Grain size effects in steels — properties of fine-grained steel Which statement best describes the typical mechanical behavior of fine-grained steel, including its tendency to distort during heat treatment?

Introduction / Context:
Prior-austenite grain size (and resulting ferrite/pearlite packet size) strongly affects strength, ductility, and toughness. Fine grains increase grain boundary area, which impedes crack initiation and slip, raising toughness while aiding dimensional stability during thermal cycles.

Given Data / Assumptions:

• Comparing fine-grained and coarse-grained steels of similar composition.
• Conventional heat treatments (normalizing, quenching, tempering).
• Distortion considered as a result of nonuniform transformation and thermal gradients.

Concept / Approach:
Hall–Petch behavior states yield strength increases as grain size decreases. Toughness also generally benefits because cracks are deflected or blunted by frequent boundaries. During heat treatment, finer and more uniform transformation structures reduce internal stresses and dimensional changes, lowering distortion risk compared with coarse-grained materials that transform nonuniformly and can exhibit higher residual stresses.

Step-by-Step Solution:

Verification / Alternative check:
Charpy data and dimensional stability studies show improved impact energy and reduced warpage for fine-grained steels after quench and temper compared with coarse-grained equivalents.

Why Other Options Are Wrong:

• Options suggesting “less tough” contradict well-known trends.
• “Greater tendency to distort” is inconsistent with finer, more uniform transformations.
• “Always more brittle” is incorrect; fine grains usually reduce brittleness.

Common Pitfalls:
Assuming higher strength always reduces ductility drastically; overlooking the role of alloy carbides and heat treatment uniformity.

Final Answer: