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Smelting of bearing steel

[Author: Jiang Rui Bearing] [Date: 2017-04-13] [heat: ]

Electric furnace process, that is, electric furnace-refining outside the furnace-continuous casting or die casting-rolling;
 Converter process, namely blast furnace-hot metal pretreatment-converter refining outside-continuous casting-rolling;
 Special smelting methods, namely vacuum induction furnace (VIM)-electroslag remelting (ESR)-rolling or forging.
Typical bearing steel production process
 Sweden SKF: 100t EF-ASEA-SKF-IC, producing steel pipes of Ø12-32mm rods, 90-200mm outer diameter and 55-110mm outer diameter;
 Sanyo, Japan: preheating of scrap steel-90 t EF (out-of-center tapping)-LF-RH-CC (vertical 3-flow, 370mm x 470mm) or IC-hot rolling (material) and cold rolling . Production of Ø102-600mm bars, etc., 50-180mm outer diameter hot-rolled steel pipes and 22-95mm outer diameter cold-rolled steel pipes;

 Datong, Japan: preheating of scrap steel-90tEAF-LF-RH-CC (370mm × 480mm);
 Kobe, Japan: blast furnace—hot metal pretreatment—80tLD-OTB top and bottom double-blown converter—slag removal—ASEA-SKF ladle refining—continuous casting (2-flow vertical bend, 300mm × 430mm), production 105mm rod and wire
 Kawasaki, Japan: blast furnace-hot metal pretreatment-converter-ladle refining-vacuum-continuous casting (4 streams 400mm × 560mm);

 Sumitomo Japan: Blast Furnace——Converter——VAD / RH——Continuous Casting / Die Casting (410mm × 560mm), rod and wire;
 Japan Nippon Steel: blast furnace-converter-LD converter-LF ladle refining-RH-continuous casting, production of Ø19-120mm bar and wire;
 Japan Aichi Steel: EAF-ladle refining-RH-continuous casting, production of Ø16-100mm bar and wire;
 Krupp, Germany: 110t UHP-EAF-ladle metallurgy-continuous casting (6 streams 260mm × 330mm), producing Ø28-80mm bar and wire.
Production process characteristics of foreign bearing steel
 Large-scale furnace; slag-free tapping; Al deoxidation; long-term stirring under vacuum or non-vacuum conditions; high-basicity slag refining; continuous casting.
 Relevant technologies are reflected in the alkalinization of ladle refractories and high temperature preheating of the ladle and the middle thin.

 The specific refining technology is embodied in: low oxidation and low temperature of primary molten steel; separation of steel slag from the primary furnace; synthesis and liquid phase of refined slag; and on-line analysis; modeling of molten steel refining (including blowing Flow, time of argon stirring and argon blowing position); slag discharge of ladle pouring steel; temperature and composition and process control of aluminum deoxidation

 Continuous casting technology is reflected in: steel retention in ladle and tundish; inertization and anti-blocking of the pouring atmosphere of steel flow; large capacity of molten steel in tundish; optimization of molten steel flow in tundish; Stability; large-scale continuous casting slab; uniformity of secondary cooling spray; multi-polarization of electromagnetic stirring; light reduction technology.
Basic conditions for bearing steel production
 Large-capacity preliminary smelting furnace to ensure low molten steel phosphorus and qualified component temperature to achieve slag-free tapping;
 Equipped with heating, vacuum and alloy fine-tuning refining device to maximize the removal of oxygen, hydrogen and other gases. Protect the casting against secondary oxidation;
 Adopt multi-pole combined electromagnetic stirring and light reduction technology to ensure the center quality of the billet and reduce the center segregation;
 The rolling mills are all twist-free and tension-free high-speed rolling mills to ensure the dimensional accuracy and surface quality of the rolled materials.

 The domestic bearing steel refining ratio has reached 100%, the average oxygen content has reached 8 × 10-4%, and a good 4 × 10-4%, but compared with advanced manufacturers such as Sweden SKF and Japan's Sanyo, the There are still gaps in the content of trace impurity elements, surface quality and internal quality stability. If the titanium content is high, it is generally above 0.003%.
 The proportion of bars in China is very large, accounting for more than 80%, the pipes are almost zero, and the proportion of wires and strips is also low.
1 EAF process for smelting bearing steel  UHP EAF-LF-VD-CC or IC as an example. The process is: electric furnace tapping-LF block station (start of bottom blowing argon)-temperature measurement-power supply slag making- —Deoxidation and desulfurization—adjusting ingredients—temperature measurement—VD station—vacuum refining—feeding line (aluminum deoxidation or calcium treatment, bottom blowing argon) —continuous casting platform temperature measurement—continuous casting machine casting . Central task: Deoxidation and removal of non-metallic inclusions and their control.
Super high power electric arc furnace
 Main tasks: melting scrap steel, decarburization, dephosphorization and heating;
 The amount of carbon in the charge can be adjusted to 1.00% -1.3%. The ore, oxygen is used for decarburization, dephosphorization, and automatic slag flow. The steel is eccentrically removed, leaving slag and steel. When tapping, the carbon content can be controlled at the lower limit of high-carbon chromium bearing steel, and the amount of carbon refining outside the furnace is small, which is convenient for operation;
 It is required to reduce the oxidation and temperature of the molten steel in the primary furnace to prevent oxidation slag from entering the ladle.
LF ladle refining furnace
 LF refining purpose: deoxidation, sulfur reduction, alloying, composition adjustment, and control of proper pouring temperature. Central task of bearing steel: deoxidation!
 Before LF heating, use aluminum to deoxidize the molten steel precipitation, then heat, adjust the composition of the molten steel, adjust the composition of the refining slag, and stir with argon;
 Rapidly making alkaline slag-deoxidation and desulfurization;

