Family, grade and section describe different things
Stainless steel is a family of materials rather than a single alloy. Its chromium-rich passive surface film underpins corrosion resistance; composition and microstructure influence performance in a particular environment and under mechanical load. Round stainless bar describes the product form alone. Selection also needs a grade, delivery condition and service conditions.
The austenitic family includes grades such as 304L and 316L, often considered for forming and welded fabrication. Ferritic steels have a different microstructure, while martensitic grades can gain strength through suitable hardening and tempering. Duplex steels combine austenitic and ferritic phases. PH identifies precipitation-hardening steels whose properties are adjusted through ageing.
A magnet is not a grade identification instrument
Ferritic, martensitic and duplex stainless steels can respond to a magnet. Annealed austenitic material generally has a low magnetic response, but cold forming can change the microstructure of some grades and increase magnetism. Magnetic attraction alone therefore does not establish that a material is non-stainless or the wrong grade.
For identity checks, match the certificate to the batch marking on the material. Define a suitable material verification method where required. If magnetic permeability is a functional requirement, specify its limit, the processing condition and measurement method rather than relying on the family name.
Tie selection to the application
Maximum hardness, easiest welding and highest corrosion resistance may not belong to the same grade. First identify what challenges the component: fluid, temperature, wear or mechanical loading. Then consider the manufacturing sequence. A shaft machined after heat treatment and a welded process component need different purchase descriptions.
- Describe the environment and temperature during service, cleaning and shutdown.
- Distinguish requirements for strength, hardness and toughness.
- State grade together with section, delivery condition and documentation needs.
At a glance
| Family | Selection focus |
|---|---|
| Austenitic | Corrosion, forming and welding conditions |
| Ferritic | Application-specific corrosion and fabrication requirements |
| Martensitic | Hardening, tempering and final surface |
| Duplex | Environment, mechanical loads and phase balance |
| PH | Ageing condition, strength and toughness |