Heat Treatment Flashcards
What is Steel
Steel is an alloy of Iron and Carbon. It may have an element of other elements like silicon, phosphorus, sulfur, manganese, ect…
What are the classification of steel?
- Straight Carbon Steel
2. Alloy Steel
What are the 3 classification of Straight carbon Steel
- Low carbon.
- Medium Carbon
- High Carbon
What is straight carbon steel.
steel with certain percentage of carbon without substantial amount of other elements.
What gives the straight carbon the ability to be hardened
The carbon makes this possible
What is Low Carbon Steel
Contains about .05 to .20% carbon. Shouldn’t be subject to continuous wear.
What is medium Carbon Steel
.2 to .6% carbon. A medium degree of hardening can be attained
What is made from medium carbon steel
bolts, nuts, crankshafts, crane shafts, etc….
What is High Carbon steel
.6 to 1.3% carbon. Maybe heat treated and tempered. Can withstand a great deal of wear.
What is made from high carbon steel
Many tools and working parts of machinery, guide pins, rest buttons, locating pins, dies, punches, gages, bushings
What is alloy steel
Alloy steels contain elements in addition to carbon and Iron. These additional alloys give the metal particular characteristics not possessed in normal steel.
What are some of the additional elements in alloy steel
- Chromium (Kro-mee-uhm)
- Vanadium (Vuh-ney-dee uh m)
- Nickel
- Molybdenum (muh-lib-duh-nuh m)
- Tungsten
What is Chromium (Kro-mee-uhm)
This element increase the depth to which steel may be hardened. Normal amount in steel is .4 to 1%
Stainless steel has 12-25%
What is vanadium (Vuh-ney-dee uh m)
This element is to reduce internal stress. Typical alloy steel contains about .12 to 0.2%
Nickel
Increases toughness and strength of steel.
Will not increase the capacity for being hardened. Typically contains .3 to 3.75%
Stainless Steel contains as much as %
Molybdenum (Muh-lib-duh-nuh m)
Increases the depth of hardness and makes steel tough
small amount .1 to 2%
What is tungsten
used in tool steel to make a fine grain alloy which maintains a sharp cutting edge.
.5 to 1.5%
High speed steel 6-18%
What are the various heat treatment operations?
- Normalizing
- Annealing
- Quenching
- Tempering/Strain Drawing
- cyaniding
- carburizing
- Nitriding
What is normalizing
Normalizing is the heating of steel above the usual hardening temps followed by cooling freely in air. Typically used after forging or improper heat treatment
What is annealing
Heat steel slowly above the hardening temps. Keeping at that temp for 1/2 to 2 hours followed by a slow cooling (cool in the furnace if possible)
Used to soften metals for machining or to relieve internal stress from excessive machining
What is quenching
cooling a heated piece by dipping in water, brine or oil
What is Tempering/strain Drawing
A process which a degree of hardness is sacrificed to reduce brittleness and increase toughness.
Accomplished by heating between 375-500 degrees F
What are the different levels of Tempering
375-400 *F , pale yellow color, suitable for punches, scrapers, and cams
430*F , light straw color, hammers, tool bits, etc.
460*F medium straw color, dies, drills , screwdrivers
490*F dark straw color, chisels
520*F light purple, axes and needles.
High speed steel can be tempered by reheating to much higher temps which vary from 1000-1200*F
What is cyaniding
place low carbon steel in molten bath of sodium cyanide for 5-30 minutes then quench in water, brine or oil. Hard skin is formed between .01 to .015” thick. Don’t grind pieces from this treatment. This can also be referred as case hardening
Carburizing
Also case hardening. Mixture of bone, leather, charcoal and other materials placed inside a metal box with the piece. The lid is lid with fire clay and placed in a furnace at 1700*F Depth varies on length of time heated. You can grind on these parts.
What is nitriding
process of putting extremely hard surface on steel. Expose steel to hot ammonia gas for several hours The ammonia breaks down into nitrogen and hydrogen The nitrogen reacts with the steel to form a nitride case around steel.
What is hardening
Involves both heating and cooling. To heat bring the piece to the desired temp above the critical range in order to get the grain structure into the proper state for hardening. The cooling process is done by quenching the piece. This helps preserve the structure obtained by heating. For the quenching the temp must be even.
