Steel
Steel is an alloy of iron and carbon that demonstrates improved mechanical properties compared to the pure form of iron.
Characterization
Steel is usually classified based on chemical composition and microstructure as primary criteria, but real-world classification also considers heat treatment behavior, processing method, mechanical performance, surface treatment, and use case.
| Feature | Description | Common Categories |
|---|---|---|
| 🧪 Chemical Composition | Elements present in the alloy, especially carbon and alloying elements like Cr, Ni, Mo, V | - Carbon Steel - Alloy Steel - Stainless Steel - Tool Steel |
| 🧬 Microstructure | Crystalline phases (e.g., ferrite, austenite) present after heat treatment or cooling | - Ferritic - Austenitic - Martensitic - Bainitic - Pearlitic |
| 🔥 Heat Treatment Behavior | How the steel responds to processes like quenching, annealing, tempering | - Hardenable vs Non-hardenable - Air vs Water vs Oil Quenching |
| 🏭 Manufacturing Process | Method of refining, alloying, and shaping the steel | - Basic Oxygen Process - Electric Arc Furnace - Killed/Semi-killed/Rimmed |
| 🎯 Mechanical Properties | Physical characteristics like strength, hardness, ductility, toughness, and wear resistance | - High-strength - Wear-resistant - Ductile - Brittle |
| 🛡️ Corrosion Resistance | Ability to resist oxidation and chemical attack | - Stainless vs Non-stainless - Galvanized/Coated |
| ⚙️ Surface Treatment | Coatings or treatments applied to enhance properties like corrosion resistance | - Galvanized (zinc-coated) - Aluminized - Painted or Powder-coated |
| 🧰 Application/Use Case | The functional role or industry it’s designed for | - Structural - Automotive - Aerospace - Food-grade - Tooling |
| 📏 Form/Shape | Final shape/form factor (especially in standards) | - Sheet - Plate - Bar - Pipe - Rebar |
| 📐 Standards & Grades | Classification by standard bodies with grade numbers and specs | - ASTM (A36, A572) - SAE (1045, 4140) - EN, DIN, JIS |
🧩Steel Taxonomy
| Dimension | Category | Subcategory / Type | Key Characteristics | Typical Uses | Example Grades |
|---|---|---|---|---|---|
| By Composition | Carbon Steel | Low Carbon (< 0.3%) | Ductile, weldable, low cost | Construction, auto panels | A36, 1018 |
| Medium Carbon (0.3–0.6%) | Balance of strength and ductility | Gears, axles, railway tracks | 1045, 1050 | ||
| High Carbon (> 0.6%) | Hard, wear-resistant, brittle | Blades, springs | 1095, 1080 | ||
| Alloy Steel | Low-Alloy Steel | Improved strength, toughness | Pipelines, structural parts | 4140, 4340 | |
| High-Alloy Steel | Heat- or corrosion-resistant | Aerospace, high-temp service | H13, M2 | ||
| Stainless Steel | Austenitic | High corrosion resistance, non-magnetic, ductile | Kitchenware, medical tools, piping | 304, 316 | |
| Ferritic | Magnetic, moderate corrosion resistance | Appliances, exhausts | 409, 430 | ||
| Martensitic | Magnetic, hardenable, moderate corrosion resistance | Cutlery, surgical tools | 410, 420, 440C | ||
| Duplex | Mixed microstructure, strong and corrosion-resistant | Marine, chemical processing | 2205, 2507 | ||
| PH Stainless | Precipitation-hardened for strength | Aerospace, shafts, fasteners | 17-4PH, 15-5PH | ||
| Tool Steel | High-speed, Shock-resisting, etc. | Extremely hard and wear-resistant | Cutting tools, dies | M2, T1, D2, O1, A2 | |
| By Microstructure | Ferritic | — | BCC, magnetic, low hardenability | Structural sheets | 430 |
| Austenitic | — | FCC, non-magnetic, excellent corrosion resistance | Pipes, tanks, kitchen sinks | 304, 316 | |
| Martensitic | — | BCT, hard and brittle after quench | Blades, turbines | 420, 440C | |
| Bainitic | — | Tough, good strength | Rails, automotive | — | |
| Pearlitic | — | Lamellar structure, wear-resistant | Wire, rails | — | |
| By Processing Method | Electric Furnace Steel | — | Precision control over impurities | Specialty steels | — |
| Basic Oxygen Steel | — | High volume, efficient production | Construction steel | — | |
| Killed Steel | — | Fully deoxidized, uniform properties | Pressure vessels | — | |
| Semi-killed Steel | — | Partially deoxidized, lower cost | General structural use | — | |
| Rimmed Steel | — | Poorly deoxidized, good surface finish | Sheet metal | — | |
| By Surface Treatment | Galvanized Steel | Hot-dip Galvanized | Zinc-coated by immersion, thick durable layer | Roofing, guardrails, outdoor structures | G90, G60 (zinc grades) |
| Electro-galvanized | Thin zinc coating via electroplating | Automotive body panels | EG steel | ||
| Coated Steel | Aluminized, Painted | Surface-coated with aluminum, enamel, or epoxy | Mufflers, cookware, white goods | Aluminized Type 1, 2 | |
| By Application | Structural Steel | — | Strong, weldable | Frames, beams | A36, ASTM A992 |
| Automotive Steel | — | Formable, strong, lightweight | Chassis, doors | DP600, TRIP780 | |
| Pipeline Steel | — | Tough, corrosion-resistant | Oil/gas pipelines | API 5L X65 | |
| Aerospace Steel | — | Lightweight, fatigue-resistant | Aircraft, missiles | Maraging 300 | |
| Cutlery / Tooling | — | High hardness, corrosion-resistant | Knives, molds | 440C, H13, D2 |