Grade quotation brief
309S vs 310S Stainless Steel
Quote 309S when the actual component temperature, atmosphere, load, cycling and design method establish adequate oxidation and strength margin for the ordered form. Quote 310S when the same controlled analysis requires its higher displayed chromium-nickel balance. Neither grade label supplies a universal temperature, creep life or atmosphere approval, and the lower-carbon S designations must be ordered explicitly.
Quote 309S when the approved atmosphere, oxidation, load and cycling assessment establishes adequate margin for the exact component. Quote 310S when that same assessment requires its higher displayed chromium-nickel balance. Neither grade can be approved from furnace setpoint, alloy ranking or a generic maximum-temperature table; use actual metal temperatures and controlled design data.
Unsure whether 309S or 310S matches the operating temperature and chemistry? Send the service conditions with the RFQ. We quote the approved designation, product form and test plan.
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Illustrations identify the compared grade references; they are not photographs of the quoted material or proof of a mill heat.
Decision matrix
Key Differences
Full grade sheets:309S Stainless Steel/310S Stainless Steel
| Factor | 309S | 310S | Procurement decision |
|---|---|---|---|
| Alloy balance | 309S has lower displayed chromium and nickel ranges than 310S in the summarized flat-product chemistry. | 310S has higher displayed chromium and nickel ranges for a different heat-resisting alloy route. | Connect the alloy difference to a documented atmosphere and design calculation, not a universal ranking. |
| Oxidation screening | 309S can be assessed for qualified furnace parts, shields and transition components under defined exposure. | 310S can be assessed where the project needs additional oxidation margin in its defined atmosphere. | Use actual metal temperature, gas chemistry, deposits, cycling and surface condition for approval. |
| Load and creep | 309S elevated-temperature strength must come from controlled code data for the exact form and condition. | 310S also needs designation-specific allowable-stress and creep data rather than alloy-content inference. | Separate unloaded oxidation screening from loaded component design and life assessment. |
| Fabrication and supply | 309S form, filler, weld procedure, thermal processing and inspection require project confirmation. | 310S may follow a different availability, forming, filler and qualified fabrication package. | Compare delivered and fabricated scopes for the same dimensions, tests and schedule before selection. |
Service and production route
Corrosion and Fabrication Boundaries
309S corrosion screening
- For this 309S vs 310S review, 309S relies on chromium-rich scale in oxidizing hot gases, but scale growth and adhesion change with oxygen potential, temperature gradient and cycling. Sulfur compounds, carbon activity, ash or salt deposits can alter the damage mechanism and alloy ranking.
- For this 309S vs 310S review, This grade is not a wet-chloride upgrade from 304 because it has no intentional molybdenum range. Condensation during startup or shutdown can expose welds, crevices and heat-tinted areas to localized corrosion that dry-air oxidation data does not address.
310S corrosion screening
- For this 309S vs 310S review, The high chromium content supports oxide-scale formation in oxidizing hot gases, while scale stability changes with temperature, oxygen potential, thermal cycling and contamination. Sulfur-bearing, reducing, carburizing or molten-salt conditions require separate alloy evaluation.
- For this 309S vs 310S review, 310S is not a molybdenum-bearing wet-corrosion grade. Condensate, chlorides and acidic deposits during startup or shutdown can create a different damage mechanism from dry oxidation and must be assessed independently.
| Operation | 309S | 310S |
|---|---|---|
| Welding | Use a qualified procedure that controls filler composition, dilution, heat input and joint restraint for cyclic hot service. Remove surface contamination and specify weld profile because notches and local section changes can concentrate thermal strain. | Qualify filler, heat input, joint restraint and purge for the actual hot-service assembly. Weld geometry and dilution matter because local hot spots, sigma-phase exposure and cyclic strain can govern before base-metal oxidation data. |
| Forming | Annealed 309S is ductile but work hardens during forming and generally needs more force than 304. Bend allowance, springback, tooling cleanliness and any intermediate anneal must be established for the actual gauge and reduction. | 310S is formable in the annealed condition but work hardens rapidly and needs higher force than lower-alloy austenitic sheet. Allow for springback, protect the surface from carbon-steel contamination and review intermediate annealing for severe reductions. |
| Machining | Rigid setups, sharp tools and positive feed help prevent rubbing into a hardened surface. Cutting data should control heat and preserve the machining allowance needed for weld preparation and thermal-expansion features. | Use rigid setups, sharp tooling and continuous positive feed to avoid rubbing into a work-hardened surface. Control cutting heat and verify dimensional allowance for components that will later see thermal expansion. |
| Heat treatment | Solution treatment establishes the intended austenitic condition; conventional heat treatment does not harden 309S. Any post-fabrication thermal cycle must be reviewed for grain growth, sensitization, distortion and final surface condition. | Solution treatment is used to establish the specified austenitic condition; 310S is not hardened by conventional quench-and-temper practice. Thermal processing after fabrication must be reviewed against grain growth, distortion and the final service requirement. |
Reference data
Composition and Mechanical Requirements
Values below come from each grade's displayed reference dataset. Product form, thickness, condition and contracted standard can change the applicable acceptance table.
