Metal Materials
EN 1.4404 Stainless Steel: Full Guide to Properties, Uses & Fabrication
If you are building equipment for a pharmaceutical plant, a desalination facility, or a food processing line, you need a stainless steel that can withstand constant exposure to corrosive agents. Standard grades like 304 can fail after welding, becoming vulnerable to a type of corrosion that attacks the grain boundaries. EN 1.4404 stainless steel solves this problem.
What Defines EN 1.4404?
The performance of EN 1.4404 is rooted in its precise chemical composition and the stable austenitic structure it maintains. It is designed to be tough, clean, and predictable.
What Is in the Alloy?
The chemical composition of EN 1.4404 is carefully controlled to maximize corrosion resistance while maintaining excellent formability and weldability.
| Element | Content Range (%) | Its Role in the Steel |
|---|---|---|
| Chromium (Cr) | 16.5 – 18.5 | Forms a passive oxide layer, providing the foundation for corrosion resistance. |
| Nickel (Ni) | 10.0 – 13.0 | Stabilizes the austenitic structure, which gives the steel its excellent ductility and toughness. |
| Molybdenum (Mo) | 2.0 – 2.5 | The key element for chloride resistance. It significantly improves resistance to pitting and crevice corrosion. |
| Carbon (C) | ≤ 0.03 | Kept very low to prevent intergranular corrosion after welding. This is the main difference from EN 1.4401 (316). |
| Manganese (Mn) | ≤ 2.0 | Adds strength and aids in hot working. |
| Silicon (Si) | ≤ 1.0 | Acts as a deoxidizer and improves oxidation resistance. |
What Are Its Key Mechanical and Physical Properties?
EN 1.4404 offers a strong balance of strength and ductility at room temperature. Its physical properties make it easy to design with.
| Property | Typical Value | Why This Matters |
|---|---|---|
| Yield Strength | ≥ 220 MPa | A reliable baseline for structural design, ensuring components don’t permanently deform under normal loads. |
| Tensile Strength | 520 – 680 MPa | Offers a wide safety margin before failure. |
| Elongation | ≥ 40% | Exceptional ductility, meaning it can be formed into complex shapes like deep-drawn tanks without cracking. |
| Density | 8.0 g/cm³ | Slightly denser than 304, but a standard value for austenitic stainless steels. |
| Hardness (Brinell) | ≤ 215 HB | Soft enough for standard machining with proper tools. |
| PREN (Pitting Resistance Equivalent) | 23 – 25 | A calculated number indicating its resistance to pitting. This range is significantly higher than 304 (PREN ~18-20). |
A pharmaceutical company uses EN 1.4404 for its drug storage tanks. The low-carbon austenitic structure ensures that after welding, the tank’s interior remains perfectly smooth and free from micro-corrosion that could contaminate a drug batch, helping them meet strict FDA purity standards.
How Does It Resist Corrosion?
EN 1.4404’s reputation is built on its outstanding performance in corrosive environments, particularly where chlorides are present.
Immunity to Intergranular Corrosion
One of the primary advantages of EN 1.4404 is its immunity to intergranular corrosion.
- The Mechanism: When standard stainless steels (like 304 or 316) are heated to around 450-850°C, carbon can migrate to grain boundaries and form chromium carbides. This depletes the surrounding area of chromium, creating a “sensitized” zone that corrodes easily.
- The Solution: EN 1.4404’s carbon is capped at 0.03%. There is simply not enough carbon to form significant chromium carbides. This means the steel remains fully corrosion-resistant even after welding, without any need for post-weld annealing.
Superior Chloride Resistance
The addition of molybdenum gives EN 1.4404 a significant edge in chloride-rich environments.
- Pitting Resistance: Its PREN value of 23-25 means it resists pitting corrosion in saltwater and de-icing salts far better than 304L. In full seawater submersion, it has a corrosion rate of less than 0.1 mm per year.
- Stress Corrosion Cracking: It is also resistant to stress corrosion cracking (SCC) in chloride environments, a common failure mode for 304 stainless steel in hot, salty conditions.
An offshore oil rig uses EN 1.4404 for its ballast water systems. The steel’s chloride stress corrosion cracking immunity and low seawater corrosion rate keep the system leak-free for over 15 years, avoiding costly environmental incidents and downtime.
How Does It Perform Across Temperatures?
EN 1.4404 is versatile, maintaining its properties from extreme cold to high heat.
High-Temperature Performance
While primarily a corrosion-resistant grade, EN 1.4404 can handle moderate heat.
- Oxidation Resistance: It resists scaling in intermittent service up to 925°C and in continuous service up to 700°C.
- Creep Resistance: At 700°C under 100 MPa of stress, it can last over 10,000 hours before deforming.
- Note: For prolonged use above 800°C, a high-temperature grade like 310 or Inconel would be a better choice.
Low-Temperature and Cryogenic Performance
EN 1.4404 excels in cold environments.
- Toughness: It remains ductile and tough down to -196°C, the temperature of liquid nitrogen.
- Cryogenic Ductility: It retains over 90% of its room-temperature ductility at these cryogenic temperatures, making it a standard material for liquefied natural gas (LNG) and liquid nitrogen storage tanks.
