Materials and Materials Processing: Properties, Heat Treatment, and Joining
Properties, processes, and weldability
Materials questions test whether you can connect a service requirement to a property, a process, and a code allowable. Know the property definitions before the alloy names.
Concepts to master. Elastic modulus, yield and ultimate strength, ductility (percent elongation, reduction of area), hardness, toughness (Charpy), fatigue strength, creep and stress rupture; ferrous and nonferrous families (carbon and alloy steel, stainless, cast iron, aluminum, copper, titanium); heat treatment-annealing, normalizing, quench-and-temper, case hardening, nitriding; welding processes (SMAW, GMAW, GTAW, SAW), preheat and postweld heat treatment, weld defects; forming processes (casting, forging, rolling) and their anisotropy and residual stress; corrosion forms including galvanic attack and hydrogen embrittlement; NDT methods; ASME Section II (materials) and Section IX (welding qualification).
Common traps. Treating hardness as a direct strength measurement (conversions are empirical and alloy-specific); assuming any heat treatment improves toughness-quenching without tempering makes high-strength steel brittle; ignoring directionality from rolling or forging; forgetting that high-strength steels are susceptible to hydrogen embrittlement; selecting a material without checking allowable stress at the design temperature.
Worked rule of thumb (carbon equivalent). CE = C + Mn/6 + (Cr+Mo+V)/5 + (Ni+Cu)/15. For C = 0.25, Mn = 1.2, and Cr = 0.5: CE = 0.25 + 0.20 + 0.10 = 0.55. Because CE exceeds 0.40, specify preheat and a qualified welding procedure. Keeping CE at or below about 0.40 generally avoids hydrogen-assisted cracking in structural steels.