EP4685248A1 - Cold-rolled high-strength steel plate with excellent phosphating performance, and manufacturing method therefor - Google Patents

Cold-rolled high-strength steel plate with excellent phosphating performance, and manufacturing method therefor

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Publication number
EP4685248A1
EP4685248A1 EP24774250.5A EP24774250A EP4685248A1 EP 4685248 A1 EP4685248 A1 EP 4685248A1 EP 24774250 A EP24774250 A EP 24774250A EP 4685248 A1 EP4685248 A1 EP 4685248A1
Authority
EP
European Patent Office
Prior art keywords
steel plate
cold
mass percentage
strength steel
rolled high
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Pending
Application number
EP24774250.5A
Other languages
German (de)
French (fr)
Inventor
Xinyan JIN
Min Zhu
Weichen MAO
Guang Chen
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Baoshan Iron and Steel Co Ltd
Original Assignee
Baoshan Iron and Steel Co Ltd
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Baoshan Iron and Steel Co Ltd filed Critical Baoshan Iron and Steel Co Ltd
Publication of EP4685248A1 publication Critical patent/EP4685248A1/en
Pending legal-status Critical Current

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    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
    • C21D1/26—Methods of annealing
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
    • C21D1/74—Methods of treatment in inert gas, controlled atmosphere, vacuum or pulverulent material
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
    • C21D1/74—Methods of treatment in inert gas, controlled atmosphere, vacuum or pulverulent material
    • C21D1/76—Adjusting the composition of the atmosphere
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D6/00—Heat treatment of ferrous alloys
    • C21D6/005—Heat treatment of ferrous alloys containing Mn
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D6/00—Heat treatment of ferrous alloys
    • C21D6/008—Heat treatment of ferrous alloys containing Si
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D8/00—Modifying the physical properties of ferrous metals or ferrous alloys by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties of ferrous metals or ferrous alloys by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D8/00—Modifying the physical properties of ferrous metals or ferrous alloys by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties of ferrous metals or ferrous alloys by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/0221—Modifying the physical properties of ferrous metals or ferrous alloys by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the working steps
    • C21D8/0226—Hot rolling
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D8/00—Modifying the physical properties of ferrous metals or ferrous alloys by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties of ferrous metals or ferrous alloys by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/0221—Modifying the physical properties of ferrous metals or ferrous alloys by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the working steps
    • C21D8/0236—Cold rolling
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D8/00—Modifying the physical properties of ferrous metals or ferrous alloys by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties of ferrous metals or ferrous alloys by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/0247—Modifying the physical properties of ferrous metals or ferrous alloys by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the heat treatment
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D8/00—Modifying the physical properties of ferrous metals or ferrous alloys by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties of ferrous metals or ferrous alloys by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/0247—Modifying the physical properties of ferrous metals or ferrous alloys by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the heat treatment
    • C21D8/0263—Modifying the physical properties of ferrous metals or ferrous alloys by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the heat treatment following hot rolling
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D8/00—Modifying the physical properties of ferrous metals or ferrous alloys by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties of ferrous metals or ferrous alloys by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/0247—Modifying the physical properties of ferrous metals or ferrous alloys by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the heat treatment
    • C21D8/0273—Final recrystallisation annealing
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D8/00—Modifying the physical properties of ferrous metals or ferrous alloys by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties of ferrous metals or ferrous alloys by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/0278—Modifying the physical properties of ferrous metals or ferrous alloys by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips involving a particular surface treatment 
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
    • C21D9/46—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for sheet metals
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/002—Ferrous alloys, e.g. steel alloys containing In, Mg, or other elements not provided for in one single group C22C38/001 - C22C38/60
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/06—Ferrous alloys, e.g. steel alloys containing aluminium
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/12—Ferrous alloys, e.g. steel alloys containing tungsten, tantalum, molybdenum, vanadium, or niobium
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/14—Ferrous alloys, e.g. steel alloys containing titanium or zirconium
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/32—Ferrous alloys, e.g. steel alloys containing chromium with boron
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/34—Ferrous alloys, e.g. steel alloys containing chromium with more than 1.5% by weight of silicon
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/38—Ferrous alloys, e.g. steel alloys containing chromium with more than 1.5% by weight of manganese
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/46—Ferrous alloys, e.g. steel alloys containing chromium with nickel with vanadium
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/54—Ferrous alloys, e.g. steel alloys containing chromium with nickel with boron
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D2211/00—Microstructure comprising significant phases
    • C21D2211/001—Austenite
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D2211/00—Microstructure comprising significant phases
    • C21D2211/004—Dispersions; Precipitations
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D2211/00—Microstructure comprising significant phases
    • C21D2211/005—Ferrite
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D2211/00—Microstructure comprising significant phases
    • C21D2211/008—Martensite

