In the case of hot-rolled steel, residual stresses are primarily caused by
- AHigh strain rate deformation.
- BInhomogeneous cooling.Correct
- CChemical segregation during casting.
- DPoor surface finish.
Solution
Concept
Residual stresses in rolled steel come from uneven cooling after rolling.
Step-by-step solution
1. After hot rolling, the section cools in air. 2. Thin parts like flange tips and web centre cool faster than thick junctions. 3. Faster-cooling parts shrink first and become stiff. 4. Later, slower-cooling parts try to shrink but are restrained. 5. This leaves locked-in stresses (residual stresses) in the section. 6. So the main cause is inhomogeneous (uneven) cooling.
Explanation
In hot-rolled sections, different parts cool at different rates. This uneven shrinkage locks in residual stresses. Flange tips are usually in compression and the web centre and flange-web junction in tension.
Why the other options are wrong
A: strain rate is not the main cause. C: segregation affects composition, not residual stress. D: surface finish does not produce residual stress.
Shortcut
Residual stress in rolled or welded steel = uneven cooling.
Common mistake
Confusing residual stress with stress from loading or from surface defects.
Correct answer: B) Inhomogeneous cooling.