CN113215492B - Rolling method of high-toughness low-alloy high-strength steel - Google Patents

Rolling method of high-toughness low-alloy high-strength steel Download PDF

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CN113215492B
CN113215492B CN202110519204.6A CN202110519204A CN113215492B CN 113215492 B CN113215492 B CN 113215492B CN 202110519204 A CN202110519204 A CN 202110519204A CN 113215492 B CN113215492 B CN 113215492B
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rolling
strength steel
cooling
toughness
water
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CN113215492A (en
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李小龙
时涛
周敦世
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Daye Special Steel Co Ltd
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Daye Special Steel Co Ltd
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Priority to EP22784173.1A priority patent/EP4338862A1/en
Priority to KR1020237038961A priority patent/KR20240004507A/en
Priority to PCT/CN2022/092306 priority patent/WO2022214107A1/en
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    • 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
    • C21D9/0075—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for rods of limited length
    • 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
    • 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
    • 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
    • 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
    • C21D7/00—Modifying the physical properties of iron or steel by deformation
    • C21D7/13—Modifying the physical properties of iron or steel by deformation by hot working
    • 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
    • C21D8/06—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of rods or wires
    • C21D8/065—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of rods or wires 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
    • C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
    • C21D9/0062—Heat-treating apparatus with a cooling or quenching zone
    • 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
    • C22C38/04—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
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/24—Ferrous alloys, e.g. steel alloys containing chromium with vanadium
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/38—Ferrous alloys, e.g. steel alloys containing chromium with more than 1.5% by weight of manganese
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D2211/00—Microstructure comprising significant phases
    • C21D2211/005—Ferrite
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D2211/00—Microstructure comprising significant phases
    • C21D2211/009—Pearlite

Abstract

The invention provides a rolling method of high-toughness low-alloy high-strength steel, which sequentially comprises the following steps: heating, descaling, rough rolling, continuous rolling, first water-through cooling, finish rolling, second water-through cooling and cooling by a cooling bed; the converter continuous casting billet is used as a raw material, and the converter continuous casting billet comprises the following chemical components in percentage by mass: c is less than or equal to 0.20; si is less than or equal to 0.60; 1.00-1.70 parts of Mn1.00; cr is less than or equal to 0.30; p is less than or equal to 0.020; s is less than or equal to 0.020; v is 0.05-0.10; al is less than or equal to 0.03; n is less than or equal to 0.025; the balance being Fe and unavoidable impurities. The actual grain size of the low-alloy high-strength steel can be refined by adopting the rolling method, the comprehensive performance of the low-alloy high-strength steel is excellent, the metallographic structure is fine ferrite plus pearlite, the grain size reaches more than 9.0 grade, the impact energy at minus 20 ℃ is more than 100J, and the impact energy at minus 40 ℃ is more than 80J.

Description

Rolling method of high-toughness low-alloy high-strength steel
Technical Field
The invention relates to the field of steel rolling, in particular to a rolling method of high-toughness low-alloy high-strength steel.
Background
With the economic development and the technological progress of society, steel materials are widely applied to various fields, wherein low-alloy high-strength steel has high strength, good plasticity and toughness, and is widely applied to high-end fields such as aerospace, ships and the like, in particular to the fields of basic facilities such as petroleum pipelines, bridges, large buildings and the like, and engineering fields such as vehicles, containers, machinery, chemical engineering, medical engineering, light industrial equipment and the like. Low alloy high strength steel is widely used in the fields of mechanical equipment, vehicles, pipe making and the like due to high strength, excellent formability and stable comprehensive properties.
At present, the approaches for improving the strength of steel materials include solid solution strengthening, dislocation strengthening, fine crystal strengthening, precipitation strengthening of second phase particles, and the like; the fine-grain strengthening effect is most obvious, and the steel after fine-grain strengthening has better strength and toughness. Along with the grain refinement and the improvement of the crack propagation resistance, the fatigue strength of the steel is increased, the toughness is improved, and the temperature of the brittle turning point is reduced. The fine-grained steel has good strength and toughness matching, and is widely applied to the fields of automobiles, ships, bridges, engineering machinery and the like.
The strength and toughness of low-alloy high-strength steel in the prior art cannot be obtained at the same time, only a rolling method of a steel plate and a plate strip is involved in the prior art, a rolling method of round steel bars is not involved, an off-line normalizing step is required in the rolling process, the production cost is high, and the energy saving, cost reduction and green manufacturing are not facilitated.
