SUS317L is a Japanese industrial standard (JIS) designation for a low-carbon austenitic stainless steel, equivalent to the international 317L stainless steel. It is known for its excellent corrosion resistance, particularly in harsh environments containing chlorides and acids, and maintains good mechanical properties and weldability. Below is a detailed breakdown:
1. Chemical Composition (JIS G4305 Standard)
The key elements (weight percentage) are strictly regulated to ensure its performance:
Chromium (Cr): 18.0% – 20.0% (forms a passive oxide layer, the core of corrosion resistance)
Nickel (Ni): 11.0% – 15.0% (stabilizes the austenitic structure, enhancing toughness and ductility)
Molybdenum (Mo): 3.0% – 4.0% (significantly improves resistance to pitting, crevice corrosion, and chloride-induced stress corrosion cracking)
Carbon (C): ≤0.03% (low carbon content prevents carbide precipitation at grain boundaries during welding, reducing intergranular corrosion risk)
Other elements: Silicon (Si) ≤1.0%, Manganese (Mn) ≤2.0%, Phosphorus (P) ≤0.045%, Sulfur (S) ≤0.030%, with the remainder being iron (Fe).
2. Physical Properties
Density: 8.0 g/cm³
Melting point: 1371°C – 1454°C
Thermal expansion coefficient (20°C – 100°C): 16.0 × 10⁻⁶/°C
Thermal conductivity: 16.2 W/(m·K) (at 100°C)
Electrical resistivity: 72 × 10⁻⁸ Ω·m
Magnetic property: Non-magnetic (typical of austenitic stainless steels; may become slightly magnetic after cold working, but not strongly magnetic)
3. Mechanical Properties
Tensile strength: ≥485 MPa
Yield strength (0.2% offset): ≥170 MPa
Elongation (in 50 mm): ≥40%
Hardness: ≤95 HRB (Rockwell B) or ≤200 HB (Brinell)
Impact toughness: Excellent, even at low temperatures (no brittle transition, suitable for cryogenic applications down to -196°C)
4. Key Characteristics
Superior corrosion resistance: The higher molybdenum content (3.0% – 4.0%) compared to SUS316L (which has 2.0% – 3.0% Mo) makes SUS317L more resistant to pitting and crevice corrosion in chloride-rich environments (e.g., seawater, brines, and industrial effluents). It also performs well in dilute acids (sulfuric, phosphoric) and organic solvents.
Excellent weldability: Low carbon content (≤0.03%) avoids carbide precipitation during welding, eliminating the need for post-weld annealing to maintain corrosion resistance. It is compatible with common welding methods (TIG, MIG, arc welding).
Good formability: High ductility allows for bending, rolling, deep drawing, and other cold working processes. Cold working can increase its strength but may slightly reduce ductility.
Heat resistance: Maintains stability and oxidation resistance in moderate high-temperature environments (up to ~800°C in oxidizing atmospheres).
5. Heat Treatment
Solution annealing: Typically conducted at 1010°C – 1150°C, followed by rapid water quenching. This process dissolves any precipitated carbides, restores the uniform austenitic structure, and maximizes corrosion resistance.
6. Applications
SUS317L is widely used in industries requiring high corrosion resistance, including:
Chemical processing: Tanks, pipelines, valves, and pumps for handling acids, chlorides, and corrosive chemicals.
Marine engineering: Components exposed to seawater (e.g., offshore structures, heat exchangers, seawater desalination equipment).
Food and pharmaceutical industries: Equipment requiring high purity and resistance to cleaning agents (stainless steel tanks, mixers, and conveyor systems).
Wastewater treatment: Pipes and fittings for chlorinated or acidic wastewater.
Pulp and paper industry: Machinery resistant to bleach chemicals (e.g., chlorine dioxide).
Relationship with Other Standards
SUS317L is the JIS equivalent of:
ASTM/ASME 317L
DIN 1.4438
EN 1.4438
Its performance is consistent with these international counterparts, with minor differences in chemical composition ranges due to regional standard variations, but the core properties (corrosion resistance, mechanical strength) remain comparable.
In summary, SUS317L is a high-performance stainless steel ideal for aggressive environments where standard grades (like SUS304 or SUS316L) may not suffice, offering a balance of corrosion resistance, weldability, and formability.