What is 1.4404 stainless steel, and when is it the better choice than 1.4301?

Stainless steel 1.4404 is an austenitic stainless steel whose chromium, nickel and molybdenum alloy content provides greater corrosion resistance than standard stainless steel 1.4301. It is often referred to in the industry as “316L”, with the “L” standing for “Low Carbon”. This property prevents chromium carbides from precipitating at the grain boundaries during welding, significantly reducing susceptibility to intergranular corrosion. We primarily use this material where atmospheric conditions or chemical exposure require a robust, durable material grade.

Designations and synonyms

Stainless steel is identified using various national and international standards systems that are equally relevant to specifiers and engineers. Below, we summarize the most common designations for grade 1.4404 to ensure clarity in material specifications.

V4A – The Historical Origin

The designation V4A is deeply rooted in German-speaking countries and is commonly used to refer to stainless steels with enhanced corrosion resistance. Historically, the abbreviation derives from “Versuchsschmelze 4 Austenit” (“trial melt 4 austenite”). While V2A (1.4301) forms the basis, molybdenum was added to the V4A alloy. This development dates back to 1912, when researchers in Germany identified the optimum combination of corrosion resistance and mechanical strength. We still use the term V4A in customer consultations today, but for technical accuracy we specify material grade 1.4404.

AISI 316L – The US Standard

Under the American Iron and Steel Institute (AISI) system, 1.4404 is classified as 316L. The 300 series denotes austenitic steels, while 16 defines the specific alloy type. The “L” suffix is crucial here: it limits the carbon content to a maximum of 0.03%, ensuring suitability for heavy welded structures without subsequent heat treatment. For international projects supplied by mirrorINOX worldwide, this designation is the established industry standard for ordering sheet and components.

X2CrNiMo17-12-2 – The Chemical Nomenclature

The designation according to DIN EN 10088-3 directly specifies the chemical composition. The “X” denotes a high-alloy steel. The number “2” indicates the carbon content (<0.03%). The symbols and numbers that follow represent 17% chromium, 12% nickel and 2% molybdenum. This precise designation allows us to tailor the material properties exactly to the requirements of surface finishing, for example polishing to Perfect Mirror No. 10® quality.

Chemical Composition

The performance of grade 1.4404 results from its precisely balanced alloy composition. We source only raw material that meets or exceeds the strict limits of the applicable standards.

• Carbon (C): Maximum 0.030% to prevent sensitization during welding.
• Chromium (Cr): 16.50% to 18.50% for the formation of the protective passive layer.
• Nickel (Ni): 10.00% to 13.00% to stabilize the austenitic microstructure.
• Molybdenum (Mo): 2.00% to 2.50% to increase resistance to pitting corrosion and chlorides.
• Manganese (Mn): Maximum 2.00% to improve strength and workability.
• Silicon (Si): Maximum 1.00% for deoxidation during steel production.
• Phosphorus (P): Maximum 0.045% as a controlled residual element.
• Sulfur (S): Maximum 0.015% for optimized weldability and microstructural stability.

Properties

Grade 1.4404 stainless steel combines mechanical toughness with exceptional chemical resistance. This makes it the ideal base material for our finishing processes in Cleebronn.

Mechanical properties

The mechanical properties of 1.4404 ensure a high level of safety under static and dynamic loads. In our production processes, we take the following values into account:

• 0.2% proof strength (R{p0.2}): At least 190 N/mm^2 at room temperature.
• 1.0% proof strength (R{p1.0}): Approximately 250 N/mm^2 for precise structural calculations.
• Tensile strength (R{m}): A range of 520 to 670 N/mm^2 provides ample reserves.
• Elongation at break (A{5}): 40% (longitudinal) and 30% (transverse) provide excellent formability.
• Charpy impact energy (ISO-V): 100J (longitudinal) and 60J (transverse) underscore the material’s toughness.

1.4404 retains its strength even at elevated temperatures. At 100°C, the 1% proof strength is still greater than or equal to 199N/mm^2, while at 500°C it falls to greater than or equal to 128N/mm^2. The tensile strength decreases moderately over this temperature range from 430N/mm^2 to 360N/mm^2.

Physical Properties

The material is characterized by physical parameters that are crucial for the thermal and electrical design of components:

• Density: 7.95 to 8.0 kg/dm^3 for precise weight calculation.
• Hardness (Brinell): Maximum 215HB, ensuring good machinability.
• Electrical resistivity: 0.75 (Ω * mm²)/m at 20°C.
• Polishability: The material is highly polishable, forming the basis for our Perfect Mirror No. 10® finishes.

Corrosion resistance

The outstanding characteristic of 1.4404 is its resistance to non-oxidising acids and chloride-containing media. Thanks to the addition of molybdenum, the material provides effective protection against pitting corrosion. This is particularly relevant in coastal regions or swimming pools, where salt-laden air attacks standard stainless steels such as 1.4301. We therefore consistently recommend 1.4404 for exterior applications exposed to high levels of pollutants.

Magnetism

As a fully austenitic steel, 1.4404 is non-magnetic in the solution-annealed condition. Its magnetic permeability is extremely low. Only cold working can lead to the formation of strain-induced martensite, which may result in slight magnetism. As the nickel content of 1.4404 remains consistently between 10 % and 13 %, its non-magnetic properties are generally retained even after moderate processing.

Applications and Industries

The versatility of grade 1.4404 is reflected in our broad customer base. We supply finished surfaces to numerous high-end sectors.

• Architecture and construction: We manufacture façade cladding, roofing systems and elevator cabins for prestigious buildings worldwide.
• Chemical industry: Construction of reactors, vessels and piping designed to withstand aggressive chemicals.
• Food industry: Used in dairies, breweries and meat-processing plants due to its hygienic surfaces and resistance to cleaning.
• Pharmaceutical industry: We supply materials for equipment requiring the highest levels of purity and resistance to disinfectants.
• Petrochemical industry: Used in oil and gas production facilities and refineries, particularly in corrosive offshore environments.
• Shipbuilding: Thanks to its resistance to seawater, we manufacture components for yachts and maritime infrastructure.

Overview of international standard designations

For global sourcing and specification, we follow the following standards systems:

• EN (Europe): X2CrNiMo17-12-2 / Material No. 1.4404
• AISI (USA): 316L
• UNS (USA): S 31603 / Grade TP 316L
• AFNOR (France): X2CrNiMo17-12-2 / NF EN 10028-7
• BS (United Kingdom): X2CrNiMo17-12-2 / B.S. EN 10028-7
• Proprietary grade designation: V4A Supra NK

Finishing 1.4404 – What mirrorINOX Makes of It

At our Cleebronn production site, we transform 1.4404 stainless steel into aesthetic masterpieces. Since our founding in 2016, we have relied on state-of-the-art manufacturing technologies and an ISO 9001-certified quality management system. Our proprietary brands harness the full potential of this stainless steel.

Using the Perfect Mirror No. 10® process, we produce mechanically polished surfaces that achieve near-perfect reflectivity and retain their brilliance even in demanding environments. With PVD/TiN coating, we give 1.4404 stainless steel colours such as gold, champagne or black without compromising the corrosion resistance of the base material. For functional applications, we offer the nanoINOX® coating, which provides additional anti-fingerprint (AFP) and easy-to-clean (ETC) properties.

In addition, we finish sheets by grinding and glass bead blasting to create uniform, matt surfaces for architectural applications. Our customers benefit from excellent reproducibility: we guarantee consistent surface quality across large batches. Through ongoing investment in research and development, we ensure that mirrorINOX remains the technology leader in finishing 1.4404 stainless steel. We manufacture bespoke solutions that go far beyond the industry standard.