AISI M42 Cobalt-Bearing Super High-Speed Steel
AISI M42 (UNS T11342) — 8 % Co super HSS, HRC 65–69, hot hardness HRC 60–62 at 600 °C. Compare with M35 and T15.
AISI M42 (UNS T11342) is an 8 % Co modification of M2 — the highest hot hardness of any standard HSS (HRC 60–62 at 600 °C), with HRC 65–69 achievable at room temperature. Wear life is 1.5–2× M2 on abrasive substrates, at the cost of toughness. Used for high-speed slitter blades (>1,200 m/min on tissue) and high-temperature cutting with ta-C coating.
Standard composition: C 1.05–1.20 %, Cr 3.50–4.50 %, Mo 9.00–10.00 %, W 1.15–1.85 %, V 0.95–1.35 %, Co 7.75–8.75 %, Mn ≤ 0.40 %, Si ≤ 0.50 %, balance Fe
Hardness: Annealed HB 235–269; hardened HRC 65–69
Heat treatment: Austenitise 1,180–1,200 °C, oil or salt quench, double temper 510–530 °C
Properties: The 8 % Co addition gives the highest hot hardness of any standard HSS. Hardness up to HRC 69 achievable. Wear life 1.5–2× M2 on abrasive substrates. Toughness lower than M2.
Applications: High-speed slitter blades (>1,200 m/min on tissue), high-temperature cutting, foil slitting with ta-C coating.
Cross-reference: ≈ JIS SKD59, DIN 1.3247, GB W2Mo9Cr4VCo8, BS BM42.
See also.
