If you need cutting tools that stay sharp at high speeds, resist wear when machining hard metals, and deliver consistent performance—JIS SKH51 high speed steel is the industry benchmark. This premium alloy excels in demanding applications like gear cutting and hard material machining, solving common issues like premature tool failure or poor edge retention. In this guide, we’ll break down its key properties, real-world uses, manufacturing steps, and how it compares to other materials—so you can choose tools that boost productivity and reduce downtime.
1. Material Properties of JIS SKH51 High Speed Steel
JIS SKH51’s exceptional cutting performance stems from its carefully balanced chemical composition and standout properties. Let’s explore these in detail:
1.1 Chemical Composition
The elements in JIS SKH51 work together to enhance red hardness, wear resistance, and high-temperature stability—critical for high-speed cutting. Below is its standard composition (per JIS G4403):
| Element | Content Range (%) | Key Role |
|---|---|---|
| Carbon (C) | 0.80 – 0.90 | Forms hard carbides with tungsten, molybdenum, and vanadium—boosting wear resistance. |
| Manganese (Mn) | 0.15 – 0.40 | Improves hardenability and reduces brittleness during heat treatment. |
| Silicon (Si) | 0.15 – 0.40 | Enhances strength and resistance to oxidation at high temperatures. |
| Chromium (Cr) | 3.80 – 4.50 | Supports carbide formation and hardenability; improves corrosion resistance. |
| Tungsten (W) | 5.50 – 6.75 | A core element for red hardness—retains strength at 600+ °C, enabling high-speed cutting. |
| Molybdenum (Mo) | 4.50 – 5.50 | Works with tungsten to enhance red hardness; reduces brittleness and improves toughness. |
| Vanadium (V) | 1.70 – 2.20 | Forms ultra-hard vanadium carbides, critical for edge retention when machining hard materials. |
| Cobalt (Co) | 4.50 – 5.50 | Further boosts red hardness and high-temperature stability—ideal for heavy-duty cutting. |
| Sulfur (S) | ≤ 0.030 | Minimized to avoid weakening the steel and reducing tool life. |
| Phosphorus (P) | ≤ 0.030 | Kept low to prevent brittleness, especially under high heat and stress. |
1.2 Physical Properties
These properties determine how JIS SKH51 behaves during tool manufacturing and cutting—such as heat transfer and dimensional stability. All values are measured at room temperature unless noted:
- Density: 8.10 g/cm³ (higher than standard steels, due to tungsten and cobalt content).
- Melting Point: 1420 – 1480 °C (high enough to withstand forging and heat treatment without melting).
- Thermal Conductivity: 25 W/(m·K) (lower than carbon steel, which helps retain heat in the tool edge during high-speed cutting).
- Coefficient of Thermal Expansion: 11.0 × 10⁻⁶/°C (from 20 to 600 °C; low expansion ensures tools keep their cutting geometry).
- Specific Heat Capacity: 450 J/(kg·K) (efficient at absorbing heat, reducing the risk of overheating during prolonged cutting).
1.3 Mechanical Properties
JIS SKH51’s mechanical properties are optimized for cutting tools—prioritizing hardness, edge retention, and red hardness. Below are typical values after standard heat treatment (quenching + triple tempering):
| Property | Typical Value | Test Standard | Why It Matters |
|---|---|---|---|
| Hardness (HRC) | 63 – 66 | JIS Z2245 | Ultra-high hardness ensures excellent edge retention for milling cutters and drills. |
| Tensile Strength | ≥ 2400 MPa | JIS Z2241 | Handles high cutting forces without breaking—ideal for machining hard materials like alloy steel. |
| Yield Strength | ≥ 2000 MPa | JIS Z2241 | Resists permanent deformation, keeping tools’ cutting edges sharp. |
| Elongation | ≤ 5% | JIS Z2241 | Low ductility (expected for hard high speed steels; a trade-off for hardness). |
| Impact Toughness (Charpy V-notch) | ≥ 12 J (at 20 °C) | JIS Z2242 | Moderate toughness—avoids brittle fracture during light shock (e.g., tool loading). |
| Red Hardness | Retains 90% hardness at 600 °C | JIS Z2245 | Lets tools cut at speeds up to 50 m/min (for steel) without softening. |
| Fatigue Strength | ~900 MPa (10⁷ cycles) | JIS Z2273 | Resists failure from repeated cutting cycles (key for high-volume automotive or aerospace machining). |
1.4 Other Properties
- Corrosion Resistance: Moderate. Chromium content provides basic protection against rust in workshop environments, but avoid prolonged exposure to moisture or chemicals.
