AIT Material Science 3 — Questions and Answers
Question 1: Which stainless steel series is most commonly used in trade applications due to its good corrosion resistance and weldability?
- 200 series
- 300 series (austenitic) (Correct answer)
- 400 series (ferritic)
- 500 series
Correct answer: 300 series (austenitic)
The 300 series austenitic stainless steels, such as 304 and 316, are most widely used because of their excellent corrosion resistance and weldability.
Question 2: What does the Rockwell hardness test measure?
- The depth of indentation made by a standard indenter under a fixed load (Correct answer)
- The surface energy of a material
- The tensile strength at yield point
- The impact energy absorbed by a specimen
Correct answer: The depth of indentation made by a standard indenter under a fixed load
The Rockwell hardness test measures material hardness by the depth of penetration of an indenter under a specific load.
Question 3: Which alloying element is added to steel to improve its hardenability and wear resistance in tool steels?
- Lead
- Sulfur
- Chromium (Correct answer)
- Copper
Correct answer: Chromium
Chromium improves hardenability, wear resistance, and corrosion resistance in steel alloys.
Question 4: What is the primary advantage of using aluminum alloys over pure aluminum in structural applications?
- Lower cost
- Higher density for better performance
- Significantly improved strength (Correct answer)
- Better electrical conductivity
Correct answer: Significantly improved strength
Alloying aluminum with elements like copper, magnesium, or silicon greatly increases its strength while maintaining its light weight.
Question 5: In welding and metal fabrication, what is 'scale' that forms on heated steel?
- A protective zinc coating
- Iron oxide formed during heating (Correct answer)
- A flux residue from welding rods
- A type of surface finish
Correct answer: Iron oxide formed during heating
Scale is iron oxide (FeO, Fe2O3, Fe3O4) that forms on the surface of steel when it is heated in the presence of oxygen.
Question 6: Which process is used to increase the surface hardness of a steel part while keeping its core tough?
- Full annealing
- Case hardening (Correct answer)
- Stress relieving
- Spheroidizing
Correct answer: Case hardening
Case hardening (carburizing, nitriding, induction hardening) creates a hard outer shell while preserving a tough, ductile core.
Question 7: What is the primary purpose of adding manganese to steel?
- To improve electrical conductivity
- To deoxidize and increase strength and hardenability (Correct answer)
- To lower the carbon content
- To reduce brittleness at high temperatures
Correct answer: To deoxidize and increase strength and hardenability
Manganese acts as a deoxidizer, increases strength, hardenability, and counters the harmful effects of sulfur in steel.
AIT Material Science 3
Which stainless steel series is most commonly used in trade applications due to its good corrosion resistance and weldability?