Improving the mechanical properties
In order to give forgings the specific properties which make them suitable to the operating conditions and applications for which they are meant, every forged product is heat treated.
Consists in heating the particular to a temperature higher than AC3 and letting it stay there long enough for the complete austenitizing of the material, followed by cooling in still or moving air.
This is mostly done to refine and make the grain uniform, preparing it for the subsequent heat treatments.
Consists in heating to the austenitizing temperature and letting it stay there until the entire material has turned into austenite, followed by sufficiently rapid cooling to allow it to turn into martensite. It can be quenched using air, oil or water; this choice is based on the size, type of steel and whether it contains alloying elements or not.
This heat treatment is done immediately after the tempering stage and is done to remove the stresses and fragility that has been created. Consists in heating to a temperature less than AC1, keeping it there for the appropriate amount of time and finishing off with cooling in air. The tempering temperature is chosen based on the hardness and tenacity properties that you want to achieve.
This is done on particulars that have previously been tempered, from which you want to remove the stresses created, while maintaining high hardness values.
STAINLESS STEEL HARDENING
This is mainly used in austenitic stainless steels and is done to obtain the maximum soft annealing and to lend corrosive protection properties. Consists in heating to a temperature generally between 1000 and 1100°C, staying there for an appropriate amount of time and then quenching in water.
Consists in the surface carburizing of steel with a low carbon content obtained by putting the particular in a furnace with an atmosphere that’s rich in this element long enough to obtain the required depth. It then moves on to the tempering stage, thereby obtaining a very hard surface layer, whilst maintaining high core tenacity.
This treatment consists in a surface enrichment of carbon and nitrogen obtained through heating in a controlled endogas atmosphere enriched with methane and ammonia. This stage is then followed by tempering, which makes this surface layer very hard, whilst maintaining low core hardness, therefore a high tenacity.
There are different types of annealing, which are listed as follows:
– Complete annealing: Consists in heating the steel to a temperature higher than AC3 and keeping it there long enough for the complete austenitic transformation and subsequent cooling in the furnace. Very low values and good workability is achieved.
– Spheroidizing annealing: Consists in heating to slightly below AC1, keeping it there long enough and slow cooling in the furnace. The hardness achieved is even lower than what is obtained with – complete annealing and therefore has greater workability in steel with low carbon content.
– Soft or subcritical annealing: This is done by heating the steel to slightly below AC1 for as long as needed and then cooling it in air. It is used to both soften the steel and remove and residual stress.
– Isothermal annealing: Consists in heating to over AC3, followed by quick cooling to a pearlitic field temperature. It stays there long enough to complete the transformation and the subsequent cooling can be done quickly to room temperature. Considerable improvements are achieved in the workability of the tool.