EN
304 vs 304L Stainless Steel Plate: Key Differences, Welding and Buying Guide
The main difference between 304 and 304L stainless steel plate is carbon content. Both belong to the austenitic chromium-nickel stainless steel family, but the lower carbon limit of 304L is particularly relevant when welding and resistance to sensitization are part of the project requirement. For industrial purchasing, however, grade alone is not enough: the applicable standard, plate dimensions, surface condition, tolerance, inspection documents and project specification should be reviewed together.
What is the difference between 304 and 304L stainless steel?
Under commonly used ASTM flat-product specifications, Type 304 is identified as UNS S30400 and permits a higher maximum carbon content than 304L, UNS S30403. The low-carbon 304L grade limits carbon to 0.03% maximum, compared with 0.08% maximum for standard 304. Lower carbon reduces the tendency for chromium carbide precipitation and sensitization during relevant thermal exposure such as welding.
Widely specified for general fabrication, equipment, tanks and structural components where the project specification permits Type 304.
The lower-carbon version of the 304 family, commonly considered when welded fabrication and resistance to sensitization need additional attention.
304 vs 304L Stainless Steel Plate Comparison
For plate buyers, the useful comparison is not simply which grade is “better.” The important question is whether the material offered satisfies the governing standard, drawing, fabrication route and service requirement.
| Comparison | 304 Stainless Steel | 304L Stainless Steel | Buyer Interpretation |
|---|---|---|---|
| UNS designation | S30400 | S30403 | Confirm the exact designation required by the order or drawing. |
| Stainless family | Austenitic Cr-Ni stainless steel | Austenitic Cr-Ni stainless steel | They belong to the same basic grade family. |
| Maximum carbon | 0.08% | 0.03% | The lower carbon limit is the defining difference for many purchasing decisions. |
| Chromium | Typically specified around 18.0–20.0% | Typically specified around 18.0–20.0% | Always check the governing standard and actual MTC rather than a general web table. |
| Nickel | Commonly specified around 8.0–10.5% | Commonly specified around 8.0–12.0% | The exact requirement should follow the applicable material specification. |
| Welding consideration | Suitable for many welded fabrications, subject to the procedure, section thickness and service requirement. | Lower carbon reduces the tendency toward weld-related sensitization in relevant conditions. | Do not select a grade only from the word “welded”; review the complete fabrication requirement. |
| General corrosion resistance | Good in many mild to moderate service environments. | Broadly similar in comparable non-sensitized conditions. | The “L” suffix should not be interpreted as universally higher corrosion resistance. |
| Chloride / pitting resistance | Application dependent. | Application dependent. | 304L does not gain molybdenum simply because it is an L grade. Chloride exposure may require comparison with other grades. |
| Dual certification | Material may sometimes be supplied or documented as 304/304L when the applicable requirements for both designations are satisfied. | Verify the MTC and obtain project acceptance where the order requires a specific designation. | |
Buyers looking for product-specific supply information can compare 304 stainless steel plate with 304L hot-rolled stainless steel plate before preparing the final RFQ.
Why does the lower carbon content of 304L matter?
Austenitic stainless steel can experience sensitization when an unsuitable combination of temperature and time allows chromium carbides to form at grain boundaries. The surrounding area can become locally depleted in chromium, reducing resistance to intergranular corrosion in environments capable of attacking the sensitized region.
Reducing carbon limits the amount of carbon available to form these carbides. This is why low-carbon grades such as 304L are widely associated with welded corrosion-resistant fabrication.
Lower carbon primarily addresses the risk of sensitization. It does not mean that 304L automatically has substantially better resistance to every type of corrosion than 304.
For example, if the real concern is chloride-related pitting, salt exposure, coastal service or an aggressive process solution, the project may need a comparison between different stainless alloy families rather than simply choosing 304L instead of 304. For that decision, see the 304 vs 316 stainless steel comparison .
Is 304L better than 304 for welding?
304L is commonly selected for welded fabrication because its lower carbon content reduces the tendency toward sensitization during normal welding thermal cycles. That advantage is especially relevant when the completed component may operate in an environment where intergranular attack is a design concern.
However, the base-metal designation is only one part of a welded system. Welding procedure, filler material, heat input, joint design, section thickness, heat tint removal, cleaning, inspection and any post-weld treatment can all affect the finished component.
Do not interpret “304L is commonly preferred for welding” as a universal substitution rule. A drawing, code, customer specification or approved WPS may require a particular designation or additional fabrication controls.
What does 304/304L dual certified plate mean?
Stainless steel plate is sometimes offered or documented with a dual designation such as 304/304L. In procurement practice, this means the material is represented as satisfying the applicable requirements used for both designations. Buyers should still review the actual certification rather than relying only on the wording in a quotation.
Dual certification does not automatically approve the material for every contract, drawing, pressure component, welding procedure or end-user specification. If a project explicitly calls for one designation, confirm whether dual-certified material is acceptable before approving the substitution.
