Classifications

• • 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 by deformation combined with, or followed by, heat treatment
  • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
  • C21D8/0278—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips involving a particular surface treatment
• • 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
  • 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
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B22—CASTING; POWDER METALLURGY
  • B22D—CASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES
  • B22D11/00—Continuous casting of metals, i.e. casting in indefinite lengths
  • B22D11/16—Controlling or regulating processes or operations
• • 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
  • C21D1/18—Hardening; Quenching with or without subsequent tempering
• • 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 by deformation combined with, or followed by, heat treatment
  • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
  • C21D8/0205—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips of ferrous alloys
• • 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 by deformation combined with, or followed by, heat treatment
  • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
  • C21D8/021—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips involving a particular fabrication or treatment of ingot or slab
• • 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 by deformation combined with, or followed by, heat treatment
  • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
  • C21D8/0221—Modifying the physical properties 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 by deformation combined with, or followed by, heat treatment
  • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
  • C21D8/0221—Modifying the physical properties 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 by deformation combined with, or followed by, heat treatment
  • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
  • C21D8/0221—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the working steps
  • C21D8/0242—Flattening; Dressing; Flexing
• • 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 by deformation combined with, or followed by, heat treatment
  • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
  • C21D8/0247—Modifying the physical properties 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 by deformation combined with, or followed by, heat treatment
  • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
  • C21D8/0247—Modifying the physical properties 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 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 by deformation combined with, or followed by, heat treatment
  • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
  • C21D8/0247—Modifying the physical properties 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
  • 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
  • C22C38/001—Ferrous alloys, e.g. steel alloys containing N
• • 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
  • C22C38/04—Ferrous alloys, e.g. steel alloys containing 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
  • C22C38/06—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
  • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
  • C22C38/22—Ferrous alloys, e.g. steel alloys containing chromium with molybdenum or tungsten
• • 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
  • C22C38/24—Ferrous alloys, e.g. steel alloys containing chromium 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
  • C22C38/26—Ferrous alloys, e.g. steel alloys containing chromium with niobium or tantalum
• • 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
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
  • C25D3/00—Electroplating: Baths therefor
  • C25D3/02—Electroplating: Baths therefor from solutions
  • C25D3/22—Electroplating: Baths therefor from solutions of zinc
• • 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 disclosure relates to a metallic material and a method of manufacturing the same, particularly to an electro-galvanized ultra-high-strength dual-phase steel and a method of manufacturing the same.
• Delayed fracture refers to a phenomenon that a material under static stress suffers a sudden brittle failure after a certain period of time. This phenomenon is a kind of embrittlement that occurs when the material interacts with the environmental stress, and it is a form of material deterioration caused by hydrogen.
• the phenomenon of delayed fracture is a major factor that hinders the application of ultra-high-strength steel, and it may be roughly classified into the following two categories:
• the former is generally caused by the intrusion of hydrogen generated by the corrosion reaction at a corrosion pit where corrosion occurs during long-term exposure; while the latter is caused by the concentration of hydrogen in the region of stress concentration under the action of stress wherein the hydrogen intrudes into the steel during manufacturing processes such as pickling and electroplating.
• the slab is heated to 1100° C. or higher and 1300° C. or lower, hot-rolled at a finish rolling exit-side temperature of 750° C. or higher and 1000° C. or lower, coiled at 300° C. or higher and 750° C. or lower, and then descaled by pickling.
• the steel plate was held at a temperature ranging from the Ac1 transformation point+20° C. to the Ac1 transformation point+120° C. for 600 seconds or more and 21600 seconds or less, and cold rolled at a reduction rate of 30% or more. Then, the steel plate is held at a temperature ranging from the Ac 1 transformation point to the Ac 1 transformation point+100° C. for 20 seconds or more and 900 seconds or less, cooled, and then subjected to electro-galvanization.
• the method for producing the cold-rolled steel plate includes the following steps: (1) molten steel pretreatment; (2) converter smelting; (3) alloy fine-tuning station; (4) RH furnace refining; (5) continuous casting; (6) hot rolling; (7) cold rolling; (8) continuous annealing; (9) temper rolling.
• the invention can improve the surface quality of the electro-galvanized steel plate and ensure that the electro-galvanized steel plate has a good shape.
• the mechanical properties of the cold-rolled steel plate are as follows: the yield strength is 120-180 MPa, and the tensile strength is higher than 260 MPa.
• the thin steel plate is cold-rolled at a reduction rate of 70° C./s to obtain a cold-rolled thin steel plate having a thickness of 1.2 mm. This is followed by recrystallization annealing at 850° C. for 60 seconds, cooling at a cooling rate of 30° C./s, and then electroplating.
• the tensile strength grades of the products involved in the above-mentioned prior art patent documents are all less than 980 MPa, or the matrix is hot stamping steel.
• One of the objects of the present disclosure is to provide an electro-galvanized ultra-high-strength dual-phase steel that is resistant to delayed cracking.
• the composition of the electro-galvanized ultra-high-strength dual-phase steel resistant to delayed cracking according to the present disclosure is designed reasonably. That is, by reasonably designing carbon, silicon, manganese and micro-alloy elements such as niobium, vanadium, chromium, molybdenum and the like in coordination with the process, the resulting steel has both excellent resistance to delayed cracking and ultra-high strength.
• the electro-galvanized ultra-high-strength dual-phase steel resistant to delayed cracking has a yield strength of ⁇ 550 MPa, a tensile strength of ⁇ 980 MPa, an elongation after fracture of ⁇ 12%, an initial hydrogen content of ⁇ 3 ppm, preferably ⁇ 2 ppm, and it does not experience delayed cracking when it is soaked in 1 mol/L hydrochloric acid for 300 hours under a pre-stress of greater than or equal to the tensile strength.
• the electro-galvanized ultra-high-strength dual-phase steel resistant to delayed cracking does not experience delayed cracking when it is soaked in 1 mol/L hydrochloric acid for 300 hours under a pre-stress of 1.2 times the tensile strength.
• the excellent performances of the electro-galvanized ultra-high-strength dual-phase steel resistant to delayed cracking can meet the industrial requirements, and be used for manufacture of automotive safety structural parts. It is highly valuable and promising for popularization and application.
• the present disclosure provides an electro-galvanized ultra-high-strength dual-phase steel resistant to delayed cracking, having a matrix structure of ferrite+tempered martensite, wherein the electro-galvanized ultra-high-strength dual-phase steel resistant to delayed cracking comprises the following chemical elements in mass percentages, in addition to Fe:
• the mass percentages of the chemical elements are:
• the chemical elements are designed according to the following principles:
• C In the electro-galvanized ultra-high-strength dual-phase steel resistant to delayed cracking according to the present disclosure, C is a solid solution strengthening element, and it is a guarantee for the material to obtain high strength. However, it should be noted that the higher the C content in the steel, the harder the martensite and the greater the tendency for delayed cracking to occur. Therefore, when a product is designed, it's better to choose a low-carbon design. In the electro-galvanized ultra-high-strength dual-phase steel resistant to delayed cracking according to the present disclosure, the mass percentage of C is controlled at 0.07-0.1%.
• the Si and Al elements can improve the tempering resistance of martensite, and can inhibit precipitation and growth of Fe 3 C, so that the dominated precipitates formed during tempering are c carbides.
• Al is also a deoxygenating element, and it has the function of deoxygenation in the steel. Therefore, in the electro-galvanized ultra-high-strength dual-phase steel resistant to delayed cracking according to the present disclosure, the mass percentage of Si is controlled at 0.05-0.3%, and the mass percentage of Al is controlled at 0.02-0.05%.
