CNC Machining
Tool Steel
Tool steel is the cornerstone of industrial mass production. Characterized by its distinctive hardness, resistance to abrasion, and ability to hold a cutting edge at elevated temperatures, it is the ultimate material for injection molds, stamping dies, and heavy-duty cutting tools.
Core Mechanical Properties
Tool steels are defined by their response to heat treatment. Below is the typical mechanical data for common tool steels in their fully hardened and tempered state.
| Alloy Grade | Yield Strength | Tensile Strength | Hardness (Rockwell C) |
|---|---|---|---|
| D2 (High-Carbon, High-Chrome) | ~ 1650 MPa | ~ 1900 MPa | 55 - 62 HRC |
| A2 (Air-Hardening) | ~ 1400 MPa | ~ 1700 MPa | 57 - 62 HRC |
| O1 (Oil-Hardening) | ~ 1350 MPa | ~ 1650 MPa | 57 - 61 HRC |
International Grade Comparison
Matching tool steel grades globally is critical for mold making and die stamping. Use our cross-reference chart for American (AISI), European (DIN/EN), and Chinese (GB) equivalents.
| AISI / ASTM (USA) | DIN / EN (Europe) | GB (China) | Key Characteristics |
|---|---|---|---|
| D2 | 1.2379 / X153CrMoV12 | Cr12Mo1V1 | Extremely high wear resistance due to high carbon and chromium content. The absolute standard for long-run cold forming and stamping dies. |
| A2 | 1.2363 / X100CrMoV5 | Cr5Mo1V | Air-hardening steel offering a superb balance between wear resistance and toughness. Highly dimensionally stable during heat treatment. |
| O1 | 1.2510 / 100MnCrW4 | 9CrWMn | Oil-hardening steel. Very good machinability in its annealed state. Preferred for custom cutting tools, gauges, and short-run dies. |
Application Fit Matrix
Tool steel is selected for components that must survive wear, impact, heat, or repeated production contact after heat treatment.
| Application | Recommended Material | Why This Material Works | Typical CNC Process | Finish / Risk Note |
|---|---|---|---|---|
| Mold Inserts & Core Pins | H13 or P20 Tool Steel | Thermal fatigue resistance and toughness for molding cycles. | Milling, EDM, grinding | Plan heat treatment and final grinding with tolerance stack-up. |
| Punches & Dies | D2 or A2 Tool Steel | High wear resistance keeps cutting edges stable. | Milling, wire EDM, grinding | Radius stress points; D2 can be brittle. |
| Wear Blocks & Guide Rails | O1, A2, or D2 Tool Steel | Hardened surfaces resist abrasion and sliding contact. | Milling, heat treat, grinding | Leave grind stock after hardening. |
| Hot Work Tooling | H13 Tool Steel | Maintains toughness under repeated heat exposure. | Milling, drilling, EDM | Proper heat treatment prevents cracking. |
| Precision Locators & Gauges | O1 or A2 Tool Steel | Can be hardened and ground for durable references. | Milling, turning, grinding | Allow for movement during heat treatment. |
Selection Rule
Match the grade to the part's real job first: strength, heat, wear, corrosion, insulation, transparency, or cosmetic finish.
DFM Reminder
Material choice changes tolerance risk, burr control, wall thickness, thread strategy, and finishing route.
Quote Tip
Share the operating environment, mating parts, finish expectations, and inspection requirements with the drawing.
Expert Machining Tips
Machining tool steel requires a two-phase approach: roughing in the soft state, followed by hard-milling after heat treatment. Huade engineers excel in this precise workflow:
- 1
Annealed Roughing & Allowances
We perform heavy material removal while the steel is in its annealed (soft) state. Crucially, our programmers leave specific material allowances (typically 0.2mm to 0.5mm) to account for slight warping that occurs during the quenching process.
- 2
Hard Milling (HRC 50+)
After heat treatment, the steel is incredibly hard. We utilize highly rigid 5-axis machines equipped with CBN (Cubic Boron Nitride) or TiAlN-coated solid carbide end mills to "hard mill" the part to its final, exact micron tolerance.
- 3
Integration with Wire EDM
For sharp internal corners or extreme precision in stamping dies (where end mills cannot reach), we seamlessly transition the hardened tool steel blocks to our Wire Electrical Discharge Machining (EDM) centers for flawless final cutting.
Top 3 Surface Treatments
For tool steels, "surface treatment" primarily refers to thermal processing and advanced tribological coatings designed to extend tool life.
1. Vacuum Heat Treatment
An absolute necessity. The raw part is quenched and tempered in a vacuum furnace to achieve its target Rockwell hardness (HRC) without suffering from surface oxidation or decarburization.
2. PVD Coatings (TiN, TiAlN)
Physical Vapor Deposition adds an ultra-thin, extremely hard (up to 80+ HRC equivalent) and highly lubricious layer to the tool steel. This prevents wear and galling in high-friction molding and stamping applications.
3. Black Oxide & Mechanical Polishing
To prevent rust on non-cutting surfaces, Black Oxide is applied. For injection molds, the cavities are hand-polished to an optical mirror finish to ensure plastic parts eject cleanly with a pristine surface.
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