T4
Data under reviewT4 adds about 5% cobalt to the T1 base for extra red hardness in heavy cuts and roughing work. It is a legacy grade, largely replaced by M35/M42 in new tooling but still specified on older drawings.
Chemical composition
| Element | Content (%) |
|---|---|
| C | 0.70–0.80 |
| Si | ≤0.40 |
| Mn | ≤0.40 |
| Cr | 3.75–4.50 |
| W | 17.25–18.75 |
| V | 0.80–1.20 |
| Co | 4.25–5.75 |
Weight percent, per the governing standard ranges. Actual values per heat are on the mill certificate.
Properties
| Delivery condition | Annealed |
| Hardness (hardened) | 63–66 HRC |
| Density | 8.60 g/cm³ |
| Red hardness | Higher than T1 (cobalt) |
Heat treatment
Preheat 850 °C; harden 1260–1290 °C; triple temper 540–580 °C.
Equivalent grades
| Standard | Designation |
|---|---|
| din | — (HS18-0-1-5 family) |
| aisi | T4 |
| jis | SKH3 (near) |
| gb | W18Cr4VCo5 (near) |
Compare side by side: T4 vs T1 · T4 vs M35
Equivalents overlap in chemistry and use but are not always identical — see our equivalents guide before substituting in certified designs.
Applications & Processing
Applications: Roughing lathe tools, milling cutters, heavy-duty form tools.
Processing: As T1; cobalt slightly reduces toughness, so avoid interrupted cuts at full hardness.
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Ask for a quotationVisit NasteelSource: ASTM A600 published ranges · Last updated 2026-11-03. Data is indicative — verify critical values against the governing standard and mill certificate before use.