, and Sc elements (hereinafter also referred to as "X elements") within a predetermined range while taking into consideration the relationship with the inclusions formed by these elements in steel, more specifically, the oxides, nitrides, and sulfides of these elements (i.e., by setting the effective amount of the X element corresponding to the left side of formula 1 to 0.0003% or more), the recrystallization of austenite grains can be suppressed or delayed, and the recrystallization start temperature can be shifted to the higher temperature side due to such suppression or delay of recrystallization. Therefore, according to the present invention, even when hot rolling, especially finish rolling, is performed at a relatively high temperature, a steel material in which recrystallization is significantly suppressed can be obtained, thereby improving productivity and making it possible to refine the metal structure in the finally obtained steel material. As a result, it is possible to improve the properties associated with the refinement of the metal structure, such as toughness, while also reducing the manufacturing costs of the steel material and the number of manufacturing processes.

Although it is not intended to be bound by any particular theory, it is believed that the above-mentioned X elements according to the embodiment of the present invention are fixed to lattice defects such as dislocations introduced into the steel during hot rolling, and, for example, inhibit the dislocations from rearranging and moving to a stable arrangement, thereby suppressing recrystallization. Since all of the above-mentioned X elements have a larger atomic radius than Nb used in the conventional technology, it is believed that by fixing such elements having a relatively large atomic radius to lattice defects such as dislocations, the effect of inhibiting dislocation rearrangement, etc. can be enhanced, and as a result, it is believed that at least the same or higher recrystallization suppression effect can be achieved compared to conventional steel materials using Nb. Therefore, in the present invention, it can be said that it is extremely important to have a large amount of elements having such a relatively large atomic radius dissolved in the steel.

However, there is a problem that these X elements are likely to combine with O (oxygen), N (nitrogen) and S (sulfur) present in the steel to form inclusions consisting of oxides, nitrides and sulfides. If the X element forms such inclusions in the steel, the amount of the X element in solid solution that can contribute to the inhibition of recrystallization decreases, and the recrystallization inhibition effect obtained by the X element being fixed to lattice defects such as dislocations cannot be fully obtained. In the present invention, the amount of the X element in solid solution taking such inclusions into consideration is calculated as the effective amount of the X element by the above formula 1 described in detail later, and the effective amount is set within a predetermined range, i.e., 0.0003% or more, thereby making it possible to achieve a higher recrystallization inhibition effect.

As described above, the X element in the present invention is likely to combine with O, N, and S to form inclusions, and therefore it is generally difficult to ensure a specified amount of solid solution in steel. For these reasons, the recrystallization suppression effect of the X element was not previously known. However, with the recent advances in refining technology, it has become possible to reduce the contents of elements such as O, N, and S that are generally present in steel as impurities to very low levels, and this time, it has been possible to realize the solid solution of the X element within a specified range. Therefore, the recrystallization suppression effect caused by the solid solution of the X element has now been revealed for the first time by the present inventors, which is extremely unexpected and surprising.

The steel material according to the embodiment of the present invention will be described in more detail below. In the following description, the unit of content of each element, "%", means "mass %" unless otherwise specified. Furthermore, in this specification, "to" indicating a numerical range is used to mean that the numerical values before and after it are included as the lower and upper limits, unless otherwise specified.

[C: 0.001-1.000%]
Carbon (C) is an element necessary for stabilizing hardness and/or ensuring strength. In order to fully obtain these effects, the C content is 0.001% or more. The content may be 0.005% or more, 0.010% or more, or 0.020% or more. On the other hand, if the C content is excessive, the toughness, bendability, and/or weldability may decrease. , the C content is 1.000% or less. The C content may be 0.800% or less, 0.600% or less, or 0.500% or less.

[Si: 0.01 to 3.00%]
Silicon (Si) is a deoxidizing element and also contributes to improving strength. In order to fully obtain these effects, the Si content is 0.01% or more. On the other hand, if the Si content is excessive, the toughness may decrease or a surface quality defect called scale defects may occur. Therefore, the Si content is 3.00% or less. The Si content may be 2.00% or less, 1.00% or less, or 0.60% or less.

[Mn: 0.10 to 4.50%]
Manganese (Mn) is an element effective in improving hardenability and/or strength, and is also an effective austenite stabilizing element. In order to fully obtain these effects, the Mn content should be 0.10% or more. The Mn content may be 0.50% or more, 0.70% or more, or 1.00% or more. On the other hand, if Mn is contained excessively, MnS, which is detrimental to toughness, is generated and acid resistance is deteriorated. Therefore, the Mn content is 4.50% or less. The Mn content may be 4.00% or less, 3.50% or less, or 3.00% or less. good.

[P: 0.300% or less]
Phosphorus (P) is an element that is mixed in during the manufacturing process. The P content may be 0%. However, it takes time to refine the P content to less than 0.0001%, This leads to a decrease in productivity. Therefore, the P content may be 0.0001% or more, 0.0005% or more, 0.001% or more, 0.003% or more, or 0.005% or more. From the viewpoint of manufacturing costs, the P content may be 0.007% or more. On the other hand, if P is contained excessively, the workability and/or toughness of the steel material may decrease. The P content is 0.300% or less. The P content may be 0.100% or less, 0.030% or less, or 0.010% or less.

