Question

The yield point phenomenon observed in annealed low carbon steel is due to the presence of the following element

• A. Silicon
• B. Chromium
• C. Carbon
• D. Phosphorous

Hint:

The yield point effect in low carbon steel is caused by carbon (or nitrogen) atoms locking dislocations. These are released suddenly, leading to the characteristic yield drop.

Answer 1

The Correct Option is C

Step 1: Understanding yield point phenomenon The yield point in a stress-strain curve of annealed low carbon steel is characterized by an upper yield point followed by a lower yield point and a yield plateau. Step 2: Role of carbon and nitrogen The phenomenon is caused by the interaction of dislocations with interstitial atoms, primarily carbon and sometimes nitrogen. These atoms pin the dislocations. On application of stress, dislocations break free from these atoms, causing a sudden drop in stress (from upper to lower yield point). Conclusion: The yield point phenomenon is primarily due to the presence of carbon atoms in the steel that lock the dislocations before yielding.