Tungsten high-speed steel (HSS) is not a single material. Different alloying systems produce significant differences in hardness, wear resistance, red hardness, toughness, and grindability.
Understanding these differences is essential when selecting a grade for a specific cutting tool or machining application. While traditional tungsten HSS offers a balance of hardness and edge retention, high-carbon, high-vanadium, cobalt-bearing, and aluminum-alloyed grades are designed to meet more specialized performance requirements.
This guide compares the major tungsten HSS grades, explains how their alloying elements affect performance, and helps identify the right material for different operating conditions.
How Tungsten HSS Grades Differ
The performance of tungsten HSS depends on more than its total alloy content. Alloying elements influence carbide formation, microstructure, and heat-treatment response, which ultimately determine hardness, wear resistance, red hardness, and toughness.
Tungsten (W): Red Hardness and Wear Resistance
Tungsten is the primary alloying element in traditional tungsten HSS. It contributes to the formation of hard carbides and helps the steel retain its hardness at elevated temperatures.
Grades such as W18Cr4V contain approximately 18% tungsten and are known for their good red hardness and edge retention. However, higher tungsten content does not automatically guarantee better overall performance. Carbide distribution, heat treatment, and the balance of other alloying elements also influence toughness and tool life.
Carbon (C): Hardness and Carbide Formation
Carbon combines with carbide-forming elements to produce hard particles that resist wear. Increasing carbon content can improve hardness and wear resistance after appropriate heat treatment.
High-carbon grades such as 9W18Cr4V are designed for applications requiring strong wear resistance and edge retention. The trade-off is reduced toughness and a greater risk of chipping under impact or interrupted cutting.
Vanadium (V): Abrasion Resistance
Vanadium forms very hard vanadium carbides, which improve resistance to abrasive wear. High-vanadium grades, including W6Mo5Cr4V3 (M3) and W6Mo5Cr4V4 (M4), are suitable for cutting tools exposed to demanding wear conditions.
However, increased vanadium content can make grinding more difficult. These grades are most useful when improved wear resistance justifies the additional tool-manufacturing and sharpening requirements.
Cobalt (Co): High-Temperature Hardness
Cobalt improves the hot-hardness response of HSS, helping cutting edges retain their hardness at elevated temperatures. Cobalt-bearing grades such as M35 and M42 are widely associated with demanding machining applications.
They are worth considering for tools used to machine heat-resistant alloys, stainless steels, and other difficult-to-machine materials. However, cobalt does not eliminate the need for appropriate tool geometry, cutting parameters, and cooling conditions.
Molybdenum (Mo): Toughness and Alloy Balance
Molybdenum can partly replace tungsten in HSS while contributing to secondary hardening and hot-hardness performance after heat treatment.
Molybdenum-bearing grades such as M2 (W6Mo5Cr4V2) offer a useful balance of toughness, wear resistance, and manufacturing versatility. Compared with traditional W18Cr4V, M2 is often preferred for applications requiring better toughness or more uniform carbide distribution.
The actual balance depends on the complete alloy composition and processing route, rather than molybdenum content alone.
Aluminum (Al): An Alternative Route to High Performance
Aluminum-alloyed HSS grades, such as W6Mo5Cr4V2Al (501 steel), are designed to improve hot hardness and wear resistance without relying on high cobalt additions.
These grades can offer an alternative for demanding cutting applications where material cost is also a consideration. However, their heat-treatment windows can be relatively demanding, and oxidation, decarburization, and grinding requirements must be carefully controlled.
Tungsten HSS Grade Comparison
Different HSS grades are engineered for different combinations of hardness, wear resistance, red hardness, toughness, and manufacturability. The following table compares representative grades and their typical applications.
