Specification
Title of invention : Hot stamped molded product and steel plate for hot stamping
Technical field
[0001]
The present invention relates to a hot stamped product and a steel plate for hot stamping. This application claims priority based on Japanese Patent Application No. 2019-213593 filed in Japan on November 26, 2019, the content of which is incorporated herein.
Background technology
[0002]
Hot-stamped parts are used for the frame parts of the vehicle body, and are often used for reinforcing parts around the cabin to ensure the living space of the occupants and for routes to transmit the load during a collision. Hot-stamped parts are also required to have even higher strength in order to meet the weight reduction of automobile bodies for fuel efficiency regulations and the sophistication of crash tests.
However, as the strength increases, the risk of hydrogen embrittlement cracking increases, so measures to suppress hydrogen embrittlement cracking are required.
[0003]
For example, in the technique of Patent Document 1, the microstructure is controlled and the cleanliness of inclusions is specified in order to achieve both hardness stability and delayed fracture resistance. In addition, in the technique of Patent Document 2, the microstructure and precipitation amount of inclusions are controlled in order to obtain tensile strength and toughness.
prior art documents
patent literature
[0004]
Patent Document 1: International Publication No. 2015/147216
Patent Document 2: JP 2017-043825 A
SUMMARY OF THE INVENTION
Problems to be Solved by the Invention
[0005]
The present inventors conducted research on hydrogen embrittlement cracking of steel hot stamped parts with a tensile strength exceeding 1.6 GPa, and found that inclusions containing CaO—Al 2 O 3 were found at the origin of hydrogen embrittlement cracking. Confirmed it exists.
[0006]
　Ca is an element added to steel to control the morphology of sulfides. Formation of spherical CaS suppresses stretched MnS. Suppression of stretched MnS is said to improve toughness.
[0007]
However, according to the studies of the present inventors, when Ca is added, coarse inclusions containing CaO—Al 2 O 3 are formed as shown in FIG. It turned out to be In FIG. 1, black parts are inclusions containing CaO—Al 2 O 3 and white parts are steel matrix.
[0008]
The present invention has been made in view of such circumstances, and an object of the present invention is to prevent hydrogen embrittlement cracking due to coarse inclusions containing CaO—Al 2 O 3 while maintaining a desired tensile strength. To provide a hot stamped molded article and a steel sheet for hot stamping.
Means to solve problems
[0009]
(1) The hot stamped product according to one aspect of the present invention is mass%
C: 0.25% or more and 0.55% or less,
Si: 0.001% or more and 2.0% or less,
Mn: 0.3% or more and 3.0% or less,
P: 0.02% or less,
S: 0.003% or less,
Al: 0.005% or more and 1.0% or less,
Cr: 0% or more and 1.0% or less,
Mo: 0% or more and 1.0% or less,
N: 0.02% or less,
Ca: 0% or more and 0.0010% or less,
B: 0.0005% or more and 0.01% or less,
Ti: 0.005% or more and 0.5% or less, Nb: 0.005% or more and 0.5% or less, V: 0.005% or more and 0.5% or less, and Zr: 0.005% or more and 0.5% % or less, and one or more selected from the group consisting of
Ni + Cu + Sn: containing 0% or more and 2% or less,
A hot stamped product having a chemical composition consisting of Fe and impurities as the balance,
The tensile strength of the hot-stamped product left in the atmosphere at room temperature of 20-30°C for 48 hours or more exceeds 1600 MPa,
It is characterized in that the long axis of inclusions containing CaO--Al 2 O 3 contained in the hot stamped product is 50 μm or less.
(2) The hot stamped product according to one aspect of the present invention is mass%
C: 0.25% or more and 0.55% or less,
Si: 0.001% or more and 2.0% or less,
Mn: 0.3% or more and 3.0% or less,
P: 0.02% or less,
S: 0.003% or less,
Al: 0.005% or more and 1.0% or less,
Cr: 0% or more and 1.0% or less,
Mo: 0% or more and 1.0% or less,
N: 0.02% or less,
Ca: 0% or more and 0.0010% or less,
B: 0.0005% or more and 0.01% or less,
Ti: 0.005% or more and 0.5% or less, Nb: 0.005% or more and 0.5% or less, V: 0.005% or more and 0.5% or less, and Zr: 0.005% or more and 0.5% % or less, and one or more selected from the group consisting of
Ni + Cu + Sn: containing 0% or more and 2% or less,
A hot stamped product having a chemical composition consisting of Fe and impurities as the balance,
The tensile strength of the hot-stamped product left in the atmosphere at room temperature of 20-30°C for 48 hours or more exceeds 1600 MPa,
Total elongation measured using a tensile test piece of a hot-stamped molded product charged with hydrogen such that the uniform elongation is El 1 (%) and the amount of diffusible hydrogen is 0.5 ± 0.1 ppm by weight is El 2(%), (El 2/El 1)×100≧100(%) is satisfied.
[0010]
(3) In the hot stamped product described in (1) or (2) above,
The maximum length of MnS present in the center of the plate thickness may be 300 μm or less.
(4) In the hot stamped product according to any one of (1) to (3) above,
in % by mass,
Ni+Cu+Sn: 0.005% or more and 2% or less may be contained.
(5) In the hot stamped product according to any one of (1) to (4) above,
The surface may have a plating layer.
[0011]
(6) The steel sheet for hot stamping according to one aspect of the present invention is mass%
C: 0.25% or more and 0.55% or less,
Si: 0.001% or more and 2.0% or less,
Mn: 0.3% or more and 3.0% or less,
P: 0.02% or less,
S: 0.003% or less,
Al: 0.005% or more and 1.0% or less,
Cr: 0% or more and 1.0% or less,
Mo: 0% or more and 1.0% or less,
N: 0.02% or less,
Ca: 0% or more and 0.0010% or less,
B: 0.0005% or more and 0.01% or less,
Ti: 0.005% or more and 0.5% or less, Nb: 0.005% or more and 0.5% or less, V: 0.005% or more and 0.5% or less, and Zr: 0.005% or more and 0.5% % or less, and one or more selected from the group consisting of
Ni + Cu + Sn: containing 0% or more and 2% or less,
A steel sheet for hot stamping having a chemical composition consisting of the balance Fe and impurities,
After heating the steel sheet for hot stamping at 950 ° C. for 1 minute, using a tensile test piece cooled to 200 ° C. or less at an average cooling rate of 30 to 100 ° C./s, at room temperature of 20 to 30 ° C. for 48 hours or more in the atmosphere a tensile strength greater than 1600 MPa measured after being left in
It is characterized in that the long axis of inclusions containing CaO--Al 2 O 3 contained in the steel plate for hot stamping is 50 μm or less.
(7) The steel sheet for hot stamping according to one aspect of the present invention is mass%
C: 0.25% or more and 0.55% or less,
Si: 0.001% or more and 2.0% or less,
Mn: 0.3% or more and 3.0% or less,
P: 0.02% or less,
S: 0.003% or less,
Al: 0.005% or more and 1.0% or less,
Cr: 0% or more and 1.0% or less,
Mo: 0% or more and 1.0% or less,
N: 0.02% or less,
Ca: 0% or more and 0.0010% or less,
B: 0.0005% or more and 0.01% or less,
Ti: 0.005% or more and 0.5% or less, Nb: 0.005% or more and 0.5% or less, V: 0.005% or more and 0.5% or less, and Zr: 0.005% or more and 0.5% % or less, and one or more selected from the group consisting of
Ni + Cu + Sn: containing 0% or more and 2% or less,
A steel sheet for hot stamping having a chemical composition consisting of the balance Fe and impurities,
After heating the steel plate for hot stamping at 950 ° C. for 1 minute, using a tensile test piece cooled to 200 ° C. or less at an average cooling rate of 30 to 100 ° C./s, leave at room temperature of 20 to 30 ° C. for 48 hours or more. The tensile strength measured after being measured exceeds 1600 MPa,
The uniform elongation is El 3 (%), and the total elongation measured using the above tensile test piece hydrogen-charged so that the amount of diffusible hydrogen is 0.5 ± 0.1 ppm by weight is El 4 ( %), it is characterized by satisfying (El 4/El 3)×100≧100(%).
[0012]
(8) In the steel plate for hot stamping according to (6) or (7) above,
The maximum length of MnS present in the center of the plate thickness may be 300 μm or less.
(9) In the steel plate for hot stamping according to any one of (6) to (8) above,
in % by mass,
Ni+Cu+Sn: 0.005% or more and 2% or less may be contained.
(10) In the steel plate for hot stamping according to any one of (6) to (9) above,
The surface may have a plating layer.
Effect of the invention
[0013]
According to the present invention, a hot stamped molded product and a steel sheet for hot stamping that can prevent hydrogen embrittlement cracking while maintaining desired tensile strength are provided.
Brief description of the drawing
[0014]
FIG. 1 is a backscattered electron image near CaO—Al 2 O 3 observed on a hydrogen embrittlement crack fracture surface.
[Fig. 2] Fig. 2 is a schematic cross-sectional view for explaining an inclusion that becomes a starting point of hydrogen embrittlement cracking.
MODE FOR CARRYING OUT THE INVENTION
[0015]
The present inventors found that when a material containing hydrogen was subjected to a tensile test, fracture occurred due to hydrogen embrittlement, and coarse inclusions containing CaO—Al 2 O 3 were present at the starting point of the fracture. . Hydrogen embrittlement cracking originating from such inclusions as described above was confirmed.
[0016]
In addition, the present inventors have found that such coarse inclusions are few in number, and therefore difficult to find by observing a cross section of a steel material, which is commonly used to measure cleanliness.
[0017]
The present inventors performed a tensile test on a material containing hydrogen and observed the fracture surface to evaluate the size of inclusions that are the starting point of hydrogen embrittlement cracking. found to be super. From this result, the present inventors found that hydrogen embrittlement cracking can be prevented by specifying the major axis of such inclusions to be 50 μm or less.
[0018]
Embodiments of the present invention will be described below with examples, but it is obvious that the present invention is not limited to the examples described below. In the following description, specific numerical values ​​and materials may be exemplified, but other numerical values ​​and materials may be applied as long as the effects of the present invention can be obtained. Also, each component of the following embodiments can be combined with each other.
