SUS 309 Chemical Composition

Chromium (Cr): This is one of the main alloying elements of SUS 309 stainless steel, and its content is usually between 19.5%-22.0% or 17.00%-19.00% (data given

Chromium (Cr): This is one of the main alloying elements of SUS 309 stainless steel, and its content is usually between 19.5%-22.0% or 17.00%-19.00% (data given by different sources vary slightly). The addition of chromium can improve the corrosion resistance of stainless steel, especially in oxidizing media.
Nickel (Ni): Nickel is another important alloying element, and its content in SUS 309 is usually 11.5%-14.0% or 12%-15%. The addition of nickel helps stainless steel maintain austenite structure and improve its strength and corrosion resistance at high temperatures.
Molybdenum (Mo): The content of molybdenum is between 2.0% and 3.0%, and its addition can further improve the corrosion resistance of stainless steel, especially in reducing media.
In addition, SUS 309 stainless steel also contains the following elements, but the content is relatively low:

Carbon (C): The content is usually controlled below 0.08% or 0.20% to reduce the formation of carbides and avoid adverse effects on the performance of the material.
Silicon (Si): The content does not exceed 1.00%, usually added as a deoxidizer.
Manganese (Mn): The content does not exceed 2.00%, which helps to improve the processing and welding properties of stainless steel.
Sulfur (S) and phosphorus (P): As impurity elements, their contents are controlled below 0.030% and 0.035% respectively to ensure the purity and performance of the material.

These chemical components jointly determine that SUS 309 stainless steel has excellent corrosion resistance and mechanical properties in high temperature environments, and can effectively resist oxidation, acid, alkali and other corrosive media. Therefore, it is mainly used in high-temperature equipment and pipelines and other fields.

stainless steel processing

The manufacture of stainless steel involves a series of processes. First, the steel is melted, and then it is cast into solid form. After various forming steps, the steel is heat treated and then cleaned and polished to give it the desired finish. Next, it is packaged and sent to manufacturers, who weld and join the steel to produce the desired shapes.

The raw materials that constitute a stainless steel item are placed together and melted in a giant electric furnace. Intense heat is applied rigorously for a period of 8 to 12 hours during this step. Once the melting is complete, the molten steel is cast into desired semi-finished forms. Some of the most common forms or shapes include slabs, blooms (rectangular shapes), billets (these could either be round or square), rods, and tube rounds.

In the second stage, the semi-finished steel shapes undergo a series of forming operations. For instance, the stainless steel is hot rolled (heated and passed through enormous rolls). The blooms and billets mentioned above are converted to bar and wire. The slabs on the other hand are formed into plates, strips or sheets. It is very common to turn semi-finished steel shapes into bars, as it is the most versatile stainless steel form (it comes in all grades and sizes). You have round, square, octagonal, and hexagonal bars, each suitable for a different type of application.

The various stainless steel forms undergo a thorough annealing process during this step. Annealing is another name for heat treatment where the stainless steel is heated and cooled in a controlled environment. The purpose of this heat treatment is to relieve the pent-up stress inside the stainless steel and soften the material to make it more suitable for a wide variety of applications. The people in charge of carrying out the annealing process have to be very careful about the conditions as even the slightest of changes in the temperature, pressure, duration, or cooling rate could result in a faulty product.

During the annealing process, a certain amount of scale appears on the surface of the stainless steel. This scale can be removed using a number of different processes that are collectively known as descaling. Pickling is one of the more common methods of carrying out the descaling process.

The semi-finished, heat-treated, and descaled stainless steel forms are cut into specific shapes in this step. Mechanical cutting is performed with the aid of guillotine knives, blanking, nibbling, and high-speed blades.

Finishing is applied to help the stainless steel product achieve its signature aesthetically appealing appearance. Finishes are also needed to make the stainless steel product smooth and easier to clean, which is a top requirement in sanitary applications.