Tool steels occupy a middle ground in deep hole drilling difficulty. They are not as aggressive as nickel superalloys on tool wear, nor as forgiving as low-carbon steel. What makes them unique is their variability within a single material grade — the same H13 bar can be supplied at 30 HRC (annealed) or 55 HRC (hardened), and the drilling parameters must change accordingly.
This guide covers five common tool steel grades used in mold, die, and tooling applications: P20, H13, A2, D2, and S7.
Material Properties Overview
| Grade | Type | Annealed Hardness | Working Hardness | Key Characteristic |
|---|---|---|---|---|
| P20 | Mold steel | 28–32 HRC | 28–32 HRC (pre-hardened) | Good machinability, most common mold steel |
| H13 | Hot work tool steel | 20–25 HRC | 45–55 HRC | Heat resistance, for die casting and extrusion |
| A2 | Air-hardening tool steel | 20–25 HRC | 57–62 HRC | Balanced wear resistance and toughness |
| D2 | High-carbon, high-chrome | 20–25 HRC | 58–64 HRC | High wear resistance, difficult machining |
| S7 | Shock-resistant tool steel | 20–25 HRC | 48–58 HRC | High toughness, for impact applications |
Sources: Paulo (A2/D2/S7 comparison); Beskamold tool steel guide; Clarwe tool steel properties.
Practical rule: For deep hole drilling, all tool steels should ideally be drilled in the annealed condition before heat treatment. If drilling hardened tool steel is unavoidable, expect tool life reductions of 50–75% compared to the annealed state.
For applications where these tool steels are used, see the Mold & Die Deep Hole Drilling guide.
1. P20 (1.2311) — Pre-Hardened Mold Steel
P20 is the most common plastic mold steel. It is supplied pre-hardened to approximately 30 HRC and is the most machinable of the five grades covered here.
Recommended Parameters (Carbide Gun Drilling)
| Parameter | Value |
|---|---|
| Cutting speed (Vc) | 70–100 m/min |
| Feed rate (6 mm drill) | 0.015–0.035 mm/rev |
| Feed rate (10 mm drill) | 0.030–0.049 mm/rev |
| Feed rate (20 mm drill) | 0.060–0.107 mm/rev |
| Coolant pressure | 40–70 bar |
| Tool coating | TiAlN |
| Expected tool life (10 mm) | 1.5–3.0 m drilled length per regrind |
Sources: Smart Lathe deep hole parameters; KBD Cutting Tool.
P20’s uniform hardness and good chip formation make it one of the easiest tool steels to deep-hole-drill. Chip shape is typically short and well-broken at recommended feeds. Avoid reducing feed below 0.015 mm/rev to prevent work hardening.
2. H13 (1.2344) — Hot Work Tool Steel
H13 is used for die casting dies, extrusion tooling, and hot forming applications. Its machining behavior depends heavily on heat treatment state.
Parameters by Condition
| Parameter | Annealed (20–25 HRC) | Pre-Hardened (45–55 HRC) | Full Hardened (55–62 HRC) |
|---|---|---|---|
| Vc — gun drilling | 70–90 m/min | 50–80 m/min | 35–55 m/min |
| Vc — BTA drilling | 60–100 m/min | 40–70 m/min | 25–45 m/min |
| Feed rate (10 mm gun drill) | 0.025–0.045 mm/rev | 0.020–0.035 mm/rev | 0.015–0.025 mm/rev |
| Feed rate (25 mm BTA) | 0.10–0.22 mm/rev | 0.08–0.16 mm/rev | 0.06–0.12 mm/rev |
| Coolant pressure | 40–60 bar | 60–80 bar | 80–100 bar |
| Recommended coating | TiAlN | TiAlN or AlTiN | AlTiN or AlCrN |
Sources: Smart Lathe; Insight Technologies BTA data; Mitsubishi Carbide H13 reference.
H13-specific challenge: H13 has a tendency to work harden, particularly in the heat-affected zone if the tool dwells or rubs. Research on H13 CNC drilling (UTS, 2023) confirmed that increasing feed rate improves surface finish in the work-hardened layer — do not reduce feed to extend tool life in this material as it will have the opposite effect.
3. A2 (1.2363) — Air-Hardening Tool Steel
A2 offers a good balance of wear resistance and toughness, making it a common choice for general-purpose tooling. It is one of the easier high-alloy tool steels to machine.
| Parameter | Annealed (20–25 HRC) | Hardened (57–62 HRC) |
|---|---|---|
| Vc — gun drilling | 60–80 m/min | 30–50 m/min |
| Vc — BTA drilling | 50–80 m/min | 25–40 m/min |
| Feed rate (10 mm gun drill) | 0.020–0.040 mm/rev | 0.012–0.025 mm/rev |
| Coolant pressure | 40–60 bar | 60–80 bar |
| Machinability rating | 70–80% of carbon steel | 40–50% of carbon steel |
Sources: Beskamold; Clarwe; Paulo.
A2 chips are typically well-behaved in the annealed state. In the hardened state (57+ HRC), the material becomes abrasive and tool life drops significantly. If drilling hardened A2 is unavoidable, use AlTiN-coated carbide and the lowest recommended speeds.
4. D2 (1.2379) — High-Carbon, High-Chromium Tool Steel
D2 contains 1.4–1.6% carbon and 11–13% chromium, forming hard chromium carbides that make it the most abrasive of the five grades. D2 is the most difficult tool steel for deep hole drilling.
| Parameter | Annealed (20–25 HRC) | Hardened (58–64 HRC) |
|---|---|---|
| Vc — gun drilling | 40–60 m/min | 20–35 m/min |
| Vc — BTA drilling | 35–55 m/min | 18–30 m/min |
| Feed rate (10 mm gun drill) | 0.015–0.030 mm/rev | 0.010–0.020 mm/rev |
| Feed rate (25 mm BTA) | 0.08–0.16 mm/rev | 0.05–0.10 mm/rev |
| Coolant pressure | 60–80 bar | 80–120 bar |
| Tool life relative to P20 | ~40% | ~15% |
| Machinability rating | 60–70% of carbon steel | 25–35% of carbon steel |
Sources: Beskamold; Clarwe; Paulo.
D2-specific challenges:
- The high carbide content (approximately 12–15% by volume) makes D2 highly abrasive. Expect flank wear as the primary failure mode rather than edge chipping.
- Coolant filtration to < 10 μm is recommended to prevent carbide particles suspended in the coolant from accelerating guide pad wear.
- If possible, drill D2 in the annealed condition and finish with EDM or grinding after heat treatment.
5. S7 (1.2359) — Shock-Resistant Tool Steel
S7 is the toughest of the five grades, designed for impact applications such as shear blades, punches, and cold forming tools. It is also the most forgiving to machine.
| Parameter | Annealed (20–25 HRC) | Hardened (48–58 HRC) |
|---|---|---|
| Vc — gun drilling | 65–85 m/min | 40–60 m/min |
| Vc — BTA drilling | 55–80 m/min | 35–50 m/min |
| Feed rate (10 mm gun drill) | 0.020–0.040 mm/rev | 0.015–0.030 mm/rev |
| Coolant pressure | 40–60 bar | 50–70 bar |
| Machinability rating | 70–80% of carbon steel | 45–55% of carbon steel |
Sources: Beskamold; Clarwe; Southern Tool Steel.
S7’s lower alloy content compared to D2 makes it significantly easier to drill. Chip formation is generally good, and tool life in the annealed state approaches that of low-alloy steel.
Comparison Summary
| Grade | Annealed Vc | Hardened Vc | Relative Tool Life (annealed) | Relative Difficulty |
|---|---|---|---|---|
| P20 | 70–100 m/min | N/A (pre-hardened) | 100% (baseline) | Low |
| S7 | 65–85 m/min | 40–60 m/min | 85–90% | Low–Medium |
| A2 | 60–80 m/min | 30–50 m/min | 70–80% | Medium |
| H13 (annealed) | 70–90 m/min | 50–80 m/min | 80–90% | Medium |
| H13 (hardened) | — | 35–55 m/min | 40–50% | Medium–High |
| D2 | 40–60 m/min | 20–35 m/min | 35–40% | High |
For comparison with other materials, see the Nickel Superalloys Guide and the Speeds and Feeds Reference.
