310S vs 309S Stainless Steel: A Practical Buyer’s Guide for High-Temperature Service
Selecting heat-resistant stainless steel is rarely about “which grade is better.” It is about which grade survives your real operating envelope—temperature, thermal cycling, atmosphere chemistry, fabrication method, and downtime tolerance.
Two of the most commonly specified alloys for furnaces, kilns, and high-temperature process equipment are 309S (UNS S30908) and 310S (UNS S31008). Both are austenitic stainless steels (non-magnetic in annealed condition, excellent high-temperature oxidation resistance), but they are engineered for different risk levels at elevated temperature. worldstainless+1
Executive decision summary (for procurement)
Choose 309S when:
Your equipment runs in high heat but not extreme heat, and the atmosphere is primarily oxidizing (hot air/flue gas) with manageable thermal cycling.
You need a cost-controlled heat-resistant grade with good fabrication performance.
Choose 310S when:
Your components see higher peak temperature, more aggressive scaling risk, or higher thermal cycling stress.
You face carburizing conditions (or carbon pickup risk) where longer service life justifies higher alloy cost.
1) The core difference: alloying strategy (Cr + Ni)
Both grades rely on chromium (Cr) to form a protective oxide scale and nickel (Ni) to stabilize austenite and support high-temperature strength retention. The key separator is how much Ni (and Cr) you are buying.
Chemical composition (ASTM ranges)
From ASTM-based chemistry limits, the typical ranges are: ATI Materials+1
| Grade | UNS | Chromium (Cr) | Nickel (Ni) | What it means in practice |
|---|---|---|---|---|
| 309S | S30908 | 22–24% | 12–15% | Strong oxidation resistance, good value for many furnace parts |
| 310S | S31008 | 24–26% | 19–22% | Higher oxidation margin + stronger high-temp stability; better in harsher cycles/atmospheres |
Why “S” matters: 309S and 310S are the lower-carbon variants of 309/310 used to reduce carbide precipitation risk in welded fabrications—helpful when you have many weld seams or complex assemblies. ATI Materials
2) Temperature limits: what “maximum service temperature” really means
Buyers often ask for a single number. In reality, service temperature depends on (a) intermittent vs continuous exposure and (b) atmosphere chemistry. A useful baseline is maximum service temperature in dry air (scaling resistance).
Approximate maximum service temperatures in dry air
A widely used reference table reports:
| Grade (Type) | Intermittent | Continuous |
|---|---|---|
| 309 (representative for 309S) | 980°C (1796°F) | 1095°C (2003°F) |
| 310 (representative for 310S) | 1035°C (1895°F) | 1150°C (2102°F) |
A producer datasheet for 309/309S aligns closely, describing destructive scaling around 2000°F (1093°C) and advising against intermittent use above 1800°F (982°C). Space Materials Database
Procurement takeaway: if your spec routinely approaches or exceeds ~1000°C, or you have frequent starts/stops (thermal cycling), 310S is the safer purchasing decision.
3) Oxidation, carburization, and “real atmosphere” selection
Oxidation / scaling (hot air, combustion products)
Both grades perform well because of high Cr, but 310S has more margin at the top end due to higher Cr and Ni. This is why 310/310S is often chosen for the most severe furnace internals. Atlas Steels+1
Carburization resistance (carbon pickup environments)
Carburizing atmospheres (common in heat treating, petrochemical units, and some combustion zones) can drive carbon diffusion into steel, embrittling material and accelerating failure mechanisms. A high-temperature stainless reference notes that higher nickel content slows diffusion rate, specifically calling out Type 310 compared with Types 309 or 304 as advantageous. Nickel Institute
Rule of thumb: if carbon pickup is part of your failure history (cracking, brittleness, unexpected distortion), move from 309S to 310S before jumping to nickel alloys.
Thermal cycling and cracking risk
Thermal cycling can crack heat-resistant parts even when average temperature is acceptable. Practical experience documented for Type 310 shows that microstructural factors (e.g., grain condition) can materially influence cracking resistance in cyclic service. Nickel Institute
Practical implication: if your equipment sees rapid heat-up/cool-down cycles, specify 310S and add fabrication controls (weld procedure, heat input discipline, and fit-up).
