Which type of steel is mild steel and stainless steel?

Mild steel is malleable, has a poor response to heat treatment, has no resistance to corrosion, relatively lower strength as compared to stainless steel.

Stainless steel is stronger, highly resistant to corrosion, relatively harder, expensive, have self-healing ability as compared to mild steel.

Let’s dive deeper to understand the above statements.

Let us see the compositional difference between mild steel and stainless steel.

Mild steel

• Mild steel is the most common type of steel.
• The name “mild steel” refers to its mild or limited response to heat treatment compared to other types of steel.

  • Low Carbon Content: Mild steel has a low carbon content (less than 0.3% by weight). Carbon is a key element in achieving significant hardening through heat treatment processes like quenching. With minimal carbon, the internal structure of mild steel changes less drastically during heating and cooling, resulting in a milder effect on its hardness.

• This low carbon content makes mild steel relatively soft and malleable, meaning it can be easily shaped and formed.
• However, it is also more susceptible to rust and corrosion.

Stainless steel

• Stainless steel gets its name from its resistance to staining, rust, and corrosion. This resistance comes from the presence of at least 10.5% chromium, a key element in its composition.
  • Chromium Oxide Layer: When chromium in stainless steel comes into contact with oxygen (usually in the air), it forms a thin, invisible layer of chromium oxide on the surface. This layer is very stable and tightly adheres to the steel.
  • Protection Barrier: This chromium oxide layer acts as a barrier, preventing oxygen and moisture from reaching the underlying iron in the steel. Iron is susceptible to rust when it reacts with oxygen and moisture. By blocking these elements, the chromium oxide layer prevents the formation of rust and stains on the stainless steel surface.
  • Self-healing Ability: Even if the chromium oxide layer is scratched or damaged, it has a remarkable self-healing ability. When exposed to oxygen again, a new layer can quickly form, continuing to protect the steel.
• Stainless steel is also generally stronger and harder than mild steel. Higher Chromium content in stainless steel contributes to strength by forming a harder and more stable crystal structure in the steel. Many types of stainless steel also contain nickel and molybdenum, which can further enhance strength. Nickel improves work hardening, while molybdenum increases high-temperature strength.
• Stainless steel is more expensive and more difficult to work with. Stainless steel contains a higher percentage of chromium (min. 10.5%) compared to mild steel (trace amounts). Chromium is a more expensive element than iron, the main component of both steels. Additionally, some grades of stainless steel may include nickel and molybdenum, further increasing the raw material cost. Stainless steel is generally harder than mild steel due to the presence of chromium and potentially other elements. This hardness makes it more challenging to cut, drill, bend, and form compared to the softer and more malleable mild steel.
• Stainless steel is often used in applications where corrosion resistance is important, such as in cookware, cutlery, and medical instruments.