Materials
Stainless Steel: ISO 3506-1 A2-50, 70, 80 | A4-50, 70, 80
Stainless Steel ISO 3506-1 (A2 & A4 Austenitic Fasteners)
Material:
ISO 3506-1 defines the mechanical properties of stainless steel bolts, screws, and studs.
These are based on austenitic stainless steels:
A2 series → 304 / 304L equivalent (general corrosion resistance)
A4 series → 316 / 316L equivalent (molybdenum-enhanced for chloride resistance)
The suffix numbers (50, 70, 80) define minimum tensile strength levels, not chemistry.
A2 Stainless Steel (304 / 304L equivalent)
A2-50 / A2-70 / A2-80
Mechanical Properties
Strength increases by class:
A2-50 → ~500 MPa tensile strength (low strength, high ductility)
A2-70 → ~700 MPa tensile strength (most common general-purpose grade)
A2-80 → ~800 MPa tensile strength (high-strength cold-worked condition)
Excellent toughness and elongation.
Non-hardenable by heat treatment; strength comes from cold working.
Corrosion Resistance
Good resistance to:
Atmospheric environments
Fresh water
Mild industrial chemicals
Less resistant to:
Chlorides (saltwater)
Pitting and crevice corrosion in marine environments
Manufacturing Considerations
Austenitic stainless → strong work-hardening behavior during machining and forming.
No quench/temper heat treatment required.
Strength level (50 → 70 → 80) is achieved via controlled cold working.
A2-80 requires tighter process control due to reduced ductility.
Applications in Fasteners
General industrial bolting
Machinery and equipment assemblies
Interior/outdoor applications with low chloride exposure
Automotive, HVAC, and appliance fasteners
A4 Stainless Steel (316 / 316L equivalent)
A4-50 / A4-70 / A4-80
Mechanical Properties
Same strength class structure as A2:
A4-50 → ~500 MPa
A4-70 → ~700 MPa (most widely used marine stainless fastener grade)
A4-80 → ~800 MPa (high-strength cold worked marine-grade fastener)
Comparable ductility to A2, with slightly reduced machinability due to Mo content.
Corrosion Resistance
Superior to A2 due to 2–3% molybdenum addition:
Excellent resistance to chloride corrosion
Strong resistance to pitting and crevice corrosion
Better performance in saltwater, coastal, and chemical environments
Preferred for marine and offshore service
Manufacturing Considerations
Cold working is used to achieve strength classes (50/70/80).
More difficult to machine than A2 due to molybdenum.
Excellent forming and threading capability in annealed condition.
A4-80 requires strict control of cold work and inspection due to reduced ductility margin.
Applications in Fasteners
Marine and offshore bolting systems
Chemical processing equipment
Food and pharmaceutical machinery
Coastal infrastructure and outdoor installations
Pump, valve, and seawater systems
Key Takeaway for Engineered Fasteners
ISO 3506 A2 and A4 fasteners are work-hardened austenitic stainless steel systems, widely used because they balance corrosion resistance, availability, and cost efficiency.
A2 (304-based) → General-purpose stainless fasteners for non-marine environments
A4 (316-based) → Marine and chemical-grade stainless fasteners with superior chloride resistance
Strength levels define performance:
-50 → Low strength, high ductility
-70 → Standard structural stainless fastener (most common)
-80 → High-strength cold-worked fastener for demanding loads
Engineering Context For Engineered Fasteners:
A2 grades are used when corrosion risk is moderate and cost efficiency matters.
A4 grades are specified when chloride exposure, seawater, or chemical attack is expected.
Moving from 70 → 80 increases load capacity but reduces ductility and increases installation sensitivity (torque control becomes more critical).
Materials
BRASS
BRONZE
COPPER
PH STAINLESS STEEL
DOING WHATEVER IT TAKES
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