What electrodes should be used to cook 40x steel?

40X steel welding technology

Essentially a designer (mechanical engineer)
Essentially a constructor (mechanical engineer)

Previously, we used only 40X steel in production, that is, 2 parts were welded from the same steel, and after heat treatment (hardening), now the question arose about replacing the material of one of the parts with 09G2S steel. The part works in tension.

Previously, we welded with UONI electrodes using conventional arc welding, now after replacing the material, what should we cook with? will the connection be reliable?

For information: we make chains that dig the ground, these 2 parts are the chain pin and the chain jaw. The finger is welded into the cheek, so we want to replace the cheek material with 09G2S. https://forum.i-mash.ru/topic_1028

Essentially a designer (mechanical engineer)

Essentially a designer (mechanical engineer)

Essentially a designer (mechanical engineer)

ChNB

, it feels like you are still an inexperienced designer. Therefore, they don’t really listen to you, and you yourself don’t really insist. In general, designers/technologists are hired so that they can at least point out the shortcomings of designs/technologies. We must do this confidently, without hesitation or doubt. First, of course, having understood the issue. If after that they insist on their version, that’s their business. Ours is to voice the problem and propose solutions.

PS And one more thing. We didn't hear what was cooking. Maybe it would be much easier not to cook, but to make a couple of holes for fastening? I worked in one enterprise where they were used to welding equipment (also from 40X). The welding held up, although it cracked, but there were problems with the accuracy of the parts on them. I convinced it to be secured with screws/pins. The problem has disappeared. Everyone is happy.

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Welded connection technology

Step 1. Preparing metal parts:

• adjustment to size, shape;
• cleaning metal from oxidation and rust.

Step 2. Preparing metal edges for welding. This point is especially relevant when working with thick workpieces (more than 3 mm):

• gap width 1-2 mm;
• cutting angle 45-60 0 ;
• shoulder straps of joints for parts of different thicknesses.

Step 3. Preparing tools and equipment:

• requirement for the material of welding wire and electrode : their composition must correspond as closely as possible to the grade of steel being welded;
• To connect 40X steel using the welding method, it is convenient to use technical tables for setting the current value depending on the thickness of the surfaces being welded and the size of the electrode.

Step 4. Warm up the parts before welding begins.

40X steel is sensitive to temperature changes and cracking due to this. You need to warm up the part with a gas torch before any type of welding.

Step 5. Point-to-point grab the parts to be joined.

To avoid deformation or shifting of the parts being welded, it is practical to make a spot clamp along the entire length of the planned weld.

Step 6. Welding process using the selected method.

Step 7. Warming up the welded parts.

After welding, heating is needed to relieve stress in the parts and evaporate residual hydrogen. This procedure is especially important when resistance spot welding.

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Welding steel 40x

40x steel is a structural alloy metal that is widely used in industry. Technical characteristics and composition of the material are determined according to GOST 453-71. The carbon content in it should be approximately 0.4%, and chromium - 1%. Welding 40X steel is a rather complex process, since the material is a difficult-to-weld metal. To solve this problem, special technologies and methods are used.

The main problem is that when welding there is a high probability of cracks, cavities and other defects. But the characteristics of the metal itself are very useful when creating metal structures, so you have to look for suitable methods for welding 40x steel.

Welding medium and high carbon steels

Medium carbon steel structures can be welded well if the welding rules and the following additional guidelines are strictly observed.

In butt, corner and T-joints, when assembling the elements being connected, the gaps provided by GOST should be maintained between the edges so that welding transverse shrinkage occurs more freely and does not cause crystallization cracks.

In addition, starting from a steel thickness of 5 mm or more, edges are cut in butt joints, and welding is carried out in several layers. The welding current is reduced.

Welding high carbon steel

Welding high-carbon steels of grades VSt6, 45, 50 and 60 and cast carbon steels with a carbon content of up to 0.7% is even more difficult. These steels are mainly used in castings and tool making.

Their welding is possible only with preliminary and concomitant heating to a temperature of 350-400 ° C and subsequent heat treatment in heating furnaces.

When welding, the rules for medium carbon steel must be followed; we will discuss this process below.

Welding technologies for high carbon steels

Good results are achieved when welding narrow beads and small areas with cooling of each layer. After welding is completed, heat treatment is required.

