CN111926149A - RH refining method for removing inclusions in molten steel - Google Patents
RH refining method for removing inclusions in molten steel Download PDFInfo
- Publication number
- CN111926149A CN111926149A CN202010921542.8A CN202010921542A CN111926149A CN 111926149 A CN111926149 A CN 111926149A CN 202010921542 A CN202010921542 A CN 202010921542A CN 111926149 A CN111926149 A CN 111926149A
- Authority
- CN
- China
- Prior art keywords
- molten steel
- nitrogen
- inclusions
- refining
- refining method
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Pending
Links
Classifications
-
- 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
- C21C7/10—Handling in a vacuum
-
- 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
Landscapes
- Chemical & Material Sciences (AREA)
- Engineering & Computer Science (AREA)
- Materials Engineering (AREA)
- Metallurgy (AREA)
- Organic Chemistry (AREA)
- Treatment Of Steel In Its Molten State (AREA)
Abstract
The invention provides an RH refining method for removing inclusions in molten steel, which is characterized in that bottom nitrogen blowing operation is carried out before and in the middle of RH vacuum, RH lifting gas is nitrogen, a denitrification path in the molten steel is controlled, nitrogen in the molten steel is prevented from being removed from bubbles, nitrogen precipitation and nitrogen increase processes in the vacuum treatment process are carried out simultaneously, sufficient nitrogen is ensured to be precipitated from the molten steel by taking the inclusions as cores, and meanwhile, the condition that the molten steel is continuously replaced and updated in the RH refining process is utilized, so that the effect of stably removing the inclusions in the molten steel is achieved. The removal amount of small-size inclusions reaches more than 90 percent, the cleanliness of molten steel is obviously improved, and meanwhile, stable and continuous production can be realized at low cost.
Description
Technical Field
The invention belongs to the field of ferrous metallurgy refining, and particularly relates to an RH refining method for removing inclusions in molten steel. The method is used for RH refining production process of high-quality special steel with strict requirements on inclusion, including high-quality industrial wire rods such as bearings, springs, cord steel and the like, and can obviously reduce the number of inclusions (especially small-size inclusions) in the steel and improve the quality of products.
Background
The non-metallic inclusion is an important factor influencing the fatigue life of high-quality special steel such as a bearing, a spring, a cord thread and the like, and the quantity and the size of the non-metallic inclusion in the steel are important indexes for measuring the quality of products. In the existing production process flow of high-quality special steel, the non-metallic inclusions are mostly controlled by refining in links such as LF, RH or VD, and the like, but the conventional refining processes such as LF, RH or VD and the like are difficult to meet the requirements of high-quality special steel on inclusions, and the contradiction between the production efficiency and the product quality is serious.
The removal of inclusions by using bubbles in molten steel has been studied and applied by metallurgists, but the bubbles formed by externally blowing gas into molten steel have large size, are not uniformly distributed, have limited inclusion adsorption capacity and have poor inclusion removal effect. At present, a plurality of patents provide methods for removing nonmetallic inclusions by separating out tiny bubbles in steel, and the main operation key points are that firstly nitrogen or hydrogen increasing treatment is carried out on molten steel, and then vacuum treatment is carried out on the molten steel, so that bubbles are separated out from the molten steel by taking the inclusions as cores, and the effect of removing the inclusions is achieved. The main patents involved are: a method for removing microscopic non-metallic inclusions in molten steel by a nitrogen increasing and nitrogen precipitating method disclosed in publication No. CN104404205A on day 11/3/2015, a method for removing metallic inclusions by a float-up method using a dissolved gas and a pressurized vacuum induction furnace refining apparatus disclosed in publication No. CN 105779699 a on day 20/7/2016, and a method for generating fine bubbles in molten steel by a method disclosed in publication No. CN 106086315 a on day 9/11/2016. Although the above patent can reduce the amount of non-metallic inclusions in steel, it has several problems: 1. the operation of adding hydrogen (blowing hydrogen, coke oven gas and natural gas) to high-temperature liquid molten steel has great potential safety hazard, strict requirements on the sealing performance of equipment and daily gas pipeline leakage detection are met, and the enterprise management cost is increased; 2. the influence of the contents of oxygen and sulfur in steel on the mass transfer of nitrogen in steel is not considered, and the reaction rates of nitrogen increase and nitrogen precipitation cannot be effectively controlled. 3. The relationship between denitrification path (inner bubble precipitation and removal from argon bubbles) and impurity removal effect in the vacuum denitrification process is not considered. At present, nitrogen elements in molten steel are mainly removed in three ways: 1) precipitation from the surface of molten steel, 2) precipitation from molten steel argon bubbles, and 3) precipitation with inclusions as nuclei in molten steel. If most of nitrogen elements in the molten steel are removed from argon bubbles, the effect of removing micro inclusions cannot be achieved, and meanwhile, nitrogen elements precipitated by taking the inclusions as cores in the molten steel are less, so that the effect of adding nitrogen, precipitating nitrogen and removing inclusions is not obvious.
