What Material Is Sus?

In modern industrial manufacturing and household products, we often come into contact with the names and codes of various metal materials. Among them, the word "SUS" is particularly common, especially in the identification of stainless steel products, such as SUS304, SUS316, SUS430, etc. For those who are not familiar with metal materials, what material does "SUS" represent? What types are there? What scenarios are different SUS materials suitable for? This article will introduce the sus material in detail.

What Is Sus?

SUS is the abbreviation of "Steel Use Stainless", which literally means "(stainless) steel for steel". It comes from the naming system of stainless steel in Japanese Industrial Standards (JIS). In the JIS system, all stainless steel materials start with SUS, followed by numbers and letters to indicate the specific brand, for example, SUS304 represents 304 type stainless steel. Internationally, different countries have their own naming methods: for example, the United States uses AISI (American Iron and Steel Institute), China uses GB (national standard), and Japan uses JIS, among which "SUS" is one of its naming features.

Many people mistakenly believe that SUS is a special metal material. In fact, it is more like a "general term" or "code" to describe a class of stainless steel alloys with specific composition and performance. In practical applications, the number after SUS is the key factor that truly determines the performance of the material.

What Is Stainless Steel?

To understand SUS, you must first understand what stainless steel is. Stainless steel is an iron-based alloy containing at least 10.5% chromium (Cr). The role of chromium is to form a dense chromium oxide passivation film on the surface of the material, which can effectively resist corrosion and oxidation. Compared with ordinary carbon steel, stainless steel is not only corrosion-resistant and high-strength, but also has excellent toughness and processing properties. It is widely used in various environments that require high strength or high durability.

Stainless steel can be divided into several categories according to the metallographic structure, such as austenite, ferrite, martensite and duplex stainless steel, and the SUS system covers almost all of these types.

Why Does Stainless Steel Not Rust?

The reason why stainless steel is "stainless" is not because it does not undergo oxidation reaction, but because a dense chromium-rich oxide film can naturally form on its surface. This passivation film is extremely thin but very strong, which can effectively prevent oxygen and moisture from continuing to erode the metal surface.

As long as the chromium (Cr) content in the alloy exceeds 10.5%, the carbon content is less than 1.2%, and certain environmental conditions are maintained, stainless steel can maintain good corrosion resistance. This structure makes SUS series stainless steel still stable in humid, acidic or salt spray environments.

Classification Of Sus Materials

According to the differences in metallographic structure and mechanical properties, SUS stainless steel can be roughly divided into the following categories:

Austenitic stainless steel:

Austenitic SUS stainless steel is currently the most widely used type, with representative models such as SUS304, SUS316, SUS321, etc. This type of stainless steel is known for its excellent corrosion resistance, weldability and formability, and is non-magnetic in most cases. It is widely used in tableware, chemical equipment, architectural decoration and other fields. Among them, SUS304 is a "universal material", and SUS316 has improved resistance to chlorides due to the addition of molybdenum (Mo) elements, making it suitable for marine environments or chemical sites.

Ferritic stainless steel:

Ferritic SUS stainless steel is represented by SUS430, SUS409, etc. This type of steel contains a high proportion of chromium and almost no nickel, so the cost is low. They are magnetic and have moderate corrosion resistance, and are suitable for places that do not withstand high corrosion, such as interior panels and washing machine tanks.

Martensitic stainless steel:

Martensitic SUS stainless steel, such as SUS410, SUS420 and SUS440, can change hardness and strength through heat treatment, so it is often used to make parts that require high hardness, such as knives, valves, and pump shafts. However, the corrosion resistance of this type of steel is relatively poor, so you need to pay attention to rust prevention when using it.

Duplex stainless steel:

Duplex stainless steel, such as SUS329J1, combines austenite and ferrite, and has both strength and corrosion resistance. It is especially suitable for harsh environments such as shipbuilding, oil equipment and brine treatment.

Common Sus Models

Understanding the common SUS material models will help you make smarter decisions in material selection and project design:

• SUS201: It is a low-nickel austenitic stainless steel, with manganese added to reduce costs, high strength but average corrosion resistance.
• SUS304: General-purpose stainless steel with balanced performance and excellent oxidation resistance and corrosion resistance.
• SUS316: Enhanced stainless steel, strong resistance to chlorine corrosion, suitable for marine and medical environments;
• SUS430: Magnetic ferritic stainless steel, nickel-free, economical and practical, magnetic, general corrosion resistance, suitable for decoration and home appliance back panels;
• SUS410/420: High-hardness stainless steel, belonging to martensitic stainless steel. It can be hardened by heat treatment and is suitable for making knives and bearings;
• SUS310S: High-temperature corrosion-resistant type, suitable for industrial furnace equipment;
• SUS321: Add titanium to improve intergranular corrosion, often used in high-temperature continuous use environments.

Effect Of Chemical Composition On Performance

The performance of different SUS materials depends on the combination and content of their alloy elements. For example, the main components of SUS304 are chromium (18%) and nickel (8%). This "18-8" combination gives it extremely strong corrosion resistance and forming properties. On the basis of SUS316, 2-3% molybdenum is added, which greatly enhances its corrosion resistance in chloride environments.

If the nickel content is reduced and replaced by manganese, cheap stainless steel such as SUS201 will be formed. Although its cost is low, its corrosion resistance and welding performance are poor. Therefore, the selection of materials must be considered in combination with specific uses, use environment, budget requirements and other aspects.

Analysis Of Misunderstandings About Sus Materials

Many users have some misunderstandings about SUS materials. For example:

 SUS will not rust?

This is wrong. Stainless steel is not "absolutely rust-free", especially in high-salt, high-humidity, and high-pollution environments, rust spots will still appear;

 SUS is equal to 304?

No. SUS is a series code, and 304 is just one of the models;

 SUS must be non-magnetic?

Only austenite is basically non-magnetic, while ferrite and martensite are magnetic;

 The higher the price, the better?

This is not the case. The model should be selected reasonably according to the actual environment.

Correspondence Between JIS And International Standards

Different countries have different names for stainless steel, but in most cases they can correspond to each other:

SUS stainless steel is not a single material, but a representative of a series of stainless steels. Behind each of its models, it represents different alloy ratios, performance characteristics and application scenarios. As a user, choosing the right susc material can not only improve product quality, but also extend its service life.