CN115351075A - Method for controlling plate shape of 235 MPa-grade thick steel plate with thickness greater than 60mm - Google Patents
Method for controlling plate shape of 235 MPa-grade thick steel plate with thickness greater than 60mm Download PDFInfo
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- 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
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
- B21B—ROLLING OF METAL
- B21B15/00—Arrangements for performing additional metal-working operations specially combined with or arranged in, or specially adapted for use in connection with, metal-rolling mills
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- 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
- B21B37/16—Control of thickness, width, diameter or other transverse dimensions
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- 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
- B21B37/28—Control of flatness or profile during rolling of strip, sheets or plates
- B21B37/30—Control of flatness or profile during rolling of strip, sheets or plates using roll camber control
- B21B37/32—Control of flatness or profile during rolling of strip, sheets or plates using roll camber control by cooling, heating or lubricating the rolls
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- 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
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- 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
- B21B45/004—Heating the product
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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
- 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
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- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
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- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
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- C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
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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
- C22C38/06—Ferrous alloys, e.g. steel alloys containing aluminium
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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
- C22C38/12—Ferrous alloys, e.g. steel alloys containing tungsten, tantalum, molybdenum, vanadium, or niobium
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
- B21B—ROLLING OF METAL
- B21B15/00—Arrangements for performing additional metal-working operations specially combined with or arranged in, or specially adapted for use in connection with, metal-rolling mills
- B21B2015/0064—Uncoiling the rolled product
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Abstract
The invention relates to a method for controlling the shape of a 235MPa thick steel plate with the thickness of more than 60mm, which comprises the following chemical components in percentage by weight: 0.12% to 0.18% of C, 0.35% to 0.35% of Si, 0.75% to 0.95% of Mn, 0.035% to P, 0.035% to S, 0.015% to 0.045% of Ceq, 0.4% to Ceq = C + Mn/6, and the balance Fe and inevitable impurities. The width of the steel plate is more than 3000mm, and the steel plate is obtained by rolling a casting blank with the thickness of 250-360 mm by a medium plate reciprocating mill; the production process comprises the steps of heating a casting blank, rolling, hot straightening and stacking and slow cooling of a steel plate; the plate shape control requirement of the steel plate can be met without subsequent cold straightening treatment, and the problems that the once-through rate and the cost reduction rate of the steel plate are influenced due to the fact that wave shapes are easy to appear in the production of the super-thick steel plate are solved.
Description
Technical Field
The invention relates to the field of steel plate production, in particular to a plate shape control method for a steel plate with the thickness specification of more than 60mm, the width of more than 3000mm and the yield strength of 235 MPa.
Background
The 235 MPa-yield-strength steel plate belongs to a low-strength-level steel plate, and the main chemical elements of the level steel are C, si, mn, al and the like. Generally, when a 4m or more wide and thick plate mill produces a steel plate of the grade with a thin specification (below 8 mm) or a thick specification (above 60 mm), a hard bending or a poor plate shape is easy to occur in rolling, particularly, the steel plate of the grade with a thickness of above 60mm and a width of above 3000mm is easy to be flattened by a flattening machine for saving, and if the steel plate can not be flattened and is subjected to supplementary rolling, raw materials are wasted, the production efficiency is influenced, the production cost is increased, and the one-time passing rate of the steel plate is seriously influenced. Meanwhile, due to the limitation of protection parameters set by the straightener, the straightening roller catcher is easy to break or the straightening effect is not ideal when the steel plate is straightened, so that the unevenness of the steel plate is poor. The above reasons result in a significant increase in the manufacturing cost of the super-thick steel plate of the steel grade and an extension in the delivery cycle.
Therefore, how to solve the problem of the plate shape of the steel plate with the thickness specification of more than 60mm, the width of more than 3000mm and the yield strength of 235MPa is the key for developing and applying the steel plate with the specification grade by improving the one-time pass rate of the steel plate.
