How to harden stainless steel at home - Metals and their processing

How to harden stainless steel at home?

Despite the fact that such a technological procedure as hardening stainless steel products leads to a decrease in their ductility and flexibility, the use of this heat treatment method makes it possible to give them exceptional hardness.

Modern hardening technologies and their correct selection provide high quality steel, in which the proportions of strength, ductility and toughness are optimally maintained.

Products treated in this way have significantly improved performance characteristics.

Hardening of steel in an induction channel installation

Features and purpose of steel hardening

Technology such as steel hardening has been actively used by mankind for quite a long time. Back in the Middle Ages, this method of heat treatment was used to improve the strength characteristics and hardness of edged weapons, as well as tools used in agriculture.

The question of how to harden stainless steel arose when people learned to produce steel alloys on an industrial scale with exceptional anti-corrosion properties.

It was during this period that new steel hardening technologies were developed, making it possible to create materials with outstanding physical and chemical characteristics.

The hardening procedure is mainly applied to stainless steels, which have a martensitic internal structure.

A characteristic feature of such stainless steel alloys is that in their normal state they have increased hardness and a tendency to become embrittled.

If products made from such steels are subjected to heat treatment, which involves rapid tempering, then their toughness coefficient can be increased, which significantly expands the scope of their application.

Changing the heat treatment mode of steel allows you to obtain different physical and mechanical properties of the metal

Depending on the tasks being solved, hardening of products made from stainless steels can be carried out in one of two ways - with heating:

the entire product (global hardening);
only that part of the product that needs to be hardened (local hardening).

You should also be very serious about choosing a method for cooling the part to be hardened after it has been heated.

It should be borne in mind that for different grades of stainless steel, the methods of cooling products subjected to hardening or tempering may differ significantly.

If, when performing heat treatment of low-alloy steels, ordinary water is often used as a cooling medium, then substances such as oil, salt and alkaline solutions are used to cool stainless steel alloys.

Temperature selection

The most important task that should be solved when starting to harden a product made of stainless steel is the correct choice of temperature conditions. If a stainless steel product is overheated during hardening, it may lose its original strength, which is explained by a decrease in the amount of carbon in its internal structure.

Heat treatment modes of chromium steels and the resulting mechanical properties

Very often, when stainless steels are hardened, residual stresses arise in them, which can be removed by subsequent mechanical processing (rolling, etc.).

Such problems can be avoided even at the stage of heat treatment if the parts being hardened are cooled in several stages, with a gradual decrease in temperature at each of them.

This cooling technique is often used in cases where, as a result of hardening, it is necessary to obtain a product characterized by particularly high strength.

The essence of the method of gradual cooling of a hardened product made of stainless steel is that after heating it is sequentially lowered into baths containing various cooling media: solutions of salts, alkalis, mineral or synthetic oils.

The most significant advantage of this technique is that when used in the metal structure, all internal stresses that have a negative impact on its quality are completely eliminated.

Among the disadvantages of this method, the high cost of its implementation should be noted, which limits the scope of its application.

Recommendations for hardening stainless steel at home

If there is a need to improve the strength characteristics and increase the hardness of a stainless steel product, then you can harden it at home by getting acquainted with practical recommendations and studying this process in a video. As an example, we can consider in detail the hardening of a stainless steel knife blade.

In order to make a stainless steel knife harder and more durable at home, you will need the following materials and equipment:

electric oven or gas burner;
sealing wax;
ordinary turpentine.

Homemade gas forge

The very method of hardening a stainless steel knife, presented in many videos on the Internet, consists of the following sequence of actions.

The metal part of the knife (without the handle) is placed in the chamber of an unheated electric oven.
After turning on the oven, you need to heat the knife until it turns a bright scarlet color (950–10500). If you do not have an electric oven, then heating the knife can be done using a gas burner or hot coals, but then it will be difficult to achieve uniform heating of the metal.
After a short exposure at a given temperature (5–10 minutes), the knife is removed from the oven and its blade is immersed in sealing wax for 1 second. The procedure of immersion and removal should be repeated until you feel that the knife enters this material with some difficulty (like butter).
Completing the procedure for hardening a knife at home consists of cleaning it from residual sealing wax and wiping the blade with a cloth soaked in turpentine.

When hardening a stainless steel knife yourself, you should keep the following in mind: overheating the metal can cause the knife blade, becoming too hard, to lose its elasticity, and this will worsen its cutting properties.

Source: https://varimtutru.com/kak-zakalit-nerzhaveyku-v-domashnih-usloviyah/

Hardening stainless steel at home

We will not explain what hardening of metals is, using scientific terms and phrases, because our article is for people who are interested in how to harden steel at home.

And, therefore, all information devoted to this issue should be as accessible as possible to understanding and application in practice.

So, in normal language, hardening is an increase in the strength of a metal by heating it to high temperatures and then cooling it in a liquid or air environment.

How to harden?

It should be noted that by thus increasing the depravity and hardness of the metal, we simultaneously significantly reduce characteristics such as flexibility and ductility. Based on this, you should carefully select items for hardening. Since by giving it some absolutely important qualities, it can be deprived of others, no less important.

Basically, for obvious reasons, hardening of metal products is used by residents of rural areas. The reason is that in this way many zealous owners try (and they succeed) to increase the service life of household items, and not only for other purposes.

Examples include plowshares (farmers), carpentry and plumbing tools, hunting knives, axes and much more. In urban conditions, the hardening process and processing of hardened steel are possible in a special workshop.

Which significantly increases the cost of this event.

Work methodology

As a rule, the goal of improving the quality of steel in terms of strength is:

Hardening only the working edge of the tool.
Increasing the hardness of the entire body of the processed object.

Based on this, two hardening methods are used:

Heating and cooling of the cutting edge, followed by processing (sharpening).
Changing characteristics over the entire area by hot forging and hardening.

