Stainless steel can be seen everywhere in life, and there are various types, which are hard to tell apart. Today I will share with you an article to explain the knowledge points here.

Stainless steel is the abbreviation of stainless acid-resistant steel. Steels that are resistant to weak corrosive media such as air, steam, and water or have stainless properties are called stainless steels; and steels that are resistant to chemical corrosive media (acids, alkalis, salts, etc.) are called acid-resistant steels.

Stainless steel refers to steel that is resistant to weak corrosive media such as air, steam, and water and chemically corrosive media such as acids, alkalis, and salts, also known as stainless acid-resistant steel. In practical applications, steel that is resistant to weak corrosive media is often called stainless steel, while steel that is resistant to chemical media is called acid-resistant steel. Due to the difference in chemical composition between the two, the former is not necessarily resistant to chemical media corrosion, while the latter is generally rust-resistant. The corrosion resistance of stainless steel depends on the alloying elements contained in the steel.

Common classification:

Usually divided into:

Usually, according to the metallographic structure, ordinary stainless steel is divided into three categories: austenitic stainless steel, ferritic stainless steel, and martensitic stainless steel. Based on these three basic metallographic structures, duplex steel, precipitation hardening stainless steel, and high alloy steel with an iron content of less than 50% have been derived for specific needs and purposes.

1. Austenitic stainless steel.

The matrix is mainly austenitic structure (CY phase) with a face-centered cubic crystal structure, which is non-magnetic and is mainly strengthened by cold working (and may cause certain magnetism). The American Iron and Steel Association uses 200 and 300 series numbers, such as 304.

2. Ferritic stainless steel.

The matrix is mainly composed of a ferrite structure (a phase) with a body-centered cubic crystal structure. It is magnetic and generally cannot be hardened by heat treatment, but it can be slightly strengthened by cold working. The American Iron and Steel Association uses 430 and 446 as the mark.

3. Martensitic stainless steel.

The matrix is a martensitic structure (body-centered cubic or cubic), which is magnetic and can adjust its mechanical properties by heat treatment. The American Iron and Steel Association uses 410, 420 and 440 numbers. Martensite has an austenitic structure at high temperature. When cooled to room temperature at an appropriate rate, the austenitic structure can be transformed into martensite (i.e. hardened).

4. Austenitic-ferritic (duplex) stainless steel.

The matrix has both austenite and ferrite phases, in which the content of the lesser phase matrix is generally greater than 15%. It is magnetic and can be strengthened by cold working. 329 is a typical duplex stainless steel. Compared with austenitic stainless steel, duplex steel has high strength, resistance to intergranular corrosion, chloride stress corrosion and pitting corrosion. The corrosion resistance is significantly improved.

5. Precipitation hardening stainless steel.

The matrix is austenite or martensite, and the stainless steel can be hardened by precipitation hardening. The American Iron and Steel Institute uses the 600 series numbers, such as 630, which is 17-4PH.

Generally speaking, except for alloys, the corrosion resistance of austenitic stainless steel is relatively excellent. In a less corrosive environment, ferritic stainless steel can be used. In a mildly corrosive environment, if the material is required to have high strength or high hardness, martensitic stainless steel and precipitation hardening stainless steel can be used.

Performance and use

Stainless Steel Series Comparison

Series 200

ASTM Standard: 201

GB Standard (China): 1Cr17Mn6Ni5N

JIS Standard (SUS): SUS201

Properties:

Resistant to acid and alkali, high density, bubble-free and pinhole-free after polishing. Ideal material for faucets and decorative fittings.

Applications:

Primarily used for decorative pipes, industrial pipes, and shallow-drawn products.

ASTM Standard: 202

GB Standard (China): 1Cr18Mn8Ni5N

JIS Standard (SUS): SUS202

Properties:

Replaces partial nickel with Mn and N, offering excellent mechanical and corrosion resistance. A cost-effective stainless steel with higher high-temperature strength than 304 and good oxidation resistance below 800°C.

Applications:

Decorative pipes, industrial pipes, and shallow-drawn products.

ASTM Standard: 2205

GB Standard (China): 022Cr22Ni5Mo3N

JIS Standard (SUS): SUS2205

Properties:

Narrow ranges of Cr, Mo, and N elements enhance strength, corrosion resistance, and weldability. Used for high-performance welded materials like oil/gas pipelines.

Applications:

Oil refining, fertilizer, papermaking, petrochemical industries; heat exchangers and condensers for seawater/high-temperature/corrosive environments.

