Carbon & tool steels

About the material

Carbon and tool steels are classic metallic construction grades with wide-reaching industrial importance. They differ mainly in their carbon content as well as in the type and proportion of additional alloying elements.

Carbon steels – such as unalloyed structural steels and spring steels – cover a wide range of strengths, depending on the carbon content. Tool steels, on the other hand, are designed for maximum hardness and mechanical strength through targeted alloying additives.

The properties of both material groups can be specifically adjusted by means of heat treatment, such as hardening, tempering or a combination of the two.

At Studer-Biennaform, these materials are processed into cold-rolled precision flat wire – with precisely defined mechanical parameters. Typical applications include springs, stamped parts and precision mechanical components where tight tolerances and reliable strengths are required.

Carbon steels

Depending on the grade, carbon steels contain around 0.2% to more than 0.8% carbon. A distinction is made as follows:

• Below approx. 0.25% C: low carbon
• Approx. 0.25–0.6% C: medium carbon
• More than approx. 0.6% C: high carbon

The carbon content has a significant influence on the material properties. As the carbon content increases, hardness and tensile strength increase, while toughness, ductility and weldability decrease. Low-carbon steels are soft, tough and easy to weld. After hardening, high-carbon grades achieve extreme hardness values of over 60 HRC and offer high wear resistance – albeit with reduced toughness.

Unalloyed carbon steels do not contain significant amounts of chromium, nickel or other alloying elements. Accordingly, their corrosion resistance is limited – if left untreated, they tend to rust. By means of suitable heat treatments such as hardening and tempering, microstructure states such as martensite, bainite or perlite can be set in order to adapt the mechanical strength and toughness in a targeted manner.

Thanks to their versatility and cost-effectiveness, carbon steels are used in many industrial areas, including for:

• Simple mechanical components such as bolts, axles and base plates
• Stamped and moulded parts
• Spring applications: e.g. C75, C100 or – as alloyed spring steel – 51CrV4
• Compression, tension and leaf springs with high elasticity and fatigue strength (after heat treatment)
• Cold-rolled components with defined elasticity and restoring force: spring clips, circlips, watch springs
• Toothed parts and cutting tools: saw blades, files, hardened edges

Thanks to their wide range of properties and good availability, carbon steels remain a cornerstone of mechanical engineering, vehicle construction and classic steel construction.

Tool steels

Tool steels are specially developed grades for the manufacture of tools and highly stressed precision parts. In addition to carbon, they contain additional alloying elements such as chromium, vanadium, molybdenum or tungsten. These elements specifically improve hardenability, heat resistance, wear resistance and dimensional stability.

Typical properties of tool steels are very high hardness values after hardening – over 60 HRC, and even up to around 70 HRC for high-speed steels. They have good heat resistance and are suitable for applications with increased thermal loads. Wear resistance is significantly increased thanks to the targeted alloy composition. The dimensional stability is also maintained after heat treatment and ensures the shape of components subject to mechanical and thermal stress is maintained.

Tool steels are primarily used for cutting, stamping and forming tools, for example:

• Stamps, dies, scrapers, guides and knife blades
• Precision edges, shafts, gears and other highly loaded functional elements

Cold-rolled tool steels are ideal for precision mechanical components, such as:

• Watchmaking files
• Small milling cutters
• Super-hard spring contacts, blades and precision pins

Rolling bearing steel (see below) also belongs to the group of tool steels.

Rolling bearing steel

Rolling bearing steels are high-carbon chromium steels with particularly high purity and microstructure homogeneity. Most commonly seen is 100Cr6 (material no. 1.3505), a steel with approximately 1.0% carbon and 1.5% chromium. Secondary metallurgical processes such as vacuum degassing greatly reduce the proportion of non-metallic inclusions – a decisive factor in the high fatigue strength of this grade.

In the hardened state (approx. 60 HRC), 100Cr6 offers high hardness, excellent wear and contact resistance as well as a fine, uniform microstructure with small carbides. This structure improves the dimensional accuracy and ensures a uniform mechanical load-bearing capacity.

Globally, rolling bearings such as ball bearings, roller bearings and needle bearings are predominantly made of 100Cr6. In addition, rolling bearing steels are suitable for all components that are subject to dynamic compressive stress and require a long service life. Typical applications include precision axes, shafts, highly stressed small parts such as bolts and valve needles, feeler levers, drift punches and measuring tools such as templates.

In cold-rolled form, 100Cr6 is also processed into high-precision flat wire products – for example, for small spring clips or knife parts, where tight dimensional tolerances and selectively adjustable mechanical properties are required after hardening.