Hardening steel 40Х: hardness, modes, time, temperature, technology

Steel after hardening: structure and properties

Steel in its usual form is a fairly soft and malleable metal.
Some grades do not require special strength (these are the so-called ordinary quality steels, produced in accordance with the requirements of GOST 380): the indicators obtained after smelting are quite sufficient, for example, for sewer manholes or protective gratings. But there are categories of steels - structural and instrumental - for which the initial strength indicators are not enough. They must be subjected to heat treatment. Its main type is hardening. Microstructure of steel 45 after annealing and hardening

Hardening: the essence of the operation

As is known, any steel is a solid solution of carbon in the main structure of α-iron. In this case, the grade determines the percentage of carbon content (for example, the grade “65 steel” means that it contains 0.65% C, U13 steel contains about 1.3% C, and so on). However, this element is quite chemically active, therefore, during the smelting process (at 1600...2000 °C) it is actively bound by iron, resulting in the formation of Fe3C cementite. Everything else is ferrite - a fairly soft structural component. The large amount of ferrite in low-carbon steels causes their increased ductility, even in a cold state. This does not apply to steels:

alloyed (they are produced according to the requirements of GOST 4543);
bearings according to GOST 801;
spring-spring according to GOST 2052 and GOST 14959;
all types of instrumental, both alloyed and unalloyed.

To understand the effectiveness of hardening, it is necessary to refer to the structure of the steel after smelting and subsequent hot rolling into the required profile - strip, rod or special profile (angle, channel, etc.).

Any steel has a crystalline structure, which is made up of an infinite number of crystals. If steel is poured and the melt is then cooled, these crystals turn into multifaceted formations called grains. Since active saturation with oxygen occurs, voids appear between adjacent crystals, which, during the cooling of the ingot, are gradually filled with sulfur, phosphorus and other low-melting non-metallic inclusions. This not only reduces ductility (phosphorus and sulfur are very fragile chemical elements), but also contributes to the appearance of very coarse accumulations of grains, which makes the metal uneven in its density. It is impossible to process such products - the ingot will begin to split. Therefore, immediately after smelting, rolling is performed, during which the original defects are healed and the structure becomes more homogeneous. Accordingly, the density increases and surface cracks disappear.

Temperature of the workpiece depending on the color when heated

Plastic deformation has a positive effect only on the macrostructure. Hardening is responsible for changing the microstructure - a set of technological methods of heat treatment, the essence of which is to increase the strength characteristics of steel. The point of hardening is to fix a number of high-temperature components of the microstructure (giving steel resistance) for normal operating conditions of products. Accordingly, steel, without changing its chemical composition, will sharply increase the level of some of its mechanical characteristics:

limit of temporary resistance σв, MPa;
yield strength σt, MPa;
fatigue limit σi, MPa;
hardness according to Brinell HB or Rockwell HRC.

At the same time, some indicators - in particular, impact strength, relative elongation - become lower after hardening. If this is critical from the point of view of the subsequent operational durability of the part (and in most cases this is the case), then it is correct to perform a number of additional operations after hardening: tempering, aging, etc.

Equipment and materials

To heat metal during heat treatment, 4 main types of furnaces are used: - salt electrode bath - chamber furnace - continuous combustion furnace - vacuum furnace

Liquids (water, mineral oil, special water polymers (Thermat), salt solutions), air and gases (nitrogen, argon) and even low-melting metals are used as quenching media in which cooling occurs. The unit itself, where cooling occurs, is called a quenching bath and is a container in which laminar mixing of the liquid occurs. An important characteristic of the quenching bath is the quality of steam jacket removal.

40ХН2МА steel properties

σ4551/10000=686 MPa, σ4551/1000=137 MPa, σ5901/10000=13 MPa, σ5901/1000=29 MPa.

