CN114921619B - Steelmaking method capable of improving delayed cracking resistance of hot forming steel in CSP production line - Google Patents

Steelmaking method capable of improving delayed cracking resistance of hot forming steel in CSP production line Download PDF

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CN114921619B
CN114921619B CN202210562344.6A CN202210562344A CN114921619B CN 114921619 B CN114921619 B CN 114921619B CN 202210562344 A CN202210562344 A CN 202210562344A CN 114921619 B CN114921619 B CN 114921619B
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steel
less
equal
controlled
inclusions
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CN114921619A (en
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陈勇
肖厚念
胡宽辉
郎丰军
程鹏
李江文
马颖
庞涛
何嘉
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Wuhan Iron and Steel Co Ltd
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    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21C—PROCESSING OF PIG-IRON, e.g. REFINING, MANUFACTURE OF WROUGHT-IRON OR STEEL; TREATMENT IN MOLTEN STATE OF FERROUS ALLOYS
    • C21C7/00—Treating molten ferrous alloys, e.g. steel, not covered by groups C21C1/00 - C21C5/00
    • C21C7/04—Removing impurities by adding a treating agent
    • C21C7/064—Dephosphorising; Desulfurising
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
    • B21B—ROLLING OF METAL
    • B21B1/00—Metal-rolling methods or mills for making semi-finished products of solid or profiled cross-section; Sequence of operations in milling trains; Layout of rolling-mill plant, e.g. grouping of stands; Succession of passes or of sectional pass alternations
    • B21B1/22—Metal-rolling methods or mills for making semi-finished products of solid or profiled cross-section; Sequence of operations in milling trains; Layout of rolling-mill plant, e.g. grouping of stands; Succession of passes or of sectional pass alternations for rolling plates, strips, bands or sheets of indefinite length
    • 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
    • B22D11/10—Supplying or treating molten metal
    • B22D11/11—Treating the molten metal
    • 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
    • B22D11/12—Accessories for subsequent treating or working cast stock in situ
    • B22D11/128—Accessories for subsequent treating or working cast stock in situ for removing
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21C—PROCESSING OF PIG-IRON, e.g. REFINING, MANUFACTURE OF WROUGHT-IRON OR STEEL; TREATMENT IN MOLTEN STATE OF FERROUS ALLOYS
    • C21C1/00—Refining of pig-iron; Cast iron
    • C21C1/02—Dephosphorising or desulfurising
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21C—PROCESSING OF PIG-IRON, e.g. REFINING, MANUFACTURE OF WROUGHT-IRON OR STEEL; TREATMENT IN MOLTEN STATE OF FERROUS ALLOYS
    • C21C7/00—Treating molten ferrous alloys, e.g. steel, not covered by groups C21C1/00 - C21C5/00
    • C21C7/0056—Treating molten ferrous alloys, e.g. steel, not covered by groups C21C1/00 - C21C5/00 using cored wires
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21C—PROCESSING OF PIG-IRON, e.g. REFINING, MANUFACTURE OF WROUGHT-IRON OR STEEL; TREATMENT IN MOLTEN STATE OF FERROUS ALLOYS
    • C21C7/00—Treating molten ferrous alloys, e.g. steel, not covered by groups C21C1/00 - C21C5/00
    • C21C7/04—Removing impurities by adding a treating agent
    • C21C7/06—Deoxidising, e.g. killing
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21C—PROCESSING OF PIG-IRON, e.g. REFINING, MANUFACTURE OF WROUGHT-IRON OR STEEL; TREATMENT IN MOLTEN STATE OF FERROUS ALLOYS
    • C21C7/00—Treating molten ferrous alloys, e.g. steel, not covered by groups C21C1/00 - C21C5/00
    • C21C7/10—Handling in a vacuum
    • 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
    • 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
    • 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
    • C21D8/0221—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
    • C21D8/0247—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
    • C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
    • C21D9/0081—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for slabs; for billets
    • 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
    • C22C38/24—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
    • C22C38/28—Ferrous alloys, e.g. steel alloys containing chromium with 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
    • C22C38/38—Ferrous alloys, e.g. steel alloys containing chromium with more than 1.5% by weight of manganese
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
    • B21B—ROLLING OF METAL
    • B21B1/00—Metal-rolling methods or mills for making semi-finished products of solid or profiled cross-section; Sequence of operations in milling trains; Layout of rolling-mill plant, e.g. grouping of stands; Succession of passes or of sectional pass alternations
    • B21B1/22—Metal-rolling methods or mills for making semi-finished products of solid or profiled cross-section; Sequence of operations in milling trains; Layout of rolling-mill plant, e.g. grouping of stands; Succession of passes or of sectional pass alternations for rolling plates, strips, bands or sheets of indefinite length
    • B21B2001/221—Metal-rolling methods or mills for making semi-finished products of solid or profiled cross-section; Sequence of operations in milling trains; Layout of rolling-mill plant, e.g. grouping of stands; Succession of passes or of sectional pass alternations for rolling plates, strips, bands or sheets of indefinite length by cold-rolling
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
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    • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
    • Y02P10/00—Technologies related to metal processing
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  • Treatment Of Steel In Its Molten State (AREA)
  • Heat Treatment Of Steel (AREA)

Abstract

Production in CSP production line can improve hot forming steel and resistThe steelmaking method with delayed cracking performance comprises the following steps: desulfurizing molten iron; conventional; smelting; LF refining; RH vacuum treatment; pouring into a blank; heating a casting blank; cooling by laminar flow and coiling; cold rolling after conventional pickling; annealing the product; heating austenitizing under the protection of nitrogen after blanking; after hot stamping forming and conventional quenching, naturally cooling to room temperature. The invention feeds 0.15-0.40 kg/ton of steel to make Al 2 O 3 The maximum size of the inclusions is reduced from about 20 mu m to not more than 10 mu m, the irregular inclusions are changed into spherical inclusions, and the distribution density is 4.63 pieces/mm 2 Down to no more than 0.8/mm 2 The hydrogen induced delayed cracking sensitivity of the steel is reduced from 80% to less than or equal to 50%.

Description

Steelmaking method capable of improving delayed cracking resistance of hot forming steel in CSP production line
Technical Field
The invention relates to a production method of steel for automobiles, in particular to a steelmaking method capable of improving the delayed cracking resistance of hot forming steel in a CSP production line.
Background
According to statistics, the fuel efficiency can be improved by 6% -8% when the weight of the automobile is reduced by 10%. One of the most important approaches to the weight reduction of automobiles is to adopt high-strength and ultra-high-strength steel, and the hot forming steel is the ultra-high-strength steel which is most widely applied at present, has the strength level of 1300-2000 MPa and is mainly applied to the positions of A columns, B columns, front and rear bumpers, car door anti-collision beams, middle channels and the like. However, when the strength of steel exceeds 1000MPa, the problem of delayed cracking of steel has also occurred, and a lot of researches have confirmed that delayed cracking of steel is caused by hydrogen in materials and the service environment of materials, has unpredictability and suddenly, often causes serious safety problems, and has become a problem that must be solved for the weight reduction of automobiles.
Current hot-formed steels are mainly MnB series steels, which are mainly deoxidized with Al during smelting. Therefore, the inclusions in the steel generate Al due to Al deoxidization in addition to TiN 2 O 3 Inclusions. Al produced 2 O 3 The inclusions are not only large in hardness, high in melting point and irregular in shape, easy to cluster into large inclusions, but also sharp edges and corners, can generate larger stress with a steel matrix in steel, and are Al 2 O 3 The inclusion also has a high hydrogen binding energy (about 72 KJ/mol), is easy to trap hydrogen, and has a hydrogen aggregation coefficient as high as 17. The accumulation of a large amount of hydrogen also causes delayed cracking of the steel, and thus Al 2 O 3 The inclusions act as crack sources for delayed cracking, and the cracking sensitivity of the steel is very high, and the stress of the spherical inclusions and the matrix is relatively small. The delayed cracking resistance of steel is critical.