| Grade | Main alloying characteristics | Key performance strengths | Typical applications |
|---|---|---|---|
| W18Cr4V (T1) | High tungsten | Good red hardness and edge retention; good grindability | General-purpose cutting tools, taps, reamers, and gear cutters |
| 9W18Cr4V (9W18) | High tungsten and carbon | High hardness and wear resistance; lower toughness | Reamers, countersinks, and wear-resistant cutting tools |
| M2 (W6Mo5Cr4V2) | Tungsten-molybdenum | Balanced toughness, wear resistance, and hot hardness | Drills, milling cutters, taps, and gear-cutting tools |
| M3 | Tungsten-molybdenum with increased vanadium | Improved abrasive wear resistance; more demanding grinding | Long-life taps, milling cutters, and tools for difficult materials |
| M4 | Tungsten-molybdenum with high vanadium and carbon | High wear resistance and hardness | Precision cutters and tools exposed to severe wear |
| M35 | M2-type alloy with approximately 5% cobalt | Improved hot hardness and cutting performance | Drills, taps, and cutters for stainless steel and difficult-to-machine alloys |
| M42 | High cobalt and molybdenum | Very high hardness and red hardness | High-performance drills, milling cutters, and specialized cutting tools |
| T15 | High tungsten, carbon, vanadium, and cobalt | Excellent wear resistance and hot-hardness capability | Specialized tools for demanding cutting conditions |
| 501 steel | Tungsten-molybdenum with aluminum | High hardness and hot hardness without high cobalt content | Cutters and tools for difficult-to-machine materials |
| 5F-6 steel | Tungsten-molybdenum with aluminum and increased vanadium | High hardness and wear resistance | Specialized cutting tools and selected forming applications |
These comparisons describe general material characteristics, not guaranteed performance rankings. Final properties depend on the specified standard, manufacturing route, heat treatment, and finished-tool geometry. International grade designations should also be verified against the applicable material specification before procurement.
W18Cr4V vs. W6Mo5Cr4V2: Which Is Better?
W18Cr4V and W6Mo5Cr4V2 (M2) are both high-speed tool steels, but they differ in alloy composition and performance balance. W18Cr4V is a traditional high-tungsten grade, while M2 is a tungsten-molybdenum HSS designed to provide a balanced combination of hardness, wear resistance, and toughness.
Neither grade is universally better. The right choice depends on the cutting tool, workpiece material, operating conditions, and required service life.
Red Hardness
W18Cr4V is known for its red hardness, allowing the cutting edge to retain hardness at elevated temperatures. M2 also provides good hot hardness and is widely used in general-purpose cutting tools. Actual performance depends on heat treatment and cutting conditions, rather than tungsten content alone.
Toughness
M2 is often preferred when a tool must balance wear resistance with toughness, particularly under interrupted cutting or moderate impact loads. W18Cr4V can perform well in stable cutting conditions, but its carbide distribution and processing history can affect its resistance to chipping.
Wear Resistance
Both grades offer good wear resistance when properly heat-treated. W18Cr4V benefits from its high tungsten content, while M2 combines tungsten, molybdenum, and vanadium to achieve a balanced hardness and wear profile. For abrasive workpiece materials or extended cutting cycles, the actual grade, heat treatment, and tool geometry should guide selection.
Carbide Distribution
Carbide distribution influences hardness, wear resistance, toughness, and cutting-edge consistency. Traditional W18Cr4V can be more susceptible to carbide segregation, particularly in larger sections or when manufacturing controls are inadequate. M2 often offers a more uniform carbide structure, although the result depends on the steelmaking route and processing quality.
Grindability
Both grades can be ground into precision cutting tools. However, carbide content, heat treatment, and the required tool geometry affect grinding difficulty. M2 is widely used in conventional tool manufacturing, while W18Cr4V may require closer process control to achieve consistent results. Grinding parameters should be adjusted to the specific grade and heat-treated condition.
Cost
W18Cr4V's high tungsten content can increase raw material costs, although actual prices depend on market conditions, supply, and manufacturing specifications. M2 is widely available and often offers a practical balance between material cost and tool performance. Total tool cost should also account for grinding, tool life, replacement frequency, and machining downtime.
Typical Applications
· W18Cr4V: Traditional drills, taps, reamers, broaches, and other cutting tools used in suitable, relatively stable cutting conditions.
· W6Mo5Cr4V2 (M2): General-purpose drills, milling cutters, taps, reamers, and gear-cutting tools where balanced hardness, wear resistance, and toughness are important.
Which Grade Should You Choose?
Choose W18Cr4V when its hot-hardness characteristics, tool design, and established manufacturing process meet the application requirements. Consider M2 when a balanced combination of toughness, wear resistance, availability, and manufacturing consistency is the priority.
Ultimately, selection depends on tool geometry, workpiece material, cutting conditions, and required tool life. Comparing the grades under the intended operating conditions is more reliable than choosing based on tungsten content alone.
