Heat Treatment

Question 1

What is Steel

Answer 1

Steel is an alloy of Iron and Carbon. It may have an element of other elements like silicon, phosphorus, sulfur, manganese, ect…

Question 2

What are the classification of steel?

Answer 2

1. Straight Carbon Steel

2. Alloy Steel

Question 3

What are the 3 classification of Straight carbon Steel

Answer 3

1. Low carbon.
2. Medium Carbon
3. High Carbon

Question 4

What is straight carbon steel.

Answer 4

steel with certain percentage of carbon without substantial amount of other elements.

Question 5

What gives the straight carbon the ability to be hardened

Answer 5

The carbon makes this possible

Question 6

What is Low Carbon Steel

Answer 6

Contains about .05 to .20% carbon. Shouldn’t be subject to continuous wear.

Question 7

What is medium Carbon Steel

Answer 7

.2 to .6% carbon. A medium degree of hardening can be attained

Question 8

What is made from medium carbon steel

Answer 8

bolts, nuts, crankshafts, crane shafts, etc….

Question 9

What is High Carbon steel

Answer 9

.6 to 1.3% carbon. Maybe heat treated and tempered. Can withstand a great deal of wear.

Question 10

What is made from high carbon steel

Answer 10

Many tools and working parts of machinery, guide pins, rest buttons, locating pins, dies, punches, gages, bushings

Question 11

What is alloy steel

Answer 11

Alloy steels contain elements in addition to carbon and Iron. These additional alloys give the metal particular characteristics not possessed in normal steel.

Question 12

What are some of the additional elements in alloy steel

Answer 12

1. Chromium (Kro-mee-uhm)
2. Vanadium (Vuh-ney-dee uh m)
3. Nickel
4. Molybdenum (muh-lib-duh-nuh m)
5. Tungsten

Question 13

What is Chromium (Kro-mee-uhm)

Answer 13

This element increase the depth to which steel may be hardened. Normal amount in steel is .4 to 1%
Stainless steel has 12-25%

Question 14

What is vanadium (Vuh-ney-dee uh m)

Answer 14

This element is to reduce internal stress. Typical alloy steel contains about .12 to 0.2%

Question 15

Nickel

Answer 15

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 %

Question 16

Molybdenum (Muh-lib-duh-nuh m)

Answer 16

Increases the depth of hardness and makes steel tough

small amount .1 to 2%

Question 17

What is tungsten

Answer 17

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%

Question 18

What are the various heat treatment operations?

Answer 18

1. Normalizing
2. Annealing
3. Quenching
4. Tempering/Strain Drawing
5. cyaniding
6. carburizing
7. Nitriding

Question 19

What is normalizing

Answer 19

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

Question 20

What is annealing

Answer 20

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

Question 21

What is quenching

Answer 21

cooling a heated piece by dipping in water, brine or oil

Question 22

What is Tempering/strain Drawing

Answer 22

A process which a degree of hardness is sacrificed to reduce brittleness and increase toughness.
Accomplished by heating between 375-500 degrees F

Question 23

What are the different levels of Tempering

Answer 23

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

Question 24

What is cyaniding

Answer 24

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

Question 25

Carburizing

Answer 25

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.

Question 26

What is nitriding

Answer 26

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.

Question 27

What is hardening

Answer 27

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.