Classifications

• • 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
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B22—CASTING; POWDER METALLURGY
  • B22D—CASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES
  • B22D11/00—Continuous casting of metals, i.e. casting in indefinite lengths
  • B22D11/16—Controlling or regulating processes or operations
  • B22D11/22—Controlling or regulating processes or operations for cooling cast stock or mould
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B22—CASTING; POWDER METALLURGY
  • B22D—CASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES
  • B22D11/00—Continuous casting of metals, i.e. casting in indefinite lengths
  • B22D11/16—Controlling or regulating processes or operations
  • B22D11/22—Controlling or regulating processes or operations for cooling cast stock or mould
  • B22D11/225—Controlling or regulating processes or operations for cooling cast stock or mould for secondary cooling
• • 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
• • 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
  • C21C7/04—Removing impurities by adding a treating agent
  • C21C7/06—Deoxidising, e.g. killing
• • 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
  • C21C7/04—Removing impurities by adding a treating agent
  • C21C7/072—Treatment with gases
• • 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
  • C22C38/001—Ferrous alloys, e.g. steel alloys containing N
• • 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
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B22—CASTING; POWDER METALLURGY
  • B22D—CASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES
  • B22D11/00—Continuous casting of metals, i.e. casting in indefinite lengths
  • B22D11/001—Continuous casting of metals, i.e. casting in indefinite lengths of specific alloys

Definitions

• the present invention belongs to the field of continuous casting technology and specifically relates to a method for producing V-N microalloyed and surface-crack-free continuous casting blank.
• Microalloyed steel is a kind of rapidly developing steel for engineering structures in nearly past half century. It plays a role in fine-grain strengthening and precipitation strengthening by adding various alloy elements (Nb, V, Ti, etc.) to the steel, thus improving the strength and toughness of the steel. It is widely used in various fields for example bridges, buildings, ships, automobiles, high-pressure vessels, etc., and has good application prospects. It is the main product in the modern steel industry. China has abundant reserves of microalloyed elements and has significant advantages in developing microalloyed steel. Typical Q550 and Q460 grades low content alloy high-strength steel have good market applications.
• microalloying is widely used due to the strengthening effect of microalloying elements.
• the carbonitride precipitation of microalloying elements reduces the plasticity of steel, and the occurrence rate of surface cracks in continuous casting billets is significantly higher than that of ordinary carbon steel casting blank.
• Niobium, vanadium, and titanium are three relatively widely used elements in microalloyed steel, with niobium having the greatest impact on the plasticity of the steel and the most significant reduction in its thermoplastic properties. Researches have shown that the addition of Ti element can reduce the brittleness of niobium and vanadium microalloyed steels, but it is not easy to control costs.
• the present invention provides a V-N microalloyed steel of surface-crack-free continuous casting blanks .
• a surface crack free continuous casting blanks with a cross-section of (150-350) mm * (1250-2400) mm is produced, which improves the surface quality of the continuous casting blanks.
• a V-N microalloyed steel composed by mass percentage of the following chemical components: C: 0.09-0.13%, Si: 0.1-0.4%, Mn: 1.0-3.0%, P: ⁇ 0.05%, S: ⁇ 0.05%, V: 0.1-0.4%, N: 0.011-0.2%, and the balance of Fe and unavoidable impurity elements.
• the present invention takes the features of the low valley point of thermoplastic properties of vanadium containing steel, the chemical composition of microalloyed steel is reasonably designed, so as to reduce the occurrence of surface cracks on the casting blanks during continuous casting.
• the V element has a very strong affinity with the N element, and combined with TMCP method in the later stage can play the role of increasing the strength and toughness of the structure through two typical strengthening mechanisms, fine grain strengthening and precipitation strengthening.
• V-N microalloying is beneficial for reducing the production cost of continuous casting blanks.
• the present invention also provides a production method for V-N microalloyed surface-crack-free continuous casting blanks, wherein the casting blanks are produced according to the chemical composition of the V-N microalloyed steel mentioned above; and the method sequentially includes the following processes: converter smelting, LF refining, and continuous casting.