Mechanical properties of steel 40ХН2МА
GOST	Delivery condition, heat treatment mode	Section, mm	KP	σ0.2 (MPa)	σв(MPa)	δ5 (%)	ψ %	KCU (J/cm2)	NV, no more
GOST 4543-71	Bar. Hardening 850 °C, oil. Vacation 620 °C, water	25	—	930	1080	12	50	78	—
Bar. Hardening 850 °C, oil. Temperature 620 °C, oil.	25	—	835	980	12	55	98	—
GOST 8479-70	Forgings. Hardening. Vacation	500-800	440	440	635	11	30	39	197-235
300-500 500-800	490	490	655	12 11	35 30	49 39	212-248
100-300 300-500	540	540	685	13 12	40 35	49 44	223-362
100-300 300-500 500-800	590	590	735	13 12 10	40 35 30	49 44 39	235-277
100-300 300-500	640	640	785	12 11	38 33	49 44	248-293
100-300	685	685	835	12	38	49	262-311
Up to 100 100-300	735	735	880	13 12	40 35	59 49	277-321
Up to 100 100-300	785	785	930	12 11	40 35	59 49	293-331
Mechanical properties of steel 40ХН2МА depending on tempering temperature
Temperature, °C	σ0.2 (MPa)	σв(MPa)	δ5 (%)	ψ %	KCU (J/cm2)	HB
Hardening 850 °C, oil
200 300 400 500 600	1600 1470 1240 1080 860	1750 1600 1370 1170 960	10 10 12 15 20	50 50 52 59 62	59 49 59 88 147	525 475 420 350 275
Mechanical properties of steel 40ХН2МА at elevated temperatures
Test temperature, °C	σ0.2 (MPa)	σв(MPa)	δ5 (%)	ψ %	KCU (J/cm2)
Hardening 850 °C, oil. Vacation 580 °C.
20 250 400 500	950 830 770 680	1070 1010 950 700	16 13 17 18	58 47 63 80	78 109 84 54
Sample 5 mm in diameter, 25 mm long, rolled. Deformation speed 2 mm/min. Strain rate 0.001 1/s
700 800 900 100 1100 1200	— — — — — —	185 89 50 35 24 14	17 66 69 75 72 62	32 90 90 90 90 90	— — — — — —
Endurance limit of steel 40ХН2МА
σ-1, MPA	J-1, MÏÀ	n	Heat treatment
447 392 519	274 235	106	Section 100 mm. Hardening 850 °C, oil. Vacation 580 °C, σв=880 MPa. Section 400 mm. Hardening 850 °C, oil. Temperature 610 °C, σв=790 MPa, σ0.2=880 MPa, σв=1080 MPa
Impact strength of steel 40ХН2МА KCU , (J/cm2)
Т= +20 °С	Т= -40 °С	Т= -60 °С	Heat treatment
103	93	59	Hardening 860 °C, oil. Vacation 580 °C
Mechanical properties of steel 40ХН2МА depending on the section
Section, mm	Sample cutting location	σ0.2 (MPa)	σв(MPa)	δ4 (%)	ψ %	KCU (J/cm2)	HRCE
Bar. Hardening 850 °C, oil. Vacation 620 °C
40 60 80 100 120	Central Central 1/2R 1/2R 1/3R	880 830 730 670 630	1030 980 880 850 830	14 16 17 19 20	57 60 61 61 62	118 127 127 127 127	33 32 29 26 25
Hardening 850 °C, oil. Vacation 540-660 °C
up to 16 16-40 40-100 100-160 160-250	Ts ts ts ts	1000 900 800 700 650	1200-1400 1100-1300 1000-1200 900-1100 850-1000	9 10 11 12 12	— — — — —	90 50 60 60 60	— — — — —
Hardenability of steel 40ХН2МА
Distance from the end, mm	Note
1,5	3	6	9	12	15	21	27	33	42	Hardening 840 °C
49-59,5	40,5-60	50-60	50-59,5	49-59	48-59	45-56	41,5-53	41-50,5	36,5-48,5	Hardness for hardenability strips, HRC
Amount of martensite, %	Critical hardness, HRCе	Critical diameter in water	Critical diameter in oil
50 90	44-47 49-53	153 137-150	114 100-114
Physical properties of steel 40ХН2МА
T (Grad)	E 10-5 (MPa)	a 10 6 (1/Deg)	l (W/(m deg))	r (kg/m3)	C (J/(kg deg))	R 10 9 (Ohm m)
20	2.15	39	7850	331
100	2.11	11.6	38	490
200	2.01	12.1	37	506
300	1.9	12.7	37	522
400	1.77	13.2	35	536
500	1.73	13.6	33	565
600	13.9	31
700	29
800	27
Brief designations:
σв	— temporary tensile strength (tensile strength), MPa	å	— relative settlement at the appearance of the first crack, %
σ0.05	— elastic limit, MPa	Jê	— ultimate torsional strength, maximum shear stress, MPa
σ0.2	— conditional yield strength, MPa	σben	— ultimate bending strength, MPa
δ5,δ4,δ10	— relative elongation after rupture, %	σ-1	— endurance limit during bending test with a symmetrical loading cycle, MPa
σсж0.05 and σсж	— compressive yield strength, MPa	J-1	— endurance limit during torsion testing with a symmetrical loading cycle, MPa
ν	— relative shift, %	n	— number of loading cycles
sв	— short-term strength limit, MPa	R and ρ	— electrical resistivity, Ohm m
ψ	— relative narrowing, %	E	— normal modulus of elasticity, GPa
KCU and KCV	— impact strength, determined on a sample with concentrators of the types U and V, respectively, J/cm2	T	— temperature at which properties were obtained, degrees
sT	— proportionality limit (yield strength for permanent deformation), MPa	l and ë	— thermal conductivity coefficient (heat capacity of the material), W/(m °C)
HB	— Brinell hardness	C	- specific heat capacity of the material (range 20o - T), [J/(kg deg)]
H.V.	— Vickers hardness	pn and r	— density kg/m3
HRСе	— Rockwell hardness, scale C	A	— coefficient of thermal (linear) expansion (range 20o - T), 1/°С
HRB	— Rockwell hardness, scale B	σtТ	— long-term strength limit, MPa
HSD	- Shore hardness	G	— modulus of elasticity during torsional shear, GPa

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Processing methods for steel grade 40x

The material does not weld well. To eliminate this drawback, heat treatment is used. With its help, you can obtain a more universal alloy and improve its technical characteristics. Heat treatment is carried out in several stages:

Hardening. Carried out in an oil environment. Necessary for improving the quality of structure surfaces.
Cooling the part. This can be done with oil or in air. It is better to use oil, as it improves the quality of the processed workpiece. If water is used, defects may appear.
Vacation. With its help, the internal stress of the metal is eliminated. This can be done in air or with oil.

If the heat treatment was carried out correctly, the hardness increases to 217 HB. This reduces internal tension. Quenching is carried out at a temperature of 860 °C, tempering - at 200 °C. If the temperature regime has not been violated, the service life of the alloy increases.

The field of heat treatment improves the weldability of the metal; to obtain a high-quality seam, the joint must be heated before applying welding.

Steel 40x has a high cost due to the complexity of production and additional heat treatment. Alloy metal is more often used for the production of parts that are subject to heavy loads for a long time.

Heat treatment features

Heat treatment is carried out to improve the mechanical properties of 40 steel, mainly to increase strength and surface hardness. It consists of a set of operations, as a result of which the internal structure of the alloy changes. The material is subjected to strong heating, so heat treatment technology must take into account the characteristics of the alloy, for example:

melting temperature of steel 40X;
its chemical composition;
content of impurities that affect the hardness of the metal;
critical points at which the structure of the alloy changes.

GOST determines the optimal modes:

steel hardening - oil medium with a temperature of 860 degrees;
tempering - water or oil at 500 degrees;
if tempering is carried out at 200 degrees, the hardness increases to 552 MPa.

As a result, the characteristics are improved:

hardness – up to 217 MPa;
tensile strength – 980 N/m2;
impact strength – up to 59 J/cm2.

Slow cooling after tempering leads to brittleness of the steel. This can be avoided by rapid cooling, but this may result in the appearance of internal stresses that cause deformation of the metal. Flock sensitivity, that is, the formation of internal cracks and cavities, can be reduced by evacuation of the heating process and combining it with argon purging.

Specifications of Carbon Steel 45

The hardening process of 40X steel requires special attention, since it is used for the manufacture of parts that experience constant loads, for example, bushings, gears, and bolts. After the procedure, the hardness of the metal increases, but ductility and resistance to impact loads decrease. The ratio of these parameters depends on:

from the time during which heating occurs to a given temperature;
holding interval, which determines the uniformity of heating;
cooling rate.

Critical diameter after quenching in various environments

With a maximum hardness of 43 to 46 HRC3 and a martensite content of no more than 50%, the diameter ranges from 16 to 76 mm.

With a critical hardness in the range from 49 to 53 HRC3 and an amount of martensite equal to 90%, the diameter is from 6 to 58 mm.

Within the indicated limits, a rod with a cylindrical cross-section is calcined through.

Quenching modes

Since during hardening not only strength characteristics increase, but also fragility, the technology for properly conducting the process is, on the one hand, to fix as much as possible of the remaining austenite, and on the other hand, to reduce the negative manifestations of such changes

This is especially important for parts with complex shapes, where there are already stress concentrators

The problem is solved by accelerated cooling of parts heated above the austenitic transformation temperature by 30...50 °C, followed by tempering. Water or oil is used as a cooling medium, and the result of such cooling is the appearance of martensite in the microstructure - a supersaturated solid solution of carbon in iron. Martensite is a much harder structure, with a different type of crystal lattice and a needle-like crystal structure. It is considered the so-called metastable phase, which cannot exist under normal conditions.

Hardening is divided into the following types:

Isothermal, in which continuous cooling is carried out in oil or in molten salts of barium and sodium chlorides. As a result, the austenitic transformation proceeds completely, and cracking and warping are eliminated in the hardened product. Isothermal hardening and tempering are required for structures of complex shape and significant overall dimensions.
Stepwise, in which, after quenching in a bath until the martensitic transformation is completed and temperature differences are equalized across the entire cross-section, the product is removed from the quenching tank and subsequently cooled in still air.
Through, used for small-sized parts. The result is the highest uniformity of mechanical properties.

Three types of tempering after hardening

The peculiarities of hardening tool steels are that they operate under much higher operating loads: for example, for a heavily loaded tool they reach 3000...3500 MPa

Therefore, it is extremely important to ensure a satisfactory combination of all strength parameters. The fundamental difference between all hardening modes of tool steels is the mandatory tempering immediately after hardening

The best results are achieved by the following hardening modes:

Isothermal.
Quenching with spontaneous tempering, in which the heated part is briefly removed from the cooling medium (oil), cleaned of the formed oxide film, and then lowered back into the oil bath.
Clean, in which heating is carried out in furnaces with a controlled atmosphere, free of oxides.
Light when the product is heated in alkaline melts.

https://youtube.com/watch?v=I-br0B8ocpI

Heating for hardening is carried out mainly in electric furnaces or in gas furnaces, the atmosphere of which contains an inert gas. This ensures the quality and completeness of the martensitic transformation, eliminating uneven properties and surface defects.

Steel hardening methods of the 40s and their features: types and technology

In the process of manufacturing various metal structures, the metal is subjected to procedures, including heat treatment.
It is very important to competently approach this operation, fulfilling the requirements of the technology, which will give the final product improved mechanical properties. This topic is quite extensive and includes a fairly large number of important issues. However, we would like to consider the features of the steel hardening procedure, its application and technology. It may seem at first that heat treating is quite a complex procedure, but upon closer inspection it becomes clear that this is not the case at all.

Some general information

Hardening is understood as a procedure during which the crystal lattice of steel and its alloys changes , due to which it is possible to maintain a critical temperature, and the latter is selected for a specific material on an individual basis. Typically, upon reaching the required temperature level, the workpiece is subjected to rapid cooling. To complete this step, use water or oil.

An important point is that in relation to tool steels, incomplete hardening is performed. It is based on heating to a temperature at which it is possible to cause the appearance of excess phases. A number of other steel grades require full hardening. They are heated to a level 50 degrees higher than the temperature that is maintained during incomplete hardening. In the case of processing non-ferrous metals, there is no need to bring the heat treatment to a polymorphic transformation, but for steel, a polymorphic transformation is a mandatory requirement.

