Steel 40ХН

Characteristics of steel 40ХН

Steel grade 40ХН is a structural alloy steel.
It belongs to the class of chromium-nickel materials. The content of elements such as chromium and nickel gives steel its brilliant color and stainless properties. The performance characteristics and chemical composition of 40ХН steel are characterized by GOST 4543-71. This grade of steel contains 8 alloying elements.

Nickel
Manganese
Chromium
Carbon
Silicon
Iron
Sulfur
Phosphorus

See the table below and the diagram for the percentage of all elements that make up 40ХН steel.

Ni	Mn	Cr	C	Si	Fe	S	P
from 1 to 1.4	from 0.5 to 0.8	from 0.45 to 0.75	from 0.36 to 0.44	from 0.17 to 0.37	less than 0.3	less than 0.035	less than 0.035

Description and history of the alloy

The name of the alloy stands for chromium-nickel structural alloy steel. GOST 4543-71 is responsible for the quality of 40ХН steel, which classifies it as a high-strength steel for use in structural purposes (chromium-nickel steel alloy with alloying elements). That is, to obtain products used in mechanical engineering and construction. The introduction of nickel into the alloy composition improves the chemical resistance indicator.

This fact was first introduced to the public in France by the chemist Joseph Louis Proust in the 19th century. He put forward the theory that iron meteorites are practically resistant to corrosion due to the nickel they contain.

Two decades later, Michael Faraday first produced an alloy with compounds of iron and nickel, which was highly resistant to corrosion. However, it was possible to obtain an alloy with improved elasticity characteristics, anti-corrosion properties and mechanical strength only after chemical removal of malleable nickel. According to its characteristics, 40ХН has greater resistance to the corrosion process due to the addition of chromium, which also enhances the strength properties of steel.

Application of steel 40ХН

Finished parts made from this material are then widely used in industry and mechanical engineering. In this area they are presented in the form: Products made from steel 40ХН, due to the properties obtained by alloying with chromium and nickel, are not subject to abrasion. In addition, they are perfectly stamped and soldered.

axles and shafts,
gear wheels,
rolls of rail and beam and large-section mills for hot rolling of metal,
couplings and cylinders,
excavator shafts,
connecting rods,
gear shafts,
rods and levers,
bolts and spindles,
various loaded elements subject to vibration and dynamic loads during operation,
products that require increased strength and toughness.

Structural alloy steel 40ХН

Substitute

Steel 45ХН,
Steel 50ХН,
Steel 38ХГН,
Steel 40Х,
Steel 35HGF,
Steel 40ХНР,
Steel 40ХНМ,
Steel 30ХГВТ.

Analogs

Europe (EN)	1.5711
Germany (DIN, EN)	40NiCr6
USA	3140

Decoding

According to GOST 4543-2016, the name of steel grades consists of numbers and letter designations of chemical elements:

The number 40 before the letter designation indicates the average mass fraction of carbon (C) in steel in hundredths of a percent, i.e. The average carbon content in steel is 0.40%.
The letter X indicates that the steel is alloyed with chromium; the absence of a number after the letter indicates that the chromium content in the steel is up to 1.5%.
The letter H indicates that the steel is alloyed with nickel; the absence of a number after the letter indicates that the nickel content in the steel is up to 1.5%.

Type of delivery

Long products, including shaped steel: GOST 4543-71, GOST 2590-88, GOST 2591-88, GOST 2879-88, GOST 10702-78.
Calibrated rod GOST 4543-71, GOST 7417-75, GOST 8560-78, GOST 10702-78.
Polished rod and silver steel GOST 4543-71, GOST 14955 - 77.
Thick sheet TU 14-1-1930-77.
Strip GOST 103-76.
Forgings and forged blanks GOST 4543-71, GOST 1133-71, GOST 8479-70.
Rolls OST 24.013.21-85
Pipe OST 14-21-77.

Characteristics and application [3]

Steel 40ХН is a chromium-nickel structural alloy steel, it belongs to the group of improveable steel and to steels of increased hardenability, i.e. calcined in parts with a diameter of 50-75 mm.

