Perform Basic Heat Treating Processes Flashcards
Why is it important that a piece of aluminum alloy be quenched immediately after it is removed from the heat treating oven?
Any delay in quenching aluminum alloy it is removed from the oven will allow the grain structure to grow enough that intergranular corrosion is likely to form within the metal.
What is meant by normalizing a piece of steel after it has been welded or machined?
Normalizing removes stresses that are locked into the material by welding or machining.
Explain the way a steel structure is normalized after it has been welded.
Heat the steel structure to a temperature above its critical temperature and allow it to cool in still air.
Why is a piece of steel tempered after it has been hardened?
When steel is hardened, it becomes brittle. Tempering removes some of this brittleness.
How is steel annealed?
It is heated to just above its upper critical temperature until it reaches a uniform temperature throughout, then it is allowed to cool very slowly in the oven.
How is steel hardened?
It is heated to its critical temperature and quenched in water, brine, or oil.
What is meant by tempering steel?
The steel is first hardened; then some of the hardness is removed to relieve some of the internal stresses and brittleness.
What is meant by case harding?
The surface of the metal is hardened by the infusion of carbon or aluminum nitride. The interior of the metal remains strong and tough.
What are two methods of case hardening?
Carburizing and nitriding.
How is steel nitrided?
The steel part is heated in a retort in which there is an atmosphere of ammonia (a compound of nitrogen and hydrogen). Aluminum, an alloying element in the steel, combines with the nitrogen to form an extremely hard aluminum nitride on the surface of the steel.
Describe the method of solution heat treatment of an aluminum alloy.
The metal is hardened by heating it in a furnace to a specified temperature and immediately quenching it in water. It is soft when it is removed from the quench, but as it ages it regains its hardness.
Describe the method of precipitation heat treating of an aluminum alloy.
The metal is heated and quenched, then it is returned to the oven and heated to a lower temperature. It is held at this temperature for a specified time, then removed from the oven and allowed to cool in still air. This increases the strength and hardness of the metal.
What is another name for precipitation heat treatment?
Artificial aging.
