Steel SKH59
JIS SKH59 · AISI/SAE M42
SKH59 is the JIS cobalt molybdenum high-speed steel equivalent to AISI M42, in which about 8 % Co and a high Mo content raise secondary hardness to working values of 64–70 HRC.
Reference datasheet — SKH59 is not in the instant-quote catalog. Upload your part and an engineer will quote it in this grade or suggest the closest stocked equivalent.
Values for the ANN condition
SKH59 tempers and conditions
SKH59 is supplied in 6 conditions, soft to hard. ANN is the default FabDigit quotes; the values on this page are for it.
Compare all 6 conditionsHide
| Condition · open for datasheet | Best for | Yield MPa | Tensile MPa | Elong. % | Hardness | Conductivity |
|---|---|---|---|---|---|---|
Hardened & tempered, 64–66 HRC | Austenitize ~1180–1190 °C and temper high (2–3 × 550–560 °C) when interrupted cuts or larger tools need extra toughness. | 0 | 65 HRC | — | ||
Hardened & tempered, 66–68 HRC | The normal working hardness for M42/SKH59 drills, taps and end mills cutting hardened or abrasive workpieces. | 0 | 67 HRC | — | ||
ANNDefault Annealed | Standard stock condition for bar/blank supply — machine tool geometry, then harden and temper. | 600 | 900 | 12 | 25 HRC | 2.9 % IACS |
Annealed, cold drawn / centreless ground bar | Precision-ground annealed round stock for drill/tap/end-mill blanks where diameter tolerance matters. | 650 | 950 | 9 | 25 HRC | 3 % IACS |
Hardened & tempered, 68–70 HRC | High austenitizing (~1190–1200 °C) plus 540 °C tempers for maximum wear resistance on light, rigid, continuous cuts. | 2,000 | 2,100 | 0 | 69 HRC | 2.6 % IACS |
Hardened, tempered + surface treated | Core at 66–68 HRC with a nitrided or TiN/TiAlN surface for lower friction and longer tool life on abrasive work. | 2,000 | 2,200 | 1 | 67 HRC | 2.7 % IACS |
What is SKH59?
SKH59 is the JIS cobalt molybdenum high-speed steel equivalent to AISI M42, in which about 8 % Co and a high Mo content raise secondary hardness to working values of 64–70 HRC. It is selected for cutting hardened, tough or abrasive materials at high cutting speed, and is supplied as annealed and cold-drawn bar, drill and cutter blanks, and hardened or nitrided tool bodies. Cost is higher than M2 while toughness and grindability are lower, coatings and tempering must stay at or below about 500 °C to avoid over-tempering, and the 4 % Cr gives no corrosion resistance; where cost or impact resistance dominates, SKH51 (M2) is the alternative. SKH59 has a density of 7.98 g/cm³ (0.288 lb/in³), heavier than 94% of steel grades. It melts at 1,290°C (2,354 °F). SKH59 has a yield strength of 600 MPa (87 ksi) and a tensile strength of 900 MPa (131 ksi) — stronger than 77% of steel grades. Elongation at break is 12% and the elastic modulus is 225 GPa (32.6 Msi).
What is SKH59 used for?
- high-speed drills
- cutting tools for hardened steel
- gear cutters
Advantages
- Polishes to a fine finish — 80/100, better than 97% of steel grades
- High strength — 600 MPa (87 ksi), better than 77% of steel grades
Limitations
- Low fracture toughness — 22 MPa·√m (20 ksi·√in), worse than 98% of steel grades
- Poor heat conductor — 19 W/m·K (11 BTU/hr·ft·°F), worse than 97% of steel grades
- Limited formability — 10/100, worse than 95% of steel grades
- High embodied carbon — 4.2 kg CO₂/kg, worse than 95% of steel grades
- Low electrical conductivity — 2.9 % IACS, worse than 93% of steel grades
SKH59 properties
Typical room-temperature values for SKH59-ANN; bars are the position among steel grades.
Physical3
SKH59 has a density of 7.98 g/cm³ (0.288 lb/in³), heavier than 94% of steel grades. It melts at 1,290°C (2,354 °F).
Mechanical17
SKH59 has a yield strength of 600 MPa (87 ksi) and a tensile strength of 900 MPa (131 ksi) — stronger than 77% of steel grades. Elongation at break is 12% and the elastic modulus is 225 GPa (32.6 Msi).
Thermal6
SKH59 is rated for continuous service to 300°C (572 °F). It conducts heat at 19 W/m·K (11 BTU/hr·ft·°F), worse than 97% of steel grades. Thermal expansion is 10.6 µm/m·K (5.89 µin/in·°F).
Electrical3
SKH59 conducts electricity at 2.9 % IACS, worse than 93% of steel grades.
Chemical & Environmental3
Corrosion resistance is poor (18/100), better than 83% of steel grades.
Sustainability4
Producing a kilogram of SKH59 takes about 55 MJ of energy and emits 4.2 kg of CO₂ — more than 94% of steel grades. Typical recycled content is 25%.
Manufacturability7
SKH59's machinability is poor (25/100, worse than 93% of steel grades); weldability poor (15/100); formability not recommended (10/100).
Common Calculations5
Values are nominal handbook figures for design screening. Certified mill or lot data ships with every FabDigit order on request.
Strength versus weight in the steel family
Yield strength against density for every steel grade FabDigit runs. SKH59 is highlighted; hover a dot for its name, or open the interactive family chart.
Working with SKH59
Is SKH59 easy to machine?
