Stainless steel making process

2025-07-21

1. Electric Arc Furnace (EAF)

Function
The primary smelting equipment for stainless steel smelting, which melts scrap steel, ferroalloys (such as ferrochrome, ferronickel) and other raw materials into molten steel, and preliminarily adjusts the composition (such as Cr, Ni content).
Structure and working principle
Electrode system: 3 graphite electrodes are fed with high voltage current to generate an arc (temperature can reach above 3000℃), which directly heats the raw materials in the furnace.
Furnace body: Refractory lining (magnesia carbon brick or alumina brick), which can be tilted to discharge steel.
Auxiliary system
Oxygen spray gun: Assists melting and oxidizes impurities (such as phosphorus and silicon).
Dust removal system: Treats the smoke generated by smelting (including heavy metal particles)
Features of stainless steel smelting
Raw materials: Low-carbon scrap steel or direct reduced iron (DRI) must be used to avoid impurities (such as copper and tin) affecting corrosion resistance.
Alloy addition: Add ferrochrome, ferronickel, etc. in the later stage of smelting to ensure uniform composition.
Typical parameters
Capacity: 50~150 tons/furnace
Smelting time: 60~90 minutes

Power consumption: 350~500 kWh/ton of steel

2. AOD furnace (Argon Oxygen Decarburization Furnace)

Function
The core equipment of stainless steel refining, by blowing in argon oxygen mixed gas, it can achieve deep decarburization and chromium preservation (avoid chromium oxidation loss), and accurately control the composition and temperature.
Structure and working principle
Furnace body: converter structure, refractory lining (magnesia chrome brick), 360° rotation.
Gas injection system
Side wall or bottom tuyere: inject O₂, Ar, N₂ mixed gas (adjustable ratio).
Reaction principle
Stage 1 (high oxygen): O₂ oxidizes carbon to generate CO bubbles, decarburization.
Stage 2 (high argon): Ar dilutes CO partial pressure to promote carbon preferential oxidation (chromium retention).
Alloy feeding system: fine-tune the composition (such as Mo, Ti) in the later stage of refining.
Advantages of stainless steel smelting
Chromium recovery rate: can reach more than 98% (traditional converter is only 80%).
Low carbon control: can produce ultra-low carbon stainless steel (such as 304L, C≤0.03%).
Typical parameters
Processing time: 40~60 minutes/furnace
Gas consumption: O₂ 15~25 Nm³/ton, Ar 10~20 Nm³/ton
Temperature control: 1600~1700℃

3. Continuous Caster

Function
The refined molten steel is continuously cast into slabs (thickness 150~250mm) to provide raw materials for subsequent hot rolling.
Structure and process flow
Ladle turret: carries the ladle and continuously injects molten steel into the tundish.
Tundish: distributes steel flow, stabilizes casting speed, and filters inclusions.
Crystallizer:
Copper water-cooled mold, where the molten steel is initially solidified into a slab shell.
Electromagnetic stirring (EMS): improves the solidification structure of alloy steels such as stainless steel.
Secondary cooling zone: water spray accelerates the solidification of the slab shell, and the support roller controls the shape of the slab.
Bill straightening machine: pulls out and straightens the slab.
Cutting equipment: flame or hydraulic shears are cut into fixed-length slabs.
Key technologies for continuous casting of stainless steel
Protective casting: argon gas seals to prevent oxidation of molten steel (especially Ti and Al steels).
Low superheat control: reduce center segregation (e.g. 304 stainless steel superheat ≤ 20°C).
Electromagnetic brake (EMBr): inhibits stream from scouring the crystallizer and improves surface quality.
Typical parameters
Casting speed: 0.8~1.5 m/min (depending on the cross-sectional size)
Slab size: width 1000~2000mm, thickness 150~250mm

4. Equipment synergy process example

EAF smelting: scrap steel + ferrochrome → initial melting, C content is about 1.5~2.0%.
AOD refining: decarburization to 0.02~0.08%, adjust Cr/Ni to the target value (such as 304 steel: 18Cr-8Ni).
Continuous casting: molten steel → slab → hot rolled coil.

5. Key differences and industry applications

Electric arc furnace vs AOD furnace:
EAF focuses on melting and initial composition adjustment, while AOD specializes in refining (decarburization, fine-tuning).
Some steel mills use "EAF+VOD (vacuum deoxidation)" to replace AOD, but AOD is still the mainstream.
Stainless steel continuous casting vs ordinary carbon steel continuous casting:
Stainless steel has high viscosity and requires higher billet drawing force;
Sensitive to cracks (such as austenitic steel), strict cooling control is required.
The precise coordination of these equipment is the core guarantee for the production of high-quality stainless steel coils.