From the retrieved prior art:
most of the literature focuses only on basic mechanical properties of hot formed steel, and little understanding of Al in the steel is available 2 O 3 The hazard of inclusions to delayed cracking of hot formed steel, and how to deal with, for example:
the document with the Chinese patent application number of CN202110888137.5 discloses 1700 MPa-level hydrogen-induced delayed cracking resistant hot forming steel and a preparation method thereof, and relates to the technical field of automobile ultra-high strength steel. The hot forming steel comprises the following chemical components in percentage by mass: c:0.21 to 0.24 percent of Si:0.27 to 0.34 percent of Mn:1.1 to 1.3 percent of S: less than or equal to 0.005 percent, P: less than or equal to 0.01 percent, al:0.02 to 0.05 percent of Cr:0.15 to 0.2 percent, B: 0.002-0.003%, ta:0.02 to 0.06 percent of Fe: the balance; the preparation method comprises the following steps: desulphurizing molten iron, converting into smelting, casting into blanks, heating and homogenizing the blanks, hot rolling, coiling, pickling, cold rolling and hot stamping. According to the invention, by adding trace Ta and controlling a processing technology, nano-scale tantalum carbide precipitated phases are formed in steel and grains are refined, so that the strength, plasticity and hydrogen-induced delayed cracking resistance of the steel are cooperatively improved. The ta element used in the document is a rare element, so that the production cost can be greatly increased, the ta can seriously reduce the welding performance of the steel, the ta element is rarely used in the metallurgical industry, and meanwhile, the method does not pay attention to the influence of the steelmaking process on the delayed cracking performance of the product.
The patent publication No. CN 110306123A discloses a high-toughness hot forming steel with tensile strength more than or equal to 1800MPa and a production method thereof, wherein the hot forming steel comprises the following components in percentage by mass: 0.29 to 0.35 percent of C, less than or equal to 0.5 percent of Si, 0.5 to 1.5 percent of Mn, less than or equal to 0.020 percent of P, less than or equal to 0.010 percent of S, less than or equal to 0.50 percent of Cr, 0.01 to 0.06 percent of Al, 0.01 to 0.06 percent of Nb, 0.01 to 0.06 percent of V, less than or equal to 0.5 percent of Mo, and the balance of Fe and unavoidable impurities; the production process comprises the following steps: 1. smelting; 2. casting blank; 3. hot rolling; 4. cold rolling; 5. annealing; 6. and (5) thermoforming. The document aims at improving the toughness of steel, improves the cold bending performance by controlling the content and proportion of Mn/Mo and Nb/V, and obviously increases the production cost by using more noble alloys Mo, nb and V.
The document of Chinese patent publication No. CN 110423953 discloses a hot forming member with excellent cold bending performance and high tensile strength of 1800MPa grade or more and a preparation method thereof, wherein the hot forming member comprises the following chemical components in percentage by weight: c:0.29-0.35%, si: less than or equal to 0.5 percent, mn:0.5-1.5%, P: less than or equal to 0.020%, S: less than or equal to 0.010%, cr: less than or equal to 0.50 percent, al:0.01-0.06%, nb:0.01-0.06%, V:0.01-0.06%, mo: less than or equal to 0.5 percent, and the balance of Fe and unavoidable impurities; the surface layer of the hot forming component is a soft ferrite structure, the inner layer is a martensite structure, and the grain size is less than or equal to 10 mu m. The composition design of low Si, low Mn, low Cr, no Ti, no B and Mo is adopted, TMCP, continuous annealing and hot forming processes are combined to obtain high-toughness hot formed steel with uniform structure and tensile strength of more than or equal to 1800MPa, and a decarburized layer with the thickness of 15-25 mu m is obtained after hot rolling in the preparation process through control of the preparation process, so that the cold bending performance of a hot formed member is improved. The document aims at improving the toughness and cold bending performance of a component through special component design, the production cost is obviously increased by using more noble alloys Mo, nb and V, and meanwhile, the document does not describe the hydrogen induced cracking resistance and principle, does not characterize the cracking resistance in a related way, and does not propose corresponding improvement measures or schemes.
