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Case-hardening steel

Application Area

Bolts, shafts, gears, etc., with a hard surface and a tough core.

Description

Case-hardening steels have a carbon content of less than 0.25% and a small amount of alloying elements, which promote through-hardening (Cr, Mn, Ni, Mo) and form hard carbides (Cr, Mo) with the introduced carbon in the surface layer, increasing wear resistance.

Properties

Excellent combination of toughness, high wear resistance, and resistance to bending and impact loads. Very good fatigue strength due to compressive stresses in the hardened surface. Very good fatigue strength due to compressive stresses in the hardened surface.
Welding: Not weldable (C15 is very well weldable before case-hardening).
Distortion: Particularly in unalloyed steels (water hardening) and/or complex-shaped parts. 
Post-processing: Grinding of certain functional areas reduces negative effects (e.g., radial runout), improves tolerances, and refines surface roughness.

Case Hardening

Tough components are achieved by using low-carbon steels, which attain only low hardness when quenched. Therefore, carbon is introduced into the surface layer through diffusion, creating a hardenable steel layer with approximately 0.8% carbon.
During quenching, the core is tempered, and the surface layer is hardened. The case-hardening process consists of two main steps, Carburizing (introducing carbon into the surface) and Hardening (quenching and tempering).

Application Area

Bolts, shafts, gears, etc., with a hard surface and a tough core.

Description

Case-hardening steels have a carbon content of less than 0.25% and a small amount of alloying elements, which promote through-hardening (Cr, Mn, Ni, Mo) and form hard carbides (Cr, Mo) with the introduced carbon in the surface layer, increasing wear resistance.

Properties

Excellent combination of toughness, high wear resistance, and resistance to bending and impact loads. Very good fatigue strength due to compressive stresses in the hardened surface.

Tempered Steel

Application Area

Tempered Steels are used where steels such as S235, S355, etc., would result in excessively large dimensions. They are ideal for all highly stressed components in gearboxes, engines, chassis, etc., such as gears, crankshafts, engine shafts, screws, shift forks, etc.

Description

Tempered Steels are engineering steels that, due to their chemical composition, are suitable for hardening and, when tempered, exhibit good toughness at a given tensile strength.
Through tempering, engineering steels achieve the following property combinations:

  • Higher yield strength Re, Rp0.2 for higher permissible stresses
  • Increased toughness (notched impact energy Av) for significant deformation before fracture

To achieve this toughness, the microstructure must not contain too much cementite. Therefore, carbon content is limited to 0.25 to 0.6%.

Properties

A selected combination of yield strength and toughness.
Welding: Not suitable (C35 and C45 are only conditionally weldable).
Machining: Heat treatable steels can also be machined after tempering.
 

Tempering

Tempering is a heat treatment process that involves quenching engineering steels followed by tempering at higher temperatures. Objective: To achieve toughness while increasing yield strength. Steels with higher yield strength and good toughness can generally be produced using two heat treatment processes:
 

  • Tempering by annealing: 
    Tempering by annealing involves hardening (martensitic structure) followed by tempering (heating) at 450°C to 600°C, where maximum values of toughness and strength are achieved.
            1. Quenching in water. 
            2. Tempering treatment (annealing), optimizing strength and toughness.
     
  • Tempering by isothermal transformation:
    Quenching an austenitic structure to a temperature between Ms (start of martensite formation) and Ar1 (cooling transformation point), followed by holding at this temperature (isothermal process). During this time, the entire austenite transforms. The steel can then be cooled to room temperature without further changes. This process is also known as bainitic tempering.

Application Area

Tempered Steels are used where steels such as S235, S355, etc., would result in excessively large dimensions. They are ideal for all highly stressed components in gearboxes, engines, chassis, etc., such as gears, crankshafts, engine shafts, screws, shift forks, etc.

Description

Tempered Steels are engineering steels that, due to their chemical composition, are suitable for hardening and, when tempered, exhibit good toughness at a given tensile strength.
Through tempering, engineering steels achieve the following property combina

Structural steel

Application Area

After normalizing or cold forming, structural steels are primarily used in high-rise, civil, bridge, water, container, vehicle, and mechanical engineering due to their tensile strength and yield strength.

Description

Unalloyed structural steels make up the largest share of total steel production. They are typically supplied in a hot-rolled condition.

Properties

Welding: Structural steels are highly weldable.
Mechanical Properties: In condition +N, structural steels have high yield strength combined with sufficient plastic deformability, especially under impact loads. It is important to consider the temperature at which notched impact energy is tested.

Designation (27J)   RJ   J0   J2   J3   J4   J5   J6
Test Temperature °C   +20   0   -20   -30   -40   -50   -60

Technological Properties

This section describes properties such as machinability, cold formability (e.g., stamping, deep drawing for sheets), weldability, corrosion resistance, etc.

Physical Properties

Requirements related to magnetic properties, thermal conductivity, and thermal expansion.