[S: 0.0300% or less]
Sulfur (S) is an element that is mixed in during the manufacturing process. From the viewpoint of reducing inclusions formed with the X element according to the embodiment of the present invention, the less the S content, the better. Therefore, the S content is 0%. However, reducing the S content to less than 0.0001% requires a long time for refining, which leads to a decrease in productivity. Therefore, the S content is set to 0.0001% or more and 0. On the other hand, if S is contained excessively, the effective amount of the X element decreases and the toughness may decrease. Therefore, the S content is set to 0. The S content is preferably 0.0100% or less, more preferably 0.0050% or less, and most preferably 0.0030% or less.

[Al: 0.001-5.000%]
Aluminum (Al) is a deoxidizing element and is also an element effective in improving corrosion resistance and/or heat resistance. To obtain these effects, the Al content is 0.001% or more. The Al content may be 0.010% or more, 0.100% or more, or 0.200% or more. In particular, from the viewpoint of sufficiently improving the heat resistance, the Al content is 1.000% or more, 2.000% or more, or 2.000% or more. On the other hand, if the Al content is excessive, coarse inclusions are generated, which reduces toughness and causes problems such as cracks during the manufacturing process. The Al content is therefore set to 5.000% or less. The Al content is set to 4.500% or less, 4.000% or less, or 3.500% or less. In particular, from the viewpoint of suppressing a decrease in toughness, the Al content may be 1.500% or less, 1.000% or less, or 0.300% or less.

[N: 0.2000% or less]
Nitrogen (N) is an element that is mixed in during the manufacturing process. From the viewpoint of reducing inclusions formed with the X element according to the embodiment of the present invention, the less the N content, the better. Therefore, the N content is 0%. However, reducing the N content to less than 0.0001% requires a long time for refining, which leads to a decrease in productivity. Therefore, the N content is set to 0.0001% or more and 0. On the other hand, N is also an element effective in stabilizing austenite, and may be intentionally contained as necessary. In this case, N The content is preferably 0.0100% or more, and may be 0.0200% or more, or 0.0500% or more. However, if N is contained excessively, the effective amount of the X element decreases and The toughness may decrease. Therefore, the N content is 0.2000% or less. The N content may be 0.1500% or less, 0.1000% or less, or 0.0800% or less.

[O: 0.0100% or less]
Oxygen (O) is an element that is mixed in during the manufacturing process. From the viewpoint of reducing inclusions formed with the X element according to the embodiment of the present invention, the less the O content, the better. Therefore, the O content is 0%. However, reducing the O content to less than 0.0001% requires a long time for refining, which leads to a decrease in productivity. Therefore, the O content is set to 0.0001% or more and 0. On the other hand, if O is contained excessively, coarse inclusions are formed, the effective amount of the X element is reduced, and the formability and/or the steel material are deteriorated. The toughness may decrease. Therefore, the O content is 0.0100% or less. The O content may be 0.0080% or less, 0.0060% or less, or 0.0040% or less.

[At least one X element selected from the group consisting of Pr: 0-0.8000%, Sm: 0-0.8000%, Eu: 0-0.8000%, Gd: 0-0.8000%, Tb: 0-0.8000%, Dy: 0-0.8000%, Ho: 0-0.8000%, Er: 0-0.8000%, Tm: 0-0.8000%, Yb: 0-0.8000%, Lu: 0-0.8000%, and Sc: 0-0.8000%]
The X element according to the embodiment of the present invention is Pr: 0 to 0.8000%, Sm: 0 to 0.8000%, Eu: 0 to 0.8000%, Gd: 0 to 0.8000%, Tb: 0 to 0.8000%, Dy: 0 to 0.8000%, Ho: 0 to 0.8000%, Er: 0 to 0.8000%, Tm: 0 to 0.8000%, Yb: 0 to 0.8000%, Lu: 0 to 0.8000%, and Sc: 0 to 0.8000%. Praseodymium (Pr), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), lutetium (Lu), and scandium (Sc) are capable of exerting a recrystallization suppression effect by being present in austenite in a solid solution state. By exerting the recrystallization suppression effect, even when hot rolling, particularly finish rolling, is performed at a relatively high temperature, the metal structure in the finally obtained steel material can be refined, so that, for example, toughness evaluated by Charpy impact properties and the like can be improved, and productivity can be significantly improved.

The X element may be used alone or in any specific combination of two or more of the above elements. The X element may be present in an amount that satisfies formula 1, which will be described in detail later, and the lower limit is not particularly limited. However, for example, the content of each X element or the total content may be 0.0010% or more, preferably 0.0050% or more, more preferably 0.0150% or more, even more preferably 0.0300% or more, and most preferably 0.0500% or more. On the other hand, even if the X element is contained in excess, the effect is saturated, and therefore, containing the X element in the steel material more than necessary may lead to an increase in manufacturing costs. Therefore, the content of each X element may be 0.8000% or less, for example, 0.7000% or less, 0.6000% or less, 0.5000% or less, 0.4000% or less, or 0.3000% or less. In addition, the total content of the X element is 9.6000% or less, and may be, for example, 6.0000% or less, 5.0000% or less, 4.0000% or less, 2.0000% or less, 1.0000% or less, or 0.5000% or less.

