CN1247799C - Production method for reducing and fining the high-carbon chromium bearing steel D-type impurity - Google Patents

Abstract

The production method of reducing and refining high-carbon chromium bearing steel D-type inclusions is characterized in that it adopts a four-step method of initial steelmaking in an electric furnace, refining in a bottom-blown argon LF ladle furnace, degassing in a VD vacuum furnace, and die casting or continuous casting Smelting process flow: a comprehensive deoxidation process of aluminum precipitation pre-deoxidation for tapping through electric furnace primary smelting, Fe-Si powder diffusion slag deoxidation at LF station, and vacuum carbon deoxidation at VD station. At the same time, high alkalinity slag desulfurization is used at LF station , In the VD station, low-basicity slag is used to reduce the free CaO in the slag. The new refining process achieves the purpose of reducing and refining the D-type inclusions in the steel. The high-carbon chromium bearing steel produced by the patented method of the present invention has an oxygen content of ≤0.0015%, a titanium content of ≤0.0030%, and a sulfur content of ≤0.015%, which not only reduces the amount of aluminum used for deoxidation (cost savings of 25.3 yuan per ton of steel) , the more important thing is to solve the technical contradiction between the control of spherical inclusions in molten steel refining and the desulfurization process. The D-type inclusions of the finished steel meet the requirements of SKF’s Grade 3 (D fine ≤ 1.0, D coarse ≤ 0.5, Dmax ≤27μm).

Description

Production Method for Reducing and Refining Type D Inclusions in High Carbon Chromium Bearing Steel

technical field

The invention relates to a control method for bearing steel inclusions in the metallurgical industry, in particular to a production method for controlling (reducing and refining) the D-type inclusions of high-carbon chromium bearing steel.

Background technique

The cleanliness of high-carbon chromium bearing steel and the fatigue life of the bearing (the main damage form of the bearing is fatigue spalling, and the inclusions in the steel are the main cause of fatigue spalling. The fatigue life of the bearing is generally determined by the shape and size of the inclusions in the steel , Quantity and uniformity of distribution.) are closely related. In recent years, with the rapid development of the economy, bearing production and use departments require the production of bearing steel with higher purity to meet the needs of lightweight bearings and longer life.

For a long time, metallurgists have always regarded the oxygen content as an important basis for evaluating the purity of bearing steel (as the oxygen content in the steel decreases, the fatigue life of the bearing can be doubled. For a long time, bearings at home and abroad Steel production enterprises are committed to continuously reducing the oxygen content in steel.). At present, the oxygen content level ([0]≤0.0015%, 15×10 ^-6 , or 15ppm) in the national standard for bearing steel has not become a problem for most bearing steel manufacturers. When the oxygen content reaches the level of ≤10ppm, there are two different tendencies to further improve the purity of bearing steel: (A) Japanese bearing steel manufacturers represented by Sanyo are still working hard for lower oxygen content , the oxygen content of ultra-pure bearing steel has been able to be controlled at 3-5ppm, and some domestic special steel enterprises have also been able to control it at 6-7ppm, while the titanium content has also been reduced to a level of ≤15ppm (a kind of The smelting production method of ultra-pure high-carbon chromium bearing steel, which is characterized by oxygen content ≤ 7ppm, titanium content ≤ 12ppm, the patentee Baosteel Group Shanghai Wugang Company); (B) European and American companies represented by SKF pay more attention to inclusions The size, quantity and nature of the object: it is required to be small in size, small in quantity, and deformable. Experiments have proved that: when the oxygen content in the steel is ≤8ppm, the fatigue life of the bearing does not increase inversely proportional to the further reduction of the oxygen content, but is related to the size, quantity, nature and distribution of the inclusions.