So far, the plate shape control research on steel plates with the thickness of more than 60mm, the width of more than 3000mm and the yield strength of 235MPa level at home and abroad is very little. The Chinese patent application with the publication number of CN103722023A discloses a TMCP high-strength ship plate shape control method which is effective for controlling the plate shape of a rolled high-strength ship plate. However, the thickness of the steel plate applicable to the method is 30-60mm, and the shape control of the steel plate with the thickness of more than 60mm is not involved. The Chinese patent application with publication number CN101069896A discloses a method for controlling the shape of a medium plate, which can reduce the wave shape of a rolled steel plate with the thickness of 30 mm. However, the method cannot completely eliminate the wave shape of the steel plate because the last time has no rolling reduction; and because the rolling mill is only contacted with the steel plate through the upper roller and the lower roller, the plate shape defects such as warping and the like generated in the previous rolling pass cannot be eliminated when the last pass has no rolling reduction.
In journal thesis 'optimized control of production process of hot-rolled thin gauge plate' (Henan metallurgy 2020.8), the problem of plate shape control of a thin gauge steel plate with a thickness gauge of 6-10mm is solved by optimizing heating, rolling and pressing procedures, but the method cannot meet the plate shape control of a steel plate with a thickness of more than 60 mm.
Disclosure of Invention
The invention provides a method for controlling the shape of a 235MPa thick steel plate with the thickness of more than 60mm, which can meet the requirement of controlling the shape of the steel plate without subsequent cold straightening treatment and solve the problems that the production of the super-thick steel plate is easy to generate wave shape, and the one-time passing rate and the cost-to-time reduction rate of the steel plate are influenced.
In order to achieve the purpose, the invention adopts the following technical scheme:
a plate shape control method of a 235 MPa-grade thick steel plate with the thickness of more than 60mm is disclosed, wherein the steel plate production process comprises casting blank heating, rolling, hot straightening and steel plate stacking and slow cooling; the method comprises the following specific steps:
1) Heating a casting blank: heating the casting blank to 1235-1265 ℃, wherein the total heating time of the soaking section and the heating section is 4.5-5.5 h, and the total in-furnace time is 6.5-7 h; ensuring that the temperature difference between the upper surface and the lower surface of the heated billet is less than 30 ℃;
2) Rolling; the cooling water quantity of the roller way between the rolling mill and the pre-straightening machine is 150-200 m 3 H; in the rolling stage, the rollers are controlled by sectional cooling, and when the head of a casting blank is rolled to be 1/6L in length, the cooling water of the rollers is not started; when rolling the 1/6L length section of the tail part of the casting blank, the cooling water quantity of the roller is controlled to be 35-50 m 3 H; when rolling the rest length of the middle part of the casting blank, the water quantity of the roller is controlled to be 50-80 m 3 H; wherein L is the length of a casting blank corresponding to the rolling direction during each pass of rolling; during rolling, at least the first 3 passes adopt large reduction rate, the reduction rate of each pass is not lower than 15%, at least the last 3 passes adopt small reduction rate, and the reduction rate of each pass is controlled to be 1-1.5%; controlling the SKI value of the SKI coefficient of the rolling mill in the rolling widening stage, and setting the SKI value to be + 4- +8; the finishing temperature of the steel plate is 850-930 ℃; the biting speed of the billet is 2-3 m/s;
3) Carrying out thermal straightening; the roll gap tilting value is set to be 8-12 mm; the position of the leading-in roller is-2.1 to-2.5 mm, the position of the leading-out roller is-4.1 to-4.9 mm, the final correction temperature is not more than 600 ℃, and the straightening force is 8000 to 10000kN;
4) Steel plate stacking and slow cooling: and immediately transporting the steel plate after the hot straightening to a slow cooling area for stacking, wherein the slow cooling speed of the steel plate stack is 5-10 ℃/h, and the time is 24-48 h.
The steel plate comprises the following chemical components in percentage by weight: c is more than or equal to 0.12 percent and less than or equal to 0.18 percent, si is less than or equal to 0.35 percent, mn is 0.75-0.95 percent, P is less than or equal to 0.035 percent, S is less than or equal to 0.035 percent, al is 0.015-0.045 percent, ceq is less than or equal to 0.4 percent, ceq = C + Mn/6, the balance is Fe and inevitable impurities, O in the impurities is less than or equal to 0.0050 percent, and the total amount of the rest impurities is less than 0.05 percent.
The width of the steel plate is larger than 3000mm, and the steel plate is obtained by rolling a casting blank with the thickness of 250-360 mm through a medium plate reciprocating mill.
