STEEL SHEET FOR HOT STAMPING AND HOT-STAMPED MEMBER

Abstract

To provide a steel sheet for hot stamping that further improves productivity of a hot-stamped member, has excellent appearance, and has excellent spot weldability, and a hot-stamped member. A steel sheet for hot stamping according to the present invention includes, on the whole of at least one surface of the steel sheet, a surface-treated film whose emissivity at a wavelength of 8.0 ?m at 25? C. is 60% or more, in which the surface-treated film contains carbon black, and one or more of oxides selected from a group consisting of a Zr oxide, a Zn oxide, and a Ti oxide, in which the carbon black and the oxides exist while being dispersed over the entire surface-treated film, the surface-treated film has a silica content of 0 to 0.3 g/m.sup.2, and when an adhesion amount of the carbon black and an adhesion amount of the oxides are set to X.sub.CB (g/m.sup.2) and X.sub.Oxide (g/m.sup.2), respectively, an equation (1) is satisfied.

Claims

1. A steel sheet for hot stamping comprising, on the whole of at least one surface of the steel sheet, a surface-treated film whose emissivity at a wavelength of 8.0 ?m at 25? C. is 60% or more, wherein: the surface-treated film contains carbon black, and one or more of a Zr oxide, a Zn oxide, and a Ti oxide, in which the carbon black and the oxides exist while being dispersed over the entire surface-treated film; the surface-treated film has a silica content of 0 to 0.3 g/m.sup.2; and when an adhesion amount of the carbon black and an adhesion amount of the oxides are set to X.sub.CB (g/m.sup.2) and X.sub.Oxide (g/m.sup.2), respectively, an equation (1) below is satisfied,
118.9?24280/{6700/(100+76?X.sub.CB)+18000/(130+65?X.sub.Oxide)}?332.0 Equation (1).

2. The steel sheet for hot stamping according to claim 1, wherein the surface-treated film contains the carbon black of 5.0 to 40.0 vol %, and contains the oxides of 1.0 to 30.0 vol %.

3. The steel sheet for hot stamping according to claim 1, wherein a ratio X.sub.Oxide/X.sub.CB between the adhesion amount X.sub.CB (g/m.sup.2) of the carbon black and the adhesion amount X.sub.Oxide (g/m.sup.2) of the oxides is 0.20 or more and 200.00 or less.

4. The steel sheet for hot stamping according to claim 1, wherein the adhesion amount X.sub.CB of the carbon black is 0.030 g/m.sup.2 or more, and the adhesion amount X.sub.Oxide of the oxides is 0.030 g/m.sup.2 or more.

5. The steel sheet for hot stamping according to claim 1, wherein an emissivity of the surface-treated film at a wavelength of 8.0 ?m at 700? C. is 60% or more.

6. The steel sheet for hot stamping according to claim 1, wherein on one side or both sides of the steel sheet for hot stamping, a metal-plated layer is provided between a base material of the steel sheet and the surface-treated film.

7. A hot-stamped member, comprising a surface-treated film on the whole of at least one surface of a steel sheet, wherein: the surface-treated film contains one or more of a Zr oxide, a Zn oxide, and a Ti oxide, in which an adhesion amount X.sub.Oxide of the oxides is 0.030 g/m.sup.2 or more; and the surface-treated film has a silica content of 0 to 0.3 g/m.sup.2.

Description

EXAMPLES

[0100] Hereinafter, examples of the present invention will be described, in which conditions in the examples are only conditional examples employed for confirming the operability and the effects of the present invention, and the present invention is not limited by the conditional examples. The present invention can employ various conditions as long as the object of the present invention is achieved without departing from the gist of the present invention.

[0101] As a base steel sheet, it is preferable to use a steel sheet having high mechanical strength (meaning various properties regarding mechanical deformation and fracture, such as tensile strength, a yield point, elongation, drawing, a hardness, an impact value, and fatigue strength). Chemical components of base steel sheets before plating, each used for a steel sheet for hot stamping described in the following examples, are shown in Table 1 below.

TABLE-US-00001 TABLE 1 STEEL CHEMICAL COMPONENT (mass %) BALANCE IS MADE UP OF IRON AND IMPURITIES. No. C Si Mn P S Al Ti B N Cr Cu Ni Nb V Mo W Sn Ca REM S1 0.11 0.21 1.21 0.02 0.005 0.05 0.02 0.0030 0.005 S2 0.40 0.01 1.01 0.04 0.010 0.03 0.04 0.0022 0.004 S3 0.23 0.60 0.90 0.03 0.010 0.04 0.03 0.0022 0.003 S4 0.31 0.01 0.50 0.04 0.010 0.04 0.04 0.0022 0.008 S5 0.25 0.60 3.00 0.03 0.004 0.01 0.03 0.0030 0.003 S6 0.27 0.21 1.01 0.05 0.004 0.01 0.02 0.0030 0.004 S7 0.29 0.01 0.90 0.01 0.020 0.03 0.02 0.0030 0.009 S8 0.34 0.60 1.01 0.01 0.004 0.10 0.02 0.0025 0.004 S9 0.28 0.21 1.05 0.03 0.004 0.03 0.01 0.0029 0.005 S10 0.26 0.23 0.90 0.04 0.004 0.03 0.10 0.0087 0.005 0.22 0.10 S11 0.17 0.25 0.95 0.03 0.004 0.01 0.04 0.0001 0.003 0.002 0.04 S12 0.33 0.21 2.01 0.04 0.004 0.01 0.03 0.0100 0.004 0.24 0.007 0.10 S13 0.27 0.03 0.90 0.02 0.010 0.01 0.02 0.0048 0.010 0.11 S14 0.37 0.01 0.95 0.02 0.010 0.03 0.02 0.0048 0.005 0.09 S15 0.25 0.21 0.90 0.04 0.010 0.03 0.02 0.0029 0.008 0.10 S16 0.33 0.12 0.50 0.04 0.008 0.04 0.04 0.0022 0.008 0.22 0.003 S17 0.32 0.13 0.51 0.04 0.008 0.04 0.04 0.0022 0.008 0.10 S18 0.30 0.14 0.53 0.04 0.009 0.04 0.04 0.0022 0.008 0.24

[0102] To each of the base steel sheets having the chemical components shown in Table 1 (steel Nos. S1 to S18), a surface-treated film was provided. More specifically, regarding each base steel sheet, a steel sheet having a width of 100 mm?a length of 200 mm, and a sheet thickness of 1.2 mm was prepared, and to some of the steel sheets, metal plating was applied and then the surface-treated film was provided over the whole surface on one side or both sides. A part of the steel sheets was not provided with the surface-treated film for comparison.

[0103] An aqueous treatment solution obtained by adding at least one or more of compounds such as commercially available carbon black, TiO.sub.2, ZrO.sub.2, ZnO, Fe.sub.2O.sub.3, Fe.sub.3O.sub.4, CuO, SiO.sub.2, TiC, TiN, SiC, and SiN, in addition to an aqueous acrylic resin being a binder component, was applied to a surface of the base steel sheet using an industrial ink-jet printer, and then dried to provide the surface-treated film. Further, in some of the aqueous treatment solutions, silica was further contained, in addition to the above components. Besides, in some verification examples, an aqueous treatment solution to which the carbon black was added and an aqueous treatment solution to which the metal oxide was added, were separately prepared, and the respective treatment solutions were applied in a stacked state. A film thickness of the surface-treated film was set to fall within a range of 1.0 to 2.5 ?m, and when the film was provided on both sides, the same kind of film was provided on both sides.

[0104] After that, a thermocouple was connected to each of a center portion of the steel sheet provided with the surface-treated film, and a center portion of a steel sheet to which the surface-treated film was not provided, to thereby enable measurement of a temperature at each position. Further, the steel sheets were heated in an electric heating furnace at a set temperature of 920? C., and the steel sheets were taken out of the heating furnace at a point of time where the steel sheet provided with the film reached 880? C. Each of the steel sheets was rapidly cooled by a flat metal mold, to thereby obtain a hot-stamped member.

[0105] A radiation thermometer was used to measure radiation intensity at the center portion of the steel sheet provided with the surface-treated film at the wavelength of 8.0 ?m at 25? C., and the emissivity (%) was calculated from a ratio with respect to radiation intensity of a blackbody.

[0106] Note that to some of the base steel sheets, Al-10 mass % Si plating, Zn plating, Zn-11 mass % Al-3 mass % Mg-0.2 mass % Si, and Al plating were applied by a hot dipping method, or Zn-3 mass % Ni plating was applied by an electroplating method, and then the above-described surface-treated film was provided. In the case of the hot dipping method, the base steel sheet was immersed into a plating bath, and then an adhesion amount was adjusted to 70 g/m.sup.2 per one side by a gas wiping method. In the case of the electroplating method, an adhesion amount per one side was adjusted to 20 g/m.sup.2.

[0107] A film composition of the site provided with the surface-treated film, and a heating rate were examined, and in some of the examples, an appearance, spot weldability after hot stamping, paint adhesiveness, and paint film corrosion resistance after hot stamping were further examined.

[0108] Evaluation methods regarding respective evaluation items are as follows.

