Heat treatment Flashcards
XRD
X ray Diffraction. Read wavelenght to determine grain size and different phases
Quenching
The procces where metal is cooled in some type of solution at a fast cooling rate. cooled through it’s eucteoid point.
Temperature gradient
change in temperature
Tempering
The procces to change the tempeture to increase toughness. rapid cooling
Stress Relieve
Procces where you heat up to recyrazatioln and then cool down. Used to remove the different stresses, residual stresses, and inertial stresses as well as distortion.
Hot rolling
Heated at recryzalation tempeture and then strecthed out to be put through two rollers. rolled out
Surface Hardening
Proccess where the surface is treateeted to create a thin, wear resistance layer with increased harndess . the core remains soft and ductile . Done to increase hardness
Homogenizing
Procces to reduce chemical segregation one element. allows for chemical diffusion involves heating near the metling point and then slowly cooling it.
Spherodizing
results in nodules in grains turningign into spheres. results in high ductility.
Normalizing
Done outside of the furnace. Increases formability.
Ovens
Air ducts distribute heated air from separate heating chamber via recirculating fan. best at lower temperatures
Annealing
The process involves heating the metal so that the metal as well as rearranges the structure of the metal. . Done to increase ductility.
Quenching medium
The liquid material into which metal is plunged during the quenching. Process
4 stages of quenching
Steam forming. Steam coverage. Steam
Surface Hardening
Pro
4 stages of vapor film
4 stages of quenching decreases temperature throughout.
Steam formation: metal I. The beaker metal starts to cool. forms a vapor field.
Steam coverage: covered in a cloud of vapor or steam blanket. Bubbles stick to the metal and consulate if from the quenching medium.
Steam discharge: a discharge where the film of bubbles collapses. Allows the metal to again make contact with the quenching medium. Agitation can decrease time in this stage. Very violent.
Slow cooling: cools at a slower cooling rate to a normal rate. No more vapor film.
Process’s of Martempering
put in a molten salt booth just above it’s martensite start tempt. The quench is much less severe. Partial quench, hold, finish quench,reheat, hold, then quench. are done to minimize residual stress, distortion, and cracking.
Proccess of Austempering
ss
Product of Martempering
Tempered Martensite
Thermal location Dislocation
Raise the temperature to rearrange the position of atoms in the crystal structure.
Raise the temperature in tempering
will decrease yield strenght, and tensile strenght.
Interupted Quenching
- Metal is winched to martensite region. 2. Hold 3. Raised to Bainite. 4. Held at Bainite. 5. Then lowered to Martensite
Full annealing is done to
Reduce Hardness and Brittleness, ie increase ductility. done at high temperatures and turns austenite to coarse pearlite.
Normalizing is done to
increase hardness and strength. done at a faster cooling rate. forms fine pearlite
Rapid heat treating is done
changes are caused by heat, not chemical changes. Only the preheated part is hardened.
Carburizing
a process where iron absorbs carbon while it is heated in the presence of heat-treated metals. The main concern is quenching
Flame hardening
used above the torch where heat is applied to only small selected areas. no carbon or nitrogen is added. Quenches rapidly. Most commonly used on medium carbon steel.
Pack carburizing
put in a furnace with many carbon materials. gas Carbnoaceous: Carbon monoxide makes the carbon fuse into the material
The main difference between Carburirzzing and Nitritiding.
Nitriding does not require secondary heat treatment like (quenching).
Gas carburizing
Where the metal is subject to a carbonaceous gase such as carbon monoxide in an enclosed space. Then heated to a high temperature until carbon is diffused into material. A contnouoius gas is used. Longer it stays in that furnace the more parts will be produced
Liquid Carburizing
Put into salt bath containing material liek cynanide and being heated by electricity. Solution is stirred transfer is done quickly
What steels is flame hardening used for
Medium Carbon Steel is the most common. must contain enough carbon.
Induction Hardening
Uses a copper coil and the process of induction to heat the metal and then quenched. Alternating current at high frequency. Electric resistant of part is used to heat metal. Most expensive but also most efficient.
Nitriding
The steel is heated at below the Austnetic temperature where Ammonia is added to allow for the nitrogen atoms to enter the steel.
Normalizing and annealing do what to affect the crystal structure of the grains
it will return it back to original shape
How Slow cooling affects cracking
Slow cooling allows for less cracking and distortion of the surface of the material.
Rapid heat treatment hardening of metal when quenched must have
a high enough carbon content.
what composition change process produces the most hardness?
Nitriding
Normalizing
Heating 20 degrees above upper transformation line.
4 different Nitriding methods
Nitriding, Cyanididng, Carbonitriding, vacuum gas nitriding.
Laser/ Electron Beam Hardening
concentrated and precise beam sent to heat the metal. Instantaneous process.
Carbonitriding
Metalis is heated in chamber with ammonia and natural gas. induces surface with carbon and nitrogen atoms. Heat treated to temperature less than carburizing then Left to quench. Can increase wear resistance
What quenching medium is heat for low carbon steels
Water
Best Quenching medium for cast iron
Air
Lowest temp medium
Brine
Tempering happens after
Quenching and Annealing
Full Annealing
Heated to 50-100 f above utt. Held their and completely changes to Austenite
Sheropheredizing g is done on what steels
High carbon steels.
Procces Annealing
Heated below LTT. Used when time/furnace time is a concern
Die casting
Where molten metal is inserted into container under very high pressure for increased strnenght and more precise dimensions
advantages of nitriding
more corrosion resistance, less cracking, requires less cleaning than carburizing.
three issues with quenching.
cracking, distortion, and internal stresses.
