CN116426828A - NM450 steel plate with low cost, large thickness and high performance and manufacturing method thereof - Google Patents

NM450 steel plate with low cost, large thickness and high performance and manufacturing method thereof Download PDF

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CN116426828A
CN116426828A CN202310441633.5A CN202310441633A CN116426828A CN 116426828 A CN116426828 A CN 116426828A CN 202310441633 A CN202310441633 A CN 202310441633A CN 116426828 A CN116426828 A CN 116426828A
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temperature
equal
steel plate
rolling
thickness
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王琨铭
帅勇
廖桑桑
邹锦忠
吕继平
张亚君
张留洪
赵敏森
蒋星亮
孙乐飞
刘志芳
杨帆
蔡芳澜
郑景斌
熊雄
周焱民
周启航
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Xinyu Iron and Steel Co Ltd
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Xinyu 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
    • B21B3/00—Rolling materials of special alloys so far as the composition of the alloy requires or permits special rolling methods or sequences ; Rolling of aluminium, copper, zinc or other non-ferrous metals
    • B21B3/02—Rolling special iron alloys, e.g. stainless steel
    • 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
    • B21B37/76—Cooling control on the run-out table
    • 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
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    • 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
    • C21C7/0075—Treating in a ladle furnace, e.g. up-/reheating of molten steel within the ladle
    • 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
    • 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
    • C21D1/56—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering characterised by the quenching agents
    • C21D1/60—Aqueous agents
    • 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
    • C22C38/001—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
    • C22C38/005—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
    • C22C38/28—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
    • C22C38/32—Ferrous alloys, e.g. steel alloys containing chromium with boron
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D2211/00—Microstructure comprising significant phases
    • C21D2211/008—Martensite
    • 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

Abstract

The invention provides a low-cost large-thickness high-performance NM450 steel plate and a manufacturing method thereof, wherein the components are as follows: 0.17 to 0.25 percent of C, 0.1 to 0.3 percent of Si, 1.0 to 1.25 percent of Mn, less than or equal to 0.015 percent of P, less than or equal to 0.005 percent of S, 0.015 to 0.04 percent of Alt, and Cr:0.5 to 0.65 percent of Nb:0.01 to 0.03 percent of Ti:0.01 to 0.02 percent, B:0.001 to 0.003 percent of Re, 0.0015 to 0.003 percent of N, 0.003 to 0.005 percent of N, and the balance of Fe and residual elements; compared with the prior art, the invention has the advantages that the hardness of the product at the position with the thickness of 1/2 is more than or equal to 440HB, the longitudinal impact energy at the temperature of minus 40 ℃ is more than or equal to 60J, the maximum thickness of the steel plate can reach 100mm and no cutting delay crack is generated through component design and production process.

Description

NM450 steel plate with low cost, large thickness and high performance and manufacturing method thereof
Technical Field
The invention belongs to the field of alloys, and particularly relates to a low-cost high-thickness high-performance NM450 steel plate and a manufacturing method thereof.
Background
NM450 steel plate is mainly applied in mining machinery, loading transportation equipment, large-scale excavating equipment and other fields, and the application environment is abominable, and the use region is extensive, and need adopt modes such as flame cutting, welding to carry out processing, therefore, NM450 steel plate must have good wearability, low temperature toughness and crack resistance sensitivity.
In view of the above performance requirements, especially for large-thickness NM450 steel plates with thickness of 80-100mm, due to thickness effect, domestic manufacturers generally adopt to add higher alloying elements Cr, mo and Ni to improve the hardenability of the steel plate and improve the low-temperature toughness, so that the production cost is greatly increased, and the stress concentration after quenching is easily caused by the segregation of the alloying elements, so that the steel plate is cut by flame and cracked after welding.
A method for manufacturing thin high-Ti abrasion-resistant steel NM450 disclosed in publication No. CN 107099728A at 8/29 of 2017, which comprises the steps of: blast furnace molten iron, molten iron pretreatment, converter smelting, LF furnace refining, RH furnace refining, traditional slab continuous casting, heating furnaces, high-pressure water dephosphorization, hot continuous rolling units, ultra-rapid cooling, coiling, flattening, heating, quenching, tempering and finishing; the components are as follows: : =0.16 to 0.20wt% of C, 0.2 to 0.4wt% of Si, 0.8 to 1.5wt% of Mn, 0.10 to 0.20wt% of Mo, 0.30 to 0.50wt% of Cr, 0.02 to 0.05wt% of Nb, 0.10 to 0.15wt% of Ti, and 0.0005 to the average of B
0.0010wt%, P <0.015wt%, S <0.010wt%, and the balance of Fe and unavoidable impurities; the patent selects a low-cost high Ti microalloying technology, the Ti content is 0.10-0.15 wt percent, and the Ti content is high and the cost is high; and the technique cannot solve the problem of core segregation of the steel sheet.
Disclosure of Invention
According to the low-cost large-thickness high-performance NM450 steel plate and the manufacturing method thereof, through component design, B and Re are added, and alloys such as Mo, ni and the like are not added, so that the production cost is reduced; according to the production process, the obtained product reduces the core segregation of the steel plate, the effect of optimizing the uniformity of the structural performance is achieved, the produced steel plate meets the requirements that the hardness of the 1/2 part of the steel plate is more than or equal to 440HB, the longitudinal impact energy at the temperature of 40 ℃ is more than or equal to 60J, the high standards of all mechanical properties meet the national standards, the maximum thickness of the steel plate can reach 100mm, the cutting delay cracks can not be generated, and the market demand of the NM450 steel plate with large thickness of the performance of the core is met.
The specific technical scheme of the invention is as follows:
the NM450 steel plate with low cost, large thickness and high performance comprises the following components in percentage by mass:
0.17 to 0.25 percent of C, 0.1 to 0.3 percent of Si, 1.0 to 1.25 percent of Mn, less than or equal to 0.015 percent of P, less than or equal to 0.005 percent of S, 0.015 to 0.04 percent of Alt, and Cr:0.5 to 0.65 percent of Nb:0.01 to 0.03 percent of Ti:0.01 to 0.02 percent, B:0.001 to 0.003 percent of Re, 0.0015 to 0.003 percent of N, 0.003 to 0.005 percent of N, and the balance of Fe and residual elements.
In the prior art, the hardenability and low-temperature toughness of the steel plate are improved by increasing the content of the element Mn, cr, mo, ti, ni so as to ensure that the core hardness is more than or equal to 420HB and the longitudinal impact energy at minus 40 ℃ is more than or equal to 60J, but elements Mn and Cr are extremely easy to form component segregation in the center of a casting blank, a core segregation zone is generated, the surface and the core structure of the thick NM450 are uneven, the core impact toughness is deteriorated, larger thermal stress and structural stress can be generated at a processing part during hot cutting and welding, when the stress exceeds the tensile strength of the steel plate, microcracks are formed at weak positions of segregation parts, and delayed cracks are caused after expansion. The element Mo and Ni alloy has high price, and the Ni-containing billet can generate N in the heating processThe iS network structure increases the adhesiveness of the scale on the surface of the steel billet, iS difficult to remove later, and has to be coated with anti-oxidation paint, thereby increasing the manufacturing cost of the steel plate. The invention utilizes the characteristic of purifying molten steel by adding 0.0015 to 0.003 percent of rare earth Re, and the rare earth Re is compounded with (Mn, ca) S composite inclusion to be modified into Re with smaller size and more quantity 2 O 2 S and Re x S y The inclusion can provide more nucleation points for tissue nucleation in the subsequent rolling process, is beneficial to refining grains in the rolling process, improves the hardenability of the steel plate and improves the low-temperature toughness, in addition, rare earth Re, al, O, S and other elements form tiny inclusions to be concentrated at a tissue grain boundary, so that the interface energy of the grain boundary is reduced, the eccentric energy barrier of other elements at the grain boundary is increased, the eccentric phenomenon of B element at the grain boundary can be inhibited to a certain extent, the hardenability of B element is more effectively improved, and the effects of reducing the Mn and Cr contents, not adding Mo, ni and other alloys, reducing the production cost, reducing the core segregation of the steel plate and optimizing the uniformity of the tissue performance are achieved.
The thickness of the low-cost large-thickness high-performance NM450 steel plate is 80-100 mm;
the structure of the low-cost large-thickness high-performance NM450 steel plate is martensitic; the 1/4 and the 1/2 parts of the core structure are 100% martensitic;
the yield strength of the steel plate of the low-cost large-thickness high-performance NM450 steel plate is more than or equal to 1150Mpa, the tensile strength is more than or equal to 1400Mpa, the elongation is more than or equal to 20%, the longitudinal impact energy at minus 40 ℃ is more than or equal to 60J, the surface Brinell hardness is more than or equal to 450HB, and the grain size is 9-10 grades; the yield strength at the position with the thickness of 1/2 is more than or equal to 1000Mpa, the tensile strength is more than or equal to 1300Mpa, the elongation is more than or equal to 20 percent, the longitudinal impact energy at the temperature of minus 40 ℃ is more than or equal to 60J, the Brinell hardness is more than or equal to 440HB, and the grain size is 9 to 10 grades.
The invention provides a manufacturing method of a low-cost large-thickness high-performance NM450 steel plate, which comprises the working procedures of smelting, heating, rolling, cooling after rolling and heat treatment.
The smelting comprises the following steps: converter smelting-LF furnace refining-RH furnace vacuum degassing;
the smelting comprises feeding rare earth wires after RH furnace vacuum smelting and emptying;
the smelting, wherein LF refining electrifying slag is more than or equal to 10min, temperature measurement sampling is carried out, deoxidizing is carried out to produce white slag, feO+Mn0 in the white slag is ensured to be less than or equal to 1.0%, the white slag holding time is more than or equal to 10min, the desulfurization effect is ensured, and the S content in molten steel is ensured to be less than 0.005%.
The RH furnace is subjected to vacuum degassing, the vacuum treatment time is more than or equal to 8min, the vacuum degree is less than or equal to 130Pa, the ultimate vacuum holding time is more than or equal to 8min, after the RH vacuum treatment breaks the blank for 2min, seamless calcium wire (0.50-0.70) kg/ton steel is fed, the wire feeding speed (1.5-1.7) m/s is fed, rare earth alloy wire (1.0-1.2) kg/ton steel is fed, the wire feeding speed (1.3-1.5) m/s is fed, soft blowing is carried out after wire feeding, the argon pressure (0.20-0.4) MPa is blown at the bottom of a ladle, and the flow (150-300) NM is carried out 3 and/H, the time is more than or equal to 10min, and the outlet time (H) is ensured]Less than or equal to 3ppm. The rare earth alloy wire is fed after breaking, mainly modifies the composite inclusion of (Mn, ca) S remained in the molten steel after desulfurization, and as the rare earth element is extremely active, the rare earth alloy is added before breaking and can quickly react with oxygen in the steel to form rare earth oxide so as to lose the inclusion modification effect, and the [ H ] is ensured when the molten steel is discharged from a vacuum station]The hydrogen atoms in the steel are mainly prevented from being adhered to the inter-crystal gaps or defects of the steel plate in a large quantity and combined into hydrogen molecules, and the hydrogen is released in the form of hydrogen after the steel plate is cut by flame, so that hydrogen-induced delayed cracks appear in the steel plate.
The heating is as follows: adopting a hot feeding and hot charging process;
the heating is specifically as follows: hot delivery temperature of steel billet: 700-800 ℃, 500-680 ℃ of hot charging temperature and heating temperature of a billet preheating section: 500-900 ℃, one-stage temperature: 900-1150 deg.c, 1200-1260 deg.c in the second adding section, 1200-1250 deg.c in the soaking section and total heating time over 360 min.
The prior art generally needs to coat anti-oxidation paint before entering a furnace, a hot feeding and hot charging process cannot be adopted, the maximum temperature of entering the furnace is only 60 ℃, the heating energy consumption is increased, in order to achieve the temperature homogenization of the steel billet, the time of the steel billet in a soaking section must be prolonged, the coarsening risk of the structure is increased, and the hardenability of the steel plate is affected. The invention does not add Ni element, can adopt a hot feeding and hot charging process, the highest furnace charging temperature can reach 680 ℃, the whole temperature is uniform when the blank is charged into the furnace, the heating time can be greatly shortened, the heating energy consumption is reduced, the production efficiency is improved, the tissue growth risk is reduced, and the finer tissue grain size is provided for subsequent rolling and heat treatment.
The rolling is as follows: rolling in a recrystallization zone and controlling a rolling process in a non-recrystallization zone in two stages;
the rolling is specifically as follows: adopting a two-stage controlled rolling process, wherein the first stage adopts a high-temperature recrystallization zone for rolling, the initial rolling temperature is more than or equal to 1050 ℃, the final rolling temperature is more than 950 ℃, the accumulated rolling reduction is 50-60%, and the single-pass rolling reduction is 20-30 mm; in the second stage, rolling is carried out by adopting a non-recrystallization zone, the initial rolling temperature is less than or equal to 880 ℃, the final rolling temperature is 830-850 ℃, the accumulated rolling reduction is 30-40%, and the single-pass rolling reduction is less than or equal to 20mm. The rolling temperature of the first stage is controlled to be higher than 950 ℃, in the rolling process of the temperature interval, the austenite grains of the steel plate can be respectively subjected to dynamic recrystallization, sub-dynamic recrystallization and static recrystallization along with the decrease of the temperature of the steel plate, the original austenite grains grow through nucleation, the grains are thinned to a certain extent and are not easy to grow, the rolling temperature of the second stage is controlled to be between 830 and 850 ℃, the second phase grains of the microalloy element Nb are promoted to be precipitated in dislocation and grain boundary by utilizing the deformation induction precipitation effect in the rolling process, and more nucleation points are provided for subsequent relaxation cooling.
The cooling after rolling is as follows: relaxation and rapid cooling;
the cooling after rolling specifically comprises the following steps: the steel plate stays on a roller way for 100-120 s (relaxation time) before being rapidly cooled, the roller way is opened to swing, the relaxation temperature is 810-830 ℃, the steel plate is rapidly cooled after being subjected to relaxation, the opening cooling temperature is more than or equal to 800 ℃, the cooling roller way speed is 0.3-0.5 m/s, and the water quantity of a high-pressure section is 6000-7500 m 3 Water ratio of 1.2-1.6, low pressure section water quantity of 3000-5000 m 3 And/h, the water ratio is 1.2-1.6, and the reddening temperature is 300-350 ℃.
In the prior art, a large amount of alloy elements are added, so that the occurrence of cracks in the sizing process before quenching caused by the generation of larger internal stress due to rapid cooling after rolling is avoided, the cooling speed is slower by adopting a post-rolling air cooling process, and the tissue can further grow up in the cooling process, thereby influencing the hardenability and the tissue uniformity of the steel plate. The method reduces the addition of alloy elements, improves the structural uniformity and the hardenability of the steel plate crystal grains, adopts a relaxation and rapid cooling process after rolling, and ensures that NbC in the steel is fully separated out after the steel plate is rolled on a roller way for 100-120 seconds, thereby providing more nucleation points for rapid cooling phase transition and achieving the effect of refining the steel plate crystal grains. The rapid cooling mainly improves the austenite supercooling degree in the rolled steel plate, increases the nucleation rate in the phase transformation process, prevents coarsening of second-phase particles of Nb precipitated in the two-stage rolling and relaxation processes, and provides finer original grain structure for subsequent off-line quenching.
The heat treatment is as follows: quenching by adopting trinitro aqueous solution and tempering at low temperature.
The method comprises the following steps: the trinitro aqueous solution comprises the following components in percentage by mass: sodium nitrate: 15-25% of sodium nitrite: 20-30% of potassium nitrate: 20-25%, the balance being water; quenching heat preservation temperature: 890-910 deg.c and 3 XH min; h represents the thickness of the steel plate, mm, and when calculating, the numerical value before the unit is brought into a formula; the temperature of the quenched steel plate is 20-40 ℃;
the low temperature tempering: tempering temperature: 180-220 ℃ and furnace storage time: 1.5XH+150 minutes, H represents the thickness of the steel plate, mm, and the numerical value before the unit is brought into a formula during calculation.
In the prior art, water is generally used as quenching cooling medium, the cooling speed is lower than 500 ℃, a large amount of alloy is needed to be added to improve the hardenability, and the cost is higher. The invention adopts trinitro water solution as quenching cooling medium, the cooling speed is 2 times of that of water above 500 ℃, and the rare earth Re is matched to refine the structure grains, so that the segregation of the element B with strong hardenability is reduced, the hardenability of the steel plate is improved, the content of noble alloy can be further reduced, the cost is reduced, and the segregation is reduced.
Compared with the prior art, the invention obtains the steel plate with more uniform structure through component design and cooperation with production process, and the produced steel plate not only meets the national standard requirement, but also meets the hardness of 1/2 of the thickness
440HB, the longitudinal impact energy at minus 40 ℃ is more than or equal to 60J, the high standard of each mechanical property meets the national standard, and is higher than the standard, the maximum thickness of the steel plate can reach 100mm, no cutting delay crack is generated, and the market demand of producing the steel plate with large thickness NM450 of the core-protecting property is met.
Drawings
FIG. 1 is a tissue at the surface of example 1;
FIG. 2 is a 1/2 thickness tissue of example 1;
FIG. 3 is a photograph of the cut end face of example 1 after cutting.
FIG. 4 is a surface texture of example 2;
FIG. 5 is a 1/2 thickness tissue of example 2;
FIG. 6 is a photograph of the cut end face of example 2 after cutting.
FIG. 7 is a surface texture of example 3;
FIG. 8 is a 1/2 thickness tissue of example 3;
FIG. 9 is a photograph of the cut end face of example 3 after cutting.
FIG. 10 is a tissue at the surface of comparative example 1;
FIG. 11 is a view showing the structure at 1/2 of the thickness of comparative example 1;
FIG. 12 is a photograph of the cut end face of comparative example 1 after cutting.
FIG. 13 is a tissue at the surface of comparative example 2;
FIG. 14 is a structure at a thickness of 1/2 of comparative example 2;
FIG. 15 is a photograph of the cut end face of comparative example 2 after cutting.
Detailed Description
Example 1
The high-performance NM450 steel plate with low cost and large thickness has the thickness H of 80mm, and comprises the following chemical components in percentage by mass: c:0.20%, si 0.26%, mn 1.1%, P:0.009%, S:0.004%, alt 0.03%, cr:0.6%, nb 0.024%, ti 0.018%, B:0.0023%, re 0.0027%, N0.004%, and the balance of Fe and residual elements.
The manufacturing method of the steel plate for the large-thickness rare earth NM450 comprises the working procedures of smelting, heating, rolling, cooling after rolling and heat treatment, and the specific process and parameters are as follows:
smelting: smelting 100 tons of molten steel in a converter, adopting converter smelting-LF refining-RH vacuum degassing, and electrifying and deslagging the LF for 15min, deoxidizing and deslagging, wherein the hold time of the deslagging is prolonged12min, feO+Mn0 in slag is less than or equal to 1.0%, and S content in molten steel is ensured to be less than 0.005%; RH furnace vacuum treatment time 10min, vacuum degree 125Pa, ultimate vacuum holding time 8min, seamless calcium wire 60Kg after breaking the blank for 2min, wire feeding speed 1.6m/s, rare earth alloy wire 112Kg, wire feeding speed 1.5m/s, soft blowing after wire feeding, ladle bottom blowing argon pressure (0.2-0.4) MPa, flow (150-300) NM 3 and/H, soft blowing time 15min, measuring the outlet time [ H ]]：3ppm。
Heating procedure: adopting a hot feeding and hot charging process, and hot feeding the steel billet at the temperature: 780 ℃, 670 ℃ of hot charging temperature and 670 ℃ of heating temperature of a billet preheating section: 500-900 ℃, one-stage temperature: 900-1150 ℃, 1200-1260 ℃ of the second heating section, 1200-1250 ℃ of the soaking section, and total heating time: 370 minutes.
And (3) rolling: the initial rolling temperature of the first stage is 1055 ℃, the final rolling temperature is 955 ℃, the accumulated rolling reduction is 55%, the single-pass rolling reduction is 20-30 mm, the initial rolling temperature of the second stage is 872 ℃, the final rolling temperature is 836 ℃, the accumulated rolling reduction is 35%, and the single-pass rolling reduction is less than or equal to 20mm.
And (3) a post-rolling cooling procedure: the steel plate stays on a roller way for 120s (relaxation time) before entering an ultra-fast cooling device, the temperature of the steel plate is controlled between 810 and 830 ℃ in the relaxation process, the roller way is started to swing during stay, the swing speed is 0.05m/s, the steel plate is rapidly cooled after swing is completed, the cooling temperature is 802 ℃, and the total water quantity of an ultra-fast cooling high-pressure section is: 7000m 3 /h, water ratio: 1.5, a roll speed of 0.5m/s, a total water content of 4500m in the low-pressure section 3 And/h, the water ratio is 1.4, the roller speed is 0.5m/s, and the temperature of the cooled steel plate returns to 340 ℃.
And (3) a heat treatment procedure: quenching by adopting a trinitro aqueous solution and tempering at a low temperature, wherein the trinitro aqueous solution comprises the following components in percentage by mass: sodium nitrate: 20%, sodium nitrite: 25% of potassium nitrate: 20%, the balance is water, quenching and heat preservation temperature: 900 ℃ +/-10 ℃ and the furnace storage time is 240 minutes, the temperature of the quenched steel plate is 35 ℃, and the low-temperature tempering process comprises the following steps: tempering temperature: 200 ℃ +/-20 ℃ and furnace storage time: 270 minutes (H stands for steel plate thickness, mm).
The microstructure and the cutting end face conditions of the steel plate of the embodiment are shown in figures 1-3, the microstructure of the 1/4 part and the core (1/2 part) of the steel plate is 100% martensitic, the grain size of the steel plate is 9.5-10 grades, the microstructure is fine and uniform, the mechanical properties of the steel plate are shown in table 1, and the hardness properties are shown in table 2. Since the maximum thickness of NM450 in the national standard GB/T24186-2009 is 80mm, the steel plate performance detection method for manufacturing 80-100 mmNM450 refers to the NM450 steel plate standard in the national standard GB/T24186-2009, and simultaneously refers to the standard to perform performance test at the position of 1/2 of the thickness.
TABLE 1 mechanical Properties of 80mmNM450 Steel sheet in example 1
Figure BDA0004194183170000081
Figure BDA0004194183170000091
TABLE 2 hardness Properties of 80mmNM450 Steel sheet in example 1
Figure BDA0004194183170000092
As can be seen from the performance test results in tables 1 and 2, the 80mm NM450 steel plate has better mechanical properties at the 1/4 position and the 1/2 position, completely meets the requirements of corresponding standards, has good toughness matching, and has good wear resistance when the surface and core cloth hardness exceeds the standard requirements.
Example 2
The high-performance NM450 steel plate with low cost and large thickness has the thickness H of 100mm, and comprises the following chemical components in percentage by mass: c:0.23%, si 0.27%, mn 1.15%, P:0.005%, S:0.004%, alt 0.03%, cr:0.63%, nb 0.027%, ti 0.017%, B:0.002%, re 0.003%, N0.004%, and the balance of Fe and residual elements.
The production method of the low-cost large-thickness high-performance NM450 steel plate comprises the following working procedures of smelting, heating, rolling, cooling after rolling and heat treatment, and the specific process and parameters are as follows:
smelting: smelting 100 tons of molten steel by a converter, wherein the converter is adopted for smeltingLF refining-RH vacuum degassing, LF electrifying and deslagging for 16min, deoxidizing and deslagging, and keeping the white slag for 15min; ensuring FeO+Mn0 in the white slag to be less than or equal to 1.0 percent and ensuring S content in molten steel to be less than 0.005 percent; RH furnace vacuum treatment time 12min, vacuum degree 126Pa, ultimate vacuum holding time 8min, feeding seamless calcium wire 65kg after breaking for 2min, feeding rare earth alloy wire 114kg after feeding at a linear speed of 1.6m/s, feeding at a linear speed of 1.5m/s, soft blowing after feeding, ladle bottom blowing argon pressure (0.20-0.4) MPa, and flow (150-300) NM 3 /H, soft blowing time 14min, measuring out of station [ H ]]：2ppm。
Heating procedure: hot delivery temperature of steel billet: 750 ℃, 620 ℃ of hot charging temperature and heating temperature of a billet preheating section: 500-900 ℃, one-stage temperature: 900-1150 deg.c, 1200-1260 deg.c in the second heating section, 1200-1250 deg.c in the soaking section and 370 min in the total heating time.
And (3) rolling: the initial rolling temperature of the first stage is 1060 ℃, the final rolling temperature is 952 ℃, the accumulated rolling reduction is 57%, the single-pass rolling reduction is 20-30 mm, the initial rolling temperature of the second stage is 868 ℃, the final rolling temperature is 845 ℃, the accumulated rolling reduction is 33%, and the single-pass rolling reduction is less than or equal to 20mm.
And (3) a post-rolling cooling procedure: the steel plate stays on a roller way for 115s before entering an ultra-fast cooling device, the temperature of the steel plate is controlled between 810 and 830 ℃ in the relaxation process, the roller way is started to swing during stay, the swing speed is 0.05m/s, the steel plate is rapidly cooled after swing is finished, the cooling temperature is 815 ℃, and the total water quantity of an ultra-fast cooling high-pressure section is as follows: 7500m 3 /h, water ratio: 1.4, a roll speed of 0.5m/s, a total water quantity of the low-pressure section of 5000m 3 And/h, the water ratio is 1.4, the roller speed is 0.5m/s, and the temperature of the cooled steel plate returns to 321 ℃.
And (3) a heat treatment procedure: quenching by adopting a trinitro aqueous solution and tempering at a low temperature, wherein the trinitro aqueous solution comprises the following components in percentage by mass: sodium nitrate: 25%, sodium nitrite: 25% of potassium nitrate: 25%, the rest is water, quenching and heat preservation temperature: 900 ℃ +/-10 ℃ and 300 minutes of furnace storage time, and low-temperature tempering process: tempering temperature: 200 ℃ +/-20 ℃ and furnace storage time: 300 minutes (H stands for steel plate thickness, mm).
The microstructure and the cutting end face conditions of the steel plate of the embodiment are shown in figures 4-6, the 1/4 position and the 1/2 position of the core part are 100% martensitic, the grain size of the steel plate is 9.5-10 grade, and the structure is fine and uniform; the mechanical properties of the steel plates are shown in Table 3, and the hardness properties are shown in Table 4.
TABLE 3 mechanical Properties of 100mmNM450 Steel sheet in example 2
Figure BDA0004194183170000101
Figure BDA0004194183170000111
TABLE 4 hardness Properties of 100mmNM450 Steel sheet in example 2
Figure BDA0004194183170000112
As can be seen from the performance test results in tables 3 and 4, the 100mm NM450 steel plate has better mechanical properties at the 1/4 position and the 1/2 position, completely meets the requirements of corresponding standards, has good toughness matching, and has good wear resistance when the surface and core cloth hardness exceeds the standard requirements.
Example 3
The high-performance NM450 steel plate with low cost and large thickness has the thickness H of 90mm, and comprises the following chemical components in percentage by mass: c:0.17%, si 0.18%, mn 1.06%, P:0.005%, S:0.004%, alt 0.017%, cr:0.52%, nb 0.020%, ti 0.014%, B:0.0013%, re 0.0017%, N0.003%, and the balance of Fe and residual elements.
The production method of the low-cost large-thickness high-performance NM450 steel plate comprises the following working procedures of smelting, heating, rolling, cooling after rolling and heat treatment, and the specific process and parameters are as follows:
smelting: smelting 100 tons of molten steel in a converter, adopting converter smelting-LF refining-RH vacuum degassing, electrifying an LF to make slag for 12min, deoxidizing to make white slag, and keeping the white slag for 11min to ensure that FeO+Mn0 in the white slag is less than or equal to 1.0% and ensure that the S content in the molten steel is less than 0.005%; RH furnaceThe empty treatment time is 8min, the vacuum degree is 130Pa, the ultimate vacuum holding time is 8min, after the empty treatment is broken for 2min, the seamless calcium wire is fed with 63Kg, the feeding speed is 1.6m/s, the rare earth alloy wire is fed with 110Kg after the feeding is finished, the feeding speed is 1.5m/s, the soft blowing is carried out after the feeding, the argon pressure (0.20-0.4) MPa and the flow (150-300) NM are carried out on the ladle bottom blowing 3 and/H, soft blowing time 10min, measuring the outlet time [ H ]]：3ppm。
Heating procedure: hot delivery temperature of steel billet: 710 ℃, hot charging temperature 520 ℃, and heating temperature of a billet preheating section: 500-900 ℃, one-stage temperature: 900-1150 deg.c, 1200-1260 deg.c in the second adding section, 1200-1250 deg.c in the soaking section and 385 min in the total heating time.
And (3) rolling: the first stage rolling temperature is 1070 ℃, the final rolling temperature is 961 ℃, the accumulated rolling reduction is 59%, the single pass rolling reduction is 20-30 mm, the second stage rolling temperature is 875 ℃, the final rolling temperature is 842 ℃, the accumulated rolling reduction is 32%, and the single pass rolling reduction is less than or equal to 20mm.
And (3) a post-rolling cooling procedure: the steel plate stays on a roller way for 113s before entering an ultra-fast cooling device, the temperature of the steel plate is controlled between 810 and 830 ℃ in the relaxation process, the roller way is started to swing during stay, the swing speed is 0.05m/s, the steel plate is rapidly cooled after swing is completed, the cooling temperature is 811 ℃, and the total water quantity of an ultra-fast cooling high-pressure section is as follows: 6500m 3 /h, water ratio: 1.4, a roll speed of 0.5m/s, a total water content of 4500m in the low-pressure section 3 And/h, the water ratio is 1.3, the roller speed is 0.5m/s, and the temperature of the cooled steel plate returns to 316 ℃.
And (3) a heat treatment procedure: quenching by adopting a trinitro aqueous solution and tempering at a low temperature, wherein the trinitro aqueous solution comprises the following components in percentage by mass: sodium nitrate: 25%, sodium nitrite: 25% of potassium nitrate: 25%, the rest is water, quenching and heat preservation temperature: 900 ℃ +/-10 ℃ and 270 minutes of furnace storage time, and low-temperature tempering process: tempering temperature: 200 ℃ +/-20 ℃ and furnace storage time: 285 minutes (H stands for steel plate thickness, mm).
The microstructure and the cutting end face of the steel plate of the embodiment are shown in figures 7-9, the microstructure of the 1/4 part and the microstructure of the core part (1/2 part) are 100% martensite, the grain size of the steel plate is 9.5-10 grades, the microstructure is fine and uniform, the mechanical properties of the steel plate are shown in table 5, and the hardness properties are shown in table 6.
TABLE 5 mechanical Properties of 90mmNM450 Steel sheet in example 3
Figure BDA0004194183170000131
Table 6 hardness Properties of 90mmNM450 Steel sheet in example 3
Figure BDA0004194183170000132
As can be seen from the performance test results in tables 5 and 6, the 90mm NM450 steel plate has better mechanical properties at the 1/4 position and the 1/2 position, completely meets the requirements of corresponding standards, has good toughness matching, and has good wear resistance when the surface and core cloth hardness exceeds the standard requirements.
As can be seen from the microstructure diagrams of the steel plates of example 1, example 2 and example 3 and the photographs of the cut ends after flame cutting, the surface and the core structure of the steel plate are martensitic, the structure grains are finer and uniform, and the uniformity of the structure performance in the thickness direction of the steel plate is ensured. Meanwhile, no delay crack is generated on the cut end face after cutting.
Comparative example 1
NM450 steel plate, steel plate thickness 80mm, steel plate chemical composition and its mass percent are: c:0.20%, si 0.15%, mn 1.21%, P:0.004%, S:0.005%, alt:0.021%, cr:0.62%, nb 0.025%, ti 0.016%, B:0.0014%, re 0.0022%, N0.005% and the balance of Fe and residual elements.
The production method of the comparative example comprises the working procedures of smelting, heating, rolling, cooling after rolling and heat treatment, and the specific process and parameters are as follows:
smelting: smelting 100 tons of molten steel in a converter, adopting converter smelting-LF refining-RH vacuum degassing, and electrifying an LF to make slag for 13min, deoxidizing to make white slag, wherein the white slag holding time is 14min; vacuum treatment time of RH furnace is 9min, vacuum degree is 128Pa, holding time of extreme vacuum is 10min, after breaking, feeding 59kg of seamless calcium wire, feeding 1.5m/s of rare earth alloy wire, feeding 113kg of rare earth alloy wire, feeding 1.5m/s of rare earth alloy wire, carrying out soft blowing after feeding the wire,ladle bottom blowing argon pressure (0.20-0.4) MPa, flow (150-300) NM 3 /H, soft blowing time 12min, measuring out of station [ H ]]：3ppm。
Heating procedure: hot delivery temperature of steel billet: 770 ℃, 635 ℃ of hot charging temperature, and heating temperature of a billet preheating section: 500-900 ℃, one-stage temperature: 900-1150 deg.c, 1200-1260 deg.c in the second adding section, 1200-1250 deg.c in the soaking section and 377 min in the total heating time.
And (3) rolling: the initial rolling temperature of the first stage is 1055 ℃, the final rolling temperature is 957 ℃, the accumulated rolling reduction is 55%, the single pass rolling reduction is 20-30 mm, the initial rolling temperature of the second stage is 872 ℃, the final rolling temperature is 833 ℃, the accumulated rolling reduction is 35%, and the single pass rolling reduction is less than or equal to 20mm.
And (3) a post-rolling cooling procedure:the steel plate is directly put into an ultra-fast cooling device for fast cooling after being rolled,the cooling temperature is 811 ℃, and the total water quantity of the ultra-fast cooling high-pressure section is as follows: 6600m 3 /h, water ratio: 1.4, a roll speed of 0.5m/s, a total water content of 4400m in the low-pressure section 3 And/h, the water ratio is 1.4, the roller speed is 0.5m/s, and the temperature of the cooled steel plate returns to 306 ℃.