(1) Heating Rate

(Grade)

[0109] A heating rate in each steel sheet was calculated based on the temperature change obtained by the thermocouple provided to each steel sheet, and the heating time in the electric heating furnace, to thereby perform evaluation. Specifically, a heating rate until when the temperature reached 910? C. from a room temperature was calculated, and the evaluation was performed based on the following evaluation criteria. A grade 2 was set as acceptance. [0110] 2: Heating rate of 3.5? C./s or more [0111] 1: Heating rate of 2.0? C./s or more and less than 3.5? C./s

(2) Appearance

(Grade)

[0112] By using a method described in JIS Z 8781-4 (2013) of Japanese Industrial Standards, a CIE 1976 L*a*b* color space was measured at arbitrary five locations within a test piece of 100 mm?100 mm, and a ratio of a maximum value to a minimum value of L* values (RL*=L*.sub.Max/L* value.sub.Min) was evaluated. A grade 2 was set as acceptance. [0113] 2: 1.1 or more [0114] 1: 1.0 or more and less than 1.1
(3) Spot Weldability after Hot Stamping

[0115] Two pieces of sample heated for 6 minutes in the electric heating furnace whose temperature was set to 920? C. and then cooled to the room temperature, were overlapped. The overlapped portion was subjected to spot welding with a DC power source by using a CrCu electrode with a tip diameter of 6 mm at pressurizing force of 400 kg. A current value was increased in increments of 0.5 kA from 7 kA, and a value lower by 0.5 kA than a current value at which expulsion and surface flash occurred two times continuously, was set to an upper limit of an appropriate current range. On the other hand, a sample after welding was embedded, a cross section thereof was polished, a nugget diameter was calculated by a method described in JIS Z 3139 (2009) of Japanese Industrial Standards, and a current value at which the nugget diameter became 5.5 mm or more was set to a lower limit of the appropriate current range. The evaluation criteria are as follows. A grade 2 was set as acceptance.

(Grade)

[0116] 2: The appropriate current range became 1.0 kA or more. [0117] 1: The appropriate current range became less than 1.0 kA.

(4) Paint Film Adhesiveness

[0118] On the sample, phosphoric acid chemical treatment, and electrodeposition painting with a thickness of 15 ?m were performed, and baking was performed at 170? C. for 20 minutes, to thereby provide a paint film. After that, the sample was immersed in deionized water at 60? C. for 200 hours, and then a peeling state of the paint film was checked. A grade 2 was set as acceptance.

(Grade)

[0119] 2: Absence of peeling [0120] 1: Presence of partial peeling
(5) Paint Film Corrosion Resistance after Hot Stamping

[0121] The paint film provided similarly to (4) was provided with a flaw by means of a cutter, and the paint film corrosion resistance after hot stamping was measured by a method defined by JASO M609 established by Society of Automotive Engineers of Japan. A width (maximum value on one side) of a paint film blister from the cut flaw after a corrosion test of 180 cycles was measured. A grade 2 was set as acceptance.

(Grade)

[0122] 2: Blister width of less than 3 mm [0123] 1: Blister width of 3 mm or more

[0124] The evaluation results obtained by examples 1 to 4 performed under the above conditions, are shown in Tables 2, 3, 4, and 5, respectively.

Example 1

[0125] In Table 2 below, Al to A25 are invention examples, and a1 to a7 are comparative examples.

[0126] In the present example 1, when preparing the aqueous treatment solution, carbon black and at least any of titanium nitride, titanium carbide, titanium oxide, iron oxide, copper oxide, zirconium oxide, silicon nitride, cobalt oxide, and tin oxide were used as compounds other than the binder component. In the present example, the adhesion amount of the surface-treated film was adjusted, to thereby adjust the value of emissivity at the wavelength of 8.0 ?m at 25? C.

[0127] In the comparative example a1, the emissivity at the wavelength of 8.0 ?m at 25? C. was small to be 57%, and the heating rate during the hot stamping was 2.0? C./s or more and less than 3.5? C./s (grade 1). Further, in the comparative example a2 containing no metal oxide, the emissivity at the wavelength of 8.0 ?m at 25? C. became 60%, but since the metal oxide was not contained, the emissivity at 700? C. became 53%, and the heating rate during the hot stamping was 2.0? C./s or more and less than 3.5? C./s (grade 1).

[0128] In the comparative examples a3 and a4 in which the silica content was out of the range of the present invention, the evaluation regarding the spot weldability after hot stamping became 1. Further, in the comparative examples a5 and a6 in which the film of the carbon black and the film of the metal oxides were separately formed, the L* value ratio became 1.0 or more and less than 1.1, and thus the grade regarding the appearance became 1. Further, also in the comparative example a7 in which the value of the middle side of the equation (1) was out of the range of the present invention, the L* value ratio became 1.0 or more and less than 1.1, and thus the grade regarding the appearance became 1.