Disclosure of Invention
Aiming at the defects of the prior art, the invention aims to provide a rolling method of high-toughness low-alloy high-strength steel, which successfully develops and produces the rolling method of the high-toughness low-alloy high-strength steel by formulating reasonable production process control through microalloy elements and controlled rolling and controlled cooling process technologies, and removes the step of off-line normalizing in the manufacturing process of products, thereby reducing the process manufacturing flow and saving the manufacturing cost; the low-alloy high-strength steel manufactured by the process and the method has the advantages that the metallographic structure is fine ferrite and pearlite, the tensile strength is greater than 630MPa, the yield strength is greater than 500MPa, the grain size after rolling is fine and uniform, the grain size reaches over 9.0 grade, and the comprehensive mechanical property is far superior to that of the conventional rolling process.
In order to achieve the above purpose, the invention provides the following technical scheme:
a rolling method of a low-alloy high-strength steel with high toughness, which comprises the following steps in sequence: heating, descaling, rough rolling, continuous rolling, first water-through cooling, finish rolling, second water-through cooling and cooling bed cooling.
The converter continuous casting billet is used as a raw material, and the continuous casting billet of the high-toughness low-alloy high-strength steel comprises the following chemical components in percentage by mass: c is less than or equal to 0.20; si is less than or equal to 0.60; 1.00-1.70 parts of Mn1.00; cr is less than or equal to 0.30; p is less than or equal to 0.020; s is less than or equal to 0.020; v is 0.05-0.10; al is less than or equal to 0.03; n is less than or equal to 0.025; the balance of Fe and inevitable impurities.
In the rolling method of the high-toughness low-alloy high-strength steel, as a preferred embodiment, the heating step is divided into four sections, namely a preheating section, a heating section and a soaking section.
In a preferred embodiment of the rolling method of the high-toughness low-alloy high-strength steel, the temperature of the preheating section is less than or equal to 750 ℃.
In a preferred embodiment of the rolling method of the high-toughness low-alloy high-strength steel, the temperature of the first heating stage is 900 to 1050 ℃.
In a preferred embodiment of the method for rolling the high-toughness low-alloy high-strength steel, the temperature of the heating secondary stage is 1050 to 1150 ℃.
In a preferred embodiment of the method for rolling the high-toughness low-alloy high-strength steel, the temperature of the soaking section is 1150 to 1210 ℃.
In the rolling method of the high-toughness low-alloy high-strength steel, as a preferred embodiment, the total heating time of the heating step is 3 to 5 hours.
In a preferred embodiment of the rolling method of the high-toughness low-alloy high-strength steel, the soaking time of the soaking section is 30-80 min.
In a preferred embodiment of the method for rolling a high-toughness low-alloy high-strength steel, the heating step is performed in a four-stage step furnace.
In a preferred embodiment of the rolling method of the high-toughness low-alloy high-strength steel, in the rough rolling step, the inlet temperature of rough rolling is 950 to 1050 ℃, the number of rough rolling passes is 5 to 7, and preferably, the number of rough rolling mills in the rough rolling step is 6.
In a preferred embodiment, the rolling step of the high-toughness low-alloy high-strength steel includes intermediate rolling and pre-finish rolling.
In a preferred embodiment of the method for rolling the high-toughness low-alloy high-strength steel, the inlet temperature of the intermediate rolling is 900 to 1000 ℃.
In a preferred embodiment of the rolling method of the high-toughness low-alloy high-strength steel, the number of the intermediate rolling mills in the intermediate rolling is 6, and the number of the intermediate rolling passes is 5 to 7, preferably 6.
In a preferred embodiment of the method for rolling the high-toughness low-alloy high-strength steel, the outlet temperature of the pre-finish rolling is 850 to 950 ℃.
In a preferred embodiment of the method for rolling the high-toughness low-alloy high-strength steel, the number of pre-finishing mills in the pre-finishing rolling is 4, and the number of pre-finishing passes is 3 to 5, preferably 4.
As a preferred embodiment, the first water-cooling is performed to the incoming material after the continuous rolling step, wherein the water-cooling speed is 25 to 50 ℃/s, and the water pressure is 0.2 to 0.6 MPa.
In the rolling method of the high-toughness low-alloy high-strength steel, as a preferred embodiment, the entry start rolling temperature of the finish rolling in the finish rolling step is 800 to 850 ℃.
In a preferred embodiment, the rolling method of the high-toughness low-alloy high-strength steel is a finish rolling using a reducing sizing mill.
In a preferred embodiment of the method for rolling the high-toughness low-alloy high-strength steel, the reducing and sizing mill set is a three-roll reducing and sizing mill set.
In a preferred embodiment of the method for rolling a high-toughness low-alloy high-strength steel, the second water-cooling is performed by performing the second water-cooling on the steel after the finish rolling step, wherein the water-cooling rate is 25 to 100 ℃/s, and the water pressure is 0.2 to 0.6 MPa.
