For shock resisting steels used in tools and machine parts, which mechanical property must be particularly high so that the steel can absorb sudden impact loads without failure?

Introduction / Context:
This question relates to material science and mechanical engineering, focusing on the design of shock resisting steels. Such steels are used in situations where components experience sudden impact loads, like hammers, chisels, springs, and certain machine parts. Knowing which property is most important helps in selecting and designing appropriate alloys for engineering applications.

Given Data / Assumptions:

• The material is shock resisting steel.
• The application involves sudden impact or shock loads.
• We are asked which property this steel should possess.
• Options include toughness, low wear resistance, low tensile strength, low hardness, and very high brittleness.

Concept / Approach:
Toughness is the ability of a material to absorb energy before fracturing. It combines strength and ductility. For components that must withstand sudden shocks, toughness is critical because the material must absorb impact energy without cracking. Low wear resistance, low tensile strength, low hardness, or high brittleness are undesirable. Therefore, the correct answer is the property that allows energy absorption under shock loading, namely toughness.

Step-by-Step Solution:

Verification / Alternative check:
Engineering handbooks and material data sheets for shock resisting tool steels frequently highlight their impact toughness and Charpy impact values. These steels are often tempered to achieve a balance of hardness and toughness. Testing methods such as impact tests explicitly measure toughness under shock loading. In contrast, properties like low wear resistance or low hardness are not features of high performance steels for shock applications. This confirms that toughness is the desired property.

Why Other Options Are Wrong:

• Low wear resistance: Components exposed to repeated impact often also face wear; low wear resistance is not an advantage.
• Low tensile strength: Shock resisting steels must have adequate strength to carry loads, not low strength.
• Low hardness: While extreme hardness can reduce toughness, too low hardness will not provide durability or wear resistance.
• Very high brittleness: Brittle materials fail suddenly under shock, which is exactly what engineers want to avoid.

Common Pitfalls:
A common mistake is to confuse hardness with toughness. Hard materials resist scratching and indentation but are not always good at absorbing impact energy. Another error is to assume that any very strong material will also resist shock, even if it is brittle. In reality, a balance of strength and ductility is needed, and that combination is captured by the concept of toughness. Remembering this helps in many exam questions about materials used in tools, springs, and structural components.

Final Answer:
Shock resisting steels should have high Toughness so that they can absorb sudden impact loads without failure.