Steel is an alloy of metals made primarily of iron, carbon, and other elements. Depending on the amount of iron present and the proportions of other elements added, steel can be divided into wide varieties. Two of these steel varieties are mild steel and stainless steel.

In this article, we’ll discuss mild steel vs stainless steel, their similarities, differences, and applications.

What is Mild Steel?

Mild steel, just like all carbon steel, is an alloy of iron (base element) and carbon (alloying elements) mixed with traces of other chemical elements. Mild steel is low-carbon steel, with a low carbon content ranging from 0.05% to 0.25%.

Since mild steel is strictly plain carbon steel, it contains no alloying elements other than carbon. There are traces of other chemical elements, such as silicon or manganese, in their chemical composition, but their content never exceeds 1% of the total weight.

The relatively low carbon content in this type of steel makes it more ductile, machinable, and weldable. However, the drawbacks include iron oxidation, which causes the steel to corrode, reducing its durability—and the material is quite durable.

Mild steel is frequently used for signs, structural applications, furniture, cars, and fencing. Due to the various advantages it provides, it’s actually used in a very wide range of applications that don’t require precise tensile strength.

What is Stainless Steel?

Stainless steel is a form of steel alloy that has one essential characteristic—high corrosion resistance. This characteristic is attributed to the high chromium content, which ranges from 10.5% to 20% by weight. Stainless steels contain less than 1.2% carbon, which is a comparatively low amount.

The alloy's iron does not oxidize because the chromium in the substance reacts with oxygen from the air to form a passive coating of chromium oxide on the surface. Further preventing the production of iron oxide, the protective layer keeps the steel from corroding. Additionally, it promotes self-healing in the event of abrasions.

In addition to corrosion resistance, additional alloying elements like molybdenum, nickel, copper, titanium, etc., have a significant impact on the mechanical and other physical characteristics of stainless steel.

What are the Differences Between Stainless Steel and Mild Steel?

The main difference between the two is in iron content: mild steel is approximately 98% iron, and stainless steel usually contains approximately 90% of iron, depending on the grade. In fact, you’re likely to differentiate them visually; one is dull with a matte finish, while the other is often polished and lustrous.

Here’s the breakdown of the differences between mild steel and stainless steel:

Chemical Composition

Mild steel consists primarily of iron and carbon as two main elements. Other elements like Nickel, chromium, aluminium, phosphorus, sulfur, silicon, and others are present in trace amounts, but what makes mild steel different is its carbon content.

Mild steel is the most widespread type of steel on the market since it’s cost-effective, easy to form, and well-suited for applications where tensile strength isn’t a precise requirement. Mild steel comes in a variety of grades, including low alloy, high alloy, medium carbon, and high carbon steel, among others.

Stainless steel, on the other hand, contains significant amounts of alloying elements besides carbon. The most significant among these are chromium and nickel, a minimum of 10.5% and 8% by weight, respectively. These elements make the stainless steel corrosion-resistant and more formable and weldable.

It also has trace amounts of other elements like silicon, nitrogen, manganese, molybdenum, carbon nickel, and copper. The varying contents of alloying elements produce different types of stainless steel, and there are more than 150 stainless steel grades in the market.

Corrosion Resistance

Corrosion resistance is the metal’s ability to resist different forms of corrosion; a property that mild steel doesn’t possess. This type of steel actually corrodes very rapidly as iron reacts and bonds with oxygen from the atmosphere to create iron oxide. Therefore, mild steel needs further processing, such as galvanizing or painting, to give it a protective surface.

However, though it’s not corrosion-proof, stainless steel is a rather corrosion-resistant material. The added chromium bonds with the oxygen from the atmosphere, thus preventing the iron within the alloy from oxidizing. This prevents the steel from rusting, giving stainless steel its corrosion-resistant properties.

With everything said, stainless steel isn’t completely corrosion-resistant, either. Most stainless steel alloys are susceptible to corrosion caused by different corrosive chemicals. For example, SAE 304 would slowly corrode in seawater, but SAE 316 wouldn’t, thanks to the 2% molybdenum content within the alloy.

Strength

Because of the chromium it contains, stainless steel is generally stronger than mild steel. Thus, it’s often used to make stainless steel products that need to withstand impacts and repeated use. Mild steel has a rather low tensile strength compared to stainless steel, but it can be strengthened by adding carbon.

Ductility

Ductility refers to the material’s capacity for plastic deformation without breaking or cracking. Mild steel is pretty ductile due to its low carbon content, making it suitable for producing pipes and pipe fittings. Stainless steel is less ductile compared to mild steel.

Hardness

The main distinction is that stainless steel is alloyed with nickel, chromium, and other elements to give it its chemical qualities rather than being made from much carbon. As a result, stainless steel becomes particularly impact-resistant because of the chromium alloy that shields it.

Mild steel can be strengthened with extra carbon or galvanized with zinc. Without this, the mild steel itself remains extremely pliable and prone to damage without galvanization.

Weldability and Malleability

Carbon content in both materials makes it more difficult to weld; however, stainless steel contains nickel which improves weldability. Regarding malleability, mild steel is generally more malleable due to its ductility.

Do You Need Mild Steel or Stainless Steel?

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In summary, the differences between stainless steel and mild steel are substantial, and the two can be differentiated visually from one another. Additionally, they serve different purposes across all industry branches, and you’ll likely find both types of steel wherever you go.

If you want to learn more about stainless steel, visit our Engineer Resource Guides or browse our steel hardware products online.