Tool steelsUNS T41907

S7 Tool Steel

Also: AISI S7, UNS T41907, S-7, S7 shock resisting tool steel, shock resisting tool steel, S7 ground flat stock

S7 is the shock-resisting tool steel: the toughest common tool steel at 54-58 HRC, for chisels, punches, shear blades and tools that take repeated impact.

ASTM A681 (alloy tool steels)

Sourcing S7 parts or stock?

Attach a drawing (PDF or STEP) or describe the part; a U.S. shop that fits quotes it.

At a glance

S7 Tool Steel typical properties
Density	7.83 g/cm³ (0.283 lb/in³)
Tensile strength	About 1,950-2,150 MPa (285-310 ksi) at 55-58 HRC; annealed about 650-770 MPa (95-110 ksi), estimated from hardness
Yield strength	About 1,450-1,600 MPa (210-230 ksi) at 55-58 HRC
Hardness	About 187-223 HB annealed; 54-58 HRC working hardness (about 60-61 HRC as quenched)
Elongation	About 7-10% at 55-58 HRC
Modulus of elasticity	207 GPa (30 Msi)
Thermal	Solidus roughly 1,400 °C (2,550 °F); softens above its tempering temperature, 205-315 °C (400-600 °F) for cold work; tempered near 540 °C (1,000 °F) it serves light hot work
Composition	Fe, 0.45-0.55% C, 3.00-3.50% Cr, 1.30-1.80% Mo, about 0.25% V, 0.20-0.90% Mn, 0.20-1.00% Si

Typical values, Hardened (air cooled from about 940 °C / 1,725 °F, oil or fast gas quench for heavy sections) and double tempered at 205-315 °C (400-600 °F) to 54-58 HRC. Annealed stock is about 187-223 HB.. Confirm against the mill certificate and the purchase spec.

MachinabilityGood: Roughly 75% of the W1 (1% carbon tool steel) benchmark annealed; the lower carbide content makes it easier on tools than A2 or D2. Hardened S7 is ground or wire-cut.
WeldabilityFair: Repair welds well for a tool steel: TIG with an S7-type filler at a preheat of about 315-425 °C (600-800 °F) for annealed stock, or just below the last tempering temperature for a hardened tool, then a slow cool and a temper. Its lower carbon makes it less crack-prone than D2 or O1.
FormabilityPoor: Machined from bar and plate; annealed stock can be straightened, hardened stock cannot be bent.
Corrosion resistancePoor: Rusts like a carbon steel; oil, black oxide or a coating.

S7 is a shock-resisting tool steel with about 0.5% carbon, 3.25% chromium and 1.4% molybdenum. Lower carbon and a small carbide volume let it absorb heavy impact at 54-58 HRC without chipping or cracking, where D2 or A2 at the same hardness would break. It hardens in air in moderate sections, so it keeps the low distortion of an air-hardening steel.

It is the usual choice for chisels and pneumatic tool bits, rivet sets, punches for thick plate, shear blades for heavy plate and billet, bending and forming tools that take shock, and stamps. Tempered higher, into the high 40s and low 50s HRC, it also serves for hot punching and for plastic mold cavities that need toughness.

The trade-off is wear. S7 has much less carbide than A2 or D2, so on long runs of abrasive stock it wears faster. It decarburizes readily when hardened in air, and a soft skin fails early on a striking face, so it belongs in vacuum or a protective atmosphere. Heavy sections, over about 63 mm (2.5"), need an oil or fast gas quench to harden through.

Heat treatment

Preheat at 650-705 °C (1,200-1,300 °F), austenitize at 925-955 °C (1,700-1,750 °F), and cool in still air or gas for sections up to about 63 mm (2.5"); quench heavier sections in oil. Harden in vacuum or a protective atmosphere, because S7 decarburizes readily. Temper immediately, twice: about 205 °C (400 °F) for 57-58 HRC, 260-315 °C (500-600 °F) for 54-56 HRC, and 480-540 °C (900-1,000 °F) for the high 40s to low 50s HRC for hot work and molds. Anneal at about 815-845 °C (1,500-1,550 °F) with a slow furnace cool; stress relieve at 650-675 °C (1,200-1,250 °F) after heavy roughing.

Tempers and conditions

Annealed (about 187-223 HB), as stocked
Hardened and tempered, 54-58 HRC (impact and cold work)
Hardened and high-tempered, high 40s to low 50s HRC (hot punching, molds)

Stock forms

Round, square and flat bar
Plate and saw-cut blocks
Precision ground flat stock
Drill rod

Relative cost

Tier 3 of 5. Priced near or a little above A2 and D2 per pound; less widely stocked in ground flat and large blocks, so check availability for big sections.

Typical applications

Chisels, pneumatic hammer bits and demolition tools
Rivet sets and riveting tools
Punches for thick plate and heavy piercing
Shear blades for heavy plate, bar and billet
Bending, forming and swaging dies that take shock
Stamps and marking tools
Hot punches and plastic mold cavities (tempered high)

Process compatibility

How S7 takes each process, and what to specify. Each process links to its own guide and to the shops that do it.

