CN115029622A - High-surface-quality hot-rolled dual-phase steel and production process thereof - Google Patents
High-surface-quality hot-rolled dual-phase steel and production process thereof Download PDFInfo
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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
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- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
- C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
- C21D8/0205—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips of ferrous alloys
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- 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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- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
- C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
- C21D8/0247—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the heat treatment
- C21D8/0263—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the heat treatment following hot rolling
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Abstract
The invention discloses high-surface-quality hot-rolled dual-phase steel, which comprises the following chemical components in percentage by mass: 0.05-0.068% of C, less than or equal to 0.12% of Si, 1.2-1.5% of Mn1.02-0.06% of Als0.02-0.06%, 0.5-0.7% of Cr0.015-0.025% of P, 78-0.002% of S0, 0-0.006% of N0, and the balance of Fe. According to the invention, by optimizing the steel composition and the preparation process, the accurate control of the cooling process can be realized, the good surface quality is ensured, the problems of high cost, low surface quality and the like of the conventional dual-phase steel are effectively solved, and the method is suitable for popularization and application.
Description
Technical Field
The invention belongs to the technical field of hot-rolled dual-phase steel, and particularly relates to high-surface-quality hot-rolled dual-phase steel and a production process thereof.
Background
Since the 20 th century 60 years ago, the dual-phase steel has good strength and toughness matching, lower yield ratio (Rp0.2/Rm), higher elongation and higher work hardening rate, has no phenomenon of discontinuous yield, ensures that a stamping component is easy to form, has small resilience, has small abrasion of a stamping die, and plays an important role in automobile reduction due to the advantages of low cost, good performance and the like.
The hot-rolled dual-phase steel is mainly classified into a low-temperature coiling type and a medium-temperature coiling type. The low-temperature coiling type hot-rolled dual-phase steel completes the transformation of main Ferro-martensite structures after finish rolling and before coiling, the content of the alloy of the hot-rolled dual-phase steel is relatively less, the alloy cost is economic, but the control of a hot-rolling process window is strict; the medium-temperature coiling type hot-rolled dual-phase steel mainly depends on stable austenite elements (such as Cr, Mo and the like) to control a steel coil in an austenite metastable state non-phase-change transformation region for coiling, but the hot-rolled dual-phase steel has high alloy cost.
The rolling control and cooling control method, namely the TMCP method, which is commonly adopted in the existing hot continuous rolling production method is difficult to realize the accurate control of the cooling process for the low-temperature production similar to the on-line quenching process, meanwhile, the hot-rolled dual-phase steel is mainly used for car wheels and has higher requirements on the surface quality of strip steel, and the accurate control of the cooling process and the guarantee of good surface quality are difficult to realize by adopting the existing hot continuous rolling production method. Therefore, a manufacturing process of the dual phase steel with low production cost and good surface quality needs to be further explored.
Disclosure of Invention
The invention mainly aims to provide the high-surface hot-rolled dual-phase steel and the production process thereof, aiming at the problems and the defects in the prior art, so that the accurate control of the cooling process is realized, the good surface quality is ensured, and the problems of high cost, low surface quality and the like of the conventional dual-phase steel are effectively solved.
In order to realize the purpose, the invention adopts the technical scheme that:
a high-surface-quality hot-rolled dual-phase steel comprises the following chemical components in percentage by mass: 0.05-0.068% of C, less than or equal to 0.12% of Si, 1.2-1.5% of Mn, 0.02-0.06% of Als, 0.5-0.7% of Cr, 0.015-0.025% of P, 0-0.002% of S, 78-0.006% of N0, and the balance of Fe.
Preferably, in the high surface quality hot-rolled dual-phase steel, the chemical components and the mass percentages thereof comprise: 0.055-0.06% of C, less than or equal to 0.1% of Si, 1.2-1.4% of Mn, 0.02-0.06% of Als, 0.5-0.6% of Cr, 0.018-0.025% of P, 0-0.002% of S0, 0-0.006% of N and the balance of Fe.
In the above scheme, the structure of the dual-phase steel comprises soft-phase ferrite and hard-phase martensite; wherein the ferrite accounts for 75-90% of the volume fraction, and the martensite accounts for 10-25% of the volume fraction.
In the scheme, the thickness of the high-surface-quality hot-rolled dual-phase steel is 3-6 mm.