What the MTC should help verify
- grade and UNS designation;
- heat or traceability reference;
- chemical composition;
- reported mechanical test results;
- material standard and product form;
- other agreed inspection information.
What dual designation does not replace
- drawing approval;
- project-specific material selection;
- dimensional and tolerance checks;
- welding-procedure requirements;
- surface and edge requirements;
- customer or third-party acceptance.
ASTM A240 and the plate purchase specification
ASTM A240/A240M is commonly referenced for chromium and chromium-nickel stainless steel plate, sheet and strip. For a purchasing team, however, writing “ASTM A240 304L plate” is still not a complete RFQ.
The buyer should also state the exact dimensions, tolerance requirements, required surface condition, quantity, edge condition, processing needs, inspection-document requirements and any project-specific acceptance criteria. The required edition of the standard and other contractual documents should follow the purchase specification.
For a broader explanation of plate dimensions, grades and specification details, see Voyage Metal's stainless steel plate thickness, sizes, grades and ASTM standards guide .
How should a buyer evaluate a 304 vs 304L plate offer?
A useful purchasing sequence is to separate material selection from document verification. This prevents a familiar grade name from becoming an automatic approval decision.
Define the requirement
Confirm the drawing, application, required grade, product form, dimensions and governing specification.
Compare the offered material
Check whether the quotation states 304, 304L or a dual designation and whether that matches the request.
Review documents
Compare the MTC, heat reference, chemical composition, test data and agreed inspection scope with the purchase requirement.
Approve deviations
Send substitutions or specification differences to the responsible engineering or quality authority before final acceptance.
304 or 304L plate: specification checks before ordering
Treat the quotation as a complete specification package rather than comparing price per kilogram or price per sheet alone.
| Check area | What to confirm | Why it matters |
|---|---|---|
| Grade | 304, 304L or an accepted dual designation | The material description should match the project requirement. |
| Product form | Plate, sheet or another specified flat product | Product form affects dimensions, tolerances and the applicable specification. |
| Standard | ASTM, ASME, EN or customer-specific requirement | The grade name alone does not define every acceptance requirement. |
| Dimensions | Thickness × width × length | Exact dimensions are necessary for quotation, processing and tolerance review. |
| Tolerance / flatness | Project or drawing requirement | Nominal size alone may not be sufficient for fabricated components. |
| Surface | No.1, 2B, polished or other required condition | Surface condition can affect fabrication, appearance and downstream processing. |
| Edge / cutting | Mill edge, trimmed edge, cut-to-size, CNC or other processing | Processing requirements affect the finished dimensions and commercial offer. |
| Documents | MTC, dimensional report or agreed inspection records | Document scope should be defined before production or shipment. |
| Traceability | Heat, lot or project identification where required | The delivered plate should be traceable to the agreed documentation. |
| Service conditions | Welding, temperature, chemicals, chlorides and downstream fabrication | These conditions may affect grade selection and approval. |
Buyers who are still defining product form can also review the broader stainless steel plate range before preparing the final specification.
What should be included in a 304 or 304L plate inquiry?
Sending the same technical information to every bidder makes quotations easier to compare and reduces unnecessary clarification after the order is placed.
304 vs 304L Stainless Steel FAQ
What is the main difference between 304 and 304L stainless steel?
The key difference is the carbon limit. Standard 304 allows up to 0.08% carbon, while 304L limits carbon to 0.03% maximum under commonly used specifications. The lower carbon content reduces the tendency toward sensitization during relevant thermal exposure such as welding.
Is 304L always better than 304?
No. 304L provides a specific low-carbon advantage, particularly where sensitization is a concern. The correct designation still depends on the project specification, mechanical requirements, fabrication method, environment and required documentation.
Does 304L have better corrosion resistance than 304?
Not universally. Their general corrosion behavior can be broadly similar in comparable non-sensitized conditions. The principal advantage of the lower carbon content is improved resistance to sensitization-related intergranular corrosion after relevant heat exposure. It does not make 304L automatically more resistant to chloride pitting.
Can 304L be substituted for 304 stainless steel plate?
Do not approve substitution solely because the grades are closely related. Check the governing standard, drawing, mechanical requirements, MTC and customer specification, and obtain the required project approval.
What does 304/304L dual certified mean?
It normally indicates that the material has been documented as meeting the applicable requirements used for both designations. Buyers should still review the MTC and confirm that a dual designation is acceptable under the project specification.
What standard is commonly used for 304 and 304L stainless steel plate?
ASTM A240/A240M is commonly referenced for chromium and chromium-nickel stainless steel plate, sheet and strip. The exact standard edition and any supplementary project requirements should be stated in the purchase order.
Request 304 or 304L Stainless Steel Plate
Send Voyage Metal the required grade, standard, thickness × width × length, tolerance, surface or edge condition, quantity, inspection-document requirement, packing, destination and intended application. The requirement can then be reviewed against the requested product and supply scope before quotation.
Discuss Your Plate Requirement