Detailed explanation of the metal production process
The production of metal materials involves multiple steps from ore extraction to final product. The process flow of different metals (such as iron, aluminum, copper, and stainless steel) is different, but the core links are similar. The following is the industrial production process of typical metals:
1. Mining and ore dressing
(1) Ore mining
- Iron ore (hematite Fe₂O₃, magnetite Fe₃O₄)
- Bauxite (Al₂O₃)
- Copper ore (chalcopyrite CuFeS₂)
Method: open-pit mining or underground mines.
(2) Ore dressing
- Crushing & grinding: crushing the ore into fine particles.
- Flotation/magnetic separation: separating metal minerals from impurities (such as using a magnetic separator to extract iron concentrate).
- Concentrate: obtaining high-purity minerals (such as iron concentrate containing more than 60% iron).
2. Smelting (metal extraction)
(1) Pyrometallurgy (high temperature reduction)
Applicable metals: iron, copper, lead, zinc, etc.
- Blast furnace ironmaking:
- Raw materials: iron ore + coke (reducing agent) + limestone (flux).
- Reaction: Fe₂O₃ + 3CO → 2Fe + 3CO₂ (temperature 1500°C).
- Product: pig iron (containing 2-4% carbon, requiring further steelmaking).
- Converter/electric arc furnace steelmaking:
- Decarburization: blowing oxygen to reduce the carbon content in pig iron (such as converter steelmaking for 15-20 minutes).
- Alloying: adding chromium, nickel, etc. to make stainless steel.
(2) Hydrometallurgy (chemical dissolution)
Applicable metals: aluminum, gold, uranium, etc.
-Bayer process for aluminum:
1. Bauxite + NaOH → dissolve Al₂O₃.
2. Electrolyze aluminum oxide (Al₂O₃) to obtain pure aluminum (Hall-Héroult process).
(3) Electrolytic refining
Applicable metals: copper (purity 99.99%), zinc, nickel.
- Copper ore is used as anode, pure copper sheet is used as cathode, and copper sulfate solution is electrolyzed.
3. Casting and molding
(1) Casting
- Sand casting: low cost, suitable for complex shapes (such as engine cylinder).
- Continuous casting: direct production of steel billets and aluminum slabs (improved efficiency).
(2) Hot working
- Hot rolling: heating to above the recrystallization temperature and rolling (such as steel plates and copper tubes).
- Forging: pressure molding (such as crankshafts and aviation parts).
(3) Cold working
- Cold rolling/drawing: Processing at room temperature to increase strength (such as stainless steel sheets, copper wire).
- Stamping/cutting: Making final parts (such as car shells).
4. Heat treatment
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technology
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aim
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Give an example
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anneal
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Soften the metal and relieve stress
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Annealed copper wire to improve ductility
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Quenching + tempering
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Improve hardness and toughness
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Tool steel tool
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Solution treatment
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Uniform alloying elements (e.g., stainless steel)
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304 stainless steel heated to 1100°C
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5. Surface treatment
- Rust prevention: electrogalvanizing (galvanized steel), anodizing (aluminum).
- Aesthetics: polishing (mirror stainless steel), spraying (color aluminum plate).
- Functional coating: PVD coating (wear-resistant tools).
6. Quality inspection
- Composition analysis: Spectrometer to detect element content.
- Mechanical testing: tensile test, hardness test.
- Non-destructive testing: X-ray inspection, ultrasonic crack detection.
Detailed explanation of the alloy production process
Alloys are materials made of two or more metals (or metals and non-metals) through fusion, sintering or other processes, and have better properties than pure metals, such as higher strength, corrosion resistance or special functions. The following is a typical alloy production process:
1. Raw material preparation
- Main metal substrates: such as iron (Fe), aluminum (Al), copper (Cu), nickel (Ni), etc.
- Alloy elements:
- Enhanced performance: chromium (Cr), molybdenum (Mo), manganese (Mn), silicon (Si), etc.
- Improved processability: carbon (C), sulfur (S), phosphorus (P) (content must be strictly controlled).
- Auxiliary materials: flux (such as limestone CaO), deoxidizer (such as aluminum Al), protective gas (such as argon Ar).
2. Melting process
(1) Ingredient calculation
According to the target alloy composition (such as 304 stainless steel requires 18%Cr+8%Ni), accurately weigh the raw materials.