General Guidelines for Tool Steel Deep Hole Drilling
Method Selection
| Diameter | Recommended Method | Reason |
|---|---|---|
| < 20 mm | Gun drilling | Better straightness, lower tooling cost |
| 20–50 mm | Gun drilling or BTA | Evaluate based on volume |
| > 50 mm | BTA drilling | Higher MRR, indexable inserts for abrasive D2/H13 |
Tool Coating Selection
| Material State | Recommended Coating | Reason |
|---|---|---|
| Annealed (all) | TiAlN | Standard all-around, good heat resistance |
| Hardened H13/A2 | AlTiN or AlCrN | Higher thermal stability for reduced speeds |
| Hardened D2 | AlCrN | Best abrasion resistance for high-carbide materials |
| All (alternate) | TiCN | Lower friction, good for annealed tool steels |
Cooling and Filtration
Tool steels generate significant heat at the cutting edge, particularly in the hardened state. High-pressure coolant is essential:
| Condition | Recommended Pressure | Notes |
|---|---|---|
| Annealed | 40–60 bar | Standard for most tool steels |
| Hardened < 55 HRC | 60–80 bar | Manage heat at reduced speeds |
| Hardened > 55 HRC | 80–120 bar | Critical for tool life |
| D2 (any condition) | 60–80 bar minimum | Carbide abrasion requires positive chip evacuation |
Filtration to < 20 μm is required for all tool steel deep hole drilling. For D2, filtration to < 10 μm is recommended to prevent chromium carbide particles from recirculating and wearing guide pads.
Expected Surface Finish
| Grade | As-Drilled Ra (gun drilling) | As-Drilled Ra (BTA) |
|---|---|---|
| P20 | 0.4–1.2 μm | 0.8–2.0 μm |
| H13 (annealed) | 0.6–1.4 μm | 0.8–2.5 μm |
| H13 (hardened) | 0.4–1.0 μm | 0.6–1.6 μm |
| A2 | 0.5–1.4 μm | 0.8–2.0 μm |
| D2 | 0.4–1.2 μm | 0.6–1.8 μm |
| S7 | 0.5–1.4 μm | 0.8–2.0 μm |
For a detailed discussion of achievable finishes, see the Surface Finish Guide.
Summary
- P20 is the easiest tool steel for deep hole drilling — treat it similarly to medium-carbon alloy steel
- H13 requires attention to heat treatment state; parameters must be reduced as hardness increases
- A2 is manageable in the annealed state, challenging when hardened
- D2 is the most difficult — drill in the annealed state whenever possible, use AlCrN coating, and expect reduced tool life
- S7 is the most forgiving high-alloy tool steel, closest to standard alloy steel in machinability
- All tool steels should ideally be drilled before heat treatment. If hardened drilling is required, reduce cutting speed by 40–60% and increase coolant pressure
Key Sources
- Smart Lathe, “How to Select Appropriate Machining Parameters for Deep Hole Drilling” — P20 and alloy steel parameters
- KBD Cutting Tool, “Gun Drilling How to Choose Cutting Parameters” — feed rate tables
- Insight Technologies, “BTA Drilling Process” — BTA parameter ranges
- Mitsubishi Carbide, H13 solid end mill reference — hardness-dependent parameter data
- UTS (University of Technology Sydney), “Effects of Machining Parameters on H13 Die Steel Using CNC Drilling Machine,” 2023 — work hardening research
- Paulo, “S7, D2, A2: Difference in Tool Steel Properties” — hardness and property comparison
- Beskamold, “Types of Tool Steel: Grades, Properties, Applications & Selection Guide” — machinability ratings
- Clarwe, “Tool Steel for CNC Machining” — grade properties
- Southern Tool Steel, drill rod specifications — availability in annealed condition
- ISCAR Drilling Handbook — general reference for cutting parameters