D2 Air-Hardening Tool Steel
Material Specification for Canadian Fabrication & Machining — comprehensive technical data covering chemical composition, stock sizing, heat treatment, machinability, common defects, and storage guidelines for Canadian industrial operations.
Material Overview & Common Uses
D2 is a high-carbon, high-chromium air-hardening tool steel (AISI D2, UNS T30402) known for its exceptional wear resistance, high compressive strength, and good dimensional stability during heat treatment. It contains approximately 1.5% carbon and 12% chromium, placing it in the cold-work tool steel family. In Canadian fabrication and machining shops, D2 is the go-to material for long-run stamping dies, forming rolls, shear blades, slitter knives, extrusion dies, and plastic injection mold components where abrasive wear is a primary concern. It is also used for gauges, mandrels, and wear plates.
D2 is not recommended for applications requiring high toughness or impact resistance, as it is relatively brittle compared to lower-alloy tool steels like A2 or O1. Its air-hardening characteristic minimizes distortion and cracking risks during heat treatment, making it suitable for complex geometries. Common supply forms include hot-rolled annealed (HRA) plate, precision ground flat stock (PGFS), and round bar. Canadian suppliers typically stock D2 in imperial and metric sizes, with surface finishes ranging from black (hot-rolled) to decarb-free (precision ground).
Core Technical Properties & Sizing
Chemical Composition (wt%)
| Element | Weight % |
|---|---|
| Carbon | 1.40 – 1.60 |
| Chromium | 11.00 – 13.00 |
| Molybdenum | 0.70 – 1.20 |
| Vanadium | 0.50 – 1.10 |
| Manganese | 0.30 – 0.50 |
| Silicon | 0.30 – 0.50 |
| Phosphorus | max 0.030 |
| Sulfur | max 0.030 |
| Iron | Balance |
Physical & Mechanical Properties
| Property | Value |
|---|---|
| Density | 0.283 lb/in³ (7.83 g/cm³) |
| Modulus of Elasticity | 30 × 10⁶ psi (207 GPa) |
| Thermal Conductivity (at 212°F / 100°C) | 20.0 BTU/hr·ft·°F (34.6 W/m·K) |
| Coefficient of Thermal Expansion (68–400°F / 20–204°C) | 6.0 × 10⁻⁶ in/in/°F (10.8 × 10⁻⁶ m/m/°C) |
| Annealed Hardness | 217 – 255 HB (max 255 HB per ASTM A681) |
| Hardened & Tempered Hardness | 58 – 62 HRC (depending on tempering temperature) |
Heat Treatment Parameters
| Stage | Temperature Range | Notes |
|---|---|---|
| Preheating | 1200 – 1300°F (649 – 704°C) | Slow and uniform heating |
| Austenitizing | 1800 – 1875°F (982 – 1024°C) | Air hardening; soak time per thickness |
| Quenching | Still or forced air | Positive pressure vacuum acceptable |
| Tempering | 400 – 1000°F (204 – 538°C) | Target hardness dependent on temperature |
| Double Tempering | — | Recommended for full transformation |
Standard Stock Sizes (Canada) & Tolerances
| Form | Thickness | Width | Length | Tolerance |
|---|---|---|---|---|
| Hot-Rolled Annealed Plate | 1/8″ – 4″ (3 – 100 mm) | 12″, 18″, 24″, 36″ | 36″, 48″, 72″, 96″ | +0.030″ to +0.060″ (1/4″–1″ thick) per ASTM A681 |
| Precision Ground Flat Stock | 1/8″ – 2″ (±0.001″) | 1/2″ – 12″ (+0.005″/–0.000″) | 12″ – 36″ (+1/8″/–0″) | Thickness ±0.001″ Width +0.005″/–0.000″ |
| Round Bar | 1/4″ – 12″ (6 – 300 mm) | — | 12′ (3.66 m) random lengths | +0.020″ to +0.060″ (1″–4″ dia) per ASTM A681 |
Surface Condition: Hot-rolled annealed plate has black oxide scale (approx 0.005–0.015″ per side) that must be removed before machining. Precision ground flat stock is decarb-free and ready for layout.
