The application for electron beam hardening lies in treating surfaces with a hardening depth ranging from 0.1 – 1.0 (1.5) mm and is particularly used when high demands are placed on the welding process and with components that are prone to distortion.
Boundary-layer transformation is a very effective method of hardening work pieces locally. The electron beam is a very efficient tool characterized by its great precision. A narrow boundary layer (typically 0.1 – 3 mm) is heated up above the austenitic temperature and rapidly cooled down again. The process of rapid heat absorption into the surrounding cold mass is referred to as self quenching. This self quenching requires no other medium for cooling, in comparison to other procedures. High temperature gradients are achieved because of the very high power-density of the electron beam. The heat is applied locally in a very short time – typically in milliseconds. Very little heat flows away into boundary zone and therefore the body of the work-piece remains relatively cold. Electron beam hardening produces less deformation when compared to other methods.
All steels whose carbon content is sufficient for the formation of Martensite can be hardened. A fine Pearlite or hardening structure is of an advantage for the complete diffusion of carbon material due to the short time required for the formation of Austenite. Cast iron can also be hardened providing it has basic Pearlite structure. Grey cast iron can be hardened by the re-melting process. In this process, a narrow boundary zone of the work-piece experiences a re-melting procedure. Rapid solidification produces a Ledeburitic structure with very good wear resistance.
The following chart explains the possibilities for EB surface modifications. For further details please click the active buttons in the chart.
Hardening is characterised as; heating up steel to the Austenitic temperature followed by rapid quenching – producing the structural form of Martensite (hardening structure). Martensite is required in steels to achieve a considerable increase in hardness. The achievable (Martensitic) hardness is directly dependent on the carbon content of the steel.
The higher the carbon content, the greater the hardness.
Example: Transverse macro-section
Hardness profile measured from
surface to base material HV 0.3
Annealing, like hardening is another heat processes where the entire mechanical characteristics of the work-piece are changed.
Annealing is usually applied after hardening. That means; the annealing process takes place immediately after the work-piece has been rapidly quenched and has is completely cold. Depending on the composition of the steel, it can exhibit very high values of hardness. In this hardened state the component is also very brittle and therefore it cannot be used or further processed.
As a rule; the higher the hardness, the lower the toughness. When a component is annealed, the hardness is reduced until the required toughness index has been reached. The consequential loss of hardness is taken into account. Hardness and toughness are cross-related and therefore cannot be selected independently from one another.
In texturing, pre-programmed electron beam pulses are used to vaporize material or explode material away from certain areas. This requires a special beam control specific to the component and the requirements.
A small boundary layer of the work-piece is melted. The rapid solidification produces a fine Ledeburitic structure with very good wear resistance.
(Ledeburitic – eutectic structure of the iron/carbon alloys with carbon contents between 2.06% and 6.67 %).
A fine, cleanly formed structure remains after melting and cooling down.
Bsp.: Al-Si-Kolbenlegierung
links: Gussgefüge, rechts: EB-Umschmelzgefüge (im selben Maßstab)
Embedding of hard composites in aluminium, copper etc.
A hard composite in the form of small pellets (shot) or powder is embedded in the molten bath).
eingebettete Wolframkarbide
angeschmolzene Wolframkarbide
Alloying is characterised as the melting together of a metal with at least one other metal or non-metallic compound.