Process Features

Technological features associated with increasing the hardness of hardened steel include such issues as constant monitoring of the following indicators:

Uniform heating of the edge or body of the workpiece;
The absence of blue or black spots on the metal surface as a result of heating, which indicates inhomogeneous and excessive heating;
Maintaining a temperature at which 45 steel (hardened) has an even red (bright) color over the entire plane (edge) of the workpiece;
A uniform cooling process in a pre-prepared water (oil) bath.

Water or machine oil is used as a cooling liquid. To control the change in color of the surface of the workpiece when it is heated, special color tables are used.

How to drill stainless steel at home

Photo of the table indicating the heating temperature of the part for its color.

Photo of the table indicating:

steel grades (A45, U9, etc.);
heating temperature at the initial stage;
cooling medium (oil, saltpeter, wax, water) by steel grade;
cooling fluid temperature;
heating temperature of the workpiece during tempering (final heat treatment).

By default, when we talk about hardenable steel, we mean stainless steels with a martensitic internal structure.

Special equipment and tools

The following tools will be needed when hardening at home:

Pliers with long handles;
Hammers of different weights and sizes (for hot forging);
Files for further processing;
The following equipment is used for heating parts:

electric oven;
gas burner;
blowtorch;
a large fire, preferably a coal one, lined with materials that redirect the heat.

If you decide to start hardening metals at home, then the best solution would be to build a mobile, compact forge.

Detailed photo of the forge design.

Any container of suitable size and material can be used as a bath for coolant.

A practical example of hardening a kitchen knife blade at home

Required:

Gas burner or electric oven;
Sealing wax as a coolant;
Turpentine;
Ticks.

Sequence of operations performed:

The handle of the knife is removed.
The knife blade is placed in the cold oven chamber. If a torch is used, you need to make the chamber yourself. Made from refractory bricks.
Turn on the burner (oven) and heat it to a temperature at which the knife blade turns bright red. It is advisable to control the process using a color chart.
After maintaining a certain amount of time at the given temperature parameters (from 5 to 10 minutes), the workpiece is removed from the chamber and abruptly immersed in wax for one second. This action (lowering - pulling out) is carried out until the moment when physically tangible resistance is felt when the knife enters the sealing wax.
The hardening process is almost complete. After cleaning the part from the remaining sealing wax with turpentine, you can confidently say that this blade is real, hardened stainless steel.

Practical advice

Not all steel grades are subject to hardening (for example, low-carbon steel). Therefore, it is advisable to first find out which group the item intended for hardening belongs to.

It should be remembered that if the technological process is disrupted (non-uniform heating, overheating, etc.), hardening may not only fail to improve the quality characteristics of the tool subjected to heat treatment, but also lead to its irreversible damage.

By and large, working with metal hardening is not something very difficult and only requires a high degree of attention and concentration. In any case, you should initially prepare for it by studying text and video materials similar to this article.

Source: https://steelfactoryrus.com/zakalka-nerzhaveyki-v-domashnih-usloviyah/

Hardening stainless steel at home - process technology | mk-soyuz.rf

Hardening refers to the heat treatment of metal, during which intense heating is first carried out, and then sudden cooling in a liquid. During this technological procedure, the ductility and elasticity of the product decreases, but its strength increases. How to properly harden stainless steel items at home?

Why is steel hardening needed?

Humanity has been using hardening technology for many centuries. Agricultural tools and bladed weapons were hardened already in the Middle Ages. Hardening of stainless steel was thought about in the era of the industrial breakthrough, when steel alloys with anti-corrosion properties were needed. It was then that a new method of hardening steel was developed, which made it possible to impart unique chemical and physical properties to the materials.

Stainless steel has a needle-like internal structure called martensite, which makes these alloys highly durable and highly resistant to embrittlement. When heat treating such steel, the viscosity coefficient increases, which expands the scope of their application.

How to harden steel at home?

Rural residents often resort to self-hardening of metal, thus increasing the service life of household items: plow shares, carpentry and plumbing tools, hunting knives, axes. It is more difficult for a city dweller to process stainless steel - a special workshop is required.

Required Tools

In order to harden steel at home, you need to arm yourself with:

Pliers with an extended handle,
Hammers of different sizes,
Files for subsequent processing,
Electric oven,
Gas burner,
Blowtorch.

To create a cooling environment, you will need any container of appropriate size.

Hardening methods

Stainless steel can be hardened in different ways. First of all, the product heats up well. For this use:

Burner,
Electric oven,
blowtorch,
A fire on coals.

The last option will be the best; the fire will be able to provide a much higher temperature.

The most commonly used cooling medium is:

When cooling with oil, the part is dipped into it twice with a short interval of a couple of seconds. The first dive takes 3-4 seconds, and the second - 5-6 seconds. Immediately after this procedure, the steel is immersed in water until it cools completely.

In the second cooling method, the part is immersed in wax several times. If the stainless steel no longer penetrates into the liquid medium, the cooling process is considered complete. Simply clean the surface with turpentine.

How to choose a temperature mode?

The choice of temperature mode plays a big role when hardening steel. Overheating is fraught with loss of inherent strength; this occurs due to a quantitative decrease in carbon in the metal structure.

In some cases, after completion of the stainless steel hardening process, residual stresses appear; they are removed through further mechanical processing. This problem can be prevented if the product being hardened is cooled in stages, with a measured decrease in temperature conditions. This step-by-step hardening technique is used in the manufacture of parts with very high strength values.

How to gradually lower the temperature of the cooling medium? To do this, prepare several containers with different liquids: saline solution, alkaline solution, mineral oil, synthetic oil. This method allows you to completely eliminate internal stress, which negatively affects the useful properties of steel. A small disadvantage of the technique is the high cost of implementation.

Master class on hardening a kitchen knife

After hardening, the knife gains strength and elasticity. The procedure does not require a lot of time.

Take:

Gas burner or electric oven.
Wax for cooling.
Turpentine.
Ticks.