• the cross-sectional specification of the continuous casting blank is (150-350) mm * (1250-2400) mm.
• the molten iron proportion is controlled between 88.0% ⁇ 91.0% (for example, 88.0%, 89.0%, 90.0%, and 91.0%), and the top-bottom combined blowing mode is used throughout the entire process, and nitrogen gas is blown first and then argon gas is blown later during the blowing process, to stir the molten steel and promote the chemical reaction in the furnace.
• the argon blowing time shall not be less than 3 minutes (for example, 3 minutes, 5 minutes, 10 minutes, and 15 minutes).
• the blowing process adopts a one blow to end (one shot to bottom) blowing method without reblowing (supplementary blowing) process, so as to avoid excessive oxidation of molten steel and increase of inclusions during the reblowing process.
• the C content at the smelting endpoint is controlled between 0.09% ⁇ 0.13% (for example, 0.09%, 0.10%, 0.11%, 0.12%, and 0.13%), and the tapping temperature is between 1625 ⁇ 1645 °C (for example, 1625 °C, 1630 °C, 1635 °C, 1640 °C, and 1645 °C).
• the tapping temperature is determined based on the solidification temperature of the molten steel, the degree of superheat during the continuous casting process, and the process temperature drop, so as to ensure the smooth pouring of the continuous casting.
• LF refining is performed after tapping without vacuum degassing; the purpose of not performing vacuum degassing is to ensure the content of N in the molten steel.
• the continuous casting process adopts a weak water cooling method, so as to effectively reduce the occurrence of cracks on the casting blanks.
• the specific water flow of the continuous casting process is 0.7 ⁇ 1.25L/kg (for example, 0.7L/kg, 0.8Ukg, 1.0L/kg, 1.2L/kg, and 1.25Ukg).
• the degree of superheat of the continuous casting furnace is strictly controlled, and the degree of superheat of the molten steel is 10 ⁇ 25 °C (for example, 10 °C, 15 °C, 20 °C, and 25 °C).
• the casting speed is 1.0 ⁇ 1.3 m/minutes (for example, 1.0m/minute, 1.1m/minute, 1.2m/minute, and 1.3m/minute).
• the control of low degree of superheat in the present invention is beneficial for improving casting speed (drawing speed), shortening pouring time, and reducing energy consumption;
• the tundish adopts alkaline covering agent to insulate the steel ladle and remove impurities from the steel ladle.
• the protective slag in the continuous casting process is divided into powder slag layer, sintered layer, and liquid slag layer during the dissolution process.
• deoxidation alloying is carried out during the tapping process in the converter smelting process, while slag washing is also carried out.
• the specific operation method of deoxidation alloying during the tapping process in the converter smelting process is: during the tapping process, silicon containing substances are selected for deoxidation, with an addition amount of 3.5 ⁇ 4.0kg/ton of steel (for example, 3.5kg/ton of steel, 3.6kg/ton of steel, 3.8kg/ton of steel, and 4.0kg/ton of steel); silicon manganese and vanadium nitrogen alloys are selected for alloying, wherein the vanadium nitrogen alloy (V content not less than 75%) is added in amount of 1 ⁇ 2 kg/ton of steel (for example, 1kg/ton of steel, 1.2kg/ton of steel, 1.4kg/ton of steel, 1.6kg/ton of steel, 1.8kg/ton of steel, 2kg/ton of steel).
• the present invention does not use aluminum for deoxidation.
• the slag filtrating (washing) is carried out using a substance containing CaO (with a CaO content of not less than 90%), with an addition amount of 3.5 ⁇ 4.0kg/ton of steel (for example, 3.5kg/ton of steel, 3.6kg/ton of steel, 3.8kg/ton of steel, and 4.0kg/ton of steel).
• the substance containing CaO needs to be added before the molten steel reaches 3/4.
• the argon blowing amount of argon stirring is 400 ⁇ 1000 L/minute (for example, 500 L/minute, 600 L/minute, 700 L/minute, 800 L/minute, and 900 L/minute), and the argon stirring time is 3 ⁇ 4 minutes (for example, 3 minutes, 3.2 minutes, 3.5 minutes, 3.8 minutes, and 4 minutes).