Judging from the harmfulness of various inclusions in bearing steel to fatigue life: the most harmful is the spherical oxide inclusions (the oxide spherical inclusions are mainly mCaO·nAl ₂ O ₃ , and the single Al ₂ O ₃ inclusions are long strips shape), this is because the thermal expansion coefficient difference between the spherical oxide inclusions and the matrix is large, and they will not deform during the rolling process, and voids will form around the inclusions, which will become the main source of cracks; therefore, it is necessary to reduce the spherical oxide inclusions. Quantity and size, the most important thing is to reduce the Ca content in the inclusions. The research shows that the calcium in the inclusions mainly comes from the free CaO content in the refining top slag (the top slag with high alkalinity has high CaO content, and the top slag with low alkalinity has low CaO content). Under the condition of vacuum (vacuum degree ≤ 67Pa) in the VD process, the C element in the bearing steel (the C content in the finished product of this type of bearing steel is about 1%) can reduce the CaO in the slag, that is, the following reaction exists: (CaO)+ [C]=[Ca]+{CO}, the reduced Ca combines with Al and O in molten steel to form spherical oxides mainly mCaO·nAl ₂ O ₃ ; if Ca combines with S in molten steel , will generate ellipsoidal CaS inclusions with poor deformability and length/width≤5). Therefore, under the refining conditions of LF/VD, the steel slag is fully mixed, and the composition of the refining slag (the refining slag of the LF or VD process, especially the refining slag of the VD process) can directly affect the nature, composition and size of the inclusions in the steel .

At present, in the electric furnace production method of high-carbon chromium bearing steel, there are two typical advanced processes in the world: one is the LF ladle refining process represented by SKF in Sweden, EAF-LF (ASEA)/VD-IC (in Sweden In SKF Ovaco plant, after the molten steel enters the ladle from the EAF furnace, the oxidized slag is first removed by the slag removal machine. After the ASEA ladle is refined, the high-alkalinity top slag can be removed by slag replacement and replaced with low-alkalinity top slag .); The second is the RH ladle refining process represented by Sanyo, Japan: EAF-LF/RH-CC (the RH ladle refining process of Sanyo Plant is to lift part of the molten steel to a vacuum chamber for degassing treatment, and the molten steel There is no mixing process with the top slag. Although high alkalinity slag is used, the composition of the top slag has little effect on the bearing steel inclusions.). However, domestic bearing steel production plants, limited by metallurgical equipment and technology, mostly use EAF (electric furnace)-LF (ladle refining furnace)/VD (vacuum degassing refining furnace)-IC (liquid steel mold casting) )/CC (liquid steel continuous casting) process, the LF/VD refining process adopts the single slag method, in order to complete the deoxidation and desulfurization tasks at the same time, the refined top slag with high alkalinity (R=4～7) is used (in the electric furnace smelting process , the task of desulfurization is mainly completed in the tapping process and ladle furnace. According to the molecular theory of slag, CaO and SiO ₂ in the top slag can be combined to form three molecular bond compounds: CaO·SiO ₂ , 2CaO·SiO ₂ and 3CaO ·SiO ₂ . Among them, CaO·SiO ₂ and 2CaO·SiO ₂ are stable compounds, and 3CaO·SiO ₂ is an unstable compound, which is easy to decompose into 2CaO·SiO ₂ and CaO. Therefore, it is necessary to reduce the free CaO content in the slag , it is necessary to control the ratio of CaO and SiO ₂ in the slag (basicity R) to ≤2.8 (3CaO/SiO ₂ =3×56/60=2.8), preferably 1.9 (2CaO/SiO ₂ =2 ×56/60=1.9); but when there is no free GaO in the slag, the following reaction cannot occur: (CaO)+[S]=(CaS)+[O], the refining top slag has no desulfurization ability, that is to say, the desulfurization ability of too low top slag basicity is poor.), therefore, the control of spherical inclusions and desulfurization (all product standards have clear restrictions on the content of sulfur in steel, in the smelting process to reach If it is not specified, it cannot enter the next process, and the nature and state of the inclusions cannot be understood during the smelting process.) A contradiction occurred, so most bearing steel manufacturers use high-alkalinity top slag (free CaO high content) refining.

Therefore, the formation of spherical oxides in high-carbon chromium bearing steel manufactured by domestic bearing steel manufacturers is unavoidable (according to the rating required by SKF, the actual level of D-type inclusions in bearing steel in China is: D fine = 2.0～ 2.5 level; D rough = 0.5 ~ 1.0 level; Dmax = 35 ~ 50μm.), so far, there is no bearing steel manufacturer in China that has been fully recognized by the world famous bearing manufacturer Sweden SKF (SKF company D33-1 In the bearing steel standard, among ordinary 3S steel grades and high-level Grade 3 steel grades of the same variety, there are clear regulations on the rating of D-type inclusions in bearing steel, which not only expands the rating range of inclusion properties to ellipsoid Spherical oxides, titanium nitride and sulfide; also put forward restrictions on the grade and size of spherical inclusions: 3S requires D fine ≤ 1.0 grade, D coarse ≤ 1.0 grade; Grade 3 requires D fine ≤ 1.0 grade, D coarse ≤ 0.5 level, Dmax≤27μm, Dmax≤27μm is equal to Ds≤1.0 level). In today's economic globalization, obtaining the approval of SKF is an important way for bearing steel to enter overseas markets and domestic and foreign companies.

Contents of the invention

The present invention develops a production method for reducing and refining high-carbon chromium bearing steel D-type inclusions, through the pre-deoxidation of aluminum precipitation for tapping in electric furnace primary refining, the deoxidation of Fe-Si powder diffusion slag in LF station refined in ladle furnace and the Comprehensive deoxidation process of vacuum carbon deoxidation in the VD station of vacuum furnace refining. At the same time, high-basic slag desulfurization is used in the LF station, and a new refining process of low-basicity slag is used in the VD station to reduce free CaO in the slag. The oxygen content, titanium content, and sulfur content of the steel are controlled within the range of ≤0.0015%, ≤0.0030%, and ≤0.015%, respectively, to reduce and refine the D-type inclusions in high-carbon chromium bearing steel, and meet the requirements of SKF's Grade3 ( D fine ≤ 1.0 grade, D coarse ≤ 0.5 grade, Dmax ≤ 27μm).

The production method for reducing and refining high-carbon chromium bearing steel D-type inclusions provided by the present invention is characterized in that it adopts a four-step smelting process flow: initial molten steel smelting in an electric furnace; refining in a bottom-blown argon ladle furnace; degassing in a vacuum furnace; Die casting or continuous casting.

The first step is to carry out primary smelting of molten steel in the EBT type (EBT is eccentric bottom tapping technology) electric furnace (EAF):

(1) Ratio of iron and steel materials in the primary smelting furnace: 70-80% of scrap steel, 20-30% of high-quality pig iron; ensure that S ≤ 0.040%;

(2) In the electric furnace, the metal raw materials are melted by electricity, and the oxygen is input to accelerate the melting: if the second feeding is made, the first basket is powered on for 3 to 8 minutes, and then the oxygen is blown to help the melting, and the second basket is fed after 15 to 20 minutes. material; if the material is added at one time, after 5 to 20 minutes of power supply, blow oxygen to help the melting;

(3) After the molten pool is formed, spray coke powder containing more than 80% carbon to create foam slag, the height of foam slag is 500-700mm, heat up, decarburize, and protect the furnace wall; flow slag in time and add lime according to conventional operations , to ensure that the phosphorus content ≤ 0.012% and the titanium content ≤ 0.0005% when tapping (to ensure that the titanium content of the finished molten steel is ≤ 0.0030%);

(4) When the composition of the molten steel meets the requirements and the temperature of the molten steel is 1630-1650°C, the method of leaving steel and slag is adopted for tapping: the amount of steel remaining is 7-13% of the total tapping amount, and the amount of slag is the total amount of slag 5-20% of

(5) When the electric furnace is tapping, carry out alloying and deoxidation operations in the ladle, and make the first batch of LF refining slag in the ladle: when the tapping amount reaches 20-30%, add Fe-Si, Fe to the ladle -Mn, Adjust Fe-Cr and carbon powder to the middle and lower limits of Si, Mn, Cr and C respectively; when the tapping amount reaches 60-70%, add 0.5-1.0Kg/t of aluminum block (ingot) pre-deoxidation); add lime 7.0-8.5Kg/t, and change the soup brick of the conventional process into 1-2Kg/t lightly burned magnesia balls;

The second step is to deoxidize, desulfurize and remove inclusions according to the single slag method on the ladle refining furnace (LF) whose capacity matches that of the electric furnace:

(1) The steel ladle after baking, the lining is dark red or above, the lining is not seriously damaged, and there is no cold steel in the ladle; the ladle arrives at the tapping station 3 minutes before tapping the electric furnace, and turns on the argon gas after it is in place;

(2) After the ladle furnace filled with high-temperature molten steel enters the LF station, it is heated by electricity, and the molten steel is refined by bottom blowing argon in the whole process of refining in the ladle furnace;

(3) During the refining process of the ladle furnace, control the argon gas flow of the permeable brick, subject to the fact that the molten steel does not expose the slag surface; raise the temperature to melt the slag; when the top slag melts into a liquid state, add high-alkalinity slag in 2 to 3 batches: The total amount of slag is 1.0-1.5Kg/t of lime (3-5Kg/t in the conventional process), 1.0-2.0Kg/t of fluorite (not added in the conventional process); at the same time, Fe- Si powder is used for diffusion deoxidation of molten steel for top slag, the total amount of Fe-Si powder added is 0.7-1.0Kg/t, no aluminum wire is fed (0.2-0.4Kg/t of aluminum wire is fed in the conventional process); the temperature reaches 1550-1560°C When the composition is adjusted to the middle limit of the specification and the temperature reaches 1590-1600°C, add 2.0-2.5Kg/t of silica (to reduce the alkalinity of the top slag, so that the alkalinity of the top slag when the molten steel is refined in the VD furnace degree ≤ 2.5), after 3-5 minutes of power transmission and melting, hoist the ladle into the VD station;

The third step is to carry out vacuum treatment on the molten steel in the vacuum furnace (VD) whose capacity matches that of the electric furnace: after the ladle is hoisted into the VD station, the sample is taken, and the aluminum wire is fed at 0.2-0.5Kg/t (the conventional process adds Al to 0.050 %); close the lid to vacuumize, control the speed of the pump, avoid large boiling and cause gassing (conventional technology pumps fast, often gassing), and keep the vacuum for 20 to 25 minutes after the vacuum reaches 50-140Pa; take a sample after breaking the vacuum, According to the temperature situation, blow argon softly (the molten steel is not exposed) for 15-20 minutes (the conventional process does not have this operation), to achieve the purpose of cleaning the molten steel; sampling analysis, fine-tuning C, Mn, Si, Cr and other elements to the middle limit of the composition specification ( In most cases, the composition at this time has been adjusted in place), but no matter what the composition content of aluminum is, no more aluminum is fed (the conventional process adjusts aluminum to 0.025%), so as to prevent Al ₂ O ₃ from being too late to float. Remains in the steel; when the temperature reaches 1500-1510°C, the steel is poured in a ladle;

The fourth step is to cast high-temperature molten steel, die casting (IC) into qualified steel ingots or/and continuous casting (CC) into qualified steel billets:

(1) During molten steel die casting, use an inert atmosphere to fully seal the protective die casting:

(1) Conventional molten steel casting temperature: liquidus temperature +55～65℃, for example, the liquidus temperature of SKF Grade 3 high-carbon chromium bearing steel is 1450℃, and the temperature of VD station hanging bag is 1500～1510℃; steel ingot mold The inner wall is clean and free of cold steel residue; the temperature of the ingot mold is 60-80°C; the casting ingot type is not limited, but it should meet the requirements of high-carbon chromium bearing steel with low magnification and carbide grade;

(2) The flow steel bricks used in the mold casting flow steel system (center injection pipe, soup channel) adopt zirconium coating, that is, the inner wall of ordinary flow steel bricks is coated with a layer of high temperature resistant (≥1600°C) and erosion resistant Zirconia protective layer (to prevent low-magnification inclusions caused by flow steel system scouring and SiO ₂ in flow steel bricks is reduced by Al in steel to increase oxygen content in steel);

(3) The whole casting process uses argon fully enclosed protection pouring: the protection device is a refractory material cavity, the upper part communicates with the lower part of the ladle nozzle, and the lower part communicates with the upper part of the injection pipe in the mold casting, and the argon gas is connected to make the steel flow in the argon gas Inject into the steel ingot mold from the ladle nozzle and the middle injection pipe under sealing (reduce the suction and secondary oxidation of molten steel).

