Coarse-grain annealing followed by isothermal conversion is employed for subeu — tectoid steels with a C-content of 0.3 to 0.4 % (ferritic-pearlitic steel) in order to produce a coarse-grained structure with a ferrite network which is as closed as possible in which either pearlite or an intermediate structure is enclosed [RUHF58, SCHU78]. The application of coarse-grain annealing to improve ma- chinability is, however, limited by interference by strength properties and as well as financial considerations.
Annealing
Annealing (A) is used in order to rob finely lamellar pearlitic structures and lamellar pearlite with cementite of their hardness and low deformability. Pearlite consisting of as much ferrite as possible with globular cementite is aspired. Such a structure is soft and easily deformable. The machinability of such a structure becomes more favourable with respect to the abrasive wear effects on the tool, while chip formation worsens to the extent that ferrite predominates in the structure. A further annealing of this type can be designated as annealing on globular cementite (AGC), whereby temperatures are held in the A1-line longer and a complete spherical shaping of the cementite is sought.