Mild Steel has a small percent elongation at failure.

Error in Statement

The erroneous statement is option 'C', which states that mild steel has a small percent elongation at failure.

Explanation

Mild steel is a type of carbon steel that contains a low amount of carbon. It is widely used in construction, automotive, and other industries due to its excellent mechanical properties, low cost, and ease of fabrication. The correct statements about mild steel are:

a) Mild steel has two yield points: Mild steel exhibits two yield points, which are the stress levels at which the material starts to deform plastically. The first yield point is lower and corresponds to the elastic deformation of the material, while the second yield point is higher and corresponds to the onset of plastic deformation.

b) Mild steel is a ductile material: Ductility is the ability of a material to deform under tensile stress without fracturing. Mild steel is a ductile material, which means it can be easily drawn into wires or other shapes without breaking.

c) Mild steel has a high percent elongation at failure: The percent elongation at failure is a measure of the ductility of a material, which indicates how much the material can stretch before it breaks. Mild steel has a high percent elongation at failure, which is typically around 20-25%.

d) Mild steel shows strain hardening: Strain hardening is the increase in the strength of a material due to plastic deformation. Mild steel exhibits strain hardening, which means that its strength increases as it is deformed.

Conclusion

In conclusion, the correct statement about mild steel is that it has a high percent elongation at failure, and the erroneous statement is that it has a small percent elongation at failure.