[0019]
[First embodiment]
　The hot stamped product according to the first embodiment has a mass%
C: 0.25% or more and 0.55% or less,
Si: 0.001% or more and 2.0% or less,
Mn: 0.3% or more and 3.0% or less,
P: 0.02% or less,
S: 0.003% or less,
Al: 0.005% or more and 1.0% or less,
Cr: 0% or more and 1.0% or less,
Mo: 0% or more and 1.0% or less,
N: 0.02% or less,
Ca: 0% or more and 0.0010% or less,
B: 0.0005% or more and 0.01% or less,
Ti: 0.005% or more and 0.5% or less, Nb: 0.005% or more and 0.5% or less, V: 0.005% or more and 0.5% or less, and Zr: 0.005% or more and 0.5% % or less, one or more selected from the group consisting of, and
Ni+Cu+Sn: 0% or more and 2% or less is contained, and the balance is Fe and impurities.
The hot stamped article according to the first embodiment has a tensile strength of more than 1600 MPa when left in the atmosphere at room temperature of 20 to 30 ° C. for 48 hours or more, and the CaO contained in the hot stamped article - The major axis of inclusions containing Al 2 O 3 is 50 μm or less.
[0020]
The chemical composition of the hot stamped product according to the first embodiment will be explained.
[0021]
(C: 0.25% or more and 0.55% or less)
C is an element that is added to ensure the quality of the material as a martensitic structure after cooling, and it is necessary to add 0.25% or more to ensure a strength of 1600 MPa or more.be. If the addition amount is too large, it becomes difficult to ensure the strength during impact deformation, so the upper limit is made 0.55%.
[0022]
(Si: 0.001% or more and 2.0% or less)
Si is a solid-solution-strengthening alloying element and is necessary to ensure strength, but if it exceeds 2.0%, the problem of surface scale occurs. Therefore, Si is specified to be 2.0% or less. In addition, when the surface of a steel sheet is plated, the upper limit of Si is preferably 1.0% because if the amount of Si added is large, the plateability deteriorates. If the amount of Si added is reduced, there is no major problem with the quality of the material, but if the amount added is small, the cost of steelmaking increases. More preferably, the amount of Si added is in the range of 0.01 to 0.5%.
[0023]
(Mn: 0.3% or more and 3.0% or less)
Mn is an element that improves strength and hardenability. is specified in the range of 0.3 to 3.0%. The amount of Mn added is more preferably 2.2% or less.
[0024]
(Al: 0.005% or more and 1.0% or less)
Al is a necessary element used as a deoxidizer for molten steel, and it is also an element that fixes N, and its amount has a great effect on grain size and mechanical properties. A content of 0.005% or more is necessary to obtain such an effect, but if it exceeds 1.0%, the amount of nonmetallic inclusions increases and surface defects tend to occur on the product. Therefore, Al is specified in the range of 0.005 to 1.0%. The amount of Al added is more preferably 0.01% or more, and more preferably 0.5% or less.
[0025]
(S: 0.003% or less)
　S affects non-metallic inclusions in steel and deteriorates toughness and hydrogen embrittlement resistance. Therefore, S is specified to be 0.003% or less. Note that S is preferably 0.001% or less.
[0026]
(P: 0.02% or less)
Because P is an element that adversely affects toughness and resistance to hydrogen embrittlement, P is regulated to 0.02% or less. Note that P is preferably 0.015% or less. Further, P is more preferably 0.010% or less.
[0027]
The chemical composition of the hot stamped product according to the present embodiment may further contain at least one selected element from among Cr, Mo, Ca, Ni, Cu, and Sn in place of part of Fe. . These selective elements may be contained depending on the purpose. Therefore, it is not necessary to limit the lower limit of these selective elements, and the lower limit may be 0%. Moreover, even if these selective elements are contained as impurities, the effects of these selective elements are not impaired.
[0028]
(Cr: 0% or more and 1.0% or less)
　Cr is an element that improves hardenability. If it exceeds 1.0%, it stabilizes the carbides present after hot rolling, after cold rolling, or after annealing (including after plating), delaying dissolution by heating in hot stamping, and reducing hardenability. can be considered. Therefore, the upper limit of Cr is defined as 1.0%. The lower limit is not particularly defined because the hardenability required for hot stamping can be ensured by adding elements such as Mn, Mo, and Ni that provide hardenability. The amount of Cr added is more preferably 0.05% or more, and more preferably 1.0% or less.
[0029]
(Mo: 0% or more and 1.0% or less)
Mo is an element that improves hardenability. If it exceeds 1.0%, it stabilizes the carbides present after hot rolling, after cold rolling, or after annealing (including after plating), delaying dissolution by heating in hot stamping, and reducing hardenability. can be considered. Therefore, the upper limit of Mo is defined as 1.0%. The lower limit is not particularly defined because the hardenability required for hot stamping can be ensured by adding an element such as Mn or Ni that provides hardenability. The amount of Mo added is more preferably 0.05% or more, and more preferably 0.5% or less.