And (3) a heat treatment procedure:quenching by using aqueous medium+low temperature tempering, quenching heat preservation temperature: 900 ℃ +/-10 ℃ and 270 minutes of furnace storage time, and low-temperature tempering process: tempering temperature: 200 ℃ +/-20 ℃ and furnace storage time: 285 minutes (H stands for steel plate thickness, mm).
The microstructure and the cutting end face conditions of the comparative steel plate are shown in fig. 10-12, the surface structure of the steel plate is martensite, the grain size is 10 grades, the structure at 1/2 part of the steel plate is martensite and bainite, the grain size is 7.5-8 grades, the microstructure and the grain size are different, the mechanical properties of the steel plate are shown in table 7, and the hardness properties are shown in table 8.
TABLE 7 mechanical Properties of 90mmNM450 Steel sheet in comparative example 1
Figure BDA0004194183170000151
Table 8 hardness Properties of 90 mmNMNM 450 Steel plate in comparative example 1
Figure BDA0004194183170000152
As can be seen from the performance test results of tables 7 and 8, the 90mm NM450 steel plate with the rare earth elements added in comparative example 1 and without relaxation cooling and trinitro aqueous solution quenching has large differences in mechanical properties and Brinell hardness at the 1/4 position and the 1/2 position, and the performance at the 1/2 position cannot meet the standard requirement.
Comparative example 2
NM450 steel plate, steel plate thickness 80mm, steel plate chemical composition and mass percent are: c:0.20%, si 0.22%, mn 1.25%, P:0.008%, S:0.005%, alt:0.028%, cr:0.61%, nb 0.023%, ti 0.018%, B:0.0015%, N0.005%, and the balance Fe and residual elements(rare earth is not added)。
The production method of the comparative example comprises the working procedures of smelting, heating, rolling, cooling after rolling and heat treatment, and the specific process and parameters are as follows:
smelting: smelting 100 tons of molten steel in a converter, adopting converter smelting-LF refining-RH vacuum degassing, and electrifying an LF to make slag for 15min, deoxidizing to make white slag, wherein the white slag holding time is 16min; RH furnace vacuum treatment time 10min, vacuum degree 128Pa, ultimate vacuum holding time 11min, vacuum breaking time 2min, feeding seamless calcium wire 55kg, feeding wire speed 1.5m/s, soft blowing after feeding wire, ladle bottom blowing argon pressure (0.20-0.4) MPa, flow (150-300) NM 3 /H, soft blowing time 13min, measuring out of station [ H ]]：3ppm。
Heating procedure: hot delivery temperature of steel billet: 750 ℃, hot charging temperature 586 ℃, and heating temperature of a billet preheating section: 500-900 ℃, one-stage temperature: 900-1150 deg.c, 1200-1260 deg.c in the second heating section, 1200-1250 deg.c in the soaking section and 383 min in the total heating time.
And (3) rolling: the initial rolling temperature of the first stage is 1053 ℃, the final rolling temperature is 961 ℃, the accumulated rolling reduction is 53%, the single-pass rolling reduction is 20-30 mm, the initial rolling temperature of the second stage is 873 ℃, the final rolling temperature is 835 ℃, the accumulated rolling reduction is 35%, and the single-pass rolling reduction is less than or equal to 20mm.
And (3) a post-rolling cooling procedure: device for entering steel plate into ultra-fast coolingBefore the steel plate stays on a roller way for 105s, the temperature of the steel plate is controlled between 810 and 830 ℃ in the relaxation process, the roller way is started to swing during the stay, the swing speed is 0.05m/s, the steel plate is rapidly cooled after the swing is finished, the cooling temperature is 813 ℃, and the total water quantity of an ultra-fast-cooling high-pressure section is as follows: 6550m 3 /h, water ratio: 1.4, a roll speed of 0.5m/s, a total water content of 4400m in the low-pressure section 3 And/h, the water ratio is 1.3, the roller speed is 0.5m/s, and the temperature of the cooled steel plate returns to 314 ℃.
And (3) a heat treatment procedure: quenching by adopting a trinitro aqueous solution and tempering at a low temperature, wherein the trinitro aqueous solution comprises the following components in percentage by mass: sodium nitrate: 25%, sodium nitrite: 25% of potassium nitrate: 25%, the rest is water, quenching and heat preservation temperature: 900 ℃ +/-10 ℃ and 240 minutes of furnace storage time, and a low-temperature tempering process: tempering temperature: 200 ℃ +/-20 ℃ and furnace storage time: 270 minutes (H stands for steel plate thickness, mm).
The microstructure and the cutting end face of the steel plate of this example are shown in fig. 13-15, the surface structure of the steel plate is martensite, the grain size is 9.5 grade, the structure at 1/2 position of the thickness is martensite and bainite, the grain size is 7.5-8.5 grade, the microstructure and the grain size are different, the mechanical properties of the steel plate are shown in table 9, and the hardness properties are shown in table 10.
Table 9 mechanical Properties of the 80mmNM450 Steel sheet of comparative example 2
Figure BDA0004194183170000171
Table 10 hardness Properties of the 80 mmNMNM 450 Steel plate of comparative example 2
Figure BDA0004194183170000172
As can be seen from the performance test results of tables 9 and 10, the 80mm NM450 steel plate without rare earth elements has large differences in mechanical properties and Brinell hardness at 1/4 and 1/2 positions, and the performance at 1/2 cannot meet the standard requirements.
The underlined data are not in accordance with the requirements of the invention, and it can be seen from the microstructure diagrams of the steel plates of comparative examples 1 and 2 and the photographs of the cut ends after flame cutting that the surface structure of the steel plate is martensitic, but the core structure has a certain bainite and component segregation, the uneven structure in the thickness direction of the steel plate causes the difference of performance, and meanwhile, the stress of the structure and the concentration of thermal stress are easy to generate after flame cutting, so that the risk of delayed cracking of the cut is greatly increased.