- Impact Energy: It can absorb over 60 J of energy at -196°C, ensuring it will not shatter under impact in cold conditions.
How Is It Heat Treated and Fabricated?
EN 1.4404 is designed for ease of fabrication. Its austenitic structure makes it one of the most formable and weldable stainless steels.
Heat Treatment
Unlike martensitic steels, EN 1.4404 cannot be hardened by heat treatment. Its main thermal processes are for stress relief and restoring properties.
- Solution Annealing: The key process. The steel is heated to 1020-1120°C and then rapidly cooled (water quenched or rapid air cooled). This dissolves any unwanted carbides and ensures full corrosion resistance. It is typically done after heavy forming.
- Stress Relief: For components that have been heavily welded or cold-worked, a low-temperature stress relief at 300-500°C can reduce residual stresses without affecting corrosion resistance.
Welding
EN 1.4404 is one of the easiest stainless steels to weld.
- Weldability: It has excellent weldability, rated 9/10. It can be welded with TIG, MIG, or stick welding.
- No Preheat: Preheating is not required, saving time and complexity.
- Filler Metal: To maintain the low-carbon benefits, use a matching low-carbon filler like ER316L.
- Interpass Temperature: Keep the interpass temperature below 150°C to prevent any risk of overheating.
- Post-Weld Cleaning: After welding, a passivation treatment with nitric or citric acid is recommended. This removes any free iron from the surface and boosts corrosion resistance by up to 50%.
Machining
Machining EN 1.4404 is slightly more demanding than machining 304 due to its molybdenum content, which makes it more “gummy.”
- Tools: Use sharp, coated carbide tools (e.g., TiAlN coating).
- Speeds and Feeds: Use turning speeds of 120-180 m/min with a consistent feed rate. Avoid letting the tool rub, as this causes work hardening.
- Coolant: Use generous amounts of coolant to control heat and clear chips.
A brewery uses EN 1.4404 for its fermentation tanks. They weld the tanks using ER316L filler and carefully control the interpass temperature. The finished tanks resist the acids from the brewing process and the harsh cleaning chemicals for over 10 years without any signs of corrosion.
How Does EN 1.4404 Compare to Other Steels?
Choosing the right material often means comparing EN 1.4404 to its alternatives.
| Material | Key Advantage | Key Disadvantage | Best Application |
|---|---|---|---|
| EN 1.4404 (316L) | Excellent chloride resistance; weldable without sensitization | Higher cost than 304L | Welded equipment in marine, pharmaceutical, and food industries |
| EN 1.4307 (304L) | Good general corrosion resistance; lower cost | Poor resistance to chlorides | Indoor, non-marine applications |
| EN 1.4401 (316) | Same corrosion resistance as 1.4404 | May require post-weld annealing to prevent sensitization | Thick sections or applications with no welding |
| EN 1.4462 (Duplex) | Higher strength and better chloride resistance than 316L | More difficult to machine and weld | High-stress marine applications like offshore platforms |
EN 1.4404 stainless steel is the gold standard for applications demanding reliable corrosion resistance in challenging environments. Its low carbon content eliminates the risk of intergranular corrosion after welding, making it a safe choice for complex fabricated equipment. Its molybdenum content provides a crucial defense against pitting and crevice corrosion in the presence of chlorides, from de-icing salts to full seawater immersion. While it requires more careful machining than simpler grades and has a higher upfront cost, its proven durability, ease of welding, and exceptional performance in corrosive and cryogenic conditions make it the most cost-effective and reliable choice for industries where failure is not an option.
How to write a spec that gets priced correctly
A drawing is a contract. If it leaves a number open, the shop fills that number in with its own default. The default is rarely the one you had in mind. Put these five lines on every RFQ and most of the back-and-forth disappears before it starts.
- Alloy designation and the standard behind it
- Temper or heat treatment condition
- Mechanical properties you actually need
- Mill certificate and traceability requirement
- Finish and the faces it applies to
The point is not paperwork. Each line removes a decision the shop would otherwise make for you. A complete RFQ comes back priced. An incomplete one comes back guessed.
What actually drives the price
Buyers usually push on material because it is the line they can see. In practice the material is rarely the biggest number on a quote. These five lines decide most of it:
- alloy grade and mill availability
- stock size versus finished size
- heat treatment and testing
- machinability
- certification
Ask for the quote split by line. A supplier who cannot break it down is guessing, and you will pay for the guess. The line you can usually renegotiate is the tolerance band, not the raw material.
Problems you will meet, and the fix
Every process has a failure mode it prefers. The same four show up again and again on this kind of work, and none of them are mysteries once you know what to look for.
- Substituting a similar grade without telling anyone
- Hardness that varies across a single bar
- Corrosion in a weld heat-affected zone
- Distortion after heat treatment on a thin part
Catch the fault on the first part, not the hundredth. A first-article check costs an hour. A bad batch costs the whole order. Write the check into the purchase order so nobody has to remember it.
What to check on the first article
The first article is the cheapest inspection you will ever buy. Use it properly and the rest of the run becomes boring, which is exactly what you want.