 Bottom blowing argon control-too large, the reaction of the steel slag is too intense and the molten steel scours the refractory material seriously, and the oxides and titanium compounds enter the molten steel; too small the temperature, composition and reaction of the steel slag are not uniform, insufficient, deoxidation The product cannot fully float;
 Appropriate bottom-blowing argon system: Stirring at a higher argon pressure in the early stages of refining; Stirring at a lower argon pressure in the later stages of refining-makes the titanium content basically stable during the refining process, and at the same time it can make the sulfur and oxygen content active Declining. Generally controlled at 0.2-0.3MPa.
VD vacuum degassing
 The main purpose-vacuum dehydrogenation, carbon deoxidation under vacuum to continue deoxidation, and argon stirring to remove inclusions, generally nitrogen removal is not obvious;
 Before entering the VD, remove the slag, reduce the alkalinity of the slag, control the intensity of argon blowing, add Al to deoxidize before vacuuming, and slowly blow argon. The argon blowing is not more than 0.2Mpa in the early stage and below 0.1Mpa in the later stage, which can fully react the molten steel and slag, and the deoxidation products will fully float

 The vacuum time is too short-the deoxidation product cannot fully float; too long-the surface of the refractory material is washed away by the molten steel for a long time and peels into the molten steel, which is not conducive to the control of the titanium content in the steel;
 Soft argon stirring after vacuum degassing-control the content of non-metallic inclusions. 5 minutes before the end of VD treatment, depending on the aluminum content of the molten steel, supplement the aluminum feed line, and then perform weak stirring to clean the molten steel;
Continuous casting or ingot (IC)
2 Converter steelmaking  The raw material conditions are good, and the purity and quality stability of molten iron are better than scrap steel;
 Use molten iron pretreatment to further improve the purity of molten iron;
 The carbon control level at the end of the converter is high, and the steel slag reaction is more balanced than the electric furnace;
 Low gas content in converter steel;
 Continuous casting and out-of-furnace refining and process levels are comparable to electric furnaces.

 Japan and Germany use different production processes, the difference is the control of carbon at the end of steelmaking;
 Japan— "Three-strip" pretreatment, low-slag smelting high-carbon steel technology, and production of low-phosphorus and low-oxygen steel;
 Germany-Low-carbon carbon converter technology ensures the dephosphorization effect in the later period of the converter. The steel is produced by increasing the carbon content of the bearing steel.

 Hot metal pretreatment: Magnesium-based desulfurizer treatment, w [S] ≤0.005% of molten iron in the furnace, 100% slag removal after treatment;
 Converter smelting: The high-carbon drawing method is adopted, and the final carbon w [C] ≤0.40%, while controlling w [P] ≤0.010%. Aluminium, manganese and titanium warming agent is added to the scrap steel-the high-carbon control at the end point is insufficient temperature; tapping temperature is 1700 ℃, carbon content is 0.34%, phosphorus content is 0.007%

 In the tapping process, high Cr alloy, Si-Mn alloy, and carbon powder are used for alloying and carburizing in the package, and slag blocking operation is carried out. Total oxygen in the molten steel is removed by bottom blowing argon stirring;
 LF refining adopts low-basicity CaO-Al2O3 slag system, with a desulfurization rate of 50% -70%, reducing Al inclusions; it has the same composition as the deoxidation product, and the interfacial tension between the two is small, and it is easy to combine into a low melting point compound ——Strong ability to absorb Al2O3 inclusions and eliminate Ca-type D inclusions. Simultaneous bottom blowing of argon with uniform composition and temperature;

 Weak argon stirring: According to the composition analysis of the reference sample, supplement the composition with high chromium, high manganese, and carbon powder to meet internal control requirements. Weak argon stirring when the temperature is 20-30 ° C higher than the temperature of the hanging bag-inclusions Further up
 Continuous casting

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