Methods of welding steel 40X

The highest quality and most common method of welding this type of metal is welding steel with 40x argon. The electric arc apparatus provides a high enough voltage for melting, and the gas protects against the influence of foreign objects that lead to defects. In this case, filler material of the same brand as the workpiece is selected. It is also possible to cook with gas using acetylene. This is a simpler but less reliable method. It may not be suitable for very thick sheet layers, so additional preparation of the metal for welding may be required. The simplest method, which is inferior in reliability to the previous ones, is ordinary manual welding with special electrodes.

Technology and features of steel welding

In modern industry, a wide variety of steel is used for welded structures.

It can be stainless or ordinary, high or low carbon, heat resistant and so on.

Various technologies are used for welding them, but the simplest is welding with a semi-automatic machine or inverter. In this article we will talk about the features of popular types of steel and how to weld them.

Welding tool steel

Tool steel is a type of steel containing less than 1% carbon. This steel is hard and durable, but not wear-resistant, so it is used only in the manufacture of tools. In addition, it has a low purchase price, which makes production profitable.

It is recommended to weld tool steel with a special electrode and using an inverter. Electrodes must be designed specifically to work with this type of steel. We recommend UONI-13/NZh/20X13 rods and a mid-price welding inverter. Be prepared for the fact that welding tool steel will require a lot of effort and patience from you. This is due to the low carbon content.

Welding structural steel

Structural steel is used much more often than tool steel. Everything is made from it: from small parts to factory machines. It is this category that includes welding of 40x steel, 30xgsa steel, 35xgsa steel and other other grades.

What is structural steel? This is a very interesting metal in composition. It consists of various impurities, in particular phosphorus and sulfur. The more of these components there are in the composition, the more unreliable the steel will be, so you need to monitor this indicator. Structural steel can be ordinary, high-quality, high-quality and especially high-quality.

As you understand, the latter type of structural steel contains a minimum of impurities, due to which it is possible to obtain truly high-quality and durable metal.

Well, ordinary structural steel contains the most impurities; it is considered the most short-lived.

By the way, this classification also has separate subgroups (they differ in the presence of some additional chemical components). But we will not describe the classification in detail so as not to confuse you.

Choosing a method

For home use, when the product will not bear much responsibility, the simplest method is used - arc welding. After all, this is the cheapest method that does not require special preparation. To weld 40x steel, electrodes specially designed for this purpose are required. In industry, electric arc welding with argon is used for critical facilities. Despite the high cost, this is one of the most reliable methods that ensures a long service life of the structure. To make the process cheaper, you can use gas welding using acetylene. The result will be very similar, and in terms of creating ceiling and vertical seams, it will also be more convenient. Other types and methods of metal welding are used quite rarely.

Regardless of the method chosen, the surface should be carefully prepared before welding.”

Weldability of 40X steel and its properties

Metal does not weld well. If the process of melting and the formation of a weld pool occurs relatively normally, since only increased viscosity is manifested here, but the whole series of problems that arise on the seam after completion often lead to its unsuitability for use. Welding 40xn steel perfectly demonstrates its temper brittleness properties. During the welding itself, as well as after it, cracks and other defects, including deformations, may appear. This occurs due to sudden changes in temperature that are caused by an electric arc, which is especially noticeable when welding thin metal with an electrode. This also occurs when voltages are generated due to insufficient protection. Thus, additional steps are needed both before and after welding.

Tool selection

There is exactly one criterion when choosing a welding wire or electrode material. Their metal should correspond as closely as possible to the composition of that used in the blanks. You just need to pay attention to the thickness so that it matches the thickness of the parts, since the welding depth should be maximum due to the difficulties in the flexibility of this grade of steel. A more important parameter is protection. Welding 40x steel semi-automatically must be supported by a shielding gas environment, and when manually welding, the electrodes must have a coating designed to work with this grade of steel. Electrodes of the E85 brand are suitable here, which have a reduced hydrogen content in the coating, and are also resistant to cracking when working with complex metals.

Modes

To improve the quality of the joint, you should use already proven parameters, which are calculated for each workpiece thickness and the corresponding weld position. This will greatly facilitate the work process.

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Welding alloy and carbon hardenable steels

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Metal welding

Welding alloy and carbon hardenable steels

Steels that are intensively hardened during welding with the formation of martensitic and intermediate structures include the following groups of steels: – structural low- and medium-alloy medium-carbon steels with a carbon content of up to 0.5%.

