The primary difference between 8670 steel and A2 tool steel lies in their alloy composition and intended application. 8670 steel is a nickel-enriched high-carbon steel (similar to L6) renowned for its extreme impact toughness and resistance to shattering, typically hardened to 54-60 HRC. In contrast, A2 is an air-hardening tool steel that offers a superior balance of wear resistance and edge stability, commonly used at 57-62 HRC.
If your project requires the use of 8670 steel or A2 tool steel, you can contact us for a free quote.
While 8670 is the gold standard for large chopping tools and swords due to its "spring-like" resilience, A2 is the preferred choice for bushcraft knives and precision tools where maintaining a sharp edge during abrasive use is more critical than raw impact strength.
Quick Performance Comparison:
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Impact Toughness: 8670 is the clear winner; it is one of the toughest steels available.
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Edge Retention: A2 wins due to its higher chromium and carbon content forming harder carbides.
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Heat Treatment: 8670 is oil-quenched and very forgiving; A2 is air-quenched, offering better dimensional stability.
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Corrosion Resistance: Both are carbon steels and will rust; however, A2 (5% Chromium) has slightly better stain resistance than 8670 (0.5\% Chromium).
What are 8670 steel and A2 steel in metallurgical terms?
8670 steel: low alloy, hardenable, toughness biased
8670 is an SAE AISI low alloy steel containing nickel, chromium, and molybdenum in modest amounts. Carbon content sits in the medium high range compared with many structural alloys, giving useful hardness potential while keeping carbide volume relatively low. In bladesmithing and large impact tools, 8670 gained a strong reputation due to its ability to absorb shock without cracking, particularly in long blades where bending loads and vibration exist.
Typical product forms:
- bar stock and round stock.
- flat bar and plate cut stock.
- occasionally strip in specialty programs.
Typical roles:
- swords, long knives, machetes.
- axes, hatchets, striking tools.
- components needing high toughness at moderate hardness.
A2 steel: air hardening tool steel, wear biased
A2 is an air hardening cold work tool steel with higher carbon and substantially higher chromium than 8670. It develops a higher carbide fraction, including chromium rich carbides, which improves abrasive wear resistance and edge life in many cutting tasks. A2 also offers good dimensional stability relative to oil hardening tool steels, since it hardens via air or plate quench rather than aggressive liquid quenching.
Typical product forms:
- precision ground flat stock.
- rounds and blocks.
- tool steel plate
Typical roles:
- blanking dies, forming dies, punches.
- industrial knives and shear blades.
- premium hard use knives when edge retention is prioritized.
Which standards and equivalent designations apply in global purchasing?
Purchasing success begins with language that mills, distributors, and heat treat shops interpret consistently. Steel names alone can hide meaningful differences in melt practice, cleanliness, and certification.
Common standards and identifiers
| Steel | Common family name | Typical standard references | Notes relevant to procurement |
|---|---|---|---|
| 8670 | SAE AISI alloy steel | SAE J404 chemistry tables, ASTM A29 general requirements depending on product form | Often supplied as alloy bar; certification discipline varies by supplier tier |
| A2 | Cold work tool steel | ASTM A681 tool steel, AMS specifications in aerospace supply chains | Often sold as precision ground stock with tighter size tolerances |
Practical equivalency notes
A2 maps closely to DIN 1.2363 in many catalogs. Regional tool steel naming can still mask differences in cleanliness, remelting, and spheroidize condition.
8670 does not always present a simple DIN “one number equals one grade” equivalence in everyday distributor listings. Buyers should request full chemistry on the MTR and confirm that nickel, chromium, molybdenum sit within the intended band, since those elements strongly affect hardenability and toughness.
How does chemistry differ, and which elements drive toughness and wear?
High ranking comparison pages often stop at carbon and chromium. Useful, yet incomplete. Nickel and molybdenum influence toughness, hardenability, and temper response, while chromium and carbon largely set carbide population and wear behavior.
Typical composition ranges (representative; verify mill data)
| Steel | C | Cr | Ni | Mo | V | Mn | Si |
|---|---|---|---|---|---|---|---|
| 8670 | 0.65 to 0.75 | 0.40 to 0.60 | 0.40 to 0.70 | 0.15 to 0.25 | low | 0.70 to 1.00 | 0.15 to 0.35 |
| A2 | 0.95 to 1.05 | 4.75 to 5.50 | low | 0.90 to 1.40 | 0.15 to 0.50 | 0.60 to 1.00 | 0.10 to 0.50 |
Element level interpretation in knife language
Carbon
- A2 carries substantially more carbon. That enables higher carbide content and higher achievable hardness. It also pushes brittleness risk upward if heat treatment or geometry becomes aggressive.
- 8670 carries less carbon than A2 yet still enough to reach a useful hardness band in blades. Lower carbide content usually improves toughness.
Chromium
- A2 uses chromium primarily to increase hardenability and carbide formation, not stainless behavior. Despite 5 percent chromium, A2 still rusts readily in humid carry without oil.
- 8670 uses chromium at a much lower level. Chromium contribution leans toward hardenability, not wear.
Nickel
- 8670 contains nickel, a strong toughness contributor. Nickel helps resist brittle fracture and improves low temperature toughness. This feature plays well in long blades and striking tools.
- A2 typically contains minimal nickel.
Molybdenum
Both contain molybdenum, yet A2 has more. Molybdenum improves hardenability and temper resistance, supporting stable high hardness in thick tooling sections.
What microstructures form after heat treatment, and why carbide volume matters
Edge behavior depends on microstructure at the apex. Two steels at the same Rockwell C hardness can cut very differently due to carbide size, distribution, and the toughness of the martensitic matrix that holds those carbides.
8670 microstructure tendencies
With proper austenitizing and quench, 8670 forms martensite with relatively low carbide volume. Carbides present tend to be smaller and fewer than in tool steels. The result: a continuous matrix that resists crack propagation and tolerates bending and impact.
Knife outcome:
- thin edges can survive lateral stress better.
- lower abrasive wear resistance compared with high carbide tool steels.
- edge tends to lose bite via rolling or smooth wear rather than brittle chipping when hardness sits on the lower side.
A2 microstructure tendencies
A2 forms martensite plus a higher volume of chromium rich carbides. Carbide population raises wear resistance yet also creates crack initiation sites if the edge becomes too thin, hardness too high, or impact too severe.
Knife outcome:
- longer working edge in abrasive cutting.
- apex may microchip when geometry is too fine.
- sharpening tends to require harder abrasives than simpler alloys.
Carbide population comparison table
| Feature | 8670 | A2 | Practical consequence at the edge |
|---|---|---|---|
| Carbide volume | low to moderate | moderate to high | A2 holds a toothy edge longer on abrasive media |
| Carbide size | typically smaller | typically larger | 8670 supports thinner apex stability |
| Matrix toughness | high | medium | 8670 survives impact and bending better |
| Wear mode | polishing and rolling | slower wear, more microchipping risk | Edge maintenance strategy differs |
What HRC ranges are realistic, and what changes when hardness moves?
Search queries often ask “8670 vs A2 HRC.” Hardness numbers matter, yet the usable hardness band depends on blade thickness, intended use, and acceptable failure mode.
Typical hardness bands used in real products
| Steel | Common HRC in large blades and impact tools | Common HRC in utility knives | Upper practical HRC ceiling in many shops |
|---|---|---|---|
| 8670 | 52 to 56 | 54 to 58 | roughly 58 to 60 with careful process control |
| A2 | 56 to 59 in impact leaning tools | 58 to 61 | roughly 61 to 63 depending on heat treat recipe and section size |
Important nuance: pushing 8670 to very high hardness can reduce its signature toughness advantage. Pushing A2 to the top end can increase chipping risk unless edge thickness increases.
What changes when hardness increases
- higher yield strength at the apex reduces rolling.
- wear resistance rises, partly due to higher matrix hardness.
- toughness drops, raising chipping probability under impact.
- sharpening becomes slower, especially in higher carbide alloys.
How does toughness compare, and which tests actually represent knife use?
“Toughness” is an umbrella term. Engineers measure toughness using Charpy impact energy, fracture toughness KIC, or instrumented impact tests. Knife users experience toughness through edge chipping, gross fracture resistance, and ability to survive torque.
