阅读说明：本技术 一种球墨铸铁活塞铸件的热处理工艺 (Heat treatment process of nodular cast iron piston casting ) 是由 黄远霞 于 2020-12-10 设计创作，主要内容包括：本发明公开了一种球墨铸铁活塞铸件的热处理工艺,包括如下步骤：将处于室温的球墨铸铁活塞铸件装入预热设备,进行三段式预热；将球墨铸铁活塞铸件加热使其基体全部转变为奥氏体并均匀化；出炉后迅速放入油溶剂冷却介质中,急冷后从油溶剂冷却介质中取出；将球墨铸铁活塞铸件置于风冷设备中,将风冷到室温后的球墨铸铁活塞铸件取出并进行回火处理,获得球墨铸铁活塞铸件。本发明工艺设计合理,使得奥氏体化更为充分,并且可以得到更加细小的奥氏体晶粒；淬火后得到均匀分布马氏体的组织结构,并根据需求可通过工艺参数的调整进一步得到细小、粗大短针状马氏体两种组织结构,克服传统铸铁活塞铸件的热处理工艺存在的均匀性差问题。(The invention discloses a heat treatment process of a nodular cast iron piston casting, which comprises the following steps: loading the nodular cast iron piston casting at room temperature into preheating equipment for three-stage preheating; heating the nodular cast iron piston casting to convert all the matrix of the nodular cast iron piston casting into austenite and homogenizing; quickly putting the mixture into an oil solvent cooling medium after the mixture is taken out of the furnace, and taking the mixture out of the oil solvent cooling medium after the mixture is quenched; and placing the nodular cast iron piston casting in air cooling equipment, taking out the nodular cast iron piston casting after air cooling to room temperature, and tempering to obtain the nodular cast iron piston casting. The process design of the invention is reasonable, so that austenitization is more sufficient, and finer austenite grains can be obtained; the microstructure structure of evenly distributed martensite is obtained after quenching, two microstructure structures of fine and thick short needle martensite can be further obtained through adjusting technological parameters according to requirements, and the problem of poor uniformity of the heat treatment process of the traditional cast iron piston casting is solved.)

1. The heat treatment process of the nodular cast iron piston casting is characterized in that the raw materials of the nodular cast iron piston casting comprise, by mass, 3.2-4% of C, 2.3-3.2% of Si, 0.3-0.6% of Mn, 0.05-0.1% of P, 0.1-0.3% of S, 0.1-0.3% of Mo, 0.2-0.5% of Cu and the balance of Fe;

the heat treatment process of the nodular cast iron piston casting comprises the following steps:

s1, loading the nodular cast iron piston casting at room temperature into preheating equipment, wherein the preheating equipment is provided with a three-section heating area for respectively preheating the nodular cast iron piston casting in a three-section mode: heating to 400-; heating to 520 ℃ for the second time, and keeping the temperature for 15-30 min; heating to 600-650 ℃ for the third time, and keeping the temperature for 30-60min to homogenize the temperature of the nodular cast iron piston casting;

s2, after preheating, heating the nodular cast iron piston casting to 935-945 ℃, and preserving heat for 45-55min to convert all the matrix of the nodular cast iron piston casting into austenite and homogenize the matrix;

s3, taking the nodular cast iron piston casting out of the furnace, quickly putting the nodular cast iron piston casting into an oil solvent cooling medium, controlling the quenching time to be 26-32S, cooling the nodular cast iron piston casting to 500-550 ℃, and taking the nodular cast iron piston casting out of the oil solvent cooling medium;

s4, placing the nodular cast iron piston casting in air cooling equipment, wherein the air outlet end of the air cooling equipment is introduced into the first section of heating zone of the preheating equipment;

and S5, taking out the nodular cast iron piston casting which is cooled to room temperature by air, and tempering to obtain the nodular cast iron piston casting with fine short acicular martensite and a small amount of residual austenite.

2. The heat treatment process for a nodular cast iron piston casting according to claim 1, wherein: in step S1, a high-temperature resistant circulating conveyor belt for conveying the nodular cast iron piston castings is arranged at the bottom of the preheating device, and the heating time of the nodular cast iron piston castings in each heating zone is controlled by controlling the conveying speed of the high-temperature resistant circulating conveyor belt.

3. The heat treatment process for a nodular cast iron piston casting according to claim 1, wherein: in step S1, the preheating device is provided with a three-stage heating zone for respectively preheating the nodular cast iron piston casting in three stages: heating to 410 ℃ for the first time, and keeping the temperature for 20 min; heating to 510 ℃ for the second time, and keeping the temperature for 25 min; and heating to 630 ℃ for the third time, and keeping the temperature for 40min to homogenize the temperature of the nodular cast iron piston casting.

4. The heat treatment process for a nodular cast iron piston casting according to claim 1, wherein: in step S2, the nodular cast iron piston casting is heated to 940 ℃, and the temperature is kept for 50min, so that the matrix of the nodular cast iron piston casting is completely transformed into austenite and homogenized.

5. The heat treatment process for a nodular cast iron piston casting according to claim 1, wherein: and step S3, taking the nodular cast iron piston casting out of the furnace, quickly putting the nodular cast iron piston casting into an oil solvent cooling medium, controlling the quenching time to be 26-32S, cooling the nodular cast iron piston casting to 520 ℃, and taking the nodular cast iron piston casting out of the oil solvent cooling medium.

6. The heat treatment process for a nodular cast iron piston casting according to claim 1 or 5, wherein: in step S3, the temperature of the oil-solvent cooling medium is 20 to 30 °.

7. The heat treatment process for a nodular cast iron piston casting according to claim 1, wherein: in step S4, a high-speed fan is arranged at the air inlet end of the air cooling equipment.

8. The heat treatment process for a nodular cast iron piston casting according to claim 1, wherein: in step S5, the tempering temperature of the tempering treatment is 500-520 ℃, the temperature is kept for 60-80min, and then the product is discharged for air cooling.

Technical Field

The invention relates to the technical field of casting processing, in particular to a heat treatment process of a nodular cast iron piston casting.

Background

The austempered ductile iron has high comprehensive mechanical properties and good processing properties, and is widely applied to the automobile industry, such as piston castings of diesel engines. Numerous studies have shown that changing the isothermal mode and the isothermal temperature results in complex changes in the microstructure. Generally, the microstructure of ADI mainly consists of graphite, bainite and retained austenite, and the content and morphology of each phase have a large relationship with the austempering temperature and time. When the isothermal temperature is 350-400 ℃, the microstructure is graphite, a small amount of feather-shaped upper bainite and a large amount of residual austenite, and the toughness is good and the strength is low; when the isothermal temperature is 200-350 ℃, most of the microstructures are graphite, acicular lower bainite and a small amount of residual austenite, and the strength is higher and the toughness is lower. The single isothermal mode is difficult to obtain the best combination of strength and toughness, so the multiphase isothermal quenching nodular cast iron process is produced at the same time. The method aims to generate partial martensite in the quenching process, and then air-cooling the martensite after isothermal treatment for a certain time, so as to obtain the multiphase combination of graphite, martensite, bainite and residual austenite.

Research shows that if part of martensite is formed in the quenching process, the later bainite nucleation can be promoted. In addition, the martensite formed first can play a role in dividing the nodular cast iron matrix and refining the bainite formed subsequently. The method is very important for improving the comprehensive mechanical property of the nodular cast iron and further accelerating the commercial application of the nodular cast iron in piston castings.

The existing piston casting applied to the diesel engine has the defects that the heat treatment process design is not reasonable enough, the as-cast structure of the piston casting cannot form a structure with uniformly distributed martensite, casting segregation exists, and the piston casting has larger non-uniformity. Therefore, optimization improvements are needed.

Disclosure of Invention

The invention aims to overcome the problems in the prior art and provide a heat treatment process for a nodular cast iron piston casting.