These steels are distinguished by high strength combined with satisfactory ductility due to complex alloying. These include pearlitic steels 35Kh, 40Kh, 35G2, 50G2, ZOKHGT, ZOKHGSA, 35KhGSNA and martensitic steels ZZKHZNVFMA, 30Kh2NMFA, etc.

; – heat-resistant and heat-resistant steels 15X5, 15Kh5MA, 15Kh5VF, 20KhZMVF, ZOKHMA, 38KhMYuA, 25Kh1M1F, etc.; – medium and high carbon steels 30, 35, 40, 45, 50, 60, 25G, 35G, 45G.

High-carbon steels are, as a rule, not used in welded structures. The need for their welding arises during surfacing and repair.

Characteristic general difficulties in welding these steels are: – formation of hardening structures during cooling after welding and, in connection with this, a tendency to cold cracks; – danger of hot cracks; – softening of the weld joint metal compared to the base metal.

Depending on the degree of alloying and carbon content, these steels are classified as satisfactory, limited, or poorly weldable steels (see Table 2).

The difficulty in welding these steels is the formation of hardening structures and cold cracks, therefore the main metallurgical and technological measures to ensure the quality of welded joints are based on eliminating this difficulty and are common to most of the steels under consideration.

Basic measures to ensure a high-quality welded joint. Pre-welding - when developing a technology, the main attention should be paid to the rational choice of materials: base and filler metal, protective equipment. The base metal with a reduced content of carbon and impurities (sulfur, phosphorus) has higher resistance to cold and hot cracks.

To increase the ductility of the weld and increase crack resistance, the carbon content in the filler metal should be less than 0.15%; It is advisable to provide a wider groove of the edges in order to ensure the formation of the weld mainly due to a more ductile filler metal. High technological strength of the weld is achieved by limiting the content of alloying elements in the filler wire to the following limits,%: 0.15 C; 0.5 Si; 1.5 MP; 1.5 Gr; 2.5 Ni; 0.5 V; 1.0 Mg; 0.5 Nb.

As protective agents, it is necessary to use coatings and fluxes of the basic type, as well as inert gases (for alloy steels). To reduce welding stresses, which are one of the causes of crack formation, it is necessary to avoid rigid nodes, clusters of seams, intersecting and closely spaced seams during design.

During welding, the following technological measures are provided: 1. Careful preparation and assembly for welding, minimal displacement of edges (less than 10-15% of thickness), minimal clearance, high-quality tack welding and edge cleaning;2. Regulation of the thermal cycle of welding to ensure the required cooling rate of the weld and heat-affected zone.

The cooling rate is regulated by changing welding modes (current value, welding speed, heat input), using special technological methods (welding in short and long sections, applying an annealing bead, welding in a slide, cascade, etc.) and using heating, which can be preliminary or accompanying and subsequent ones.

Heating is the most radical way to regulate the cooling rate and is used when regulation of welding modes and special technological methods fail to ensure the required cooling rate and structure of the welded joint. The higher the content of carbon and alloying elements, the higher the heating temperature.3.

Reducing the hydrogen content in the weld, since hydrogen is one of the main reasons for the formation of cold cracks.

This is achieved by using electrodes with calcium fluoride coatings and basic fluxes, protective gases with low humidity; welding on direct current of reverse polarity; thorough preparation for welding of the welded and filler metal (cleaning, dehydration) and protective materials (drying, calcination).

4. Rational sequence of sutures in order to reduce residual stresses and deformations.

After welding, to prevent cold cracks, high tempering is immediately performed to relieve residual stresses and stabilize the structure.

To ensure equal strength of the welded joint, after welding, a complete heat treatment of the product is carried out, which consists of hardening and subsequent high tempering or normalization.

If the dimensions of the product and the available equipment allow complete heat treatment, then the chemical composition of the weld metal should be close to the chemical composition of the base metal.

If complete heat treatment is not possible, then the problem of equal strength is solved by selecting welding modes and alloying through a filler wire.

When welding hardening steels, the main types of fusion welding are used - manual arc, submerged arc, shielding gas, electron beam, electroslag using welding materials that provide the specified strength and chemical composition of the weld.

Read more:

Welding of high alloy steels

Source: https://pereosnastka.ru/articles/svarka-legirovannykh-i-uglerodistykh-zakalivayushchikhsya-stalei

Features and requirements for steel 40X

All manufactured metal products, including 40X steel, must meet the requirements of state standards.

GOST 4543 of 2016 determines the composition and required performance qualities of the material.

Each type of product made from this steel has its own GOSTs, which regulate the features of the entire product range.

The steel rolling industry produces three types of blanks from 40X steel: circle, hexagon and sheet.

Steel 40X: characteristics, application, hardness and weldability of steel 40X

Steel grade: 40Х (substitutes 45Х, 38ХА, 40ХН, 40ХС, 40ХФ, 40ХР).

Class: alloy structural steel.

Industrial use: axles, shafts, pinion shafts, plungers, rods, crankshafts, camshafts, rings, spindles, mandrels, racks, sponge rings, bolts, axle shafts, bushings and other high-strength upgradeable parts.

Hardness: HB 10 -1 = 217 MPa

Weldability of the material: difficult to weld. Welding methods: RDS, ESW, heating and subsequent heat treatment are required. KTS - subsequent heat treatment is required.

Forging temperature, oC: beginning 1250, end 800. Sections up to 350 mm are cooled in air.

Flock sensitivity: sensitive.

Tendency to temper brittleness: prone.

Type of delivery:

• Long products, including shaped steel: GOST 4543-71, GOST 2590-2006, GOST 2591-2006, GOST 2879-2006, GOST 10702-78.
• Calibrated rod GOST 7417-75, GOST 8559-75, GOST 8560-78, GOST 1051-73.
• Polished rod and silver GOST 14955-77.
• Thick sheet GOST 1577-93, GOST 19903-74.
• Strip GOST 103-2006, GOST 1577-93, GOST 82-70.
• Forgings GOST 8479-70.
• Pipes GOST 8731-74, GOST 8733-74, GOST 13663-86.

Steel 40X and its characteristics

In our company you can order a variety of metal products used in everyday life, construction and industry. Its qualities, properties and characteristics depend on the material from which rolled metal is made.

We invite you to familiarize yourself with the various types of steel. For example, steel grade 40X, which belongs to the structural alloy class, is especially popular. In this section you will learn more about this material.

If you have questions about products or want to place an order, then call our specialists! Company managers work around the clock.

This material contains 0.40 percent carbon and less than one and a half percent chromium.

This material is difficult to weld. You can weld using the manual arc method or the electroslag method, but first you need to preheat the steel and then perform heat treatment. Resistance spot welding also requires further heat treatment.

The hardness of steel 40X is as follows: HB 10 -1 = 217 MPa.

Substitutes for this material can be brands 45X, 38XA, 40XH, 40XC, 40ХФ, 40XP.

If you are going to forge this steel, then at the beginning of the process you need to heat it to 1,250 degrees Celsius, and at the end cool it to 800 degrees. If products with a cross-section of up to 350 millimeters were forged, they must be cooled in air.

You can find out more information from the tables located on the website.

Properties and composition

This grade of steel has the required properties due to its chemical composition:

• iron (up to 97%);
• silicon;
• manganese;
• nickel;
• sulfur;
• phosphorus;
• copper;
• chromium.

The letter X indicates the presence of an alloying element - chromium (0.8-1.1%), which increases the steel's resistance to corrosion. 40 is an indicator of carbon concentration (0.44%).

Along with the advantages, this brand also has disadvantages that you need to know and take into account when working with products made from it:

• fragility , susceptibility to shock;
• poor weldability.

According to the degree of weldability of the structure, steel 40X belongs to group 4.

Used for making:

• shafts - gears of gearboxes;
• gear wheels of reducers;
• sheet metal is used for stamping;
• frame structures are sheathed with sheets;
• pipes : heating systems and transportation of liquids;

Also used in mechanical engineering, transport, in the construction of railway bridges, etc.

Steel 40Х

Among all the different materials that are used in mechanical engineering and other fields, steel is the most widely used.
It is available in a wide variety of designs; performance largely depends on the chemical composition. The alloying process allows you to give the material certain performance qualities. For example, a high concentration of chromium leads to increased corrosion resistance. 40X steel has become quite widespread. It is represented by an alloyed structure that can withstand minor exposure to moisture and some chemicals.

