SUS304 Stainless Steel vs SS304: What’s the Difference?

SUS304 (SUS meaning Steel Use Stainless) stainless steel austenite is typically known as the Japanese name for SS304 or AISI 304. The main difference between the two materials is not any physical property or feature, but how it is referenced in American and Japanese grades. However, that has not stopped various people from attempting to explain the mechanical differences between the two grades.

SUS304 (Japanese JIS Standard) is one of the most widely used versions of stainless steel. It is made up of 18% Cr (Chromium) and 8% Ni (Nickel). In high and low temperatures, it can maintain its strength and heat resistance. It also has great weldability, mechanical properties, cold workability and corrosion resistance at room temperature.

SS304 (AISI 304) is the most frequently used stainless steel when making other stainless steel materials and is typically bought in a cold or annealed condition. Similar to SUS304, SS304 also contains 18% Cr and 8% Ni and is, therefore, referred to as 18/8.

SS304 has great weldability, heat and corrosion resistance, low-temperature strength, processability, mechanical properties, no hardening from heat treatment, and great warm workability like bending and stamping. SS304 is used in a vast array of applications in many industries, including food, medical and decoration work.

Chemical compositions of SUS304 and SS 304

  SUS304 SS 304
Carbon (C) ≤ 0.08 ≤ 0.07
Silicon (Si) ≤ 1.00 ≤ 0.75
Manganese (Mn) ≤ 2.00 ≤ 2.00
Phosphorus (P) ≤ 0.045 ≤ 0.045
Sulfur (S) ≤ 0.03 ≤ 0.03
Chromium (Cr) 18.00 - 20.00 17.50 - 19.50
Nickel (Ni) 8.00 - 10.50 8.00 - 10.50

 

Corrosion resistance of stainless steel 304

Stainless steel 304 is known to be excellent in a wide variety of atmospheric settings and in the company of various corrosive media. However, in a warm chloride environment, it can be liable to pitting, crevice corrosion, and stress corrosion when the temperature goes above 60 °C.

It is also considered to be resistant to drinkable water up to around 200 mg/L of chloride, at ambient temperatures.

Physical properties of SUS304 and SS304

Density (g/cm3) 7.8 - 8.2
Melting point (℃) 1,230 - 1,480
Specific heat (J/kg·℃) 440 - 500
Electrical resistivity (Ω·m) (20℃)

7.3*10-7 - 8.5*10-7

Coefficient of thermal expansion (1/K) 1.7*10-5 - 1.9*10-5
Thermal conductivity (W/m·K) 14 - 20


Both materials are extremely close to one another in physical and chemical properties, so it can easily be said that they are the same materials as per these properties.

Again, the main difference between the two is the standardisation between the American and Japanese nations. This means that each material can be used alternatively to the other unless there are specific regulations or requirements stated by the state or customer.

Welding of stainless steel 304

As mentioned above, stainless steel 304 has great weldability both including and not including filler materials. It is also applicable to all of the conventional welding techniques.

If the highest corrosion resistance is required, segments that have been substantially welded may be annealed post-weld. However, this is not needed for 304L. If a big area of welding is required and heat treatment post-weld is not an option, then stainless steel grade 321 can be used as an alternative to 304.

In the hot section of the weld, intrinsic corrosion, which is referred to as intergranular corrosion, can occur as stainless steel is being welded. If weldability is a priority for the application, stainless steel 304 is specifically resistant to this certain type of corrosion.

Stainless steels, in general, also become quite fragile and may crack in very extreme temperatures, such as those in a cryogenic environment. However, SUS304 has a high fracture toughness when subjected to a situation like this.

In many austenitic stainless steels, the difference between the steels comes from what alloy components have been added or removed. Therefore, SUS304 is referred to as the mother of many other SUS materials.

Grade specification comparison

Grade UNS No Old British Euronorm Swedish SS Japanese JIS
BS En No Name
304 S30400 304S31 58E 1.4301 X5CrNi18-10 2332 SUS 304
304L S30403 304S11 1.4306 X2CrNi19-11 2352 SUS 304L
304H S30409 304S51 1.4948 X6CrNi18-11

 

Applications of SUS304 and SS304

Both of these stainless steels have a wide range of applications spanning nearly every industry. Each variant can be roll-formed or baked into components used for industrial applications, like processing equipment, machinery parts, car headers, and also many household applications (including screws, food handling, food utensils and many more).

Architects also use stainless steel 304 for accents to exterior designs like fire and water features, railings, trim and panelling.

Grade 304 has a really balanced austenitic structure that allows it to be extremely deep drawn with the need for intermediate annealing. This means that it is the dominant material for the creation of drawn stainless steel parts like hollow-ware, saucepans and sinks.

Do you have any experience with any of these two stainless steels? They both have a vast array of applications and it is likely that anyone who has worked with stainless steel in the past has come across some version of grade 304 stainless steel.

  • The main difference between both SUS304 and SS304 is how the material is referenced as a Japanese or American grade.
  • SS304 and SUS304 are both very widely used stainless steel variants.
  • They are very close in chemical and physical properties.
  • Both have many uses in industrial and household applications.

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