CN116397161B - Normalizing steel plate with uniform thickness direction performance and preparation method thereof - Google Patents

Normalizing steel plate with uniform thickness direction performance and preparation method thereof Download PDF

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Publication number
CN116397161B
CN116397161B CN202310186435.9A CN202310186435A CN116397161B CN 116397161 B CN116397161 B CN 116397161B CN 202310186435 A CN202310186435 A CN 202310186435A CN 116397161 B CN116397161 B CN 116397161B
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steel plate
equal
temperature
cooling
steel
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CN116397161A (en
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梁宝珠
刘文斌
鲍海燕
王志衡
张渊普
黄道昌
易勋
余宏伟
杨波
王孝东
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Baowu Group Echeng Iron and Steel Co Ltd
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Baowu Group Echeng Iron and Steel Co Ltd
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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
    • C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
    • 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
    • B21B1/46—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 metal immediately subsequent to continuous casting
    • B21B1/463—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 metal immediately subsequent to continuous casting in a continuous process, i.e. the cast not being cut before rolling
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
    • B21B—ROLLING OF METAL
    • B21B37/00—Control devices or methods specially adapted for metal-rolling mills or the work produced thereby
    • B21B37/74—Temperature control, e.g. by cooling or heating the rolls or the product
    • 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
    • C21C7/0006—Adding metallic additives
    • 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
    • C21C7/04—Removing impurities by adding a treating agent
    • C21C7/064—Dephosphorising; Desulfurising
    • 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
    • C21D1/28—Normalising
    • 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
    • C21D11/00—Process control or regulation for heat treatments
    • 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
    • C21D11/00—Process control or regulation for heat treatments
    • C21D11/005—Process control or regulation for heat treatments for cooling
    • 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
    • C21D8/0247—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
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C33/00—Making ferrous alloys
    • C22C33/04—Making ferrous alloys by melting
    • C22C33/06—Making ferrous alloys by melting using master alloys
    • 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
    • C22C38/005—Ferrous alloys, e.g. steel alloys containing rare earths, i.e. Sc, Y, Lanthanides
    • 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
    • C22C38/26—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
    • C22C38/38—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
    • 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
    • C21D2211/009—Pearlite
    • 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
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
    • Y02P10/00—Technologies related to metal processing
    • Y02P10/20—Recycling

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  • Physics & Mathematics (AREA)
  • Thermal Sciences (AREA)
  • Crystallography & Structural Chemistry (AREA)
  • Heat Treatment Of Steel (AREA)

Abstract

The invention relates to a normalized steel plate with uniform performance in the thickness direction and a preparation method thereof, wherein the normalized steel plate consists of ：C：≤0.20%,Si：0.20～0.45%,Mn：1.30～1.80%,Cr：0.20～0.40%,Nb：0.020～0.050%,La：0.020～0.050%,Als：0.020～0.045%,P≤0.020%,S≤0.010%,N≤50ppm,O≤20ppm,H≤10ppm,N+O+H≤60ppm,As≤0.005%,As+Sb+Bi+Sn+Pb≤0.05%,CEV≤0.45%, of the following chemical components in percentage by mass, and the balance of Fe and unavoidable impurities; the normalized steel plate prepared by the method has the yield strength of more than 370MPa, the tensile strength of more than 530MPa, the low-temperature impact energy of-20 ℃ of more than 120J, the thickness of 50-100 mm and good welding performance; the invention can be implemented on the existing equipment, has low cost and good economic benefit, and can be produced in industrial large scale.

Description

Normalizing steel plate with uniform thickness direction performance and preparation method thereof
Technical Field
The invention relates to the technical field of metal material manufacturing, in particular to a normalized steel plate with uniform thickness direction performance and a preparation method thereof.
Background
Along with the continuous development of economy, environmental protection pressure is increased, ideas such as carbon peak reaching and carbon neutralization are deep, the service life of a fixed storage tank and a pipeline is effectively prolonged, carbon emission is reduced, the conventional performance is required in the design process, the strength, the toughness and the welding performance of the steel plate along the thickness direction are required, and normalizing delivery is required for ensuring the overall stability of the steel plate. Therefore, development of a normalized steel plate having uniform properties in the thickness direction has been a development direction.
