Steel vs Stainless Steel: Understanding the Key Differences

Steel and stainless steel share many similarities; they are both primarily composed of Iron, contain carbon, and are used extensively in both industrial and domestic products.

Despite this, the distinction between the two is significant, with certain applications being unsuitable for either one. In this article, we will explain what sets them apart and why engineers choose one over the other.

The Differences Between Steel and Stainless Steel

• Stainless steel is corrosion resistant – steel corrodes readily in the presence of moisture
• Steel is predominantly made up of iron and carbon – stainless steel typically contains relatively large amounts of other alloying elements such as chromium and nickel
• Stainless Steel has a shiny appearance and can be polished to a mirror finish

Decoding Steel Grades: A Simple Guide

Steel comes in many different grades, each one having slightly different properties, be as higher strength, better machinability, etc. Here are some of the most common steel grades you need to know:

• ASTM A36 grade – this is a commercial grade steel often found in low-stress applications such as medium duty structures and supporting steelwork
• ASTM A572 grade – another steel commonly used for structural components, within A572, multiple sub-grades vary in strength, from grade 42 to 65.
• AISI 1018 – a low-medium carbon steel grade often found in bar form, commonly used for machined components, it has a reasonable level of strength with excellent weldability and machineability
• AISI 1045 – a medium carbon steel, good for machining strong parts from, with average to low weldability depending on application

Stainless Steel Grades Explained: Choosing the Right One

Stainless steel’s corrosion proof nature and high strength make it incredibly versatile. But just like steel, there are numerous different grades available. Some of the most common ones are explained below:

• 304 – all 300 series stainless steels are Austenitic chromium-nickel alloys. They have excellent corrosion resistance. 304 grade is generally slightly cheaper than other 300 series, such as 316 or 310. 304 grade is easy to machine, weld and form.
• 316 – often referred to as marine-grade, 316 stainless steel is great at resisting seawater environments. It has similar strength and manufacturing properties to 304 grade.
• 400 series – this group of stainless steel grades is often used for their cost-effectiveness compared to 300 series grades. They are ferritic, meaning they are usually magnetic. The 400 series still has good corrosion resistance but are not recommended for acidic environments.
• Duplex – grades such as 2205 and 2507 are termed duplex because they have both austenitic and ferritic phases in the same material. Duplex grades typically have excellent corrosion and heat resistance, often being capable of withstanding extremely high temperatures.

Steel and Stainless Steel Applications: Where Each Excels

With stainless steel and steel having such similar properties when it comes to density, hardness and strength, the differences come mainly from their resistance to corrosion.

Cost

If up front expense is the deciding factor, mild steel will generally win out, as stainless can be up to 4x times more expensive. Not only that, the welding wire and fasteners made from it are much more expensive.

However, if the components are designed to be used in any kind of harsh environment – including just being outside – for any period of time, the preventative and ongoing maintenance of painting or coating can significantly narrow the gap, depending on the application.

Appearance

Stainless steel can be polished to a mirror finish, whereas mild steel cannot. This often makes stainless steel better suited to architectural and aesthetic parts than mild steel.

Even in mill or brushed finish, stainless steel often gives a higher end appearance compared to painted or coated mild steel.

Maintenance

If you have a mild steel part that has an old painted or plated finish, it can be extremely time consuming and expensive to strip and re-coat, only to need the same treatment again in X no of years.

Stainless steel, whilst it does scratch and tarnish, can be polished back to a nice sheen with relative ease.

Maintaining Steel and Stainless Steel: Best Practices

Even a component made from a highly corrosion resistant material, such as stainless steel, needs maintenance, a part made from steel even more so.

Maintaining Stainless Steel

Stainless is pretty durable to most cleaners and household products, but be sure to proceed with caution on polished or brushed finish surfaces. Clean with mild detergents and try to work with any grainy surface.

When using chemicals, try a conspicuous area first, which will let you check the abrasiveness and products will not scratch or discolour the surface.

Maintaining Mild Steel

If used inside, and not in any kind of humid environment, mild steel can be used untreated, e.g., unpainted or plated tools. However, if the part is to be exposed to the elements or gets wet regularly, it should be protected from corrosion with a paint or plating process.

Once protected, the coating should be checked regularly for signs of corrosion, which initially form as bubbling and discoloration. Some coatings, such as powder coating, can allow rust to form under the surface and hide it from view.

If a part needs to be low maintenance, galvanising is one of the best ways to protect it long-term. Galvanised finishes can be painted over with the right type of prep and paint.