CN114378114A - Method for producing medium plate with excellent quality by utilizing defective continuous casting slab - Google Patents
Method for producing medium plate with excellent quality by utilizing defective continuous casting slab Download PDFInfo
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- 238000009749 continuous casting Methods 0.000 title claims abstract description 36
- 238000004519 manufacturing process Methods 0.000 title claims abstract description 18
- 230000002950 deficient Effects 0.000 title claims abstract description 11
- 238000005096 rolling process Methods 0.000 claims abstract description 122
- 238000001816 cooling Methods 0.000 claims abstract description 52
- 230000009467 reduction Effects 0.000 claims abstract description 43
- 238000010438 heat treatment Methods 0.000 claims abstract description 42
- 230000007547 defect Effects 0.000 claims abstract description 39
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims abstract description 37
- 238000000034 method Methods 0.000 claims abstract description 30
- 230000008569 process Effects 0.000 claims abstract description 9
- 238000007689 inspection Methods 0.000 claims abstract description 5
- 229910000831 Steel Inorganic materials 0.000 claims description 31
- 239000010959 steel Substances 0.000 claims description 31
- 239000012535 impurity Substances 0.000 claims description 6
- 229910052698 phosphorus Inorganic materials 0.000 claims description 6
- 239000007921 spray Substances 0.000 claims description 6
- 238000005507 spraying Methods 0.000 claims description 6
- 229910052717 sulfur Inorganic materials 0.000 claims description 6
- 239000000126 substance Substances 0.000 claims description 3
- 238000002791 soaking Methods 0.000 abstract description 6
- 238000012797 qualification Methods 0.000 abstract description 4
- 238000010079 rubber tapping Methods 0.000 abstract description 4
- 238000005266 casting Methods 0.000 description 27
- 230000000694 effects Effects 0.000 description 14
- 230000035515 penetration Effects 0.000 description 8
- 239000000047 product Substances 0.000 description 8
- 238000001514 detection method Methods 0.000 description 7
- 230000002349 favourable effect Effects 0.000 description 7
- UQSXHKLRYXJYBZ-UHFFFAOYSA-N Iron oxide Chemical compound [Fe]=O UQSXHKLRYXJYBZ-UHFFFAOYSA-N 0.000 description 6
- XEEYBQQBJWHFJM-UHFFFAOYSA-N iron Substances [Fe] XEEYBQQBJWHFJM-UHFFFAOYSA-N 0.000 description 5
- 239000002344 surface layer Substances 0.000 description 5
- 230000009286 beneficial effect Effects 0.000 description 4
- 239000012466 permeate Substances 0.000 description 4
- UFHFLCQGNIYNRP-UHFFFAOYSA-N Hydrogen Chemical compound [H][H] UFHFLCQGNIYNRP-UHFFFAOYSA-N 0.000 description 3
- 238000003723 Smelting Methods 0.000 description 3
- 229910052799 carbon Inorganic materials 0.000 description 3
- 239000002131 composite material Substances 0.000 description 3
- 229910052739 hydrogen Inorganic materials 0.000 description 3
- 239000001257 hydrogen Substances 0.000 description 3
- 239000000463 material Substances 0.000 description 3
- 229910001562 pearlite Inorganic materials 0.000 description 3
- 238000005204 segregation Methods 0.000 description 3
- 238000010583 slow cooling Methods 0.000 description 3
- 230000035882 stress Effects 0.000 description 3
- 238000003466 welding Methods 0.000 description 3
- 229910000859 α-Fe Inorganic materials 0.000 description 3
- 238000005452 bending Methods 0.000 description 2
- 230000008901 benefit Effects 0.000 description 2
- 238000009792 diffusion process Methods 0.000 description 2
- 238000011160 research Methods 0.000 description 2
- 230000008646 thermal stress Effects 0.000 description 2
- 239000002918 waste heat Substances 0.000 description 2
- OAICVXFJPJFONN-UHFFFAOYSA-N Phosphorus Chemical compound [P] OAICVXFJPJFONN-UHFFFAOYSA-N 0.000 description 1
- NINIDFKCEFEMDL-UHFFFAOYSA-N Sulfur Chemical compound [S] NINIDFKCEFEMDL-UHFFFAOYSA-N 0.000 description 1
- 230000015572 biosynthetic process Effects 0.000 description 1
- 230000015556 catabolic process Effects 0.000 description 1
- 238000006731 degradation reaction Methods 0.000 description 1
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- 238000012986 modification Methods 0.000 description 1
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- 230000008092 positive effect Effects 0.000 description 1
- 230000003449 preventive effect Effects 0.000 description 1
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- 238000007711 solidification Methods 0.000 description 1
- 230000008023 solidification Effects 0.000 description 1
- 238000006467 substitution reaction Methods 0.000 description 1
- 239000011593 sulfur Substances 0.000 description 1
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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
- B21B1/24—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 in a continuous or semi-continuous process
- B21B1/26—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 in a continuous or semi-continuous process by hot-rolling, e.g. Steckel hot mill
