CN116949342A - Method for improving flaw detection qualification rate of Q355D thick steel plate - Google Patents

Method for improving flaw detection qualification rate of Q355D thick steel plate Download PDF

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CN116949342A
CN116949342A CN202310643564.6A CN202310643564A CN116949342A CN 116949342 A CN116949342 A CN 116949342A CN 202310643564 A CN202310643564 A CN 202310643564A CN 116949342 A CN116949342 A CN 116949342A
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宋维兆
雷洪
吾塔
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Xinjiang Bayi Iron and Steel Co Ltd
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Xinjiang Bayi Iron and Steel Co Ltd
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    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C33/00—Making ferrous alloys
    • C22C33/04—Making ferrous alloys by melting
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21C—PROCESSING OF PIG-IRON, e.g. REFINING, MANUFACTURE OF WROUGHT-IRON OR STEEL; TREATMENT IN MOLTEN STATE OF FERROUS ALLOYS
    • C21C5/00—Manufacture of carbon-steel, e.g. plain mild steel, medium carbon steel or cast steel or stainless steel
    • C21C5/28—Manufacture of steel in the converter
    • C21C5/30—Regulating or controlling the blowing
    • C21C5/35—Blowing from above and through the bath
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21C—PROCESSING OF PIG-IRON, e.g. REFINING, MANUFACTURE OF WROUGHT-IRON OR STEEL; TREATMENT IN MOLTEN STATE OF FERROUS ALLOYS
    • C21C7/00—Treating molten ferrous alloys, e.g. steel, not covered by groups C21C1/00 - C21C5/00
    • C21C7/0006—Adding metallic additives
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21C—PROCESSING OF PIG-IRON, e.g. REFINING, MANUFACTURE OF WROUGHT-IRON OR STEEL; TREATMENT IN MOLTEN STATE OF FERROUS ALLOYS
    • C21C7/00—Treating molten ferrous alloys, e.g. steel, not covered by groups C21C1/00 - C21C5/00
    • C21C7/0056—Treating molten ferrous alloys, e.g. steel, not covered by groups C21C1/00 - C21C5/00 using cored wires
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21C—PROCESSING OF PIG-IRON, e.g. REFINING, MANUFACTURE OF WROUGHT-IRON OR STEEL; TREATMENT IN MOLTEN STATE OF FERROUS ALLOYS
    • C21C7/00—Treating molten ferrous alloys, e.g. steel, not covered by groups C21C1/00 - C21C5/00
    • C21C7/0075—Treating in a ladle furnace, e.g. up-/reheating of molten steel within the ladle
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21C—PROCESSING OF PIG-IRON, e.g. REFINING, MANUFACTURE OF WROUGHT-IRON OR STEEL; TREATMENT IN MOLTEN STATE OF FERROUS ALLOYS
    • C21C7/00—Treating molten ferrous alloys, e.g. steel, not covered by groups C21C1/00 - C21C5/00
    • C21C7/10—Handling in a vacuum
    • 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
    • C22C38/14—Ferrous alloys, e.g. steel alloys containing titanium or zirconium
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/42—Ferrous alloys, e.g. steel alloys containing chromium with nickel with copper
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
    • Y02P10/00—Technologies related to metal processing
    • Y02P10/20—Recycling

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  • Materials Engineering (AREA)
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  • Organic Chemistry (AREA)
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  • Manufacturing & Machinery (AREA)
  • Treatment Of Steel In Its Molten State (AREA)

Abstract

The invention discloses a method for improving the flaw detection qualification rate of a Q355D thick steel plate, which comprises the following steps: molten iron desulfurization pretreatment, top-bottom combined blown converter smelting, converter tapping deoxidization alloying, LF refining, RH vacuum treatment, slab continuous casting, slab hot-charging rolling, thick plate rolling, flaw detection, and finished product packaging and warehousing; Q355D thick steel plate component composition: c:0.15 to 0.18 weight percent; si:0.25 to 0.35 weight percent; mn:1.45 to 1.55 weight percent; ti:0.010 to 0.020wt%; p: less than or equal to 0.015wt%; s: less than or equal to 0.004 wt percent; al: 0.015-0.035-wt%; cr is less than or equal to 0.10 and wt percent; ni is less than or equal to 0.030 and wt percent; cu is less than or equal to 0.020 and wt percent; [ N ]: less than or equal to 0.0045 and wt percent, [ H ]: less than or equal to 0.00015 percent wt percent, and the balance of iron and unavoidable impurities; except for the first plate blank of the casting furnace and the last plate blank of one casting time, rolling the second-stage and lower-stage flaw detection plates instead, and rolling all the first-stage flaw detection plates by the rest plate blanks, wherein flaw detection of the rolled plates is all qualified.

Description

Method for improving flaw detection qualification rate of Q355D thick steel plate
Technical Field
The invention relates to a method for improving the flaw detection qualification rate of a Q355D thick steel plate.
Background
The flaw detection defect is one of main quality defects of the thick plate. Therefore, in order to ensure the product quality, a large number of unsteady state slabs are generated in the steelmaking and continuous casting production process to carry out degradation and improvement, the degradation and improvement rate of the slabs reaches 10% at most, and the flaw detection qualification rate of the rolled thick plates is 95-96.5%. If the production process is unstable, the flaw detection failure rate of the steel plate is multiplied, large quality objections occur, and serious quality accidents can be caused. The internal quality defect is found by nondestructive inspection of the steel sheet, and is a method generally adopted for thick steel sheets. Ultrasonic flaw detection is a main method for nondestructive detection of the internal quality of a thick steel plate, and can detect internal defects such as layering, shrinkage cavity, holes, inclusions, white spots, bubbles, internal cracks, looseness, segregation, serious coarse crystals and the like of the steel plate.
Disclosure of Invention
The invention aims to provide a method for improving the flaw detection qualification rate of a Q355D thick steel plate, which can eliminate the unqualified flaw detection factors from the source and improve the product quality.
The technical scheme adopted by the invention is that the method for improving the flaw detection qualification rate of the Q355D thick steel plate is implemented according to the following steps:
a step A of, in the first step,
1) The process route for preparing Q355D thick steel comprises the following steps: molten iron desulfurization pretreatment, top-bottom combined blown converter smelting, converter tapping deoxidization alloying, LF refining, RH vacuum treatment, slab continuous casting, slab hot-charging rolling, thick plate rolling, flaw detection, and finished product packaging and warehousing; Q355D thick steel plate component composition: c:0.15 to 0.18 weight percent; si:0.25 to 0.35 weight percent; mn:1.45 to 1.55 weight percent; ti:0.010 to 0.020wt%; p: less than or equal to 0.015wt%; s: less than or equal to 0.004 wt percent; al: 0.015-0.035-wt%; cr is less than or equal to 0.10 and wt percent; ni is less than or equal to 0.030 and wt percent; cu is less than or equal to 0.020 and wt percent; [ N ]: less than or equal to 0.0045 and wt percent, [ H ]: less than or equal to 0.00015 percent wt percent, and the balance of iron and unavoidable impurities;
2) Molten iron charging into a converter requires: the weight percentage of the blast furnace molten iron [ P ] is less than or equal to 0.120 percent, the weight percentage of the [ S ] is less than or equal to 0.06 percent, and the temperature of the molten iron is more than or equal to 1280 ℃; the sulfur content of molten iron entering the converter after the molten iron desulfurization treatment is not more than 0.004%, slag must be removed after the molten iron desulfurization, and the slag removal amount is more than 90% of the total amount of top slag of a molten iron ladle;
3) Bottom argon blowing stirring is carried out in the whole smelting process of the top-bottom combined blowing converter, the steel tapping component of the converter is required to have the phosphorus content not more than 0.012wt percent, the sulfur content not more than 0.008wt percent, the carbon content is controlled to be 0.08-0.12 wt percent, and the steel tapping temperature of the converter is 1650-1680 ℃;
4) The tapping requirement of the converter, baking and drying of the ladle, baking of the drainage sand filled in the ladle, and baking of the drainage sand at 200-250 ℃ are carried out, so that the tapping target time t is more than or equal to 3.5min, and slag discharge detection and slide plate slag stopping are ensured;
5) Refining in an LF furnace: heating, adjusting components, desulfurizing, deoxidizing and removing impurities, feeding calcium wire for treatment, wherein the initial sulfur content of the LF refining ladle molten steel is not more than 0.011wt%, the time for reducing the LF white slag is not less than 10min, the aluminum content in the LF treated finished steel is 0.040-0.050 wt%, the CaO content of the LF refining final slag component is 52-55 wt%, the MgO content is less than or equal to 2%, and the Al content is not less than 10min 2 O 3 30-33 wt% of SiO 2 The content is 5-10wt%, the LF treatment time is less than 40min, the treatment process is to prevent nitrogen increase of molten steel, shorten the electrifying time, and add silicon carbide and limestone into top slag for submerged arc refining;
6) Calcium treatment of molten steel, namely feeding a calcium wire into the molten steel, then carrying out ladle bottom argon blowing for more than 5 minutes, and detecting that the calcium content in the steel is controlled to be in the range of 0.0025-0.0040 wt% after soft blowing is finished, wherein aluminum iron cannot be added into the steel after the calcium wire feeding treatment;
7) RH vacuum treatment, and circulator flow is more than or equal to 80m 3 Adding ferrotitanium after RH treatment, wherein the RH minimum vacuum degree is less than or equal to 67Pa, and the RH treatment time is not less than 14min; the pure degassing time is not less than 9 minutes; RH minimum vacuum degree is less than or equal to 133Pa, RH treatment time is not less than 16min, and pure degassing time is not less than 11 min; RH minimum vacuum degree is less than or equal to 180Pa, RH treatment time is not less than 18min, and pure degassing time is not less than 13 min; RH treatment capacity reaches 15 furnaces, continuous casting is stopped, RH must be processed by vacuum groove cooling steel operation, RH treatment is finished by molten steel hydrogen determination operation, when the hydrogen content in molten steel is not more than 1.0PPm, a plate blank can be conveyed by adopting a heat preservation vehicle, and stacked and slowly cooled in a steel rolling stock area for 8 hours and then put inHeating and rolling in a furnace; when the hydrogen content in the steel is 1.0-1.5 PPm, the slab is stacked and slowly cooled for 48 hours and then can be charged and rolled; when the hydrogen content in the steel is 1.51-1.8 PPm, stacking and slowly cooling the slabs for 72 hours, loading the slabs into a furnace for rolling, and slowly cooling the rolled steel plates for 24 hours;
8) The superheat degree of the continuous casting molten steel is 15-30 ℃, and the pulling speed range of the plate blank is: 0.85+/-0.1 m/min; light-weight of plate blank 4-5 mm, and smelting finished component molten steel [ N ]]Internal control standard, head furnace: not more than 45PPm, not more than 40PPm in a normal continuous casting furnace, adopting dry materials for the lining of a continuous casting tundish, and baking for more than 2.5 hours; the tundish covering agent is kept dry, H 2 The O is not more than 0.5%, argon is introduced into a tundish before continuous casting and pouring for 200-L/min, argon is blown between nozzle plates for 10-12L/min, stopper rod argon is blown for 4-6L/min, argon protection is performed on a large ladle long nozzle for 200L/min, and the slab straightening temperature is not less than 950 ℃;
a step B of, in which the step B,
1) The holding time of the steel-making LF white slag is not less than 10 minutes, and the LF outlet strictly forbids aluminum addition and deoxidation of molten steel; the strictly controlled S component of the steel component is not more than 0.005%, and the nitrogen content is not more than 0.0045%; h content in hot-rolling slab steel is not more than 1.0ppm, RH treatment: the flow rate of the circulating argon is not less than 80m 3 And (h) strictly prohibiting the steel ladle molten steel temperature from being high, adding scrap steel for temperature adjustment, and strictly executing 15-furnace steel casting;
2) The superheat degree of the continuous casting molten steel is 15-30 ℃; and the control range of the slab pulling speed is as follows: 0.85+/-0.1 m/min; light pressing weight of slab light pressing: 4-5 mm under light pressure;
3) The internal control standard of molten steel [ N ] of smelting finished components is that a casting furnace is started: the nitrogen content of the smelting finished product is not more than 45ppm, and the nitrogen content of a normal continuous casting furnace is not more than 40ppm;
4) The continuous casting tundish adopts dry materials, and the baking time is longer than 2.5 hours; the water content in the tundish covering agent is not more than 0.5%, all interfaces of the tundish are fully sealed before continuous casting is started, argon is introduced into the tundish, the flow is 200L/min, the argon introducing time is more than 10min, argon is blown between nozzle plates for 10-12L/min, the stopper rod is blown for 4-6L/min, the ladle is protected by long nozzle circular seam argon, and the flow is 200L/min; the slab continuous casting straightening temperature is not less than 950 ℃;
5) When the hydrogen content in the molten steel is less than 1.0PPm, hot-charging and rolling the plate blank; when the hydrogen content in the molten steel is 1.01-1.2 PPm, the plate blanks are stacked and slowly cooled for 8 hours and then rolled, and when the hydrogen content in the molten steel is 1.21-1.50 PPm, the plate blanks are stacked and slowly cooled for 36 hours and then rolled.
Through trial production, the method provided by the invention has the advantages that the superheat degree of the continuous casting molten steel is 15-29 ℃, the continuous casting slab pulling speed is 0.84-0.86 m/min, and the center segregation of the slab is 2.2 grade (Mannesmann standard) at the highest. The maximum nonmetallic inclusion is class D or DS fine system 0.5 grade. Except for the first plate blank of the casting furnace and the last plate blank of one casting time, rolling the second-stage and lower-stage flaw detection plates instead, and rolling all the first-stage flaw detection plates by the rest plate blanks, wherein flaw detection of the rolled plates is all qualified. See table 1.
。
Description of the embodiments
A method for improving the flaw detection qualification rate of Q355D thick steel plates is implemented according to the following steps,
a step A of, in the first step,
1) The preparation process comprises the following steps: molten iron desulfurization pretreatment, top-bottom combined blown converter smelting, converter tapping deoxidization alloying, LF refining, RH vacuum treatment, slab continuous casting, slab hot-charging rolling, thick plate rolling, flaw detection, and finished product packaging and warehousing;
Q355D thick steel plate component composition: c:0.15 to 0.18 weight percent; si:0.25 to 0.35 weight percent; mn:1.45 to 1.55 weight percent; ti:0.010 to 0.020wt%; p: less than or equal to 0.015wt%; s: less than or equal to 0.004 wt percent; al: 0.015-0.035-wt%; cr is less than or equal to 0.10 and wt percent; ni is less than or equal to 0.030 and wt percent; cu is less than or equal to 0.020 and wt percent; [ N ]: less than or equal to 0.0045 and wt percent, [ H ]: less than or equal to 0.00015 percent wt percent, and the balance of iron and unavoidable impurities;
2) Nonmetallic manganese sulfide inclusions in steel seriously affect the internal quality of the steel plate, and the nonmetallic manganese sulfide inclusions are rarely generated, rather than a large amount of manganese sulfide inclusions generated and removed in LF refining and RH refining processes. Molten iron charging into a converter requires: the weight percentage of the blast furnace molten iron [ P ] is less than or equal to 0.120 percent, the weight percentage of the [ S ] is less than or equal to 0.06 percent, and the temperature of the molten iron is more than or equal to 1280 ℃; the sulfur content of molten iron entering the converter after the molten iron desulfurization treatment is not more than 0.004 percent. Slag must be removed after desulfurization of molten iron, and the slag removal amount is more than 90% of the total amount of top slag of the ladle.
3) Smelting by a top-bottom combined blown converter, namely smelting by a top-bottom combined blown converter, wherein the whole process of bottom blowing argon stirring is performed, the converter tapping component requirement is that the phosphorus content is not more than 0.012wt%, the sulfur content is not more than 0.008wt% and the carbon content is controlled to be 0.08-0.12 wt%. The tapping temperature of the converter is 1650-1680 ℃.
4) The tapping requirement of the converter, baking and drying of the ladle, baking of the drainage sand filled in the ladle, and 200-250% of baking temperature of the drainage sand, ensuring that the continuous casting ladle molten steel flows automatically, and tapping target time t is more than or equal to 3.5min, slag discharge detection and slide plate slag stopping.
5) Refining in an LF furnace: heating, adjusting components, desulfurizing, deoxidizing, removing impurities, and feeding calcium wire for treatment. The initial sulfur content of the LF refining ladle molten steel is not more than 0.011wt%, the LF white slag reduction time is not less than 10min, the aluminum content in the LF treated finished steel is 0.040-0.050 wt%, the CaO content of the LF refining final slag component is 52-55 wt%, the MgO content is less than or equal to 2%, and the Al content is less than or equal to 10min 2 O 3 30-33 wt% of SiO 2 The content is 5-10wt%, the LF treatment time is less than 40min, the treatment process is to prevent nitrogen increase of molten steel, shorten the electrifying time, and the top slag is added with silicon carbide and limestone for submerged arc refining.
6) And (3) calcium treatment of molten steel, namely feeding a calcium wire into the molten steel, and then carrying out ladle bottom argon blowing for more than 5 minutes, wherein the content of calcium in the steel is controlled to be in the range of 0.0025-0.0040 wt% after soft blowing is finished, and aluminum iron cannot be added into the steel after the calcium wire feeding treatment.
7) RH vacuum treatment, and circulator flow is more than or equal to 80m 3 And/h, adding ferrotitanium at the end of RH treatment. The processing time is determined based on the minimum vacuum level achievable by RH. RH minimum vacuum degree is less than or equal to 67Pa, RH treatment time is not less than 14min, and pure degassing time is not less than 9 min; the method comprises the steps of carrying out a first treatment on the surface of the RH minimum vacuum degree is less than or equal to 133Pa, RH treatment time is not less than 16min, and pure degassing time is not less than 11 min; RH minimum vacuum degree is less than or equal to 180Pa, RH treatment time is not less than 18min, and pure degassing time is not less than 13 min. RH treatment capacity reaches 15 furnaces, continuous casting is stopped, and RH has to perform vacuum groove cooling operation. After RH treatment, carrying out molten steel hydrogen determination operation, and when the hydrogen content in the molten steel is not more than 1.0PPm, carrying out heat transfer on a plate blank by adopting a heat preservation vehicle, stacking and slowly cooling in a steel rolling stock area for 8 hours, and heating and rolling in a furnace; when the hydrogen content in the steel is 1.0-1.5 PPm, stacking and slowly cooling the plate blanks for 48 hoursThen charging and rolling; when the hydrogen content in the steel is 1.51-1.8 PPm, the plate blank is stacked and slowly cooled for 72 hours, and then the plate can be charged and rolled, and the rolled steel plate is slowly cooled for 24 hours.
8) The superheat degree of the continuous casting molten steel is 15-30 ℃, and the pulling speed range of the plate blank is: 0.85+/-0.1 m/min; the light pressing amount of the plate blank is 4-5 mm. Molten steel [ N ] as a component of a finished product]Internal control standard, head furnace: not more than 45PPm, and the normal continuous casting furnace not more than 40PPm. The continuous casting tundish lining adopts dry materials, and the baking time is longer than 2.5 hours; the tundish covering agent is kept dry, H 2 And the O is not more than 0.5%, 200-L/min of argon is introduced into the tundish before continuous casting, 10-12L/min of argon is blown between nozzle plates, 4-6L/min of argon is blown by a stopper rod, and 200L/min of argon is protected by a large ladle long nozzle. The straightening temperature of the plate blank is not less than 950 ℃.
A step B of, in which the step B,
1) The holding time of the steel-making LF white slag is not less than 10 minutes, and the LF outlet strictly forbids aluminum addition and deoxidation of molten steel; the strictly controlled S component of the steel component is not more than 0.005%, and the nitrogen content is not more than 0.0045%; h content in hot-rolling slab steel is not more than 1.0ppm, RH treatment: the flow rate of the circulating argon is not less than 80m 3 And (h) strictly prohibiting the steel ladle molten steel temperature from being high, adding scrap steel for temperature adjustment, and strictly executing 15-furnace steel casting;
2) The superheat degree of the continuous casting molten steel is 15-30 ℃; and the control range of the slab pulling speed is as follows: 0.85+/-0.1 m/min; light pressing weight of slab light pressing: 4-5 mm under light pressure;
3) The internal control standard of molten steel [ N ] of smelting finished components is that a casting furnace is started: the nitrogen content of the smelting finished product is not more than 45ppm, and the nitrogen content of a normal continuous casting furnace is not more than 40ppm;
4) The continuous casting tundish adopts dry materials, and the baking time is longer than 2.5 hours; the water content in the tundish covering agent is not more than 0.5%, all interfaces of the tundish are fully sealed before continuous casting is started, argon is introduced into the tundish, the flow is 200L/min, the argon introducing time is more than 10min, argon is blown between nozzle plates for 10-12L/min, the stopper rod is blown for 4-6L/min, the ladle is protected by long nozzle circular seam argon, and the flow is 200L/min; the slab continuous casting straightening temperature is not less than 950 ℃;
5) When the hydrogen content in the molten steel is less than 1.0PPm, hot-charging and rolling the plate blank; when the hydrogen content in the molten steel is 1.01-1.2 PPm, the plate blanks are stacked and slowly cooled for 8 hours and then rolled, and when the hydrogen content in the molten steel is 1.21-1.50 PPm, the plate blanks are stacked and slowly cooled for 36 hours and then rolled.
Examples
Smelting the components of a finished product: c:0.155 to 0.18 weight percent; si:0.27 to 0.33wt%; mn:1.45 to 1.55 weight percent; ti:0.010 to 0.020wt%; p: 0.011-0.015 wt%; s: 0.002-0.0035 wt%; al:0.025 to 0.032 weight percent; cr is less than or equal to 0.03wt%; ni is less than or equal to 0.01wt%; cu is less than or equal to 0.03wt%; [ N ]: less than or equal to 0.0045 and wt percent, [ H ]:0.00010 to 0.00015 percent wt percent. Through trial production, the method provided by the invention has the advantages that the superheat degree of the continuous casting molten steel is 15-29 ℃, the continuous casting slab pulling speed is 0.84-0.86 m/min, and the center segregation of the slab is 2.2 grade (Mannesmann standard) at the highest. The maximum nonmetallic inclusion is class D or DS fine system 0.5 grade. Except for the first plate blank of the casting furnace and the last plate blank of one casting time, rolling the second-stage and lower-stage flaw detection plates instead, and rolling all the first-stage flaw detection plates by the rest plate blanks, wherein flaw detection of the rolled plates is all qualified.

Claims (1)

1. The method for improving the flaw detection qualification rate of the Q355D thick steel plate is characterized by comprising the following steps of:
a step A of, in the first step,
1) The process route for preparing Q355D thick steel comprises the following steps: molten iron desulfurization pretreatment, top-bottom combined blown converter smelting, converter tapping deoxidization alloying, LF refining, RH vacuum treatment, slab continuous casting, slab hot-charging rolling, thick plate rolling, flaw detection, and finished product packaging and warehousing; Q355D thick steel plate component composition: c:0.15 to 0.18 weight percent; si:0.25 to 0.35 weight percent; mn:1.45 to 1.55 weight percent; ti:0.010 to 0.020wt%; p: less than or equal to 0.015wt%; s: less than or equal to 0.004 wt percent; al: 0.015-0.035-wt%; cr is less than or equal to 0.10 and wt percent; ni is less than or equal to 0.030 and wt percent; cu is less than or equal to 0.020 and wt percent; [ N ]: less than or equal to 0.0045 and wt percent, [ H ]: less than or equal to 0.00015 percent wt percent, and the balance of iron and unavoidable impurities;
2) Molten iron charging into a converter requires: the weight percentage of the blast furnace molten iron [ P ] is less than or equal to 0.120 percent, the weight percentage of the [ S ] is less than or equal to 0.06 percent, and the temperature of the molten iron is more than or equal to 1280 ℃; the sulfur content of molten iron entering the converter after the molten iron desulfurization treatment is not more than 0.004%, slag must be removed after the molten iron desulfurization, and the slag removal amount is more than 90% of the total amount of top slag of a molten iron ladle;
3) Bottom argon blowing stirring is carried out in the whole smelting process of the top-bottom combined blowing converter, the steel tapping component of the converter is required to have the phosphorus content not more than 0.012wt percent, the sulfur content not more than 0.008wt percent, the carbon content is controlled to be 0.08-0.12 wt percent, and the steel tapping temperature of the converter is 1650-1680 ℃;
4) The tapping requirement of the converter, baking and drying of the ladle, baking of the drainage sand filled in the ladle, and baking of the drainage sand at 200-250 ℃ are carried out, so that the tapping target time t is more than or equal to 3.5min, and slag discharge detection and slide plate slag stopping are ensured;
5) Refining in an LF furnace: heating, adjusting components, desulfurizing, deoxidizing and removing impurities, feeding calcium wire for treatment, wherein the initial sulfur content of the LF refining ladle molten steel is not more than 0.011wt%, the time for reducing the LF white slag is not less than 10min, the aluminum content in the LF treated finished steel is 0.040-0.050 wt%, the CaO content of the LF refining final slag component is 52-55 wt%, the MgO content is less than or equal to 2%, and the Al content is not less than 10min 2 O 3 30-33 wt% of SiO 2 The content is 5-10wt%, the LF treatment time is less than 40min, the treatment process is to prevent nitrogen increase of molten steel, shorten the electrifying time, and add silicon carbide and limestone into top slag for submerged arc refining;
6) Calcium treatment of molten steel, namely feeding a calcium wire into the molten steel, then carrying out ladle bottom argon blowing for more than 5 minutes, and detecting that the calcium content in the steel is controlled to be in the range of 0.0025-0.0040 wt% after soft blowing is finished, wherein aluminum iron cannot be added into the steel after the calcium wire feeding treatment;
7) RH vacuum treatment, and circulator flow is more than or equal to 80m 3 Adding ferrotitanium after RH treatment, wherein the RH minimum vacuum degree is less than or equal to 67Pa, and the RH treatment time is not less than 14min; the pure degassing time is not less than 9 minutes; RH minimum vacuum degree is less than or equal to 133Pa, RH treatment time is not less than 16min, and pure degassing time is not less than 11 min; RH minimum vacuum degree is less than or equal to 180Pa, RH treatment time is not less than 18min, and pure degassing time is not less than 13 min; RH treatment capacity reaches 15 furnaces, continuous casting is stopped, RH must be processed by vacuum groove cooling steel operation, RH treatment is finished by molten steel hydrogen determination operation, when the hydrogen content in molten steel is not more than 1.0PPm, a plate blank can be conveyed by adopting a heat preservation vehicle, and stacked and slowly cooled in a steel rolling stock area for 8 hours and then put into the furnace for heating and rolling; when the hydrogen content in the steel is 1.0-1.5 PPm, the slab is stacked and slowly cooled for 48 hours and then can be charged and rolled; when the hydrogen content in the steel is 1.51-1.8 PPm, stacking and slowly cooling the slabs for 72 hours, loading the slabs into a furnace for rolling, and slowly cooling the rolled steel plates for 24 hours;
8) The superheat degree of the continuous casting molten steel is 15 to the upper30 ℃, and the pulling speed range of the plate blank: 0.85+/-0.1 m/min; light-weight of plate blank 4-5 mm, and smelting finished component molten steel [ N ]]Internal control standard, head furnace: not more than 45PPm, not more than 40PPm in a normal continuous casting furnace, adopting dry materials for the lining of a continuous casting tundish, and baking for more than 2.5 hours; the tundish covering agent is kept dry, H 2 The O is not more than 0.5%, argon is introduced into a tundish before continuous casting and pouring for 200-L/min, argon is blown between nozzle plates for 10-12L/min, stopper rod argon is blown for 4-6L/min, argon protection is performed on a large ladle long nozzle for 200L/min, and the slab straightening temperature is not less than 950 ℃;
a step B of, in which the step B,
1) The holding time of the steel-making LF white slag is not less than 10 minutes, and the LF outlet strictly forbids aluminum addition and deoxidation of molten steel; the strictly controlled S component of the steel component is not more than 0.005%, and the nitrogen content is not more than 0.0045%; h content in hot-rolling slab steel is not more than 1.0ppm, RH treatment: the flow rate of the circulating argon is not less than 80m 3 And (h) strictly prohibiting the steel ladle molten steel temperature from being high, adding scrap steel for temperature adjustment, and strictly executing 15-furnace steel casting;
2) The superheat degree of the continuous casting molten steel is 15-30 ℃; and the control range of the slab pulling speed is as follows: 0.85+/-0.1 m/min; light pressing weight of slab light pressing: 4-5 mm under light pressure;
3) The internal control standard of molten steel [ N ] of smelting finished components is that a casting furnace is started: the nitrogen content of the smelting finished product is not more than 45ppm, and the nitrogen content of a normal continuous casting furnace is not more than 40ppm;
4) The continuous casting tundish adopts dry materials, and the baking time is longer than 2.5 hours; the water content in the tundish covering agent is not more than 0.5%, all interfaces of the tundish are fully sealed before continuous casting is started, argon is introduced into the tundish, the flow is 200L/min, the argon introducing time is more than 10min, argon is blown between nozzle plates for 10-12L/min, the stopper rod is blown for 4-6L/min, the ladle is protected by long nozzle circular seam argon, and the flow is 200L/min; the slab continuous casting straightening temperature is not less than 950 ℃;
5) When the hydrogen content in the molten steel is less than 1.0PPm, hot-charging and rolling the plate blank; when the hydrogen content in the molten steel is 1.01-1.2 PPm, the plate blanks are stacked and slowly cooled for 8 hours and then rolled, and when the hydrogen content in the molten steel is 1.21-1.50 PPm, the plate blanks are stacked and slowly cooled for 36 hours and then rolled.
CN202310643564.6A 2023-06-01 2023-06-01 Method for improving flaw detection qualification rate of Q355D thick steel plate Pending CN116949342A (en)

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