In the scheme, the yield strength Rp0.2 of the dual-phase steel is 300-375 MPa, the tensile strength Rm is 590-650 MPa, the yield ratio is 0.5-0.60, and the total elongation after fracture is 24-30%; the surface has no defects such as tiger skin lines, short strip iron sheets, edge black lines, edge hairlines and the like.
The preparation method of the high-surface-quality hot-rolled dual-phase steel comprises the following steps of:
carrying out corner cutting treatment on the edge of a continuous casting billet with the thickness of 230-250 mm, and then sending the continuous casting billet to a rolling mill for rolling; the plate blank after corner cutting can eliminate the linear defect of the hot rolling edge curling part caused by large temperature drop of the edge part during rolling;
heating, wherein the heating temperature is controlled to be 1250-1320 ℃, the heating time is 150-220 min, the tapping temperature is 1280-1320 ℃, and the heating temperature is controlled in the range, so that the tiger skin lines on the surface can be effectively reduced;
carrying out rough rolling and finish rolling on the heated continuous casting billet; in rough rolling, in order to further reduce the temperature drop of the edge of the strip steel and prevent the edge of the strip steel from generating linear defects, the vertical roll adopts a baffle water-stop device to prevent water from contacting with the edge of the strip steel (see attached figure 3); removing scale on the surface by using a descaling pressure larger than 350Bar (preferably 370-380 Bar) before finish rolling; controlling the discharge temperature of rough rolling to be 1080-1110 ℃, the bite temperature of finish rolling to be 970-982 ℃, the finish rolling temperature to be 790-830 ℃ and the rolling speed to be 3.7-6 m/s;
performing cooling control after hot rolling, performing ultra-fast cooling on the finish-rolled continuous casting billet, controlling the temperature drop to be 100-130 ℃, controlling the cooling speed to be 100-140 ℃/s, and then performing air cooling for 7-12 s; and cooling to below 150 ℃ by laminar flow at a cooling speed of 85-115 ℃/s.
Rolling and finishing the coiled material within 24 hours at a finishing speed of 20-50 m/min; drying treatment is carried out in the flattening process, the drying temperature is 150-250 ℃, the air pressure is 20-30 Kpa, and the flow is 1100-1100 m 3 Drying the water on the surface of the strip steel, evaporating the accumulated water on the surface, and preventing the surface of the strip steel from being rusted and pocked due to the accumulated water on the surface; wherein, the air knife drying device is adopted in the drying process and is arranged at the position of the side guide roll between the pinch roll and the withdrawal and straightening machine.
In the scheme, the corner cutting treatment step is to cut off the corners at two sides (the corners at two sides) of the upper surface of the casting blank along the angle direction which is parallel to the casting blank surface by 40-50 degrees (preferably 45 degrees), and the length and the width of the cut-off corners are preferably 280-320 mm.
The principle of the invention is as follows:
1) composition design
Directly influencing the volume fraction of martensite and the carbon content of the martensite in the dual-phase steel, and avoiding the precipitation of the martensite by controlling the enrichment of C in a metastable austenite region so as to obtain a dual-phase structure in which island-shaped martensite is dispersedly distributed on a polygonal ferrite matrix; generally, the carbon content increases, the strength of the dual-phase steel increases, and the ductility decreases; meanwhile, the welding performance and the like can be influenced by increasing the content of C, but the content of C is too low, and a two-phase structure is not easy to obtain; the optimal C content in the dual-phase steel system is about 0.05-0.068%, which is beneficial to obtaining the dual-phase steel with 15-20% of martensite fraction and reasonable matching of obdurability.