Chemical composition (wt%)
| Element | 309S | 310S |
|---|---|---|
| C | ≤0.08 | ≤0.08 |
| Mn | ≤2.00 | ≤2.00 |
| Si | ≤0.75 | ≤1.50 |
| Cr | 22.0–24.0 | 24.0–26.0 |
| Ni | 12.0–15.0 | 19.0–22.0 |
| P | ≤0.045 | ≤0.045 |
| S | ≤0.030 | ≤0.030 |
Mechanical properties
| Property | 309S | 310S |
|---|---|---|
| Tensile strength | ≥515 MPa (75 ksi) | ≥515 MPa (75 ksi) |
| Yield strength (0.2%) | ≥205 MPa (30 ksi) | ≥205 MPa (30 ksi) |
| Elongation (50 mm) | ≥40% | ≥40% |
| Hardness | ≤217 HBW | ≤217 HBW |
Quotation workflow
Application Decisions
- For furnace internals, provide measured or calculated metal temperature, atmosphere composition, pressure, velocity, deposits, load, support geometry and cycle profile.
- For radiant tubes and burner parts, add internal and external atmospheres, heat flux, restraints, weld locations, creep method and inspection intervals.
- For heat-treatment fixtures, document load, distortion tolerance, pickup or scaling limits, quench exposure, repair welding and retirement criteria.
- For dissimilar joints or overlays, identify both base materials, dilution, filler classification, PWHT, thermal fatigue and governing welding code.
Quote 309S when
- Furnace shells, heat shields and transition pieces qualified for an S30908 route
- Dissimilar-joint or overlay systems whose approved welding specification names a 309 family
- Cyclic hot components supported by measured metal temperatures and designation-specific data
- Orders where the required 309S form, thickness, weld package and inspection scope are available
Quote 310S when
- Furnace internals whose project oxidation review needs the displayed 310S alloy balance
- Burner parts, radiant tubes or fixtures with approved S31008 thermal-design data
- Oxidizing service whose gas chemistry, deposits, load and cycles have been defined
- Traceable supply packages that preserve 310S product, welding and equipment-code requirements
Hold point
Do Not Substitute Without Review
- Do not replace 309S with 310S, or 310S with 309S, without authorized review of atmosphere, thermal design, welding and product-form requirements.
- Do not convert furnace-air setpoint or an oxidation chart into a guaranteed component metal-temperature limit.
- Do not infer allowable stress, creep rupture or design life from room-temperature properties or chromium-nickel content.
- Do not substitute a non-S family designation or apply flat-product values to tube, pipe or fabricated equipment without the governing standard.
Specification boundary
Standards, Temperature and Approval
Product and project approval
ASTM A240/A240M and EN 10088 can govern specified flat products, while tubular or fabricated furnace components require the applicable product, welding and equipment specifications. The current edition, exact UNS designation, form, condition, atmosphere basis, design code and authorized technical reviewer control acceptance.
Temperature boundary
This comparison publishes no fixed operating-temperature range for 309S or 310S. Actual metal temperature can differ from furnace setpoint, while oxygen potential, sulfur, carbon activity, combustion products, deposits, cycling, load, creep duration, section and weld condition set separate boundaries.
Commercial comparison
Cost and Availability Factors
Quote 309S and 310S on one RFQ with the same product form, dimensions, tests and documents. This page does not represent current stock, price or lead time.
Cost factors
- Current alloy inputs and mill availability for the exact grade, form, thickness, condition and delivery window.
- Design section, forming, machining, weld consumables, thermal processing and qualified fabrication hours.
- Oxidation coupons, elevated-temperature tests, PMI, NDE, inspection documents and witness requirements.
- Fabricated-component yield, repair strategy, quantity, packing, freight, Incoterm and requalification scope.
Inputs for a like-for-like quotation
- UNS S30908 or S31008, product form, material and dimensional standards, equipment code and substitution policy.
- Dimensions, thickness, quantity, delivery condition, finish, tolerance, formed geometry and end preparation.
- Actual metal-temperature profile, furnace setpoint, gas chemistry, oxygen and sulfur potential, deposits, load and cycles.
- Joining process, filler, WPS/PQR, dilution, heat treatment, surface cleaning, distortion and NDE requirements.
- MTC, heat traceability, PMI, elevated-temperature or oxidation tests, inspection, destination, Incoterm and schedule.
Continue the specification
Related Grades, Standards and Applications
Grade references
Standards
Buyer questions
Frequently Asked Questions
Is 310S always better than 309S?
No. Its different alloy balance can provide added oxidation margin in some atmospheres, but carburizing, sulfur-bearing, reducing or condensing conditions can change the ranking. Match the exact grade to atmosphere, load, cycles and code data.
What does the S suffix mean?
The S designation identifies the specified lower-carbon variant within each grade family. It remains a distinct ordered material: state S30908 or S31008 and verify heat chemistry against the current product standard.
Can these grades be used in sulfur-bearing atmospheres?
Nickel-bearing alloys can behave differently as sulfur potential, oxygen potential, temperature and deposits change. Provide the complete gas and shutdown chemistry and obtain a specialist high-temperature corrosion review before approval.
Published by Tsingshan (Shandong) Iron & Steel Co., Ltd..Sources, update policy and technical limitations.
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