In order to achieve the technical purpose and achieve the technical effect, the invention is realized by the following technical scheme:

the heat treatment process of the nodular cast iron piston casting comprises the following raw materials, by mass, 3.2-4% of C, 2.3-3.2% of Si, 0.3-0.6% of Mn, 0.05-0.1% of P, 0.1-0.3% of S, 0.1-0.3% of Mo, 0.2-0.5% of Cu, and the balance of Fe;

the heat treatment process of the nodular cast iron piston casting comprises the following steps:

s1, loading the nodular cast iron piston casting at room temperature into preheating equipment, wherein the preheating equipment is provided with a three-section heating area for respectively preheating the nodular cast iron piston casting in a three-section mode: heating to 400-; heating to 520 ℃ for the second time, and keeping the temperature for 15-30 min; heating to 600-650 ℃ for the third time, and keeping the temperature for 30-60min to homogenize the temperature of the nodular cast iron piston casting;

s2, after preheating, heating the nodular cast iron piston casting to 935-945 ℃, and preserving heat for 45-55min to convert all the matrix of the nodular cast iron piston casting into austenite and homogenize the matrix;

s3, taking the nodular cast iron piston casting out of the furnace, quickly putting the nodular cast iron piston casting into an oil solvent cooling medium, controlling the quenching time to be 26-32S, cooling the nodular cast iron piston casting to 500-550 ℃, and taking the nodular cast iron piston casting out of the oil solvent cooling medium;

s4, placing the nodular cast iron piston casting in air cooling equipment, wherein the air outlet end of the air cooling equipment is introduced into the first section of heating zone of the preheating equipment;

and S5, taking out the nodular cast iron piston casting which is cooled to room temperature by air, and tempering to obtain the nodular cast iron piston casting with fine short acicular martensite and a small amount of residual austenite.

Further, in the heat treatment process of the nodular cast iron piston casting as described above, in step S1, the bottom of the preheating device is provided with a high temperature resistant circulating conveyor belt for conveying the nodular cast iron piston casting, and the heating time of the nodular cast iron piston casting in each heating zone is controlled by controlling the conveying speed of the high temperature resistant circulating conveyor belt.

Further, in the heat treatment process of the nodular cast iron piston casting, as described above, in step S1, the preheating device is provided with a three-stage heating zone to respectively preheat the nodular cast iron piston casting in three stages: heating to 410 ℃ for the first time, and keeping the temperature for 20 min; heating to 510 ℃ for the second time, and keeping the temperature for 25 min; and heating to 630 ℃ for the third time, and keeping the temperature for 40min to homogenize the temperature of the nodular cast iron piston casting.

Further, in the heat treatment process of the nodular cast iron piston casting, in step S2, the nodular cast iron piston casting is heated to 940 ℃, and the temperature is kept for 50min, so that the matrix of the nodular cast iron piston casting is completely transformed into austenite and homogenized.

Further, in the heat treatment process of the nodular cast iron piston casting, in step S3, the nodular cast iron piston casting is taken out of the furnace and then is quickly placed into the oil solvent cooling medium, the quenching time is controlled to be 26-32S, the nodular cast iron piston casting is cooled to 520 ℃, and the nodular cast iron piston casting is taken out of the oil solvent cooling medium.

Further, in the heat treatment process of the nodular cast iron piston casting as described above, in step S3, the temperature of the oil solvent cooling medium is 20 to 30 °.

Further, in the heat treatment process of the nodular cast iron piston casting, in step S4, a high-speed fan is arranged at the air inlet end of the air cooling device.

Further, in the heat treatment process of the nodular cast iron piston casting, in the step S5, the tempering temperature of the tempering treatment is 500-520 ℃, the temperature is kept for 60-80min, and then the nodular cast iron piston casting is discharged from the furnace and cooled in air.

The invention has the beneficial effects that:

1. the heat treatment process of the nodular cast iron piston casting is reasonable in design, so that austenitization is more sufficient, and finer austenite grains can be obtained; the microstructure of evenly distributed martensite is obtained after quenching, two microstructure of fine short needle martensite and coarse short needle martensite can be further obtained through adjusting technological parameters according to requirements, and the problems of casting segregation and large nonuniformity existing in the heat treatment process of the traditional cast iron piston casting are solved.

