WO2021114394A1 - Isothermal quenching technology with oil or oil atmosphere as cooling medium - Google Patents

Abstract

A technology of cooling with an oil medium and isothermal quenching with an oil or gas medium (SFPID). A heat treatment object continuously completes a heating procedure and a quenching procedure. A quenching process is performed in an oil medium in an oxygen-free environment. The technology comprises the steps of: S1, heating a heat treatment object in a device and austenitizing the heat treatment object; S2, rapidly cooling, in an oil medium, an austenitized heat treatment object to a lower bainite area; S3, performing, in the oil medium, isothermal treatment on a lower-bainitized heat treatment object and obtaining a lower bainitic structure; and S4, cleaning the heat treatment object that completes the quenching process. Oil is adopted, and a device (an SFPID special furnace) capable of insulating oil from air (oxygen) is used so that the oil is not in contact with oxygen, thereby preventing an oil product from burning or aging due to an excessive temperature.

Description

Austempering process with oil or oil atmosphere as cooling medium Technical field

The invention relates to the technical field of heat treatment of metal materials, in particular to an austempering process that uses oil medium to cool down and uses oil or gas medium for isothermal transformation.

Background technique

Academically, austempering is to keep the austenitized metal workpiece at a certain temperature above the Ms point in the salt bath for a long enough time to transform it into the lower bainite structure, and finally cool it in the air. This kind of quenching The method is called austempering.

For example, in order to obtain good comprehensive mechanical properties of ductile iron, the currently widely used heat treatment process is austempering. That is, the ductile cast iron is heated to 850～920℃, after the austenite is homogenized, it is quickly put into the nitrate furnace with the temperature above the Ms point (the starting temperature of martensite transformation) and stays at a constant temperature for a period of time, so The body transforms into the lower bainite structure. However, using nitrate as the quenching medium will cause serious pollution to the environment, and its discharge does not meet the environmental standards, and the secondary treatment will greatly increase the cost.

In addition, "salt bath" quenching usually uses equipment such as salt bath furnaces, roller furnaces, or manual treatment, and the cooling rate of the salt bath is slow. Because of the limitations of these factors, the size of the workpiece to be processed is limited. Especially for larger size workpieces, austempering is extremely difficult.

In addition to the academic austempering process, there is also a popular austempering in the folk, which is to keep the austenitized metal workpiece at a certain temperature below the Ms point in the salt solution for a long enough time to transform it into a horse. Stenite structure to obtain more ideal material properties. For example, the tool will have a certain degree of toughness after popular austempering, so that it can prevent its cracking.

However, whether it is an academic austempering process or a popular austempering method, it is inseparable from the use of "salt bath" for isothermal transformation of metals. However, there will be a "fatal problem" for metal workpieces, that is, 1. The cooling rate is slow, 2. The nitrate medium or salt solution is very easy to remain on the surface of the metal workpiece, especially in the ravine-like structure, and it is easy to clean inconveniently. The metal workpiece is corroded.

Therefore, it is urgent to develop a new type of austempering medium, equipment and process to replace the currently widely used nitrate austempering, which has important engineering application significance.

Summary of the invention

The technical scheme of the present invention is: an austempering process based on oil, oil-atmosphere medium, including: continuously completing the heating process and the quenching process of the heat-treated object.

Taking traditional austempering as an example, the metal workpiece is heated above Ac1 (the starting temperature of austenite transformation) to make it a uniform austenite structure, and then the austenite is supercooled at a rapid cooling rate To a certain temperature above the Ms point (being the starting temperature of martensite transformation), and isothermal holding at this temperature, the microstructure obtained is bainite and retained austenite, which has good comprehensive mechanical properties. The specific steps include:

1. Heat the metal workpiece to the austenite zone and keep it for a certain period of time to austenitize it.

2. The austenitized metal workpiece is quickly cooled to a certain point above Ms in a salt bath furnace, and avoids the S-curve nose.

3. In the salt bath furnace, the metal workpiece is isothermal in the bainite zone, and the lower bainite structure is obtained.

Although this traditional austempering process can effectively perform isothermal transformation, its process has many problems:

First, the quenching medium used in the salt bath furnace is nitrate, which is a pollutant and is difficult to discharge and handle.

Second, the nitrate is not easy to clean, and it is easy to remain on the surface of the quenched workpiece, which is very easy to corrode.

Third, the workpiece heating and quenching are two processes, so they are completed in their respective furnaces, and the middle is conveyed through the roller furnace, thus limiting the size of the workpiece.