Si: good action as non-carbide forming element in dual phase steels: the alpha + gamma region of the Fe-C phase diagram is enlarged, the treatment range of the critical region is widened, the technological performance of the dual-phase steel is improved, and the strength of the dual-phase steel is kept; secondly, the austenite form formed when the critical area is heated is changed, and the hardenability of austenite is improved, so that fine and uniformly distributed martensite can be obtained more easily; thirdly, Si accelerates the carbon to be deviated to austenite, so that ferrite is further purified, the clearance solid solution strengthening is avoided, and the production of coarse carbide during cooling can be avoided; si can influence the interaction of dislocation, increase the work hardening rate and the uniform extension under a given strength level;
however, the high Si content is not beneficial to the control of the surface quality of the plate, the Si element is easy to form Fe2SiO4/FeO (the melting point is 1173 ℃), and the iron scale defects which are difficult to remove are formed by pinning at the interface of the iron scale matrix; the actual condition of production quality control and the high surface quality requirement of the wheel are combined, the Si content in the steel is greatly reduced and is selected to be less than or equal to 0.12 percent, and the surface quality of the strip steel is improved;
mn: the pearlite transformation is delayed, the hardenability of austenite formed during heating in a critical zone can be effectively improved, and the effects of solid solution strengthening and ferrite grain refinement are achieved; meanwhile, Mn reduces critical points A3 and A1, and has a good effect of delaying bainite transformation while delaying pearlite transformation; in the dual-phase steel produced by adopting the rapid heating process, the content of Mn is generally higher, and uniform martensite structure and more uniform performance are obtained after cooling; however, too high Mn content easily causes severe banded structure, which reduces plasticity; therefore, in the invention, the content of Mn is set between 1.2 and 1.5 percent, and Mn is the optimal component;
p: the strengthening effect of P on ferrite is greater than that of Si, the formation temperature of ferrite can be increased, a two-phase region is enlarged, the form of a martensite island can be obviously changed, and the addition of proper P is favorable for obtaining fine and dispersedly distributed martensite; properly increasing the P content is advantageous for improving the processing of dual phase steelA rate of hardening; when P is excessively increased, processability is easily deteriorated; under the same rolling process, the addition of P content is favorable for improving the Si-system-containing iron scale, and P forms a low-melting-point ternary eutectic compound (FeO + Fe) at the interface of a substrate and the iron scale 2 SiO 4 +Fe 3 PO 4 ) The method is beneficial to removing the iron scale, so that more than 0.035 percent of P is adopted to improve the defect of the iron scale in the production process of many double-phase steels; however, considering the problems of segregation and poor workability caused by a high P content, the optimal range of P in the present invention is 0.012-0.025%, and Si-based scale is improved in cooperation with optimization of rolling process (ultra-high pressure descaling, high tapping temperature, etc.).
S is a component which becomes a starting point of cracks and deteriorates workability by forming sulfide inclusions such as MnS, and therefore, the content of S is preferably as small as 0.002%.
Cr: elements that stabilize austenite; cr can also remarkably improve the hardenability of steel, increase the supercooling capability of austenite, refine the structure, strongly delay pearlite transformation and bainite transformation, promote the diffusion of carbon to austenite, reduce the yield strength of ferrite and be more beneficial to obtaining the low-yield-strength dual-phase steel. In the invention, Cr is set to be 0.5-0.7%.
Als promotes martensite to be in a fibrous form, Al can also form AlN to be precipitated, and the function of refining grains is achieved to a certain extent. The range of Als in the invention is 0.02-0.06%.
N: n is mainly present in the form of harmful elements in the steel, the problem of aging strain of N is that the formability is rapidly reduced along with the increase of the content of N, and the range of N is less than or equal to 0.006 percent in the invention.
2) Design of the process
According to the invention, the edge of the continuous casting billet is subjected to corner cutting treatment, so that the linear defect of the hot-rolled edge rolling part caused by large temperature drop of the edge during rolling can be effectively eliminated; then, by controlling the heating temperature and conditions of the casting blank, tiger skin stripes on the surface are effectively reduced; then, in the rough rolling process, the vertical rolls adopt a baffle water-stop device to prevent water from contacting the edge of the strip steel, further reduce the temperature drop of the edge of the strip steel and prevent the edge of the strip steel from generating linear defects; removing scale on the surface by adopting a descaling pressure of more than 350Bar before finish rolling; meanwhile, by optimizing the steps and conditions of the rough rolling and finish rolling processes, adopting ultra-fast cooling conditions and optimizing drying conditions, the surface accumulated water is evaporated, and the surface corrosion pits caused by the accumulated water on the surface of the strip steel are effectively prevented. At present, residual water on the surface of the steel plate is serious in the production process, so that residual water stains and rust stains on the surface of the steel plate influence the quality of the plate surface. The production speed can only be reduced in order to eliminate water marks in the production process. At present, the speed of the plate passing is only 15 m/min. In order to solve the problems existing at present, a leveling water blowing device is additionally arranged. The method is mainly used for dewatering and drying the surfaces of steel plates in a production line, does not damage the surfaces of the plates, and does not have negative influence on the quality of strip steel. The production efficiency and the quality are improved.