Disclosure of Invention
The invention aims to provide a normalized steel plate with uniform thickness direction performance and a preparation method thereof according to the current market demand, and the normalized steel plate prepared by the invention has the advantages of yield strength of more than 370MPa, tensile strength of more than 530MPa, low-temperature impact energy of-20 ℃ of more than 120J, thickness of 50-100 mm and good welding performance.
The normalized steel plate has uniform performance in the thickness direction, and consists of the following chemical components in percentage by mass ：C：≤0.20%,Si：0.20～0.45%,Mn：1.30～1.80%,Cr：0.20～0.40%,Nb：0.020～0.050%,La：0.020～0.050%,Als：0.020～0.045%,P≤0.020%,S≤0.010%,N≤50ppm,O≤20ppm, H≤10ppm,N+O+H≤60ppm, As≤0.005%,As+Sb+Bi+Sn+Pb≤0.05%,CEV≤0.45%, and the balance of Fe and unavoidable impurities.
Preferably, the normalized steel plate with uniform thickness direction performance is prepared from the following chemical components in percentage by mass ：C：≤0.185%,Si：0.25～0.42%,Mn：1.32～1.49%,Cr：0.22～0.37%,Nb：0.026～0.043%,La：0.023～0.045%,Als：0.022～0.043%,P≤0.020%,S≤0.010%,N≤50ppm,O≤20ppm, H≤10ppm,N+O+H≤60ppm, As≤0.005%,As+Sb+Bi+Sn+Pb≤0.05%,CEV≤0.45%, and the balance of Fe and unavoidable impurities.
The normalized steel plate prepared by the method has the yield strength of more than 370MPa, the tensile strength of more than 530MPa, the low-temperature impact energy of-20 ℃ of more than 120J, the thickness of 50-100 mm and good welding performance.
The invention relates to a preparation method of a normalized steel plate with uniform thickness direction performance, which comprises the following steps:
(1) Charging molten iron: s content is less than or equal to 0.040%, temperature is more than or equal to 1350 ℃, and slag skimming treatment is not needed;
(2) Smelting in a converter: smelting by adopting a double slag method, and controlling a terminal point C: 0.06-0.08%; adding ferrochrome along with molten iron, adding ferromanganese and ferrosilicomanganese when the tapping amount reaches 1/3, adding a slag baffle when the tapping amount reaches 5/6-7/8, and strictly prohibiting point blowing in the tapping process to avoid nitrogen increase;
(3) Refining outside a furnace: argon is blown in the whole process, the refining time is more than or equal to 30min, the alkalinity of white slag is controlled to be 4.5-6.5, and the argon blowing time after the alloy is finely adjusted is more than or equal to 4min;
(4) Vacuum treatment: the vacuum degree is less than or equal to 67Pa, the holding time of the extreme vacuum is more than or equal to 10min, the La wire and the Ca-Fe wire are fed, and the argon blowing time is more than or equal to 10min; wherein the La content of La line is more than or equal to 90 percent according to weight percentage;
(5) Continuously casting into a casting blank, wherein the superheat degree is 6-15 ℃, the pulling speed is 0.70-0.75 m/min, and the slow cooling time of the casting blank is not less than 48 hours;
(6) The casting blank is heated to the tapping temperature of 1180-1250 ℃, and is tapped for primary high-pressure water descaling;
(7) Rolling and cooling: the initial rolling temperature of rough rolling is more than or equal to 1100 ℃, the initial rolling temperature of finish rolling is less than or equal to 960 ℃, the final rolling temperature is 840-870 ℃, the steel plate is subjected to laminar cooling after pre-straightening, the cooling speed is more than or equal to 20 ℃/S, and the steel plate is subjected to air cooling and offline after straightening by adopting a thermal straightener;
(8) And (3) carrying out normalizing treatment on the rolled steel plate by adopting a vacuum radiation heat treatment furnace, wherein the normalizing treatment temperature is as follows: 900-940 ℃, and cooling the steel plate by air after the steel plate is discharged from the furnace for (h+30-60) min, wherein h is the thickness value of the finished product in mm.
