Is stainless steel magnetic, and what causes it?

What is magnetic stainless steel?

Magnetic stainless steel is a material whose atomic structure allows its elementary magnetic moments to align. In materials science, we primarily distinguish between ferritic, martensitic and austenitic steels. While ferritic and martensitic steels are ferromagnetic due to their body-centred cubic lattice structure, austenitic steels have a face-centred cubic structure that is generally paramagnetic and therefore appears “non-magnetic” to the layperson. Magnetic permeability determines how strongly a material responds to external magnetic fields. mirrorINOX makes targeted use of these physical distinctions to create the right surface solution for every industrial requirement – from mechanical engineering to electrical engineering.

Designations and Synonyms – Relevant Standards and Names

In international trade and manufacturing, designers encounter various designation systems that are often used synonymously but have different origins. A thorough understanding of these standards is essential for material procurement and ensuring the required material properties.

V2A and V4A – The Classics

The designations V2A (test melt 2 austenite) and V4A are historically established terms widely used in German-speaking countries. V2A generally refers to grade 1.4301, while V4A denotes grades such as 1.4404, which offer greater resistance to chlorides due to the addition of molybdenum. Both belong to the austenitic stainless steel group and are largely non-magnetic in the annealed condition.

AISI Standards – The US Standard

The American Iron and Steel Institute (AISI) uses a three-digit numbering system. The 300 series (e.g. AISI 304, AISI 316) designates austenitic chromium-nickel steels, which are generally non-magnetic. By contrast, the 400 series (e.g. AISI 430) comprises ferritic and martensitic chromium steels. These grades are strongly attracted to magnets and are often used where magnetic adhesion or specific coefficients of thermal expansion are required.

DIN EN 10088 – The European Standard

European standards use five-digit material numbers. The 1.4xxx series denotes stainless steels. For example, 1.4016 is a classic magnetic ferritic chromium steel. Grade 1.4301 is the standard austenitic stainless steel. At mirrorINOX, we stock a wide range of these grades to ensure short lead times for architectural and industrial projects.

Chemical Composition

The chemical analysis determines the microstructure and thus the magnetism of the stainless steel. The proportions of the alloying elements shift the balance between ferrite- and austenite-forming elements.

• Iron (Fe): The base element of steel. Depending on the alloying elements present, it forms either a magnetic (ferritic/martensitic) or a non-magnetic (austenitic) crystal lattice.
• Chromium (Cr): A minimum content of 10.5% is required to form the passive layer and provide corrosion resistance.
• Nickel (Ni): The most important austenite-forming element; transforms the magnetic ferritic lattice into a non-magnetic austenitic lattice.
• Molybdenum (Mo): Increases resistance to pitting corrosion, but only indirectly affects magnetism.
• Carbon (C): Influences hardenability, particularly in martensitic steels.
• Manganese (Mn): Serves as a partial substitute for nickel and also stabilizes the austenitic microstructure.

Properties

The physical and mechanical properties of stainless steel vary considerably between magnetic and non-magnetic grades. The grade selected must therefore always be matched to the final requirements profile.

Mechanical properties

Ferritic, magnetic stainless steels are characterised by good thermal conductivity and lower thermal expansion compared with austenitic grades. They can be readily cold-formed, but exhibit less work hardening than chromium-nickel steels. Martensitic grades, by contrast, can be hardened by heat treatment and achieve high strength levels, making them ideal for cutting tools. We take these factors into account when selecting our finishing processes, such as grinding or polishing.

Physical Properties

The key difference lies in relative permeability. While austenitic steels have a permeability close to 1, that of ferritic grades is many times higher. Cold forming is an important consideration: even normally non-magnetic austenitic steels can form strain-induced martensite as a result of extensive forming (e.g. deep drawing or bending), causing them to exhibit magnetic properties in these areas. This is a purely physical effect and does not indicate any reduction in material quality.

Corrosion resistance

Contrary to popular belief, magnetism is not an indicator of susceptibility to rust. A ferritic stainless steel such as 1.4016 is highly resistant in moderate environments. Corrosion resistance is determined primarily by the chromium and molybdenum content and the surface finish. A mirror-polished surface from mirrorINOX, such as Perfect Mirror No. 10®, further enhances corrosion resistance by offering the corrosive medium virtually no surface to attack.

Magnetism

In industrial practice, magnetism is often relevant to production processes. Magnetic stainless steels can be secured on magnetic chucks, simplifying the machining of precision components. In the food industry, magnetisability is advantageous for detecting broken tool fragments in the product stream. Our team in Cleebronn will be pleased to advise you on selecting the optimum material, taking these functional aspects into account.

Applications and industries

The applications of stainless steel are as diverse as its alloys. Depending on the sector, its magnetic properties play a crucial role in the functionality of the end product.

• Household appliance industry: Ferritic grades are used for refrigerator fronts (magnetic adhesion) and the bases of induction cookware.
• Automotive engineering: Used in exhaust systems due to the thermal properties and corrosion resistance of magnetic chromium steels.
• Medical technology: Non-magnetic austenitic stainless steels are essential here to prevent interference with magnetic resonance imaging (MRI) scanners.
• Mechanical engineering: Use of magnetic grades for detectability and specific sensor requirements.
• Architecture and façades: mirrorINOX generally supplies non-magnetic grades (1.4301, 1.4404) for maximum durability in exterior applications.
• Elevator industry: A combination of aesthetics and functionality, often using our VIBES or BEADS textures on a non-magnetic substrate.

Overview of international standard designations

For global applications, the correlations between standards are crucial. Our ISO 9001-certified processes ensure the traceability and standards compliance of all finished sheets.

• 1.4301 corresponds to AISI 304 (austenitic, non-magnetic)
• 1.4404 corresponds to AISI 316L (austenitic, non-magnetic, acid-resistant)
• 1.4016 corresponds to AISI 430 (ferritic, magnetic)
• 1.4541 corresponds to AISI 321 (titanium-stabilized austenitic stainless steel, non-magnetic)
• 1.4006 corresponds to AISI 410 (martensitic, magnetic, hardenable)

Refining stainless steel – what mirrorINOX makes of it

Since 2016, mirrorINOX has been producing high-end stainless steel surfaces at its Cleebronn production facility. We finish both magnetic and non-magnetic sheet metal using state-of-the-art processes. Our proprietary Perfect Mirror No. 10® finish sets the standard for reflection quality and is produced on high-precision polishing lines. For colour accents, we use the PVD process to apply coatings in Gold, Black or Rose Gold without compromising the metallic feel.

The reproducibility of our finishes is our core quality promise. Through automated processes, we ensure that repeat orders for large-scale projects are visually identical to the original order. With nanoINOX®, we also offer a sol-gel-based coating that provides anti-fingerprint properties and enhanced corrosion protection. Whether vibration finishing (VIBES), bead blasting (BEADS) or complex design patterns, we process sheet sizes up to 4.000 x 16.000 mm, meeting the most demanding requirements of international architecture and industry.