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KR-102962163-B1 - Hot-stamped steel parts including cracks with a thin coating having excellent spot weldability and excellent paint adhesion

KR102962163B1KR 102962163 B1KR102962163 B1KR 102962163B1KR-102962163-B1

Abstract

A hot-stamped coated steel part comprising a steel substrate and an aluminum alloy coating on at least one surface of the steel substrate, wherein the coating extends outwardly from the steel substrate and comprises an interdiffusion layer and an outer layer, and the total thickness e of the coating and the thickness e of the interdiffusion layer are given by the following conditions: 16 ≤ E pc < 40, Satisfying, Here, And, The above hot-stamped coated steel part comprises an undeformed portion having a thickness e Pflat of 0.6 mm to 3.5 mm and at least one deformed portion, and the linear density (lineic density: dC) of cracks in the coating in the undeformed portion is greater than or equal to the minimum linear density of cracks dC min (e Pflat ) as defined below:

Inventors

  • 필리뽀 끌레망
  • 세라 도리안
  • 살몽 르가뇌 위베르
  • 뒤소수아 다비

Assignees

  • 아르셀러미탈

Dates

Publication Date
20260508
Application Date
20240209
Priority Date
20230630

Claims (20)

  1. A hot-stamped coated steel part comprising a steel substrate and an aluminum alloy coating on at least one surface of the steel substrate, The above coating extends outward from the steel substrate and includes an interdiffusion layer and an outer layer, and the total thickness e coating of the above coating and the thickness e IDL of the interdiffusion layer are under the following conditions: 16 ≤ E pc < 40, Satisfying, Here, And, Here, e IDL represents the thickness (μm) of the interdiffusion layer, and e coating represents the total thickness (μm) of the coating, The hot-stamped coated steel part comprises an undeformed portion having a thickness e Pflat of 0.6 mm to 3.5 mm and at least one deformed portion, wherein the linear density (lineic density: dC) of cracks in the coating in the undeformed portion is greater than or equal to the minimum linear density of cracks dC min (e Pflat ) as defined below: Here, dC and dC min (e Pflat ) are expressed as the number of cracks per mm, and e Pflat represents the thickness (mm) of the undeformed portion, and A hot-stamped coated steel part, wherein the linear density of the cracks is determined by the ratio between the total number of cracks observed in various cross-sections of the undeformed portion with a bright-field optical microscope over a total observation length of at least 5 mm in a direction parallel to the surface of the steel substrate.
  2. In paragraph 1, A hot-stamped coated steel part in which the linear density dC of cracks in the coating in the above-mentioned undeformed portion is 4*dC min (e Pflat ) or less.
  3. In paragraph 1 or 2, The above hot-stamped coated steel part is a hot-stamped coated steel part having a uniform thickness e P between 0.6 mm and 3.5 mm.
  4. In paragraph 1 or 2, The hot-stamped coated steel part has a variable thickness, the hot-stamped coated steel part is composed of two or more regions each having distinct thicknesses e Pi between 0.6 mm and 3.5 mm, and the hot-stamped coated steel part has an average thickness e P between 0.6 mm and 3.5 mm.
  5. In paragraph 1 or 2, The hot-stamped coated steel part comprises two or more undeformed portions each having a thickness e pflat (i) of 0.6 mm to 3.5 mm, and in each undeformed portion, the linear density dC(i) of cracks in the coating is greater than or equal to dC min (e pflat (i)); and: Here, And, Here, e pflat (i) represents the thickness of the considered undeformed portion expressed in mm, where i = 1...n, n≥2, and dC(i) and dC min (e pflat (i)) represent the number of cracks per mm, respectively, representing the linear density of cracks and the minimum linear density of cracks in the coating of the considered undeformed portion of the thickness e pflat (i), a hot-stamped coated steel part.