Step by step process:

Remove the handle from the product.
Place the blade in the stove compartment. When using a burner, the chamber is made by hand using refractory bricks.
Turn on the stove (burner). Heat the knife until it acquires a rich red hue. If possible, control the heating by checking the color you purchase against the color chart.
Soak the stainless steel until it turns bright red and remove from the compartment.
Immediately immerse the metal in the prepared sealing wax for a couple of seconds. Pull it out. Repeat the procedure many times until the part no longer fits into the sealing wax.
Clean the stainless steel with turpentine to remove wax residues.

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Master class on hardening an ax

Sometimes the manufacturer violates the technology of heat treatment of steel, and the ax turns out to be very soft, quickly begins to dull and form dents, or brittle, then the blade becomes covered with cracks and loses color. The situation can be corrected.

Take:

Electric oven,
wire circle,
water,
Machine oil,
2 containers for water and oil.

Step by step process:

Blunt the cutting edge to 0.1 cm.
Heat the ax blade to 750-760°C.
To determine the heating temperature, apply a magnet to the stainless steel; it is not attracted to stainless steel at 768°C.
Cool slowly to 550°C.
The cooling procedure takes up to 10 hours. No special cooler is required; just leave the ax in the switched off oven.
Clean the stainless steel from scale using a wire wheel.
Heat the blade to 800-830°C until a rich fiery red hue.
Cool first in water (30°C), lowering for 3-4 seconds. Move the stainless steel quickly in the container, this will help avoid the formation of a steam cushion.
Cool in machine oil.
Preheat oven to 300°C. Keep the part in it for an hour.
Cool outdoors.

On a note

After removing the hot steel from the furnace (burner), it will be elastic and soft, so there is a high probability of damage. To avoid unpleasant consequences, you need to immerse it in a cooling medium smoothly and carefully.

When choosing steel products, pay attention to foreign manufacturers; in their tools, the percentage of stainless metal content exceeds Russian GOST standards.

Long and strong heating of the metal makes the hardening process deeper, resulting in a hard and elastic blade. After this, it will be less strong and gradually lose its cutting qualities.

The same stainless steel should not be hardened many times: the metal begins to tire and wastes the necessary qualities.

Hardening steel for the first time is a responsible undertaking that requires continuous monitoring. When heated, the product is removed every 3-4 seconds, this allows you to strictly observe the color of the metal. In case of overheating, the steel takes on a white tint; in case of underheating, it becomes dark blue.

To harden stainless steel at home, you must arm yourself with a gas burner, an electric oven, a blowtorch, or light a fire. In addition, the process cannot be carried out without a coolant (water, sealing wax or machine oil). You will need long-handled pliers and special gloves. Self-hardening of stainless steel requires constant monitoring of color changes in the material.

Source: https://xn----ntbhhmr6g.xn--p1ai/metallyi/osobennosti-zakalki-nerzhaveyki-v-domashnih-usloviyah

Features of steel hardening

Heat treating a metal changes its characteristics. Tempering steel makes it harder and stronger. In some cases, heat treatment is carried out to refine the grain and level the structure. A simple heating and rapid cooling technology for small parts can be done at home. It is necessary to know the grade of steel and its heating temperature for hardening.

What is metal hardening?

One type of heat treatment is metal hardening. It consists of several stages performed in a certain sequence:

Heating metal to a certain temperature. Dwell time for leveling over the entire depth of the part.
Fast cooling.
Tempering to relieve stress and correct hardness to a specified value.

During the manufacturing process, complex parts can undergo several different types of hardening.

Based on the depth of treatment, hardening is divided into two types:

Basically, in mechanical engineering, volumetric heat treatment is used, when the part is heated to its entire depth. As a result of sudden cooling, after the completion of heat treatment, the hardness inside and outside differs by only a few units.

Surface hardening is used for parts that must be hard on top and ductile on the inside. The inductor heats the steel to a depth of 3–20 mm and immediately behind it there is a sprayer that pours water on the hot metal.

The steel is heated to austenite state. Each brand has its own temperature, determined from the table of the state of iron-carbon alloys. During sudden cooling, carbon remains inside the grain and does not enter the intercrystalline space. The transformation of the structure does not have time to occur, and the internal structure contains pearlite and ferrite. The grain becomes finer, the metal itself becomes harder.

What steels can be hardened?

When heated and rapidly cooled, internal changes in structure occur in all steels. Hardness increases only with carbon content greater than 0.4%. St. 35 according to GOST has it 0.32 - 0.4%, which means it can “get hot” - slightly change the hardness if the carbon is located at the upper limit.

Steels starting from CT45 and higher in carbon content are considered hardenable. At the same time, hardening of stainless steel with low carbon content, type 3X13, is possible. Chromium and some other alloying elements replace it in the crystal lattice and increase the hardenability of the metal.

High-alloy carbon steels contain substances that accelerate the cooling process and increase the steel's ability to harden. They require a complex step cooling system and high temperature tempering.

Temperature and heating rate

The heating temperature for hardening increases with the content of carbon and alloying substances in the steel. For St45 it is, for example, 630–650⁰, St 90HF - more than 800⁰.

High-carbon and high-alloy steels, when heated quickly, can “crack” - form small cracks on the surface and inside. They are heated in several stages. At temperatures of 300⁰ and 600⁰, exposure is done. In addition to equalizing the temperature throughout the depth, there is a structural change in the crystal lattice and a transition to other types of internal structure.

Properties of steel after hardening

After hardening of parts, structural changes occur that affect the technical characteristics of the metal:

increases hardness and strength;
grain decreases;
flexibility and ductility decreases;
fragility increases;
abrasion resistance increases;
fracture resistance decreases.

It is easy to obtain a high class of cleanliness on the surface of a hardened part. Raw steel is not polished, it drags on and on.

Types of steel hardening

The main parameters for hardening steel: heating temperature and cooling rate. They completely depend on the grade of steel - carbon content and alloying substances.

Hardening in one environment

When hardening steel, the environment determines the cooling rate. The greatest hardness is obtained when the part is dipped in water. This way you can heat medium-carbon low-alloy steels and some stainless steels.

