What is stronger than HSS? A guide to superior cutting materials

September 22, 2025 •

5 min read

High-Speed Steel (HSS) is a versatile, cost-effective cutting tool material, but it's not the strongest available for demanding applications. While HSS is suitable for general-purpose use, materials like cobalt and carbide offer a significant upgrade in hardness and heat resistance. So, what is stronger than HSS, and when should you use it?

Quick Summary

Materials superior to High-Speed Steel (HSS) include cobalt, carbide, ceramics, and Cubic Boron Nitride (CBN), each offering greater hardness, wear resistance, and heat resistance for specific, demanding applications. The best choice depends on the workpiece material, required cutting speed, and budget.

Key Points

Cobalt (HSCO): A blend of HSS with 5-8% cobalt, offering higher heat and wear resistance for cutting harder metals like stainless steel.
Carbide: Significantly harder and more rigid than HSS, carbide is ideal for high-speed machining of very hard materials but is brittle and costly.
Ceramics: Used for extremely high-speed machining of hardened metals and cast iron, ceramics offer exceptional heat resistance but have very low toughness.
Cubic Boron Nitride (CBN): Second only to diamond in hardness, CBN is reserved for machining and grinding the hardest materials and superalloys.
Powder Metallurgy (PM): A manufacturing process that creates a more uniform HSS with a finer grain structure, improving its toughness and wear resistance.
Coatings vs. Solid: Coatings like TiN enhance the surface properties of HSS tools, while solid carbide or cobalt offer inherent strength throughout the material.

Understanding High-Speed Steel (HSS)

High-Speed Steel, or HSS, is a type of tool steel commonly used for general-purpose cutting tools such as drill bits, end mills, and saw blades. Its versatility and affordability make it a popular choice for many applications, especially with softer metals, wood, and plastics. HSS maintains its hardness at relatively high temperatures, distinguishing it from conventional carbon steel, but it has its limitations when faced with harder materials or high-speed machining.

Cobalt Steel (HSCO): A Step Up in Performance

Cobalt steel, often marked as HSCO or M35, is a significant upgrade from standard HSS. It is an alloy blend that incorporates 5% to 8% cobalt, enhancing its properties. The addition of cobalt provides several key advantages:

Increased Hardness: Cobalt significantly boosts the material's hardness, allowing it to withstand higher cutting forces.
Superior Heat Resistance: HSCO maintains its hardness at higher operating temperatures than HSS. This 'red hardness' is crucial for high-speed applications and machining tougher materials like stainless steel and cast iron without losing its cutting edge.
Extended Tool Life: The improved wear resistance and heat tolerance mean cobalt tools last longer and can handle more demanding tasks before requiring replacement or resharpening.

While more expensive and slightly more brittle than standard HSS, cobalt steel provides an excellent balance of performance and value for many metalworking applications.

Carbide: The Hardness Champion

For extreme hardness and high-speed cutting, carbide is the undisputed champion among common tool materials. Typically made from tungsten carbide particles bonded with a metallic binder like cobalt, carbide tools are substantially harder and more rigid than any steel.

Extreme Hardness: Carbide's hardness allows it to cut through hardened steels, cast iron, and other abrasive materials with ease.
High-Speed Capability: Carbide tools can be run at much higher speeds than HSS, leading to increased productivity and shorter cycle times.
Excellent Wear Resistance: The material's durability results in an exceptionally long tool life, justifying its higher initial cost.
High Brittleness: The trade-off for carbide's hardness is its brittleness. It is prone to chipping or breaking under impact or excessive vibration, making it unsuitable for manual drills and requiring rigid machine setups.

Beyond Carbide: The Realm of Advanced Materials

For applications that push the boundaries of machining, even carbide has its limitations. Advanced ceramic and superhard materials offer specialized performance for the most demanding tasks.

Ceramic Tools: Constructed from compounds like alumina or silicon nitride, ceramic tools possess extreme hardness, high thermal conductivity, and chemical stability. They are ideal for ultra-high-speed machining of hardened materials and cast iron, where the heat generated would destroy other tools. However, they are even more brittle than carbide and require precise, vibration-free machining conditions.
Cubic Boron Nitride (CBN): As the second-hardest material known, CBN is used for the most difficult grinding and machining tasks. It is exceptionally durable and heat-resistant, making it perfect for grinding superalloys and very hard steels (above 45 HRC). The high cost of CBN limits its use to specific high-performance applications where other materials fail.
Diamond: The hardest material available, polycrystalline diamond (PCD) is used for extreme-hardness materials like ceramics, stone, and non-ferrous alloys. It is not suitable for ferrous metals due to a chemical reaction with the high heat, but it provides unmatched abrasion resistance for specific non-ferrous applications.