High-Carbon vs. High-Vanadium Tungsten HSS
High-carbon and high-vanadium tungsten high-speed steels are designed to address different performance requirements. Higher carbon content can support greater hardness after heat treatment, while increased vanadium promotes the formation of hard vanadium carbides that improve abrasive wear resistance. However, neither element determines performance on its own; the full alloy composition and heat treatment also matter.
| Property | High-Carbon Tungsten HSS | High-Vanadium Tungsten HSS |
|---|---|---|
| Hardness | Can achieve high hardness after proper heat treatment | Can achieve high hardness, depending on composition and heat treatment |
| Wear resistance | Good, depending on carbide content and distribution | Generally strong abrasive wear resistance due to hard vanadium carbides |
| Toughness | Excess carbon can increase brittleness and chipping risk | High carbide content can also reduce toughness |
| Grinding | Depends on carbide structure and hardness | Often more difficult to grind because of hard vanadium carbides |
| Heat treatment | Requires careful control of austenitizing, quenching, and tempering | Requires careful control to develop the desired hardness and carbide structure |
| Typical applications | Cutting tools and applications requiring high hardness and edge retention | Tools exposed to severe abrasive wear, including selected milling cutters and precision cutting tools |
Which Type Should You Choose?
Choose a high-carbon grade when high hardness and edge retention are the primary requirements. A high-vanadium grade is worth considering when abrasive wear limits tool life.
For either type, excessive hardness or carbide content can increase edge-chipping risk. The best choice depends on whether the application is limited mainly by edge wear, abrasive wear, or mechanical impact.
Cobalt Tungsten HSS vs. Non-Cobalt HSS
Cobalt-bearing HSS is designed to retain hardness more effectively at elevated cutting temperatures. Non-cobalt grades, such as W18Cr4V and M2, can still provide good hot hardness and are suitable for many conventional cutting applications.
The main difference is not simply whether a grade contains cobalt, but how well its overall composition matches the cutting temperature, workpiece material, and required tool life.
| Property | Cobalt-Bearing HSS | Non-Cobalt HSS |
|---|---|---|
| Red hardness | Generally improved at elevated temperatures | Good, but typically lower than comparable cobalt-bearing grades under demanding hot-cutting conditions |
| High-temperature cutting | Better suited to conditions that generate substantial cutting heat | Suitable for many conventional cutting conditions with appropriate speeds and cooling |
| Difficult-to-machine materials | Often preferred for heat-resistant alloys, certain stainless steels, and other demanding materials | Can work well when tool geometry, grade selection, and cutting parameters are appropriate |
| Cost | Generally higher due to cobalt alloying and material costs | Often more economical and widely available |
| Toughness | Depends on the specific grade; increased hot hardness does not automatically mean greater toughness | Also grade-dependent; some non-cobalt grades offer an effective balance of toughness and wear resistance |
When Is Cobalt HSS Worth the Extra Cost?
Cobalt-bearing grades such as M35 and M42 are worth considering when cutting temperatures are high and maintaining edge hardness is critical. They can help extend tool life in demanding applications, provided the tool design and cutting parameters are appropriate.
Non-cobalt grades are often a practical choice for general-purpose drilling, milling, tapping, and reaming where cutting temperatures and wear demands are more moderate.
Cobalt HSS is not automatically tougher or more economical over the tool's lifetime. Compare the purchase price with tool life, regrinding requirements, replacement frequency, and machine downtime. The best grade is the one that delivers the required performance at an acceptable total tooling cost.
Tungsten HSS vs. Molybdenum HSS
Tungsten HSS and molybdenum HSS are two major high-speed steel alloying approaches. Tungsten-rich grades such as W18Cr4V rely heavily on tungsten, while molybdenum-containing grades such as M2 (W6Mo5Cr4V2) combine tungsten and molybdenum to balance hardness, wear resistance, and toughness.
Neither type is universally superior. Performance depends on the specific grade, manufacturing route, heat treatment, and intended cutting conditions.
Key Differences
| Factor | Tungsten-Rich HSS | Molybdenum-Containing HSS |
|---|---|---|
| Red hardness | Can provide strong hot-hardness performance | Also offers good red hardness when properly heat-treated |
| Wear resistance | Depends on carbide type, distribution, and hardness | Benefits from a balanced alloy system with tungsten, molybdenum, and vanadium |
| Toughness | Can be affected by carbide segregation and processing quality | M2 often provides a practical balance of toughness and wear resistance |
| Manufacturing | Some traditional grades require careful control of carbide distribution | M2 is widely used in tool manufacturing and is available in many product forms |
| Cost | High tungsten content can increase material costs | Often offers a cost-effective balance of performance and availability |
| Typical applications | Traditional drills, taps, reamers, and specialized cutting tools | General-purpose drills, milling cutters, taps, and gear-cutting tools |
Which Type Should You Choose?
Consider tungsten-rich HSS when its performance characteristics and established tool-manufacturing process suit the application. Molybdenum-containing HSS, particularly M2, is often a strong choice when balanced toughness, wear resistance, availability, and cost matter.
The decision should be based on the complete grade specification and actual tool performance—not simply on whether tungsten or molybdenum is the dominant alloying element.
Tungsten HSS vs. Tungsten Carbide
First, an important distinction: tungsten high-speed steel is not the same material as tungsten carbide. Tungsten HSS is an alloy steel containing tungsten and other alloying elements. Tungsten carbide tools are typically made from cemented carbide, in which hard carbide particles are bonded together using a metallic binder.
Both materials are widely used for cutting tools, but they perform differently under heat, wear, and impact.
Key Performance Differences
| Factor | Tungsten HSS | Cemented Tungsten Carbide |
|---|---|---|
| Hardness | High hardness after heat treatment | Generally much harder |
| Red hardness | Good hot hardness for many cutting applications | Typically retains hardness at higher cutting temperatures |
| Wear resistance | Good, but generally lower than carbide | Generally superior for abrasive wear and high-speed cutting |
| Toughness | Generally better resistance to impact and edge chipping | Usually more brittle, particularly in sharp or unsupported cutting edges |
| Impact resistance | Often better for interrupted cutting and variable loads | Depends on carbide grade; tougher grades are available, but impact can cause chipping or fracture |
| Cutting speed | Usually suited to lower cutting speeds | Often enables significantly higher cutting speeds |
| Grindability | Can be ground using conventional tool-grinding processes with suitable wheels | Requires appropriate diamond grinding or other specialized processes |
| Cost | Often lower initial material and tooling costs | Typically higher initial cost, although longer tool life may offset it |
| Tool geometry | Suitable for complex shapes, sharp edges, and tools that require frequent regrinding | Suitable for rigid, wear-resistant cutting edges; edge preparation is important |
| Difficult-to-machine materials | Can work well in selected applications, particularly where toughness matters | Often preferred for high-speed machining of hard or abrasive materials, subject to material and setup requirements |
Which Is Better: HSS or Tungsten Carbide?
Choose tungsten carbide when cutting speed, dimensional consistency, and wear resistance are the main priorities. It is often suitable for high-volume production and demanding machining applications where the machine and setup provide sufficient rigidity.
Choose tungsten HSS when toughness, complex tool geometry, regrinding, or lower initial tooling cost matters more. It remains useful for drills, taps, broaches, and other tools operating under conditions where carbide's brittleness may be a disadvantage.
For difficult-to-machine materials such as heat-resistant alloys, carbide can offer higher productivity, but the result depends on the specific workpiece, cutting conditions, and tool grade. Cobalt-bearing HSS can also be effective in selected applications.
Ultimately, compare tool life, achievable cutting speed, edge failure risk, regrinding costs, and downtime. The best material is the one that meets the machining requirements at the lowest practical total cost—not necessarily the one with the highest hardness.
Is Tungsten Steel Harder Than HSS?
Yes, if “tungsten steel” refers to cemented tungsten carbide, it is generally harder than high-speed steel (HSS). However, the term tungsten steel is ambiguous, so the materials must be identified before making a reliable comparison.
In some markets, particularly in Chinese manufacturing terminology, “tungsten steel” commonly refers to cemented carbide. In English, however, the term can also be used loosely to describe tungsten-alloyed steels, including tungsten HSS.
Tungsten Steel vs. Tungsten HSS: What Is the Difference?
· Cemented tungsten carbide: A composite material made primarily from hard tungsten carbide particles bonded with a metallic binder. It offers very high hardness and wear resistance but is generally more brittle than HSS.
