Rules for hardening metal at home

Features of 9ХС steel

In the manufacture of various construction tools, special steel 9ХС is used. Products made from such metal will be distinguished by maximum strength, reliability and durability. Today we will talk about the features of this material, its advantages and disadvantages.

Advantages and disadvantages

Metal 9ХС has a number of advantages.

• Unique technical characteristics . This metal is considered quite durable. It produces wear-resistant products that are practically not subject to mechanical stress; they are very resistant to bending and torsion. Even with constant use, they will not become deformed. In addition, cracks and other small defects practically do not form on their surface.
• Increased hardness . It is achieved after annealing. Also, after this procedure, the material becomes absolutely susceptible to calcination.
• Corrosion protection. This steel contains chromium, which protects the material from the negative effects of water.
• Hardness _ Tools made from such steel can easily cut other metals and dense wood.
• Same carbide distribution. This provides advantages when using this metal in the manufacture of thread-cutting devices that have a fine thread pitch.

In addition, it can be noted that the metal is characterized by increased hardenability and elasticity. It can hold an edge for a long time.

But 9ХС grade steel also has some disadvantages.

• Appearance . This metal will not shine; a peculiar pattern can be seen on its surface.
• Relatively high cost . Products made from this metal are produced by hand forging, which is why their price is quite high.
• Difficulty of processing . Even small errors in the manufacture of such steel can lead to a decrease in its quality. It behaves rather capriciously during heat treatment and sharpening.
• Loses its properties at elevated temperatures. When heated above 200 degrees, the cutting qualities of the tools are primarily reduced. It should also be noted that this variety is not suitable for the production of welded structures. During heat treatment, the material will require compliance with a specific optimal temperature regime.
• Care requirements. Chrome and silicon will not fully protect steel, so you will need to carefully wipe and dry tools after contact with water. Otherwise, over time it will begin to rust.

Structural transformations during heat treatment.

We subject the steel to incomplete hardening and heat it until austenite and secondary cementite are formed. Next, we keep it at this temperature (840 ºС) to obtain homogeneous austenite.

Subsequent cooling in oil at a rate greater than Vcrit (lower cooling rate at which austenite turns into martensite) ensures the production of fine-grained martensite.

Let us consider the transformation in oil that occurs in 9ХС steel upon heating the initial equilibrium structure F+C. In practice, at normal heating rates (in an electric furnace) for hardening, pearlite retains its lamellar or granular structure up to the Ac1 temperature (770 ºС for 9ХС steel). At temperature Ac1 in steel, pearlite transforms into austenite. Austenite crystals (grains) nucleate mainly at the boundaries of the ferrite and cementite phases. The formation of austenite grains occurs at a faster rate than the dissolution of pearlite cementite, therefore it is necessary to hold the steel at the quenching temperature to completely dissolve cementite and obtain homogeneous austenite.

Changes in steel structure during oil quenching

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During continuous cooling in steel with Vcool > Vcrit, austenite transforms into martensite. Martensitic transformation develops in steel at a high speed (1000-7000 m/s) in the temperature range Mn...Mk. It is necessary to take into account that with an increase in the carbon content in steel, the temperatures Mn and Mk decrease (points Mn and Mk change their position on the graph). The introduction of alloying elements also changes the position of points Mn and Mk. For example, the introduction of silicon and chromium increases them. As a result of hardening of 9ХС steel, its structure has

except martensite and a certain amount of retained austenite (6-8%).

The formation of martensite as a result of hardening leads to high residual stresses, increased hardness and strength, but at the same time the tendency to brittle fracture increases, which requires additional subsequent tempering.

Tempering is the heating of hardened steels to temperatures not exceeding Ac1

During vacation, several processes occur. The main one is the decomposition of martensite, which consists of the release of carbon in the form of carbides. In addition, retained austenite decomposes, carbide transformation and coagulation of carbides occur, imperfections in the crystalline structure of the solid solution and residual stresses are reduced.

Let us consider transformations in hardened steel during tempering. The first transformation during tempering develops in the range of 80.200ºС and leads to the formation of a tempered martensite structure. As a result, the specific volume of martensite decreases and the residual stresses decrease. The second transformation during tempering develops in the temperature range of 200.260 o C and consists of the following stages:

1) transformation of retained austenite into tempered martensite;

2) decomposition of tempered martensite

3) reduction of residual stresses;

4) some increase in volume associated with the transition A rest

M otp.

The third transformation during tempering develops in the range of 300.400ºС. This completes the decomposition of tempered martensite and the process of carbide formation. A ferrite-carbide mixture is formed, and residual stresses are significantly reduced.

The structure of steel after low tempering (up to 250 C) is called tempered martensite; steel structure after an average tempering of 350.500ºС – troostite tempering; after a high tempering of 500.600 ºС – tempering with sorbitol.

In 9XC steel, after incomplete quenching in oil and low tempering at 170ºC, a tempered martensite structure is formed.

Steel 9ХС. Basic data

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GOST 5950-73. Tool alloy steels.

Purpose: drills, reamers, taps, dies, combs, cutters, machine dies, stamps for cold work. Critical parts, the material of which must have increased wear resistance, fatigue strength during bending, torsion, contact loading, as well as elastic properties.

Main characteristics

The main characteristics of this steel can be found in GOST 5950-2000 and GOST 2590-2006. First, we will analyze the chemical composition of this metal. It includes the following components:

Chromium in the metal provides, among other things, increased hardness and strength. It is also responsible for the corrosion resistance of the material. Silicon , has the same property . Due to it, the strength of the steel increases, but at the same time the toughness and ductility decrease.

Chemical composition

To create 9ХС steel, 13 substances are used, the combination of which in the right quantities results in qualitatively better physical, mechanical and operational characteristics.

Here are the components that make up 9ХС steel:

• iron (Fe) – 94%;
• silicon (Si) – up to 1.6%, but not less than 0.9%;
• chromium (Cr) – up to 1.25%, but not less than 0.95%;
• carbon (C) – 0.9%;
• manganese (Mn) – up to 0.6%;
• nickel (Ni) – 0.35%;
• copper (Cu) – 0.3%;
• molybdenum (Mo) – 0.2%;
• tungsten (W) – 0.2%;
• vanadium (V) – 0.15%;
• sulfur (S) – 0.03%
• phosphorus (P) – 0.03%;
• titanium (Ti) – less than 0.03%.

Percentages may vary slightly among different manufacturers. Deviations should not exceed 1/10 of a percent, otherwise the properties of the resulting alloy may differ.

Analogs

There are various analogues of this steel.

• HVG . This domestic substitute includes tungsten, chromium and manganese. It differs from 9ХВ steel in its increased carbon content. This material is not used for welded structures.
• HVSG . This domestic analogue is a deep calcination steel. It has increased strength and hardness.
• 90CrSi5 . This foreign substitute is alloy tool steel. It is produced in Germany.

It should be noted that the replacement of HVSG and HVG has a higher manganese content compared to 9ХС. This increases the metal's tendency to deform. All analogues are created in the same way, but their chemical composition may change.

Explanation of markings

For marking steels and other materials, certain standards are being developed, the use of which makes it possible to simplify the process of determining the chemical composition. This steel is deciphered as follows:

1. In the instrumental group, the first digit indicates the carbon content (in tenths of a percent), that is, in this case, 0.9% carbon. This element is considered the main one, as it determines the characteristics of the crystal lattice, hardness, strength, fragility and other qualities.
2. As previously noted, the steel was alloyed to change some performance characteristics. Chromium and silicon, of which no more than 1.5%, were used as alloying materials.

In addition to the above elements, the composition contains many others that are an integral part of steels.

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Application

9ХС grade steel can be used in the manufacture of a wide variety of devices. Most often it is used to create sharp and reliable knives and blades. It can also be perfect for the production of cutting parts for tools, including axes.

Knives and blades made from this metal are perfect for hunting and fishing. They are often taken for hiking trips.

They easily tolerate the effects of unfavorable environmental conditions. Such knives can withstand strong impacts and twisting. At the same time, they will retain excellent cutting properties for a long time. All of them are made by hand. Sometimes these cutting tools are also used for the needs of the food industry.

Sometimes 9ХС steel is used in the manufacture of various drills. But at the same time, they can only be used for working with soft materials, most often with wood of various species. Cylindrical reamers are also produced from it. They are used to improve the dimensional accuracy of holes and to remove roughness.

Heat treatment and sharpening

There are certain requirements for heat treatment of steel of this grade that must be observed. A preliminary analysis and x-ray of the structure are performed. This will allow timely identification of all defects present on the surface. At this stage, the hardness of the alloy is monitored. To properly harden the material, it will be necessary to maintain the recommended temperature.

The heat treatment itself occurs by heating the metal and then cooling it. Most often it is carried out either at the intermediate or at the final stage of manufacturing. It should be remembered that it directly affects the strength of steel. Cooling of the metal, as a rule, occurs in a special oil.

Most often, this hardening is carried out in special electric furnaces equipped with a sealed casing. As a rule, such equipment is equipped with a special system for adjusting and maintaining optimal temperature conditions. During processing, the hardness of the steel is periodically checked.

Sharpening the material allows you to remove a small layer from it and give it the desired shape.

After such a procedure, small marks will remain on the metal surface. As a rule, after this the product is also polished and fine-tuned. They are carried out in order to give it its final shape, the sharpening angle.

Most often, a variety of abrasives are used for sharpening. This procedure is carried out not only during the steel production process, but also in the future as the products are used.

After all the processing, the steel is produced in the form of large sheets. They may vary depending on length and thickness.

Source

Methods for hardening metal at home

To harden metal at home, you will need a heat source and a container of coolant. The heat source can be an open fire from a fire, a gas burner, or a specially shaped electric oven (muffle furnace). The bath or container must be deep enough to completely immerse the part inside it.

Hardening on an open fire

The work is performed in the following sequence:

The meaning of metal color when hardening over an open fire

• Make a fire and wait for a large formation of burning coals;
• Pour oil into one container and water into another;
• When the flame reaches a bright crimson color, metal objects that require hardening are laid out on the coals;
• Using the heating table by color, monitor the state of metal heating;
• Once the required temperature is reached, the workpieces are removed using pliers and quickly lowered into the liquid;
• The optimal cooling mode is at intervals of three seconds, with a gradual increase in the time interval;
• When the metal has lost its color, continue to cool it with water.

Hardening in a muffle furnace

A muffle furnace is an electric heating device that resembles a tunnel, around which there is a nichrome electric spiral. The entire structure is coated with refractory clay, the rear end of the tunnel is tightly closed, the front end has a door through which the necessary workpieces can be placed inside the furnace. It is advisable to equip the door with a viewing window made of fireproof glass (to monitor the heating process of the workpiece).

After the metal reaches the required temperature, the rest of the cooling process occurs as described in the section: “Hardening over an open fire.”