What you need to know about knife steels. And is it necessary to strive for high hardness?

The concept of metal hardness was previously known only to graduates of technical universities, workers of machine-building plants and blacksmiths. This term came into use with the modern knifeman with the adoption of the law on weapons and GOST standards, which provide signs on the basis of which a knife can be classified as a bladed weapon.

One of the mandatory characteristics by which a particular product is classified as a bladed weapon is the hardness of the steel from which the knife blade is made (or, as it is called in GOST, the warhead of a bladed weapon). And starting from this moment, the nyfomaniacs in Russia began to slowly read reference books that provide the characteristics of different steels, explanations of the differences between powder and laminated steels, and of course the steel hardness indicators, those very noticeable HRC.

If one car enthusiast can ask another about how many “cubes are in the engine,” then an advanced knifomaniac, looking at the characteristics of a field knife that says “57-59 HRC,” can seriously determine that this is a flimsy model for bushcraft and it belongs on kitchen.

This article will tell you in a simple and understandable form what kind of beast this HRC is, where it came from and why it is needed at all.

Interesting fact : On American and European websites, among the parameters indicated by sellers or manufacturers, it is extremely rare to find such a parameter as steel hardness. This issue is not regulated in any way by law, so the average inexperienced buyer does not need this parameter.

So, what do we need to know about the hardness of metals?

Since ancient times, man has encountered the concept of hardness of materials. I also quickly realized that different materials differ from each other in hardness and strength. If you hit a stone with a stick, the stick will either break or bounce off. If you hit a stick with a stone, the stick will break. If a coconut falls from a tree onto a pebble beach, it will break. And if you hit a softer stone with flint for a long time and diligently, then you can quite easily make a head for a stone axe.

Gradually, in the process of evolution, our ancestors realized that different materials have different hardness, and depending on this hardness, they do or do not have the desired properties. Thus was born a method for determining the hardness of a material by comparing it with a certain standard.

Thus, a good carpenter can determine the degree of shrinkage of a log by tapping it with a mallet made of a harder type of wood. Using a special hammer, a potter can determine the degree of readiness of pottery. Willingly or unwittingly, each of us at least once in our lives has resorted to a similar method of determining the hardness of an object.

However, until recently, the most common method for determining the hardness of a material was the sclerometric method. Sclerometry is a physical process where the material being tested scratches (or scratches) a reference sample. If the material being tested scratches the standard, it means the material being tested is harder.

If the material being tested cannot leave a mark on the standard and is easily scratched by the standard, then the material being tested has a hardness less than that of the standard. Now this procedure seems ridiculous to us, but until recently, this was the only way to determine the hardness of a material. How else could the ancient Sumerians determine that it was possible to write inscriptions with a sharp stick on almost dried clay?

The issue of determining the hardness of materials (especially stones and metals) became acute at the end of the 18th and beginning of the 19th centuries, with the development of geology and the beginning of the flowering of mechanical engineering.

It was at this time that the “Mohs scale”, known to all physicists and archaeologists, appeared. However, the first to propose measuring the hardness of metals by comparing them with a standard was the French naturalist of the mid-18th century, Rene Antoine Reaumur.

Reaumur actively conducted experiments related to the melting and processing of metals and therefore he was faced with the acute question of determining the various characteristics of the alloys that he obtained in the process of his research.

His ideas were picked up and developed by the German naturalist and geologist Karl Friedrich Christian Mohs. In 1811, he came up with a system for standard comparison of minerals, which now bears his name. Until about the middle of the 20th century, this scale was actively used by geological exploration parties around the world.

The Mohs scale is a comparative table in which known minerals of different hardness are indicated and their hardness is measured in the following criteria:

• Scratched with a fingernail;
• Scratched by copper;
• Scratched by glass;
• Scratches glass;
• Processed only with diamond.

