Steel hardness 65g as delivered. Optimal technological processes of material heat treatment

19.07.2018

Trying to insert a bunch of tables.
Steel 65G
General information
Substitute
steels: 70, U8A, 70G, 60S2A, 9Khs, 50HFA, 60S2, 55S2.
Delivery type
Long products, including shaped: GOST 14959-79, GOST 2590-71, GOST 2591-71, GOST 2879-69, GOST 7419.0-78 - GOST 7419.8-78. Calibrated bar GOST 14959-79, GOST 7417-75, GOST 8559-75, GOST 8560-78, GOST 1051-73. Polished rod and silver thread GOST 14955-77, GOST 7419.0-78 - GOST 7419.8-78. Sheet thick GOST 1577-81. Tape GOST 1530-78, GOST 2283-79, GOST 21996-76, GOST 21997-76, GOST 10234-77, GOST 19039-73. Strip GOST 103-76, GOST 4405-75. Wire GOST 11850-72. Forgings and forged blanks GOST 1133-71.
Purpose
springs, leaf springs, thrust washers, brake bands, friction discs, gears, flanges, bearing housings, clamping and feed collets and other parts that require increased wear resistance and parts that work without shock loads.
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Chemical composition
Chemical element %
Silicon (Si) 0.17-0.37
Copper (Cu), no more than 0.20
Manganese (Mn) 0.90-1.20
Nickel (Ni), no more than 0.25
Phosphorus (P), no more than 0.035
Chromium (Cr), no more than 0.25
Sulfur (S), no more than 0.035
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Mechanical properties
Mechanical properties
Heat treatment, delivery condition Cross section, mm 0.2, MPa B, MPa 5, % , % HRCe
Steel categories: 3.3A, 3B, 3V, 3G, 4.4A, 4B. Hardening 830 °С, oil, tempering 470 °С. Samples 785 980 8 30
Sheets normalized and hot rolled 80 730 12
Hardening 800-820 °C, oil. Vacation 340-380 °C, air. 20 1220 1470 5 10 44-49
Hardening 790-820 °C, oil. Vacation 550-580 °С, air. 60 690 880 8 30 30-35
Mechanical properties at elevated temperatures
test t, °C 0.2, MPa B, MPa 5, % , %
Hardening 830 °C, oil. Holiday 350 °С.
200 1370 1670 15 44
300 1220 1370 19 52
400 980 1000 20 70
Mechanical properties depending on tempering temperature
tempering t, °С 0.2, MPa B, MPa 5, % , % KCU, J/m2 HRCe
Hardening 830 °C, oil.
200 1790 2200 4 30 5 61
400 1450 1670 8 48 29 46
600 850 880 15 51 76 30
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Technological properties
Forging temperature
Beginning 1250, late 780-760. Cooling of workpieces with a cross section of up to 100 mm is carried out in air, sections of 101-300 mm - in a trough.
Weldability
not applicable to welded structures. KTS - no restrictions.
Machinability
In the hardened and tempered state at HB 240 and B = 820 MPa K solid. = 0.85, K b.st. = 0.80.
Propensity for letting go
inclined at Mn content>=1\%
Floken sensitivity
insensitive
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Temperature of critical points
Critical point °C
AC1 721
Ac3 745
Ar3 720
Ar1 670
Mn 270
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impact strength
Impact strength, KCU, J/cm2
Delivery condition, heat treated +20 0 -20 -30 -70
Hardening 830 C. Tempering 480 C. 110 69 27 23 12
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endurance limit
-1, MPa -1, MPa B, MPa 0.2, MPa Heat treatment, steel condition
725 431 Hardening 810 C, oil. Vacation 400 C.
480 284 Hardening 810 C, oil. Vacation 500 C.
578 1470 1220 HB 393-454
647 1420 1280 HB 420
725 1690 1440 HB 450
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Hardenability
Hardening 800 °C.
Distance from the end, mm / HRC e
1.5 3 4.5 6 9 12 15 18 27 39
58,5-66 56,5-65 53-64 49,5-62,5 41,5-56 38,5-51,5 35,5-50,5 34,5-49,5 35-47,5 31-45
Quantity of martensite, % Crit.diam. in water, mm Crit. dia. in oil, mm Crit. hardness, HRC
50 30-57 10-31 52-54
90 Up to 38 Up to 16 59-61
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Physical properties
Test temperature, °C 20 100 200 300 400 500 600 700 800 900
Modulus of normal elasticity, Е, GPa 215 213 207 200 180 170 154 136 128
Modulus of elasticity under torsional shear G, GPa 84 83 80 77 70 65 58 51 48
Density, pn, kg/cm3 7850 7830 7800 7730
Thermal conductivity W/(m °С) 37 36 35 34 32 31 30 29 28
Test temperature, °C 20-100 20-200 20-300 20-400 20-500 20-600 20-700 20-800 20-900 20-1000
Linear expansion coefficient (a, 10-6 1/°C) 11.8 12.6 13.2 13.6 14.1 14.6 14.5 11.8
Specific heat (C, J/(kg °C)) 490 510 525 560 575 590 625 705

If necessary, I can throw this file on the soap ...

Polished rod and silver:, GOST 7419.0-78, GOST 7419.8-78. Sheet thick: . Tape:, GOST 1530-78, GOST 19039-73. Band: , . Wire: . Forgings and forged blanks: .
Class: Structural spring-spring steel
Industrial use: springs, leaf springs, thrust washers, brake bands, friction discs, gears, flanges, bearing housings, clamping and feed collets and other parts that require increased wear resistance and parts that work without shock loads.

Chemical composition in% steel 65G
C	0,62 - 0,7
Si	0,17 - 0,37
Mn	0,9 - 1,2
Ni	up to 0.25
S	up to 0.035
P	up to 0.035
Cr	up to 0.25
Cu	up to 0.2
Fe	~97

Mechanical properties of steel 65G
GOST	Delivery condition, heat treatment mode	section, mm	σ 0.2 (MPa)	σ in(MPa)	δ5 (%)	ψ %	HRC, no more
GOST 14959-79	Steel categories: 3, 3A, 3B, 3B, 3G, 4, 4A, 4B. Hardening 830 °C, oil. Holiday 470 °С	Samples	785	980	8	30	-
GOST 1577-93	Sheets normalized and hot rolled Hardening 800-820 °C, oil. Vacation 340-380 °С, air Hardening 790-820 °C, oil. Vacation 550-580 °С, air	80 20 60	-1220 690	730 1470 880	12 5 8	-10 30	-44-49 30-35

Hardenability of steel 65G
Distance from the end, mm										Note
1,5	3	4,5	6	9	12	15	18	27	39	Hardening 800 °С
58,5-66	56,5-65	53-64	49,5-62,5	41,5-56	38,5-51,5	35,5-50,5	34,5-49,5	35-47,5	31-45	Hardness for hardenability bands, HRC

Physical properties of steel 65G
T(grad)	E 10 - 5(MPa)	a 10 6(1/deg)	l(W/(m deg))	r(kg / m 3)	C(J/(kg deg))	R109(Ohm m)
20	2.15		37	7850
100	2.13	11.8	36	7830	490
200	2.07	12.6	35	7800	510
300	2	13.2	34		525
400	1.8	13.6	32	7730	560
500	1.7	14.1	31		575
600	1.54	14.6	30		590
700	1.36	14.5	29		625
800	1.28	11.8	28		705

The use of steel 65G and heat treatment of products: spiral springs, sheet and spring washers are made of steel 65G and other spring steels. Spring steel is used to make springs. The hardness of the springs is within R c = 40-50, and spring washers R c = 40-48. Upon acceptance, the springs are checked for hardness and elasticity. The test method should, as far as possible, approximate the actual operating conditions of the springs (tension, compression or bending).

