On the Cutting Edge: Understanding Blade Hardness (And Why It Matters to You)
In food production, your blades don’t just cut — they define your efficiency, consistency, and ultimately your product quality. Whether you’re slicing fresh loaves or processing protein, the hardness of your blade steel plays a critical role in performance.
Hardness is typically measured using the Rockwell “C” scale (HRC). To measure HRC, a diamond point is pressed into the steel under force, and the depth of the indentation it makes is the measure of hardness:
• Shallower indentation = harder steel
• Deeper indentation = softer steel
While it’s easy to assume that harder is always better, that’s only half the story.
“Hardness gives you a sharp cutting edge, but the harder your blade is, the more brittle it is. Blades need to be balanced between hardness and toughness, based on what you’re cutting, at what speeds, and at what temperatures.” – Mikko Brunner, MD & Lead Engineer, Renlaw
The Balancing Act: Hardness vs Toughness
In practice, blade performance is a balance between:
• Hardness → edge retention, wear resistance
• Toughness → resistance to chipping, cracking, and shock
For example:
In high-speed slicing (e.g. bread lines, continuous processing), higher hardness improves wear life and reduces downtime.
In impact-heavy applications (e.g. bone contact, dense product, frozen goods), lower hardness improves durability and reduces breakage, to a point.
When you’re cutting pork frozen at below 20 degrees, you will need to go harder again to retain the sharp life on your blade, and just make sure to handle it very carefully.
Common Blade Materials (And Where They Work Best)
Different materials achieve hardness in different ways, and each comes with advantages and disadvantages.
Choosing the wrong steel hardness can cause prematurely blunt blades or chipped edges which lead to additional blade changes, unexpected downtime, and an overall increased cost per cut.
The processing method of your blade steels is also critical. Contaminants from machining, incorrect heat treatment, and rough or impassive surface finishes can all lower the blade’s corrosion resistance. Choosing the wrong steel can also affect the resistance to chemical attacks, i.e. an 0.5% Molybdenum content can significantly increase a steels resistance to Chloride (salt) attacks.
Tungsten Carbide (TC)
Extremely hard with unmatched edge retention. Tungsten is best for: High-volume, repetitive cutting of predictable substances.
• Advantages: Exceptional “sharp-life” ; handles high cutting temperatures without losing structural integrity.
• Limitations: It’s brittle and prone to chipping and cracking if not handled with appropriate caution. It’s extremely expensive and is generally only available in smaller sizes.
High-Speed Steel (HSS)
A balance of hardness and toughness. HSS is the hardest wearing of the alloy steel range, while softer than tungsten carbide, it is also tougher. HSS is very successful in high-speed production environments.
• Advantages: Withstands high temperatures (600°C+); Available in a wider range of sizes; Easier to work with than Tungsten.
• Limitations: High cost compared with regular tool steels; requires specialised Heat Treatment to harden which increases production lead times and cost on the blades themselves.
Tool Steels (e.g. D2 / 1.2379)
This is a broad term for quality alloy steels. There is an enormous range of these steels, and they have a wide range of applications. High quality Tool Steels are your best choice for general-purpose cutting. Make sure your steel is coming from a reputable steel supplier, though, as quality does fluctuate depending on where and how it is made.
Renlaw steels are all imported from Germany.
• Advantages: Good wear resistance and durability, Available in a wide range of sizes, versatile.
• Limitations: Requires correct heat treatment for optimal results, especially where a harder cutting edge is required.
Martensitic Stainless Steels
Martensitic Stainless steels are often used in medical and food processing blades. These differ from fabrication stainless steels in that they are magnetic. Due to the addition of elements to make them hardenable and wear resistant, they unfortunately are more prone to corrosion.
“In food production, material choice isn’t just about performance. Hygiene and corrosion resistance play a vital role in this highly regulated sector.” – Mikko Brunner
High Carbon Steels
High Carbon Steels have a carbon content of 0.61-1.5%. These steels typically have a four-figure lack the alloying elements which make a quality knife steel. Carbon steels are cheaper than the above material choices, but are mostly used in budget tooling ranges.
How Hardness is Achieved
Blade steels don’t start out at optimum hardness. They are engineered to the right hardness for your application.
The blade manufacturing process typically involves:
1. Machining in a softer state
2. Hardening (heat treatment)
3. Tempering
4. (Optional) Cryogenic treatment
5. Grinding, toothing, sharpening, and finishing (this usually includes deburring and polishing)
At Renlaw, blades are almost exclusively hardened in vacuum furnaces to minimise warpage and preserve surface integrity.
The Heat Treatment Process: blades are heated slowly to 1050-1200°C and subsequently quenched in Nitrogen to change the metallic structure and harden the steel.
At this point the steel is very hard, but also brittle. Subsequent reheating to 300-500°C (tempering) toughens the structure of the steel and allows us to adjust the hardness and toughness of the steel to suit the application. In some cases, the finished blades are cryogenically treated by chilling them to -70°C to -260°C to further stabilise the metallic structure and improve the steels qualities
Why This Matters on Your Line
Understanding hardness isn’t just technical — it directly affects your operation:
• Downtime: harder blades last longer (in the right application)
• Product quality: cleaner cuts, less tearing
• Cost efficiency: lower replacement frequency
• Food safety: correct material reduces corrosion and contamination risk
So, What Should You Choose?
There’s no universal “best” hardness – only the right fit for your process.
Ask yourself:
• Is your process high-speed or high-impact?
• Are you cutting soft, fresh, frozen, or abrasive materials?
• Do you need corrosion resistance (e.g. wet, salty, or acidic environments)?
“The best blade is the one that’s built for your application.” – Mikko Brunner