In a preferred embodiment of the method for rolling high-toughness low-alloy high-strength steel, the descaling step is performed by descaling with high-pressure water having a water pressure of 15 to 20MPa and having a scale removed mesh.
More preferably, the water pressure of the high-pressure water is 17-20 MPa.
In a preferred embodiment, the rolling method of the high-toughness low-alloy high-strength steel is used to obtain a high-toughness low-alloy high-strength steel bar, wherein the steel bar is about 60 to 120mm in length.
In a preferred embodiment of the method for rolling a high-toughness low-alloy high-strength steel, the cooling-bed cooling is a method in which a steel material obtained by cooling the steel material in a second pass through water is cooled in a cooling bed.
Compared with the prior art, the invention has the beneficial effects that:
(1) in the chemical components of the continuous casting billet, the microalloy element vanadium V is added, so that the hardenability of steel is improved, the deformation of steel is reduced, cracks are avoided, and the impact toughness is improved; because the microalloy element vanadium V only has a delay effect on recrystallization below 900 ℃, the microalloy element vanadium V is almost completely dissolved after austenite transformation, meanwhile, the microalloy element N further strengthens the impact toughness of the microalloy element, the precipitation strengthening effect of the microalloy element vanadium V and nitrogen N is fully utilized, the impact toughness is improved by adding the microalloy element V, and meanwhile, the microalloy element vanadium V has the strengthening effect of dissolving into ferrite to form stable carbide and refine grains.
Meanwhile, an online TMCP process is adopted, the precipitation process of nitrides is controlled, ferrite and pearlite structures are formed, grains are refined again by adopting lower finish rolling temperature and cooling rate, the strength of the steel is improved in the process of refining the grains, the plasticity and impact toughness of the steel are improved, and high-strength control of mechanical properties is realized.
The actual grain size of the low-alloy high-strength steel can be refined by adopting the rolling method, the obtained low-alloy high-strength steel has excellent comprehensive performance, the metallographic structure is fine ferrite and pearlite, the tensile strength is more than 630MPa, the yield strength is more than 500MPa, the grain size after rolling is fine and uniform, the grain size reaches more than 9.0 grade, the impact energy at-20 ℃ is more than 100J, the impact energy at-40 ℃ is more than 80J, and the comprehensive mechanical property of the low-alloy high-strength steel is far beyond that of the conventional rolling process;
(2) off-line normalizing treatment is not carried out in the rolling process, and the mechanical property can meet the use requirement, so that the processing time can be saved, and the cost can be reduced and the efficiency can be improved.
Drawings
FIG. 1 is a metallographic structure obtained in a manner that the rolling time of comparative example 2 is 80mm in the middle of the rolling process;
FIG. 2 shows the grain size (grade 7.5) obtained in 80mm gauge in the middle of rolling in comparative example 2;
FIG. 3 shows a metallographic structure obtained by 80mm before the rolling in example 2 of the present invention;
FIG. 4 shows the grain size (grade 9.0) obtained in 80mm gauge in the middle of rolling in example 2 of the present invention.
Detailed Description
The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the 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.
The rolling method disclosed by the invention is designed according to continuous rolling process parameters, combines solid-state phase change and plastic deformation of a rolling principle, adopts a four-section stepping heating furnace heating process system and a rolling reduction system to perform plastic forming, performs forming through rough rolling, intermediate rolling and finish rolling deformation systems, and finally controls metal solid-state phase change through a controlled cooling process to obtain a high-quality tissue form and excellent tissue mechanical properties of a required product.
The technical solution of the present invention is further described in detail by way of example with reference to the accompanying drawings.
A rolling method of a low-alloy high-strength steel with high toughness, which comprises the following steps in sequence: heating, descaling, rough rolling, continuous rolling, first water-through cooling, finish rolling, second water-through cooling and cooling by a cooling bed; the converter continuous casting billet is used as a raw material, and the converter continuous casting billet comprises the following chemical components in percentage by mass: c is less than or equal to 0.20; si is less than or equal to 0.60; 1.00-1.70 parts of Mn1.00; cr is less than or equal to 0.30; p is less than or equal to 0.020; s is less than or equal to 0.020; v is 0.05-0.10; al is less than or equal to 0.03; n is less than or equal to 0.025; the balance being Fe and unavoidable impurities.
In the chemical components of the continuous casting billet, a microalloy element vanadium V is added, so that the hardenability of steel is improved, the deformation and cracks of the steel are reduced, and the impact toughness is improved; because the microalloy element vanadium V only has a delay effect on recrystallization at the temperature of below 900 ℃, the microalloy element vanadium V is almost completely dissolved after austenite transformation, meanwhile, the microalloy element N further strengthens the impact toughness of the microalloy element vanadium V, and the precipitation strengthening effect of the microalloy element vanadium V and nitrogen N is fully utilized.
