SUS303 vs SUS304: Which Stainless Steel for Precision-Machined Parts?

SUS303 and SUS304 are austenitic stainless steels commonly specified for shafts, bushings, fittings, brackets, housings and equipment components. Their appearance is similar, but their behavior during machining and in service is not the same. SUS303 is generally selected when machining productivity and chip control are priorities. SUS304 is usually preferred when corrosion resistance, forming or welding matters more. The two grades should therefore not be interchanged simply because both are called stainless steel.

SUS303 is useful for parts with extensive turning, multiple threads or holes, and relatively high production quantities when the service environment is mild. Examples include small shafts, spacers, bushings, fittings, pins and indoor mechanism components. It should not be selected automatically for chloride exposure, repeated contact with water or chemicals, food-contact requirements, or welded assemblies. In these cases, the designer should confirm the appropriate stainless grade for the actual environment.

SUS304 provides a practical balance of corrosion resistance, strength, formability and weldability. It is commonly considered for brackets, plates, housings, equipment components and parts used in ordinary humid environments. However, SUS304 is not immune to corrosion. Chlorides, temperature, crevices, surface roughness and iron contamination can damage its passive condition. Marine or aggressive chemical service may require a higher-alloyed stainless steel rather than a simple change from SUS303 to SUS304.

Only with approval from the designer or customer. A substitution may reduce machining time but can change corrosion resistance, welding behavior and suitability for the intended service. For build-to-print work, VietTech uses the specified material or requests written confirmation before applying an alternative. An RFQ should state the material standard, product form, certificate requirement, surface condition, welding requirement and service environment where relevant. This prevents a quotation based on one stainless grade from being applied to a part that needs the properties of another.

VietTech manufactures build-to-print components using CNC milling, CNC turning, grinding and wire EDM as appropriate to the geometry and technical requirements. Inspection planning follows the critical dimensions, datums and tolerances shown on the drawing. Surface treatment or specialist operations, where requested, are coordinated with suitable partners and checked according to the order requirements. Actual feasibility depends on part size, tolerance, quantity, material availability and inspection requirements. VietTech does not apply one universal machining condition to every stainless-steel component.

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メインキーワード: SUS303 SUS304 違い