Steel M48-HT68
Heat-treated state
AISI/SAE M48 · UNS T11348
HT68 = hardened & triple tempered
Standard cutting-tool condition: austenitize ~1200-1220 °C, quench, triple temper ~540-560 °C for maximum hot hardness and wear life.
Values for the HT68 condition
Other M48 tempers and conditions
M48 is listed in 3 conditions; see the grade overview at M48.
Compare all 3 conditionsHide
| Condition · open for datasheet | Best for | Yield MPa | Tensile MPa | Elong. % | Hardness | Conductivity |
|---|---|---|---|---|---|---|
ANNDefault Annealed | The as-supplied condition for bar, blanks and forgings — soft enough to machine tool geometry before hardening. | 620 | 950 | 10 | 26 HRC | 23 W/m·K |
HT68This page Hardened & triple tempered | Standard cutting-tool condition: austenitize ~1200-1220 °C, quench, triple temper ~540-560 °C for maximum hot hardness and wear life. | — | 2,100 | 0 | 68 HRC | — |
Hardened & triple tempered | Pick when some edge toughness is needed (interrupted cuts, larger cutters) at slightly reduced red hardness. | — | 2,300 | 0 | 66 HRC | — |
What is M48-HT68?
M48-HT68 is M48 heat treated to HT68 — standard cutting-tool condition: austenitize ~1200-1220 °C, quench, triple temper ~540-560 °C for maximum hot hardness and wear life. M48-HT68 has a yield strength of 620 MPa (89.9 ksi) and a tensile strength of 2,100 MPa (305 ksi) — stronger than 78% of steel grades. Elongation at break is 0% and the elastic modulus is 225 GPa (32.6 Msi). M48-HT68 has a density of 8.15 g/cm³ (0.294 lb/in³), heavier than 97% of steel grades. It melts at 1,250°C (2,282 °F). ANN is the default condition FabDigit quotes; HT68 is available on request or by drawing note.
Advantages
- High service temperature — 620°C (1,148 °F), better than 99% of steel grades
- Polishes to a fine finish — 70/100, better than 87% of steel grades
- High strength — 620 MPa (89.9 ksi), better than 78% of steel grades
Limitations
- Limited ductility — 0%, worse than 100% of steel grades
- Low fracture toughness — 13 MPa·√m (11.8 ksi·√in), worse than 100% of steel grades
- Difficult to machine — 3/100, worse than 100% of steel grades
- Limited formability — 1/100, worse than 100% of steel grades
- Difficult to weld — 8/100, worse than 99% of steel grades
M48-HT68 properties
Typical room-temperature values for M48-HT68; 17 are specific to this condition. Other listed values are M48 reference data and may not represent this condition. Bars are the position among steel grades.
Physical3
M48-HT68 has a density of 8.15 g/cm³ (0.294 lb/in³), heavier than 97% of steel grades. It melts at 1,250°C (2,282 °F).
Mechanical15
M48-HT68 has a yield strength of 620 MPa (89.9 ksi) and a tensile strength of 2,100 MPa (305 ksi) — stronger than 78% of steel grades. Elongation at break is 0% and the elastic modulus is 225 GPa (32.6 Msi).
Thermal6
M48-HT68 is rated for continuous service to 620°C (1,148 °F). It conducts heat at 23 W/m·K (13.3 BTU/hr·ft·°F), worse than 92% of steel grades. Thermal expansion is 10.3 µm/m·K (5.72 µin/in·°F).
Electrical3
M48-HT68 conducts electricity at 2.9 % IACS, worse than 93% of steel grades.
Chemical & Environmental2
Corrosion resistance is poor (15/100), better than 75% of steel grades.
Sustainability4
Producing a kilogram of M48-HT68 takes about 60 MJ of energy and emits 5.5 kg of CO₂ — more than 96% of steel grades. Typical recycled content is 35%.
Manufacturability8
M48-HT68's machinability is not recommended (3/100, worse than 100% of steel grades); weldability not recommended (8/100); formability not recommended (1/100).
Values are nominal handbook figures for design screening. Confirm any required mill or lot documentation when quoting.
Working with M48-HT68
Is M48 easy to machine?
Machine only in the annealed condition with rigid setups, sharp cobalt-HSS or coated carbide, low speeds and heavy coolant; after hardening only grinding (CBN/SG wheels) or EDM — beware grinding burn and cracks.
Can M48 be welded?
Essentially non-weldable structurally; repair only by TIG/laser with matched HSS filler, 500-550 °C preheat and immediate multiple tempers.
Can M48 be formed, bent or molded?
Hot forge 1100-1150 °C, finish above 950 °C, slow cool then full spheroidize anneal (~870 °C, ≤20 °C/h to 600 °C); no cold forming.
What surface finishes work on M48?
Finish by grinding/lapping; protect with black oxide, steam oxide, nitriding or PVD TiN/TiAlN — never anodize; oil or VCI wrap for storage.
M48 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 |
|---|---|---|
| C | 1.42 – 1.52 | 1.47 |
| Mn | 0.15 – 0.4 | 0.28 |
| Si | 0.15 – 0.4 | 0.28 |
| Cr | 3.5 – 4 | 3.75 |
| W | 9.5 – 10.5 | 10 |
| Mo | 4.75 – 5.5 | 5.1 |
| V | 2.75 – 3.25 | 3 |
| Co | 8 – 10 | 9 |
| P | ≤ 0.03 | — |
| S | ≤ 0.03 | — |
| Fe | balance | — |
M48-HT68 — frequently asked
What is M48-HT68 used for?
M48-HT68 is typically used for heavy-duty milling cutters, broaches for hard/heat-resistant alloys, high-performance drills and taps and cutting tools for superalloys. In short: highest cobalt in family; exceptional red hardness; hardens to 68 HRC.
What is the yield strength of M48-HT68?
M48-HT68 has a typical yield strength of 620 MPa (89.9 ksi) and a tensile strength of 2,100 MPa (305 ksi) — stronger than 78% of steel grades. Strength varies by condition: see the 3 listed tempers.
Is M48-HT68 easy to machine?
Not especially — machinability is rated not recommended (3/100, worse than 100% of steel grades). Machine only in the annealed condition with rigid setups, sharp cobalt-HSS or coated carbide, low speeds and heavy coolant; after hardening only grinding (CBN/SG wheels) or EDM — beware grinding burn and cracks.
Can M48-HT68 be welded?
Not readily — weldability is rated not recommended (8/100). Essentially non-weldable structurally; repair only by TIG/laser with matched HSS filler, 500-550 °C preheat and immediate multiple tempers.
What surface finishes work on M48-HT68?
Finish by grinding/lapping; protect with black oxide, steam oxide, nitriding or PVD TiN/TiAlN — never anodize; oil or VCI wrap for storage.
Can M48-HT68 be formed, bent or molded?
Hot forge 1100-1150 °C, finish above 950 °C, slow cool then full spheroidize anneal (~870 °C, ≤20 °C/h to 600 °C); no cold forming.
What is the maximum service temperature of M48-HT68?
M48-HT68 is rated for continuous use to about 620°C (1,148 °F). Strength falls off well before that limit — check the elevated-temperature data for load-bearing parts.
Sources
- ASTM A600 — Tool Steel High Speed Tool Steels — ASTM International (2021)
- ASM Handbook Vol.1 — Properties and Selection: Irons, Steels, and High-Performance Alloys (High-Speed Tool Steels) — ASM International (1990)
- ASM Specialty Handbook — Tool Materials — ASM International (1995)
- ASM Handbook Vol.16 — Machining — ASM International (1989)
Property data is compiled from published supplier and standards handbooks and normalised for comparison. Nothing on this page is a certification — request mill certs, CoC or material test reports with your order.