The basic chemical composition of the steel material according to the embodiment of the present invention is as described above. Furthermore, the steel material may contain one or more of the following optional elements as necessary. For example, the steel material may contain one or more of Nb: 0-3.000%, Ti: 0-0.500%, Ta: 0-0.500%, V: 0-1.00%, Cu: 0-3.00%, Ni: 0-60.00%, Cr: 0-30.00%, Mo: 0-5.00%, W: 0-2.00%, B: 0-0.0200%, Co: 0-3.00%, Be: 0-0.050%, and Ag: 0-0.500%. The steel may contain one or more of Zr: 0-0.5000%, Hf: 0-0.5000%, Ca: 0-0.0500%, Mg: 0-0.0500%, and at least one of La, Ce, Nd, Pm, and Y: 0-0.5000% in total. The steel may contain one or two of Sn: 0-0.300%, and Sb: 0-0.300%. The steel may contain one or two of Te: 0-0.100%, Se: 0-0.100%, As: 0-0.050%, Bi: 0-0.500%, and Pb: 0-0.500%. These optional elements will be described in detail below.

[Nb: 0 to 3.000%]
Niobium (Nb) is an element that contributes to precipitation strengthening and suppression of recrystallization. The Nb content may be 0%, but in order to obtain these effects, the Nb content should be 0.003% or less. % or more. For example, the Nb content may be 0.005% or more or 0.010% or more. In particular, from the viewpoint of achieving sufficient precipitation strengthening, the Nb content is preferably 1.000 % or more, or 1.500% or more. On the other hand, if Nb is contained excessively, the effect becomes saturated and the workability and/or toughness may be reduced. Therefore, the Nb content is set to 3. The Nb content may be 2.800% or less, 2.500% or less, or 2.000% or less. In particular, from the viewpoint of suppressing the deterioration of the toughness of the weld heat affected zone (HAZ), Therefore, the Nb content is preferably 0.100% or less, and may be 0.080% or less, 0.050% or less, or 0.030% or less.

[Ti: 0 to 0.500%]
Titanium (Ti) is an element that contributes to improving the strength of steel materials through precipitation strengthening, etc. The Ti content may be 0%, but in order to obtain such an effect, the Ti content should be less than 0. The Ti content may be 0.010% or more, 0.050% or more, or 0.080% or more. On the other hand, an excessive Ti content may cause a large amount of precipitates. may be generated and cause a decrease in toughness. Therefore, the Ti content is 0.500% or less. The Ti content is 0.300% or less, 0.200% or less, or 0.100% or less. Good too.

[Ta: 0 to 0.500%]
Tantalum (Ta) is an element effective for controlling the morphology of carbides and increasing strength. The Ta content may be 0%, but in order to obtain these effects, the Ta content should be 0.001%. % or more. The Ta content may be 0.005% or more, 0.010% or more, or 0.050% or more. On the other hand, if Ta is excessively contained, fine Ta carbides are formed. Ta precipitates in large quantities, which may lead to an excessive increase in the strength of the steel material, resulting in a decrease in ductility and cold workability. Therefore, the Ta content is 0.500% or less. . 300% or less, 0.100% or less, or 0.080% or less.

[V: 0-1.00%]
Vanadium (V) is an element that contributes to improving the strength of steel materials by precipitation strengthening, etc. The V content may be 0%, but in order to obtain such an effect, the V content should be less than 0. The V content may be 0.01% or more, 0.02% or more, 0.05% or more, or 0.10% or more. On the other hand, an excessive V content In this case, a large amount of precipitates may be formed, which may reduce toughness. Therefore, the V content is set to 1.00% or less. The V content is set to 0.80% or less, 0.60% or less, or 0. It may be 50% or less.

[Cu: 0-3.00%]
Copper (Cu) is an element that contributes to improving strength and/or corrosion resistance. The Cu content may be 0%, but in order to obtain these effects, the Cu content should be 0.001% or more. The Cu content may be 0.01% or more, 0.10% or more, 0.15% or more, 0.20% or more, or 0.30% or more. Excessive Cu content may cause deterioration of toughness and weldability. Therefore, the Cu content is 3.00% or less. The Cu content is 2.00% or less, 1.50% or less, 1.00% or less. % or less, or 0.50% or less.

[Ni: 0-60.00%]
Nickel (Ni) is an element that contributes to improving strength and/or heat resistance, and is also an effective austenite stabilizing element. The Ni content may be 0%, but in order to obtain these effects, The Ni content is preferably 0.001% or more. The Ni content is preferably 0.01% or more, 0.10% or more, 0.50% or more, 0.70% or more, 1.00% or more, or In particular, from the viewpoint of sufficiently improving the heat resistance, the Ni content may be 30.00% or more, 35.00% or more, or 40.00% or more. On the other hand, excessive Ni content increases the alloy cost, and the deformation resistance during hot working increases, which may increase the equipment load. Therefore, the Ni content is set to 60.00% or less. The Ni content may be 55.00% or less, or 50.00% or less. In particular, from the viewpoint of economy and/or suppressing deterioration of weldability, the Ni content is 15.00% or less, 10.00% or less, 6.00% or less, or 4.00% or less. This is also fine.

[Cr: 0-30.00%]
Chromium (Cr) is an element that contributes to improving strength and/or corrosion resistance. The Cr content may be 0%, but in order to obtain these effects, the Cr content should be 0.001% or more. The Cr content may be 0.01% or more, 0.05% or more, 0.10% or more, or 0.50% or more. In particular, from the viewpoint of sufficiently improving the corrosion resistance, The Cr content may be 10.00% or more, 12.00% or more, or 15.00% or more. On the other hand, if Cr is excessively contained, the alloy cost increases and the toughness decreases. Therefore, the Cr content is 30.00% or less. The Cr content may be 28.00% or less, 25.00% or less, or 20.00% or less. In particular, weldability and/or Alternatively, from the viewpoint of suppressing a decrease in workability, the Cr content may be 10.00% or less, 9.00% or less, or 7.50% or less.