The softest reference mineral is talc, and the hardest mineral is diamond. The hardness of talc on the Mohs scale is “1”, the hardness of diamond is “10”. Between talc and diamond, as hardness increases, there are: gypsum (hardness 2), calcite (hardness 3), fluorite (hardness 4), apatite (hardness 5), orthoclase (hardness 6), quartz (hardness 7), topaz (hardness 8 ), corundum (hardness 9). This simple method of determining the hardness of minerals turned out to be indispensable in field conditions.

In addition to the Mohs scale, there are other methods for determining the hardness of materials, which were actively developed at the end of the 19th and beginning of the 20th centuries. There are usually four most well-known methods for determining the hardness of metals:

• Brinell method;
• Vickers method;
• Shore method;
• Rockwell method.

Looking ahead , we note: all these methods are similar to each other, since they are based on pressing a reference sample into the surface of the metal. Only the shape of the standard, the pressure force, and the formula for calculating the value differ.

The element that is pressed into the surface of the metal is called an “indenter”. A steel ball (Brinell method), a diamond cone (Rockwell method), or a diamond pyramid (Vickers and Shore methods) can be used as an indenter.

The demand for these methods of measuring metal hardness is explained by their following features:

• all the methods described make it possible to measure each finished sample separately, which undoubtedly improves the quality of serial products;
• there is no destruction of the finished product (for example, a knife) and in the future it can be used for its intended purpose;
• high measurement speed, which means high productivity of the method.

Important : Test results using different methods are not comparable.

Let's consider each method separately, paying special attention to the Rockwell method.

Brinell method

This method was proposed by the Swede Johan August Brinell in the early 20th century. At that time, this was the most accurate way to determine the hardness of metals. Steel balls of various diameters (from 1.2 to 10 millimeters) are used as an indenter. The diameter of the ball is selected depending on the expected hardness of the metal.

Brinell divided metals into several groups, combining them by hardness. The group with minimal hardness included tin, lead and their alloys. The group with the highest hardness included titanium, nickel and steel alloys. For metals with minimal hardness, a ball of the smallest diameter is used; for metals of high hardness, a ball of the largest diameter is used.

Measurements take place according to the following algorithm: the sample being tested is placed on a special table, and an indenter is pressed into the sample from above with a gradually increasing load. This happens over a short period of time from 2 to 8 seconds. After reaching the maximum level of dynamic load, the load is maintained in a static state for approximately 10 seconds. After completing the procedure, the diameter of the indentation is measured on the sample being tested.

Hardness is calculated using a formula that takes into account the applied load, the diameter of the indenter and the diameter of the indentation. Hardness is indicated in the format kgf/mm2, display format HBW.

Rockwell method

Among all existing methods for determining the hardness of steels and non-ferrous metals, the most common and most accurate is the Rockwell method.

Rockwell method - determination of metal hardness

Carrying out measurements and determining the Rockwell hardness number is regulated by the relevant documents of GOST 9013-59

. This method is implemented by pressing indenters—a diamond cone or a carbide ball—into the material being tested. Diamond indenters are used for testing hardened steels and carbide alloys, while carbide balls are used for testing less hard and relatively soft metals. Measurements are carried out using mechanical or electronic hardness testers.

The Rockwell method provides for the possibility of using a number of hardness scales A, B, C, D, E, F, G, H (54 in total), each of which provides the greatest accuracy only in its own relatively narrow measurement range.

To measure high hardness values ​​with a diamond cone, the “A” and “C” scales are most often used. They are used to test samples made of hardened tool steels and other hard steel alloys. And comparatively softer materials, such as aluminum, copper, brass, and annealed steel are tested with ball indenters on the “B” scale.

Example of Rockwell hardness designation: 58 HRC or 42 HRB.

The numbers in front indicate a number or a conventional unit of measurement. The two letters after them are the Rockwell hardness symbol, the third letter is the scale on which the tests were carried out.

(!)

Two identical values ​​from different scales are not the same thing, for example, 58 HRC ≠ 58 HRA. Rockwell numerical values ​​can only be compared if they belong to the same scale.

Rockwell scale ranges according to GOST 8.064-94:

Locksmith tool

Tools for manual metal processing (chopping, cutting, filing, branding, punching, marking) are made from carbon and alloy tool steels. Their working parts are subjected to hardening to a certain hardness, which should be within the following limits:

Installation tool

This includes various wrenches, screwdrivers, and pliers. The hardness standard for their working parts is set by current standards. This is a very important indicator, which determines how wear-resistant the tool is and can resist crushing. Sufficient values ​​for some instruments are given below:

Metal cutting tool

This category includes consumable equipment for metal cutting, used on machine tools or with hand tools. For its manufacture, high-speed steels or hard alloys are used, which retain hardness in cold and overheated states.

Note:

Some milling cutter manufacturers indicate in the marking the hardness not of the cutter itself, but of the material that it can process.

Fasteners

There is a relationship between the strength class of a fastener and its hardness. For high-strength bolts, screws, and nuts, this relationship is reflected in the table:

If for bolts and nuts the main mechanical characteristic is the strength class, then for such fasteners as lock nuts, washers, set screws, hardness is no less important.

The following minimum/maximum Rockwell values ​​are established by the standards:

Vickers method

When measuring hardness using the Vickers method, a pyramid-shaped tip is used as an indenter, the edges of which converge at an angle of 136 degrees. To ensure the accuracy of the test, it is important to observe several points:

• the load must be placed strictly in the center of the diamond tip;
• the load application vector must be strictly perpendicular to the surface of the test sample.

Measurements take place according to the following algorithm: the sample being tested is placed on a special table, and the indenter is pressed into the sample from above immediately with the required load level (the maximum possible value is up to 100 kgf). Next, the indenter is held under load for 10-15 seconds. After removing the indenter, the indentation depth and indentation diagonal are measured.

Next, a calculation takes place according to the form, which takes into account the ratio of the applied load to the diagonal of the indentation and the time during which the test took place. Hardness is indicated in kgf/mm2 format, display format HV. The Vickers method, due to the use of a diamond tip, allows for more accurate measurements than the Brinell method.

Tool steels

Now let's talk about knives made of tool steels. What is it and why are they needed?

Tool alloy steels are usually called steels with a high carbon content (from 0.8 to 1.6%) and a noticeable percentage of alloying additives (from 2.5%). Such steels “hold” the cutting edge much better than most stainless steels. They are typically hardened to 60 to 64 HRC. But you need to remember that such steels are not stainless and therefore require maintenance.

Conventionally, tool knife steels can be divided into two groups.

Steels - analogues of American D2

• Russian X12MF;
• European 1.2379, K110, Z160, etc.;
• Chinese Cr12MoV.

Typically, these steels are used for the production of cutting and skinning knives, as well as for utility and work knives. Sometimes blades for folding pocket knives are made from such steels. These steels contain a high amount of carbon (1.5-1.6%), and high is a content of more than 1.0%. These knives have excellent cutting properties and hold the cutting edge perfectly, but they tend to rust a little. I would like to note that D2 steel is produced only in the USA. If “D2” is written on the blade of a knife made in Russia or China, then, of course, there is no D2 there, but its local analogue. A good replacement for D2 is the Austrian-Swedish K110, a very popular steel, in no way inferior to the American one, but it is easier to get and costs less.

So-called “eight percent” steels

• American CPM S3V;
• Austrian-Swedish K340 and Vanadis 10.

They are called “eight percent”, because they contain approximately 8.0% chromium. Such steels rust more strongly than D2, but are much superior to D2 in strength (but D2 is superior to them in wear resistance of the cutting edge). It is best to make long-bladed cutting weapons from such steels. That is, for small “dexterous” knives D2 is good, and for knives with a long blade (from 150-250 mm) CPM S3V or K340 is better.

Shore method

This method is a continuation of the well-known “tapping” method, when by tapping a part or workpiece, the master tries to determine its hardness. The method was proposed by the American engineer Albert Shore at the beginning of the 20th century. The essence of the method is that the hardness of the metal is determined by the height of the indenter's rebound.

The device for measuring hardness consists of a hollow tube, on which a cut is made along its entire length with marked divisions. The tube is installed on the surface of the sample being measured and a striker with a diamond tip is dropped into it. The hardness of the metal is determined visually by the rebound height of the striker. Essentially, this device is a “sclerometer”.

This type of measurement does not provide high accuracy, but is excellent for express assessment of the hardness of alloys in metallurgical production, when you need to quickly determine the hardness of a large part or a part that has a complex surface.

Shore hardness display format HSD (or HSC, depending on the scale used).

Stainless steels

Stainless steels (the most popular nowadays) are the most versatile. They can be used to make a knife for almost any purpose. Their main difference from other steels is their ability to successfully resist corrosion (rust). To do this, an alloying additive, chromium (Cr), is usually added to the steel. A chromium content of thirteen percent or more makes the material resistant to rust. Here you need to understand that under unfavorable conditions (in salt water, for example), stainless steel can also corrode. There are no absolutely stainless knife steels, but still, under normal everyday conditions, these steels are practically not susceptible to corrosion. So what exactly are these steel grades?

Inexpensive stainless steels

• Russian 40Х13, 65Х13, EP-107, etc.;
• European 1.4116, 12C27, etc.;
• Japanese SUS420J2, AUS-4, AUS-6, etc.;
• American 420, 425, 420HC, etc.;
• Chinese 4Cr13MoV, 5Cr13MoV, etc.

Typically, inexpensive kitchen and utility knives are made from these steels. Knives made from such steels resist corrosion well, but they don’t hold an edge well. They can be heat treated (hardened) to a hardness of 50-54 HRC, which is extremely insufficient. A decent knife should have a cutting edge hardness (CU) of at least 55 HRC. Pleasant exceptions include the Swedish brand 12C27, Japanese AUS-6 and American 420HC. Knives made from the three listed steels have good cutting edge stability. Such knives are hardened to a hardness of approximately 55-58 HRC, which is quite sufficient for most kitchen work and work on a camping trip or fishing.

Average cost stainless steels

• Russian 95Х18, 110Х18, etc.;
• European 1.4125, 14C28N, N690, etc.;
• Japanese AUS-8, AUS-10, VG-1, etc.;
• American 440A, 440B, 440C, etc.;
• Chinese 7Cr13MoV, 8Cr13MoV, 9Cr13MoV, etc.

As a rule, such steels produce inexpensive but very good knives. They are perfectly hardened to a hardness of 57-59 HRC (sometimes higher). I would especially like to highlight the modern Austrian-Swedish brand N690. This steel is very stable. Good heat treatment. Many manufacturers around the world are switching to it. Including here in Russia, because Our stainless steels are capricious and not always stable.

We propose to clarify the question: “What is an inexpensive knife, and what is an average and, finally, an expensive one?” Historically, over the past 15-20 years, the United States has been the center of interest in knife topics and the trendsetter. Therefore, the cost of knives is usually measured in US dollars. So:

• an inexpensive knife costs up to $100;
• average knife from 100 to 300 dollars;
• expensive knife from $300 and up.

That is, a knife for 400 rubles. and a knife for 4000 rubles. are considered cheap. And knives for 30,000 rubles. and for 300,000 rubles. both will be expensive. Maybe there is a strong simplification here, but this is how it happened...

Expensive stainless steels:

• Russian EP-766;
• European Elmax, M390, etc.;
• Japanese VG-10, ATS-34, R-2, ZDP-189, etc.;
• American 154CM, CPM S30V, CPM S35VN, etc.