Chinese patent publication No. CN 108754319A discloses hot forming steel with tensile strength of more than or equal to 1800MPa grade produced by ESP production line, and comprises the following components in percentage by weight: c:0.28 to 0.40 percent, si:0.15 to 0.40 percent, mn:1.40 to 1.60 percent, P is less than or equal to 0.01 percent, S is less than or equal to 0.01 percent, als:0.015 to 0.050 percent, cr is less than or equal to 0.80 percent, N is less than or equal to 0.005 percent, and B: 0.002-0.005%, mo is less than or equal to 0.50%, nb+Ti:0.025 to 0.090 percent; the production method comprises the following steps: smelting and continuously casting into a plate blank; rough rolling; soaking treatment; performing finish rolling after conventional high-pressure descaling; laminar cooling; heating; acid washing and stamping to form. According to the invention, elements such as Nb, ti and the like in the components are added in a compounding way, and Cr, B, mo and the like are controlled, and ESP short flow process is adopted to produce the hot stamping forming steel with the tensile strength of 1800MPa, so that the mechanical property of the hot stamping forming steel can be ensured, the procedures of repeated heating, uncoiling and the like of a coil in the production process can be reduced, the procedures of cold rolling and annealing heat treatment can be eliminated, the production cost is reduced, and the delayed cracking sensitivity is not reduced. The document aims at emphasizing that the ESP process is used for finishing the output of the product, has lower cost, but the ESP product is a hot rolled product, has poorer surface quality compared with the traditional cold rolled product, and is difficult to meet higher surface quality requirements of the automobile industry, and meanwhile, the method does not describe the hydrogen induced cracking resistance and principle of the ESP product, does not pay attention to the influence of inclusions on the cracking delay, and does not carry out related characterization on the cracking delay performance.
The document of Chinese patent publication No. CN101275200A discloses a hot-formed martensitic steel which is mainly suitable for hot-stamping thin-thickness parts with tensile strength of 1.3-1.7 GPa. The main chemical components (weight percent) of the composition are: 0.10 to 0.33 percent of C, 0.50 to 2.30 percent of Si, 0.50 to 2.00 percent of Mn, less than or equal to 0.020 percent of P, less than or equal to 0.015 percent of S, 0.015 to 0.060 percent of Al, less than or equal to 0.002 percent of [ O ], 0.002 to 0.015 percent of [ N ] and the balance of Fe and unavoidable impurities. In addition, any one or more of B0.0005-0.0050%, ti 0.02-0.10%, nb 0.02-0.10%, V0.02-0.15% and RE 0.001-0.050% are added. Compared with the existing hot forming martensitic steel 22MnB5 steel, the tensile strength of the steel is improved from 1.0-1.5 GPa to 1.3-1.7 GPa, the steel has good plasticity and elongation more than 15%, and the hydrogen-induced delayed fracture sensitivity is obviously reduced, so that a foundation is provided for the weight reduction and the high safety performance of automobiles. However, the document does not address the effect of TiN inclusions on delayed cracking. The literature mainly reduces the sensitivity of delayed cracking by adding microalloy elements such as Nb, V, ti and the like, but does not pay attention to the influence of TiN inclusions on delayed cracking, and has some defects in the literature, firstly, the literature aims to develop a steel for thin-thickness parts, but does not use a sheet sample for mechanical test, but uses a round bar sample for tensile test, and the bar sample and the plate sample have different sectional shapes, so that the stress-strain states received in the tensile process are different, and the result is inappropriate to use the bar sample instead of the sheet sample, so that the result has no guiding significance to practical application. Secondly, mechanical tests using a bar-shaped test piece of phi 12 instead of a sheet test piece showed that these test steels were not sufficiently rolled, and the final rolled thickness was not less than 12mm, which greatly differs from the actual sheet thickness, and it was found that the inventors did not sufficiently recognize the influence of the rolling process on the mechanical properties of the material. Thirdly, the heating system of the tested hydrogen induced cracking tensile sample is 900-950 ℃ for x30min, the actual formed plate-shaped heating system is 900-950 ℃ for x5min, the process difference between the two is huge, the performance of the steel obtained by the method can be greatly different, and the obtained result is not convincing.
Chinese patent publication nos. CN110079743a and CN110157864a, which are also incorporated herein by reference, respectively disclose two types of hot forming steels with low delayed cracking sensitivity, in which both documents, the delayed cracking performance is improved by adding micro-alloying elements such as Nb and Ti to the steel to produce a fine precipitated phase, and the influence of inclusions in the steel on the delayed cracking is not taken into consideration, and no corresponding improvement measures and act are given in the smelting process.
Disclosure of Invention
The invention aims to overcome the defects existing in the prior art,provides a steelmaking method capable of improving the delayed cracking resistance of hot forming steel in CSP production line, which ensures that Al in the steel 2 O 3 The maximum size of the inclusions is reduced from about 20 mu m to not more than 10 mu m, the irregular inclusions are changed into spherical inclusions, and the distribution density is 4.63 pieces/mm 2 Down to no more than 0.8/mm 2 The hydrogen induced delayed cracking sensitivity of the steel is reduced from 80% to less than or equal to 50%.
