Coarse grain annealing

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The coarse grain annealing (also referred to as full annealing) is one of the heat treatment process for steel and serves to improve machinability .

The grain size results from the solidification of metals as crystallites and their subsequent processing through forming and heat treatment; it is an important material property . The controlled heating, soaking and cooling of metals to achieve defined material properties is called annealing in materials science .

The coarse-grain annealing takes place at a temperature above the hardening temperature with appropriate cooling in order to achieve a coarser grain.

The aim of coarse-grain annealing of semi-finished products and workpieces is to improve the machinability of components that are subject to large-scale machining. This happens at temperatures between 950 ° C and 1100 ° C. The holding time must be long enough (1–4 hours) to achieve the desired coarsening of the grain. This makes the process relatively expensive. As the grain growth goes hand in hand with a deterioration in the component properties, the structural condition must be converted back into a fine-grained condition in the course of the final heat treatment (hardening, quenching and tempering, case hardening etc.) According to DIN  8580, annealing is one of the manufacturing processes by changing material properties .