S7 Tool Steel process compatibility
Process	Rating	Notes
CNC Machining	GoodGood	Annealed; easier on tools than A2 or D2. Leave clean-up stock for decarburization and grinding.
CNC Grinding	GoodGood	Finishes punches, blades and striking faces after hardening; grind off any decarburized skin.
Wire EDM	GoodGood	Cuts hardened punches and blade profiles; skim-cut the recast layer, which is brittle on an impact tool.
Sinker EDM	GoodGood	For mold cavities and forming tools in hardened stock; remove the white layer.
Vacuum Heat Treating	ExcellentExcellent	Prevents the decarburization S7 is prone to; a gas quench hardens sections up to about 63 mm (2.5") through.
Heat Treating	GoodGood	Conventional shops need a protective atmosphere or a wrap; heavy sections get an oil quench.
Stress Relieving	GoodGood	At 650-675 °C (1,200-1,250 °F) after heavy roughing and before hardening, to limit movement.
Nitriding	FairFair	Only on S7 tempered high for hot work or molds; low-tempered S7 would soften, and a hard case gives up some of the toughness S7 is bought for.
Black Oxide	GoodGood	A cheap, common finish on punches and chisels; oil it for rust resistance.
Hard Chrome Plating	FairFair	Used on mold cavities; bake for hydrogen right after plating.
Waterjet Cutting	GoodGood	Blanks for blades and punches with no heat-affected zone.
Welding	FairFair	Repair welding with a 315-425 °C (600-800 °F) preheat on annealed stock and a post-weld temper; more forgiving than D2 or O1.
Carburizing	Not recommendedNot recommended	A high-carbon case would throw away the toughness S7 is chosen for; if the tool is wearing out, pick A2 or D2 instead.

Design and sourcing tips

Choose S7 when the tool fails by chipping or cracking from impact; when it fails by wear, move toward A2 or D2.
Match hardness to the job: about 56-58 HRC for chisels and light punches, 54-56 HRC for heavy impact and thick-plate shear blades.
Ask for vacuum or protective-atmosphere hardening and leave clean-up stock; a decarburized, soft skin mushrooms and cracks on a striking face.
Radius corners and chamfer striking edges; even the toughest tool steel starts fatigue cracks at sharp corners under repeated impact.
Sections over about 63 mm (2.5") need an oil or fast gas quench to harden through; put the section and the target hardness on the heat treat note.

Frequently asked questions

What is S7 tool steel used for?: Tools that take impact: chisels, pneumatic hammer bits, rivet sets, punches for thick plate, shear blades for heavy plate and billet, and bending and forming tools that see shock. Tempered higher it is also used for hot punching and plastic mold cavities.
S7 vs A2: which is better?: For impact, S7. With about half the carbon of A2 and much less carbide, S7 absorbs far more energy before it chips or cracks at a similar hardness. A2 wears longer on abrasive stock and holds size a little better. Use S7 for chisels, heavy punches and shear blades; A2 for general dies and punches where wear, not shock, ends tool life.
How hard should S7 be?: Most S7 tools run 54-58 HRC. Chisels and light punches are commonly 56-58 HRC; heavy-impact tools and thick-plate shear blades 54-56 HRC for more toughness. As quenched it reaches about 60-61 HRC, and tempered at 480-540 °C (900-1,000 °F) it drops to the high 40s or low 50s HRC for hot work.
Can S7 be welded?: Yes, for repair, and more forgivingly than D2 or O1 because of its lower carbon. Preheat to about 315-425 °C (600-800 °F) for annealed stock, or just below the last tempering temperature for a hardened tool so it does not soften, weld by TIG with an S7-type filler, cool slowly and temper. Skipping the preheat or the temper leaves a brittle heat-affected zone that cracks under the first heavy blow.

Processes that commonly use it

Wire EDM Sinker EDM CNC Grinding Heat Treating Vacuum Heat Treating

Related materials

A2 Tool Steel H13 Tool Steel D2 Tool Steel O1 Tool Steel 4340 Steel

Where to verify these values

ASTM A681 (chemistry and annealed hardness limits)
Producer data sheets for S7, such as Crucible S7
ASM Handbook Vol. 4, Heat Treating (tool steel hardening and tempering)
Roberts, Krauss and Kennedy, Tool Steels, 5th ed. (ASM International)

At a glance

S7 Tool Steel typical properties
Density	7.83 g/cm³ (0.283 lb/in³)
Tensile strength	About 1,950-2,150 MPa (285-310 ksi) at 55-58 HRC; annealed about 650-770 MPa (95-110 ksi), estimated from hardness
Yield strength	About 1,450-1,600 MPa (210-230 ksi) at 55-58 HRC
Hardness	About 187-223 HB annealed; 54-58 HRC working hardness (about 60-61 HRC as quenched)
Elongation	About 7-10% at 55-58 HRC
Modulus of elasticity	207 GPa (30 Msi)
Thermal	Solidus roughly 1,400 °C (2,550 °F); softens above its tempering temperature, 205-315 °C (400-600 °F) for cold work; tempered near 540 °C (1,000 °F) it serves light hot work
Composition	Fe, 0.45-0.55% C, 3.00-3.50% Cr, 1.30-1.80% Mo, about 0.25% V, 0.20-0.90% Mn, 0.20-1.00% Si

MachinabilityGood

Roughly 75% of the W1 (1% carbon tool steel) benchmark annealed; the lower carbide content makes it easier on tools than A2 or D2. Hardened S7 is ground or wire-cut.