If the metal contains more than 0.5% carbon and alloying elements, then when cooled in water, the part will crack - become covered with cracks or completely collapse.

High-alloy steels increase their hardness even when cooled in air.

When quenching in water, alloy steel is heated to 40–60⁰. The cold liquid will bounce off the hot surface, forming a steam jacket. The cooling rate will be significantly reduced.

Step hardening

Hardening of steels with complex composition can be carried out in several stages. To speed up the cooling of large parts made of high-alloy steels, they are first dipped in water. The residence time of the part is determined by several minutes. After this, quenching continues in oil.

Water quickly cools the metal on the surface. After this, the part is dipped in oil and cools to the critical temperature of structural transformations of 300–320⁰. Further cooling is carried out in air.

If you heat massive parts only in oil, the temperature from the inside will slow down the cooling and significantly reduce the hardness.

Isothermal hardening

It is difficult to harden metal with a high carbon content, especially tools made of tool steel - axes, springs, chisels. When rapidly cooled, strong stresses are formed in it. High temperature tempering removes some of the hardness. Hardening is carried out in stages:

Normalization to improve structure.
Heating to hardening temperature.
Dipping into a bath of saltpeter, heated to 300–350⁰, and soaking in it.

After hardening in a saltpeter bath, tempering is not necessary. Stresses are released during slow cooling.

Light hardening

There is no technical term for “light hardening”. When alloy steels are hardened, including heating, in a vacuum or inert gases, the metal does not darken. Hardening in a protective gas environment is expensive and requires special equipment separately for each type of part. It is used only for mass production of the same type of product.

In a vertical furnace, the part is heated, passing through an inductor, and immediately lowered below - into a salt or nitrate bath. The equipment must be sealed. After each cycle, the air is pumped out of it.

Hardening with self-tempering

During rapid cooling during the hardening process of steel, heat remains inside the part, which gradually leaves and releases the material - relieving stress. Self-tempering can only be done by specialists who know how much the time a part remains in the coolant can be reduced.

Self-tempering can be done at home if you need to slightly increase the hardness of fasteners or small parts. It is necessary to lay them on heat-insulating material and cover with asbestos on top.

Cooling methods during hardening

Methods of cooling metal during water and oil quenching are widely used in industry. The most ancient composition for hardening swords and other thin-walled objects is saline solution. Hardening was carried out by blacksmiths using forging heat and the heat generated by deformation.

Red sabers, swords, knives were dipped into the urine of red-haired guys. In Europe they were simply stuck into the bodies of living slaves. The colloidal composition containing salts and acids made it possible to cool the steel at an optimal speed and not create unnecessary stresses and leads.

Currently, various sodium salt solutions, saltpeter and even plastic shavings are used.

How to harden steel at home

The decision on how to heat metal is made based on several parameters:

steel grades;
required hardness;
operating mode of the part;
dimensions

Not all heat treatment methods are available to amateurs. You should choose the simplest ones. Most often, at home, you have to harden stainless steel when making knives and other home cutting tools.

The hardening temperature of chromium-containing steels is 900–1100⁰C. Heating should be checked visually. The metal should have a light orange - dark yellow color, uniform over the entire surface.

You can dip a thin stainless steel into hot water, lifting it into the air and lowering it again. The higher the carbon content, the more time the steel spends in air. One cycle lasts approximately 5 seconds.

Plain weldable steels are heated to a cherry color and cooled in water. Medium alloy materials should have a red color before immersion in water. After 10–30 seconds, they are transferred to oil, then placed in the oven.

When hardening, the maximum hardness that steel gives with this technology is obtained. Then it is reduced to the required value by high-temperature tempering.

Hardening at home

Equipment

Metal is heated in various ways. You just need to remember that the combustion temperature of wood cannot provide heating to the metal.

If you need to improve the quality of 1 part, just light a fire. It must be lined with bricks around the perimeter and, after laying the workpiece, partially closed on top, leaving gaps for air access. It's better to burn coal.

A separate area and a small part are heated with a gas and kerosene burner, constantly running the flame and heating it from all sides.

Making a muffle furnace requires a lot of time and resources. It is advisable to build it for constant use.

The coolant can be in a bucket or any other container that will ensure complete immersion of the part with an oil thickness of the 5 largest sections of the part:

one part under the hardened product;
two on top.

The part must be moved slowly in the coolant. Otherwise, a steam jacket will form.

Self-production of a chamber for hardening metal

The simplest semblance of a muffle furnace is made from refractory brick, fireclay clay and asbestos:

Wind copper wire onto the mandrel. For home voltage, a cross section of 0.8 mm is suitable. Leave long ends.
Place the spiral inside the bricks and fix it with clay, coating the entire inner surface.
Make a pallet inside - a platform for placing workpieces. To do this, you need to mix clay with asbestos.
Thermal insulating material can also be placed outside, reducing the heat transfer of the walls.
Connect the ends of the wire to the wires with a plug.
At the back, seal the hole between the bricks hermetically.
Build a lid in front that will open.

All materials should dry at room temperature.
This will take several days. Then you can lay the part on the insulating material and heat it. Hardening an ax at home.

Defects during hardening of steel

When hardening steel, 2 groups of defects arise:

The first are associated with uneven, spotty hardening and the discrepancy between the resulting hardness and the requirements in the drawing. Such defects are mainly caused by improper cooling or poorly performed heat treatment.

Uncorrectable items include chips, cracks, and complete destruction of parts. The reason most often lies in low-quality metal.

Hardening significantly changes the structure and performance properties of the metal. You can do it yourself using simple parts. It is necessary to know exactly the grade of steel, its hardening temperature and the cooling medium.

Source: https://metalloy.ru/obrabotka/termo/zakalka-stali

Instructions on how to harden steel at home

We will not explain what hardening of metals is, using scientific terms and phrases, because our article is for people who are interested in how to harden steel at home.

And, therefore, all information devoted to this issue should be as accessible as possible to understanding and application in practice.

So, in normal language, hardening is an increase in the strength of a metal by heating it to high temperatures and then cooling it in a liquid or air environment.