Definitions

  • the present invention relates to a steel plate and a manufacturing method therefor, and particularly relates to a cold-rolled steel plate and a manufacturing method therefor.
  • High-strength steel is a material that is being used more and more widely at present.
  • Cold-rolled high-strength steel usually requires an addition of relatively high contents of alloying elements such as C, Si, Mn, Cr, and Al, combined with the continuous annealing process and phase transformation strengthening to achieve certain strength and formability.
  • Phosphating is a pretreatment process before automotive electrophoretic coating.
  • phosphating solution By immersing a steel plate or a part made of a steel plate in phosphating solution, a layer of insoluble phosphating film is formed on the surface of the steel plate or the part, thereby improving the adhesion of the paint film.
  • alloying elements such as Si and Mn in the steel can form external oxidation on a surface of a strip steel after annealing.
  • the external oxidation of Si and Mn on the surface of a steel plate can affect the nucleation and growth of the phosphating film, thereby affecting the coating quality of automotive parts. Therefore, in recent years, the phosphating performance of high-strength steel has gradually attracted attention.
  • the Chinese patent application with publication number CN107419185A, publication date December 1, 2017 , and titled "A Cold-rolled Steel Plate with Good Phosphating Performance and Production Method Therefor” mainly produces a cold-rolled plate with good phosphating performance by precisely controlling the composition, and simultaneously through hot rolling, pickling, five-stand full six-roller cold rolling, continuous annealing, and leveling process.
  • the Chinese patent application with publication number CN111910123A, publication date November 10, 2020 , and titled "Cold-Rolled Continuous Annealing Ultra-High Strength Steel with Good Phosphating Performance and Preparation Method Therefor” discloses an annealing process for obtaining good phosphating performance of cold-rolled continuously annealing ultra-high strength steel. It specifies that a H 2 content of an annealing atmosphere is 6% to 15%, a dew point is -45 °C to -41 °C, and an oxygen content is 2 ppm to 5 ppm, whose purpose is to inhibit the selective oxidation of alloying elements through the above parameters, thereby achieving good phosphating performance.
  • controlling the annealing atmosphere is another method for improving the phosphating performance of a cold-rolled steel plate with high alloy content.
  • a method of controlling both dew point and oxygen content at a relatively low level is rather difficult and costly; while a method of controlling a dew point at a relatively high level will cause decarburization on the surface of a steel plate, therefore this method also has certain limitations.
  • One object of the present invention is to provide a cold-rolled high-strength steel plate with excellent phosphating performance, which achieves excellent phosphating performance by controlling Mn and Si elements not enriching on the surface of the steel plate.
  • the present invention provides a cold-rolled high-strength steel plate with excellent phosphating performance, wherein, on an element mass percentage content-depth distribution curve with a depth in the range of 0-1000 nm from the surface of the steel plate, a mass percentage peak value of Mn element Mn p is ⁇ 10.0%, and a mass percentage peak value of Si Si p is ⁇ 4.0%, and both the mass percentage peak value of Mn element Mn p and the mass percentage peak value of Si element Si p are located at a depth of ⁇ 50 nm from the surface of the steel plate.
  • GDOES glow discharge optical emission spectroscopy
  • the key to achieving excellent phosphating performance of a cold-rolled high-strength steel is that on an element mass percentage content-depth distribution curve with a depth in the range of 0-1000 nm from a surface layer of a steel plate detected by glow discharge optical emission spectroscopy (GDOES), a mass percentage peak value of Mn Mn p is ⁇ 10.0%, and a mass percentage peak value of Si Si p is ⁇ 4.0%.
  • GDOES glow discharge optical emission spectroscopy
  • the mass percentage peak values of Mn or Si on the surface of the steel plate can reach several to dozens of times that of the matrix Mn or Si. These oxides will hinder the reaction between the phosphating solution and the steel plate, thereby affecting the phosphating performance of the high-strength steel.
  • the present invention controls Mn p ⁇ 10% and Si p ⁇ 4%.
  • the present invention controls Mn p ⁇ 8.5% and Si p ⁇ 3.0%.
  • Mn p is between 5.0 and 10.0%, and Si p is between 0.1 and 3.0%.
  • the present invention controls a depth of Mn p t pMn to ⁇ 50 nm and a depth of Si p t pSi to ⁇ 50 nm. This is because through research the inventors have found that when a depth of Mn p and a depth of Si p are less than 50 nm, even if Mn p is ⁇ 10% or Si p is ⁇ 4%, external oxidation of Si and Mn at local positions cannot be avoided, and the local phosphating performance is poor.
  • the mass percentage peak value of Mn element Mn p and the mass percentage peak value of Si element Si p are located at a depth of 50-500 nm from the surface of the steel plate.
  • a preferred t pMn of the present invention is ⁇ 500 nm, and t pSi is ⁇ 500 nm.
  • the present invention controls t pMn between 100 nm and 450 nm, and t pSi between 100 nm and 450 nm.
  • a mass percentage peak value of Fe element Fe p is ⁇ 85%, and a mass percentage peak value of Fe element Fe p is located within a depth range of 0-t pSi from the surface of the steel plate, wherein t pSi represents a depth position where a mass percentage peak value of Si element Si p appears.
  • Fe p refers to a mass percentage peak value of Fe element with a depth in the range of 0-t pSi from the surface of the steel plate.
  • a cold-rolled high-strength steel plate with excellent phosphating performance of the present invention comprises a base layer, a surface layer and a transition layer between the base layer and the surface layer in the thickness direction; wherein a microstructure of the surface layer is ferrite.
  • a thickness of the surface layer is 50-500 nm.
  • the thickness of the surface layer i.e., the ferrite layer
  • the thickness of the surface layer is 50-500 nm
  • a mass percentage peak value of Mn Mn p and a mass percentage peak value of Si element Si p are located at a depth t p of 50-500 nm, on the element mass percentage content-depth distribution curve detected by glow discharge optical emission spectroscopy (GDOES).
  • GDOES glow discharge optical emission spectroscopy
  • the Mn and Si elements that diffuse outward from the matrix during annealing are primarily enriched in a transition layer.
  • the ferrite surface layer can effectively prevent alloying elements such as Mn and Si from diffusing to the surface of the ferrite, thereby ensuring that a mass percentage peak value of Mn Mn p and a mass percentage peak value of Si Si p are located at a depth t p of 50-500 nm, on the element mass percentage content-depth distribution curve detected by glow discharge optical emission spectroscopy (GDOES).
  • GDOES glow discharge optical emission spectroscopy
  • a microstructure of the base layer is martensite + ferrite, or martensite + ferrite + residual austenite.
  • the transition layer comprises oxides of Mn, Si, and Fe and/or composite oxides of Mn, Si, and Fe.
  • Oxides of Mn, Si, and Fe refer to oxides of Mn, oxides of Si, or oxides of Fe.
  • Composite oxides of Mn, Si, and Fe refer to oxides of two or three elements of Mn, Si, and Fe.
  • the oxides of Mn, Si and Fe are at least one of the following: MnO, MnO 2 , SiO 2 , FeO, Fe 2 O 3 and Fe 3 O 4 ;
  • the composite oxides of Mn, Si and Fe are at least one of the following: MnSiO 3 , Mn 2 SiO 4 , Mn 2 FeO 3 , Mn 2 FeO 4 , FeSiO 3 , Fe 2 SiO 3 and Fe 2 SiO 4 .
  • a cold-rolled high-strength steel plate with excellent phosphating performance of the present invention has a tensile strength of ⁇ 780 MPa. Further, a cold-rolled high-strength steel plate with excellent phosphating performance of the present invention has a tensile strength of ⁇ 980 MPa. Further, a cold-rolled high-strength steel plate with excellent phosphating performance of the present invention has a tensile strength of ⁇ 1180 MPa.
  • a cold-rolled high-strength steel sheet with excellent phosphating performance of the present invention comprises the following elements with mass percentages as follows: C: 0.07-0.30%, Si: 0.07-3.0%, Mn: 1.5-5.0%.
  • the mass percentages of each chemical elements of a cold-rolled high-strength steel sheet with excellent phosphating performance of the present invention are as follows: C: 0.07-0.30%, Si: 0.07-3.0%, Mn: 1.5-5.0%, and one or more of Nb, Ti, Al, B, Cr, Mo, Ni, and V, with a total mass percentage of Nb, Ti, Al, B, Cr, Mo, Ni, and V being less than or equal to 2.0%; and a balance of Fe and inevitable impurities.
  • the inevitable impurities are mainly S and P, and their contents are expected to be as low as possible.
  • P can be controlled to be ⁇ 0.05% and S can be controlled to be ⁇ 0.02%.
  • C Carbon is a solid solution strengthening element necessary for ensuring strength in steel.
  • the C content of the present invention is controlled at 0.07-0.30%.
  • Si Silicon has an effect of improving both the strength and formability of the steel, but when the Si content is too high, the difficulty of production and manufacturing increases. Therefore, the Si content of the present invention is controlled at 0.07-3.0%.
  • Mn Manganese is an element that increases the stability of austenite, has the effect of reducing the critical cooling rate during quenching of steel and improving the hardenability of steel. Mn can also improve the work hardening performance of steel, thereby increasing the strength of steel. Therefore, the Mn content of the present invention is controlled at 1.5-5.0%.
  • Nb, Ti, Al, B, Cr, Mo, Ni, and V elements have the effects of solid solution strengthening, refining microstructure, and improving hardenability. Adding a small amount helps to further improve the strength and toughness of steel. Therefore, the present invention may also comprise one or more of Nb, Ti, Al, B, Cr, Mo, Ni, and V elements, and their total amount by mass percentage is controlled to be less than or equal to 2.0%.
  • the content of Nb when present, the content of Nb may be 0.01-0.1%, the content of Ti may be 0.01-0.05%, the content of Al may be 0.01-1.5%, the content of B may be 0.0002-0.0008%, the content of Cr may be 0.01-0.5%, the content of Mo may be 0.1-0.3%, the content of Ni may be 0.0001-0.03%, and the content of Ni may be 0.01-0.1%.
  • Another object of the present invention is to provide a manufacturing method for the cold-rolled high-strength steel plate with excellent phosphating performance.
  • the manufacturing method adopts a unique continuous annealing process to control the enrichment position and enrichment amount of the Mn and Si elements in the steel plate, thereby achieving excellent phosphating performance.
  • the present invention provides a manufacturing method for the above cold-rolled high-strength steel sheet with excellent phosphating performance, comprising the following steps of: smelting, casting, hot rolling, pickling, cold rolling, and continuous annealing; wherein, in the continuous annealing step, a first-stage heating is performed to the cold-rolled sheet in an oxidizing atmosphere, then a second-stage heating and soaking are performed in a reducing atmosphere, followed by cooling and coiling.
  • the purpose of adopting an oxidizing atmosphere in the first-stage heating is to form iron oxide on the surface of the steel plate during the first-stage heating process
  • the purpose of adopting a reducing atmosphere in the second-stage heating and soaking is to reduce the iron oxide formed during the first-stage heating process to form ferrite, thereby forming a surface layer composed entirely of ferrite, so that Mn and Si elements cannot be enriched on the surface of the steel plate.
  • the oxidizing atmosphere of the first-stage heating is obtained by controlling the air-fuel ratio of the direct-fired furnace to be 0.95-1.05.
  • an oxidizing atmosphere can be achieved by adjusting the air-fuel ratio.
  • the air-fuel ratio is less than 0.95, oxidation is insufficient; when the air-fuel ratio is greater than 1.05, excessive oxidation occurs. Therefore, the air-fuel ratio is controlled to be 0.95-1.05.
  • the oxidizing atmosphere of the first-stage heating is a mixture gas of N 2 and O 2 , wherein the volume percentage of O 2 is 0.01-1%.
  • an oxidizing atmosphere is achieved by using a mixed gas of N 2 and O 2 .