Disclosure of Invention
The invention provides an RH refining method for removing inclusions in molten steel, which is characterized in that the method comprises the steps of controlling a removing path of nitrogen elements in the molten steel, spontaneously precipitating tiny nitrogen bubbles by taking fine inclusions as cores of the nitrogen elements in the molten steel under a vacuum condition, removing the inclusions after bubbles float upwards, fully considering the relation between a denitrification path (internally precipitating the bubbles and removing the bubbles from argon bubbles) and an inclusion removing effect in a vacuum denitrification process, precipitating the tiny nitrogen bubbles by taking the inclusions as cores of the nitrogen elements in the molten steel as much as possible, floating the bubbles and removing the inclusions.
The specific technical scheme of the invention is as follows:
an RH refining method for removing inclusions in molten steel comprises the following steps:
1) carrying out low-vacuum treatment on the molten steel in the middle before and after RH refining, wherein the bottom blowing and lifting gases of the steel ladle are nitrogen;
2) and carrying out high vacuum degree treatment on the molten steel in the later stage of RH refining, and switching the lifting gas into argon.
Furthermore, the [ O ] in the RH incoming molten steel is required to be less than 20ppm, [ S ] is required to be less than 20ppm and [ Cr ] is required to be less than 5 percent, and the Cr content is too high to facilitate denitrification; the content of the components is controlled by mass fraction;
preferably, the ladle used in the vacuum treatment is provided with a bottom blowing element which is positioned right below the RH ascending immersion pipe, and the bottom blowing element is mainly used for keeping the nitrogen content in the molten steel and simultaneously has no adverse effect on the flow field of the molten steel in the RH vacuum refining process;
further, in the step 1), the vacuum degree in the middle before RH refining (after RH station entry) is maintained at 150-200 Pa;
further, after the RH station enters, opening a steel ladle right below the lifting impregnation pipe for bottom blowing, wherein the bottom blowing gas is nitrogen, the flow rate is 0.30-1.75NL/(min.t), and starting vacuum treatment; the vacuum degree is kept at 150-200 Pa;
in step 1), the lift gas is nitrogen, and the flow rate is 5.20-7.10 NL/(min.t).
In the step 1), the ladle bottom blowing and the lifting gas treatment are carried out synchronously, and the treatment time is 15-18 min.
Namely, the RH refining metaphase in the step 1) refers to the period of time of carrying out ladle bottom blowing and lifting gas treatment for 15-18min after RH enters the station.
In the step 1), bottom blowing nitrogen is carried out before and in the middle period of RH vacuum, RH lifting gas is nitrogen, the denitrification path in the molten steel is controlled, the nitrogen element in the molten steel is prevented from being separated out in bubbles formed by the lifting gas, and sufficient nitrogen element is ensured to be spontaneously separated out and float in the molten steel by taking small-size inclusion as a core, so that the purpose of removing the inclusion is achieved.
After the treatment in the step 1), closing the bottom blowing of the steel ladle, namely entering the step 2), and switching the lifting gas of the dip pipe into argon.
In the step 2), the molten steel is subjected to high vacuum degree treatment in the later RH refining stage, namely the vacuum degree of a vacuum groove is less than 100 Pa;
further, in the step 2), the lifting gas of the dip pipe is switched to argon gas, the flow rate of the lifting gas is 6.90-8.70NL/(min.t), and the treatment time is more than 6 min. The treatment time for the steel grade with lower nitrogen content of the finished product is longer, and meanwhile, because the contents of [ O ] and [ S ] in the molten steel are very low, the treatment time is not too long, and the production rhythm is not influenced.
Further, in the treatment process of the step 2), the content of the S element in the steel is adjusted, and the adding time of the sulfur-containing alloy is 3-5 minutes before the blank breaking.
In the step 2), the molten steel is subjected to high-vacuum-degree treatment in the later stage of RH refining, the lifting gas is argon, nitrogen in the steel is rapidly separated out in lifting argon bubbles by utilizing a vacuum condition, and the nitrogen content in the molten steel is reduced so as to meet the requirement of the molten steel on the nitrogen content.
The physical meaning of the unit NL/(min.t) is the blowing amount required by unit mass of molten steel in unit time.
The design idea of the invention is that if the effect of removing small-size inclusions is considered, the removal path of nitrogen elements in molten steel must be controlled, and nitrogen elements in molten steel are precipitated by taking the inclusions as cores as much as possible to precipitate the inclusions so as to ensure good and stable inclusion removal effect.
Compared with the prior art, the method disclosed by the invention has the advantages that the removal path of the nitrogen element in the molten steel is controlled, the principle that the inclusion is removed by precipitating micro bubbles in the molten steel is utilized, the relation between a denitrification path (internally precipitating bubbles and removing the bubbles from argon bubbles) and the inclusion removing effect in the vacuum denitrification process is fully considered, and the nitrogen element in the molten steel is precipitated by taking the inclusion as a core and the inclusion is removed as much as possible. The bottom blowing nitrogen operation is carried out before and in the middle period of RH vacuum, RH lifting gas is nitrogen, the denitrification path in the molten steel is controlled, the nitrogen element in the molten steel is prevented from being removed from bubbles (in a lifting gas pipeline), the nitrogen precipitation and nitrogen increase processes are carried out simultaneously in the vacuum treatment process, the nitrogen content in the molten steel can be effectively ensured by the lower vacuum degree in the early period, the sufficient volume of the molten steel in a vacuum tank is further ensured to carry out denitrification reaction, the sufficient nitrogen element is precipitated from the molten steel by taking impurities as a core, and meanwhile, the condition of continuous replacement and updating of the molten steel in the RH refining process is utilized, so that the effect of stably removing the impurities in the molten steel is achieved. The later high vacuum degree aims at rapid denitrification and reaches the target range of steel grades. The removal amount of small-size inclusions reaches more than 90 percent, the cleanliness of molten steel is obviously improved, and meanwhile, stable and continuous production can be realized at low cost.
Detailed Description
Example 1
An RH refining method for removing inclusions in molten steel comprises the following steps:
1) the RH incoming molten steel (all the mass fractions) is required to have [ O ] less than 20ppm, [ S ] less than 20ppm and [ Cr ] less than 5% (the content is too high to be beneficial to denitrification); the ladle used in the vacuum treatment needs a bottom blowing element positioned right below the RH ascending dipping pipe; and opening the ladle bottom blowing right below the lifting immersion pipe after the RH station (the middle period before vacuum treatment) with the flow rate of 0.30-1.75NL/(min.t), starting vacuum treatment, keeping the vacuum degree at 150-200Pa, using nitrogen as lifting gas with the flow rate of 5.20-7.10NL/(min.t), and treating for 15-18 min.