Steel 40X, the characteristics of which can be improved by heat treatment, has a number of features, which we will discuss in more detail later.

Steel 40x

Decoding steel 40X

In the CIS, the GOST 4543-2016 standard is used, which allows you to determine not only the chemical composition, but also the various performance qualities of the material.

Download GOST 4543-2016

Steel 40X GOST defines the following substances in its composition:

1. The first number 40 is used to indicate the main element in the composition, which is carbon. As a rule, most of the composition is iron, and carbon, the concentration of which is 0.44%, determines the main performance characteristics.
2. The next letter X indicates that the composition contains an alloying element represented by chromium. The absence of a number after the letter indicates that the concentration of the element is 1.1%. As previously noted, chromium increases the corrosion resistance of the structure. However, the steel grade in question, 40X, is not characterized by high anti-corrosion qualities.
3. Considering 40X GOST, we note that the composition includes a fairly large amount of nickel, silicon and manganese. They determine some of the performance characteristics of the metal, but they are not noted in the markings.

Deciphering allows you to determine the chemical composition and basic performance qualities of the material. It is worth considering that foreign manufacturers use different standards when labeling materials, but the chemical composition of analogues is approximately similar.

Chemical composition of steel

As previously noted, the chemical composition of 40X steel is determined by markings. However, it does not reflect the entire composition. Steel grade 40X is characterized by the following features:

1. The carbon concentration in the composition ranges from 0.36% to 0.44%. Note that manufacturers cannot provide a more accurate indicator due to the complexity of the metal production process.
2. Chromium is the main alloying element; the metal contains 0.8-1.1%.
3. The alloy production process determines that nickel, silicon and manganese are included in the metal. Their concentration is no more than 1%, but even a small amount leads to a change in performance characteristics.
4. The composition contains harmful elements, for example, phosphorus and sulfur. Their concentration is strictly regulated.
5. Copper is also included in the composition, but it is about 0.035%. That is why the concentration of this element does not change the basic performance characteristics.

Chemical composition of steel 40x according to GOST

Refining of the structure with various alloying elements is carried out using strong deoxidizers, after which slag is introduced, treated with silicon and carbon.

Physical and mechanical properties

When considering the mechanical properties of 40X steel, it should be taken into account that it has high hardness and strength, the structure can withstand significant loads and is not subject to destruction during operation. Steel 40X is characterized by the following positive qualities:

1. Quite high corrosion resistance, which is achieved by including chromium in the composition.
2. High strength indicators. Hardness is measured in various indices, HRC and HB are often used. The hardness indicator corresponds to a value of 217 MPa.
3. When choosing a more suitable material, attention is paid to specific gravity. The density of 40X steel is 7820 kg/m3.

Properties of St 40x

The elastic modulus and yield strength can vary over a fairly wide range, depending on temperature. For example, with a significant increase in temperature, the elastic modulus decreases. The yield strength determines how applicable the alloy is when producing workpieces by casting.

The alloy also has several significant disadvantages:

1. Tempering fragility. After hardening, the structure becomes very susceptible to impact loads. The likelihood of increased brittleness can be reduced by following heat treatment technology.
2. High tendency to form flakes. It is characteristic of quite a large number of different alloys.
3. Poor weldability complicates the manufacturing process of various products. If desired, a variety of welding technologies can be used. The process is greatly simplified by preheating the structure. In addition, the structure is difficult to cut when using welding equipment.
4. Flock sensitivity is a property that determines the high probability of internal cracks appearing after casting various products. Such defects often occur during hot deformation of alloy steel. Such defects cause high concentrations of hydrogen during heat treatment. The likelihood of defects can be reduced by strictly observing the temperature regime.

Welding steel

Recently, the method of vacuumization of the alloy has been quite often used, due to which the hydrogen concentration is reduced. That is why the quality of the resulting structure increases significantly.

Application area

According to the degree of weldability of the structure, it belongs to group 4. The weld seam can cause various cracks to form. That is why the 40X material is preheated before performing welding work, which avoids simply a huge number of problems with the operation of the resulting product.

In addition, it is necessary to carry out preliminary preparation of the edges for arc welding. When using contact point technology, heat treatment is required.