Powder Metallurgy: A Modern Manufacturing Method

Powder Metallurgy (PM) is a modern manufacturing technique that significantly enhances the properties of tool steels, including HSS. Instead of traditional melting and casting, PM involves consolidating and sintering fine metal powders. This process results in a finer, more uniform grain structure and better control over the material's composition. PM HSS offers superior toughness, wear resistance, and less chipping compared to conventional HSS, effectively bridging the performance gap between traditional HSS and carbide.

Coatings vs. Solid Materials

Sometimes, a tool's performance is improved not by changing the base material but by applying a protective coating. Coatings like Titanium Nitride (TiN), Titanium Carbonitride (TiCN), and Aluminum Titanium Nitride (AlTiN) can increase the surface hardness, wear resistance, and heat resistance of HSS tools.

Benefits: Coatings increase tool life and enable faster cutting speeds on HSS tools, providing a cost-effective upgrade.
Limitations: Unlike solid materials like carbide or cobalt, the enhanced properties of coated HSS are only on the surface. Once the coating wears away, the tool reverts to the performance of the base HSS material.

How to Choose the Right Material

Selecting the best tool material depends on a few critical factors:

Workpiece Material: For general use on softer materials, HSS is fine. For hardened steel and stainless steel, cobalt is a better choice. For masonry, concrete, and high-speed machining of hardened metals, carbide, ceramics, or CBN are necessary.
Production Volume: For high-volume production, the initial higher cost of carbide or CBN is often justified by the increased cutting speeds and longer tool life, which reduce overall costs.
Equipment Rigidity: The brittleness of carbide and ceramics means they require a rigid machine setup with minimal vibration. Handheld tools are not suitable for these materials, where HSS or cobalt's greater toughness is an advantage.

Comparison of Cutting Tool Materials


Feature	HSS	Cobalt (HSCO)	Carbide	Ceramic	CBN
Hardness	Medium	High	Very High	Extremely High	Extremely High
Toughness	High	Medium-High	Low	Very Low	Low
Heat Resistance	Medium	High	Very High	Extremely High	Extremely High
Wear Resistance	Medium	High	Very High	Extremely High	Extremely High
Cost	Low	Medium	High	Very High	Highest
Best For	Soft metals, wood, plastics, general use	Stainless steel, cast iron, harder metals	Hardened materials, high speed machining	Ultra-high speed machining of hard materials	Superalloys, very hard steels

Conclusion: Matching the Tool to the Task

When asking what is stronger than HSS, the answer is not a single material but a range of options, each with a specific purpose. For the toughest jobs, HSS is simply not adequate, and a material with higher hardness and heat resistance is required. By understanding the performance trade-offs between HSS, cobalt, carbide, and more exotic materials like ceramics and CBN, manufacturers and hobbyists can select the right tool for the task, improving efficiency, extending tool life, and achieving superior results.

Choosing the right CNC tool material is a critical decision that impacts productivity and quality.

Frequently Asked Questions

The primary difference lies in their composition and heat resistance. Cobalt tools are an alloy of HSS with 5-8% cobalt, which gives them superior 'red hardness'—the ability to maintain a sharp edge at higher temperatures. HSS is more affordable and tougher, while cobalt is better for harder metals and higher speeds.

Yes, carbide is significantly harder and more rigid than HSS. However, it is also much more brittle. While carbide excels at high-speed cutting of hard materials, HSS offers better toughness for applications involving impact or vibration.

You should consider a ceramic tool for ultra-high-speed machining of very hard materials where heat generation is extreme. Ceramic tools are even harder and more heat-resistant than carbide but are also more brittle and require a highly rigid machine setup.

CBN is second only to diamond in hardness and is the superior choice for machining ferrous metals like hardened steel and superalloys. Diamond tooling, while harder, is not suitable for ferrous materials due to a chemical reaction at high temperatures, but it is excellent for non-ferrous materials.

PM HSS is tougher and more wear-resistant than conventional HSS. The powder metallurgy process results in a more uniform and finer grain structure, which reduces the brittleness typically associated with high hardness in conventional HSS.

No. Coatings on HSS improve the surface hardness and wear resistance but do not make the underlying tool as strong as a solid carbide tool. The enhanced performance is limited to the thin surface layer, and the tool will lose its superior properties once the coating wears off.

It is generally not recommended to use carbide drill bits in a handheld drill. Carbide's high brittleness makes it susceptible to chipping and breaking under the vibration and inconsistent pressure common with manual operation. HSS or cobalt bits are better suited for these applications due to their higher toughness.