JP2009046721A - Steel sheet for heat treatment - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a steel sheet for hot press forming in which, on hot press forming, oxide scales adhere firmly at the forming and most of the oxide scales peel off after cooling and also the remaining scales can be easily peeled off by shot blasting. <P>SOLUTION: The steel sheet has a chemical composition consisting of 0.1 to 0.5% C, 0.5 to 3.0% Mn+Cr, one or more selected from the group consisting of ≤0.5% Si, ≤2% Ni, ≤1% Cu, ≤1% V and ≤1% Al and the balance Fe with impurities. Moreover, the product of the center line average roughness (Ra)(μm) of the surface of the steel sheet and the number (PPI), per 25.4 mm, of a pair of a peak of ≥0.3175 μm from the center line of a surface roughness curve and a valley of ≥0.3175 μm ranges from 10 to 300. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  In the present invention, the oxide scale produced when the steel sheet is heated in the atmosphere or in a low oxygen concentration atmosphere is prevented from peeling from the base steel during heat treatment such as quenching, while easy in subsequent descaling treatment. The present invention relates to a steel plate for heat treatment that is peeled off.

  In recent years, in order to reduce the weight of automobiles, efforts have been made to increase the strength of steel materials and reduce the weight used. In thin steel plates widely used in automobiles, press formability decreases with increasing steel plate strength, making it difficult to manufacture products with complex shapes. Specifically, problems such as a decrease in ductility and breakage at a site with a high degree of processing, a springback and wall warpage increase, and dimensional accuracy deteriorates. Therefore, it is not easy to produce a part by press molding using a steel plate having a high strength, particularly a tensile strength of 780 MPa or higher. According to roll forming instead of press forming, it is possible to process a high-strength steel sheet, but it can be applied only to parts having a uniform cross section in the longitudinal direction.

  On the other hand, as shown in Patent Document 1, in a method called hot press for press-forming a heated steel plate, the steel plate is soft and highly ductile at a high temperature, so that a complicated shape is formed with high dimensional accuracy. Is possible. In the hot press, the steel sheet is heated in the austenite region and rapidly cooled (quenched) in the mold at the time of forming, so that high strength of the steel sheet can be achieved at the same time by martensitic transformation.

  Patent Document 2 discloses a pre-press quench method that simultaneously achieves high strength and forming of a steel sheet by forming into a predetermined shape at room temperature, heating to an austenite region, finishing forming in a mold and quenching. Is disclosed.

Patent Document 3 discloses that a scale is attached to the surface of a hot press-molded product and it is necessary to remove it by means such as shot blasting.
Patent Document 4 discloses that, during hot press forming, the surface average roughness is specified to be 3.0 μm or less and the generation of oxide scale is reduced by specifying the surface oxide structure of the steel sheet. Yes.
British Patent Publication No. 1490535 Japanese Patent Laid-Open No. 10-96031 JP 2004-290108 A JP-A-2005-133180

  Such a hot press method and a pre-press quench method are excellent molding methods that can ensure high strength and formability of the member at the same time, but are subjected to heat treatment heated to a high temperature of 800 to 1000 ° C., The problem that the steel plate surface is oxidized arises. As a result of this oxidation, the scale made of iron oxide formed on the surface of the steel sheet falls off during pressing and adheres to the mold, resulting in decreased productivity, or such oxidized scale remains in the product after pressing. The appearance may be poor.

  In addition, when such an oxide scale remains, the adhesion between the steel sheet and the coating film is inferior in the case of coating in the next step, which may lead to a decrease in corrosion resistance. Further, as disclosed in Patent Document 3, it has been pointed out that a welding failure such as electrode welding occurs during spot welding. Therefore, after press molding, oxide scale removal treatment such as shot blasting is required.

  In Patent Document 4, the generation of oxide scale itself is suppressed, but once the oxide scale has been generated, it is necessary to remove it after hot press molding, followed by brush water cleaning, further acid cleaning and alkali cleaning. .

  Therefore, as a characteristic required for the oxide scale generated on the surface of the steel sheet during the heat treatment in the hot press method or the pre-press quench method, it is suppressed that the scale peeling off during quenching (hot press etc.), In the descaling process (shot blasting process, etc.), it is easily peeled and removed.

  For example, the heating of the steel sheet when subjected to normal hot pressing is often performed in a non-oxidizing atmosphere (for example, gas furnace-air-fuel ratio 0.9) in order to suppress generation of oxide scale. Nevertheless, ordinary steel plates have a large amount of oxide scale produced, and the problem is that the oxide scale peels off during hot pressing, and the mold is easily contaminated.

  On the other hand, in patent document 4, the steel plate surface characteristic is changed by wash | cleaning the steel plate surface with a special washing | cleaning method, and the said subject is solved. Although this method is an excellent method, since it involves an increase in steps in the steel plate manufacturing process, a method that can solve the above-described problems without an increase in such steps is desired.

  Although the present inventors allow the generation of oxide scale during heating, scale peeling and dropping are suppressed during quenching (hot pressing, etc.), and descaling treatment after completion of heat treatment (shot blasting, etc.) As a result of intensive investigations to obtain a steel sheet that is easily peeled and removed, sometimes such an oxide scale can be obtained by appropriately controlling the chemical composition and surface properties of the steel sheet. Newly discovered.

  In the present invention, by adjusting the adhesion between the oxide scale generated during heating and the base steel, it does not peel off during heat treatment, especially during hot press forming, but it can be easily peeled off after forming, for example, by shot peening. Therefore, it has been found that it is only necessary to adjust the unevenness of the surface of the steel sheet and utilize the so-called scale anchor effect.

  According to the present invention, it is understood that the unevenness state of the steel sheet surface can be defined by the unevenness depth and the unevenness density of a predetermined depth, thereby quantitatively evaluating the scale anchor effect described above. It was.

  Here, the depth of the unevenness corresponds to the center line average roughness Ra. The number of irregularities corresponds to the number PPI per 25.4 mm of a pair of a peak of 0.3175 μm or more and a valley of 0.3175 μm or more from the center line of the surface roughness curve.

  As described above, it has been found that the uneven state of the steel sheet surface greatly affects the scale peelability according to the present invention, but the scale peelability is changed by the concave portion because of the scale anchor effect due to the concave portion and the scale peeling. It is surmised that this is caused by the fact that the propagation of is suppressed by the recess. For this reason, it is assumed that if the deep concave portions exist at a high density, the scale anchor effect increases, and conversely, the scale anchor effect decreases. However, the results of the experiments by the inventors revealed that, in fact, this is not the case, and each element does not affect the scale anchor effect alone, but influences each other. did.

  In other words, in the present invention, from the result of subsequent trial and error, the product of the depth of the unevenness and the density of the unevenness of the predetermined depth, that is, the product of Ra and PPI, between the oxide scale and the base steel. It was found that the adhesion strength of can be properly evaluated.

The present invention completed based on this finding is as follows.
(1) By mass%, C: 0.1 to 0.5% and Mn + Cr: 0.5 to 3.0%, Si: 0.5% or less, Ni: 2% or less, Cu: 1% or less, V: 1% or less, and Al: 1% or less selected from the group consisting of 1% or less, and a steel plate having a chemical composition consisting of Fe and impurities, the center of the surface The product of the line average roughness Ra (μm) and the number PPI per 25.4 mm of a pair of a peak of 0.3175 μm or more and a valley of 0.3175 μm or more from the center line of the surface roughness curve is 10 or more and 300 A steel sheet for heat treatment, characterized in that:
(2) The steel sheet for heat treatment according to the above (1), wherein the chemical composition contains B: 0.01% or less in mass% instead of part of Fe.
(3) The chemical composition contains one or two selected from the group consisting of Nb: 1.0% or less and Mo: 1.0% or less in mass%, instead of a part of Fe. The steel sheet for heat treatment as described in (1) or (2) above.
(4) The steel sheet for heat treatment according to any one of (1) to (3), wherein the chemical composition contains Ti in an amount satisfying the following formula (1) instead of a part of Fe:
3.42N + 0.001 ≦ Ti ≦ 3.42N + 0.5 (1)
Here, Ti and N in a formula show content (unit: mass%) of each element in steel.
(5) The steel sheet for heat treatment according to any one of (1) to (4), wherein the chemical composition contains Ca: 0.005% or less in mass% instead of part of Fe.
(6) With respect to one or more of P, S and N which are impurities as the chemical composition, P: 0.015% or less, S: 0.010% or less and N: 0.010 in mass% % Steel sheet for heat treatment according to any one of the above (1) to (5), which satisfies one condition or two conditions or more.
(7) The steel sheet for heat treatment as described in any one of (1) to (6) above, which is for hot press forming.

  Next, the reason why the present invention is limited to each range will be described. In the following description, “%” for alloy elements represents “mass%”.

C: 0.1 to 0.5%
In order to ensure the strength of the product after heat treatment, the C content is 0.1% or more, preferably 0.15% or more. On the other hand, if the C content exceeds 0.5%, generation of oxide scale is suppressed during the heat treatment, and the present invention does not need to be used. Therefore, the C content is 0.1% or more and 0.5 or less. Usually, the C content of a steel sheet used in hot pressing or the like is generally 0.2 to 0.35%, and the present invention exhibits a remarkable effect with respect to the C content in this range. .

Mn + Cr: 0.5-3.0%
Mn and Cr are very effective elements in order to increase the hardenability of the steel sheet and to ensure a stable strength after quenching. However, if the total content of Mn and Cr (hereinafter also referred to as “(Mn + Cr) content”) is less than 0.5%, the effect is not sufficient, while the (Mn + Cr) content exceeds 3.0%. And the effect is saturated, and on the contrary, it is difficult to secure a stable strength. A more desirable (Mn + Cr) content is 0.8 to 2.0%.

B: 0.01% or less B is an optional additive element, and is effective for enhancing the hardenability of the steel sheet and further enhancing the effect of ensuring the stability of the strength after quenching. It is also an important element in that it segregates at grain boundaries to increase grain boundary strength and improve toughness. However, when the B content exceeds 0.01%, the effect is saturated and the cost is increased. A more desirable B content is 0.001 to 0.0030%.

Si: 0.5% or less, Ni: 2% or less, Cu: 1% or less, V: 1% or less, Al: 1% or less These elements enhance the hardenability of the steel sheet and ensure stable strength after quenching. It is an effective element and is contained in at least one kind. However, even if each element is contained in excess of each upper limit, the effect is small and the cost is unnecessarily increased. Therefore, when contained, the content of each alloy element is set to the above range.

Nb: 1.0% or less Nb is an optional additive element that suppresses recrystallization and forms fine carbides to make austenite grains fine when the steel sheet is heated to Ac ₃ points or more. Has the effect of greatly improving toughness. However, when the Nb content exceeds 1.0%, the effect is saturated and the cost is increased unnecessarily. The Nb content is more preferably 0.01 to 0.2%, and further preferably 0.04 to 0.15%.

Mo: 1.0% or less Mo is an optional additive element, and when the steel sheet is heated to Ac ₃ points or more, fine carbides are formed to make the austenite grains fine. Have However, when the Mo content exceeds 1.0%, the effect is saturated and the cost is unnecessarily increased. A more desirable Mo content is 0.01 to 0.2%, and further desirably 0.04 to 0.15%.

Formula: 3.42N + 0.001 ≦ Ti ≦ 3.42N + 0.5
Ti is an optional additive element, and has the effect of greatly improving toughness because it suppresses recrystallization and forms fine carbides to make austenite grains fine when the steel sheet is heated to Ac ₃ points or more. . In order to surely obtain such an effect, the Ti content is preferably (3.42N + 0.001) or more when the steel N content is represented by “N”. On the other hand, when the Ti content exceeds (3.42N + 0.5), the effect is saturated and the cost is unnecessarily increased. A more desirable Ti content is 3.42N + 0.02 ≦ Ti ≦ 3.42N + 0.08.

Ca: 0.005% or less Ca is an optional additive element, and has the effect of refining inclusions in steel and improving toughness after quenching. In order to reliably obtain such an effect, the Ca content is preferably set to 0.001% or more. On the other hand, when the Ca content exceeds 0.005%, the effect is saturated. A more desirable Ca content is 0.002 to 0.004%.

In the steel composition, P, S, and N are usually contained as impurities. In the present invention, at least one of them is preferably within the following range.
P: 0.015% or less P is an element that greatly deteriorates the toughness after quenching and greatly deteriorates the adhesion between the base steel and the oxide scale, and is preferably 0.015% or less. More desirably, it is 0.010% or less, and further desirably is 0.008% or less.

S: 0.010% or less Since S is an element that greatly deteriorates the toughness after quenching and greatly deteriorates the adhesion between the base steel and the oxide scale, it is preferably 0.010% or less. More desirably, it is 0.008% or less, and further desirably is 0.005% or less.

N: 0.010% or less N is an element that forms inclusions in steel and deteriorates the toughness after quenching, and is therefore preferably 0.010% or less. More desirably, it is 0.008% or less, and further desirably is 0.005% or less.

As can be seen from the above description, in the present invention, the steel composition and the surface irregularity state of the steel sheet are not directly related, but when the object of the present invention is a hot press-formed steel sheet, for example, A preferred chemical composition is as follows:
In mass%, C: 0.1 to 0.5%, Mn: 0.01 to 3.0%, Cr: 0.01 to 3.0%, provided that Mn + Cr: 0.5 to 3.0%, Si: 0.5% or less, Al: 1% or less, and P: 0.015% or less, S: 0.010% or less, and N: 0.010% or less, respectively, Ni: 2% or less, Cu: 1% or less, and V: 1% or more selected from the group consisting of 1% or less, and the balance consisting of Fe and impurities.

Further, the following elements may be included as necessary.
(1) B: 0.01% or less.
(2) One or two selected from the group consisting of Nb: 1.0% or less and Mo: 1.0% or less.

(3) Ti in an amount satisfying the following formula (1).
3.42N + 0.001 ≦ Ti ≦ 3.42N + 0.5 (1)
Here, Ti and N in a formula show content (unit: mass%) of each element in steel.

(4) Ca: 0.005% or less.

About surface unevenness In the present invention, the roughness of the surface of the steel sheet, that is, the state of the unevenness on the surface of the steel sheet is defined by the depth of the unevenness and the number of the unevenness.

  Here, the depth of the unevenness corresponds to the center line average roughness Ra. The number of irregularities corresponds to the number PPI per 25.4 mm of a pair of a peak of 0.3175 μm or more and a valley of 0.3175 μm or more from the center line of the surface roughness curve.

  According to the present invention, when the product of Ra and PPI (hereinafter referred to as Ra × PPI value) is less than 10, the adhesion between the oxide scale generated on the steel sheet surface by heating and the base steel is low, and during hot pressing It is not possible to suppress the scale peeling at the etc. On the other hand, if the Ra × PPI value exceeds 300, the adhesion between the oxide scale produced on the steel sheet surface by heating and the base steel becomes too high, and the descaling process becomes difficult. More preferably, it is 20 or more and 280 or less, More preferably, it is 30 or more and 260 or less.

  In addition, since the glossiness after coating may fall when the value of Ra or PPI is excessive, Ra is preferably 3 μm or less and PPI is 1000 or less. On the other hand, the lower limit of Ra and PPI values is not particularly limited as long as the above conditions are satisfied. However, Ra is preferably 0.05 μm or more and PPI is 1 or more because of manufacturing constraints.

  In the present invention, the uneven surface state of the steel sheet as described above is, for example, the relationship between rolling conditions (lubricant, reduction amount, sheet thickness, rolling roll surface state, etc.) in cold rolling or skin pass rolling and the surface state obtained thereby. By checking the above and empirically obtaining the rolling conditions for obtaining the target surface irregularity state, it is possible to make it appear by adjusting the rolling conditions.

Next, a heat treatment condition and a heat treatment method in which the effect of the present invention is exhibited will be described.
Usually, in order to perform the quenching treatment, it is necessary to first heat the steel sheet to a temperature range of two phases (ferrite and austenite) or higher, that is, to a point of _Ac1 or higher. Therefore, it is desirable that steel containing 0.5% or less of C is heated to 700 ° C. or higher and held at that temperature for 1 minute or longer. The upper limit of the holding time is not particularly set, but it is desirable to set the upper limit to about 10 minutes in consideration of the efficiency in actual production.

About the cooling rate after heating, in order to obtain high strength after heat treatment, it is sufficient to secure a cooling rate at least equal to or higher than the upper critical cooling rate of the steel.
“Heat treatment” in the present specification can be exemplified by quenching, and a preferable example thereof is rapid cooling in a mold during hot press molding, that is, quenching. The same heat treatment conditions as described above may be used for hot press forming, but more specifically, after heating to 700 to 1000 ° C., cooling at about 50 ° C./sec or more simultaneously with press forming in the mold. Cooled and quenched at speed.

About heating atmosphere, what is necessary is just the conditions which an oxide scale produces | generates in air | atmosphere or low oxygen concentration atmosphere.
The quenching method includes a partial quenching method in which water is cooled immediately after high-frequency heating, or a method in which the entire member is heated by a heating furnace or the like, such as hot press or pre-press quench method, and then mold cooling or oil cooling. Any method may be used as long as it is a rapid cooling method. The scale anchor effect of the present invention is particularly exerted when a considerable shear force is applied to the oxide scale as in the hot press molding or pre-quenching method.

  Thus, the heating conditions prior to the heat treatment are not particularly limited, and normal heating conditions may be employed. Although depending on the oxygen concentration in the heating atmosphere and the heating temperature, the thickness of the oxide scale is usually 1 to 30 μm. Therefore, the thickness of the oxide scale is 1 to 30 μm in order to exert the effects of the present invention. What is necessary is just to heat-oxidize on such conditions.

  In the present invention, with a thin oxide scale of 1 to 2 μm, the peeling stress is small, the scale peeling hardly occurs, and the descaling is very difficult. Therefore, the scale thickness is preferably more than 2 μm. However, in most cases, the oxide scale thickness exceeds 2 μm. The present invention is effective for such an oxide scale.

  The steel sheet of the present invention is usually used once heated in the austenite region or in the vicinity of the austenite region for heat treatment, that is, quenching. Therefore, the mechanical properties at room temperature before heating are not important, and the metal structure before heating is not particularly specified. That is, any of a hot-rolled steel plate and a cold-rolled steel plate (full hard material, annealed material) may be used, and the manufacturing method is not particularly limited. However, from the viewpoint of productivity, a preferable manufacturing method is described below.

  The hot rolling is preferably performed in the austenite region from the viewpoint of rolling stability. When the coiling temperature is low, the strength increases due to the martensite-based structure, and when used as a base material for cold rolling, cold rolling becomes difficult, and the pre-press quench method is used without performing cold rolling. When provided, cold working becomes difficult. On the other hand, if the coiling temperature is high, the oxide scale becomes thick and the efficiency of the subsequent pickling is reduced. Therefore, the winding temperature is preferably 500 to 600 ° C.

  In pickling, an oxidized scale formed on the surface of the steel sheet during hot rolling is removed using an aqueous hydrochloric acid solution or an aqueous sulfuric acid solution. Usually, the acid concentration is about 3 to 10% with hydrochloric acid and about 15 to 25% with sulfuric acid, and the liquid temperature is usually about 80 to 100 ° C. Moreover, in order to prevent a per-acid pickling state (dissolution of base iron), a very small amount of pickling inhibitor is usually added. This inhibitor forms a film on the surface of the steel, which prevents corrosion of the steel by acid.

  Cold rolling is performed by a conventional method. The steel sheet of the present invention often has a high C content for the purpose of improving strength by quenching. For this reason, if the cold rolling is performed at an excessively high reduction ratio, the burden on the mill increases. Further, if the strength after cold rolling becomes too high due to work hardening, the welding strength and the line threading ability at the time of coil connection become a problem in the subsequent steps such as annealing. Therefore, the rolling reduction is preferably 80% or less, and more preferably 70% or less. In addition, since cold rolling increases the cost, it is preferable to omit the cold rolling and use a hot-rolled and pickled steel plate for a steel plate having a thickness and width that can be manufactured by hot rolling. .

  In addition, when pre-forming is involved, the type and structure of the steel plate are not limited, but it is desirable that the steel plate be as soft and ductile as possible. For example, TS is preferably about 590 MPa or less. In a hot-rolled steel sheet and a cold-rolled steel sheet, it is preferable to perform annealing in order to obtain a soft steel sheet, and the annealing temperature is preferably a recrystallization temperature or higher and 900 ° C. or lower. Moreover, it is preferable that the average cooling rate to room temperature after annealing is less than the upper critical cooling rate. Examples of the annealing method include box annealing and continuous annealing.

Examples of the present invention are shown below.
A steel plate (thickness: 1.0 mm) having the chemical composition shown in Table 1 was subjected to hot rolling and pickling or hot rolling and pickling and cold rolling on a slab melted in a laboratory. Manufactured.

  Test steel sheets with various surface irregularities were produced from the steel sheets thus obtained. In this example, the roughness of the steel sheet surface was adjusted by skin pass rolling. That is, the surface unevenness of the cold-rolled steel sheet, which is the starting material, was varied, but considering this, the rolling conditions for skin pass rolling were reduced, for example, the skin pass was lightly applied to a steel sheet with a shallow recess, The steel plate with a large recess depth was subjected to adjustment such as strong skin pass rolling.

As a result, the value of Ra × PPI was greatly changed.
In addition, Ra and PPI regarding the surface roughness of a steel plate were measured based on JIS-B0601 and SAEJ911.

  From these steel plates, a test plate having a size of 1.0 t × 80 w × 320 L (mm) was cut and heated in a gas furnace (air-fuel ratio 0.85 to 1.1) under the conditions shown in Table 2. Immediately after taking out from the heating furnace, a hat-type hot press was performed.

  FIG. 1 is a schematic explanatory view of the hat forming method of this example. The hot press molding conditions at this time were a molding height of 70 mm, Rd (die shoulder R) 8 mm, Rp (punch shoulder R) 8 mm, clearance 1.0 mm, and wrinkle holding force 12.7 kN.

  Thereafter, the appearance of the hot press-hat-molded product was observed, and when the area where the scale was peeled was 10% or less of the total surface area, the test was accepted and subjected to the next descaling treatment. The descaling process was performed by shot blasting. The conditions at that time were an iron ball having a diameter of 300 μm, an arc height value of 0.1 to 0.2 mmN, and a coverage of 100%.

  The quantitative evaluation of the remaining state of the oxide scale was evaluated by the method of Example 1 of Patent Document 3. That is, when the electrical resistance value measured by the method of Example 1 of Patent Document 3 was 15 mΩ or less, it was determined as acceptable.

  In Comparative Examples 6 and 7, since the Ra × PPI value was small, there was a lot of scale peeling immediately after hot pressing, which was unacceptable. Further, in Comparative Examples 8, 9, and 10, since the Ra × PPI value was large, the adhesion of the scale was too high, and the descaling process did not go well and failed. On the other hand, in the example of the present invention, since the Ra × PPI value is in an appropriate range, there was little scale peeling immediately after hot pressing, and there was no problem even in the descaling process.

  The scope of the present invention is shown in FIG. The circles in the figure are examples of the present invention, and the crosses are comparative examples.

It is a typical explanatory view of the hat forming method used for hot press forming in the example of the present invention. It is a graph which shows the result of the Example of this invention.

Claims (7)

In mass%, C: 0.1-0.5% and Mn + Cr: 0.5-3.0%, Si: 0.5% or less, Ni: 2% or less, Cu: 1% or less V: 1% or less and Al: 1% or less selected from the group consisting of 1% or less, a steel plate having a chemical composition consisting of the remainder Fe and impurities, the center line average roughness of the surface The product of the depth Ra (μm) and the number PPI per 25.4 mm of a pair of a peak of 0.3175 μm or more and a valley of 0.3175 μm or more from the center line of the surface roughness curve is 10 or more and 300 or less A steel sheet for heat treatment characterized by the above. The steel sheet for heat treatment according to claim 1, wherein the chemical composition contains B: 0.01% or less in mass% instead of part of Fe. The chemical composition contains one or two selected from the group consisting of Nb: 1.0% or less and Mo: 1.0% or less in mass%, instead of part of Fe. Or the steel plate for heat processing of 2. The steel sheet for heat treatment according to any one of claims 1 to 3, wherein the chemical composition contains Ti in an amount satisfying the following formula (1) instead of a part of Fe:
3.42N + 0.001 ≦ Ti ≦ 3.42N + 0.5 (1)
Here, Ti and N in a formula show content (unit: mass%) of each element in steel. The steel sheet for heat treatment according to any one of claims 1 to 4, wherein the chemical composition contains Ca: 0.005% or less in mass% instead of part of Fe. With respect to one or more of P, S and N which are impurities, the chemical composition is P: 0.015% or less, S: 0.010% or less and N: 0.010% or less in terms of mass%. The steel sheet for heat treatment according to any one of claims 1 to 5, which satisfies one condition or two conditions or more. The steel sheet for heat treatment according to any one of claims 1 to 6, which is for hot press forming.

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