The reason why the grain refinement improves the plasticity and toughness is that the fine grains provide better conditions for the occurrence and propagation of plastic deformation. All factors that lower the austenite to ferrite transformation temperature Ar3 tend to be grain refined. The impact toughness is improved by adding the content of the microalloy element V, and meanwhile, the microalloy element V is dissolved in ferrite to play a reinforcing role, form stable carbide and refine grains.
The rolling method sequentially comprises the following steps:
(1) heating of
The heating step is carried out in a four-section stepping heating furnace; the heating step is divided into four sections, namely a preheating section, a heating section and a soaking section.
The temperature of the preheating section is less than or equal to 750 ℃ (such as 600 ℃, 650 ℃, 665 ℃, 700 ℃, 750 ℃ and any two temperatures in the section or section point); that is, if the furnace temperature exceeds 750 ℃, the heat transfer rate of the steel billet may be too high, and the temperature difference between the steel billet and the heating furnace may be too large, thereby causing cracks on the surface of the cast billet or the final rolled product.
The temperature of the first heating section is 900-1050 ℃ (such as 900 ℃, 950 ℃, 980 ℃, 1000 ℃, 1010 ℃, 1050 ℃ and any two temperatures between the two sections or interval points). The temperature of the second heating section is 1050-1150 ℃ (such as 1050 ℃, 1080 ℃, 1100 ℃, 1110 ℃, 1130 ℃, 1150 ℃ and any two temperatures in the section or interval). The main functions of the first heating section and the second heating section are as follows: the energy consumption is reduced, and the oxidation burning loss of the steel billet is reduced.
The temperature of the soaking section is 1150-1210 deg.C (such as 1150 deg.C, 1160 deg.C, 1165 deg.C, 1170 deg.C, 1185 deg.C, 1190 deg.C, 1205 deg.C, 1210 deg.C, and any two temperatures between the two zones or intervals). The main functions of the soaking section are as follows: the energy consumption is reduced, the oxidation burning loss of the steel billet is reduced, and the decarburization of the steel billet is reduced.
The total heating time of the heating step is 3-5 h (such as 3.5h, 4h, 4.5h, 4.8h and time points between any two of the time periods); the soaking time of the soaking section is 30-80 min (such as 30min, 35min, 40min, 45min, 50min, 55min, 60min, 70min, 75min, 80min and the time point between any two time periods).
The heating step achieves the following four goals: firstly, the energy consumption can be reduced and the cost can be saved by omitting the step of off-line normalizing; secondly, the oxidation burning loss of the steel billet is reduced in the four-section heating process; thirdly, the decarburization of the steel billet is reduced; fourthly, the surface cracks of the final rolled material caused by overlong heating time are reduced.
(2) Descaling
Descaling the heated billet by adopting high-pressure water to remove scale, wherein the pressure of the high-pressure water is 15-20 MPa (such as 15MPa, 16.5MPa, 17MPa, 18MPa, 20MPa and the pressure value between any two pressure values); the pressure value of the high-pressure water is preferably 17-20 MPa. The scale on the surface of the steel is removed by using high-pressure water, and the scale on the surface is not cleaned completely and thoroughly under the pressure lower than 15MPa, so that the rolling effect of the steel is influenced.
(3) Rough rolling
Preferably, 6 roughing mills are arranged in the roughing step; wherein the inlet temperature of rough rolling is 950-1050 ℃ (such as 950 ℃, 980 ℃, 1000 ℃, 1020 ℃, 1035 ℃, 1050 ℃ and any two temperature intervals or interval points), and the rough rolling pass is 5-7; the rough rolling pass is preferably 6 passes. The rough rolling step adopts a continuous rolling method, the surface size of the billet is changed mainly through plastic deformation, the hole pattern design adopts a box-shaped hole design, and the section shape of the billet is changed and reduced through a large reduction process.
(4) Continuous rolling
The continuous rolling step comprises intermediate rolling and pre-finish rolling, wherein the inlet temperature of the intermediate rolling is 900-1000 ℃ (such as 905 ℃, 920 ℃, 940 ℃, 950 ℃, 970 ℃, 1000 ℃ and any two temperature intervals or interval points), 6 intermediate rolling mills are preferably arranged in the intermediate rolling step, and the number of intermediate rolling passes is 5-7; the intermediate rolling pass is preferably 6 passes. The hole pattern design mainly adopts ellipse and round hole pattern design, and the section shape of the blank is close to the shape of a finished product through a rolling process.
