At around what temperature does steel begin losing its strength?

• A. 700
• B. 570
• C. 500
• D. 400

Answer: (B)

When steel is heated, its internal structure softens and becomes easier for dislocations to move, so the material’s yield strength and overall stiffness drop. This weakening starts only after the metal reaches high temperatures and becomes more pronounced as temperature rises into the fire-range. Among the temperatures given, the one in the upper portion of the list aligns with the point where steel begins to lose noticeable strength. That’s why this value is the best choice, reflecting how structural steel can rapidly weaken under fire exposure and why protective measures are crucial.