Overview
ISO 4948-1 classifies steels by chemical composition into unalloyed and alloyed groupings. It is a classification framework for technical communication, not a product specification, grade equivalence table or independent basis for ordering steel.
Designation and acceptance
ISO 4948-1:1982 remains the published current edition confirmed by ISO while a replacement ISO/FDIS 4948-1 is under development. The published document classifies steels using specified compositional criteria. A draft or FDIS should not be presented as the contractual current standard unless the parties expressly adopt it.
Members and selection
| Designation | Selection context |
|---|---|
| Unalloyed steels | Classification depends on defined limits for specified elements; product quality and performance remain separate questions. |
| Alloy steels | Crossing one or more classification thresholds identifies an alloy category but does not identify an orderable grade. |
| Element thresholds | Apply the edition-specific rules to the specified composition rather than relying on marketing terms such as low alloy. |
| Revision pathway | Keep the confirmed 1982 edition distinct from the under-development FDIS when documenting requirements. |
Comparison framework
| Criterion | Decision context |
|---|---|
| Classification versus designation | ISO 4948-1 groups steels; national systems and product standards assign orderable names and requirements. |
| Specified versus measured chemistry | Classification rules refer to defined composition criteria and should not be improvised from one heat analysis. |
| Product requirements | Dimensions, tolerances, properties, heat treatment and tests are outside the classification alone. |
| Edition control | The published standard and the revision project have different status and must be cited accurately. |
Performance
- Composition classification cannot predict delivered yield strength or toughness without condition, size and product requirements.
- Alloy classification is not a universal weldability or corrosion-resistance ranking.
- Service performance must be assessed from the exact grade, processing route and design environment.
Orderable product scope
- Flat and long products must be purchased to an applicable national, regional or ISO product specification.
- Pipe, tube and pressure products require code-compatible product documents and service controls.
- Forgings and castings require manufacturing-route-specific standards rather than a broad chemistry class.
Processing
- Use the classification early in material taxonomy, not as a replacement for manufacturing instructions.
- Confirm actual chemistry before welding or heat-treatment planning, including residuals where relevant.
- Record the edition used when databases or specifications assign alloy/unalloyed categories.
Applications
- Building a controlled metals database across multiple national naming systems.
- Explaining why two steels fall into a broad chemistry class without asserting interchangeability.
- Scoping candidate materials before product-standard and service-specific selection.
Selection
- Use the current published ISO classification rule for the intended documentation purpose.
- Then identify a specific grade and product standard covering the required form and condition.
- Validate mechanical properties, fabrication, tests and service approval independently.
Procurement
- Do not place an order using only an ISO 4948 classification.
- State the exact grade, product specification and contract edition.
- Define form, dimensions, delivery condition, chemistry and required properties.
- Specify tests, inspection, certification, marking and any code or end-use approval.
Sources and review
01
ISO 4948-1:1982 — Steels: Classification by chemical composition
02International Organization for Standardization · Edition 1, confirmed 2021; current while under revision
ISO/FDIS 4948-1 — Steels: Classification by chemical composition
International Organization for Standardization · Under development