Measures for achieving the above object:
a steelmaking method capable of improving the delayed cracking resistance of hot forming steel in a CSP production line comprises the following production steps:
1) Desulfurizing molten iron, controlling S in the molten iron to be less than or equal to 0.002%, and controlling the exposed surface of the molten iron after slag skimming to be not less than 96%;
2) Conventionally carrying out electric furnace or converter smelting, and controlling the smelting end point in molten steel: c: 0.05-0.06%, T [ O ] is less than or equal to 0.025%;
adding deoxidizer to pre-deoxidize before tapping, and keeping argon blowing in the whole process in the deoxidizing alloying process;
3) LF refining, and conventional soft blowing for 3-5 min with T [ O ] less than or equal to 0.0020%;
in slag making, caO/Al in the slag is controlled 2 O 3 1.6 to 2.0;
4) RH vacuum treatment is carried out, and the vacuum degree is not more than 150Pa;
after RH vacuum treatment is finished, calcium wire feeding treatment is carried out, and the calcium wire quantity is fed according to 0.15-0.40 kg/ton of steel;
soft argon blowing is carried out on molten steel, the soft argon blowing time is 5-10 min, the argon flow is controlled to be 30-50 Nl/min, and the molten steel is strictly forbidden to be exposed in the argon blowing process;
5) Pouring into a blank, and controlling the superheat degree of the ladle molten steel to be 10-15 ℃ in the continuous casting process; the blank pulling speed is 4.0-6.0 m/min; spherical inclusions in casting blanks are formed by CaS, mgO and (CaO) 12 (Al 2 O 3 ) 7 The composition is that the particle diameter of the spherical inclusion is controlled to be less than or equal to 10 mu m;
6) Heating the casting blank, wherein the heating temperature is controlled to be 1100-1200 ℃;
7) Hot rolling, wherein the final rolling temperature is controlled to be 830-910 ℃;
8) Cooling laminar flow to coiling temperature, coiling, and controlling the coiling temperature to 615-665 ℃;
9) Cold rolling to the thickness of a finished product after conventional pickling, and controlling the total rolling reduction to be 55-65%;
10 Then annealing the product, wherein the annealing temperature is controlled between 780 and 840 ℃;
11 Cutting and blanking the steel plate, heating under the protection of nitrogen to austenitize, wherein the austenitize temperature is 850-910 ℃, and preserving the temperature for 4-6 min;
12 After hot stamping forming, conventional quenching is carried out, and then the mixture is naturally cooled to room temperature.
Preferably: in slag making, caO/Al in the slag is controlled 2 O 3 1.7 to 1.93.
Preferably: the vacuum degree is not more than 120Pa.
Preferably: the particle diameter of the spherical inclusions is controlled to be less than or equal to 9.0 mu m.
Preferably: the blank pulling speed is 4.5-5.5 m/min.
Description: the invention is suitable for the composition and the content of components with tensile strength not lower than 1000 MPa.
The action and mechanism of the main process in the invention
The invention controls CaO/Al in slag making 2 O 3 CaO/Al in the slag is preferably controlled within 1.6 to 2.0 2 O 3 1.7 to 1.93, because the slag has small alkalinity, is favorable for adsorbing more Al 2 O 3 The sulfur capacity of the slag alkalinity is moderately increased, and the desulfurization capability is enhanced.
The vacuum degree is controlled to be not more than 150Pa, preferably not more than 120Pa in RH vacuum treatment, because high vacuum can effectively reduce the quantity of inclusions and improve the cleanliness of steel, but the vacuum time and energy consumption required by overhigh vacuum degree are also increased, the production rhythm is also prolonged, the cost control is not facilitated, and the vacuum degree is required to be moderately controlled.