[0030]
(Ca: 0% or more and 0.0010% or less)
It is desirable not to add Ca in order to suppress the formation of CaO-Al2O3, which can be the starting point of hydrogen embrittlement cracking. However, even in the case of no additives, there is a possibility of contamination from ladle slag during smelting or powder used during casting. Therefore, it is necessary to suppress this, and the upper limit of Ca is limited to 0.0010%. Within this range, the possibility of forming coarse CaO--Al 2 O 3 that can serve as a starting point for hydrogen embrittlement cracking is low. However, depending on the refining conditions, a small amount of CaO—Al 2 O 3 may aggregate and coarsen, so it is important to use a refining method that prevents coarsening.
[0031]
(B: 0.0005% or more and 0.01% or less)
B is added to improve hardenability during press forming or cooling after press forming, but 0.0005% or more of addition is necessary to exhibit this effect. However, if the addition amount is unreasonably increased, there is concern about hot cracking and the effect is saturated, so the upper limit of B is preferably 0.01%.
[0032]
(Ti: 0.5% or less, Nb: 0.5% or less, V: 0.5% or less, and Zr: 0.5% or less)
Ti, Nb, V, and Zr are added for the purpose of fixing N, which forms a compound with B, in order to effectively exhibit the effect of B. Ti, Nb, V, and Zr also have the effect of improving toughness and resistance to hydrogen embrittlement by forming carbides/nitrides and suppressing grain growth of austenite during heating to make grains finer. However, excessive addition deteriorates the toughness, so the upper limit of the amount of these additions is set at 0.5%. The amount of these elements to be added is 0.005% or more, respectively, from the viewpoint of the amount of addition necessary for exhibiting the effect.
[0033]
(N: 0.02% or less)
When N exceeds 0.02%, the toughness tends to deteriorate due to coarsening of nitrides. Therefore, it is preferable to specify N to be 0.02% or less. N is more preferably 0.01% or less.
[0034]
(Ni+Cu+Sn: 0% or more and 2% or less)
The hot stamped product according to the first embodiment may contain, as a chemical composition, Ni+Cu+Sn (total of Ni, Cu and Sn): 0% or more and 2% or less in mass %.
[0035]
By adding these elements, Ni, Cu and Sn can improve plating adhesion. Furthermore, improvement in corrosion resistance can also be expected. In order to obtain this effect, it is preferable to add Ni, Cu and Sn in a total amount of 0.005% or more. However, excessive addition increases the alloy cost, so the upper limit of the sum of these elements is set to 2%. More preferably, Ni+Cu+Sn has an upper limit of 1.0% and a lower limit of 0.05%.
[0036]
Mg, Y, As, Sb, and REM are considered to change the shape of MnS, which is the main sulfide, to improve impact properties and delayed fracture properties, so they may be added. However, excessive addition deteriorates workability, so the upper limit is preferably 0.1% or less.
Also, even if other elements such as Se and W, which are not defined above, are contained, there is no major problem with the characteristics as long as the content does not exceed 0.1%.
[0037]
There are no particular restrictions on O, but excessive addition causes the generation of oxides that adversely affect toughness, and also generates oxides that cause fatigue fracture, so the content of O is 0.015% or less. is desirable. Note that the hot stamped product according to the present embodiment contains impurities. The term "impurities" refers to substances mixed in from raw materials such as ores, scraps, or the manufacturing environment during the industrial production of steel. Among these impurities, P, S, O and N are preferably restricted as described above. Also, since it is preferable that the content of impurities is small, there is no need to limit the lower limit, and the lower limit of impurities may be 0%.
[0038]
Next, features of inclusions in the hot stamped product according to the first embodiment will be described.
[0039]
CaO-Al2O3 is an inclusion that becomes the starting point for hydrogen embrittlement cracking that occurs in a tensile test when hydrogen is contained in a certain amount or more. This is confirmed by observing the fracture surface of the test piece by a tensile test.
[0040]
It is believed that other coarse inclusions such as TiN are present, but according to the research of the present inventors, no example of hydrogen embrittlement cracking originating from TiN or the like was observed. Therefore, it is inferred that CaO--Al 2 O 3 has the characteristics of starting hydrogen embrittlement cracking.
[0041]
When CaO—Al 2 O 3 contains more than a certain amount of hydrogen, the cause of hydrogen embrittlement cracking occurring in a tensile test is speculated as follows.
That is, from the observation results of the fracture surface, cracks often occur in CaO-Al2O3, which is thought to have been the starting point, and it is inferred that it is brittle compared to other precipitates/inclusions. Therefore, when a tensile stress is applied to the inclusions, fracture is likely to occur, and it is presumed that the fracture causes hydrogen embrittlement cracking of the steel material.
[0042]
In addition, the stress applied to inclusions depends on the major diameter of the inclusions, and it is speculated that the larger the major diameter, the higher the stress applied to the inclusions, causing the inclusions to break and trigger hydrogen embrittlement cracking.
That is, the length of the major axis of inclusions is important, and it is thought that by limiting this, it is possible to suppress the fracture of inclusions and suppress hydrogen embrittlement cracking.
[0043]
Here, if the major axis of inclusions is 50 μm or less, hydrogen embrittlement cracking does not occur, so it is preferable to define the major axis of inclusions to be 50 μm as the upper limit. In addition, the long diameter of inclusions is more preferably 30 μm or less in order to ensure the above effect.