The outlet temperature of the pre-finish rolling is 850-950 ℃ (such as 855 ℃, 870 ℃, 890 ℃, 900 ℃, 910 ℃, 920 ℃, 930 ℃, 940 ℃, 950 ℃ and any two temperatures in the interval or interval point); and preferably arranging 4 pre-finishing mills in the pre-finishing step, wherein the number of pre-finishing passes is 3-5, and the number of pre-finishing passes is preferably 4. The hole pattern design mainly adopts ellipse and round hole pattern design, and the section shape of the blank is close to the shape of a finished product through a rolling process.
(5) First pass water cooling
And (2) carrying out first water-through cooling on the incoming material after the continuous rolling step, wherein the temperature after the first water-through cooling is 750-800 ℃ (such as 750 ℃, 765 ℃, 780 ℃, 795 ℃, 798 ℃, 800 ℃ and any two temperatures in the range of a section or a section point), the water-through cooling speed of the first water-through cooling is 25-50 ℃/s, and the water pressure is 0.2-0.6 MPa. And controlling the temperature of the steel before finish rolling by controlling the temperature and the water cooling speed of the first water cooling, so as to obtain the target temperature required by finish rolling.
(6) Finish rolling
And (3) rolling the rolled material obtained in the step (5) in a sizing reduction finishing mill group, wherein the sizing reduction finishing mill group is preferably a three-roll sizing reduction finishing mill group, namely a KOCKS sizing reduction finishing mill group, and the entry starting rolling temperature is 800-850 ℃ (such as 800 ℃, 810 ℃, 820 ℃, 824 ℃, 832 ℃, 850 ℃ and any two temperature intervals or interval points). The three-roller reducing sizing mill set is adopted for finish rolling, so that low-temperature rolling can be better implemented, the grain size and the comprehensive mechanical property of the non-quenched and tempered steel are improved, and excellent properties of the non-quenched and tempered steel are provided for production of the non-quenched and tempered steel.
(7) Second pass water cooling
And carrying out secondary water-through cooling on the steel after the finish rolling, wherein the temperature of the secondary water-through cooling on the steel after the finish rolling step is 600-700 ℃ (such as 600 ℃, 625 ℃, 640 ℃, 662 ℃, 683 ℃, 700 ℃ and any two temperatures in the section or section point), wherein the water cooling speed is 25-100 ℃/s, and the water pressure is 0.2-0.6 MPa. And after finish rolling, carrying out secondary water-through cooling, controlling the temperature and the water-cooling speed of the secondary water-through cooling, and controlling the temperature of the steel to obtain the final required metallographic structure and mechanical property of the steel.
(8) Cooling bed cooling, i.e. cold bed air cooling
And air cooling the steel obtained after the second water cooling in a cooling bed to finally obtain the finished product steel.
The controlled rolling and controlled cooling technology from the step (1) to the step (8) is a main step for refining the grain size of high-carbon steel, and the purposes of refining the actual grain size and improving the rigidity and toughness of steel are achieved by combining the control of heating temperature, deformation degree and cooling speed.
Meanwhile, an online TMCP (thermal mechanical control) process (namely a thermo-mechanical control process) is adopted to control the precipitation process of nitrides to form uniform ferrite and pearlite structures, and grains are refined again by adopting lower finish rolling temperature and cooling rate, so that the strength of the steel is improved, the plasticity and impact toughness of the steel are improved, and the high-strength control of mechanical properties is realized.
The rolling method of the high-toughness low-alloy high-strength steel is unique, the combined action of trace alloy elements and a rolling control cooling technology of a thermal mechanical control process is adopted to realize on-line control, the actual grain size of the high-toughness low-alloy high-strength steel can be refined by adopting the process method, the high-toughness low-alloy high-strength steel is excellent in comprehensive performance, the metallographic structure is fine ferrite plus pearlite, the tensile strength is greater than 630MPa, the yield strength is greater than 500MPa, the grain size after rolling is fine and uniform, the grain size reaches above 9.0 grade, the charpy V-shaped impact power of 20 ℃ is greater than 100J, the charpy V-shaped impact power of 40 ℃ is greater than 80J, and the comprehensive mechanical property of the high-toughness low-alloy high-strength steel is far beyond the conventional rolling method.
The off-line normalizing treatment is not carried out on the high-toughness low-alloy high-strength steel in the manufacturing process, and the mechanical property can meet the use requirement, so that the processing time can be saved, and the cost can be reduced and the efficiency can be improved.
Example 1
Embodiment 1 provides a rolling method of high-toughness low-alloy high-strength steel, the specification of a required finished product is 65mm in the middle and the middle, and a continuous casting billet with a section of 300 x 400mm is selected; wherein, the mass percentage of each chemical component in the continuous casting billet is 100 percent as shown in the table 2; the method comprises the following steps:
(1) heating: cutting off the section continuous casting billet, and then putting the section continuous casting billet into a four-section stepping heating furnace for heating in a cold delivery mode, wherein the temperature of a preheating section is 685 ℃, the temperature of a first heating section is 1005 ℃, the temperature of a second heating section is 1086 ℃, and the temperature of a soaking section is 1175 ℃; the total heating time in the heating step is 3.8h, and the soaking time in the soaking section is 43 min.
