CFS Fastener Materials & Manufacturing 3 — Questions and Answers
Question 1: Which stainless steel grade is most susceptible to sensitization (carbide precipitation) when welded?
- Type 304 (Correct answer)
- Type 316L
- Type 347
- Type 410
Correct answer: Type 304
Type 304 stainless steel is susceptible to sensitization because its carbon content can form chromium carbides at grain boundaries during welding.
Question 2: What is the Rockwell hardness scale typically used to measure hardness of standard steel fasteners?
- Rockwell A (HRA)
- Rockwell B (HRB)
- Rockwell C (HRC) (Correct answer)
- Rockwell F (HRF)
Correct answer: Rockwell C (HRC)
The Rockwell C scale (HRC) is the standard for measuring hardness of heat-treated steel fasteners, using a diamond indenter.
Question 3: Silicon bronze fasteners are preferred in marine environments primarily because they offer:
- Higher tensile strength than stainless steel
- Excellent corrosion resistance without galvanic issues with copper alloy fittings (Correct answer)
- Lower cost than carbon steel
- Better thread engagement than aluminum
Correct answer: Excellent corrosion resistance without galvanic issues with copper alloy fittings
Silicon bronze resists corrosion in marine environments and is galvanically compatible with copper alloy fittings, preventing galvanic corrosion.
Question 4: Which cold heading operation forms the head of a bolt by upsetting the wire blank?
- Trimming
- Pointing
- Extrusion
- Upsetting (Correct answer)
Correct answer: Upsetting
Upsetting compresses the end of a wire blank axially, causing the metal to flow radially outward to form the fastener head.
Question 5: What minimum tensile strength (psi) is required for an SAE Grade 5 bolt?
- 60,000 psi
- 74,000 psi
- 120,000 psi (Correct answer)
- 150,000 psi
Correct answer: 120,000 psi
SAE Grade 5 bolts have a minimum tensile strength of 120,000 psi for diameters up to 1 inch.
Question 6: The term 'proof load' for a fastener refers to:
- The load at which the fastener fractures
- The maximum axial load the fastener must withstand without permanent deformation (Correct answer)
- The torque required to seat the fastener
- The load applied during proof testing before shipment
Correct answer: The maximum axial load the fastener must withstand without permanent deformation
Proof load is the specified load a fastener must sustain without any measurable permanent deformation, representing the elastic limit.
Question 7: Which material property describes a fastener's ability to absorb energy before fracturing?
- Hardness
- Toughness (Correct answer)
- Yield strength
- Elastic modulus
Correct answer: Toughness
Toughness is the ability of a material to absorb energy (area under the stress-strain curve) without fracturing, combining strength and ductility.
CFS Fastener Materials & Manufacturing 3
Which stainless steel grade is most susceptible to sensitization (carbide precipitation) when welded?