EAF process, namely furnace - refining - continuous casting or die casting - rolling;
BOF process, namely blast - hot metal pretreatment - external converter refining - casting - rolling;
Special smelting method, namely a vacuum induction furnace (VIM) - electroslag remelting (ESR) - rolling or forging。
A typical bearing steel production process
Swedish SKF: 100t EF-ASEA-SKF-IC, production Ø12-32mm wire rod, diameter and outer diameter 55-110mm 90-200mm steel;
Japan's Sanyo: scrap preheating --90 t EF (eccentric bottom tapping) - LF - RH - CC (Vertical 3 stream, 370mm × 470mm) or IC-- hot-rolled (wood) and cold。 Production Ø102-600mm bars, etc。, diameter 50-180mm hot-rolled steel, cold rolled steel tube outer diameter 22-95mm;
Japan Datong: scrap preheating --90tEAF - LF - RH - CC (370mm × 480mm);
Kobe, Japan: Blast - hot metal pretreatment --80tLD-OTB top and bottom blowing converter - Cleaner --ASEA-SKF ladle - Casting (2 stream vertical bending type, 300mm × 430mm), production Ø18-105mm wire rod;
Kawasaki, Japan: Blast - hot metal pretreatment - Converter - Ladle - Vacuum - Casting (4 streams 400mm × 560mm);
Sumitomo: BF - BOF --VAD / RH-- casting / molding (410mm × 560mm), rod and wire;
Nippon Steel: BF - BOF converter --LF --LD --RH-- casting ladle refining, production Ø19-120mm wire rod;
Aichi Steel: EAF-- ladle --RH-- casting, production Ø16-100mm wire rod;
German Krupp: 110t UHP- EAF-- ladle metallurgy - Casting (6 flow 260mm × 330mm), wire rod production Ø28-80mm.
The characteristics of the production process abroad bearing steel
Stove large; no slag tapping; Al-deoxy; under vacuum and non-vacuum conditions for extended periods stir; high alkalinity slag refining; casting.
Related technologies embodied in: alkaline refractory ladle and ladle of thin and intermediate temperature to warm up.
Specific refining technology embodied in: the beginning of liquid steel and low temperature oxidation of low; furnace slag tapping early separation; refining slag synthesis and analysis of liquid-based and online; liquid steel refining modeling (including argon stir traffic, time and argon position); pouring steel ladle slag; temperature and composition as well as aluminum deoxidation process control technology.
Casting technology embodied in: stay steel ladle and tundish; steel stream pouring inert atmosphere and attempts to prevent; Tundish large capacity; Tundish flow optimization; mold steel surface stability ; large slab; uniform secondary cooling spray; multipolar electromagnetic stirring; soft reduction technology。
The basic conditions for the production of bearing steel
Large-capacity furnace early to ensure steel phosphorus, ingredients temperature qualified, slag-free tapping;
With heating, vacuum refining apparatus for fine tuning the alloy, the maximum oxygen removal, hydrogen and other gases. Protection of casting anti-secondary oxidation;
Using a combination of multi-pole magnetic stirring and soft reduction technology to ensure the quality of the billet center, reducing the central segregation;
No twisting mill are tension-free high-speed rolling mill, rolled to ensure dimensional accuracy and surface quality。
Domestic bearing steel refining ratio has reached 100 percent, the average oxygen content has reached 8 × 10-4%, good reach 4 × 10-4%, but compared with the Swedish SKF, Japan Sanyo and other advanced manufacturers in steel trace impurity elements, surface quality and internal quality stability are still gaps。 As the high titanium content, generally above 0。003%。
A large proportion of bars, accounting for more than 80%, almost zero pipe, wire, strip the proportion is lower.
An electric arc furnace smelting process bearing steel
UHP EAF-LF-VD-CC or IC, for example, process: electric furnace steel --LF seat contracting position (bottom blowing argon start) - Temperature - Power slagging - deoxidation and desulfurization - adjust ingredients - temperature --VD station - vacuum refining - feed line (aluminum killed or calcium treatment, argon bottom end) - casting platform temperature - continuous casting machine casting. Central task: deoxygenation and removal of non-metallic inclusions and control.
