STAINLESS STEEL OVERVIEW: TUTORIAL
Third Branch
Nickel Containing:
When nickel is added and the chromium level is increased, the structure changes
again and it is called "Austenitic" and they have the following
characteristics:
- Are NOT magnetic
- CANNOT be hardened by "heat treatment" BUT CAN be hardened by cold working
- Have the "BEST" corrosion resistance
- Can be easily welded
- Have excellent cleanability and hygiene characteristics
- Have exceptional resistance to both high and low temperature
Common Uses:
- Kitchen sinks
- Architectural applications such as roofs and gutters, doors and windows, tubular frames
- Food processing equipment
- Restaurant food preparation areas
- Chemical vessels
- Ovens
- Heat exchangers
Common Grades:
Stainless is designated by three different systems
- Metallurgical structure - Austenitic
- Grade: 304 (most used), 310 (for high temperature), 316 (for better corrosion resistance), 317 (for best corrosion resistance)
- Unified Numbering System UNS: S30400, S31000, S31600, S31700 (Note chemistry and properties given for 304 and 316)
Some Limitations:
Austenitic stainless steels have some limitations:
- The maximum temperature under oxidizing conditions is 925ºC (see heat resisting stainless steels)
- They are suitable only for low concentrations of reducing acid (Super Austenitics are available for higher acid levels)
- In cervices and shielded areas, there might not be enough oxygen to maintain the passive oxide film and crevice corrosion might occur (Super Austenitics, Duplex and Super Ferritic are available in these situations)
- Very high levels of halide ions, especially the chloride ion can also breakdown the passive surface film
(Super Austenitics and Duplex are available to withstand these conditions)
Information on Super Ferritic and Super Austenitic material is available from the list of Stainless Producers.