Question

The advantage of pack carburising is

• A. Close control of surface carbon is possible
• B. Suited for production of thin carburized cases
• C. Prepared atmosphere is not required
• D. Components can be directly quenched from carburizing temperature

Hint:

Compare surface hardening methods:

• Pack Carburizing: Simple, low-cost, good for thick cases, poor process control.

• Gas Carburizing: Excellent control, good for mass production, requires complex furnaces.

• Liquid Carburizing (Cyaniding): Fast, uniform, but uses toxic salts.

• Nitriding: Produces very hard case, low distortion, but slow process.

Answer 1

The Correct Option is C

Step 1: Picture the setup of pack carburizing.
In pack carburizing, the workpiece is simply buried inside a sealed steel box, packed with a solid carburizing compound, usually charcoal mixed with an energizer such as barium carbonate, and the whole box is placed in a furnace.
Step 2: Trace where the carbon actually comes from.
As the box heats up, the energizer reacts with the charcoal to generate carbon monoxide gas right there inside the sealed container. This CO then disproportionates at the hot steel surface to deposit active carbon, which diffuses inward. Every ingredient needed for this reaction is already packed inside the box.
Step 3: What this means practically.
Because the carburizing "atmosphere" is generated in situ from the pack itself, there is no need for an external gas supply, gas mixing system, or atmosphere controlled furnace, unlike gas carburizing which needs a carefully metered endothermic gas atmosphere. This makes pack carburizing simple and usable even with a basic box furnace.
Step 4: Checking the other choices.
Precise control of surface carbon and thin case depths are actually weaknesses of this slow, hard to monitor process, and direct quenching from the carburizing box is generally avoided because it coarsens the grains, so those cannot be the advantage. The genuine advantage is that pack carburizing needs no externally prepared atmosphere.
\[ \boxed{\text{Prepared atmosphere is not required}} \]