Removing the hardening

In accordance with the technology, when cooling the product, a vacation must be carried out. Its purpose is to increase the ductility and reduce the brittleness of the material. At the same time, it is important to ensure the constant strength of the workpiece. This problem is solved by keeping the product in an oven heated to a temperature of 150 to 650 degrees , where it gradually cools. It is customary to distinguish three types of vacations:

Low temperature. The main effect here is to give the workpiece increased wear resistance characteristics. At the same time, such steel can better withstand dynamic loads. The treatment procedure itself takes place at a temperature of 260 degrees. This type of tempering is carried out for products made of low-alloy and carbon steels.
Medium temperature. To carry it out, the temperature is maintained in the range from 350 to 500 degrees. It is usually used in relation to springs, leaf springs, dies, etc. The effect of such tempering is to increase the elasticity and endurance of the product.
High temperature. It is carried out at temperatures of 500 and 680 degrees. Such processing allows you to give the product higher strength and ductility. This procedure is usually carried out on parts that will subsequently experience significant loads.

Hardening steel at home

There are situations when a home craftsman is faced with the problem of increasing the strength characteristics of a household tool. Moreover, to solve this problem there is no need to contact specialists, since he can do everything himself . You can cope with this task with a minimum of equipment and knowledge.

Let's take a closer look at the situation on the axe. If you are considering a Soviet-made instrument , then there is no doubt about its high quality of workmanship. At the same time, the same cannot be said about the products that are sold today. If there are signs of jamming or chipping, then from this we can conclude that the requirements of the hardening technology have been violated. However, it is within the power of every master to correct this situation.

The first thing to do is light a fire with coals. It is advisable to bring it to such a state that the coals are as white as possible. This way you can understand that they have heated up to the highest possible temperature. In addition, we will need two containers. In the first one we will pour oil, which can be used as regular machine oil. The other tank should be filled with clean cold water.

After waiting until the edge of the tool turns crimson, the ax is removed from the fire. To avoid burns due to exposure to high temperatures, it is recommended to use blacksmith's tongs or any other alternative. After this, you need to quickly place the ax in a container with oil and hold it there for 3 seconds . After this time, the ax is removed, allowed to cool for the same 3 seconds, after which the operation is repeated. The procedure of immersing the ax in oil must be carried out until the tool loses its bright light.

Next, we have to immerse the ax in a container of water, and it is important to stir the liquid periodically. This operation completes the hardening of steel at home.

Details about heating metal

If you follow the technology, metal hardening requires 3 stages:

Heating steel;
Excerpt. Thanks to this operation, it is possible to complete all structural transformations and ensure through-through heating;
Cooling.

If you have to deal with structures made of carbon steels, then they are hardened in chamber furnaces . A special feature of this procedure is that there is no need for preheating. This is due to the ability of the material to perfectly tolerate such unpleasant phenomena as warping and cracking. If it is necessary to harden such complex structures as sharp transitions and thin edges, then preheating is indispensable. This procedure can be performed in two ways:

Using salt furnaces, in which the workpiece must be immersed for 3-4 seconds in three stages;
Using separate ovens, in which a temperature regime of 400-500 degrees Celsius should be created.

An important point in hardening metal is that this procedure must be carried out with uniform heating. It happens that such a problem cannot be solved in one session. In this case, the conditions for through heating must be maintained. Particular attention should be paid to the number of products that are planned to be hardened.

As their number increases, it is necessary to increase the duration of their heating. For example, if a disk cutter with a diameter of 2.4 cm , then it must be heated for 13 minutes.

If it is planned to subject a dozen similar products to such processing, then the heating time should be increased to 18 minutes.

Steel hardening methods

The following methods have become most widespread recently:

Chemical composition

The number 40 in the marking indicates that the percentage of carbon in the alloy ranges from 0.36 to 0.44, and the letter x indicates the presence of the alloying element chromium in an amount of no less than 0.8 and no more than 1.1 percent. Alloying steel with chromium gives it the property of resistance to corrosion in an oxidizing environment and atmosphere. In other words, steel acquires stainless properties. In addition, chromium determines the structure of the alloy, its technological and mechanical characteristics.

The remaining chemical elements are included in steel x 40 in the following quantities:

no more than 97% iron;
0.5 - 0.8% manganese;
0.17 - 0.37% silicon;
no more than 0.3% copper;
no more than 0.3% nickel;
no more than 0.035% phosphorus;
no more than 0.035% sulfur.

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.

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

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.
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.
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.

physical characteristics

Almost all physical properties of metals depend directly or inversely on temperature. Indicators such as resistivity, coefficient of linear expansion and specific heat capacity increase with increasing temperature, while the density of steel, its modulus of elasticity and thermal conductivity, on the contrary, decrease with increasing temperature.

Another physical characteristic, called mass, does not depend on practically anything. The sample can be subjected to heat treatment, cooled, processed, given different shapes, and the mass will remain unchanged.

The physical characteristics of all known grades of domestic steels and alloys, including the grade described, are summarized in tables and placed in reference books on metal science.

Induction installation

The HDTV induction heat treatment unit is a high-frequency generator and inductor for HDTV hardening. The part to be hardened can be located in or near the inductor. The inductor is made in the form of a coil, with a copper tube wound on it. It can have any shape depending on the shape and size of the part. When alternating current passes through the inductor, an alternating electromagnetic field appears in it, passing through the part. This electromagnetic field causes eddy currents known as Foucault currents to occur in the workpiece. Such eddy currents, passing through layers of metal, heat it to a high temperature.