This grade of steel is one of the best examples of structural steel. The combination of nickel and chromium allows the use of 40ХН steel for the manufacture of critical parts, for example:

axles,
shafts,
connecting rods,
gear wheels,
excavator shafts,
couplings,
gear shafts,
spindles,
bolts,
levers,
stocks,
cylinders and other critical loaded parts subjected to vibration and dynamic loads, which are subject to requirements for increased strength and toughness.
Rolls of rail and beam and large-section mills for hot rolling of metal.

Since nickel is completely dissolved in a solid solution, it contributes to a more significant increase in the hardness and strength of ferrite than chromium. It is especially important that hardening here is also accompanied by an increase in ductility. With the simultaneous presence of nickel and chromium in steel, a good combination of mechanical properties (strength and toughness), as well as high hardenability, is achieved.

40ХН steel is widely used in petroleum engineering for the manufacture of the most critical parts, for example:

especially loaded lifting, transmission and intermediate shafts,
gear couplings,
sprockets of valuable gears of drilling rigs,
plates and rollers of bush-roller chains,
axes of traveling blocks,
trunk swivel,
latches and axes of elevators.

When using chromium-nickel steel, it must be borne in mind that it has a tendency to temper brittleness, especially in the temperature range 450-550°C. Therefore, parts made of this steel should be cooled quickly after high tempering (in water or oil). When a small amount of molybdenum is added to 40ХН steel, the tendency to temper brittleness decreases.

Recommendations for the use of steel 40X for parts of valves and pneumatic actuators that do not operate under pressure and are not subject to welding, intended for operation at low temperatures (GOST 33260-2015)

steel grade	Quenching + tempering at temperature, °C	Approximate level of strength, N/mm (kgf/mm2)	Application temperature not lower, °C	Use in thickness no more than, mm
40ХН	500	1000(100)	-80	50

Temperature of critical points, °C

Ac1	Ac3	Ar3	Ar1	Mn
735	768	700	660	305

Chemical composition, % (GOST 4543-71)

C	Si	Mn	Cr	Ni	P	S	Cu
					no more
0,36-0,44	0,17-0,37	0,50-0,80	0,45-0,75	1,00-1,40	0,035	0,035	0,30

Chemical composition, % (GOST 4543-2016)

Mass fraction of elements, %
C	Si	Mn	Cr	Ni	Mo	Al	Ti	V	IN
0,36-0,44	0,17-0,37	0,50-0,80	0,45-0,75	1,00-1,40	—	—	—	—	—

NOTE: The sign “-” means that the mass fraction of this element is not standardized or controlled, unless otherwise specified in 7.1.2.3 (GOST 4543-2016).

Recommended temperatures for hardening annealed steel 40ХН when heating with high-frequency frequency [1]

Steel grade	Heating temperature in °C at a heating rate above Ac1 deg/sec
	30-60	100-200	400-500
	Heating duration above Ac1 sec
	2-4	1,0-1,5	0,5-0,8
40ХН	900-940°C	920-960°C	960-1020°C

Mode of softening treatment of steel 40ХН [1]

Steel grade	Operation	Heating temperature in °C	Cooling conditions*
40ХН	Annealing	800-820	30-40° S/h

Approximate heat treatment regimes for steel 40ХН [1]

Steel grade	Heating temperature for hardening and normalization in °C	Cooling medium	Temperature in °C	Mechanical properties
				Hardness		Tensile strength σв in kg/mm2	δ in %
				HB	H.R.C.
40ХН	800-840	Oil	180-200	—	45-50	150	8
			550-600	255-286	—	85-95	14-16

NOTE. Cool at the specified rate to 500°C and then in air.