  • the volume percentage of O 2 is less than 0.01%, oxidation is insufficient; when the volume percentage of O 2 is greater than 1%, further increasing O 2 will lead to excessive oxidation. Therefore, the volume percentage of O 2 is controlled to be 0.01-1%.
  • the heating rate of the first-stage heating is 1-50 °C/s
  • the first-stage heating is heating from room temperature to T 1
  • T 1 and the mass percentage of Si satisfy: 570 + 4000xSi ⁇ T 1 ⁇ 600 + 9000 ⁇ Si.
  • the thickness of the oxide layer on the surface of the steel plate will increase as the end temperature T 1 of the first-stage heating increases. Therefore, in order to obtain an appropriate thickness of an oxide layer, the upper and lower limits of the T 1 temperature need to be controlled.
  • the inventors found that, when the T 1 temperature is the same, the thickness of the iron oxide on the surface of the steel plate is also affected by a composition of a steel plate, with the Si content having the most significant influence. When the Si content in a steel plate is relatively high, a higher T 1 temperature is required to obtain the iron oxide with same thickness during the first-stage heating.
  • T 1 temperature and the Si content of a steel plate satisfy the following relationship: 570 + 4000 ⁇ Si ⁇ T 1 ⁇ 600 + 9000 ⁇ Si.
  • T 1 is 580 °C - 800 °C.
  • the thickness of an oxide layer formed during the first-stage heating is 50-500 nm.
  • a dew point of the oxidizing atmosphere of the first-stage heating is ⁇ -50°C, preferably ⁇ -40°C. In some embodiments, a dew point of the oxidizing atmosphere of the first-stage heating is between -50°C and 50°C. In some embodiments, a dew point of the oxidizing atmosphere of the first-stage heating is between -50 °C and 0 °C.
  • a dew point of the reducing atmosphere of the second-stage heating and soaking is ⁇ 10 °C, such as ⁇ 0 °C, ⁇ -10°C or ⁇ -20°C.
  • a dew point of the reducing atmosphere of the second-stage heating and soaking is 10 °C to -50 °C, such as 0 °C to -50 °C or -20 °C to -50 °C.
  • a dew point of the atmosphere of the first-stage heating, the second-stage heating and soaking is not a necessary technical feature of this case.
  • a product characteristic of a mass percentage peak value of Mn Mn p ⁇ 10.0% and a mass percentage peak value of Si Si p ⁇ 4.0% on an element mass percentage content-depth distribution curve with a depth in the range of 0-1000 nm from the surface of the steel plate can be obtained.
  • the present invention differs from existing techniques, which promote the internal oxidation of alloy elements and reduce external oxidation by increasing the dew point of reducing atmosphere.
  • a dew point of the oxidizing atmosphere of the first-stage heating is beneficial for lowering the T 1 temperature. This is because, increasing the dew point of the atmosphere during the first-stage heating will increase the internal oxidation of alloying elements, thereby reducing oxidation of alloying elements at the interface of iron oxide/substrate, especially the oxidation of Si element. Therefore, preferably, a dew point of the oxidizing atmosphere of the first-stage heating is controlled to be ⁇ -40 °C. Since an excessively high dew point of the second-stage heating and soaking can lead to decarburization, preferably, a dew point of the atmosphere of the second-stage heating and soaking is controlled to be ⁇ -20 °C.
  • the reducing atmosphere of the second-stage heating and soaking is a mixture gas of N 2 and H 2 , wherein the volume percentage of H 2 is 0.5-20%.
  • the heating rate of the second-stage heating is 1-20 °C/s
  • the second-stage heating is heated from T 1 to a soaking temperature of 720-920 °C
  • a soaking time is 30-200 s.
  • the soaking temperature T 2 is controlled to be 720-920 °C, and the soaking time is controlled to be 30-200 s, mainly to obtain an appropriate mechanical property of a cold-rolled high-strength steel, which has little correlation with the phosphating performance.
  • the cold-rolled high-strength steel plate with excellent phosphating performance of the present invention has the following beneficial effects:
  • the present invention solves the problem of poor phosphating performance of cold-rolled high-strength steel by controlling the mass percentage peak values of Mn and Si and their depth positions on an element mass percentage content-depth distribution curve of a steel plate, thereby improving the coating performance of a cold-rolled high-strength steel.
  • Table 1 lists the composition ratios of the steel grades adopted in each example and comparative example of the present invention.
  • Table 1 (wt%, with a balance of Fe) Steel plate code C Si Mn P S Al Nb Ti B Cr Mo V Ni A 0.08 0.4 2.2 0.012 0.002 - 0.04 0.03 - - - - - B 0.2 1.8 2.3 0.007 0.001 0.03 - 0.02 - - - - - C 0.07 0.07 2.1 0.010 0.0008 0.6 - 0.01 0.0006 - - - D 0.13 0.26 2.4 0.011 0.0017 - - - - 0.4 - - - E 0.22 1.8 2.8 0.014 0.0014 0.03 - 0.02 - - - - - F 0.11 1.2 1.5 0.006 0.0007 - - - - - - - G 0.3 3 3 0.022 0.005 1.5 - - - - - - -
  • the oxidizing atmosphere of the first-stage heating is a mixture gas of N 2 and O 2 , wherein the volume percentage of O 2 is 0.01-1%.
  • the dew point of the oxidizing atmosphere of the first-stage heating is ⁇ -40 °C
  • the dew point of the reducing atmosphere of the second-stage heating is ⁇ -20 °C.
  • the heating rate of the second-stage heating is 1-20 °C/s
  • the second-stage heating is heated from T 1 to a soaking temperature of 720-920 °C
  • a soaking time is 30-200 s.
  • examples with an air-fuel ratio indicated by "/” indicate that the oxidizing atmosphere adopted in these examples is a mixed gas of N 2 and O 2 .
  • the air-fuel ratio and oxygen content of Comparative Examples A1-A4, D1-D2, E1-E3, F1, and G1-G2 are all indicated by “/”, indicating that no oxidizing atmosphere is used in the first-stage heating in these comparative examples.
  • the codes "A,” “B,” ..., “H,” and “I” of each example and comparative example in Table 2 indicate that the composition of the steel plate corresponding to the code in Table 1 is used.
  • Table 3 lists the characteristics of the steel plates of each example and comparative example produced using the compositions of the steel plates of A-I and the process parameters listed in Table 2, as well as the phosphating performance corresponding to each steel plate, wherein Mn p , Si p , t pSi , t pMn , and Fe p are detected by GDOES.
  • Table 3 No. Mn p Si p t pMn t pSi Fe p phosphating performance mass% mass% nm nm mass% Ex. A1 6.4 1.2 224 228 87.5 ⁇ Ex. A2 8.2 0.8 272 275 92.0 ⁇ Ex. A3 7.2 1 420 427 85.0 ⁇ Ex.
  • Figures 1, 2 , and 3 respectively show the element mass percentage content-depth distribution curves of Mn, Si, and Fe with a depth in the range of 0-1000 nm from the surface of the steel plate of Example A1 and Comparative Example A1.
  • the characteristic values Mn p , Si p , Fe p , and t p are marked on the curves.
  • t p in Figure 1 represents t pMn
  • t p in Figure 2 represents t pSi
  • t p in Figure 3 represents t pSi .
  • Example A1 undergoes the first-stage heating in an oxidizing atmosphere, while it is heated to 580 °C at a heating rate of 10 °C/s.
  • the oxidizing atmosphere is a mixture gas of N 2 and O 2 , wherein a volume percentage of O 2 is 0.2%, and a dew point is -50 °C.
  • the second-stage heating and soaking are carried out in a reducing atmosphere, wherein a heating rate is 4 °C/s, a soaking temperature is 820 °C, and a soaking time is 100 s.
  • the reducing atmosphere in the second-stage heating and soaking is a mixture gas of N 2 and H 2 , wherein a volume percentage of H 2 is 2%, and a dew point of the atmosphere is -50 °C.
  • GDOES is used to detect the element depth distribution on a surface of an annealed steel plate, and the element mass percentage content-depth distribution curves of Mn, Si, and Fe with a depth in the range of 0-1000 nm as shown in Figures 1 to 3 are obtained.
  • Comparative Example A1 undergoes the first-stage heating, the second-stage heating and soaking in a reducing atmosphere, with a heating rate, a temperature and a time all being the same as those of Example A1.
  • the element mass percentage content-depth distribution curves of Mn, Si, and Fe with a depth in the range of 0-1000 nm from a surface of Comparative Example A1 after annealing are shown in Figures 1 to 3 .
  • Example A1 and Comparative Example A1 are subjected to phosphating treatment under the same conditions.
  • the phosphating film on the surface of Example A1 is uniform and dense, and the phosphating performance meets the requirements (in Table 2-2 indicated by "o").
  • the phosphating film on the surface of Comparative Example A1 is sparse, with a large area not covered by the phosphating film, and the phosphating performance does not meet the requirements (in Table 2-2 indicated by " ⁇ ").
  • phosphating performance is judged by observing the phosphating film on the surface of the steel plate after phosphating treatment.
  • a coverage rate of the phosphating film is 100%, a size of phosphating crystals is less than 12 microns, and a weight of the phosphating film is more than 2 g/m 2 , indicating that the phosphate performance meets the requirements.
  • Phosphating treatment is carried out using commercially available treatment agents. The specific steps and processes are as follows: (1) pre-degreasing spray: 45-55 °C, 1 min; (2) degreasing spray: 45-55 °C, 2.0 min; (3) second water cleaning spray: room temperature, 1 min; (4) surface conditioning spray: room temperature, 1 min; (5) phosphating spray: 50-60 °C, 2.0 min; (6) water cleaning spray: room temperature, 1 min; (7) Drying.
  • Figures 4 , 5, and 6 respectively show the mass percentage content-depth distribution curves of Mn, Si, and Fe elements with a depth in the range of 0-1000 nm from the surface of the steel plate of Example B1 and Comparative Example B1.
  • the characteristic values Mn p , Si p , Fe p , and t p are marked on the curves.
  • t p in Figure 4 represents t pMn
  • t p in Figure 5 represents t pSi
  • t p in Figure 6 represents t pSi .
  • Example B1 undergoes the first-stage heating in an oxidizing atmosphere, while it is heated to 650°C at a heating rate of 50 °C/s.
  • the oxidizing atmosphere is achieved by a direct-fired heating furnace, with an air-fuel ratio of 0.95 and a dew point of 50 °C.
  • the second-stage heating and soaking are carried out in a reducing atmosphere, wherein a heating rate is 5 °C/s, a soaking temperature is 870 °C, and a soaking time is 180 s.
  • the atmosphere of the second-stage heating and soaking is a mixed gas of N 2 and H 2 , wherein a volume percentage of H 2 is 2%, and a dew point of the atmosphere is -40 °C.
  • GDOES is used to detect the element depth distribution on a surface of an annealed steel plate, and the element mass percentage content-depth distribution curves of Mn, Si, and Fe with a depth in the range of 0-1000 nm as shown in Figures 4 to 6 are obtained.
  • the sample of Example B1 is subjected to phosphating treatment, the phosphating film is uniform and dense, and the phosphating performance meets the requirements.
  • Comparative Example B1 undergoes the first-stage heating, the second-stage heating and soaking in a reducing atmosphere.
  • the reducing atmosphere is a mixed gas of N 2 and H 2 , wherein a volume percentage of H 2 is 2% and a dew point of the atmosphere is -20 °C.
  • the soaking temperature and soaking time are the same as those of Example B1.
  • the element mass percentage content-depth distribution curves of Mn, Si, and Fe with a depth in the range of 0-1000 nm from the surface of the steel plate after annealing of Comparative Example B1 are shown in Figures 4-6 .
  • the sample of Comparative Example B1 is subjected to phosphating treatment, and the phosphating film is uneven and non-dense, with some local positions not covered by the phosphating film, thus the phosphating performance did not meet the requirements.
  • the inventors also adapt the method of using scanning electron microscopy to observe the cross-sectional metallography after erosion by nitric acid alcohol solution to detect the microstructures of each example and comparative example.
  • Cross-sectional transmission electron microscopy samples of the surface layer and transition layer are prepared using a focused ion beam microscope. The thickness of the surface layer is measured and the types of oxides in the transition layer are analyzed under a transmission electron microscope, and the test results are listed in Table 4.
  • Table 4 No. Thickness of surface layer (nm) Microstructure of surface layer Microstructure of base layer Oxides of Mn, Si, Fe and/or composite oxides of Mn, Si, Fe in the transition layer Ex.
  • a cold-rolled steel plate manufactured by the present invention exhibits excellent phosphating performance while also having relatively high strength.