WeldabilityFair

Repair welds well for a tool steel: TIG with an S7-type filler at a preheat of about 315-425 °C (600-800 °F) for annealed stock, or just below the last tempering temperature for a hardened tool, then a slow cool and a temper. Its lower carbon makes it less crack-prone than D2 or O1.

FormabilityPoor

Machined from bar and plate; annealed stock can be straightened, hardened stock cannot be bent.

Corrosion resistancePoor

Rusts like a carbon steel; oil, black oxide or a coating.

Heat treatment

Typical applications

Chisels, pneumatic hammer bits and demolition tools

Rivet sets and riveting tools

Punches for thick plate and heavy piercing

Shear blades for heavy plate, bar and billet

Bending, forming and swaging dies that take shock

Stamps and marking tools

Hot punches and plastic mold cavities (tempered high)

Process compatibility

How S7 takes each process, and what to specify. Each process links to its own guide and to the shops that do it.

S7 Tool Steel process compatibility
Process	Rating	Notes
CNC Machining	GoodGood	Annealed; easier on tools than A2 or D2. Leave clean-up stock for decarburization and grinding.
CNC Grinding	GoodGood	Finishes punches, blades and striking faces after hardening; grind off any decarburized skin.
Wire EDM	GoodGood	Cuts hardened punches and blade profiles; skim-cut the recast layer, which is brittle on an impact tool.
Sinker EDM	GoodGood	For mold cavities and forming tools in hardened stock; remove the white layer.
Vacuum Heat Treating	ExcellentExcellent	Prevents the decarburization S7 is prone to; a gas quench hardens sections up to about 63 mm (2.5") through.
Heat Treating	GoodGood	Conventional shops need a protective atmosphere or a wrap; heavy sections get an oil quench.
Stress Relieving	GoodGood	At 650-675 °C (1,200-1,250 °F) after heavy roughing and before hardening, to limit movement.
Nitriding	FairFair	Only on S7 tempered high for hot work or molds; low-tempered S7 would soften, and a hard case gives up some of the toughness S7 is bought for.
Black Oxide	GoodGood	A cheap, common finish on punches and chisels; oil it for rust resistance.
Hard Chrome Plating	FairFair	Used on mold cavities; bake for hydrogen right after plating.
Waterjet Cutting	GoodGood	Blanks for blades and punches with no heat-affected zone.
Welding	FairFair	Repair welding with a 315-425 °C (600-800 °F) preheat on annealed stock and a post-weld temper; more forgiving than D2 or O1.
Carburizing	Not recommendedNot recommended	A high-carbon case would throw away the toughness S7 is chosen for; if the tool is wearing out, pick A2 or D2 instead.

Design and sourcing tips

Choose S7 when the tool fails by chipping or cracking from impact; when it fails by wear, move toward A2 or D2.

Match hardness to the job: about 56-58 HRC for chisels and light punches, 54-56 HRC for heavy impact and thick-plate shear blades.

Ask for vacuum or protective-atmosphere hardening and leave clean-up stock; a decarburized, soft skin mushrooms and cracks on a striking face.

Radius corners and chamfer striking edges; even the toughest tool steel starts fatigue cracks at sharp corners under repeated impact.

Sections over about 63 mm (2.5") need an oil or fast gas quench to harden through; put the section and the target hardness on the heat treat note.

Frequently asked questions

What is S7 tool steel used for?

Tools that take impact: chisels, pneumatic hammer bits, rivet sets, punches for thick plate, shear blades for heavy plate and billet, and bending and forming tools that see shock. Tempered higher it is also used for hot punching and plastic mold cavities.

S7 vs A2: which is better?

For impact, S7. With about half the carbon of A2 and much less carbide, S7 absorbs far more energy before it chips or cracks at a similar hardness. A2 wears longer on abrasive stock and holds size a little better. Use S7 for chisels, heavy punches and shear blades; A2 for general dies and punches where wear, not shock, ends tool life.

How hard should S7 be?

Most S7 tools run 54-58 HRC. Chisels and light punches are commonly 56-58 HRC; heavy-impact tools and thick-plate shear blades 54-56 HRC for more toughness. As quenched it reaches about 60-61 HRC, and tempered at 480-540 °C (900-1,000 °F) it drops to the high 40s or low 50s HRC for hot work.

Can S7 be welded?

Yes, for repair, and more forgivingly than D2 or O1 because of its lower carbon. Preheat to about 315-425 °C (600-800 °F) for annealed stock, or just below the last tempering temperature for a hardened tool so it does not soften, weld by TIG with an S7-type filler, cool slowly and temper. Skipping the preheat or the temper leaves a brittle heat-affected zone that cracks under the first heavy blow.