Fourth, the quenching cooling rate of nitrate salt is slow, and the workpiece with large effective size cannot be quenched.

In summary, the traditional austempering process has many shortcomings. Based on the shortcomings, targeted technological innovation design is carried out to form two technical solutions in the content of the present invention.

That is, first, the cooling and isothermal process of quenching is completely performed in an oil medium in an oxygen-free environment. Second, the quenching cooling process is carried out in an oil medium in an oxygen-free environment, and the quenching isothermal process is carried out in a suitable gas atmosphere.

The first type: austempering process based on oil medium. The steps include:

S1. Heat the heat-treated object to its austenitization in the equipment;

S2. The austenitized heat treatment object is rapidly cooled in the oil medium to a point above the lower bainite transformation temperature (ie Ms point), and the oil temperature is controlled so that the heat treatment object completes the isothermal transformation in the oil medium;

S3. Clean the heat-treated objects that have completed the austempering process.

Preferably, the oil medium is in an oxygen-free atmosphere, and the vaporization point of the oil medium is higher than the lower bainitizing temperature of the heat treatment object. Therefore, the oil medium will not burn due to excessive temperature, and it will not be easy to age and will not vaporize.

The second type: oil-gas medium hierarchical austempering process. The steps include:

S1. Heat the heat-treated object to its austenitization in the equipment;

S2. Quickly cool the austenitized heat treatment object in an oil medium to a point above the lower bainite transformation temperature (ie Ms point);

S3. Then place the heat-treated object in a suitable gas atmosphere for isothermal transformation and obtain a uniform lower bainite structure;

S4. Clean the heat-treated objects that have completed the austempering process.

Preferably, the oil medium is in an oxygen-free atmosphere, and the vaporization point of the oil medium is higher than the lower bainitizing temperature of the heat treatment object. Therefore, the oil medium should not burn due to excessive temperature, and it will not vaporize when it is aged.

Preferably, the lower bainitizing heat treatment object undergoes isothermal transformation in a suitable gas atmosphere to avoid oxidation.

The advantages of the present invention are:

1. This scheme uses oil, and uses the SFPID special furnace to make the oil not in contact with oxygen, which can prevent the oil from burning or aging due to excessive temperature.

2. With oil as the medium, oil isothermal or oil cooling protective atmosphere isothermal can also be used according to different parts.

3. A reasonable heat treatment process is used to avoid excessive oil loss and excessive aging caused by long-term operation of oil products at high temperatures and improve the safety of oil products.

Description of the drawings

The present invention will be further described below in conjunction with the accompanying drawings and embodiments:

Figure 1 is a process curve diagram of austempering heat treatment;

Figure 2 is a 100 times enlarged view of the metallographic structure of the workpiece after the process of the present invention;

Figure 3 is a 500-fold enlarged view of the metallographic structure of the workpiece after the process of the present invention.

Detailed ways

Example 1:

An austempering process based on oil medium, which uses oil as the medium for austempering, and at the same time uses SFPID special furnace for process control.

Among them, the characteristic that the oil medium needs is its own high vaporization point. In order to meet the austempering temperature of the metal workpiece, the vaporization point of the oil medium must be at least higher than the holding temperature of the austempering.

Then, different metals have different Ms points, and different oils can be used as quenching media for different metals.

The following are examples of the Ms points of several different texture carbon steels:

Quenched and tempered steel	Ms point (℃)	Spring steel	Ms point (℃)	Tool steel	Ms point (℃)
30	380	85	220	T 7	280
50Mn	320	60Mn	270	T 8	220～230
40Cr	355	60Si 2 Mn	305	T 8 Mn	180
50CrNi	300	50CrV	270	T 9	190
45CrNiMoVA	275	To	To	T 10	210
35CrNiMo	350	Bearing steel	Ms point (℃)	9SiCr	160
30CrNiAl	330	GCr 15	240	Cr 2	240
5CrMn	400	GCr 15 SiMn	210	4CrW 2 Si	315
20Cr 2 Ni 4	305	To	To	Cr 4 W 2 MoV	142
40CrV	218	To	To	3Cr 2 W 8 V	380

In summary, the vaporization point of high-temperature oil is higher than the Ms point of metal, so it should not vaporize due to excessive temperature. At the same time, the oil medium and the isothermal transformation process are both in an air-isolated (mainly oxygen) environment, which can not only avoid combustion problems, but also prevent the aging of high-temperature oil.

Example 2

Based on the above scheme, the austempering process based on oil medium includes the following steps:

S1. The heat-treated object is heated and austenitized in the SFPID special furnace;

S2. The austenitized heat-treated object is rapidly cooled to the lower bainite transformation temperature in oil, and the heat-treated object that has begun to be lowered bainite is subjected to isothermal treatment in the oil to obtain a uniform lower bainite structure ；

S3. Clean the heat-treated objects that have completed the quenching process.

Based on the above scheme, the steps of the hierarchical austempering process based on oil and gas medium include:

S1. The heat-treated object is heated and austenitized in the SFPID special furnace;

S2. The austenitized heat-treated object is rapidly cooled to the lower bainite transformation temperature in oil;

S3. Then the lower bainite heat treatment object is placed in a suitable gas atmosphere for isothermal transformation and a uniform lower bainite structure is obtained;

S4. Clean the heat-treated objects that have completed the quenching process.

Compare this process with the traditional "salt bath" quenching process, as shown in the following table:

Example 3

With nodular cast iron as the quenching object, the hierarchical austempering process of oil and gas medium is adopted. The specific steps include:

S1. Heat the ductile cast iron to 840℃～910℃ in the equipment to make it austenitize;

S2. Quickly cool the austenitized ductile iron in an oil medium to the lower bainite transformation temperature, with a cooling point of 230°C to 350°C;

S3. Isothermally treat the spheroidal graphite cast iron that has begun to lower bainite in an oil medium to obtain a lower bainite structure, where the temperature holding point is 240°C to 350°C;

S4. Clean the heat-treated objects that have completed the quenching process.

Based on the above parameter range, this embodiment provides multiple sets of example values to illustrate the advantages of the solution of the present invention, as shown in the following table:

To	Test date	Material	Furnace batch number	tensile strength	Yield Strength	Elongation
1	19-11-14	QT1200-3	191078	1363.1	850.7	5
2	19-11-14	QT1200-3	194078	1301	866.1	6
3	19-11-14	QT1200-3	191079	1339.8	844.8	4.5
4	19-11-14	QT1200-3	191079	1298	939.2	5
5	19-11-20	QT1200-3	191080	1520	998	4
6	19-11-20	QT1200-3	191080	1525	1001	4

The above-mentioned embodiments only exemplarily illustrate the principles and effects of the present invention, and are not used to limit the present invention. Anyone familiar with this technology can modify or change the above-mentioned embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or changes made by those with ordinary knowledge in the technical field without departing from the spirit and technical idea of the present invention should still be covered by the claims of the present invention.

Claims (4)

1. An austempering process based on an oil medium includes: continuously completing heating and quenching processes on a heat-treated object; characterized in that: the austenitized heat-treated object is placed in an oil medium and cooled to the lower bainite transformation temperature. Perform isothermal transformation in the oil medium; and the oil medium is in an atmosphere insulated from oxygen; the steps include:

   S1. Heating and austenitizing the heat-treated object;

   S2. Rapidly cool the austenitized heat-treated object to the lower bainite transformation temperature in an oil medium in an oxygen-free environment, and complete the isothermal transformation of the heat-treated object in the oil medium;

   S3. Clean the heat-treated objects that have completed the austempering process.
2. The austempering process according to claim 1, wherein the vaporization point of the oil medium is higher than the lower bainite transformation temperature of the heat-treated object.
3. A hierarchical austempering process based on oil and gas medium, including: heating and quenching the heat treatment object continuously; it is characterized in that the austenitized heat treatment object is placed in an oil medium and cooled to lower bainite transformation After the temperature, it is placed in a gas atmosphere for isothermal transformation; and the oil medium and the isothermal transformation process are both in an oxygen-free gas atmosphere; the steps include:

   S1. Heating and austenitizing the heat-treated object;

   S2. Quickly cool the austenitized heat treatment object to the lower bainite transformation temperature in an oil medium in an oxygen-free environment;

   S3. Perform isothermal treatment on the heat-treated object of lower bainite in an oxygen-free gas atmosphere and obtain the lower bainite structure;

   S4. Clean the heat-treated objects that have completed the austempering process.
4. The hierarchical austempering process according to claim 3, characterized in that: the vaporization point of the oil medium is higher than the lower bainite transformation temperature of the heat treatment object; the oil medium is in an atmosphere isolated from oxygen; the heat treatment is completed in a gas atmosphere Isothermal transformation of the subject.

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