Weldability

Due to the significant role of welding as a joining process in structural steels, the following explanations clarify the concept of weldability:

  • Welding suitability: A steel is considered weldable if, based on its metallurgical, chemical, and physical properties, a weld can be produced that meets the required specifications.
  • Welding safety:This is not determined by the steel manufacturer but by the fabricator. Welding safety is ensured when the welded component remains safe in operation (brittle fracture and crack-free) under the intended service conditions. It is influenced by Design aspects (plate thickness, weld type and arrangement, notch effect), Load conditions (type, magnitude, and multi-axiality of stresses, strain rate, operating temperature).
  • Welding feasibility: It indicates whether the respective joint can be produced under the selected manufacturing conditions. The three influencing factors interact with each other.A steel is considered weldable if, during rapid cooling, the microstructure formed in the heat-affected zone (HAZ) remains sufficiently deformable. To achieve this, martensite formation must be avoided, or the carbon content must be limited so that any resulting martensite remains sufficiently ductile.In addition to carbon, alloying elements also influence the crack susceptibility of the hardened zones in the HAZ. The combined effect of carbon and alloying elements is often expressed using the carbon equivalent (Ceq). A commonly used formula for structural steels is: Ceq = C + Mn/6 + (Cr + Mo + V)/5 + (Ni+Cu)/15 [%]. Alloying elements in this equation are expressed as mass percentages. Compared to carbon, they contribute less significantly to crack susceptibility.

The alloying elements in this equation are expressed as mass percentages. Compared to carbon, they contribute significantly less to crack susceptibility. In general, depending on the workpiece thickness, steel with Ceq ≥ 0.45% is preheated to 100°C – 150°C before welding. This reduces the cooling rate in the heat-affected zone (HAZ), which effectively decreases the amount of martensite. As a result, the hardness in the HAZ is reduced, minimizing the risk of cracking.

Application Area

After normalizing or cold forming, structural steels are primarily used in high-rise, civil, bridge, water, container, vehicle, and mechanical engineering due to their tensile strength and yield strength.

Description

Unalloyed structural steels make up the largest share of total steel production. They are typically supplied in a hot-rolled condition.

Properties

Welding: Structural steels are highly weldable.
Mechanical Properties: In condition +N, structural steels have high yield strength combined with sufficient plastic deform

Bearing steel

Application Area

Components that must meet high requirements for hardness, durability, wear resistance, and dimensional stability, such as tools, guide rails, bushings, spacer rings, spindles, shafts, rollers, gears, cutting rollers, etc.

Description

100Cr6 is the classic steel used in the bearing industry. In addition to its application in ball, needle, and roller bearings, it is also suitable for wear-resistant machine components. It can be surface-hardened or through-hardened depending on the requirements. For thicker surface-hardened layers, 100CrMo7-3 is a better choice.

Eigenschaften

  • Welding: Bearing steels are not weldable.
     
  • Heat Treatment:              Normalizing: 870° - 900°C followed by air cooling
                                              Annealing: 750°C – 800°C soft annealed to obtain spheroidized cementite
                                              Stress relieving: 600° - 650°C followed by air cooling
                                              Hardening: 80° - 870°C quenched in oil
     

Application Area

Components that must meet high requirements for hardness, durability, wear resistance, and dimensional stability, such as tools, guide rails, bushings, spacer rings, spindles, shafts, rollers, gears, cutting rollers, etc.

Description

100Cr6 is the classic steel used in the bearing industry. In addition to its application in ball, needle, and roller bearings, it is also suitable for wear-resistant machine components. It can be surface-hardened or through-hardened depending on the requirements. For thicker surface-hardened layers

Gear steel

Application Area

Designed for highly stressed gears requiring sufficiently high surface hardness on the tooth flanks, high bending strength in the tooth root, and good impact toughness to withstand sudden loads. Gears made from CV58Z exhibit high wear resistance and are resistant to pitting formation. This steel is also suitable for other components, such as cam discs.

Description

Typically, components with these requirements are made from case-hardening steel. However, for economic reasons, flame hardening or inductive hardening of quenched and tempered steels is often used. In these processes, the tooth flanks are heated and quenched in a feed process. However, this hardening method is only effective for spur gears with module > 6. Bevel gears and gear modules below 6 cannot be hardened with satisfactory results using this method. To overcome this limitation, the circumferential hardening process was developed, enabling consistent hardness results even for smaller gears. A crucial requirement was developing a steel with high surface hardness while maintaining sufficient elasticity to absorb shock loads during operation.

Properties

  • Oil-hardening steel, specifically designed for circumferential hardening.
  • Not suitable for processes requiring water quenching.
  • Requires strict metallurgical conditions and suitable testing procedures to ensure consistent steel properties for circumferential hardening.
  • Supplied in either annealed or quenched and tempered condition.

