general materials and processes Flashcards
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 critical temperature and quenched in water, brine, 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 hardening
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
Carbonizing 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, and alloy element and steel, combines with nitrogen to form an extremely hard aluminum nitride on the surface of the steel 
What is 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 it’s hardness. 
What is 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 the temperature for a specified time, then removed from a oven and allowed to cool in still air this increases the strength and hardness of the metal precipitation heat treating is also called artificial aging
What is another name for precipitation heat treatment?
Artificial aging
identify and explain the differences between heat treated and non heat treated aluminum alloys
heat treated aluminum alloy designations are normally followed with a -T, followed by a number (1-10) that designates the type of heat treat. a common aircraft aluminum alloy is 2024-T3 heat treated aluminum is stronger than non heat treated aluminum
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 after it is removed from the oven will allow the grain structure to grow enough that inter granular corrosion is likely to form in the metal