Such steels are used for the manufacture of designer knives and knives - luxury items. As a rule, knives made from such steels are not cheap at all. I would like to highlight from the general list:

• Russian steel EP-766 (95Х13М3К3Б2Ф) - it’s still nice that we haven’t forgotten how to work!
• American 154CM - the steel was originally developed for gas turbine blades.
• Japanese VG-10 - simple and reliable, time-tested!
• Austrian-Swedish Elmax - until recently, this steel was the “last word” in the production of knives.
• Austrian-Swedish M390 – probably the most modern, but a little overpriced at the height of fashion.

Blades made from such steels usually have a hardness of 58 to 61 HRC.

When choosing a knife: what is HRC and what is its optimal indicator?

Greetings to you, visiting. When choosing a knife online and looking at the many models you like, you can notice not only external differences, but also different performance indicators. Regarding the length of the blade and the material of the handle, everything is very clear, but among the list of technical characteristics (TX) you can find a designation that is not entirely clear to everyone - HRC.

Knife lovers are probably familiar with this designation, but some ordinary people, and even people who are passionate about knives, often have a misunderstanding of this characteristic.

What is HRC?

HRC is a designation for the measure of steel hardness; in the case of a knife, the hardness of the blade steel. Often, in the characteristics of a knife we ​​see “Blade steel hardness: 59-60 HRC;

1. Where 59-60
   is the quantitative value (indicator) of hardness.
2. HR
   is a method of measuring hardness - namely (Hard Rocwel) a method that was invented by Stanley Rockwell back in 1908.
3. C
   is the instrument scale used to measure the hardness of steel (there are 11 in total).

The most important process in knife making is the heat treatment of steel. The only hint about the results of this treatment is the hardness indicator, that is, in simple words, the manufacturer does not provide any data on the properties of the steel after its heat treatment - except for its hardness.

Thus, when choosing a knife, it remains to rely on the hardness of the blade. But do not forget that hardness is not the strength of a knife.

The hardness of steel is only one of the strength characteristics of steel.

Which hardness rating should I choose?

When you come to the store, you will not be able to experimentally test the plasticity of the blade and its ability to retain primary and secondary sharpness. To put it very simply, the higher the hardness, the more fragile the blade, but it will retain the sharpness of the blade longer, and actually vice versa.

This ratio is conditional, since at the moment there are alloys that have high hardness and maximum ductility.

The pursuit of great hardness promises sharpening costs, since sharpening is correct

at home, a blade with a hardness of 65 HRC will be very problematic without experience and special skills. abrasives.

Characteristics of steel 40x13, scope and reviews

Any steel has certain properties inherent only to a specific brand. And metallurgists try to make every effort to obtain the highest and highest quality characteristics of the material. But, since it is not entirely possible to obtain an ideal steel structure, it all comes down to selecting the optimal capabilities for certain purposes. After all, everyone knows that a knife made of soft steel is easier to sharpen than one made of harder steel. Hard steel, on the contrary, is highly resistant to mechanical stress.

With a complex chemical composition, the production process of steel itself slows down, which is why the cost of the finished product increases.

The quality of a knife may not always depend on a specific grade of steel. High-quality heat treatment of the product plays a big role here . The most popular steel for making knives is considered to be 40x13 steel. It has all the necessary properties and characteristics.

What characteristics does steel 40x13 have?

Steel grade 40x13 has the following characteristics:

1. Has powerful heat resistance.
2. Resistance to various corrosions.
3. It is considered an absolutely non-rusting material.

Steel acquires its anti-corrosion properties thanks to a complex technological process that involves special hardening. As a result of this procedure the carbide is completely dissolved , which provides anti-corrosion protection for the material. One of the reasons for the decrease in resistance to corrosion is the reduced chromium content in the carbide or a decrease in the melting point of steel to 600 degrees. But, if the technological process is provided correctly, then this should not happen.