CN111304520B - Method for smelting CB2 material by electric arc furnace - Google Patents
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Abstract
The invention belongs to the technical field of casting, and mainly relates to a smelting process method of a high-temperature heat-resistant material CB2, wherein the CB2 material is mainly ZG12Cr9Mo1Co1 NiVNbNB; the method mainly comprises the following steps: preparing materials, smelting in an EAF furnace, smelting in an LF furnace, smelting in a VD furnace, adjusting components in the LF furnace, and pouring; by adopting the smelting method, the VD treatment is used for smelting the casting with the C content of about 0.1 percent, the secondary oxidation of the molten steel can be avoided, the content of oxides in the molten steel is reduced, the recovery rate of easily-oxidized elements such as B, Nb, V and the like is improved, and the content of S can be reduced to be lower. And the smelting time is shortened by half, the one-time smelting yield reaches more than 95%, the rejection rate is reduced to zero, the production cost is greatly reduced, and the production efficiency is improved.
Description
Technical Field
The invention belongs to the technical field of casting, and mainly relates to a smelting process method of a high-temperature heat-resistant material CB 2.
Background
With the rapid development of social economy, the energy shortage becomes the bottleneck of social development, and the realization of environment-friendly economic growth is the main direction of the development of the current international energy industry. Energy conservation and emission reduction, increase of the investment in the original energy source and the proportion of novel energy sources, and increase of the utilization rate of the existing energy sources are very important. The ultra-supercritical steam turbine with high power, high parameter, high thermal efficiency, high temperature resistance and high pressure resistance is the development direction of the current steam turbine technology, and the utilization rate of energy can be obviously improved by improving the temperature and the pressure of steam, so the key point for improving the efficiency of the steam turbine is to improve the high temperature resistance and the high pressure resistance of materials.
The high-alloy heat-resistant steel casting can work in a severe environment with the temperature of 620 ℃ and the pressure of more than 25MPa due to good high-temperature strength, particularly high-temperature oxidation resistance and high-temperature creep resistance, and becomes an ideal high-temperature and high-pressure resistant part for large-scale high-end gas and steam generating sets. The CB2 material mainly comprises ZG12Cr9Mo1Co1NiVNbNB, ZG13Cr9Mo2Co1NiVNbNB and other materials, wherein 14 elements need to be controlled in the smelting process, the types of the elements are 2 times of those of common materials, particularly Co, B and other elements, the elements are applied to steel making only in recent years, and the element characteristics and the action mechanism in steel need to be further researched. Many domestic manufacturers can not well master the smelting method of the material due to lack of experience in the aspect, so that the situations that some elements are scrapped due to low recovery rate, large amount of added alloy, waste of cost and even some elements exceed the standard are generally caused. Therefore, how to master the smelting method of the CB2 material and control 14 elements in place becomes the focus of the current research.
Disclosure of Invention
According to the invention, through research on the smelting method of the CB2 material, various problems encountered in the smelting process of the CB2 material are mainly solved, the one-time smelting yield is improved, the rejection rate is reduced, and the production cost is reduced.
A method for smelting CB2 material in an electric arc furnace comprises the following steps:
preparing materials: the charging materials are scrap steel and pig iron, and the adding amount ratio of the scrap steel to the pig iron is 8: 2;
smelting in an EAF furnace: firstly, distributing materials, namely adding charging materials into an EAF furnace, and simultaneously adding lime accounting for 5 percent of the total amount of molten steel to remove P in advance; blowing oxygen for decarburization after the temperature of the molten steel reaches 1620 ℃, and not reducing in an EAF furnace; when the P content is less than or equal to 0.005 percent and the C content is less than or equal to 0.05 percent, tapping the steel to an LF furnace for smelting when the temperature reaches 1640-1670 ℃;
smelting in an LF furnace: firstly, adding Al particles of 2 kg/ton steel to 3 kg/ton steel to fully reduce the molten steel until the oxygen activity is reduced to be below 5PPM, adding 1000kg to 1200kg of active lime to reduce electrode recarburization, then adding 50kg to 80kg of fluorite, adjusting the argon flow to be 0.4MPa to 0.6MPa to remove S, reducing the S content to be below 0.01 percent, taking a spectrum sample to analyze chemical components, adjusting the molten steel components until the content of each element in the molten steel meets the standard range, and tapping to VD furnace for smelting when the temperature is adjusted to be 1620 ℃ to 1640 ℃;
and (3) smelting in a VD furnace: firstly, high vacuum is pumped, the vacuum degree reaches below 67pa, and nonmetallic inclusions, N, H, O and other harmful gases in the steel are removed through the high vacuum; after keeping for 15min, VD is finished, 1 kg/ton steel to 1.5 kg/ton steel Al particles are added, after keeping for 5min, tapping is carried out to an LF furnace to adjust components;
adjusting components in an LF furnace: adjusting the pressure of argon gas to 0.2-0.25 Mpa to prevent the molten steel from violently rolling, and if the argon gas is too large, the recovery rate of N is low; then adding ferrochromium nitride, sampling and analyzing after 5min, tapping and pouring;
pouring: and (3) adopting an argon blowing ring to protect pouring, preventing the molten steel from further secondary oxidation, and supplementing 300 kg-500 kg of heat insulating agent after pouring to prevent the pouring defect from being generated.
As a further scheme of the invention, in the smelting step of the EAF furnace, 40 percent of the total amount of lime in the material distribution process is placed at the bottom of the furnace burden for bottom padding, and 60 percent of the total amount of lime is added in the middle of the furnace burden; so that molten steel in the melting stage can fully react with lime, the molten steel can be fully contacted with the lime after being melted, and the efficiency of removing P is improved.
As a further scheme of the invention, in the smelting step of the EAF furnace, when the oxygen blowing decarbonization amount is more than 0.2 percent, the furnace door is inclined downwards by 30 degrees to start slag flowing, when the slag flowing amount is more than 90 percent of the total amount of steel slag, the slag flowing is stopped, a second batch of lime is added from a high-level bunker, the adding amount is 2 to 3 percent of the total amount of molten steel, the oxygen blowing decarbonization is continued until the P content is less than or equal to 0.005 percent, and the removal amount of the oxidation slag in the furnace is ensured to be more than or equal to 95 percent after the oxygen blowing is finished; therefore, the P removed from the steel slag is reduced to have reversible reaction to generate simple substance P which returns to the molten steel again, and the content of the P is increased.
As a further scheme of the invention, in the smelting step of the EAF furnace, 2kg/t of aluminum blocks are put into a ladle during tapping, and 300kg of an S removing agent is simultaneously put into the ladle during tapping; and the tapping adopts rapid tapping to prevent residual oxidizing slag from entering a ladle.
As a further scheme of the invention, in the smelting step of the LF furnace, the alloy which is not easy to oxidize is added firstly when the components of the molten steel are adjusted, and the alloy is added in small amount in batches, wherein the adding amount is less than 300kg each time; the alloy which is not easy to oxidize comprises: ferrochromium, ferromolybdenum, electrolytic cobalt and electrolytic nickel.
Furthermore, when electrolytic cobalt is added, the temperature of the molten steel is increased to be over 1590 ℃, the flow of argon is adjusted to be 0.4-0.6 Mpa, the melting point of the electrolytic cobalt is about 1495 ℃, and the electrolytic cobalt belongs to elements which are not easy to oxidize, and by the method, the recovery rate of the electrolytic cobalt can reach over 95 percent.
As a further scheme of the invention, in the smelting step of the LF furnace, the alloy which is not easy to oxidize is added, then sampling analysis is carried out, if the carbon content is less than 0.12%, easily-oxidizable elements are continuously added, and the easily-oxidizable elements comprise Mn, Si, V, Nb and B; according to the content of each element in the steel, firstly controlling the Mn, Si and V elements to be within the standard, and then adjusting the Nb and B elements; by the method, the recovery rate of ferrocolumbium can reach 80-85%, and the recovery rate of ferroboron can reach 60-65%.
As a further scheme of the invention, in the VD furnace smelting step, the thickness of a slag layer is kept between 180mm and 220 mm; if the slag layer exceeds the thickness, the excess slag is scraped off.
Furthermore, in the smelting step of the VD furnace, the size of argon is observed at any time through the observation hole, the rolling diameter of the molten steel is within the range of 600 mm-800 mm, and the too large or too small rolling diameter is not beneficial to degassing and inclusion removal of the molten steel.
As a further aspect of the present invention, in the LF furnace, the amount of ferrochrome nitride added (kg) ═ the target value of nitrogen content-0.05% >. the weight of molten steel ]/(recovery rate of ferrochrome nitride · the nitrogen content in ferrochrome nitride) is adjusted in separate steps.
Further, in the adjusting and dividing steps of the LF furnace, in the process of sampling and analyzing the content, if the N content does not meet the standard requirement, the ferrochromium nitride is continuously added, after all the components are qualified, the argon pressure is adjusted to be 0.1-0.15 Mpa for soft blowing for a period of time, and after the temperature reaches 1585 ℃, tapping and pouring are carried out.
As a further scheme of the invention, in the pouring step, the cavity is blown with argon 30min before pouring, the oxygen concentration of the cavity is measured during pouring, and the pouring can be carried out after the oxygen concentration is less than 5%.
The method of the invention has the following beneficial effects:
the method for smelting the CB2 material in the electric arc furnace provided by the invention applies VD treatment to smelt a casting with the C content of about 0.1%, can avoid secondary oxidation of molten steel, reduce the content of oxides in the molten steel, improve the recovery rate of easily-oxidized elements such as B, Nb and V, and simultaneously can reduce the S content to be lower.
The content of N in molten steel is required to be 0.015-0.025% in the smelting process of the CB2 material, the content of N in the range exceeds the content of nitrogen contained in the original molten steel, but the adding amount is quite small, the recovery rate of N after the ferrochrome nitride is added is different along with the adding amount, the recovery rate of N in the range is summarized to be about 85% through experiments and data collection and arrangement, meanwhile, the rationality of the recovery rate is verified through subsequent practical production, and the content of N once conforms to 100% by adopting the smelting method provided by the invention.
The CB2 material belongs to a material containing B with low melting point, low density and easy oxidation, and because of the particularity of the element B, the adding process of the element B is summarized through tests before smelting, ferroboron is added before VD instead of VOD, so that the recovery rate of the element B is improved from 50% to 80%, and the smelting time is shortened by 40%.
The EAF + LF + VD smelting process is adopted to replace the EAF + LF + VOD process, the smelting time is shortened by half, the one-time smelting qualification rate reaches more than 95%, the rejection rate is reduced to zero, the production cost is greatly reduced, and the production efficiency is improved.
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Detailed Description
The technical solution of the present invention is further described in detail with reference to the following examples. In the present invention, unless otherwise specifically defined and limited, terms are to be construed broadly, and specific meanings of the terms in the present invention may be understood by those skilled in the art according to specific situations.
The embodiment of the invention provides a method for smelting a CB2 material in an electric arc furnace, wherein the CB2 material is mainly ZG12Cr9Mo1Co1NiVNbNB, elements to be controlled reach 14, and the specific chemical component contents meet the following requirements: c: 0.10 to 0.14%, Si: 0.20 to 0.4%, Mn: 0.60-0.90%, P: less than or equal to 0.015 percent, S: less than or equal to 0.010 percent, Cr: 9.00-9.60%, Mo: 1.40-1.60%, Ni: 0.10-0.25%, N: 0.015 to 0.025%, Co: 0.95-1.15%, B: 0.008-0.01%, V: 0.18 to 0.25%, Al: less than or equal to 0.010 percent, Nb: 0.05-0.07%, Cu: less than or equal to 0.2 percent; the specific smelting method comprises the following steps:
preparing materials: because the P content of the finished product of the material is less than or equal to 0.015 percent, and the P content brought by the return of molten steel to P in the later reduction period and the refining process and the alloying process is added, the P content of EAF tapping needs to be controlled below 0.005 percent; therefore, the charging materials are scrap steel and pig iron, and the adding amount ratio of the scrap steel to the pig iron is 8: 2.
Preparing a ladle: the steel ladle is built by adopting magnesia-chrome bricks, so that the recarburization of refractory materials in the smelting process is prevented, steel slag must be cleaned, residues are prevented from entering molten steel, a P removing product in the residues is subjected to reversible reaction to generate a simple substance P, the content of the P in the molten steel is increased, the steel ladle is baked in advance, and the temperature of the steel ladle is higher than 700 ℃ before tapping; ensuring smooth argon before tapping.
Smelting in an EAF furnace: firstly, distributing materials, namely adding charging materials into an EAF furnace, and simultaneously adding lime accounting for 5 percent of the total amount of molten steel to remove P in advance; blowing oxygen for decarburization after the temperature of the molten steel reaches 1620 ℃, and not reducing in an EAF furnace; when the P content is less than or equal to 0.005 percent and the C content is less than or equal to 0.05 percent, tapping the steel to an LF furnace for smelting when the temperature reaches 1640-1670 ℃.
In the step, specifically, 40% of the total amount of lime in the material distribution process is placed at the bottom of the furnace burden for bottom padding, and 60% of the total amount of lime is added in the middle of the furnace burden; so that molten steel in the melting stage can fully react with lime, the molten steel can be fully contacted with the lime after being melted, and the efficiency of removing P is improved.
Specifically, when the oxygen blowing decarbonization amount is more than 0.2%, the furnace door is inclined downwards by 30 degrees to start slag flowing, when the slag flowing amount is more than 90% of the total amount of steel slag, the slag flowing is stopped, a second batch of lime is added from a high-level stock bin, the adding amount is 2% -3% of the total amount of molten steel, the oxygen blowing decarbonization is continued until the content of P is less than or equal to 0.005%, and the removal amount of oxidized slag in the furnace is ensured to be more than or equal to 95% after the oxygen blowing is finished; therefore, the P removed from the steel slag is reduced to have reversible reaction to generate simple substance P which returns to the molten steel again, and the content of the P is increased.
Specifically, 2kg/t of aluminum blocks are put into a ladle during tapping, and 300kg of an S removing agent is simultaneously put into the ladle; and the tapping adopts rapid tapping to prevent residual oxidizing slag from entering a ladle.
It should be noted that, the conventional product needs to be added with Al particles for reduction operation after the EAF is blown with oxygen, but because CB2 material casting has strict requirement on P content, the reduction is not carried out during smelting in an EAF furnace.
Smelting in an LF furnace: firstly, adding Al particles of 2 kg/ton steel to 3 kg/ton steel to fully reduce the molten steel until the oxygen activity is reduced to be below 5PPM, adding 1000kg to 1200kg of active lime to reduce electrode recarburization, then adding 50kg to 80kg of fluorite, adjusting the argon flow to be 0.4MPa to 0.6MPa to remove S, reducing the S content to be below 0.01 percent, taking a spectrum sample to analyze chemical components, adjusting the molten steel components until the content of each element in the molten steel meets the standard range, and tapping to a VD furnace for smelting when the temperature is adjusted to be 1620 ℃ to 1640 ℃.
In the step, specifically, alloy which is not easy to oxidize is added firstly when the components of the molten steel are adjusted, and the alloy is added in small amount in batches, wherein the adding amount is less than 300kg each time; wherein the non-oxidizable alloy comprises: ferrochromium, ferromolybdenum, electrolytic cobalt and electrolytic nickel.
Specifically, when electrolytic cobalt is added, the temperature of the molten steel is raised to be over 1590 ℃, the flow of argon is adjusted to be 0.4-0.6 Mpa, the melting point of the electrolytic cobalt is about 1495 ℃, and the electrolytic cobalt belongs to elements which are not easy to oxidize, and by the method, the recovery rate of the electrolytic cobalt can reach over 95 percent.
Specifically, sampling and analyzing after adding the alloy which is not easy to oxidize, and if the carbon content is less than 0.12%, continuously adding the elements which are easy to oxidize, wherein the elements which are easy to oxidize comprise Mn, Si, V, Nb and B; according to the content of each element in the steel, firstly controlling the Mn, Si and V elements to be within the standard, and then adjusting the Nb and B elements; because Nb and B elements have low melting points and are easy to oxidize, the molten steel must be fully reduced before addition, after the oxygen activity of the molten steel is less than a certain value and the Al content in the steel is more than a fixed value, the molten steel is proved to be fully reduced, and at the moment, two alloys of ferrocolumbium and ferroboron can be sequentially added; by the method, the recovery rate of ferrocolumbium can reach 80-85%, and the recovery rate of ferroboron can reach 60-65%.
It should be noted that, when the alloy which is not easily oxidized is added, a small amount of the alloy is added in batches, if too much alloy is added each time, the electrode is easily broken, energy is wasted, and the carburization is serious, and if the electrode is broken, only VOD can be carried out, so that the final total oxygen content and S content are high.
And (3) smelting in a VD furnace: firstly, high vacuum is pumped, the vacuum degree reaches below 67pa, and nonmetallic inclusions, N, H, O and other harmful gases in the steel are removed through the high vacuum; and after keeping for 15min, finishing VD, adding 1-1.5 kg/ton of steel Al particles, keeping for 5min, and tapping to an LF furnace to adjust components.
In the step, specifically, the thickness of the slag layer is kept between 180mm and 220 mm; if the slag layer exceeds the thickness, the excess slag is scraped off. And the size of the argon is observed at any time through the observation hole, the rolling diameter of the molten steel is within the range of 600 mm-800 mm, and the too large or too small rolling diameter is not beneficial to degassing and inclusion removal of the molten steel.
Adjusting components in an LF furnace: adjusting the pressure of argon gas to 0.2-0.25 Mpa to prevent the molten steel from violently rolling, and if the argon gas is too large, the recovery rate of N is low; and adding ferrochromium nitride, sampling and analyzing after 5min, tapping and pouring.
In this step, specifically, the amount (kg) of ferrochrome nitride added is [ (target value of nitrogen content-0.05%) of weight of molten steel ]/(recovery rate of ferrochrome nitride ] of nitrogen content in ferrochrome nitride).
Specifically, in the process of sampling and analyzing the content, if the N content does not meet the standard requirement, the ferrochrome nitride is continuously added, after all the components are qualified, the argon pressure is adjusted to be 0.1-0.15 Mpa for soft blowing for a period of time, and after the temperature reaches 1585 ℃, tapping and pouring are carried out.
It should be noted that the Al content is not too high and is easy to form AlN with N before adding the ferrochrome nitride, so that the recovery rate of N is reduced.
Pouring: and (3) adopting an argon blowing ring to protect pouring, preventing the molten steel from further secondary oxidation, and supplementing 300 kg-500 kg of heat insulating agent after pouring to prevent the pouring defect from being generated.
In the step, specifically, in order to prevent the loss of alloy elements and the generation of inclusions caused by secondary oxidation of molten steel in the pouring process, argon is blown into a cavity 30min before pouring, the oxygen concentration of the cavity is measured during pouring, and the cavity can be poured after the oxygen concentration is less than 5%.
Although the present invention has been described in detail with reference to the foregoing embodiments, it will be apparent to those skilled in the art that modifications may be made to the embodiments or portions thereof without departing from the spirit and scope of the invention.
Claims (8)
1. The method for smelting the CB2 material by using the electric arc furnace is characterized by comprising the following steps of:
preparing materials: the charging materials are scrap steel and pig iron, and the adding amount ratio of the scrap steel to the pig iron is 8: 2;
smelting in an EAF furnace: firstly, distributing materials, namely adding charging materials into an EAF furnace, and simultaneously adding lime accounting for 5 percent of the total amount of molten steel; blowing oxygen for decarburization after the temperature of the molten steel reaches 1620 ℃, and not reducing in an EAF furnace; when the P content is less than or equal to 0.005 percent and the C content is less than or equal to 0.05 percent, tapping the steel to an LF furnace for smelting when the temperature reaches 1640-1670 ℃;
smelting in an LF furnace: firstly, adding AL particles to fully reduce molten steel until the oxygen activity is reduced to be below 5ppm, adding active lime to reduce electrode recarburization, adding fluorite, adjusting the argon flow to be 0.4-0.6 MPa to remove S, reducing the S content to be below 0.01%, taking a spectrum sample to analyze chemical components, adjusting the components of the molten steel until the content of each element in the molten steel meets the standard range, and tapping to a VD furnace for smelting when the temperature is adjusted to be 1620-1640 ℃;
and (3) smelting in a VD furnace: firstly, vacuumizing to a high vacuum degree below 67pa, keeping the vacuum degree for 15min, then finishing VD, adding 1-1.5 kg/ton of steel Al particles, keeping the vacuum degree for 5min, and then tapping to an LF furnace to adjust components;
adjusting components in an LF furnace: adjusting argon pressure to 0.2-0.25 MPa, adding ferrochrome nitride, wherein the addition amount (kg) of the ferrochrome nitride is [ (the target value of nitrogen content-0.05%). the weight of molten steel ]/(the recovery rate of the ferrochrome nitride is the nitrogen content in the ferrochrome nitride), sampling and analyzing after 5min, tapping and pouring;
pouring: argon blowing ring protection pouring is adopted, and a heat preservation agent is added after pouring.
2. The method of claim 1, wherein in the EAF furnace smelting step, 40% of the total amount of lime is placed at the bottom of the burden for bedding, and 60% of the total amount of lime is added in the middle of the burden during burden distribution.
3. The method for smelting the CB2 material by using the electric arc furnace as claimed in claim 1, wherein in the smelting step of the EAF furnace, when the oxygen blowing decarburization quantity is more than 0.2%, the furnace door is inclined downwards by 30 degrees to start slag flowing, when the slag flowing quantity is more than 90% of the total steel slag quantity, the slag flowing is stopped, a second batch of lime is added from a high-level bin, the adding quantity is 2% -3% of the total molten steel quantity, the oxygen blowing decarburization is continued until the P content is less than or equal to 0.005%, and the removal quantity of the oxidized slag in the furnace is ensured to be more than or equal to 95% after the oxygen blowing is finished.
4. The method for smelting CB2 material in an electric arc furnace according to claim 1, wherein in the EAF furnace smelting step, 2kg/t of aluminum blocks are charged into a ladle while tapping, and 300kg of a desulfurizing agent is charged at the same time.
5. The method for smelting the CB2 material by using the electric arc furnace as claimed in claim 1, wherein in the smelting step of the LF furnace, the alloy which is not easy to oxidize is added firstly when the components of the molten steel are adjusted, and the alloy is added in small quantities in batches, wherein each addition is less than 300 kg.
6. The method for smelting CB2 material by using an electric arc furnace as claimed in claim 5, wherein the sample is taken for analysis after adding the alloy which is not easy to oxidize, and if the carbon content is less than 0.12%, the elements which are easy to oxidize are continuously added, and the elements which are easy to oxidize comprise Mn, Si, V, Nb and B; according to the content of each element in the steel, firstly, three elements of Mn, Si and V are controlled within the standard, and then two elements of Nb and B are adjusted.
7. The method for smelting CB2 material by using the electric arc furnace as claimed in claim 1, wherein the thickness of the slag layer is kept between 180mm and 220mm in the VD furnace smelting step.
8. The method for smelting CB2 material by using the electric arc furnace as claimed in claim 1, wherein in the step of pouring, argon is blown into the cavity 30min before pouring, the oxygen concentration of the cavity is measured during pouring, and the pouring is carried out after the oxygen concentration is less than 5%.
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