• the argon stirring time is 3 ⁇ 4 minutes (for example, 3 minutes, 3.2 minutes, 3.5 minutes, 3.8 minutes, and 4 minutes).
• weak argon stirring is adopted in the middle stage and end stage of LF refining, with the same argon blowing flow rate.
• the argon blowing amount of argon stirring is 100 ⁇ 200 L/minute (for example, 120 L/minute, 140 L/minute, 160 L/minute, and 180 L/minute), and the time of argon stirring is ⁇ 5 minutes; the total refining time is controlled within 40 ⁇ 50 minutes (for example, 40 minutes, 42 minutes, 45 minutes, 48 minutes, and 50 minutes), and the obtained N content is 100 ⁇ 2000 ppm (for example, 100 ppm, 500 ppm, 1000 ppm, 1500 ppm, 2000 ppm).
• the other component content meets the required molten steel composition content in the smelting process.
• the different water volume distribution is selected based on the different specifications of the casting blanks and the composition of the steel grade during the continuous casting process.
• the specific distribution of water volume in the continuous casting process is as follows: the water volume in the inner and outer arcs of the wide-side foot-roller of the casting blank accounts for about 8.0 ⁇ 10.0% of the total water volume (for example, 8.0%, 8.5%, 9.0%, 9.5%, and 10.0%), the water volume in the narrow-side foot-roller accounts for 3.4 ⁇ 4.5% of the total water volume (for example, 3.4%, 3.8%, 4.0%, 4.2%, and 4.5%), and the water volume in the inner and outer arcs of the second zone of the vertical bending section accounts for 11.0 ⁇ 15.9% of the total water volume (for example, 11.0%, 12.0%, 13.0%, 14.0%, 15.0%, 15.5%, and 15.9%), the water volume in the inner and outer arcs of the third zone accounts for 13.0 ⁇ 15.9% of the total water volume (for example, 13.0%, 14.0%, 15.0%, 15.5%, and 15.9%), the water volume in the inner and outer arcs of the third zone accounts for 13.0 ⁇ 15.9% of the total water volume (
• the beneficial effects of the present invention are: the production method for V-N microalloyed and surface-crack-free continuous casting blank presented by the invention improves the thermoplastic properties of the continuous casting blanks through reasonable composition design of V-N microalloying, combined with appropriate smelting and continuous casting processes, avoiding high-temperature brittle zones or having sufficient thermoplastic properties in the straightening range of the blanks to prevent surface cracks from occurring.
• the surface quality of the billets is good, without the need for cleaning the casting blanks, and the production efficiency is improved.
• the present invention provides a surface-crack-free continuous casting blanks V-N microalloyed steel.
• the V-N microalloyed steel is composed of the following chemical components by mass percentage: C: 0.09-0.13%, Si: 0.1-0.4%, Mn: 1.0-3.0%, P: ⁇ 0.05%, S: ⁇ 0.05%, V: 0.1-0.4%, N: 0.011-0.2%, and the balance of Fe and a small amount of unavoidable impurity elements.
• the present invention also provides a production method for preparing surface-crack-free microalloyed steel for continuous casting blanks with the above-mentioned chemical components, the method sequentially includes the following processes: converter smelting, LF refining, and continuous casting.
• the alkaline covering agent and low-carbon steel protective slag used in the production process of the continuous casting blank of the present invention are commonly used commercial products for producing microalloyed steel.
• the plasticity of steel is decreased, the occurrence rate of surface cracks of continuous casting blank is significantly higher than that of ordinary carbon steel blank, and problems such as transverse cracks, longitudinal cracks, and shape cracks occur.
• the contents of C are controlled, S is reduced, the use of a deoxidant is controlled, the inclusion morphology is changed, and the purity of steel is improved.
• a microalloyed steel with fine grains and good plasticity is obtained, thereby reducing the occurrence of surface cracks in a continuous casting blank of microalloyed steel , improving the surface quality of a continuous casting blank.
• This example provides a V-N microalloyed continuous casting blank and its production method, and the chemical composition of the continuous casting blank is shown in Table 1 by mass percentage.
• Table 1 The chemical component of the V-N microalloyed continuous casting blank from Example 1 Example chemical component (wt%), the balance of Fe and unavoidable impurity elements C Si Mn P S V N 1 0.10 0.23 1.62 0.014 0.007 0.12 0.012
• the production method sequentially includes the following processes: converter smelting, LF refining and continuous casting.
• a 120t converter is used for smelting, the smelting raw materials are molten iron and steel scrap, and the ratio of molten iron is controlled at 90%; nitrogen gas is used for blowing in the early stage of blowing and argon gas used for blowing in the later stage with 4 minutes of the argon gas blowing, and a gun-to-bottom type for blowing is carried out in the blowing process, absolutely eliminating the supplementary blowing process, thereby preventing the molten steel from being peroxided so as to improve the cleanliness of the molten steel.
• the C content at the smelting endpoint is controlled at 0.10wt%, and the tapping temperature is 1632 °C; deoxidation alloying and slag filtrating are carried out during tapping, silicon containing material is selected as deoxidizing agent with the addition amount of about 3.6kg/t steel; the alloyed raw material is vanadium nitrogen alloy (with a V content of 77 wt%) with an addition of about 1.6kg/ton of steel; and a substance containing CaO is selected for slag filtrating (with a CaO content of 90 wt%) with an added amount of 3.8kg/ton of steel.
• the steel ladle is directly transferred to the LF refining station for argon blowing refining after tapping; in the early stage of refining, the argon blowing rate at 400L/minute is selected for argon blowing stirring for 3 minutes , then silicon containing substances are added for deoxygenation, and a small amount of silicon manganese is added to adjust the Mn content; at the end stage of refining, the argon blowing rate is adjusted to 150L/minute and stirred for 6 minutes; the total refining time is controlled at 45 minutes, the N content obtained is 120 ppm and the content of other components meets the requirements of molten steel composition in the composition control process.
• the large ladle is protected with a long water port and a conical asbestos pad is added to ensure the air-tightness of the connection.
• a coal gas flame is firstly used to check air-tightness of the lower water port of the ladle and the bowl part of long water port. If the flame is sucked in, it indicates poor sealing at this location, and a new long water port is jointed. If the air-tightness meets the requirements, argon gas is introduced into the bowl part connection of the long water port to form an argon sealing state during the pouring process, further preventing oxygen and nitrogen increase in the molten steel caused by the loose connection between the bowl part of long water port and the lower water port of the ladle due to air intake .
• This example is the third furnace for casting, that is, a third furnace steel which is cast after the start of continuous casting.
• the degree of superheat is 20 °C, and the actual drawing speed is 1.1m/minute.
• the specific distribution of water volume with a specific water flow (specific amount of water) of 1.2 Ukg is as follows: the amount of water in the inner and outer arcs of the wide-side foot-roller of the casting blank accounts for about 8.6% of the total amount of water, the amount of water in the narrow-side foot-roller accounts for 3.5% of the total amount of water, and the amount of water in the inner and outer arcs of the second zone of the vertical bending section accounts for 15.8% of the total amount of water, the water volume in the inner and outer arcs of the third zone accounts for 15.6% of the total water volume, the water volume in the inner and outer arcs of the fourth zone accounts for 12.9% of the total water volume, the water volume in the inner and outer arcs of the fifth zone of arc section 1 accounts for 9.3% of the total water volume, the water volume in the inner and outer arcs of the sixth zone corresponding to arc sections 2 and 3 accounts for 12.4% of the total water volume, the water volume in the inner and outer arcs of
• the continuous casting blank obtained from the multi furnace steel cast by the above method has a cross-sectional area of 200mm * 2000mm, good surface quality, no cracks detected at low magnification, and no cracks observed on the surface of the casting blank during hot state observation, without the need for casting blank cleaning.
• This example provides a V-N microalloyed continuous casting blank, and the chemical composition of the continuous casting blank is shown in Table 2 by mass percentage.
• Table 2 The chemical component of the V-N microalloyed continuous casting blank from Example 2 Example chemical component (wt%), the balance of Fe and unavoidable impurity elements C Si Mn P S V N 2 0.09 0.40 1.00 0.014 0.006 0.25 0.032
• the production method sequentially includes the following processes: converter smelting, LF refining, and continuous casting.
• a 120t converter is used for smelting, the smelting raw materials are molten iron and steel scrap, and the ratio of molten iron is controlled at 89%; nitrogen gas is used for blowing in the early stage of blowing and argon gas used for blowing in the later stage with 3 minutes of the argon gas blowing, and a gun-to-bottom type for blowing is carried out in the blowing process, absolutely eliminating the supplementary blowing process .
• the C content at the smelting endpoint is controlled at 0.09t%, and the tapping temperature is 1630 °C.
• Deoxidation alloying and slag filtrating are carried out during tapping, and silicon containing material is selected as deoxidizing agent (that is, silicon carbide) with the addition amount of about 3.8 kg/t steel; the alloyed raw material is vanadium nitrogen alloy (with a V content of 77 wt%) with an addition of about 1.3 kg/ton of steel; and a substance containing CaO is selected for slag filtrating (with a CaO content of 90 wt%) with an added amount of 3.6 kg/ton of steel.
• silicon containing material that is, silicon carbide
• the alloyed raw material is vanadium nitrogen alloy (with a V content of 77 wt%) with an addition of about 1.3 kg/ton of steel
• a substance containing CaO is selected for slag filtrating (with a CaO content of 90 wt%) with an added amount of 3.6 kg/ton of steel.
• the steel ladle is directly transferred to the LF refining station for argon blowing refining after tapping, in the early stage of refining, the argon blowing rate at 400 L/minute is selected for argon blowing stirring for 4 minutes,and then silicon containing substances are added for deoxygenation; at the end stage of refining, the argon blowing rate is adjusted to 150L/minute and stirred for 7 minutes; the total refining time is controlled at 48 minutes, the N content obtained is 100 ppm, and the content of other components meets the requirements of molten steel composition in the composition control process.
• the large ladle is protected with a long water port and a conical asbestos pad is added to ensure the air-tightness of the connection.
• a coal gas flame is firstly used to check air-tightness of the lower water port and the bowl part of the long water port. If the flame is sucked in, it indicates poor sealing at this location, and a new long water port is jointed. If the air-tightness meets the requirements, argon gas is introduced into the bowl part connection of the long water port to form an argon sealing state during the pouring process, further preventing oxygen and nitrogen increase in the molten steel caused by the loose connection between the long water port bowl part and the lower water port of the ladle due to air intake.
• This example is the fourth furnace of steel poured after the continuous casting start.
• the degree of superheat is 15 °C, and the actual drawing speed is 1.2m/minute.
• the specific distribution of water volume with a specific water flow of 1.0L/kg is as follows: the water volume in the inner and outer arcs of the wide-side foot-roller of the casting blank accounts for about 8.1% of the total water volume, the water volume in the narrow-side foot-roller accounts for 4.3% of the total water volume, and the water volume in the inner and outer arcs of the second zone of the vertical bending section accounts for 11.4% of the total water volume, the water volume in the inner and outer arcs of the third zone accounts for 13.1% of the total water volume, the water volume in the inner and outer arcs of the fourth zone accounts for 12% of the total water volume, the water volume in the inner and outer arcs of the fifth zone of arc section 1 accounts for 9.0% of the total water volume, the water volume in the inner and outer arcs of the sixth zone corresponding to arc sections 2 and 3 accounts for 13.6% of the total water volume, the water volume in the inner and outer arcs of the seventh zone of the sections 4 ⁇ 5 accounts for
• the continuous casting blank obtained from the multi furnace steel cast by the above method has a cross-sectional area of 250 mm * 1800 mm, good surface quality, no cracks detected at low magnification, and no cracks observed on the surface of the casting blank during hot state observation, without the need for casting blank cleaning.

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• 2020
  • 2020-09-18 CN CN202010990234.0A patent/CN111996466B/zh active Active
• 2021
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