[Mo: 0-5.00%]
Molybdenum (Mo) is an element that improves the hardenability of steel, contributes to improving strength, and also contributes to improving corrosion resistance. The Mo content may be 0%, but these effects can be achieved by adding 0% Mo. In order to obtain the above, the Mo content is preferably 0.001% or more. The Mo content is preferably 0.01% or more, 0.02% or more, 0.50% or more, or 1.00% or more. On the other hand, if Mo is contained excessively, the deformation resistance during hot working increases, and the load on the equipment may become large. Therefore, the Mo content is 5.00% or less. Mo Content may be 4.50% or less, 4.00% or less, 3.00% or less, or 1.50% or less.

[W: 0-2.00%]
Tungsten (W) is an element that improves the hardenability of steel and contributes to improving its strength. The W content may be 0%, but in order to obtain such an effect, the W content should be 0%. The W content is preferably 0.01% or more, 0.02% or more, 0.05% or more, 0.10% or more, or 0.50% or more. However, if W is contained excessively, ductility and weldability may decrease. Therefore, the W content is 2.00% or less. The W content is 1.80% or less, 1.50% or less, or It may be 1.00% or less.

[B: 0 to 0.0200%]
Boron (B) is an element that contributes to improving strength. The B content may be 0%, but in order to obtain such an effect, the B content must be 0.0001% or more. The B content may be 0.0003% or more, 0.0005% or more, or 0.0007% or more. On the other hand, if B is contained excessively, the toughness and/or weldability may decrease. Therefore, the B content is 0.0200% or less. The B content may be 0.0100% or less, 0.0050% or less, 0.0030% or less, or 0.0020% or less.

[Co: 0-3.00%]
Cobalt (Co) is an element that contributes to improving hardenability and/or heat resistance. The Co content may be 0%, but in order to obtain these effects, the Co content should be 0.001% or less. % or more. The Co content may be 0.01% or more, 0.02% or more, 0.05% or more, 0.10% or more, or 0.50% or more. If Co is contained excessively, the hot workability may be deteriorated, and the raw material cost may increase. Therefore, the Co content is 3.00% or less. The Co content is 2.50% or less. It may be 2.00% or less, 1.50% or less, or 0.80% or less.

[Be: 0-0.050%]
Beryllium (Be) is an element that is effective in increasing the strength of the base material and refining the structure. The Be content may be 0%, but in order to obtain such effects, the Be content is The Be content is preferably 0.0003% or more. The Be content may be 0.0005% or more, 0.001% or more, or 0.010% or more. On the other hand, excessive Be content may cause the molding The Be content is therefore 0.050% or less. The Be content may be 0.040% or less, 0.030% or less, or 0.020% or less.

[Ag: 0-0.500%]
Silver (Ag) is an element that is effective in increasing the strength of the base material and refining the structure. The Ag content may be 0%, but in order to obtain such effects, the Ag content The Ag content is preferably 0.001% or more. The Ag content may be 0.010% or more, 0.020% or more, 0.030% or more, or 0.050% or more. If it is contained excessively, the formability may decrease. Therefore, the Ag content is 0.500% or less. The Ag content is 0.400% or less, 0.300% or less, or 0.200% or less. It's fine.

[Zr: 0 to 0.5000%]
Zirconium (Zr) is an element that can control the morphology of sulfides. The Zr content may be 0%, but in order to obtain such an effect, the Zr content must be 0.0001% or more. On the other hand, even if Zr is contained in an excessive amount, the effect is saturated, and therefore, the inclusion of more Zr than necessary in the steel material may lead to an increase in manufacturing costs. is not more than 0.5000%.

[Hf: 0-0.5000%]
Hafnium (Hf) is an element that can control the morphology of sulfides. The Hf content may be 0%, but in order to obtain such an effect, the Hf content must be 0.0001% or more. On the other hand, even if Hf is contained in an excessive amount, the effect is saturated, and therefore, the inclusion of more Hf than necessary in the steel material may lead to an increase in manufacturing costs. is not more than 0.5000%.

[Ca: 0-0.0500%]
Calcium (Ca) is an element that can control the morphology of sulfides. The Ca content may be 0%, but in order to obtain such an effect, the Ca content must be 0.0001% or more. On the other hand, even if an excessive amount of Ca is contained, the effect is saturated, and therefore, the inclusion of more Ca than necessary in the steel material may lead to an increase in the manufacturing cost. is not more than 0.0500%.

[Mg: 0 to 0.0500%]
Magnesium (Mg) is an element that can control the morphology of sulfides. The Mg content may be 0%, but in order to obtain such an effect, the Mg content must be 0.0001% or more. The Mg content may be more than 0.0015%, 0.0016% or more, 0.0018% or more, or 0.0020% or more. On the other hand, an excessive Mg content is not effective. The Mg content is saturated, and the cold formability and/or toughness may decrease due to the formation of coarse inclusions. Therefore, the Mg content is 0.0500% or less. The Mg content is 0.0400 % or less, 0.0300% or less, or 0.0200% or less.

[At least one of La, Ce, Nd, Pm and Y: 0 to 0.5000% in total]
Lanthanum (La), cerium (Ce), neodymium (Nd), promethium (Pm) and yttrium (Y) are elements that can control the morphology of sulfides, similar to Ca and Mg. The total content of at least one of La, Ce, Nd, Pm and Y may be 0%, but in order to obtain such an effect, it is preferable that it is 0.0001% or more. The total content of at least one of La, Ce, Nd, Pm and Y may be 0.0002% or more, 0.0003% or more, or 0.0004% or more. On the other hand, even if these elements are contained excessively, the effect may be saturated, and coarse oxides or the like may be formed, resulting in a decrease in cold formability. Therefore, the total content of at least one of La, Ce, Nd, Pm and Y may be 0.5000% or less, 0.4000% or less, 0.3000% or less, or 0.2000% or less.

[Sn: 0 to 0.300%]
Tin (Sn) is an element that is effective in improving corrosion resistance. The Sn content may be 0%, but to obtain this effect, the Sn content must be 0.001% or more. The Sn content may be 0.010% or more, 0.020% or more, 0.030% or more, or 0.050% or more. On the other hand, if Sn is contained excessively, the toughness, particularly This may result in a decrease in low temperature toughness. Therefore, the Sn content is 0.300% or less. The Sn content may be 0.250% or less, 0.200% or less, or 0.150% or less. .

[Sb: 0 to 0.300%]
Antimony (Sb) is an element that is effective in improving corrosion resistance, similar to Sn, and the effect can be increased by including it in combination with Sn. The Sb content may be 0%, but In order to obtain the effect of improving corrosion resistance, the Sb content is preferably 0.001% or more. However, excessive Sb content may result in a decrease in toughness, particularly low-temperature toughness. Therefore, the Sb content is 0.300% or less. may be 0.250% or less, 0.200% or less, or 0.150% or less.

[Te: 0 to 0.100%]
Tellurium (Te) is an element that is effective in improving the machinability of steel because it forms low-melting point compounds with Mn and S to enhance the lubricating effect. Even if the Te content is 0%, However, in order to obtain such an effect, the Te content is preferably 0.001% or more. The Te content is preferably 0.010% or more, 0.020% or more, 0.030% or more, or The content of Te may be 0.040% or more. On the other hand, if Te is contained excessively, the effect is saturated and the alloy cost increases. Therefore, the Te content is 0.100% or less. The amount may be 0.090% or less, 0.080% or less, or 0.070% or less.

[Se: 0-0.100%]
Selenium (Se) is an effective element for improving the machinability of steel because the selenides formed in steel change the shear plastic deformation of the workpiece material, making chips more likely to be crushed. The Se content may be 0%, but in order to obtain such an effect, the Se content is preferably 0.001% or more. However, if Se is excessively contained, the effect is saturated and the alloy cost increases. Therefore, the Se content The Se content may be 0.090% or less, 0.080% or less, or 0.070% or less.

[As: 0 to 0.050%]
Arsenic (As) is an effective element for improving the machinability of steel. The As content may be 0%, but in order to obtain such an effect, the As content should be 0%. The As content is preferably 0.001% or more. The As content may be 0.005% or more or 0.010% or more. On the other hand, if As is excessively contained, the hot workability may be deteriorated. Therefore, the As content is 0.050% or less. The As content may be 0.040% or less, 0.030% or less, or 0.020% or less.

[Bi: 0-0.500%]
Bismuth (Bi) is an element effective in improving the machinability of steel. The Bi content may be 0%, but in order to obtain such an effect, the Bi content must be 0%. The Bi content is preferably 0.001% or more. The Bi content may be 0.010% or more, 0.020% or more, 0.030% or more, or 0.050% or more. On the other hand, when Bi is excessively added, Even if Bi is contained, the effect is saturated and the alloy cost increases. Therefore, the Bi content is 0.500% or less. The Bi content is 0.400% or less, 0.300% or less, or 0.200% or less. It may be the following.

[Pb: 0 to 0.500%]
Lead (Pb) is an element that is effective in improving the machinability of steel because it melts when the temperature rises during cutting and promotes the growth of cracks. The Pb content may be 0%, but In order to obtain such an effect, the Pb content is preferably 0.001% or more. The Pb content may be 0.050% or more. On the other hand, if the Pb content is excessive, the hot workability may be deteriorated. Therefore, the Pb content is 0.500% or less. It may be 400% or less, 0.300% or less, or 0.200% or less.

In the steel material according to the embodiment of the present invention, the remainder other than the above elements consists of Fe and impurities. Impurities are components that are mixed in due to various factors in the manufacturing process, including raw materials such as ores and scraps, when industrially manufacturing steel material.

[Effective amount of X element]
According to an embodiment of the present invention, the effective amount of the X element consisting of Pr, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, and Sc is determined by the left side of the following formula 1, and the value is set to satisfy the following formula 1.
0.40[Pr]+0.37[Sm]+0.37[Eu]+0.36[Gd]+0.35[Tb]+0.34[Dy]+0.34[Ho]+0. 33[Er]+0.33[Tm]+0.32[Yb]+0.32[Lu]+1.24[Sc]-2.33[O]-3.99[N]-1.74[S] ≧ 0.0003 ... Formula 1
Here, [Pr], [Sm], [Eu], [Gd], [Tb], [Dy], [Ho], [Er], [Tm], [Yb], [Lu], [Sc], [O], [N], and [S] are the contents [mass %] of each element, and are 0 when the element is not contained.

