Hot working characteristics — surface finish and accuracy During hot working of metals, which of the following statements best describes typical outcomes regarding finish, scale formation, and tolerance control?

Introduction / Context:
Hot working (deforming above recrystallisation temperature) improves ductility and reduces flow stress, but it also has drawbacks affecting product finish and dimensional accuracy. Recognizing these trade-offs guides selection between hot and cold processes.

Given Data / Assumptions:

• Typical steels or nonferrous alloys hot worked in air.
• Conventional industrial equipment such as rolling mills, presses, and hammers.
• No special protective atmospheres unless stated.

Concept / Approach:
At elevated temperatures, metals oxidize readily, forming scale that marks the surface. Thermal gradients, elastic springback differences, and equipment clearances impede tight tolerance control. Although hot working refines grains, it rarely achieves the fine finishes and close tolerances obtainable by cold finishing or machining.

Step-by-Step Solution:
Hot temperatures cause oxidation → oxide scale forms → surface finish deteriorates.Thermal expansion and die clearances shift dimensions → difficult to hold close tolerances.Therefore, poor(er) surface finish, scale formation, and reduced tolerance control are all expected outcomes.

Verification / Alternative check:
Mill-scale removal (shot blasting, pickling) is standard after hot rolling or forging; cold finishing passes are often scheduled to restore tolerance and finish.

Why Other Options Are Wrong:
Choosing any single effect ignores the others; 'None of these' contradicts well-established hot working behavior.

Common Pitfalls:
Assuming hot working always yields better quality; neglecting decarburization in steels; forgetting that protective atmospheres or controlled environments can mitigate, but not fully eliminate, scale and tolerance issues.

Final Answer:
All of these