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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
- B21B45/04—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 de-scaling, e.g. by brushing
- B21B45/08—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 de-scaling, e.g. by brushing hydraulically
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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
- C22C38/002—Ferrous alloys, e.g. steel alloys containing In, Mg, or other elements not provided for in one single group C22C38/001 - C22C38/60
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
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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
- C22C38/04—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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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/14—Ferrous alloys, e.g. steel alloys containing titanium or zirconium
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Abstract
The invention belongs to the technical field of medium plate production, and particularly provides a method for producing a medium plate with excellent quality by using a defective continuous casting billet, which comprises the following steps: heating → high-pressure water descaling → rough rolling → finish rolling → ACC laminar cooling → hot straightening → stacking cooling → inspection and warehousing; the slab is preheated, slowly heated in multiple stages, the soaking temperature and the tapping temperature are high, high-pressure water descaling control is matched, rough rolling is carried out at a low rolling speed, descaling is carried out between all stages, a process slab with internal heat, external cold, internal soft and external hard is formed in the rolling process, and then a medium slab with the thickness of 250mm and the defect slab with the maximum thickness of 60mm can be rolled out by virtue of reasonable rolling reduction and rolling control and cooling processes, the mechanical qualification rate is more than or equal to 99%, and the qualification rate under the GB/T2970I-level standard is 100%.
Description
Technical Field
The invention belongs to the technical field of medium plate production, and particularly provides a method for producing a medium plate with excellent quality by using a defective continuous casting blank, particularly a method for producing a medium plate with excellent quality, high performance qualified rate of more than or equal to 99%, high flaw detection qualified rate of 100% and thickness specification of less than or equal to 60mm by using a continuous casting blank with serious internal cracks such as intermediate cracks, triangular zone cracks and the like.
Background
In the large-scale mass production activity, the condition that serious defects exist in the continuous casting billet sometimes happens, and even the condition that serious slab crack defects appear in a large scale is not lacked.
The severe slab crack means that an internal median crack or a triangular region crack or the like reaches 2.0 grade or more, or a severe central crack is generated. As solidification proceeds, inclusions or harmful elements are aggregated during the formation of cracks, and the crack front is also segregated by elements such as C, Mn. The problems that the mechanical properties, especially the plasticity indexes (cold bending, elongation after fracture and the like) of the rolled steel plate are unqualified, the tensile fracture is layered, and the internal tearing occurs in the processing and using process of a user are caused, so that the use requirements cannot be met.
According to the conventional production process method, generally, the method directly aims at the generation reason of casting blank cracks, measures such as controlling the content of phosphorus and sulfur in molten steel, pouring with low superheat degree, optimizing the process system of a continuous casting secondary cooling area, improving the equipment precision and the maintenance frequency and the like are taken, so that good casting blank quality is obtained, and the internal quality of a subsequent steel plate is ensured. However, the above measures still have uncertainty in the mass production process and do not work well in the face of sudden situations or difficulties in organizing production. The measures are all preventive measures, casting blanks with serious defects can not be recovered, the plasticity index of steel plates produced by the casting blanks with the defects is poor, and the product degradation rate is high; for the problem, the research is pointed at present.
For the produced continuous casting plate blank with serious defects, in the actual production, how to obtain the product with qualified quality by the subsequent process has important practical significance.
Disclosure of Invention
Aiming at the technical problems in the prior art, the invention provides a method for producing a medium plate with excellent quality by utilizing a defective continuous casting billet.