By making the effective amount of the X element satisfy the above formula 1, the amount of these elements present in the steel in a solid solution state can be increased, so that the recrystallization of austenite grains can be suppressed or delayed, and the recrystallization start temperature can be shifted to a higher temperature due to such suppression or delay of recrystallization. To explain in more detail, these X elements (hereinafter, also simply referred to as "X") tend to combine with O (oxygen), N (nitrogen) and S (sulfur) present in the steel to form inclusions consisting of oxides ( _X2O3 ), nitrides (XN) and sulfides ₍ XS). Once the inclusions are formed, at least the X elements in these inclusions cannot contribute to suppressing the recrystallization of austenite grains. Therefore, in order to suppress the recrystallization of austenite grains, it is necessary to increase the amount of X elements present in the steel in a solid solution state without forming inclusions (i.e., the amount of X elements in the steel).

Here, the amount of the X element in solid solution in steel can be roughly calculated by subtracting the maximum amount that can be consumed to form inclusions (oxides, nitrides, and sulfides) from the amount of the X element contained in the steel. Therefore, in the embodiment of the present invention, the amount of the X element in solid solution roughly calculated in this manner is the amount of the X element effective for suppressing the recrystallization of austenite grains (i.e., the "effective amount of the X element"), and is specifically defined by the following formula A.
Effective amount of X element [atomic %] = Σ(M _[Fe] /M _[X] ) x [X] - (M _[Fe] /M _[O] ) x [O] x 2/3 - (M _[Fe] /M _[N] ) x [N] - (M _[Fe] /M _[S] ) x [S] ... Formula A
Here, X represents each of the X elements Pr, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, and Sc, M _[X] represents the atomic weight of the X element, M _[Fe] represents the atomic weight of Fe, M _[O] represents the atomic weight of O, M _[N] represents the atomic weight of N, and M _[S] represents the atomic weight of S. [X], [O], [N], and [S] are the contents [mass%] of the corresponding elements, and are 0 when the element is not contained.

The above formula A will be explained in detail below. First, although various alloy elements are contained in the steel material according to the embodiment of the present invention, it is clear that the steel material as a whole is composed almost entirely of Fe, or, when the optional elements Ni and/or Cr are contained relatively in large amounts (the maximum contents are 60.00% and 30.00%, respectively), the steel material is composed almost entirely of Ni and/or Cr in addition to Fe. On the other hand, it is well known that the atomic weights of Ni and Cr are equivalent to the atomic weight of Fe. Therefore, even if the steel material contains a relatively large amount of Ni and/or Cr, the atomic percentages of each of the X elements Pr, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, and Sc can be approximately calculated by multiplying the content [mass%] of each X element by the ratio of the atomic weight of Fe to the atomic weight of each X element, that is, (M _[Fe] / M _[X] ) × [X]. Therefore, the atomic percentage of all X elements can be calculated by adding up the amount of each X element calculated by (M _[Fe] /M _[X] )×[X] (i.e., by calculating Σ(M _[Fe] /M _[X] )×[X]).

Next, the amount of the X element in the steel that can effectively suppress the recrystallization of austenite grains can be calculated by subtracting the maximum amount (atomic %) that can be consumed to form oxides (X ₂ O ₃ ), nitrides (XN) and sulfides (XS) from the total atomic % of the X element. Here, the maximum amount (atomic %) of the X element that can be consumed to form oxides (X ₂ O ₃ ), nitrides (XN) and sulfides (XS) can be approximately calculated as (M _[Fe] / M _{[o] ) × [O] × 2/3, (M [Fe] / M [N]} ) × [N] and (M _{[ Fe]} / M _{[S ]} ) × [S] using the atomic weights of Fe, O, N and S in the steel and the contents of O, N and S, respectively, for the same reason as described above. Therefore, the effective amount of the X element for suppressing the recrystallization of austenite grains can be defined by the following formula A.
Effective amount of X element [atomic %] = Σ(M _[Fe] /M _[X] ) x [X] - (M _[Fe] /M _[O] ) x [O] x 2/3 - (M _[Fe] /M _[N] ) x [N] - (M _[Fe] /M _[S] ) x [S] ... Formula A

Here, the atomic weights of Fe, O, N, S and each X element are Fe: 55.845, O: 15.9994, N: 14.0069, S: 32.068, Pr: 140.908, Sm: 150.36, Eu: 151.964, Gd: 157.25, Tb: 158.925, Dy: 162.500, Ho: 164.930, Er: 167.259, Tm: 168.934, Yb: 173.045, Lu: 174.967, Sc: 44.9559. Therefore, by substituting the atomic weights of each element into the above formula A and rearranging it, the effective amount of the X element in atomic % can be approximately represented by the following formula B.
Effective amount = 0.40 [Pr] + 0.37 [Sm] + 0.37 [Eu] + 0.36 [Gd] + 0.35 [Tb] + 0.34 [Dy] + 0.34 [Ho] + 0.33 [Er] + 0.33 [Tm] + 0.32 [Yb] + 0.32 [Lu] + 1.24 [Sc] - 2.33 [O] - 3.99 [N] - 1.74 [S] ... Formula B
Here, [Pr], [Sm], [Eu], [Gd], [Tb], [Dy], [Ho], [Er], [Tm], [Yb], [Lu], [Sc], [O], [N], and [S] are the contents [mass %] of each element, and are 0 when the element is not contained.

In an embodiment of the present invention, in order to suppress the recrystallization of austenite grains, the effective amount of the X element calculated by the above formula B must be 0.0003% or more, that is, it must satisfy the following formula 1.
0.40[Pr]+0.37[Sm]+0.37[Eu]+0.36[Gd]+0.35[Tb]+0.34[Dy]+0.34[Ho]+0. 33[Er]+0.33[Tm]+0.32[Yb]+0.32[Lu]+1.24[Sc]-2.33[O]-3.99[N]-1.74[S] ≧ 0.0003 ... Formula 1
The effective amount of the X element may be, for example, 0.0005% or more or 0.0007% or more, preferably 0.0010% or more, more preferably 0.0015% or more, even more preferably 0.0030% or more, and most preferably 0.0050% or more or 0.0100% or more. Also, as is clear from the above formula 1, in order to stably secure the effective amount, it is preferable to reduce the contents of O, N and S in the steel as much as possible. Here, the upper limit of the effective amount of the X element is not particularly limited, but even if the effective amount of the X element is excessively increased, the effect is saturated and the manufacturing cost increases (the alloy cost increases with the increase in the content of the X element and/or the refining cost increases for O, N and S), which is not necessarily preferable. Therefore, the effective amount of the X element is preferably 2.0000% or less, and may be, for example, 1.8000% or less, 1.5000% or less, 1.2000% or less, 1.0000% or less, or 0.8000% or less.

The steel material according to the embodiment of the present invention may be any steel material and is not particularly limited. The steel material according to the embodiment of the present invention includes, for example, steel material before exerting the recrystallization suppression effect, such as slabs, billets, and blooms that are steel material before hot rolling, and steel material after exerting the recrystallization suppression effect, such as steel material after hot rolling. The steel material after hot rolling is not particularly limited, but includes, for example, thick steel plate, thin steel plate, and even steel bar, wire rod, shaped steel, and steel pipe.

The steel material according to the embodiment of the present invention can be manufactured by any suitable method known to those skilled in the art depending on the form of the final product, etc. For example, when the steel material is a thick steel plate, the manufacturing method includes the steps generally applied when manufacturing a thick steel plate, for example, a step of casting a slab having the above-described chemical composition, a step of hot rolling the cast slab, including a finish rolling that ends at a temperature lower than the recrystallization start temperature, and a step of cooling the obtained rolled material, and may further include an appropriate heat treatment step and a tempering step, etc., as necessary. For example, the steel material according to the embodiment of the present invention is particularly suitable for applying a thermomechanical control process (TMCP) that combines controlled rolling and accelerated cooling.

In addition, when the steel material is a thin steel plate, the manufacturing method includes the steps generally applied when manufacturing a thin steel plate, for example, a step of casting a slab having the above-described chemical composition, a step of hot rolling the cast slab, including a finish rolling step that ends at a temperature lower than the recrystallization start temperature, and a step of cooling and coiling the obtained rolled material, and may further include a cold rolling step, an annealing step, etc. as necessary. Similarly, the manufacturing method of steel bars and other steel materials includes the steps generally applied when manufacturing steel bars and other steel materials, for example, a steelmaking step of forming molten steel having the above-described chemical composition, a step of casting slabs, billets, blooms, etc. from the formed molten steel, a step of hot rolling the cast slabs, billets, blooms, etc., including a finish rolling step that ends at a temperature lower than the recrystallization start temperature, and a step of cooling the obtained rolled material, and other steps can be appropriately selected and performed from appropriate steps known to those skilled in the art for manufacturing those steel materials. The specific conditions for each of the above steps are not particularly limited, and appropriate conditions may be appropriately selected depending on the type of steel, the type and shape of the steel material, etc. In the production of the steel material according to the embodiment of the present invention, it is important to ensure an effective amount of the X element, and for this purpose, it is extremely important to sufficiently reduce the contents of O, N and S, which can form inclusions in the steel together with the X element, in the refining step.

The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples in any way.

In this example, first, molten steels having various chemical compositions were melted using a vacuum melting furnace, and ingots of approximately 50 kg were produced using an ingot casting method. The chemical compositions of samples taken from each of the resulting ingots were analyzed and found to be as shown in Table 1 below. Next, a compression processing test was carried out using cylindrical test material (φ8 mm × height 12 mm) obtained from the ingots, and the recrystallization inhibition effect of the steel material was evaluated based on the softening rate calculated from the results of the test.

Specifically, according to the test conditions of the compression working test shown in Fig. 1, first, a cylindrical test material was heated to 950-1300°C, and then two compression working tests were performed under the conditions of a working temperature of 950°C, a true strain ε = 0.4, a strain rate ε/t = 5s ^-1 , and an interpass time of 10s (Working 1 and Working 2 in Fig. 1), and the softening rate was measured from the stress-strain curves measured by Working 1 and Working 2. More specifically, as shown in Fig. 2 (excerpted from Naoki Maruyama et al., "State of Nb in the Early Stage of Recovery and Recrystallization of Hot-Worked Austenitic Structure of Steel", Journal of the Japan Institute of Metals, Vol. 60, No. 11 (1996), pp. 1051-1057), when the yield stresses during the first and second compression working are _σ1 and _σ2 , respectively, and the maximum stress during the first compression working is _σm , the softening rate _Xs can be calculated from the following formula.
X _s = (σ _m - σ ₂ )/(σ _m - σ ₁ )

If recrystallization has progressed sufficiently between the first compression and the second compression, the stress-strain curves measured by the processing 1 and the processing 2 will show similar behavior, so σ ₂ will be close to σ ₁ , and therefore the softening rate X _s will approach 1. On the other hand, if the progress of recrystallization is suppressed between the first compression and the second compression, the dislocation density will increase during the second compression, causing work hardening, so the yield stress σ ₂ will increase, and as a result, the softening rate X _s will approach 0. Therefore, by measuring the softening rate X _s of a steel material, it is possible to evaluate the recrystallization suppression effect of the steel material. In this embodiment, when the softening rate X _s is 0.20 or less, the steel material was evaluated as having an improved recrystallization suppression effect. The results are shown in Table 1 below.

With reference to Table 1, in Comparative Examples 84 to 91, the effective amount of the X element consisting of Pr, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, and Sc was low, so that a sufficient recrystallization suppression effect could not be exhibited. More specifically, in Comparative Example 84, since the X element was not included, a sufficient recrystallization suppression effect could not be exhibited. In addition, in Comparative Examples 85 to 91, although the above-mentioned X element was included, its content was low in a relative relationship with O, N, and/or S, in other words, the content of O, N, and/or S was excessive with respect to the X element, so that it is considered that a relatively large amount of inclusions was generated between the X element and these elements. As a result, the effective amount of the X element was low, and a sufficient recrystallization suppression effect could not be exhibited. In contrast to this, in all the examples according to the present invention, a high recrystallization suppression effect could be exhibited by setting the effective amount of the X element to 0.0003% or more.

The steel material according to the embodiment of the present invention is, for example, a slab, billet, bloom, which is a steel material before hot rolling, or a steel material after hot rolling. Examples of the steel material after hot rolling include thick steel plates used for applications such as bridges, architecture, shipbuilding, and pressure vessels, thin steel plates used for applications such as automobiles and home appliances, and also steel bars, wire rods, shaped steel, and steel pipes. When the steel material according to the embodiment of the present invention is applied to these materials, the recrystallization suppression effect makes it possible to manufacture steel materials without impairing productivity, and since the metal structure in the steel material can be refined, it is possible to significantly improve the properties related to the refinement of such metal structure, such as toughness.

Claims (5)

In mass percent,
C: 0.001-1.000%,
Si: 0.01-3.00%,
Mn: 0.10 to 4.50%,
P: 0.300% or less,
S: 0.0300% or less,
Al: 0.001-5.000%,
N: 0.2000% or less,
O: 0.0100% or less,
at least one X element selected from the group consisting of Pr: 0 to 0.8000% , Eu : 0 to 0.8000%, Gd: 0 to 0.8000%, Tb: 0 to 0.8000%, Dy: 0 to 0.8000%, Ho: 0 to 0.8000%, Er: 0 to 0.8000%, Tm: 0 to 0.8000%, Yb: 0 to 0.8000%, Lu: 0 to 0.8000%, and Sc: 0 to 0.8000%,
Nb: 0 to 3.000%,
Ti: 0 to 0.500%,
Ta: 0-0.500%,
V: 0-1.00%,
Cu: 0 to 3.00%,
Ni: 0 to 60.00%,
Cr: 0-10.00 %,
Mo: 0-5.00%,
W: 0-2.00%,
B: 0-0.0200%,
Co: 0-3.00%,
Be: 0 to 0.050%,
Ag: 0-0.500%,
Zr: 0 to 0.5000%,
Hf: 0-0.5000%,
Ca: 0-0.0500%,
Mg: 0 to 0.0500% (excluding 0.0001 to 0.0015%)
At least one of La, Ce, Nd, Pm, and Y: 0 to 0.5000% in total,
Sn: 0-0.300%,
Sb: 0 to 0.300%,
Te: 0 to 0.100%,
Se: 0-0.100%,
As: 0 to 0.050%,
Bi: 0-0.500%,
Pb: 0 to 0.500%, and the balance: Fe and impurities;
A steel material having a chemical composition that satisfies the following formula 1.
0.40[Pr ]+ 0.37[Eu]+0.36[Gd]+0.35[Tb]+0.34[Dy]+0.34[Ho]+0.33[Er]+0.33[Tm]+0.32[Yb]+0.32[Lu]+1.24[Sc]-2.33[O]-3.99[N]-1.74[S] ≧ 0.0003...Formula 1
Here, [Pr] , [ Eu], [Gd], [Tb], [Dy], [Ho], [Er], [Tm], [Yb], [Lu], [Sc], [O], [N], and [S] are the contents [mass %] of each element, and are 0 when the element is not contained. The chemical composition, in mass%,
Nb: 0.003 to 3.000%,
Ti: 0.005-0.500%,
Ta: 0.001 to 0.500%,
V: 0.001-1.00%,
Cu: 0.001 to 3.00%,
Ni: 0.001 to 60.00%,
Cr: 0.001-10.00 %,
Mo: 0.001 to 5.00%,
W: 0.001-2.00%,
B: 0.0001 to 0.0200%,
Co: 0.001-3.00%,
Be: 0.0003 to 0.050%, and Ag: 0.001 to 0.500%
The steel material according to claim 1, comprising one or more of the following: The chemical composition, in mass%,
Zr: 0.0001 to 0.5000%,
Hf: 0.0001-0.5000%,
Ca: 0.0001-0.0500%,
Mg: 0.0001 to 0.0500% (excluding 0.0001 to 0.0015%) , and at least one of La, Ce, Nd, Pm and Y: 0.0001 to 0.5000% in total
The steel material according to claim 1 or 2, comprising one or more of the following: The chemical composition, in mass%,
Sn: 0.001 to 0.300%, and Sb: 0.001 to 0.300%
The steel material according to any one of claims 1 to 3, comprising one or two of the following: The chemical composition, in mass%,
Te: 0.001 to 0.100%,
Se: 0.001 to 0.100%,
As: 0.001 to 0.050%,
Bi: 0.001 to 0.500%, and Pb: 0.001 to 0.500%
The steel material according to any one of claims 1 to 4, comprising one or more of the following:

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