Principal Engineering Alloys

Question 1

What are High Strength Low Alloy (HSLA) steels. How are they produced and what are their typical yield strength?

Answer 1

Microalloyed Steel

Combined effect of selective alloying and thermo-mechanical (accurately controlled) treatment.

Yield SStrength: 450-600 MPa

Question 2

What is the effect of grain size on strength ?

What is the relationship that governs this?

Answer 2

Fine grain size; increased yield strength.

Hall-Petch Relationship:

Question 3

Benefits of HSLA ?
5 Points
(I Hate All Ginger Inbreds)

Answer 3

1. Improved low temp toughness
2. High strength to weight ratio.
3. Available in sheet bar, plate and tube.
4. Good manufacturability.
5. Increased yeild strength.

Question 4

Define weld decay?

Answer 4

intergranular corrosion
only applies to austenitic steels
result of sensitization in the heat-affected zone during the welding operation.
The corrosive attack is restricted to the heat affected zone (HAZ).

Question 5

Prevention action for weld decay?

Answer 5

(1) subjecting the sensitized material to a high-temperature heat treatment
to redissolve chromium carbide particles
(2) lowering the carbon
content below 0.03 wt% C so that carbide formation is minimal, and (3) alloying
the stainless steel with another metal such as niobium or titanium, which has a
greater tendency to form carbides than does chromium so that the Cr remains in
solid solution.

Question 6

Prevention action for weld decay? (3 points)

Answer 6

(1) subjecting the sensitized material to a high-temperature heat treatment
to redissolve chromium carbide particles
(2) lowering carbon
content below 0.03 wt% C so that carbide formation is minimal
(3) alloying the stainless steel with another metal such as niobium or titanium, these carbides will remain in
solid solution.

Question 7

What are stainless steels ? (4 Points)

Answer 7

1. Corrosion Resistant ferrous Alloys containing at least 11wt% Cr
2. Chromium forms passive, corrosion resistant layer on steel surface.
3. There are different types of steels with specific attributes.
4. final properties dictated by:
   - Alloy comp
   - Processing
   - Microstructure

Question 8

8 benefits of stainless steel?

Answer 8

1. Many grades available
2. Good Corrosion resistance
3. Very high strength (duplex and superaustenitics)
4. Austenitics are non magnetic
5. Aesthetically appealing
6. Good low temperature
7. Reasonable manufacturability
8. wide range of applications

Question 9

4 strong points and 2 limitations of stainless steel?

Answer 9

Strong Points:

1. Low Density
2. High Electrical&Thermal conductivity
3. High corrosion resistance
4. High Ductility

Limitations:

1. Low melting point.
2. High coefficient of thermal expansion.

Question 10

Define precipitation hardening?

Answer 10

Formation of extremely small uniformly dispersed particles of a second phase with the original phase matrix.

Accomplished by phase transformations.

New phases are called precipitates.