[0129] On the other hand, in the invention examples Al to A25, the emissivity at the wavelength of 8.0 ?m at 25? C. was 60% or more. As a result of this, the heating rate became 3.5? C./s or more (grade 2), and regarding the appearance and the spot weldability after hot stamping as well, the grade became 2.

TABLE-US-00002 TABLE 2 STEEL SHEET FOR HOT STAMPING ADHESION AMOUNT CON- EMISS- EMISS- OF TENT IVITY IVITY ADHESION CARBON OF REFER- AT AT AMOUNT BLACK CARBON ENCE STEEL TYPE OF FILM FORMING 25? C. 700? C. OF SILICA X.sub.CB BLACK No. No. PLATING METHOD (%) (%) (g/m.sup.2) (g/m.sup.2) (VOL %) INVEN- A1 S1 Al-10 MASS % Si MIXED LAYER 60 55 0 0.012 0.50 TION A2 S2 Zn MIXED LAYER 66 70 0 0.021 5.00 EXAM- A3 S13 Zn-11 MASS % MIXED LAYER 65 73 0 0.054 4.43 PLE Al-3 MASS % Mg- 0.2 MASS % Si A4 S6 Al-10 MASS % Si MIXED LAYER 86 82 0 0.800 25.64 A5 S7 Al-10 MASS % Si MIXED LAYER 88 83 0 0.880 23.66 A6 S4 Al-10 MASS % Si MIXED LAYER 84 85 0 0.480 8.89 A7 Al-10 MASS % Si MIXED LAYER 81 85 0 0.210 4.86 A8 S5 Al-10 MASS % Si MIXED LAYER 89 86 0 1.440 23.53 A9 S6 Al-10 MASS % Si MIXED LAYER 93 87 0 3.000 35.21 A10 S8 AI MIXED LAYER 60 54 0 0.012 0.24 A11 S10 Al-10 MASS % Si MIXED LAYER 65 58 0 0.034 0.91 A12 S11 Zn-3 MASS % MIXED LAYER 83 87 0 0.480 16.67 Ni PLATING A13 S12 Al-10 MASS % Si MIXED LAYER 80 85 0 0.060 0.82 A14 S14 Al-10 MASS % Si MIXED LAYER 89 86 0 1.230 16.80 A15 S15 Al-10 MASS % Si MIXED LAYER 93 87 C 3.000 32.89 A16 S16 Al-10 MASS % Si MIXED LAYER 88 85 0 0.800 16.26 A17 S17 Al-10 MASS % Si MIXED LAYER 60 54 0 0.012 0.31 A18 S18 Al-10 MASS % Si MIXED LAYER 66 55 0 0.028 0.67 A19 S8 Al-10 MASS % Si MIXED LAYER 65 57 0 0.065 1.32 A20 S13 Al-10 MASS % Si MIXED LAYER 88 81 0 0.800 10.93 A21 S3 Al-10 MASS % Si MIXED LAYER 82 83 0 0.480 8.51 A22 S8 Al-10 MASS % Si MIXED LAYER 89 84 0 1.480 17.37 A23 S14 Al-10 MASS % Si MIXED LAYER 93 85 0 3.000 25.51 A24 S2 Al-10 MASS % Si MIXED LAYER 89 86 0.3 1.400 15.56 A25 S14 Al-10 MASS % Si MIXED LAYER 93 88 0.3 3.000 26.88 COMPAR- a1 S1 Al-10 MASS % Si MIXED LAYER 57 54 0 0.008 0.33 ATIVE a2 S3 Al-10 MASS % Si MIXED LAYER 60 53 0 0.018 0.75 EXAM- a3 S2 Al-10 MASS % Si MIXED LAYER 63 81 0.6 0.090 1.47 PLE a4 S4 Al-10 MASS % Si MIXED LAYER 68 85 1.0 0.160 2.61 a5 S5 Al-10 MASS % Si LOWER LAYER CB .fwdarw. 