A toolmaker needs to case harden the surface of a mild steel gear wheel so that the teeth resist wear while the core remains tough. (a) State what case hard...
Question 1 Report
A toolmaker needs to case harden the surface of a mild steel gear wheel so that the teeth resist wear while the core remains tough.
(a) State what case hardening does to the surface of mild steel. [1]
(b) Name the carbon-rich material used in the pack cementation method of case hardening. [1]
Answer Details
(a) Case hardening increases the carbon content of the surface layer of mild steel, transforming it into a hard, wear-resistant outer case. [1] Mild steel normally contains only about 0.1-0.3% carbon, which is too soft for surfaces that must resist abrasion. By adding carbon to the outer 1-2 mm, the surface becomes significantly harder while the inner core retains its original toughness and ductility. This combination is ideal for a gear wheel: the teeth resist wear at the contact surfaces, yet the body of the gear can absorb shock loads without fracturing.
(b) Charcoal (carbon powder or granules). [1] In the pack cementation method, the mild steel component is packed into a heat-resistant box surrounded by charcoal and heated to approximately 900-950 °C for several hours. At this temperature, carbon atoms migrate from the charcoal into the steel surface by diffusion. Bone meal or proprietary compounds such as Kasenit are also accepted as the carbon-rich packing material.
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