· Tungsten high-speed steel: An alloy steel containing tungsten, carbon, chromium, vanadium, and other elements. Heat treatment develops its hardness and cutting performance, while its steel matrix generally provides better toughness than cemented carbide.
Which Material Is Harder?
| Property | Cemented Tungsten Carbide | Tungsten HSS |
|---|---|---|
| Hardness | Generally higher | Lower, but still very hard after heat treatment |
| Wear resistance | Generally superior | Good for many cutting-tool applications |
| Toughness | Generally lower; susceptible to chipping or fracture | Generally better impact resistance |
| Typical cutting speeds | Often higher | Usually lower |
| Common applications | Carbide inserts, end mills, wear-resistant tooling | Drills, taps, reamers, broaches, and complex cutting tools |
Exact hardness values depend on the carbide grade, binder content, HSS composition, and heat treatment. Their hardness scales may also differ, so values should only be compared using appropriate test methods.
Which Should You Choose?
Choose cemented carbide when high cutting speeds and wear resistance are the priorities and the machine setup can support its cutting edges. Choose tungsten HSS when toughness, complex tool geometry, regrinding, or resistance to impact is more important.
The key is to distinguish cemented tungsten carbide from tungsten high-speed steel. If a material specification simply says “tungsten steel,” confirm the grade or composition before comparing hardness, selecting a cutting tool, or specifying a component.
How to Select the Right Tungsten HSS Grade
Selecting the right tungsten high-speed steel grade requires more than comparing hardness or tungsten content. The grade must match the workpiece material, cutting conditions, tool geometry, and expected service life. A higher-alloy grade is not always the most economical choice if its additional performance is unnecessary for the application.
Consider Workpiece Material
Start with the material being machined. General-purpose steels may be handled effectively by standard HSS grades such as M2 or W18Cr4V. Stainless steels and heat-resistant alloys can generate more heat and cutting resistance, making cobalt-bearing grades such as M35 or M42 worth evaluating. Abrasive workpiece materials may benefit from grades with higher vanadium content.
Consider Cutting Speed
Higher cutting speeds generate more heat at the cutting edge. If thermal softening limits tool life, a grade with stronger red-hardness performance may be appropriate. Cobalt-bearing HSS is often considered for demanding high-temperature cutting, while standard grades remain suitable for many conventional cutting conditions.
Consider Tool Geometry
Complex tools, narrow cutting edges, and intricate profiles require careful consideration of grindability and edge strength. Select a grade that can achieve the required geometry and surface quality without excessive grinding difficulty or edge damage.
Consider Impact and Interruption
Interrupted cutting, variable loads, and unstable machining conditions increase the risk of edge chipping. In these situations, toughness and edge preparation are particularly important. Avoid selecting a grade based on maximum hardness alone; a slightly different hardness-wear balance may deliver more reliable tool life.
Consider Wear Requirements
Identify the main cause of tool failure. If abrasive wear is the primary limitation, high-vanadium grades may be worth considering. If the cutting edge softens under high temperatures, prioritize red hardness. If chipping occurs before significant wear develops, investigate toughness, tool geometry, and cutting stability before moving to a harder grade.
Consider Grinding Requirements
Grinding affects dimensional accuracy, edge quality, and production cost. High-vanadium grades can be more difficult to grind because of their hard carbides. Confirm that the available grinding equipment, wheel selection, and process controls can achieve the required tool geometry consistently.
Consider Tool Cost and Production Volume
For low-volume production or tools that require frequent regrinding, a standard HSS grade may provide the best overall value. In high-volume production, a more specialized grade may justify its higher material cost if it reduces tool changes, downtime, or scrap. Compare total tooling cost rather than purchase price alone.
A Practical Tungsten HSS Selection Process
Use this sequence to narrow down the appropriate grade: Workpiece → Cutting Condition → Tool Geometry → HSS Grade
1. Workpiece: Identify the material's hardness, abrasiveness, and machinability.
2. Cutting condition: Assess cutting speed, temperature, coolant use, and whether cutting is continuous or interrupted.
3. Tool geometry: Define the required edge sharpness, profile, dimensional accuracy, and grinding requirements.
4. HSS grade: Select a grade that balances hardness, red hardness, wear resistance, toughness, and cost.
Finally, verify the grade's material specification and heat-treatment requirements. When several grades appear suitable, trial cutting under representative production conditions is the most reliable way to confirm tool life and overall cost-effectiveness.
