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A product of a displacive transformation. In carbon steel, rapid cooling can trap carbon in a distorted iron lattice, producing high hardness and low as-quenched toughness.

As-quenched martensite generally has greater hardness and strength, but lower ductility and toughness, than ordinary pearlitic steel. Its supersaturated carbon and distorted lattice impede dislocation glide; quench stresses also promote cracking. Pearlite combines hard cementite lamellae with more deformable ferrite, with finer spacings generally giving greater strength. Austenitize, quench to martensite, then temper to obtain a useful compromise between indentation resistance and resistance to fast fracture. Tempering below the austenitizing range relieves stresses and develops a fine carbide-containing microstructure. It trades some maximum hardness for improved toughness; the temperature and time must suit the required balance.

Both outer faces of the cantilever are loaded, so use the pine's lower longitudinal compressive strength, $40\mathrm{MPa}$, rather than its $85\mathrm{MPa}$ tensile strength. Consistent SI units give $M_A$ values $(2.564,2.143,0.7273)\times 10^5{\mathrm{m}}^2{\mathrm{s}}^{-2}$ for steel, aluminium and pine respectively. Their $M_B$ values are $5.734,8.748,11.499\mathrm{P}{\mathrm{a}}^{1/2}{\mathrm{m}}^3\mathrm{k}{\mathrm{g}}^{-1}$. Hence Design A: steel best, pine worst; Design B: pine best, steel worst. Aluminium is intermediate in both cases. These rankings concern the stated strength constraint; a toughness or deflection constraint could change feasibility.

Check stiffness and tip deflection using Young's modulus, failure from existing cracks using fracture toughness or the supplied critical energy-release rate, local crushing at supports, shear failure, buckling, fatigue and joint design. In a simple linear-elastic crack model, $K_c^2\simeq E^{\prime }{G}_c$, so toughness cannot be inferred from strength alone. Wood also has grain-direction dependence, moisture sensitivity, natural defects, property scatter and time-dependent creep; the design must control grain alignment and compression-side stability. Metals raise issues of corrosion, mass, joining, machining, residual stress and heat-treatment state. Cost, availability, reproducibility, service temperature and end-of-life treatment can decide between otherwise feasible designs. A high merit index is a screening result, not a complete safety specification.

Heating quenched steel below the austenitizing range to adjust its microstructure and relieve stresses. Carbon redistribution and carbide formation can improve toughness at a cost in hardness.