CN116287593A - High-hardenability 20CrNiMoH steel and heat treatment process for improving hardenability of 20CrNiMoH steel - Google Patents

High-hardenability 20CrNiMoH steel and heat treatment process for improving hardenability of 20CrNiMoH steel Download PDF

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CN116287593A
CN116287593A CN202310347391.3A CN202310347391A CN116287593A CN 116287593 A CN116287593 A CN 116287593A CN 202310347391 A CN202310347391 A CN 202310347391A CN 116287593 A CN116287593 A CN 116287593A
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steel
hardenability
20crnimoh
quenching
heat treatment
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陈文杰
朱心昆
刘逸枫
刘洋
罗军
赵康
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Kunming University of Science and Technology
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    • C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
    • C21D1/55—Hardenability tests, e.g. end-quench tests
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    • C21D9/0075—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for rods of limited length
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    • G01N2001/2873—Cutting or cleaving
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Abstract

The invention relates to high-hardenability 20CrNiMoH steel and a heat treatment process for improving the hardenability of the 20CrNiMoH steel, belonging to the technical field of heat treatment processes of steel. According to the invention, the original steel is subjected to cutting processing, normalizing treatment in a salt bath furnace, annealing treatment, end quenching and quenching treatment by using salt water in sequence, so that the hardenability of the steel can be obviously improved. On one hand, the characteristics of high heating speed, uniform temperature, no contact between steel and air, difficult oxidization and decarburization and small deformation during heat treatment are utilized, and the hardenability of the steel is improved. On the other hand, the quenching is performed by using the salt solution, the quenching is deeper, the quenching effect is better, and when the steel is cooled by the salt solution, the salt crystals are separated out while the vapor film is formed, and the vapor film is broken by bursting, so that the hardness is relatively high and uniform, and meanwhile, the cooling is uniform, and the tendency of deformation and cracking is low.