- Wear Resistance: Excellent. Tungsten, molybdenum, and vanadium carbides create a hard surface that resists abrasive wear—even when machining hard materials like stainless steel or heat-resistant alloys.
- Machinability: Poor (in hardened state). Most shaping is done when the steel is annealed (softened to HRC 24–28); post-hardening machining requires diamond grinding or EDM (electrical discharge machining).
- Hardenability: Excellent. It hardens evenly across thick sections (up to 30 mm), so large tools like gear cutting tools have consistent performance.
- High-temperature Stability: Outstanding. Maintains strength and hardness at temperatures up to 650 °C—far better than standard tool steels or carbon steel.
2. Applications of JIS SKH51 High Speed Steel
JIS SKH51’s red hardness and wear resistance make it ideal for high-speed, high-heat cutting tasks. Here are its most common uses, with real examples:
2.1 Cutting Tools
- Examples: Milling cutters, turning tools, drills, and reamers for machining metals like alloy steel, stainless steel, or cast iron.
- Why it works: Red hardness lets tools cut at high speeds without softening. A Japanese machine shop used JIS SKH51 end mills for alloy steel parts—tool life increased by 200% vs. standard high speed steel (HSS).
2.2 Broaches and Reamers
- Examples: Internal broaches for creating splines or keyways, and precision reamers for tight-tolerance holes (e.g., 0.001 mm).
- Why it works: Wear resistance keeps broach teeth and reamer edges sharp through hundreds of cuts. A U.S. aerospace supplier used JIS SKH51 reamers for titanium parts—reamer life jumped from 50 to 200 holes per tool.
2.3 Gear Cutting Tools
- Examples: Hob cutters, shaping tools, and shaving tools for manufacturing automotive or industrial gears.
- Why it works: Precision edge retention ensures gear teeth have accurate geometry. A German gear maker used JIS SKH51 hob cutters—gear quality improved (fewer surface defects) and tool changes dropped by 60%.
2.4 Machining of Hard Materials
- Examples: Tools for machining hardened steel (up to HRC 45), stainless steel, or super-alloys like Inconel (used in aerospace).
- Why it works: Ultra-hard carbides resist wear from tough materials. A Chinese automotive manufacturer used JIS SKH51 drills for hardened steel engine blocks—drill life increased from 100 to 350 holes.
3. Manufacturing Techniques for JIS SKH51 High Speed Steel
Turning JIS SKH51 into high-performance cutting tools requires precise, specialized steps. Here’s a step-by-step breakdown:
- Melting: Raw materials (iron, tungsten, cobalt, etc.) are melted in an electric arc furnace (EAF) or induction furnace at 1550–1650 °C. Strict control ensures uniform mixing of high-value elements.
- Casting: Molten steel is poured into small ingot molds (5–20 kg) to avoid internal defects like carbide segregation. Slow cooling (10–20 °C/hour) refines grain structure.
- Forging: Ingots are heated to 1100–1180 °C and hammered or pressed into tool blanks (e.g., 10x10x100 mm for drill bits). Forging breaks up large carbides, improving tool strength.
- Heat Treatment: The most critical step for maximizing performance:
- Annealing: Heat to 850–900 °C, hold 2–4 hours, cool slowly. Softens steel to HRC 24–28 for machining.
- Preheating: Heat to 800–850 °C, hold 1 hour. Prepares the steel for quenching to avoid thermal shock.
- Austenitizing: Heat to 1200–1240 °C, hold 15–30 minutes. Critical for dissolving carbides evenly.
- Quenching: Cool rapidly in oil or air (depending on tool size). Hardens steel to HRC 64–67.
- Triple Tempering: Reheat to 540–580 °C, hold 1–2 hours, cool. Repeat 3 times. Reduces brittleness and sets final hardness (HRC 63–66).
- Machining: Most shaping (milling, drilling) is done before quenching (annealed state). Carbide tools are recommended for best results.
- Grinding: Precision CNC grinding creates sharp cutting edges and tight tolerances (±0.001 mm for reamers or hob cutters).
- Surface Treatment (Optional):
- Coating: Add TiN (titanium nitride) or TiAlN (titanium aluminum nitride) coatings to boost wear resistance by 50–100%.
- Nitriding: Creates a hard surface layer (HRC 70+) for tools needing extra protection against abrasive wear.
4. Case Study: JIS SKH51 in Gear Hobbing Tools
A Korean automotive gear manufacturer faced a problem: their standard HSS hob cutters were wearing out every 800 gears when machining alloy steel gear shafts (HRC 35). They switched to JIS SKH51 hobs (coated with TiAlN), and here’s what happened:
- Process: Hobs were forged, annealed, machined to tooth geometry, heat-treated (1220 °C quenching + triple tempering at 560 °C), ground to precision, and coated with TiAlN.
- Results:
- Hob life increased to 3200 gears (300% improvement) thanks to JIS SKH51’s red hardness and TiAlN coating.
- Machining speed increased from 30 to 45 m/min (50% faster), cutting production time per gear by 25%.
- Gear quality improved: tooth surface roughness dropped from Ra 1.6 μm to Ra 0.8 μm (smoother gears reduce noise in automotive transmissions).
- Why it works: Tungsten and cobalt in JIS SKH51 retained the hob’s hardness at the high cutting temperatures (500+ °C), while the TiAlN coating reduced friction between the hob teeth and gear steel—minimizing wear.
5. JIS SKH51 vs. Other Cutting Materials
How does JIS SKH51 compare to common alternatives for cutting tools? Let’s evaluate key properties:
| Material | Hardness (HRC) | Red Hardness (600 °C) | Wear Resistance | Machinability | Cost (vs. JIS SKH51) | Best For |
|---|---|---|---|---|---|---|
| JIS SKH51 High Speed Steel | 63 – 66 | Excellent | Excellent | Poor (hardened) | 100% | High-speed cutting of hard metals, gear hobbing |
| Standard HSS (JIS SKH40) | 60 – 63 | Good | Good | Fair (hardened) | 60% | General cutting (mild steel, low speeds) |
| Carbide Tools | 85 – 90 (HV) | Excellent | Very Good | Very Poor | 300% | Ultra-high-speed cutting (50+ m/min), brittle materials |
| Ceramic Tools | 90 – 95 (HV) | Outstanding | Very Good | Extremely Poor | 500% | Machining super-alloys (e.g., Inconel), no shock loading |
| Carbon Steel (1095) | 55 – 60 | Poor | Poor | Excellent | 20% | Low-speed cutting (soft wood, plastic) |
| Alloy Steel (4140) | 30 – 40 | Very Poor | Fair | Excellent | 30% | Non-cutting tools (e.g., tool holders, jigs) |
Key takeaway: JIS SKH51 offers the best balance of red hardness, wear resistance, and toughness for high-speed cutting of hard metals. It’s cheaper than carbide or ceramic tools and far more durable than standard HSS or carbon steel—making it the most cost-effective choice for demanding machining tasks.
Yigu Technology’s View on JIS SKH51 High Speed Steel
At Yigu Technology, JIS SKH51 is our top recommendation for clients needing high-performance cutting tools—from automotive gear hobbing to aerospace super-alloy machining. Its unique carbide blend solves the biggest pain point: tool softening at high speeds, which leads to frequent replacements. We often pair it with TiAlN or TiCN coatings to extend tool life by 50–100%, helping clients cut downtime and boost productivity. For manufacturers focused on precision and efficiency, JIS SKH51 isn’t just a tool material—it’s a way to achieve consistent, high-quality results in the toughest machining applications.
FAQ About JIS SKH51 High Speed Steel
1. Can JIS SKH51 be used for machining non-metallic materials like plastics or wood?
While JIS SKH51 is technically capable, it’s overkill for non-metallic materials. Its high hardness and red hardness are designed for metal cutting, and using it for plastics/wood would be costly and unnecessary. For non-metals, choose standard HSS or carbon steel tools instead.
2. What’s the maximum cutting speed JIS SKH51 can handle for machining alloy steel?
JIS SKH51 can cut alloy steel (HRC 30–35) at speeds up to 50 m/min when coated with TiAlN. For uncoated tools, we recommend reducing speed to 30–35 m/min to avoid excessive wear. Always use cutting fluid to cool the tool and workpiece.
3. Is JIS SKH51 more expensive than standard HSS (JIS SKH40)?
Yes, JIS SKH51 costs about 60–70% more than JIS SKH40 due to its higher tungsten and cobalt content. But it’s worth the investment: JIS SKH51 tools last 2–3x longer, reduce downtime from tool changes, and let you machine at faster speeds—saving money in the long run.