In the step 2), before rolling, the casting blank after being taken out of the heating furnace is descaled by using high-pressure water, the descaling time is 0.5-1 min, and the pressure of a descaler is 20-25 MPa.
The flatness of the finished steel plate is below 5mm/2 m.
Compared with the prior art, the invention has the beneficial effects that:
1) The higher heating temperature is adopted, and the furnace time of the soaking section and the heating section is ensured at the same time, so that the temperature difference between the upper surface and the lower surface of the heated casting blank is controlled within 30 ℃, the temperature difference between the surface of the casting blank and the core part is reduced, and the transverse and longitudinal metal flow uniformity of the surface of the steel plate is improved; the total furnace time is controlled, thereby effectively inhibiting the excessive growth of austenite grains and ensuring the performance of the steel plate.
2) The flow rate of the roller table cooling water is controlled, and the rollers adopt a segmented cooling process, so that the phenomenon that a large amount of cooling water flows on the surface of a steel plate to cause uncontrolled temperature drop on the surface of the steel plate is avoided, and the rolling pass is increased; the cooling water quantity of the roller is reasonably controlled, the roller shape is effectively controlled, and the problems of irregular deviation, camber and the like generated in the rolling process due to uneven head-middle-tail temperature distribution of the steel billet are greatly improved; meanwhile, pass rolling reduction of different stages of rolling is optimized, and the final rolling temperature and the rolling speed are controlled, so that the initial plate shape of a rolled steel plate is effectively ensured, and the internal stress of the steel plate is reduced; in addition, the coefficient SKI value of the SKIs of the rolling mill, the biting speed of the steel billet and the rolling speed in the rolling widening stage are controlled to ensure that the intermediate billet is kept in a horizontal or slightly upwarping state, so that the initial shape of the rolled steel plate is ensured.
3) The method comprises the steps of adopting three ways of thermal straightening, a semi-automatic straightening mode, manual steel plate thickness input and the like to realize inclined roll gap straightening, and ensuring the straightened steel plate to be straight and have good plate shape by setting the initial guide-in roll position, the guide-out roll position, the straightening temperature and the straightening pressure; meanwhile, a lower final straightening temperature is set, so that the temperature drop interval of the steel plate in the cooling process is smaller, the generation of larger internal stress due to phase change is avoided, the control of the shape of the steel plate is facilitated, the occurrence probability of the shape problems of the buckle head and the buckle tail plate is reduced, and the input cost of subsequent cold straightening equipment is saved.
4) The steel plate after hot straightening is immediately transported to a slow cooling area for stacking, steel plate stacking slow cooling and asbestos heat preservation treatment are carried out, meanwhile, the slow cooling temperature and the stacking speed of the steel plate are strictly limited, the temperature drop of the steel plate is guaranteed to be consistent, a phase change interval with large internal stress at 400 ℃ is avoided, the final flatness of the finished steel plate is guaranteed to meet the requirement below 5mm/2m, and the subsequent flattening and straightening process cost is saved.
Detailed Description
The invention relates to a method for controlling the shape of a 235MPa thick steel plate with the thickness of more than 60mm, wherein the steel plate production process comprises casting blank heating, rolling, hot straightening and steel plate stacking and slow cooling; the method comprises the following specific steps:
1) Heating a casting blank: heating the casting blank to 1235-1265 ℃, wherein the total heating time of the soaking section and the heating section is 4.5-5.5 h, and the total furnace time is 6.5-7 h; ensuring that the temperature difference between the upper surface and the lower surface of the heated billet is less than 30 ℃;
2) Rolling; the cooling water quantity of the roller way between the rolling mill and the pre-straightening machine is 150-200 m 3 H; in the rolling stage, the rollers are controlled by sectional cooling, and when the head of a casting blank is rolled to be 1/6L in length, the cooling water of the rollers is not started; when rolling the 1/6L length section of the tail part of the casting blank, the cooling water quantity of the roller is controlled to be 35-50 m 3 H; when rolling the rest length of the middle part of the casting blank, the water quantity of the roller is controlled to be 50-80 m 3 H; wherein L is the length of a casting blank corresponding to the rolling direction during each pass of rolling; during rolling, at least the first 3 passes adopt large reduction rate, the reduction rate of each pass is not lower than 15%, at least the last 3 passes adopt small reduction rate, and the reduction rate of each pass is controlled to be 1-1.5%; controlling the SKI value of the SKI coefficient of the rolling mill in the rolling and widening stage, and setting the SKI value to be + 4- +8; the finishing temperature of the steel plate is 850-930 ℃; the biting speed of the billet is 2-3 m/s;
3) Carrying out thermal straightening; the roll gap tilting value is set to be 8-12 mm; the position of the leading-in roller is-2.1 to-2.5 mm, the position of the leading-out roller is-4.1 to-4.9 mm, the final correction temperature is not more than 600 ℃, and the straightening force is 8000 to 10000kN;
4) Steel plate stacking and slow cooling: and immediately transporting the steel plate after the hot straightening to a slow cooling area for stacking, wherein the slow cooling speed of the steel plate stack is 5-10 ℃/h, and the time is 24-48 h.
The steel plate comprises the following chemical components in percentage by weight: c is more than or equal to 0.12 percent and less than or equal to 0.18 percent, si is less than or equal to 0.35 percent, mn is 0.75-0.95 percent, P is less than or equal to 0.035 percent, S is less than or equal to 0.035 percent, al is 0.015-0.045 percent, ceq is less than or equal to 0.4 percent, ceq = C + Mn/6, the balance is Fe and inevitable impurities, O in the impurities is less than or equal to 0.0050 percent, and the total amount of the rest impurities is less than 0.05 percent.
The width of the steel plate is larger than 3000mm, and the steel plate is obtained by rolling a casting blank with the thickness of 250-360 mm through a medium plate reciprocating mill.
In the step 2), before rolling, the casting blank discharged from the heating furnace is descaled by using high-pressure water, the descaling time is 0.5-1 min, and the pressure of a descaler is 20-25 MPa.
The flatness of the finished steel plate is below 5mm/2 m.
The action principle of the plate shape control method of the 235 MPa-grade thick steel plate with the thickness of more than 60mm is as follows:
1. a casting blank heating procedure;
feeding a casting blank (with the thickness of 250-360 mm, preferably a continuous casting blank) into a stepping heating furnace for heating, wherein the casting blank is heated to 1235-1265 ℃, the total heating time of a soaking section and a heating section is 4.5-5.5 hours, and the total in-furnace time is 6.5-7 hours; the higher heating temperature is adopted, the temperature difference between the upper surface and the lower surface of the heated casting blank is ensured to be less than 30 ℃, the temperature difference between the surface of the casting blank and the core part is shortened, and the horizontal and longitudinal metal flow uniformity of the surface of the steel plate is improved; the total furnace time is controlled, the excessive growth of austenite grains is effectively inhibited, and the mechanical property of the steel plate is ensured.
2) Descaling and rolling by high-pressure water;
before rolling, descaling the casting blank after the casting blank is taken out of the heating furnace by using high-pressure water, wherein the descaling time is 0.5-1 min, and the pressure of a descaling machine is 20-25 MPa; meanwhile, the roller bed cooling water between the rolling mill and the pre-straightening area is reduced to 150-200 m 3 And h, the uncontrolled temperature drop of the surface of the steel plate caused by the flow of a large amount of cooling water on the lower surface of the steel plate is avoided, the rolling pass is increased, and meanwhile, the control of the intermediate billet to keep a horizontal or slightly upwarping state is facilitated.
In the rolling stage, sectional cooling control is adopted for the roller; when the head of the rolled casting blank is set to a set length section, the cooling water of the roller is not started, and when the middle of the rolled casting blank is set to a set length section, the cooling water quantity of the roller is 50-80 m 3 H, starting; when the tail part of the casting blank is rolled to set the length section, the roller is cooledThe water cooling amount is 35-50 m 3 And/h is started. By adjusting the cooling water quantity of the roller, the roller shape is effectively controlled, and the defects of irregular deviation, camber and the like generated in the rolling process due to uneven head-middle-tail temperature distribution of the steel billet are greatly improved. In addition, preferably, the rolling reduction rate of the first three times of rolling is high, the rolling reduction rate of each time is not lower than 15%, and the rolling reduction rate of the last three times of rolling is controlled to be 1-1.5%; the capacity of the rolling mill is exerted as much as possible in three passes before rolling, the plate shape of the steel plate can be flattened and the internal stress of the steel plate is reduced by adopting large reduction rate and rolling in the last three passes because the temperature reduction deformation resistance of the steel plate is increased and adopting small reduction rate. And controlling the SKI value of the SKI board coefficient of the rolling mill in the rolling widening stage, and setting the SKI value to be + 4- +8, so that the intermediate billet is kept in a horizontal or slightly upwarping state, and the billet is favorably and quickly bitten in the rolling widening stage. Controlling the finishing temperature of the steel plate to be 850-930 ℃. In order to ensure the rolled shape of the steel plate, the biting speed of the steel billet is controlled to be 2-3 m/s.