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Abstract

Disclosed in the present invention is a cold-rolled high-strength steel plate with excellent phosphating performance. On the element mass percentage content-depth distribution curve with a depth in the range of 0-1000 nm from the surface of the steel plate, the Mn mass percentage peak Mnp is less than or equal to 10.0%, the Si mass percentage peak Sip is less than or equal to 4.0%, and the Mn mass percentage peak Mnp and the Si mass percentage peak Sip are both located at a depth position greater than or equal to 50 nm from the surface of the steel plate. Correspondingly, further disclosed in the present invention is a manufacturing method for the cold-rolled high-strength steel plate, and a unique continuous annealing process is used in the manufacturing method.

Description

    Technical Field
  • The present invention relates to a steel plate and a manufacturing method therefor, and particularly relates to a cold-rolled steel plate and a manufacturing method therefor.
    • Background Art
  • High-strength steel is a material that is being used more and more widely at present. Cold-rolled high-strength steel usually requires an addition of relatively high contents of alloying elements such as C, Si, Mn, Cr, and Al, combined with the continuous annealing process and phase transformation strengthening to achieve certain strength and formability.
  • Phosphating is a pretreatment process before automotive electrophoretic coating. By immersing a steel plate or a part made of a steel plate in phosphating solution, a layer of insoluble phosphating film is formed on the surface of the steel plate or the part, thereby improving the adhesion of the paint film.
  • However, when using continuous annealing to produce cold-rolled high-strength steel, alloying elements such as Si and Mn in the steel can form external oxidation on a surface of a strip steel after annealing. The external oxidation of Si and Mn on the surface of a steel plate can affect the nucleation and growth of the phosphating film, thereby affecting the coating quality of automotive parts. Therefore, in recent years, the phosphating performance of high-strength steel has gradually attracted attention.
  • For example, the Chinese patent application with publication number CN107419185A, publication date December 1, 2017 , and titled "A Cold-rolled Steel Plate with Good Phosphating Performance and Production Method Therefor" mainly produces a cold-rolled plate with good phosphating performance by precisely controlling the composition, and simultaneously through hot rolling, pickling, five-stand full six-roller cold rolling, continuous annealing, and leveling process.
  • For another example, the Chinese patent application with publication number CN111910123A, publication date November 10, 2020 , and titled "Cold-Rolled Continuous Annealing Ultra-High Strength Steel with Good Phosphating Performance and Preparation Method Therefor" discloses an annealing process for obtaining good phosphating performance of cold-rolled continuously annealing ultra-high strength steel. It specifies that a H2 content of an annealing atmosphere is 6% to 15%, a dew point is -45 °C to -41 °C, and an oxygen content is 2 ppm to 5 ppm, whose purpose is to inhibit the selective oxidation of alloying elements through the above parameters, thereby achieving good phosphating performance.
  • It can be seen from this that in the prior art, controlling the content of alloying elements is a method for obtaining excellent phosphating performance, but limiting the content of alloy elements will affect the properties of the material.
  • In addition, controlling the annealing atmosphere is another method for improving the phosphating performance of a cold-rolled steel plate with high alloy content. However, a method of controlling both dew point and oxygen content at a relatively low level is rather difficult and costly; while a method of controlling a dew point at a relatively high level will cause decarburization on the surface of a steel plate, therefore this method also has certain limitations.
  • Based on this, it is desired to provide a novel cold-rolled high-strength steel plate that achieves excellent phosphating performance.
    • Summary
  • One object of the present invention is to provide a cold-rolled high-strength steel plate with excellent phosphating performance, which achieves excellent phosphating performance by controlling Mn and Si elements not enriching on the surface of the steel plate.
  • Based on the above-mentioned object, the present invention provides a cold-rolled high-strength steel plate with excellent phosphating performance, wherein, on an element mass percentage content-depth distribution curve with a depth in the range of 0-1000 nm from the surface of the steel plate, a mass percentage peak value of Mn element Mnp is ≤10.0%, and a mass percentage peak value of Si Sip is ≤4.0%, and both the mass percentage peak value of Mn element Mnp and the mass percentage peak value of Si element Sip are located at a depth of ≥50 nm from the surface of the steel plate. Herein, a mass percentage peak value of Mn element Mnp and a mass percentage peak value of Si element Sip are detected by glow discharge optical emission spectroscopy (GDOES).
  • In the present invention, the key to achieving excellent phosphating performance of a cold-rolled high-strength steel is that on an element mass percentage content-depth distribution curve with a depth in the range of 0-1000 nm from a surface layer of a steel plate detected by glow discharge optical emission spectroscopy (GDOES), a mass percentage peak value of Mn Mnp is ≤ 10.0%, and a mass percentage peak value of Si Sip is ≤ 4.0%. This is because in a cold-rolled high-strength steel produced through continuous annealing, alloying elements, such as Mn and Si, form external oxidation on the annealed steel plate, and the Si and Mn elements will be significantly enriched on the surface. The mass percentage peak values of Mn or Si on the surface of the steel plate can reach several to dozens of times that of the matrix Mn or Si. These oxides will hinder the reaction between the phosphating solution and the steel plate, thereby affecting the phosphating performance of the high-strength steel.
  • Through research, the inventors have found that when a mass percentage peak value of Mn Mnp exceeds 10% or a mass percentage peak value of Si Sip exceeds 4%, on an element mass percentage content-depth distribution curve with a depth in the range of 0-1000 nm from a surface layer of a steel plate, the phosphating performance of a steel plate is poor. Therefore, the present invention controls Mnp ≤ 10% and Sip ≤ 4%. In some embodiments, the present invention controls Mnp ≤ 8.5% and Sip ≤ 3.0%. In some embodiments, Mnp is between 5.0 and 10.0%, and Sip is between 0.1 and 3.0%.
  • To achieve excellent phosphating performance, the present invention controls a depth of Mnp tpMn to ≥ 50 nm and a depth of Sip tpSi to ≥ 50 nm. This is because through research the inventors have found that when a depth of Mnp and a depth of Sip are less than 50 nm, even if Mnp is ≤ 10% or Sip is ≤ 4%, external oxidation of Si and Mn at local positions cannot be avoided, and the local phosphating performance is poor.
  • Further, in the cold-rolled high-strength steel plate with excellent phosphating performance of the present invention, the mass percentage peak value of Mn element Mnp and the mass percentage peak value of Si element Sip are located at a depth of 50-500 nm from the surface of the steel plate.
  • Although the phosphating performance of a cold-rolled high-strength steel is also excellent when tpMn is > 500 nm and tpSi is> 500 nm, achieving these values requires a higher pre-oxidation temperature and a longer pre-oxidation time. Therefore, a preferred tpMn of the present invention is ≤ 500 nm, and tpSi is ≤ 500 nm. In some embodiments, the present invention controls tpMn between 100 nm and 450 nm, and tpSi between 100 nm and 450 nm.
  • Further, in the cold-rolled high-strength steel plate with excellent phosphating performance of the present invention, on an element mass percentage content-depth distribution curve with a depth in the range of 0-1000 nm from the surface of the steel plate, a mass percentage peak value of Fe element Fep is ≥85%, and a mass percentage peak value of Fe element Fep is located within a depth range of 0-tpSi from the surface of the steel plate, wherein tpSi represents a depth position where a mass percentage peak value of Si element Sip appears. In the present invention, Fep refers to a mass percentage peak value of Fe element with a depth in the range of 0-tpSi from the surface of the steel plate.
  • When Fep is ≥85%, it can be ensured that during the phosphating process of a cold-rolled high-strength steel, there is sufficient Fe on the surface to react with the phosphating solution, thereby achieving excellent phosphating performance.
  • Further preferably, when Fep is ≥90%, the phosphating performance is even better.
  • Further, a cold-rolled high-strength steel plate with excellent phosphating performance of the present invention comprises a base layer, a surface layer and a transition layer between the base layer and the surface layer in the thickness direction; wherein a microstructure of the surface layer is ferrite.
  • Further, in a cold-rolled high-strength steel plate with excellent phosphating performance of the present invention, a thickness of the surface layer is 50-500 nm.
  • When the thickness of the surface layer, i.e., the ferrite layer, is 50-500 nm, it can be ensured that a mass percentage peak value of Mn Mnp and a mass percentage peak value of Si element Sip are located at a depth tp of 50-500 nm, on the element mass percentage content-depth distribution curve detected by glow discharge optical emission spectroscopy (GDOES).
  • In a high-strength steel with excellent phosphating performance of the present invention, when a thickness of a surface layer is 50-500 nm, the Mn and Si elements that diffuse outward from the matrix during annealing are primarily enriched in a transition layer. The ferrite surface layer can effectively prevent alloying elements such as Mn and Si from diffusing to the surface of the ferrite, thereby ensuring that a mass percentage peak value of Mn Mnp and a mass percentage peak value of Si Sip are located at a depth tp of 50-500 nm, on the element mass percentage content-depth distribution curve detected by glow discharge optical emission spectroscopy (GDOES).
  • Further, in a cold-rolled high-strength steel plate with excellent phosphating performance of the present invention, a microstructure of the base layer is martensite + ferrite, or martensite + ferrite + residual austenite.
  • Further, in a cold-rolled high-strength steel plate with excellent phosphating performance of the present invention, the transition layer comprises oxides of Mn, Si, and Fe and/or composite oxides of Mn, Si, and Fe. Oxides of Mn, Si, and Fe refer to oxides of Mn, oxides of Si, or oxides of Fe. Composite oxides of Mn, Si, and Fe refer to oxides of two or three elements of Mn, Si, and Fe.
  • Furthermore, the oxides of Mn, Si and Fe are at least one of the following: MnO, MnO2, SiO2, FeO, Fe2O3 and Fe3O4; the composite oxides of Mn, Si and Fe are at least one of the following: MnSiO3, Mn2SiO4, Mn2FeO3, Mn2FeO4, FeSiO3, Fe2SiO3 and Fe2SiO4.
  • Further, a cold-rolled high-strength steel plate with excellent phosphating performance of the present invention has a tensile strength of ≥ 780 MPa. Further, a cold-rolled high-strength steel plate with excellent phosphating performance of the present invention has a tensile strength of ≥ 980 MPa. Further, a cold-rolled high-strength steel plate with excellent phosphating performance of the present invention has a tensile strength of ≥ 1180 MPa.
  • There are no special restrictions on the type and elemental composition of a cold-rolled high-strength steel in this application. Various cold-rolled high-strength steels known in the art are prepared by the method of the present invention, thereby having the structure (such as the element distribution described herein) and phosphating performance described herein.
  • In some embodiments, a cold-rolled high-strength steel sheet with excellent phosphating performance of the present invention comprises the following elements with mass percentages as follows:
    C: 0.07-0.30%, Si: 0.07-3.0%, Mn: 1.5-5.0%.
  • Furthermore, the mass percentages of each chemical elements of a cold-rolled high-strength steel sheet with excellent phosphating performance of the present invention are as follows:
    C: 0.07-0.30%, Si: 0.07-3.0%, Mn: 1.5-5.0%, and one or more of Nb, Ti, Al, B, Cr, Mo, Ni, and V, with a total mass percentage of Nb, Ti, Al, B, Cr, Mo, Ni, and V being less than or equal to 2.0%; and a balance of Fe and inevitable impurities.
  • The inevitable impurities are mainly S and P, and their contents are expected to be as low as possible. In some embodiments, P can be controlled to be ≤ 0.05% and S can be controlled to be ≤ 0.02%.
  • The design principles of the above elements are as follows:
    C: Carbon is a solid solution strengthening element necessary for ensuring strength in steel. When the C content is too low, the strength of the steel is relatively low, while when the C content is too high, the weldability of the steel is poor. Therefore, the C content of the present invention is controlled at 0.07-0.30%.
  • Si: Silicon has an effect of improving both the strength and formability of the steel, but when the Si content is too high, the difficulty of production and manufacturing increases. Therefore, the Si content of the present invention is controlled at 0.07-3.0%.
  • Mn: Manganese is an element that increases the stability of austenite, has the effect of reducing the critical cooling rate during quenching of steel and improving the hardenability of steel. Mn can also improve the work hardening performance of steel, thereby increasing the strength of steel. Therefore, the Mn content of the present invention is controlled at 1.5-5.0%.
  • Nb, Ti, Al, B, Cr, Mo, Ni, and V elements have the effects of solid solution strengthening, refining microstructure, and improving hardenability. Adding a small amount helps to further improve the strength and toughness of steel. Therefore, the present invention may also comprise one or more of Nb, Ti, Al, B, Cr, Mo, Ni, and V elements, and their total amount by mass percentage is controlled to be less than or equal to 2.0%. In some embodiments, when present, the content of Nb may be 0.01-0.1%, the content of Ti may be 0.01-0.05%, the content of Al may be 0.01-1.5%, the content of B may be 0.0002-0.0008%, the content of Cr may be 0.01-0.5%, the content of Mo may be 0.1-0.3%, the content of Ni may be 0.0001-0.03%, and the content of Ni may be 0.01-0.1%.
  • Another object of the present invention is to provide a manufacturing method for the cold-rolled high-strength steel plate with excellent phosphating performance. The manufacturing method adopts a unique continuous annealing process to control the enrichment position and enrichment amount of the Mn and Si elements in the steel plate, thereby achieving excellent phosphating performance.
  • Based on the above object, the present invention provides a manufacturing method for the above cold-rolled high-strength steel sheet with excellent phosphating performance, comprising the following steps of: smelting, casting, hot rolling, pickling, cold rolling, and continuous annealing; wherein, in the continuous annealing step, a first-stage heating is performed to the cold-rolled sheet in an oxidizing atmosphere, then a second-stage heating and soaking are performed in a reducing atmosphere, followed by cooling and coiling.
  • In the manufacturing method of the present invention, smelting, casting, hot rolling, pickling and cold rolling all adopt existing conventional processes. In an exemplary method, in the hot rolling step, a heating temperature is controlled to be 1150-1260 °C, a start temperature of the finishing rolling is 1100-1220 °C, and a final temperature of the finishing rolling is 900-950 °C. In the cold rolling step, a cold rolling reduction ratio is controlled to be ≥50%. In some embodiments, commercially available cold-rolled steel can be used to implement the annealing process of the present application.
  • In the continuous annealing step, the purpose of adopting an oxidizing atmosphere in the first-stage heating is to form iron oxide on the surface of the steel plate during the first-stage heating process, and the purpose of adopting a reducing atmosphere in the second-stage heating and soaking is to reduce the iron oxide formed during the first-stage heating process to form ferrite, thereby forming a surface layer composed entirely of ferrite, so that Mn and Si elements cannot be enriched on the surface of the steel plate.
  • Further, in some embodiments of the manufacturing method of the present invention, the oxidizing atmosphere of the first-stage heating is obtained by controlling the air-fuel ratio of the direct-fired furnace to be 0.95-1.05.
  • In some embodiments, when the first-stage heating is performed using a direct-fired furnace, an oxidizing atmosphere can be achieved by adjusting the air-fuel ratio. When the air-fuel ratio is less than 0.95, oxidation is insufficient; when the air-fuel ratio is greater than 1.05, excessive oxidation occurs. Therefore, the air-fuel ratio is controlled to be 0.95-1.05.
  • Further, in other embodiments of the manufacturing method of the present invention, the oxidizing atmosphere of the first-stage heating is a mixture gas of N2 and O2, wherein the volume percentage of O2 is 0.01-1%.
  • In other embodiments, when the first-stage heating is performed using an infrared radiation furnace, an oxidizing atmosphere is achieved by using a mixed gas of N2 and O2. When the volume percentage of O2 is less than 0.01%, oxidation is insufficient; when the volume percentage of O2 is greater than 1%, further increasing O2 will lead to excessive oxidation. Therefore, the volume percentage of O2 is controlled to be 0.01-1%.
  • Further, in the manufacturing method of the present invention, the heating rate of the first-stage heating is 1-50 °C/s, the first-stage heating is heating from room temperature to T1, and T1 and the mass percentage of Si satisfy: 570 + 4000xSi ≤ T1 ≤ 600 + 9000×Si.
  • The thickness of the oxide layer on the surface of the steel plate will increase as the end temperature T1 of the first-stage heating increases. Therefore, in order to obtain an appropriate thickness of an oxide layer, the upper and lower limits of the T1 temperature need to be controlled. Through research, the inventors found that, when the T1 temperature is the same, the thickness of the iron oxide on the surface of the steel plate is also affected by a composition of a steel plate, with the Si content having the most significant influence. When the Si content in a steel plate is relatively high, a higher T1 temperature is required to obtain the iron oxide with same thickness during the first-stage heating. An appropriate thickness of an oxide layer can be obtained when the T1 temperature and the Si content of a steel plate satisfy the following relationship: 570 + 4000 × Si ≤ T1 ≤ 600 + 9000 × Si. In some embodiments, T1 is 580 °C - 800 °C. Preferably, the thickness of an oxide layer formed during the first-stage heating is 50-500 nm.
  • Further, in the manufacturing method of the present invention, a dew point of the oxidizing atmosphere of the first-stage heating is ≥ -50°C, preferably ≥ -40°C. In some embodiments, a dew point of the oxidizing atmosphere of the first-stage heating is between -50°C and 50°C. In some embodiments, a dew point of the oxidizing atmosphere of the first-stage heating is between -50 °C and 0 °C.
  • Further, in the manufacturing method of the present invention, a dew point of the reducing atmosphere of the second-stage heating and soaking is ≤ 10 °C, such as ≤0 °C, ≤-10°C or ≤-20°C. In some embodiments, a dew point of the reducing atmosphere of the second-stage heating and soaking is 10 °C to -50 °C, such as 0 °C to -50 °C or -20 °C to -50 °C.
  • It should be particularly noted here that, in the present invention, a dew point of the atmosphere of the first-stage heating, the second-stage heating and soaking is not a necessary technical feature of this case. In other words, even without special control over the dew point of the atmosphere of the first-stage heating, the second-stage heating and soaking, a product characteristic of a mass percentage peak value of Mn Mnp ≤ 10.0% and a mass percentage peak value of Si Sip ≤ 4.0% on an element mass percentage content-depth distribution curve with a depth in the range of 0-1000 nm from the surface of the steel plate can be obtained. This is because, during the first-stage heating, when iron oxide is formed, some Mn in the matrix oxidizes along with Fe, but the oxides formed by Si are primarily located in the transition layer. During the second-stage heating and soaking, when the reduced iron is reduced, regardless of the atmosphere's dew point, the selective oxidation of alloying elements such as Mn and Si in the matrix is primarily concentrated below the ferrite formed after the iron oxide is reduced, i.e., in the transition layer, and does not enrich on the surface of ferrite. Therefore, the present invention differs from existing techniques, which promote the internal oxidation of alloy elements and reduce external oxidation by increasing the dew point of reducing atmosphere.
