Heat treatment JOD & AMcC (Heat treating is a manufacturing process…
Heat treatment JOD & AMcC
Heat treating is a manufacturing process used to alter the physical and chemical properties of a material .
Main types of Heat treatment
Annealing of a piece is used to make the piece more ductile, it also reduces its hardness making it more workable
Material is heated up to a temperature between 80-180 degrees celcius below the lower critical temp.
It is then allowed to soak for a specific time and then cooled normally in air
Crystallization occurs and as the temperature is relatively lower in the new grains they are small.
Higher carbon steels are heated up to a higher temperature, just 30 degrees Celsius below the lower critical temp.
This annealing process is called sheroidising, where cemintite is formed into spheres. this improves its machinability
Normalizing relives stress , This improves Ductility and toughness .
Hardening is a process used to increase the hardness of a piece , It is used commonly when manufacturing Machine cutting tools e.g Drill bits
Tempering is used to increase the toughness of a piece . Usually preformed after the hardening process
To remove some of the brittleness caused by hardening process , steel is heated to a temperature below lower critical temperaturre of 723 degrees C.
Usually heated to a range between 230-300 Degrees C.
Heating at a low temperature reduces stresses in the material.
Allows for Martensite to change to ferrite and perlite.
the resultant of tempering process is a steel hard enough to do the required job, and also tough enough to withstand wear and tear.
Quenching is the rapid cooling of a workpiece in water, oil or in air to obtain certain material properties.
the process of quenching
piece is heated to between 815 and 900 degrees making shure the piece is heated evenly and is not overheated .
The piece is taken from the oven to the quenching station where it is dipped in oil or water, the person quenching must make shure to go into the liquid straight so not to bend or warp the piece. piece can also be cooled in Air.
water is used where maximum Hardness is needed but may cause tiny cracking and distortions in the piece
when hardness can be sacrificed oil is used. The cooling rate of oil is much less then water.