  6. In paragraph 1 or 2, A hot-stamped coated steel part, wherein, in a cross-section, cracks in the coating of the undeformed portion extend from the uppermost surface of the coating toward the steel substrate in a direction orthogonal to the surface of the steel substrate over a depth of at least 5 μm, and each of the cracks has a width of less than 2 μm in a direction parallel to the surface of the steel substrate.
  7. In paragraph 1 or 2, The hot-stamped coated steel part is a monolithic part, or a hot-stamped welded part comprising at least two hot-stamped coated sub-parts and at least one hot-stamped weld that joins the hot-stamped coated sub-parts together.
  8. In Paragraph 7, The steel substrate of the hot-stamped coated steel part or the steel substrate of each hot-stamped coated sub-part has a structure consisting of at least 60 volume% martensite, up to 20 volume% bainite, up to 5 volume% ferrite, and up to 15 volume% austenite, the hot-stamped coated steel part.
  9. In Paragraph 7, The steel in the above hot-stamped coated steel part or each hot-stamped coated sub-part is in weight percent, 0.062% ≤ C ≤ 0.4% 0.4% ≤ Mn ≤ 3.9% 0.10% ≤ Si ≤ 1.5% 0.005% ≤ Al ≤ 1.0% 0.001% ≤ Cr ≤ 2.0% 0.001% ≤ Ti ≤ 0.2% 0.0005% ≤ B ≤ 0.010% Ni ≤ 2% Nb ≤ 0.1% Mo ≤ 0.65 % W ≤ 0.30% N ≤ 0.010% 0.0001% ≤ S ≤ 0.05% 0.0001% ≤ P ≤ 0.1% Contains Ca ≤ 0.005%, and A hot-stamped coated steel part having a chemical composition in which the remainder of the above composition consists of iron and inevitable impurities resulting from refinement.
  10. In Paragraph 9, The steel in the above hot-stamped coated steel part or at least one hot-stamped coated sub-part is in weight percent, 0.062% ≤ C ≤ 0.095% 1.4% ≤ Mn ≤ 1.9% 0.2% ≤ Si ≤ 0.5% 0.020% ≤ Al ≤ 0.070% Includes 0.02% ≤ Cr ≤ 0.1%, and Here, 1.5% ≤ (C + Mn +Si + Cr) ≤ 2.7%, and 0.0035% ≤ Ti ≤ 0.072% 0.0002% ≤ B ≤ 0.004% Includes 0.04% ≤ Nb ≤ 0.06%, and Here, 0.044% ≤ (Nb+Ti) ≤ 0.09%, and 0.001% ≤ N ≤ 0.009% 0.0005% ≤ S ≤ 0.003% 0.0001% ≤ P ≤ 0.020% Contains Ca ≤ 0.005%, and A hot-stamped coated steel part having a chemical composition in which the remainder of the above composition consists of iron and inevitable impurities resulting from refinement.
  11. In Paragraph 9, The steel in the above hot-stamped coated steel part or at least one hot-stamped coated sub-part is in weight percent, 0.15% ≤ C ≤ 0.30% 0.5% ≤ Mn ≤ 3.0% 0.10% ≤ Si ≤ 0.50% 0.005% ≤ Al ≤ 0.1% 0.01% ≤ Cr ≤ 1.0% 0.001% ≤ Ti ≤ 0.2% 0.0002% ≤ B ≤ 0.010% 0.0005% ≤ N ≤ 0.010% 0.0001% ≤ S ≤ 0.05% 0.0001% ≤ P ≤ 0.1% Contains Ca ≤ 0.005%, and Hot-stamped coated steel parts having a chemical composition in which the remainder is Fe and inevitable impurities resulting from refinement.
  12. In Paragraph 9, The steel in the above hot-stamped coated steel part or at least one hot-stamped coated sub-part is in weight percent, 0.3% ≤ C ≤ 0.4% 0.5% ≤ Mn ≤ 1.0% 0.40% ≤ Si ≤ 0.80% 0.01% ≤ Al ≤ 0.1% 0.1% ≤ Cr ≤ 1.0% 0.008% ≤ Ti ≤ 0.03% 0.0005% ≤ B ≤ 0.003% Ni ≤ 0.5% 0.01% ≤ Nb ≤ 0.1% 0.1% ≤ Mo ≤ 0.5 % N ≤ 0.005% 0.0001% ≤ S ≤ 0.004% 0.0001% ≤ P ≤ 0.02% Contains Ca ≤ 0.0010%, and A hot-stamped coated steel part having a chemical composition in which the remainder of the above composition consists of iron and inevitable impurities resulting from refinement.
  13. A method for manufacturing hot-stamped coated steel parts, The following consecutive steps: - A step of providing a steel blank having an average thickness e B of 0.6 mm to 3.5 mm, wherein the steel blank comprises, on at least one surface, an aluminum or aluminum alloy pre-coating, and the pre-coating has an average thickness between 8.0 μm and 19.90 μm, said blank - A step of heating the steel blank in a furnace to a heating temperature T between 850℃ and 970℃ and maintaining the steel blank at the heating temperature T to obtain a fully austenitic structure in the steel blank, - A step of transferring the heated steel blank to a die, and then closing the die, - A step of obtaining a hot-stamped blank comprising an undeformed portion and at least one deformed portion by hot-stamping the blank in the above die, such that a flat portion of the steel blank having a thickness e Bflat of 0.6 mm to 3.5 mm is not deformed and at least one portion of the steel blank is deformed through hot-stamping, - Includes the step of cooling the above hot-stamped blank to a temperature of less than 400 ℃ to obtain a hot-stamped coated steel part, and When the die is closed, the temperature T close of the steel blank is between 720°C and 820°C, and the time t M consumed by the steel blank during heating, holding, transfer, and hot-stamping at a temperature exceeding the melting temperature T melt of the pre-coating is between a minimum time t M min and a maximum time t M max , and and And, Here, t Mmin and t Mmax are expressed in seconds, and T heat is A method for manufacturing a hot-stamped coated steel part, wherein the heating temperature (°C) of the blank is indicated, T melt is indicated as the melting temperature (°C) of the pre-coating, and e Bflat is indicated as the thickness (mm) of the portion of the steel blank that has not undergone deformation.
  14. In Paragraph 13, A method for manufacturing a hot-stamped coated steel part, wherein the above pre-coating is an aluminum-alloy pre-coating comprising 7 to 15 weight% silicon, 2 to 4 weight% iron, and optionally 0.0015 to 0.0030 weight% calcium, and the remainder being aluminum and unavoidable impurities.
  15. In Paragraph 14, A method for manufacturing a hot-stamped coated steel part, wherein the above pre-coating is an aluminum-alloy pre-coating comprising 8 to 11 weight% silicon, 2 to 4 weight% iron, optionally 0.0015 to 0.0030 weight% calcium, and the remainder being aluminum and unavoidable impurities.
  16. In paragraph 13 or 14, A method for manufacturing a hot-stamped coated steel part, wherein when the steel blank is hot-stamped in the die, two or more flat sections of the steel blank having a thickness e Bflat (i) of 0.6 mm to 3.5 mm each are not deformed, and the time t M consumed by the steel blank at a temperature greater than the melting temperature T melt of the pre-coating is between the minimum time t M min (Max(e Bflat(i) ) ) required for the flat section having the highest thickness and the maximum time t M max (Min(e Bflat(i) )) required for the flat section having the lowest thickness.
  17. In paragraph 13 or 14, A method for manufacturing a hot-stamped coated steel part, wherein the blank having a variable thickness is in the range of a minimum thickness e Bmin to a maximum thickness e Bmax when the steel blank is hot-stamped in the die, and the time t M consumed by the steel blank above the melting temperature T melt of the pre-coating is between the minimum time t Mmin (e Bmax ) required for the maximum thickness e Bmax and the maximum time t Mmax ( e Bmin ) required for the minimum thickness e Bmin.
  18. In paragraph 13 or 14, A method for manufacturing a hot-stamped coated steel part, wherein the steel blank is a monolithic blank, a tailor-rolled blank, or a tailor-welded blank manufactured by welding at least two sub-blanks together.
  19. In Paragraph 18, The above blank or each sub-blank is in weight percent, 0.062% ≤ C ≤ 0.4% 0.4% ≤ Mn ≤ 3.9% 0.10% ≤ Si ≤ 1.5% 0.005% ≤ Al ≤ 1.0% 0.001% ≤ Cr ≤ 2.0% 0.001% ≤ Ti ≤ 0.2% 0.0005% ≤ B ≤ 0.010% Ni ≤ 2% Nb ≤ 0.1% Mo ≤ 0.65 % W ≤ 0.30% N ≤ 0.010% 0.0001% ≤ S ≤ 0.05% 0.0001% ≤ P ≤ 0.1% Contains Ca ≤ 0.005%, and A method for manufacturing a hot-stamped coated steel part, which is manufactured by cutting a pre-coated steel sheet having a chemical composition in which the remainder of the above composition consists of iron and inevitable impurities resulting from refinement.
  20. In Paragraph 19, The chemical composition of the above blank or at least one sub-blank is in weight percent, 0.062% ≤ C ≤ 0.095% 1.4% ≤ Mn ≤ 1.9% 0.2% ≤ Si ≤ 0.5% 0.020% ≤ Al ≤ 0.070% Includes 0.02% ≤ Cr ≤ 0.1%, and Here, 1.5% ≤ (C + Mn +Si + Cr) ≤ 2.7% and 0.0035% ≤ Ti ≤ 0.072% 0.0002% ≤ B ≤ 0.004% Includes 0.04% ≤ Nb ≤ 0.06%, and Here, 0.044% ≤ (Nb+Ti) ≤ 0.09% and, 0.001% ≤ N ≤ 0.009% 0.0005% ≤ S ≤ 0.003% 0.0001% ≤ P ≤ 0.020% Contains Ca ≤ 0.005%, and A method for manufacturing a hot-stamped coated steel part, wherein the remainder of the above composition consists of iron and inevitable impurities resulting from refinement:

Description

Hot-stamped steel parts including cracks with a thin coating having excellent spot weldability and excellent paint adhesion The present invention relates to a hot-stamped coated steel part comprising a steel substrate and an aluminum alloy coating on at least one surface of the steel substrate, wherein the coating has an optimized crack density and the part has excellent paint adhesion and excellent spot weldability. The present invention also relates to a method for manufacturing a hot-stamped coated steel part. These parts can also be used in the automotive industry, for example, for the manufacture of structural elements for intrusion prevention or energy absorption functions. In this type of application, it is desirable to have steel parts that combine high mechanical strength, high impact resistance, good corrosion resistance, and dimensional accuracy. Automotive parts, e.g., front or rear rails, roof rails, B-pillars, and chassis parts, e.g., lower control arms, engine cradles, require these characteristics in particular. To satisfy these requirements, such parts are currently generally manufactured by a hot-stamping process (also referred to as press-hardening). In a hot-stamping process, particularly as disclosed in FR 2 780 984 and FR 2 807 447, a blank cut from a steel sheet pre-coated with a metal or metal alloy is heated in a furnace to a temperature at which the ferrite and cementite microstructure of the low-carbon steel is at least partially transformed into austenite and subsequently hot-stamped in a die. During stamping, the part is held in the die to achieve rapid cooling, thereby causing the formation of a desired hardened microstructure and the acquisition of desired mechanical properties. The pre-coating may be aluminum or an aluminum alloy. During heating in the furnace, the pre-coating is alloyed with the steel substrate to form a compound that provides protection to the surface of the steel against decarburization and scale formation. Recently, the focus has been on how the coating of parts affects the properties of the parts after hot-stamping and during use. In WO 2008/053273A1, it was proposed to limit the pre-coating thickness to 20 to 33 μm at all locations and to control the hot-stamping process, particularly the heating rate and austenitization parameters, to achieve preferred continuity and shape of continuous layers in the coating of the part, thereby inducing improved weldability. However, it is still desirable to provide hot-stamped steel parts having further improved spot weldability and improved paint adhesion that can be manufactured with a lower pre-coating thickness. Furthermore, even if paint adhesion can be improved in some cases, since such improvement is achieved at the expense of spot weldability, it is still desirable to provide a part that combines excellent paint adhesion and excellent spot weldability. - FIG. 1 schematically illustrates an example of a hot-stamped coated steel part according to the present invention. - FIG. 2 is a cross-section of a coating on an undistorted portion of a part according to the present invention as observed within a given field of view, and - Figure 3 illustrates an example of a coating cross-section of an undeformed part of another part where the linear density of cracks is insufficient. The present invention relates to a hot-stamped coated steel part. Hot-stamped coated steel parts are non-planar parts manufactured by hot-stamping a blank. The term "steel plate" refers to a flat steel plate. Here, the term refers to a hot-rolled or cold-rolled steel plate that is in coil form or cut from such a coil. A steel plate has an upper face and a lower face, which are also referred to as the upper side and lower side or the upper surface and lower surface. The distance between these faces is designated as the thickness of the plate. The thickness can be measured, for example, using a micrometer, with its spindle and anvil positioned on the upper and lower faces, and the axis between the spindle and the anvil perpendicular to the surface of the steel plate. In a similar manner, the thickness can also be measured on a formed part. Similarly, the thickness can also be measured on a blank and on a part. A steel blank refers to a flat steel plate cut into any shape suitable for use, or a blank produced by cutting two or more steel plate materials, which may have different thicknesses or different compositions, into the required shape and assembling them together, particularly welded together. The average thickness of a part or part of a part refers to the overall average thickness of the material constituting the part after it has been formed into a three-dimensional part from an initial flat plate. Uniform thickness means that the thickness of the blank, part, plate, or its area or part being considered is constant, with the maximum variation in thickness of the blank, part, plate, or its area or part being greater than or less than the a