JP-7856670-B2 - Highly formable hot-dip galvanized or hot-dip galvanized aluminum-magnesium plated duplex steel and its rapid heat treatment hot-dip galvanizing manufacturing method

JP7856670B2JP 7856670 B2JP7856670 B2JP 7856670B2JP-7856670-B2

Inventors

王健
楊奕
李俊
張理揚
杜小峰
丁志龍
劉華飛
任玉苓
杜瑤
林傳華

Assignees

宝山鋼鉄股▲分▼有限公司

Dates

Publication Date: 20260511
Application Date: 20220331
Priority Date: 20210402

Claims (17)

A steel sheet having a highly formable aluminum-zinc coating or zinc-aluminum-magnesium coating with a tensile strength of ≥ 590 MPa, wherein the steel sheet is composed of a duplex steel sheet and the highly formable aluminum-zinc coating or zinc-aluminum-magnesium coating on the surface of the duplex steel sheet. The mass percentage of the chemical composition of the aforementioned duplex steel sheet is as follows: C: 0.045-0.12%, Si: 0.1-0.5%, Mn: 1.0-2.0%, P ≤ 0.02%, S ≤ 0.006%, Al: 0.02-0.055%, optionally containing one or two of Cr, Mo, Ti, Nb, and V, with Cr + Mo + Ti + Nb + V ≤ 0.5%, and the remainder being Fe and other unavoidable impurities. The steel sheet having the highly formable aluminum-zinc coating or zinc-aluminum-magnesium coating has a yield strength of ≥ 300 MPa, a tensile strength of ≥ 590 MPa, an elongation of ≥ 20%, a strength-ductility product of ≥ 15 GPa%, and a strain-hardening index n 90 value greater than 0.20; and the metal structure of the steel sheet having the highly formable aluminum-zinc coating or zinc-aluminum-magnesium coating is a two-phase structure of uniformly distributed ferrite and martensite, with an average grain size of 1 to 5 μm.
The C content is 0.045 to 0.105%; and/or the Si content is 0.15 to 0.25%; and/or the Mn content is 1.0% to 1.5%; and/or the Cr + Mo + Ti + Nb + V ≤ 0.4%; and/or the steel sheet having the highly formable aluminum zinc coating or zinc aluminum magnesium coating has a yield strength of 300 to 560 MPa, a tensile strength of 590 to 860 MPa, an elongation of 20 to 30%, and a strength-ductile product of 15 to 21 GPa% as described in claim 1.
The C content is 0.05 to 0.12%; and/or the Si content is 0.1 to 0.4%; and/or the Mn content is 1.2 to 2.0%; and/or the Cr + Mo + Ti + Nb + V ≤ 0.2%; and/or the steel sheet having the highly formable aluminum-zinc coating or zinc-aluminum-magnesium coating has a yield strength of 300 to 400 MPa, a tensile strength of 630 to 860 MPa, an elongation of 20 to 30%, and a strength-ductile product of 15 to 21 GPa% as described in claim 2.
The C content is 0.065 to 0.085%; and/or the Mn content is 1.2% to 1.35%; and/or the steel sheet having the highly formable aluminum-zinc coating or zinc-aluminum-magnesium coating has a yield strength of 450 to 560 MPa, a tensile strength of 590 to 860 MPa , an elongation of 20 to 30%, and a strength-ductility product of 15 to 21 GPa%, as described in claim 2.
The steel sheet having a highly formable aluminum-zinc coating or zinc-aluminum-magnesium coating according to claim 2, wherein the C content is 0.07 to 0.10%; and/or the Mn content is 1.5 to 1.8%.
The steel sheet having a highly formable aluminum-zinc coating or zinc-aluminum-magnesium coating with a tensile strength ≥ 590 MPa has the following mass percentage chemical composition: C: 0.045 to 0.105%, Si: 0.1 to 0.4%, Mn: 1.0 to 1.5%, P ≤ 0.02%, S ≤ 0.006%, Al: 0.02 to 0.055%, and may further contain one or two of Cr, Mo, Ti, Nb, and V, and Cr + Mo + Ti + Nb + V ≤ 0.3%, with the remainder being Fe and other unavoidable impurities, as described in claim 1.
Duplex steel sheets have a carbon content of 0.065 to 0.085%; and/or Duplex steel sheets have a Si content of 0.15 to 0.25%; and/or Duplex steel sheets have a Mn content of 1.2% to 1.35%; and/or A steel sheet having a highly formable aluminum-zinc coating or zinc-aluminum-magnesium coating according to claim 6, wherein in a duplex steel sheet , Cr + Mo + Ti + Nb + V ≤ 0.2%; and/or the steel sheet having the highly formable aluminum-zinc coating or zinc-aluminum-magnesium coating has an average grain size of 1 to 3 μm; and/or the steel sheet having the highly formable aluminum-zinc coating or zinc-aluminum-magnesium coating has a yield strength of 300 to 400 MPa, a tensile strength of 630 to 700 MPa, an elongation of 22 to 30%, a strength-ductility product of 15 to 20 GPa%, and a strain-hardening index n 90 value greater than 0.21.
