CN111996466B - V-N microalloyed steel and production method of V-N microalloyed continuous casting billet without surface cracks - Google Patents

V-N microalloyed steel and production method of V-N microalloyed continuous casting billet without surface cracks Download PDF

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CN111996466B
CN111996466B CN202010990234.0A CN202010990234A CN111996466B CN 111996466 B CN111996466 B CN 111996466B CN 202010990234 A CN202010990234 A CN 202010990234A CN 111996466 B CN111996466 B CN 111996466B
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continuous casting
steel
water amount
microalloyed
blowing
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CN111996466A (en
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霍孝新
杜林秀
麻衡
陈爱娇
王中学
杜传治
宁伟
刘悦
吴红艳
何康
赵立峰
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Laiwu Steel Group Yinshan Section Steel Co Ltd
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Laiwu Steel Group Yinshan Section Steel Co Ltd
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Priority to PCT/CN2021/118337 priority patent/WO2022017545A1/en
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    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/12—Ferrous alloys, e.g. steel alloys containing tungsten, tantalum, molybdenum, vanadium, or niobium
    • 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

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  • Engineering & Computer Science (AREA)
  • Materials Engineering (AREA)
  • Metallurgy (AREA)
  • Organic Chemistry (AREA)
  • Mechanical Engineering (AREA)
  • Manufacturing & Machinery (AREA)
  • Treatment Of Steel In Its Molten State (AREA)
  • Continuous Casting (AREA)

Abstract

The invention discloses a V-N microalloyed steel and a production method of a V-N microalloyed continuous casting billet without surface cracks. The V-N microalloyed steel comprises the following chemical components in percentage by mass: c: 0.09-0.13%, Si: 0.1-0.4%, Mn: 1.0-3.0%, P: less than or equal to 0.05 percent, S: less than or equal to 0.05 percent, V: 0.1-0.4%, N: 0.011-0.2%, and the balance of Fe and inevitable impurity elements. The continuous casting billet is subjected to component control according to the chemical components of the V-N microalloyed steel; the production method sequentially comprises the following steps: converter smelting, LF refining and continuous casting. According to the invention, through reasonable component design and smelting continuous casting process, the thermoplasticity of the continuous casting blank is improved, a high-temperature brittle region is avoided in a casting blank straightening region, or the thermoplasticity is good enough, so that no surface crack is generated, the surface quality of the casting blank is good, the casting blank does not need to be cleaned, and the production efficiency is improved.

Description

V-N microalloyed steel and production method of V-N microalloyed continuous casting billet without surface cracks
Technical Field
The invention belongs to the field of continuous casting processes, and particularly relates to a production method of a V-N microalloyed continuous casting billet without surface cracks.
Background
Microalloyed steel is steel for engineering structure which has been rapidly developed in nearly half a century, has the effects of fine grain strengthening and precipitation strengthening in steel by adding various alloy elements (Nb, V, Ti and the like), improves the strength and toughness of steel, is widely applied to various fields such as bridges, buildings, ships, automobiles, high-pressure containers and the like, has better application prospect, and is a main product in the modern steel industry. The reserves of the microalloy elements in China are rich, and the microalloy steel has obvious advantages in the aspect of developing microalloy steel. Typical Q550 and Q460 grade low alloy high strength steels have good market applications.
In the industrial production process, the microalloying is widely applied due to the strengthening effect of microalloy elements, but in the continuous casting process, the plasticity of steel is reduced due to the precipitation of carbonitrides of the microalloy elements, the occurrence rate of cracks on the surface of a continuous casting billet is obviously higher than that of a plain carbon steel casting billet, the problems of transverse cracking, longitudinal cracking, shape cracking and the like occur, the quality of the continuous casting billet is influenced, and the large-scale production is not facilitated, which is a typical problem of microalloying casting billets. The three elements of niobium, vanadium and titanium are three elements which are relatively widely applied to microalloy steel, wherein the niobium element has the largest influence on the plasticity of the steel and has the most obvious effect on reducing the thermoplasticity of the steel. Researches show that the addition of Ti can reduce the brittleness of niobium and vanadium microalloy steel, but the cost is not easy to control.
Therefore, the problem of cost and micro-alloy steel casting blank cracks is comprehensively considered, and the development of a casting blank production process with low cost and no casting blank cracks is a typical process difficulty, so that the performance of the micro-alloy steel is ensured, the normal operation of a continuous casting process is ensured, and the surface quality of the casting blank is improved.
Disclosure of Invention
Aiming at the problem that cracks are easy to appear on the surface of a casting blank during continuous casting of microalloyed steel in the prior art, the invention provides V-N microalloyed steel for a continuous casting blank without surface cracks, wherein the continuous casting blank without surface cracks with the section of (150-350) mm (1250-2400) mm is produced through reasonable component design and smelting continuous casting process, and the surface quality of the continuous casting blank is improved.
In order to achieve the purpose, the technical scheme adopted by the invention is as follows:
the V-N microalloyed steel comprises the following chemical components in percentage by mass: c: 0.09-0.13%, Si: 0.1-0.4%, Mn: 1.0-3.0%, P: less than or equal to 0.05 percent, S: less than or equal to 0.05 percent, V: 0.1-0.4%, N: 0.011-0.2%, and the balance of Fe and inevitable impurity elements.
According to the invention, the chemical components of the microalloyed steel are reasonably designed by utilizing the characteristic of low thermoplastic valley point of the vanadium-containing steel, so that the occurrence of surface cracks of the casting blank during continuous casting of the microalloyed steel is reduced.
In the invention, the V element and the N element have extremely strong affinity, and the later period of combination with the TMCP method can play a role in increasing the strength and toughness of the tissue through two typical strengthening mechanisms of fine grain strengthening and precipitation strengthening.
Meanwhile, the reserves of vanadium ores in partial areas of China are rich, such as Chengde and Panzhihua areas, and the like, have good cost advantages, and the price of N is relatively low. Therefore, the V-N microalloying is adopted, which is beneficial to reducing the production cost of the continuous casting billet.
The invention also provides a production method of the V-N microalloyed continuous casting billet without surface cracks, which produces the continuous casting billet according to the chemical composition of the V-N microalloyed steel; the method sequentially comprises the following steps: converter smelting, LF refining and continuous casting.
In the above production method, as a preferable mode, the cross-sectional specification of the continuous casting slab is (150 to 350) mm × (1250 to 2400) mm.
In the above production method, preferably, in the converter smelting step, the molten iron ratio is controlled to be 88.0% to 91.0% (e.g., 88.0%, 89.0%, 90.0%, 91.0%), a top-bottom combined blowing mode is adopted throughout the process, and nitrogen gas is blown first and then argon gas is blown during the blowing process, thereby stirring the molten steel and promoting the progress of the chemical reaction in the converter. Wherein the argon blowing time is not less than 3min (e.g., 3min, 5min, 10min, 15 min).
In the production method, as a preferable mode, in the smelting process of the converter, the blowing process adopts a one-gun bottom-up blowing process without a blowing-supplementing process so as to avoid molten steel peroxidation in the blowing-supplementing process and increase of inclusions.
In the above production method, preferably, in the converter smelting step, the content of the smelting end point C is controlled to be 0.09 to 0.13% (e.g., 0.09%, 0.10%, 0.11%, 0.12%, 0.13%), the tapping temperature is 1625 to 1645 ℃ (e.g., 1625 ℃, 1630 ℃, 1635 ℃, 1640 ℃, and 1645 ℃), and the tapping temperature is determined based on the molten steel solidification temperature, the degree of superheat during continuous casting, and the process temperature drop, thereby ensuring smooth casting.
In the production method, as a preferred mode, LF refining is carried out after tapping, and vacuum degassing refining is not carried out; the purpose of not performing vacuum degassing is to secure the N content in the molten steel.
In the above production method, as a preferable mode, in the continuous casting process, a weak water cooling mode is adopted in the continuous casting process, so that the occurrence of casting blank cracks is effectively reduced.
In the production method, as a preferred mode, in the continuous casting process, protective casting is adopted, the water gap is immediately closed by a large ladle when the alarm is given at the final stage of casting, the water gap is strictly forbidden to be opened again after being closed, the tundish is covered by an alkaline covering agent, the liquid level is ensured to be well covered, and the crystallizer is made of low-carbon steel covering slag.
In the above production method, preferably, the specific water amount in the continuous casting process is 0.7 to 1.25L/kg (e.g., 0.7L/kg, 0.8L/kg, 1.0L/kg, 1.2L/kg, 1.25L/kg).
In the above production method, preferably, in the continuous casting step, the degree of superheat of the molten steel is controlled strictly to be 10 to 25 ℃ (for example, 10 ℃, 15 ℃, 20 ℃, 25 ℃).
In the above production method, as a preferable mode, in the continuous casting step, the drawing rate is 1.0 to 1.3m/min (e.g., 1.0m/min, 1.1m/min, 1.2m/min, 1.3m/min) during the continuous casting.
The invention controls low superheat degree, is beneficial to improving the pulling speed, shortening the pouring time and reducing the energy consumption; the tundish adopts an alkaline covering agent for preserving the heat of the ladle and removing impurities in the ladle.
In the above production method, as a preferable mode, in the continuous casting process, the mold flux is divided into a powder layer, a sintered layer, and a liquid layer during the dissolution.
In the above production method, as a preferable mode, in the converter smelting step, deoxidation alloying is performed during tapping, and slag washing is performed at the same time.
In the above production method, as a preferred aspect, in the converter smelting step, the specific operation method of the deoxidation alloying in the tapping process is: deoxidizing by using silicon-containing substances in the tapping process, wherein the adding amount of the silicon-containing substances is 3.5-4.0 kg/ton steel (for example, 3.5 kg/ton steel, 3.6 kg/ton steel, 3.8 kg/ton steel and 4.0 kg/ton steel); silicon-manganese and vanadium-nitrogen alloys are selected for alloying, wherein the addition amount of the vanadium-nitrogen alloys (the V content is not less than 75%) is 1-2 kg/ton steel (for example, 1 kg/ton steel, 1.2 kg/ton steel, 1.4 kg/ton steel, 1.6 kg/ton steel, 1.8 kg/ton steel and 2 kg/ton steel). The invention does not use aluminum for deoxidation.
In the above production method, as a preferable mode, in the converter smelting step, the slag washing is performed with a CaO-containing substance (CaO content is not less than 90%) added in an amount of 3.5 to 4.0 kg/ton of steel (for example, 3.5 kg/ton of steel, 3.6 kg/ton of steel, 3.8 kg/ton of steel, 4.0 kg/ton of steel) before the molten steel is discharged to 3/4 in the tapping process.
In the production method, as a preferable mode, in the LF refining, in an early stage of the LF refining, an argon blowing amount for argon blowing stirring is 400 to 1000L/min (e.g., 500L/min, 600L/min, 700L/min, 800L/min, 900L/min), an argon blowing stirring time is 3 to 4min (e.g., 3min, 3.2min, 3.5min, 3.8min, 4min), no bare molten steel is paid attention to while stirring, and then a silicon-containing substance is used for deoxidation, and the components are finely adjusted under the argon blowing stirring condition.
In the production method, as a preferable mode, in the LF refining, weak argon is adopted for stirring in the middle stage and the final stage of the LF refining, and the argon blowing flow is the same.
In the production method, as a preferable mode, in the LF refining, the argon blowing amount for argon blowing and stirring is 100-200L/min (for example, 120L/min, 140L/min, 160L/min, 180L/min) at the final stage of the LF refining, and the argon blowing and stirring time is not less than 5 min; the total refining time is controlled to be 40-50 min (for example, 40min, 42min, 45min, 48min and 50min), the obtained N content is 100-2000 ppm (for example, 100ppm, 500ppm, 1000ppm, 1500ppm and 2000ppm), and the content of other components meets the content of molten steel components required in the smelting process.
In the continuous casting process, different water distribution is selected according to different specifications of the casting blank and different steel type components in the continuous casting process.
In the above production method, as a preferred mode, in the continuous casting step, the water amount in the continuous casting process is specifically distributed as follows: the water content of the inner and outer arcs of the wide-face foot roll of the casting blank is about 8.0-10.0% (e.g., 8.0%, 8.5%, 9.0%, 9.5%, 10.0%) of the total water content, the water content of the narrow-face foot roll is 3.4-4.5% (e.g., 3.4%, 3.8%, 4.0%, 4.2%, 4.5%) of the total water content, the water content of the inner and outer arcs of the two zones of the vertical bending section is 11.0-15.9% (e.g., 11.0%, 12.0%, 13.0%, 14.0%, 15.0%, 15.5%, 15.9%) of the total water content, the water content of the inner and outer arcs of the three zones is 13.0-15.9% (e.0%, 14.0%, 15.5%, 15.9%) of the water content of the inner and outer arcs of the four zones is 12.0-13.0% (e.0%, 12.2%, 12.6%, 12.8%, 13.0%, 1.0% of the total water content of the inner and the outer arcs of the total water content of the five zones is 12.0% (e.0%, e.5% of the total water content of the inner and the outer arcs of the total water content of the inner and the arcs of the segments is 0% (e.0% of the total water content of the arcs of the segments is 12.0% of the segments, 12.0%, 12.5%, 13.0%, 13.5%, 13.8%, 13.0%), 8.0-11.5% of the total water amount of the inner and outer arcs of the seven regions of the 4-5 sections (for example, 8.0%, 8.5%, 9.0%, 9.5%, 10.0%, 11.0%, 11.5%, 10.0%), 8.0-11.5% of the total water amount of the inner and outer arcs of the eight regions of the 6-7 and 8 sections for straightening (for example, 8.0%, 8.5%, 9.0%, 9.5%, 10.0%, 11.0%, 11.5%, 10.0%), and the rest of the water amount is distributed to the horizontal section.
In the invention, the technical characteristics can be freely combined to form a new technical scheme under the condition of not conflicting with each other.
The steps and processes not described in detail in the production method provided by the present invention are conventional processes in the art.
Compared with the prior art, the invention has the beneficial effects that:
according to the production method of the V-N microalloyed continuous casting billet without surface cracks, the thermoplasticity of the continuous casting billet is improved through reasonable component design of V-N microalloying and a proper smelting continuous casting process, so that a high-temperature brittleness area is avoided in a casting billet straightening area, or the thermoplasticity is good enough to prevent surface cracks from being generated, the surface quality of the casting billet is good, the casting billet does not need to be cleaned, and the production efficiency is improved.
Detailed Description
The technical solution of the present invention will be described in detail with reference to the following examples. The various examples are provided by way of explanation of the invention, and not limitation of the invention. In fact, it will be apparent to those skilled in the art that modifications and variations can be made in the present invention without departing from the scope or spirit thereof. For instance, features illustrated or described as part of one embodiment, can be used with another embodiment to yield a still further embodiment. It is therefore intended that the present invention encompass such modifications and variations as fall within the scope of the appended claims and equivalents thereof.
According to the embodiment of the invention, the V-N microalloyed steel for the continuous casting billet without the surface cracks comprises the following chemical components in percentage by mass: c: 0.09-0.13%, Si: 0.1-0.4%, Mn: 1.0-3.0%, P: less than or equal to 0.05 percent, S: less than or equal to 0.05 percent, V: 0.1-0.4%, N: 0.011-0.2%, and the balance of Fe and a small amount of inevitable impurity elements.
The invention also provides a production method for preparing the microalloy steel of the continuous casting billet without the surface cracks, which sequentially comprises the following working procedures: converter smelting, LF refining and continuous casting.
The alkaline covering agent and the low-carbon steel covering slag used in the production process of the continuous casting slab are common commercial products for producing the microalloy steel.
Because carbon nitride is separated out in the continuous casting process, the plasticity of steel is reduced, the incidence rate of surface cracks of the continuous casting billet is obviously higher than that of a plain carbon steel casting billet, and the problems of transverse cracks, longitudinal cracks, shape cracks and the like occur.
Example 1
In the V-N microalloyed continuous casting billet and the production method thereof provided by the embodiment, the chemical components of the continuous casting billet are shown in the table 1 according to the mass percentage.
TABLE 1 chemical composition of V-N microalloyed steel continuous casting billet in example 1
Figure BDA0002690612670000061
The production method sequentially comprises the following steps: converter smelting, LF refining and continuous casting.
(1) Smelting in a converter:
a120 t converter is adopted for smelting in the converter smelting process, smelting raw materials are molten iron and scrap steel, the molten iron ratio is controlled to be 90%, nitrogen gas is adopted for blowing in the blowing early stage, argon gas is adopted for blowing in the later stage, the argon blowing time is 4min, the blowing process adopts a one-gun bottom-to-bottom blowing mode, and the reblowing process is firmly stopped, so that molten steel is prevented from being oxidized excessively, and the cleanliness of the molten steel is improved.
Controlling the content of C at the smelting end point to be 0.10 wt%, and controlling the tapping temperature to be 1632 ℃; deoxidizing alloying and slag washing are carried out in the tapping process, a silicon-containing substance is selected as a deoxidizing agent, and the addition amount of the silicon-containing substance is about 3.6kg per ton of steel; the alloying raw material is vanadium-nitrogen alloy (V content is 77 wt%), and about 1.6 kg/ton steel is added; the slag washing is carried out by using CaO-containing substances (CaO content is 90 wt%) and adding 3.8kg of CaO per ton of steel.
(2) LF refining:
directly transferring the steel ladle to an LF refining station for argon blowing refining after tapping, selecting 400L/min for argon blowing and stirring at the early stage of refining, adding a silicon-containing substance for deoxidation after 3min, and adding a small amount of silicomanganese to adjust the Mn content; adjusting the argon blowing amount to 150L/min at the final stage of refining and stirring for 6 min; the total refining time is controlled at 45min, the obtained N content is 120ppm, and the content of other components meets the content of molten steel components required in the component control process.
(3) Continuous casting:
in the protective casting link, the ladle is protected by a long nozzle, and a conical asbestos pad is added to ensure the tightness of the joint.
After casting is started, firstly, gas flame is utilized to carry out airtightness test on a ladle down nozzle and a long nozzle bowl, if flame is absorbed, the airtightness of the position is not good, and the long nozzle is sleeved again. If the tightness meets the requirement, argon is introduced into the joint of the long nozzle bowl part in the casting process to form an argon sealing state, so that the condition that the oxygen and nitrogen of molten steel are increased due to air suction caused by untight connection between the long nozzle bowl part and the ladle drain nozzle is further prevented.
The ladle alarms at the end of pouring to immediately close the water gap, and the water gap is strictly forbidden to be opened again after being closed. The tundish is covered by an alkaline covering agent, and the crystallizer is protected by low-carbon steel protective slag (P0050 special for Pinchuan 250).
In the example, the steel of the 3 rd furnace is poured after the 3 rd furnace is poured, namely the superheat degree is 20 ℃, and the actual drawing speed is 1.1 m/min.
In the continuous casting process, the specific water amount of 1.2L/kg is specifically distributed as follows: the water content of the inner arc and the outer arc of the wide-surface foot roll of the casting blank is about 8.6 percent of the total water content, the water content of the narrow-surface foot roll is 3.5 percent of the total water content, the water content of the inner arc and the outer arc of the second region of the vertical bending section is 15.8 percent of the total water content, the water content of the inner arc and the outer arc of the third region is 15.6 percent of the total water content, the water content of the inner arc and the outer arc of the fourth region is 12.9 percent of the total water content, the water content of the inner arc and the outer arc of the fifth region of the arc 1 section is 9.3 percent of the total water content, the water content of the inner arc and the outer arc of the sixth region corresponding to the arc 2 and 3 sections is 12.4 percent of the total water content, the water content of the inner arc and the outer arc of the seventh region of the 4-5 sections is 8.1 percent of the total water content, and the water content of the inner arc and the outer arc and the inner arc and the outer arc of the eight regions of the straightening sections 6, 7 and 8 sections is distributed to the horizontal section.
The implementation effect is as follows: the continuous casting billet obtained by the multi-furnace steel poured by the method has the advantages that the section is 200 mm-2000 mm, the surface quality is good, no crack is generated in low-power detection, no crack is generated on the surface of the casting billet in thermal state observation, and the casting billet does not need to be cleaned.
Example 2
In this example, a V-N microalloyed continuous casting slab without surface cracks was produced, the chemical composition of which is shown in Table 2 by mass%.
TABLE 2 chemical composition of V-N microalloyed steel continuous casting billet in example 2
Figure BDA0002690612670000081
The production method sequentially comprises the following working procedures: converter smelting, LF refining and continuous casting.
(1) Smelting in a converter:
a120 t converter is adopted for smelting in the smelting process, the smelting raw materials are molten iron and scrap steel, the molten iron ratio is controlled to be 89%, nitrogen gas blowing is adopted in the blowing early stage, argon gas blowing is adopted in the later stage, the argon blowing time is 3min, a one-gun bottom blowing mode is adopted in the blowing process, and the reblowing process is firmly avoided.
The smelting end point C content is controlled to be 0.09 wt%, and the tapping temperature is 1630 ℃.
Deoxidizing alloying and slag washing are carried out in the tapping process, and a silicon-containing substance (namely silicon carbide) is selected as a deoxidizing agent, and the addition amount of the deoxidizing agent is about 3.8 kg/ton of steel; the alloying raw material is vanadium-nitrogen alloy (V content is 77 wt%), and about 1.3 kg/ton steel is added; the slag washing is carried out by using CaO-containing substances (CaO content is 90 wt%) and adding 3.6 kg/ton steel.
(2) LF refining:
directly transferring the steel ladle to an LF refining station for argon blowing refining after tapping, wherein the argon blowing amount in the early stage of refining is 400L/min for argon blowing and stirring for 4min, and then adding a silicon-containing substance for deoxidation; adjusting the argon blowing amount to 150L/min at the final stage of refining and stirring for 7 min; the total refining time is controlled at 48min, the obtained N content is 100ppm, and the content of other components meets the content of molten steel components required in the component control process.
(3) Continuous casting:
in the protective casting link, the ladle is protected by a long nozzle, and a conical asbestos pad is added to ensure the tightness of the joint. After casting is started, firstly, gas flame is utilized to carry out airtightness test on a ladle down nozzle and a long nozzle bowl, if flame is absorbed, the airtightness of the position is not good, and the long nozzle is sleeved again. If the tightness meets the requirement, argon is introduced into the joint of the long nozzle bowl part in the casting process to form an argon sealing state, so that the condition that the oxygen and nitrogen of molten steel are increased due to air suction caused by untight connection between the long nozzle bowl part and the ladle drain nozzle is further prevented. The ladle alarms at the end of pouring to immediately close the water gap, and the water gap is strictly forbidden to be opened again after being closed. The tundish is covered by an alkaline covering agent, and the crystallizer is protected by low-carbon steel covering slag (special P0027-3 for Pinchuan 250).
The example is the 4 th furnace steel which is continuously cast after casting, the superheat degree is 15 ℃, and the actual drawing speed is 1.2 m/min.
In the continuous casting process, the specific water amount of 1.0L/kg is specifically distributed as follows: the water content of the inner arc and the outer arc of the wide-surface foot roller of the casting blank is about 8.1 percent of the total water content, the water content of the narrow-surface foot roller is 4.3 percent of the total water content, the water content of the inner arc and the outer arc of the second region of the vertical bending section is 11.4 percent of the total water content, the water content of the inner arc and the outer arc of the third region is 13.1 percent of the total water content, the water content of the inner arc and the outer arc of the fourth region is 12 percent of the total water content, the water content of the inner arc and the outer arc of the fifth region of the arc 1 section is 9.0 percent of the total water content, the water content of the inner arc and the outer arc of the sixth region corresponding to the arc 2 and 3 sections is 13.6 percent of the total water content, the water content of the inner arc and the outer arc of the seventh region of the 4-5 sections is 11.2 percent of the total water content, and the water content of the inner arc and the outer arc of the eight regions of the straightening sections 6, 7 and 8 sections is 11.3 percent, and the rest water content is distributed to the horizontal section.
The implementation effect is as follows: the continuous casting billet obtained by the multi-furnace steel poured by the method has the specification of 250mm x 1800mm, good surface quality, no obvious cracks in low-power detection, no obvious cracks on the surface of the casting billet in thermal state observation, and no need of cleaning the casting billet.
The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention, and various modifications and changes may be made by those skilled in the art. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims (6)

1. The V-N microalloyed continuous casting billet without surface cracks is characterized by comprising the following chemical components in percentage by mass: c: 0.09-0.13%, Si: 0.1-0.4%, Mn: 1.0-3.0%, P: less than or equal to 0.05 percent, S: less than or equal to 0.05 percent, V: 0.1-0.4%, N: 0.011-0.2%, and the balance of Fe and inevitable impurity elements; the production method of the V-N microalloyed continuous casting billet without surface cracks sequentially comprises the following steps: converter smelting, LF refining and continuous casting;
in the LF refining process, in the early stage of LF refining, the argon blowing amount for argon blowing and stirring is 400-1000L/min, the argon blowing and stirring time is 3-4 min, a silicon-containing substance is adopted for deoxidation, and the components are finely adjusted under the condition of argon blowing and stirring; in the final stage of LF refining, the argon blowing amount for argon blowing and stirring is 100-200L/min, and the argon blowing and stirring time is more than or equal to 5 min; controlling the total refining time to be 40-50 min, wherein the obtained N content is 100-2000 ppm;
in the continuous casting procedure, a weak water cooling mode is adopted in the continuous casting process; protective pouring is adopted in the continuous casting process, the water gap is closed immediately when the large ladle alarms at the final stage of pouring, the water gap is strictly forbidden to be opened again after being closed, the tundish is covered by an alkaline covering agent, and the crystallizer is made of low-carbon steel covering slag; the specific water amount in the continuous casting process is 0.7-1.25L/kg; the superheat degree of the molten steel is 10-25 ℃; in the continuous casting process, the drawing speed is 1.0-1.3 m/min.
2. The V-N microalloyed surface crack-free billet as claimed in claim 1, wherein the cross-sectional gauge of the billet is (150-350) mm (1250-2400) mm.
3. The V-N microalloyed continuous casting slab without surface cracks as claimed in claim 1 or 2, wherein in the converter smelting process, the molten iron ratio is controlled to be 88.0wt% -91.0 wt%, a top-bottom combined blowing mode is adopted in the whole process, and nitrogen is blown firstly and then argon is blown in the blowing process; wherein the argon blowing time is not less than 3 min;
the blowing process adopts a one-gun bottom-reaching type blowing without a complementary blowing process;
the content of C at the smelting end point is controlled to be 0.09-0.13 wt%, and the tapping temperature is 1625-1645 ℃.
4. The V-N microalloyed continuous casting billet without surface cracks as claimed in claim 3, characterized in that LF refining is carried out after tapping, and a vacuum degassing refining process is not carried out.
5. The V-N microalloyed continuous casting billet without surface cracks as claimed in claim 1, wherein in the converter smelting process, deoxidation alloying is carried out during tapping, and simultaneously slag washing is carried out;
the specific operation method of the deoxidation alloying comprises the following steps: deoxidizing by using a silicon-containing substance in the tapping process, wherein the adding amount is 3.5-4.0 kg per ton of steel; alloying by using silicomanganese and vanadium-nitrogen alloy, wherein the addition amount of the vanadium-nitrogen alloy is 1-2 kg per ton of steel;
the slag washing is carried out by using CaO-containing substances, the addition amount is 3.5-4.0 kg/ton of steel, and the CaO-containing substances need to be added before molten steel is discharged to 3/4.
6. The V-N microalloyed continuous casting billet without surface cracks as claimed in claim 1, wherein the water amount in the continuous casting process is specifically distributed as follows: the water amount of the inner arc and the outer arc of the wide-surface foot roller of the casting blank accounts for 8.0-10.0% of the total water amount, the water amount of the narrow-surface foot roller accounts for 3.4-4.5% of the total water amount, the water amount of the inner arc and the outer arc of the second region of the vertical bending section accounts for 11.0-15.9% of the total water amount, the water amount of the inner arc and the outer arc of the third region accounts for 13.0-15.9% of the total water amount, the water amount of the inner arc and the outer arc of the fifth region of the arc 1 section accounts for 8.5-9.5% of the total water amount, the water amount of the inner arc and the outer arc of the six regions corresponding to the arc 2 and the 3 sections accounts for 12.0-14.0% of the total water amount, the water amount of the inner arc and the outer arc of the seven regions of the 4-5 sections accounts for 8.0-11.5% of the total water amount, the inner arc and the outer arc of the eight regions of the 6-straightening section and the 8 section, and the rest water amount is distributed to the horizontal section.
CN202010990234.0A 2020-09-18 2020-09-18 V-N microalloyed steel and production method of V-N microalloyed continuous casting billet without surface cracks Active CN111996466B (en)

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