Key Differences Between Stainless Steel Grades SUS304 and SUS316

Have you ever wondered about the meaning behind those cryptic codes like "SUS304" or "SUS316" engraved on stainless steel products? These aren't random numbers—they serve as the material's unique identifier, containing crucial information about its composition and properties.

The prefix "SUS" stands for "Steel Use Stainless," indicating stainless steel under the Japanese Industrial Standards (JIS) system. Similar to how identification numbers begin with regional codes, SUS serves as the standard marker for stainless steel materials in this classification system.

Beyond SUS, other letters in JIS steel codes carry specific meanings:

• F: Ferrum (Iron) - e.g., FC360 indicates cast iron
• S: Steel - e.g., SS400 represents general structural steel
• A: Aluminium - e.g., A1050 denotes pure aluminum
• C: Copper - e.g., C1020 signifies pure copper
• N: Nickel - e.g., NW2200 represents nickel alloy

• K: Tool steel (Kogu) - e.g., SK85 is carbon tool steel
• KS: Alloy tool steel - e.g., SKS51
• C: Cast steel - e.g., FC350
• F: Forged steel - e.g., SF490
• S: Structural steel - e.g., SS400
• UJ: Bearing steel - e.g., SUJ2
• UP: Spring steel - e.g., SUP10

The three digits following SUS indicate specific steel grades, with the first digit representing the primary classification:

• 200 Series: Chromium-nickel-manganese austenitic stainless steel. These grades use manganese as a partial nickel substitute, offering lower cost but reduced corrosion resistance compared to 300 series.
• 300 Series: Chromium-nickel austenitic stainless steel. The most widely used group, known for excellent corrosion resistance, weldability, and mechanical properties. Common examples include SUS304 and SUS316.
• 400 Series: Chromium-based stainless steel, divided into martensitic and ferritic types. While offering higher strength and hardness than 300 series, they have lower corrosion resistance. Examples include SUS430 and SUS420J2.
• 600 Series: Precipitation-hardening chromium-nickel stainless steel. These grades achieve exceptional strength through heat treatment, often used for high-strength components. Examples include SUS631 and SUS632J1.

The last two digits serve to differentiate specific grades within each category.

Additional letters or numbers in steel grades convey special characteristics:

• L: Low carbon content (e.g., SUS304L, SUS316L) - improves weldability and resistance to intergranular corrosion
• J1/J2: Special Japanese grades (e.g., SUS420J2, SUS329J1)
• XM: Special grades under ASTM standards (e.g., SUSXM7)
• N: Nitrogen-added (e.g., SUS304N1) - enhances strength and corrosion resistance

Other suffixes indicate material form:

• B: Bar stock
• WR: Wire rod
• HP: Hot-rolled plate
• CP: Cold-rolled plate

• SUS304: The most common austenitic stainless steel, offering excellent corrosion resistance, heat resistance, and mechanical properties. Widely used in food processing, medical equipment, and chemical applications.
• SUS304L: Low-carbon version of 304, with improved weldability and intergranular corrosion resistance.
• SUS316: Enhanced version of 304 with added molybdenum for superior corrosion resistance, particularly in chloride environments. Common in marine and chemical processing equipment.
• SUS316L: Low-carbon variant of 316 with better welding characteristics.
• SUS430: Ferritic stainless steel with good corrosion resistance and formability, but lower strength. Frequently used in kitchenware and appliances.
• SUS420J2: Martensitic stainless steel offering high strength and hardness, though with limited corrosion resistance. Used for cutlery and valves.

Different standardization systems worldwide use varying designations for the same materials. Below is a reference table showing equivalent grades across major standards:

Understanding these stainless steel grade designations enables informed material selection for various applications. With this knowledge, those mysterious codes on metal products become clear indicators of a material's properties and intended uses.