A method for controlling the sulfur content of heavy rail steel

Abstract

The application provides a refining method for controlling the sulfur content of heavy rail steel, and the steps are as follows: step one, after the ladle reaches the LF station, argon is blown from the bottom; step two, the ladle is heated for the first time, after 10 minutes of heating, slagging materials are added for slagging, argon is blown from the bottom in multiple stages with different flow rates, and then the station is exited; step three, after the ladle exited in step two reaches the RH station, temperature measurement and sampling are performed, the composition is analyzed, and then vacuum treatment is performed; step four, after 12-16 minutes of vacuum treatment, the vacuum treatment is ended, and whether calcium treatment needs to be performed is determined according to the [S] content of the RH inlet; step five, when the [S] content is greater than or equal to 0.006%, calcium-containing powder is sprayed from the argon blowing hole for calcium treatment; step six, after the calcium treatment, argon is blown from the bottom, and then the station is exited; step seven, after the molten steel exited in step six reaches the continuous casting platform for continuous casting and rolling, the heavy rail steel is prepared. The application can improve the Ca yield while optimizing the desulfurization kinetic conditions, so as to achieve the purposes of desulfurization and improvement of the molten steel quality.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of steel metallurgical refining, in particular, and especially relates to a refining method for controlling the sulfur content of heavy rail steel. BACKGROUND

[0002] Rail is one of the important components of railway, which contacts with wheels in the process of railway transportation, provides effective support and guidance for locomotive, and needs to bear the huge vertical pressure and strong lateral friction force from the wheels. Modern railway transportation is developing at a rapid speed, especially the railway transportation in China is continuously tending to be high speed and heavy load, which puts forward more strict requirements on the quality of rail. The rail bears the variable load of locomotive back and forth in a loop when contacting with the wheels, and the purity has an important influence on the fatigue life of the rail. Since the manganese sulfide is precipitated in the solidification process of the casting blank by combining the sulfur element with the manganese element, it has the characteristics of low melting point, and thus is gathered in specific regions such as the grain boundary, interdendritic and center region of the casting blank, causing loose, segregation and other hazards; the manganese sulfide inclusion can make the steel produce hot brittleness, and the gathered manganese sulfide inclusion is elongated in the rail rolling process, which cuts the matrix of the steel and reduces the transverse mechanical properties, such as affecting the low temperature transverse impact toughness of the steel. Therefore, it is necessary to strictly control the sulfur content in the heavy rail steel.

[0003] Calcium treatment is a refining method developed in the 1970s, and its main purposes include: reducing harmful elements such as oxygen and sulfur in steel; changing the composition and morphology of inclusions in steel, reducing nozzle clogging, etc. According to the literature research, methods such as directly adding calcium alloy into the ladle and spraying calcium alloy into the molten steel are known, but they have been gradually eliminated due to unstable treatment effect or high cost, and now the ladle calcium wire feeding method is mainly applied, that is, the calcium alloy (Ca, Ca-Si, Ca-Fe, etc.) is wrapped with steel sheet to make a cored wire, which is fed into the molten steel at high speed by a wire feeder.

[0004] At present, some steel grades with high requirements on sulfur content generally feed a certain amount of calcium wire into the molten steel after refining to perform calcium treatment, and then perform soft blowing for a certain time to make the inclusions in the steel float up for easy removal, but since calcium is very active and has a large vapor pressure, after the calcium wire is fed into the molten steel, a violent reaction usually occurs, which may even cause molten steel spatter, resulting in volatilization of calcium and secondary oxidation of the molten steel, reducing the yield of calcium and contaminating the molten steel. In addition, since the molten steel can avoid nozzle clogging after calcium treatment, the molten steel for continuous casting is usually treated by calcium.

[0005] CN202210561937.0: The application discloses a heavy rail ultra-low sulfur control method. Without changing the heavy rail production process, timing and slag consumption, the method promotes the transformation of MnS complex inclusions into complex inclusions wrapped with CaS by increasing the calcium content in the silicon-calcium-barium alloy, which is more conducive to the floating of desulfurization products and further promotes desulfurization. Secondly, the calcium and barium in the silicon-calcium-barium alloy can quickly complete the deoxidation task in the early stage of refining, and the key process control point is in the converter tapping-LF refining position. At this time, the silicon content in the molten steel is very low, and the desulfurization thermodynamic condition is good. The high-calcium-barium deoxidizing alloy has a larger density and can quickly enter the lower part of the molten steel. The calcium and sulfur produced by deoxidation reaction optimize the desulfurization kinetics. The method is suitable for heavy rail steel and can ensure that [S] is less than or equal to 0.005%. The patent promotes desulfurization by increasing the calcium content in the silicon-calcium-barium alloy. The added calcium is prone to violent reaction with molten steel, which may cause molten steel spatter.

[0006] CN201810833929.0: The application discloses a smelting method for improving the cleanliness of heavy rail steel and belongs to the technical field of iron and steel metallurgy. The technical problem solved by the application is that the cleanliness of existing domestic heavy rail steel is difficult to meet the requirements of high-speed railways. The method comprises the following steps: hot metal pretreatment, converter smelting, LF refining, RH refining and continuous casting. In the method, 6-10 m / t of ferrocalcium wire is used for calcium treatment in the RH refining. Through the above steps, the content of P, S, O, N and H in the steel rail can be controlled to be less than or equal to 0.0060%, 0.0030%, 0.0010%, 0.0050% and 0.00015% respectively, the content of P+S+O+N+H is less than or equal to 160 ppm, and the rating of various inclusions is less than or equal to 1.0 grade, so that the cleanliness of the heavy rail steel is remarkably improved, and the method has certain social benefits and is worthy of popularization and application. The patent uses ferrocalcium wire for calcium treatment, which is a conventional operation and may cause spatter.

[0007] CN201510427458.X: The application discloses a control method of heavy rail steel inclusions. The application provides a control method of heavy rail steel inclusions. The method comprises the following steps: converter smelting, LF furnace refining, RH vacuum treatment and continuous casting. The application adopts active lime in the converter and active lime, silicon carbide and quartz sand slagging in the refining process to control the mass content of S in the molten steel to be less than 0.006% and ensure that the inclusion rating of the steel is less than or equal to 2.0. The application uses relatively high alkalinity, has high and stable desulfurization efficiency, and obviously improves various inclusions in the molten steel. The patent controls the sulfur content by the slagging method, and the slagging process is complicated and has obvious limitations.

[0008] CN201910323204.1: The application discloses a calcium treatment method for a RH refining furnace vacuum process. The method comprises the following steps: adding calcium-containing alloy into molten steel circulating in a vacuum chamber of an RH alloy bin during a vacuum circulation treatment process of an RH vacuum refining furnace, and modifying inclusions in the molten steel. The calcium treatment process is stable and controllable, the calcium composition of the molten steel is stable and accurate after the treatment is completed, the calcium yield reaches more than 20%, the inclusions in the molten steel are fully modified, the flaw detection qualified rate is high, and the inclusion rating is within 1.5. The application successfully solves the problem of secondary oxidation caused by molten steel turbulence and exposure during calcium treatment by feeding a pure calcium wire after the vacuum treatment of the RH refining furnace is completed, stabilizes the calcium treatment effect, reduces the inclusion content, improves the cleanliness of the molten steel and the flaw detection qualified rate of finished steel plates, reduces the production cost, and greatly improves the economic benefit. The patent adds calcium-containing alloy to the molten steel circulating in the vacuum chamber of the RH alloy bin. Calcium is very active and has a large vapor pressure, which easily causes vacuum air pressure fluctuations and affects refining.

[0009] CN202010592806.X: The application discloses an RH vacuum furnace calcium treatment process method, which comprises KR molten iron pretreatment-converter smelting-RH vacuum refining-continuous casting of slabs. The RH vacuum refining comprises decarburization, deoxidization alloying and calcium treatment. In the decarburization, a slag surface deoxidizer is added to the surface of the slag in the middle and late stages of decarburization, the addition amount is 1.0-2.0 kg / ton of steel, the ladle slag is modified, and (T.Fe+MnO) in the slag is less than or equal to 5 wt%. In the deoxidization alloying, alloy and carbon powder are added for deoxidization alloying. In the calcium treatment, a seamless pure calcium wire is fed 5 minutes after the deoxidization alloying is completed for calcium treatment. During the calcium treatment, the pressure in the vacuum chamber is increased to more than 200 mbar. After the calcium treatment is completed, the pressure in the vacuum chamber is reduced to less than 2 mbar, and the vacuum chamber is broken after 6 minutes of static circulation. The process method of the application feeds a seamless calcium wire after deoxidization alloying, utilizes RH molten steel circulation stirring to make the distribution of Ca elements in the molten steel uniform, realizes modification of Al2O3 inclusions, reduces the oxidation amount of Ca elements, improves the calcium yield, and stabilizes the calcium treatment effect. The patent uses the feeding of a seamless calcium wire for calcium treatment. The added calcium wire is easy to react violently with the molten steel, which may cause molten steel spatter, calcium volatilization and secondary oxidation of the molten steel.

[0010] Based on the above analysis, in order to improve the calcium yield, it is necessary to propose a refining method for controlling the sulfur content of heavy rail steel to solve the existing problems. SUMMARY

[0011] The application provides a refining method for controlling the sulfur content of heavy rail steel.

[0012] The application adopts the following technical means:

[0013] The refining method for controlling the sulfur content of heavy rail steel comprises the following steps.

[0014] Step one: after the ladle reaches the LF station, argon bottom blowing is started;

[0015] Step two: the ladle is heated for the first time, and after 10 minutes of heating, slagging materials are added for slagging, multi-stage argon bottom blowing with different flow rates is carried out, and then the station is exited;

[0016] Step three: after the ladle is exited in step two and reaches the RH station, temperature measurement and sampling are carried out, the composition is analyzed, and then vacuum treatment is carried out;

[0017] Step four: after 12-16 minutes of vacuum treatment, the vacuum treatment is ended, and whether calcium treatment needs to be carried out is determined according to the [S] content of the RH inlet station;

[0018] Step five: when the [S] content is greater than or equal to 0.006%, calcium powder is sprayed from the argon blowing hole for calcium treatment;

[0019] Step six: after the calcium treatment, argon bottom blowing is carried out, and then the station is exited;

[0020] Step seven: after the molten steel is exited in step six and reaches the continuous casting platform, the molten steel is continuously cast and rolled to prepare heavy rail steel.

[0021] Further, in step one, the argon bottom blowing flow rate is controlled to be 150-200 NL / min.

[0022] Further, in step two, the multi-stage argon bottom blowing with different flow rates is as follows: when slagging, the argon bottom blowing flow rate is adjusted to be 100-150 NL / min; after the molten steel is heated to 1560-1580 DEG C, the ladle is subjected to small-flow argon bottom blowing, the argon blowing flow rate is controlled to be 50-80 NL / min, soft blowing is carried out for 5-6 minutes, and the molten steel liquid surface is not exposed during the argon blowing process.

[0023] Further, in step three, the vacuum degree is controlled to be below 3 mbar, and the lifting gas flow rate is controlled to be 1200-1400 NL / min.

[0024] Further, in the step five, the calcium-containing powder is limestone powder with a particle size of 0-1.5 mm, and the blowing amount of the calcium-containing powder is set according to the content of [S] in the molten steel.

[0025] Further, in the step five, the calcium-containing powder is blown into the ladle from the bottom blowing argon hole under the carrying of inert gas Ar with a flow rate of 50-100 NL / min.

[0026] Further, in the step six, the argon gas is blown at a flow rate of 50-80 NL / min for 5-8 min.

[0027] Compared with the prior art, the present application has the following advantages:

[0028] 1. The present application provides a refining method for controlling the sulfur content of heavy rail steel, which avoids the disadvantages of calcium treatment operation, such as large fluctuation of Ca recovery rate, violent chemical reaction in calcium treatment process, secondary oxidation of molten steel, etc., greatly improves the effective contact area, optimizes the desulfurization kinetics conditions while improving the Ca recovery rate, and thus achieves the purposes of desulfurization and improvement of molten steel quality.

[0029] 2. The present application provides a refining method for controlling the sulfur content of heavy rail steel, which performs calcium treatment by bottom blowing calcium-containing powder during RH refining process, has high and stable calcium absorption rate, reduces the inclusions in molten steel, reduces the S content in steel, improves the nozzle clogging situation, and achieves the purpose of improving the quality of molten steel.

[0030] 3. The present application provides a refining method for controlling the sulfur content of heavy rail steel, which can improve the calcium treatment effect of RH refining, control the mass content of S in molten steel to be reduced to below 0.006%, and has obvious improvement effect on the quality of finished steel. The present application has created obvious economic benefits after being implemented in a certain factory. The present application can be widely applied in the same industry in China.

[0031] 4. The present application provides a refining method for controlling the sulfur content of heavy rail steel, which can avoid the disadvantages of calcium treatment operation, such as large fluctuation of Ca recovery rate, violent chemical reaction in calcium treatment process, large steel slag spatter, secondary oxidation of molten steel, etc., greatly improves the effective contact area and thus improves the Ca recovery rate, and thus achieves the purposes of desulfurization and improvement of molten steel quality.

[0032] Based on the above reasons, the present application can be widely applied in the field of steel metallurgical refining. BRIEF DESCRIPTION OF DRAWINGS

[0033] In order to more clearly illustrate the technical solutions of the embodiments of the present application or the prior art, the accompanying drawings needed to be used in the embodiments or prior art description will be briefly introduced. Obviously, the accompanying drawings in the following description are some embodiments of the present application, and other drawings can be obtained by those skilled in the art without any creative effort on the basis of these drawings.

[0034] Figure 1 The flowchart of the method of the present application. DETAILED DESCRIPTION

[0035] It should be noted that the embodiments in the present application and the features in the embodiments can be combined with each other without conflict. The present application will be described in detail below with reference to the accompanying drawings and in combination with the embodiments.

[0036] In order to make the purpose, technical solutions and advantages of the embodiments of the present application clearer, the technical solutions of the embodiments of the present application will be described clearly and completely below in combination with the accompanying drawings of the embodiments of the present application. Obviously, the described embodiments are only some of the embodiments of the present application, but not all the embodiments. The description of the at least one exemplary embodiment is actually only illustrative, but not as any limitation on the present application and its application or use. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without any creative effort belong to the scope of protection of the present application.

[0037] It should be noted that the terms used herein are only for the purpose of describing specific embodiments, and are not intended to limit the exemplary embodiments according to the present application. As used herein, the singular form is intended to include the plural form unless the context clearly indicates otherwise, and furthermore, it should be understood that when the terms "comprise" and / or "include" are used in the specification, there is a feature, step, operation, device, component and / or combination thereof.

[0038] The relative arrangement of parts and steps, numerical expressions, and values set forth in the examples herein are not intended to limit the scope of the application unless otherwise specifically stated. It is to be understood that the drawings are not necessarily to scale as the dimensions of the parts shown are for the purpose of illustration and description only and not limitation of the scope of the application. Techniques, methods, and apparatus known to those of ordinary skill in the relevant art can not be discussed in detail but are intended to be part of the scope of the application. In all examples shown and discussed herein, any specific value is to be interpreted as illustrative only and not as a limitation. Thus, other examples of exemplary embodiments can have different values. It is noted that like numbers and letters refer to like elements throughout the several views of the drawings and, as such, no further discussion with regard thereto is needed.

[0039] As Figure 1 shown, the present application provides a refining method for controlling sulfur content of heavy rail steel, comprising the following steps:

[0040] (1) After the ladle reaches the LF station, start bottom argon blowing, and control the bottom argon blowing flow rate at 150-200 NL / min;

[0041] (2) Perform first heating, after 10 min of heating, add slagging material to form slag, and adjust the bottom argon blowing flow rate to 100-150 NL / min. When the molten steel is heated to 1560-1580℃, the ladle uses small flow rate bottom argon blowing, and the argon blowing flow rate is controlled at 50-80 NL / min, soft blowing for 5-6 min, and the argon blowing process controls the molten steel liquid surface not to be exposed, and then the station is exited;

[0042] (3) The ladle reaches the RH station, temperature measurement and sampling are performed, and then vacuum treatment operation is started, the vacuum degree is controlled below 3 mbar, and the lifting gas flow rate is controlled at 1200-1400 NL / min;

[0043] (4) After 12-16 min of vacuum treatment, the treatment is ended, and whether calcium treatment needs to be performed is confirmed according to the RH station [S] content;

[0044] (5) When [S]≥0.006%, calcium-containing powder is sprayed from the argon blowing hole to perform calcium treatment;

[0045] (6) The sprayed powder selects limestone powder, the particle size is 0-1.5 mm, and the blowing amount is set according to the [S] content in the molten steel;

[0046] (7) The calcium-containing powder is carried by inert gas Ar, and is blown into the ladle at a flow rate of 50 NL-100 / min from the bottom gas blowing hole of the ladle;

[0047] (8) After calcium treatment, soft blowing for 5-8 min at a bottom blowing flow rate of 50-80 NL / min, and then leaving the station;

[0048] (9) After leaving the station, the molten steel reaches the continuous casting platform for continuous casting and rolling to produce heavy rail steel.

[0049] The advantages of the present application are that, by bottom blowing calcium powder, the drawbacks caused by calcium wire feeding treatment operation, such as large Ca yield fluctuation, intense chemical reaction in calcium treatment process, secondary oxidation of molten steel, etc., can be avoided, the effective contact area can be greatly improved, the Ca yield can be improved, the desulfurization kinetics condition can be optimized, and thus the purposes of desulfurization and improving molten steel quality can be achieved.

[0050] The present application performs calcium treatment by bottom blowing calcium-containing powder during RH refining process, the calcium absorption rate is high and stable, the inclusions in molten steel are reduced, the S content in steel is reduced, the nozzle clogging condition is improved, and the purpose of improving molten steel quality is achieved.

[0051] The present application can improve the calcium treatment effect of RH refining, control the mass content of S in molten steel to be reduced to below 0.006%, and obviously improve the quality of finished steel. After the implementation of the present application in a certain factory, obvious economic benefits are created. The present application can be popularized and applied in the same industry in China.

[0052] After the application of the present application, the drawbacks caused by calcium wire feeding treatment operation, such as large Ca yield fluctuation, intense chemical reaction in calcium treatment process, large steel slag spatter, secondary oxidation of molten steel, etc., can be avoided, the effective contact area can be greatly improved, and thus the Ca yield can be improved, the purposes of desulfurization and improving molten steel quality can be achieved. After the implementation of the present application in a certain factory, obvious economic benefits are created, and it is expected to create more than 3.5 million yuan per year.

[0053] Example 1

[0054] For a 120 t ladle, when producing heavy rail steel, the process steps are as follows:

[0055] (1) After the ladle reaches the LF station, bottom argon blowing is started, and the bottom argon blowing flow rate is controlled at 150-200 NL / min;

[0056] (2) First heating is performed, after heating for 10 min, slagging material is added for slagging, and the bottom argon blowing flow rate is adjusted to 100-150 NL / min. When the molten steel is heated to 1560-1580℃, the ladle is bottom blown with small flow rate, the argon blowing flow rate is controlled at 50-80 NL / min, soft blowing is performed for 5-6 min, the molten steel surface is not exposed during the argon blowing process, and then the station is left;

[0057] (3) The ladle reaches the RH station, temperature measurement and sampling are performed, and the composition is analyzed;

[0058] (4) After the insertion tube enters the liquid steel, the RH starts normal treatment operation;

[0059] (5) After the RH treatment is completed, the liquid steel is treated with calcium according to the [S] content;

[0060] (6) Calcium-containing powder is blown in at a bottom blowing flow rate of 100 NL / min;

[0061] (7) Soft argon blowing is used for stirring, the soft blowing time is 6 min, and the soft blowing gas flow rate is controlled at 50 NL / min.

[0062] In this way, the calcium yield reaches 23%, the S content is controlled below 0.006%, the number of inclusions in the steel is significantly reduced, and the water nozzle clogging during continuous casting is improved.

[0063] Example 2

[0064] For a 150 t ladle, when producing heavy rail steel, the process steps are as follows:

[0065] (1) After the ladle reaches the LF station, argon bottom blowing is started, and the argon bottom blowing flow rate is controlled at 150-200 NL / min;

[0066] (2) First heating is performed, after 10 min of heating, slagging materials are added for slagging, and the argon bottom blowing flow rate is adjusted to 100-150 NL / min. When the liquid steel is heated to 1560-1580°C, the ladle is subjected to low-flow argon bottom blowing, the argon blowing flow rate is controlled at 50-80 NL / min, soft blowing is performed for 5-6 min, the argon blowing process controls the liquid surface of the molten steel not to be exposed, and then the station is exited;

[0067] (3) The ladle reaches the RH station, temperature sampling is performed, and the composition is analyzed;

[0068] (4) After the insertion tube enters the liquid steel, the RH starts normal treatment operation;

[0069] (5) After the RH treatment is completed, the liquid steel is treated with calcium according to the [S] content;

[0070] (6) Calcium-containing powder is blown in at a bottom blowing flow rate of 120 NL / min;

[0071] (7) Soft argon blowing is used for stirring, the soft blowing time is 6 min, and the soft blowing gas flow rate is controlled at 80 NL / min.

[0072] In this way, the calcium yield reaches 24.2%, the S content is controlled below 0.006%, the number of inclusions in the steel is significantly reduced, and the water nozzle clogging during continuous casting is improved.

[0073] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present application, and are not intended to limit the present application; although the present application has been described in detail with reference to the above embodiments, those skilled in the art should understand that the technical solutions recorded in the above embodiments can be modified, or some or all of the technical features can be replaced by equivalents; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present application.

Claims

1. A refining method for controlling the sulfur content of heavy rail steel, characterized by, It comprises the following steps: Step one, after the ladle reaches the LF station, argon is blown from the bottom; Step two, the ladle is heated for the first time, after 10 minutes of heating, slagging materials are added for slagging, argon is blown from the bottom at different flow rates in multiple stages, and then the ladle is sent out; Step three, after the ladle sent out in step two reaches the RH station, temperature measurement and sampling are performed, the composition is analyzed, and then vacuum treatment is performed; Step four, after vacuum treatment for 12-16 minutes, vacuum treatment is ended, and whether calcium treatment is needed is determined according to the [S] content of the RH inlet; Step five, when the [S] content is greater than or equal to 0.006%, calcium-containing powder is sprayed from the argon blowing hole for calcium treatment; Step six, after calcium treatment, argon is blown from the bottom, and then the ladle is sent out; Step seven, the molten steel sent out in step six reaches the continuous casting platform for continuous casting and rolling to prepare heavy rail steel; In step five, the calcium-containing powder sprayed is limestone powder with a particle size of 0-1.5 mm; the calcium-containing powder is carried by inert gas Ar and blown into the ladle from the bottom blowing hole at a flow rate of 50-100 NL / min.

2. The method of refining heavy rail steel to control sulfur content according to claim 1, wherein, In step one, the argon blowing flow rate is controlled at 150-200 NL / min.

3. The method of refining heavy rail steel to control sulfur content according to claim 1, wherein, In step two, the argon blowing flow rate is controlled at 150-200 NL / min.

4. The method of refining heavy rail steel to control sulfur content according to claim 1, wherein, In step two, the argon blowing flow rate is controlled at 150-200 NL / min.

5. The method of refining heavy rail steel to control sulfur content according to claim 1, wherein, In step three, the vacuum degree is controlled below 3 mbar, and the lifting gas flow rate is controlled at 1200-1400 NL / min.

6. The method of refining heavy rail steel to control sulfur content according to claim 1, wherein, In step five, the amount of calcium-containing powder blown is set according to the [S] content in the molten steel. In step six, the argon blowing flow rate is controlled at 50-80 NL / min for soft blowing for 5-8 min. In step five, the amount of calcium-containing powder blown is set according to the [S] content in the molten steel. In step six, the argon blowing flow rate is controlled at 50-80 NL / min for soft blowing for 5-8 min.

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