The steel sheet having the highly formable aluminum-zinc coating or zinc-aluminum-magnesium coating has a yield strength of 304 to 398 MPa, a tensile strength of 630 to 698 MPa, an elongation of 22.3 to 29.4%, a strength-ductile product of 15.3 to 19.4 GPa%, and a strain hardening index n 90 value greater than 0.21, as described in claim 7.
The steel sheet having a highly formable aluminum-zinc coating or zinc-aluminum-magnesium coating with a tensile strength of ≥ 590 MPa, The mass percentage of the chemical composition of the duplex steel sheet is as follows: C: 0.05-0.12%, Si: 0.1-0.5%, Mn: 1.2-2.0%, P ≤ 0.015%, S ≤ 0.003%, Al: 0.02-0.055%, and may further contain one or two of Cr, Mo, Ti, Nb, and V, and Cr + Mo + Ti + Nb + V ≤ 0.5 %, with the remainder being Fe and other unavoidable impurities, the steel sheet having a highly formable aluminum-zinc coating or zinc-aluminum-magnesium coating according to claim 1.
Duplex steel sheets have a carbon content of 0.07 to 0.10%; and/or Duplex steel sheets have a Si content of 0.1 to 0.4%; and/or The duplex steel sheet has a Mn content of 1.5 to 1.8%; and/or Cr + Mo + Ti + Nb + V ≤ 0.4%; and/or the steel sheet having the highly formable aluminum-zinc coating or zinc-aluminum-magnesium coating has a yield strength of 470 to 560 MPa, a tensile strength of 780 to 860 MPa, an elongation of 20 to 25%, a strength-ductility product of 16 to 21 GPa%, and a strain-hardening index n 90 value greater than 0.20, as described in claim 9 .
The steel sheet having the highly formable aluminum-zinc coating or zinc-aluminum-magnesium coating has a yield strength of 476 to 556 MPa, a tensile strength of 786 to 852 MPa, an elongation of 20.1 to 24.8%, a strength-ductile product of 16.7 to 20.2 GPa%, and a strain hardening index n90 value greater than 0.20, as described in claim 10.
A method for producing a steel sheet having a highly formable aluminum-zinc coating or zinc-aluminum-magnesium coating with a tensile strength ≥ 590 MPa according to any one of claims 1 to 11, comprising the following steps: 1) Smelting and casting The chemical composition is described in any one of claims 1 to 7, 9, and 10 , and the mixture is cast into a slab; 2) Hot rolling and winding; the winding temperature shall be 550 to 680°C; 3) Cold rolling: The cold rolling reduction ratio shall be 40-85%, and after cold rolling, rolled hardened strip steel or steel plate shall be obtained; 4) Rapid heat treatment, hot-dip aluminum zinc plating, or hot-dip zinc aluminum magnesium plating A ) Rapid heating: Cold-rolled steel strip or steel sheet is rapidly heated from room temperature to the endpoint temperature of the austenite-ferrite two-phase region, which is 750 to 845°C, and the rapid heating is performed in one or two stages; When using a single-stage rapid heating system, the heating rate shall be 15 to 500°C/s; In a two-stage rapid heating system, the first stage involves heating from room temperature to 550-650°C at a heating rate of 15-500°C/s, and the second stage involves heating from 550-650°C to 750-845°C at a heating rate of 30-500°C/s. B ) Soaking: Soaking is performed at 750-845°C, which is the endpoint temperature of the austenite-ferrite two-phase region, with a soaking time of 10-60 seconds. C ) Cooling After the soaking of the steel strip or steel plate is complete, it is slowly cooled to 670-770°C at a cooling rate of 5-15°C/s; then rapidly cooled to 580-600°C at a cooling rate of 50-200°C/s; D ) Hot-dip aluminum zinc plating or hot-dip zinc-aluminum magnesium plating: After rapid cooling to 580-600°C, the steel strip or steel plate is immersed in a zinc oven to perform hot-dip aluminum zinc plating or hot-dip zinc-aluminum magnesium plating; E ) After molten aluminum zinc plating, rapidly cool to room temperature at a cooling rate of 30 to 200°C/s to obtain an aluminum zinc AZ product; or, After molten zinc-aluminum-magnesium plating, the product is rapidly cooled to room temperature at a cooling rate of 10 to 300°C/s to obtain a zinc-aluminum-magnesium AM product.
Step 4) The entire process of rapid heat treatment and molten aluminum zinc plating or molten zinc aluminum magnesium plating takes 29 to 159 seconds; and/or Step 2) The hot rolling end temperature ≥ Ar3 ; and/or Step 2) The winding temperature is 580 to 650°C; and/or Step 3) The cold rolling reduction ratio is 60 to 80%; and/or Step 4) When the rapid heating is a single-stage heating, the heating rate is 50 to 300°C/s; and/or Step 4) The rapid heating is a two-stage heating, where in the first stage the temperature is raised from room temperature to 550 to 650°C at a heating rate of 15 to 300°C/s, and in the second stage the temperature is raised from 550 to 650°C to 750 to 845°C at a heating rate of 50 to 300°C/s; and/or In step 4), the final temperature of the rapid heating is 770 to 830°C; and/or in the soaking process of step 4), the steel strip or steel plate is heated to the endpoint temperature of the austenite and ferrite two-phase region, and then the temperature is kept constant and soaked; and/or in the soaking process of step 4), the steel strip or steel plate is subjected to a small increase or decrease in temperature during the soaking time, with the temperature after the increase being 845°C or less and the temperature after the decrease being 750°C or more; and/or the soaking time is 10 to 40 s; The method according to claim 12.
In step A), when single-stage rapid heating is performed, the heating rate is 50 to 500°C/s; and/or in step A), when two-stage rapid heating is performed, in the first stage the rolled hardened strip or steel sheet is heated from room temperature to 550 to 650°C at a heating rate of 15 to 500°C/s, and in the second stage it is heated from 550 to 650°C to 750 to 845°C at a heating rate of 50 to 500°C/s; and/or in step C), after soaking is complete, the strip or steel sheet is slowly cooled to 670 to 770°C at a cooling rate of 5 to 15°C/s, and then rapidly cooled to 580 to 600°C at a cooling rate of 50 to 150°C/s; and/or in step E), after molten aluminum zinc plating, the steel sheet is rapidly cooled to room temperature at a cooling rate of 30 to 150°C/s to obtain an aluminum zinc AZ product; and/or In step E), after molten zinc-aluminum-magnesium plating, the product is rapidly cooled to room temperature at a cooling rate of 30 to 180°C/s to obtain a zinc-aluminum-magnesium AM product. The method according to claim 12.
The entire process of the rapid heat treatment and molten aluminum zinc plating or molten zinc aluminum magnesium plating according to step 4) takes 29 to 122 seconds; and/or in step 4), the rapid heating is a two-stage heating, in which the strip or steel plate is heated from room temperature to 550 to 650°C in the first stage at a heating rate of 30 to 300°C/s, and in the second stage at a heating rate of 80 to 300°C/s to heat from 550 to 650°C to 750 to 845°C; In step 4), after molten zinc-aluminum-magnesium plating, the steel sheet is rapidly cooled to room temperature at a cooling rate of 30 to 250°C/s to obtain a zinc-aluminum-magnesium AM product; The method according to claim 13.
A method according to claim 12, The above method is as follows: (1) The steel strip or steel sheet has the following mass percentages of chemical composition: C: 0.045 to 0.105%, Si: 0.1 to 0.4%, Mn: 1.0 to 1.5%, P ≤ 0.02%, S ≤ 0.006%, Al: 0.02 to 0.055%, and may further contain one or two of Cr, Mo, Ti, Nb, and V, and Cr + Mo + Ti + Nb + V ≤ 0.3%, with the remainder being Fe and other unavoidable impurities, provided that after molten aluminum zinc plating, it is cooled to room temperature at a cooling rate of 30 to 200°C/s to obtain an aluminum zinc AZ product, or after molten zinc aluminum magnesium plating, it is cooled to room temperature at a cooling rate of 30 to 180°C/s to obtain a zinc aluminum magnesium AM product; or the above method is as follows: (2) The steel strip or steel sheet has the following mass percentages of chemical composition: C: 0.05 to 0.12%, Si: 0.1 to 0.5%, Mn: 1.2 to 2.0%, P ≤ 0.015%, S ≤ 0.003%, Al: 0.02 to 0.055%, and may further contain one or two of Cr, Mo, Ti, Nb, and V, and Cr + Mo + Ti + Nb + V ≤ 0.5%, with the remainder being Fe and other unavoidable impurities, provided that after molten aluminum zinc plating, it is rapidly cooled to room temperature at a cooling rate of 30 to 150°C/s to obtain an aluminum zinc AZ product, or after molten zinc aluminum magnesium plating, it is rapidly cooled to room temperature at a cooling rate of 10 to 300°C/s to obtain a zinc aluminum magnesium AM product; method.
The method according to claim 16, (1) In step 4), the entire process of the rapid heat treatment and molten aluminum zinc plating or molten zinc aluminum magnesium plating takes 29 to 122 seconds; or (2) The method wherein the entire process of the rapid heat treatment and molten aluminum zinc plating or molten zinc aluminum magnesium plating takes 29 to 159 seconds.