(II) Continuous casting of high-temperature molten steel into qualified steel billets:

(1) Equipment preparation: (A) There is no serious damage to the copper plate on the inner wall of the crystallizer, no seepage or water leakage is allowed, and the wear depth of the corner is ≯1.5mm; (B) The size of the crystallizer should match the specification of the finished material: for bearings For the steel of ferrules, the compression ratio of blank → material is > 10; for the steel used for bearing rolling elements (rollers and needle rollers), the compression ratio of blank → material is > 50; continuous casting steel is not suitable for manufacturing bearing balls; (C ) The baking temperature of the tundish is 1000～1200℃;

(2) Conventional molten steel casting temperature, high carbon chromium bearing steel VD station hanging bag temperature is: liquidus temperature + 55 ~ 60 ℃, the first bag is liquidus temperature + 60 ~ 65 ℃, tundish The heat temperature is 5-35°C; that is to say, the liquidus temperature of high-carbon chromium bearing steel is 1450°C, the temperature of the VD station hanging bag is 1505-1510°C (1510-1515°C for the first bag), and the temperature of the molten steel in the tundish is 1455°C ~1485°C;

(3) During the entire process from the ladle to the crystallizer, the high-temperature molten steel is always in a protective state isolated from the atmosphere: from the ladle to the tundish, the long nozzle is sealed by argon blowing; from the tundish to the mold, the intrusion is used type nozzle; tundish and crystallizer, covered with mold slag;

(4) The crystallizer and the secondary cooling end adopt electromagnetic stirring; the casting speed of the continuous casting slab and the amount of cooling water in each section are selected as conventional parameters; to remove gas, inclusions, uniform composition and temperature, reduce segregation, and ensure the slab C segregation C/CO ≤ 1.10, equiaxed crystal ratio ≥ 45%, and occurrence rate of various cracks ≤ 2.5%. When the inert atmosphere is fully enclosed to protect the mold casting and casting of high-temperature molten steel, the coated flow steel brick used in the mold casting flow steel system (center injection pipe, soup channel), the high temperature resistant and erosion resistant zirconia inner wall coating needs to be baked Manufactured, the baking temperature is 250-400°C, and the coating thickness is 1-5mm.

Compared with the prior art, the present invention has the following advantages:

1. The ladle furnace process is operated by the single slag method, and the process is simple and convenient;

2. Strong versatility of equipment and process: there is no need to add additional special equipment. All EBT electric furnaces, equipped with basic equipment such as ladle furnaces and vacuum furnaces with corresponding capacities, can meet production needs;

3. The high basicity of LF furnace refining top slag and the low basicity of VD furnace refining top slag reduce the content of sulfur and calcium in steel, which not only meets the standard requirements, but also reduces and refines the content of sulfur and calcium in high-carbon chromium bearing steel Type D inclusions;

4. Due to the reduction of the amount of aluminum used, the Al ₂ O ₃ inclusions in the steel are significantly reduced, thereby reducing the nodulation probability of the continuous casting intrusive nozzle, increasing the number of continuous casting furnaces, and reducing production costs.

specific implementation plan

A steel company implements the patented method of the present invention and adopts a four-step smelting process: 30-100 tons of electric arc furnace initial steelmaking liquid; corresponding capacity of bottom-blown argon ladle furnace refining; corresponding capacity of vacuum furnace degassing; mold casting production line , successfully produced SKF's Grade 3 high-carbon chromium bearing steel.

The first step is to carry out primary smelting of molten steel in an EBT electric furnace: (1) The ratio of steel materials in the primary smelting furnace: scrap steel 75%, high-quality pig iron 25%; Melting: secondary feeding, the first basket is fed and melted after feeding, oxygen is blown to help the melting after 5 minutes of power supply, and the second basket is fed after 17 minutes of power supply; (3) When the molten pool is formed, spray 80 carbon % coke powder to make foam slag, the foam slag height is 500-700mm; depending on the phosphorus content in the steel, flow the slag in time and add lime to ensure that the phosphorus content ≤ 0.012% and titanium content ≤ 0.0005% when tapping; (4) When the composition of the molten steel meets the requirements and the temperature of the molten steel is 1630-1650°C, the method of leaving steel and slag is adopted for tapping: the amount of steel remaining is 10% of the total tapping amount, and the amount of slag tapping is 15% of the total slag amount; 5) When tapping the electric furnace, carry out alloying and deoxidation operations in the ladle, and make the first batch of LF refining slag in the ladle: when the amount of steel tapping reaches 1/4, add Fe-Si, Fe-Mn to the ladle , Fe-Cr, and carbon powder, respectively adjust Si, Mn, Cr, and C to the middle and lower limits of the specifications; when the tapping amount reaches 2/3, add 0.7Kg/t of aluminum block (ingot) to the ladle; add 7.5Kg of lime /t, and 1.5Kg/t lightly burned magnesium balls.

The second step is to deoxidize, desulfurize and remove inclusions according to the single slag method on the LF refining furnace whose capacity matches that of the electric furnace: (1) After baking, the lining of the ladle is dark red or above, and the lining is not seriously damaged. There is no cold steel residue in the ladle; the ladle arrives at the tapping station 3 minutes before tapping the electric furnace, and the argon gas is turned on; (2) After the ladle furnace containing the high-temperature molten steel enters the LF station, it is heated by electricity and is refined in the ladle furnace (3) During the refining process of the ladle furnace, the argon flow rate of the permeable brick is controlled, subject to the fact that the molten steel does not expose the slag surface; Add high-alkalinity slag in batches, the total amount of slag is lime 1.25Kg/t, fluorite 1.50Kg/t; at the same time, Fe-Si powder is added to the ladle slag surface in two batches to carry out diffusion deoxidation of molten steel on top slag, Fe-Si The total amount of powder added is 0.88Kg/t; when the temperature reaches 1550-1560°C, take samples to adjust the composition; when the composition is adjusted to the middle limit of the specification and the temperature reaches 1590-1600°C, add 2.25Kg/t of silica, and melt 4 Minutes, hoist the ladle into the VD station.

The third step is to carry out vacuum treatment on the molten steel in the vacuum furnace (VD) whose capacity matches that of the electric furnace: after the ladle is hoisted into the VD station, the sample is taken and the aluminum wire is fed at 0.3Kg/t; the lid is closed to vacuumize and the pumping speed is controlled , to avoid outgassing caused by large boiling; keep the vacuum for 20 minutes after reaching 0.5 Torr (66.7Pa); take a sample after breaking the vacuum, and blow argon softly (the molten steel is not exposed) for 15 to 20 minutes according to the temperature to achieve the cleaning of molten steel Purpose: Sampling analysis, fine-tuning C, Mn, Si, Cr and other elements to the middle limit of the composition specification, but no matter what the composition content of aluminum is, no more aluminum is fed; the temperature reaches 1500-1510 ° C, and the steel is poured.

The 4th step, casting high-temperature molten steel, die-casting becomes qualified steel ingot or/and continuous casting becomes qualified steel billet: (1) when molten steel die-casting, adopt inert atmosphere fully-enclosed protection die-casting casting: (1) conventional molten steel casting temperature , such as SKFGrade3 high-carbon chromium bearing steel VD station bag temperature is 1500 ~ 1510 ℃; the inner wall of the ingot mold is clean, no cold steel residue; the use temperature of the ingot mold is 60 ~ 80 ℃; the casting ingot type is not limited, but should meet High-carbon chromium bearing steel with low magnification and carbide grade requirements; (2) The flow steel brick used in the mold casting flow steel system adopts zirconium coating, that is, the inner wall of ordinary flow steel brick is coated with a layer of high temperature resistance (≥1600℃) , Erosion-resistant zirconia protective layer, the zirconia inner wall coating needs to be baked at a temperature of 250-400 ℃, and the thickness is 1-5mm; (3) The whole casting process is fully enclosed with argon gas to protect the casting: the protection device is a fire-resistant The upper part of the material cavity communicates with the lower part of the ladle nozzle, and the lower part communicates with the upper part of the injection pipe of the mold casting, and the argon gas is connected to make the steel flow into the ingot mold from the ladle nozzle and the injection pipe under the argon seal. (II) Continuous casting of high-temperature molten steel into qualified steel billets: (1) Equipment preparation: (A) The copper plate on the inner wall of the crystallizer is not seriously damaged, no seepage or water leakage is allowed, and the wear depth of the corners is ≯1.5mm; (B) The crystallizer The size should match the specifications of the finished product: for steel used for bearing rings, the compression ratio of billet → material is > 10; for steel used for bearing rolling elements, the compression ratio of billet → material is > 50; continuous casting steel is not suitable for manufacturing Bearing balls; (C) tundish baking temperature 1000-1200°C; (2) molten steel casting temperature, VD station hanging bag temperature is 1505-1510°C (the first bag is 1510-1515°C), tundish superheat ≤35℃; (3) During the whole process from the ladle to the crystallizer, the high-temperature molten steel is always in a protective state isolated from the atmosphere: from the ladle to the tundish, the long nozzle is sealed by argon blowing; from the tundish to the crystallization The tundish and crystallizer are covered with mold slag; (4) The crystallizer and the secondary cooling end are electromagnetically stirred; the casting speed of the continuous casting slab and the amount of cooling water in each section are selected from conventional parameters.

8 furnaces of 600 tons of SKF Grade 3 high-carbon chromium bearing steel produced by implementing the patented method of the present invention, the oxygen content in the steel is ≤0.0015%, the titanium content is ≤0.0030%, and the sulfur content is ≤0.015%, which not only reduces the amount of aluminum used for deoxidation (1 ton of steel can save the cost of 25.3 yuan), and more importantly, it solves the technical contradiction between the control of spherical inclusions in molten steel refining and the desulfurization process, greatly reduces the content of free CaO in the slag, and makes the finished billet, steel (die casting The final steel ingot is processed according to the conventional process, hot-processed and rolled to open the billet, and the quality of the rolled product meets the requirements of SKF's D33-1 standard (high-level Grade3 steel code B10101). , use the Strurers Abraplan-2 automatic sample grinding machine to sample, observe and grade at 100 times, the D-type inclusions meet D fine ≤ 1.0 grade, D coarse ≤ 0.5 grade, Dmax ≤ 27μm; reach SKF company (foreign advanced level) Require.

Claims (2)

1, the production method of minimizing and refinement high-carbon chromium bearing steel D-type impurity is characterized in that adopting four step rule smelting technology flow process, and electric furnace is just made steel liquid; The BOTTOM ARGON BLOWING ladle furnace refining; The vacuum oven degassing; Die casting or continuous casting: the first step, in EBT type electric furnace, carry out molten steel and just refine:

(1) first furnace iron and steel stock proportioning: steel scrap 70～80%, high duty pig iron 20～30%; The clear S of guaranteeing≤0.040%;

(2) in electric furnace, energising deposite metal starting material, input oxygen quickens fusing: if secondary charging, send after the first basket charging electricity after 3～8 minutes oxygen blast flux, send electricity 15～20 minutes laggard second basket material; If once reinforced, send electricity after 5～20 minutes oxygen blast flux;

(3) after the molten bath forms, spray into the coke powder making foamed slag of carbon containing more than 80%, the foamy slag height is 500～700mm, heats up decarburization, protection furnace wall; Operation is in time flowed slag and is added lime, the phosphorus content when guaranteeing to tap≤0.012%, titanium content≤0.0005% routinely;

(4) when molten steel component arrival requirement, when molten steel temperature was 1630～1650 ℃, adopt and stay steel to stay the slag mode to tap: staying the steel amount was 7～13% of total tap, and going out the quantity of slag is 5～20% of total quantity of slag;

(5) during electric furnace steel tapping, in ladle, carry out alloying, deoxidation operation, and in ladle, make first LF refining slag: when tap reaches 20～30%, in ladle, add the lower limit that Fe-Si, Fe-Mn, Fe-Cr, carbon dust transfer to Si, Mn, Cr, C specification respectively; Tap reaches at 60～70% o'clock, adds the aluminium block 0.5～1.0Kg/t of precipitation pre-deoxidation in ladle; The calcined magnesite ball that adds lime 7.0～8.5Kg/t, 1～2Kg/t;

Second step, on the LF ladle refining furnace that capacity and electric furnace are complementary, by single slag process deoxidation, desulfurization, remove inclusion:

(1) ladle after the baking, more than cylinder-packing was dark red, cylinder-packing did not have badly damaged, no cold steel in the bag; Ladle arrived the tapping station in preceding 3 minutes at electric furnace steel tapping, opened argon gas after putting in place;

(2) after the ladle furnace that fills high-temperature molten steel enters the LF station, the energising heating, whole process is carried out the BOTTOM ARGON BLOWING refining liquid steel in ladle furnace refining;

(3) in the ladle furnace refining process, the argon flow amount of control gas permeable brick is as the criterion with the not exposed top of the slag of molten steel; The intensificationization slag; When top slag fusing was in a liquid state, divide 2～3 batches to add the high basicity slag material: the slag charge total amount was lime 1.0～1.5Kg/t, fluorite 1.0～2.0Kg/t; The ladle top of the slag divides 2～3 batches of adding Fe-Si powder to carry out the molten steel diffusive deoxidation of top slag simultaneously, and it is 0.7～1.0Kg/t that the Fe-Si powder adds total amount, does not feed aluminum steel; When temperature reached 1550～1560 ℃, composition was adjusted in sampling; Limit when composition is adjusted in the specification, when temperature reaches 1590～1600 ℃, add silicon stone 2.0～2.5Kg/t, send electrofusion after 3～5 minutes, ladle is hung in the VD station;

In the 3rd step, on the VD vacuum oven of capacity and electric furnace coupling, molten steel is carried out vacuum-treat: aluminum steel 0.2～0.5Kg/t taken a sample, feeds by ladle after hanging in the VD station; Close lid and vacuumize, pump speed is advanced in control, avoids big boiling to cause venting, and vacuum tightness kept 20～25 minutes after reaching 50～140Pa; Take a sample behind the vacuum breaker, according to temperature conditions, the soft blow argon cleaned molten steel in 15～20 minutes, was not as the criterion so that molten steel is exposed; Sampling analysis, fine setting C, Mn, elements such as Si, Cr are limit to the composition specification, but no matter how many component contents of aluminium be, all hello aluminium no longer; Temperature reaches 1500～1510 ℃, and bull ladle waters steel;

In the 4th step, the casting high-temperature molten steel is molded into qualified steel ingot or/and continuous casting becomes qualified steel billet:

(I) during the molten steel die casting, adopt the totally-enclosed protection die casting casting of inert atmosphere:

(1) conventional molten steel pouring temperature, VD station bull ladle temperature is: liquidus temperature+55～65 ℃; Ingot mold inwall cleaning does not have cold steel residue; 60～80 ℃ of ingot mold use temperatures; The cast ingot shape is unrestricted, but should satisfy high-carbon-chromium bearing steel low power and carbide rank demand;

(2) feed trumpet, the Tang Dao of die casting stream steel system, the runner brick of use adopts zirconium matter coating, and the inwall at common runner brick scribbles the anti-1600 ℃ of high temperature of one deck, erosion resistant zirconium white protective layer exactly;

(3) the casting whole process is used the totally-enclosed protection cast of argon gas: protector is a refractory materials cavity, top communicates with the ladle nozzle bottom, the bottom communicates with die casting feed trumpet top, connect argon gas and make steel stream under the argon gas sealing, inject ingot mold, reduce the air-breathing and secondary oxidation of molten steel from ladle nozzle, feed trumpet;

(II) the high-temperature molten steel continuous casting becomes qualified steel billet:

(1) equipment is prepared: (A) crystallizer inwall copper coin does not have major injury, forbidden to have ooze, drainage, bight wearing depth ≯ 1.5mm; (B) the crystallizer size should be complementary with finished product material specification: be used for the steel of bearing ring, the compression ratio of base → material＞10; The steel that are used for bearing roller, the compression ratio of base → material＞50; The continuous casting steel are not suitable for the manufacturing bearing ball; (C) the tundish storing temperature is 1000～1200 ℃;

(2) conventional molten steel pouring temperature, VD station bull ladle temperature is: liquidus temperature+55～60 ℃, first bag is liquidus temperature+60～65 ℃, 5～35 ℃ of tundish superheating temperature;

(3) from big whole process of wrapping crystallizer, high-temperature molten steel is in the guard mode with isolated from atmosphere all the time: big Baogang water adopts Argon to seal long nozzle to tundish; The tundish molten steel adopts the intrusive mood mouth of a river to crystallizer; Tundish and crystallizer cover with covering slag;

(4) crystallizer and two cold ends adopt induction stirring; The consumption of continuously cast bloom pulling rate and each section water coolant is selected conventional parameter.

2, the production method of minimizing according to claim 1 and refinement high-carbon chromium bearing steel D-type impurity; it is characterized in that: when adopting the totally-enclosed protection die casting casting of inert atmosphere high-temperature molten steel; the coating runner brick that die casting stream steel system uses; high temperature resistant, erosion resistant zirconium white inside coating need toast to be made; 250～400 ℃ of storing temperatures, coat-thickness 1～5mm.