TS · tool steel
Tool Steel S7 (shock resisting)
The toughness grade. Machines like a medium alloy steel in the annealed state and hardens to 55–57 HRC without becoming brittle - that combination is what you pay for.
Quoting this material
- Typical lead time
- 12–20 working days
- Condition
- Annealed, or hardened and tempered for service
- Achievable finish
- Ra 0.8 µm after grinding typical · Ra 0.4 µm best
Machined in-house to your drawing: see the precision CNC machining service and the machine and inspection capability it runs on.
Machinability
Our own 1–10 shop ranking, not a published index: 10 is free-cutting brass C360, 1 is Inconel 718. It ranks how a material behaves on the floor - cycle time, chip control and tool life together. Where a published index exists it is quoted in the note.
The toughness grade. Machines like a medium alloy steel in the annealed state and hardens to 55–57 HRC without becoming brittle - that combination is what you pay for.
Properties as supplied
| Parameter | Value | Unit |
|---|---|---|
| Hardness (working) | 55–57 | HRC |
| Impact toughness | Highest of the common tool steels | - |
| Wear resistance | Moderate | - |
| Distortion in hardening | Low to moderate | - |
| Thermal conductivity | 40 | W/m·K |
| Modulus of elasticity | 205 | GPa |
Hardness, tensile and thermal figures are typical published values for the condition stated. Actual mill certificates govern; send the specification with the drawing and we confirm against the certificate before the material is cut.
Condition
Annealed, or hardened and tempered for service
Heat treatment
Austenitise around 940–980 °C, quench in air or oil, temper at 200–540 °C. It is designed to be hardened at a lower hardness than D2 and keep more toughness - that is the trade it exists to make.
Achievable surface finish
Ra 0.8 µm after grinding
Ra 0.4 µm
Grinds acceptably; not usually chosen for a polished surface, so finish matter less than on a mould steel.
Tooling and cutting parameters
Cutting speed
- 100–180 m/min annealed (carbide) · 50–80 m/min at 56 HRC
Feed
- 0.10–0.25 mm/rev turning · 0.06–0.15 mm/tooth milling
Tooling
- Coated carbide annealed; CBN for hardened
Coolant
- Flood
Starting points for carbide on a rigid setup, not a guarantee. The right numbers depend on the machine, the toolholder and the fixturing - ask and we will say what we would actually run.
Typical applications
- Punches and chisels
- Shear and chipper blades
- Jackhammer and impact tooling
- Forging hammer dies
- Toughness-critical machine components
DFM notes for this grade
- Choose it for shock, not wear: it will outlast D2 under impact and under-perform it under abrasion
- The 55–57 HRC working range is deliberate - pushing it to 60 HRC destroys the toughness that is the reason for buying it
- Where a part both impacts and wears, a D2 insert in an S7 body is often better than one material trying to do both
Questions buyers ask
- When is S7 the right choice over D2?
- When the failure mode is chipping or cracking rather than wear. A punch that breaks, a blade that chips on a hard spot, a die that cracks from impact - those are S7 problems. A die that gradually wears its edge away is a D2 problem.
- Can S7 be welded for a repair?
- With preheat and a matching filler, and it is one of the more repairable tool steels. The repaired area still needs re-tempering, and on a high-cycle tool the heat-affected zone is the next place something will fail.