What are stainless steel quarto plates and what are they used for?

The term quarto plate refers to hot-rolled heavy plate with a minimum thickness of 3.0 mm. The name derives directly from the manufacturing process using so-called four-high rolling mills. This type of rolling mill consists of four rolls: two inner work rolls that come into direct contact with the stainless steel, and two outer backup rolls that withstand the immense rolling pressure. Unlike strip-rolled sheet (coils), quarto plates are produced as individual plates or sheets in multiple lengths.

The production process begins by heating stainless steel slabs to temperatures of up to 1,250 °C. Under pressures of several thousand tonnes, they are gradually rolled to the target thickness. As these plates are not wound into coils, they have significantly lower residual stress. We receive these mill-finished products as raw material and, depending on the requirements, subject them to further levelling processes to create a flat, distortion-free base for our surface finishing in Cleebronn.

Designations and Synonyms – Relevant Standards and Names

Quarto plates are known by various designations, which differ depending on the region, industry or standard. For purchasers and engineers, precise identification of the grade is crucial to its subsequent processability and corrosion resistance.

V2A and V4A – The Classic Designations

The terms V2A (Versuchsschmelze 2 Austenit) and V4A remain the most common designations for stainless steel in German-speaking countries. While V2A generally refers to grade 1.4301, V4A denotes molybdenum-alloyed steels such as 1.4404, which offer greater resistance to chlorides. mirrorINOX processes both categories as quarto plates for exterior and marine applications.

AISI and ASTM – The US Standard

International projects often use the classification system of the American Iron and Steel Institute (AISI). In this system, quarto plates in grade 1.4301 correspond to AISI 304, while 1.4404 is designated as AISI 316L. These designations are particularly relevant in shipbuilding and for international art installations, which we support with our polishing processes.

DIN EN 10088 – The European Standard

In the EU, DIN EN 10088 is the key standard for stainless steels. It defines their chemical composition and physical properties. Quarto plates are often designated as "P" (Plate). For every order, we document compliance with these standards by providing the relevant mill certificates, ensuring the traceability of our finished surfaces.

Chemical Composition – The Basis of Corrosion Resistance

The chemical composition of quarto plates determines their suitability for use in aggressive environments. The proportions of the elements vary depending on the alloy to achieve specific properties.

• Chromium (Cr): Minimum content of 10.5% to form the protective passive layer.
• Nickel (Ni): Stabilizes the austenitic microstructure and improves formability.
• Molybdenum (Mo): Increases resistance to pitting corrosion and is essential in V4A grades (e.g. 1.4404).
• Carbon (C): Reduced in L grades (low carbon) to prevent intergranular corrosion after welding.
• Manganese (Mn): Used for deoxidation and improves the strength properties of the heavy plate.

Properties of stainless steel quarto plates

The physical and mechanical properties of quarto plates make them the preferred material for structurally critical components and components exposed to chemical stress.

Mechanical Properties

Quarto plates are characterized by high tensile strength and excellent elongation at break. The hot-rolling process gives them a homogeneous microstructure, ensuring consistent load-bearing capacity even at extreme plate thicknesses. This is particularly important in bridge construction and heavy machinery manufacturing, where we supply processed plates with high mechanical strength.

Physical Properties

The coefficient of thermal expansion of austenitic quarto plates is higher than that of ferritic steels. We take this into account when installing our Perfect Mirror No. 10® panels over large façade areas. These plates also offer good thermal conductivity, making them suitable for tank construction in the food industry.

Corrosion resistance

Alloyed with chromium and molybdenum, quarto plates provide passive protection against oxidation. mirrorINOX enhances this natural resistance through surface finishing processes such as electropolishing or the nanoINOX® coating (sol-gel process). These finishes reduce surface roughness and minimise the adhesion of corrosive particles.

Magnetism

Austenitic quarto plates such as 1.4301 or 1.4404 are virtually non-magnetic in the solution-annealed condition. This is a crucial factor for applications in medical technology or specialised research facilities. Cold forming, for example during levelling after rolling, can produce a small proportion of deformation-induced ferrite, but this does not adversely affect corrosion resistance.

Applications and Industries

The versatility of quarto plates makes them suitable for use in sectors where safety and durability are top priorities.

• Architecture and façade construction: Used as large-format, mirror-polished façade elements for iconic buildings worldwide.
• Yacht and shipbuilding: Use of corrosion-resistant V4A grades for deck cladding and prestigious design elements in marine applications.
• Tank and plant construction: Manufacture of tanks for the pharmaceutical and food industries that meet the highest standards of hygiene and cleanability.
• Art installations: Creation of monumental sculptures, including large-scale projects using 70 tonnes of stainless steel finished by mirrorINOX.
• Bridge and structural engineering: Utilization of high structural load-bearing capacity combined with corrosion protection in major infrastructure projects.
• Special-purpose machinery: Components for the chemical industry that must withstand extreme pressures and temperatures.

Overview of international standard designations

For the global sourcing of quarto plates, we manufacture in accordance with various international standards to ensure compatibility with your projects.

• Europe: DIN EN 10088-2 / DIN EN 10028-7 (material grades such as 1.4301, 1.4404, 1.4462).
• USA: ASTM A240 / ASME SA240 (grades such as 304, 304L, 316, 316L, 318LN).
• Japan: JIS G4304 (designations such as SUS304, SUS316L).
• China: GB/T 4237 (grades such as 06Cr19Ni10).

Finishing quarto plates – mirrorINOX expertise

mirrorINOX specializes in the functional and aesthetic enhancement of stainless steel quarto plates. At our production facility in Cleebronn, we transform the raw material into high-end products. One example demonstrating our capabilities was the supply of a 16.0 mm thick V4A quarto plate measuring 14,973 x 3,347 mm for a world-renowned artist. It was polished to a mirror finish using our Perfect Mirror No. 10® finish—a process that achieves a quality of reflection far exceeding conventional industry standards.

In addition to high-gloss polishing, we offer processes such as vibration polishing and glass bead blasting. Our proprietary brand nanoINOX® also enables coloured finishes and anti-fingerprint sealing for quarto plates. Our ISO 9001-certified processes and extensive experience since 2016 ensure complete documentation and unrivalled reproducibility of surface finishes, even for batch sizes of several hundred tonnes.