Steel knives - CPM 121 REX - red-resistant steel

Steel knives - CPM 121 REX - red-resistant steel

CPM 121 REX - red-resistant steel

Crazy knife steel with extreme hardness (CPM REX 121). Removes shavings from N690

The CPM Rex 121 tool steel composition was developed in Sweden in the middle of the 19th century. The American company Crucible Industries LLC produces a powder high-speed cutting alloy.

Characteristics of steel

CPM Rex 121 steel knife
The CPM Rex 121 brand alloy occupies an intermediate position between high-alloy (high-strength) and hard alloy steels. The material of this brand is intended for the manufacture of cutting tools with high wear resistance and a hardness of 70-72 HRC.

For products made of this steel, it is better to use coarse sharpening, since its grinding, and therefore sharpening, are performed with great difficulty. REX 121 contains 1% more carbon and 3% more vanadium than the competing Carpenter CTS alloy.

Knives made of CPM Rex 121 steel.

The CPM Rex 121 brand alloy occupies an intermediate position between high-alloy (high-strength) and hard alloy steels. The material of this brand is intended for the manufacture of cutting tools with high wear resistance and a hardness of 70-72 HRC.

For products made of this steel, it is better to use coarse sharpening, since its grinding, and therefore sharpening, are performed with great difficulty. REX 121 contains 1% more carbon and 3% more vanadium than the competing Carpenter CTS alloy.

The SRM REX 121 brand has low impact strength parameters. Products made of this material are prone to breakage when exposed to them. Fits small.

Pros and cons for knives

Alloys obtained by the method of powder metallurgy have a uniform structure of small grains. It is this condition that gives the products special cutting properties. CPM REX tool steel is used in the production of metal cutting tools. The tools have the following advantages:

the resistance of the knife blade to bending is provided by the alloying procedure, the addition of elements that contribute to the increase of this parameter;
increasing the mechanical parameters of the blade, its strength depends on the content of additives in the material: tungsten, nickel, chromium and other elements;
hardening, heat treatment of metal in the form of heating it to the critical point (the limit temperature at which the destruction of the crystal structure of the metal is observed) and its sharp cooling. The procedure is designed to increase strength and hardness.
Knives made of powder tool steel have the following disadvantages:

limit parameters of alloying, i.e. alloying components can be added in certain quantities while observing their ratio. Otherwise, the properties will not meet the specified requirements;
powder steel, in addition to alloying additives, contains non-metallic extraneous inclusions. This error can be overcome by modern production and processing technologies;
The high cost of the material is caused by the high cost of production and the limited dimensions of the blanks.

As a result, CPM 121 REX brand powder steel is a unique material for the manufacture of cutting tools of special strength.
 

Chemical composition
Steel is an alloy, the main components are iron and carbon, the ratio of which determines the grade. Additives are important, they are used to develop alloys of the desired composition.

CPM 121 REX iron-carbon alloy has the following composition:

carbon content (C) – 3.4%, its presence in the alloy ensures strength and hardness of the material;
the amount of chromium (Cr) is 4.0%, its presence supports the ability to be hardened, increases resistance to wear and corrosion. It is a mandatory element of all grades of steel;
the molybdenum (Mo) percentage of this grade is 5.0 units. The silver-white metal from Mendeleev's periodic table represents a refractory element. Its presence provides a certain rigidity, stability when heated to high temperatures, prevents brittleness and fragility of products;
V (vanadium) is a shiny grayish-white element that makes up 9.5% of the alloy. As a metal of high hardness, vanadium increases the properties of chromium. Inertness to aggressive environments provides the addition of this element;
the content of W (tungsten) according to the production technology of this brand is 10.0%. The melting point of tungsten, a gray metal, is 33800C. Addition of tungsten to the metal gives it high strength characteristics. It is a mandatory component in high-speed steel alloys;
9.0% (Co) of cobalt in the alloy ensures the heat resistance of the steel and its mechanical characteristics. Cobalt is a silver-white or yellowish metal, it can have a pink or blue tint. Alloys with the addition of cobalt are used for the manufacture of tools intended for processing materials - drills, cutters, milling cutters, etc.;
The presence of S (sulfur) is necessary to increase the machinability characteristics of products. But its content is absorbed in 0.12%. A higher content of this element affects such characteristics as impact strength, abrasion resistance, and corrosion resistance.
 

SRM Rex 121 steel, due to its properties, is used for the manufacture of high-speed cutting products, which increases their effect on the processed materials.
 

CPM
in the marking stands for Crucible Particle Metallurgy.

Knife made of SRM Rex 121 steel.

Properties

Steel is a unique material whose mechanical, physical and technological properties are determined by its composition. CPM steel is obtained using modern, constantly improving technologies, which include powder. This type of tool steel has the following properties.

Mechanical:

high hardness and strength, they are provided by carbon, the percentage of which is 3.4%;
high indicators of wear resistance depends on the 9% cobalt content;
unsurpassed cutting ability and stability of the blade at small sharpening angles.
Chemical:

steel is inert, it is not oxidized by oxygen, does not react with harmful substances;
has high indicators of corrosion resistance;
has high heat resistance, it retains its strength properties.

Technological:

characteristic resistance to such loads as shocks, bends and others to which knives and cutting tools are subjected;
liquid fluidity is characteristic of molten steel, in this state it fills the entire space in which it is located;
hardly amenable to cutting. Special diamond equipment is required for blade sharpening.
Machining recommendations
CPM Rex 121 alloy is a very hard high-speed steel with numerous advantages. However, the advantages, in some cases, turn into disadvantages. Difficulties are revealed when using ready-made products, namely knives.

This type of product made of powder steel is difficult to sharpen, so it is better to use the services of specialists to perform this procedure.
 

This is due to the fact that unskilful actions can lead to the appearance of microcracks, irregularities, staining of the edge of the blade.
Application
Powder steels are expensive materials, so their use is quite limited. Blades made of CPM Rex 121 steel are found in souvenir and collectible edged weapons, as well as gift items. Exclusive gift knives can be purchased in specialized stores and online marketplaces:

Analogues of steel CPM Rex 121

Comparison of CPM Rex 121.
HAP 72 is a Japanese analogue of the knife metal of the American company Crucible Industries LLC. The purpose of this brand is the production of premium class knives and cutting tools of a high category of strength, hardness, and wear resistance. In knife production, the HAP 72 brand is recognized as the best. The composition of the components of this grade of steel in percentages: Carbon - 2.10%, Chromium - 4.0%, Molybdenum - 8.2%, Vanadium - 5.0%, Cobalt - 9.5%, Tungsten - 9.5%.

Analogues of CPM REX 121 knife steel, the American manufacturer Crucible Industries LLC presents a series of grades S60V, S90V, CPM3V, produced by Crucible Particle Metallurgy (CPM) technology.

Machining recommendations
CPM Rex 121 alloy is a very hard high-speed steel with numerous advantages. However, the advantages, in some cases, turn into disadvantages. Difficulties are revealed when using ready-made products, namely knives.

This type of product made of powder steel is difficult to sharpen, so it is better to use the services of specialists to perform this procedure.
This is due to the fact that unskilful actions can lead to the appearance of microcracks, irregularities, staining of the edge of the blade.
Application
Powder steels belong to expensive materials, so their use is quite limited. Blades made of CPM Rex 121 steel are found in souvenir and collectible edged weapons, as well as gift items. Exclusive gift knives can be purchased in specialized stores and online marketplaces:

Comparison of CPM Rex 121.
HAP 72 is a Japanese analogue of the knife metal of the American company Crucible Industries LLC. The purpose of this brand is the production of premium class knives and cutting tools of a high category of strength, hardness, and wear resistance. In knife production, the HAP 72 brand is recognized as the best. The composition of the components of this grade of steel in percentages: Carbon - 2.10%, Chromium - 4.0%, Molybdenum - 8.2%, Vanadium - 5.0%, Cobalt - 9.5%, Tungsten - 9.5%.

Analogues of CPM REX 121 knife steel, the American manufacturer Crucible Industries LLC presents a series of grades S60V, S90V, CPM3V, produced using Crucible Particle Metallurgy (CPM) technology.

Cons:

• Strength.  This is its main disadvantage. No heavy work, because steel with such hardness does not have high impact strength;
• Corrosion resistance.  It rusts, oxidizes, becomes stained. In general, without digestion anywhere;
• Due to this hardness, there may be difficulties with sharpening.  Grinds only on diamonds;
• Space price tag.