Smelting Process of Bearing Steel
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Electric furnace process, that is, electric furnace - refining outside furnace - continuous casting or die casting - rolling;
Converter process, that is, blast furnace - hot metal pretreatment - converter refining - continuous casting - rolling;
Special smelting methods, namely vacuum induction furnace (VIM) - electroslag remelting (ESR) - rolling or forging.
Typical production process of bearing steel
Swedish SKF: 100t EF-ASEA-SKF-IC, producing 12-32MM rod and wire rod, 90-200mm outer diameter and 55-110mm outer diameter steel pipe.
Shanyang, Japan: scrap preheating - 90 t EF (eccentric bottom tapping) - LF - RH - CC (vertical 3-stream, 370 mm *470 mm) or IC - hot rolling (material) and cold rolling. Production of 102-600 mm bar, 50-180 mm hot-rolled steel pipe with outer diameter, 22-95 mm cold-rolled steel pipe with outer diameter;
Datong, Japan: scrap preheating - 90tEAF - LF - RH - CC (370mm *480mm);
Kobe, Japan: BF - hot metal pretreatment - 80tLD - OTB top and bottom combined blowing converter - slag removal - ASEA - SKF ladle refining - continuous casting (2 vertical bend, 300mm * 430mm), producing 18 - 105mm rods and wires;
Kawasaki, Japan: Blast Furnace - Hot Metal Pretreatment - Converter - Ladle Refining - Vacuum - Continuous Casting (4 streams 400 mm x 560 mm);
Japanese Sumitomo: Blast Furnace - Converter - VAD / RH - Continuous Casting / Mold Casting (410mm x 560mm), Bar and Wire;
Nippon Iron Co. of Japan: Blast Furnace - Converter - LD Converter - LF ladle refining - RH - continuous casting, production of 19 - 120 mm bar and wire rod;
Aichi Steel of Japan: EAF - ladle refining - RH - continuous casting, producing 16 - 100mm bar and wire rod;
Krupp, Germany: 110t UHP - EAF - ladle metallurgy - continuous casting (6 streams 260mm x 330mm), producing 28 - 80mm bar and wire.
Production Process Characteristics of Bearing Steel Abroad
Large-scale furnace; slag-free tapping; Al deoxidation; long-time stirring under vacuum or non-vacuum conditions; high basicity slag refining; continuous casting.
Relevant technologies are embodied in the alkalinization of refractories for ladles and high temperature preheating of ladles and intermediate thin layers.
Specific refining technologies are as follows: low oxidation and low temperature of molten steel in primary smelting; separation of steel slag from primary smelting furnace tapping; synthesis and liquidization of refining slag as well as on-line analysis; modelling of liquid steel refining (including flow rate, time and position of argon blowing); slagging of ladle casting; process control of temperature and composition as well as aluminium deoxidation process.
The continuous casting technology is embodied in the following aspects: steel ladle and tundish; inertness and blockage prevention of steel flow casting atmosphere; large capacity of tundish steel water; optimization of water flow in tundish steel; stabilization of liquid steel level of mould; large scale of continuous casting billet; uniformity of two cold spray; multi polarization of electromagnetic stirring; soft reduction technology.
Basic Conditions for Bearing Steel Production
Large capacity primary smelting furnace ensures low phosphorus content of molten steel, qualified composition temperature and slag-free tapping.
It is equipped with heating, vacuum, alloy fine-tuning refining equipment to remove oxygen, hydrogen and other gases to the maximum extent. Protective casting to prevent secondary oxidation;
Multi-pole electromagnetic stirring and soft reduction technology are adopted to ensure the center quality of billet and reduce center segregation.
Rolling mills are all non-twisting tension-free high-speed rolling mills to ensure the dimensional accuracy and surface quality of the rolled products.
The refining ratio of domestic bearing steel has reached 100%, the average oxygen content has reached 8 x 10-4%, and the good value has reached 4 x 10-4%. However, compared with Sweden SKF, Japan Shanyang and other advanced manufacturers, there are still gaps in the content of trace impurities, surface quality and internal quality stability of steel. If the content of titanium is on the high side, it is generally above 0.003%.
In our country, the proportion of bars is very large, accounting for more than 80%, the proportion of pipes is almost zero, and the proportion of wires and strips is also low.
1 EAF Process for Bearing Steel Smelting
UHP EAF-LF-VD-CC or IC for example, the process flow is as follows: tapping of electric furnace - LF seat package station (starting from bottom argon blowing) - temperature measurement - power supply slagging - deoxidization and desulfurization - adjustment component - temperature measurement - VD Station - vacuum refining - feeding line (aluminum deoxidization or calcium treatment, end of bottom argon blowing) - continuous casting platform temperature measurement - continuous casting machine. Central task: Deoxidation and non-metallic inclusion removal and control.
Preliminary smelting of ultra-high power electric arc furnace
Main tasks: melting scrap, decarbonization, dephosphorization and heating;
Carbon content in burden can be allocated to 1.00% - 1.3%. Decarbonization with ore, oxygen, dephosphorization, automatic slag flow, eccentric tapping and slag retention are used. Carbon content can be controlled at the lower limit of high carbon chromium bearing steel when tapping. Carbon increment in refining outside the furnace is very small and easy to operate.
It is required that the molten steel of the primary smelting furnace be low oxidized and low temperature, so as to prevent the oxidized slag from entering the ladle.
ladle furnace
Purpose of LF refining: Deoxidation, sulfur reduction, alloying, composition adjustment and proper pouring temperature control. The central task of bearing steel: deoxidation!
Before LF heating, the molten steel is precipitated and deoxidized by aluminium, then heated, adjusted the composition of molten steel, adjusted the composition of refining slag and stirred by argon blowing.
Fast alkaline slag - deoxidization and desulfurization;
Control of bottom argon blowing - excessive, excessive slag reaction and severe erosion of refractories by molten steel, oxide and titanium entering molten steel; excessive small molten steel temperature, composition and slag reaction are not uniform, insufficient, deoxidized products can not fully float;
Suitable bottom argon blowing system: stirring with larger argon pressure in the early stage of refining; stirring with smaller argon pressure in the later stage - making the content of titanium basically stable in the refining process, and at the same time making the activity of sulfur and oxygen content decrease continuously. Generally controlled at 0.2-0.3 MPa.
VD vacuum degassing
The main purposes are vacuum dehydrogenation and continuous deoxidation of carbon under vacuum.
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