68 79 0 0.090 4.17 UPPER LAYER OXIDE a6 S1 Al-10 MASS % Si LOWER LAYER OXDE .fwdarw. 68 89 0 0.160 3.25 UPPER LAYER CB a7 S3 Al-10 MASS % Si MIXED LAYER 94 88 0 3.800 29.87 PROPERTY SPOT STEEL SHEET FOR HOT STAMPING WELD- METAL OXIDE APPEAR- ABILITY ADHESION CON- ADHESION MIDDLE ANCE AFTER REFER- AMOUNT TENT AMOUNT SIDE OF (COLOR HOT ENCE X.sub.oxide (VOL RATIO EQUATION HEATING UNIFORM- STAM- No. TYPE (g/m.sup.2) %) X.sub.oxide/X.sub.CB (1) RATE ITY) PING INVEN- A1 ZrO.sub.2 0.012 0.50 1.00 119.0 2 2 2 TION A2 ZrO.sub.2 0.018 4.28 0.86 119.5 2 2 2 EXAM- A3 ZrO.sub.2 0.061 5.00 1.13 122.2 2 2 2 PLE A4 ZrO.sub.2 0.510 16.34 0.64 159.7 2 2 2 A5 ZrO.sub.2 0.510 13.70 0.58 161.4 2 2 2 A6 ZrO.sub.2 1.410 26.11 2.94 186.3 2 2 2 A7 ZrO.sub.2 2.160 50.00 10.29 195.3 2 2 2 A8 ZrO.sub.2 2.350 38.39 1.63 253.8 2 2 2 A9 ZrO.sub.2 3.000 35.21 1.00 320.3 2 2 2 A10 ZnO 0.012 0.24 1.00 119.0 2 2 2 A11 ZnO 0.051 1.37 1.50 121.2 2 2 2 A12 ZnO 1.320 45.83 2.75 183.2 2 2 2 A13 ZnO 2.450 33.46 40.83 192.2 2 2 2 A14 ZnO 2.410 32.92 1.96 249.2 2 2 2 A15 ZnO 3.000 32.89 1.00 320.3 2 2 2 A16 ZnO 0.510 10.36 0.64 159.7 2 2 2 A17 TiO.sub.2 0.012 0.31 1.00 119.0 2 2 2 A18 TiO.sub.2 0.018 0.42 0.64 119.7 2 2 2 A19 TiO.sub.2 0.048 0.97 0.74 122.0 2 2 2 A20 TiO.sub.2 0.510 6.96 0.64 159.7 2 2 2 A21 TiO.sub.2 1.320 23.40 2.75 183.2 2 2 2 A22 TiO.sub.2 2.310 27.11 1.56 253.5 2 2 2 A23 TiO.sub.2 3.000 25.51 1.00 320.3 2 2 2 A24 ZrO.sub.2 2.310 25.66 1.65 251.1 2 2 2 A25 TiO.sub.2 3.000 26.88 1.00 320.3 2 2 2 a1 ZrO.sub.2 0.200 0.13 0.38 118.5 1 2 2 a2 1 2 2 COMPAR- a3 ZrO.sub.2 2.100 34.31 23.33 186.4 2 2 1 ATIVE a4 ZrO.sub.2 1.600 26.14 10.00 177.7 2 2 1 EXAM- a5 ZrO.sub.2 0.140 6.48 1.56 126.4 2 1 2 PLE a6 ZrO.sub.2 0.510 10.36 3.19 142.8 2 1 2 a7 ZrO.sub.2 3.000 23.58 0.79 334.4 2 1 2