Machine only in the annealed condition with sharp, rigid setups and low speeds (≈25% of 1212 free-machining steel); after hardening, finish by grinding with SG/CBN wheels and generous coolant — grindability is poorer than M2 because of the Co and high Mo carbides.
Can SKH59 be welded?
Not a structural welding grade; repair or bimetal band-saw joining only by EB, laser or friction welding with preheat 500–550 °C and immediate re-temper to avoid quench cracks.
Can SKH59 be formed, bent or molded?
Hot work at 1050–1100 °C (stop above 900 °C) with slow furnace cooling and spheroidize anneal 850–870 °C; no meaningful cold formability.
SKH59 chemical composition (wt %)
Limits by weight percent from the governing specification, written the way the spec states them — a single maximum for impurities, a range for alloying elements, and the base element as balance. Nominal is the typical mid-range value.
| Element | Spec limit (wt %) | Nominal |
|---|---|---|
| CJIS G4403 SKH59 / AISI M42 | 1 – 1.15 | 1.08 |
| Si | ≤ 0.5 | 0.3 |
| Mn | ≤ 0.4 | 0.25 |
| P | ≤ 0.03 | |
| S | ≤ 0.03 | |
| Cr | 3.5 – 4.5 | 3.9 |
| Mo | 9 – 10 | 9.5 |
| W | 1.2 – 1.9 | 1.5 |
| V | 0.9 – 1.4 | 1.15 |
| Cocobalt gives red hardness | 7.5 – 8.5 | 8 |
| Fe | balance |
What surface finishes work on SKH59?
Harden 1180–1200 °C in vacuum/salt, quench and triple temper 540–560 °C; finish with steam-oxide, black oxide, nitriding or TiN/TiAlN PVD (≤500 °C so as not to over-temper) and keep oiled — the 4% Cr does not make it stainless.
Surface treatments FabDigit runs on steel parts — pick them in the quote configurator or call them out on the drawing. Each links to its datasheet in the surface-finish library (thickness, specs, call-out, material verdicts).
Organic Coating
Black / Phosphate
Thermal Spray
Equivalent designations
Standards and trade names that resolve to Steel SKH59 in FabDigit's catalog. Equivalence is nominal — check the exact specification when certification matters.
How much does SKH59 cost?
SKH59 is a high-cost steel ($$$$), pricier than about 78% of the materials FabDigit quotes. Part price depends far more on geometry, tolerance and quantity than on the raw stock — upload a CAD file for a live quote.
SKH59 — frequently asked
What is SKH59 used for?
SKH59 is typically used for high-speed drills, cutting tools for hardened steel and gear cutters. In short: highest-hardness cobalt HSS; for hardened-material cutting; poorest grindability in family.
What is the yield strength of SKH59?
SKH59 has a typical yield strength of 600 MPa (87 ksi) and a tensile strength of 900 MPa (131 ksi) — stronger than 77% of steel grades. Strength varies by condition: see the 6 listed tempers.
Is SKH59 easy to machine?
Not especially — machinability is rated poor (25/100, worse than 93% of steel grades). Machine only in the annealed condition with sharp, rigid setups and low speeds (≈25% of 1212 free-machining steel); after hardening, finish by grinding with SG/CBN wheels and generous coolant — grindability is poorer than M2 because of the Co and high Mo carbides.
Can SKH59 be welded?
Not readily — weldability is rated poor (15/100). Not a structural welding grade; repair or bimetal band-saw joining only by EB, laser or friction welding with preheat 500–550 °C and immediate re-temper to avoid quench cracks.
What surface finishes work on SKH59?
Harden 1180–1200 °C in vacuum/salt, quench and triple temper 540–560 °C; finish with steam-oxide, black oxide, nitriding or TiN/TiAlN PVD (≤500 °C so as not to over-temper) and keep oiled — the 4% Cr does not make it stainless.
Can SKH59 be formed, bent or molded?
Hot work at 1050–1100 °C (stop above 900 °C) with slow furnace cooling and spheroidize anneal 850–870 °C; no meaningful cold formability.
What is the maximum service temperature of SKH59?
SKH59 is rated for continuous use to about 300°C (572 °F). Strength falls off well before that limit — check the elevated-temperature data for load-bearing parts.
What is the difference between SKH59-ANN and SKH59 QT68-70?
ANN is the default condition — standard stock condition for bar/blank supply — machine tool geometry, then harden and temper. QT68-70: high austenitizing (~1190–1200 °C) plus 540 °C tempers for maximum wear resistance on light, rigid, continuous cuts. Yield strength is 600 MPa in ANN versus 2,000 MPa in QT68-70.
How much does SKH59 cost?
SKH59 is a high-cost steel ($$$$), pricier than about 78% of the materials FabDigit quotes. Part price depends far more on geometry, tolerance and quantity than on the raw stock — upload a CAD file for a live quote.
Sources
- JIS G 4403 High speed tool steel materials — JSA (2015)
- ASTM A600 Standard Specification for Tool Steel High Speed — ASTM (2016)
- ASM Handbook Vol. 1: Properties and Selection: Irons, Steels, and High-Performance Alloys — ASM International (1990)
- ASM Handbook Vol. 16: Machining — ASM International (1989)
- M42 / HS2-9-1-8 cobalt high speed steel datasheet — Böhler / Erasteel (2022)
Property data is compiled from published supplier and standards handbooks and normalised for comparison; hardness values on non-Brinell scales are converted approximately for charting only. Manufacturability limits are FabDigit quote-engine defaults and may be relaxed by engineering review. Nothing on this page is a certification — request mill certs, CoC or material test reports with your order.