Other properties of the material in question determine its wide application. The following types of workpieces are supplied to production sites:

1. Sheets. Sheet metal is widely used, for example, in cold or hot stamping. In addition, metal sheets are used for sheathing frame structures.
2. Forgings are used as a basis for creating various products.
3. Pipes are very common today, for example, when creating a heating system or for transporting various liquids.
4. Rolled metal is used in the mechanical engineering field as a blank for various parts.

Circle f 160 st 40X with turning

After heat treatment, Steel 40 can be used to produce nozzles, reamers and tap bodies.

An analogue of 40X steel can be used to produce various critical structures, for example, axles, shafts, gears, bolts or plungers.

Foreign analogues can be used to manufacture parts that will be used outdoors at low temperatures. An example is the elements of bridges and railway structures.

To significantly increase the performance characteristics of the resulting products, various heat treatments are carried out.

Hardening leads to a significant increase in surface hardness, but brittleness can only be reduced by tempering. It is possible to achieve the required indicators only if the specific features of the technology are observed.

Heat treatment

In many cases, heat treatment can significantly improve the performance of the metal. Heat treatment of 40X steel is carried out taking into account the structural features. Recommendations for performing such a procedure are as follows:

1. Hardening of 40X steel is carried out in an oil environment. This allows you to significantly improve the quality of the surface layer of the structure.
2. The 40X hardening is carried out with subsequent cooling of the workpiece. For this purpose, a conventional air or oil medium can be used. Oil can significantly improve the quality of the resulting product, while cooling in air occurs at larger sizes. The use of an aqueous environment may result in scale and other defects.
3. A vacation is required to reduce internal stress. Tempering is carried out in oil or in air.

Heat treatment of 40X steel is carried out depending on the loads for which the products are designed. The calculation is carried out depending on three critical points. Hardening is carried out at a temperature of 860 degrees Celsius.

The hourly interval is 4 hours. Tempering in air can be carried out at a temperature of 200 degrees Celsius; when using an oil bath, the figure rises to 500 degrees Celsius.

In some cases, steel 40X is normalized.

When heat treatment is carried out correctly, the hardness after hardening is approximately 217 HB. At the same time, internal stresses are significantly reduced, due to which the service life of the resulting product is significantly extended.

Properties of St 40x at elevated temperatures

In conclusion, we note that the steel in question is quite difficult to manufacture, due to which the cost increases significantly. That is why alloyed alloy is used in the manufacture of critical products that must have exceptional strength.

The surface is characterized by a fairly high resistance to moisture, but the indicator does not correspond to stainless steel. This is due to the fact that stainless steel contains chromium with a concentration of about 18%.

The inclusion of other chemical elements makes it possible to expand the range of applications of alloys.

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Welding methods for 40X steel. What to give preference to?

The main problem when welding such steel is the appearance of cracks and internal defects.

This metal can be welded using three types of welding:

• electric arc;
• electroslag;
• contact-point.

To reduce the possible occurrence of cracks, the following steps must be followed:

1. Pre-heat treatment.
2. Heating during welding.
3. When resistance spot welding, heat treatment is also performed at the end.

Arc welding

Welding seams are made by burning an electric arc.

• arc ignition - by touching the electrode to the metal part;
• maintaining arc length during operation;
• moving the electrode along the weld.

The welding connection of parts made of steel 40X is carried out with a direct current of reverse polarity, when the electrode is connected to the “plus”, and the product is connected to the “minus”. This connection of the terminals ensures rapid and significant heating of the connection area itself, and the part practically does not heat up.

There are three options for electric arc welding:

1. Manual arc . This is the simplest and most accessible method for a home craftsman or in a small workshop where great responsibility for quality is not required. It does not require special training. Minimum set of equipment: special electrode for alloy steels E85 UONI - 13/85, coated with a low hydrogen content; welding transformers and rectifiers or welding inverters.
2. Electric arc with argon , which is the most used and high-quality method of welding 40X steel. To protect the welding site from gases contained in the air, argon protection is used. Argon arc welding is an industrial option for joining alloy steel. Can be semi-automatic or automatic. The filler material is used of the same grade as the metal being welded.
3. Gas welding using acetylene . This is a cheaper and simpler method than argon welding, but less reliable. It is not suitable for thick sheets and this makes the job more difficult.

Hardening steel 40x: hardness, modes, time, temperature, technology - Turner

17.12.2019

Of all the materials used in mechanical engineering, machine tool building, instrument making and other industrial fields, steel is the most widely used.

