Stainless steels

About the material

Stainless steels are the most commonly used material group in precision engineering. They are characterised by their corrosion resistance, durability and versatility. The decisive factor is their chromium content of at least 11%, which forms a protective passive layer – the basis for their high resistance to chemical and physical influences.

Depending on the microstructure – such as austenite, ferrite or martensite – and on alloying additives such as nickel, molybdenum or nitrogen, specifically defined properties are created: from high ductility and heat resistance to hardness and wear resistance.

Studer-Biennaform processes these materials into cold-rolled precision flat wire. In doing so, we guarantee tight tolerances, precisely defined mechanical strengths and consistently reproducible quality – for demanding applications in medical technology, electronics, watchmaking and automotive technology.

Austenitic stainless steels

Austenitic grades (e.g. V2A / 1.4301, V4A / 1.4404) are the most commonly used stainless steels. They contain chromium (approx. 16–26%) and nickel (approx. 8–22%), often with molybdenum added to further increase corrosion resistance.

These grades have an FCC microstructure (face-centered cubic), are not magnetisable when in the annealed state and cannot be hardened by heat treatment. However, their mechanical strength can be adjusted in a targeted manner by work hardening. Austenitic stainless steels are characterised by excellent corrosion resistance – the stable chromium oxide layer provides reliable protection against rust, even in aggressive environments. They are highly ductile, easy to form, weldable, and are tough and fracture-resistant, even at low temperatures.

These properties make austenitic stainless steels extremely versatile. They are used in chemically aggressive environments such as chemical plants or in food technology, and retain their mechanical properties over a wide temperature range.

Typical applications are:

• Springs, such as leaf and compression springs made of 1.4310 spring steel
• Contact parts in electrical engineering
• Precision components
• Decorative components with high requirements in terms of polishing capability and freedom from corrosion

Austenitic spring steels such as 1.4310 provide high restoring forces. 1.4301 or 1.4404 are preferred for decorative components.

Martensitic stainless steels

Martensitic grades combine moderate corrosion resistance with high hardness and mechanical strength. They typically contain 12 to 19% chromium and an increased carbon content of between 0.1 and 1.2%. Unlike austenitic grades, they can be hardened by heat treatment – such as quenching and tempering.

The resulting BCT microstructure (body-centered tetragonal) makes them magnetic in the hardened and tempered state. After appropriate heat treatment, martensitic stainless steels achieve hardness values of 55 to 60 HRC. They are characterised by high tensile strength, good wear resistance and – compared to other stainless steel grades – limited corrosion resistance. Their reduced toughness means careful component design is required to prevent brittle fractures.

Typical applications can be found wherever high strength, hardness and wear resistance are required – especially in:

• Cutting tools and knives, e.g. scalpels and industrial blades made of 1.4034
• Surgical instruments such as shears or forceps
• Technical functional parts, such as valves, shafts or ball bearing components
• Precision components with high mechanical loads, e.g. made of 1.4112 or 1.4125
• Tools used in the watchmaking industry, e.g. for opening the case

Thanks to their hardness and hardenability, martensitic stainless steels are ideal for moving and cutting components with a long service life – especially in oily or dry environments where moderate corrosion resistance is sufficient.

Ferritic stainless steels

Ferritic stainless steels consist mainly of chromium – typically 11 to 18% – with a very low carbon content (below 0.1%) and low to no nickel content. They have a purely ferritic, body-centered cubic structure (BCC), are magnetic and cannot be hardened by heat treatment. An increase in strength is only possible to a limited extent by cold working.

They are characterised by good corrosion resistance in slightly aggressive media such as water or humid atmospheres. In addition, they have very good resistance to oxidation at raised temperatures – a significant advantage over other stainless steel groups. Mechanically, ferritic grades offer moderate strength, good formability and comparatively limited toughness. Embrittlement can occur, particularly at low temperatures. Suitability for welding is limited, as grain growth and embrittlement can occur during welding. Titanium- or niobium-stabilised grades offer improved properties here.

Ferritic stainless steels are considered a cost-effective material solution for numerous mass applications. Typical areas of application are:

• Household appliances and white goods
• Architecture and construction
• Automotive technology, e.g. exhaust systems (1.4512 / AISI 409), decorative strips
• Containers, sockets and structures with moderate requirements in terms of mechanical strength and corrosion protection

Specially alloyed variants such as 1.4742 with around 25% chromium are suitable for applications at high temperatures. They exhibit outstanding scaling resistance up to approximately 800 to 900 °C and are used in heating elements and furnace components.

Duplex and superduplex steels

Duplex stainless steels combine ferritic and austenitic microstructure components in roughly equal proportions. This two-phase structure gives them very high mechanical strength – with approximately twice the yield strength compared to standard austenites – as well as good toughness even at low temperatures.

The typical chemical composition includes 19 to 28% chromium, 5 to 8% nickel, up to 4% molybdenum and around 0.1 to 0.3% nitrogen. The interplay of microstructure and alloy ensures excellent corrosion resistance – especially against stress-corrosion cracking and pitting in media containing chlorides. The chloride resistance is significantly higher than that of purely austenitic grades.

Due to their properties, duplex stainless steels are preferred in areas subject to corrosion, such as in chemical engineering, energy and process engineering, as well as in offshore and seawater systems.