Heat treatment

The combination of processes for the targeted modification of the properties of metallic materials is called heat treatment. With a total of eleven different furnaces, the Silbitz Group is one of the largest foundry companies that successfully serve the steel processing sector of heat treatment. In most cases, they are materials that are heated during the treatment for a limited time to the required temperatures. This allows the material properties to be targetedly improved. The decisive influencing factores in the processes are the atmosphere, temperature, heating and holding time as well as quenching or cooling. The basic heat treatment processes include annealing, hardening and tempering in chronical order. For example, hardened steel can first be annealed and then hardened in three stages before the material retains its required toughness and strength.

Annealing in the heat treatment involves three basic operations. First, the workpiece is heated slowly to a certain temperature. This remains for a certain time corresponding to the goal before it finally comes back to a slow cooling. If the material is annealed shortly before the first transformationline to obtain only low hardness and strength, this is referred to as soft annealing. A similar effect for cast materials is shown by the ferrite which dissolves free and perlite-bound cementite in ferrite and graphite. To reduce residual stresses, the so-called stress relief annealing is used as a special branch of the heat treatment.

The actual hardening process during the heat treatment takes places in three stages. In the first two steps, which are also called austenitizing, the material is initially heated only slowly, so that the workpiece parts are not overstretched or burned. Thereafter, it is quickly increased to the required hardening temperature. In the second step, the hardening temperature is maintained for uniform soaking. The third stage of the heat treatment is quenching, with the heated material cooling in a very short time. The cooling rate affects the hardness of the workpiece and is among others depending on the particular deterrent. The Silbitz Group offers three variants: the normal form of water, oil and moving air. Basins of up to 40 cubic meters are available for both liquids. For high alloy steels (air hardening), the quenching agent used in the heat treatment is moving air generated by fans in a cooling chamber with a maximum load of 60 tons.

Construction materials, which are not only required to be particularly strong, but also have a high toughness, are tempered during the heat treatment. These include for example waves, wedges or screws. This is a tempering process that creates an extremely strong, fine-grained material structure at temperatures up to 700°C.

During tempering, the workpiece is reheated to up to 350°C.The result is a compensation structure that optimizes the mechanical properties while reducing the hardness-related brittleness and any internal stresses for the respective application.

The typical tasks of heat treatment include the reduction of solidification and stress in the component as well as the targeted adjustment of component and material properties such as wear resistance, tensile strength, toughness and hardness. The aim of the heat treatment in the Silbitz Group is to increase the service life of tools or components through special qualities, thus increasing cost-effectiveness. Results that are difficult to achieve with conventional methods.

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