Engineering · Past QCAA questions All past questions
2025 · Section 2 · Short response

Question 12

[5 marks] Likely simple familiar
Topic guidesPremiumTopic guide 10 · Contrasting two steelsTopic guide 10 · Microstructures and the properties they give
Game plansPremiumTemplate T4 Compare or contrast4.4 Explaining or comparing a steel
The question

An engineer is developing a knife for use in an industrial workshop. They have access to mild carbon steel (0.25% carbon) and high carbon steel (1.1% carbon).

Compare the mechanical properties of the materials to determine the most appropriate choice for the application. Justify your choice with reference to the microstructures.

Watch the situation first

The soft ferrite in mild steel lets its edge wear away, while the cementite in high carbon steel keeps the edge sharp

Two blade edges, seen end on, make the same four cuts. Watch the tip of each edge after every cut. The wear is exaggerated so you can see it.

Two knife edges: mild steel and high carbon steel Each edge makes the same cuts, again and again The softer mild steel edge wears and goes blunt The harder high carbon steel edge stays sharp mild steel0.25% carbon high carbon steel1.1% carbon material being cut blunt tip still a sharp point ferrite pearlite pearlite mostly ferrite, about 30% pearlite pearlite, cementite at the grain boundaries

At 1.1% carbon the steel holds about 4.4 times as much hard cementite as at 0.25%. That cementite is what keeps a cutting edge sharp.

Now for the engineering

Build the comparison and see which of the five marks it earns

Pick the sentences you would write. Watch the difference between naming a property and comparing it, because QCAA pays for both. Your answer builds up in order below the two microstructures.

mild, 0.25% Chigh carbon, 1.1% C
Your answer

Your sentences
Marks earned

QCAA marking guide · 5 marks

Work through the solution one mark at a time

An identify mark and a compare mark for each steel, then one for the choice. Try each step yourself before you reveal it.

Step 11 mark

Place both steels first. 0.25% carbon is mild steel, which the 2025 syllabus calls low carbon steel. It is hypoeutectoid, so it is about 70% ferrite and 30% pearlite. 1.1% carbon is high carbon steel, hypereutectoid, so it is pearlite with cementite at the grain boundaries.

Then give a property of the mild steel. The guide’s notes accept “low strength” and “low hardness”, and the sample says softer and more ductile.

QCAA’s sample: “Mild carbon steel is softer and more ductile …”

Marker: identifies a suitable property of mild carbon steel [1 mark]

Step 21 mark

Compare that property with the other steel, and give the microstructure as the reason. “Than” is the word that turns a description into a comparison.

QCAA’s sample: “… than high carbon steel as it contains a high amount of ferrite.”

Marker: makes a comparison regarding the property [1 mark]

Step 31 mark

Now a property of the high carbon steel. The guide’s note names “high strength”, and the sample uses harder and more wear resistant.

QCAA’s sample: “Conversely, high carbon steel is harder and more wear resistant …”

Marker: identifies a suitable property of high carbon steel [1 mark]

Step 41 mark

Compare it back to the mild steel, again with the microstructure as the reason. At 1.1% carbon the steel has about 16.5% cementite in it, against about 3.7% at 0.25%.

QCAA’s sample: “… than mild carbon steel because it contains a higher amount of cementite.”

Marker: makes a comparison regarding the property [1 mark]

Step 51 mark

Make the choice in its own sentence, with the job as the reason. A knife has to be sharp and stay sharp, which is hardness and wear resistance.

QCAA’s sample: “Industrial knives are required to be very sharp and to maintain their sharpness; therefore, high carbon steel is the most suitable material for this application.”

Mild carbon steel (0.25% C) is softer and more ductile than high carbon steel, because its microstructure contains a high amount of ferrite. Conversely, high carbon steel (1.1% C) is harder and more wear resistant than mild carbon steel, because its pearlite and grain-boundary cementite give it a higher amount of cementite. An industrial knife must be very sharp and stay sharp, so high carbon steel is the most appropriate choice.

Marker: identifies that high carbon steel is the most appropriate material for industrial knives [1 mark]

Putting it all together

Each phrase of the question gave you something

“a knife for use in an industrial workshop”
Industrial knives are on the high carbon list, which tells you the answer before you start. The job is cutting, so sharpness and wear resistance decide it.
“mild carbon steel (0.25% carbon) and high carbon steel (1.1% carbon)”
Low carbon and hypoeutectoid against high carbon and hypereutectoid. That is mostly ferrite against pearlite with extra cementite.
“Compare the mechanical properties”
Four marks. Identify a property of each steel and compare each one, with “than” in the sentence.
“to determine the most appropriate choice”
One mark for saying high carbon steel, in its own sentence.
“with reference to the microstructures”
No dot point names it, but the sample puts ferrite and cementite inside the comparisons as the reasons. Do the same.
What makes this simple familiar

QCAA did not publish a band for this question. It reads as simple familiar because both steels and the application are straight off the syllabus lists, and the comparison is the standard ferrite against cementite one. For 2026, 0.25% carbon is low carbon steel and 1.1% is still high carbon steel, with industrial knives on its list, so the question works as it stands once you read mild as low carbon.

If I had to guess where you might lose marks, it would be describing each steel in its own paragraph without comparing them. That earns the two identify marks and loses both compare marks. The other trap is choosing high carbon steel because it is “stronger” and stopping. The choice mark is safest when the reason is the job: sharp, and staying sharp.

Only mark this done when you could do it without help. Reading the solution does not count.

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Question wording, any figures and marking-guide steps are from the 2025 QCAA Engineering external assessment, © State of Queensland (QCAA) 2025, licensed under CC BY 4.0, and have been adapted, except where a third-party source is named. Tangent Tuition is not affiliated with the QCAA.

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