Explain why a fully hardened steel would need to be tempered. Support your answer with a labelled sketch of the resulting tempered microstructure. (4 marks) --- 7 WORK AREA LINES (style=lined) --- Exemplar solution 1: → Steel in its fully hardened state exhibits extreme brittleness, limiting its practical applications and making it vulnerable to failure. → When exposed to abrupt forces or stress concentrations, fully hardened steel can develop cracks or break catastrophically due to its inability to deform. → The tempering process plays a vital role in optimising steel’s mechanical properties, creating an essential balance between hardness and toughness. → Through careful tempering, the steel’s characteristics can be precisely tuned to match specific operational requirements, ensuring reliable performance across diverse applications. → Martensite by hardening: Exemplar solution 2: → The tempering process serves as a crucial follow-up treatment after quenching, specifically designed to mitigate the steel’s brittle characteristics. → The procedure involves carefully reheating the hardened steel to a temperature below its critical point, followed by another cooling cycle. → This methodical heating and cooling sequence helps release internal stresses that developed during the initial quenching phase. → Through tempering, manufacturers can precisely adjust the balance between the steel’s hardness and toughness to achieve desired mechanical properties. → Ferrite and finely dispersed cementite: Exemplar solution 1: → Steel in its fully hardened state exhibits extreme brittleness, limiting its practical applications and making it vulnerable to failure. → When exposed to abrupt forces or stress concentrations, fully hardened steel can develop cracks or break catastrophically due to its inability to deform. → The tempering process plays a vital role in optimising steel’s mechanical properties, creating an essential balance between hardness and toughness. → Through careful tempering, the steel’s characteristics can be precisely tuned to match specific operational requirements, ensuring reliable performance across diverse applications. → Martensite by hardening: Exemplar solution 2: → The tempering process serves as a crucial follow-up treatment after quenching, specifically designed to mitigate the steel’s brittle characteristics. → The procedure involves carefully reheating the hardened steel to a temperature below its critical point, followed by another cooling cycle. → This methodical heating and cooling sequence helps release internal stresses that developed during the initial quenching phase. → Through tempering, manufacturers can precisely adjust the balance between the steel’s hardness and toughness to achieve desired mechanical properties. → Ferrite and finely dispersed cementite:
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♦♦ Mean mark 32%.
