Steel metallurgy involves the study of iron-carbon alloys containing less than 2% carbon

1. Mechanical requirements: Strength, ductility, hardness, fatigue, impact (CVN).
2. Environmental conditions: Corrosion (humidity, salt, chemicals), temperature (cryogenic, elevated).
3. Manufacturing constraints: Weldability, machinability, formability, heat treatment capability.
4. Cost & availability: Carbon steel << HSLA < stainless steel << specialty alloys.
5. Standards & certification: ASTM, ASME, API, ISO, EN.

| Property | Definition | Typical Unit | | :--- | :--- | :--- | | Tensile Strength (UTS) | Maximum stress steel can withstand while being stretched before breaking. | MPa or psi | | Yield Strength | Stress at which steel begins to deform plastically (0.2% offset). | MPa or psi | | Elongation | A measure of ductility; the percentage of permanent stretch before fracture. | % | | Hardness | Resistance to indentation (Rockwell, Brinell, Vickers scales). | HRC, HB, HV | | Toughness | Ability to absorb energy before fracture (Charpy V-notch test). | Joules (J) | | Modulus of Elasticity | Stiffness; ratio of stress to strain within elastic limit (steel ~200 GPa). | GPa |

Common standards summary

• ASTM: wide range (A36, AISI steels, A240 for stainless).
• EN: S235/S275/S355 (structural), EN 10083 (alloy steels), EN 10088 (stainless).
• SAE/ASTM AISI: carbon and alloy designation series (10xx, 41xx, 86xx).

5.5 Stainless Steel Applications

• 304: Kitchen sinks, piping, brewery tanks.
• 316: Marine hardware, chemical tankers (Mo added for chloride resistance).
• 440C: Ball bearings, high-end knives (martensitic, hardenable).

Example Decision Flow:

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