2. According to the invention, the air cooling equipment communicated with the preheating equipment is arranged, so that heat released in the cooling process of the nodular cast iron piston casting can be recycled, and the energy-saving and environment-friendly effects are achieved.

Of course, it is not necessary for any one product that embodies the invention to achieve all of the above advantages simultaneously.

Drawings

In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the description of the embodiments will be briefly introduced below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and it is obvious for those skilled in the art that other drawings can be obtained according to the drawings without creative efforts.

FIG. 1 is a microstructure view of a nodular cast iron piston casting processed according to example 1;

FIG. 2 is a microstructure view of a nodular cast iron piston casting in example 2 after being processed;

fig. 3 is a microscopic structure view of the nodular cast iron piston casting in comparative example 1 after being processed.

Detailed Description

The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

Example 1

The present embodiment is a heat treatment process for a nodular cast iron piston casting, which comprises, by mass, 3.6% of C, 2.8% of Si, 0.4% of Mn, 0.08% of P, 0.2% of S, 0.2% of Mo, 0.4% of Cu, and the balance Fe;

the heat treatment process of the nodular cast iron piston casting comprises the following steps:

s1, loading the nodular cast iron piston casting at room temperature into preheating equipment, wherein the preheating equipment is provided with a three-section heating area for respectively preheating the nodular cast iron piston casting in a three-section mode: heating to 410 ℃ for the first time, and keeping the temperature for 20 min; heating to 510 ℃ for the second time, and keeping the temperature for 25 min; heating to 630 ℃ for the third time, and keeping the temperature for 40min to homogenize the temperature of the nodular cast iron piston casting; the bottom of the preheating device is provided with a high-temperature resistant circulating conveyor belt for conveying the nodular cast iron piston castings, and the heating time of the nodular cast iron piston castings in each heating area is controlled by controlling the conveying speed of the high-temperature resistant circulating conveyor belt;

s2, after preheating is finished, heating the nodular cast iron piston casting to 940 ℃, and preserving heat for 50min to convert all the matrix of the nodular cast iron piston casting into austenite and homogenize the matrix;

s3, taking the nodular cast iron piston casting out of the furnace, quickly putting the nodular cast iron piston casting into an oil solvent cooling medium, controlling the temperature of the oil solvent cooling medium to be 20-30 degrees, controlling the quenching time to be 26-32S, cooling the nodular cast iron piston casting to 520 ℃, and taking the nodular cast iron piston casting out of the oil solvent cooling medium;

s4, placing the nodular cast iron piston casting in air cooling equipment, wherein a high-speed fan is arranged at the air inlet end of the air cooling equipment, and the air outlet end of the air cooling equipment is introduced into a first section heating area of preheating equipment;

s5, taking out the nodular cast iron piston casting which is cooled to room temperature by air, tempering at the temperature of 510 ℃, keeping the temperature for 70min, and then discharging from the furnace for air cooling; the nodular cast iron piston casting with the structure of fine short acicular martensite and a small amount of residual austenite as shown in figure 1 is obtained.

Example 2

The present embodiment is a heat treatment process for a nodular cast iron piston casting, which comprises, by mass, 3.6% of C, 2.8% of Si, 0.4% of Mn, 0.08% of P, 0.2% of S, 0.2% of Mo, 0.4% of Cu, and the balance Fe;

the heat treatment process of the nodular cast iron piston casting comprises the following steps:

s1, loading the nodular cast iron piston casting at room temperature into preheating equipment, wherein the preheating equipment is provided with a three-section heating area for respectively preheating the nodular cast iron piston casting in a three-section mode: heating to 40 deg.C for the first time, and maintaining the temperature for 15 min; heating to 520 deg.C for the second time, and maintaining the temperature for 30 min; heating to 600 ℃ for the third time, and keeping the temperature for 30min to homogenize the temperature of the nodular cast iron piston casting; the bottom of the preheating device is provided with a high-temperature resistant circulating conveyor belt for conveying the nodular cast iron piston castings, and the heating time of the nodular cast iron piston castings in each heating area is controlled by controlling the conveying speed of the high-temperature resistant circulating conveyor belt;

