Materials and Manufacturing Processes
What this domain tests
Materials and Manufacturing Processes covers property definitions, material selection trade-offs, and the process signatures that create defects. Expect questions on heat treatment, weldability, and matching a manufacturing route to a tolerance and volume.
Core rules
- Yield strength marks the onset of plastic strain; ultimate tensile strength is the maximum stress; hardness is resistance to indentation; toughness is energy absorbed to fracture.
- Annealing softens and relieves stress; normalising refines grain structure; quench-and-temper trades hardness against toughness.
- Weldability is estimated by carbon equivalent: CE = C + Mn/6 + (Cr + Mo + V)/5 + (Ni + Cu)/15. Values above roughly 0.40 typically call for preheat and a qualified welding procedure.
- Each process has a signature defect: casting gives porosity and shrinkage; welding gives lack of fusion and a hardened heat-affected zone; machining gives residual stress and tool marks; additive manufacturing gives anisotropy and porosity.
Worked example
A steel has C 0.18, Mn 1.20, Cr 0.10, Mo 0.02, Ni 0.05, Cu 0.02 (wt%). CE = 0.18 + 1.20/6 + (0.10 + 0.02)/5 + (0.05 + 0.02)/15 = 0.18 + 0.20 + 0.024 + 0.005 ≈ 0.41. That sits just above the 0.40 threshold, so the correct answer is to specify preheat and a qualified WPS, or to select a lower-CE grade - not to assume the parent metal chemistry is adequate.
Traps
Comparing hardness values across different material classes as if they were strength; assuming a matching filler metal gives matching properties; ignoring the heat-affected zone as the likely weakest point; and specifying a tolerance or surface finish the chosen process cannot hold in production.