2) After the treatment of the step 1), closing ladle bottom blowing, entering the later stage of RH vacuum treatment, wherein the vacuum degree of a vacuum tank is less than 100Pa, the lifting gas of a dip pipe is switched into argon, the flow rate of the lifting gas is 6.90-8.70NL/(min.t), the treatment time is more than 6min, and if the content of the S element in the steel needs to be adjusted, the sulfur-containing alloy can be added into molten steel 3min before the break.
The method is used in the smelting process of treating 7-furnace bearing steel poured in a certain plant, the mass of the steel ladle molten steel is about 115 +/-1 tons, the oxygen and sulfur contents in the steel are controlled by adopting an LF furnace process, and the inclusion is removed by adopting an RH process according to the method. Wherein the conditions of the station entry and the bottom blowing of the RH refined molten steel are shown in Table 1, and the conditions of the RH process are shown in Table 2. During the production process, the removal conditions of inclusions with different sizes in molten steel before and after RH are inspected, compared and analyzed, and the comparison result is shown in Table 3.
TABLE 1 RH refining molten steel arrival and bottom blowing conditions
The flow units in the table are NL/min.
TABLE 2 lifting gas implementation of RH refining procedure
The removal of inclusions before and after the RH refining process in each furnace by the ASPEX inclusion analysis is shown in table 3.
TABLE 3 table of the amount of inclusions removed before and after RH refining
The method can be obtained from the process control condition of the embodiment and the conditions of impurity removal before and after the RH refining process, the process control and impurity removal effects of the invention are good, and the molten steel cleanliness and product quality improvement effects are obvious.
The method disclosed by the invention has the advantages that by controlling the removal path of nitrogen elements in the molten steel, the principle that the nitrogen elements in the molten steel spontaneously precipitate tiny nitrogen bubbles by taking tiny impurities as cores under the vacuum condition and the impurities are removed after the bubbles float upwards is utilized, the relation between a denitrification path (internally precipitate the bubbles and remove the bubbles from the argon bubbles) and the impurity removal effect in the vacuum denitrification process is fully considered, so that the nitrogen elements in the molten steel precipitate tiny nitrogen bubbles by taking impurities as cores as much as possible, and the bubbles float upwards and remove the impurities. The bottom blowing nitrogen operation is carried out before and in the middle period of RH vacuum, RH lifting gas is nitrogen, the denitrification path in molten steel is controlled, the nitrogen element in the molten steel is prevented from being removed from bubbles, the nitrogen precipitation and nitrogen increase processes in the vacuum treatment process are carried out simultaneously, sufficient nitrogen element is ensured to be precipitated from the molten steel by taking inclusions as cores, and meanwhile, the continuous replacement and updating conditions of the molten steel in the RH refining process are utilized, so that the effect of stably removing the inclusions in the molten steel is achieved. The removal amount of small-size inclusions reaches more than 90 percent, the cleanliness of molten steel is obviously improved, and meanwhile, stable and continuous production can be realized at low cost.
Claims (10)
1. An RH refining method for removing inclusions in molten steel, comprising the steps of:
1) carrying out low-vacuum treatment on the molten steel in the middle before and after RH refining, wherein the bottom blowing and lifting gases of the steel ladle are nitrogen;
2) and carrying out high vacuum degree treatment on the molten steel in the later stage of RH refining, and switching the lifting gas into argon.
2. The RH refining method for removing inclusions in molten steel according to claim 1, wherein [ O ] is required to be less than 20ppm, [ S ] is required to be less than 20ppm, and [ Cr ] is required to be less than 5% in the RH incoming molten steel.
3. The RH refining method for removing inclusions in molten steel according to claim 1, wherein a ladle used in the vacuum treatment is located immediately below the RH dip pipe with a bottom blowing member.
4. The RH refining method for removing inclusions in molten steel according to claim 1, wherein the mid-stage vacuum degree before RH refining in step 1) is maintained at 150-200 Pa.
5. The RH refining method for removing inclusions in molten steel according to any one of claims 1 to 4, wherein after the RH is in-station, a ladle bottom blowing just below the lifting dip pipe is opened, and a bottom blowing gas is nitrogen at a flow rate of 0.30-1.75 NL/(min.t).
6. The RH refining method for removing inclusions in molten steel according to claim 1, wherein in the step 1), the lift gas is nitrogen gas, and a flow rate is 5.20 to 7.10 NL/(min.t).
7. The RH refining method for removing inclusions in molten steel according to claim 1, wherein the treatment time of the step 1) is 15 to 18 min.
8. An RH refining method for removing inclusions in molten steel according to claim 1, wherein in the step 2), a degree of vacuum in the vacuum vessel at a later stage of RH refining is less than 100 Pa.
9. The RH refining method for removing inclusions in molten steel according to claim 1, wherein the dip tube lift gas is switched to argon gas in the step 2), the lift gas flow rate is 6.90-8.70NL/(min.t), and the treatment time is more than 6 min.
10. The RH refining method for removing inclusions in molten steel according to claim 1, wherein in the step 2), when the content of S element in steel is adjusted, the timing of adding the sulfur-containing alloy is 3 to 5 minutes before the break.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN202010921542.8A CN111926149A (en) | 2020-09-04 | 2020-09-04 | RH refining method for removing inclusions in molten steel |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN202010921542.8A CN111926149A (en) | 2020-09-04 | 2020-09-04 | RH refining method for removing inclusions in molten steel |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CN111926149A true CN111926149A (en) | 2020-11-13 |
Family
ID=73310224
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CN202010921542.8A Pending CN111926149A (en) | 2020-09-04 | 2020-09-04 | RH refining method for removing inclusions in molten steel |
Country Status (1)
| Country | Link |
|---|---|
| CN (1) | CN111926149A (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN112646954A (en) * | 2020-11-23 | 2021-04-13 | 首钢集团有限公司 | RH refining method for improving removal rate of ultra-low carbon steel inclusions |
Citations (7)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JP2007224367A (en) * | 2006-02-23 | 2007-09-06 | Jfe Steel Kk | Method for producing high-nitrogen steel |
| CN104404205A (en) * | 2014-10-27 | 2015-03-11 | 北京科技大学 | Method for removing microscopic nonmetallic inclusion in molten steel by using nitrogen-increasing nitrogen-precipitating process |
| CN107686871A (en) * | 2017-08-25 | 2018-02-13 | 武汉钢铁有限公司 | A kind of non-hardened and tempered steel production method |
| CN109652615A (en) * | 2019-01-25 | 2019-04-19 | 钢铁研究总院 | A method of improving RH refining process molten steel circular flow |
| CN110387455A (en) * | 2019-08-29 | 2019-10-29 | 马鞍山钢铁股份有限公司 | A kind of sulfur bearing steel accurately controls nitrogen method |
| CN110453029A (en) * | 2019-09-25 | 2019-11-15 | 敬业钢铁有限公司 | The method of the inexpensive accurate control siliceous low-alloy steel nitrogen content of high nitrogen |
| CN110592322A (en) * | 2019-09-19 | 2019-12-20 | 北京科技大学 | Method for generating micro-bubbles in RH refined molten steel |
-
2020
- 2020-09-04 CN CN202010921542.8A patent/CN111926149A/en active Pending
Patent Citations (7)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JP2007224367A (en) * | 2006-02-23 | 2007-09-06 | Jfe Steel Kk | Method for producing high-nitrogen steel |
| CN104404205A (en) * | 2014-10-27 | 2015-03-11 | 北京科技大学 | Method for removing microscopic nonmetallic inclusion in molten steel by using nitrogen-increasing nitrogen-precipitating process |
| CN107686871A (en) * | 2017-08-25 | 2018-02-13 | 武汉钢铁有限公司 | A kind of non-hardened and tempered steel production method |
| CN109652615A (en) * | 2019-01-25 | 2019-04-19 | 钢铁研究总院 | A method of improving RH refining process molten steel circular flow |
| CN110387455A (en) * | 2019-08-29 | 2019-10-29 | 马鞍山钢铁股份有限公司 | A kind of sulfur bearing steel accurately controls nitrogen method |
| CN110592322A (en) * | 2019-09-19 | 2019-12-20 | 北京科技大学 | Method for generating micro-bubbles in RH refined molten steel |
| CN110453029A (en) * | 2019-09-25 | 2019-11-15 | 敬业钢铁有限公司 | The method of the inexpensive accurate control siliceous low-alloy steel nitrogen content of high nitrogen |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN112646954A (en) * | 2020-11-23 | 2021-04-13 | 首钢集团有限公司 | RH refining method for improving removal rate of ultra-low carbon steel inclusions |
Similar Documents
| Publication | Publication Date | Title |
|---|---|---|
| CN110527775B (en) | RH refining furnace chemical temperature rising method suitable for low-carbon aluminum killed steel | |
| CN111926149A (en) | RH refining method for removing inclusions in molten steel | |
| CN115612920A (en) | Steel for flexible bearing of harmonic speed reducer of robot and production method thereof | |
| CN1710366A (en) | Top-bottom reblowing vacuum inductive stove | |
| CN111944940A (en) | Method for controlling inclusions in IF steel | |
| CN110565030A (en) | low-silicon low-aluminum martensitic stainless steel containing rare earth elements and smelting method thereof | |
| CN114317996A (en) | Method for manufacturing low-gas-content high-titanium low-aluminum nickel-cobalt alloy electroslag remelting electrode | |
| CN111944953B (en) | Method for reducing number of small-size nonmetallic inclusions in steel | |
| CN2859419Y (en) | A top and bottom compound blow vacuum inductive stove | |
| CN109022661B (en) | Method for reducing heavy rail steel rail damage rate | |
| CN117845145A (en) | Super-purity 316LVV stainless steel cast ingot, triple smelting process and application thereof | |
| Ardelean et al. | Researches regarding the influence of vacuum parameters on the efficiency of gas removal from the liquid steel | |
| CN106086315A (en) | A kind of method generating micro-bubble in molten steel | |
| CN111057938A (en) | Processing technology of heat-resistant, wear-resistant and corrosion-resistant high-chromium heat-resistant alloy | |
| CN113388740B (en) | Method for improving cleanliness of pressurized electroslag remelting high-nitrogen martensite stainless steel | |
| CN113943902B (en) | Low-gas-content controlled smelting method for high-silicon high-titanium aluminum-containing stainless steel | |
| CN110592324B (en) | RH refining method for reducing tapping temperature of IF steel converter | |
| Shevtsova et al. | Aspects of the formation of sulfide inclusions and their effect on the quality of low-alloy structural steels | |
| CN115652181B (en) | Manufacturing method of steel large round billet for high-carbon low-alloy hot roller | |
| CN111270081A (en) | Method for controlling gas element content in 9Ni steel ingot of more than 40 tons | |
| CN117551838B (en) | Control method for low-magnification pocking defects of large-specification martensitic stainless steel forging | |
| CN115181829B (en) | Production method for controlling manganese in converter smelting | |
| CN113106322B (en) | Smelting method of ultrapure ferrite stainless steel | |
| CN113584372B (en) | Casting blank smelting method for reducing black lines on surface of pickled plate | |
| CN211339585U (en) | VD furnace shielding cover |
Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| PB01 | Publication | ||
| PB01 | Publication | ||
| SE01 | Entry into force of request for substantive examination | ||
| SE01 | Entry into force of request for substantive examination |