CN114378114B - Method for producing medium plate with excellent quality by using defective continuous casting blank - Google Patents
Method for producing medium plate with excellent quality by using defective continuous casting blank Download PDFInfo
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- CN114378114B CN114378114B CN202111504848.4A CN202111504848A CN114378114B CN 114378114 B CN114378114 B CN 114378114B CN 202111504848 A CN202111504848 A CN 202111504848A CN 114378114 B CN114378114 B CN 114378114B
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- 238000009749 continuous casting Methods 0.000 title claims abstract description 37
- 230000002950 deficient Effects 0.000 title claims abstract description 34
- 238000004519 manufacturing process Methods 0.000 title claims abstract description 18
- 238000005096 rolling process Methods 0.000 claims abstract description 123
- 238000001816 cooling Methods 0.000 claims abstract description 60
- 238000010438 heat treatment Methods 0.000 claims abstract description 57
- 230000009467 reduction Effects 0.000 claims abstract description 41
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims abstract description 37
- 238000000034 method Methods 0.000 claims abstract description 26
- 238000002791 soaking Methods 0.000 claims abstract description 21
- 230000007547 defect Effects 0.000 claims abstract description 16
- 230000008569 process Effects 0.000 claims abstract description 9
- 238000010079 rubber tapping Methods 0.000 claims abstract description 7
- 239000007921 spray Substances 0.000 claims description 12
- 229910052717 sulfur Inorganic materials 0.000 claims description 7
- 239000012535 impurity Substances 0.000 claims description 6
- 239000000126 substance Substances 0.000 claims description 3
- 238000001514 detection method Methods 0.000 abstract description 8
- 238000012797 qualification Methods 0.000 abstract description 5
- 238000005266 casting Methods 0.000 description 27
- 229910000831 Steel Inorganic materials 0.000 description 22
- 239000010959 steel Substances 0.000 description 22
- XEEYBQQBJWHFJM-UHFFFAOYSA-N iron Substances [Fe] XEEYBQQBJWHFJM-UHFFFAOYSA-N 0.000 description 11
- 230000035515 penetration Effects 0.000 description 9
- 230000000694 effects Effects 0.000 description 8
- 239000000463 material Substances 0.000 description 6
- 239000002344 surface layer Substances 0.000 description 5
- 230000008901 benefit Effects 0.000 description 4
- 229910052799 carbon Inorganic materials 0.000 description 4
- 229910052698 phosphorus Inorganic materials 0.000 description 4
- 238000010583 slow cooling Methods 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
- 230000009286 beneficial effect Effects 0.000 description 3
- 229910052739 hydrogen Inorganic materials 0.000 description 3
- 239000001257 hydrogen Substances 0.000 description 3
- 229910052742 iron Inorganic materials 0.000 description 3
- 229910001562 pearlite Inorganic materials 0.000 description 3
- 238000005204 segregation 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
- 208000037656 Respiratory Sounds Diseases 0.000 description 2
- 238000005452 bending Methods 0.000 description 2
- 238000005336 cracking Methods 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
- 230000004075 alteration Effects 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
- 230000006866 deterioration Effects 0.000 description 1
- 238000007689 inspection Methods 0.000 description 1
- 238000011009 performance qualification Methods 0.000 description 1
- 239000011574 phosphorus Substances 0.000 description 1
- 230000008092 positive effect Effects 0.000 description 1
- 230000003449 preventive effect Effects 0.000 description 1
- 238000012545 processing Methods 0.000 description 1
- 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
Classifications
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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
-
- 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
-
- 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
-
- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
-
- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/06—Ferrous alloys, e.g. steel alloys containing aluminium
-
- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/12—Ferrous alloys, e.g. steel alloys containing tungsten, tantalum, molybdenum, vanadium, or niobium
-
- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/14—Ferrous alloys, e.g. steel alloys containing titanium or zirconium
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- Chemical & Material Sciences (AREA)
- Engineering & Computer Science (AREA)
- Mechanical Engineering (AREA)
- Materials Engineering (AREA)
- Metallurgy (AREA)
- Organic Chemistry (AREA)
- Metal Rolling (AREA)
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 blank, which comprises the following steps: heating, descaling by high-pressure water, rough rolling, finish rolling, ACC laminar cooling, hot straightening, cold piling, checking and warehousing; the slab is preheated, slowly heated in multiple stages, the soaking temperature and the tapping temperature are high, the high-pressure water descaling control is matched, the rough rolling is performed at a low rolling speed and the descaling is performed in the whole process, a process blank with internal heat and external cooling, internal heat and external hardness is formed in the rolling process, and the defect slab with the thickness of 250mm can be rolled into a medium plate with excellent quality and the maximum thickness of 60mm by means of reasonable rolling reduction and controlled rolling and controlled cooling processes, so that the mechanical qualification rate is more than or equal to 99%, and the flaw detection qualification rate under 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, in particular to a method for producing a medium plate with excellent quality, high performance qualification rate of more than or equal to 99%, flaw detection qualification 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 middle cracks and triangular area cracks.