3. A thermal straightening process;
carrying out three-pass thermal straightening on the rolled steel plate, and setting the roll gap tilting value to be 8-12 mm by adopting a semi-automatic straightening mode; the position of the leading-in roller is-2.1 to-2.5 mm, the position of the leading-out roller is-4.1 to-4.9 mm, the final straightening temperature is not more than 600 ℃, and the straightening force is 8000 to 10000 kN. And the straightening mode, the proper roll gap, the straightening force and the straightening times are set, so that the straightened steel plate is straight and has good plate shape. Meanwhile, a lower final straightening temperature is set, so that the temperature drop interval of the steel plate in the cooling process is smaller, the generation of larger internal stress caused by phase change is avoided, the probability of the problems of head buckling and tail buckling of the steel plate is reduced, and the input cost of subsequent cold straightening and flattening equipment is saved.
4. A steel plate stacking and slow cooling process;
and (3) immediately transporting the steel plates after the hot straightening to a slow cooling area for stacking, wherein the temperature of the stacked steel plates is more than 450 ℃, the number of the stacked steel plates is not less than 10, simultaneously carrying out heat preservation treatment on the upper side, the lower side and the two sides of the stacked steel plates by using asbestos, and carrying out plasma cutting after the steel plates are stacked for 24-48 hours. Because the cooling speed of the lower surface, the upper surface and the two sides of the thick steel plate is different, the temperature drop of the steel plate can be ensured to be consistent by adopting steel plate stacking slow cooling and asbestos heat preservation, and meanwhile, a phase change interval with larger internal stress at 400 ℃ is avoided, and the final plate shape of the finished steel plate is ensured.
The invention combines chemical components with controlled rolling and controlled cooling process, overcomes the defects of the prior art, and solves the plate shape control problem of the steel plate with thickness specification of more than 60mm, width of more than 3000mm and yield strength of 235 MPa. The flatness of the finished steel plate is below 5mm/2m, and the technical requirements are met.
The following examples are carried out on the premise of the technical scheme of the invention, and detailed embodiments and specific operation processes are given, but the scope of the invention is not limited to the following examples.
[ examples ] A method for producing a compound
In the embodiment, the chemical components of the steel plate are shown in the table 1, and the heating system of the casting blank and the high-pressure water descaling process parameters before rolling are shown in the table 2; table 3 shows the rolling process parameters of the steel sheets; table 4 shows the hot straightening and slow cooling process parameters of the steel plate and the flatness of the finished steel plate.
TABLE 1 chemical composition of steel sheet (wt%)
| Examples | C | Si | Mn | Al | Ceq |
| 1 | 0.13 | 0.33 | 0.95 | 0.016 | 0.289 |
| 2 | 0.14 | 0.27 | 0.82 | 0.035 | 0.276 |
| 3 | 0.18 | 0.25 | 0.88 | 0.040 | 0.326 |
| 4 | 0.12 | 0.26 | 0.93 | 0.043 | 0.345 |
| 5 | 0.16 | 0.35 | 0.76 | 0.026 | 0.286 |
| 6 | 0.17 | 0.28 | 0.79 | 0.015 | 0.301 |
Note: the impurity elements P in the steel are less than or equal to 0.035 percent, and S is less than or equal to 0.035 percent; 0 percent or less than 0.0050 percent and the total amount of other impurity elements is less than 0.05 percent.