Springs made from heat-treated (patented) wire or tape of classes H, P and B undergo additional tempering at a temperature of 250-350 ° to relieve internal stresses that have arisen during their manufacture and to improve the elastic properties of the wire.

Spring release is best done in saltpeter baths for 5-10 minutes, depending on the cross section of the material. When tempering in oil or electric furnaces, special attention should be paid to the uniformity of heating. Vacation time in these furnaces is 20-40 minutes.

Springs made of annealed steel are quenched and tempered. In the case of making springs from wire with a diameter of more than 6 mm, before hardening, a high tempering is performed at a temperature of 670-720 ° to eliminate hardening resulting from cold winding. Hot-wound springs are normalized before hardening.

For heating for quenching, the springs are placed in chamber furnaces or salt baths heated to the required temperature. To avoid deformation, large springs are heated in a special device.

Small springs are loaded into the oven on a baking sheet. Exposure in the furnace should be the smallest - to prevent oxidation and decarburization. To reduce the residence time in the oven, small springs are placed on a preheated baking sheet. In the absence of a protective atmosphere in the furnace, the springs are packed in an insulating environment, or small amounts of charcoal are thrown into the furnace. Cool the springs in oil. It is not recommended to cool the springs in water to avoid cracking. If hardening in water is necessary, the exposure should be no more than 2-3 seconds. followed by cooling in oil.

Before release, the springs are cleaned of oil by washing in a soda solution or thoroughly rubbing in sawdust. Oil that is not removed from the springs flares up during vacation and changes the vacation conditions, which leads to uneven heating and low hardness. The tempering temperature is 300-420°. The annealing of the extreme turns is carried out in a lead bath.

Large springs are put on pipes before release to eliminate warping.

Attention should be paid to the surface of the material used for the manufacture of springs. Risks, hair lines and other defects lead to the formation of cracks, and the decarburized layer leads to a decrease in the elastic properties of the spring.

Quite often, anti-corrosion coatings used on a number of springs make them brittle due to hydrogen saturation of the metal during etching and during the coating process. This is especially noticeable on springs made of wire or tape of small cross section. This brittleness, called etching or hydrogen, is eliminated by heating the finished springs in oil, glycerin or an oven at a temperature of 150-180 ° for 1-2 hours.

However, during prolonged etching, the metal is saturated with hydrogen so strongly that the indicated temperature does not eliminate brittleness and the springs must be annealed. To avoid deep hydrogenation, springs made of thin wire or tape should not be pickled before coating, but should be sandblasted and heated after coating, as indicated above.

Short designations:
σ in	- tensile strength (ultimate tensile strength), MPa	ε	- relative settlement at the appearance of the first crack, %
σ 0.05	- elastic limit, MPa	J to	- torsion strength, maximum shear stress, MPa
σ 0.2	- conditional yield strength, MPa	σ bend	- ultimate strength in bending, MPa
δ5,δ4,δ 10	- relative elongation after rupture, %	σ-1	- endurance limit during bending test with symmetrical loading cycle, MPa
σ compress0.05 And σ compress	- compressive yield strength, MPa	J-1	- endurance limit during torsion test with a symmetrical loading cycle, MPa
ν	- relative shift, %	n	- number of loading cycles
s in	- 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, respectively, of the type U and V, J / cm 2	T	- temperature at which the properties are obtained, deg
s T	- limit of proportionality (yield strength for permanent deformation), MPa	l And λ	- coefficient of thermal conductivity (heat capacity of the material), W/(m °C)
HB	- Brinell hardness	C	- specific heat capacity of the material (range 20 o - T), [J / (kg deg)]
HV	- Vickers hardness	p n And r	- density kg / m 3
HRC e	- Rockwell hardness, C scale	but	- coefficient of temperature (linear) expansion (range 20 o - T), 1/°C
HRB	- Rockwell hardness, scale B	σ t T	- ultimate strength, MPa
HSD	- Shore hardness	G	- modulus of elasticity at shear by torsion, GPa

Structural high carbon steel brand 65G supplied accordingly technical requirements GOST 14959, is a steel of the spring-spring group. It must combine high surface hardness (for which up to 1% manganese is introduced into its composition) and increased elasticity. All these characteristics are provided as a result of the implementation of proper heat treatment products made from the steel in question.

The initial chemical composition of steel and the requirements for parts made from it

Relating to the category of sparingly alloyed steel, 65G steel is relatively cheap, which leads to its wide and effective use. Among its main components are:

carbon (within 0.62 ... 0.70%);
manganese (within 0.9 ... 1.2%);
chromium and nickel (up to 0.25 ... 0.30%).

All other components are copper, phosphorus, sulfur, etc. - refer to impurities, and are allowed in the chemical composition of this material in quantities limited by the state standard.

With sufficient hardness (for example, after surface normalization, it should be at least 285 HB), and tensile strength (at least 750 MPa), steel 65G has a sufficiently high impact strength for its class - 3.0 ... 3.5 kg∙m /cm 2 . This makes it possible to use the material for the production of critical parts of material handling equipment (in particular, traveling wheels of overhead cranes, rollers), as well as spring washers and springs for non-critical purposes.

It should be noted that spring parts made of 65G steel are poorly welded, and also cannot withstand periodically occurring tensile stresses (relative elongation does not exceed 9%), and therefore cannot be used in one-piece structures of machines and mechanisms. During the processes of cold plastic deformation, steel becomes very low-plastic even at small (up to 10%) deformations, therefore, if it is necessary to manufacture large springs from it, it is necessary to apply heating of the initial blanks, even for sheet stamping. However, even in the hot state, the limiting degrees of deformation of steel 65G do not exceed 50 ... 60%.

Despite the fact that in the course of strain hardening the limit of material tensile strength increases to 1200...1300 MPa, these indicators are not enough to give the final product (for example, springs) the necessary operational strength. Therefore, hardening and tempering of steel 65G are mandatory.

Optimal technological processes of material heat treatment

The choice of heat treatment mode is dictated by production requirements. In most cases, to give the proper physical and mechanical characteristics, use:

normalization;
hardening followed by tempering.

The temperature-time parameters of heat treatment and the choice of its type depend on the initial structure of the steel. This material belongs to steels of the hypoeutectoid type, therefore, at temperatures above the lower point of austenite transformation - 723 ° C - by 30 ... 50 ° C, it contains austenite in the form of a solid mechanical mixture with a small amount of ferrite. Since austenite is a harder structural component than ferrite, the quenching temperature range for 65G steel will be significantly lower than for structural steels with a lower percentage of carbon. Thus, the temperature interval for hardening steel of this grade should be within the range of no more than 800 ... 830 ° C.

Approximately the same temperature range is also used to carry out normalization - a technological operation of heat treatment, which is used to correct the structure of the material of the product, to relieve internal stresses, and with subsequent machining semi-finished product - and to improve its machinability.

Since the impact strength of hardened steel 65G is low, after hardening the products made from it, in particular springs, must necessarily undergo high tempering. The martensite-austenite transformations that occur during tempering reduce the level of internal stresses that occur during hardening, reduce brittleness, and slightly increase the impact strength.

The transition of high tempering is excluded from the mode only when the workpiece is isothermally hardened. As a result of high tempering, steel 65G acquires the structure of sorbitol, characteristic features which are the fineness of the structure while maintaining the initially high hardness, which fully meets the operational requirements.

Modes of hardening steel 65G

In order to comply with the specifications specifications for the operation of parts, when choosing a hardening mode, the following components are taken into account:

method and equipment for heating products to the required temperatures;
setting the desired temperature range of hardening;
selection of the optimal holding time at a given temperature;
choice of the type of quenching medium;
technology for cooling the part after hardening.

The intensity of heating determines the quality of the resulting structure. For low-alloy steels, the process is carried out quite quickly, since this minimizes the risk of decarburization of the material, and, as a result, the loss of its strength parameters by the part. However, too fast heating causes other troubles. In particular, for large parts with large differences in cross sections, this can cause uneven heating of the metal, with the prospect of further occurrence of hardening cracks, chipping of corners and edges.

To achieve the maximum degree of heating uniformity, the steel is first heated in the preliminary chambers of thermal furnaces to temperatures somewhat lower than the hardening ones - from 550 to 700 ° C, and only then the part is sent directly to the hardening furnace. Heating is fastest in molten salts, slower in gas furnaces, and even slower in electric furnaces. That is why the surface hardening of products from steel 65G in induction furnaces performed quite rarely. The inductor, as a hardening unit, is used only for products with a small cross section. When choosing the type of heating device, the composition of the atmosphere that is created in it is also important. In particular, for thermal furnaces operating on gas, they try in every possible way to reduce the duration of the part's stay in the furnace, since otherwise a part of the carbon of the surface layer will burn out.

Based on the normalized for steel 65G hardening temperature of 800 ... 820 ° C, the limiting value of the decarburized layer should not be more than 50 ... 60 microns.

The temperature range of hardening temperatures can be adjusted depending on the configuration of the product. For example, if the part has a complex shape, small dimensions and is made of sheet metal, then the lower limit of the above range will be the optimal temperature. By controlling the hardening temperature (for example, using automatic temperature sensors), it is possible to change the thickness of the hardened layer and the size of the zone that has been hardened less than the others. Such technical solutions are resorted to when different parts of the part work in different operating conditions.

Steel 65G is not afraid of overheating, however, when hardened to the upper value of the temperature range, the impact strength of the material begins to decrease, which is accompanied by the growth of grains in the microstructure.

To reduce warping of parts that have thin ribs and bridges, they use heating in salt hardening baths. More often, a melt of sodium chloride is used, and for deoxidation, borax or ferrosilicon is added to the working volume of the bath.

Exposure during hardening of products from steel 65G at a given temperature range occurs until the pearlite transformation completely occurs. This process depends on the size of the cross section of the part and the method of heating. For the most common cases, you can use the table data:

Heating and holding time depending on the hardening medium and workpiece dimensions

largest overall size details, mm	Hardening in a flame furnace		Hardening in an electric furnace
largest overall size details, mm	Heating time, min	Holding time, min	Heating time, min	Holding time, min
Up to 50	40	10	50	10
Up to 100	80	20	88	20
Up to 150	120	30	130	30
up to 200	160	40	175	40

Cooling of products after hardening is carried out not in water, but in oil, this avoids possible danger cracking.

Post-vacation technology

As already mentioned, to obtain the structure of sorbitol, products made of steel 65G are subjected only to high tempering at temperatures of 550 ... 600 ° C, with cooling in still air. For particularly critical parts, an additional low vacation is sometimes carried out. Its temperature range is 160…200 °С, followed by slow air cooling. This technology avoids the accumulation of thermal stresses in the product, and increases its durability. For tempering, you can use not only fiery, but also electric furnaces equipped with devices for forced air circulation. The exposure time of products in such furnaces is from 110 to 160 minutes (increased time standards correspond to details of complex configuration and significant cross sections).

It is not recommended to use water and aqueous solutions of salts as working media during hardening of steel 65G. The acceleration of the cooling process, which causes water, is often accompanied by uneven ignition.

The final quality control of hardening consists in assessing the macro- and microstructure of the metal, as well as in determining the final hardness of the product. The surface hardness of products made of steel 65G should be in the range of 35 ... 40 HRC after normalization, and 40 ... 45 HRC - after hardening with high tempering.

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