SUS 304 stainless steel is the most versatile and widely used grade of stainless steel globally, valued for its superior combination of strength, workability, and corrosion resistance. The designation SUS stands for “Steel Use Stainless” and originates from the Japanese Industrial Standards (JIS) system. SUS 304 is functionally equivalent to the globally recognized AISI 304 designation, sharing almost identical chemical and mechanical properties. Its widespread adoption is due to its balanced characteristics, making it the preferred material for a vast array of applications, from industrial components to everyday household items.
The Chemical Makeup of SUS 304
SUS 304 is categorized as an austenitic stainless steel, characterized by a face-centered cubic crystal structure. This structure is primarily stabilized by the inclusion of nickel, a defining element of the 300-series stainless steels. The composition is famously known as the “18/8” grade because of its two primary alloying elements: Chromium and Nickel.
The alloy contains Chromium content that typically ranges between 18% and 20% by weight, which is the foundational component responsible for the material’s rust resistance. Nickel is present in a range of 8% to 10.5%, contributing to the alloy’s strength, ductility, and resistance to various corrosive agents.
Carbon is also included, kept at a maximum of 0.08%. Keeping the carbon content low helps maintain the steel’s ductility and its resistance to a specific type of corrosion that can occur after welding. Other trace elements, such as Manganese and Silicon, are included to improve the alloy’s structural integrity and oxidation resistance.
Defining Performance Characteristics
The high chromium content allows SUS 304 to develop a thin, continuous, and self-healing Chromium Oxide layer on its surface, known as the passive layer. This invisible film acts as a barrier, preventing oxygen from reaching the underlying iron, which resists rust and general atmospheric corrosion. This passive layer is the most important feature that makes the alloy “stainless.”
Despite its excellent general corrosion resistance, the material is vulnerable to chlorides, such as those found in salt water. Exposure to warm, concentrated chloride environments can lead to pitting corrosion and crevice corrosion. At temperatures above approximately 60°C, it becomes susceptible to stress corrosion cracking, which is why a similar grade, like 316 stainless steel (which includes Molybdenum), is often chosen for marine environments.
The austenitic structure, stabilized by nickel, gives the steel excellent ductility and formability. This allows manufacturers to easily deep-draw the material into complex shapes, such as kitchen sinks and hollow-ware, without requiring intermediate annealing. SUS 304 exhibits excellent weldability and can be joined using all common fusion welding techniques, simplifying its fabrication in industrial settings.
The alloy is non-magnetic in the annealed condition. The austenitic crystal structure prevents the formation of magnetic phases typically found in other steel types. However, cold working (mechanically deforming the steel) can introduce localized phase changes, making the material become slightly magnetic.
Widespread Industrial and Household Uses
The blend of corrosion resistance, strength, and ease of fabrication makes SUS 304 highly utilized across numerous sectors. In the food and beverage industry, its non-reactive and hygienic surface is relied upon for manufacturing kitchen equipment, including sinks, cutlery, and food processing machinery. It is also the standard material for brewing tanks and dairy equipment because it resists the mild acids found in these products.
The construction and architectural fields utilize its durability and aesthetic appeal for both functional and decorative purposes. This includes applications such as building facades, handrails, staircases, and outdoor fixtures that must withstand weather exposure. Its resilience and clean finish ensure that these elements maintain their appearance over a long service life.
In the automotive and industrial sectors, SUS 304 is used for components in moderately corrosive conditions. Common applications include exhaust systems, engine parts, storage tanks, and piping for chemical and pharmaceutical processing equipment. Its blend of heat resistance and mechanical strength is leveraged in these demanding environments where continuous operation is paramount.