HDTV induction heater

A distinctive feature of induction heating using HDTV is the passage of eddy currents on the surface of the heated part. This way, only the outer layer of the metal is heated, and the higher the frequency of the current, the smaller the depth of heating, and, accordingly, the depth of hardening of the high-frequency frequency. This makes it possible to harden only the surface of the workpiece, leaving the inner layer soft and tough to avoid excessive brittleness. Moreover, you can adjust the depth of the hardened layer by changing the current parameters.

The increased frequency of the current allows you to concentrate a large amount of heat in a small area, which increases the heating rate to several hundred degrees per second. Such a high heating rate moves the phase transition to a higher temperature zone. In this case, the hardness increases by 2-4 units, to 58-62 HRC, which cannot be achieved with volumetric hardening.

For the correct implementation of the HDTV hardening process, it is necessary to ensure that the same clearance is maintained between the inductor and the workpiece over the entire hardening surface, and mutual touching must be avoided. This is ensured, if possible, by rotating the workpiece in the centers, which allows for uniform heating, and, as a consequence, the same structure and hardness of the surface of the hardened workpiece.

The essence of the process

The normalization procedure is as follows. The part is heated to temperatures that exceed the maximum permissible parameters (Ac1, Ac3) by 30 - 50 degrees Celsius, then it is kept at this temperature for some time, after which it is cooled.

The temperature is selected based on the steel grade. Thus, alloys containing 0.8% carbon, so-called hypereutectoid, are processed at temperatures lying between the critical points Ac1 and Ac3.

What are critical points? This is the name given to the temperatures at which phase changes and structure of the alloy occur when it is heated or cooled.

The result of this is that a certain volume of carbon enters the solid solution and austenite is fixed. That is, a structure consisting of martensite and cementite appears. It is cementite that leads to an increase in wear resistance and hardness. Heating high-carbon steel above ac3 leads to an increase in internal stresses. This is due to the fact that the amount of austenite increases due to an increase in carbon concentration.

When heated above the critical point Ac3, steel with a carbon content of less than 0.8% acquires increased viscosity. This happens because in steel of this type austenite (fine-grained) appears, turning into martensite (fine-grained).

Hypoeutectoid steel is not processed at temperatures in the range Ac1 - Ac3. Since in this case ferrite appears, which reduces the hardness parameters.

Time required to complete the operation

It takes some time to obtain a homogeneous structure of the alloy at a certain temperature. This time will be determined as the holding time of steel during normalization. It was experimentally determined that a layer of metal 25 mm thick becomes homogeneous after an hour. Thus. and determine the normalization time.

The final stage is cooling

The cooling rate plays a significant role in the formation of perlite volume and the size of its plates. Numerous studies have shown that high cooling rates increase the amount of perlite and the steel gains increased hardness and strength. Low cooling intensity leads to steel losing hardness and strength.

When processing parts with significant differences in size, for example. shafts, it is advisable to remove stresses arising under the influence of temperature fluctuations. To do this, they are preheated in a container filled with different salts. When the temperature drops, it is possible to speed up this process by placing hot parts in water or specially selected oil.

In other words, steel normalization eliminates stress inside the part and minimizes its structure. That is, it has a direct effect on changes in the microstructure of steel alloys.

The purpose of steel normalization

The purposes of steel normalization can be different: for example, to both increase and decrease strength and hardness, depending on the thermal and mechanical history of the product.

The purposes of normalization often overlap or even get confused with annealing, heat hardening, and stress-relieving tempering. Normalization is used, for example, to improve the machinability of a part by cutting, refine the grain, homogenize the grain structure, or reduce residual stresses. A comparison of temperature-time cycles for normalization and annealing is shown in Figure 2.

Figure 2 ─ Comparison of temperature-time cycles of normalization and full annealing. Slower cooling during annealing results in a higher ferrite-pearlite transformation temperature and a coarser microstructure than normalization.

For steel castings, normalization is used to homogenize their dendritic structure, reduce residual stresses and make them more susceptible to subsequent thermal hardening.

Products obtained by pressure treatment can be normalized to reduce banding of the structure after rolling or different grain sizes after forging.

Normalization followed by tempering is used instead of conventional hardening when products have a complex shape or sudden changes in cross-section. This is done to avoid cracking, warping and excessive thermal stress.

Decoding steel 40X

Grade 40X is classified as structural, alloyed. As a result of the fact that the steel can contain from 0.36 and 0.44% carbon and from 0.8 to 1.1% chromium, it becomes difficult to weld. That is, to obtain a high-quality seam it is necessary to perform a number of additional technological operations. Before welding begins, the edges of the parts must be heated to 300 ºC. After the seam is obtained, annealing must be performed.

Full composition of 40X:

The chemical composition of 40X steel allows it to be used for the production of parts with high strength parameters. These details include:

Analogs

By the way, when choosing a bar made of 40X steel as the main material, the designer must remember that there is the possibility of using domestic analogues, such as 45X, 38ХА, 40ХН, 40ХС, 40ХФ, 40ХР. Among the steels produced abroad, there are the following analogues:

G51400, H51350 - USA;

37Cr4, 41Cr4, 41CrS4 - Germany;

35Cr, 38CrA, 40Cr, 40CrA - China.

Steel hardening

Hardening is a heat treatment operation of metal. It consists of heating the metal to a critical temperature at which the crystal lattice of the material changes, or to a temperature at which the phase dissolves in the matrix, which exists at a low temperature.