The reasons for the composition and production process setting of the steel of the present invention are described in detail below.
1. Reasons for the limited amount of chemical components (C, si, mn, P, S, cr, nb, la, etc)
The steel is considered to be mainly to ensure uniformity of strength and toughness in the thickness direction. Therefore, the purity of molten steel is strictly controlled during steelmaking. C. The design components of Si, mn and Cr ensure the strength and toughness of the steel and prevent P, S content from affecting the low-temperature toughness of the steel. The requirements on P, S, as and gas elements are raised, and considering that the influence of the elements on the brittleness of the steel is large, the content of the elements is strictly limited, so that the tissue segregation tendency of the steel is reduced.
(1) Influence of alloying elements on Steel Properties
C is the most effective element for improving the strength of steel, and as the content of C increases, fe 3 C in the steel increases, the hardenability also increases, and the tensile strength and yield strength of the steel are improved. However, increasing the C content in the steel increases the tissue segregation degree of the steel plate, which is unfavorable for the uniformity of thickness performance, low-temperature toughness and welding performance. Therefore, the C content of the steel of the present invention should be controlled to be 0.20% or less.
Si has a solid solution strengthening effect, so that strength and hardness of ferrite are improved, but plasticity and toughness are reduced. The deoxidizing capability is strong, the deoxidizing agent is a deoxidizing agent commonly used in steelmaking, silicon is also commonly present in steel as silicate inclusions of Fe and Mn, various performances of the steel can be reduced, and the plasticity is lower than that of sulfide. Therefore, the Si content of the steel of the invention is limited to 0.20-0.45% and can meet the requirement.
Mn has strong affinity with carbon, is an effective element for expanding an austenite phase region, refining grains and ensuring comprehensive performance, is an element easy to segregate, and can generate a martensite phase in the production and welding processes of steel when the content of Mn and C in the segregated region reaches a certain proportion, and the phase can show high hardness. Therefore, the Mn content is limited to a range of 1.30 to 1.80% in designing the steel.
Cr is a ferrite forming element and reduces the gamma zone, so that in the absence of austenitizing elements, high Cr steels will exhibit a ferrite structure. There are many valuable properties: high hardness, high strength, yield point and high wear resistance, and has little influence on plasticity and toughness, high oxidation resistance and corrosion resistance. Cr is a medium carbide forming element, and among all kinds of carbides, chromium carbide is the smallest one, which can be uniformly distributed in the steel volume, and thus has high strength, hardness, yield point and high wear resistance. Because it can refine and uniformly distribute the structure, the plasticity and toughness are also good. Therefore, the Cr content in the steel is controlled to be in the range of 0.20-0.40%.
Nb is an element for obviously improving the dynamic recrystallization of austenite, can effectively refine matrix grains, and can obviously refine austenite grains by matching with large reduction in the rolling process. The refined grains can simultaneously improve the strength and the low-temperature toughness level of the steel plate. However, an excessive Nb content causes an increase in the second phase particle size, which affects the welding performance. Therefore, in the steel of the present invention, the added Nb is controlled to be in the range of 0.020 to 0.050%.
La: sulfur, oxygen and the like in the steel react with added La elements to generate spherical La sulfide or sulfur oxide to replace strip manganese sulfide (MnS) inclusion, and the sulfide form is controlled, so that the toughness and plasticity of the steel, particularly the transverse impact performance, are improved, and the anisotropy of the steel is improved. In addition, la converts angular high-hardness alumina inclusions into spherical La oxysulfide and aluminum La, which is beneficial to improving the fatigue performance of steel and the like. Therefore, as long as the La addition amount is proper, la element not only can denature impurities, but also can reduce the quantity of impurities and refine the impurities. Therefore, the La content in the steel is controlled to be in the range of 0.020-0.050%.
