# S7 tool steel

Shock-resisting tool steel: product identification, heat-treatment response, dimensional allowances and tooling selection limits.

Reviewed: 2026-11-01

Tags: materials, steel, tool-steel, heat-treatment

## What S7 identifies

The Steel Store's S7 guide estimates **0.001 in per inch expansion** after **air quenching from the proper hardening temperature**. Applied to a **200 mm feature**, that gives **0.20 mm** estimated growth. Bow, twist and geometry can change the finishing allowance. [Steel Store dimensional-stability guide](https://www.steelstore.com/app/uploads/sites/187/2025/01/Steel-Store-S7-Data-Sheet_1.pdf)

S7 is an air-hardening, shock-resisting tool steel used where impact loading matters. Carpenter identifies its product as AISI S7, UNS T41907; **CarTech** is its producer trademark. The generic designation does not establish a particular supplier, melting route, surface finish or finished-tool hardness. [Carpenter product identification](https://www.carpentertechnology.com/alloy-finder/S7)

Carpenter's nominal composition, by mass, is 0.50% carbon, 0.70% manganese, 0.30% silicon, 3.25% chromium and 1.40% molybdenum, balance iron. These are nominal figures, not a purchase specification's permitted ranges. Its technical bulletin describes high impact resistance and resistance to softening at moderately elevated temperatures, with both cold- and hot-work uses. This establishes a selection direction; it does not certify a tool against breakage. [Carpenter S7 technical bulletin](https://www.carpentertechnology.com/hubfs/7407324/Material%20Saftey%20Data%20Sheets/S7.pdf)

Industeel supplies an S7 plate product, whereas Ellwood's **ExELL S7 SMDQ** is a named premium die-and-mold product. Do not silently substitute an international cross-reference for the ordered material: Industeel marks its 1.2355 correspondence approximately, rather than declaring every product under that number interchangeable. [Industeel S7](https://industeel.arcelormittal.com/wp-content/uploads/2022/10/DS-TOOL-S7.pdf), [Ellwood S7](https://esmusa.elwd.com/product/s7/)

## Choose against the failure mode

Typical applications include punches, chisels, shears and blanking tools. Industeel also lists support and backing plates. Ellwood lists forming tools and plastic molds, emphasizing cleanliness, polishability and a homogeneous structure for its particular product. Application lists describe candidates, not guaranteed service life or a universal optimum. [Industeel S7](https://industeel.arcelormittal.com/wp-content/uploads/2022/10/DS-TOOL-S7.pdf), [Ellwood S7](https://esmusa.elwd.com/product/s7/)

For a tooling decision, record what ended the previous tool's life: chipped edge, bulk fracture, progressive wear, plastic deformation or dimensional drift. These are different requirements. Specify the working hardness and support geometry alongside the grade, then validate the result in the actual operation. A higher hardness reading alone cannot demonstrate improved impact performance. A replacement trial should hold workpiece material, clearance, lubrication and operating load sufficiently consistent to make the comparison useful.

If surface polish matters, request the exact cleanliness and inspection requirements. Ellwood describes ladle metallurgy, vacuum degassing, forging reductions and spheroidizing anneal for SMDQ. That description should not be converted into an unsupported assertion that every S7 product is remelted, mold quality or equally polishable. [Ellwood product manufacturing description](https://esmusa.elwd.com/product/s7/)

## Supplied condition and heat treatment

Separate annealed stock from hardened tooling. Industeel specifies delivery annealed at **225 HB maximum**, with a published thickness program of 9–100 mm continuous-cast material and 101–220 mm ingot-cast/forged material. These are producer-specific delivery statements, not universal availability or finished-tool requirements. [Industeel S7, April 2022](https://industeel.arcelormittal.com/wp-content/uploads/2022/10/DS-TOOL-S7.pdf)

Carpenter's historical bulletin gives hardening at 1700–1750°F (927–954°C), followed by quenching and prompt tempering. Its air-cooling guidance is limited to sections up to 2½ inches; heavier sections call for oil quenching. It warns about decarburization during thermal processing. Thus, “air hardening” does not mean that any size or furnace load will harden adequately in still air. [Carpenter heat-treatment guidance](https://www.carpentertechnology.com/hubfs/7407324/Material%20Saftey%20Data%20Sheets/S7.pdf)

A newer supplier sheet illustrates a different, complete set of instructions: The Steel Store specifies a 1250°F preheat, hardening at 1700–1780°F, circulated-air/inert-gas or positive-pressure inert-gas quenching to 150°F, and mandatory double tempering. It requires cooling to room temperature between tempers and gives a minimum two-hour hold with the tool at temperature. Use the supplying producer's approved procedure and the heat treater's qualified equipment/load plan; combining isolated settings from different sheets creates an unverified procedure. [Steel Store S7, Rev_1](https://www.steelstore.com/app/uploads/sites/187/2025/01/Steel-Store-S7-Data-Sheet_1.pdf)

Record section geometry, furnace atmosphere, quench and temper history with hardness and dimensional results.

## Read hardness and impact data with their conditions

The Steel Store's temper-response table uses **1-inch-diameter specimens, 3 inches long, air hardened from 1725°F**. It reports approximately 57 HRC after a 400°F temper, 55 HRC at 500°F and 51 HRC at 1000°F. The sheet explicitly presents its values as estimating guidance. Those rows do not guarantee the hardness of a large die or define a permissible service temperature. [Steel Store specimen and tempering table](https://www.steelstore.com/app/uploads/sites/187/2025/01/Steel-Store-S7-Data-Sheet_1.pdf)

Industeel's impact table supplies joule values but does not identify enough specimen/notch details to make them a general comparison with other producers' tests. Avoid ranking steels using that table against an unrelated Charpy test. For acceptance, request the test method, specimen geometry, orientation, test temperature and treatment condition, as well as the required result. [Industeel mechanical-property table](https://industeel.arcelormittal.com/wp-content/uploads/2022/10/DS-TOOL-S7.pdf)

## Dimensional allowance: bounded example

The Steel Store estimates approximately **0.001 inch per inch expansion** after air quenching from the proper hardening temperature, while warning that geometry and bending, bowing or twisting add variation. [Steel Store dimensional-stability guidance](https://www.steelstore.com/app/uploads/sites/187/2025/01/Steel-Store-S7-Data-Sheet_1.pdf)

Include finishing and any surface treatment in the thermal plan. Ellwood directs users to consult it for welding, EDM, grinding and nitriding details. Do not infer a qualified repair-weld or coating cycle from the S7 designation alone. [Ellwood toolmaking guidance](https://esmusa.elwd.com/product/s7/)

## Order and source boundaries

An actionable order identifies producer/product, governing specification and edition, form and dimensions, annealed or hardened condition, surface allowance, hardness requirements and any agreed inspection. Keep chemistry acceptance separate from the final tool's dimensional and performance acceptance. See [grades, tempers and conditions](../grades-tempers-and-conditions.md).

Source editions checked here are Carpenter's **July 1, 1986** bulletin, whose footer also carries a 2020 copyright; Industeel **DS-TOOL-S7, 04/2022**; and The Steel Store **SS-DS003, Rev_1, January 20, 2025**. Copyright and upload dates are not new technical editions. Ellwood's live page does not display a technical revision date and contains transcription defects; confirm critical treatment details directly rather than treating the page as a current signed process specification.