  • However, the inventors have found that increasing the dew point of the oxidizing atmosphere of the first-stage heating is beneficial for lowering the T1 temperature. This is because, increasing the dew point of the atmosphere during the first-stage heating will increase the internal oxidation of alloying elements, thereby reducing oxidation of alloying elements at the interface of iron oxide/substrate, especially the oxidation of Si element. Therefore, preferably, a dew point of the oxidizing atmosphere of the first-stage heating is controlled to be ≥ -40 °C. Since an excessively high dew point of the second-stage heating and soaking can lead to decarburization, preferably, a dew point of the atmosphere of the second-stage heating and soaking is controlled to be ≤ -20 °C.
  • Further, in the manufacturing method of the present invention, the reducing atmosphere of the second-stage heating and soaking is a mixture gas of N2 and H2, wherein the volume percentage of H2 is 0.5-20%.
  • Further, in the manufacturing method of the present invention, the heating rate of the second-stage heating is 1-20 °C/s, the second-stage heating is heated from T1 to a soaking temperature of 720-920 °C, and a soaking time is 30-200 s.
  • The soaking temperature T2 is controlled to be 720-920 °C, and the soaking time is controlled to be 30-200 s, mainly to obtain an appropriate mechanical property of a cold-rolled high-strength steel, which has little correlation with the phosphating performance.
  • The cold-rolled high-strength steel plate with excellent phosphating performance of the present invention has the following beneficial effects:
    The present invention solves the problem of poor phosphating performance of cold-rolled high-strength steel by controlling the mass percentage peak values of Mn and Si and their depth positions on an element mass percentage content-depth distribution curve of a steel plate, thereby improving the coating performance of a cold-rolled high-strength steel.
  • In some more preferred embodiments, a steel plate with excellent phosphating performance also has a tensile strength of ≥ 780 MPa.
    • Description of the Drawing
    • Fig. 1 is a comparison of mass percentage content-depth distribution curves of Mn element with a depth in the range of 0-1000 nm from the surface of the steel plate of Example A1 and Comparative Example A1 of the present invention.
    • Fig. 2 is a comparison of mass percentage content-depth distribution curves of Si element with a depth in the range of 0-1000 nm from the surface of the steel plate of Example A1 and Comparative Example A1 of the present invention.
    • Fig. 3 is a comparison of mass percentage content-depth distribution curves of Fe element with a depth in the range of 0-1000 nm from the surface of the steel plate of Example A1 and Comparative Example A1 of the present invention.
    • Fig. 4 is a comparison of mass percentage content-depth distribution curves of Mn element with a depth in the range of 0-1000 nm from the surface of the steel plate of Example B1 and Comparative Example B1 of the present invention.
    • Fig. 5 is a comparison of mass percentage content-depth distribution curves of Si element with a depth in the range of 0-1000 nm from the surface of the steel plate of Example B1 and Comparative Example B1 of the present invention.
    • Fig. 6 is a comparison of mass percentage content-depth distribution curves of Fe element with a depth in the range of 0-1000 nm from the surface of the steel plate of Example B1 and Comparative Example B1 of the present invention.
    Detailed Description
  • The cold-rolled high-strength steel plate with excellent phosphating performance and the manufacturing method therefor of the present invention will be further explained and illustrated below with reference to specific embodiments and drawings. However, such explanations and descriptions do not constitute an improper limitation on the technical solution of the present invention.
  • Table 1 lists the composition ratios of the steel grades adopted in each example and comparative example of the present invention. Table 1 (wt%, with a balance of Fe)
    Steel plate code C Si Mn P S Al Nb Ti B Cr Mo V Ni
    A 0.08 0.4 2.2 0.012 0.002 - 0.04 0.03 - - - - -
    B 0.2 1.8 2.3 0.007 0.001 0.03 - 0.02 - - - - -
    C 0.07 0.07 2.1 0.010 0.0008 0.6 - 0.01 0.0006 - 0.2 - -
    D 0.13 0.26 2.4 0.011 0.0017 - - - - 0.4 - - -
    E 0.22 1.8 2.8 0.014 0.0014 0.03 - 0.02 - - - - -
    F 0.11 1.2 1.5 0.006 0.0007 - - - - - - - -
    G 0.3 3 3 0.022 0.005 1.5 - - - 0.5 - - -
    H 0.09 0.8 1.8 0.0091 0.02 0.03 - - 0.0004 0.03 - 0.0003 0.07
    I 0.2 0.5 5 0.05 0.0017 1.5 - - - - - 0.02 -
  • Based on the composition of a steel plate in Table 1, the steel plates of each example and comparative example of the present invention are prepared according to the following steps, and the specific process parameters of the continuous annealing steps of each example and comparative example are listed in Table 2:
    1. (1) conventional smelting;
    2. (2) conventional casting;
    3. (3) conventional hot rolling;
    4. (4) conventional pickling and cold rolling;
    5. (5) continuous annealing: heating the cold-rolled sheet in an oxidizing atmosphere for the first-stage heating; wherein the heating rate of the first-stage heating is 1-50 °C/s, the first-stage heating is heated from room temperature to T1, and T1 and the mass percentage of Si satisfy: 570 + 4000×Si ≤ T1 ≤ 600 + 9000×Si; then performing the second-stage heating and soaking in a reducing atmosphere, the reducing atmosphere in the second-stage heating is a mixture gas of N2 and H2, wherein the volume percentage of H2 is 0.5-20%; followed by cooling and coiling.
  • In some embodiments, the oxidizing atmosphere of the first-stage heating is a mixture gas of N2 and O2, wherein the volume percentage of O2 is 0.01-1%.
  • In other embodiments, the oxidizing atmosphere of the first-stage heating is obtained by controlling the air-fuel ratio of the direct-fired furnace to be 0.95-1.05.
  • In some embodiments, the dew point of the oxidizing atmosphere of the first-stage heating is ≥ -40 °C, the dew point of the reducing atmosphere of the second-stage heating is ≤ -20 °C.
  • In some embodiments, the heating rate of the second-stage heating is 1-20 °C/s, the second-stage heating is heated from T1 to a soaking temperature of 720-920 °C, and a soaking time is 30-200 s. Table 2
    No. Steel plate composition code First-stage heating Second-stage heating Soaking
    Air-fuel ratio O2 content H2 content Dew point Heating rate Temperature T1 H2 content Dew point Heating rate Temperature T2 H2 content Dew point Time
    Volume% Volume % °C °C/s °C Volume % °C °C/s °C Volume % °C s
    Ex. A1 A / 0.2 / -50 10 580 2 -50 4 820 2 -50 100
    Ex. A2 A / 0.01 / -20 5 600 5 -40 4 820 5 -40 100
    Ex. A3 A / 0.5 / -10 20 580 5 -10 4 800 5 -10 150
    Ex. A4 A / 1 / -40 1 600 5 -40 5 780 5 -40 120
    Ex. A5 A / 1 / -40 10 600 5 -20 1 780 5 -20 120
    Ex. A6 A / 1 / -40 10 600 0.5 0 5 780 0.5 0 120
    Comp. Ex. A1 A / / 2 -50 10 580 2 -50 4 820 2 -50 100
    Comp. Ex. A2 A / / 5 -40 10 600 5 -40 5 780 5 -40 120
    Comp. Ex. A3 A / / 5 -20 1 600 5 -20 5 780 5 -20 120
    Comp. Ex. A4 A / / 5 0 10 600 5 0 5 780 5 0 120
    Ex. B1 B 0.95 / / 50 50 650 2 -40 5 870 2 -40 180
    Ex. B2 B 1 / / 50 50 680 2 -40 5 870 2 -40 180
    Ex. B3 B 1.05 / / 50 50 700 20 -40 20 870 20 -40 180
    Ex. B4 B / 0.5 / -10 10 730 5 -10 4 920 5 -10 180
    Comp. Ex. B1 B / / 2 -20 10 700 2 -20 4 870 2 -20 200
    Comp. Ex. B2 B 0.9 / 5 -40 35 570 5 -40 10 870 5 -40 180
    Comp. Ex. B3 B 1 / 5 10 50 550 5 10 20 870 5 10 180
    Ex. C1 C / 0.5 / -35 15 580 10 -20 5 720 10 -20 30
    Ex. C2 C 0.95 / / 40 25 580 5 -20 5 780 5 -20 120
    Comp. Ex. C1 C / / 5 -20 15 570 10 -20 5 780 10 -20 30
    Ex. D1 D / 0.5 / 0 10 590 5 0 5 780 5 0 120
    Ex. D2 D / 0.5 / 0 10 620 5 0 5 780 5 0 120
    Comp. Ex. D1 D / / 5 0 10 590 5 0 5 780 5 0 120
    Comp. Ex. D2 D / / 5 -10 10 620 5 -10 5 780 5 -10 120
    Ex. E1 E / 0.2 / -40 10 750 5 -40 5 840 5 -40 120
    Ex. E2 E / 0.2 / -40 10 750 5 -20 5 840 5 -20 120
    Ex. E3 E / 0.2 / -40 10 750 5 0 5 840 5 0 120
    Comp. Ex. E1 E / / 5 -40 10 750 5 -40 5 840 5 -40 120
    Comp. Ex. E2 E / / 5 -40 10 750 5 -20 5 840 5 -20 120
    Comp. Ex. E3 E / / 5 -40 10 750 5 0 5 840 5 0 120
    Ex. F1 F 0.95 / / 42 50 618 5 0 5 800 5 -30 200
    Comp. Ex. F1 F / / 5 -30 20 630 5 -30 5 845 5 -30 150
    Ex. G1 G / 0.05 / 10 10 800 2 -40 10 850 2 -40 120
    Ex. G2 G / 0.05 / 10 10 800 2 -10 10 850 2 -10 120
    Ex. G3 G / 0.05 / 10 10 800 2 10 10 850 2 10 120
    Comp. Ex. G1 G / / 2 10 10 700 2 -40 10 850 2 -40 120
    Comp. Ex. G2 G / / 2 10 10 700 2 -10 10 850 2 -10 120
    Ex. H H / 0.5 / -50 25 602 5 10 5 780 5 10 120
    Ex. I I / 0.5 / -50 25 590 5 -30 5 845 5 -30 240
  • In Table 2 above, examples with an air-fuel ratio indicated by "/" indicate that the oxidizing atmosphere adopted in these examples is a mixed gas of N2 and O2. The air-fuel ratio and oxygen content of Comparative Examples A1-A4, D1-D2, E1-E3, F1, and G1-G2 are all indicated by "/", indicating that no oxidizing atmosphere is used in the first-stage heating in these comparative examples. The codes "A," "B," ..., "H," and "I" of each example and comparative example in Table 2 indicate that the composition of the steel plate corresponding to the code in Table 1 is used.
  • Table 3 lists the characteristics of the steel plates of each example and comparative example produced using the compositions of the steel plates of A-I and the process parameters listed in Table 2, as well as the phosphating performance corresponding to each steel plate, wherein Mnp, Sip, tpSi, tpMn, and Fep are detected by GDOES. Table 3
    No. Mnp Sip tpMn tpSi Fep phosphating performance
    mass% mass% nm nm mass%
    Ex. A1 6.4 1.2 224 228 87.5 ○
    Ex. A2 8.2 0.8 272 275 92.0 ○
    Ex. A3 7.2 1 420 427 85.0 ○
    Ex. A4 6.2 1.2 181 188 90.1 ○
    Ex. A5 7.2 1 188 298 89.1 ○
    Ex. A6 6 1 213 222 88.7 ○
    Comp. Ex. A1 25.3 3.2 6.0 7.5 23.0 ×
    Comp. Ex. A2 30.7 3.6 11.8 13.2 15.6 ×
    Comp. Ex. A3 29.8 3.8 12.7 13.8 26.0 ×
    Comp. Ex. A4 25.5 2.7 9.3 10.2 37.0 ×
    Ex. B1 9.1 2.1 316 323 91.4 ○
    Ex. B2 5.2 3.5 380 390 88.8 ○
    Ex. B3 6.5 2.8 450 455 93.2 ○
    Ex. B4 8.3 2.3 280 283 89.1 ○
    Comp. Ex. B1 30.3 12.2 15.9 16.4 5.4 ×
    Comp. Ex. B2 33.1 12.9 9.7 11.2 4.2 ×
    Comp. Ex. B3 17.9 4.9 5.4 6.8 34.9 ×
    Ex. C1 7.4 0.2 170 174 92.1 ○
    Ex. C2 5.9 0.1 120 123 91.2 ○
    Comp. Ex. C1 59.3 2.9 12.5 13.0 20.2 ×
    Ex. D1 6.1 1.2 165 171 87.9 ○
    Ex. D2 7.2 1.3 248 261 91.2 ○
    Comp. Ex. D1 46.3 1.9 4.6 5.5 27.7 ×
    Comp. Ex. D2 53.9 3.1 2.1 3.2 14.3 ×
    Ex. E1 9.2 2.1 298 305 90.8 ○
    Ex. E2 7.4 1.9 306 324 90.6 ○
    Ex. E3 6.6 2.1 305 320 88.1 ○
    Comp. Ex. E1 29.5 11.8 24.1 25.3 12.5 ×
    Comp. Ex. E2 23 9.3 11.2 13.4 26.5 ×
    Comp. Ex. E3 17.7 5.6 6.5 8.0 37.7 ×
    Ex. F1 7.8 2.1 230 237 93.2 ○
    Comp. Ex. F1 51.2 6.8 9.5 11.0 5.9 ×