Background
In the large-scale mass production activities, the situation that serious defects exist in continuous casting billets occurs, and even the situation that serious slab cracking defects exist in large batches is not poor.
Severe slab cracking means that internal intermediate cracks, triangular cracks, etc. reach a level of 2.0 or more, or severe central cracks are generated. As solidification proceeds, during the formation of cracks, inclusions or harmful elements are accumulated, and at the same time, the crack front is segregated by C, mn and other elements. The problems brought by the method are that the mechanical properties of the rolled steel plate, especially the plastic property indexes (cold bending, elongation after breaking, and the like) are unqualified, the tensile fracture is layered, and the user has internal tearing in the processing and using processes, so that the use requirements cannot be met.
According to the conventional production process method, the method generally aims at the generation reasons of casting blank cracks directly, adopts measures of controlling the content of phosphorus and sulfur in molten steel, pouring with low superheat degree, optimizing a continuous casting secondary cooling zone process system, improving equipment precision, overhauling frequency and the like, 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 factors in mass production and do not work well in the face of sudden conditions or difficulties in organizational production. The measures are preventive measures, the casting blank with serious defects can not be recovered, the steel plate produced by the casting blank with the defects is poor in plasticity index, and the degradation rate of the product is high; there is currently little research aimed at this problem.
For the continuous casting slab with serious defects which is produced, in the actual production, how to obtain the qualified product by means of the subsequent procedures 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 using a defective continuous casting blank.
The invention adopts the technical proposal for solving the technical problems in the prior art that:
The invention aims to protect a method for producing a medium plate with excellent quality by using a defective continuous casting blank, wherein the defective continuous casting blank comprises the following chemical components in percentage by mass: 0.15 to 0.20 percent, si:0.25-0.31%, mn:1.45 to 1.50 percent, P: less than or equal to 0.020%, S: less than or equal to 0.020%, less than or equal to 0.030% Nb, less than or equal to 0.030% Ti, less than or equal to 0.050% Alt, and the balance of Fe and unavoidable impurities; intermediate cracks of 2.0 and above, and/or triangular cracks of 0.5 and above, it should be understood that the defect levels described herein are merely indicative of the applicability of the present invention to severe slab defects and are not intended to limit the invention.
The method comprises the following steps: heating, descaling by high-pressure water, rough rolling, finish rolling, ACC laminar cooling, hot straightening, cold piling, checking and warehousing.