It is important to understand:

After reaching a critical temperature, the metal undergoes rapid cooling.
After hardening, the steel acquires the structure of martensite (named after Adolph Martens) and therefore becomes hard.
Hardening increases the strength of steel. The metal becomes even harder and more wear-resistant.
A distinction should be made between conventional quenching of the material and quenching to obtain excess vacancies.

Hardening modes differ in the speed of the process and heating temperature. There are also differences in the duration of exposure at a given temperature and cooling rate.

Optimal heat treatment mode

The electric furnace is heated to a temperature close to 860 degrees Celsius. With standard oven power, this takes about 40 minutes.
The holding time of the workpiece in the chamber is assumed to be 10–15 minutes. Visually, the color of 40x steel should acquire a uniform yellow tint.
An oil medium is often used for cooling, and water is less often used.

You can more accurately calculate the heating time of a metal product using the rule: for each cubic millimeter you need to allow 1.5 to 2 minutes for the part to remain inside the electric furnace chamber.

As practice has shown, for 40x steel the most effective method of hardening is by heating the metal with high frequency currents (HFC). Such heating is characterized by rapid achievement of the specified temperature, as well as improved indicators of the strength of the product during operation.

Characteristics of the material. Steel 40ХН.

Brand	steel 40ХН
Substitute:	steel 45ХН, steel 50ХН, steel 38ХГН, steel 40Х, steel 35ХГФ, steel 40ХНР, steel 40ХНМ, steel 30ХГВТ
Classification	Alloyed structural steel. Chrome-nickel
Application	axles, shafts, connecting rods, gears, excavator shafts, couplings, gear shafts, spindles, bolts, levers, rods, cylinders and other critical loaded parts subject to vibration and dynamic loads, which are subject to increased strength and toughness requirements. Rolls of rail and beam and large-section mills for hot rolling of metal.

Chemical composition in % of material 40ХН

C	Si	Mn	Ni	S	P	Cr	Cu
0.36 – 0.44	0.17 – 0.37	0.5 – 0.8	1 – 1.4	up to 0.035	up to 0.035	0.45 – 0.75	up to 0.3

The temperature of the critical points of the material is 40ХН.

Ac1 = 735, Ac3(Acm) = 768, Ar3(Arcm) = 700, Ar1 = 660, Mn = 305

Mechanical properties at T=20oC of material 40ХН.

Assortment	Size	Eg.	sв	sT	d5	y	KCU	Thermal change
–	mm	–	MPa	MPa	%	%	kJ/m2	–
Bar	ø 25	980	785	11	45	690	Quenching and tempering

The hardness of the material is 40ХН after annealing,

HB 10 -1 = 207 MPa

Physical properties of material 40ХН.

T	E 10- 5	a 10 6	l	r	C	R 10 9
hail	MPa	1/Grad	W/(m deg)	kg/m3	J/(kg deg)	Ohm m
20	2	7820
100	11.8	44	7800
200	12.3	43	7770
300	13.4	41	7740
400	14	39	7700
500	37
T	E 10- 5	a 10 6	l	r	C	R 10 9

Technological properties of material 40ХН.

Weldability:	difficult to weld.
Flock Sensitivity:	sensitive.
Tendency to temper brittleness:	inclined.

Designations:

Mechanical properties :
sв	– Short-term strength limit,
sT	– Proportional limit (yield strength for permanent deformation),
d5	– Elongation at break,
y	– Relative narrowing,
KCU	– Impact strength, [kJ/m2]
HB	– Brinell hardness,

Physical properties:
T	– Temperature at which these properties were obtained,
E	– Modulus of elasticity of the first kind,
a	– Coefficient of thermal (linear) expansion (range 20o – T), [1/degree]
l	– Thermal conductivity coefficient (heat capacity of the material), [W/(m deg)]
r	– Material density, [kg/m3]
C	– Specific heat capacity of the material (range 20o – T), [J/(kg deg)]
R	– Electrical resistivity,

Weldability:
no limits	– welding is performed without heating and without subsequent heat treatment
limited weldability	– welding is possible when heated to 100-120 degrees. and subsequent heat treatment
difficult to weld	– to obtain high-quality welded joints, additional operations are required: heating to 200-300 degrees. during welding, heat treatment after welding - annealing

Buy steel 40ХН. Structural alloy steel. Chromium-nickel steel group.

Pipe Angle Channel Strip Circle Hexagon Reinforcement Square Beam Sheet

Heat treatment of steel 45, 40x, 20, 30xgsa, 65g, 40, 40xn, 35, and steel 20x13

In mechanical engineering steel 45 (as a substitute for 40Х, 50, 50Г2), steel 40х (as a substitute for steel 38х, 40хр, 45х, 40хс, 40хф, 40хн), steel 20 (as a substitute for 15, 25), are most often subjected to heat treatment. steel 30khgsa (substitutes 40khfa, 35khm, 40khn, 25khgsa, 35khgsa), steel 65g, steel 40khn, steel 35, and steel 20x13, also

Heat treatment of steel 45

Heat treatment of steel 45 - structural carbon. After preliminary heat treatment of steel 45 - normalization, it can be machined quite easily. Turning, milling, etc. Parts are obtained, for example, such as pinion shafts, crankshafts and camshafts, gears, spindles, bandages, cylinders, cams.

After the final heat treatment of steel 45 (hardening), the parts acquire high strength and wear resistance. Often sanded. The high carbon content (0.45%) ensures good hardenability and, accordingly, high surface hardness and strength of the product. 45 steel is hardened “on water”. That is, after calcination, the part is cooled in water. After cooling, the part is subjected to low-temperature tempering at a temperature of 200-300 degrees Celsius.

With this heat treatment of steel 45, a hardness of about 50 HRC is obtained.

Heat treatment of steel 45 and use of products: The jaws of machine chucks, according to GOST instructions, are made from steels 45 and 40X. Hardness Rc = 45 -50. In the jaws of four-jaw chucks, the thread hardness should be in the range Rc = 35-42. Tempering of cams from steel 45 is carried out at a temperature of 220-280°, from steel 40X at 380-450° for 30-40 minutes.

Interpretation of steel grade 45: grade 45 means that the steel contains 0.45% carbon, C 0.42 - 0.5; Si 0.17 - 0.37; Mn 0.5 - 0.8; Ni up to 0.25; S up to 0.04; P up to 0.035; Cr up to 0.25; Cu up to 0.25; As up to 0.08.

Heat treatment of steel 40Х

Heat treatment of steel 40X - alloy structural steel is intended for high-strength parts such as axles, shafts, gear shafts, plungers, rods, crank and cam shafts, rings, spindles, mandrels, racks, sponge rings, bolts, axle shafts, bushings and other parts increased strength. 40X steel is also often used to produce forgings, stampings and pipe fittings. However, the last listed parts require additional heat treatment, which consists of quenching through water in oil or simply in oil, followed by tempering in oil or air.

Decoding steel grade 40X. The number 40 indicates that the steel contains 0.4% carbon. Chromium content is less than 1.5%. In addition to the usual impurities, it contains specially introduced elements in certain quantities, which are designed to provide specially specified properties. In this case, chromium is used as an alloying element, as indicated by the corresponding marking.

Heat treatment of steel 20

Heat treatment of steel 20 - high-quality structural carbon steel. Widely used in boiler making, for pipes and heating pipelines for various purposes; in addition, the industry produces rods and sheets. The starting temperature for forging steel 20 is 1280° C, the end temperature is 750° C, the forging is cooled by air. Steel 20 is non-floczen sensitive and not prone to tempering.

After carburization and cyanide plating, steel 20 can be used to produce parts that require high surface hardness and allow low core strength: cam rollers, fasteners, spindles, sprockets, studs, rod forks and gear shift shafts, valve lifters, oil pump shafts.

Steel 20 is used for the production of lightly loaded parts (pins, axles, copiers, stops, gears), cemented parts for long and very long service (operation at temperatures not exceeding 350 ° C), thin parts exposed to abrasion and other parts of automotive and agricultural mechanical engineering.

Heat treatment of steel 30khgsa

Heat treatment of steel 30xgsa - refers to medium-alloy structural steel.

Steel 30xgsa undergoes improvement - hardening followed by high tempering at 550-600 ° C, therefore it is used in the creation of improved parts (except for aircraft parts, these can be various casings, axles and shafts, blades of compressor machines that operate at 400 ° C, and much more), levers, pushers, critical welded structures operating under alternating loads, fasteners operating at low temperatures. Steel 30xgsa has good endurance, excellent impact strength, and high strength. It also has excellent weldability.

Welding 30xgsa steel also has its own characteristics. It is carried out with preheating of the material to 250-300 ° C, followed by slow cooling. This procedure is very important because cracks may appear due to the sensitivity of the steel to sudden temperature changes after welding. Therefore, upon completion of welding work, the torch should be withdrawn slowly, while heating the material at a distance of 20-40 mm from the welding site.

Also, no more than 8 hours after completion of welding, welded joints of 30KhGSA steel require quenching with heating to 880 °C, followed by high tempering. Next, the product is cooled in oil at 20-50 °C. Tempering is carried out by heating to 400 - 600 ° C and cooling in hot water. Welding must be performed as quickly as possible in order to avoid burnout of alloying elements.

Steel normalization

Normalization of steel is often considered from two points of view - thermal and microstructural.

In the thermal sense and classical sense, steel normalization is the heating of steel to an austenitic state, followed by cooling in still air. Sometimes normalization also includes operations with accelerated air cooling.

The location of the normalization temperature on the iron-carbon phase diagram is shown in Figure 1.

Figure 1 – Simplified iron-carbon phase diagram. The shaded strip is the normalization temperature of steels

From the point of view of microstructure, pearlite is considered a normalized structure for steel with a carbon content of 0.8%, and for steels with a lower carbon content - hypoeutectoid steels - a mixture of pearlite and ferrite.

The normalization operation is used for most steels, including steel castings. Very often, welded steel seams are normalized to refine the steel structure in the zone of influence of welding.

The purpose of steel normalization

The purposes of steel normalization can be different: for example, to both increase and decrease strength and hardness, depending on the thermal and mechanical history of the product.

For steel castings, normalization is used to homogenize their dendritic structure, reduce residual stresses and make them more susceptible to subsequent thermal hardening.

Products obtained by pressure treatment can be normalized to reduce banding of the structure after rolling or different grain sizes after forging.

Steel cooling rate during normalization

The cooling rate during normalization is usually not a critical value. However, when the product has large differences in cross-sectional dimensions, measures are taken to reduce thermal stresses to avoid warping.

Holding at normalization temperature

The role of the duration of exposure at the normalization temperature is only to ensure homogenization of the austenitic structure before cooling begins. One hour of exposure for every 25 mm of section thickness is the norm.

The cooling rate during normalization significantly affects the amount of perlite, its size and the thickness of the pearlite plates. The higher the cooling rate, the more perlite is formed, and its plates become thinner and closer to each other. Increasing the proportion of pearlite in the structure and its grinding increases the strength and hardness of steel. Lower cooling rates mean less strong and harder steel.

After the products have cooled uniformly across their cross-section below the lower critical point Ar1, they can be cooled in water or oil to reduce the overall cooling time.

Heat treatment of non-ferrous metals

Alloys based on other metals do not respond to hardening as well as steel, but their hardness can also be increased by heat treatment. Typically a combination of hardening and pre-annealing (heating above the phase transformation point with slow cooling) is used.

Bronzes (copper alloys) are annealed at a temperature just below the melting point, and then quenched with water cooling. Quenching temperature from 750 to 950C depending on the composition of the alloy. Tempering at 200-400C is carried out for 2-4 hours. The highest hardness values, up to HV300 (about HRC 34), can be obtained for products made of beryllium bronze.
The hardness of silver can be increased by annealing to a temperature close to the melting point (dull red color) and then quenching.
Various nickel alloys are annealed at 700-1185C, such a wide range is determined by the variety of their compositions. For cooling, salt solutions are used, particles of which are then removed with water or protective gases that prevent oxidation (dry nitrogen, dry hydrogen).

Metal	Annealing temperature, C°	Cooling medium
Copper Brass L96 Brass L90-L62 Cupronickel Nickel silver Silver Aluminum Duralumin	500 — 600 540 — 600 600 — 700 650 — 700 700 — 750 650 — 700 300 — 350 360 — 380	Water Outdoor Outdoor Water Water Water Outdoor Oven Cooling

Applying an improvement

After improvement, carbon steels are used to produce parts that require increased strength. These are parts such as shaft, bushing, gear, gear, bushing. The use of carbon steels is due to low cost of production and manufacturability.

Steel improvement is used in the manufacture of worm shaft

Materials with a high carbon content (60, 65) after improvement are used for the manufacture of spring and spring products.

The introduced alloying elements make it possible to manufacture from these steels critical parts with larger diameters that experience greater loads. After heat treatment, they retain their viscosity and plasticity with increased strength and hardness, and the cold brittleness threshold is reduced.

Steel 40X. Application in production

40X steel is a structural carbon alloy steel. After hardening and appropriate tempering, Steel 40X acquires high strength while maintaining sufficient ductility, allowing it to be used in the production of gear shafts of the first stage of RM type gearboxes, such as the RM 250 gearbox, the RM 350 gearbox, the RM 750 gearbox, the RM 850 gearbox and the gearbox RM 1000. Also, gear wheels of Ts2N type gearboxes are made from Steel 40X. These are the Ts2U 400 gearbox, the Ts2N 450 gearbox, the Ts2N 500 gearbox, the Ts2N 630 gearbox and the Ts2N 710 gearbox. All detailed characteristics of these mechanisms are given in our catalog.

Use of special coolants

During the technological process, water is mainly used to cool parts. The quality of the coolant can be changed by adding soda or special salts, which can affect the cooling process of the workpiece.

To preserve the hardening process, it is strictly forbidden to use the water contained in it for extraneous operations. The water must be clean and have a temperature of 20 to 30 °C. It is forbidden to use running water to harden steel.

Composition of mixtures of salts and alkalis used as quenching media

This hardening method is used only for cemented products or those with a simple shape.

Products with complex shapes made from special structural steel are cooled in a 5% caustic soda solution at a temperature of 50-60 °C. The hardening operation is carried out in a room equipped with exhaust ventilation. Mineral oils are used to harden workpieces made of high-alloy steel, and the cooling rate in an oil bath does not depend on the oil temperature. Mixing oil and water is unacceptable, as this can lead to cracks in the metal.

Advantages and disadvantages

Hardening of parts using HDTV has both advantages and disadvantages. The advantages include the following:

After high-frequency quenching, the part retains a soft center, which significantly increases its resistance to plastic deformation.
The cost-effectiveness of the process of hardening HDTV parts is due to the fact that only the surface or zone that needs to be hardened is heated, and not the entire part.
During mass production of parts, it is necessary to set up the process and then it will be automatically repeated, ensuring the required quality of hardening.
The ability to accurately calculate and adjust the depth of the hardened layer.
The continuous-sequential hardening method allows the use of low-power equipment.
A short heating and holding time at high temperature contributes to the absence of oxidation, decarburization of the top layer and the formation of scale on the surface of the part.
Rapid heating and cooling does not result in large warpage and distortion, which allows for a reduction in finishing allowance.

But it is economically feasible to use induction installations only for mass production, and for single production, purchasing or manufacturing an inductor is unprofitable. For some parts with complex shapes, induction production is very difficult or impossible to obtain a uniform hardened layer. In such cases, other types of surface hardening are used, for example, gas-flame or volumetric hardening.

Source of the article: https://stankiexpert.ru/spravochnik/materialovedenie/zakalka-tvch.html

Cooling parts

Cooling is the second important stage of the hardening process; the quality and hardness of the entire surface depends on its speed and uniformity. Cooling occurs in coolant tanks or by spray. For high-quality hardening, it is necessary to maintain a stable temperature of the coolant and prevent it from overheating. The holes in the sprayer must be of the same diameter and spaced evenly, this way the same metal structure on the surface is achieved.

To prevent the inductor from overheating during operation, water is constantly circulated through the copper tube. Some inductors are made combined with a workpiece cooling system. Holes are cut in the inductor tube through which cold water enters the hot part and cools it.

Hardening with high frequency currents