The Differences Between SUS303 and SUS304
2025/9/29
SUS303 and SUS304 are two of the most common stainless steel grades, with both being classified as austenitic stainless steels and containing nickel. Both are readily available, with SUS304 in particular being the most widely used stainless steel grade due to its high availability and low cost. This article explains some of the key differences between these two commonly used stainless steel grades!
SUS303 and SUS304 Physical Composition Comparison
Material Name | Carbon (C) | Silicon (Si) | Manganese (Mn) | Phosphorus (P) | Sulfur (S) | Nickel (Ni) | Chromium (Cr) |
|---|---|---|---|---|---|---|---|
SUS303 | 0.15% or less | 1% or less | 2% or less | 0.20% or less | 0.15% or less | 8.0 - 10.0% or less | 17.0-19.0% |
SUS304 | 0.08% or less | 1% or less | 2% or less | 0.045% or less | 0.030% or less | 8.0 – 10.50% | 18.0-20.0% |
Appearance (Visual Differences)
There is virtually no difference in appearance between SUS303 and SUS304, so it is difficult to distinguish them by visual inspection alone.
Magnetic Properties
Both SUS303 and SUS304 are non-magnetic, so they cannot be identified with a magnet. However, work-hardened areas caused by machining may develop some magnetism due to structural changes.
Machinability
SUS304 is tough and has a tendency to stick to cutting tools, which makes its machinability relatively poor. SUS303, on the other hand, contains phosphorus and sulfur, making it easier to machine by sticking less to cutting tools.
Weldability
SUS303 contains higher amounts of phosphorus and sulfur, which negatively affects its weldability. If welding is required, SUS304 is more suitable.
Corrosion Resistance
Stainless steel is known for its excellent corrosion resistance, and SUS304 offers better corrosion resistance than SUS303. For applications involving exposure to water or corrosive environments, SUS304 is preferred.
Galling Resistance
SUS304 can suffer from galling (seizure) when metal surfaces rub against each other and stick. SUS303 is more resistant to galling, making it better suited for environments where metal-to-metal contact and friction occur.
Differences in Chips During Machining
As previously mentioned, SUS303, which contains phosphorus and sulfur, has less stickiness, while SUS304 is more ductile and sticky. When machined on a lathe, SUS303 tends to produce powdery chips, while SUS304 tends to generate continuous, ribbon-like chips due to its higher ductility.
Key Points
SUS303 and SUS304 share similar mechanical properties, but depending on the application and machining method, one may be more suitable than the other.
For machining, SUS303 performs better, while for welding, SUS304 performs better.
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