(2) Melting method
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Smelting mode
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Application scenario
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peculiarity
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Electric Arc Furnace (EAF)
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Stainless steel, special alloy
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High temperature (1600°C+), precise composition control
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Induction furnace
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Small batch high purity alloys (such as nickel-based alloys)
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No pollution, uniform composition
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Converter (AOD/VOD)
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Stainless steel decarbonization refining
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Lower carbon content and reduce chromium loss
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Key steps:
- Melting: Heating the metal to liquid state (e.g. about 1500-1600°C for iron-based alloys).
- Alloying: Adding alloying elements (e.g. chromium, nickel) and stirring to ensure uniform mixing.
- Refining:
- Deoxidation: Adding aluminum/silicon to remove oxygen impurities.
- Desulfurization/phosphorus: Removing harmful elements through flux (e.g. CaO) reaction.
3. Casting or continuous casting
- Mold casting: Liquid alloy is poured into a mold and cooled to form (suitable for small batches of complex parts).
- Continuous casting: Directly casting into slabs, square billets or round billets (suitable for large-scale production, such as stainless steel coils).
4. Hot working
- Hot rolling: Heating to above the recrystallization temperature (e.g. 1100-1250°C for stainless steel) and rolling into plates, bars, etc.
- Forging: Forming by pressure (e.g. aviation alloy forgings).
5. Cold working (optional)
- Cold rolling/drawing: Processing at room temperature to increase strength (such as stainless steel sheets, copper alloy wires).
- Annealing: Eliminate work hardening and restore toughness (such as annealing temperature of 304 stainless steel 1010-1120°C).
6. Surface treatment
- Pickling: Remove oxide scale (HNO₃+HF mixture for stainless steel).
- Polishing/plating: such as electrogalvanizing (galvanized steel), PVD coating (colored stainless steel).
7. Quality inspection
- Composition analysis: Spectrometer detects element content.
- Mechanical property test: hardness, tensile strength, impact test.
- Non-destructive testing: X-ray flaw detection, ultrasonic detection of internal defects.
The difference between metals and alloys
1. Metal (pure metal)
- Definition: A material consisting of a single metallic element (e.g., pure iron, pure copper, pure aluminum).
- Features:
- Good electrical/thermal conductivity, but poor mechanical properties (soft, easy to deform).
- Active chemical properties (such as pure iron easy to rust).
- Typical use: wire (copper), aluminum foil (aluminum) and other scenes with high purity requirements.
2. Alloy
- Definition: material formed by the fusion of two or more metals (or metal and non-metal).
- Features:
- Optimizes properties (strength, corrosion resistance, etc.) by adjusting the composition.
- Cost control (such as replacing part of nickel with manganese to reduce the cost of stainless steel).
- Typical examples:
- Stainless steel (iron + chromium + nickel),
- Brass (copper + zinc),
- Aluminum alloy (aluminum + magnesium/silicon).
Why choose stainless steel products?
Stainless steel (such as 304, 316) is a classic representative of iron based alloys, and its core advantages are as follows:
1. Corrosion resistance
- The role of chromium: when the chromium content is more than 10.5%, a dense chromium oxide (Cr₂O₃) passivation film is formed on the surface to isolate water oxygen.
- Comparison:
- Ordinary carbon steel: easy to rust, need additional galvanizing/painting.
Aluminum: Although resistant to atmospheric corrosion, but not resistant to acid and alkali.
2. High strength and durability
- Work hardening: The strength can be significantly improved after cold rolling (such as 304 tensile strength increased by 50% after cold rolling).
- High temperature performance: Austenitic stainless steel (such as 310S) remains stable at 800 ° C.
3. Hygiene and aesthetics
- No coating: No plating or painting is required to avoid coating contamination (food grade applications such as kitchen equipment, surgical instruments).
- Surface diversity: polished (mirror), brushed (matte), plated (PVD), etc.
4. Environmentally friendly and recyclable
- 100% recyclable: Waste stainless steel can be directly remelted without performance attenuation.
- Long life: the life of stainless steel used in construction (such as 316L curtain wall) can reach more than 50 years, reducing resource waste.
5. Economics (long-term perspective)
- Initial cost: stainless steel is 2 to 3 times higher than carbon steel, but it is maintenance-free (no anti-rust treatment is required).
- Case:Chemical storage tank: carbon steel needs to be replaced regularly, stainless steel one-time investment is more cost-effective.
When not to choose stainless steel?
1. Extreme budget constraints: carbon steel + anti-rust coating can be used for short-term projects.
2. Ultra-lightweight demand: aluminum alloy or titanium alloy lighter (such as aerospace).
3. Ultra-high temperature environment: Nickel-based alloys (such as Inconel) are more heat resistant.
