Before we explore everything about alloy steel, let’s get amazed by a few facts about steel I bet you have never heard of before.
- Steel is around one thousand times stronger than the purest form of iron and it can be recycled without losing this strength.
- The steel industry opens up homes for more than 2 million people worldwide as its employment rates increase.
- 25% of an average computer is made up by steel.
- When heated, steel and iron expand. This property of steel increases the height of the Eiffel tower by six inches in summer.
- 200 billion cans are made every year from steel.
- More than eighty million tons of steel are recycled in North America every year.
- Roofs made from steel last more than fifty years while traditional roofs only last for seventeen years.
Pretty interesting right? In this article, we will be discussing alloy steel and its relationship with stainless and carbon steel.
What Is Alloy Steel?
Everyone has for sure heard of stainless steel before. It is the best material for cookware like pots and pans. But do you know what stainless steel is made up of? It is a mixture of iron, chromium, silicon, carbon and manganese (all added in different portions). Any mixture of metals is known as an alloy. Another example of an alloy that we will be discussing today is an alloy steel. It is a type of steel which is mixed with different levels of one or more of the following elements: manganese, silicon, nickel, titanium, copper, chromium and aluminum. The difference between stainless steel and alloy steel is that alloy steel is made up of elements such as nickel and copper.
- Manganese strengthens the steel at higher temperatures as it eliminates the formation of unneeded compounds such as iron sulphide.
- Nickel and copper increase the strength and hardness of the steel in addition to maintaining resistance to corrosion and oxidisation.
- Copper is added in very small amounts, but it also adds to the strength and corrosion resistance of the steel.
- Aluminium limits the formation and growth of any impurities such as austenite grains.
- Chromium is a key alloying element which acts a significant corrosion and wear & tear resistant. It also helps the steel harden as it has a positive response to heat treatments.
Let’s look at some properties of alloy steel: Thermal conductivity (the ability of a material to conduct heat) of alloy steel is around 26-48.6 W/m-k which is considered low. As most alloy steels contain titanium and nickel, which have low thermal conductivity. Tensile strength of alloy steels is between 758-1882 MPa which is higher than the tensile strength of stainless steel. Steel is mixed with the other elements to enhance their mechanical properties, hardening the steel making the alloy steel more durable and resistant to corrosion.
There are two types of alloy steel: high & low alloy steel. This depends on the percentage of the alloying elements; high alloy steel has a higher percentage. Low alloy steel usually has 1-5% of alloying elements, making it more suitable for applications which require mechanical properties. The most common example of high alloy steel is stainless steel. The level of chromium varies, giving rise to different types of stainless steel. There are at least 12% of chromium and it can increase to 27% in some steels; depending on their use. Fun fact, did you know that stainless steel can remove odors from the surface of the skin! Low alloy steel has increased hardness and wear & tear resistance, but it doesn’t have the same tensile strength as high alloy steel. High alloy steel can also resist wear and tear even under high temperatures.
What Are The Uses of Alloy Steel?
Alloy steel is one of the common steels that are used frequently. There is a wide range of applications of alloy steel including:
- Pipes used in energy-related applications such as oil and gas drilling. They have the ability to withstand the stress and pressure that will be applied in those machine parts.
- Bearings are made from alloy steel as it gives them strength to resist any cracking or rolling contact fatigue.
- Architecture uses alloy steel to avoid corrosion, high alloy steel is used in construction.
- Railways, security safes and armour plating are other common uses of alloy steel. Manganese and Nickel found in alloy steel are both mainly responsible for this application.
- Household items such as the cookware, cutlery, counter-tops, etc. are made from stainless steel, as they are easy to shape with high temperatures.
- Artwork has integrated steel alloys as a medium for fine art. Artists use it as the base of the canvas to give the art piece shine.
Alloy steel is used in nearly all industries. In addition to the uses listed above, steel can be used in transportation, housing, energy and machinery.
Alloy Steel VS Carbon Steel
“Persistence is to the character of man as carbon is to steel”, Napoleon Hill.
Another type of steel to introduce in this article is carbon steel. The main element in this type of steel is not iron, it is carbon. The higher the amount of carbon, the easier you can harden the metal as you heat it. There is also low, medium and high carbon steel. In low carbon steel, the carbon content doesn’t exceed 0.25% mixed with 0.4% manganese. This is the cheapest carbon steel, yet they can be used in a lot of applications as they can be easily shaped. Medium carbon steel is made up of a maximum of 0.54% carbon and 1.65% of manganese. The higher carbon content makes this type of steel stronger in addition to giving it resistance to wear. This, however, decreases their ability to be shaped easily. While high carbon steel has a carbon content that can reach 0.9%.
This type of carbon steel is the strongest and hardest to shape, therefore it is only used when it really is needed. Some of its applications are springs, wires and knives. If you are a chemistry lover, you would know that various forms of carbon are very strong. Diamonds, which are the strongest material on earth, is actually made from carbon. So, that might explain why when carbon is mixed with iron, it is enough on its own with no further elements to strengthen it.
Now that we have established a good base for what is carbon steel, let’s dive into the differences between carbon steel and alloy steel. Their composition is very different from each other. Carbon steel is made from a maximum of 2.1% of carbon (very high carbon steel) and iron. Any other element found in this type of steel is seen as an impurity.
However, alloy steel wouldn’t be alloy without the additional elements added to enhance their properties. This is what makes the alloy steel more resistant to corrosion, has higher tensile strength and hardness. The higher the alloying elements content, the more-used the alloy steel is. On the other hand, the higher the carbon content, the harder and less usable the steel becomes. Nonetheless, carbon steel scores point in the price category. Carbon steel is relatively cheaper, especially as the carbon content is lower. Alloy steel can get very expensive due to the alloying elements added and their amount.
How Much Is It?
First, let’s consider the pros and cons of alloy steels before you make your purchase. Alloy steels have a high strength-to-weight ratio. They also have low densities, decreasing their weight so they are able to withstand stress and pressure. With the aid of heat, they can be shaped in any required form which increases their application options. On the other hand, when compared to stainless steel, alloy steel have a lower strength overall (especially at higher temperatures) as well as a higher chance of getting corroded.
When you are looking at alloy steel, there are a few things to consider: the shape of the alloy steel, thickness, width and length of the steel pipes. As well as the pipe grade, which is the percentage of alloying elements. The top two common places that supply alloy steel are India and China. The United States comes in third place. According to online global trading websites (such as Alibaba.com and made-in-china), the price of alloy steel starts at $450 and can reach $2800 per tonne. One tonne is the minimum weight to order.
In conclusion, everywhere you look you will find steel in any form. It has been integrated into almost every aspect of life. Depending on the elements that iron is mixed with, different types of steel are formed. Each type of steel, whether it is alloy, carbon or stainless steel have their own set of properties that make them more suitable for specific applications. But the properties that they all share in general is their strength, hardness and their ability to be shaped into the desired form. The uses of steel varies widely from cookware to industries, construction and farming.