Description

This invention belongs to the field of rapid heat treatment of materials, and more particularly to highly formable molten aluminum zinc plated or molten zinc-aluminum-magnesium plated duplex steel (including molten aluminum zinc plated AZ products and molten zinc-aluminum-magnesium plated AM products) and a method for rapidly heat-treating and molten molten steel therefor. As public concern for energy conservation and material safety increases, numerous automobile manufacturers are using high-strength steel for automotive materials. For example, materials used in automobile exhaust systems require high strength, toughness, corrosion resistance, and certain heat resistance properties. Meanwhile, materials for home appliances and construction require high strength and thinness for substrate materials, and good corrosion resistance for coatings. Thus, in fields such as automobiles, home appliances, and construction, the demands on coatings and plated products for corrosion resistance, dent resistance, durability, large deformation impact strength, and safety are becoming increasingly stringent. In the field of hot-dip galvanized high-strength steel for automobiles, hot-dip galvanized duplex steel is the most widely applied and has the greatest potential. Low-carbon, low-alloy hot-dip galvanized duplex steel is characterized by a low yield ratio, high initial work hardening rate, and a good balance of strength and ductility. Currently, it is widely used as a high-strength, highly formable steel for press-forming automotive structures. However, as the demands for corrosion resistance in steel products become increasingly stringent, hot-dip pure zinc plating no longer meets these requirements, necessitating the development of new varieties with superior corrosion-resistant coatings. Therefore, research into hot-dip aluminum-zinc plating and hot-dip zinc-aluminum-magnesium plating coatings, which offer superior corrosion resistance, is becoming increasingly active. In response, hot-dip aluminum-zinc plating and hot-dip zinc-aluminum-magnesium plating high-strength steel products are also emerging. Currently, the main methods for modifying molten aluminum-zinc plated and molten zinc-aluminum-magnesium plated duplex steels involve altering the microstructure and properties of the molten-plated duplex steel by adding alloying elements and adjusting the soaking temperature, time, and cooling rate in the critical annealing process. Chinese patent application CN201710994660.X discloses "550 MPa grade structural hot-dip aluminum-galvanized steel sheet and method for producing the same," whose chemical composition is C: 0.02–0.07%, Si ≤ 0.03%, Mn: 0.15–0.30%, P ≤ 0.020%, Si ≤ 0.020%, Nb: 0.015–0.030%, Als: 0.020–0.070%. Cold rolling is performed at a low cold rolling reduction ratio of 55–60%, resulting in a yield strength of 550 MPa or higher, a tensile strength of 560 MPa, and an elongation of approximately 10%. This patented steel sheet has the problem of low elongation and a high yield strength ratio, which affects subsequent processing steps. Chinese patent application CN102363857B discloses a method for producing structural coated boards with a yield strength of 550 MPa, wherein Ti and Nb do not exceed 0.05% and 0.045%, respectively, the yield strength Rp 0.2 reaches 550-600 MPa, the tensile strength R m is 560-610 MPa, and the elongation after fracture A 80 mm ≥ 6%. The strengthening method is mainly based on low-temperature annealing, which retains most of the uncrystallized band structure, increasing strength but resulting in poor plasticity and affecting molding. Chinese patent application CN100529141C discloses "Fully Hardened Aluminum-Zinc Plated Steel Sheet and Method for Producing the Same." The steel sheet produced by this method has a yield strength of 600 MPa or higher, a fracture elongation of ≤7%, and a total Ti and Nb content of 0.15%–0.100%. The annealing temperature is 630–710°C, and the fully hardened steel sheet is obtained using a low-temperature recovery annealing method. However, the elongation of the steel sheet product obtained by this method is too low to meet current processing and formability requirements. Chinese patent application CN201911161556.8 discloses "Hot-dip zinc-aluminum-magnesium plated high-strength steel, manufacturing method and application." The hot-dip zinc-aluminum-magnesium plated high-strength steel includes a base material and a zinc-aluminum-magnesium alloy coating on the surface of the base material. Through component design and control of the production process based on the component design, a production method and core production technology are provided, centering on a CSP thin slab continuous casting and continuous rolling production line and a conventional hot-dip galvanizing production line, encompassing smelting, hot rolling, cold rolling, and annealing processes. The above-mentioned hot-dip zinc-aluminum-magnesium plated high-strength steel has a yield strength