Al is the main deoxidizing element in steel, and the maximum solubility in austenite is about 0.6%. Al and N in the steel combine to form AlN particles, so that the growth of crystal grains is hindered, the effect of refining the crystal grains is achieved, the impact toughness is improved, and the hot workability, the welding performance and the cutting workability of the steel are affected by the excessive content of Al. So the Als content in the steel is controlled to be in the range of 0.020-0.45 percent.
P is a harmful element in steel, has a great damaging effect on the mechanical properties of the steel plate, especially the low-temperature impact toughness, the elongation, the weldability and the SR property of a welded joint, and theoretically has lower and better requirements; however, in view of steel-making operability and steel-making cost, the P content needs to be controlled to 0.020% or less.
S is used as a harmful inclusion in steel and has a great damage effect on low-temperature toughness of a quality-improved steel plate, more importantly, S is combined with Mn in the steel to form MnS inclusion, in the hot rolling process, the plasticity of MnS enables MnS to extend along the rolling direction to form a strip along the rolling direction of the MnS inclusion, the low-temperature impact toughness, uniform elongation, Z-direction performance and weldability of the steel plate are seriously damaged, and meanwhile, S is a main element generating hot shortness in the hot rolling process, and theoretically, the lower the requirement is, the better; however, in view of steel-making operability and steel-making cost, the S content needs to be controlled to 0.010% or less.
N, O, H is used as a gas element in steel, N and O in the steel have adverse effects on low-temperature toughness, excessive N and O in the steel form particles or inclusions with elements such as Nb, ti and the like, grain growth is hindered, toughness of a welding heat affected zone is further damaged, and steel cleanliness is reduced, so that the N and O content in the steel is reduced as much as possible. The steel has high H content, which is easy to generate bubbles and easy to cause cracks and the variability of performance, so that N is less than or equal to 50ppm, O is less than or equal to 20ppm and H is less than or equal to 10ppm; meanwhile, the N+O+H is less than or equal to 60ppm.
As is a harmful element in steel, increases cold brittleness of steel, deteriorates welding performance, and is liable to form defects such As segregation and inclusions, so that it is preferable that As is lower in steel. Meanwhile, the total amount of the rest residual elements is limited, and As+Sb+Bi+Sn+Pb is less than or equal to 0.05 percent.
2. Reasons for setting production Process
(1) Steelmaking process
The S content of the incoming molten iron is controlled to achieve the effect of low S, so that the slag skimming procedure is reduced, the cost is reduced, and the production rhythm is improved. The content of tapping C is controlled through smelting of a 130t top-bottom combined blown converter, and alloy is added when the tapping amount reaches 1/3, so that the alloy is effectively dissolved in molten steel, slag blocking plate operation is adopted, the excessive thickness of a slag layer is avoided, and the point blowing is strictly forbidden to avoid nitrogen and oxygen increasing. The external refining time is controlled to be more than or equal to 30min so as to remove sulfur and oxygen as much as possible, avoid damaging impact toughness due to high S and O content, and promote the uniformity of the components and temperature of molten steel in an argon blowing mode. The vacuum process adopts a circulating degassing process, the vacuum degree is controlled, the ultimate vacuum treatment time is ensured, and the impurity and gas content in the steel can be well reduced. Meanwhile, la wires and Ca-Fe wires are added, so that the types of inclusions in molten steel are changed, the inclusions are promoted to float upwards fully, and the steel is ensured to have high purity and low-temperature toughness. The superheat degree is controlled to be 6-15 ℃, the drawing speed is controlled to be 0.70-0.75 m/min, and the slow cooling of the casting blank is used for reducing the central porosity and segregation of the casting blank and improving the internal quality.
(2) Steel rolling process
The invention controls the heating and tapping temperature of the casting blank within a certain range, and aims to ensure the full austenitization and homogenization of the casting blank, lighten the internal defects of the casting blank such as center segregation and the like and control the size of austenite grains within a proper range. The initial rolling temperature, the finish rolling temperature and the final rolling temperature of rough rolling and the cooling mode are controlled, so that the purpose is to perform I-stage rough rolling in a complete austenite recrystallization zone, perform II-stage finish rolling in a non-recrystallization zone, prevent mixed crystals and obtain proper grain size. So as to obtain the product of the invention with uniform thickness direction performance.
