Stainless steel is an iron-based alloy that resists rust and corrosion. This resistance comes from chromium — at least 10.5% — which forms a thin, invisible oxide layer on the surface. If scratched, this layer self-repairs in the presence of oxygen.

Key Properties

• Corrosion resistance – Performs well in moist, acidic, or salty environments.
• Strength – Many grades are stronger than ordinary carbon steel, especially at elevated or cryogenic temperatures.
• Formability – Can be rolled, drawn, bent, or deep-drawn into various shapes.
• Weldability – Most austenitic grades weld easily with standard techniques.
• Appearance – Readily accepts polished, brushed, or matte finishes.

Common Grade Families

Austenitic (300 series)

Non-magnetic, excellent toughness, and very weldable.

• 304 – The most widely used. Suitable for kitchenware, tanks, piping, and architectural trim.
• 316 – Contains molybdenum for saltwater and chemical resistance. Used in marine hardware, pharmaceutical equipment, and outdoor structures.

Ferritic (400 series)

Magnetic, lower cost, but less formable than austenitic grades.

• 430 – Common in appliance panels, automotive trim, and indoor decorative applications.

Martensitic (400 series)

Magnetic, heat-treatable to high hardness.

• 410 and 420 – Used for cutlery, valves, shafts, and surgical instruments where wear resistance matters.

Precipitation-hardening

• 17-4 PH – Combines high strength with moderate corrosion resistance. Often specified for aerospace and high-stress components.

Surface Finishes

• No. 2B – Smooth, reflective finish for general industrial use.
• No. 4 – Brushed finish, common on kitchen equipment and handrails.
• BA (Bright Annealed) – Mirror-like surface for decorative or sanitary applications.
• Matte – Non-reflective, often bead-blasted or etched.

Limitations to Know

• Stainless steel is more expensive than carbon steel or aluminum.
• It has lower thermal conductivity and higher thermal expansion than plain carbon steel.
• Galling (cold welding) can occur when stainless threads are tightened without lubricant.
• In low-oxygen environments or with long-term chloride exposure, some grades can suffer pitting or crevice corrosion.

Choosing the Right Grade

For indoor, dry conditions → 304 is often sufficient.

For coastal or chemical exposure → 316 is recommended.

For high hardness and wear resistance → Consider 420 or 17-4 PH.

For magnetic response or lower cost → Look at ferritic grades like 430.