TABLE 2 heating system of casting blank and high-pressure water descaling process parameters before rolling
TABLE 3 Rolling Process parameters of the Steel plates
TABLE 4 Hot straightening, slow Cooling Process parameters for Steel plates and flatness of finished Steel plates
Therefore, the method solves the problem of the shape of hot rolled steel plates with the thickness of more than 60mm, the width of more than 3000mm and the yield strength of 235MPa grade produced by casting blanks with the thickness of 250-360 mm, and the flatness of the steel plates meets the technical requirement of less than 5mm/2 m.
The above description is only for the preferred embodiment of the present invention, but the scope of the present invention is not limited thereto, and any person skilled in the art should be considered to be within the technical scope of the present invention, and the technical solutions and the inventive concepts thereof according to the present invention should be equivalent or changed within the scope of the present invention.
Claims (5)
1. A plate shape control method of a 235 MPa-grade thick steel plate with the thickness of more than 60mm is characterized in that the production process of the steel plate comprises the steps of heating a casting blank, rolling, hot straightening and stacking and slow cooling of the steel plate; the method comprises the following specific steps:
1) Heating a casting blank: heating the casting blank to 1235-1265 ℃, wherein the total heating time of the soaking section and the heating section is 4.5-5.5 h, and the total furnace time is 6.5-7 h; ensuring that the temperature difference between the upper surface and the lower surface of the heated billet is less than 30 ℃;
2) The cooling water quantity of the roller way between the rolling mill and the pre-straightening machine is 150-200 m 3 H; in the rolling stage, the rollers are controlled by sectional cooling, and when the head of a casting blank is rolled to be 1/6L in length, the cooling water of the rollers is not started; when the 1/6L length section of the tail part of the casting blank is rolled, the cooling water quantity of the roller is controlled to be 35-50 m 3 H; when rolling the rest length of the middle part of the casting blank, the water quantity of the roller is controlled to be 50-80 m 3 H; wherein L is the length of a casting blank corresponding to the rolling direction during each pass of rolling; during rolling, at least the first 3 passes adopt large reduction rate, the reduction rate of each pass is not lower than 15%, at least the last 3 passes adopt small reduction rate, and the reduction rate of each pass is controlled to be 1-1.5%; controlling the SKI value of the SKI coefficient of the rolling mill in the rolling and widening stage, and setting the SKI value to be + 4- +8; the finishing temperature of the steel plate is 850-930 ℃; the biting speed of the billet is 2-3 m/s;
3) Hot straightening; the roll gap tilting value is set to be 8-12 mm; leading in the position of the roller at minus 2.1 to minus 2.5mm, leading out the position of the roller at minus 4.1 to minus 4.9mm, wherein the final straightening temperature is not more than 600 ℃, and the straightening force is 8000 to 10000KN;
4) Steel plate stacking and slow cooling: and immediately transporting the steel plate after the hot straightening to a slow cooling area for stacking, wherein the slow cooling speed is 5-10 ℃/h, and the time is 24-48 h.
2. The method for controlling the shape of a 235MPa thick steel plate with a thickness greater than 60mm according to claim 1, wherein the steel plate comprises the following chemical components in percentage by weight: c is more than or equal to 0.12 percent and less than or equal to 0.18 percent, si is less than or equal to 0.35 percent, mn is 0.75-0.95 percent, P is less than or equal to 0.035 percent, S is less than or equal to 0.035 percent, al is 0.015-0.045 percent, ceq is less than or equal to 0.4 percent, ceq = C + Mn/6, the balance is Fe and inevitable impurities, O in the impurities is less than or equal to 0.0050 percent, and the total amount of the rest impurities is less than 0.05 percent.
3. The method for controlling the shape of a 235MPa thick steel plate with the thickness of more than 60mm according to claim 1, wherein the width of the steel plate is more than 3000mm, and the steel plate is obtained by rolling a casting blank with the thickness of 250-360 mm through a medium plate reciprocating mill.
4. The method for controlling the shape of a 235MPa grade thick steel plate with a thickness of more than 60mm according to claim 1, wherein in the step 2), before rolling, the cast blank after being taken out of the heating furnace is descaled by using high-pressure water, the descaling time is 0.5-1 min, and the pressure of a descaler is 20-25 MPa.
5. A method for controlling the shape of a 235MPa grade thick steel plate with a thickness greater than 60mm according to claim 1, wherein the flatness of the finished steel plate is below 5mm/2 m.
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