Which factor most improves the fatigue resistance of steel?

Which factor most improves the fatigue resistance of steel?

• A. Higher hardness
• B. Refined grain structure through heat treatment
• C. Increased brittleness
• D. Decreased toughness

Answer: (B)

Refining the grain structure in steel improves fatigue resistance. Finer grains create more grain boundaries, which act as barriers to dislocation motion and to the growth of cracks under cyclic loading. This makes crack initiation harder and slows crack propagation, boosting the fatigue life. The effect is often described by the Hall–Petch relationship: smaller grain size increases strength and toughness, helping the material withstand repeated stresses without developing or growing fatigue cracks. Heat treatment can achieve this refinement by controlling heating and cooling to produce a finer, more uniform microstructure. Higher hardness alone doesn’t guarantee better fatigue life; it can reduce toughness and make cracks easier to propagate. Increased brittleness or decreased toughness generally harms fatigue performance, so the grain-refining approach through heat treatment best enhances fatigue resistance.

Refining the grain structure in steel improves fatigue resistance. Finer grains create more grain boundaries, which act as barriers to dislocation motion and to the growth of cracks under cyclic loading. This makes crack initiation harder and slows crack propagation, boosting the fatigue life. The effect is often described by the Hall–Petch relationship: smaller grain size increases strength and toughness, helping the material withstand repeated stresses without developing or growing fatigue cracks. Heat treatment can achieve this refinement by controlling heating and cooling to produce a finer, more uniform microstructure.

Higher hardness alone doesn’t guarantee better fatigue life; it can reduce toughness and make cracks easier to propagate. Increased brittleness or decreased toughness generally harms fatigue performance, so the grain-refining approach through heat treatment best enhances fatigue resistance.