If we try to remember our chemistry classes back in our school days, we will recall that iron (Symbol Fe) is pure metal. Whereas steel is an alloy of iron and carbon. We all know that iron gets impacted by the weather and starts rusting easily by forming ferrous oxide.
However, steel resists corrosion better and hence is more favored in the construction industry, automobile manufacturing industry, and heavy machinery manufacturing industry. Stainless steel is steel that is even better at resisting corrosion than steel. Materials have been added to steel to make it stainless steel. This means that it won’t rust or tarnish as fast. For this reason, it is often used for outdoor installations and even pots and pans. Let’s study the differences between steel and stainless steel in more detail.
What is the difference between steel and stainless steel?
Steel and stainless steel are both alloys of iron and are broadly used in multiple industries across the globe. Based on their strength, hardness, cost, ductility, and malleability, they are differentiated into separate categories. Let’s look at the main differences between both the alloys-
1. Steel contains iron, carbon, and a few other elements in small proportions. Iron contains impurities like silicon (Si), sulfur (S), phosphorus (P), and manganese (Mn). During the process of manufacturing steel, all these impurities are removed. When steel is made by adding carbon to it, it is known as mild steel. It has a low melting point and hence is very hard. Other elements such as nickel and chromium have been added to stainless steel to make it more resistant to moisture.
Stainless steel contains 10.5% or more chromium (Cr). While converting it into stainless steel, nickel (Ni), nitrogen (N), and molybdenum (Mo) are also added in different proportions to steel. Due to the chromium content, it resists corrosion to a very large extent.
2. Steel is comparatively stronger than stainless steel as it has a higher carbon content. Steel is even harder than stainless steel.
3. If we compare the magnetic properties of stainless steel, it is completely non-magnetic. Some of the cheaper versions of stainless steel that do not contain nickel, like series 3xx and 4xx have slightly magnetic properties.
4. Steel does not look very aesthetically appealing due to its carbon content. It has a matte finish. Stainless steel looks shiny and due to the chromium content, it is quite lustrous and has a great aesthetic appeal. Utensils made of stainless steel look good, and some manufacturers use stainless steel to produce artifacts too. Since people decorate their homes with it, we will surely say that it looks quite appealing.
5. The thermal conductivity of steel is higher than that of stainless steel. This means that steel is better at transmitting heat.
6. Stainless steel is heavier than steel. During the manufacturing process, stainless steel has lesser occupancy, and hence, compared to steel, it is difficult to handle during the manufacturing process.
7. Steel is cheaper than stainless steel, and hence it is widely used to manufacture bigger machinery, automobile cases, and equipment. Given a choice, people would have used stainless steel for the same purposes as it does not rust. However, since the costs would go up by manifolds, the heavy equipment manufacturers stick to mild steel.
8. Steel is normally classified based on its carbon content. There are different qualities of steel. They are known as low carbon content steel, medium carbon content steel, and high carbon content steel. Stainless steel is classified based on its micro-structures.
Stainless steel is grouped in five broad categories- ferritic stainless steel, austenitic stainless steel, precipitation-hardened (PH), duplex stainless steel, and martensitic stainless steel. Amongst these five broad categories, more than 100 sub-categories of stainless steel are produced.
Steel is also used in electrical appliances due to its magnetic properties. Since welding can be done easily on steel compared to stainless steel, it is used in any product that needs joining.
Ferritic stainless steel contains more than 12% chromium and less than 0.20% carbon content in the steel alloy. Some of the varieties of ferritic steel contain even up to 30% chromium. This variety cannot be hardened using heat treatment.
Austenitic stainless steel is highly corrosive resistant and is known for its strength and durability. It is aesthetically pleasing and, hence, many industries use it to build items and structures that are visible to others. It has exceptional resistance to heat. It is low on maintenance and it is easy to clean. The demand for this variety is due to its environment-friendly feature. It is used extensively in the construction, medical, aerospace, and automobile industries.
Austenitic stainless steel has a face-centered cubic (FCC) type of structure. It contains nickel and nitrogen elements in the stainless steel alloy, which makes it aesthetically more appealing compared to other varieties of stainless steel.
The tensile strength of precipitation hardening (PH) stainless steel can be three or four times higher than that of austenitic stainless steel. This type of steel is used extensively in the oil and gas, nuclear, and aerospace industries. Since the strength of this variety of steel is extremely high and it has very high corrosion resistance, it is favored in many high-end industries. This alloy contains aluminum, copper, molybdenum, and titanium, sometimes used separately or in combination.
The metallurgical structure of Duplex stainless steel consists of two phases. It is a combination of austenite and ferrite in approximately equal proportions. The chromium content of this variety of steel can be anything between 20-28%. They also contain higher molybdenum, up to 5%; lower nickel, up to 9%, and 0.05–0.50% nitrogen.
Martensitic stainless steel contains chromium between 11.5-18%, 1.2% carbon, and nickel. This steel is very hard and is extensively used in mechanical valves and instruments, medical instruments, turbine parts, and other various applications.
Usage of steel
Steel is used for manufacturing die tools and cutting tools. They are also used extensively in sheeting welding and tooling. Steel is an important component in construction sites. It is used to reinforce concrete. It is used in manufacturing automobiles, cars, aviation structures, ships, missiles, satellites, etc. It resists corrosion to a great extent if painted with good quality anti-corrosion paints.
Usage of stainless steel
As mentioned earlier, different varieties of stainless steel have their usage in different industries. Broadly they are used in utensils manufacturing and equipment manufacturing industries on a very large scale.
Does stainless steel tarnish?
Steel is prone to rust and stains. Though it is much more resistant to environmental effects compared to raw iron, it is not completely change-proof like stainless steel. If you use stainless steel utensils in your kitchen, you will know that stainless steel does not rust or tarnish. It remains as-is for years together.
The longevity of stainless steel makes it so popular amongst utensil manufacturers. Unlike bone china, it does not break. It is very economical and hence most home appliances like mixer grinders, food processors, vacuum cleaners, etc. use stainless steel to manufacture the body parts of the gadgets.
Stainless steel costs more as more elements have been added but it can last for a long time. This is why it is used in devices that have to deal with moisture such as dishwashers, washing machines, and so on. This is also the reason why it is used for pots and pans; These can last several decades without any issues.
If the stainless steel gets scratched or damaged, it is possible that it will tarnish as the protection of the other metals might be removed and the exposed steel gets damaged by moisture and tarnishes or rusts.
Stainless steel is also used for outdoor plumbing and electricity as the brackets won’t rust over time. It is dangerous to use steel as this can break over time. This can make electric wires or drains fall and damage property or even harm people. For this reason, it is essential that stainless steel brackets are used. Some people want to save by using steel brackets but this is not a great idea.
To conclude, we can state that the main difference between steel and stainless steel is that elements have been added to stainless steel so that it doesn’t rust or stain as fast as steel. This makes it last longer in moist conditions. The drawback is that it is more expensive than steel though so it is not always used.