[0044]
The major axis of inclusions can be obtained by observing the fracture surface of a test piece that has been fractured by a tensile test using a SEM (scanning electron microscope). In many cases, the inclusions present on the fractured surface that fractured in the tensile test are destroyed, and not all of them remain. can be regarded as the major axis of the inclusion.
Further, when the thickness of the inclusion in the plate thickness direction is small, it is possible to define the major axis of the inclusion as the range where the inclusion is packed in the depression.
[0045]
The major diameter of inclusions can be directly measured from images or photographs taken using an SEM.
[0046]
FIG. 2 is a schematic cross-sectional view for explaining inclusions that act as starting points for hydrogen embrittlement cracking, and represents a cross section of a plane perpendicular to the direction in which the hot-stamped steel S is rolled at the time of manufacture. ing.
The starting point of the fracture in the tensile test is the inclusion at the center of the elliptical intergranular fracture surface. When there are two or more elliptical grain boundary fracture surfaces, the longest diameter of the inclusion is taken as the starting point of fracture, and this longest diameter is taken as the major diameter of the inclusion. In the example of FIG. 2, an inclusion A exists at the center of the intergranular fracture surface SA, an inclusion B exists at the center of the intergranular fracture surface SB, and an inclusion C exists at the center of the intergranular fracture surface SC.
[0047]
In the example of FIG. 2, "(major axis l A of inclusion A)>(major axis l B of inclusion B)", and among inclusions A to C, the major axis l A of inclusion A is the longest. Therefore, it is determined that inclusion A is the starting point of hydrogen embrittlement cracking, and hydrogen embrittlement cracking does not occur if the major axis lA of inclusion A is 50 μm or less.
[0048]
The hot stamped article according to the first embodiment has a tensile strength of 1600 MPa measured using a tensile test piece of the hot stamped article left in the atmosphere at room temperature of 20 to 30 ° C. for 48 hours or more. Exceed.
By leaving the hot stamped product after quenching in the air at room temperature of 20-30°C for 48 hours or more, hydrogen is sufficiently released from the inside of the hot stamped product.
[0049]
　The tensile test piece of the hot stamped product is preferably taken from a flat part of the hot stamped product because it ensures the accuracy of the tensile test result.
[0050]
In the hot stamped product according to the first embodiment, the maximum length of MnS present in the central portion of the plate thickness may be 300 μm or less. In this embodiment, the plate thickness central portion, means the range from the center of the plate thickness to the thickness of 1/3 of the plate thickness in the plate thickness direction of the hot stamped product. Moreover, the maximum length of the MnS is more preferably 200 μm or less.
[0051]
Since MnS is elongated during rolling, when stress is applied, it is thought that stress concentration will occur at the ends, which will become starting points for hydrogen embrittlement cracking. As the length of MnS increases, the stress generated at the ends increases, which promotes the occurrence of hydrogen embrittlement cracking. In addition, since MnS tends to occur in the central segregation part, the largest precipitates exist in the central part of the sheet thickness. Therefore, it is preferable to define the maximum length of MnS present in the central portion of the sheet thickness to be 300 μm or less. The length of MnS can be obtained by mirror-polishing a cross section of the target steel material in the rolling direction and observing MnS at the center of the plate thickness with a metallographic microscope at a magnification of 200 to 500 times. MnS can be confirmed by elemental analysis with SEM-EDS (EDS-equipped scanning electron microscope) or EPMA (Electron Probe Micro Analyzer). It is desirable to observe about 10 fields of view.
[0052]
　Central segregation, in which the solute elements are macro-concentrated, occurs at the center of the thickness of the slab during continuous casting. Center segregation is the concentration of surrounding concentrated molten steel at the center due to the flow of the liquid phase generated by bulging, solidification shrinkage, and the like. In the center segregation part, the solute elements are more concentrated than in the normal solidified part, and coarse MnS is likely to be generated even if the S concentration is lowered. In order to suppress the center segregation, a method is known in which flow is generated in the molten steel by light reduction in which the slab is reduced to compensate for the solidification shrinkage, or by electromagnetic stirring, so that the molten steel is equiaxed. Either method can reduce the center segregation and suppress the generation of coarse MnS. Moreover, if the S concentration is reduced to 0.0030% by mass or less by implementing such measures against center segregation, problematic coarse MnS is hardly generated. In addition, if the S concentration can be reduced to 0.0010% by mass or less, the generation of MnS itself can be suppressed.
[0053]
Also, the hot stamped product according to the first embodiment may have a plating layer on its surface.
[0054]
The steel plate for the hot stamped product as described above may be subjected to aluminum plating, aluminum-zinc plating, or zinc plating. The composition of the plating is mainly composed of aluminum and zinc, but elements such as Ni may be added to improve the characteristics. Elements such as Fe may also be included as impurities.
[0055]
Regarding the method of manufacturing steel sheets for hot stamped products as described above, pickling and cold rolling may be carried out by conventional methods, and the subsequent aluminum plating process, aluminum-zinc plating process, and zinc plating process may also be carried out by conventional methods. OK.
