Steel is primarily a solid solution of iron and carbon (typically
High-strength steels (>1200 MPa tensile) absorb atomic hydrogen, becoming brittle. Prevention: Bake immediately after plating. Use low-hydrogen welding rods.
The ability to resist surface indentation and abrasion, often increased by adding chromium or vanadium.
Standards: AISI/ASTM tool steel designations. Steel is primarily a solid solution of iron
Material selection requires matching the steel's properties to the stresses it will encounter during its service life. Mechanical Properties
| Series | Structure | Corrosion Resistance | Example | Application | |--------|-----------|----------------------|---------|-------------| | 300 (Austenitic) | FCC, non-magnetic | Excellent | 304, 316 | Food equipment, chemical plants | | 400 (Ferritic/Martensitic) | BCC, magnetic | Good | 410, 430 | Cutlery, automotive trim | | 200 series | Austenitic, Mn-substituted | Moderate | 201 | Utensils, architectural |
| Property | Definition | Typical Unit | | :--- | :--- | :--- | | | 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 | The ability to resist surface indentation and abrasion,
): The stress at which material deformation becomes permanent. Ductility/Elongation (
Widely used in structural engineering and piping. Common designations include ASTM A36 (structural carbon steel) and ASTM A325 (high-strength bolts).
The maximum stress a material can withstand before breaking under tension. Mechanical Properties | Series | Structure | Corrosion
The maximum engineering stress that a material can withstand before catastrophic fracture.
Machinery parts, tool making, and heavy equipment.
| Grade | C% | Tensile (MPa) | Yield (MPa) | Hardness (HB) | Common Use | |-------|----|--------------|-------------|---------------|-------------| | A36 | 0.26 | 400–550 | 250 | 120–160 | Structural beams | | 1018 | 0.18 | 440 | 370 | 130 | Shafts, pins | | 4140 (Q&T) | 0.40 | 950 | 655 | 300 | Axles, gears | | 304 SS | 0.08 | 515 | 205 | 150 | Food equipment | | 17-4PH (H900) | 0.07 | 1310 | 1170 | 400 | Aerospace fittings |
Steel is fundamentally an alloy consisting primarily of iron (Fe) and a small percentage of carbon (C), typically between 0.02% and 2.1% by weight. The addition of carbon, along with other alloying elements, significantly alters the mechanical and physical properties of pure iron, resulting in a versatile engineering material. 1.1 The Role of Carbon Carbon is the most important alloying element in steel.
Steel Metallurgy: Properties, Specifications, and Applications