Relative toughness expectations
In most heat treated conditions used in blades, 8670 tends to exceed A2 in impact toughness at similar hardness. Nickel content and lower carbide fraction drive this.
A2 remains tougher than many very high carbide alloys, yet it usually cannot match the shock tolerance of nickel bearing low alloy steels at the same HRC.
Which test correlates best with blade behavior?
- Charpy V notch gives a quick comparative picture, yet notch geometry and sample orientation matter.
- Lateral bend tests on heat treated coupons can reflect long blade behavior better than Charpy in certain cases.
- Edge impact tests, such as cutting into hardwood knots or controlled impact on brass rod, reflect apex behavior, though results become geometry dependent.
Toughness comparison table (qualitative, heat treat dependent)
| Category | 8670 expectation | A2 expectation | Notes |
|---|---|---|---|
| Resistance to catastrophic breakage | high | medium | critical in long blades and striking tools |
| Resistance to gross chipping | high | medium | depends strongly on HRC and edge thickness |
| Resistance to microchipping at thin apex | high | medium | A2 improves with thicker edge geometry |
| Dimensional stability during hardening | medium | high | A2 air hardening reduces quench stress |
How does edge retention compare on abrasive media versus clean slicing?
Edge retention has multiple mechanisms:
- abrasive wear on carbides and matrix.
- adhesive wear
- microfracture at the apex.
- deformation and rolling.
A2 tends to show stronger performance in abrasive wear, since carbide volume is higher. 8670 can still cut well, yet its working edge generally fades sooner in high abrasion.
Task based expectations
| Cutting media | 8670 typical result | A2 typical result | Explanation |
|---|---|---|---|
| Cardboard, fiberboard | moderate | strong | abrasive wear dominates, A2 carbides help |
| Rope, webbing | moderate | strong | toothy edge longevity favors A2 |
| Wood carving | strong feel, stable | strong, slightly less forgiving | microchipping risk rises in A2 if too thin |
| Food prep | moderate | moderate | both rust without care; geometry dominates performance |
| Plastic strapping | moderate | strong | A2 resists wear in plastic additives and dust |
A2 edge retention trade
A2 often holds a working edge longer, yet that edge can turn toothy. Users expecting very high push cutting performance may prefer 8670 with a refined, polished apex that stays continuous, especially if the cutting media is not highly abrasive.
Which steel resists chipping better, and how geometry shifts the outcome?
Chipping is not solely a steel issue. It is the interaction between:
- hardness
- carbide size and distribution.
- edge angle
- edge thickness behind the apex.
- cutting technique and impact events.
General chipping tendency
- 8670 tends to chip less in impact and mixed cutting, particularly in thin geometries.
- A2 can chip when pushed to high hardness with thin edges, yet it performs well when geometry is tuned to its microstructure.
Geometry tuning rules that work in practice
8670
- supports thinner edges and lower inclusive angles without immediate chipping.
- excels in long blades where bending loads occur.
- benefits from a hardness target that preserves toughness.
A2
- prefers moderate inclusive angles and a slightly thicker edge behind the apex.
- benefits from careful tempering to avoid brittle behavior.
- excels when cutting media contains abrasion and impacts stay limited.
Edge geometry matrix (starting point ranges, adjust per product)
| Steel | Typical inclusive edge angle range | Behind edge thickness approach | Primary risk if geometry is extreme |
|---|---|---|---|
| 8670 | lower angles tolerated | can run thin | rolling if hardness too low, wear if media abrasive |
| A2 | moderate angles preferred | keep slightly thicker | microchipping if too thin, especially at high HRC |
What heat treatment variables swing results more than the steel name?
High ranking pages frequently list austenitize and temper temperatures. In production, repeatability depends on:
- furnace uniformity and soak control.
- decarb prevention.
- quench method consistency.
- temper time and multiple temper cycles.
- cryogenic step decisions.
- section size and heat extraction.
Heat treatment overview (high level reference, verify with data sheets)
| Steel | Austenitizing temperature band | Quench style | Tempering approach | Notes |
|---|---|---|---|---|
| 8670 | typically in the mid to upper range used in alloy blade steels | oil quench common, fast plates in thin sections | double temper common | avoid decarb, control grain growth |
| A2 | typically higher than 8670 tool steel recipes | air or plate quench | multiple tempers common | aim to control retained austenite |
- 8670 in open atmosphere heat treat can decarburize at the surface. A thin decarb layer ruins edge stability even if core hardness reads fine.
- A2 can grow grain if overheated. Coarse grain raises brittle fracture risk, which shows up in chipping complaints.
Retained austenite and stability in A2
A2 can retain austenite after hardening. Proper temper cycles, and optional cryogenic processing in some shops, reduce retained austenite and improve dimensional stability and wear behavior.
Why two “A2” knives behave differently
A2 sold as “A2” can vary in:
- melt practice (standard electric melt versus ESR remelt).
- cleanliness and inclusion content.
- spheroidize quality prior to hardening.
- heat treat recipe and quench setup.
MWalloys recommends buyers treat “A2” and “8670” as a beginning, then lock in the supplier, certification, and process window.
How do grinding, machining, and distortion risk compare in production?
Machining and stock removal
- 8670 machines similarly to other low alloy steels in annealed condition. Tool wear tends to remain moderate.
- A2 in annealed condition machines acceptably, yet carbide volume and chromium content can raise tool wear. In hardened condition, A2 becomes significantly more abrasive on belts and wheels.
Grinding burn sensitivity
Both steels can suffer grinding burn and microcracking if aggressive belts, dull abrasives, or poor coolant practice occurs. A2 at high hardness is especially sensitive since surface microcracks can propagate along carbides.
Distortion risk during hardening
- A2 air hardening reduces quench shock, often resulting in better dimensional control in flat tooling and thick sections.
- 8670 typically needs an oil quench, which can increase warpage risk in thin blades without good fixturing and normalization steps.
Manufacturing comparison table
| Production concern | 8670 | A2 |
|---|---|---|
| Stock removal effort after hardening | moderate | high |
| Dimensional stability in hardening | medium | high |
| Risk of quench cracking | low to medium | low |
| Belt and abrasive consumption | moderate | high |
| Sensitivity to decarb | high | medium |
What corrosion and patina behavior should users expect in the field?
Neither 8670 nor A2 qualifies as stainless. Chromium content in A2 slows rust slightly relative to simple carbon steels, yet it still stains and pits in humid, salty, or acidic exposure.
Field corrosion expectations
- 8670: rust develops quickly without oil, especially in wet sheaths and humid environments.
- A2: rust still develops; patina may appear slower in some conditions, yet it remains a non stainless steel.
Practical care requirements
- wipe down after use
- oil the blade prior to storage.
- avoid long term wet sheath storage.
- rinse and dry after food acids, salt exposure, or sweat contact.
Purchasing teams selling into marine or kitchen heavy markets should consider stainless alternatives unless end users accept maintenance.
Which applications favor 8670, and which favor A2?
8670 best fit scenarios
- long blades needing high resistance to breakage.
- machetes and choppers used in brush and wood contact.
- axes and striking tools requiring shock absorption
- training swords and blades subject to bending loads.
- products where a tough, stable edge matters more than maximum wear resistance.
A2 best fit scenarios
- industrial knives and shear blades cutting abrasive materials.
- punches and dies where wear resistance matters.
- hard use utility knives cutting cardboard and fiberboard daily.
- blades needing air hardening to reduce distortion in thick cross sections.
- customers who accept slower sharpening in exchange for longer cutting intervals.
Application decision matrix
| Application | 8670 rating | A2 rating | Why the rating trends that way |
|---|---|---|---|
| Sword length blade | high | medium | bending and impact loads favor toughness |
| Axe or hatchet | high | medium | shock loading favors nickel alloy toughness |
| Warehouse box cutting | medium | high | abrasive wear favors tool steel carbides |
| Wood carving knife | high | medium to high | thin edge stability favors 8670 |
| Die blanking, punches | low to medium | high | A2 designed around cold work tooling |
| Outdoor knife in humid climate | medium | medium | both need oil, stainless would outperform |
How should buyers specify 8670 or A2 to avoid mixed lots and heat treat disputes?
Many returns and warranty issues trace back to vague specifications. A purchase order should define grade, standard, delivery condition, and certification requirements. Heat treat responsibility should be explicit.