For aluminum plating, the suitable Si concentration in the bath is 5-12%, and for aluminum-zinc plating, the suitable Zn concentration in the bath is 40-50%.
[0056]
Also, even if Mg or Zn is mixed in the aluminum plating layer or Mg is mixed in the aluminum-zinc plating layer, steel sheets with similar characteristics can be produced without any particular problems.
Regarding the atmosphere in the plating process, plating can be performed under normal conditions in both continuous plating equipment with a non-oxidizing furnace and continuous plating equipment without a non-oxidizing furnace, and special control is required only for this steel sheet. It does not impede productivity because it does not In addition, as long as it is a galvanizing method, any method such as hot-dip galvanizing, electro-galvanizing, galvannealing, or the like may be adopted.
[0057]
Under the above manufacturing conditions, the surface of the steel sheet is not pre-plated with metal before plating, but there is no particular problem with pre-plating with Ni or Fe, or other metal pre-plating that improves plating properties. In addition, the surface of the plating layer may be plated with a different kind of metal or coated with an inorganic or organic compound.
[0058]
[Second embodiment]
　The hot stamped product according to the second embodiment has a mass%
C: 0.25% or more and 0.55% or less,
Si: 0.001% or more and 2.0% or less,
Mn: 0.3% or more and 3.0% or less,
P: 0.02% or less,
S: 0.003% or less,
Al: 0.005% or more and 1.0% or less,
Cr: 0% or more and 1.0% or less,
Mo: 0% or more and 1.0% or less,
N: 0.02% or less,
Ca: 0% or more and 0.0010% or less,
B: 0.0005% or more and 0.01% or less,
Ti: 0.005% or more and 0.5% or less, Nb: 0.005% or more and 0.5% or less, V: 0.005% or more and 0.5% or less, and Zr: 0.005% or more and 0.5% % or less, one or more selected from the group consisting of, and
Ni+Cu+Sn: 0% or more and 2% or less is contained, and the balance is Fe and impurities.
The hot stamped product according to the second embodiment has a tensile strength of more than 1600 MPa and a uniform elongation of El 1 (%) when left in the atmosphere at room temperature of 20 to 30 ° C. for 48 hours or more. When the total elongation measured using a tensile test piece of a hot stamped molded product charged with hydrogen so that the amount of diffusible hydrogen is 0.5 ± 0.1 ppm by weight is El 2 (%) , (El 2/El 1)×100≧100(%).
[0059]
The chemical composition of the hot-stamped article according to the second embodiment is the same as that of the hot-stamped article according to the first embodiment.
[0060]
The hot stamped molded article according to the second embodiment is a hot stamped molded article left in the atmosphere at room temperature of 20 to 30 ° C. for 48 hours or more, similarly to the hot stamped molded article according to the first embodiment. The tensile strength exceeds 1600 MPa and the uniform elongation is El 1 (%), measured using test pieces.
[0061]
In addition, the hot stamped molded article according to the second embodiment was measured using a tensile test piece of a hot stamped molded article charged with hydrogen so that the amount of diffusible hydrogen was 0.5 ± 0.1 ppm by weight. When the total elongation is El 2 (%), it satisfies (El 2/El 1) x 100 ≥ 100 (%).
[0062]
If coarse inclusions containing CaO—Al 2 O 3 exist inside the tensile test piece, hydrogen acts and causes hydrogen embrittlement. When a tensile test is performed using a tensile test piece in which hydrogen embrittlement has occurred, the tensile test piece does not undergo sufficient plastic deformation, and brittle fracture occurs before reaching the original tensile strength. As a result, elongation becomes a small number.
The original tensile properties (tensile strength and elongation) can be confirmed by conducting a tensile test using a tensile test piece with hydrogen released.
[0063]
When judging the quality of hot stamped products, hydrogen embrittlement does not occur if the elongation ratio, that is, (El 2 /El 1) x 100 is 100% or more. Originally, the two elongations should be compared with each other at the same uniform elongation. is difficult to measure accurately. Therefore, instead of the uniform elongation, the total elongation (elongation at break) measured after breaking is measured and evaluated.
Evaluation based on such total elongation is a stricter evaluation than uniform elongation.
[0064]
In the hot stamped product according to the second embodiment, the tensile properties are as follows: a tensile test piece of a hot stamped product in a normal state in which hydrogen is released; .5 ± 0.1 ppm by weight) using tensile specimens of hot-stamped articles charged with hydrogen.
The amount of diffusible hydrogen can be measured by the thermal desorption method.
[0065]
[Third embodiment]
　The steel sheet for hot stamping according to the third embodiment has a mass%
C: 0.25% or more and 0.55% or less,
Si: 0.001% or more and 2.0% or less,
Mn: 0.3% or more and 3.0% or less,
P: 0.02% or less,
S: 0.003% or less,
Al: 0.005% or more and 1.0% or less,
Cr: 0% or more and 1.0% or less,
Mo: 0% or more and 1.0% or less,
N: 0.02% or less,
Ca: 0% or more and 0.0010% or less,
B: 0.0005% or more and 0.01% or less,
Ti: 0.005% or more and 0.5% or less, Nb: 0.005% or more and 0.5% or less, V: 0.005% or more and 0.5% or less, and Zr: 0.005% or more and 0.5% % or less, one or more selected from the group consisting of, and
A steel sheet for hot stamping having a chemical composition containing Ni+Cu+Sn: 0% or more and 2% or less, with the balance being Fe and impurities.
