A shock-resisting tool steel built for impact. With about 0.50% carbon, 3.25% chromium and molybdenum, S7 absorbs heavy blows that would shatter a high-carbon die steel, while still hardening to a useful 54 – 58 HRC.
What Is S7 Tool Steel?
S7 sits in the shock-resisting family of tool steels. The chromium-molybdenum chemistry gives it very high impact toughness, so it is the steel you reach for when the tool is hit, dropped or used to shear thick, hard material.
It air-hardens with little distortion and keeps a working hardness around 54 – 58 HRC. It is not a high-wear or high-heat grade — for long abrasive runs, a cold-work grade such as DC53 is the better pick.
Supply Forms and Sizes
Every form is available soft-annealed (for further forming and machining) or heat-treated to your hardness window.
| Form | Condition | Size Range | Typical Use |
|---|---|---|---|
| Round bar | Annealed / pre-hardened | 10 – 150 mm | Punches, chisels, die blocks |
| Flat bar | Annealed | 8 – 80 mm thick | Shear blades, holders |
| Blocks | Annealed | up to 250 mm | Impact die sections |
| Forging stock | Hot rolled | 40 – 200 mm | Large impact tools |
Chemical Composition (AISI S7)
| C | Mn | Si | Cr | Mo | V | P max | S max |
|---|---|---|---|---|---|---|---|
| 0.45 – 0.55 | 0.20 – 0.80 | 0.20 – 1.00 | 3.00 – 3.50 | 1.30 – 1.80 | 0.20 – 0.30 | 0.030 | 0.030 |
Heat analysis is reported on the mill certificate for every lot. If your drawing calls for tighter limits than the standard, flag it at enquiry — ladle-refined heats usually meet it without a surcharge.
Physical Properties
| Property | Value |
|---|---|
| Density | 7.85 g/cm³ |
| Elastic modulus (E) | ~200 GPa |
| Shear modulus (G) | ~79 GPa |
| Thermal conductivity | ~40 W/m·K at room temperature |
| Coefficient of thermal expansion | ~12 ×10⁻₆ /K (20 – 200 °C) |
Mechanical Properties
Typical values for S7 hardened and tempered in the impact-resistance range. The mill certificate is the binding document.
| Condition | Hardness | Tensile Strength | Impact (Charpy) | Notes |
|---|---|---|---|---|
| Annealed | ≤ 229 HB | — | — | For machining |
| H&T 54 HRC | 52 – 56 HRC | ~1700 MPa | very high | Max toughness |
| H&T 58 HRC | 56 – 60 HRC | ~1900 MPa | high | Wear + impact mix |
Equivalent Grades
| Standard | Designation |
|---|---|
| USA AISI | S7 |
| No exact DIN/EN twin | — |
| Closest shock grades | 5CrNiMo, 4Cr5MoSiV (hot-work, similar role) |
Heat Treatment and Processing
Preheat slowly, then raise to the grade forging range. Work above the lower limit and cool slowly after forging to avoid cracks.
815 – 845 °C, soak, slow furnace cool to ~595 °C then air. Delivers soft condition for machining.
Air harden from 925 – 955 °C; oil may be used for heavy sections.
Around 205 – 540 °C; lower temp (~200 °C) keeps peak hardness, higher temp trades hardness for toughness.
After machining or forming, 200 – 350 °C for 1 – 2 hours, air cool, to stabilise dimensions and relieve residual stress.
Heat-treated bars and plates are supplied with the hardness and test certificate you specify. For critical parts we can control decarburisation depth and supply a spheroidized or soft-annealed structure on request.
Applications of S7 Tool Steel
Cushions the shock of cold heading and riveting without cracking.
Outlasts brittle die steels when cutting thick plate and bars.
Absorbs repeated impact on demolition and construction tools.
Takes the hammering transmitted through punches and forming dies.
For sheets and strips too thick for a fragile high-carbon die.
Springy toughness keeps the die alive under cyclic load.
S7 Tool Steel vs Alternative Grades
| Grade | vs S7 Tool Steel | Choose It When |
|---|---|---|
| S7 | — | Impact and shock loads dominate and hardness can stay moderate. |
| DC53 / D2 | Far higher wear resistance, but more brittle | Long abrasive runs, little impact |
| H13 (hot work) | Better red-hardness | Tools that run hot, e.g. hot stamping |
| A2 | Better dimensional stability in heat treat | Precision tools where low distortion matters |
Quality Control and Mill Certificates
Every shipment ships with an EN 10204 3.1 mill certificate covering heat chemical analysis, hardness and the mechanical test on record. On request we add: ultrasonic test on heavy bar and plate, magnetic particle inspection on machined surfaces, and third-party inspection (SGS / BV) before loading. Dimensional tolerances follow the relevant EN / ASTM / JIS standard or your drawing.
Frequently Asked Questions
What is S7 tool steel used for?
Impact tools: punches, chisels, shear blades for thick stock, die blocks and concrete-breaker parts — anywhere the tool takes heavy, repeated blows.
What hardness does S7 reach?
Usually 54 – 58 HRC after hardening and tempering; it can be taken higher at the cost of some toughness.
Is S7 air hardening?
Yes. It air-hardens with low distortion; oil quench is only needed for very heavy sections.
Does S7 rust?
It is not stainless. Keep oiled or coated in storage and in humid service.
What is the minimum order quantity?
Mill lots typically start at 500 kg per item; smaller trial sizes are often available from stock.
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