The technical scheme adopted by the invention for solving the technical problems in the prior art is as follows:
the invention aims to protect the method for producing the medium plate with excellent quality by utilizing the defect continuous casting billet, wherein the defect continuous casting billet comprises the following chemical components in percentage by mass: 0.15% -0.20%, Si: 0.25 to 0.31%, Mn: 1.45-1.50%, P: less than or equal to 0.020%, S: less than or equal to 0.020 percent, less than or equal to 0.030 percent of Nb, less than or equal to 0.030 percent of Ti, less than or equal to 0.050 percent of Alt, and the balance of Fe and inevitable impurities; intermediate cracks of the order of 2.0 and above and/or triangular cracks of the order of 0.5 and above, it being understood that the defect levels described herein are merely illustrative of the serious slab defects to which the present invention may be applied and are not intended to be limiting.
The method comprises the following steps: heating → high-pressure water descaling → rough rolling → finish rolling → ACC laminar cooling → hot straightening → stacking cooling → inspection and warehousing.
S1, firstly, cold blank preheating is carried out on the defect continuous casting blank, the cold blank of the defect continuous casting blank and the lower line hot plate blank are alternately stacked and stacked for 30-45 hours before rolling, the average surface temperature of the lower line hot plate blank is ensured to be not less than 700 ℃, and the surface temperature of the defect continuous casting blank after preheating reaches 400-500 ℃; the cold blank preheating of the defective casting blank is carried out by utilizing the waste heat of the hot blank, so that the internal crack expansion or the casting blank fracture caused by the influence of thermal stress in the heating process of the casting blank is prevented;
s2, in the heating stage, adopting a four-section heating method in a heating furnace, wherein the preheating section is less than or equal to 800 ℃, the first heating section is 850-; the four-stage heating (preheating stage, first heating stage, second heating stage, soaking stage) can keep a gentle heating rate and inhibit the propagation of internal cracks. The high soaking temperature plays an important role in internal cracks of the welding, the reasons are that atom diffusion is facilitated, the strength of the steel billet is reduced, the surface layer cooling speed is high, the casting blank is beneficial to forming internal heat external cooling and internal soft and external hard, the rolling force permeates to the heart, and the core cracks of the continuous casting blank are convenient to eliminate;
s3, in the high-pressure water descaling stage, the pressure of descaling spraying water is required to be more than or equal to 22MPa, and the roller speed is less than or equal to 0.5 m/S; compared with the conventional dephosphorization, the key difference of the step is that the large descaling pressure and the slow roller table speed are adopted, and the method has the main effects that firstly, thick and much iron oxide scales generated by high-temperature heating in the step two can be completely removed, and secondly, a certain steel plate surface layer cooling effect can be realized in the step, so that the method is beneficial to forming casting blanks with internal heat, external cold, soft and hard inside and external hard outside, and is convenient for the rolling force to permeate into cracks of the heart;
s4, in the rough rolling stage, ensuring that all rolling passes adopt an inter-pass descaling process, the descaling water spray pressure is more than or equal to 20MPa, the biting speed in the rough rolling stage is not more than 1.2m/S, and the maximum rolling speed is 1.8 m/S; high-pressure water descaling is adopted among all passes and is matched with a slow rolling speed, the effect is mainly that the slow rolling speed is favorable for the penetration of rolling force to a centripetal part, and the effect of high-pressure water descaling is matched, so that the rolling surface temperature can be further effectively reduced, the blank is favorable for forming 'internal heat, external cold, internal soft and external hard' by passing, and the penetration of the rolling force to the centripetal part is further promoted;
in the rough rolling stage, at least 1 longitudinal rolling pass reduction is more than or equal to 30mm, 1 longitudinal rolling pass reduction is more than or equal to 25mm, and the target reduction rate of the final pass of rough rolling is more than or equal to 20%; the high total pass reduction rate and the single pass reduction amount control ensure that the deformation and penetration of the core part can be fully ensured in rolling;
s5, the start temperature range of finish rolling is 850-900 ℃, and the end temperature range is 770-830 ℃; the total pass reduction rate of the finish rolling stage is required to be more than or equal to 45 percent, and the final pass target reduction rate of the finish rolling is more than or equal to 10 percent; the total pass reduction rate and the final pass reduction rate in the finish rolling stage are required to be ensured, and the aim is to improve the internal microstructure and improve the toughness of the material;
s6, in the cooling stage, the cooling speed is controlled at 6-15 ℃/S, and the final cooling temperature is controlled at 620-630 ℃; after straightening, the steel plate is stacked and slowly cooled at the highest speed, the stacking and cooling temperature is 400-500 ℃, and the stacking and cooling time is 25-36 h. This step has the effect of improving the strength by laminar cooling, followed by the release of hydrogen and stress by slow cooling, improving the internal quality of the steel sheet.