- Every dimension on the drawing, with the measured value written beside it.
- The material certificate, matched to the heat or lot number on the parts.
- The finish against the sample you approved, under the same light.
- Fit against the mating part, assembled rather than measured.
- Packaging, because parts that arrive damaged were never in tolerance.
Check in this order: datums, then mating features, then cosmetic faces. If the datums are wrong, every number after them is noise. Keep the report on file. When a problem shows up in month six, that document is the only thing that tells you what changed.
How to compare two quotes fairly
Two numbers are not comparable unless the scope matches. Line them up before you decide, because a low number with three gaps is not a low number.
Same drawing, same material, same finish, same inspection. Anything else is a different job wearing the same part number. Then look at what each quote leaves out. Freight, packaging, certificates and tooling are the usual gaps.
Ask each supplier to state their assumptions in writing. The one who does is usually the one who has run the process before.
Scaling from one part to a batch
The first part teaches you the process. The hundredth teaches you the process cost.
Watch three things as volume grows: setup amortisation, tool wear, and how much hand work the finish still needs. If the unit price barely moves between ten and a hundred, the cost sits in material or in hand work, not in setup. Ask which, because only one of them is negotiable.
Lead time behaves the same way. A one-off is scheduled around other jobs. A repeat order is scheduled around your forecast. Give the shop a forecast and the lead time gets shorter, not longer.
How to read a supplier's quote
A quote is a short document with a long shadow. Four things in it decide whether the job runs smoothly, and only one of them is the price.
- The scope line. It should name the process, the material and the finish, not just the part.
- The tolerance basis. General tolerance or the drawing, and which standard it follows.
- The exclusions. Tooling, freight, certificates and inspection are the usual omissions.
- The validity date. Material prices move, and an open-ended quote is a promise nobody can keep.
Read the exclusions before you read the total. A quote that leaves out tooling is not cheaper. It is a quote for a different job.
What to send with the first order
The first order sets the pattern for every order after it. Send a complete package once and the shop files it, and the second order takes a fraction of the time.
- A STEP or native model plus a PDF drawing carrying the same revision letter.
- The material callout by standard number, not by trade name.
- The finish and the exact faces it applies to.
- Any test the part must pass: fit, seal, drop, salt spray, dielectric.
- A contact who can answer a question inside one working day.
Then write down what was agreed. An email that confirms the material, the finish and the date is worth more than a longer purchase order that leaves them open.
When this is the wrong choice
A good supplier tells you when the process does not fit. These are the cases where we say so.
- The volume is so low that setup costs more than the parts are worth.
- The tolerance is tighter than the process can hold without a second operation.
- The geometry cannot be made without a tool feature that will not pay back.
- The material you need is not available in the form the process requires.
- The schedule is shorter than the tooling or setup time, and nobody has said so yet.
None of these are refusals. They are reasons to look at a different route, and the earlier that conversation happens the cheaper it is. The most expensive mistake in manufacturing is a process chosen before the question was understood.
Our solution for EN 1.4404 Stainless Steel: Full
YiguProto runs metal sourcing and machining in house, from a single prototype to a production batch. We quote the process, the material and the finish as separate lines, so you can see where the money goes instead of arguing with one number.
Send a STEP file or a drawing and you get a DFM report in one to two business days. It flags the features that add cost and the features that will not hold tolerance on the process you picked.
Every order ships with an inspection report on the features you call out. If a part misses, we make it again. Ready to price a part? Start with a free quote and DFM review, or read more about our metal sourcing and machining. You can also talk to an engineer before you commit to a drawing.
FAQ about EN 1.4404 Stainless Steel: Full
Does the process work for prototypes as well as production?
Yes, and that is usually the point. Running the prototype on the production process removes a whole class of surprises, because the part you test is made the same way as the part you sell.
How do I compare two quotes fairly?
Match the scope first: same drawing, same material, same finish, same inspection. Then read the exclusions. Freight, tooling and certificates are the usual gaps, and a low number with three gaps is not a low number.
What should I check before approving the parts?
Datums first, then the features that mate, then the cosmetic faces. Ask for a dimensional report, a material certificate and a finish sample. A part can be inside every tolerance and still not fit, so assemble one before you sign.
What happens if a part is out of specification?
We measure it against the same drawing you approved and, if it misses, we make it again. What matters is that the report exists, because a disagreement without data is just an opinion.
Is there a minimum order quantity?
No hard minimum. One part is fine. What changes with volume is which costs dominate, so a single unit is priced mostly on setup and a thousand units are priced mostly on cycle time and material.
What is EN 1.4404 Stainless Steel: Full used for?
EN 1.4404 Stainless Steel: Full turns up wherever the part has to do a real job at a predictable cost: brackets, housings, fixtures, covers and the fittings that hold them together. The honest test is whether the properties match the load and the environment, not whether the material is fashionable.
The short version
EN 1.4404 Stainless Steel: Full rewards the buyer who reads the data sheet and the drawing together. Pick the option for the property that matters, not for the price per kilo.
Tighten only what mates. Test a sample before the run. Then let the process do the rest.