Only proper heat treatment will show the hidden qualities of forged steel, whether it is a specific surface hardness to resist wear, easy machinability for future machining procedures, or very high toughness values in deep temperature ranges.
The necessary mechanical properties of the forging that are required for its future application can only be accomplished by using the proper heat treatment. Our furnaces use state-of-the-art technology that allows us to use cost-effective and environmentally friendly, well-established heat treatment procedures. In doing so, we apply generally accepted standards or we work according to your particular specifications.
For the forging, rolling, and heat-treating of the rings, we have developed an integrated combination of system. It allows us to manufacture the workpiece on a direct path from an upsetting and perforating press, through the rolling mill to the tempering system. Furthermore, by applying selective heat transfer in this combination of the production steps, the system becomes energy-efficient and thus, environmentally friendly.
Overview of the common heat treatments at Dirostahl
The objective of tempering is to achieve an optimal combination of hardness and yield/tensile strength. The process is a combination of hardening (quenching) and subsequent reheating (tempering). For hardening, the component is austenitized and quickly cooled back down after a corresponding holding time. When quenched, the steel becomes hard, but also brittle. The subsequent tempering increases the yield point and tensile strength and breaks up the high strain and toughness values.
The objective of normalising is a close-grained, uniform microstructure with optimal tensile and deformability properties. All microstructure irregularities and property changes which appeared through other procedures are removed once again. To do so the steel is heated above the austenite temperature and it is cooled back down once fully heated in still air.
Solution annealing (+AT)
Solution annealing is used to improve the corrosion resistance of stainless steels through equal distribution of the alloying element. Depending on the steel it is effected in a temperature range between 1020 °C and 1200 °C. This annealing process is also used after shape-changing procedures in lieu of the recrystallisation annealing.
Soft annealing (+A)
The objective of soft annealing is an improved machinability and formability. Soft annealing results in a very low hardness. To do so a temperature just below AC1 (approx. 680 °C – 700 °C) is chosen. After a corresponding holding time the workpiece is cooled down in the furnace. This procedure is used for low eutectoid steels (<0.8% carbon).
Spheroidising (annealing on spherical cementite) is comparable with soft annealing. The objective is to achieve the highest possible degree of spheroidisation of the cementite. It is used for hypereutectoid roller bearing steels (carbon content > 0.8%). For this purpose, the temperature oscillates within the conversion line (AC1). In this case, after a corresponding holding time, the workpiece is also cooled down in the furnace.
Ferrite-Perlite annealing (+FP)
Ferrite-Perlite annealing is used for an improved machinability of case-hardened steels. In the past this procedure was known as process annealing. According to the new standards, today it is officially known as isothermal annealing or Ferrite-Perlite annealing. In this annealing process, the cooling curve after coarse grain annealing is interrupted and kept in Perlite range, until a pure Ferrite-Perlite microstructure is formed.
Stress relief annealing (+SR)
The objective of stress relief annealing is the reduction of internal stresses in the material. Such stresses occur, for example, due to microstructure transformations, cold formation and through machining treatment. A good result not only requires the correct temperature, but also a careful cool down. This is the only way in which new stress formations are avoided. Usually stress relief annealing is effected in temperatures around 600 °C (in case of previously annealing components however, 30 - 50 °C below the first temperature).