    Ex. G1 9.3 3.5 198 212 89.7 ○
    Ex. G2 8 2.9 192 200 90.5 ○
    Ex. G3 6.1 2.9 211 220 91.0 ○
    Comp. Ex. G1 51.9 5.3 4.5 6.2 19.9 ×
    Comp. Ex. G2 52.5 3.3 4.7 6.2 23.1 ×
    Ex. H1 6.4 2.9 50 53 86.8 ○
    Ex. I1 9.8 1.4 120 128 85.2 ○
  • Figures 1, 2, and 3 respectively show the element mass percentage content-depth distribution curves of Mn, Si, and Fe with a depth in the range of 0-1000 nm from the surface of the steel plate of Example A1 and Comparative Example A1. The characteristic values Mnp, Sip, Fep, and tp are marked on the curves. tp in Figure 1 represents tpMn, tp in Figure 2 represents tpSi, and tp in Figure 3 represents tpSi.
  • As shown in Table 2, Example A1 undergoes the first-stage heating in an oxidizing atmosphere, while it is heated to 580 °C at a heating rate of 10 °C/s. The oxidizing atmosphere is a mixture gas of N2 and O2, wherein a volume percentage of O2 is 0.2%, and a dew point is -50 °C. Then the second-stage heating and soaking are carried out in a reducing atmosphere, wherein a heating rate is 4 °C/s, a soaking temperature is 820 °C, and a soaking time is 100 s. The reducing atmosphere in the second-stage heating and soaking is a mixture gas of N2 and H2, wherein a volume percentage of H2 is 2%, and a dew point of the atmosphere is -50 °C.
  • GDOES is used to detect the element depth distribution on a surface of an annealed steel plate, and the element mass percentage content-depth distribution curves of Mn, Si, and Fe with a depth in the range of 0-1000 nm as shown in Figures 1 to 3 are obtained.
  • Comparative Example A1 undergoes the first-stage heating, the second-stage heating and soaking in a reducing atmosphere, with a heating rate, a temperature and a time all being the same as those of Example A1. The element mass percentage content-depth distribution curves of Mn, Si, and Fe with a depth in the range of 0-1000 nm from a surface of Comparative Example A1 after annealing are shown in Figures 1 to 3.
  • Example A1 and Comparative Example A1 are subjected to phosphating treatment under the same conditions. The phosphating film on the surface of Example A1 is uniform and dense, and the phosphating performance meets the requirements (in Table 2-2 indicated by "o"). However, the phosphating film on the surface of Comparative Example A1 is sparse, with a large area not covered by the phosphating film, and the phosphating performance does not meet the requirements (in Table 2-2 indicated by "×"). Herein, phosphating performance is judged by observing the phosphating film on the surface of the steel plate after phosphating treatment. A coverage rate of the phosphating film is 100%, a size of phosphating crystals is less than 12 microns, and a weight of the phosphating film is more than 2 g/m2, indicating that the phosphate performance meets the requirements. Phosphating treatment is carried out using commercially available treatment agents. The specific steps and processes are as follows: (1) pre-degreasing spray: 45-55 °C, 1 min; (2) degreasing spray: 45-55 °C, 2.0 min; (3) second water cleaning spray: room temperature, 1 min; (4) surface conditioning spray: room temperature, 1 min; (5) phosphating spray: 50-60 °C, 2.0 min; (6) water cleaning spray: room temperature, 1 min; (7) Drying.
  • Figures 4, 5, and 6 respectively show the mass percentage content-depth distribution curves of Mn, Si, and Fe elements with a depth in the range of 0-1000 nm from the surface of the steel plate of Example B1 and Comparative Example B1. The characteristic values Mnp, Sip, Fep, and tp are marked on the curves. tp in Figure 4 represents tpMn, tp in Figure 5 represents tpSi, and tp in Figure 6 represents tpSi.
  • Example B1 undergoes the first-stage heating in an oxidizing atmosphere, while it is heated to 650°C at a heating rate of 50 °C/s. The oxidizing atmosphere is achieved by a direct-fired heating furnace, with an air-fuel ratio of 0.95 and a dew point of 50 °C. Then, the second-stage heating and soaking are carried out in a reducing atmosphere, wherein a heating rate is 5 °C/s, a soaking temperature is 870 °C, and a soaking time is 180 s. The atmosphere of the second-stage heating and soaking is a mixed gas of N2 and H2, wherein a volume percentage of H2 is 2%, and a dew point of the atmosphere is -40 °C.
  • GDOES is used to detect the element depth distribution on a surface of an annealed steel plate, and the element mass percentage content-depth distribution curves of Mn, Si, and Fe with a depth in the range of 0-1000 nm as shown in Figures 4 to 6 are obtained. The sample of Example B1 is subjected to phosphating treatment, the phosphating film is uniform and dense, and the phosphating performance meets the requirements.
  • Comparative Example B1 undergoes the first-stage heating, the second-stage heating and soaking in a reducing atmosphere. The reducing atmosphere is a mixed gas of N2 and H2, wherein a volume percentage of H2 is 2% and a dew point of the atmosphere is -20 °C. The soaking temperature and soaking time are the same as those of Example B1. The element mass percentage content-depth distribution curves of Mn, Si, and Fe with a depth in the range of 0-1000 nm from the surface of the steel plate after annealing of Comparative Example B1 are shown in Figures 4-6. The sample of Comparative Example B1 is subjected to phosphating treatment, and the phosphating film is uneven and non-dense, with some local positions not covered by the phosphating film, thus the phosphating performance did not meet the requirements.
  • The inventors also adapt the method of using scanning electron microscopy to observe the cross-sectional metallography after erosion by nitric acid alcohol solution to detect the microstructures of each example and comparative example. Cross-sectional transmission electron microscopy samples of the surface layer and transition layer are prepared using a focused ion beam microscope. The thickness of the surface layer is measured and the types of oxides in the transition layer are analyzed under a transmission electron microscope, and the test results are listed in Table 4. Table 4
    No. Thickness of surface layer (nm) Microstructure of surface layer Microstructure of base layer Oxides of Mn, Si, Fe and/or composite oxides of Mn, Si, Fe in the transition layer
    Ex. A1 217 F F+M MnO, SiO2, FeO, Mn2SiO4, Mn2FeO3, Mn2FeO4
    Ex. A2 266 F F+M MnO, SiO2, FeO, Mn2SiO4, Mn2FeO3, Mn2FeO4
    Ex. A3 410 F F+M MnO, SiO2, FeO, Mn2SiO4, Mn2FeO3, Mn2FeO4
    Ex. A4 176 F F+M MnO, SiO2, FeO, Mn2SiO4, Mn2FeO3, Mn2FeO4
    Ex. A5 180 F F+M MnO, SiO2, FeO, Mn2SiO4, Mn2FeO3, Mn2FeO4
    Ex. A6 203 F F+M MnO, SiO2, FeO, Mn2SiO4, Mn2FeO3, Mn2FeO4
    Comp. Ex. A1 - - F+M Without transition layer
    Comp. Ex. A2 - - F+M Without transition layer
    Comp. Ex. A3 - - F+M Without transition layer
    Comp. Ex. A4 - - F+M Without transition layer
    Ex. B1 303 F F+M+R MnO, MnO2, SiO2, MnSiO3 FeSiO3, Fe2SiO3, Fe2SiO4
    Ex. B2 370 F F+M+R MnO, MnO2, SiO2, MnSiO3 FeSiO3, Fe2SiO3, Fe2SiO4
    Ex. B3 440 F F+M+R MnO, MnO2, SiO2, MnSiO3 FeSiO3, Fe2SiO3, Fe2SiO4
    Ex. B4 265 F F+M+R MnO, MnO2, SiO2, MnSiO3 FeSiO3, Fe2SiO3, Fe2SiO4
    Comp. Ex. B1 - - F+M+R Without transition layer
    Comp. Ex. B2 - - F+M+R Without transition layer
    Comp. Ex. B3 - - F+M+R Without transition layer
    Ex. C1 160 F F+M MnO, MnO2, Mn2FeO3, Mn2FeO4
    Ex. C2 108 F F+M MnO, MnO2, Mn2FeO3, Mn2FeO4
    Comp. Ex. C1 - - F+M MnO, MnO2, Mn2FeO3, Mn2FeO4
    Ex. D1 157 F F+M MnO, MnO2, SiO2, Mn2FeO3, Mn2FeO4
    Ex. D2 238 F F+M MnO, MnO2, SiO2, Mn2FeO3, Mn2FeO4
    Comp. Ex. D1 - - F+M Without transition layer
    Comp. Ex. D2 - - F+M Without transition layer
    Ex. E1 283 F F+M+R MnO, MnO2, SiO2, MnSiO3 FeSiO3, Fe2SiO3, Fe2SiO4
    Ex. E2 290 F F+M+R MnO, MnO2, SiO2, MnSiO3 FeSiO3, Fe2SiO3, Fe2SiO4
    Ex. E3 295 F F+M+R MnO, MnO2, SiO2, MnSiO3 FeSiO3, Fe2SiO3, Fe2SiO4
    Comp. Ex. E1 - - F+M+R Without transition layer
    Comp. Ex. E2 - - F+M+R Without transition layer
    Comp. Ex. E3 - - F+M+R Without transition layer
    Ex. F1 220 F F+M+R MnO, MnO2, SiO2, MnSiO3 FeSiO3, Fe2SiO3, Fe2SiO4
    Comp. Ex. F1 - - F+M+R Without transition layer
    Ex. G1 192 F F+M+R MnO, MnO2, SiO2, FeO, Fe2O3, Fe3O4, MnSiO3, Mn2SiO4, Mn2FeO3, Mn2FeO4, FeSiO3, Fe2SiO3, Fe2SiO4
    Ex. G2 184 F F+M+R MnO, MnO2, SiO2, FeO, Fe2O3, Fe3O4, MnSiO3, Mn2SiO4, Mn2FeO3, Mn2FeO4, FeSiO3, Fe2SiO3, Fe2SiO4
    Ex. G3 204 F F+M+R MnO, MnO2, SiO2, FeO, Fe2O3, Fe3O4, MnSiO3, Mn2SiO4, Mn2FeO3, Mn2FeO4, FeSiO3, Fe2SiO3, Fe2SiO4
    Comp. Ex. G1 - - F+M+R Without transition layer
    Comp. Ex. G2 - - F+M+R Without transition layer
    Ex. H1 50 F F+M+R MnO, MnO2, SiO2, FeO, Fe2O3, Fe3O4
    Ex. I1 112 F F+M+R MnO, MnO2, SiO2, FeO, Fe2O3, Fe3O4
    Note: in Table 4, F represents ferrite, M represents martensite, and R represents residual austenite. The surface layer of each comparative example is denoted by "-", indicating that the comparative examples do not have a surface layer.
  • The inventors also test the tensile strength of each example and comparative example by the tensile test in accordance with the national standard GB/T 228.1, and the test results are listed in Table 5. Table 5
    No. Tensile strength (MPa)
    Ex. A1 1043
    Ex. A2 1074
    Ex. A3 1090
    Ex. A4 986
    Ex. A5 1025
    Ex. A6 1048
    Comp. Ex. A1 1050
    Comp. Ex. A2 1078
    Comp. Ex. A3 1100
    Comp. Ex. A4 1002
    Ex. B1 1210
    Ex. B2 1123
    Ex. B3 1024
    Ex. B4 1030
    Comp. Ex. B1 1190
    Comp. Ex. B2 1110
    Comp. Ex. B3 1030
    Ex. C1 798
    Ex. C2 810
    Comp. Ex. C1 830
    Ex. D1 817
    Ex. D2 812
    Comp. Ex. D1 806
    Comp. Ex. D2 820
    Ex. E1 1320
    Ex. E2 1200
    Ex. E3 1380
    Comp. Ex. E1 1310
    Comp. Ex. E2 1210
    Comp. Ex. E3 1370
    Ex. F1 857
    Comp. Ex. F1 846
    Ex. G1 1511
    Ex. G2 1493
    Ex. G3 1522
    Comp. Ex. G1 1488
    Comp. Ex. G2 1497
    Ex. H1 1052
    Ex. I1 1543
  • It can be seen from this that a cold-rolled steel plate manufactured by the present invention exhibits excellent phosphating performance while also having relatively high strength.
  • It should be noted that the combination of the various technical features in this case is not limited to the combination described in the claims of this case or the combination described in the specific embodiments. All technical features described in this case can be freely combined or combined in any way unless there is a contradiction between them.
  • It should also be noted that the embodiments listed above are only specific embodiments of the present invention. Obviously, the present invention is not limited to the above embodiments. Similar changes or modifications made therewith are directly derived from the contents disclosed in the present invention or can be easily associated with by those skilled in the art and should all fall within the scope of protection of the present invention.

