SOLUTION HEAT TREATMENT AND AGING – PRECIPITATION HARDENING
Austenitic steels, as well as other alloys – mainly non-ferrous metals – that do not exhibit allotropic transformations but are characterized by variable solubility of one of the components in the solid solution, can undergo precipitation hardening.
We offer processes that combine the following technological operations:
• Solution Heat Treatment
• Aging
Solution Heat Treatment
This process involves heating the alloy to a temperature approximately 30–50°C above the solubility limit to dissolve the precipitated component (most commonly tertiary cementite in steels) into the solid solution. The alloy is held at this temperature to achieve equilibrium and then rapidly cooled. As a result, the alloy acquires a single-phase structure.
In the case of austenitic steels, the resulting structure consists of austenite supersaturated with carbon. Although the strength properties of steel slightly decrease after solution heat treatment, its plastic properties significantly improve.
Aging
This process involves heating a previously solution-treated alloy to a temperature below the solubility limit, holding it at this temperature, and then cooling. During aging, excess components precipitate from the supersaturated solid solution in the form of highly dispersed phases.
In some cases, aging occurs with the involvement of intermediate phases and Guinier–Preston zones, which are complexes where solute atoms segregate within the solvent lattice.
Aging leads to strengthening, manifested by an increase in mechanical strength and a decrease in plasticity.
When the temperature is too high, overaging can occur. This effect involves the coalescence of precipitates and the loss of their coherence, which prevents further hardening and can even lead to a reduction in hardness compared to the solution-treated state.
In some cases, aging can occur at room temperature, in which case it is referred to as natural aging.
However, aging can also be an undesirable process, such as in deep-drawing sheets or boiler steels, where it reduces plasticity and increases brittleness.
Max. dimensions of the working chamber for solution heat treatment and aging:
We offer the execution of precipitation hardening processes in vacuum furnaces with a maximum capacity of 1200 kg, in atmospheric furnaces with a maximum gross capacity of 1800 kg, and in pit furnaces. The size of the working chamber is as follows.
a = max 1200mm
b = max 900mm
c = max 750mm
The dimensions apply to processes such as hardening and carburizing (cooling in oil or gas), aging, solution heat treatment, tempering, annealing, and brazing in a vacuum chamber furnace.
Aging, tempering, and annealing in an atmospheric furnace:
a = max 1500mm
b = max 1000mm
c = max 900mm
Nitriding, sulfonitriding, tempering, aging, and annealing in a pit furnace:
h = max 1900mm
r = max 1000mm