The hot stamping steel sheet according to the third embodiment uses a tensile test piece obtained by heating the hot stamping steel sheet at 950 ° C. for 1 minute and then cooling it to 200 ° C. or less at an average cooling rate of 30 to 100 ° C./s, The tensile strength measured after being left in the atmosphere at room temperature of 20 to 30°C for 48 hours or more exceeds 1600 MPa, and the major diameter of inclusions containing CaO—Al 2 O 3 contained in the hot stamped product is 50 μm or less. be.
[0066]
The chemical composition of the hot stamping steel sheet according to the third embodiment is the same as that of the hot stamped product according to the first embodiment.
[0067]
The hot stamping steel sheet according to the third embodiment uses a tensile test piece obtained by heating the hot stamping steel sheet at 950 ° C. for 1 minute and then cooling it to 200 ° C. or less at an average cooling rate of 30 to 100 ° C./s, The tensile strength measured after being left in the air at room temperature of 20-30° C. for 48 hours or more exceeds 1600 MPa. Even if the steel sheet for hot stamping is not hot stamped, it can simulate the strength level and hydrogen embrittlement resistance when processed into a hot stamped product by heating and quenching under the above conditions and performing a tensile test. can be predicted and evaluated.
[0068]
In the hot stamping steel sheet according to the third embodiment, inclusions containing CaO—Al 2 O 3 contained in the hot stamping steel sheet have a major axis of 50 μm or less, like the hot stamped product according to the first embodiment.
[0069]
[Fourth embodiment]
　The steel sheet for hot stamping according to the fourth embodiment has a mass%
C: 0.25% or more and 0.55% or less,
Si: 0.001% or more and 2.0% or less,
Mn: 0.3% or more and 3.0% or less,
P: 0.02% or less,
S: 0.003% or less,
Al: 0.005% or more and 1.0% or less,
Cr: 0% or more and 1.0% or less,
Mo: 0% or more and 1.0% or less,
N: 0.02% or less,
Ca: 0% or more and 0.0010% or less,
B: 0.0005% or more and 0.01% or less,
Ti: 0.005% or more and 0.5% or less, Nb: 0.005% or more and 0.5% or less, V: 0.005% or more and 0.5% or less, and Zr: 0.005% or more and 0.5% % or less, one or more selected from the group consisting of, and
A steel sheet for hot stamping having a chemical composition containing Ni+Cu+Sn: 0% or more and 2% or less, with the balance being Fe and impurities.
The hot stamping steel sheet according to the fourth embodiment uses a tensile test piece obtained by heating the hot stamping steel sheet at 950 ° C. for 1 minute and then cooling it to 200 ° C. or less at an average cooling rate of 30 to 100 ° C./s. The tensile strength exceeds 1600 MPa, the uniform elongation is El 3 (%), and the amount of diffusible hydrogen is 0.5 ± When the total elongation measured using the tensile test piece charged with hydrogen to 0.1 weight ppm is El 4 (%), (El 4 / El 3) × 100 ≥ 100 (%) Be satisfied.
[0070]
The chemical composition of the hot stamping steel sheet according to the fourth embodiment is the same as that of the hot stamped product according to the first embodiment.
[0071]
The hot stamping steel sheet according to the fourth embodiment is a hot stamped molded article left in the atmosphere at room temperature of 20 to 30 ° C. for 48 hours or more in the same manner as the hot stamped molded article according to the first embodiment. The tensile strength measured with a strip is over 1600 MPa and the uniform elongation is El 3 (%).

The scope of the claims

[Claim 1]
in % by mass
C: 0.25% or more and 0.55% or less,
Si: 0.001% or more and 2.0% or less,
Mn: 0.3% or more and 3.0% or less,
P: 0.02% or less,
S: 0.003% or less,
Al: 0.005% or more and 1.0% or less,
Cr: 0% or more and 1.0% or less,
Mo: 0% or more and 1.0% or less,
N: 0.02% or less,
Ca: 0% or more and 0.0010% or less,
B: 0.0005% or more and 0.01% or less,
Ti: 0.005% or more and 0.5% or less, Nb: 0.005% or more and 0.5% or less, V: 0.005% or more and 0.5% or less, and Zr: 0.005% or more and 0.5% % or less, one or more selected from the group consisting of, and
Ni + Cu + Sn: containing 0% or more and 2% or less,
A hot stamped product having a chemical composition consisting of Fe and impurities as the balance,
The tensile strength of the hot-stamped molded article left in the atmosphere at room temperature of 20-30°C for 48 hours or more exceeds 1600 MPa,
The long axis of inclusions containing CaO-Al2O3 contained in the hot stamped product is 50 μm or less
A hot stamp molded product characterized by:
[Claim 2]
in % by mass
C: 0.25% or more and 0.55% or less,
Si: 0.001% or more and 2.0% or less,
Mn: 0.3% or more and 3.0% or less,
P: 0.02% or less,
S: 0.003% or less,
Al: 0.005% or more and 1.0% or less,
Cr: 0% or more and 1.0% or less,
Mo: 0% or more and 1.0% or less,
N: 0.02% or less,
Ca: 0% or more and 0.0010% or less,
B: 0.0005% or more and 0.01% or less,
Ti: 0.005% or more and 0.5% or less, Nb: 0.005% or more and 0.5% or less, V: 0.005% or more and 0.5% or less, and Zr: 0.005% or more and 0.5% % or less, one or more selected from the group consisting of, and
Ni + Cu + Sn: containing 0% or more and 2% or less,
A hot stamped product having a chemical composition consisting of Fe and impurities as the balance,
The tensile strength of the hot stamped product left in the air at room temperature of 20 to 30°C for 48 hours or more exceeds 1600 MPa,
The total tensile strength measured using a tensile test piece of the hot-stamped molded product hydrogen-charged so that the uniform elongation is El 1 (%) and the amount of diffusible hydrogen is 0.5 ± 0.1 ppm by weight Satisfies (El 2/El 1) x 100 ≥ 100 (%) when the elongation is El 2 (%)
A hot stamp molded product characterized by:
[Claim 3]
　The maximum length of MnS existing in the central part of the plate thickness is 300 μm or less
The hot-stamped article according to claim 1 or 2, characterized in that:
[Claim 4]
in % by mass,
Ni + Cu + Sn: containing 0.005% or more and 2% or less
The hot-stamped article according to any one of claims 1 to 3, characterized in that:
[Claim 5]
　Plating layer on the surface
The hot-stamped molded article according to any one of claims 1 to 4, characterized in that:
[Claim 6]
in % by mass
C: 0.25% or more and 0.55% or less,
Si: 0.001% or more and 2.0% or less,
Mn: 0.3% or more and 3.0% or less,
P: 0.02% or less,
S: 0.003% or less,
Al: 0.005% or more and 1.0% or less,
Cr: 0% or more and 1.0% or less,
Mo: 0% or more and 1.0% or less,
N: 0.02% or less,
Ca: 0% or more and 0.0010% or less,
B: 0.0005% or more and 0.01% or less,
Ti: 0.005% or more and 0.5% or less, Nb: 0.005% or more and 0.5% or less, V: 0.005% or more and 0.5% or less, and Zr: 0.005% or more and 0.5% % or less, one or more selected from the group consisting of, and
Ni + Cu + Sn: containing 0% or more and 2% or less,
A steel sheet for hot stamping having a chemical composition consisting of the balance Fe and impurities,
After heating the steel plate for hot stamping at 950 ° C. for 1 minute, using a tensile test piece cooled to 200 ° C. or less at an average cooling rate of 30 to 100 ° C./s, at room temperature of 20 to 30 ° C. for 48 hours or more in the atmosphere a tensile strength greater than 1600 MPa measured after being left in
The major axis of inclusions containing CaO—Al 2 O 3 contained in the steel plate for hot stamping is 50 μm or less
A steel plate for hot stamping characterized by:
[Claim 7]
in % by mass
C: 0.25% or more and 0.55% or less,
Si: 0.001% or more and 2.0% or less,
Mn: 0.3% or more and 3.0% or less,
P: 0.02% or less,
S: 0.003% or less,
Al: 0.005% or more and 1.0% or less,
Cr: 0% or more and 1.0% or less,
Mo: 0% or more and 1.0% or less,
N: 0.02% or less,
Ca: 0% or more and 0.0010% or less,
B: 0.0005% or more and 0.01% or less,
Ti: 0.005% or more and 0.5% or less, Nb: 0.005% or more and 0.5% or less, V: 0.005% or more and 0.5% or less, and Zr: 0.005% or more and 0.5% % or less, one or more selected from the group consisting of, and
Ni + Cu + Sn: containing 0% or more and 2% or less,
A steel sheet for hot stamping having a chemical composition consisting of the balance Fe and impurities,
After heating the steel plate for hot stamping at 950 ° C. for 1 minute, using a tensile test piece cooled to 200 ° C. or less at an average cooling rate of 30 to 100 ° C./s, at room temperature of 20 to 30 ° C. for 48 hours or more in the atmosphere a tensile strength greater than 1600 MPa, measured after being left in
The uniform elongation is El 3 (%), and the total elongation measured using the tensile test piece hydrogen-charged so that the amount of diffusible hydrogen is 0.5 ± 0.1 ppm by weight is El 4 ( %), it satisfies (El 4/El 3) × 100 ≥ 100 (%)
A steel plate for hot stamping characterized by:
[Claim 8]
　The maximum length of MnS existing in the central part of the plate thickness is 300 μm or less
The steel plate for hot stamping according to claim 6 or 7, characterized in that:
[Claim 9]
in % by mass,
Ni + Cu + Sn: containing 0.005% or more and 2% or less
The steel sheet for hot stamping according to any one of claims 6 to 8, characterized in that:
[Claim 10]
　Plating layer on the surface
The steel sheet for hot stamping according to any one of claims 6 to 9, characterized in that: