JP2015113500A - Hot press component - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a hot press component having excellent delayed fracture resistance which cannot be achieved by prior art even for a hot roll press component to which tensile strength of 1180 MPa or more is added.SOLUTION: There is provided a hot press component having a composition component containing, by mass%, C:0.1 to 0.4%, Si:2.0% or less (excluding 0%), Mn:0.3 to 3.5% and Ti:0.01 to 0.2% and the balance iron with inevitable impurities, a micro structure containing martensite and retained austenite with an area ratio of 80% or more and the balance ferrite, and containing alloy carbonitride:0.05 mass% or more, the alloy carbonitride having consistency with a parent phase of 5.0×10/mor more and cementite of 2 mass% or less.

Description

  The present invention relates to a hot-pressed part requiring high strength, such as used for a structural member of an automobile part.

  In recent years, in order to achieve both improvement in automobile fuel efficiency and improvement in collision safety, it has been demanded to increase the strength of automobile steel plates as much as possible. However, as the strength of the steel sheet increases, the elongation and r value decrease, and the press formability and shape freezeability deteriorate.

  In order to solve such a problem, the steel sheet is heated to a temperature at which it becomes an austenite phase to reduce the strength, and in a state in which forming is facilitated, a mold having a temperature lower than that of the steel sheet (for example, room temperature) is used. A hot press forming method is used for producing parts by forming a steel sheet by forming and at the same time performing quenching utilizing the temperature difference between the two to ensure strength after forming.

  However, a part manufactured by the hot press molding method is hardened simultaneously with molding from a high temperature in order to obtain high strength, and therefore has a martensite-based structure. For this reason, there is a concern about delayed fracture due to hydrogen embrittlement particularly in ultra-high strength parts having a tensile strength of 1180 MPa or more.

  Heretofore, in order to improve the hydrogen embrittlement resistance of parts manufactured by the press molding method, the following proposals have been made.

  For example, in Patent Document 1, a predetermined amount of an alloy carbonitride-forming element is added, and after forming a microstructure of martensite 60% or more by hot pressing, heat treatment is performed at a temperature range of 150 to 700 ° C. for 1 to 1000 minutes. In addition, a method for manufacturing a member for an automobile having excellent hydrogen embrittlement resistance has been proposed. According to this method, hydrogen embrittlement resistance is improved by uniformly and finely dispersing the alloy carbonitride as hydrogen trap sites in the member after hot pressing.

  However, simply dispersing the alloy carbonitride in the member and heat-treating it after hot pressing inevitably results in a reduction in strength of the member, and cementite becomes coarse and causes a decrease in hydrogen embrittlement resistance. Is required.

  Patent Document 2 discloses a method of reducing residual stress and improving hydrogen embrittlement resistance by performing shearing in the vicinity of bottom dead center after hot pressing, and Patent Document 3 discloses a shear angle after hot pressing. A method of reducing residual stress and improving hydrogen embrittlement resistance by performing a shearing process using a punch or a die tool having a material, Patent Document 4 discloses that a part of a part is melted and cut after hot pressing. Methods have been proposed for improving the hydrogen embrittlement resistance by reducing the residual stress by processing.

  As described above, the technology for preventing the delayed fracture of the cut portion is often seen, but the reality is that there is almost no technology for improving the delayed fracture resistance of the base material.

Japanese Patent No. 4288201 JP 2006-104526 A JP 2008-266721 A JP 2006-110713 A

  The present invention has been made paying attention to the above circumstances, and the purpose thereof is excellent delayed fracture resistance that could not be obtained by the prior art even in a hot press part having a tensile strength of 1180 MPa or more. An object of the present invention is to provide a hot-pressed part having properties.

The invention described in claim 1
Ingredient composition is in mass% (hereinafter the same for chemical ingredients)
C: 0.1 to 0.4%
Si: 2.0% or less (excluding 0%),
Mn: 0.3 to 3.5%
Ti: 0.01 to 0.2%
And the balance is composed of iron and inevitable impurities, and the microstructure is
Martensite + retained austenite is included in the area ratio 80% or more, the remainder is made of ferrite,
Alloy carbonitride: 0.05% by mass or more,
The alloy carbonitride having consistency with the parent phase: 5.0 × 10 ¹⁰ pieces / m ² or more,
Cementite: A hot-pressed part excellent in delayed fracture resistance, characterized by containing 2% by mass or less.

The invention described in claim 2
Ingredient composition further
Cu: 0.005 to 5%,
Ni: 0.005 to 5%
Cr: 0.001 to 3%,
Mo: 0.001 to 3%,
B: 0.0002 to 0.1%
The hot-pressed part according to claim 1, comprising at least one selected from the group consisting of:

The invention according to claim 3
Ingredient composition further
V: 0.001 to 0.1%
Nb: 0.001 to 0.1%
It is a hot press part of Claim 1 or 2 containing at least 1 sort (s) chosen from the group which consists of.

  According to the present invention, by securing a predetermined amount of alloy carbonitride having consistency with the base material, even a hot-pressed part having a tensile strength of 1180 MPa or more could not be obtained by the prior art. It has become possible to provide hot-pressed parts having excellent delayed fracture resistance.

  Hereinafter, the present invention will be described in more detail.

  First, the microstructure characterizing the hot-pressed part according to the present invention (hereinafter also referred to as “the present invention part”) will be described.

[Microstructure of parts of the present invention]
As described above, the component of the present invention has a microstructure including martensite + residual austenite (hereinafter also referred to as “residual γ”) in an area ratio of 80% or more, and the balance is composed of ferrite, and alloy carbonitride. : 0.05% by mass or more, the alloy carbonitride having consistency with the parent phase: 5.0 × 10 ¹⁰ pieces / m ² or more, cementite: 2% by mass or less, respectively. .
The reason why such numerical limitation is a requirement will be described below.

<Martensite + retained austenite: area ratio 80% or more, balance: ferrite>
If too much ferrite is present, the strength of the component cannot be secured, so the total amount of martensite and retained austenite is 80% or more in terms of area ratio. Further, if ferrite is present halfway, it becomes a crack generation site and its propagation path, so the total amount of martensite and retained austenite is preferably 90% or more, and more preferably 100%. .

<Alloy carbonitride: 0.05% by mass or more, alloy carbonitride having consistency with parent phase: 5.0 × 10 ¹⁰ pieces / m ² or more>
In addition to ensuring the precipitation amount of alloy carbonitrides, a part or all of them are precipitated with good consistency with the parent phase, thereby increasing the hydrogen trapping ability and improving delayed fracture resistance. In order to exhibit such an action effectively, the precipitation amount of the alloy carbonitride needs to be 0.05% by mass or more, preferably 0.08% by mass or more, more preferably 0.10% by mass. The amount of precipitation of the alloy carbonitride having consistency with the parent phase (hereinafter also referred to as “consistent precipitate”) needs to be 5.0 × 10 ¹⁰ pieces / m ² or more, preferably 1. It is 0 × 10 ¹¹ pieces / m ² or more, more preferably 2.0 × 10 ¹¹ pieces / m ² or more.

<Cementite: 2% by mass or less>
Cementite is formed by performing self-tempering in the cooling process during quenching and / or heat treatment after quenching. Cementite tends to be formed along the old γ grain boundary and lowers the strength of the old γ grain boundary, so that delayed fracture is likely to occur. In addition, if undissolved cementite remains during heating, the cementite coarsens and becomes a stress concentration source, especially if it remains in the vicinity of the old γ grain boundary, it acts as a crack initiation site. Deteriorating delayed fracture resistance. Therefore, by reducing the amount of cementite precipitation as a whole, the amount of cementite formed at the former γ grain boundary of martensite can be reduced, the strength of the former γ grain boundary can be prevented from decreasing, and the delayed fracture resistance can be improved. . In order to effectively exhibit such an action, the amount of cementite deposited must be 2% by mass or less, preferably 1.8% by mass or less, and more preferably 1.5% by mass or less.

[Measurement method of area ratio of each phase]
The hot pressed part sample is mirror-polished, then subjected to nital corrosion, observed with an optical microscope, ferrite, martensite, bainite and pearlite are identified, and the area ratio of each phase is calculated. At this time, for martensite, since retained austenite is contained in martensite, the area ratio is calculated by the total amount of martensite + residual austenite.

[Measurement method of precipitate content]
A predetermined amount of hot-pressed part sample is electrolyzed to disperse particles such as precipitates in the electrolytic solution, and the electrolytic solution is filtered through a mesh having pores with a diameter of 0.1 μm to extract the particles. An X-ray diffraction peak profile was collected using an X-ray diffractometer. Then, the kind of extracted particle | grains was identified by the peak fitting method. In addition, it has been confirmed that cementite (Fe ₃ C), alloy carbonitride ((Ti, V, Nb) (C, N)), and manganese sulfide (MnS) are present in the component sample of the present invention. Among these particle peaks, for cementite (Fe ₃ C), the (002) plane and (200) plane, for manganese sulfide (MnS), the (200) plane, alloy carbonitride ((Ti, V, (Nb) (C, N)), the peak intensity (Yn, where n = Fe ₃ C, MnS, (Ti, V, Nb) (C, N)) on the (111) plane is In 1), the relative concentration (Cn; mass%) in the extracted particles was calculated.

Cn = Yn × An / Σ (Yi × Ai) (1)
Here, An: relative sensitivity coefficient, Fe ₃ C: 1.000, MnS: 0.118, (Ti, V, Nb) (C, N): 0.700.

  And the absolute precipitation amount (= content; mass%) in the hot-pressed part sample was calculated | required by following formula (2).

    [Absolute precipitation amount] = [Relative concentration in extracted particles] × [Total mass of extracted particles] / [Total mass dissolved by electrolysis] Formula (2)

[Method for measuring number density of alloy carbonitride having consistency with parent phase]
A thin film sample of a hot pressed part sample is prepared and observed with a transmission electron microscope. When the observation is adjusted so that the incident direction of the electron beam is parallel to the <001> direction of the parent phase (martensite), one of the three types of diffraction patterns shown in FIG. 1 is obtained. (See HJKestenbach et al: Acta Microscopica, vol. 7 (1998), p22). A white circle in FIG. 1 is a diffraction pattern from the precipitate. A dark field image using a diffraction pattern marked with a white circle is taken. At this time, if white granular particles are observed in the captured dark field image, they are alloy carbonitrides (hereinafter also referred to as “matched precipitates”) having consistency with the parent phase. Therefore, the field of view incident on the parent phase from the <001> direction is observed more than five times at 100,000 times or more, and the number density of the particles specified by the above means is calculated at that time, and it is matched with the parent phase. The number density of the alloy carbonitride having the properties was determined.

  Next, the component composition which comprises this invention components is demonstrated. Hereinafter, all the units of chemical components are mass%.

[Component composition of the parts of the present invention]
C: 0.1 to 0.4%
C is an important element in securing the strength of the steel sheet. In particular, it is an essential element for generating a hard phase such as martensite and austenite and increasing the strength. In order to obtain a tensile strength of 1180 MPa or more, 0.1% or more, preferably 0.12% or more, more preferably Is required to be 0.15% or more. On the other hand, if too much is included, the cementite that is the starting point of brittle fracture is increased, and hydrogen embrittlement is likely to occur, so 0.4% or less, preferably 0.35% or less, more preferably 0.3% or less. And

Si: 2.0% or less (excluding 0%)
Si is an element effective for improving the hardenability, increasing the strength of the steel sheet, and suppressing the precipitation of cementite. However, if the content is too large, the cost for removing the scale in hot rolling is high and the economy is high. Therefore, it is 2.0% or less, preferably 1.7% or less, and more preferably 1.5% or less. Although the lower limit is not particularly defined, it is desirable that the content be close to 0% because bringing the content close to 0% causes an increase in manufacturing cost.

Mn: 0.3 to 3.5%
Mn is an element having a deoxidizing and desulfurizing action in the steel making process. Furthermore, it is an element effective for improving hardenability. In order to effectively exhibit such an action, the content is 0.3% or more, preferably 0.5% or more, and more preferably 0.8% or more. On the other hand, if the content is too large, the impact properties after quenching and tempering are promoted, the amount of Mn-based inclusions is increased, and cold workability and fatigue resistance properties are deteriorated. Is 3.0% or less, more preferably 2.5% or less.

Ti: 0.01 to 0.2%
Ti is an important element that acts as a hydrogen trap site by existing as fine carbonitride in steel and contributes to the improvement of delayed fracture resistance. In particular, if it is deposited so as to match the martensite which is the parent phase, the hydrogen trapping capability is enhanced, and the effect of further improving the delayed fracture resistance can be obtained. In order to effectively exhibit such an action, the content is 0.01% or more, preferably 0.02% or more, and more preferably 0.03% or more. On the other hand, if the content is too large, a large amount of coarse precipitates are produced, and the workability and delayed fracture resistance deteriorate, so that it is 0.2% or less, preferably 0.15% or less, more preferably 0.1 % Or less.

  The component of the present invention basically contains the above components, with the balance being iron and inevitable impurities. Inevitable impurities include P, S, N, and O, but it is preferable not to include these elements as much as possible. P is 0.020% or less, S is 0.010% or less, and N is It is desirable to limit it to 0.008% or less and O to 0.002% or less.

  The component of the present invention can contain the following permissible components as long as the effects of the present invention are not impaired.

Cu: 0.005 to 5%,
Ni: 0.005 to 5%
Cr: 0.001 to 3%,
Mo: 0.001 to 3%,
B: 0.0002 to 0.1%
At least one selected from the group consisting of these elements suppresses ferrite transformation, pearlite transformation, and bainite transformation, and thus prevents formation of ferrite, pearlite, and bainite during cooling after heating, and martensite + retained austenite It works effectively to ensure. In order to exhibit such an action effectively, it is preferable to contain each lower limit value or more. Considering only the characteristics, it is preferable that the content is large. However, since the cost of alloy addition increases, it is preferable to set the content to the upper limit value or less. More preferable lower limits of the content of these elements are 0.02% for Cu, 0.02% for Ni, 0.02% for Cr, 0.02% for Mo, and 0.0003% for B, and more preferable. The upper limit is 1% for Cu, 1% for Ni, 1% for Cr, 1% for Mo, and 0.01% for B.

V: 0.001 to 0.1%
Nb: 0.001 to 0.1%
At least one selected from the group consisting of V and Nb, like Ti, is an element that acts as a hydrogen trap site by existing as fine carbonitride in steel and contributes to the improvement of delayed fracture resistance. . In order to exhibit such an action effectively, it is preferable to contain each 0.001% or more. However, if the content of these elements is excessive, coarse carbonitrides are formed and the ductility is deteriorated by becoming the starting point of destruction. Therefore, the content is preferably 0.1% or less. The more preferable lower limit of the content of these elements is 0.01%, respectively, and the more preferable upper limit is 0.05%.

  Next, a preferred manufacturing method for obtaining the above-described component of the present invention will be described below.

[Preferred manufacturing method of the present invention part]
There are no particular limitations on the steps of melting the steel, casting the steel slab, and charging the steel slab into the heating furnace (hot rolling heating furnace) of the hot rolling line. For example, (1) casting You may charge a hot-rolling heating furnace without cooling a steel slab after, (2) After cooling the steel slab after casting once, you may insert into a hot-rolling heating furnace, 3) The steel slab may be charged into a hot-rolling heating furnace after the ingot after casting is subjected to ingot rolling.

And after hot rolling, it winds at 500-750 degreeC, and does not give cold rolling, or even if it gives, it is set as the small reduction of 45% or less of cold rolling. Here, when hot-plating a steel plate before hot pressing, the annealing temperature may be set to 650 ° C. or lower. Next, the rolled steel sheet or hot-dipped steel sheet is subjected to a hot pressing step as it is rolled. The heating rate of these steel sheets is 20 ° C./s or more, the heating temperature is 900 to 1200 ° C., the heating time is 1 to 600 s, and the press is performed. It is recommended that the average cooling rate from the end point to 400 ° C. is 30 ° C./s or more, and the average cooling rate from 400 ° C. to 200 ° C. is 10 ° C./s or more.
In addition, when further heat-processing to the components after a hot press, it is recommended to carry out on the conditions of 100-250 degreeC x 1-60min.
The reason why such a condition is recommended will be described below.

<Winding temperature: 500 to 750 ° C.>
By winding at a high temperature of 500 ° C. or higher, ferrite-pearlite transformation can be performed, and at the same time, precipitates (alloy carbonitrides) can be dispersed inside the structure so as to match the parent phase. However, if the coiling temperature is too high, the consistency with the parent phase is lost, and therefore it is preferable to set the temperature to 750 ° C. or lower.

<No cold rolling or cold rolling rate: 45% or less>
When the steel sheet is strongly squeezed cold, the consistency of the precipitates (alloy carbonitride) dispersed so as to be consistent with the parent phase is lost. Therefore, even when hot rolling or cold rolling is performed, The ductility is preferably 45% or less.

<In the case of hot dip plated steel sheet, annealing temperature: 650 ° C. or less>
By limiting the annealing temperature in the continuous hot dipping line to a low temperature of 650 ° C. or lower, plating can be applied without recrystallizing the parent phase. A large amount of (nitride) can be left. On the other hand, when the annealing temperature is higher than 650 ° C., recrystallization of the parent phase occurs, and the consistency with the precipitate (alloy carbonitride) is lost. It becomes difficult to secure precipitates (alloy carbonitrides) having consistency with the phases. In addition, although annealing time is not specifically limited, It is preferable to set it as 30-600 s.

<Heating rate of steel sheet to be subjected to hot pressing: 20 ° C./s or more, heating temperature: 900 to 1100 ° C., heating time: 1 to 600 s>
By rapidly heating a steel sheet containing precipitates (alloy carbonitrides) that are consistent with the parent phase, some of the precipitates are transformed into the parent phase by reverse transformation without recrystallizing the parent phase as much as possible. However, it is possible to reversely transform the remaining precipitates while maintaining the consistency with the parent phase. As a result, even when the parent phase is transformed into martensite in the subsequent hot pressing and quenching steps, a large amount of precipitates can be left while maintaining consistency with the parent phase.
In order to effectively exhibit such an effect, the heating rate of the steel sheet to be subjected to hot pressing is preferably 20 ° C./s or more, more preferably 50 ° C./s or more, and particularly preferably 100 ° C./s or more.
The heating temperature and heating time of the steel sheet subjected to hot pressing change the microstructure of the steel sheet to austenite (to make the microstructure of the part martensite by subsequent quenching), and the cementite remains in an insoluble state during heating. In order to prevent this, it is necessary to heat at a high temperature for a predetermined time. However, if it is heated for a long time at a high temperature, the precipitate that has been dispersed with consistency with the matrix phase will dissolve, and it will not be possible to ensure the consistent precipitate in the part after hot pressing.
For this reason, the heating temperature of the steel sheet to be subjected to hot pressing is 900 to 1100 ° C., further 950 to 1070 ° C., particularly 1000 to 1050 ° C., and the heating time is 1 to 600 s, further 1 to 300 s, particularly 1 to 150 s. It is preferable to do this.

<Average cooling rate from the end of pressing to 400 ° C .: 30 ° C./s or more, average cooling rate from 400 ° C. to 200 ° C .: 10 ° C./s or more>
In order to prevent the formation of ferrite, pearlite, bainite and the like during quenching, the average cooling rate from the end of pressing to 400 ° C. is preferably 30 ° C./s or more, more preferably 40 ° C./s or more.
Further, by maintaining a high cooling rate from 400 ° C. to 200 ° C., the delayed fracture resistance can be improved by preventing the precipitation of cementite. In order to effectively exhibit such an action, the average cooling rate from 400 ° C. to 200 ° C. is preferably 10 ° C./s or more, more preferably 15 ° C./s or more.

<Heat treatment conditions after hot pressing: 100-250 ° C. × 1-60 min>
In addition, reheating or tempering in a range where no formation of cementite occurs after hot pressing is effective in improving the toughness of low carbon steel. Generally, heat treatment is performed at 100 to 250 ° C. for 1 to 60 minutes.

  Hereinafter, the present invention will be described in more detail with reference to examples. However, the following examples are not intended to limit the present invention, and may be implemented with appropriate modifications within a range that can meet the purpose described above and below. These are all possible and are within the scope of the present invention.

  Using a vacuum induction furnace (VIF), a test steel containing chemical components shown in Table 1 was melted, cast into a 50 kg ingot, and cooled. After heating the obtained ingot to 1200 ° C., it was once hot-rolled to a plate thickness of 25 mm and used as a test material. After heating this test material to 1200 ° C. again, it is hot-rolled to a plate thickness at a finish rolling temperature of 900 ° C., and then rapidly cooled at a cooling rate of 20 ° C./s in order to simulate winding, Rapid cooling was stopped at each coiling temperature, and the steel sheet was placed in an atmospheric furnace heated to the coiling temperature and held for 30 minutes. And this hot-rolled sheet was cold-rolled to obtain a cold-rolled sheet having a thickness of 1.4 mm. This cold-rolled sheet is divided into what is subjected to hot pressing as it is and what is subjected to hot pressing after plating the surface, and the latter is heated to each annealing heating temperature using a plating simulator, It was immersed in a plating bath and plated to give a hot-dip plated plate.