s2, after preheating, heating the nodular cast iron piston casting to 945 ℃, and preserving heat for 55min to convert all the basal bodies of the nodular cast iron piston casting into austenite and homogenize the basal bodies;

s3, taking the nodular cast iron piston casting out of the furnace, quickly putting the nodular cast iron piston casting into an oil solvent cooling medium, controlling the temperature of the oil solvent cooling medium to be 20-30 degrees, controlling the quenching time to be 26-32S, cooling the nodular cast iron piston casting to 500 ℃, and taking the nodular cast iron piston casting out of the oil solvent cooling medium;

s4, placing the nodular cast iron piston casting in air cooling equipment, wherein a high-speed fan is arranged at the air inlet end of the air cooling equipment, and the air outlet end of the air cooling equipment is introduced into a first section heating area of preheating equipment;

s5, taking out the nodular cast iron piston casting which is cooled to room temperature by air, tempering at the tempering temperature of 520 ℃, preserving heat for 60min, and then discharging from the furnace for air cooling; the nodular cast iron piston casting with the structure shown in figure 2 being coarse short acicular martensite and a small amount of retained austenite is obtained.

Comparative example 1

The present embodiment is a heat treatment process for a nodular cast iron piston casting, which comprises, by mass, 3.6% of C, 2.8% of Si, 0.4% of Mn, 0.08% of P, 0.2% of S, 0.2% of Mo, 0.4% of Cu, and the balance Fe;

the heat treatment process of the nodular cast iron piston casting comprises the following steps:

s1, loading the nodular cast iron piston casting at room temperature into preheating equipment, wherein the preheating equipment is provided with a three-section heating area for respectively preheating the nodular cast iron piston casting in a three-section mode: heating to 410 ℃ for the first time, and keeping the temperature for 20 min; heating to 510 ℃ for the second time, and keeping the temperature for 25 min; heating to 630 ℃ for the third time, and keeping the temperature for 40min to homogenize the temperature of the nodular cast iron piston casting; the bottom of the preheating device is provided with a high-temperature resistant circulating conveyor belt for conveying the nodular cast iron piston castings, and the heating time of the nodular cast iron piston castings in each heating area is controlled by controlling the conveying speed of the high-temperature resistant circulating conveyor belt;

s2, after preheating is finished, heating the nodular cast iron piston casting to 900 ℃, and preserving heat for 75min to convert all the basal bodies of the nodular cast iron piston casting into austenite and homogenize the basal bodies;

s3, taking the nodular cast iron piston casting out of the furnace, quickly putting the nodular cast iron piston casting into an oil solvent cooling medium, controlling the temperature of the oil solvent cooling medium to be 20-30 degrees, controlling the quenching time to be 26-32S, cooling the nodular cast iron piston casting to 520 ℃, and taking the nodular cast iron piston casting out of the oil solvent cooling medium;

s4, placing the nodular cast iron piston casting in air cooling equipment, wherein a high-speed fan is arranged at the air inlet end of the air cooling equipment, and the air outlet end of the air cooling equipment is introduced into a first section heating area of preheating equipment;

s5, taking out the nodular cast iron piston casting which is cooled to room temperature by air, tempering at the temperature of 510 ℃, keeping the temperature for 70min, and then discharging from the furnace for air cooling; a nodular cast iron piston casting having the structure shown in fig. 3 was obtained.

The preferred embodiments of the invention disclosed above are intended to be illustrative only. The preferred embodiments are not intended to be exhaustive or to limit the invention to the precise embodiments disclosed. Obviously, many modifications and variations are possible in light of the above teaching. The embodiments were chosen and described in order to best explain the principles of the invention and the practical application, to thereby enable others skilled in the art to best utilize the invention. The invention is limited only by the claims and their full scope and equivalents.