The choice of its grades is huge; depending on its composition, any steel has certain qualities and belongs to different groups according to its indicators.

Steel 40X belongs to the class of structural alloy steels.

Chemical components included in the composition

If we consider the percentage composition of the presented alloy, the number 40 means that it contains a percentage of carbon up to 0.44%, the letter X determines the presence of an alloying additive - chromium up to 1.1%.
A more detailed composition of the chemical components is presented in the table below. An equivalent replacement for this grade can be alloys such as 40ХН, 45Х, 40ХН, 40ХС. Chemical composition of steel grade 40X

Alloy steels are produced by remelting or production using fresh charge.

If a charge is used, a preliminary calculation of the chromium content in it should take into account losses during smelting, but this value should not exceed 0.4%, otherwise the process will produce highly alloyed waste.

Refining of the metal with alloying elements is carried out with strong deoxidizers, after which slag treated with carbon and silicon is introduced. After exposure to the reducing slag, the structural steel is well deoxidized, which ensures good hardening.

Qualitative indicators

A durable and hard material that can withstand heavy loads and not be destroyed - this is how 40X steel can be assessed. Characteristics it has:

• good corrosion properties;
• resistance to temperature fluctuations;
• high strength indicators;
• aesthetic qualities.

But in addition to positive indicators, 40X steel also has negative properties. This may include:

• tendency to form flakes;
• temper brittleness;
• poor weldability.

Flock sensitivity

This is a defect that occurs during accelerated cooling of the alloy after casting, in the form of internal cracks. It can occur during hot deformation of alloy steel. It can also appear on the surface in the form of clear oval or zigzag areas.

The formation of this defect can occur due to an excess of hydrogen evolution during heat treatment. This disadvantage can be combated using high-temperature heat treatment and optimal cooling mode.

You can also use the method of vacuumizing the alloy, which will help reduce the hydrogen content as a percentage.

Tempering brittleness

It occurs during slow cooling of alloyed structural steels after tempering and is caused by a sharp decrease in viscosity.

For comparison, the viscosity value can drop by 5-10 times compared to the same indicator when the steel is rapidly cooled. Slow cooling only affects the impact strength; it does not reduce the other characteristics of the steel.

Cooling too quickly can cause internal stresses, which can lead to deformation of the product.

Welding difficulties

Steel 40X belongs to the fourth group in terms of weldability. Welding seams can lead to the formation of cracks. The manifestation of these defects can be reduced by preheating. Preliminary edge preparation is also required.

Welding work of this brand can be performed using arc welding: manual or electroslag; you can also use resistance welding. After contact point, additional heat treatment will be required. For manual welding, special electrodes for alloy steels E85 UONI-13/85 are used.

The type and position of the welded seam can be any.

Steel hardening

Hardening is a heat treatment operation consisting of heating to temperatures above the upper critical point AC3 for hypoeutectoid steel and above the lower critical point AC1

for hypereutectoid steel and holding at a given temperature followed by rapid cooling (in water, oil, aqueous solutions of salts, etc.).

• As a result of hardening, steel acquires a martensite structure and, as a result, becomes hard.
• Hardening increases the strength of structural steels and imparts hardness and wear resistance to tool steels.
• Hardening modes are determined by the heating rate and temperature, the duration of exposure at this temperature, and especially the cooling rate.
• Choice of hardening temperature.

The heating temperature of steel for hardening depends mainly on the chemical composition of the steel. When hardening hypoeutectoid steels, heating should be carried out to a temperature 30 - 50 ° above the AC3 point.

In this case, the steel has the structure of homogeneous austenite, which, upon subsequent cooling at a rate exceeding the critical hardening rate, turns into martensite. This type of hardening is called complete .

When hypoeutectoid steel is heated to temperatures AC1 - AC3, a certain amount of ferrite remaining after hardening is retained in the martensite structure, which reduces the hardness of the hardened steel. This type of hardening is called incomplete.

For hypereutectoid steel, the best quenching temperature is 20-30° above AC1, i.e. incomplete quenching. In this case, the preservation of cementite during heating and cooling will contribute to an increase in hardness, since the hardness of cementite is greater than the hardness of martensite.

Hypereutectoid steel should not be heated to a temperature above AC1, since the hardness is lower than when quenched from a temperature above AC1, due to the dissolution of cementite and an increase in the amount of retained austenite.

In addition, when cooling from higher temperatures, greater internal stresses can arise.

Cooling rate.

To obtain the martensite structure, it is necessary to supercool the austenite by rapidly cooling the steel at the temperature of the lowest stability of austenite, i.e. at 650-550 ° C.

In the martensitic transformation temperature zone, i.e., below 240°C, on the contrary, it is more advantageous to use slow cooling, since the resulting structural stresses have time to level out, and the hardness of the resulting martensite practically does not decrease.

The correct choice of quenching medium is of great importance for successful heat treatment.

The most common quenching media are water, a 5-10% aqueous solution of caustic soda or table salt, and mineral oil. For hardening carbon steels, water with a temperature of 18° C can be recommended; and for hardening most alloy steels - oil.

Hardenability and hardenability of steel.

When hardening steel, it is important to know its hardenability and hardenability. These characteristics should not be mixed.

Hardenability shows the ability of steel to increase hardness when hardened. Some steels have poor hardenability, that is, they have insufficient hardness after hardening. Such steels are said to “not accept” hardening.

The hardenability of steel depends mainly on its carbon content. This is explained by the fact that the hardness of martensite depends on the degree of distortion of its crystal lattice. The less carbon in martensite, the less distorted its crystal lattice will be and, therefore, the lower the hardness of the steel will be.

Steels containing less than 0.3% carbon have low hardenability and therefore, as a rule, are not hardened.

The hardenability of steel is characterized by its ability to be hardened to a certain depth.

When hardening, the surface of the part cools faster, since it is in direct contact

The core of the part cools much more slowly; heat from the central part of the part is transferred through the mass of metal to the surface and is absorbed only at the surface by the coolant.

The hardenability of steel depends on the critical quenching speed: the lower the critical speed, the greater the depth of quenching of steel parts.

For example, steel with large natural austenite grains (coarse-grained), which has a low critical hardening rate, is annealed to a greater depth than steel with small natural austenite grains (fine-grained), which has a high critical hardening rate.

Therefore, coarse-grained steel is used for the manufacture of parts that must have deep or through hardenability, while afine-grained steel is used for parts with a hard surface hardened crust and a viscous unhardened core.

1. The depth of hardenability is also influenced by the initial structure of the steel being hardened, the heating temperature for hardening and the quenching medium.
2. The hardenability of steel can be determined by fracture, microstructure and hardness.
3. Types of steel hardening .
4. There are several hardening methods used depending on the composition of the steel, the nature of the workpiece, the hardness to be achieved, and the cooling conditions.

Quenching in one environment is shown schematically in Fig. 1 in the form of curve 1.

Such hardening is easier to perform, but it cannot be used for every steel and not for all parts, since rapid cooling of parts with variable cross-sections in a wide temperature range contributes to the occurrence of temperature unevenness and large internal stresses, which can cause warping of the part, and sometimes cracking ( if the magnitude of internal stresses exceeds the tensile strength).

The more carbon in steel, the greater the volumetric changes and structural stresses, the greater the risk of cracks.

Rice. 1 . Cooling curves for different quenching methods

Hypereutectoid steels are hardened in one environment if the parts have a simple shape (balls, rollers, etc.). If parts have complex shapes, either hardening in two environments or step hardening is used.

Hardening in two environments (curve 2) is used for tools made of high-carbon steel (taps, dies, cutters). The essence of the method is that the part is first soaked in water, quickly cooling it to 300-400 ° C, and then transferred to oil, where it is left until completely cooled.

Step hardening (curve 3) is performed by rapidly cooling the parts in a salt bath, the temperature of which is much higher than the temperature at which the martensitic transformation begins (240-250 ° C).

Holding at this temperature should ensure equalization of temperatures across the entire cross-section of the part.

The parts are then cooled to room temperature in oil or in still air, thereby eliminating thermal internal stresses.

Step hardening reduces internal stress, warping and the possibility of cracking.

The disadvantage of this type of hardening is that hot traces cannot provide a high cooling rate at a temperature of 400-600 ° C. In this regard, step hardening can be used for parts made of carbon steel with a small cross-section (up to 8-10 mm). For alloy steels with a low critical hardening rate, step hardening is applicable to large cross-section parts (up to 30 mm).