(2) Descaling: and descaling the heated billet by adopting high-pressure water to remove the scale, wherein the pressure of the high-pressure water is 18.0 MPa.
(3) Rough rolling: sending the descaled steel billets into a high-rigidity roughing mill (6 frames) for roughing to obtain rough rolling steel billets; the rough rolling inlet temperature is 1015 ℃, and the rough rolling pass is 6.
(4) Continuous rolling: and (4) sending the rough rolling billet obtained in the step (3) into a continuous rolling unit, wherein the inlet temperature of intermediate rolling is 925 ℃, the intermediate rolling pass is 6 passes, the outlet temperature of the pre-finish rolling billet is 910 ℃, and the pre-finish rolling billet pass is 4 passes.
(5) First water cooling: carrying out primary water cooling on the rolled material subjected to pre-finish rolling; cooling to 790 deg.C; the water cooling speed is 40 ℃/s, and the water pressure is 0.5 MPa.
(6) Finish rolling: and rolling the rolled material which is 80mm in the middle of the specification obtained after pre-finish rolling through a KOCKS reducing sizing mill set, wherein the inlet temperature of the rolled material is 845 ℃ during rolling of the reducing sizing mill set, and the obtained specification is the middle of the 65mm steel bar.
(7) And (3) second-time through water cooling: carrying out secondary water cooling on the rolled material after finish rolling; cooling to 685 deg.C; the water cooling speed is 75 ℃/s, and the water pressure is 0.6 MPa.
(8) Cooling bed cooling (cooling bed air cooling): and (5) performing air cooling on the steel bar material with the specification of 65mm in the middle in the step (7) in a cooling bed to finally obtain the finished product steel bar material.
The hot rolled structure of the high toughness low alloy high strength steel obtained in example 1 was uniform ferrite and pearlite, the actual grain size was 9.0 grade, and the mechanical properties of the steel product are shown in table 3. The hot rolled structure of the high toughness low alloy high strength steel obtained in example 1 was uniform ferrite and pearlite, the actual grain size was 9.0 grade, and it is clear from table 3 that the steel products thereof were excellent in mechanical properties.
Example 2
Embodiment 2 provides a rolling method of high-toughness low-alloy high-strength steel, the specification of a required finished product is 80mm in the middle and long, and a continuous casting billet with a section of 300 x 400mm is selected; wherein, the mass percentage of each chemical component in the continuous casting billet is 100 percent as shown in the table 2; the rolling method sequentially comprises the following steps: (1) heating, (2) descaling, (3) rough rolling, (4) continuous rolling, (5) first water cooling, (6) finish rolling, (7) second water cooling and (8) cooling by a cooling bed (cooling bed air cooling), the processing steps of example 2 are the same as those of example 1, the processing parameters of the specific steps are shown in table 1, and the mechanical properties of steel products are shown in table 3.
The hot rolled structure of the high toughness low alloy high strength steel obtained in example 2 was uniform ferrite and pearlite as shown in fig. 3; the actual grain size was on the order of 9.0 as shown in FIG. 4. As can be seen from Table 3, the steel products are superior in mechanical properties.
Example 3
Embodiment 3 provides a rolling method of a high-toughness low-alloy high-strength steel, the specification of a required finished product is 100mm in the middle; selecting a continuous casting billet with a section of 300 x 400 mm; wherein, the mass percentage of each chemical component in the continuous casting billet is 100 percent as shown in the table 2; the rolling method sequentially comprises the following steps: (1) heating, (2) descaling, (3) rough rolling, (4) continuous rolling, (5) first water cooling, (6) finish rolling, (7) second water cooling and (8) cooling by a cooling bed (cooling bed air cooling), the processing steps of example 3 are the same as those of example 1, the processing parameters of the specific steps are shown in table 1, and the mechanical properties of steel products are shown in table 3.
The hot rolled structure of the high-toughness low-alloy high-strength steel obtained in example 3 was uniform ferrite and pearlite, the actual grain size was 9.0 grade, and it is clear from table 3 that the steel product was excellent in mechanical properties.
The specific process step parameters for examples 1-3 are shown in Table 1.
Figure 379466DEST_PATH_IMAGE001
The chemical compositions of the selected slabs of examples 1 to 3 are shown in Table 2.
Figure 315060DEST_PATH_IMAGE002
The properties of the high-toughness low-alloy high-strength steels obtained in examples 1 to 3 are shown in Table 3.