(3) Heat treatment process
The steel plate manufactured by the method can be used for manufacturing fixed storage tanks, pressure pipelines and the like, and the uniformity of the thickness performance of the steel plate is not required. Therefore, the heat treatment process is designed to be normalizing, the normalizing temperature, the normalizing time and the cooling speed are controlled within a certain range, and the oversize or too fine grain size caused by improper temperature and time is prevented, so that a stable tissue is obtained. The structure of the steel after normalizing is a stable ferrite and pearlite structure, and the martensitic structure with great influence on the low-temperature toughness does not appear in the steel.
The invention has the advantages that the N, O, H content is strictly controlled in the steelmaking process, the vacuum circulation is carried out to ensure the purity of the molten steel, meanwhile, the La line and the Ca-Fe line are added, the type of the inclusions in the molten steel is changed, the inclusions are promoted to float up sufficiently to enable the inclusions to be spheroidized and thinned, and the fluidity of the molten steel is improved. The steel plate with thick specification is rolled, and after normalizing treatment, the steel plate has uniform performance in the thickness direction and can be used for reinforcing a fixed storage tank or a pressure pipeline. The invention can be implemented on the existing equipment, has low cost and good economic benefit, and can realize industrial mass production.
Detailed Description
In order to better explain the technical solution of the present invention, the following description of the technical solution of the present invention is given by way of example only and not by way of limitation in any way, in conjunction with specific examples. All changes and equivalents that do not depart from the gist of the invention are intended to be within the scope of the invention.
Table 1 below shows the chemical composition and weight percent (wt%) value list of the steel plate according to each embodiment of the present invention;
table 2 below is a list of values of the technological parameters of the smelting process of the steel plate according to each embodiment of the invention;
Table 3 below is a list of values of process parameters for the rolling process and the heat treatment process of the steel sheet according to various embodiments of the present invention;
Table 4 below shows the results of mechanical properties of the finished steel sheet produced in accordance with the examples of the present invention.
The normalized steel plate provided by the embodiment of the invention has uniform performance in the thickness direction, and consists of the following chemical components in percentage by mass ：C：≤0.20%,Si：0.20～0.45%,Mn：1.30～1.80%,Cr：0.20～0.40%,Nb：0.020～0.050%,La：0.020～0.050%,Als：0.020～0.045%,P≤0.020%,S≤0.010%,N≤50ppm,O≤20ppm, H≤10ppm,N+O+H≤60ppm, As≤0.005%,As+Sb+Bi+Sn+Pb≤0.05%,CEV≤0.45%, and the balance of Fe and unavoidable impurities.
The preparation method of the normalized steel plate with uniform thickness direction performance comprises the following steps:
(1) Charging molten iron: s content is less than or equal to 0.040%, temperature is more than or equal to 1350 ℃, and slag skimming treatment is not needed;
(2) Smelting in a converter: smelting by adopting a double slag method, and controlling a terminal point C: 0.06-0.08%; adding ferrochrome along with molten iron, adding ferromanganese and ferrosilicomanganese when the tapping amount reaches 1/3, adding a slag baffle when the tapping amount reaches 5/6-7/8, and strictly prohibiting point blowing in the tapping process to avoid nitrogen increase;
(3) Refining outside a furnace: argon is blown in the whole process, the refining time is more than or equal to 30min, the alkalinity of white slag is controlled to be 4.5-6.5, and the argon blowing time after the alloy is finely adjusted is more than or equal to 4min;
(4) Vacuum treatment: the vacuum degree is less than or equal to 67Pa, the holding time of the extreme vacuum is more than or equal to 10min, the La wire and the Ca-Fe wire are fed, and the argon blowing time is more than or equal to 10min; wherein the La content of La line is more than or equal to 90 percent by weight percent.
