Mechanical design—properties required for shock resisting steels Shock resisting steels should predominantly exhibit high which property?

Introduction / Context:
Components subjected to impact, sudden loads, or dynamic conditions require steels capable of absorbing energy without fracturing. The material choice for chisels, hammers, pneumatic tools, and impact-loaded parts emphasizes resistance to crack initiation and propagation under shock loading.

Given Data / Assumptions:

• Service involves sudden or repeated impact rather than steady static loads.
• Failure modes include brittle fracture and fatigue crack growth under dynamic stress.

Concept / Approach:
Toughness is the ability to absorb energy up to fracture and is the key property for shock resistance. While hardness contributes to wear resistance and tensile strength describes load-bearing capacity under static conditions, neither alone ensures survival under impact. A balanced microstructure with adequate ductility prevents brittle cracks from advancing. Alloy design and heat treatment aim to produce tempered martensite or bainitic structures with high Charpy impact energy, ensuring reliable performance under shock.

Step-by-Step Solution:

Verification / Alternative check:
Standards for shock resisting tool steels (e.g., S-series) specify high impact toughness values and tempered microstructures, confirming design emphasis on toughness.

Why Other Options Are Wrong:

• Hardness: improves wear resistance but can increase brittleness if excessive.
• Tensile strength: valuable for static loads; high strength without toughness can be catastrophic under shock.
• Wear resistance: useful for abrasion, not chiefly for impact survival.

Common Pitfalls:
Over-hardening a steel for wear without ensuring sufficient toughness, leading to spalling or brittle fracture under impact.

Final Answer:
toughness