阅读说明：本技术 一种高铝高钒板坯n含量的控制方法 (Control method for N content of high-aluminum high-vanadium plate blank ) 是由 王军 邝春福 彭友全 杨晓东 卓钧 邱伟 张彦恒 于 2020-07-29 设计创作，主要内容包括：本发明提供了一种高铝高钒板坯N含量的控制方法,包括依次进行的LD-LF-RH-CC,包括以下步骤：在LD阶段：在高铝高钒钢冶炼中采用底吹供气模式,吹炼后期采用低枪位操作,在冶炼后期加入炉渣发泡剂；在RH阶段：真空室本体与浸入管对接焊接后采用渗透法进行探伤并焊补,所述浸入管寿命≤50次；在CC阶段：采用双氩封长水口浇注。本申请在LD阶段、RH阶段以及CC阶段严格控制N的引入,而使得最终制备的高铝高钒板坯N含量较低；经过工业生产,本申请生产的高铝高钒板坯N含量≤40ppm。(The invention provides a method for controlling the N content of a high-aluminum high-vanadium plate blank, which comprises the steps of sequentially performing LD-LF-RH-CC and the following steps: in the LD stage: a bottom blowing gas supply mode is adopted in the smelting of high-aluminum high-vanadium steel, the low lance position operation is adopted in the later stage of blowing, and a slag foaming agent is added in the later stage of smelting; in the RH phase: carrying out flaw detection and welding repair by adopting a penetration method after butt welding of the vacuum chamber body and the immersion pipe, wherein the service life of the immersion pipe is less than or equal to 50 times; in the CC stage: and (4) pouring by adopting a double-argon-sealed long nozzle. The introduction of N is strictly controlled in an LD stage, an RH stage and a CC stage, so that the finally prepared high-aluminum high-vanadium plate blank has low N content; through industrial production, the content of N in the high-aluminum high-vanadium plate blank produced by the method is less than or equal to 40 ppm.)

1. The method for controlling the N content of the high-aluminum high-vanadium slab comprises the steps of LD-LF-RH-CC which are sequentially carried out, and is characterized by comprising the following steps:

in the LD stage: a bottom blowing gas supply mode is adopted in the smelting of high-aluminum high-vanadium steel, the low lance position operation is adopted in the later stage of blowing, and a slag foaming agent is added in the later stage of smelting;

in the RH phase: carrying out flaw detection and welding repair by adopting a penetration method after butt welding of the vacuum chamber body and the immersion pipe, wherein the service life of the immersion pipe is less than or equal to 50 times;

in the CC stage: and (4) pouring by adopting a double-argon-sealed long nozzle.

2. The control method according to claim 1, characterized in that the bottom-blowing air supply intensity in the bottom-blowing air supply mode is > 0.03m³V (min. t) steel; and the gas in the bottom blowing gas supply mode is argon.

3. The control method according to claim 1, characterized in that in the LD stage, the scrap consumption is less than or equal to 40kg/t of high-aluminum high-vanadium steel; the end point carbon is 0.04-0.05%.

4. A control method according to claim 1, characterized in that titanium alloying is carried out with a titanium sponge alloy in the RH stage.

5. The control method according to claim 1, wherein an argon protection pipeline is arranged outside the tundish in the CC stage, and a fiber sealing ring is arranged outside the argon protection pipeline.

6. The control method according to claim 1, wherein in the CC stage, a flow field of the tundish is optimized so that a maximum flow velocity of the molten steel surface of the tundish is 0.158 m/s.

7. The control method of claim 1, wherein after the LD stage is completed, the nitrogen content of the molten steel is controlled from 19 × 10 on average^-6To less than 13 × 10^-6。

8. The method of claim 1, wherein the nitrogen content of the molten steel after the RH stage is completed is controlled to be 6 × 10 on average^-6The above is reduced to less than 2 × 10^-6。

9. The control method according to any one of claims 1 to 8, wherein the high-aluminum high-strength slab comprises the following components: 0.33-0.35 wt% of C, 0.50-0.70 wt% of Si, 1.70-1.90 wt% of Mn, 0.20-0.28 wt% of Cr, 0.030-0.040 wt% of Nb, 0.15-0.17 wt% of V, 0.0015-0.0030 wt% of B, 0.50-0.60 wt% of Als, and the balance Fe.

Technical Field

The invention relates to the technical field of high-aluminum high-vanadium steel smelting, in particular to a method for controlling the N content of a high-aluminum high-vanadium plate blank.

Background

Nitrogen is a harmful element in high-grade steel represented by automobile panels, which reduces the plasticity and impact toughness of steel, causes cold brittleness of steel like phosphorus, and forms nitride inclusions with elements such as titanium, aluminum and the like in steel, which deteriorates the surface quality of steel and reduces the yield^-6The following. The LD-LF-RH-CC process flow is adopted in the high-grade steel production represented by an automobile panel in the West Chang steel plant, because semisteel is adopted for steel making, the initial carbon content in the semisteel is lower, the difficulty of converter denitrification is higher than that of other steel plants, an LF process is added in the process flow, the nitrogen absorption probability of molten steel is increased, and meanwhile, the nitrogen increase amount in the RH and continuous casting steel casting processes is higher. The problem of controlling the nitrogen content has become a bottleneck for restricting the research and development of high-grade steel represented by automobile panels and an important restriction factor for comprehensively utilizing vanadium and titanium resources in Panxi area.

The vanadium titano-magnetite in Panxi area is a composite ore which mainly contains iron and contains multiple metal elements such as titanium, vanadium, chromium and the like. The titanomagnetite is extracted by adopting blast furnace ironmaking-converter vanadium extractionAnd (5) processing. The existing process only recycles iron and vanadium, and a large amount of titanium enters blast furnace slag and has low content (TiO in the slag)₂About 22 percent) of the vanadium-titanium magnetite, the smelted molten iron is rich in a large amount of vanadium elements, the molten iron is subjected to a vanadium extraction process, vanadium is removed in the form of vanadium slag and then enters a vanadium product process for recycling, the remaining molten iron is called semi-steel, and the converter raw material of the Xichang steel vanadium smelting plant adopts semi-steel for smelting, and the smelting process has the remarkable characteristics that the smelting heat source is insufficient, the silicon elements in the molten iron are completely oxidized after the vanadium extraction process, in order to ensure the grade of the vanadium slag, a large amount of cooling agent is added into the vanadium extraction converter while oxygen is blown, the temperature in the converter is controlled, and the carbon content in the semi-steel is low^-6The nitrogen content in the molten steel begins to decrease after oxygen blowing in the converter smelting begins, the nitrogen content in the molten steel reaches the minimum when the carbon is drawn, and the molten steel absorbs nitrogen to different degrees when the carbon is drawn and the smelting endpoint appears, statistics shows that the average denitrification rate of the molten steel entering the converter to the carbon drawing converter can reach 75.4 percent, the denitrification rate of the molten steel entering the converter to the endpoint is reduced to 57.8 percent, and the average nitrogen of the molten steel is only 11 × 10 when the carbon is drawn^-6The average nitrogen of the end point molten steel reaches 17 × 10^-6The above. Therefore, the nitrogen content of the molten steel is at a lower level during carbon drawing, and the nitrogen absorption of the molten steel is more serious from the carbon drawing to the end point of the converter. Compared with other domestic plants, the high-grade steel grades of semisteel smelting represented by automobile panels are influenced by a semisteel furnace-entering heat source, the end temperature of the converter is insufficient, and the nitrogen content of the end molten steel is high due to the fact that the end molten steel is over oxidized. Therefore, in order to improve the application of high-strength high-aluminum high-vanadium steel, it is necessary to provide a method for effectively reducing the content of N.

Disclosure of Invention

The invention aims to provide a method for controlling the N content of a high-aluminum high-vanadium plate blank, and the method can effectively reduce the N content.

In view of the above, the application provides a method for controlling the N content of a high-aluminum high-vanadium slab, which includes the sequential steps of LD-LF-RH-CC, and includes the following steps:

in the LD stage: a bottom blowing gas supply mode is adopted in the smelting of high-aluminum high-vanadium steel, the low lance position operation is adopted in the later stage of blowing, and a slag foaming agent is added in the later stage of smelting;

in the RH phase: carrying out flaw detection and welding repair by adopting a penetration method after butt welding of the vacuum chamber body and the immersion pipe, wherein the service life of the immersion pipe is less than or equal to 50 times;

in the CC stage: and (4) pouring by adopting a double-argon-sealed long nozzle.

