Designation systems
| System | Origin | Example for a cast 316-type steel | Remarks |
|---|---|---|---|
| EN name and number | Europe | GX5CrNiMo19-11-2, 1.4408 | Number system inherited from the German Werkstoffnummer; cast steel names begin with G |
| DIN | Germany | G-X6CrNiMo18-10 (historical) | Largely replaced by EN standards; old names survive on drawings |
| ASTM / ACI grade | USA | CF8M | Defined in ASTM specifications such as A351 and A743 |
| ASME | USA | SA-351 CF8M | ASME adopts ASTM specifications for pressure equipment, with the prefix SA or SB |
| UNS | USA | J92900 | An identification number for a composition, not a specification |
| AISI / SAE | USA | 316 (wrought counterpart) | AISI numbers designate wrought steels; castings use ACI grades |
| JIS | Japan | SCS14 | Defined in JIS G 5121 for stainless steel castings |
| ISO | International | ISO designations for cast steels | Used less often on purchase documents than EN or ASTM |
| GB/T | China | ZG-prefixed grades | Verification against the current GB/T standard is required case by case |
Why "equivalent" is rarely exact
Two specifications that describe a similar alloy can differ in:
- composition limits, including residual elements and nitrogen;
- required heat treatment and permitted alternatives;
- minimum mechanical properties and test temperature;
- the test piece (separately cast, attached or cut from the casting) and test frequency;
- rules for repair welding, non-destructive testing and documentation;
- the product form and application for which the standard was written.
A casting can satisfy both specifications only if it is made and tested to the stricter requirement of each, and is certified accordingly ("dual certification"). This is possible for some pairs and impossible for others.
Classification used in the LOSTWAX database
| Class | Meaning |
|---|---|
| Recognised equivalent | The same material under another designation, for example a UNS number assigned to an ASTM grade |
| Similar composition | Cast grades of different standards with largely overlapping composition ranges; properties and test requirements still differ |
| Comparable properties | Grades for the same application with different composition balance, or the wrought counterpart of a cast grade |
| Functional alternative | A grade that may fulfil the same function after engineering review; not a like-for-like replacement |
| Not directly interchangeable | No sufficiently close counterpart is identified |
Where no entry is given for a system, no relationship has been verified and the question requires engineering assessment. No relationship is assigned merely because chemical compositions look alike.
Cast and wrought grades
Cast stainless steels deliberately differ from their wrought namesakes. Silicon is higher for fluidity, and the chromium-nickel balance is set so that austenitic grades contain some ferrite, which improves resistance to hot tearing. As a result, cast and wrought versions differ in strength, magnetic response and, in some environments, corrosion behaviour. A drawing that states only "AISI 316" for a casting is incomplete; the cast grade and standard should be agreed.
Recommended practice for substitution
- Start from the governing specification on the drawing or order, in its current edition.
- Compare composition, heat treatment, properties and test requirements line by line.
- Check design-code implications, for example pressure-equipment rules that list permitted materials.
- Obtain written approval from the party responsible for the design.
- Record the agreed specification on the order and the inspection certificate.
The material comparison tool supports step 2 for the grades in the database; the standards library lists the governing documents.