Figure 55746DEST_PATH_IMAGE003
Examples 4 to 7
Examples 4 to 7 provide a rolling method of a low alloy high strength steel of high toughness, which sequentially passes through the following steps: (1) heating, (2) descaling, (3) rough rolling, (4) continuous rolling, (5) first water cooling, (6) finish rolling, (7) second water cooling and (8) cooling by a cooling bed (cooling by air in the cooling bed), wherein the processing steps and mechanical parameters of examples 4-7 are the same as those of example 1; the chemical components contained in the continuous casting slabs used in examples 4 to 7 were contained in mass percentages, as shown in table 4, and the mass fractions were 100% in total.
Figure 571041DEST_PATH_IMAGE005
The properties of the high toughness low alloy high strength steels obtained in examples 4 to 7 are shown in Table 5.
Figure 962839DEST_PATH_IMAGE006
As is clear from Table 5, the hot rolled structures of the high toughness low alloy high strength steels obtained in examples 4 to 7 were uniform ferrite and pearlite, the actual grain size was 9.0 grade, and the mechanical properties of the steel products were excellent.
Comparative example 1
The specification of the required finished product is 65mm as far as the shaft, and a continuous casting billet with a section of 300 multiplied by 400mm is selected; the continuous casting billet comprises the following chemical components in percentage by weight: c0.45; si 0.28; mn1.46; 0.16 of Cr; v0.06; n0.010; 0.020 of Al; p is less than or equal to 0.020; s is less than or equal to 0.020; the balance of Fe and inevitable impurities. The alloy steel processing steps and parameters are shown in table 7.
As shown in Table 6, since the C content in the chemical composition of the slab was 0.45%, that is, C >0.20, the elongation of the rolled steel was 18% as shown in Table 8, and the Charpy V work at-20 ℃ was 32J; the Charpy V-type impact energy at-40 ℃ is 17J.
Comparative example 2
The specification of the required finished product is 80mm as far as the shaft, and a continuous casting billet with a section of 300 multiplied by 400mm is selected; the continuous casting billet comprises the following chemical components in percentage by weight: c0.16; 0.30 of Si; 0.8 of Mn; 0.15 of Cr; v0.07; n0.012; 0.020 of Al; p is less than or equal to 0.020; s is less than or equal to 0.020, and the balance of Fe and inevitable impurities. The alloy steel processing steps and parameters are shown in table 7.
As shown in Table 6, since the Mn content of the chemical composition of the slab is 0.8, that is, Mn is less than 1.0, as shown in Table 8, the elongation of the rolled steel is 26%, and the Charpy V-type impact energy at-20 ℃ is 54J; the Charpy V-type impact energy at-40 ℃ is 25J.
Comparative example 3
The specification of the required finished product is 100mm as far as the shaft, and a continuous casting billet with a section of 300 multiplied by 400mm is selected; the continuous casting billet comprises the following chemical components in percentage by weight: c0.16; 0.30 of Si; mn1.40; 0.15 of Cr; n0.011; 0.022 of Al; p is less than or equal to 0.020; s is less than or equal to 0.020; the balance being Fe and unavoidable impurities. The alloy steel processing steps and parameters are shown in table 7.
As shown in Table 6, since vanadium V is not added to the chemical components of the continuous casting slab, as shown in Table 8, the elongation of the rolled steel is 25%, and the Charpy V-type impact energy at-20 ℃ is 35J; the Charpy V-type impact energy at-40 ℃ is 19J.
Comparative example 4
The specification of the required finished product is that the middle section is 90mm, and a continuous casting billet with a section of 300 multiplied by 400mm is selected; the continuous casting billet comprises the following chemical components in percentage by weight: c0.16; si 0.32; mn1.47; 0.15 of Cr; v0.06; n0.040; 0.020 of Al; p is less than or equal to 0.020; s is less than or equal to 0.020; the balance being Fe and unavoidable impurities. The alloy steel processing steps and parameters are shown in table 7.
As shown in Table 6, since the content of nitrogen N in the chemical composition of the slab was 0.040, that is, N was >0.025, as shown in Table 8, the elongation of the rolled steel was 27%, and the Charpy V work at-20 ℃ was 62J; the Charpy V-type impact energy at-40 ℃ is 37J.
As can be seen from Table 8, the Charpy V-type impact energy at-20 ℃ in the mechanical properties of the steels obtained by the rolling methods of comparative examples 1 to 4 is less than 100J; the Charpy V-shaped impact energy at minus 40 ℃ is less than 80J, and the grain size of the rolled alloy steel is less than 9.0 grade.
Figure 803756DEST_PATH_IMAGE007
The processing steps and parameters of the alloy steels of comparative examples 1 to 4 are shown in Table 7.
Figure 530272DEST_PATH_IMAGE008
The properties of the alloy steels obtained in comparative examples 1 to 4 are shown in Table 8.