Further, the thickness of the defect continuous casting blank is 250 mm; the thickness of the finished product is 50-60 mm.
Furthermore, the mechanical properties of the finished product are as follows: the upper yield strength ReH is more than or equal to 370 MPa; the tensile strength Rm is more than or equal to 510 MPa; the reduction of area A is 25%; the charpy V-shaped longitudinal impact at the temperature of minus 20 ℃ is more than or equal to 81J; the Charpy V-shaped longitudinal impact at 0 ℃ is more than or equal to 99J; the Charpy V-shaped longitudinal impact at 20 ℃ is more than or equal to 108J.
The invention has the advantages and positive effects that:
the invention adopts the processes of heating → high-pressure water descaling → rough rolling → finish rolling → ACC laminar cooling → hot straightening → stacking cold → inspection and warehousing to roll the continuous casting slab with serious defects into the medium plate with excellent quality, thereby solving the problems of low percent of pass of plasticity indexes such as elongation and cold bending after the fracture of the defect slab, delamination of the fracture, improper flaw detection and the like.
Specifically, the method comprises the following steps: 1) the four-section heating process is adopted in the heating stage, so that the slow heating rate can be kept, the expansion of internal cracks is inhibited, and meanwhile, the high soaking temperature plays an important role in welding the internal cracks of the continuous casting billet;
2) in the high-pressure water descaling stage, the large descaling pressure and the slow roller table speed are adopted, so that not only can thick and much iron oxide scales generated by high-temperature heating in the step two be removed completely, but also a certain steel plate surface layer cooling effect can be achieved in the stage, the casting blank is favorable for forming internal heat, external cold, soft and hard, and the rolling force is convenient for permeating cracks on the radial part;
3) in the rough rolling stage, high-pressure water descaling is adopted between all passes and is matched with a slow rolling speed, the effect is mainly that the slow rolling speed is favorable for the penetration of rolling force to a centripetal part, and the effect of high-pressure water descaling is matched, so that the rolling surface temperature can be further effectively reduced, the blank is favorable for forming 'internal heat, external cold, internal soft and external hard' by passes, and the penetration of the rolling force to the centripetal part is further promoted;
4) in the finish rolling stage, the total pass reduction rate and the final pass reduction rate in the finish rolling stage are well controlled, and the purpose is to improve the internal microstructure and improve the toughness of the material;
5) and in the cooling stage, the strength is improved through laminar cooling, and then the hydrogen and the stress are released through slow cooling, so that the internal quality of the steel plate is improved.
The method has the significance that under the condition of conventional rolling capability, the internal cracks of the casting blank are welded together in the subsequent rolling process while the internal cracks of the casting blank are inhibited from being seriously deteriorated, so that the defect casting blank is effectively utilized. The qualification rate of the mechanical properties of the steel plate reaches 99%, the flaw detection meets the GB/T2970I standard, the qualification rate is 100%, the quality loss is reduced, and the economic benefit is improved.
Drawings
FIG. 1 is a low magnification of a cast slab before rolling in example 1;
FIG. 2 shows a metallographic structure (100X) at a thickness of 1/4 of the steel sheet obtained in example 1;
FIG. 3 is a low magnification of a cast slab before rolling in example 2;
FIG. 4 shows a metallographic structure (100X) at a thickness 1/4 of the steel sheet obtained in example 2;
FIG. 5 is a low magnification of a cast slab before rolling in example 3;
FIG. 6 shows a metallographic structure (100X) at a thickness of 1/4 of the steel sheet obtained in example 3;
Detailed Description
For a further understanding of the invention, its nature and utility, reference should be made to the following examples, which are set forth in the following detailed description, taken in conjunction with the accompanying drawings, in which:
a method for producing a medium plate with excellent quality by using a defective continuous casting slab comprises the following chemical components in percentage by mass: 0.15% -0.20%, Si: 0.25 to 0.31%, Mn: 1.45-1.50%, P: less than or equal to 0.020%, S: less than or equal to 0.020 percent, less than or equal to 0.030 percent of Nb, less than or equal to 0.030 percent of Ti, less than or equal to 0.050 percent of Alt, and the balance of Fe and inevitable impurities; with finished product thicknesses of 50-60mm and median cracks on the order of 2.0 and above, and/or triangular cracks on the order of 0.5 and above, it should be understood that the defect levels described herein are merely illustrative of the serious slab defects to which the present invention may be applied, and are not intended to limit the invention.