Description

High-hardenability 20CrNiMoH steel and heat treatment process for improving hardenability of 20CrNiMoH steel
Technical Field
The invention belongs to the technical field of heat treatment processes of steel, and particularly relates to high-hardenability 20CrNiMoH steel and a heat treatment process for improving the hardenability of the 20CrNiMoH steel.
Background
Steel heat treatment refers to a process of obtaining desired properties by heating, maintaining and cooling steel in a solid state to change its internal structure. The heat treatment plays an important role in machine manufacturing, and can improve the service performance of metal materials, save metal and prolong the service life of machines. In addition, the heat treatment can improve the technological performance of the metal material and improve the productivity and the processing quality.
At present, the heat treatment process commonly adopted for steel is as follows: original steel material, normalizing, annealing, machining a standard sample with the diameter of 25mm at the tail end, and performing an end quenching test. When the steel is subjected to heat treatment, the size, the heating temperature, the cooling mode and the like of the steel influence the hardenability of the steel to different degrees, and the steel is heated unevenly and is poor in uniformity during normalizing treatment due to the large influence of the original steel specification, and a box-type resistance furnace which is usually adopted during heating treatment can cause the phenomena of oxidation and decarburization of the steel, so that the hardenability of the steel is reduced.
Disclosure of Invention
Aiming at the defects of the prior art, the invention provides high-hardenability 20CrNiMoH steel and a heat treatment process for improving the hardenability of the 20CrNiMoH steel.
In order to achieve the above purpose, the technical scheme adopted by the invention is as follows:
a heat treatment process for improving hardenability of 20CrNiMoH steel comprises the following steps:
s1: machining the raw steel into a heat-treated blank sample, wherein the diameter of the blank sample is
Figure BDA0004160266710000011
S2: normalizing the blank sample, and then cooling to room temperature; the normalizing treatment is carried out in a salt bath furnace;
s3: annealing the sample subjected to the S2 normalizing treatment, and cooling to obtain an annealed sample;
s4: processing the annealed sample into
Figure BDA0004160266710000021
Is a terminal quenching standard sample of (2);
s5: will be
Figure BDA0004160266710000022
End quenching test was performed on the end standard samples of (c), and quenching was performed using flowing brine after end quenching.
The invention improves the hardenability of the steel by: firstly, the original steel is cut into the steel blank with the diameter of 28-33 mm, and the volume of the steel blank is smaller, so that the steel blank is heated more uniformly during heat treatment, the cooling speed is higher after discharging, and the hardenability of the steel can be improved. Secondly, different from the traditional heat treatment using a box-type resistance furnace, the normalizing treatment process of the steel is performed in a salt bath furnace, the salt bath furnace has high heating speed and relatively uniform heating, the steel is not in direct contact with air during the heat treatment, the oxidation decarburization is reduced, and the hardenability of the steel is improved. Thirdly, according to the invention, when the steel blank sample is quenched, the sample blank is placed in flowing saline water, the quenching depth in the saline water can reach 15mm, compared with the quenching depth in oil or water, the saline water has deeper quenching depth and better quenching effect, and when the saline water cools the steel, crystals of salt can be separated out in the cooling process and burst to break a steam film, the cooling speed of the saline water is about twice that of clear water, so that the saline water quenching can obtain relatively high and uniform hardness, and meanwhile, the deformation cracking tendency is smaller than that of the clear water due to uniform cooling.
The end quenching test is carried out according to national standard GB 5216-2014.
In the preferred embodiment of the present invention, in S2, ventilation and exhaust are performed when the salt bath furnace is used, and the vapor of the heating medium of the salt bath furnace is discharged into the room.
When the salt bath furnace is used, ventilation and exhaust are needed, steam of a heating medium of the salt bath furnace is discharged into a room, the room is cooled, and quenching is performed in brine after end quenching, so that the steel smelting production cost is not increased under the condition that the chemical components of steel are not regulated, a large amount of energy consumption is saved, and the heat treatment cost is reduced.
In a preferred embodiment of the present invention, in S2, the normalizing temperature is 30 to 50 ℃ higher than Ac3, and the temperature is kept for 60 minutes after reaching the normalizing temperature.
In a preferred embodiment of the present invention, in S2, the cooling mode is air cooling combined with air blowing cooling.
In a preferred embodiment of the present invention, in S3, the annealing treatment specifically includes heating the sample after the normalizing treatment in S2 to 770 ℃ and preserving heat for 3 hours, then cooling to 650 ℃ along with the furnace, and finally cooling with the discharging air.
In the S5 of the invention, during the end quenching test, the hardness of the quenched end face of the steel is detected by a full-automatic end quenching hardness tester.
Compared with the prior art, the invention has the beneficial effects that: firstly, the raw steel is subjected to cutting processing, normalizing treatment in a salt bath furnace, annealing treatment, end quenching test and quenching treatment by using salt water in sequence, so that the hardenability of the steel can be obviously improved. The main principle comprises: on one hand, the characteristics of high heating speed, uniform temperature, no contact between steel and air, difficult oxidization and decarburization and small deformation during heat treatment are utilized, and the hardenability of the steel is improved. On the other hand, the quenching is performed by using the salt solution, the quenching is deeper, the quenching effect is better, and when the steel is cooled by the salt solution, the salt crystals are separated out while the vapor film is formed, and the vapor film is broken by bursting, so that the hardness is relatively high and uniform, and meanwhile, the cooling is uniform, and the tendency of deformation and cracking is low.
Drawings
FIG. 1 is a diagram of an experimental apparatus for end quenching treatment according to the present invention.
FIG. 2 is a graph showing comparative hardenability curves of the heat-treated steel products according to example 1 and comparative example 3 of the present invention, in which the modified process is the heat-treatment process according to example 1 and the conventional process is the heat-treatment process according to comparative example 3.