Claims (10)

1. The low-cost large-thickness high-performance NM450 steel plate is characterized by comprising the following components in percentage by mass:
C:0.17～0.25％、Si:0.1～0.3％、Mn:1.0～1.25％、P≤0.015％、S≤0.005％、Alt:0.015～0.04％、Cr：0.5～0.65％、Nb：0.01～0.03％、Ti：0.01～0.02％、B：
0.001 to 0.003 percent of Re, 0.0015 to 0.003 percent of N, 0.003 to 0.005 percent of N, and the balance of Fe and residual elements.
2. The low-cost high-thickness high-performance NM450 steel sheet according to claim 1, wherein the thickness of the low-cost high-thickness high-performance NM450 steel sheet is 80 to 100mm.
3. The low-cost high-thickness high-performance NM450 steel plate according to claim 1, wherein the yield strength of the steel plate of the low-cost high-thickness high-performance NM450 steel plate is equal to or more than 1150Mpa, the tensile strength is equal to or more than 1400Mpa, the elongation is equal to or more than 20%, the longitudinal impact energy at minus 40 ℃ is equal to or more than 60J, the surface Brinell hardness is equal to or more than 450HB, and the grain size is 9-10 grades; the yield strength at the position with the thickness of 1/2 is more than or equal to 1000Mpa, the tensile strength is more than or equal to 1300Mpa, the elongation is more than or equal to 20 percent, the longitudinal impact energy at the temperature of minus 40 ℃ is more than or equal to 60J, the Brinell hardness is more than or equal to 440HB, and the grain size is 9 to 10 grades.
4. A method of manufacturing a low cost, high thickness, high performance NM450 steel sheet according to any one of claims 1-3, comprising the steps of smelting, heating, rolling, post-rolling cooling and heat treatment.
5. The manufacturing method according to claim 4, characterized in that the smelting comprises LF furnace refining, in particular: the refining and electrifying slag of the LF furnace is more than or equal to 10min, the temperature measurement and sampling are carried out, the deoxidization is carried out to prepare white slag, feO+Mn0 in the white slag is ensured to be less than or equal to 1.0%, the retention time of the white slag is more than or equal to 10min, and the S content in molten steel is ensured to be less than 0.005%.
6. The method according to claim 4, wherein the smelting comprises vacuum degassing of an RH furnace, in particular: vacuum treatment time is more than or equal to 8min, vacuum degree is less than or equal to 130Pa, holding time of extreme vacuum is more than or equal to 8min, RH vacuum treatment breaks the air for 2min, seamless calcium wire (0.50-0.70) kg/ton steel is fed, and wire feeding speed is high
(1.5-1.7) m/s, then feeding rare earth alloy wire (1.0-1.2) kg/ton steel, feeding wire at the speed (1.3-1.5) m/s, carrying out soft blowing after wire feeding, and carrying out ladle bottom blowing argon pressure (0.20-0.4) MPa and flow (150-300) NM 3 and/H, the time is more than or equal to 10min, and the outlet time (H) is ensured]≤3ppm。
7. The method of manufacturing according to claim 4, wherein the heating is: adopting a hot feeding and hot charging process, and hot feeding the steel billet at the temperature: 700-800 ℃, 500-680 ℃ of hot charging temperature and heating temperature of a billet preheating section: 500-900 ℃, one-stage temperature: 900-1150 deg.c, 1200-1260 deg.c in the second adding section, 1200-1250 deg.c in the soaking section and total heating time over 360 min.
8. The method according to claim 4, wherein the rolling is performed in a high temperature recrystallization zone, the initial rolling temperature is equal to or higher than 1050 ℃, the final rolling temperature is equal to or higher than 950 ℃, the cumulative rolling reduction is 50-60%, and the single pass rolling reduction is 20-30 mm; and then rolling in a non-recrystallization zone, wherein the initial rolling temperature is less than or equal to 880 ℃, the final rolling temperature is 830-850 ℃, the accumulated rolling reduction is 30-40%, and the single-pass rolling reduction is less than or equal to 20mm.
9. The method of manufacturing according to claim 4, wherein the post-rolling cooling is: relaxation and rapid cooling; the cooling after rolling specifically comprises the following steps: the steel plate stays on a roller way for 100 to 120 seconds before being rapidly cooled, the roller way is started to swing, the relaxation temperature is 810 to 830 ℃, and the steel plate enters ultra-fast cooling equipment for rapid cooling after the relaxation is finishedRapidly cooling, wherein the cooling temperature is more than or equal to 800 ℃, the cooling roller way speed is 0.3-0.5 m/s, and the water quantity of the high-pressure section is 6000-7500 m 3 Water ratio of 1.2-1.6, low pressure section water quantity of 3000-5000 m 3 And/h, the water ratio is 1.2-1.6, and the reddening temperature is 300-350 ℃.
10. The method of manufacturing according to claim 4, wherein the heat treatment is: quenching by adopting trinitro aqueous solution and tempering at low temperature; the trinitro aqueous solution comprises the following components in percentage by mass: sodium nitrate: 15-25% of sodium nitrite: 20-30% of potassium nitrate: 20-25%, the balance being water; quenching heat preservation temperature: 890-910 deg.c and 3 XH min; h represents the thickness of the steel plate, and mm; the temperature of the quenched steel plate is 20-40 ℃; the low temperature tempering: tempering temperature: 180-220 ℃ and furnace storage time: 1.5 XH+150 minutes.
CN202310441633.5A 2023-04-23 2023-04-23 NM450 steel plate with low cost, large thickness and high performance and manufacturing method thereof Pending CN116426828A (en)

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