AISI O1 Oil-Hardening Cold-Work Tool Steel
AISI O1 (UNS T31501) — oil-hardening cold-work tool steel, HRC 58–64, low distortion. Compare with A2 and D2 for short-run tooling.
AISI O1 (UNS T31501, DIN 1.2510, JIS SKS3) is the standard oil-hardening cold-work tool steel — 0.9 % C, 0.5 % Cr, 0.5 % W. Hardened to HRC 58–64 with minimal distortion when quenched in oil, it remains popular for short-run tooling, prototype knives and gauges where the convenience of oil-hardening offsets the air-hardening trend.
Standard composition: C 0.85–1.00 %, Cr 0.40–0.70 %, Mn 1.00–1.40 %, W 0.40–0.70 %, V ≤ 0.30 %, Si 0.20–0.40 %, balance Fe
Hardness: Annealed HB 183–212; hardened HRC 58–64
Heat treatment: Austenitise 780–820 °C, oil quench, double temper 175–200 °C
Properties: Excellent dimensional stability on oil quenching. Hardness up to HRC 64 achievable. Lower wear resistance than D2 (low Cr and V). Used for precision parts where dimensional control matters more than wear.
Applications: Precision gauges, dies for short-run blanking, master tools, low-volume slitter blades, draw dies for sheet metal.
Cross-reference: ≈ JIS SKS3, DIN 1.2510, GB 9Mn2V, BS BO1.
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