205
- drawback - heating of the tempered steel is lower than temperatures of phase
transformations and cooling for removal of residual tension after training. If
drawback is spent at the room temperature or a little exceeding, it is called as
aging.
Annealing and normalization.
Annealing - heat treatment at which steel heats up to a certain temperature, is
maintained at it and then slowly cooled in the furnace for receiving equilibrium,
less firm structure, free from residual tension.
Annealing of 1 sort treat:
- diffusive annealing (or homogenization) - heating to 1000-1100 for elimination
of the chemical heterogeneity formed at crystallization of metal. To
homogenization subject ingots or castings high-alloyed by the steel.
- re-crystallization annealing which is applied to cold
work removal after cold
plastic deformation. Heating temperature most often is in limits 650-700z.
- annealing for removal of internal tension. Apply for the purpose of reduction
of tension formed in metal at molding, welding, processing by cutting, etc.
Temperature of annealing is in limits 200-700zs, is more often 350-600zs.
Annealing of 2 sorts (or phase re-crystallization) can be full and incomplete:
- full annealing - heating became on 30-50z above the top critical point with the
subsequent slow cooling. At this annealing there is a full re-crystallization: when
heating the ferritic-pearlitny
structure passes in austenitic, and when cooling
austenite turns back into ferrite and pearlite.
To full annealing subject castings, forgings, hire for crushing of grain, removal
of internal tension. Thus plasticity and viscosity increase.
- incomplete annealing differs from full that heat steel to lower temperature (on
30-50z higher than temperature of pearlitny transformation). Thus there will be a
re-crystallization of only a pearlitny component. It is more economic operation,
than full annealing as heating is made up to lower temperatures.
At incomplete annealing the workability cutting
as a result of decrease in
hardness and increase of plasticity of steel improves.
Isothermal annealing consists in heating and endurance at a temperature on
30-50z above the top critical point, cooling to 600-700zs, endurance at this
temperature before full transformation of austenite into pearlite and the
subsequent cooling on air.
Normalization - an annealing version. At normalization cooling is carried out
on quiet air. Cooling speed is slightly more, than at usual annealing that defines
some difference of properties of the annealed and normalized steel.
Достарыңызбен бөлісу: