Materials science — approximate recrystallisation temperature of steel For process planning in hot working and annealing, what is a representative recrystallisation temperature for plain carbon steel?

Introduction / Context:
Recrystallisation temperature defines the threshold above which cold-worked metals form new strain-free grains during annealing, drastically reducing hardness and restoring ductility. For steels, this value guides heat-treatment schedules and distinguishes cold from hot working regimes.

Given Data / Assumptions:

• Material: plain carbon steel with prior cold work.
• Seeking a representative temperature rather than an exact value for all compositions and degrees of deformation.
• Ambient to elevated temperature processing environment.

Concept / Approach:
Recrystallisation temperature is often approximated as 0.3–0.5 times the absolute melting temperature. For steel, practical shop guidance pegs typical recrystallisation around 450–600° C, with 600° C commonly cited in examination settings as a representative value ensuring complete recrystallisation for many conditions.

Step-by-Step Solution:

Verification / Alternative check:
Metallography after annealing shows equiaxed, strain-free grains above the recrystallisation threshold, with hardness dropping significantly from the cold-worked condition.

Why Other Options Are Wrong:

• 400° C: typically below full recrystallisation for many steels.
• 800° C: closer to austenitizing temperatures, exceeding the need for simple recrystallisation.
• “None of these”: 600° C is a valid representative value.
• 200° C: far too low for steel recrystallisation.

Common Pitfalls:
Confusing stress-relief (lower temperatures) with full recrystallisation; assuming a single exact temperature for all steels regardless of prior work.

Final Answer: