smc-3719-35-Tempering/Hardening

ENGINEERING, PPT 2024 HSC 24d

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)

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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:

Show Worked Solution

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:

♦♦ Mean mark 32%.

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:

ENGINEERING, PPT 2018 HSC 14 MC

Which row of the table correctly describes the property changes that occur after tempering quench-hardened steel?

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`A`

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Tempering of hardened steel is designed to reduce the brittleness of the material without significantly impacting its hardness (minimal loss).
This increases the toughness as tempering usually involves an increase in ductility.

`=>A`

Mean mark 51%.

ENGINEERING, PPT 2020 HSC 25b

Members of steel trusses are often connected using metal rivets as shown.

Describe the hot working process that the rivet has undergone to create the resulting structure. Support your answer by completing and labelling the diagram of the sectioned rivet. (3 marks)

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For hot working to be successful, the rivet has to be heated above the recrystallisation temperature of the material.
A riveting gun is then used to hot forge the head of the rivet into place.
This causes grain flow to form around the head of the rivet, as shown in the image above.

Show Worked Solution

For hot working to be successful, the rivet has to be heated above the recrystallisation temperature of the material.
A riveting gun is then used to hot forge the head of the rivet into place.
This causes grain flow to form around the head of the rivet, as shown in the image above.

♦♦♦ Mean mark 26%.

ENGINEERING, PPT 2020 HSC 18 MC

The grain structure of a material has changed over time from that shown in microstructure `A` to that shown in microstructure `B`.

What heat treatment process has the material undergone to cause this change?

Tempering
Normalising
Quench hardening
Precipitation hardening

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`D`

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Of the answers presented, precipitation hardening is the only form of heat treatment that causes `alpha` and `beta` to dissolve into a single phase alloy as shown in Microstructure B.

`=>D`

♦♦ Mean mark 33%.