[0130] In the following example, silica was not contained in the aqueous treatment solution used for forming the surface-treated film. The evaluation of the paint film adhesiveness was performed while focusing attention on the contents of the carbon black and the metal oxides in the surface-treated film. The obtained results are shown in Table 3 below.

[0131] In Table 3, in invention examples B1, B6 to B8, B13 to B15, B20, and B21 in which the content of carbon black (CB) in the surface-treated film was less than 5 vol % or greater than 40 vol %, or the content of metal oxides in the surface-treated film was less than 1 vol % or greater than 30 vol %, peeling occurred at a part of the paint film, and thus the grade regarding the paint film adhesiveness became 1. On the other hand, in invention examples B2 to B5, B9 to B12, and B16 to B19 in which the content of carbon black (CB) in the surface-treated film was 5 to 40 vol %, and the content of metal oxides in the surface-treated film was 1 to 30 vol %, peeling did not occur in the paint film, and thus the grade regarding the paint film adhesiveness became 2.

[0132] From the above results, it was clarified that when the carbon black was contained by 5 to 40 vol % and the metal oxides were contained by 1 to 30 vol %, it was possible to improve the paint film adhesiveness.

TABLE-US-00003 TABLE 3 STEEL SHEET FOR HOT STAMPING ADHESION AMOUNT EMISS- EMISS- OF IVITY IVITY ADHESION CARBON REFER- FILM AT AT AMOUNT BLACK ENCE STEEL TYPE OF FORMING 25? C. 700? C. OF SILICA X.sub.CB No. No. PLATING METHOD (%) (%) (g/m.sup.2) (g/m.sup.2) INVENTION B1 S1 Al-10 MASS % Si MIXED LAYER 60 55 0 0.012 EXAMPLE B2 S2 Al-10 MASS % Si MIXED LAYER 74 56 0 0.060 B3 S11 Al-10 MASS % Si MIXED LAYER 77 58 0 0.160 B4 S8 Al-10 MASS % Si MIXED LAYER 81 76 0 0.210 B5 S5 Al-10 MASS % Si MIXED LAYER 84 74 0 0.480 B6 S12 Al-10 MASS % Si MIXED LAYER 86 58 0 0.800 B7 S1 Al-10 MASS % Si MIXED LAYER 80 71 0 0.090 B8 S6 Al-10 MASS % Si MIXED LAYER 65 56 0 0.034 B9 S7 Al-10 MASS % Si MIXED LAYER 74 56 0 0.060 B10 S8 Al-10 MASS % Si MIXED LAYER 77 58 0 0.160 B11 SS Al-10 MASS % Si MIXED LAYER 83 75 0 0.460 B12 S10 Al-10 MASS % Si MIXED LAYER 83 71 0 0.480 B13 S13 Al-10 MASS % Si MIXED LAYER 86 58 0 0.800 B14 S14 Al-10 MASS % Si MIXED LAYER 80 71 0 0.100 B15 S15 Al-10 MASS % Si MIXED LAYER 60 54 0 0.012 B16 S12 Al-10 MASS % Si MIXED LAYER 74 56 0 0.060 B17 S3 NO PLATING MIXED LAYER 77 68 0 0.160 B18 S4 Al-10 MASS % Si MIXED LAYER 79 75 0 0.390 B19 S5 Al-10 MASS % Si MIXED LAYER 82 72 0 0.480 B20 S5 Al-10 MASS % Si MIXED LAYER 84 58 0 0.800 B21 S10 Al-10 MASS % Si MIXED LAYER 79 78 0 0.080 STEEL SHEET FOR HOT STAMPING CON- CON- METAL OXIDE TENT TENT ADHESION ADHESION OF OF MIDDLE PROPERTY REFER- AMOUNT AMOUNT CARBON METAL SIDE OF PAINT ENCE X.sub.oxide RATIO BLACK OXIDE EQUATION ADHESIVE- No. TYPE (g/m.sup.2) X.sub.oxide/X.sub.CB (VOL %) (VOL %) (1) NESS INVENTION B1 ZrO.sub.2 0.012 1.00 1.0 0.2 119.0 1 EXAMPLE B2 ZrO.sub.2 0.070 1.17 5.0 1.0 122.7 2 B3 ZrO.sub.2 0.510 3.19 13.3 7.1 142.8 2 B4 ZrO.sub.2 2.160 10.29 17.5 30.0 195.3 2 B5 ZrO.sub.2 1.410 2.94 40.0 19.6 186.3 2 B6 ZrO.sub.2 0.510 0.64 66.7 7.1 159.7 1 B7 ZrO.sub.2 2.450 27.22 7.5 34.0 194.3 1 B8 ZrO.sub.2 0.051 1.50 2.8 0.7 121.2 1 B9 ZrO.sub.2 0.070 1.17 5.0 1.0 122.7 2 B10 ZrO.sub.2 0.510 3.19 13.3 7.1 142.8 2 B11 ZrO.sub.2 2.160 4.70 14.3 30.0 208.9 2 B12 ZrO.sub.2 1.320 2.75 40.0 18.3 183.2 2 B13 ZrO.sub.2 0.510 0.64 66.7 7.1 159.7 1 B14 ZrO.sub.2 2.450 24.50 8.3 34.0 195.0 1 B15 TiO.sub.2 0.012 1.00 1.0 0.2 119.0 1 B16 TiO.sub.2 0.070 1.17 5.0 1.0 122.7 2 B17 TiO.sub.2 0.510 3.19 13.3 7.1 142.8 2 B18 TiO.sub.2 2.160 5.54 32.5 30.0 205.3 2 B19 TiO.sub.2 1.320 2.75 40.0 18.3 183.2 2 B20 TiO.sub.2 0.510 0.64 66.7 7.1 159.7 1 B21 TiO.sub.2 2.450 30.63 6.7 34.0 193.6 1

[0133] In the following example, silica was not contained in the aqueous treatment solution used for forming the surface-treated film. The evaluation of the heating rate was performed while focusing attention on the ratio of adhesion amounts of the carbon black and the metal oxides in the surface-treated film. Note that in the present example, the evaluation was performed regarding the heating rate until when the temperature reached 910? C. from, not the room temperature but 500? C. The evaluation criteria are as follows. The obtained results are shown in Table 4 below.

(Grade)

[0134] 2: Heating rate of 1.3? C./s or more [0135] 1: Heating rate of less than 1.3? C./s

[0136] In Table 4, in C1, C7, C8, C14, C15, and C21 in which the ratio X.sub.Oxide/X.sub.CB between the adhesion amount of the carbon black and the adhesion amount of the metal oxides was less than 0.20 or greater than 200.00, the heating rate until when the temperature reached 910? C. from 500? C. became less than 1.3? C./s, and thus the grade became 1. On the other hand, in C2 to C6, C9 to C13, and C16 to C20 in which the ratio X.sub.Oxide/X.sub.CB between the adhesion amount of the carbon black and the adhesion amount of the metal oxides was 0.20 to 200.00, the heating rate until when the temperature reached 910? C. from 500? C. became 1.3? C./s or more, and thus the grade became 2.

TABLE-US-00004 TABLE 4 STEEL SHEET FOR HOT STAMPING ADHESION AMOUNT EMISS- EMISS- OF IVITY IVITY ADHESION CARBON REFER- AT AT AMOUNT BLACK ENCE STEEL TYPE OF FILM FORMING 25? C. 700? C. OF SILICA X.sub.CB No. No. PLATING METHOD (%) (%) (g/m.sup.2) (g/m.sup.2) INVENTION C1 S1 Al-10 MASS % Si MIXED LAYER 84 53 0 1.050 EXAMPLE C2 S5 Al-10 MASS % Si MIXED LAYER 94 61 0 3.000 C3 S8 Al-10 MASS % Si MIXED LAYER 60 63 0 0.012 C4 S8 Al-10 MASS % Si MIXED LAYER 64 61 0 0.037 C5 S3 Al-10 MASS % Si MIXED LAYER 65 60 0 0.042 C6 S11 Al-10 MASS % Si MIXED LAYER 63 74 0 0.015 C7 S12 Al-10 MASS % Si MIXED LAYER 62 61 0 0.010 C8 S14 Al-10 MASS % Si MIXED LAYER 72 51 0 0.850 C9 S2 Al-10 MASS % Si MIXED LAYER 92 63 0 2.000 C10 S16 Al-10 MASS % Si MIXED LAYER 60 61 0 0.012 C11 S17 Al-10 MASS % Si MIXED LAYER 66 68 0 0.035 C12 S18 Al-10 MASS % Si MIXED LAYER 74 70 0 0.024 C13 S8 Al-10 MASS % Si MIXED LAYER 71 75 0 0.012 C14 S5 Al-10 MASS % Si MIXED LAYER 74 71 0 0.009 C15 S10 Al-10 MASS % Si MIXED LAYER 75 53 0 0.910 C16 S7 Al-10 MASS % Si MIXED LAYER 93 60 0 2.100 C17 S1 Al-10 MASS % Si MIXED LAYER 60 59 0 0.015 C18 S3 Al-10 MASS % Si MIXED LAYER 72 63 0 0.033 C19 S2 Al-10 MASS % Si MIXED LAYER 66 68 0 0.020 C20 S4 Al-10 MASS % Si MIXED LAYER 68 73 0 0.014 C21 S5 Al-10 MASS % Si MIXED LAYER 69 71 0 0.010 STEEL SHEET FOR HOT STAMPING CON- PROPERTY TENT METAL OXIDE HEATING OF ADHESION CON- ADHESION MIDDLE RATE AT REFER- CARBON METAL AMOUNT TENT AMOUNT SIDE OF 500? C. ENCE BLACK OXIDE Xoxide (VOL RATIO EQUATION OR No. (VOL %) TYPE (g/m2) %) X.sub.oxide/X.sub.CB (1) MORE INVENTION C1 24.30 ZrO.sub.2 0.120 2.77 0.11 144.6 1 EXAMPLE C2 35.20 ZrO.sub.2 0.600 7.04 0.20 191.3 2 C3 0.30 ZrO.sub.2 0.012 0.30 1.00 119.0 2 C4 0.75 ZrO.sub.2 0.580 11.78 15.68 140.8 2 C5 2.33 ZrO.sub.2 0.053 2.94 1.26 121.5 2 C6 0.20 ZrO.sub.2 3.000 40.98 200.00 199.6 2 C7 0.16 ZrO.sub.2 2.300 37.58 230.00 185.5 1 C8 22.84 ZrO.sub.2 0.012 0.32 0.01 136.1 1 C9 39.60 ZrO.sub.2 0.400 7.93 0.20 171.0 2 C10 0.71 ZrO.sub.2 0.021 1.25 1.75 119.4 2 C11 0.91 ZrO.sub.2 0.950 24.73 27.14 152.6 2 C12 0.80 ZrO.sub.2 1.350 45.00 56.25 163.5 2 C13 0.28 ZrO.sub.2 2.400 57.14 200.00 187.7 2 C14 0.25 ZrO.sub.2 2.100 60.34 233.33 181.1 1 C15 22.30 TiO.sub.2 0.012 0.29 0.01 137.0 1 C16 34.31 TiO.sub.2 0.420 6.86 0.20 173.1 2 C17 0.69 TiO.sub.2 0.025 1.15 1.67 119.6 2 C18 1.30 TiO.sub.2 1.030 40.87 31.21 154.9 2 C19 0.57 TiO.sub.2 1.530 43.96 76.50 168.1 2 C20 0.22 TiO.sub.2 2.800 45.75 200.00 195.8 2 C21 0.16 TiO.sub.2 2.300 36.85 230.00 185.5 1

[0137] In the following example, silica was not contained in the aqueous treatment solution used for forming the surface-treated film. The evaluation of the paint film corrosion resistance after hot stamping was performed while focusing attention on the adhesion amounts of the carbon black and the metal oxides in the surface-treated film. The obtained results are shown in Table 5 below.

[0138] In Table 5, in invention examples D1, D4, and D7 in which the adhesion amount of the carbon black was less than 0.030 g/m.sup.2 or the adhesion amount of the metal oxides was less than 0.030 g/m.sup.2, the blister width of the paint film after the hot stamping became 3 mm or more, and thus the grade became 1. On the other hand, in invention examples D2, D3, D5, D6, D8, and D9 in which the adhesion amount of the carbon black was 0.030 g/m.sup.2 or more and the adhesion amount of the metal oxides was 0.030 g/m.sup.2 or more, the blister width of the paint film after the hot stamping became less than 3 mm, and thus the grade became 2.

TABLE-US-00005 TABLE 5 STEEL SHEET FOR HOT STAMPING ADHESION AMOUNT EMISS- EMISS- OF IVITY IVITY ADHESION CARBON REFER- AT AT AMOUNT BLACK ENCE STEEL TYPE OF FILM FORMING 25? C. 700? C. OF SILICA X.sub.CB No. No. PLATING METHOD (%) (%) (g/m.sup.2) (g/m.sup.2) INVENTION D1 S10 Al-10 MASS % Si MIXED LAYER 64 56 0 0.014 EXAMPLE D2 S7 Al-10 MASS % Si MIXED LAYER 65 57 0 0.030 D3 S1 Al-10 MASS % Si MIXED LAYER 71 63 0 0.110 D4 S5 Al-10 MASS % Si MIXED LAYER 65 55 0 0.015 D5 S2 Al-10 MASS % Si MIXED LAYER 67 56 0 0.030 D6 S15 Al-10 MASS % Si MIXED LAYER 81 62 0 0.350 D7 S10 Al-10 MASS % Si MIXED LAYER 63 54 0 0.012 D8 S7 Al-10 MASS % Si MIXED LAYER 69 58 0 0.030 D9 S1 Al-10 MASS % Si MIXED LAYER 80 67 0 0.280 STEEL SHEET FOR HOT STAMPING CON- PROPERTY TENT METAL OXIDE PAINT FILM OF ADHESION CON- ADHESION MIDDLE CORROSION REFER- CARBON AMOUNT TENT AMOUNT SIDE OF RESISTANCE ENCE BLACK Xoxide (VOL RATIO EQUATION AFTER HOT No. (VOL %) TYPE (g/m2) %) X.sub.oxide/X.sub.CB (1) STAMPING INVENTION D1 1.45 ZrO.sub.2 0.013 1.35 0.93 119.1 1 EXAMPLE D2 1.78 ZrO.sub.2 0.030 1.79 1.00 120.2 2 D3 6.54 ZrO.sub.2 0.280 16.67 2.55 132.5 2 D4 0.35 ZnO 0.011 0.26 0.73 119.0 1 D5 1.04 ZnO 0.030 1.04 1.00 120.2 2 D6 11.21 ZnO 0.220 7.05 0.63 136.7 2 D7 0.32 TiO.sub.2 0.017 0.46 1.42 119.2 1 D8 2.27 TiO.sub.2 0.030 2.27 1.00 120.2 2 D9 16.66 TiO.sub.2 0.250 14.80 0.89 136.2 2

[0139] Preferred embodiments of the present invention have been described above in detail, but the present invention is not limited to the embodiments. It should be understood that various changes and modifications are readily apparent to those skilled in the art who has the common general knowledge in the technical field to which the present invention pertains, within the scope of the technical spirit as set forth in claims, and they should also be covered by the technical scope of the present invention.