The invention is toAfter the RH vacuum treatment is finished, calcium wire feeding treatment is carried out, and the feeding amount of the calcium wire is controlled to be 0.15-0.40 kg/ton steel, because the inclusion can be modified by adopting the calcium treatment after RH, the calcium wire is prepared from Al 2 O 3 The inclusions are converted into C12A7 inclusions with low melting point, and the shapes of the inclusions are irregularly converted into spheres, so that the stress of the inclusions and steel base is greatly reduced, and the sensitivity of delayed cracking is reduced; the thin slab is adopted for continuous casting in the continuous casting process and the high-speed drawing is kept, so that calcium aluminate inclusions can be effectively prevented from gathering and growing in the continuous casting process, the size of the inclusions is reduced, and the effect of reducing stress in steel can be achieved. Compared with the prior art, the invention has obviously changed size, shape and quantity of the inclusions, the maximum size is reduced from about 20 mu m to not more than 10 mu m, the irregular inclusions are changed into spherical inclusions, and the distribution density is 4.63 pieces/mm 2 Down to 0.8 pieces/mm 2 The hydrogen induced delayed cracking sensitivity of the steel is reduced from 80% to less than or equal to 50%.
The invention controls the superheat degree of the ladle molten steel at 10-15 ℃ and the blank pulling speed at 4.0-6.0 m/min, and is beneficial to rapid blank pulling due to low superheat degree, thereby controlling the growth of inclusions in the steel.
The invention controls the heating temperature of the casting blank to 1100-1200 ℃, which is unfavorable for plate shape control because the temperature is too low and the rolling resistance is large, the obtained tissue is also uneven, and the too high temperature causes excessive burning loss of the casting blank.
Compared with the prior art, the invention ensures that the Al is fed by 0.15-0.40 kg/ton of steel of calcium line quantity 2 O 3 The maximum size of the inclusions is reduced from about 20 mu m to not more than 10 mu m, the irregular inclusions are changed into spherical inclusions, and the distribution density is 4.63 pieces/mm 2 Down to no more than 0.8/mm 2 The hydrogen induced delayed cracking sensitivity of the steel is reduced from 80% to less than or equal to 50%.
Detailed Description
The present invention will be described in detail below:
table 1 shows the values of chemical components under different intensities for the processes of the examples and comparative examples of the present invention;
table 2 is a list of the main process parameters for each example and comparative example of the present invention;
table 3 shows a list of performance tests for each example and comparative example of the present invention;
the embodiments of the invention were produced according to the following steps
1) Desulfurizing molten iron, controlling S in the molten iron to be less than or equal to 0.002%, and controlling the exposed surface of the molten iron after slag skimming to be not less than 96%;
2) Conventionally carrying out electric furnace or converter smelting, and controlling the smelting end point in molten steel: c: 0.05-0.06%, T [ O ] is less than or equal to 0.025%; adding deoxidizer to pre-deoxidize before tapping, and keeping argon blowing in the whole process in the deoxidizing alloying process;
3) LF refining, conventional soft blowing for 3-5 min, and controlling T [ O ]]Less than or equal to 0.0020 percent; in slag making, caO/Al in the slag is controlled 2 O 3 1.6 to 2.0;
4) RH vacuum treatment is carried out, and the vacuum degree is not more than 150Pa;
after RH vacuum treatment is finished, calcium wire feeding treatment is carried out, and the calcium wire quantity is fed according to 0.15-0.40 kg/ton of steel;
soft argon blowing is carried out on molten steel, the soft argon blowing time is 5-10 min, the argon flow is controlled to be 30-50 Nl/min, and the molten steel is strictly forbidden to be exposed in the argon blowing process;
5) Pouring into a blank, and controlling the superheat degree of the ladle molten steel to be 10-15 ℃ in the continuous casting process; the blank pulling speed is 4.0-6.0 m/min; spherical inclusions in casting blanks are formed by CaS, mgO and (CaO) 12 (Al 2 O 3 ) 7 The composition is that the particle diameter of the spherical inclusion is controlled to be less than or equal to 10 mu m;
6) Heating the casting blank, wherein the heating temperature is controlled to be 1100-1200 ℃;
7) Hot rolling, wherein the final rolling temperature is controlled to be 830-910 ℃;
8) Cooling laminar flow to coiling temperature, coiling, and controlling the coiling temperature to 615-665 ℃;
9) Cold rolling to the thickness of a finished product after conventional pickling, and controlling the total rolling reduction to be 55-65%;
10 Then annealing the product, wherein the annealing temperature is controlled between 780 and 840 ℃;
11 Cutting and blanking the steel plate, heating under the protection of nitrogen to austenitize, wherein the austenitize temperature is 850-910 ℃, and preserving the temperature for 4-6 min;
12 After hot stamping forming, conventional quenching is carried out, and then the mixture is naturally cooled to room temperature.