How to harden?

Which significantly increases the cost of this event.

How to harden stainless steel at home: instructions and safety precautions

When working with metal, people often wonder how to harden stainless steel. There are several ways. Hardening metal is a labor-intensive procedure. It is necessary for the products to be strong.

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Currently, industrial metal hardening is used. It is produced in special thermal ovens. Many people are interested in how to harden stainless steel at home. This is difficult to do without special equipment. At home, you can make stainless steel harder and remove softness. In today's article we will look at how to achieve this.

Why is this necessary?

Before hardening stainless steel, you need to understand why this procedure is necessary. If you temper steel properly, it will not bend easily. After heat treatment, the product will not crumble.

It is important not to overdo it with hardening, otherwise the metal will become very brittle. In this case, the product will have to be released. Many people do not know how to harden a knife so that the blade is strong and does not bend when cutting. This type of work can be done at home if you follow safety rules. It must be remembered that steel should not be overheated. If it becomes too hard, the knife will not cut well.

There are two options: the entire product is hardened, or only part of it. The first option is called global hardening of the metal, and the second – local.

General sequence of work

To properly harden a stainless steel knife, you need:

Heat the metal part of the product. There is no need to heat the handle.
Wait until the knife turns scarlet. The metal should heat up evenly.
You need to heat the blade for no more than 10 minutes, after which it is placed in sealing wax and immediately removed.

After work, you need to remove any remaining sealing wax from the blade. Next, wipe the surface with turpentine.

What do you need to work with stainless steel?

It is necessary to prepare the necessary materials in advance and take care of good equipment. If the house does not have an electric stove, then a regular gas burner is suitable for the operation. You need to purchase wax and turpentine.

How does the metal change during the work?

Many people make blanks for knives at home. This job requires certain skills. Before you harden a knife at home, you should find out how the process works and what happens to the metal.

During operation, the steel becomes hot. Depending on the material from which the sheet is made, it acquires a red or white tint. During the hardening process, the metal becomes stronger than it was before the procedure. Strength increases in the following cases:

When the alloy heats up to a certain point. The process of destruction of the crystal structure begins.
The metal is transformed into a soft mass. Crystals become mobile. They become fine-grained. After the product is cooled, the grains do not lose their structure. A strong bond develops between them. As a result, the steel becomes strong, but at the same time brittle.

Many people are interested in how to harden a knife. Experts advise working only with the cutting edge. In this case, the product will last a long time.

Method of testing metal for hardness

Many people use a stainless steel knife in everyday life. If they don’t know whether it needs heat treatment to increase wear resistance, they look at the degree of hardness of the metal.

What it is? The hardness of a metal is usually understood as its resistance to loads from strong objects. There is a special Rockwell technique. It consists of pressing a steel ball. Strong balls and diamond cones with an apex angle of 120° and a rounded sharp end are used as indenters.

Due to its simplicity, this method is one of the most common methods for testing materials.

How to determine the degree of hardness of a metal without special devices?

At home, you can determine the degree of hardness of a product without a device. To do this, you should stock up on a needle file. It can be used to determine the hardness of a flat surface. This method also works with rounded surfaces. If the edge of the product is very sharp, a piece of glass is taken to check the strength.

If the metal is soft, then it will not cut the glass (at most it will leave a couple of scratches). When the metal is hard, it is difficult to take it with a file. After some effort, it may leave a noticeable mark on the glass.

If the metal has been subjected to strong hardening, then it is almost impossible to take it with a needle file. The product cuts glass easily. During the process you can hear a specific crunch.

What are the types of home hardening?

Before hardening stainless steel, you should find out what methods are available for working at home. Much depends on the correct task. It is important to consider what grade of steel the stainless steel is. There are different modes of metal hardening:

Hardening in a single environment. It is considered one of the simplest methods. It must be remembered that the method is not suitable for metal that contains a lot of carbon. If you take a sheet of this type, cracks will appear on it as a result of hardening. The product becomes fragile and in most cases loses its shape. The method is excellent for products with a low percentage of carbon.
Intermittent hardening method. It occurs in two stages. The product is cooled in water, after which it is placed in oil. You can leave the metal in the air. This method is suitable for metal with a high carbon content. It allows steel to be hardened without cracking. The method is considered difficult to perform at home. It should be used for products with high carbon content.
To harden stainless steel in stages, you must first heat the metal, and then lower it into hot water with added salt. Keep the product in the salt bath for up to 5 minutes. Gradual cooling occurs. The product will not suffer from thermal stress. The advantage of this method is that it avoids cracks and other damage to the metal. The final stage is to cool the sheet in the fresh air. This method is intended for thin metal that contains a lot of carbon.
Surface hardening of metal. It is often called partial. Many people want to figure out how to harden stainless steel using this method. In this case, you can see that the products gain surface strength. The metal core remains ductile. The method is perfect for hardening parts that can withstand heavy loads.
Subsequent release method. It is interesting because you can set the hardness of the metal to the desired depth. This method is used when working on percussion instruments. The strength of such products increases.

What is used to cool stainless steel at home?

At home, for cooling after hardening the metal, use:

Water. It quickly copes with the function of a metal cooler. It is not recommended to place metal containing a high percentage of carbon in water. The product may become deformed. This environment is suitable for low carbon stainless steel.
If a person wants to cool the product evenly after hardening, then he will need mineral oil. It allows the metal to cool slowly and does not cause deformation. This method is excellent for alloy steel.
Sodium chloride or hydroxide present in aqueous solution. The concentration of the substance should not exceed 10 percent. The metal product will cool evenly. The required method is applied to steel with a high carbon content.
Various polymer solutions. These include detergents. The method is good because it does not cause deformation of the material. There will be no defects in the product.

Table of metal cooling temperature after hardening

Recommended environment for cooling hardened metal	Suitable temperature
Water	From 20 to 80 degrees
Oil	From 20 to 200 degrees
Saline solutions	From 20 degrees and above to infinity

What do you need to know to carry out the stainless steel hardening procedure at home?