S1, firstly, preheating a cold blank of a defective continuous casting blank, and alternately stacking the cold blank of the defective continuous casting blank and a lower line hot plate blank for 30-45 hours before rolling, so that the average surface temperature of the lower line hot plate blank is more than or equal to 700 ℃, and the surface temperature of the preheated defective continuous casting blank is 400-500 ℃; cold blank preheating of a defective casting blank is performed by utilizing the waste heat of a hot blank, so that internal crack expansion or casting blank fracture caused by the influence of thermal stress of the casting blank in the heating process is prevented;
S2, in a heating stage, a four-section heating method is adopted in a heating furnace, wherein the preheating section is less than or equal to 800 ℃, the first heating section is 850-1050 ℃, the second heating section is 1100-1220 ℃, the target soaking temperature of the soaking section is 1250+/-20 ℃, the soaking time is more than or equal to 30min, the total heating time in the furnace is 280-300min, and the tapping temperature requirement is more than or equal to 1200 ℃; four-section heating (preheating section, first heating section, second heating section, soaking section) can keep gentle heating rate, suppresses the extension of inside crackle. The high soaking temperature plays an important role on welding internal cracks, firstly, atomic diffusion is facilitated, secondly, the strength of the steel billet is reduced, thirdly, the surface layer is fast in cooling speed, the internal heat, the external cooling, the internal softness and the external hardness of a casting blank are facilitated to be formed, rolling force penetrates into the core, and the core cracks of the continuous casting blank are conveniently eliminated;
S3, in a high-pressure water descaling stage, the water spray pressure requirement for descaling is more than or equal to 22MPa, and the roller speed is less than or equal to 0.5m/S; the key difference of the step compared with the conventional dephosphorization is that the large descaling pressure and the slow roller speed are adopted, and the effect is mainly that firstly, thick and much iron scales generated by high-temperature heating in the second step can be removed completely, secondly, a certain cooling effect on the surface layer of the steel plate can be achieved at the stage, so that 'internal heat, external cooling, internal softness and external hardness' of a casting blank are formed, and the penetration of rolling force to cracks of the central part is facilitated;
S4, in the rough rolling stage, ensuring that all rolling passes adopt an inter-pass descaling process, wherein 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 1.8m/S; the high-pressure water descaling among all passes is adopted, and the slow rolling speed is matched, so that the slow rolling speed is beneficial to the penetration of the rolling force to the center, and the high-pressure water descaling is matched, so that the temperature of the rolling surface can be further effectively reduced, the inner heat, the outer cooling, the inner softness and the outer hardness of a blank can be formed by passes, and the penetration of the rolling force to the center is further promoted;
at least 1 reduction of longitudinal rolling passes in the rough rolling stage is more than or equal to 30mm,1 reduction of longitudinal rolling passes is more than or equal to 25mm, and the target reduction of the last pass of rough rolling is more than or equal to 20%; the high total pass reduction rate and single pass reduction control ensure the deformation penetration of the core during rolling;
S5, finishing rolling at a starting temperature of 850-900 ℃ and an ending temperature of 770-830 ℃; the total pass reduction rate of the finish rolling stage is more than or equal to 45%, and the final pass target reduction rate of the finish rolling is more than or equal to 10%; the total pass reduction rate and the final pass reduction rate of 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, controlling the cooling speed to be 6-15 ℃/S and the final cooling temperature to be 620-630 ℃ in the cooling stage; after straightening, stacking and slowly cooling at the fastest speed, wherein the stacking cooling temperature is 400-500 ℃ and the stacking cooling time is 25-36h. The effect of this step is to increase the strength by laminar cooling, followed by 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 250mm; the thickness of the finished product is 50-60mm.
Further, the mechanical properties of the finished product are as follows: the upper yield strength ReH is more than or equal to 370MPa; tensile strength Rm is more than or equal to 510MPa; shrinkage a=25%; the Charpy V-shaped longitudinal impact at the temperature of minus 20 ℃ is more than or equal to 81J; 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, cold piling, inspection and warehousing to roll the continuous casting slab with serious defects into a medium plate with excellent quality, and solves the problems of low percent of pass of plastic indexes such as elongation after breaking, cold bending and the like of the defective slab, layering of fracture, failure in flaw detection and the like.
Specific: 1) The four-section heating process is adopted in the heating stage, so that the gentle heating rate can be kept, the expansion of internal cracks is restrained, and meanwhile, the high soaking temperature plays an important role in welding the internal cracks of the continuous casting blank;
2) In the high-pressure water descaling stage, large descaling pressure and slow roller speed are adopted, so that thick and much iron scales generated by high-temperature heating in the second step can be removed completely, a certain steel plate surface layer cooling effect can be achieved at the stage, the internal heat, the external cooling, the internal softness and the external hardness of a casting blank are formed, and the penetration of rolling force to cracks of the central part is facilitated;
3) In the rough rolling stage, high-pressure water descaling among all passes is adopted, and slow rolling speed is matched, so that the slow rolling speed is beneficial to permeation of rolling force centripetal parts, and meanwhile, the high-pressure water descaling is matched, so that the rolling surface temperature can be further effectively reduced, inner heat, outer cooling, inner soft and outer hardness of blanks are formed in a pass-by-pass mode, and permeation of rolling force centripetal parts 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 controlled well, and the aim 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 advantages that under the condition of the capability of a conventional rolling mill, the internal cracks are welded in the subsequent rolling process while the internal crack deterioration of the serious casting blank is restrained, so that the defective casting blank is effectively utilized. The steel plate has the mechanical property qualification rate reaching 99 percent, the flaw detection meets the GB/T2970I level standard, the qualification rate is 100 percent, the quality loss is reduced, and the economic benefit is improved.
Drawings
FIG. 1 is a low-power casting billet before rolling in example 1;
FIG. 2 is a metallographic structure (100X) at 1/4 of the thickness of the steel sheet obtained in example 1;
FIG. 3 is a low-power cast slab before rolling in example 2;
FIG. 4 is a metallographic structure (100X) at 1/4 of the thickness of the steel sheet obtained in example 2;
FIG. 5 shows a low power of a cast slab before rolling in example 3;
FIG. 6 is a metallographic structure (100X) at 1/4 of the thickness of the steel sheet obtained in example 3;
Detailed Description
For a further understanding of the invention, its features and advantages, reference is now made to the following examples, which are illustrated in the accompanying drawings in which:
A method for producing a medium plate with excellent quality by using a defective continuous casting blank comprises the following chemical components in percentage by mass: 0.15 to 0.20 percent, si:0.25-0.31%, mn:1.45 to 1.50 percent, P: less than or equal to 0.020%, S: less than or equal to 0.020%, less than or equal to 0.030% Nb, less than or equal to 0.030% Ti, less than or equal to 0.050% Alt, and the balance of Fe and unavoidable impurities; the finished product thickness is 50-60mm, the median crack reaches a level of 2.0 and above, and/or the delta crack reaches a level of 0.5 and above, it being understood that the defect levels described herein are merely indicative of the applicability of the present invention to severe slab defects, and are not intended to limit the invention.
The method comprises the following steps: heating, descaling by high-pressure water, rough rolling, finish rolling, ACC laminar cooling, hot straightening, cold piling, checking and warehousing.
S1, firstly, preheating a cold blank of a defective continuous casting blank, and alternately stacking the cold blank of the defective continuous casting blank and a lower line hot plate blank for 30-45 hours before rolling, so that the average surface temperature of the lower line hot plate blank is more than or equal to 700 ℃, and the surface temperature of the preheated defective continuous casting blank is 400-500 ℃; cold blank preheating of a defective casting blank is performed by utilizing the waste heat of a hot blank, so that internal crack expansion or casting blank fracture caused by the influence of thermal stress of the casting blank in the heating process is prevented;
S2, in a heating stage, a four-section heating method is adopted in a heating furnace, wherein the preheating section is less than or equal to 800 ℃, the first heating section is 850-1050 ℃, the second heating section is 1100-1220 ℃, the target soaking temperature of the soaking section is 1250+/-20 ℃, the soaking time is more than or equal to 30min, the total heating time in the furnace is 280-300min, and the tapping temperature requirement is more than or equal to 1200 ℃; four-section heating (preheating section, first heating section, second heating section, soaking section) can keep gentle heating rate, suppresses the extension of inside crackle. The high soaking temperature plays an important role on welding internal cracks, firstly, atomic diffusion is facilitated, secondly, the strength of the steel billet is reduced, thirdly, the surface layer is fast in cooling speed, the internal heat, the external cooling, the internal softness and the external hardness of a casting blank are facilitated to be formed, rolling force penetrates into the core, and the core cracks of the continuous casting blank are conveniently eliminated;
S3, in a high-pressure water descaling stage, the water spray pressure requirement for descaling is more than or equal to 22MPa, and the roller speed is less than or equal to 0.5m/S; the key difference of the step compared with the conventional dephosphorization is that the large descaling pressure and the slow roller speed are adopted, and the effect is mainly that firstly, thick and much iron scales generated by high-temperature heating in the second step can be removed completely, secondly, a certain cooling effect on the surface layer of the steel plate can be achieved at the stage, so that 'internal heat, external cooling, internal softness and external hardness' of a casting blank are formed, and the penetration of rolling force to cracks of the central part is facilitated;
S4, in the rough rolling stage, ensuring that all rolling passes adopt an inter-pass descaling process, wherein 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 1.8m/S; the high-pressure water descaling among all passes is adopted, and the slow rolling speed is matched, so that the slow rolling speed is beneficial to the penetration of the rolling force to the center, and the high-pressure water descaling is matched, so that the temperature of the rolling surface can be further effectively reduced, the inner heat, the outer cooling, the inner softness and the outer hardness of a blank can be formed by passes, and the penetration of the rolling force to the center is further promoted;
at least 1 reduction of longitudinal rolling passes in the rough rolling stage is more than or equal to 30mm,1 reduction of longitudinal rolling passes is more than or equal to 25mm, and the target reduction of the last pass of rough rolling is more than or equal to 20%; the high total pass reduction rate and single pass reduction control ensure the deformation penetration of the core during rolling;
S5, finishing rolling at a starting temperature of 850-900 ℃ and an ending temperature of 770-830 ℃; the total pass reduction rate of the finish rolling stage is more than or equal to 45%, and the final pass target reduction rate of the finish rolling is more than or equal to 10%; the total pass reduction rate and the final pass reduction rate of 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, controlling the cooling speed to be 6-15 ℃/S and the final cooling temperature to be 620-630 ℃ in the cooling stage; after straightening, stacking and slowly cooling at the fastest speed, wherein the stacking cooling temperature is 400-500 ℃ and the stacking cooling time is 25-36h. The effect of this step is to increase the strength by laminar cooling, followed by release of hydrogen and stress by slow cooling, improving the internal quality of the steel sheet.
Example 1
The embodiment relates to a 60mm thick Q355B medium plate, which comprises the following smelting components in percentage by mass: 0.18% C, 1.47% Mn, 0.29% Si, 0.018% Alt, 0.017% P, 0.016% S, 0.002% Nb, 0.005% Ti; the balance of Fe and unavoidable impurities. Thickness of casting blank: 250mm, severe internal cracks exist, and the low-power rating result is center segregation B0.5, center porosity 0.5, middle crack 3.0 grade, and triangle crack 0.5 grade. The main equipment is a conventional 3500mm medium plate mill, and the maximum rolling force is 70000KN.
The subsequent rolling method of the casting blank with serious internal crack defect comprises the following steps:
S1, firstly, cold blank preheating is carried out on a defective casting blank, the cold material of the defective continuous casting blank and an 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 preheated defective continuous casting blank is ensured to reach 480 ℃;
S2, in a heating stage, a four-section heating method is adopted in a heating furnace, wherein the temperature of a preheating section is 700-800 ℃, the temperature of a first heating section is 900-1050 ℃, the temperature of a second heating section is 1100-1200 ℃, the soaking temperature is 1240-1260 ℃, the soaking time is 30min, and the total heating time in the furnace is 280min; the tapping temperature is 1220 ℃;
s3, in a high-pressure water descaling stage, the descaling water spray pressure is 22MPa, and the roller speed is 0.5m/S;
s4, in the rough rolling stage, high-pressure water is adopted for descaling, the water spray pressure for descaling is 21MPa, the biting speed in the rough rolling stage is 1.2m/S, and the maximum rolling speed is 1.6m/S; the rough rolling stage has 1 reduction of 32mm in longitudinal rolling pass, 1 reduction of 28mm in longitudinal rolling pass and the target reduction of the last pass of rough rolling is 22%.
S5, the finish rolling starting temperature range is 885 ℃ and the finish rolling ending temperature range is 825 ℃; the total pass reduction rate of the finish rolling stage is 48%, and the final pass target reduction rate of the finish rolling stage is 11%;
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; after straightening, stacking and slow cooling at the fastest speed, wherein the stacking cooling temperature is 485 ℃, and the stacking cooling time is 25h.
The mechanical properties of example 1 are shown in Table 1, and the comprehensive mechanical properties are excellent, and the strength and toughness are good.
TABLE 1 mechanical properties data sheet for the finished product of example 1
The metallographic structure (100×) at 1/4 of the thickness 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 of the example 1 are shown in Table 4, and the GB/T2970I grade requirement is met.
Example 2
The embodiment relates to a 50mm thick Q355C medium plate, which comprises the following smelting components in percentage by mass: 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 unavoidable impurities; thickness of casting blank: 250mm, severe internal cracks exist, and the low-power grading result is center segregation B0.5, center porosity 0.5, middle cracks 2.0 grade, and triangular area cracks 1.0 grade; the main equipment is a conventional 3500mm medium plate mill, and the maximum rolling force is 70000KN.
The subsequent rolling method of the casting blank with serious internal crack defect comprises the following steps:
S1, firstly, cold blank preheating is carried out on a defective casting blank, the defective continuous casting blank cold material and an off-line hot plate blank are alternately stacked and stacked for 40 hours before rolling, the average surface temperature of the off-line hot plate blank is 710 ℃, and the surface temperature of the preheated defective continuous casting blank is ensured to reach 420 ℃;
S2, in the heating stage, a four-stage heating method is adopted in a heating furnace, wherein the temperature of a preheating stage is 700-800 ℃, the temperature of a first heating stage is 880-1030 ℃, the temperature of a second heating stage is 1110-1210 ℃, the soaking temperature is 1230-1260 ℃, the soaking time is 35min, and the total heating time is 285min. The tapping temperature is 1225 ℃;
s3, in a high-pressure water descaling stage, the descaling water spray pressure is 23MPa, and the roller speed is 0.3m/S;
S4, in the rough rolling stage, high-pressure water is adopted for descaling, the water spray pressure for descaling is 21MPa, the biting speed in the rough rolling stage is 1.2m/S, and the maximum rolling speed is 1.5m/S. The rough rolling stage has 1 reduction of 35mm of longitudinal rolling pass, 1 reduction of 30mm of longitudinal rolling pass and the target reduction of the last pass of rough rolling;
S5, finishing rolling at a starting temperature range of 850 ℃ and an ending temperature range of 775 ℃; the total pass reduction rate of the finish rolling stage is 53%, and the final pass target reduction rate of the finish rolling stage is 11%;
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; after straightening, stacking and slowly cooling at the fastest speed, wherein the stacking cooling temperature is 450 ℃, and the stacking cooling time is 30h.
The mechanical properties of example 3 are shown in Table 3, and the comprehensive mechanical properties are excellent, and the strength and toughness are good.
TABLE 2 mechanical properties data sheet for the finished product of example 2
The metallographic structure (100×) at 1/4 of the thickness 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 of the example 1 are shown in Table 4, and the GB/T2970I grade requirement is met.
Example 3
The embodiment relates to a 50mm thick Q355D medium plate, which comprises the following smelting components in percentage by mass: 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 unavoidable impurities. Thickness of casting blank: 250mm, severe internal cracks exist, and the low-power rating result is center segregation B0.5, center porosity 0.5, middle crack 2.0 grade, and triangle crack 0.5 grade. The main equipment is a conventional 3500mm medium plate mill, and the maximum rolling force is 70000KN.
The subsequent rolling method of the casting blank with serious internal crack defect comprises the following steps:
S1, firstly, cold blank preheating is carried out on a defective casting blank, the defective continuous casting blank cold material and an off-line hot plate blank are alternately stacked and stacked for 45 hours before rolling, the average surface temperature of the off-line hot plate blank is 800 ℃, and the surface temperature of the preheated defective continuous casting blank is ensured to reach 450 ℃;
S2, in the heating stage, a four-stage heating method is adopted in a heating furnace, wherein the temperature of a preheating stage is 700-800 ℃, the temperature of a first heating stage is 850-1000 ℃, the temperature of a second heating stage is 1100-1220 ℃, the soaking temperature is 1230-1270 ℃, the soaking time is 30min, and the total heating time in the furnace is 300min. Tapping temperature 1215 ℃;
s3, in a high-pressure water descaling stage, the descaling water spray pressure is 22MPa, and the roller speed is 0.3m/S;
s4, in the rough rolling stage, high-pressure water is adopted for descaling, the water spray pressure for descaling is 21MPa, the biting speed in the rough rolling stage is 1.0m/S, and the maximum rolling speed is 1.5m/S. The rough rolling stage has 1 reduction of 35mm of longitudinal rolling pass, 1 reduction of 30mm of longitudinal rolling pass and the target reduction of the last pass of rough rolling;
S5, finishing rolling is started at a temperature range of 855 ℃ and ended at a temperature range of 795 ℃; the total pass reduction rate of the finish rolling stage is 53%, and the final pass target reduction rate of the finish rolling stage is 11%;
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. After straightening, stacking and slowly cooling at the fastest speed, wherein the stacking cooling temperature is 420 ℃, and the stacking cooling time is 36h.
The mechanical properties of example 3 are shown in Table 3, and the comprehensive mechanical properties are excellent, and the strength and toughness are good.
TABLE 3 mechanical properties data sheet for the finished product of example 3
The metallographic structure (100X) of the steel sheet obtained in this example at 1/4 of the thickness is shown in FIG. 6. Is a typical ferrite + pearlite structure. The flaw detection results of the steel plate of the example 1 are shown in Table 4, and the GB/T2970I grade requirement is met.
TABLE 4 flaw detection results
The embodiments described herein are only some, not all, embodiments of the invention. Based on the explanation and guidance of the above description, those skilled in the art can make alterations, improvements, substitutions, etc. to the embodiments based on the present invention and the examples, but all other examples obtained without making innovative research are included in the protection scope of the present invention.
Claims (3)
1. A method for producing a medium plate with excellent quality by using a defective continuous casting blank is characterized by comprising the following steps: the defective continuous casting blank comprises the following chemical components in percentage by mass: 0.15 to 0.20 percent, si:0.25-0.31%, mn:1.45 to 1.50 percent, P: less than or equal to 0.020%, S: less than or equal to 0.020%, less than or equal to 0.030% Nb, less than or equal to 0.030% Ti, less than or equal to 0.050% Alt, and the balance of Fe and unavoidable impurities;
the method comprises the following steps: heating, descaling by high-pressure water, rough rolling, finish rolling, ACC laminar cooling, hot straightening, cold piling, checking and warehousing; specific:
s1, firstly, preheating a cold blank of a defective continuous casting blank, and alternately stacking the cold blank of the defective continuous casting blank and a lower line hot plate blank for 30-45 hours before rolling, so that the average surface temperature of the lower line hot plate blank is more than or equal to 700 ℃, and the surface temperature of the preheated defective continuous casting blank is 400-500 ℃;
S2, in a heating stage, a four-section heating method is adopted in a heating furnace, wherein the preheating section is less than or equal to 800 ℃, the first heating section is 850-1050 ℃, the second heating section is 1100-1220 ℃, the target soaking temperature of the soaking section is 1250+/-20 ℃, the soaking time is more than or equal to 30min, the total heating time in the furnace is 280-300min, and the tapping temperature requirement is more than or equal to 1200 ℃;
S3, in a high-pressure water descaling stage, the water spray pressure requirement for descaling is more than or equal to 22MPa, and the roller speed is less than or equal to 0.5m/S;
S4, in the rough rolling stage, ensuring that all rolling passes adopt an inter-pass descaling process, wherein 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 1.8m/S;
At least 1 reduction of longitudinal rolling passes in the rough rolling stage is more than or equal to 30mm,1 reduction of longitudinal rolling passes is more than or equal to 25mm, and the target reduction of the last pass of rough rolling is more than or equal to 20%;
S5, finishing rolling at a starting temperature of 850-900 ℃ and an ending temperature of 770-830 ℃; the total pass reduction rate of the finish rolling stage is more than or equal to 45%, and the final pass target reduction rate of the finish rolling is more than or equal to 10%;
S6, controlling the cooling speed to be 6-15 ℃/S and the final cooling temperature to be 620-630 ℃ in the cooling stage; after straightening, stacking and slowly cooling at the fastest speed, wherein the stacking cooling temperature is 400-500 ℃ and the stacking cooling time is 25-36h.
2. The method for producing a medium plate of excellent quality by using a defective continuous casting billet according to claim 1, wherein: the thickness of the defect continuous casting blank is 250mm; the thickness of the finished product is 50-60mm.
3. The method for producing a medium plate of excellent quality by using a defective continuous casting billet according to claim 1, wherein the mechanical properties of the finished product are as follows: the upper yield strength ReH is more than or equal to 370MPa; tensile strength Rm is more than or equal to 510MPa; shrinkage a=25%; the Charpy V-shaped longitudinal impact at the temperature of minus 20 ℃ is more than or equal to 81J; 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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| CN104525560A (en) * | 2014-12-29 | 2015-04-22 | 天津钢铁集团有限公司 | Effective control method for pitted surface of plain carbon steel/Nb-containing steel plate of 20-30 mm thickness |
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| CN104525560A (en) * | 2014-12-29 | 2015-04-22 | 天津钢铁集团有限公司 | Effective control method for pitted surface of plain carbon steel/Nb-containing steel plate of 20-30 mm thickness |
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