Exam III

Question 1

CORROSION

Explain cathodic protection.

Example?

Answer 1

The protection of a cathode by a sacrificial anode that takes on the corrosion.

Magnesium plate on steel pipe.

Question 2

CORROSION

Explain anodic protection.

Example?

Answer 2

Creation of a passive film on the surface of the anode to block corrosion by passing electric current through the anode and changing it’s potential.

304 stainless steel in phosphoric acid can be protected with it.

Question 3

CORROSION

What is a sacrificial anode?

Example?

Answer 3

A piece of metal (typically high on the galvanic chart) that is delibrately corroded to protect another metal.

Zinc corroding instead of Copper!

Question 4

CORROSION

What are the 8 design changes to reduce corrosion?

Answer 4

1) Crevice control
2) No metals mixing
3) Corrosion allowance
4) Anodic protection
5) Cathodic protection
6) Welding practices
7) Stagnant areas
8) Hot spots

Question 5

CORROSION

What are the 7 environmental controls that reduce corrosion?

Answer 5

1) pH
2) Temperature
3) Velocity
4) Concentration
5) Inhibitors
6) Cleaning
7) Aeration

Question 6

CORROSION

What are the 6 material selectoins that reduce corrosion?

Answer 6

1) Coatings
2) Cladding
3) Heat treatment
4) Diffusion treatments
5) Corrosion data
6) Surface finish

Question 7

CORROSION

Explain galvanizing.

Answer 7

It is the act of putting a physical coundary in place to protect a metal (i.e. cathodic protection or zinc coating).

Question 8

CORROSION

Define cladding.

How different from coating?

Answer 8

It is when a protective layer is bonded to the base metal!

Is thick while coating is thin.

Question 9

STAINLESS STEELS

Which stainless steel is described?
* magnetic
* poor weldability
* BCC
* non-heat treatable
* <0.2% C & 15-20% Cr

Answer 9

Ferritic Stainless Steel

Question 10

STAINLESS STEELS

Which stainless steel is described?
* magnetic
* poor weldability
* BCT
* heat treatable
* <1.2% C & 12-18% Cr

Answer 10

Martensitic Stainless Steel

Question 11

STAINLESS STEELS

Which stainless steel is described?
* non-magnetic
* weldability
* FCC
* non-heat treatable
* v low C, 16-26% Cr, 8-24% Nickel

Also, has ternary phase diagram

Answer 11

Austenitic Stainless Steel

Question 12

STAINLESS STEELS

What is the sigma phase? When does it occur and is it desirable?

Answer 12

Sigma phase is a hard, brittle intermetallic phase that forms during long-term exposure to high temps or post-weld heat treatments. It’s undesirable because it makes it more brittle and less tough/ corrosion resistant.

Question 13

STAINLESS STEELS

Physical Properties of Stainless Steel:
density, thermal conductivity, electrical resistivity, series number, coefficient of thermal expansion, & modulus of elasticity?

(Compared to steel)

Answer 13

1) Density: about the same
2) Thermal conductvity: less than half
3) Electrical resistivity: x6 as much
4) Series number: 300 series
5) Coef. of Thermal Expansion: 50% greater
6) Modulus of Elasticity: 28-29 x 10^6 psi (slightly lower)

Question 14

STAINLESS STEELS

Mechanical Properties of Stainless Steel:
tensile strength, yield strength, percent elongation, and impact strenght?

(Compared to steel)

Answer 14

1) Tensile Strength: all stainless are greater
2) Yield Strength: all stainless are same or greater
3) Percent Elongation: all greater except 430, 446, 430F, 420, & 440C
4) Impact Strength: all much greater except 430, 446, 430F, & 440C

Question 15

STAINLESS STEELS

How/why/what sensitization develops, what it is?

Answer 15

It is when chromium makes CrC instead of CrO; caused for elongated heat exposure and high carbon (800-1500); leads to intergranular attacks bc CrC gathers at grain boundaries.

Question 16

STAINLESS STEELS

What are the times needed to allow sensitization for stainless steel? (304 & 304L)

Answer 16

304: 2-3 minutes
304L: 1 hour

Question 17

STAINLESS STEELS

What are 4 methods used to prevent sensitization?

Answer 17

1) low-carbon stainless steel
2) adding alloy (like titanium) to bond w/ C instead of Cr
3) annealing (heat to high temp and quench to dissolve bonds)
4) avoid sensitization temperature range all together

Question 18

STAINLESS STEELS

What are stabilized stainless steels? What alloying elements support this?

Answer 18

Alloyed steels that have increased protection from intergranular attacks. Elements: titanium, niobium, and tantalum.

Question 19

STAINLESS STEELS

Define stress corrosion cracking.

Answer 19

A form of corrosion where a material under tensile stress is weakened by a corrosive environment, leading to crack initiation and propagation.

Question 20

STAINLESS STEELS

What are the 3 uses for: ferritic stainless steels?

Which ones are the focus?

Answer 20

1) Atmospheric corrosion
2) Elevated temperatures
3) Decorative

430, 430F, 446

Question 21

STAINLESS STEELS

What are the 3 uses for: martensitic stainless steels?

Which ones are the focus?

Answer 21

1) Structural components
2) Cutting devices
3) Tools

403, 410, 416, 420, 440C

Question 22

STAINLESS STEELS

What are the 3 uses for: austenitic stainless steels?

Which ones are the focus?

Answer 22

1) Chemical resistances
2) Tanks
3) Piping

302, 303, 304, 316, 304L, 316L

Question 23

STAINLESS STEEL

What are all of the things that stainless is generally susceptible to?

Answer 23

• pitting
• crevice corrosion
• attack in chloride and reducing acids (bleach/sea)
• stress corrosion cracking
• intergranular corrosion when sensitized
• galvanic corrosion between grains

Question 24

STAINLESS STEEL

What are the applications of ferritic stainless steel’s 430, 430F, & 446?

Answer 24

403: corrosion resistance to acids, cheap cutlery, resistant to stress corrosion cracking
430F: sulfur added for machinability, fasteners
446: high Cr, scaling resistance, furnace parts

Question 25

# STAINLESS STEEL What are the applications of **martensitic stainless steel**'s 403, 416, 420, & 440C?

Answer 25

**403**: high temperature turbine parts **416**: free machining, fasteners **420**: cutlery, surgical instruments, tools, wear **440C**: tooling, wear, highest hardness and abrasion resistance

Question 26

# STAINLESS STEEL What are the applications of **austenistic stainless steel**'s 302, 303, 304, 304L, 316, 316L?

Answer 26

**302**: gasoline **303**: sulfur for free machining, not as good corrosion resistance **304**: gasoline **304L**: same as 304 when welding/stress relieving are required **316**: resists sulfuric acid (extreme temps) and nitric acid (reg temp), good gasoline, chemical service **316L**: same as 316 when welding/stress relieving are required

Question 27

# STAINLESS STEEL What are the alloys of each series? | 200, 300, 400, 500

Answer 27

**200**: Cr, Ni, Mn **300**: Cr, Ni **400**: Cr, Fe **500**: Cr

Question 28

# CAST IRONS What are the 4 types of cast iron and purposes?

Answer 28

1) White: hard and wear resistant 2) Malleable: heat treated for ductility 3) Grey: general purpose 4) Ductile: some ductility as cast

Question 29

# CAST IRONS As grade of **grey** cast iron increases, what else increases? What decreases?

Answer 29

**Increase:** * all strengths * quality of finish * wear resistance * modulus of elasticity **Decrease:** * ability to dampen vibrations * resistance to thermal shock * machinability * castability