Short answer: In an SK4 vs SK5 comparison, both are former JIS carbon tool steel symbols: SK4 corresponds to SK95 and SK5 corresponds to SK85. SK4/SK95 has the higher specified carbon range, but it is not automatically better for a blade or formed part. Select against the governing standard, drawing, delivery condition, manufacturing route and acceptance criteria.
Comparison at a Glance
| Question | SK5 | SK4 |
|---|---|---|
| Grade family | JIS carbon tool steel; identify the applicable JIS standard and edition in the order. | |
| Nominal distinction | Lower specified carbon range than SK4 | Higher specified carbon range than SK5 |
| Selection basis | Part design, manufacturing route, required condition, target properties and validation—not grade name alone. | |
| Automatic substitution | No. Compare the full specifications and obtain engineering approval. | |
Why Carbon Range Is Only One Part of the Decision
Carbon range helps distinguish the two grade designations, but final strip and component behavior also depends on the delivered microstructure, surface and edge condition, thickness, forming strain, heat-treatment cycle and final geometry. Two coils with the same grade name can perform differently if these controls are not aligned.
Questions to Answer Before Selecting SK5 or SK4
- Which standard and edition controls the material? Do not order by the short grade name alone.
- Will the component be formed before heat treatment? Describe blanking, bending, stamping and machining operations.
- Which condition is required at delivery? State annealed or an agreed hardened-and-tempered condition and the applicable acceptance criteria.
- What must the finished component do? Include cutting material, load, flexing, impact, temperature and corrosion environment where relevant.
- How will the strip be inspected? Define dimensions, edge, surface, property testing, sampling and documents.
Blade and Saw Applications
It is unsafe to select a blade material from “hardness” alone. A saw or cutting blade must balance edge or tooth requirements with the flexibility and toughness required by its geometry and service. Band saw backing, circular blades, hand saws and industrial cutting rules do not impose the same conditions. The blade manufacturer should validate the grade together with the heat treatment and finished blade design.
Approximate Cross-References Need Approval
Cross-reference tables can help buyers identify candidate grades, but they do not prove full equivalence. National standards may differ in chemistry limits, product form, test methods, tolerances, surface requirements and delivery conditions. Put the required standard on the purchase order and compare both documents before changing designations.
Frequently Asked Questions
What is the main difference between SK5 and SK4?
They are former JIS symbols: SK5 corresponds to SK85 and SK4 corresponds to SK95; SK95 has the higher specified carbon range in the cited JIS-based catalogue. The final choice must also account for product form, delivery condition, heat treatment, geometry and acceptance requirements.
Is SK4 always better than SK5 for blades?
No. A higher-carbon grade is not automatically better for every blade. Blade geometry, forming route, heat treatment, hardness target, toughness requirement and service loading must be considered.
Can an international equivalent replace SK5 or SK4 directly?
Do not substitute an approximate cross-reference without comparing the complete standards and obtaining engineering approval.
Prepare the RFQ
Send the exact standard, thickness, width, tolerances, condition, edge, surface, end use, testing, quantity and destination. Use the precision steel strip RFQ checklist to avoid missing fields.
Related products: SK4 steel strip, SK5 steel strip, hardened and tempered steel strip, and saw blade steel strip applications.