Before carrying out this operation at home, you should learn some rules:

If the metal has increased hardness, then it needs to be heated as much as possible. It is best to wait until the product turns crimson.
If the steel contains a large amount of carbon, then you need to be careful about the cooling process.
If the product requires hardening over the entire surface, then it should be heated evenly on each side.
Do not allow the stainless steel to overheat. No stains should appear on the surface as a result of incandescence.
Before starting work, you need to prepare special tongs. You will need a container to cool the metal.

Expert advice

Experts advise hardening stainless steel over an open fire. The flame of a fire is best suited for these purposes. It is recommended to use ready-made coals. They maintain the desired temperature for quite a long time.

If the product requires partial hardening, a blowtorch should be used. It is suitable for working with cutting edges and other small parts. It is important not to overexpose the parts to the fire.

Beginners often ask how to harden stainless steel according to instructions. It is also important to know what safety precautions should be followed when working with it. If the cooling phase uses oil, you must keep a distance from the container to avoid burns.

How to reduce the hardness of stainless steel by tempering?

Tempering is used to eliminate increased hardness of the metal. The product is heated to maximum temperature, and then gradually cooled in air.

For holidays, you can use temperatures not exceeding 250 degrees. In this case, the material does not lose its strength. In this mode they work with knives and other piercing objects.

It is recommended to heat springs and spirals to 500 degrees. If a person is working on parts intended for shock loads, then he can use a temperature range from 500 to 700 degrees.

How to harden stainless steel? Safety precautions

To ensure that working with metal does not harm human health, the following safety rules must be observed:

The room in which the metal hardening process takes place should be regularly ventilated. It is recommended to install a special hood in the room. Children and animals should not be allowed into the room where work is taking place.
During the process you need to use special gloves. As soon as the instruments begin to heat up, they are immersed in water until completely cooled.
When working with fire, you should follow fire regulations and do not approach the fire with flammable liquids.
If the product is hardened in oil, then the container is tightly closed with a lid.
You need to work in special protective clothing. Sleeves and legs must be covered, as there is a risk of burns to the extremities.

So, we looked at how to harden stainless steel. As you can see, this operation can be done with your own hands at home. The main thing is not to forget about safety precautions and follow the instructions exactly.

Source: https://labuda.blog/191713

How to harden metal yourself at home

Heat treatment of metals is one of the main ways to improve their mechanical and physical-chemical characteristics: hardness, strength and others.

One type of heat treatment is hardening. It has been successfully used by man in a handicraft way since ancient times. In the Middle Ages, this method of heat treatment was used to improve the strength and hardness of metal household items: axes, sickles, saws, knives, as well as military weapons in the form of spears, sabers and others.

And now they use this method of improving the characteristics of metal, not only on an industrial scale, but also at home, mainly for hardening metal household items.

What is metal hardening and its types

Hardening is understood as a type of heat treatment of a metal, consisting of heating it to a temperature, upon reaching which a change in the structure of the crystal lattice occurs (polymorphic transformation) and further accelerated cooling in water or an oil medium. The purpose of this heat treatment is to increase the hardness of the metal.

Hardening is also used, in which the heating temperature of the metal prevents a polymorphic transformation from taking place. In this case, its state is recorded, which is characteristic of the metal at the heating temperature. This state is called a supersaturated solid solution.

Polymorphic transformation hardening technology is used mainly for products made of steel alloys. Non-ferrous metals are subjected to hardening without achieving a polymorphic change.

After such treatment, steel alloys become harder, but at the same time they become more brittle, losing their ductility.

To reduce unwanted brittleness after heating with polymorphic change, a heat treatment called tempering is used. It is carried out at a lower temperature with gradual further cooling of the metal. In this way, the stress of the metal is relieved after the hardening process, and its fragility is reduced.

When hardening without polymorphic transformation, there is no problem with excessive brittleness, but the hardness of the alloy does not reach the required value, therefore, during repeated heat treatment, called aging, it is, on the contrary, increased due to the decomposition of the supersaturated solid solution.

Features of steel hardening

Mainly stainless steel products and alloys intended for their manufacture are hardened. They have a martensitic structure and are characterized by increased hardness, leading to brittleness of products.

If you heat treat such products by heating to a certain temperature followed by rapid tempering, you can achieve an increase in viscosity. This will allow the use of such products in various fields.

Types of steel hardening

Depending on the purpose of stainless steel products, it is possible to harden the entire item or only that part of it that must be functional and have increased strength characteristics.

Therefore, hardening of stainless steel products is divided into two methods: global and local.

Cooling medium

Achieving the required properties of stainless materials largely depends on the choice of cooling method.

Different grades of stainless steel undergo cooling differently. If low-alloy steels are cooled in water or its solutions, then for stainless alloys oil solutions are used for these purposes.

Important: When choosing a medium in which to cool the metal after heating, it should be taken into account that cooling occurs faster in water than in oil! For example, water at a temperature of 18°C can cool an alloy by 600°C in a second, but oil by only 150°C.

In order to obtain high metal hardness, cooling is carried out in running cold water. Also, to increase the hardening effect, a brine solution is prepared for cooling by adding about 10% table salt to the water, or an acidic medium containing at least 10% acid (usually sulfuric) is used.

In addition to the choice of cooling medium, the cooling mode and speed are also important. The temperature decrease rate must be at least 150°C per second. Thus, in 3 seconds the temperature of the alloy should drop to 300°C. A further decrease in temperature can be carried out at any speed, since the structure fixed as a result of rapid cooling will no longer be destroyed at low temperatures.

Important: Cooling the metal too quickly leads to its excessive fragility! This should be taken into account when hardening yourself.

The following cooling methods are distinguished:

Using one medium, when the product is placed in a liquid and kept there until completely cooled.
Cooling in two liquid media: oil and water (or saline solution) for stainless steels. Products made of carbon steel are first cooled in water, since it is a fast cooling medium, and then in oil.
Using the jet method, when the part is cooled with a stream of water. This is very convenient when you need to harden a specific area of the product.
Using the method of step cooling in compliance with temperature conditions.

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Temperature

The correct temperature regime for hardening stainless steel products is an important condition for their quality. To achieve good characteristics, they are uniformly heated to 750-850°C, and then quickly cooled to a temperature of 400-450°C.

Important: Heating the metal above the recrystallization point leads to a coarse-grained structure, which worsens its properties: excessive brittleness, leading to cracking!

To relieve stress after heating the metal to the desired hardening temperature, step-by-step cooling of products is sometimes used, gradually lowering the temperature at each heating stage. This technology allows you to completely remove internal stress and obtain a durable product with the required hardness.

How to harden metal at home

Using basic knowledge, you can harden steel at home. Heating of metal is usually carried out using a fire, electric muffle furnaces or gas burners.

Hardening an ax at the stake and in the oven

If you need to give additional strength to household tools, for example, to make an ax more durable, then the easiest way to harden it can be done at home.

During manufacture, axes are stamped with a mark by which you can identify the grade of steel. We will look at the hardening process using U7 tool steel as an example.

The technology must be performed in compliance with the following rules:

1. Annealing . Before processing, dull the sharp edge of the blade and place the ax in a burning brick oven to heat. The heat treatment procedure must be carefully monitored to prevent overheating (permissible heating is 720-780°C). More advanced craftsmen recognize the temperature by the color of the heat.

And beginners can find out the temperature using a magnet. If the magnet stops sticking to the metal, it means the ax has heated up above 768°C (red-burgundy color) and it’s time to cool down.

Use a poker to move the hot ax to the oven door, remove the heat deeper, close the door and valve, leave the heated metal in the oven for 10 hours. Let the ax gradually cool down with the stove.

2. Hardening of steel . Heat the ax over a fire, potbelly stove or stove until dark red - temperature 800-830°C (the magnet has stopped magnetizing, wait another 2-3 minutes).

Quenching is performed in heated water (30°C) and oil. Lower the ax blade into the water 3-4 cm, moving it vigorously.

Next, place the ax in a container with oil; if the oil catches fire, cover the container with a thick cloth. Keep in oil until completely cool.

3. Release of the ax blade . Tempering reduces the brittleness of steel and relieves internal stress. Sand the metal with sandpaper to better distinguish the colors of the paint.

Place the ax in the oven for 1 hour at a temperature of 270-320°C. After standing, remove and cool in air.

heat treatment of an ax at home, three stages: annealing, hardening, tempering.

Hardening the knife

It is advisable to use furnaces to harden metals yourself. For household items in the form of knives, axes, drills and others, small muffle furnaces are the most suitable. In them you can achieve a hardening temperature much higher than on a fire and it is easier to achieve uniform heating of the metal.

You can make such a stove yourself. You can find many simple design options on the Internet. In such ovens, a metal product can be heated to 700-900°C.

Let's look at how to harden a stainless steel knife at home using an electric muffle furnace. For cooling, instead of water or oil, melted sealing wax is used (can be obtained from a military unit).

The sequence of the hardening process is as follows:

the knife (without a handle, if it is wooden) is placed in a cold oven;
turning on the closed oven, heat it together with the knife until the blade turns bright red (800-900°C);
Using a hot knife blade, cut the sealing wax up to 10 times, plunging 1.5 cm into it;
the procedure is repeated up to 5 times, heating the knife blade and cooling in wax;
Remains of sealing wax are removed with turpentine using a dampened cloth.

It is better to do the procedure in the fresh air; sealing wax smells terrible when melted. Also, the knife blade can be heated over an open fire.

other ways to harden a knife at home.

Source: https://plavitmetall.ru/obrabotka/zakalka-stali-v-domashnix-usloviyax.html

Hardening stainless steel at home - Metals, equipment, instructions

Hardening the metal increases the hardness of the product by 3-4 times.

The need for this procedure arises when you need a metal object to cut glass without effort.

It happens that the need to harden a metal tool arises due to the fact that it is either not hardened to the required degree, or, conversely, it was overdone in hardening it.

In the first case, metal objects, such as drills, become jammed, in the second they literally crumble.

It is unlikely that you will be able to check in the store how well a metal tool is hardened.

Although the possibility of such verification exists. You need to take a file and run it along the edge of a cutting object - a knife or an ax.

The fact that the file sticks and sticks to the metal means that the product has not been hardened enough.

In this case, its edge will be too soft and pliable.

If the file moves away from the object with ease and seems to be stroking it, and the hand does not feel any uneven places while pressing, then the product has become overloaded on the face.

If you still have metal equipment in your hands that needs additional hardening, then it’s okay.

You can harden a knife with your own hands, even without resorting to complex technologies, that is, at home.

The only thing you need to remember: it is forbidden to harden low-carbon steels.

But it is quite possible to increase the strength of carbon and tool steels.

Hardening technique

Simply put, hardening technology consists of two actions - heating the sample to a high temperature and cooling it.

Just don’t assume that everything is elementary, because groups of metals differ in their unique structure and characteristics.

Do-it-yourself heat treatment of metal is justified if:

there is an urgent need to strengthen the material, for example, to “strengthen” the cutting edges of kitchen utensils or tools, such as a chisel or chisel;
it is necessary to increase the ductility of the object, which makes it easier to work with metal, for example, the hot forging process.

The price of professional hardening of 1 kg is 100-200 rubles. Hardening small parts will cost less. The price for this service ranges from 6 to 20 rubles.

If you harden equipment at home, it is important to know some of the subtleties of this process.

Heating requires uniformity; it must occur without the appearance of black or blue spots on the object. Under no circumstances should the sample be heated to extreme levels.

The fact that the product is heating up correctly will be indicated by its coloring in a bright red color.

For hardening a metal object such as a drill, equipment such as an electric furnace or thermal oven, as well as a blowtorch and a large fire are suitable.

What is more suitable - a furnace, an electric furnace or an open fire depends on the temperature required by the type of metal being processed.

