O1 Oil-Hardening Tool Steel Technical Material Specification
Comprehensive technical specification for O1 oil-hardening tool steel (AISI/SAE O1, UNS T31501), covering Canadian stock sizing, machinability, heat treatment, common defects, and storage guidelines for fabrication and machining shops.
Material Overview & Common Uses
O1 is a high-carbon, oil-hardening tool steel (AISI/SAE O1, UNS T31501) known for its excellent dimensional stability during heat treatment, good wear resistance, and ease of machining in the annealed condition. It is a staple in Canadian tool and die shops, mold making, and precision machining. Common applications include cutting tools (drills, taps, reamers), blanking dies, forming rolls, gauges, jigs, fixtures, and woodworking plane irons and chisels. O1 is supplied in the annealed condition (typically 190-210 HB) and is hardened by heating to 790-815°C (1450-1500°F) followed by oil quenching, then tempering to desired hardness (typically 58-62 HRC). Its predictable shrinkage (approx. 0.001-0.002 in/in) makes it ideal for precision tooling.
Core Technical Properties & Sizing
| Property | Value / Detail |
|---|---|
| Chemical Composition (wt%) | C 0.85-1.00, Mn 1.00-1.40, Si 0.50 max, Cr 0.40-0.60, W 0.40-0.60, V 0.20 max, S 0.030 max, P 0.030 max |
| Physical Properties | Density 7.85 g/cm³, Modulus of Elasticity 207 GPa, Thermal Conductivity 24 W/m·K at 100°C |
| Hardness (Annealed) | 190-210 HB (typical) |
| Hardness (Hardened & Tempered) | 58-62 HRC |
| Flat Stock Thickness (Precision Ground) | 1/16" (1.6 mm) to 4" (101.6 mm) in 1/16" inc. up to 1", then 1/8" inc. |
| Flat Stock Width | 1/8" (3.2 mm) to 12" (304.8 mm) in 1/8" inc. up to 6", then 1/4" inc. |
| Flat Stock Tolerances (Thickness) | ±0.0005" for ≤1", ±0.001" for 1-2", ±0.002" for 2-4" |
| Drill Rod Diameter (Canadian Standard) | 1/16" to 1" in 1/64" inc. Metric: 1 mm to 25 mm in 0.5 mm inc. |
| Drill Rod Tolerances (Diameter) | +0.0000" / -0.0005" for ≤1/2", +0.0000" / -0.001" for 1/2" to 1" |
Machinability, Tooling & Feeds
O1 in the annealed condition has a machinability rating of approximately 85-90% of AISI 1112 free-machining steel. It produces short, brittle chips and responds well to carbide tooling. Recommended cutting parameters for carbide tools are detailed below.
| Operation | Tooling | Speed (SFM) | Feed | Depth of Cut |
|---|---|---|---|---|
| Turning | Carbide | 150-250 | 0.005-0.015 IPR | 0.050-0.150" |
| Milling | Carbide | 200-300 | 0.003-0.008 IPT | 0.030-0.100" |
| Drilling | Carbide | 80-120 | 0.002-0.006 IPR | — |
| Grinding | Al₂O₃ (46-60 grit, J-K) | — | — | Avoid overheating |
| Heat Treatment | Pre-heat 650-700°C, Austenitize 790-815°C, Quench in warm oil (50-70°C) | — | — | Temper at 150-260°C |
Common Defects & Quality Control
| Defect | Description | Detection / Inspection |
|---|---|---|
| Decarburization | Surface carbon loss during hot rolling or heat treatment, visible as a soft, discolored layer. | Visual / ASTM A681 (Acceptable depth: 0.005" per side for ≤1") |
| Carbide Segregation | Banding of carbides leading to anisotropic wear and cracking. | Microetch (2% nital) at 100-400X |
| Grinding Cracks | Fine, perpendicular cracks from excessive heat during grinding. | Magnetic particle (MT) or dye penetrant (PT) |
| Quench Cracks | Longitudinal or radial cracks from too rapid cooling or insufficient tempering. | Visual / MT / PT |
| Dimensional Distortion | Warpage or growth/shrinkage beyond 0.002 in/in. | Micrometers, surface plate |
| Inclusions | Non-metallic inclusions (sulfides, oxides). | ASTM E45 Method A (Worst field rating < 2.0) |
| Surface Scale | Heavy oxide scale from annealing. | Visual (Must be removed before precision grinding) |
Storage, Handling & Racking Guidelines
Store O1 tool steel in a dry, indoor environment with relative humidity below 60% to prevent surface rust. Precision ground flat stock should be stored vertically in dedicated racking with padded dividers to prevent edge damage and scratches. Drill rod should be stored horizontally in tubes or on racks with full-length support to avoid bending. Apply a light rust-preventive oil (e.g., LPS-3 or equivalent) if storage exceeds 30 days. Do not store near acids, chlorides, or moisture sources. For long-term storage (over 6 months), wrap in VCI (Vapor Corrosion Inhibitor) paper. Racking should be sturdy, with a load capacity of at least 500 lbs per shelf for flat stock bundles. Implement FIFO (First-In, First-Out) inventory rotation. Use Ryxen SupplyGrid to track stock levels and set reorder points at 2 weeks of average consumption. When receiving, inspect for transit damage, verify dimensions and hardness with a portable hardness tester (e.g., Leeb rebound), and check for decarburization on cut edges.