Claims (15)

  1. A cold-rolled high-strength steel plate with excellent phosphating performance, wherein on an element mass percentage content-depth distribution curve with a depth in the range of 0-1000 nm from a surface of the steel plate, a mass percentage peak value of Mn element Mnp is ≤10.0%, and a mass percentage peak value of Si element Sip is ≤4.0%, and both the mass percentage peak value of Mn element Mnp and the mass percentage peak value of Si element Sip are located at a depth of ≥50 nm from the surface of the steel plate.
  2. The cold-rolled high-strength steel plate with excellent phosphating performance according to claim 1, wherein the mass percentage peak value of Mn element Mnp and the mass percentage peak value of Si element Sip are located at a depth of 50-500 nm from the surface of the steel plate.
  3. The cold-rolled high-strength steel plate with excellent phosphating performance according to claim 1, wherein on an element mass percentage content-depth distribution curve with a depth in the range of 0-1000 nm from the surface of the steel plate, a mass percentage peak value of Fe element Fep is ≥85%, and the mass percentage peak value of Fe element Fep is located within a depth range of 0-tpSi from the surface of the steel plate, wherein tpSi represents a depth position where the mass percentage peak value of Si element Sip appears.
  4. The cold-rolled high-strength steel plate with excellent phosphating performance according to any one of claims 1 to 3, wherein the steel plate comprises a base layer, a surface layer and a transition layer between the base layer and the surface layer in the thickness direction; wherein the microstructure of the surface layer is ferrite.
  5. The cold-rolled high-strength steel plate with excellent phosphating performance according to claim 4, wherein a thickness of the surface layer is 50-500 nm.
  6. The cold-rolled high-strength steel plate with excellent phosphating performance according to claim 4, wherein a microstructure of the base layer is martensite + ferrite, or martensite + ferrite + residual austenite.
  7. The cold-rolled high-strength steel plate with excellent phosphating performance according to claim 4, wherein the transition layer comprises oxides of Mn, Si, and Fe and/or composite oxides of Mn, Si, and Fe.
  8. The cold-rolled high-strength steel plate with excellent phosphating performance according to claim 7, wherein the oxides of Mn, Si and Fe are at least one of the following: MnO, MnO2, SiO2, FeO, Fe2O3 and Fe3O4; and the composite oxides of Mn, Si and Fe are at least one of the following: MnSiO3, Mn2SiO4, Mn2FeO3, Mn2FeO4, FeSiO3, Fe2SiO3 and Fe2SiO4.
  9. The cold-rolled high-strength steel plate with excellent phosphating performance according to claim 1, wherein the cold-rolled high-strength steel plate has a tensile strength of ≥780MPa.
  10. The cold-rolled high-strength steel plate with excellent phosphating performance according to claim 1, wherein the cold-rolled high-strength steel plate comprises the following elements with mass percentages as follows: C: 0.07-0.30%, Si: 0.07-3.0%, Mn: 1.5-5.0%.
  11. The cold-rolled high-strength steel plate with excellent phosphating performance according to claim 10, wherein the mass percentages of each chemical elements are:
    C: 0.07-0.30%, Si: 0.07-3.0%, Mn: 1.5-5.0%, and one or more of Nb, Ti, Al, B, Cr, Mo, Ni, and V, with a total mass percentage of Nb, Ti, Al, B, Cr, Mo, Ni, and V being less than or equal to 2.0%; and a balance of Fe and inevitable impurities.
  12. A manufacturing method for the cold-rolled high-strength steel plate with excellent phosphating performance according to any one of claims 1 to 11, comprising the following steps of: smelting, casting, hot rolling, pickling, cold rolling, and continuous annealing; wherein in the continuous annealing step, a first-stage heating is performed to a cold-rolled plate in an oxidizing atmosphere, then a second-stage heating and soaking are performed in a reducing atmosphere, followed by cooling and coiling.
  13. The manufacturing method according to claim 12, wherein the oxidizing atmosphere of the first-stage heating is obtained by controlling an air-fuel ratio of a direct-fired furnace to be 0.95-1.05; alternatively, the oxidizing atmosphere of the first-stage heating is a mixture gas of N2 and O2, wherein the volume percentage of O2 is 0.01-1%.
  14. The manufacturing method according to claim 12, wherein a heating rate of the first-stage heating is 1-50 °C/s, the first-stage heating is heated from room temperature to T1, and T1 and a mass percentage of Si satisfy: 570 + 4000×Si ≤ T1 ≤ 600 + 9000×Si; preferably, T1 is 580-800 °C.
  15. The manufacturing method according to claim 12, wherein the manufacturing method has one or more of the following features:
    a dew point of the oxidizing atmosphere in the first-stage heating is ≥ -50 °C;
    the reducing atmosphere in the second-stage heating and soaking is a mixture gas of N2 and H2, wherein a volume percentage of H2 is 0.5-20%;
    a dew point of the reducing atmosphere in the second-stage heating and soaking is ≤ 10 °C;
    a heating rate in the second-stage heating is 1-20 °C/s, the second-stage heating is heated from T1 to a soaking temperature of 720-920 °C, and a soaking time is 30-200 s.
EP24774250.5A 2023-03-23 2024-03-22 Cold-rolled high-strength steel plate with excellent phosphating performance, and manufacturing method therefor Pending EP4685248A1 (en)

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CN202310292931.2A CN118685699B (en) 2023-03-23 2023-03-23 Cold-rolled high-strength steel plate with excellent phosphating performance and manufacturing method thereof
PCT/CN2024/083228 WO2024193686A1 (en) 2023-03-23 2024-03-22 Cold-rolled high-strength steel plate with excellent phosphating performance, and manufacturing method therefor

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CN107419185A (en) 2017-08-16 2017-12-01 马钢(集团)控股有限公司 A kind of cold-rolled steel sheet and production method with excellent phosphorus characteristic
CN111910123A (en) 2020-07-13 2020-11-10 首钢集团有限公司 A kind of cold-rolled and continuously degraded ultra-high-strength steel with excellent phosphating performance and preparation method thereof

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CN103160654B (en) * 2011-12-14 2015-03-11 鞍钢股份有限公司 Manufacturing method of ultrahigh-strength surface active steel plate and steel plate thereof
CN103805840B (en) * 2012-11-15 2016-12-21 宝山钢铁股份有限公司 A kind of high formability galvanizing ultrahigh-strength steel plates and manufacture method thereof
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CN106350731B (en) * 2016-08-30 2018-08-10 宝山钢铁股份有限公司 A kind of cold rolling high strength steel plate and its manufacturing method with excellent phosphorus characteristic and formability

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CN107419185A (en) 2017-08-16 2017-12-01 马钢(集团)控股有限公司 A kind of cold-rolled steel sheet and production method with excellent phosphorus characteristic
CN111910123A (en) 2020-07-13 2020-11-10 首钢集团有限公司 A kind of cold-rolled and continuously degraded ultra-high-strength steel with excellent phosphating performance and preparation method thereof

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KR20250167586A (en) 2025-12-01
JP2026509920A (en) 2026-03-25

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