TABLE 1 list of chemical component values (wt%) for various examples and comparative examples of the present invention at various intensities
TABLE 2 list of the main process parameters for each example and comparative example of the present invention
Continuous table 2
The test steel and the comparison steel are subjected to conventional mechanical property comparison, and the results are shown in Table 3; meanwhile, the hydrogen-induced delayed cracking performance of the test steel and the comparative steel is compared, the test steel and the comparative steel are carried out in 0.2mol/L NaOH, and the charging current is dynamically applied, and the charging current density is 0.5mA/cm 2 Tensile strain rate 1.0X10 -5 /s, by calculating the elongation loss (hydrogen embrittlement index I HE )To evaluate the hydrogen induced delayed cracking resistance, I ε Smaller values represent better hydrogen induced delayed cracking resistance.
TABLE 3 Performance test results for each example and comparative example of the present invention
As can be seen from the test results of Table 3, each embodiment has better performance, al 2 O 3 The form, size and quantity of inclusion impurities are obviously changed, and the hydrogen induced delayed cracking sensitivity is reduced from 80% to less than or equal to 50%.
This embodiment is merely a best example and is not intended to limit the implementation of the technical solution of the present invention.

Claims (3)

1. A steelmaking method capable of improving the delayed cracking resistance of hot forming steel in a CSP production line comprises the following production steps:
1) Desulfurizing molten iron, controlling S in the molten iron to be less than or equal to 0.002%, and controlling the exposed surface of the molten iron after slag skimming to be not less than 96%;
2) Conventionally carrying out electric furnace or converter smelting, and controlling the smelting end point in molten steel: c: 0.05-0.06%, T [ O ] is less than or equal to 0.025%;
adding deoxidizer to pre-deoxidize before tapping, and keeping argon blowing in the whole process in the deoxidizing alloying process;
3) LF refining, and soft blowing for 3-5 min with T [ O ] being less than or equal to 3 min
0.0020%; in slag making, caO/Al in the slag is controlled 2 O 3 1.6 to 2.0;
4) Carrying out RH vacuum treatment, wherein the treatment time is 10-15 min, and the vacuum degree is not more than 150Pa;
after RH vacuum treatment is finished, calcium wire feeding treatment is carried out, and the calcium wire quantity is fed according to 0.15-0.40 kg/ton of steel;
soft argon blowing is carried out on molten steel, the soft argon blowing time is 5-10 min, the argon flow is controlled to be 30-50 Nl/min, and the molten steel is strictly forbidden to be exposed in the argon blowing process;
5) Pouring into a blank, and controlling the superheat degree of the ladle molten steel to be 10-15 ℃ in the continuous casting process; the blank pulling speed is 5.2-6.0 m/min;
spherical inclusions in casting blanks are formed by CaS, mgO and (CaO) 12 (Al 2 O 3 ) 7 The composition is that the particle diameter of the spherical inclusion is controlled to be less than or equal to 10 mu m;
6) Heating the casting blank, wherein the heating temperature is controlled to be 1100-1148 ℃;
7) Hot rolling, wherein the final rolling temperature is controlled to be 830-856 ℃;
8) Cooling laminar flow to coiling temperature, coiling, and controlling the coiling temperature to 651-665 ℃;
9) Cold rolling to the thickness of a finished product after conventional pickling, and controlling the total rolling reduction to be 55-65%;
10 Then annealing the product, wherein the annealing temperature is controlled between 780 and 840 ℃;
11 Cutting and blanking the steel plate, and heating under the protection of nitrogen to austenitize;
12 After hot stamping forming, austenitizing at 850-910 deg.c, maintaining the temperature for 4-6 min for conventional quenching, and cooling naturally to room temperature.
2. A steelmaking process for improving the delayed cracking resistance of a hot formed steel in a CSP line as defined in claim 1 wherein: the vacuum degree is not more than 120Pa.
3. A steel-making process for improving delayed cracking resistance of a hot formed steel in a CSP line as claimed in claim 1,
the method is characterized in that: the particle diameter of the spherical inclusions is controlled to be less than or equal to 9.0 mu m.
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