How hard should be the metal of a knife? Using TKM-459CE UCI hardness tester to measure the hardness of a steel blade

There are numerous types of knives – for fishing, hunting, surgery, and garden works, for kitchen, throwing, or box cutting. There are many piercing and cuttin instruments on the market, which manufacturers are offering. How should we accurately choose between the options and select the one that will satisfy all our needs and serve to fulfill all necessary functions?

The first factor to be looked into is the hardness of the blade. It is a characteristic that correlates directly with the toughness, durability, and reliability of the knife.

The balanced hardness provides the durable initial factory sharpening while reducing the risk of breakage, deformation, and crumbling of metal during usage.

What must be known about blade steel?

Fine-grained steel can be sharpened easily, but there is a risk of rapid corrosion. Powdered steel has excellent cutting features, but the cutting edge made from this type of metal is usually hard to finish.

To correctly choose a knife for a specific purpose, we should consider the material it was made from.

As a rule, the fine-grained steel knives belong to a higher class of products.

- High-carbon steel is a metal alloy containing at least 0.6 % of carbon (C). The level of carbon defines the hardness and toughness of the product. For example, Japanese ZDP-189 blades may have a 2.9% up to 3.0% carbon rate, which permits forging the steel up to 69 HRC.
- Stainless steel contains more than 10.5% chromium (Cr) and at least 50% iron (Fe).

There is steel forging that combines extraordinary features of both steel types listed above. As a result, the blades become hard, enduring, and rust-resistant. They are also highly resistant to mechanical damage and coloring, aside from keeping a long-term sharpness.

Very often, additions of such elements as cobalt (Co), molybdenum (Mo), and vanadium (V), among others, can be found in high-carbon stainless steels. They positively affect the metal quality features, increasing toughness and cutting characteristics between sharpenings.

It is worth mentioning that the high rate of sharpness for specific piercing and cutting tools is far from advantageous.

In particular, knives for general purposes, or knives for tourism and diving, are highly valued by the users for their excellent rust resistance and simplicity in sharpening, but a lower carbon rate is required in that case. Such blades have a hardness rate below 60 HRC, but they are quite reliable and are resistant to shock loads very well. The cutting edge is not subjected to great deformation, and one can sharp such a blade easily in the field.

The higher the knife's hardness rate, the longer it stays sharp, but it is also more difficult to sharpen it correctly. In case the hardness rate is too high and the usage is quite frequent, the blade may start to crumble and break down! Hence, it is crucial to consider the purposes of the chosen knife and the steel grade (as a rule, the information about steel grade can be found on the blade or knife clip surface) from which the blade was manufactured.

How to measure the hardness of a knife?

The hardness index of knives steel also indicates its hardening quality and other features.

Rockwell's HRC scale is used to determine hardness. Usually, to keep this feature under control, stationary and portable hardness testers are used. 

The hardness of top-quality blades

Knife type	Hardness
Kitchen, universal, touristic	from 48 up to 57 HRC
Hunting	from 55 up to 60 HRC
Surgical	from 25 up to 62 HRC
Axes	from 62 up to 70 HRC

Universal and UCI hardness testers of the TKM series can be used to measure the hardness of a knife blade. The TKM-459CE tester can perform all necessary measurements with the highest precision without leaving any visible prints on a tested object's surface.

The Rockwell values range is between 20 and 70 HRC.

To perform the tests of the blades, we can provide you with a UCI tester with an "A" and/or "H" type of probe.

What is the difference between "A" and "H" probes?

Tester	Load	Length/Diameter	Weight/thickness*/roughness	Application
«А»	50H (5 kg/110.23 lb)	148/26 mm	1 kg (2.22 lb)/3 мм/Ra 1,6	General purposes
«H»	10H (1 kg/2.2 lb)	148/26 mm	1 kg (2.22 lb)/2 mm/Ra 0,8	Thin objects with a smooth surface

* In case of specific conditions, the tested object's thickness may be less than indicated in the table.

"A" probe was designed for general purposes and is included in all sets of UCI testers of the TKM series.

"H" type of probe provides more reliable results because it will show the hardness of the surface, regardless of the thickness of a given blade. It is usually used to test objects, which thickness starts with 2 mm. The imprint left after the measurements is smaller in radius and depth than the one left by the "A" type. This can be extremely important in the case of premium knives.

Sizes of imprints left after hardness measurements

Parameters of the imprints	Examples of hardness values	“A” type of probe	“H” type of probe
Average possible diameters of imprints (mm) left on the product surface	42,5 HRC	0,13	0,07
	63,0 HRC	0,09	0,05
Average possible diameters of imprints (mm) left on the product surface	42,5 HRC	0,037	0,020
	63,0 HRC	0,025	0,014

We can produce unique probes with features different from those listed above on demand.

The best way to choose a hardness tester to measure the hardness of a knife is to trust our professional team from "Mashproekt". We will tell you about all differences between TKM series testers and offer you the one that will cover your needs.