• Mn In the electro-galvanized ultra-high-strength dual-phase steel resistant to delayed cracking according to the present disclosure, Mn is an element that strongly improves the hardenability of austenite, and it can improve the strength of the steel effectively by forming more martensite. Therefore, in the electro-galvanized ultra-high-strength dual-phase steel resistant to delayed cracking according to the present disclosure, the mass percentage of Mn is controlled at 2.0-2.6%.
• Cr In the electro-galvanized ultra-high-strength dual-phase steel resistant to delayed cracking according to the present disclosure, Cr can improve the tempering resistance of martensite effectively, which is very conducive to improvement of delayed cracking.
• the mass percentage of Cr in the electro-galvanized ultra-high-strength dual-phase steel resistant to delayed cracking according to the present disclosure is controlled at 0.2-0.6%.
• Mo In the electro-galvanized ultra-high-strength dual-phase steel resistant to delayed cracking according to the present disclosure, addition of an appropriate amount of the Mo element can help to form dispersively distributed fine precipitates, which is conducive to gathering of dispersed hydrogen.
• the Mo element can form a large quantity of MoC precipitates in the steel, which is conducive to gathering of dispersed hydrogen in local areas, and thus very helpful to reduce delayed cracking of the steel. Therefore, in the electro-galvanized ultra-high-strength dual-phase steel resistant to delayed cracking according to the present disclosure, the mass percentage of Mo is controlled at 0.1-0.25%.
• the Nb element is an element for precipitation of carbonitrides. It can refine grains, precipitate carbonitrides, and increase material strength. At the same time, the coherent micro-alloy precipitates are conducive to gathering of dispersed hydrogen, which helps to reduce delayed cracking. Therefore, in the electro-galvanized ultra-high-strength dual-phase steel resistant to delayed cracking according to the present disclosure, the mass percentage of Nb is controlled at 0.02-0.04%.
• V In the electro-galvanized ultra-high-strength dual-phase steel resistant to delayed cracking according to the present disclosure, V may play a role in refining grains. At the same time, the coherent micro-alloy precipitates are conducive to gathering of dispersed hydrogen. Therefore, in the electro-galvanized ultra-high-strength dual-phase steel resistant to delayed cracking according to the present disclosure, the mass percentage of V is controlled at 0.06-0.2%.
• electro-galvanized ultra-high-strength dual-phase steel resistant to delayed cracking according to the present disclosure further comprises 0.0015-0.003% of element B.
• the electro-galvanized ultra-high-strength dual-phase steel resistant to delayed cracking according to the present disclosure may also comprise a small amount of element B.
• B is used as a strong element for hardenability.
• An appropriate amount of B can increase the hardenability of the steel, and promote formation of martensite.
• the unavoidable impurities include the P, S and N elements, and the contents thereof are controlled to be at least one of the following: P ⁇ 0.012%, S ⁇ 0.003%, N ⁇ 0.005%.
• P, S and N are all unavoidable impurity elements in the steel. It's better to lower the contents of the P, S and N elements in the steel as far as possible. S tends to form MnS inclusions which will seriously affect the hole expansion rate.
• the P element may reduce the toughness of the steel, which is not conducive to the delayed cracking performance. An unduly high content of the N element in the steel is prone to causing cracks on the surface of the slab, which will greatly affect the performances of the steel.
• the mass percentage of P is controlled at P ⁇ 0.012%; the mass percentage of S is controlled at S ⁇ 0.003%; and the mass percentage of N is controlled at N ⁇ 0.005%.
• the phase proportion (by volume) of the tempered martensite is >50%.
• the carbide particles include MoC, VC, Nb (C, N), and the carbide particles are all distributed in the matrix structure in a coherent form.
• the carbide particles have a size of ⁇ 60 nm.
• the tempered martensite further comprises coherently distributed ⁇ carbides.
• the performances of the electro-galvanized ultra-high-strength dual-phase steel resistant to delayed cracking meet at least one of the following: yield strength ⁇ 550 MPa, tensile strength ⁇ 980 MPa, elongation after fracture ⁇ 12%, initial hydrogen content ⁇ 3 ppm; no delayed cracking when soaked in 1 mol/L hydrochloric acid for 300 hours under a pre-stress of greater than or equal to the tensile strength.
• the performances of the electro-galvanized ultra-high-strength dual-phase steel resistant to delayed cracking meet the following: yield strength ⁇ 550 MPa, tensile strength ⁇ 980 MPa, elongation after fracture ⁇ 12%, initial hydrogen content ⁇ 3 ppm; no delayed cracking when soaked in 1 mol/L hydrochloric acid for 300 hours under a pre-stress of greater than or equal to the tensile strength.
• the yield ratio of the electro-galvanized ultra-high-strength dual-phase steel resistant to delayed cracking according to the present disclosure is in the range of 0.55-0.70.
• another object of the present disclosure is to provide a method for manufacturing an electro-galvanized ultra-high-strength dual-phase steel resistant to delayed cracking.
• the electro-galvanized ultra-high-strength dual-phase steel resistant to delayed cracking manufactured by this method has a yield strength of ⁇ 550 MPa, a tensile strength of ⁇ 980 MPa, an elongation after fracture of ⁇ 12%, an initial hydrogen content of ⁇ 3 ppm, preferably ⁇ 2 ppm, and it does not experience delayed cracking when it is soaked in 1 mol/L hydrochloric acid for 300 hours under a pre-stress of greater than or equal to the tensile strength.
• the present disclosure provides a method for manufacturing the above electro-galvanized ultra-high-strength dual-phase steel resistant to delayed cracking, comprising steps:
• Annealing heating to an annealing soaking temperature of 780-820° C., preferably 790-810° C. at a heating rate of 3-10° C./s, the annealing time being 40-200 s, preferably 40-160 s; and then rapidly cooling at a rate of 30-80° C./s, preferably 35-80° C./s, a starting temperature of the rapid cooling being 650-730° C.;
• Tempering tempering temperature: 200-280° C., preferably 210-270° C.; tempering time: 100-400 s, preferably 120-300 s;
• a medium to low temperature tempering treatment is utilized to control the relevant process parameters. This not only helps to reduce the hardness of martensite, but can also effectively avoid precipitation of coarse-grained martensite, which is very beneficial to the delayed cracking performance of the steel.
• step (1) a drawing speed in the continuous casting is controlled at 0.9-1.5 m/min.
• step (1) the continuous casting may be performed in a secondary cooling mode with a large amount of water.
• step (2) the cast slab is controlled to be soaked at a temperature of 1200-1260° C., preferably 1210-1245° C.; then rolled with a finishing rolling temperature being controlled at 840-900° C.; then cooled at a rate of 20-70° C./s after rolling; then coiled at a coiling temperature of 580-630° C.; and then subjected to heat preservation treatment or slow cooling treatment after coiling.
• the heat preservation treatment is performed for 1-5 hours, or the slow cooling treatment is performed at a cooling rate of 3-5° C./s.
• step (2) in order to ensure the stability of the rolling load, the heating temperature is controlled at 1200° C. or higher. Meanwhile, the upper limit of the heating temperature is controlled to be 1260° C. in order to prevent increase of oxidative burning loss. Therefore, the cast slab is finally controlled to be soaked at a temperature of 1200-1260° C.
• step (2) the heat preservation after hot-rolling and coiling or the slow cooling after coiling is conducive to full precipitation of dispersive precipitates.
• Various types of dispersively distributed precipitates are conducive to adsorption of a small amount of hydrogen and dispersive distribution of hydrogen, thereby avoiding gathering of hydrogen. This helps to resist delayed cracking.
• step (3) the cold rolling reduction rate is controlled at 45-65%.
• step (3) the cold rolling reduction rate is controlled at 45-65%. Before the cold rolling, the iron oxide scale on the surface of the steel plate can be removed by pickling.
• step (6) the temper rolling reduction rate is controlled at ⁇ 0.3%.
• step (6) in order to guarantee the flatness of the steel plate, a certain amount of temper rolling needs to be performed, but an excessively large amount of temper rolling will increase the yield strength of the steel too much. Therefore, in the manufacturing method according to the present disclosure, the temper rolling reduction rate is controlled at ⁇ 0.3%.
• step (7) may be performed by a conventional electro-galvanizing method.
• double-side plating is performed, and the weight of the plating layer on one side is in the range of 10-100 g/m 2 .
• the electro-galvanized ultra-high-strength dual-phase steel resistant to delayed cracking and the method of manufacturing the same according to the present disclosure have the following advantages and beneficial effects:
• composition of the electro-galvanized ultra-high-strength dual-phase steel resistant to delayed cracking is designed reasonably. That is, by reasonably designing carbon, silicon, manganese and micro-alloy elements such as niobium, vanadium, chromium, molybdenum and the like in coordination with the process, the resulting steel has both excellent resistance to delayed cracking and ultra-high strength.
• the electro-galvanized ultra-high-strength dual-phase steel resistant to delayed cracking has a yield strength of ⁇ 550 MPa, a tensile strength of ⁇ 980 MPa, an elongation after fracture of ⁇ 12%, an initial hydrogen content of ⁇ 3 ppm, and delayed cracking does not occur when it is soaked in 1 mol/L hydrochloric acid for 300 hours under a pre-stress of greater than or equal to the tensile strength.
• the excellent performances of the electro-galvanized ultra-high-strength dual-phase steel resistant to delayed cracking can meet the industrial requirements, suitable for manufacture of automotive safety structural parts. It is highly valuable and promising for popularization and application.
• the interior of the steel plate, especially the surface layer is free of TiN, which is conducive to reducing gathering of hydrogen in the interior of the steel plate and improving the delayed cracking performance of the steel.
• a combination of high temperature soaking and medium temperature tempering is adopted.
• the high temperature soaking gives rise to more austenite transformation, and thus more martensite is obtained during the subsequent rapid cooling, which finally guarantees higher strength before tempering.
• medium to low temperature tempering treatment and controlling relevant process parameters not only reduction of the hardness of martensite is favored, but precipitation of coarse-grained martensite is also avoided effectively, so that the yield ratio of the material is moderate, and on the other hand, the delayed cracking performance of the steel is greatly favored.
• the tempering temperature used is too low, it is not conducive to reducing the hardness of martensite; if the tempering temperature is too high, martensite will decompose, and the final strength will be lower than 980 MPa.
• the use of high temperature soaking and medium temperature tempering in combination according to the present disclosure effectively ensures that the prepared electro-galvanized ultra-high-strength dual-phase steel resistant to delayed cracking has the characteristics of excellent delayed-cracking resistance and low initial hydrogen content.
• Table 1 lists the mass percentages of various chemical elements in the steel grades corresponding to the electro-galvanized ultra-high-strength dual-phase steels resistant to delayed cracking in Examples 1-6 and the steels in Comparative Examples 1-14.
• Annealing The temperature was raised to the annealing soaking temperature of 780-820° C. at a heating rate of 3-10° C./s, wherein the annealing time was 40-200 s. Then, rapid cooling was performed at a rate of 30-80° C./s, wherein the starting temperature of the rapid cooling was 650-730° C.;
• tempering temperature was 200-280° C., and the tempering time was 100-400 s;
• Temper rolling The temper rolling reduction rate was controlled at ⁇ 0.3%;
• Double-side electro-galvanization The weight of the plating layer on each side was 10-100 g/m 2 .
• Tables 2-1 and 2-2 list the specific process parameters for the electro-galvanized ultra-high-strength dual-phase steels resistant to delayed cracking in Examples 1-6 and the steels in Comparative Examples 1-14.
• Step (3) Drawing Step (2) Cold speed in Finishing rolling continuous Soaking rolling Cooling Coiling reduction Steel casting temperature temperature rate temperature rate No. grade (m/min) (° C.) (° C.) (° C./s) (° C.) (%)
• Ex. 1 A 0.9 1230 885 35 585 50 Ex. 2 B 1.1 1240 860 30 595 60 Ex. 3 C 1.5 1220 890 65 605 65 Ex. 4 D 1.3 1215 875 40 625 55 Ex. 5 E 1.1 1224 880 35 615 48 Ex. 6 F 1.5 1230 890 60 600 58 Comp. Ex. 1 G 1.4 1235 895 60 595 50 Comp. Ex. 2 H 1.2 1200 875 65 620 64 Comp. Ex.
• Step (6) Starting Temper Annealing Rapid temperature Step (5) rolling Heating soaking Annealing cooling of rapid Tempering Tempering reduction rate temperature time rate cooling temperature time rate No. (° C./s) (° C.) (s) (° C./s) (° C.) (° C.) (s) (%) Ex. 1 5 795 60 55 710 260 100 0.1 Ex. 2 8 790 80 35 680 240 300 0.1 Ex. 3 7 785 120 80 650 210 250 0.3 Ex. 4 4 794 160 45 730 270 200 0.1 Ex. 5 3 810 40 45 670 230 120 0.2 Ex. 6 10 806 160 72 660 265 300 0.1 Comp. Ex.
• Table 3 lists the performance test results for the electro-galvanized ultra-high-strength dual-phase steels resistant to delayed cracking in Examples 1-6 and the steels in Comparative Examples 1-14.
• GB/T 13239-2006 Metallic Materials—Tensile Testing At Low Temperature was referred to.
• a standard sample was prepared, and subjected to static stretching on a tensile testing machine to obtain a corresponding stress-strain curve. After data processing, the parameters of yield strength, tensile strength and elongation after fracture were obtained finally.
• Method for measurement of hydrogen content The sample was heated to a certain temperature, and a hydrogen analyzer was used to measure the concentration of hydrogen released along with the change (rise) of the temperature, thereby judging the initial hydrogen content in the steel.
• each Example according to the present disclosure had a yield strength of ⁇ 550 MPa, a tensile strength of ⁇ 980 MPa, an elongation after fracture of ⁇ 12%, and an initial hydrogen content of ⁇ 3 ppm.
• the electro-galvanized ultra-high-strength dual-phase steel resistant to delayed cracking in each Example had an ultra-high strength and a delayed cracking performance that was significantly better than that of a comparative steel grade of the same level. No delayed cracking occurred when the steel plate was soaked in 1 mol/L hydrochloric acid for 300 hours under a pre-stress of greater than or equal to the tensile strength.
• the excellent performances of the electro-galvanized ultra-high-strength dual-phase steel resistant to delayed cracking according to the present disclosure can meet the industrial requirements, suitable for manufacture of automotive safety structural parts. It is highly valuable and promising for popularization and application.

Landscapes

• Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Materials Engineering (AREA)
• Metallurgy (AREA)
• Organic Chemistry (AREA)
• Mechanical Engineering (AREA)
• Thermal Sciences (AREA)
• Crystallography & Structural Chemistry (AREA)
• Physics & Mathematics (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Electrochemistry (AREA)
• Heat Treatment Of Sheet Steel (AREA)
• Coating With Molten Metal (AREA)
• Electroplating Methods And Accessories (AREA)
• Continuous Casting (AREA)

Applications Claiming Priority (3)

Publications (1)

Family

ID=78722980

Family Applications (1)

Country Status (6)

Families Citing this family (2)

Family Cites Families (19)

• 2020
  • 2020-05-27 CN CN202010459228.2A patent/CN113737108A/zh active Pending
• 2021
  • 2021-05-25 JP JP2022572382A patent/JP2023527197A/ja active Pending
  • 2021-05-25 EP EP21813639.8A patent/EP4159887A4/en active Pending
  • 2021-05-25 US US17/927,771 patent/US20230243008A1/en active Pending
  • 2021-05-25 WO PCT/CN2021/095802 patent/WO2021238915A1/zh unknown
  • 2021-05-25 CA CA3180458A patent/CA3180458A1/en active Pending

Also Published As

Similar Documents

Legal Events