Preferably, the intensity of bottom-blowing air supply in the bottom-blowing air supply mode is greater than 0.03m³V (min. t) steel; and the gas in the bottom blowing gas supply mode is argon.

Preferably, in the LD stage, the consumption of scrap steel is less than or equal to 40kg/t of high-aluminum high-vanadium steel; the end point carbon is 0.04-0.05%.

Preferably, titanium alloying is performed with a titanium sponge alloy in the RH stage.

Preferably, in the CC stage, an argon protection pipeline is arranged outside the tundish, and a fiber sealing ring is arranged outside the argon protection pipeline.

Preferably, in the CC stage, a flow field of the tundish is optimized in the tundish, so that the maximum flow velocity of the molten steel surface of the tundish is 0.158 m/s.

Preferably, after the LD stage is finished, the nitrogen content of the molten steel is controlled to be 19 × 10 on average^-6To less than 13 × 10^-6。

Preferably, after the RH stage is completed, the nitrogen content of the molten steel is from 6 × 10 to 10 on average^-6The above is reduced to less than 2 × 10^-6。

Preferably, the high-aluminum high-strength slab specifically comprises the following components: 0.33-0.35 wt% of C, 0.50-0.70 wt% of Si, 1.70-1.90 wt% of Mn, 0.20-0.28 wt% of Cr, 0.030-0.040 wt% of Nb, 0.15-0.17 wt% of V, 0.0015-0.0030 wt% of B, 0.50-0.60 wt% of Als, and the balance Fe.

The application provides a method for controlling the N content of a high-aluminum high-vanadium plate blank, which comprises the steps of sequentially carrying out LD-LF-RH-CC, and strictly controlling the introduction of N in the LD stage, the RH stage and the CC stage, so that the finally prepared high-aluminum high-vanadium plate blank has lower N content; through industrial production, the content of N in the high-aluminum high-vanadium plate blank produced by the method is less than or equal to 40 ppm.

Drawings

FIG. 1 is a schematic structural diagram of a tundish argon blowing system in a CC stage;

FIG. 2 is a schematic diagram of the structure of the inner cavity of a tundish 1/4 of the original current stabilizer in the CC stage;

fig. 3 is a schematic diagram of the structure of the inner cavity of a tundish 1/4 of the current stabilizer at stage CC;

FIG. 4 is a structural schematic view of a bowl part of a long nozzle before CC stage improvement;

fig. 5 is a structural schematic diagram of a long nozzle bowl after CC stage improvement.

Detailed Description

For a further understanding of the invention, reference will now be made to the preferred embodiments of the invention by way of example, and it is to be understood that the description is intended to further illustrate features and advantages of the invention, and not to limit the scope of the claims.

The control method of the N content of the high-strength high-aluminum high-vanadium plate blank can be widely used in domestic steel enterprises, the systematic research is carried out on the problems that the nitrogen content of the converter end point is higher, the steel tapping and refining are finished until the nitrogen content of the tundish molten steel is seriously increased in the production of high-grade steel represented by an automobile panel, on the basis of investigation and analysis of the change rule of the nitrogen content of the molten steel in the steel-making process, the nitrogen content control technology of the high-grade steel represented by the semi-steel smelting automobile panel is applied, the nitrogen content of the converter end point and the nitrogen content of the converter process of the high-grade steel represented by the automobile panel are effectively reduced, the nitrogen content of a finished product is reduced, the integral control level of the nitrogen content of the high-grade steel represented by the automobile panel is improved, and the quality stability of the steel varieties such as the high-grade steel represented by the automobile panel, electric steel, ultra-low-carbon deep drawing steel, phosphorus-high, provides technical support for the production of low-nitrogen steel. The technical improvement or the process provides a solution for manufacturers in the steel industry and adopting semi-steel smelting (duplex method) to produce high-grade steel represented by automobile panels. The embodiment of the invention discloses a method for controlling the N content of a high-aluminum high-vanadium plate blank, which comprises the steps of sequentially performing LD-LF-RH-CC, and comprises the following steps:

in the LD stage: a bottom blowing gas supply mode is adopted in the smelting of high-aluminum high-vanadium steel, the low lance position operation is adopted in the later stage of blowing, and a slag foaming agent is added in the later stage of smelting;

in the RH phase: carrying out flaw detection and welding repair by adopting a penetration method after butt welding of the vacuum chamber body and the immersion pipe, wherein the service life of the immersion pipe is less than or equal to 50 times;

in the CC stage: and (4) pouring by adopting a double-argon-sealed long nozzle.

The method is characterized in that the high-aluminum high-vanadium steel plate blank for the automobile panel is required to have low N content, and the production process of the plate blank comprises the steps of sequentially performing LD-LF-RH-CC; in the following description, only the modifications in the above steps are described, and the modifications are not performed according to the conventional art.

According to the invention, in the LD stage, the top oxygen blowing is adopted in the current steelmaking converter stage, and a bottom blowing air supply mode is introduced in the invention, so that a top-bottom combined blowing mode is realized, the uniformity of molten steel in the blowing process is improved, the over oxidation is prevented, and the oxygen in the steel is reduced; for the high-aluminum high-vanadium steel, argon is uniformly selected in a low-blowing gas supply mode in the whole blowing process, so that nitrogen increase in the blowing process is prevented and reduced; the strength of bottom blowing gas supply is more than 0.03m³L (min. t) steel.

In the stage, the consumption of scrap steel is strictly controlled to be less than or equal to 40kg/t of high-aluminum high-vanadium steel; meanwhile, the control of the rotary terminal is enhanced, and the low lance position operation is adopted in the later stage of converting, so that the over-blowing of molten steel during converting or the local high temperature of the molten steel at the top of a converter molten pool are reduced, and the nitrogen absorption of the molten steel is reduced. The solubility of nitrogen in steel increases with the increase of temperature, and the higher the temperature is, the higher the partial pressure of nitrogen is; during smelting of semisteel, because heating elements such as silicon, manganese and the like are trace, the reaction in the furnace at the initial stage is mainly carbon-oxygen reaction, but the reaction is not violent and the temperature is not high; in the middle stage of smelting, the carbon-oxygen reaction is vigorously carried out, and a large amount of CO bubbles generated by the reaction greatly reduce the partial pressure of nitrogen and reduce the probability of contact of nitrogen and molten steel; when the final stage of blowing is reached, the decarburization speed in the furnace is reduced, the partial pressure in the furnace is less than that outside the furnace, so that air enters the furnace, the nitrogen partial pressure in the furnace is increased, the nitrogen increasing speed in the furnace is higher than the denitrification speed, and the temperature in the furnace is also high, so that the final stage of blowing is a period with the highest nitrogen solubility, nitrogen is easily absorbed from the air as long as molten steel is contacted with the air, and the nitrogen absorption of the molten steel can be effectively avoided by low-lance-position blowing; meanwhile, the low-lance blowing can also improve the one-time carbon drawing hit rate, reduce the complementary blowing and avoid the deep blowing, and the end point carbon is 0.04-0.06%. And a slag foaming agent is added at the later stage of smelting, so that the nitrogen removal at the later stage of smelting is promoted, and the carbon drawing to key molten steel nitrogen increase is reduced. In the application, the blowing period (the continuous time period of blowing argon from the top and the bottom of an oxygen lance into the converter) in the converter blowing period is about 13 minutes on average, and the later period of blowing refers to the time period of continuously blowing the top and the bottom by combined blowing to 9-13 minutes; the smelting period of the steel-making converter refers to the period from the beginning of iron adding of the steel-making converter to the end of steel tapping of the converter, and the later smelting period mainly refers to the period from the beginning of steel tapping after the end of blowing of the converter to the end of steel tapping; the latter stage of the blowing and the latter stage of the smelting are time periods well known to those skilled in the art, and the present application is not particularly limited.

For the smelting technology of high-grade steel, high-strength, high-aluminum and high-vanadium steel represented by an automobile panel through the control of an LD stage, the nitrogen content of the molten steel at the end point of the converter is controlled to be 19 × 10 on average^-6To less than 13 × 10^-6And the fluctuation range is smaller, and the control is more stable.

In the RH stage, the method mainly aims at controlling nitrogen increase in the process, namely flaw detection and welding repair are carried out on the vacuum chamber body and the immersed tube by adopting a penetration method after butt welding, so that the welding defects are eliminated, the welding quality is improved, and the nitrogen increase in the molten steel treatment process is reduced. The service life of the immersion pipe is less than or equal to 50 times so as to realize the control of the nitrogen increasing amount of the molten steel. The titanium alloying is carried out by adopting the low-nitrogen sponge titanium alloy so as to reduce the introduction of N.

The nitrogen increasing amount in the RH stage is from 6 × 10 on average^-6The above is reduced to 2 × 10^-6The nitrogen increasing amount is stably controlled to 2 × 10^-6Hereinafter, the fluctuation range is smaller.

In the CC stage, the method is mainly used for improving the poor pouring protection effect in the continuous casting process. In the stage, double-argon-sealed long nozzle pouring is mainly adopted, so that the contact probability of the molten steel in the pouring process and air is reduced, and nitrogen absorption of the molten steel in the pouring process is reduced as much as possible; the double-argon-seal long nozzle pouring specifically comprises the following steps: the long nozzle and the ladle down nozzle are in a meshing connection mode,in actual production, a certain gap always exists between the ladle and the tundish, when ladle molten steel flows to the tundish through the long nozzle at a high speed, a certain negative pressure is formed at the inlet end of the long nozzle, so that a large amount of air at the joint is sucked into the long nozzle, and the nitrogen increase of the molten steel is continuously caused, and in part of steel works in the prior art, the nitrogen increase of the molten steel from the ladle to the tundish is controlled to be 3 × 10 by adopting a mode of protective pouring by matching the long nozzle with a sealing ring^-6The same method is adopted by the applicant to protect the pouring nitrogen increasing amount to be 7 × 10^-6Above, it can be seen that the sealing performance of the ladle drain nozzle and the long nozzle is relatively poor, and the research and optimization of the structure of the long nozzle are necessary.

Aiming at the problem of nitrogen increase of molten steel from a ladle to a tundish, the continuous casting long nozzle is redesigned, and the structures of the front long nozzle bowl and the rear long nozzle bowl are respectively improved as shown in figures 4 and 5; the newly designed long nozzle mainly changes the design of a bowl part, the inner side of the bowl part consists of two contact surfaces with different tapers, the taper of the lower half part is consistent with that of the lower nozzle of a steel ladle, the taper of the upper half part is slightly larger, and an argon blowing ring is added. Comparing fig. 4 and fig. 5, it can be known that the contact part of the long nozzle bowl part before the improvement and the ladle lower nozzle is in line contact, and the contact part of the improved long nozzle bowl part in the structure is in surface contact with the ladle lower nozzle, so that the possibility of tilting the nozzle sleeve is reduced, and the sealing performance of the ladle lower nozzle and the upper nozzle is improved; secondly, the improved long nozzle is provided with an argon blowing protection at the bowl opening, and is also provided with an annular seam argon chamber at a position which is about 30mm away from the bowl opening, and an argon chamber can be formed at the position after argon blowing, so that the function of double-layer argon protection pouring is achieved; the design also solves the problem that the local argon sealing effect is poor due to the blockage of the argon sealing when the residual steel is cleaned and the steel overflowing is caused.

The flow field of the tundish is improved so that the maximum flow velocity of the molten steel surface of the tundish is 0.158 m/s; the method specifically comprises the following steps: in the casting process, the tundish is divided into a three-layer distribution structure of molten steel, tundish covering agent and air, and the covering agent covers the surface of the molten steel after being melted, so that the tundish mainly has the functions of isolating air and preventing secondary oxidation and nitrogen increase of the molten steel. In the actual production process, the high-speed molten steel flowing into the tundish forms partial ascending turbulence after passing through the flow stabilizer, and the covering is easy to be openedThe protective layer of the agent causes the molten steel around the long nozzle to be exposed, and the exposed molten steel is directly contacted with air, thereby causing the nitrogen increase of the molten steel in the tundish. In order to reduce the liquid level rollover of the tundish, the novel flow regulators are adopted, the inner cavity structures of the tundish of the two flow regulators are shown in figures 2 and 3, only the tundish of 1/4 is simulated due to the symmetry of the structure of the tundish, and the inner cavity structure of the tundish of 1/4 is shown in figures 2 and 2. When two flow regulators are used, the flow speed of the positions of the liquid level of the tundish, the ladle wall and the like is compared; the calculation conditions are as follows: the liquid level of the tundish is 1200mm, the steel flux is 5.56t/min, and the insertion depth of the ladle long nozzle is 200 mm. The calculation results show that the internal longitudinal section of the original current stabilizer consists of a plurality of broken lines and arcs, the transition is smooth, the size of the outlet edge is small, the kinetic energy attenuation of the molten steel injected in the current stabilizer is small, and the outlet area of the current stabilizer is smaller than that of the new current stabilizer, so that the flow velocity of the molten steel flow at the outlet of the current stabilizer is high. The height of the original current stabilizer is higher, the distance from the outlet of the current stabilizer to the liquid surface is shorter, and the attenuation of the molten steel is smaller in the process of flowing to the liquid surface, so that the surface flow velocity of the molten steel is larger than that of a new current stabilizer when the original current stabilizer is used; the maximum flow velocity of the surface of the molten steel is 0.232m/s when the original current stabilizer is used, and the maximum flow velocity of the surface of the molten steel is 0.158m/s when the new current stabilizer is used, which is very beneficial to reducing liquid level rollover. The floating rate of the inclusion with different grain diameters is compared when two flow regulators are used, and the simulated inclusion has the density of 3000kg/m³The inclusion is added into the tundish from the ladle long nozzle. The calculation result shows that the floating rate of the inclusion with each grain diameter is higher than that of the original current stabilizer when the new current stabilizer is used. The numerical simulation result shows that the new current stabilizer is superior to the original current stabilizer in reducing the surface rollover of molten steel and is favorable for promoting the floating and removal of inclusions.

An argon protection pipeline is further arranged outside the tundish, and a fiber sealing ring is arranged outside the argon protection pipeline; the argon protection pipeline is shown in figures 1 and 2; before the casting machine (CC) begins to cast steel, argon is blown into the tundish to replace oxygen and nitrogen in the tundish, so that secondary oxidation and nitrogen increase of molten steel in the casting process can be obviously reduced. On the basis of the original tundish cover, holes are respectively formed in a stopper rod hole A cover, an injection hole B cover and a stopper rod hole C cover, argon pipelines are arranged (as shown in figure 1), argon is blown into the tundish in the casting process, and an argon protection atmosphere is formed above tundish molten steel, so that the function of reinforcing tundish protection casting is achieved.

The slab specific to the control method for the N content of the high-aluminum high-vanadium slab comprises the following components: 0.33-0.35 wt% of C, 0.50-0.70 wt% of Si, 1.70-1.90 wt% of Mn, 0.20-0.28 wt% of Cr, 0.030-0.040 wt% of Nb, 0.15-0.17 wt% of V, 0.0015-0.0030 wt% of B, 0.50-0.60 wt% of Als, and the balance of Fe; in a specific embodiment, the high-aluminum high-vanadium slab is specifically 34MnB 5V.

In order to further understand the invention, the method for controlling the N content of the high-aluminum high-vanadium slab provided by the invention is described in detail below with reference to the following examples, and the scope of the invention is not limited by the following examples.

The method for controlling the N content of the high-aluminum high-vanadium plate blank is widely applied, and particularly provides an effective solution for realizing mass production of high-grade steel grades and low-cost production in a steel mill which is about to try or produce the high-grade steel grades represented by automobile panels. The following further illustrates in an embodiment form that the slab production in the following embodiment includes LD-LF-RH-CC process flows performed in sequence, the process flows only illustrate specific differences of N control, and other parts are the same as those of the existing process flows;