4) Mechanical performance at elevated temperature (what buyers should ask for)
For high-temperature parts, the real concern is not room-temperature yield strength—it is creep deformation and strength retention over time.
A major producer datasheet emphasizes these alloys’ use for elevated temperature applications and notes their ability to retain a larger fraction of room-temperature strength than common austenitics like 304. ATI Materials+1
Buyer note: If your component is load-bearing at high temperature (hangers, supports, structural furnace frames), discuss whether an “H” grade (309H/310H) is more appropriate than “S”. The “S” variants prioritize weldability; “H” variants are often chosen when creep strength dominates.
5) Weldability and fabrication (where projects lose money)
309S and 310S are generally weldable using common austenitic stainless methods, but they require disciplined practice because of austenitic thermal expansion and distortion sensitivity. Space Materials Database+1
Filler metal guidance (typical):
Match grade intent: ER/E309 for 309S work; ER/E310 for 310S work.
For dissimilar joints or buttering layers, engineering review is recommended before finalizing filler selection.
If you also purchase consumables with base metal, align filler selection with your WPS to avoid a strong base metal paired with an underperforming weld metal.
6) Applications: where each grade is typically specified
A producer application summary lists broad use across the heat treatment industry (conveyors, rollers, burner parts, refractory supports, retorts, oven linings, tube hangers, baskets/trays) as well as chemical processing environments involving hot concentrated media. ATI Materials+1
309S typical applications
Furnace baffles, liners, and ducting where temperatures are high but not at the extreme end
Heat shields, boiler baffles, high-temperature containers
Sections where cost control matters and scaling conditions are manageable
310S typical applications
Radiant tubes, retorts, high-temperature burner zones
Kiln and furnace internals with higher peak temperature and cycling
Heat-treat fixtures where carburization and repeated cycles shorten 309S life
7) Cost and ROI: how to justify 310S to a project manager
The cost gap is primarily driven by nickel content—310S carries substantially more Ni than 309S. ATI Materials+1
Instead of quoting a fixed percentage premium (which fluctuates with alloy surcharges), a more defensible purchasing argument is:
If failure triggers shutdown, replacement labor, or refractory rework, the lifecycle cost of a cheaper grade can exceed the upfront savings quickly.
If service conditions stay comfortably below the 309S oxidation envelope and carburization is not present, 309S usually delivers the best cost-performance ratio.
8) RFQ
When requesting a quote for 309S or 310S, include:
Grade & standard: 309S / 310S, product form standard (e.g., ASTM A240 for plate/sheet/coil)
Product form: coil/strip, sheet/plate, pipe/tube
Dimensions: thickness, width, length (or OD/WT/length for pipe)
Quantity: total tons + split by size
Surface & finish: 2B / BA / No.4 / HL / pickled, plus protective film needs
Service conditions: max temperature, continuous vs intermittent, number of cycles/day, and atmosphere (oxidizing, carburizing, sulfur-bearing, etc.)
Fabrication: welding process, PWHT/no PWHT, and inspection requirements
Documentation: MTC/EN 10204 3.1, PMI, third-party inspection (if needed)
Logistics: Incoterms + destination port + packing requirements
A complete RFQ shortens lead time and avoids “non-comparable” offers.
Why source heat-resistant stainless from LYH Steel
LYH Steel supplies stainless steel in the forms most commonly specified for high-temperature equipment—sheet/plate, strip/coil, and pipe/tube—with quotation support based on application conditions. LYH Steel+2LYH Steel+2
If you want the fastest, cleanest quotation cycle, use the RFQ checklist above and submit through LYH Steel’s contact channel. LYH Steel
FAQ
Q1: Is 309S “good enough” for furnace parts?
Often yes—if your peak temperature and cycling stay within the 309 oxidation/scaling envelope in your specific atmosphere.
Q2: Does 310S always last longer than 309S?
Not always. 310S has more margin at higher temperature and in carburizing risk, but service life is dominated by atmosphere chemistry, cycling, design stress, and fabrication quality. Nickel Institute+1
Q3: Which is easier to weld: 309S or 310S?
Both are weldable; the “S” versions are commonly selected for welded fabrications because of their lower carbon design intent. Final weld performance depends on WPS control and filler selection. ATI Materials+1