What Is AISI 316 Stainless Steel?
AISI 316 is a grade designation within the American Iron and Steel Institute (AISI) numbering system for stainless steels. It identifies a specific austenitic stainless steel alloy defined primarily by its chemical composition — roughly 16–18.5% chromium, 10–14% nickel, and 2–3% molybdenum. The AISI system focuses on classifying alloys by their chemistry rather than product form or mechanical properties.
What Is ASTM 316 Stainless Steel?
ASTM 316 refers to 316 stainless steel products that meet specifications published by ASTM International (formerly the American Society for Testing and Materials). Unlike the AISI grade designation, ASTM standards define complete product specifications — including chemical composition ranges, mechanical property requirements, dimensional tolerances, testing methods, and delivery conditions for specific product forms such as sheet, plate, bar, tube, and pipe.
Chemical Composition (Identical for Both)
Element
316 (UNS S31600)
316L (UNS S31603)
C (Carbon)
≤ 0.08%
≤ 0.03%
Si (Silicon)
≤ 0.75%
≤ 0.75%
Mn (Manganese)
≤ 2.00%
≤ 2.00%
P (Phosphorus)
≤ 0.045%
≤ 0.045%
S (Sulfur)
≤ 0.030%
≤ 0.030%
Cr (Chromium)
16.0 – 18.0%
16.0 – 18.0%
Ni (Nickel)
10.0 – 14.0%
10.0 – 14.0%
Mo (Molybdenum)
2.00 – 3.00%
2.00 – 3.00%
N (Nitrogen)
≤ 0.10%
≤ 0.10%
Fe (Iron)
Balance
Balance
Mechanical Properties (ASTM A240 — Plate/Sheet)
Property
316 (S31600)
316L (S31603)
Units
Tensile Strength (min)
75,000 psi (515 MPa)
70,000 psi (485 MPa)
ksi
Yield Strength 0.2% (min)
30,000 psi (205 MPa)
25,000 psi (170 MPa)
ksi
Elongation (2″ gauge, min)
40%
40%
%
Reduction of Area (min)
50%
50%
%
Hardness (max, HBW)
217
217
HBW
Hardness (max, HRB)
95
95
HRB
2025 Revision Changes (ASTM A240-2025)
Parameter
A240-2022
A240-2025
Impact
Max S in 316L
0.030%
0.0225%
Reduces hot cracking in multipass welding
Min Tensile (CR 316L, ≤0.5 mm)
485 MPa
515 MPa
+5% strength for thin gauge
Min Elongation (CR 316L, ≤0.5 mm)
35%
40%
Improved formability guarantee
Applicable ASTM Product Standards by Form
Product Form
ASTM Standard
Typical Use
Plate, Sheet, Strip
A240 / A240M
Pressure vessels, general fabrication
Welded/Unwelded Tube
A312 / A312M
Piping, heat exchangers
Seamless Tube
A213 / A269
Boilers, general purpose
Bar, Rod, Shape
A276 / A276M
Shafts, pins, structural
Forgings
A182 / A182M
Valves, flanges, fittings
Wire
A580 / A586
Springs, cables, welding wire
Flanges
A182 / B16.5
Piping connections
Castings
A351 / A743
Valve bodies, pump housings
Fasteners
A193 / A325
Bolts, studs
Clad Plate
A403 / A466
Corrosion-resistant overlay
Q1: Are AISI 316 and ASTM 316 the same?
Yes, they refer to the same alloy. "AISI 316" is the grade designation, whereas "ASTM 316" refers to Grade 316 stainless steel supplied in accordance with specific ASTM product standards (such as A240, A312, A276, etc.). There is no difference in the material itself.
Q2: What is the ASTM equivalent for AISI 316?
There is no single "ASTM equivalent standard." The universal cross-reference designations are UNS numbers S31600 (316) or S31603 (316L). The applicable ASTM standard depends on the product form: A240 (plate/sheet), A312 (welded pipe), A276 (bar), or A182 (pipe fittings).
Q3: If I order "AISI 316," can I receive material that meets the ASTM A240 standard?
In practice, yes—most steel mills produce material that complies with both standards. However, for engineering review and compliance purposes, your purchase order (PO) should clearly specify the ASTM product standard (e.g., "ASTM A240 Type 316L"). Specifying only "AISI 316" is insufficient as a formal technical specification.
Q4: What is the difference between 316 and 316L?
The only compositional difference is the carbon content: 316 allows for up to 0.08% carbon, whereas 316L is limited to ≤ 0.03%. This makes 316L more suitable for welding applications (due to the absence of sensitization risk), though it has slightly lower strength (yield strength of 25 ksi vs. 30 ksi).
Q5: Which material should be specified for welded chemical vessels?
You should specify 316L in accordance with ASTM A240 (or ASME SA-240 for pressure vessels). The low carbon content eliminates the need for post-weld annealing, and the molybdenum (Mo) content enables resistance to chloride-containing process media. Q6: What is the PREN value of 316 stainless steel?
PREN = %Cr + 3.3×%Mo + 16×%N. For 316/316L: approximately 24–26. Comparison: 304 ≈ 18, 317L ≈ 29, 2205 duplex steel ≈ 35, 904L ≈ 43.
Q7: Is 316 magnetic?
No. In the annealed condition, 316 is non-magnetic (fully austenitic structure). Cold working may induce slight magnetism, but this can be eliminated by re-annealing.
Q8: What is the maximum service temperature for 316/316L?
Up to 870°C (1,598°F) for general applications. For ASME-compliant pressure vessel applications, the upper temperature limit is typically between 800°C and 850°C, depending on thickness and design specifications.
Q9: How much higher is the price of 316 compared to 304?
As of 2026, the price of 316 is approximately 30%–50% higher than that of 304. In the US market: 304 ≈ $2,900–$3,050 per metric ton, while 316 ≈ $3,800–$5,600 per metric ton (depending on product form and the specific quarter).