Figure 849258DEST_PATH_IMAGE009
While the preferred embodiments of the present invention have been described, additional variations and modifications in those embodiments may occur to those skilled in the art. Therefore, the appended claims should be construed to include preferred embodiments and all such variations and modifications as fall within the scope of the invention.
The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention, and various modifications and changes may be made by those skilled in the art. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims (16)

1. A rolling method of low-alloy high-strength steel with high toughness is characterized by sequentially comprising the following steps of:
heating, descaling, rough rolling, continuous rolling, first water-through cooling, finish rolling, second water-through cooling and cooling bed cooling;
the converter continuous casting slab is used as a raw material, and comprises the following chemical components in percentage by mass: c is less than or equal to 0.20; si is less than or equal to 0.60; 1.37-1.70 parts of Mn; cr is less than or equal to 0.30; p is less than or equal to 0.020; s is less than or equal to 0.020; v is 0.07-0.10; al is less than or equal to 0.03; 0.008-0.025% of N; the balance of Fe and inevitable impurities;
the temperature after the first water penetration cooling is 765-800 ℃;
in the finish rolling step, the entry start rolling temperature of finish rolling is 832-850 ℃;
performing secondary water-through cooling, wherein the temperature of performing the secondary water-through cooling on the steel after the finish rolling step is 600-700 ℃, the water-cooling speed is 25-100 ℃/s, and the water pressure is 0.2-0.6 MPa;
and the cooling bed cooling means that the steel obtained after the secondary water cooling is cooled in the cooling bed by air.
2. The rolling method of a high-toughness low-alloy high-strength steel according to claim 1, characterized in that: the heating step is divided into four sections, namely a preheating section, a heating section and a soaking section,
the temperature of the preheating section is less than or equal to 750 ℃;
the temperature of the first heating section is 900-1050 ℃;
the temperature of the second heating section is 1050-1150 ℃;
the temperature of the soaking section is 1150-1210 ℃.
3. The rolling method of a high toughness low alloy high strength steel according to claim 2, characterized in that: the total heating time of the heating step is 3-5 h; the soaking time of the soaking section is 30-80 min.
4. The rolling method of a high toughness low alloy high strength steel according to claim 2, characterized in that: the heating step is performed in a four-stage step furnace.
5. The rolling method of a high-toughness low-alloy high-strength steel according to claim 1 or 2, characterized in that: in the rough rolling step, the inlet temperature of rough rolling is 950-1050 ℃, and the rough rolling pass is 5-7.
6. The rolling method of a high toughness, low alloy, high strength steel according to claim 5, wherein: the number of the rough rolling mills in the rough rolling step is 6; the rough rolling pass is 6.
7. The rolling method of a high-toughness low-alloy high-strength steel according to claim 6, wherein: the continuous rolling step comprises medium rolling and pre-finish rolling,
the inlet temperature of the medium rolling is 900-1000 ℃, and the medium rolling pass is 5-7;
the outlet temperature of the pre-finish rolling is 850-950 ℃, and the pre-finish rolling pass is 3-5.
8. The rolling method of a high toughness, low alloy, high strength steel as claimed in claim 7, wherein: the number of the middle rolling mills in the middle rolling is 6; the middle rolling pass is 6 passes.
9. The rolling method of a high toughness, low alloy, high strength steel as claimed in claim 7, wherein: the number of pre-finishing mills is 4 in the pre-finishing; the pre-finish rolling pass is 4.
10. The rolling method of a high toughness, low alloy, high strength steel according to claim 5, wherein: and carrying out primary water cooling on the incoming material after the continuous rolling step, wherein the water cooling speed is 25-50 ℃/s, and the water pressure is 0.2-0.6 MPa.
11. The rolling method of a high toughness, low alloy, high strength steel according to claim 5, wherein: and (5) performing finish rolling by adopting a reducing sizing mill set.
12. The rolling method of a high toughness low alloy high strength steel according to claim 11, characterized in that: the reducing sizing machine set is a three-roller reducing sizing machine set.
13. The rolling method of a high toughness, low alloy, high strength steel according to claim 5, wherein: in the descaling step, high-pressure water with scale removed as a mesh is used for descaling, and the water pressure of the high-pressure water is 15-20 MPa.
14. The method of rolling a high toughness, low alloy, high strength steel according to claim 13, wherein: the water pressure of the high-pressure water is 17-20 MPa.
15. The rolling method of a high-toughness low-alloy high-strength steel according to any one of claims 1 to 2, characterized in that: the low-alloy high-strength steel bar with high toughness is obtained by the rolling method.
16. The method of rolling high toughness low alloy high strength steel as claimed in claim 15, wherein: the specification of steel bar is in the same side 60 ~ 120 mm.
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