When it is necessary to harden not the entire surface of a metal object, but only a certain place, jet hardening is used. It assumes that a stream of cold water is directed at the object pointwise.

The cooling method for a drill, screwdriver, chisel or crimp may vary. It can be carried out in several stages, one-time and abruptly, or gradually. It all depends on the type of metal.

If you plan to carry out an operation with one cooler, then special equipment, such as a bucket or barrel, is prepared. Even a bath is suitable for this.

This cooling method is ideal for products made from carbon or alloy steel.

When a two-stage cooling scheme is needed to lower the temperature of a metal object, two different media are used. This procedure also ensures the tempering of the metal.

Cooling with oil is carried out secondarily, since there is a risk of ignition due to high temperature.

Temperature conditions and other hardening indicators are reflected in the table below.

Hardening steel over an open fire

It is possible to harden metal at home. For an easy and useful hardening process, you need to light a fire and prepare two large containers. There should be a lot of hot coals in the fire.

Diesel or motor oil is poured into one container, clean water, preferably from a well, is poured into the other. You should first prepare a tool with which you will need to hold the hot product.

It is advisable to find blacksmith pliers, but if they are not among the tools, you can arm yourself with something else similar to pliers.

When the preliminary work is done, metal drills or other objects are placed in the very center of the flame, that is, on hot coals.

The rich white coals are hotter than the rest. It is important to watch the hardening process - the flame should be crimson, not white. If the fire is painted in the latter color, there is a risk of overheating and even burning of the metal.

It is necessary that the color is distributed evenly across the entire area of the fire. Black spots should not appear on the edge of the product that is being hardened.

And if the metal turns blue in places, this indicates that the material has softened too much and become too plastic. This should not be allowed under any circumstances.

Therefore, the process requires increased care, because you can overdo it and heat the ax blade white-hot.

When the metal equipment is heated in the fire, it is time to remove it from the high heat.

A hot object must be lowered into a container of oil many times with a frequency of 3 seconds, gradually increasing this period of time.

You cannot hesitate with these actions; you need to carry out operations to harden the metal edge quickly and sharply.

When working with your own hands, the element should be dipped into a container with liquid until the color loses its saturation and brightness.

Next, the object is immersed in a bucket filled with water, which will have to be shaken a little.

At this stage, do not forget to be careful, as oil droplets on a knife or ax may burst into flames if they end up in water.

The table shows how to correctly and incorrectly immerse various parts, including drills and disc cutters, in water:

Very often there is a need to harden drills. It is not recommended to immerse thin long elements flat into water, otherwise the lower layer of metal, cooled first, will shrink.

Drills should be lowered into the liquid with the thicker end.

If you follow all the rules and precautions, then hardening yourself will not seem like a complicated and dangerous procedure. It will bring the desired guaranteed effect.

But sometimes at home you have to harden steel equipment or melt non-ferrous metal. Such operations require extremely high temperatures, 700-900 degrees.

And only a muffle furnace or an electric furnace can heat metal objects to this level. You can make a muffle furnace yourself. It is unlikely that you can make an electric oven at home.

How to make a chamber for hardening metal?

A homemade muffle furnace is a must-have in the household today. It allows you to heat treat the product without unnecessary steps.

To make a stove with your own hands, you will need fireproof clay, which is used to cover boilers. A chamber no more than 1 cm thick is created from this material.

Welding stainless steel semi-automatically in argon

And its dimensions must fit into the following parameters of length, height and width - 210 * 105 * 75 mm.

When fashioning a muffle furnace with your own hands, you need to have a mold made from cardboard in advance. It is better to soak it in paraffin so that it does not stick.

The clay is spread on the mold from the wrong side, because this way it will not shrink during drying. When the clay hardens, it will move away from the edges of the mold on its own.

The same refractory clay will serve as the material for making the oven door. Then the homemade muffle furnace in the form of two parts should dry in the open air.

Then it is completely dried in an oven at a temperature of one hundred degrees.

Then the door and chamber are fired, gradually increasing the temperature to 900 degrees. These parts should then gradually cool in the oven itself.

Then the door is attached to the oven, carefully using a file and sanding the surface with sandpaper.

You need to wind 18 meters of nichrome wire around the camera. Its thickness should be 0.75 mm. The first and last turns are twisted.

To avoid the risk of a short circuit, the distances between the turns of the wire are smeared with clay. Another layer about 12 cm thick is spread on the dried layer of clay.

To make the case easy to assemble, it is better to make it with two removable covers, which are secured with screws.

A door is attached to the front lid on a hinge; it should open horizontally. It is necessary to install a ceramic part on this door using bolts and gaskets.

The remaining gaps are again filled with clay, and the edges of the wire are removed onto the back cover of the frame.

Then a connector and a standard cord with a plug are prepared. All holes between the heating elements and the frame must be filled with asbestos chips.

To install a thermocouple and be able to monitor the heating process, it is advisable to make two holes in the chamber.

The first is 1 cm in diameter, the second is 2 cm. Closable metal curtains need to be attached to these holes.

The homemade stove design weighs 10 kg and can heat up to 950 degrees within an hour.

Its presence facilitates the process of hardening a drill, file, matrix and many other metal products. How a homemade stove hardens metal equipment is shown in the video.

Although muffle equipment that hardens metal is not the only option. Heat treatment can be performed by chamber and flame equipment, electric furnace, thermal furnace, as well as bath furnaces.

In any case, making a hardening device yourself is more profitable than buying it. For example, the average price of a muffle furnace is 40 thousand.

An electric furnace is used to harden metal at a temperature of about 1300 degrees and the electric furnace costs much more.

Source: https://spb-metalloobrabotka.com/zakalka-nerzhaveyki-v-domashnih-usloviyah/

How to harden stainless steel at home: video, tips, nuances

Modern hardening technologies and their correct selection provide high quality steel, in which the proportions of strength, ductility and toughness are optimally maintained.

Products treated in this way have significantly improved performance characteristics.

Hardening of steel in an induction channel installation