Strength Properties in Delivery Condition

  • Annealed to spheroidized cementite.
  • Quenched and tempered for higher strength (although higher strengths are not recommended due to machining difficulties).
  • During circumferential hardening, a tooth root strength of approximately 1470 N/mm² is achieved.
  • Quenched and tempered condition is recommended for smaller gears (outer diameter ≤ 200 mm) and when the bore is broached (e.g., keyway profiles) or the teeth are hobbed.

    • Lower distortion during hardening.
    • Achieves higher hardness of 62 – 64 HRC (approx. 2–3 HRC higher than annealed material).

  • Annealed material can be used for larger gears since longer heating times during hardening ensure proper hardness results.

Warmformgebung und Wärmebehandlung

   Tempering 
Forging °CAnnealing (spheroidized cementite)
°C		Normalizing °CHardening °CTempering °C
8050 - 1050710 - 740*850 - 880830 - 850180 - 210

*) Annealing temperature depends on the required microstructure and processing conditions.

To ensure consistent and reproducible results, CV 58 Z is produced using special melting techniques and carefully controlled heat treatment.

Distortion During Hardening

In practical applications, hardening distortion is measured by the change in the pressure angle and the major pitch deviation before and after hardening.

Comparative studies between CV 58 Z and 16 MnCr 5 show that:

  • Hardening distortion in CV 58 Z is on average 45% and 30% lower, respectively, than in 16 MnCr 5.
  • This results in improved dimensional stability after heat treatment.

Circumferential Hardening

Circumferential hardening, also called rotational hardening, is used to harden the circumference of rotating components.

Process:

  • This method is similar to stationary hardening but with the key difference that the workpiece rotates during heating and quenching.
  • A machined gear blank, in either an annealed or pre-hardened state, is locally heated and then quenched in oil.

Objectives:

  • High surface hardness for wear resistance
  • High bending strength
  • Good impact toughness

Hardened Zones

In case-hardening steel 16 MnCr 5, the hard case layer and the soft core are clearly visible as two distinct structural zones. In CV 58 Z, the gear tooth exhibits an almost fully hardened microstructure, with a gradual transition into the softer structure of the gear rim. This results in higher load-bearing capacity and better impact resistance compared to conventional case-hardened steels.

Application Area

Designed for highly stressed gears requiring sufficiently high surface hardness on the tooth flanks, high bending strength in the tooth root, and good impact toughness to withstand sudden loads. Gears made from CV58Z exhibit high wear resistance and are resistant to pitting formation. This steel is also suitable for other components, such as cam discs.

Description

Typically, components with these requirements are made from case-hardening steel. However, for economic reasons, flame hardening or inductive hardening of quenched an

Seamless Steel Tubes / Rolled Rings

We are the official representative of Ovako Steel AB,Hofors and Hällefors, in Switzerland. In addition to our comprehensive on-site consultation, we offer direct access to the extensive expertise of the steelworks whenever needed. This enables us to provide tailor-made solutions based on the in-depth knowledge and innovative technologies of Ovako Steel AB. Whether for specific applications or general challenges in the steel industry, we are your competent partner in ensuring the successful realization of your projects.

Application Areas

Ovako® steels are used in demanding applications such as bearings, fuel injection nozzles in Common Rail diesel engines, hydraulic cylinders, rollers, highly stressed gearboxes like those in wind turbines, and complex mechanical engineering components. These steels are available as seamless steel tubes, rolled or forged rings with diameters of up to three meters, or as bar material. While many steel grades are available from the Embrach service center, Ovako® also manufactures other high-quality steels, which can be supplied directly from the factory with the appropriate lead time and quantity.

Description

  • Seamless Engineering Steel Tube Ovako® 280: Ovako® 280 is made from high-purity steel and is seamless. It is available in various dimensions, with a maximum outer diameter of 256.5 mm.
  • Bearing Steel Tubes Ovako® 803 and Ovako® 824: These steels are characterized by high resistance to fatigue and wear.
    Ovako® 803 offers excellent fatigue and wear resistance. The tubes are supplied in an annealed condition, making them easy to machine. Through martensitic hardening and tempering, hardness levels of up to 60–65 HRC can be achieved.
    Ovako® 824 is suitable for through-hardening of thicker wall sections. This steel also provides high fatigue strength, excellent wear resistance, and good toughness. It is suitable for both martensitic and bainitic hardening.

Find out more about Ovako® here.

We are the official representative of Ovako Steel AB,Hofors and Hällefors, in Switzerland. In addition to our comprehensive on-site consultation, we offer direct access to the extensive expertise of the steelworks whenever needed. This enables us to provide tailor-made solutions based on the in-depth knowledge and innovative technologies of Ovako Steel AB. Whether for specific applications or general challenges in the steel industry, we are your competent partner in ensuring the successful realization of your projects.

Application Areas

Ovako®

Round Steel

Square Steel

Flat Steel

Do you need help or advice? We are here for you.

Which steel grade could be suitable for your application? Are there alternative products? How is availability developing? We are happy to put our expertise to work for you and ensure that you receive the right material at the desired time.

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