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

  • The main difference between both SUS304 and SS304 is how it is referenced to with regards to American and Japanese grades
  • 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

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 to in American and Japanese grades.

However, that has not stopped various people from attempting to explain the mechanical differences between the two steels. In one instance a sample of SS304 that was obtained from an American source, and a sample of SUS304 that was gathered from a Japanese source were both sent to a testing laboratory.

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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 keep its heat and strength resistance, while also having 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 steels and is typically bought in a cold or annealed condition. Similar to SUS304, SS304 also contains 18% Cr and Ni, and therefore is also 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 decorational work etc. Read more in our AISI 304 Stainless Steel: Specification and Datasheet article.

SUS304, SS304: Chemical Composition

Temperature Range
Steel Grade SUS304 SS 304
C ≤ 0.08 0.07
Si ≤ 1 0.75
Mn ≤ 2 2
P ≤ 0.045 0.045
S ≤ 0.03 0.03
Cr 18.00-20.00 17.5-19.5
Ni 8.00-10.50 8.0-10.5

Corrosion Resistance

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 also stresses corrosion when the temperature is approximately above 60 degrees celsius. It is also considered to be resistant to drinkable water up to around 200 mg/L of chloride, at ambient temperatures.

SUS304, SS304: Physical Properties

Density (g/cm3) Melting point (℃) Specific heat (J/kg·℃)
SUS304 Material 7.93 1,400-1,450 460-502
SS 304 Material 7.93 1398-1454 500 at 0-100℃
Electrical resistivity (μΩ·m) (20℃) Thermal expansion (10-6/K) Thermal conductivity (W/m·K)
SUS304 Material 0.73 16.3 (20-100℃) 16.8 (100℃)
Physical Properties ≤ 17.8 (20-300℃)
18.4 (20-500℃)
SS 304 Material 0.73 17.2 (0-100℃) 16.3 (100 ℃)
Physical Properties 17.8 (0-300℃
18.4 (0-500℃)

As can be seen from the above table, 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 standardization between the American and Japanese nations. This means that each material can be used alternatively to each other, unless there are specific regulations or requirements stated by the state or customer.

Welding

As mentioned above stainless steel 304 has great weldability including and not including filler materials, and through 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 when 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 high 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

SUS304, SS304: Applications

Both of these stainless steels have a wide range of applications spanning across 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 like 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 paneling.

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 draw 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 any one that has worked with stainless steel in the past has come across some version of grade 304 stainless steel.

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