Series 300

ASTM Standard: 304

GB Standard (China): 1Cr18Ni9 (06Cr18Ni10)

JIS Standard (SUS): SUS304

Properties:

Versatile steel with excellent corrosion/heat resistance, low-temperature strength, and mechanical properties. Good hot-workability (e.g., stamping/bending), no hardening after heat treatment (non-magnetic, service temperature: -196°C to 800°C).

Applications:

Food industry, household items (tableware, cabinets, indoor pipes, water heaters, boilers, bathtubs).

JIS Standard (SUS): SUS304J1

Properties:

Contains added Cu, improving formability (especially ductility) and resistance to aging cracks. Suitable for complex shapes. Corrosion resistance matches 304.

Applications:

Thermos cups, kitchen sinks, pots, lids, lunchboxes, door handles, textile machinery.

ASTM Standard: 304L

GB Standard (China): 022Cr19Ni10

JIS Standard (SUS): SUS304L

Properties:

Low-carbon version of 304. Similar corrosion resistance but superior intergranular corrosion resistance post-welding/stress relief. Maintains performance without heat treatment (non-magnetic, -196°C to 800°C).

Applications:

Chemical, coal, and petroleum industries (outdoor equipment); heat-resistant parts where heat treatment is impractical.

ASTM Standard: 321

GB Standard (China): 1Cr18Ni9Ti

JIS Standard (SUS): SUS321

Properties:

Titanium (Ti) is added to 304 steel to prevent intergranular corrosion. Suitable for use at 430°C–900°C.

Applications:

Agriculture, ship components, nuclear industry, aircraft, exhaust pipes, boiler drums, automotive parts (windshield wipers, mufflers, molded products).

ASTM Standard: 316

GB Standard (China): 0Cr17Ni12Mo2

JIS Standard (SUS): SUS316

Properties:

Molybdenum (Mo) is added, providing exceptional corrosion resistance, atmospheric corrosion resistance, and high-temperature strength. Can be used in harsh conditions. Work-hardening properties (non-magnetic).

Applications:

Marine applications; chemical, dye, papermaking, oxalic acid, and fertilizer production equipment; photography/food industry; coastal facilities; cables, CD rods, bolts, nuts.

ASTM Standard: 316L

GB Standard (China): 00Cr17Ni14Mo2

JIS Standard (SUS): SUS316L

Properties:

Low-carbon version of 316 steel. Shares the same properties as 316 but with superior intergranular corrosion resistance.

Applications:

Products requiring enhanced intergranular corrosion resistance in 316 steel applications.

ASTM Standard: 309S

GB Standard (China): 0Cr23Ni13Mo2

JIS Standard (SUS): SUS309S

Properties:

High-alloy steel (23Cr-13Ni) with excellent corrosion resistance and strength. Suitable for parts operating at 1000°C.

Applications:

Exhaust systems, heat treatment furnaces, heat exchangers.

ASTM Standard: 310S

GB Standard (China): 0Cr25Ni20Si2

JIS Standard (SUS): SUS310S

Properties:

Outstanding oxidation resistance, corrosion resistance, and high-temperature performance. High chromium/nickel content ensures sustained operation under extreme heat.

Applications:

Boilers, exhaust systems, heat treatment furnaces, heat exchangers.

Series 400 (Ferritic/Martensitic Steels)

ASTM Standard: 409L

GB Standard (China): 00Cr12Ti

JIS Standard (SUS): SUS409L

Properties:

Most economical grade. Titanium (Ti) improves high-temperature corrosion resistance and strength. Ferritic stainless steel (chromium steel).

Applications:

Automotive exhaust pipes, heat exchangers, containers requiring post-weld non-heat treatment.

ASTM Standard: 410

GB Standard (China): 1Cr13

JIS Standard (SUS): SUS410

Properties:

Representative martensitic steel. High strength but unsuitable for highly corrosive environments. Good machinability; hardens after heat treatment (magnetic).

Applications:

Blades, mechanical parts, petroleum refining equipment, bolts, nuts, shafts, cutlery (knives, forks).

420J1 (GB: 2Cr13 / SUS420J1):

High hardness post-quenching, good corrosion resistance (magnetic).

Applications: Cutlery (knives), turbine blades.

420J2 (GB: 3Cr13 / SUS420J2):

Higher hardness than 420J1 after quenching (magnetic).

Applications: Blades, nozzles, valves, rulers, cutlery (scissors, knives).

ASTM Standard: 430

GB Standard (China): 1Cr17

JIS Standard (SUS): SUS430

Properties:

Representative ferritic steel. Low thermal expansion, excellent formability, and oxidation resistance.

Applications:

Heat-resistant utensils, burners, home appliances, Class 2 cutlery, kitchen sinks, exterior decor, bolts, nuts, CD rods, screens.

444

Applications:

Dedicated water tank panels.

Stainless steel Surface treatment

NO.1 Finish

Appearance: Silver-white, matte (non-reflective).

Manufacturing Process:

Hot-rolled to specified thickness, then annealed and descaled to produce a rough, non-reflective surface.

Applications:

Used where surface gloss is not required.

NO.2D Finish

Appearance: Silver-white, slightly brighter than NO.1 but still matte.

Manufacturing Process:

Cold-rolled, then heat-treated and acid-cleaned. Sometimes given a final light roll with dull rolls to achieve a uniform matte finish.

Applications:

General-purpose materials, deep-drawing applications where surface aesthetics are not critical.

NO.2B Finish

Appearance: Brighter than NO.2D with a smooth, lightly reflective surface.

Manufacturing Process:

NO.2D material undergoes additional light cold-rolling with polishing rollers to achieve a controlled gloss. This is the most common surface finish and can serve as a base for further polishing.

Applications:

General-purpose materials.

BA (Bright Annealed) Finish

Appearance: Mirror-like, highly reflective.

Manufacturing Process:

No formal standard, but typically involves bright annealing to produce an ultra-smooth, reflective surface.

Applications:

Architectural materials, kitchenware.

NO.3 Finish

Appearance: Coarsely ground, semi-reflective.

Manufacturing Process:

NO.2D or NO.2B material is ground with 100–200-grit abrasive belts.

Applications:

Architectural materials, kitchenware.

NO.4 Finish

Appearance: Medium-gloss, with visible "grain" and uniform reflectivity.

Manufacturing Process:

NO.2D or NO.2B material is polished with 150–180-grit abrasive belts to create a standardized reflective surface.

Applications:

Similar to NO.3 (architecture, kitchenware).

Stainless steel thickness

Because during the rolling process of the steel mill machinery, the rollers are slightly deformed by heat, resulting in deviations in the thickness of the rolled plates, which are generally thick in the middle and thin on both sides. When measuring the thickness of the plate, the state stipulates that the middle part of the plate head should be measured.

What kind of stainless steel is not easy to rust?

There are three main factors that affect the corrosion of stainless steel:

1. The content of alloy elements.

Generally speaking, steel with a chromium content of 10.5% is not easy to rust. The higher the content of chromium and nickel, the better the corrosion resistance. For example, the nickel content of 304 material is 8-10%, and the chromium content reaches 18-20%. Such stainless steel will not rust under normal circumstances.

2. The smelting process of the production enterprise will also affect the corrosion resistance of stainless steel.

Large stainless steel plants with good smelting technology, advanced equipment and advanced technology can ensure the control of alloy elements, removal of impurities and control of billet cooling temperature. Therefore, the product quality is stable and reliable, the internal quality is good, and it is not easy to rust. On the contrary, some small steel plants have backward equipment and backward technology. During the smelting process, impurities cannot be removed, and the products produced will inevitably rust.

3. External environment, dry and well-ventilated environment is not easy to rust.

However, areas with high air humidity, continuous rainy weather, or high acidity and alkalinity in the air are prone to rust. 304 stainless steel will also rust if the surrounding environment is too bad.

How to deal with rust on stainless steel?

1. Chemical method

Use pickling paste or spray to assist the rusted parts to passivate again to form a chromium oxide film to restore its corrosion resistance. After pickling, it is very important to rinse with clean water properly to remove all pollutants and acid residues. After all treatments, re-polish with polishing equipment and seal with polishing wax. For local slight rust, you can also use a 1:1 gasoline and engine oil mixture with a clean rag to wipe off the rust.

2. Mechanical method

Sandblasting, shot blasting with glass or ceramic particles, annihilation, brushing and polishing. Mechanical methods may wipe off the pollution caused by previously removed materials, polishing materials or annihilation materials. All kinds of pollution, especially foreign iron particles, may become a source of corrosion, especially in humid environments. Therefore, the mechanically cleaned surface should preferably be cleaned formally under dry conditions. The mechanical method can only clean the surface, and cannot change the corrosion resistance of the material itself. Therefore, it is recommended to re-polish with polishing equipment after mechanical cleaning and seal with polishing wax.

Foshan Sucelsteel Co., Ltd. is a premier manufacturer and global exporter of high-end stainless steel products. We specialize in decorative stainless steel sheets, tile trims, metal meshes, and custom-made stainless steel solutions.

With a strong focus on design, quality, and customer satisfaction, Sucelsteel proudly serves clients across the architecture, interior design, and construction industries worldwide.