Machinability, Tooling & Feeds
D2 in the annealed condition (217–255 HB) has a machinability rating of approximately 40–50% of 1212 free-machining steel. It is abrasive due to high chromium carbides, causing rapid tool wear. Carbide tooling is strongly recommended for production runs.
| Operation | Tooling | Surface Speed (SFM) | Feed | Depth of Cut | Notes |
|---|---|---|---|---|---|
| Turning | Carbide inserts (C2–C6) | 80 – 120 (24 – 37 m/min) | 0.005 – 0.015 in/rev | 0.050 – 0.150″ | Use ample coolant; avoid HSS |
| Milling | Coated carbide end mills (TiAlN / AlTiN) | 100 – 150 (30 – 46 m/min) | 0.002 – 0.005 in/tooth | Axial 0.020 – 0.080″ Radial 30–50% | Climb milling preferred |
| Drilling | Carbide or cobalt HSS drills | 40 – 60 (12 – 18 m/min) | 0.002 – 0.005 in/rev | — | Peck cycle recommended |
| Tapping | Spiral point taps, TiN coated | 20 – 30 (6 – 9 m/min) | — | — | Use cutting fluid; watch for galling |
| Grinding | Aluminum oxide or CBN wheels | Moderate | Light | — | Prone to burn/cracking; use ample coolant |
| EDM (Wire / Sinker) | — | — | — | — | Suitable; recast layer may be hard — stress relief recommended |
| Welding | D2 filler rod | — | — | — | Not for load-bearing; preheat 500–600°F; post-weld stress relief 1100–1200°F for 1 hr/in |
Common floor defects during machining: decarburization (soft skin), carbide segregation (banding), and residual stress from prior operations.
Common Defects & Quality Control
Incoming inspection should verify hardness (annealed: 217–255 HB), surface condition (no deep pits, cracks, or excessive decarb), and dimensional compliance per ASTM A681.
| Defect | Description | Inspection Method | Acceptable Limit |
|---|---|---|---|
| Decarburization | Soft, carbon-depleted layer on hot-rolled surfaces; depth 0.010–0.060″ per side | Microscopic examination or hardness traverse | ≤0.015″ per side for precision ground stock |
| Carbide Segregation (Banding) | Uneven distribution of chromium carbides; anisotropic wear and cracking risk | Microscopic examination per ASTM E768 | Minimized by proper forging and annealing |
| Cracking | From improper heat treatment (rapid cooling, inadequate tempering) or grinding stress | Dye penetrant or magnetic particle testing | Zero cracks in critical areas |
| Soft Spots | Incomplete austenitization or improper quenching | Hardness tester (Rockwell or Brinell) | Within ±10 HB of specified range |
| Dimensional Distortion | Non-uniform heating or cooling during heat treatment | Calipers, micrometers, CMM | Per print tolerance; measure after heat treat |
| Surface Scale | Black oxide on hot-rolled plate | Visual inspection | Must be removed before machining |
| Laps & Seams | Rolling defects; linear surface discontinuities | Visual inspection, dye penetrant | Not acceptable on precision ground stock |
QC Procedures: Verify mill test report (MTR) per ASTM A681; perform hardness test on each bar/plate; check thickness and width with calipers; inspect for visible defects. For critical applications, perform ultrasonic testing (UT) to detect internal voids or inclusions. Surface roughness ≤125 μin Ra for ground stock.
Storage, Handling & Racking Guidelines
D2 tool steel should be stored in a dry, indoor environment with controlled humidity (≤50% RH) to prevent rust and corrosion. Store flat stock horizontally on wooden or rubber-cushioned racks to avoid bending or warping; maximum unsupported span for 1/4″ plate is 24″. Round bars should be stored on V-shaped racks or in vertical tubes to prevent rolling and damage.
Do not stack heavy plates on top of thin sheets to avoid distortion. Use lifting magnets or vacuum lifters for heavy plates; never drag plates across each other to avoid scratching. Apply a light rust-preventive oil (e.g., LPS-3, Boeshield T-9) on machined surfaces if storing for more than 30 days. Keep material away from moisture sources (leaky roofs, condensation).
Implement FIFO (first-in, first-out) inventory rotation to prevent age-related surface degradation. For long-term storage (>6 months), wrap in VCI (vapor corrosion inhibitor) paper or plastic. Racking should be sturdy, with capacity rated for the heaviest stock (e.g., 4″ thick plate at 40 lb/ft³ = 160 lb/ft²). Label each rack location with material grade, size, heat number, and date received.
Use Ryxen SupplyGrid to track inventory levels and auto-generate reorder points when stock falls below minimum thresholds (e.g., 2 weeks of average usage).