Classifications of Metals and Alloys (Module 1-2)

Question 1

Metals and alloys can be classified as what two types?

Answer 1

Ferrous and non-ferrous

Question 2

These alloys have iron as their primary constituent.

Answer 2

Ferrous alloys

Question 3

These alloys are widely used due to the constituent’s abundance, various types of production, and versatility.

Answer 3

Ferrous alloys

Question 4

What are the two types of ferrous alloys?

Answer 4

Steels and Cast Irons

Question 5

What are the two types of steels?

Answer 5

Plain Carbon or Low Alloy Steels and High Alloy/Alloyed Steels

Question 6

What are the four types of Low Alloy Steels?

Answer 6

a. Low Carbon Steels
b. High Strength Low Alloy Steels
c. Medium Carbon Steels
d. High Carbon Steels

Question 7

What are the two types of high alloy/alloyed steels?

Answer 7

a. Tool Steels

b. Stainless Steels

Question 8

What are the three types of stainless steels?

Answer 8

a. Martensitic Stainless Steels
b. Ferritic Stainless Steels
c. Austenitic Stainless Steels

Question 9

What are the four types of cast irons?

Answer 9

a. Gray Cast Iron
b. Ductile or Nodular Cast Iron
c. White Cast Iron
d. Malleable Cast Iron

Question 10

These are the type of alloys containing less than or equal to 2 wt% of carbon.

Answer 10

Steels.

Question 11

These are steels containing residual concentrations of impurities (other than carbon) and a little Mn, S, and P.

Answer 11

Plain Carbon or Low Alloy Steels

Question 12

These are low alloy steels that contain less than 0.25 wt% carbon but are produced in greatest quantities. These are used in automobile parts and structural shapes.

Answer 12

Low Carbon Steels

Question 13

These low alloy steels contain 0.05-0.25 wt% carbon and other alloying elements such as Cu, V, Ni, and Mo (~10 wt% total). These are stronger that low carbon steels are not made to meet specific chemical composition, but rather to meet specific mechanical properties.

Answer 13

High Strength Low Alloy Steels

Question 14

This low alloy steel is heat-treatable with tempered martensite as the most common form. This is used in tracks, gears, and high strength structural components. It contains 0.25-0.60% carbon.

Answer 14

Medium Carbon Steels

Question 15

This low alloy steel is wear resistant and is capable of holding sharp edges. It is used in cutting tools, dies, razors, blades, springs, and high strength wires. It contains 0.60-1.40 wt% carbon.

Answer 15

High Carbon Steels

Question 16

This type of steel has alloying elements that are intentionally added in specific concentrations to improve specific properties.

Answer 16

High Alloy Steels

Question 17

This type of high alloy steel is mainly used for general machine parts where strength, wear resistance, and dimensional stability are required. These are mainly used for tools.

Answer 17

Tool Steels

Question 18

This type of high alloy steel is highly resistant to corrosion in a variety of environments. They are utilized in gas turbines, high temperature boilers, heat treating furnaces, and aircrafts. It contains at least 11% Cr that forms chromium oxide, a film that effective protects the steel against many corrosive media (passivation effect).

Answer 18

Stainless Steel

Question 19

This type of stainless steel responds to heat treatment. It contains 11.5-18% Cr.

Answer 19

Martensitic Stainless Steel

Question 20

This stainless steel does not respond to heat treatment but is hardenable by cold working. It contains ~14-27% Cr and is low in carbon content. Its primary constituent exists at room temperature.

Answer 20

Ferritic Stainless Steel (ferrite, alpha)

Question 21

This stainless steel has its primary constituent at room temperature. It is the chromium-nickel (3xx) and chromium-nickel-manganese (2xx) type of stainless steel. The total Ni and Cr content is at least 23%. It is not heat-treatable but is hardenable by cold working.

Answer 21

Austenitic Stainless Steel

Question 22

This is the type of a ferrous alloy that has low melting points but are generally brittle. It is characterized by the existence of graphite instead of cementite. The graphite formation is promoted by the presence of silicon in amounts greather than 1 wt% and slow cooling rates. It contains more than 2 wt% carbon.

Answer 22

Cast Irons

Question 23

This is the type of cast iron that contains 2.5-4.0 wt% carbon (hypoeutectic) and 1.0-3.0 wt% silicon. The graphite exists in the form of flakes and acts as stress concentrator. It is effective in damping vibrational energy and is wear resistant. It is also the least expensive among metals.

Answer 23

Gray Cast Iron

Question 24

This type of cast iron has magnesium. It is stronger and more ductile, and is commonly applied in valves, pump bodies, and gears. The presence of magnesium promotes the formation of spheroids. It is also called spheroidal graphite iron or spherulitic iron.

Answer 24

Nodular or ductile cast iron

Question 25

This cast iron contains low amounts of silicon, hence carbon exists as cementite and not graphite. All cast irons under this classification are hypoeutectic alloys. Its typical microstructure contains dendrites of transformed austenite (pearlite) in an interdendritic network of cementite. It is harder, more brittle, and difficult to machine. It serves as the starting material for malleable iron.

Answer 25

White Cast Iron

Question 26

This cast iron is produced from heating up white cast irons to 800-900 deg. Celsius for a prolonged period of time causing decomposition of cementite and eventually forming graphite (tempered carbon). It is relatively high in strength and has appreciable ductility. It is used for connecting rods, transmission gears, differential cases for cars, pipe fittings, valve parts for railroad, marine, and other heavy-duty services. The tempered carbon exists in clusters or rosettes.

Answer 26

Malleable Cast Iron

Question 27

These classification of alloys is utilized primarily because of their unique properties in specific applications.

Answer 27

Non-ferrous Alloys