Workshop practice — heat treatment at the cutting edge of a hand chisel For durable service in general fitting and bench work, the cutting edge of a cold chisel should be finished by which treatment so that it is hard enough to cut yet not so brittle that it chips during use?

Introduction / Context:A bench or cold chisel is a common hand tool used to cut or shear metals. If its edge is too soft, it will mushroom or blunt quickly; if it is too hard, it may chip and fail dangerously. This question tests your understanding of the correct heat-treatment sequence for a tough yet wear-resistant cutting edge.

Given Data / Assumptions:

• The tool is a carbon steel or alloy steel hand chisel used on mild steel or similar materials.
• Service requires a balance between hardness (edge retention) and toughness (resistance to chipping).
• Heat treatments available: hardening, tempering, case hardening, normalizing.

Concept / Approach:Hardening (austenitize then quench) produces a very hard martensitic structure, but also a highly brittle edge. Tempering (reheating below the critical range) reduces brittleness and restores toughness by controlled relief of internal stresses and transformation of martensite to tempered martensite. The combination “harden + temper” is standard for cutting tools that experience impact and wedging, such as chisels.

Step-by-Step Solution:Heat the cutting end to the appropriate austenitizing temperature (colour indications are often used in workshop practice).Quench (commonly in water or oil) to harden the edge fully; the edge is now very hard but brittle.Immediately temper by reheating to a lower temperature (observing temper colours such as pale straw to purple depending on the required hardness) and then quench or air cool.Result: tempered martensite at the edge gives adequate hardness with improved toughness.

Verification / Alternative check:Practical guides prescribe hardening and tempering for chisels; a simple shop test is to observe reduced chipping and sustained sharpness after tempering versus untempered hardened tools.

Why Other Options Are Wrong:

• Hardened only: too brittle, prone to chipping.
• Tempered only: tempering without prior hardening cannot create a hard edge.
• Case hardened: creates a thin hard case on low-carbon steels, not ideal for a shock-loaded wedge.
• Normalized only: refines grain but lacks the required high edge hardness.

Common Pitfalls:Confusing tempering with annealing; annealing softens too much, while tempering fine-tunes hardness after quenching.

Final Answer:hardened and tempered