  The cold-rolled plate and hot-dip plated plate thus produced were heated to a predetermined heating temperature at each heating rate with an electric heating device, and then held at that temperature for each predetermined time. Immediately after that, pressing was performed and mold hardening was performed. Then, after reaching 400 ° C., the cooling is continued with a mold, taken out into the atmosphere and air-cooled, or covered with glass wool and cooled together with the mold from 400 ° C. to 200 ° C. The hot-pressed part sample was produced by changing the cooling rate. In addition, some of the hot-dip plated plates were further subjected to heat treatment at a predetermined temperature for a predetermined time after cooling to produce hot pressed part samples. Each manufacturing condition is shown in Table 2.

  Each hot-pressed part sample thus obtained (hereinafter, also simply referred to as “part sample”) is subjected to the measurement method described in the above [Mode for carrying out the invention] The area ratio of each phase, the content of precipitates, and the number density of alloy carbonitride having consistency with the parent phase were investigated. In addition, about the number density of the alloy carbonitride which has consistency with a parent phase, it measured also on the cold rolled sheet before a hot press process.

  Further, in order to evaluate the mechanical characteristics of each of the above component samples, tensile strength and delayed fracture resistance were measured by the methods described below.

<Tensile strength>
A No. 5 test piece described in JIS Z 2201 was produced, a tensile test was performed according to JIS Z 2241, and a tensile strength was measured.

<Delayed fracture resistance>
A strip-shaped test piece of 100 mm × 30 mm was prepared, subjected to U-bending with a bending radius of 10 mm, and then immersed in hydrochloric acid at a concentration of 3% by mass with a stress of 800 MPa and 1000 MPa, respectively, for a maximum of 96 hours. It was held and examined for the presence of cracks. A sample in which no crack was generated even after being held for 96 hours was set as “> 96h”, and when a crack occurred in the middle, a holding time until the crack was generated was recorded. The delayed fracture resistance was determined based on the holding time until the occurrence of cracking when a stress of 1000 MPa was applied, with 48 hours or longer being accepted and those less than 48 hours being rejected.

  The measurement results are shown in Table 3 below.

  As shown in Table 3 above, Test No. Reference numerals 14 to 16, 18 to 20, 22 to 25, 27, and 29 are comparative parts that do not satisfy at least one of the requirements of the component composition and microstructure defined in the present invention, and any of tensile strength and delayed fracture resistance Does not meet the acceptance criteria.

  In contrast, test no. 1 to 13, 17, 21, 26 and 28 all satisfy the requirements of the microstructure definition of the present invention as a result of being manufactured under the recommended manufacturing conditions using steel types satisfying the range of the component composition of the present invention. It is an invention part, both tensile strength and delayed fracture resistance satisfy the acceptance criteria, and it is hot superior in delayed fracture resistance than the hot-pressed parts obtained by the prior art at ultra-high strength of 1180 MPa or higher. It was confirmed that press parts were obtained.

  As shown in the table, in any test, the number density of matched precipitates (carbonitride having consistency with the parent phase) is determined by hot pressing, that is, from cold-rolled sheets to hot-pressed parts. However, it can be seen that the number density exceeding the specified amount is still secured in the invention parts.

Claims (3)

Ingredient composition is in mass% (hereinafter the same for chemical ingredients)
C: 0.1 to 0.4%
Si: 2.0% or less (excluding 0%),
Mn: 0.3 to 3.5%
Ti: 0.01 to 0.2%
And the balance is composed of iron and inevitable impurities, and the microstructure is
Martensite + retained austenite is included in the area ratio 80% or more, the remainder is made of ferrite,
Alloy carbonitride: 0.05% by mass or more,
The alloy carbonitride having consistency with the parent phase: 5.0 × 10 ¹⁰ pieces / m ² or more,
Cementite: Hot pressed parts with excellent delayed fracture resistance characterized by containing 2% by mass or less. Ingredient composition further
Cu: 0.005 to 5%,
Ni: 0.005 to 5%
Cr: 0.001 to 3%,
Mo: 0.001 to 3%,
B: 0.0002 to 0.1%
The hot-pressed part according to claim 1, comprising at least one selected from the group consisting of: Ingredient composition further
V: 0.001 to 0.1%
Nb: 0.001 to 0.1%
The hot-pressed part according to claim 1 or 2, comprising at least one selected from the group consisting of: