Introduction
Stainless steel is used for a wide range of things in both the industrial and consumer markets because it is strong, doesn’t rust, and looks good.
But how does stainless steel get from trash or refined ores to its final shape and use?
Most stainless steel starts out the same way before it is made into something else. This process determines both the actual composition of the steel alloy and its many different properties.
So, to learn how stainless steel is made, we must first look at what it is made of.
HOW DOES STAINLESS STEEL WORK AND ITS MEANING?
Stainless steel is a chromium-iron alloy.
Even though stainless steel must have at least 10.5% chromium, the exact parts and ratios will change depending on the grade and how it will be used.
Other common additives include:
Nickel
Carbon
Manganese
Molybdenum
Nitrogen
Sulfur
Copper
Silicon
During the alloying process, the exact parts of an alloy are measured and evaluated to make sure that the steel has the properties that were wanted.
Some of the most common reasons for adding other metals and gases to a stainless steel alloy are as follows:
Corrosion resistance improved
Resistance to high temperatures
Temperature resistance is low.
Increased power
The weldability has been improved.
Formability has improved.
Magnetism management
But the composition of your stainless steel isn’t the only thing that makes it unique…
How steel is made will change its properties even more.
WHERE DOES STAINLESS STEEL COME FROM?
In the later stages, the exact method will change depending on the grade of stainless steel. How a type of steel is formed, worked, and finished has a big effect on how it looks and how it works.
Before you can make steel that can be sold, you must first make the molten alloy.
So, the first stages of making most types of steel are the same.
1) Melting
In an electric arc furnace, scrap metal and other things are melted together to make stainless steel. The EAF uses high-power electrodes to heat the metals slowly over a long period of time. This creates a slurry of molten metal that flows easily.
Because stainless steel can be recycled over and over again, up to 60% of the steel in many stainless steel orders comes from recycled steel. This not only helps keep costs down, but it also makes less of an impact on the environment.
Temperatures will vary based on the type of steel used.
2) Carbon Content Removal
Carbon is a part of what makes iron strong and hard. On the other hand, if there is too much carbon, it could cause problems, like carbides forming when welding.
Before casting molten stainless steel, it needs to be calibrated and have its carbon content brought down to the right level.
Foundries can control the amount of carbon in two ways.
The first way is to use Argon Oxygen Decarburization (AOD). By injecting an argon gas mixture into molten steel, the amount of carbon in the steel can be lowered with minimal loss of other important parts.
Another method used is vacuum oxygen decarburization. During this process, molten steel is moved to a separate chamber where oxygen is added while heat is applied. The gases that were let out are then taken out of the chamber using a vacuum, which lowers the amount of carbon even more.
Both processes allow for precise control over the amount of carbon in the steel, which leads to correct mixing and precise properties in the final product.
3) Tuning
After the carbon has been taken out, the temperature and chemistry are finally in balance and uniform. This makes sure that the metal meets the requirements for the grade it was made for and that the composition of the steel stays the same throughout the batch.
Samples are put to the test and judged. The mix is then changed until it has the quality that was wanted.
4) CASTING OR FORMING
Now, the foundry needs to make the basic shape that will be used to cool and shape the molten steel. The exact shape and size will depend on the end result.
Here are some common examples of shapes:
The Blooms, Billets, Slabs, Rods, Tubes, and Forms are then given a number so that the batch can be tracked as it goes through the different operations.
The next steps will depend on the target grade and the final product or purpose. Slabs are used to make plates, strips, and sheets. Blooms and billets are used to make bars and wires.
Depending on the grade or format, steel may go through some of these steps more than once to get the look or properties that are needed.
The steps that follow are the most common.
Rolling in the heat
This process, which is done at temperatures higher than the steel’s recrystallization temperature, helps set the rough dimensions of the steel. During the whole process, the temperature is carefully controlled to keep the steel flexible enough to work with without changing the structure.
Using repeated passes, the size of the steel is slowly changed. Most of the time, the right thickness can only be reached by rolling through many mills over time.
Rolling in the Cold
Cold rolling is a precise process that happens below the temperature at which steel re-crystallizes. Several rollers are used to help shape the steel. This method makes a finish that looks better and is more consistent.
It can, however, change the structure of the steel, so it needs to be heated to get back to its natural microstructure.
Annealing
Most steel goes through a process called “annealing” after it has been rolled. There needs to be a controlled cycle of heating and cooling. These cycles help soften the steel and get rid of the stress inside it.
Depending on the quality of the steel, the actual temperatures and times will be different. The heating and cooling rates also have an effect on the final product.
Pickling or descaling
When steel goes through different processes, scale forms on its surface.
This buildup is more than just ugly. It can also change the steel’s ability to resist stains, last long, and be welded. This scale needs to be taken off to make the oxide barrier that makes stainless resistant to corrosion and stains.
Descaling or pickling is a way to get rid of the scale. Acid baths (acid pickling) or controlled heating and cooling in an oxygen-free environment are both ways to do this.
Depending on what the final product will be, the metal may be rolled or pushed through a die again. Then there are phases of annealing until the right properties are reached.
Cutting
After the steel has been worked on and is ready, it is cut to the specifications of the order.
Most of the time, mechanical ways are used, like cutting with guillotine knives, circular knives, high-speed blades, or pounding with dies.
On the other hand, flame cutting or plasma jet cutting can be used to make shapes with more detail.
The best solution will depend on the type of steel that is needed and the shape of the finished product.
Finishing
There are many different ways to finish stainless steel, from matte to mirror. Finishing is one of the last steps in the process of making something. Common processes include etching with acid or sand, sandblasting, belt grinding, belt buffing, and belt polishing.
Now that the steel is in its final form, it is ready to be sent to the buyer. Rolls and coils are often used to store and ship large amounts of stainless steel, which is used in many industrial processes. But the final shape will depend on the type of steel and other factors that are unique to each order.
FINAL CONCLUSIONS
Understanding the right grades and types of stainless steel for different uses and environments is important for long-term performance and saving money. You can find a stainless steel alloy that fits your needs, whether you need something strong and resistant to corrosion for marine use or something beautiful and easy to clean for a restaurant.