CN113201688A - 700 MPa-grade thick-specification high-strength steel and production method thereof - Google Patents

700 MPa-grade thick-specification high-strength steel and production method thereof Download PDF

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CN113201688A
CN113201688A CN202110435974.2A CN202110435974A CN113201688A CN 113201688 A CN113201688 A CN 113201688A CN 202110435974 A CN202110435974 A CN 202110435974A CN 113201688 A CN113201688 A CN 113201688A
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steel
less
rolling
argon
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CN113201688B (en
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赵任
秦哲
楚斌
刘启森
林承江
王欢龙
徐剑
王军荣
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Rizhao Steel Holding Group 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
    • B21B1/22—Metal-rolling methods or mills for making semi-finished products of solid or profiled cross-section; Sequence of operations in milling trains; Layout of rolling-mill plant, e.g. grouping of stands; Succession of passes or of sectional pass alternations for rolling plates, strips, bands or sheets of indefinite length
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • 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
    • B21B37/58—Roll-force control; Roll-gap control
    • 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
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
    • B21B—ROLLING OF METAL
    • B21B45/00—Devices for surface or other treatment of work, specially combined with or arranged in, or specially adapted for use in connection with, metal-rolling mills
    • B21B45/02—Devices for surface or other treatment of work, specially combined with or arranged in, or specially adapted for use in connection with, metal-rolling mills for lubricating, cooling, or cleaning
    • B21B45/0203—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
    • C21D6/00—Heat treatment of ferrous alloys
    • C21D6/005—Heat treatment of ferrous alloys containing Mn
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D6/00—Heat treatment of ferrous alloys
    • C21D6/008—Heat treatment of ferrous alloys containing Si
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D8/00—Modifying the physical properties 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
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
    • C21D9/0081—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for slabs; for billets
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/002—Ferrous alloys, e.g. steel alloys containing In, Mg, or other elements not provided for in one single group C22C38/001 - C22C38/60
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/04—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
    • C22C38/12—Ferrous alloys, e.g. steel alloys containing tungsten, tantalum, molybdenum, vanadium, or niobium
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/14—Ferrous alloys, e.g. steel alloys containing titanium or zirconium
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
    • B21B—ROLLING OF METAL
    • B21B1/00—Metal-rolling methods or mills for making semi-finished products of solid or profiled cross-section; Sequence of operations in milling trains; Layout of rolling-mill plant, e.g. grouping of stands; Succession of passes or of sectional pass alternations
    • B21B1/22—Metal-rolling methods or mills for making semi-finished products of solid or profiled cross-section; Sequence of operations in milling trains; Layout of rolling-mill plant, e.g. grouping of stands; Succession of passes or of sectional pass alternations for rolling plates, strips, bands or sheets of indefinite length
    • B21B2001/225—Metal-rolling methods or mills for making semi-finished products of solid or profiled cross-section; Sequence of operations in milling trains; Layout of rolling-mill plant, e.g. grouping of stands; Succession of passes or of sectional pass alternations for rolling plates, strips, bands or sheets of indefinite length by 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
    • C21D2211/00—Microstructure comprising significant phases
    • C21D2211/002—Bainite
    • 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
    • C21D2211/003—Cementite
    • 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

Abstract

The invention relates to the technical field of high-strength steel production, in particular to 700 MPa-grade thick-specification high-strength steel and a production method thereof, wherein the thickness is 10-16 mm, and the chemical components are as follows: 0.05 to 0.07%, Si < 0.15%, Mn: 1.5-1.8%, P < 0.015%, S < 0.003%, Alt: 0.025 to 0.05%, Nb: 0.03 to 0.04%, Ti: 0.095-0.12%, N < 0.0055%, B: 0.002-0.004%, and the balance of Fe and inevitable impurities; the production method comprises converter smelting, LF refining, continuous casting, slab heating, rough rolling, finish rolling, layer cooling, coiling and warehousing slow cooling. The invention does not need to carry out pretreatment and vacuum refining on the molten iron, has lower cost, and the tensile strength of the steel plate can reach more than 700MPa, and the impact energy at minus 20 ℃ is stabilized to more than 200J.

Description

700 MPa-grade thick-specification high-strength steel and production method thereof
Technical Field
The invention relates to the technical field of high-strength steel production, in particular to 700 MPa-level thick-specification high-strength steel and a production method thereof.
Background
700MPa high-strength steel is mainly applied to main beams of special vehicles such as trailers and the like, and the 700MPa high-strength steel with lower low-temperature toughness is easy to have girder fracture accidents in alpine regions or in winter after being made into the trailers, so that the traffic safety risk is increased, and therefore the 700MPa high-strength steel has high strength and also has high low-temperature impact resistance. However, with the increase of the thickness of the steel plate, particularly when the thickness reaches 10.0-16.0 mm, the production difficulty of the 700MPa grade high-strength steel is increased sharply, the ideal metallographic structure is more difficult to obtain, and the phenomenon of uneven crystal grains of the core part of the product is obvious. Therefore, the research on the uniformity of the thick-specification high-strength steel structure and the optimal matching of chemical components and the rolling process by the controlled rolling and controlled cooling process is the key point for developing the thick-specification high-strength steel.
The traditional process production mode requires molten iron pretreatment and vacuum refining treatment, steel rolling requires long-time heating to ensure sufficient solid solution of the alloy so as to ensure the precipitation strengthening effect after coiling, the grain size difference of a core part of a product after controlled rolling and controlled cooling process is large, the metallographic structure is ferrite, cementite and pearlite, and the non-uniformity of the grain size of the ferrite and the precipitation of a brittle phase of the pearlite are all adverse effects on the low-temperature toughness of the product.
The C700L steel plate is manufactured by adopting a Nb, V and Ti composite micro-alloying process and a controlled rolling and cooling process on a 1780mm hot rolling production line by Wangqi et al (Wangqi et al, C700L high-strength automobile girder steel development, Hebei metallurgy, No. 8 of 2014), but the low-temperature impact toughness of the steel plate at-20 ℃ is lower.
The Chinese patent application CN 201811268002.3 discloses a 700 MPa-grade automobile beam steel strip with the thickness of 14.0mm, the impact power at minus 20 ℃ is 153-168J, the preparation method of the steel strip needs molten iron desulphurization, decarburization and dephosphorization pretreatment, and needs vacuum refining, the steel-making cost is higher, and the steel-making method is not suitable for steel mills without molten iron pretreatment process and vacuum refining furnace to produce. And the metallographic structure obtained at the coiling temperature of 580-620 ℃ is ferrite plus pearlite, a part of large-size ferrite grains still exist in the core part, and both the strength and the low-temperature toughness have a space for improving.
The Chinese invention patent ZL 201410126294.2 discloses a low-brittleness 700MPa grade steel for automobile beams, which comprises the following chemical components: 0.05 to 0.07%, Si < 0.012%, Mn: 1.45 to 1.75%, P < 0.012%, S < 0.005%, Al: 0.020-0.070%, Nb: 0.035 to 0.050%, Ti: 0.08-0.1% of N, less than 0.005% of N, and the balance of iron and inevitable impurities, the preparation method needs molten iron desulphurization pretreatment and vacuum refining, has high steel making cost, is not suitable for steel mills without molten iron pretreatment process and vacuum refining furnace to produce, is suitable for producing steel plates with the thickness of 3-12 mm, and does not describe the production method of high-strength steel with the thickness of more than 12 mm.
Disclosure of Invention
Aiming at the technical problem that the steel-making cost is high due to the fact that molten iron pretreatment and vacuum refining are needed in the conventional method for improving the low-temperature toughness of the 700MPa grade high-strength steel with the thick specification, the invention provides the 700MPa grade high-strength steel and the production method thereof, the production method adopts the process flow of blast furnace molten iron → converter → LF furnace → slab continuous casting → stacking slow cooling → rolling → laminar cooling → coiling → warehousing slow cooling, the molten iron is not required to be subjected to desulfurization pretreatment and vacuum refining, the steel-making cost is relatively lower, the purity of the molten steel is ensured through the fine control of molten iron selection and the steel-making process, the grain refinement of the material is ensured through adding alloy elements with high hardenability, adopting proper heating temperature and furnace time, reasonably distributing rough rolling and finish rolling reduction, selecting reasonable rolling temperature and cooling process after rolling, and avoiding the formation of pearlite brittle phase through adopting proper coiling temperature, thereby ensuring that the material has excellent comprehensive mechanical properties; the tensile strength of the steel plate obtained by the production method can reach more than 700MPa, the impact energy at minus 20 ℃ is stabilized at more than 200J, the steel plate can be well adapted to the low-temperature environment in alpine regions or winter, and the steel plate is suitable for being used as a main beam material of special vehicles such as trailers and the like.
In a first aspect, the invention provides a production method of 700 MPa-level thick-specification high-strength steel,
the thickness of the high-strength steel is 10.0-16.0 mm, and the chemical components and the contents are as follows:
c: 0.05-0.07%, Si < 0.15%, Mn: 1.50-1.80%, P < 0.015%, S < 0.003%, Alt: 0.025 to 0.050%, Nb: 0.030-0.040%, Ti: 0.095% -0.120%, N < 0.0055%, B: 0.002% -0.004%, and the balance of Fe and inevitable impurities;
the production method comprises the following steps:
(1) smelting in a converter; (2) LF refining; (3) continuous casting;
(4) heating the plate blank: the heating temperature is 1240-1270 ℃, the in-furnace time is 180-260 min, the slab undergoes austenite → ferrite → austenite phase change circulation, the effect of slab grain refinement is achieved, particularly, the slab core grain refinement is beneficial to improving the toughness, the proper heating temperature and the in-furnace time can avoid abnormal growth of local grains of the slab caused by overlong in-furnace time or overhigh heating temperature, and the precipitation of the nano-scale titanium nitride after coiling is facilitated;
(5) rough rolling: 1+ 5-pass rolling or 0+ 5-pass rolling is adopted, the temperature of a final secondary outlet is 1040-1080 ℃, and the final secondary reduction is more than 20%, so that the deformation and recrystallization temperature of coarse rolling recrystallization are ensured, the rolled material can realize complete austenite recrystallization, the abnormal growth of austenite grains is avoided, and the austenite grains are refined;
(6) finish rolling: seven stands are subjected to hot continuous rolling, a second rolling mill and a fifth rolling mill are thrown for rolling, the sum of the reduction ratios of the first two rolling mills is more than or equal to 60 percent, the front-section stand is prevented from entering a partial recrystallization zone, the mixed crystal risk is reduced, the integral reduction ratio of the rear-section stand is ensured, the compression ratio of a non-recrystallization zone is ensured, enough nucleation points are provided for subsequent phase change, the grain refinement is ensured, and the temperature of a last secondary outlet is 830-860 ℃;
(7) layer cooling: selecting a front section cooling mode, controlling the temperature of a front section cooling outlet at 580-600 ℃, wherein the cooling speed is more than or equal to 35 ℃/s, improving the supercooling degree of a core part, refining ferrite grains, wherein the refining of the ferrite grains can increase the number and the area of crystal boundaries under a unit area, and the corresponding dislocation amount and the impurity amount of each unit crystal boundary are relatively reduced, so that the stress concentration can be relieved, the crack expansion is inhibited, the brittle fracture sensitivity along the crystal is weakened, and the low-temperature toughness of the material is improved;
(8) coiling: the coiling temperature is 540-560 ℃, and the sequence of the ductile-brittle transition temperature is as follows: pearlite > upper bainite > ferrite, can inhibit pearlite from precipitating and forming upper bainite with the lower coiling temperature, the interface of ferrite/pearlite is relatively weak, facilitate the production and spread of the crackle, make the ductile-brittle transition temperature of the material rise, thus will cause the low-temperature impact toughness of the material to be worsened, therefore the material containing ferrite + bainite tissue has better ability to resist low-temperature impact than the material of ferrite + pearlite tissue;
(9) and (4) warehousing and slow cooling: and warehousing, stacking and slow cooling the steel coil.
Further, the 700MPa grade thick specification high-strength steel comprises the following chemical components in percentage by weight:
c: 0.063%, Si: 0.06%, Mn: 1.58%, P: 0.014%, S: 0.003%, Alt: 0.035%, Nb: 0.035%, Ti: 0.099%, N: 0.0034%, B: 0.003% and the balance of Fe and inevitable impurities.
Further, in the step (1), the S of the molten iron entering the furnace is less than or equal to 0.030 percent, the Si is more than 0.30 percent, the temperature of the molten iron is greater than or equal to 1290 ℃, the TSO is measured at the end point, the T is greater than or equal to 1610 ℃, the O is less than or equal to 800ppm, the point blowing is not allowed, the argon is switched after the converter is blown for 5 minutes, the pressure of a furnace mouth is controlled at the micro-positive pressure, the target N content of a tundish is less than or equal to 40ppm, the shape of a steel tapping hole is good, the tapping time is 4-8 minutes, 30 seconds before tapping, the air in the ladle is emptied by introducing the argon, the scattered flow tapping is not allowed, the alloy is not allowed to be replenished for the second time, the whole argon blowing is required in the tapping process, a feeding pipe is aligned with the impact part of the steel flow, the accumulation of alloy materials and the slag in the slag ladle is prevented from being accumulated, the slag thickness is less than or equal to 100mm in the converter, the argon station is blown tightly, and the explosion blowing is not more tightly restricted, and the molten steel is not more than or less than 20 cm.
Further, in the step (2), the station entering temperature is more than or equal to 1520 ℃, a bypass is opened at the early stage to carry out large stirring, the air permeability of the steel ladle is improved, the steel ladle is heated and heated at the station, white slag is formed in 15min, aluminum particles are used for carrying out slag deoxidation in the process, a small amount of aluminum particles are batched, the aluminum particles are uniformly scattered on the slag surface, and the final slag system is CaO: 53% -58% of Al2O3：26％～32％，SiO2The method comprises the following steps of less than or equal to 8%, MgO less than or equal to 10%, FeO + MnO less than or equal to 1.2%, refining time more than or equal to 50min, heating time less than or equal to 30min, white slag time more than or equal to 10min, micro-positive pressure operation is adopted in a whole argon blowing furnace, foam slag covers the liquid level of steel, Ca wires are added into the furnace at a rate of 80-110 m/furnace, the pressure of bottom blowing argon is strictly controlled in the wire feeding process, two-stage soft blowing is adopted, soft blowing before calcium is more than or equal to 5min, the diameter of argon flowers is 200-300 mm, soft blowing after calcium is more than or equal to 15min, the creep diameter of slag surfaces is 100-200 mm, the creep process ensures that slag surfaces creep and molten steel are not exposed, aluminum, alloy and heating operations are forbidden in the soft blowing and calcium treatment processes, alloy supplementation is forbidden in the 8min before soft blowing, argon blowing flow of a single-permeable brick is 30-150 NL/min, and the air permeability difference furnace is based on the diameter of argon flowers.
Further, in the step (3), argon replacement of the tundish is continuously carried out from closing of the ladle baking device to pouring of the ladle, the blowing flow of an argon seal of the ladle is 30-80L/min, argon is blown by a stopper rod for 2-5L/min, a covering agent is coated in a high-alkalinity tundish, no molten steel is exposed in the process, delta Als of the ladle is less than 40ppm, delta Alt is less than 60ppm, Als/Alt of the tundish is more than or equal to 0.92, N of the tundish is less than or equal to 50ppm, a long nozzle sealing gasket is intact, a long nozzle sleeve is right vertical to the liquid level of the tundish, the service time of the long nozzle is less than or equal to 4 hours, the insertion depth of the ladle nozzle is more than or equal to 200mm, the insertion depth of an immersion nozzle is 120-140 mm, slag falling of the ladle is strictly controlled, and 3 tons of steel are left in the ladle at the tail stage of casting for self-circulation; deslagging every 3 furnaces of the tundish for 1 time, using a large-chamfer crystallizer, keeping the reduction at 4mm under electric soft reduction, keeping the electromagnetic stirring current intensity at 340A, keeping the frequency at 5Hz, keeping the pulling speed at 1.0-1.15 m/min, keeping the pulling speed variation at less than or equal to 0.05m/min, keeping the liquid level fluctuation of the crystallizer at less than 3mm, keeping the superheat degree of the tundish at 10-25 ℃, and keeping the plate blank off-line stacking and slow cooling at more than or equal to 24 hours.
The steps (1), (2) and (3) ensure that high-quality qualified casting blanks can be obtained without molten iron pretreatment and a vacuum refining furnace.
Further, in the step (4), the temperature difference of the surface of the strip steel is less than or equal to 30 ℃.
Further, in the step (6), the finish rolling temperature is 950-1020 ℃, the finish rolling temperature is 830-860 ℃, the water between the frames is fully opened, the rolling speed is less than or equal to 2.5m/s, and the finish rolling temperature is controlled in a closed loop mode.
In a second aspect, the invention provides 700MPa thick-specification high-strength steel prepared by the production method.
The beneficial effect of the invention is that,
on the first hand, the production method of the invention improves the hardenability of the material by adding 0.002-0.004% of B element in the components, which is beneficial to the refinement of crystal grains at the central part in the layer cooling process; the material is optimized and guaranteed to have better comprehensive mechanical property through steel rolling temperature control, rough rolling, finish rolling reduction distribution and layer cooling;
in the second aspect, the structure of the high-strength steel with h being more than or equal to 10.0mm and less than or equal to 16.0mm prepared by the production method is an ideal structure which is combined by polygonal ferrite and a small amount of cementite and bainite, large-grain ferrite grains in the core are eliminated, the average grain size of the ferrite in the core is less than 4 mu m, the tensile strength is stably controlled to be more than 700MPa, and the impact energy at-20 ℃ is stably more than 200J.
Drawings
In order to more clearly illustrate the embodiments or technical solutions in the prior art of the present invention, the drawings used in the description of the embodiments or prior art will be briefly described below, and it is obvious for those skilled in the art that other drawings can be obtained based on these drawings without creative efforts.
FIG. 1 is a metallographic photograph at 1000X magnification of the structure of a high strength steel core according to example 1 of the present invention;
FIG. 2 is a metallographic photograph at 1000 Xmagnification of the structure of a high strength steel core according to example 2 of the present invention.
Detailed Description
In order to make those skilled in the art better understand the technical solution of the present invention, the technical solution in the embodiment of the present invention will be clearly and completely described below with reference to the drawings in the embodiment of the present invention, and it is obvious that the described embodiment is only a part of the embodiment of the present invention, and not all embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
Example 1
The 12.0 x 1500mm 700MPa grade thick specification high-strength steel comprises the following chemical components in percentage by weight:
c: 0.063%, Si: 0.06%, Mn: 1.58%, P: 0.014%, S: 0.003%, Alt: 0.035%, Nb: 0.035%, Ti: 0.099%, N: 0.0034%, B: 0.003%, and the balance of Fe and inevitable impurities;
the production method of the high-strength steel adopts the process flow of blast furnace molten iron → a converter → an LF furnace → slab continuous casting → stacking slow cooling → 2150 line rolling → laminar cooling → coiling → warehousing slow cooling, and specifically comprises the following steps:
(1) smelting in a converter: charging molten iron S: 0.016%, Si: 0.51 percent, the temperature of molten iron is 1310 ℃, TSO is measured at the end point, T is 1630 ℃, and [ O ] is 650ppm, the process is free of point blowing, argon is switched after the converter blows for 5 minutes, the pressure of a furnace mouth is controlled by micro positive pressure, the content of N in a tundish is 35ppm, the shape of a steel tapping hole is good, the tapping time is 6 minutes, 30 seconds before tapping, argon is introduced into the ladle to evacuate the air in the ladle, no scattered flow is used for tapping, no secondary alloy is added, argon is blown in the whole tapping process, a charging pipe is aligned to a steel flow impact part, no lump is contained in an alloy material and a slag material bag, the thickness of steel slag discharged from the converter is less than or equal to 100mm, and the molten steel is exposed by about 15 cm;
(2) LF refining: the entering temperature is 1540 ℃, a bypass is opened at the early stage to carry out large stirring, the temperature is raised by heating when the station arrives, white slag is formed in about 12min, aluminum particles are used for carrying out slag deoxidation in the process, a small amount of aluminum particles are batched, the aluminum particles are uniformly scattered on the slag surface, and the final slag system is CaO: 54% of Al2O3：29％，SiO2: 6.5%, MgO: 7.8%, FeO + MnO: 0.9 percent, refining time is 51min, heating time is 26min, white slag time is 11min, micro-positive pressure operation is adopted in an argon blowing furnace in the whole process, foam slag covers the liquid level of steel, a Ca wire is added into a furnace with the thickness of 105m, the argon bottom blowing pressure is controlled in the wire feeding process, no big turnover is caused, two-stage soft blowing is adopted, soft blowing is carried out before calcium is carried out for 10min, the diameter of an argon flower is about 250mm, soft blowing is carried out after calcium is carried out for 5min, the creep diameter of a slag surface is about 150mm, the slag surface creeps in the soft blowing process, molten steel is not exposed, aluminum supplement, alloy and heating operation are not carried out in the soft blowing and calcium treatment processes, and the argon blowing flow rate of a single air brick is 90 NL/min;
(3) continuous casting: continuously replacing argon in the tundish from closing of the ladle baking device to pouring of the ladle, wherein the flow of argon seal blowing of the ladle is 55L/min, the flow of argon seal blowing of the stopper rod is 4L/min, a covering agent is coated in a high-alkalinity tundish, no molten steel is exposed in the process, and the ladle is covered with delta Als: 20ppm, Δ Alt: 25ppm, medium packet Als/Alt is 0.96, medium packet N: 41ppm, the long nozzle sealing gasket is intact, the long nozzle sleeve is right vertical to the liquid level of the tundish, the service time of the long nozzle is 2 hours, the insertion depth of the ladle nozzle is 260mm, the insertion depth of the immersion nozzle is 140mm, the ladle slag discharging is strictly controlled, and 3 tons of steel are left in the ladle for self-circulation at the end of casting; deslagging every 3 furnaces of the tundish for 1 time, using a large-chamfer crystallizer, keeping the reduction at 4mm under electric soft reduction, keeping the electromagnetic stirring current intensity at 340A, keeping the frequency at 5Hz, keeping the pulling speed at 1.1m/min, keeping the pulling speed at less than or equal to 0.05m/min, keeping the liquid level fluctuation of the crystallizer at less than 3mm, keeping the superheat degree of the tundish at 20 ℃, and performing off-line stacking and slow cooling for 27 hours on the plate blank to finally obtain the plate blank with the thickness of 227 mm;
(4) heating the plate blank: the temperature of the third heating section and the soaking section is controlled to be 1265 ℃, the temperature difference of the surface of the strip steel is less than or equal to 30 ℃, and the furnace time is 240 min;
(5) rough rolling: 1+5 passes of rolling are adopted, the reduction rate of each pass is 20.5%, 23.05%, 22.95%, 21.8%, 21.4% and 21.0%, the outlet temperature of the last pass is 1050-1080 ℃, the thickness of the intermediate blank is 52mm, and the rolling descaling is complete;
(6) finish rolling: the initial rolling temperature is 950-1020 ℃, seven frames are subjected to hot continuous rolling, the second and fifth rolling mills are thrown for rolling, the reduction rate of each pass is 32.50%, 0%, 30.30%, 25.40%, 0%, 22.02%, 12.50%, the outlet temperature of the last pass is 835 ℃, the water between the frames is fully opened, the highest rolling speed is 2.5m/s, and the final rolling temperature is subjected to closed-loop control;
(7) layer cooling: selecting a front-section cooling mode, wherein the temperature of a front-section cooling outlet is 590 ℃, and the cooling speed is 35 ℃/s;
(8) coiling: the coiling temperature is 560 ℃;
(9) and (4) warehousing and slow cooling: and warehousing and stacking the steel coils for slow cooling for 24 hours.
The metallographic photograph of the high-strength steel is shown in fig. 1, the structure is polygonal ferrite, cementite and a small amount of bainite, the average grain size of the ferrite at 1/4 is 3.7 μm, the grain size of the core is 12.0 grade, the average grain size of the ferrite is 3.3 μm, and large abnormal ferrite grains are not detected.
The high-strength steel is subjected to mechanical property tests, the yield strength is 677Mpa, the tensile strength is 734Mpa, the elongation is 16.5 percent, the impact energy (10 x 50mm) at the temperature of minus 20 ℃ is 236J, 237J and 209J respectively, and the average value is 227J.
Example 2
The 14.0 x 1500mm 700 MPa-grade thick-specification high-strength steel comprises the following chemical components in percentage by weight:
c: 0.064%, Si: 0.08%, Mn: 1.65%, P: 0.012%, S: 0.002%, Alt: 0.035%, Nb: 0.033%, Ti: 0.11%, N: 0.0040%, B: 0.003%, and the balance of Fe and inevitable impurities;
the production method of the high-strength steel adopts the process flow of blast furnace molten iron → a converter → an LF furnace → slab continuous casting → stacking slow cooling → 2150 line rolling → laminar cooling → coiling → warehousing slow cooling, and specifically comprises the following steps:
(1) smelting in a converter: charging molten iron S: 0.017%, Si: 0.46 percent, the temperature of molten iron is 1325 ℃, TSO is measured at the end point, T is 1640 ℃, and [ O ] is 620ppm, the process is free of point blowing, argon is switched after converter blowing is carried out for 5 minutes, the pressure of a furnace mouth is controlled by micro-positive pressure, the content of N in a tundish is 32ppm, the shape of a steel tapping hole is good, the tapping time is 8 minutes, 30 seconds before tapping, argon is introduced into the ladle to evacuate the air in the ladle, no scattered flow is used for tapping, no secondary alloy is added, argon is blown in the whole tapping process, a charging pipe is aligned to a steel flow impact part, no lump is contained in an alloy material and a slag material bag, the thickness of steel slag discharged from the converter is less than or equal to 100mm, and the bare thickness of the molten steel is about 18 cm;
(2) LF refining: the station-entering temperature is 1525 ℃, a bypass is opened at the early stage to carry out large stirring, the station-entering temperature is raised by heating, white slag is formed in about 13min, aluminum particles are used for carrying out slag deoxidation in the process, a small amount of aluminum particles are batched and uniformly scattered on the slag surface, and the final slag system is CaO: 55% of Al2O3：30％，SiO2: 5.5%, MgO: 6.5%, FeO + MnO: 0.95 percent, the refining time is 55min, the heating time is 28min, the white slag time is 12min, the micro-positive pressure operation is adopted in the argon blowing furnace in the whole process, the foam slag covers the liquid level of steel, the Ca wire is added into the furnace at a rate of 100 m/furnace, the argon bottom blowing pressure is controlled in the wire feeding process without big turnover, two-stage soft blowing is adopted, the soft blowing is carried out before calcium for 9min, the diameter of an argon flower is about 250mm, the soft blowing is carried out after calcium for 6min, the creep diameter of a slag surface is about 150mm, the slag surface creeps in the soft blowing process, the molten steel is not exposed, the aluminum supplement, the alloy and the heating operation are not carried out in the soft blowing and calcium treatment processes, and the argon blowing flow rate of a single air brick is 90 NL/min;
(3) continuous casting: continuously replacing argon in the tundish from closing of the ladle baking device to pouring of the ladle, wherein the flow of argon seal blowing of the ladle is 50L/min, the flow of argon seal blowing of the stopper rod is 4L/min, a covering agent is coated in a high-alkalinity tundish, no molten steel is exposed in the process, and the ladle delta Als is large: 22ppm,. DELTA.Alt: 28ppm, medium packet Als/Alt is 0.97, medium packet N: 42ppm, the long nozzle sealing gasket is intact, the long nozzle sleeve is right vertical to the liquid level of the tundish, the service time of the long nozzle is 2.5h, the insertion depth of the ladle nozzle is 260mm, the insertion depth of the immersion nozzle is 125mm, the slag discharging of the ladle is strictly controlled, and 3 tons of steel are left in the ladle in the tail casting period for self-circulation; deslagging every 3 furnaces of the tundish for 1 time, using a large-chamfer crystallizer, keeping the reduction at 4mm under electric soft reduction, keeping the electromagnetic stirring current intensity at 340A, keeping the frequency at 5Hz, keeping the pulling speed at 1.05m/min, keeping the pulling speed at less than or equal to 0.05m/min, keeping the liquid level fluctuation of the crystallizer at less than 3mm, keeping the superheat degree of the tundish at 25 ℃, and performing off-line stacking and slow cooling on the plate blank for 24 hours to finally obtain the plate blank with the thickness of 227 mm;
(4) heating the plate blank: the temperature of the third heating section and the soaking section is controlled to be 1270 ℃, the temperature difference of the surface of the strip steel is less than or equal to 30 ℃, and the furnace time is 258 min;
(5) rough rolling: 1+5 passes of rolling are adopted, the reduction rate of each pass is 20.5%, 22.80%, 22.90%, 21.50%, 22.05% and 21.0%, the outlet temperature of the last pass is 1040-1070 ℃, the thickness of the intermediate billet is 52mm, and the rolling descaling is fully performed;
(6) finish rolling: the initial rolling temperature is 960-1030 ℃, seven frames are subjected to hot continuous rolling, the second and fifth rolling mills are thrown for rolling, the reduction rate of each pass is 30.50%, 0%, 30.30%, 23.25%, 0%, 17.02%, 12.36%, the last pass outlet temperature is 840 ℃, the water between the frames is fully opened, the highest rolling speed is 2.2m/s, and the final rolling temperature is subjected to closed-loop control;
(7) layer cooling: selecting a front-section cooling mode, wherein the temperature of a front-section cooling outlet is 580 ℃, and the cooling speed is 36 ℃/s;
(8) coiling: the coiling temperature is 540 ℃;
(9) and (4) warehousing and slow cooling: and warehousing and stacking the steel coils for slow cooling for 24 hours.
The metallographic photograph of the high-strength steel is shown in fig. 2, the structure is polygonal ferrite, cementite and a small amount of bainite, the average grain size of the ferrite at 1/4 is 3.9 μm, the grain size of the core is 12.0 grade, the average grain size of the ferrite is 3.5 μm, and large abnormal ferrite grains are not detected.
The mechanical property test of the high-strength steel is carried out, the yield strength is 662Mpa, the tensile strength is 728Mpa, the elongation is 18.5 percent, and the impact energy (10X 50mm) at the temperature of minus 20 ℃ is respectively 208J, 225J and 213J, and the average value is 215J.
Although the present invention has been described in detail by referring to the drawings in connection with the preferred embodiments, the present invention is not limited thereto. Various equivalent modifications or substitutions can be made on the embodiments of the present invention by those skilled in the art without departing from the spirit and scope of the present invention, and these modifications or substitutions are within the scope of the present invention/any person skilled in the art can easily conceive of the changes or substitutions within the technical scope of the present invention.

Claims (8)

1. The production method of the 700 MPa-grade thick-specification high-strength steel is characterized in that the thickness of the high-strength steel is 10.0-16.0 mm, and the chemical components and the contents are as follows:
c: 0.05-0.07%, Si < 0.15%, Mn: 1.50-1.80%, P < 0.015%, S < 0.003%, Alt: 0.025 to 0.050%, Nb: 0.030-0.040%, Ti: 0.095% -0.120%, N < 0.0055%, B: 0.002% -0.004%, and the balance of Fe and inevitable impurities;
the production method comprises the following steps:
(1) smelting in a converter; (2) LF refining; (3) continuous casting;
(4) heating the plate blank: heating at 1240-1260 ℃, and keeping the furnace for 180-260 min;
(5) rough rolling: 1+ 5-pass rolling or 0+ 5-pass rolling is adopted, the last-pass outlet temperature is 1040-1080 ℃, and the last-pass secondary reduction amount is more than 20%;
(6) finish rolling: hot continuous rolling with seven stands, throwing a second rolling mill and a fifth rolling mill for rolling, wherein the sum of the reduction rates of the first two rolling mills is more than or equal to 60 percent, and the temperature of a last secondary outlet is 830-860 ℃;
(7) layer cooling: selecting a front section cooling mode, controlling the temperature of a front section cooling outlet at 580-600 ℃, and controlling the cooling speed to be more than or equal to 35 ℃/s;
(8) coiling: the coiling temperature is 540-560 ℃;
(9) and (4) warehousing and slow cooling: and warehousing, stacking and slow cooling the steel coil.
2. The production method according to claim 1, wherein the high-strength steel has the following chemical components and contents:
c: 0.063%, Si: 0.06%, Mn: 1.58%, P: 0.014%, S: 0.003%, Alt: 0.035%, Nb: 0.035%, Ti: 0.099%, N: 0.0034%, B: 0.003% and the balance of Fe and inevitable impurities.
3. The production method of claim 1, wherein in the step (1), the molten iron S in the furnace is less than or equal to 0.030 percent, Si is greater than 0.30 percent, the temperature of the molten iron is greater than or equal to 1290 ℃, TSO is measured at the end point, T is greater than or equal to 1610 ℃, O is less than or equal to 800ppm, point blowing is not allowed, argon is switched after 5 minutes of converter blowing, the pressure of a furnace mouth is controlled under micro-positive pressure, the target N content of a tundish is less than or equal to 40ppm, the shape of a steel tapping hole is good, the steel tapping time is 4-8 minutes, 30 seconds before steel tapping, the air in the ladle is emptied by introducing argon, the steel is not allowed to scatter and tap, secondary alloy supplement is not allowed, argon is required to be blown in the whole process of steel tapping, a feeding pipe is aligned to an impact part of steel flow, the lump accumulation in an alloy material and a slag ladle is prevented, the slag quantity is strictly controlled during steel tapping, the slag thickness is less than or equal to 100mm, argon station is blown to be strictly blown, and the molten steel is not more than or less than 20 cm.
4. The production method according to claim 1, wherein in the step (2), the station entering temperature is more than or equal to 1520 ℃, a bypass is opened at the early stage for large stirring to improve the air permeability of the steel ladle, the steel ladle is heated and heated at the station, white slag is formed in 15min, the slag deoxidation is carried out by using aluminum particles in the process, and the final slag system is CaO: 53% -58% of Al2O3：26％～32％，SiO2The method comprises the following steps of less than or equal to 8%, MgO less than or equal to 10%, FeO + MnO less than or equal to 1.2%, refining time more than or equal to 50min, heating time less than or equal to 30min, white slag time more than or equal to 10min, micro-positive pressure operation is adopted in a whole argon blowing furnace, foam slag covers the liquid level of steel, Ca wires are added into the furnace at a rate of 80-110 m/furnace, the pressure of bottom blowing argon is strictly controlled in the wire feeding process, large overturning is strictly prohibited, two-stage soft blowing is adopted, soft blowing before calcium is more than or equal to 5min, the diameter of argon flowers is 200-300 mm, soft blowing after calcium is more than or equal to 15min, the creep diameter of slag surfaces is 100-200 mm, the creep of slag surfaces is guaranteed and the molten steel is not exposed, aluminum, alloy and heating operations are prohibited in the soft blowing and calcium treatment processes, alloy replenishment is prohibited in the soft blowing process, Al is prohibited in the soft blowing process at 8min, and argon blowing flow rate of single-permeable bricks is 30-150 NL/min.
5. The production method according to claim 1, wherein in the step (3), argon replacement of the tundish is continuously carried out from closing of the ladle baking device to pouring of the ladle, the blowing flow of the ladle argon seal is 30-80L/min, the stopper rod blows argon for 2-5L/min, a tundish covering agent with high alkalinity is used, no molten steel is exposed in the process, delta Als of the tundish is less than 40ppm, delta Alt is less than 60ppm, the ratio of the Als/Alt of the tundish is more than or equal to 0.92, the ratio of the N of the tundish is less than or equal to 50ppm, a long nozzle sealing gasket is intact, a long nozzle sleeve is right perpendicular to the tundish liquid level, the service time of the long nozzle is less than or equal to 4h, the insertion depth of the ladle nozzle is more than or equal to 200mm, the insertion depth of an immersion nozzle is 120-140 mm, slag dropping of the ladle is controlled, and 3 tons of steel are left in the ladle at the tail stage of casting for self-circulation; deslagging every 3 furnaces of the tundish for 1 time, using a large-chamfer crystallizer, keeping the reduction at 4mm under electric soft reduction, keeping the electromagnetic stirring current intensity at 340A, keeping the frequency at 5Hz, keeping the pulling speed at 1.0-1.15 m/min, keeping the pulling speed variation at less than or equal to 0.05m/min, keeping the liquid level fluctuation of the crystallizer at less than 3mm, keeping the superheat degree of the tundish at 10-25 ℃, and keeping the plate blank off-line stacking and slow cooling at more than or equal to 24 hours.
6. The production method according to claim 1, wherein in the step (4), the temperature difference between the surfaces of the steel strip is 30 ℃ or less.
7. The production method according to claim 1, wherein in the step (6), the finish rolling temperature is 950-1020 ℃, the finish rolling temperature is 830-860 ℃, the water between stands is fully boiled, the rolling speed is less than or equal to 2.5m/s, and the finish rolling temperature is controlled in a closed loop mode.
8. 700MPa grade thick gauge high strength steel prepared by the production method according to any one of claims 1 to 7.
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* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP2000328187A (en) * 1999-05-20 2000-11-28 Nippon Steel Corp High strength hot rolled steel sheet for working excellent in endurance fatigue property and small in variation of material and its production
CN102226250A (en) * 2011-06-13 2011-10-26 马鞍山钢铁股份有限公司 Hot rolled steel plate with yield strength being 700MPa and preparation method thereof
CN102409233A (en) * 2011-11-03 2012-04-11 首钢总公司 Low-temperature steel for engineering machinery and production method thereof
CN107881420A (en) * 2016-09-29 2018-04-06 上海梅山钢铁股份有限公司 A kind of tensile strength 550Mpa level hot rolled steel plates and its manufacture method
CN112281075A (en) * 2020-11-06 2021-01-29 安阳钢铁股份有限公司 Method for improving integral rolling performance stability of niobium-titanium composite reinforced 700MPa girder steel

Patent Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP2000328187A (en) * 1999-05-20 2000-11-28 Nippon Steel Corp High strength hot rolled steel sheet for working excellent in endurance fatigue property and small in variation of material and its production
CN102226250A (en) * 2011-06-13 2011-10-26 马鞍山钢铁股份有限公司 Hot rolled steel plate with yield strength being 700MPa and preparation method thereof
CN102409233A (en) * 2011-11-03 2012-04-11 首钢总公司 Low-temperature steel for engineering machinery and production method thereof
CN107881420A (en) * 2016-09-29 2018-04-06 上海梅山钢铁股份有限公司 A kind of tensile strength 550Mpa level hot rolled steel plates and its manufacture method
CN112281075A (en) * 2020-11-06 2021-01-29 安阳钢铁股份有限公司 Method for improving integral rolling performance stability of niobium-titanium composite reinforced 700MPa girder steel

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Denomination of invention: A 700MPa thick specification high-strength steel and its production method

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