A heat treatment process for low alloy steel castings

Abstract

The application discloses a heat treatment process of low-alloy steel castings, and the heat treatment process of the low-alloy steel castings controls the chemical element content of the low-alloy steel castings reasonably, so that the strength of the steel castings is higher; the heating temperature in the heat treatment process is appropriately increased, and the holding time is prolonged, so that the structure transformation of the steel is sufficient, and the mechanical performance and the impact toughness are effectively improved. The heat treatment process adopts a process flow of preheating + normalizing + tempering + quenching + annealing, and compared with a traditional heat treatment process, the heat treatment process has the advantages that the grains are further refined and uniform, the grain size is maximally increased, and good structure conditions are prepared for subsequent heat treatment.

Description

Technical Field

[0001] This invention relates to the field of heat treatment technology for steel castings, and more specifically, to a heat treatment process for low alloy steel castings. Background Technology

[0002] Due to the extremely uneven global distribution of metal ores, ore procurement is affected not only by local economic conditions but also by factors such as weather and transportation. Consequently, the production of high-alloy steel castings, which require a large amount of alloying elements, is also affected. Furthermore, high-alloy steel castings are expensive and priced high. If low-alloy steel castings can meet certain performance requirements of high-alloy steel castings, they can replace them. This is because the production of low-alloy steel castings is less constrained and limited, and they can save significant costs. The complex microstructure of steel can be controlled through heat treatment, with the quenching process being a key factor. Therefore, the quenching of low-carbon alloy steel castings becomes particularly important.

[0003] Currently, the heat treatment process for low-alloy steel castings generally involves normalizing, quenching, and tempering. The quenching medium is quenching oil, used in a 1:10 weight ratio (1 ton of casting to 10 tons of quenching oil) to ensure effective quenching. However, after a period of use, the quenching oil's viscosity increases and its volume decreases due to oxide powder from the casting and carbonization of the oil medium, necessitating the addition of new oil, leading to high oil quenching costs. Furthermore, oil quenching is prone to ignition, posing a safety hazard, and generates large amounts of harmful substances, causing environmental pollution. Additionally, existing heat treatment processes often result in low-alloy steel castings with poor toughness, failing to meet the requirements for high toughness. Summary of the Invention

[0004] The purpose of this invention is to provide a heat treatment process for low alloy steel castings to solve the technical problems existing in the background art.

[0005] The present invention provides a heat treatment process for low alloy steel castings, comprising the following steps:

[0006] S1, steel castings are prepared using the following raw materials in the following mass percentages: carbon 0.2-0.25%, manganese 1-1.5%, silicon 0.3-0.5%, chromium 0.2-0.3%, molybdenum 0.2-0.4%, nickel 0.6-0.8%, with the balance being iron, and the sum of the above raw material mass percentages is 100%;

[0007] S2, the low-alloy steel castings after casting are placed in a high-temperature furnace for preheating treatment;

[0008] S3. After the preheating treatment is completed, the low alloy steel casting is moved to the normalizing furnace for normalizing treatment.

[0009] S4. The low alloy casting is transported to a vacuum quenching furnace, first heated to 650-700℃, held for 1-2 hours, then heated to quenching temperature of 820-850℃, held for 2-3 hours, and then water-cooled to room temperature.

[0010] S5. After quenching and air cooling, place the casting in a heat treatment furnace and heat it to 350-420℃. Hold it at this temperature for 2-3 hours, with the heating rate controlled at 20-30℃ / min. Then heat it to 550-600℃, with the heating rate controlled at 15-20℃ / min. Hold it at this temperature for 5-7 hours. Then remove the casting and air cool it.

[0011] In a preferred embodiment, the raw materials for preparing low-alloy steel castings are: 0.24% carbon, 1.2% manganese, 0.4% silicon, 0.2% chromium, 0.3% molybdenum, 0.7% nickel, and the balance being iron, with the sum of the above raw material mass percentages being 100%.

[0012] In a preferred embodiment, the raw materials for preparing low-alloy steel castings are: 0.2% carbon, 1% manganese, 0.3% silicon, 0.2% chromium, 0.2% molybdenum, 0.6% nickel, and the balance being iron, with the sum of the above raw material mass percentages being 100%.

[0013] In a preferred embodiment, the raw materials for preparing low-alloy steel castings are: 0.25% carbon, 1.5% manganese, 0.5% silicon, 0.3% chromium, 0.4% molybdenum, 0.8% nickel, and the balance being iron, with the sum of the above raw material mass percentages being 100%.

[0014] In a preferred embodiment, the preheating conditions in S2 are: a preheating temperature of 300-350°C, a preheating rate of 10-15°C / min, and a time of 2-2.5h.

[0015] In a preferred embodiment, the normalizing process in S3 is as follows: during the normalizing process, the normalizing furnace is heated at a rate of ≤80℃ / h until the temperature inside the furnace reaches 900-950℃, at which point the heating is stopped, and the furnace is held for 3-4 hours. Finally, the low-alloy steel casting is removed and air-cooled.

[0016] In a preferred embodiment, the processing conditions for the water cooling process in S4 are: casting water cooling transfer time of 40-60s, water temperature of 20-30℃, and water cooling time of 5-8min.

[0017] The beneficial effects of the technical solution of this invention are:

[0018] The heat treatment process for low-alloy steel castings of the present invention achieves higher strength by rationally controlling the chemical element content of the low-alloy steel castings; by appropriately increasing the heating temperature and extending the holding time during the heat treatment process, the microstructure of the steel can be fully transformed, thereby effectively improving mechanical properties and impact toughness.

[0019] The heat treatment process of this invention adopts a process flow of preheating + normalizing + tempering + quenching + annealing. Compared with the traditional heat treatment process, its advantages are that it further refines and homogenizes the grains, maximizes the grain size, and prepares good microstructure conditions for subsequent heat treatment. Detailed Implementation

[0020] The present invention will now be described in further detail with reference to specific embodiments. The embodiments of the present invention are given for the purpose of illustration and description, and are not intended to be exhaustive or to limit the invention to the disclosed forms. Many modifications and variations will be apparent to those skilled in the art. The embodiments were chosen and described to better illustrate the principles and practical application of the invention, and to enable those skilled in the art to understand the invention and design various embodiments with various modifications suitable for a particular purpose.

[0021] Example 1

[0022] The present invention provides a heat treatment process for low alloy steel castings, comprising the following steps:

[0023] S1, steel castings are prepared using the following raw materials in the following mass percentages: carbon 0.24%, manganese 1.2%, silicon 0.4%, chromium 0.2%, molybdenum 0.3%, nickel 0.7%, and the balance being iron, the sum of the above raw material mass percentages being 100%;

[0024] S2, the low-alloy steel castings after casting are placed in a high-temperature furnace for preheating treatment;

[0025] S3. After the preheating treatment is completed, the low alloy steel casting is moved to the normalizing furnace for normalizing treatment.

[0026] S4. The low alloy casting is transported to a vacuum quenching furnace, first heated to 650-700℃, held for 1-2 hours, then heated to quenching temperature of 820-850℃, held for 2-3 hours, and then water-cooled to room temperature.

[0027] S5. After quenching and air cooling, place the casting in a heat treatment furnace and heat it to 350-420℃. Hold it at this temperature for 2-3 hours, with the heating rate controlled at 20-30℃ / min. Then heat it to 550-600℃, with the heating rate controlled at 15-20℃ / min. Hold it at this temperature for 5-7 hours. Then remove the casting and air cool it.

[0028] The preheating conditions in S2 are: preheating temperature of 300-350℃, preheating rate of 10-15℃ / min, and time of 2-2.5h.

[0029] The normalizing process in S3 is as follows: During the normalizing process, the normalizing furnace is heated at a rate of ≤80℃ / h until the temperature inside the furnace reaches 900-950℃. The heating is then stopped, and the furnace is held for 3-4 hours. Finally, the low-alloy steel casting is removed and air-cooled.

[0030] The processing conditions for water cooling in S4 are as follows: water cooling transfer time for casting is 40-60 seconds, water temperature is 20-30℃, and water cooling time is 5-8 minutes.

[0031] Example 2

[0032] The present invention provides a heat treatment process for low alloy steel castings, comprising the following steps:

[0033] S1, steel castings are prepared using the following raw materials in the following mass percentages: carbon 0.2%, manganese 1%, silicon 0.3%, chromium 0.2%, molybdenum 0.2%, nickel 0.6%, and the balance being iron, with the sum of the above raw material mass percentages being 100%;

[0034] S2, the low-alloy steel castings after casting are placed in a high-temperature furnace for preheating treatment;

[0035] S3. After the preheating treatment is completed, the low alloy steel casting is moved to the normalizing furnace for normalizing treatment.

[0036] S4. The low alloy casting is transported to a vacuum quenching furnace, first heated to 650-700℃, held for 1-2 hours, then heated to quenching temperature of 820-850℃, held for 2-3 hours, and then water-cooled to room temperature.

[0037] S5. After quenching and air cooling, place the casting in a heat treatment furnace and heat it to 350-420℃. Hold it at this temperature for 2-3 hours, with the heating rate controlled at 20-30℃ / min. Then heat it to 550-600℃, with the heating rate controlled at 15-20℃ / min. Hold it at this temperature for 5-7 hours. Then remove the casting and air cool it.

[0038] The preheating conditions in S2 are: preheating temperature of 300-350℃, preheating rate of 10-15℃ / min, and time of 2-2.5h.

[0039] The normalizing process in S3 is as follows: During the normalizing process, the normalizing furnace is heated at a rate of ≤80℃ / h until the temperature inside the furnace reaches 900-950℃. The heating is then stopped, and the furnace is held for 3-4 hours. Finally, the low-alloy steel casting is removed and air-cooled.

[0040] The processing conditions for water cooling in S4 are as follows: water cooling transfer time for casting is 40-60 seconds, water temperature is 20-30℃, and water cooling time is 5-8 minutes.

[0041] Example 3

[0042] The present invention provides a heat treatment process for low alloy steel castings, comprising the following steps:

[0043] S1. Steel castings are prepared using the following raw materials in the following mass percentages: The raw materials for preparing low-alloy steel castings are: carbon 0.25%, manganese 1.5%, silicon 0.5%, chromium 0.3%, molybdenum 0.4%, nickel 0.8%, and the balance is iron. The sum of the above raw material mass percentages is 100%.

[0044] S2, the low-alloy steel castings after casting are placed in a high-temperature furnace for preheating treatment;

[0045] S3. After the preheating treatment is completed, the low alloy steel casting is moved to the normalizing furnace for normalizing treatment.

[0046] S4. The low alloy casting is transported to a vacuum quenching furnace, first heated to 650-700℃, held for 1-2 hours, then heated to quenching temperature of 820-850℃, held for 2-3 hours, and then water-cooled to room temperature.

[0047] S5. After quenching and air cooling, place the casting in a heat treatment furnace and heat it to 350-420℃. Hold it at this temperature for 2-3 hours, with the heating rate controlled at 20-30℃ / min. Then heat it to 550-600℃, with the heating rate controlled at 15-20℃ / min. Hold it at this temperature for 5-7 hours. Then remove the casting and air cool it.

[0048] The preheating conditions in S2 are: preheating temperature of 300-350℃, preheating rate of 10-15℃ / min, and time of 2-2.5h.

[0049] The normalizing process in S3 is as follows: During the normalizing process, the normalizing furnace is heated at a rate of ≤80℃ / h until the temperature inside the furnace reaches 900-950℃. The heating is then stopped, and the furnace is held for 3-4 hours. Finally, the low-alloy steel casting is removed and air-cooled.

[0050] The processing conditions for water cooling in S4 are as follows: water cooling transfer time for casting is 40-60 seconds, water temperature is 20-30℃, and water cooling time is 5-8 minutes.

[0051] The performance of the low-alloy steel castings obtained by the heat treatment processes in Examples 1-3 was tested, and the results are as follows:

[0052] As shown in Table 1:

[0053]

[0054] Table 1

[0055] The heat treatment process for low-alloy steel castings of the present invention achieves higher strength by rationally controlling the chemical element content of the low-alloy steel castings; by appropriately increasing the heating temperature and extending the holding time during the heat treatment process, the microstructure of the steel can be fully transformed, thereby effectively improving mechanical properties and impact toughness.

[0056] Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. All other embodiments obtained by those skilled in the art and related fields based on the embodiments of the present invention without inventive effort should fall within the scope of protection of the present invention. Structures, devices, and operating methods not specifically described and explained in the present invention, unless otherwise specified or limited, shall be implemented according to conventional means in the art.

Claims

1. A heat treatment process for low-alloy steel castings, characterized in that, Includes the following steps: S1, steel castings are prepared using the following raw materials in the following mass percentages: carbon 0.2-0.25%, manganese 1-1.5%, silicon 0.3-0.5%, chromium 0.2-0.3%, molybdenum 0.2-0.4%, nickel 0.6-0.8%, with the balance being iron, and the sum of the above raw material mass percentages is 100%; S2, the low-alloy steel castings after casting are placed in a high-temperature furnace for preheating treatment; S3. After the preheating treatment is completed, the low alloy steel casting is moved to the normalizing furnace for normalizing treatment. S4. The low alloy casting is transported to a vacuum quenching furnace, first heated to 650-700℃, held for 1-2 hours, then heated to quenching temperature of 820-850℃, held for 2-3 hours, and then water-cooled to room temperature. S5. After quenching and air cooling, place the casting in a heat treatment furnace and heat it to 350-420℃. Hold it at this temperature for 2-3 hours, with the heating rate controlled at 20-30℃ / min. Then heat it to 550-600℃, with the heating rate controlled at 15-20℃ / min. Hold it at this temperature for 5-7 hours. Then remove the casting and air cool it.

2. The heat treatment process for low-alloy steel castings according to claim 1, characterized in that, The raw materials for preparing low alloy steel castings are as follows: carbon 0.24%, manganese 1.2%, silicon 0.4%, chromium 0.2%, molybdenum 0.3%, nickel 0.7%, and the balance is iron. The sum of the above raw material mass percentages is 100%.

3. The heat treatment process for low-alloy steel castings according to claim 1, characterized in that, The raw materials for preparing low alloy steel castings are as follows: carbon 0.2%, manganese 1%, silicon 0.3%, chromium 0.2%, molybdenum 0.2%, nickel 0.6%, and the balance is iron. The sum of the above raw material mass percentages is 100%.

4. The heat treatment process for low-alloy steel castings according to claim 1, characterized in that, The raw materials for preparing low alloy steel castings are as follows: carbon 0.25%, manganese 1.5%, silicon 0.5%, chromium 0.3%, molybdenum 0.4%, nickel 0.8%, and the balance is iron. The sum of the above raw material mass percentages is 100%.

5. The heat treatment process for low-alloy steel castings according to claim 1, characterized in that, The preheating conditions in S2 are: preheating temperature of 300-350℃, preheating rate of 10-15℃ / min, and time of 2-2.5h.

6. The heat treatment process for low-alloy steel castings according to claim 1, characterized in that, The normalizing process in S3 is as follows: During the normalizing process, the normalizing furnace is heated at a rate of ≤80℃ / h until the temperature inside the furnace reaches 900-950℃. The heating is then stopped, and the furnace is held for 3-4 hours. Finally, the low-alloy steel casting is removed and air-cooled.

7. The heat treatment process for low-alloy steel castings according to claim 1, characterized in that, The processing conditions for water cooling in S4 are as follows: water cooling transfer time for casting is 40-60 seconds, water temperature is 20-30℃, and water cooling time is 5-8 minutes.

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