Compared with the prior art, the invention has the beneficial effects that:
1) the product obtained by the invention has thin specification and uniform longitudinal performance of the steel plate; valuable elements are not required to be added, so that the cost of raw materials can be effectively reduced; the obtained finished product has good surface quality, does not have tiger skin lines, spot iron sheets and edge hairline defects, and has superior performance and surface quality;
2) by carrying out corner cutting treatment on the edge of a continuous casting billet, optimizing rolling, cooling and drying conditions and controlling the temperature and air cooling time after primary cooling, the yield strength and the tensile strength of the continuous casting billet are accurately controlled, wherein Rp0.2300-375 MPa, Rm is 590-650 MPa, the yield ratio is 0.56-0.60, and the total elongation after fracture is 24-30%.
Drawings
FIG. 1 is a schematic view of a process flow of the high surface quality hot rolled dual phase steel according to the present invention;
FIG. 2 is a schematic view of a chamfer of a continuous casting slab according to example 1 of the present invention;
FIG. 3 is a diagram of a water cutting device arranged on the vertical roll in the rough rolling process of the present invention;
fig. 4 is a schematic structural diagram of a drying device adopted in the present invention, wherein (a) is a shape of an air knife, (b) is a schematic structural diagram of an air knife protection frame (air knife drying device), and (c) is a schematic mounting position diagram of the air knife protection frame (air knife drying device).
Detailed Description
In order to better understand the present invention, the following embodiments are further illustrated, but the present invention is not limited to the following embodiments.
Example 1
A hot-rolled dual-phase steel with high surface quality has a process flow diagram as shown in figure 1; the preparation method comprises the following steps:
1) and (3) post-heating the edge chamfer (the chamfer angle is shown in a schematic diagram in figure 2, and the chamfer angle is in a direction of 45 degrees along the surface of the continuous casting slab) of the continuous casting slab with the thickness of 230 mm: controlling the heating temperature to 1300 ℃, soaking time to 150min, tapping temperature to 1292 ℃, and the components in the continuous casting billet in percentage by weight: 0.06% of C, 0.08% of Si, 1.30% of Mn, 0.54% of Cr, 0.015% of P, 0.0015% of S, 0.045% of Als, 0.003% of N and the balance of Fe and inevitable impurities;
2) rolling the continuous casting billet: during rough rolling, the vertical roll adopts a baffle water-stop device to prevent water from contacting the edge of the strip steel (a real object figure is shown in figure 3); removing surface iron scale by using a descaling pressure 380Bar before finish rolling; controlling the discharging temperature of rough rolling to be 1110 ℃, the finish rolling biting temperature to be 971 ℃, the finish rolling temperature to be 820 ℃ and the rolling speed to be 5.8 m/s;
3) after hot rolling, cooling control is carried out, firstly, ultra-fast cooling is carried out until the temperature is reduced to 130 ℃, and the cooling speed is 120 ℃/S; then air cooling for 8 s; then cooling to 150 ℃ by laminar flow at a cooling speed of 85 ℃/s;
4) coiling at the coiling temperature of 110 ℃; leveling (leveling speed is 30m/min) by a leveling machine within 24 hours after coiling, wherein a drying device (the specific structure is shown in figure 4) is used for removing residual moisture on the surface of the steel plate in the leveling process to prevent water accumulation between steel coil layers, the adopted drying temperature is 150 ℃, the wind pressure is 27Kpa, and the flow is 1050m 3 /h。
The steel plate obtained in the embodiment comprises the following chemical components in percentage by mass: 0.05% of C, 0.1% of Si, 1.21% of Mn, 0.5% of Cr, 0.0015% of S, 0.045% of Als, 0.003% of N, 0.019% of P and the balance of Fe and inevitable impurities; the thickness is 3.56 mm; the metallographic structure comprises a soft phase ferrite and a hard phase martensite, wherein the ferrite accounts for 85% by volume, and the martensite accounts for 15%; the yield strength Rp0.2 is 335MPa, the tensile strength Rm is 612MPa, the yield ratio is 0.547, and the total elongation after fracture is 26%; the surface has no tiger skin lines, short strip iron sheet, black lines on the edge and hairline defects on the edge.