The method comprises the following steps: heating → high-pressure water descaling → rough rolling → finish rolling → ACC laminar cooling → hot straightening → stacking cooling → inspection and warehousing.
S1, firstly, cold blank preheating is carried out on the defect continuous casting blank, the cold blank of the defect continuous casting blank and the lower line hot plate blank are alternately stacked and stacked for 30-45 hours before rolling, the average surface temperature of the lower line hot plate blank is ensured to be not less than 700 ℃, and the surface temperature of the defect continuous casting blank after preheating reaches 400-500 ℃; the cold blank preheating of the defective casting blank is carried out by utilizing the waste heat of the hot blank, so that the internal crack expansion or the casting blank fracture caused by the influence of thermal stress in the heating process of the casting blank is prevented;
s2, in the heating stage, adopting a four-section heating method in a heating furnace, wherein the preheating section is less than or equal to 800 ℃, the first heating section is 850-; the four-stage heating (preheating stage, first heating stage, second heating stage, soaking stage) can keep a gentle heating rate and inhibit the propagation of internal cracks. The high soaking temperature plays an important role in internal cracks of the welding, the reasons are that atom diffusion is facilitated, the strength of the steel billet is reduced, the surface layer cooling speed is high, the casting blank is beneficial to forming internal heat external cooling and internal soft and external hard, the rolling force permeates to the heart, and the core cracks of the continuous casting blank are convenient to eliminate;
s3, in the high-pressure water descaling stage, the pressure of descaling spraying water is required to be more than or equal to 22MPa, and the roller speed is less than or equal to 0.5 m/S; compared with the conventional dephosphorization, the key difference of the step is that the large descaling pressure and the slow roller table speed are adopted, and the method has the main effects that firstly, thick and much iron oxide scales generated by high-temperature heating in the step two can be completely removed, and secondly, a certain steel plate surface layer cooling effect can be realized in the step, so that the method is beneficial to forming casting blanks with internal heat, external cold, soft and hard inside and external hard outside, and is convenient for the rolling force to permeate into cracks of the heart;
s4, in the rough rolling stage, ensuring that all rolling passes adopt an inter-pass descaling process, the descaling water spray pressure is more than or equal to 20MPa, the biting speed in the rough rolling stage is not more than 1.2m/S, and the maximum rolling speed is 1.8 m/S; high-pressure water descaling is adopted among all passes and is matched with a slow rolling speed, the effect is mainly that the slow rolling speed is favorable for the penetration of rolling force to a centripetal part, and the effect of high-pressure water descaling is matched, so that the rolling surface temperature can be further effectively reduced, the blank is favorable for forming 'internal heat, external cold, internal soft and external hard' by passing, and the penetration of the rolling force to the centripetal part is further promoted;
in the rough rolling stage, at least 1 longitudinal rolling pass reduction is more than or equal to 30mm, 1 longitudinal rolling pass reduction is more than or equal to 25mm, and the target reduction rate of the final pass of rough rolling is more than or equal to 20%; the high total pass reduction rate and the single pass reduction amount control ensure that the deformation and penetration of the core part can be fully ensured in rolling;
s5, the start temperature range of finish rolling is 850-900 ℃, and the end temperature range is 770-830 ℃; the total pass reduction rate of the finish rolling stage is required to be more than or equal to 45 percent, and the final pass target reduction rate of the finish rolling is more than or equal to 10 percent; the total pass reduction rate and the final pass reduction rate in the finish rolling stage are required to be ensured, and the aim is to improve the internal microstructure and improve the toughness of the material;
s6, in the cooling stage, the cooling speed is controlled at 6-15 ℃/S, and the final cooling temperature is controlled at 620-630 ℃; after straightening, the steel plate is stacked and slowly cooled at the highest speed, the stacking and cooling temperature is 400-500 ℃, and the stacking and cooling time is 25-36 h. This step has the effect of improving the strength by laminar cooling, followed by the release of hydrogen and stress by slow cooling, improving the internal quality of the steel sheet.
Example 1
The embodiment relates to a Q355B medium-thickness plate with the thickness of 60mm, and the smelting components are as follows according to mass percentage: 0.18% of C, 1.47% of Mn, 0.29% of Si, 0.018% of Alt, 0.017% of P, 0.016% of S, 0.002% of Nb and 0.005% of Ti; the balance of Fe and inevitable impurities. Casting blank thickness: 250mm, serious internal cracks exist, and the low-power rating results are that the center segregation B is 0.5, the center porosity is 0.5, the middle cracks are 3.0 grade, and the triangular region cracks are 0.5 grade. The main equipment is a conventional 3500mm medium and heavy plate mill, and the maximum rolling force is 70000 KN.
The subsequent rolling method of the casting blank with the serious internal crack defect comprises the following steps:
s1, firstly, cold blank preheating is carried out on the defect casting blank, the cold blank of the defect continuous casting blank and the off-line hot plate blank are alternately stacked and stacked for 30 hours before rolling, the average surface temperature of the off-line hot plate blank is 750 ℃, and the surface temperature of the defect continuous casting blank after preheating is guaranteed to reach 480 ℃;
s2, in the heating stage, a four-stage heating method is adopted in the heating furnace, wherein the temperature of the preheating section is 700-; the tapping temperature is 1220 ℃;
s3, in the high-pressure water descaling stage, the descaling water spray pressure is 22MPa, and the roller speed is 0.5 m/S;
s4, in the rough rolling stage, descaling all passes by adopting high-pressure water, wherein the descaling water spraying pressure is 21MPa, the biting speed in the rough rolling stage is 1.2m/S, and the maximum rolling speed is 1.6 m/S; in the rough rolling stage, the reduction of 1 longitudinal rolling pass is 32mm, the reduction of 1 longitudinal rolling pass is 28mm, and the target reduction rate of the final pass of rough rolling is 22%.
S5, the precision rolling starting temperature range is 885 ℃, and the finishing temperature range is 825 ℃; the total pass reduction rate of the finish rolling stage is 48 percent, and the final pass target reduction rate of the finish rolling is 11 percent;
s6, in the cooling stage, the water inlet temperature is 803 ℃, the final cooling temperature is controlled at 622 ℃, and the cooling speed is 8 ℃/S; and after straightening, the steel plates are off-line stacked and slowly cooled at the highest speed, the stacking cooling temperature is 485 ℃, and the stacking cooling time is 25 hours.
The mechanical properties of example 1 are shown in Table 1, and the composite material has excellent comprehensive mechanical properties, good strength and good toughness.
Table 1 table of mechanical properties data of the finished product in example 1
The metallographic structure (100 ×) at a thickness of 1/4 of the steel sheet obtained in example 1 is a typical ferrite + pearlite structure as shown in fig. 1. The flaw detection results of the steel plate in the embodiment 1 are shown in a table 4, and the steel plate meets the GB/T2970I grade requirement.
Example 2
The embodiment relates to a Q355C medium-thickness plate with the thickness of 50mm, and the smelting components are as follows according to mass percentage: 0.18% C, 1.49% Mn, 0.31% Si, 0.029% Alt, 0.009% P, 0.009% S, 0.003% Nb, 0.005% Ti; the balance of Fe and inevitable impurities; casting blank thickness: 250mm, serious internal cracks exist, and the low-power rating result is that the center segregation B is 0.5, the center porosity is 0.5, the middle cracks are 2.0 grade, and the triangular region cracks are 1.0 grade; the main equipment is a conventional 3500mm medium and heavy plate mill, and the maximum rolling force is 70000 KN.
The subsequent rolling method of the casting blank with the serious internal crack defect comprises the following steps:
s1, firstly, cold blank preheating is carried out on the defect casting blank, the cold blank of the defect continuous casting blank and the lower line hot plate blank are alternately stacked and stacked for 40 hours before rolling, the average surface temperature of the lower line hot plate blank is 710 ℃, and the surface temperature of the defect continuous casting blank after preheating is ensured to reach 420 ℃;
s2, in the heating stage, a four-stage heating method is adopted in the heating furnace, wherein the temperature of the preheating section is 700-. The tapping temperature is 1225 ℃;
s3, in the high-pressure water descaling stage, the descaling water spray pressure is 23MPa, and the roller speed is 0.3 m/S;
s4, in the rough rolling stage, all passes adopt high-pressure water to descale, the descaling water spraying pressure is 21MPa, the biting speed in the rough rolling stage is 1.2m/S, and the maximum rolling speed is 1.5 m/S. In the rough rolling stage, the reduction of 1 longitudinal rolling pass is 35mm, the reduction of 1 longitudinal rolling pass is 30mm, and the target reduction rate of the final pass of rough rolling is 22%;
s5, the precision rolling starting temperature range is 850 ℃, and the finishing temperature range is 775 ℃; the total pass reduction rate of the finish rolling stage is 53 percent, and the final pass target reduction rate of the finish rolling is 11 percent;
s6, in the cooling stage, the water inlet temperature is 760 ℃, the final cooling temperature is controlled at 630 ℃, and the cooling speed is 12 ℃/S; and after straightening, the steel plates are off-line stacked and slowly cooled at the highest speed, wherein the stacking cooling temperature is 450 ℃, and the stacking cooling time is 30 hours.
The mechanical properties of example 3 are shown in Table 3, and the composite mechanical properties are excellent, and the strength and toughness are good.
Table 2 table of mechanical properties of the finished product in example 2
The metallographic structure (100 ×) at a thickness of 1/4 of the steel sheet obtained in this example is a typical ferrite + pearlite structure as shown in fig. 4. The flaw detection results of the steel plate in the embodiment 1 are shown in a table 4, and the steel plate meets the GB/T2970I grade requirement.
Example 3
The embodiment relates to a Q355D medium-thickness plate with the thickness of 50mm, and the smelting components are as follows according to mass percentage: 0.16% C, 1.46% Mn, 0.31% Si, 0.029% Alt, 0.009% P, 0.009% S, 0.015% Nb, 0.015% Ti; the balance of Fe and inevitable impurities. Casting blank thickness: 250mm, serious internal cracks exist, and the low-power rating results are that the center segregation B is 0.5, the center porosity is 0.5, the middle cracks are 2.0 grades, and the triangular region cracks are 0.5 grades. The main equipment is a conventional 3500mm medium and heavy plate mill, and the maximum rolling force is 70000 KN.
The subsequent rolling method of the casting blank with the serious internal crack defect comprises the following steps:
s1, firstly, cold blank preheating is carried out on the defect casting blank, the cold blank of the defect continuous casting blank and the lower line hot plate blank are alternately stacked and stacked for 45 hours before rolling, the average surface temperature of the lower line hot plate blank is 800 ℃, and the surface temperature of the defect continuous casting blank after preheating is guaranteed to reach 450 ℃;
s2, in the heating stage, a four-stage heating method is adopted in the heating furnace, wherein the temperature of the preheating section is 700-. Tapping temperature is 1215 ℃;
s3, in the high-pressure water descaling stage, the descaling water spray pressure is 22MPa, and the roller speed is 0.3 m/S;
s4, in the rough rolling stage, all passes adopt high-pressure water to descale, the descaling water spraying pressure is 21MPa, the biting speed in the rough rolling stage is 1.0m/S, and the maximum rolling speed is 1.5 m/S. In the rough rolling stage, the reduction of 1 longitudinal rolling pass is 35mm, the reduction of 1 longitudinal rolling pass is 30mm, and the target reduction rate of the final pass of rough rolling is 22%;
s5, wherein the finish rolling starting temperature range is 855 ℃, and the finishing temperature range is 795 ℃; the total pass reduction rate of the finish rolling stage is 53 percent, and the final pass target reduction rate of the finish rolling is 11 percent;
s6, in the cooling stage, the water inlet temperature is 784 ℃, the final cooling temperature is controlled at 620 ℃, and the cooling speed is 13 ℃/S. And after straightening, the steel plates are off-line stacked and slowly cooled at the highest speed, wherein the stacking cooling temperature is 420 ℃, and the stacking cooling time is 36 h.
The mechanical properties of example 3 are shown in Table 3, and the composite mechanical properties are excellent, and the strength and toughness are good.
Table 3 table of mechanical properties data of the finished product of example 1
The metallographic structure (100 ×) at a thickness 1/4 of the steel sheet obtained in this example is shown in fig. 6. A typical ferrite + pearlite structure. The flaw detection results of the steel plate in the embodiment 1 are shown in a table 4, and the steel plate meets the GB/T2970I grade requirement.
TABLE 4 results of flaw detection
The embodiments described herein are only some, and not all, embodiments of the invention. Based on the above explanations and guidance, those skilled in the art can make modifications, improvements, substitutions, and the like on the embodiments based on the present invention and examples, but all other embodiments obtained without innovative research fall within the scope of the present invention.
Claims (3)
1. A method for producing a medium plate with excellent quality by utilizing a defective continuous casting slab is characterized by comprising the following steps: the defect continuous casting slab comprises the following chemical components in percentage by mass: 0.15% -0.20%, Si: 0.25 to 0.31%, Mn: 1.45-1.50%, P: less than or equal to 0.020%, S: less than or equal to 0.020 percent, less than or equal to 0.030 percent of Nb, less than or equal to 0.030 percent of Ti, less than or equal to 0.050 percent of Alt, and the balance of Fe and inevitable impurities;
the method comprises the following steps: heating → high-pressure water descaling → rough rolling → finish rolling → ACC laminar cooling → hot straightening → stacking cooling → inspection and warehousing; specifically, the method comprises the following steps:
s1, firstly, cold blank preheating is carried out on the defect continuous casting blank, the cold blank of the defect continuous casting blank and the lower line hot plate blank are alternately stacked and stacked for 30-45 hours before rolling, the average surface temperature of the lower line hot plate blank is ensured to be not less than 700 ℃, and the surface temperature of the defect continuous casting blank after preheating reaches 400-500 ℃;
s2, in the heating stage, adopting a four-section heating method in a heating furnace, wherein the preheating section is less than or equal to 800 ℃, the first heating section is 850-;
s3, in the high-pressure water descaling stage, the pressure of descaling spraying water is required to be more than or equal to 22MPa, and the roller speed is less than or equal to 0.5 m/S;
s4, in the rough rolling stage, ensuring that all rolling passes adopt an inter-pass descaling process, the descaling water spray pressure is more than or equal to 20MPa, the biting speed in the rough rolling stage is not more than 1.2m/S, and the maximum rolling speed is 1.8 m/S;
in the rough rolling stage, at least 1 longitudinal rolling pass reduction is more than or equal to 30mm, 1 longitudinal rolling pass reduction is more than or equal to 25mm, and the target reduction rate of the final pass of rough rolling is more than or equal to 20%;
s5, the start temperature range of finish rolling is 850-900 ℃, and the end temperature range is 770-830 ℃; the total pass reduction rate of the finish rolling stage is required to be more than or equal to 45 percent, and the final pass target reduction rate of the finish rolling is more than or equal to 10 percent;
s6, in the cooling stage, the cooling speed is controlled at 6-15 ℃/S, and the final cooling temperature is controlled at 620-630 ℃; after straightening, the steel plate is stacked and slowly cooled at the highest speed, the stacking and cooling temperature is 400-500 ℃, and the stacking and cooling time is 25-36 h.
2. The method for producing a medium plate of good quality using a defective slab as set forth in claim 1, wherein: the thickness of the defect continuous casting billet is 250 mm; the thickness of the finished product is 50-60 mm.
3. The method for producing a medium plate with excellent quality by using a defective continuous casting slab as claimed in claim 1, wherein the mechanical properties of the finished product are as follows: the upper yield strength ReH is more than or equal to 370 MPa; the tensile strength Rm is more than or equal to 510 MPa; the reduction of area A is 25%; the charpy V-shaped longitudinal impact at the temperature of minus 20 ℃ is more than or equal to 81J; the Charpy V-shaped longitudinal impact at 0 ℃ is more than or equal to 99J; the Charpy V-shaped longitudinal impact at 20 ℃ is more than or equal to 108J.
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