Minimum specification package (MWalloys recommended)
- Grade plus governing standard.
- Product form and size tolerances.
- Delivery condition: annealed, spheroidized, or pre hardened.
- Chemistry limits, confirmed via MTR per heat.
- Cleanliness requirement when relevant (inclusion limits, ESR option).
- Surface condition: decarb limits, scale control, ground finish needs.
- Traceability: heat number on bundles plus label discipline.
- Heat treat acceptance criteria: target HRC range, sampling plan, test method.
- Straightness, flatness, warp limits after heat treat if supplier performs hardening.
- Change control: no substitute heats or alternate mills without written approval.
Example procurement language snippets
- “A2 tool steel per ASTM A681, annealed and spheroidized, with MTR and heat traceability.”
- “8670 alloy steel per SAE J404 chemistry, supplied annealed, normalized option stated, MTR required.”
Incoming inspection checklist
| Check | Method | Purpose |
|---|---|---|
| Chemistry verification | MTR review, PMI spot check in higher risk programs | prevents grade mix ups |
| Microhardness near surface | sample coupon after heat treat | catches decarb issues |
| HRC testing | calibrated Rockwell C | verifies heat treat outcome |
| Straightness | straightedge or fixture | reduces scrap in long blades |
| Surface defects | visual plus magnetic particle in critical tools | catches seams and cracks |
Summary tables and selection checklist
Side by side comparison summary
| Attribute | 8670 | A2 |
|---|---|---|
| Primary strength | toughness, shock resistance | wear resistance, stable high HRC |
| Edge retention on abrasive media | moderate | strong |
| Chipping resistance in thin geometry | strong | medium, geometry sensitive |
| Max practical hardness in many knife shops | moderate high | high |
| Distortion control in hardening | medium | strong |
| Corrosion behavior | rusts readily | rusts readily, slightly improved relative behavior |
| Sharpening speed | faster | slower |
Quick selection checklist
Choose 8670 when the product sees impact, bending, chopping, or mixed media contact, and when failure must remain ductile rather than brittle.
Choose A2 when cutting media is abrasive, when long working edge matters, and when air hardening dimensional stability reduces manufacturing risk.
FAQs
S7 Shock-Resisting Tool Steel: 10/10 Technical FAQ
1. What makes S7 the "king" of shock resistance?
S7 is a chromium-molybdenum tool steel designed to provide maximum impact toughness. Its unique chemistry allows it to absorb massive energy during a strike without fracturing. In Charpy V-Notch tests, S7 consistently outperforms almost all other air-hardening tool steels, making it the premier choice for jackhammer bits and heavy-duty chisels.
2. Is S7 steel air-hardening or oil-hardening?
3. Can S7 be used for knives and blades?
4. How does S7 compare to D2 tool steel?
They are opposites. D2 is a "wear-resistance monster" with high carbon/chromium but is brittle. S7 is a "toughness monster" that can withstand impact but wears down faster in abrasive environments. If you are cutting cardboard, use D2; if you are smashing concrete, use S7.
5. What is the ideal HRC range for S7 tools?
The "sweet spot" for S7 depends on the tool:
- Heavy Impact (Chisels/Hammers): 54 - 56 HRC.
- Medium Impact (Punches/Dies): 56 - 58 HRC.
- Heavy-Duty Knives: 57 - 58 HRC.
Tempering higher than 58 HRC begins to rapidly diminish the shock-resisting properties.
6. Can S7 handle high-temperature applications?
7. Is S7 easy to machine and grind?
8. Does S7 rust? (Corrosion Resistance)
9. What is the "Charpy" value of S7?
At a typical hardness of 57 HRC, S7 can show Charpy V-Notch values of over 125-150 ft-lbs (in certain heat-treat configurations). To put that in perspective, a standard D2 steel often tests at less than 20 ft-lbs. This massive difference is why S7 survives where other steels shatter.
10. What are the top 3 applications for S7?
1. Pneumatic Tools: Rivet sets, breaker bits, and moil points.
2. Master Hobs: Cold-forming dies that must withstand extreme compression.
3. Heavy-Duty Cutters: Notching dies, shear blades for thick metal, and "demolition" style knives.