Example 2
A preparation method of high-surface-quality hot-rolled dual-phase steel comprises the following steps:
1) after-heating the edge of a 230mm thick slab (same as example 1): controlling the heating temperature of 1300 ℃, soaking time of 150min and tapping temperature of 1280 ℃, wherein the continuous casting billet comprises the following components in percentage by weight: 0.06% of C, 0.07% of Si, 1.25% of Mn, 0.54% of Cr, 0.018% of P, 0.0018% of S, 0.044% of Als, 0.0028% of N, and the balance of Fe and inevitable impurities;
2) rolling the continuous casting billet: during rough rolling, the vertical roll adopts a baffle water-stop device to prevent water from contacting the edge of the strip steel; removing surface iron scale by using a descaling pressure 380Bar before finish rolling; controlling the rough rolling temperature to be 1100 ℃, the finish rolling bite temperature to be 973 ℃, the finish rolling temperature to be 800 ℃ and the rolling speed to be 4.4 m/s;
3) and (3) cooling control is carried out after hot rolling, firstly, ultra-fast cooling is carried out, the temperature is reduced to 130 ℃, the cooling speed is 120 ℃/s, then, air cooling is carried out for 11s, and laminar cooling is carried out to 150 ℃, and the cooling speed is 85 ℃/s.
4) Finally, coiling at the coiling temperature of 110 ℃; leveling by using a leveling machine within 24 hours after coiling (the leveling speed is 35m/min), wherein a drying device is used for removing residual moisture on the surface of a steel plate in the leveling process to prevent water accumulation between steel coil layers, the drying temperature is 150 ℃, the wind pressure is 27Kpa, and the flow is 1050m 3 /h。
The steel plate prepared in the embodiment comprises the following chemical components in percentage by mass: 0.05% of C, 0.1% of Si, 1.23% of Mn, 0.5% of Cr, 0.0018% of S, 0.044% of Als, 0.0028% of N, 0.0182% of P, and the balance of Fe and inevitable impurities; the thickness is 4.2 mm; the metallographic structure comprises soft-phase ferrite and hard-phase martensite, the volume fraction of the ferrite is 87%, and the martensite is 13%; the yield strength Rp0.2 of the material is 315MPa, the tensile strength Rm is 602MPa, the yield ratio is 0.554, and the total elongation after fracture is 26%; the surface has no defects of tiger skin lines, short strip iron sheets, edge black lines, edge hairlines and the like.
Example 3
A preparation method of high-surface-quality hot-rolled dual-phase steel comprises the following steps:
1) after-heating the edge of a 230mm thick slab (same as example 1): controlling the heating temperature of 1300 ℃, soaking time of 150min and tapping temperature of 1280 ℃, wherein the continuous casting billet comprises the following components in percentage by weight: 0.0625% of C, 0.06% of Si, 1.37% of Mn, 0.55% of Cr, 0.0178% of P, 0.001% of S, 0.04% of Als, 0.0038% of N and the balance of Fe and inevitable impurities;
2) rolling the continuous casting billet: during rough rolling, the vertical roll adopts a baffle water-stop device to prevent water from contacting the edge of the strip steel; removing surface iron scale by using a descaling pressure 380Bar before finish rolling; controlling the rough rolling temperature to 1110 ℃, the finish rolling bite temperature to 980 ℃, the finish rolling temperature to 810 ℃ and the rolling speed to 3.4 m/s;
3) performing cooling control after hot rolling, firstly performing ultra-fast cooling, cooling to 130 ℃, cooling at a speed of 120 ℃/s, then performing air cooling for 8s, and performing laminar cooling to 150 ℃, cooling at a speed of 85 ℃/s;
4) finally, coiling at the coiling temperature of 110 ℃; leveling (leveling speed is 30m/min) by a leveling machine within 24 hours after coiling, wherein a drying device is used for removing residual moisture on the surface of the steel plate in the leveling process to prevent water accumulation between steel coil layers, the adopted drying temperature is 150 ℃, the wind pressure is 27Kpa, and the flow is 1050m 3 /h。
The steel plate prepared in the embodiment comprises the following chemical components in percentage by mass: 0.058% of C, 0.05% of Si, 1.230% of Mn, 0.5% of Cr0.0018% of S, 0.044% of Als, 0.0028% of N, 0.018% of P and the balance of Fe and inevitable impurities; the thickness is 5.0 mm; the metallographic structure comprises soft-phase ferrite and hard-phase martensite, the volume fraction of the ferrite is 87%, the martensite is 13%, the yield strength Rp0.2 is 369MPa, the tensile strength Rm is 618MPa, the yield ratio is 0.597, and the total elongation after fracture is 26.4%; the surface has no defects of tiger skin lines, short strip iron sheets, edge black lines, edge hairlines and the like.