Approximate modes of preliminary heat treatment of steel 40ХН [2]

steel grade	Heat treatment operation	Temperature, °C	Cooling method	Hardness HB
40ХН	Normalization	840-860	On air	207-255
40ХН	Annealing	800-830	Slow	187-241

Mechanical properties

Source	Delivery status	Section, mm	KP	Yield strength σ0.2, MPa	Tensile strength σв, MPa	Relative elongation after break δ5 (δ4), %	Relative narrowing ψ, %	KCU, J/cm2	Hardness HB, no more
Source	Delivery status	Section, mm	KP	no less					Hardness HB, no more
GOST 4543-71	Bar. Quenching at 820°C in water or oil; tempering at 500°C, cool. in water or oil	25	—	785	980	11	45	69	—
GOST 8479-70	Forging. Normalization	100-300	315	315	570	14	35	34	167-207
		300-500	12	30	29	167-207
		500-800	11	30	29	167-207
	Forging. Quenching+tempering	300-500	345	345	590	14	38	49	174-217
		Up to 100	395	395	615	17	45	59	187-229
		100-300	15	40	54
		300-500	13	35	49
		500-800	11	30	39
		Up to 100	440	440	635	16	45	59	197-235
		100-300	14	40	54
		300-500	13	35	49
		500-800	11	30	39
		Up to 100	490	490	655	16	45	59	212-248
		100-300	13	40	54
		Up to 100	540	540	685	15	45	59	223-262
		100-300	13	40	49
		Up to 100	590	590	735	14	45	59	235-277
		100-300	13	40	49

Mechanical properties of rolled products depending on the section [2]

Section, mm	Yield strength σ0.2, MPa	Tensile strength σв, MPa	Relative elongation after rupture δ5, %	Relative narrowing ψ, %	Hardness HB
40	780	960	18	58	325
80	730	920	20	54	302
120	710	910	—	50	300

NOTE. Normalization at 870-925°C; hardening at 790°C in oil; tempering at 540°C.

Mechanical properties depending on tempering temperature

ttp, °С	Yield strength σ0.2, MPa	Tensile strength σв, MPa	Relative elongation after rupture δ5, %	Relative narrowing ψ, %	KCU, J/cm2	Hardness HB
400	1220	1370	10	41	32	387
600	1080	1160	14	51	46	302
600	760	910	20	60	83	241

NOTE. Hardening at 820°C in oil.

Mechanical properties at elevated temperatures

tsp, °С	Tensile strength σв, MPa	Relative elongation after rupture δ5, %	Relative narrowing ψ, %
Normalization at 850°C
20	790	18	48
200	750	—	50
300	690	20	—
400	540	25	65
500	480	25	79
600	350	27	85
Sample 6 mm in diameter, 30 mm in length, forged and normalized. Deformation speed 50mm/min, strain rate 0.031/s
700	225	36	92
800	130	57	96
900	91	71	100
1000	62	75	100
1100	45	76	100
1200	31	—	100

Endurance limit

Strength characteristics	σ-1, MPa	τ-1, MPa
Yield strength σ0.2=780 MPa; Tensile strength σв=980 MPa;НВ 300-320	490	294
Yield strength σ0.2=690 MPa; Tensile strength σв=880 MPa;НВ 270-300	441	274
Yield strength σ0.2=570 MPa; Tensile strength σв=780 MPa;НВ 200-240	392	235
Tensile strength σв=790 MPa; normalization; HB 197	314-392(n=107)	—

Impact strength KCU

Delivery status	KSU, J/cm2 at temperature, °C
Delivery status	+20	-20	-40	-60
Forging 200×30mm. Quenching+tempering	116	116	93	80

NOTE. σ4252.6/10000=103 MPa, σ4256/10000=138 MPa, σ4256.1/100000=69 MPa; σ5353.2/10000=21 MPa.

Technological properties

Forging temperature, °	At first 1250, at the end 830. Sections up to 50 mm are cooled in air, sections from 51 to 200 mm are cooled in a mold, sections from 201 to 300 mm are cooled with a furnace.
Weldability	Difficult to weld. Welding method - RDS, ADS submerged arc, ESW. Heating and subsequent heat treatment are required.
Machinability	Kv tv.sp. = 1.0 and Kv b.st. = 0.9 in the hot-rolled state at HB 166-170 and Tensile strength σв = 690 MPa.
Flock sensitivity	Highly sensitive.
Tendency to temper brittleness	Inclined

Hardenability

The hardenability band for steel 40ХН after normalization at 850°С and quenching from 820°С is shown in the figure below.

Critical diameter d after quenching in various environments

Amount of martensite,%	Critical hardness HRCе	d, mm after hardening
Amount of martensite,%	Critical hardness HRCе	in water	In oil
50	44-47	60-112	34-76
90	50-53	40-86	18-56

Density ρп kg/cm3 at test temperature, °С

Steel	20	100	200	300	400
40ХН	7820	7800	7770	7740	7700

Linear expansion coefficient α*106, K-1

steel grade	α*106, K-1 at test temperature, °C
steel grade	20-100	20-200	20-300	20-400
40ХН	11,8	12,3	13,4	14,0

Thermal conductivity coefficient λ W/(m*K)

Steel grade	λ W/(m*K), at test temperature, °C
Steel grade	20	100	200	300	400	500
40ХН	—	44	43	41	39	37

Young's modulus (normal elasticity) E, GPa

Steel grade	At test temperature
Steel grade	20°C
40ХН	200

Bibliography

I.S. Kamenichny. A short reference book for the thermal technologist. 1963
Firger I.V. Heat treatment of alloys: Handbook. 1982
Schreiber G.K., S.M.Perlin, B.F.Shibryaev. Structural materials in the oil, petrochemical and gas industries. 1969

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Properties of steel 40ХН

The specific gravity of the material is 7820 kg/m3. Heat treatment is carried out using hardening and tempering.

The initial forging temperature is +1250°C, the final temperature is +830°C. Products with a cross-section up to 50 mm are cooled in air, parts with a cross-section from 51 mm to 201 mm are cooled in a mold, elements with a cross-section up to 300 mm are cooled in a furnace.

Heat treatment of steel 40ХН

Quenching and tempering. Forging temperature, °C: beginning 1250, end 830.

Welding process

Welding activities with alloy steels are quite difficult, due to the features that cause the formation of brittle elements in the heat-affected zone due to hardening (that is, welding must be performed using a certain technology). In the best case, it is better to carry out welding work before releasing the product during heating or before annealing, but only after welding. The temperature effect on the 40ХН alloy consists of hardening the alloy, accompanied by further tempering of the product. After such manipulations, the properties of the steel acquire twice the resistance to cracking compared to the state before welding. The endurance limit of steel increases 6 times.

To weld elements made from this steel, it is necessary to initially achieve hardness H = 2860-3020 MPa. This is helped by heat treatment of 40ХН steel, followed by tempering at temperatures from 550 to 860 degrees Celsius. Next, the product is reheated in an electric furnace at temperatures from 350 to 400 degrees Celsius.

Then the welding process itself is carried out in two layers with the obligatory cleaning of slag from the seams in the welding current mode from 160 to 200 A. It is important that the current be constant with reverse polarity. For welding, high-quality electrodes marked UONI 13/55 type E50A with a diameter of 4 millimeters and a weld leg of 8 millimeters are usually used.

Processing and hardening

After welding, the finished part is cooled by lowering the temperature when the furnace is turned off, while being under strict control. As a result of such manipulations, the seam obtained on the product under X-ray irradiation will show the absence of defects. The presence of surface cracks is checked by cleaning and grinding the seams, followed by applying a layer of acid.

The quality of the welding joint is also checked using modern macro-sections.

Products manufactured using this technology successfully undergo macro studies, which reveal the structural density of the deposited metal in the weld zone and the zones closest to it. The microstructure in these places changes from ferrite-pearlite to serbite-like pearlite. Also, samples of parts made of 40ХН steel undergo a hardness test, the purpose of which is to confirm the invariance of the steel structure in the weld zone after welding.

Hardening of products made from this material occurs during the process of immersion in oil, however, large parts are sometimes hardened in water and then, as soon as possible, they are moved into oil or exposed to low tempering. The process of hardening with high-frequency currents, after heating with which tempering is carried out, is also not uncommon. Ultimately, such manipulations increase the hardness of the surface of the product.