Judging by the name, you might assume that stainless steel never stains—but you’d be wrong.
Stainless steel stains less easily than other iron-based metals, but it’s not literally “stainless”. Just like standard steel, stainless can get marked up by fingerprints and grease, discolor, and eventually rust. The difference is resilience. Stainless steel can withstand much more time and abuse before showing signs of wear.
What is stainless steel?
Stainless steel is an alloy of iron that is resistant to rusting and corrosion. It contains at least 11% chromium and may contain elements such as carbon, other nonmetals and metals to obtain other desired properties. Stainless steel‘s resistance to corrosion results from the chromium, which forms a passive film that can protect the material and self-heal in the presence of oxygen.
The resistance to corrosion and luster are used in many applications. Stainless steel can be rolled into sheets, plates, bars, wire, and tubing. These can be used in cookware, cutlery, surgical instruments, major appliances, vehicles, construction material in large buildings, industrial equipment (e.g., in paper mills, chemical plants, water treatment), and storage tanks and tankers for chemicals and food products.
The biological cleanability of stainless steel is superior to both aluminium and copper, having a biological cleanability comparable to glass.Its cleanability, strength, and corrosion resistance have prompted the use of stainless steel in pharmaceutical and food processing plants.
Different types of stainless steel are labeled with an AISI three-digit number,The ISO 15510 standard lists the chemical compositions of stainless steels of the specifications in existing ISO, ASTM, EN, JIS, and GB standards in a useful interchange table.
Common stainless steels
The two most common stainless steel grades are 304 and 316. The key difference is the addition of molybdenum, an alloy which drastically enhances corrosion resistance, especially for more saline or chloride-exposed environments.
316 stainless steel contains molybdenum. 304 stainless steel does not.
For outdoor furnishings like rails and bollards, stainless steel is an ideal corrosion-resistant material, but it will only withstand long-term exposure if the grade is appropriate for its environment. 304 is an economical and practical choice for most environments, but it doesn’t have the chloride resistance of 316. The slightly higher price point of 316 is well worth it in areas with high chloride exposure, especially near the ocean or by heavily salted roadways. Each application for stainless steel has unique demands and needs a stainless steel that’s up to the task.
Other common consumer stainless steels include 409 and 430.
304 Stainless Steel
SAE 304 stainless steel is the most common stainless steel. The steel contains both chromium (between 18% and 20%) and nickel (between 8% and 10.5%) metals as the main non-iron constituents. 304 stainless steel is an austenitic stainless steel. 304 stainless steel is less electrically and thermally conductive than carbon steel. 304 stainless steel is magnetic, but less magnetic than steel. 304 stainless steel has a higher corrosion resistance than regular steel and is widely used because of the ease in which it is formed into various shapes.
The composition was developed by W. H. Hatfield at Firth-Vickers in 1924 and was marketed under the trade name “Staybrite 18/8”.304 stainless steel is specified by SAE International as part of its SAE steel grades. Outside the US it is commonly known as A2 stainless steel, in accordance with ISO 3506 for fasteners.In the commercial cookware industry it is known as 18/8 stainless steel. In the unified numbering system it is UNS S30400 The Japanese equivalent grade of this material is SUS304. It is also specified in European norm 1.4301.
Common uses for 304 stainless steel:
- Storage tanks
- Fasteners and finishing hardware (screws, nuts, bolts, plates, handles)
- Pots and pans
- Residential sinks and sink parts
- Indoor architectural/decorative hardware (panels, sculptures, sconces)
- Equipment tubing
Residential appliances
316 Stainless Steel
316 grade is the second-most common form of stainless steel. It has almost the same physical and mechanical properties as 304 stainless steel, and contains a similar material make-up. The key difference is that 316 stainless steel incorporates about 2 to 3 percent molybdenum. The addition increases corrosion resistance, particularly against chlorides and other industrial solvents.316 stainless steel has additional molybdenum that gives it resistance to chlorides and other processing chemicals.
316 stainless steel is commonly used in many industrial applications involving processing chemicals, as well as high-saline environments such as coastal regions and outdoor areas where de-icing salts are common. Due to its non-reactive qualities, 316 stainless steel is also used in the manufacture of medical surgical instruments.
Alternative 300-series grades can contain up to 7 percent molybdenum. They provide even better chloride resistance, but such heavy-duty resistance is only necessary in industrial or high concentration exposure conditions.
Common uses for 316 stainless steel:
- We now see 316 stainless steel routinely diagnosed for processing and construction applications as varied as:
- Heat exchangers;
- Pharmaceutical equipment;
- Food contact and processing equipment;
- Pasteurization and fermentation tanks.