Types of pig iron: the pig iron obtained from a blast furnace that is well fired with ample fuel at very high temperature (promoting graphitic carbon) is called what? (Choose the grade commonly preferred for foundry castings.)

Introduction / Context:
Pig iron is classified by the form in which carbon occurs after solidification, heavily influenced by furnace temperature and chemistry. Foundries prefer a graphitic form of carbon for fluidity and machinability. The question asks which pig iron results from a hot, well-fueled furnace condition.

Given Data / Assumptions:

• High-temperature, well-fueled operation favors graphitization in the solidified iron.
• Grey pig iron contains carbon mostly as free graphite flakes.
• White pig iron contains combined carbon as cementite due to relatively rapid solidification/low silicon.

Concept / Approach:
Ample fuel and high temperature in the furnace, together with sufficient silicon, promote the separation of carbon as graphite during solidification, yielding grey pig iron. This improves fluidity for intricate castings and enhances machinability compared with white iron, which is hard and brittle.

Step-by-Step Solution:

Verification / Alternative check:
Foundry metallurgy texts relate higher silicon and furnace heat to grey iron formation preferred for casting.

Why Other Options Are Wrong:

• Bessemer pig: process label, not directly indicative of carbon form.
• White or forge pig: combined carbon → poor machinability.
• Mottled pig: mixed structure; not the ideal foundry grade.

Common Pitfalls:
Assuming higher hardness (white iron) is always desirable; for casting complexity and machining, grey iron is favored.

Final Answer:
Grey or foundry pig