(5) Continuously casting into a casting blank, wherein the superheat degree is 6-15 ℃, the pulling speed is 0.70-0.75 m/min, and the slow cooling time of the casting blank is not less than 48 hours;
(6) The casting blank is heated to the tapping temperature of 1180-1250 ℃, and is tapped for primary high-pressure water descaling;
(7) Rolling and cooling: the initial rolling temperature of rough rolling is more than or equal to 1100 ℃, the initial rolling temperature of finish rolling is less than or equal to 960 ℃, the final rolling temperature is 840-870 ℃, the steel plate is subjected to laminar cooling after pre-straightening, the cooling speed is more than or equal to 20 ℃/S, and the steel plate is subjected to air cooling and offline after straightening by adopting a thermal straightener;
(8) And (3) carrying out normalizing treatment on the rolled steel plate by adopting a vacuum radiation heat treatment furnace, wherein the normalizing treatment temperature is as follows: 900-940 ℃, and cooling the steel plate by air after the steel plate is discharged from the furnace for (h+30-60) min, wherein h is the thickness value of the finished product in mm.
Table 1 list of chemical components and weight percentage (wt%) values of the steel sheet according to each embodiment of the present invention
Table 2 list of values of process parameters in the smelting process of the steel sheet according to the embodiments of the present invention
Table 3 list of values of process parameters of the rolling process and the heat treatment process of the steel sheet according to the embodiments of the present invention
Table 4 list of values of process parameters in the rolling process of the steel sheet according to the embodiments of the present invention
As can be seen from tables 1 to 4, the steel plate of the invention has simple manufacturing process and the mechanical properties as follows: the yield strength is more than or equal to 370MPa, the tensile strength is more than or equal to 530MPa, the elongation A is more than or equal to 23%, the low-temperature impact energy at minus 20 ℃ is more than 120J, and the inspection performance at different thickness positions is uniform. Completely meets the requirements of manufacturing equipment such as fixed storage tanks, pressure pipelines and the like.
The above-described embodiments are merely specific examples of the present invention for illustrating the present invention and are not to be construed as limiting the present invention in any way, and any insubstantial changes made in the above-described embodiments without departing from the scope of the claims of the present invention should be construed as falling within the scope of the claims of the present invention.

Claims (5)

1. The normalized steel plate with uniform performance in the thickness direction is characterized by comprising the following chemical components in percentage by mass ：C：≤0.20%,Si：0.20～0.45%,Mn：1.30～1.80%,Cr：0.20～0.40%,Nb：0.020～0.050%,La：0.020～0.050%,Als：0.020～0.045%,P≤0.020%,S≤0.010%,N≤50ppm,O≤20ppm, H≤10ppm,N+O+H≤60ppm, As≤0.005%,As+Sb+Bi+Sn+Pb≤0.05%,CEV≤0.45%, and the balance of Fe and unavoidable impurities;
The preparation method of the normalized steel plate with uniform thickness direction performance comprises the following steps:
(1) Charging molten iron: s content is less than or equal to 0.040%, temperature is more than or equal to 1350 ℃, and slag skimming treatment is not needed;
(2) Smelting in a converter: smelting by adopting a double slag method, and controlling a terminal point C: 0.06-0.08%; adding ferrochrome along with molten iron, adding ferromanganese and ferrosilicomanganese when the tapping amount reaches 1/3, adding a slag baffle when the tapping amount reaches 5/6-7/8, and strictly prohibiting point blowing in the tapping process to avoid nitrogen increase;
(3) Refining outside a furnace: argon is blown in the whole process, the refining time is more than or equal to 30min, the alkalinity of white slag is controlled to be 4.5-6.5, and the argon blowing time after the alloy is finely adjusted is more than or equal to 4min;
(4) Vacuum treatment: the vacuum degree is less than or equal to 67Pa, the holding time of the extreme vacuum is more than or equal to 10min, the La wire and the Ca-Fe wire are fed, and the argon blowing time is more than or equal to 10min;
(5) Continuously casting into a casting blank, wherein the superheat degree is 6-15 ℃, the pulling speed is 0.70-0.75 m/min, and the slow cooling time of the casting blank is not less than 48 hours;
(6) The casting blank is heated to the tapping temperature of 1180-1250 ℃, and is tapped for primary high-pressure water descaling;
(7) Rolling and cooling: the initial rolling temperature of rough rolling is more than or equal to 1100 ℃, the initial rolling temperature of finish rolling is less than or equal to 960 ℃, the final rolling temperature is 840-870 ℃, the steel plate is subjected to laminar cooling after pre-straightening, the cooling speed is more than or equal to 20 ℃/S, and the steel plate is subjected to air cooling and offline after straightening by adopting a thermal straightener;
(8) And (3) carrying out normalizing treatment on the rolled steel plate by adopting a vacuum radiation heat treatment furnace, wherein the normalizing treatment temperature is as follows: 900-940 ℃, and cooling the steel plate by air after the steel plate is discharged from the furnace for (h+30-60) min, wherein h is the thickness value of the finished product in mm.
2. The normalized steel plate with uniform thickness direction performance according to claim 1, wherein the normalized steel plate is composed of the following chemical components by mass percent ：C：≤0.185%,Si：0.25～0.42%,Mn：1.32～1.49%,Cr：0.22～0.37%,Nb：0.026～0.043%,La：0.023～0.045%,Als：0.022～0.043%,P≤0.020%,S≤0.010%,N≤50ppm,O≤20ppm, H≤10ppm,N+O+H≤60ppm, As≤0.005%,As+Sb+Bi+Sn+Pb≤0.05%,CEV≤0.45%, and the balance of Fe and unavoidable impurities.
3. A normalized steel plate having uniform thickness direction property according to claim 1 or 2, characterized in that: the normalized steel plate has yield strength of more than 370MPa, tensile strength of more than 530MPa, low-temperature impact energy of more than 120J at minus 20 ℃ and thickness of 50-100 mm, and good welding performance.
4. The method for producing a normalized steel plate having uniform thickness-direction properties according to claim 1 or 2, characterized by comprising the steps of:
(1) Charging molten iron: s content is less than or equal to 0.040%, temperature is more than or equal to 1350 ℃, and slag skimming treatment is not needed;
(2) Smelting in a converter: smelting by adopting a double slag method, and controlling a terminal point C: 0.06-0.08%; adding ferrochrome along with molten iron, adding ferromanganese and ferrosilicomanganese when the tapping amount reaches 1/3, adding a slag baffle when the tapping amount reaches 5/6-7/8, and strictly prohibiting point blowing in the tapping process to avoid nitrogen increase;
(3) Refining outside a furnace: argon is blown in the whole process, the refining time is more than or equal to 30min, the alkalinity of white slag is controlled to be 4.5-6.5, and the argon blowing time after the alloy is finely adjusted is more than or equal to 4min;
(4) Vacuum treatment: the vacuum degree is less than or equal to 67Pa, the holding time of the extreme vacuum is more than or equal to 10min, the La wire and the Ca-Fe wire are fed, and the argon blowing time is more than or equal to 10min;
(5) Continuously casting into a casting blank, wherein the superheat degree is 6-15 ℃, the pulling speed is 0.70-0.75 m/min, and the slow cooling time of the casting blank is not less than 48 hours;
(6) The casting blank is heated to the tapping temperature of 1180-1250 ℃, and is tapped for primary high-pressure water descaling;
(7) Rolling and cooling: the initial rolling temperature of rough rolling is more than or equal to 1100 ℃, the initial rolling temperature of finish rolling is less than or equal to 960 ℃, the final rolling temperature is 840-870 ℃, the steel plate is subjected to laminar cooling after pre-straightening, the cooling speed is more than or equal to 20 ℃/S, and the steel plate is subjected to air cooling and offline after straightening by adopting a thermal straightener;
(8) And (3) carrying out normalizing treatment on the rolled steel plate by adopting a vacuum radiation heat treatment furnace, wherein the normalizing treatment temperature is as follows: 900-940 ℃, and cooling the steel plate by air after the steel plate is discharged from the furnace for (h+30-60) min, wherein h is the thickness value of the finished product in mm.
5. The method for producing a normalized steel plate having uniform thickness-direction properties according to claim 4, wherein: and (3) the La wire used in the step (4) contains more than or equal to 90% of La in percentage by weight.
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