Example 4
A preparation method of high-surface-quality hot-rolled dual-phase steel comprises the following steps:
1) after-heating the edge of a 230mm thick slab (same as example 1): controlling the heating temperature of 1300 ℃, soaking time of 150min and tapping temperature of 1280 ℃, wherein the continuous casting billet comprises the following components in percentage by weight: 0.061% of C, 0.09% of Si, 1.30% of Mn, 0.548% of Cr, 0.0164% of P, 0.00102% of S, 0.0499% of Als, 0.00357% of N, and the balance of Fe and inevitable impurities;
2) rolling the continuous casting billet: during rough rolling, the vertical roll adopts a baffle water-stop device to prevent water from contacting the edge of the strip steel; removing surface iron scale by using a descaling pressure 380Bar before finish rolling; controlling the rough rolling temperature to be 1110 ℃, the finish rolling bite temperature to be 982 ℃, the finish rolling temperature to be 830 ℃ and the rolling speed to be 5.9 m/s;
3) performing cooling control after hot rolling, firstly performing ultra-fast cooling, cooling to 130 ℃, cooling at a speed of 120 ℃/s, then performing air cooling for 8s, and performing laminar cooling to 150 ℃, cooling at a speed of 85 ℃/s;
4) finally, coiling at the coiling temperature of 110 ℃; leveling (leveling speed 38m/min) with a leveling machine within 24 hours after coiling, wherein a drying device (see figure 4) is used for removing residual moisture on the surface of the steel plate in the leveling process to prevent water accumulation between steel coil layers, the adopted drying temperature is 175 ℃, the wind pressure is 27Kpa, and the flow is 1050m 3 /h。
The steel plate prepared in the embodiment comprises the following chemical components in percentage by mass: 0.061% of C, 0.09% of Si, 1.30% of Mn, 0.548% of Cr0.0174% of P, 0.00102% of S, 0.0499% of Als, 0.00357% of N, and the balance of Fe and inevitable impurities; the thickness is 3.56 mm; the metallographic structure comprises a soft-phase ferrite and a hard-phase martensite, wherein the volume fraction of the ferrite is 86%, the martensite is 14%, the yield strength Rp0.2 is 364MPa, the tensile strength Rm is 624MPa, the yield ratio is 0.583, and the total elongation after fracture is 25.9%; the surface has no defects of tiger skin lines, short strip iron sheets, edge black lines, edge hairlines and the like.
Comparative example 1
A preparation method of high-surface-quality hot-rolled dual-phase steel comprises the following steps:
1) post-heating a continuous casting billet with the thickness of 230 mm: controlling the heating temperature to be 1300 ℃, soaking time to be 153min, discharging temperature to be 1290 ℃, and the continuous casting billet comprises the following components in percentage by weight: 0.072% of C, 0.07% of Si, 1.25% of Mn, 0.55% of Cr, 0.0144% of P, 0.00122% of S, 0.0419% of Als, 0.00327% of N, and the balance of Fe and inevitable impurities;
2) rolling the continuous casting billet, controlling the rough rolling temperature to be 1110 ℃, enabling the vertical roll not to adopt a water retaining device, enabling the pressure of finish rolling and descaling to be more than 350Bar, enabling the finish rolling bite temperature to be 1080 ℃, enabling the finish rolling temperature to be 830 ℃, and enabling the rolling speed to be 5.9 m/s;
3) and (3) cooling control is carried out after hot rolling, firstly, ultra-fast cooling is carried out, the temperature drop is 130 ℃, the cooling speed is 120 ℃/S, then, air cooling is carried out for 8S, and laminar cooling is carried out to 150 ℃, and the cooling speed is 85 ℃/S.
Finally, coiling is carried out, wherein the coiling temperature is 110 ℃.
And the upper leveling machine uses a drying device to remove residual moisture on the surface of the steel plate within 24 hours after coiling, so that water accumulation between steel coil layers is prevented.
The steel plate prepared in the embodiment comprises the following chemical components in percentage by mass: 0.072% of C, 0.07% of Si, 1.25% of Mn, 0.55% of Cr0.55%, 0.0144% of P, 0.00122% of S, 0.0419% of Als, 0.00327% of N, and the balance of Fe and inevitable impurities; and unavoidable impurities; the thickness is 3.56 mm; the structure is soft phase ferrite and hard phase martensite, the volume fraction of the ferrite is 78%, the martensite is 22%, the yield strength Rp0.2 is 414MPa, the tensile strength Rm is 674MPa, the yield ratio is 0.614, the total elongation after fracture is 25.2%, and the tensile strength and the yield ratio are both higher because the carbon content exceeds the upper limit; the surfaces of the composite material have no tiger skin lines and short strip iron sheets, but have the defects of edge black lines, edge hairlines and the like.
Comparative example 2
A preparation method of high-surface-quality hot-rolled dual-phase steel comprises the following steps:
1) heating the edge of a 230 mm-thick continuous casting blank after corner cutting: controlling the heating temperature to 1300 ℃, soaking time to 150min, tapping temperature to 1280 ℃, wherein the continuous casting billet comprises the following components in percentage by weight: 0.064% of C, 0.12% of Si, 1.38% of Mn, 0.57% of Cr, 0.0084% of P, 0.00152% of S, 0.0479% of Als, 0.00227% of N, and the balance of Fe and inevitable impurities;
2) rolling the continuous casting billet, controlling the rough rolling temperature to be 1113 ℃, the finish rolling descaling pressure to be more than 350Bar, the finish rolling bite temperature to be 980 ℃, the finish rolling temperature to be 810 ℃ and the rolling speed to be 5.9 m/s;
3) and (3) performing cooling control after hot rolling, firstly performing ultra-fast cooling with the temperature reduced to 130 ℃ and the cooling speed of 120 ℃/S, then performing air cooling for 8S, and performing laminar cooling to 150 ℃ and the cooling speed of 85 ℃/S.
Finally, coiling is carried out, wherein the coiling temperature is 110 ℃.
And the upper leveling machine uses a drying device to remove residual moisture on the surface of the steel plate within 24 hours after coiling, so that water accumulation between steel coil layers is prevented.
The steel plate prepared by the comparative example comprises the following chemical components in percentage by mass: 0.064% of C, 0.12% of Si, 1.38% of Mn, 0.57% of Cr0.57%, 0.0084% of P, 0.00152% of S, 0.0479% of Als, 0.00227% of N, and the balance of Fe and inevitable impurities; the thickness is 3.5 mm; the structure is soft phase ferrite and hard phase martensite, the volume fraction of the ferrite is 78 percent, the martensite is 22 percent, the yield strength Rp0.2 is 342MPa, the tensile strength Rm is 614MPa, the yield ratio is 0.557, and the total elongation after fracture is 26.4 percent; because the silicon content exceeds the standard upper limit and the phosphorus content exceeds the lower limit, tiger skin lines exist on the edge part of the surface, but the defects of short strip-shaped iron sheet, edge black lines, edge hairlines and the like do not exist.
Comparative example 3
A preparation method of high-surface-quality hot-rolled dual-phase steel comprises the following steps:
1) heating a continuous casting billet with the thickness of 230 mm: controlling the heating temperature of 1300 ℃, soaking time of 150min and tapping temperature of 1280 ℃, wherein the continuous casting billet comprises the following components in percentage by weight: 0.064% of C, 0.08% of Si, 1.31% of Mn, 0.52% of Cr, 0.018% of P, 0.00132% of S, 0.0479% of Als, 0.00227% of N, and the balance of Fe and inevitable impurities;
2) rolling the continuous casting billet, controlling the discharging temperature of rough rolling to be 1110 ℃, not using a rough rolling water retaining device, controlling the finish rolling descaling pressure to be more than 350Bar (380Bar), controlling the finish rolling bite temperature to be 980 ℃, controlling the finish rolling temperature to be 813 ℃, and controlling the rolling speed to be 5.7 m/s;
3) and (3) performing cooling control after hot rolling, firstly performing ultra-fast cooling, cooling to 130 ℃, cooling at the speed of 120 ℃/s, then performing air cooling for 8s, and performing laminar cooling to 150 ℃, and cooling at the speed of 87 ℃/s.
Finally, coiling is carried out, wherein the coiling temperature is 110 ℃.
And the upper leveling machine uses a drying device to remove residual moisture on the surface of the steel plate within 24 hours after coiling, so that water accumulation between steel coil layers is prevented.
The steel plate prepared by the comparative example comprises the following chemical components in percentage by mass: 0.062% of C, 0.08% of Si, 1.38% of Mn, 0.57% of Cr0.0184% of P, 0.00152% of S, 0.0479% of Als, 0.00227% of N, and the balance of Fe and inevitable impurities; the thickness is 3.5 mm; the structure is soft phase ferrite and hard phase martensite, the volume fraction of the ferrite is 79 percent, the martensite is 21 percent, the yield strength Rp0.2 is 352MPa, the tensile strength Rm is 609MPa, the yield ratio is 0.578, and the total elongation after fracture is 26.8 percent; the slab has no corner cut and no rough rolling water retaining device, and the edge has the defects of black lines, edge hairlines and the like.
The above embodiments are merely illustrative of the technical ideas and features of the present invention, and the purpose thereof is to enable those skilled in the art to understand the contents of the present invention and implement the present invention, and not to limit the protection scope of the present invention. All equivalent changes and modifications made according to the spirit of the present invention should be covered in the protection scope of the present invention.
Claims (10)
1. The high-surface-quality hot-rolled dual-phase steel is characterized by comprising the following chemical components in percentage by mass: 0.05-0.068% of C, less than or equal to 0.12% of Si, 1.2-1.5% of Mn, 0.02-0.06% of Als, 0.5-0.7% of Cr, 0.015-0.025% of P, 0-0.002% of S, 0-0.006% of N, and the balance of Fe.
2. The high surface quality hot rolled dual phase steel as claimed in claim 1, wherein the chemical components and their mass percentages are as follows: 0.055-0.06% of C, less than or equal to 0.1% of Si, 1.2-1.4% of Mn, 0.02-0.06% of Als, 0.5-0.6% of Cr, 0.018-0.025% of P, 0-0.002% of S, 0-0.006% of N and the balance of Fe.
3. The high surface quality hot rolled dual phase steel according to claim 1, wherein the structure of the dual phase steel comprises soft phase ferrite and hard phase martensite; wherein the ferrite accounts for 75-90% of the volume fraction, and the martensite accounts for 10-25% of the volume fraction.
4. The method for preparing high surface quality hot rolled dual phase steel according to any one of claims 1 to 3, comprising the steps of performing corner cutting treatment on the edge of a continuous casting slab, heating, rolling, performing controlled cooling after rolling, coiling and leveling; in the rolling step, a baffle water-stop device is adopted by a vertical roller during rough rolling to prevent water from contacting the edge part of the strip steel, and descaling pressure is more than 350Bar before finish rolling; after rolling, controlled cooling adopts an ultra-fast cooling process.
5. The preparation method according to claim 4, wherein the heating temperature in the heating step is controlled to be 1250-1320 ℃, the heating time is 150-220 min, and the tapping temperature is 1280-1320 ℃.
6. The production method according to claim 4, wherein in the rolling step, the rough rolling tapping temperature is controlled to be 1080 to 1110 ℃, the finish rolling biting temperature is 970 to 982 ℃, the finish rolling temperature is 790 to 830 ℃, and the rolling speed is 3.1 to 6 m/s.
7. The preparation method according to claim 4, wherein in the ultra-fast cooling process, the temperature drop is controlled to be 100-130 ℃, the cooling speed is 100-140 ℃/s, and then air cooling is carried out for 7-12 s; and cooling to below 250 ℃ by laminar flow at a cooling speed of 85-115 ℃/s.
8. The production method according to claim 4, wherein the coiling temperature is 50 to 150 ℃.
9. The method according to claim 4, wherein the leveling is performed within 24 hours after the coiling, and the leveling speed is 20 to 50 m/min.
10. The method according to claim 4, wherein the drying is performed during the leveling process, the drying temperature is 150 to 250 ℃, the wind pressure is 20 to 30Kpa, and the flow rate is 1000 to 1100m 3 /h。
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