FIG. 3 is a diagram showing the structure of 7mm of the end of the heat-treated end-quenched sample according to example 1 and comparative example 3 of the present invention; wherein FIG. 3 (a) is a 7mm texture chart of the end of the heat-treated end-quenched sample described in example 1, and FIG. 3 (b) is a 7mm texture chart of the end of the heat-treated end-quenched sample described in comparative example 3.
Detailed Description
For a better description of the objects, technical solutions and advantages of the present invention, the present invention will be further described with reference to the following specific examples.
The chemical components of the original 20CrNiMoH steel comprise the following components in percentage by mass: 0.17 to 0.23 percent of C, 0.17 to 0.37 percent of Si, 0.60 to 0.95 percent of Mn, 0.35 to 0.65 percent of Cr, 0.35 to 0.75 percent of Ni, and Mo:0.15 to 0.25 percent, less than or equal to 0.30 percent of P and less than or equal to 0.35 percent of S.
Inventive example 1 and comparative examples 1-3 the heat treated end quenched samples were placed in a centering device as in fig. 1 and quenched with fresh water or brine through a water supply line below the device.
Example 1
A heat treatment process for improving hardenability of 20CrNiMoH steel comprises the following steps:
s1: machining the raw steel into a heat-treated blank sample, wherein the diameter of the blank sample is
Figure BDA0004160266710000041
S2: normalizing the blank sample in a salt bath furnace, and then cooling the blank sample to room temperature by air; the normalizing treatment temperature is 30-50 ℃ higher than Ac3, and the temperature is kept for 60min after reaching the normalizing temperature;
s3: heating the sample subjected to S2 normalizing treatment to 770+/-5 ℃ for 3 hours, cooling to 650+/-5 ℃ along with a furnace, and finally discharging and air cooling to obtain an annealed sample;
s4: processing the annealed sample into
Figure BDA0004160266710000042
Is a terminal quenching standard sample of (2);
s5: will be
Figure BDA0004160266710000043
End quenching test was performed on the end standard samples of (c), and quenching was performed using flowing brine after end quenching.
Comparative example 1
A heat treatment process for improving hardenability of 20CrNiMoH steel comprises the following steps:
s1: machining the raw steel into a heat-treated blank sample, wherein the diameter of the blank sample is
Figure BDA0004160266710000044
S2: normalizing the blank sample in a box-type resistance furnace, and then cooling the blank sample to room temperature by air; the normalizing treatment temperature is 30-50 ℃ higher than Ac3, and the temperature is kept for 60min after reaching the normalizing temperature;
s3: heating the sample subjected to S2 normalizing treatment to 770+/-5 ℃ for 3 hours, cooling to 650+/-5 ℃ along with a furnace, and finally discharging and air cooling to obtain an annealed sample;
s4: processing the annealed sample into
Figure BDA0004160266710000045
Is a terminal quenching standard sample of (2);
s5: will be
Figure BDA0004160266710000046
End quenching test was performed on the end standard samples of (c), and quenching was performed using flowing brine after end quenching.
Comparative example 2
A heat treatment process for improving hardenability of 20CrNiMoH steel comprises the following steps:
s1: machining the raw steel into a heat-treated blank sample, wherein the diameter of the blank sample is
Figure BDA0004160266710000051
S2: normalizing the blank sample in a salt bath furnace, and then cooling the blank sample to room temperature by air; the normalizing treatment temperature is 30-50 ℃ higher than Ac3, and the temperature is kept for 60min after reaching the normalizing temperature;
s3: heating the sample subjected to S2 normalizing treatment to 770+/-5 ℃ for 3 hours, cooling to 650+/-5 ℃ along with a furnace, and finally discharging and air cooling to obtain an annealed sample;
s4: processing the annealed sample into
Figure BDA0004160266710000052
Is a terminal quenching standard sample of (2);
s5: will be
Figure BDA0004160266710000053
End quenching test was performed on the end standard samples of (c), and quenching was performed using flowing water after end quenching.
Comparative example 3
A heat treatment process for improving hardenability of 20CrNiMoH steel comprises the following steps:
s1: machining the raw steel into a heat-treated blank sample, wherein the diameter of the blank sample is
Figure BDA0004160266710000056
S2: normalizing the blank sample in a box-type resistance furnace, and then cooling the blank sample to room temperature by air; the normalizing treatment temperature is 30-50 ℃ higher than Ac3, and the temperature is kept for 60min after reaching the normalizing temperature;
s3: heating the sample subjected to S2 normalizing treatment to 770+/-5 ℃ for 3 hours, cooling to 650+/-5 ℃ along with a furnace, and finally discharging and air cooling to obtain an annealed sample;
s4: processing the annealed sample into
Figure BDA0004160266710000057
Is a terminal quenching standard sample of (2);
s5: will be
Figure BDA0004160266710000054
End quenching test was performed on the end standard samples of (c), and quenching was performed using flowing water after end quenching.
The end hardenability hardness results of the raw steels after the heat treatment processes of examples and comparative examples are shown in table 1.
Table 1 shows the end hardenability hardness results of the heat treatments of the examples and comparative examples for the raw steel
Figure BDA0004160266710000055
Figure BDA0004160266710000061
Compared with the comparative example, the heat treatment of the embodiment of the invention can obviously improve the end hardenability hardness of 20CrNiMoH steel. Compared with comparative example 1, the embodiment shows that the quenching property of the steel is improved by adopting the characteristics that the steel is not contacted with air, is not easy to oxidize and decarbonize and has small deformation when the salt bath furnace is used for heat treatment. According to the examples, the quenching was performed with saline solution, the quenching was deeper, and the quenching effect was better than that of comparative example 2. According to the present invention, the quenching effect of the steel material is superior to that of the conventional heat treatment process according to the example and the comparative example 3.
Meanwhile, according to the hardness distribution curve of FIG. 2, the end hardening curve of the steel treated by the heat treatment process is obviously higher, the overall hardness is higher, and the hardenability is better. As can be seen from FIG. 3, the metallographic structure of the steel treated by the heat treatment process according to the present invention is a substantially bainitic structure, whereas the metallographic structure of the steel treated by the heat treatment process according to comparative example 3 is a mixed structure of martensite and bainite.
Finally, it should be noted that the above embodiments are only for illustrating the technical solution of the present invention and not for limiting the scope of the present invention, and although the present invention has been described in detail with reference to the preferred embodiments, it should be understood by those skilled in the art that the technical solution of the present invention may be modified or substituted equally without departing from the spirit and scope of the technical solution of the present invention.

Claims (5)

1. A heat treatment process for improving hardenability of 20CrNiMoH steel is characterized by comprising the following steps:
s1: machining an original steel material into a heat treatment blank sample, wherein the diameter of the blank sample is phi 28-33 mm;
s2: normalizing the blank sample, and then cooling to room temperature; the normalizing treatment is carried out in a salt bath furnace;
s3: annealing the sample subjected to the S2 normalizing treatment, and cooling to obtain an annealed sample;
s4: processing the annealed sample into a terminal quenching standard sample with the diameter of 25 mm;
s5: end quenching test is carried out on a standard end sample with the diameter of 25mm, and flowing saline is used for end quenching after end quenching.
2. The heat treatment process for improving the hardenability of 20CrNiMoH steel according to claim 1, wherein in the step S2, the normalizing temperature is 30-50 ℃ higher than Ac3, and the heat is preserved for 60min after reaching the normalizing temperature.
3. The heat treatment process for improving hardenability of 20CrNiMoH steel according to claim 1, wherein in S2, ventilation and exhaust are performed when using a salt bath furnace, and the vapor of the heating medium of the salt bath furnace is exhausted into the room.
4. The heat treatment process for improving the hardenability of 20CrNiMoH steel according to claim 1, wherein in the step S3, the annealing treatment specifically comprises heating the sample after the normalizing treatment of the step S2 to 770 ℃ +/-5 ℃ for 3 hours, then cooling to 650 ℃ +/-5 ℃ along with a furnace, and finally cooling the sample by discharging air.
5. A high hardenability 20CrNiMoH steel prepared by a heat treatment process for improving the hardenability of 20CrNiMoH steel as defined in any one of claims 1 to 4.
CN202310347391.3A 2023-04-04 2023-04-04 High-hardenability 20CrNiMoH steel and heat treatment process for improving hardenability of 20CrNiMoH steel Pending CN116287593A (en)

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