UHP early refining
Main tasks: melting scrap, decarbonization, dephosphorization and heating;
Charge in the amount of carbon can be equipped with the 1.00% -1.3%, with ore, oxygen decarbonization, dephosphorization, automatic flow slag, eccentric tapping, leaving residue remaining steel. When the carbon content of the steel can be controlled to limit carbon chromium bearing steel, refining increase the amount of carbon is small, easy to operate;
Require early furnace steel cryogenic liquid compounds of hypoxia, to prevent oxidation of slag into the ladle.
LF Ladle Furnace
LF refining purposes: oxygen, sulfur reduction, alloying, adjust the composition, suitable pouring temperature control。 Central task of bearing steel: deoxy!
Before LF heating, aluminum deoxidation of liquid steel precipitation, and then heated, adjust steel liquid ingredients, adjust refining slag composition, argon stirring;
Quick made basic slag - deoxy desulfurization;
Bottom argon control - too big, too intense and steel slag reaction solution on the serious erosion of refractory oxide and titanium compound into the liquid steel; too small steel liquid temperature, composition and slag reactions are uneven and inadequate, deoxy product not fully floating;
Suitable argon blowing: Refined early argon pressure greater agitation; late in smaller argon pressure agitation - titanium content in the refining process is basically stable, while allowing sulfur content and oxygen content activity continuously decline. General control 0.2-0.3MPa.
VD vacuum degassing
The main purpose - Vacuum dehydrogenase, vacuum carbon deoxidation continue oxygen, argon gas stirring to inclusion, general denitrification is not obvious;
Before entering VD, removing slag, slag reduce alkalinity control argon strength, before the final vacuum plus Al deoxidation, slow argon. Argon is not greater than the pre-0.2Mpa, 0.1Mpa late in less liquid steel and slag can fully react deoxy product fully floating;
Vacuum time is too short - deoxy product can not be fully floating; too long - refractory surface is liquid steel into the long-term erosion and spalling of liquid steel, titanium steel is not conducive to control the content;
After vacuum degassing soft argon stirring - control the content of non-metallic inclusions. VD treatment before the end of 5min, depending on the amount of supplemental feeding liquid steel containing aluminum wire, then stir in the weak wash liquid steel;
Casting or ingot (IC)
Material conditions are good, purity and quality are superior stability of iron scrap;
Using hot metal pretreatment, to further improve the purity of molten iron;
BOF endpoint control high levels of carbon, the reaction tends to be more balanced than the slag furnace;
BOF steel gas content is low;
Outer casting and refining furnace and technological level and fairly.
Japan and Germany, using different production processes, the difference - carbon steel end control;
Japan - "three off" pretreatment, less high-carbon steel slag smelting technology to produce low-phosphorus hypoxia steel;
Germany - pull converter low carbon technology to ensure that post-converter dephosphorization effect, relying on the steel is produced by carbon bearing steel.
Hot metal pretreatment: magnesium based desulfurization agent treatment, into the furnace hot metal w [S] ≤0.005%, 100% slag processing will hold in addition;
BOF: high pull carbon method, the end carbon w [C] ≤0。40%, while controlling the w [P] ≤0。010%。 Blended with scrap aluminum and manganese titanium mention warm agents - Supplementary end high carbon control the temperature enough; tapping temperature 1700 ℃, the carbon content of 0。34%, phosphorus content of 0。007 percent;
Tapping process in packages of high Cr alloy, Si-Mn alloy, carbon black and by alloying carbon and slag operation, the use of bottom argon stirring the molten steel to remove the entire oxygen;
LF refining low alkalinity CaO-Al2O3 slag system, desulfurization rate of 50% -70% lower Al inclusions; consistent with deoxy product components, small interfacial tension between the two compounds into a low melting point is easy to combine - - strong ability to absorb Al2O3 inclusions, eliminate class D inclusions containing CaO. Meanwhile bottom argon uniform composition, temperature;
Argon weak agitation: According to the reference sample of component analysis, complementary high chromium, high manganese, charcoal be adjusted to meet the internal composition requirements, argon at a temperature higher than the temperature of 20-30 ℃ weak hanging bag stir - Inclusion further float;