Heat treatment process of nodular cast iron male die casting

Abstract

A heat treatment process of a nodular cast iron terrace die casting belongs to the technical field of lost foam nodular cast iron heat treatment. According to the method, the cleaned nodular cast iron male die casting is sequentially subjected to two-section type preheating treatment, high-temperature quenching heat preservation, tempering treatment and cleaning and drying. The two-stage preheating treatment has a heat preservation process, so that the overall temperature of the nodular cast iron male die casting is uniformly increased. And the heat source of the preliminary preheating treatment is heat recovery in the subsequent cooling process, so that the energy is saved. And through high-temperature quenching and heat preservation treatment, an original matrix is converted into tempered martensite and retained austenite, so that the casting has high hardness and certain toughness, the lubricating property of graphite is reserved, and the wear resistance is enhanced. The ethylene-propylene-diene copolymer added into the quenching oil is a cooling accelerant and can accelerate the cooling process, the added high-temperature amine antioxidant can prevent part of tissues of a casting from being oxidized in the high-temperature quenching process, and the added fatty glyceride can reduce the surface activity of the quenching oil, so that rapid heat exchange is realized.

Description

Technical Field

[0001] The invention belongs to the technical field of lost foam ductile iron heat treatment, and in particular relates to a heat treatment process for a ductile iron male mold casting. Background Art

[0002] Ductile iron is a type of cast iron in which carbon is precipitated as spherical graphite through spheroidization and inoculation, and the graphite is distributed in a spherical shape. It has good castability, wear resistance, and machinability. Ductile iron has excellent mechanical properties and process properties, and its mechanical properties can be further improved through heat treatment. Therefore, it can be used to manufacture parts with large loads and complex forces, and can even replace steel to manufacture certain important parts, such as diesel engine crankshafts, connecting rods, gears, machine tool spindles, etc., and has broad application prospects. The punch is an important component of the automotive mold, which requires sufficient strength and rigidity, good thermal conductivity, high temperature resistance, high pressure resistance, corrosion resistance, and wear resistance.

[0003] The as-cast structure of ductile iron punch castings currently produced is mainly composed of spheroidal graphite structure and austenite structure. The tensile strength is low and the complex structure castings are easy to deform. The tensile strength and wear resistance of the castings cannot meet the requirements of automotive mold parts, especially the tensile strength and wear resistance of drawing mechanism molds. They must be interfered and adjusted through corresponding effective heat treatment methods to meet the mechanical properties of the products and customer requirements.

[0004] Therefore, a new technical solution is urgently needed in the prior art to solve this problem. Summary of the invention

[0005] The technical problem to be solved by the present invention is to provide a heat treatment process for ductile iron male mold castings to solve the technical problems in the prior art that the tensile strength is low and the castings with complex structures are easy to deform, and their tensile strength and wear resistance do not meet the requirements of automobile mold parts.

[0006] A heat treatment process for a ductile iron male die casting comprises the following steps, and the following steps are performed in sequence: Step 1: Pretreatment of castings; The casting pretreatment includes cleaning and preheating of the outer surface of the ductile iron male mold casting; the preheating treatment includes preliminary preheating treatment and active preheating treatment; The preliminary preheating treatment uses a heat recovery preheating device, which recovers the waste heat generated during quenching and tempering to preheat and keep the ductile iron male mold casting warm; In the active preheating treatment, an active preheating device is used to preheat the ductile iron male mold casting after preliminary preheating and keep it warm, so that the temperature of the ductile iron male mold casting reaches 440 to 480 degrees Celsius; Step 2: quenching treatment; The preheated ductile iron male mold casting is heated to between 865 and 898 degrees Celsius by a heating device and kept warm for 30 to 35 minutes, and then the heated ductile iron male mold casting is quickly placed in quenching oil for 50 to 75 seconds to reduce the temperature of the ductile iron male mold casting to 360 to 420 degrees Celsius, and the original matrix is ​​converted into tempered martensite and residual austenite by quenching; Step 3: Tempering treatment; The quenched ductile iron male mold casting is placed in a tempering device, the ductile iron male mold casting is heated to 480-500 degrees Celsius, and kept warm for 50-60 minutes, and then the temperature of the ductile iron male mold casting is lowered to room temperature through an air cooling device; and the heat generated by the air heat exchange is recovered through a heat recovery preheating device; Step 4: Clean and dry.

[0007] In the step 1, the temperature of the ductile iron male mold casting reaches 230 to 260 degrees Celsius after preliminary preheating treatment, and the insulation time is 15 to 17 minutes.

[0008] In the step 1, the heat preservation time of the ductile iron male mold casting after preheating treatment is 20 to 23 minutes.

[0009] The components of the quenching oil in step 2 are: No. 10 machine oil, EPDM copolymer, high temperature amine antioxidant and fatty acid glyceride, wherein the mass ratio of each component is: 100 parts of No. 10 machine oil, 8 parts of EPDM copolymer, 5 parts of high temperature amine antioxidant and 6 parts of fatty acid glyceride.

[0010] In the step 2, the initial temperature of the quenching oil is 60 to 75 degrees Celsius. After the quenching treatment, the heat generated by the heat exchange of the quenching oil is recovered by the heat recovery preheating device to restore the temperature to 60 to 75 degrees Celsius. In the step 3, the heat generated by the air heat exchange in the air cooling device is recovered by the heat recovery preheating device.

[0011] The cleaning and drying in step 4 is specifically as follows: spraying cleaning liquid on the outer surface of the ductile iron male mold casting after tempering, brushing the ductile iron male mold casting with a brushing device, drying it, and then evenly applying a layer of protective oil on the outer surface of the ductile iron male mold casting to isolate the air and prevent oxidation.

[0012] Through the above design scheme, the present invention can bring the following beneficial effects: The present invention performs a two-stage preheating treatment on the cleaned ductile iron male mold casting. First, the ductile iron male mold casting is preliminarily preheated by a heat recovery preheating device. The heat source of this treatment process is the heat recovery during the subsequent cooling process, which saves energy. In the two-stage preheating treatment, the overall temperature of the ductile iron male mold casting is uniformly increased by heat preservation treatment, thereby avoiding the problem of uneven heating during the heating process.

[0013] The present invention makes the original matrix completely austenitized by high-temperature quenching and heat preservation treatment, and then converts the original matrix into tempered martensite and residual austenite structure in the process of cooling the ductile iron male mold casting by the cooling effect of quenching oil. The casting after quenching treatment has high hardness and certain toughness, retains the lubrication property of graphite, and has enhanced wear resistance. By adding ethylene propylene copolymer as a cooling agent in the quenching oil, the cooling process of oil quenching can be effectively accelerated, and by adding a high-temperature amine antioxidant, the problem of partial organization being oxidized in the ductile iron male mold casting during high-temperature quenching is avoided, and by adding a fatty acid glyceride surfactant, the surface activity of the quenching oil can be effectively reduced, thereby achieving the purpose of rapid heat exchange.

[0014] The present invention performs tempering treatment on the ductile iron male die casting, so that the original matrix is ​​converted into tempered martensite and residual austenite structure, the original spheroidal graphite morphology remains unchanged, the treated casting has high hardness and certain toughness, the lubrication property of graphite is retained, and the wear resistance is enhanced. Through the coordination of multiple heat treatment processes, the treated ductile iron male die casting has high strength, high toughness and good comprehensive mechanical properties. Finally, a layer of protective oil is applied on its outer surface to isolate the ductile iron male die casting from the air, slow down the oxidation process of the ductile iron male die casting, and ensure the stability of various properties of the ductile iron male die casting after heat treatment. The casting after heat treatment of the present invention can meet the mechanical properties of automobile mold castings and customer use requirements. DETAILED DESCRIPTION

[0015] The present invention is further described in detail below in conjunction with embodiments: The invention provides a heat treatment process for a ductile iron male mold casting, which comprises the following steps: Step 1: Pretreatment of castings; Casting pretreatment includes cleaning and preheating of the outer surface of ductile iron male castings.

[0016] Immerse the ductile iron male mold casting completely in the cleaning liquid for 5 minutes, then use the brushing device to fully brush the outer surface of the casting, and finally rinse the casting with clean water. Clean the impurities attached to the outer surface of the ductile iron male mold casting as clean as possible to avoid certain components carried by the impurities during the heat treatment process, which may affect the properties of the ductile iron male mold casting.

[0017] The cleaned ductile iron male die casting is subjected to a two-stage preheating treatment: First, the cleaned ductile iron male mold casting is preheated by a heat recovery preheating device, so that the temperature of the ductile iron male mold casting reaches 230-260 degrees Celsius and is kept warm for 15-17 minutes. The heat source of this process is the heat recovery during the subsequent cooling process, so the temperature of the initial preheating treatment is limited.

[0018] Then, the ductile iron male mold casting is preheated by an active preheating device so that the temperature of the ductile iron male mold casting reaches 440 to 480 degrees Celsius, and the temperature is kept for 20 to 23 minutes.

[0019] In both preheating treatments, it is necessary to keep the castings warm for a period of time. Through a long period of heat preservation, the overall temperature of the ductile iron male casting can be evenly increased, thus avoiding the problem of uneven heating during the heating process.

[0020] Step 2: quenching treatment; The preheated ductile iron male mold casting is heated to between 865 and 898 degrees Celsius by a heating device and kept warm for 30 to 35 minutes. The heated ductile iron male mold casting is then quickly placed in the quenching oil and soaked for 50 to 75 seconds to reduce the temperature of the ductile iron male mold casting to 360 to 420 degrees Celsius. The components of the quenching oil are: No. 10 machine oil, EPDM copolymer, high-temperature amine antioxidant, and fatty acid glyceride. The mass ratio of each component is: No. 10 machine oil 100 parts, EPDM copolymer 8 parts, high-temperature amine antioxidant 5 parts, and fatty acid glyceride 6 parts. The initial temperature of the quenching oil is 60 to 75 degrees Celsius. The heat generated by the heat exchange of the quenching oil is recovered by a heat recovery preheating device for preheating the ductile iron male mold casting, and the temperature of the quenching oil is restored to 60 to 75 degrees Celsius.

[0021] In this embodiment, the original matrix is ​​completely austenitized through high-temperature quenching and heat preservation treatment, and then the original matrix is ​​converted into tempered martensite and residual austenite structure during the cooling process of the ductile iron male mold casting through the cooling effect of the quenching oil. The casting after quenching has high hardness and certain toughness, retains the lubricating properties of graphite, and has enhanced wear resistance. By adding ethylene propylene diene copolymer as a cooling agent to the quenching oil, the cooling process of oil quenching can be effectively accelerated. By adding high-temperature amine antioxidants, the problem of partial oxidation of the structure of the ductile iron male mold casting during high-temperature quenching can be avoided. By adding fatty acid glyceride surfactants, the surface activity of the quenching oil can be effectively reduced, thereby achieving the purpose of rapid heat exchange.

[0022] Step 3: Tempering treatment; The quenched ductile iron male mold casting is quickly placed in the tempering device, and the ductile iron male mold casting is gradually heated to 480-500 degrees Celsius and kept warm for 50-60 minutes. The temperature of the ductile iron male mold casting is gradually reduced to room temperature through an air cooling device, and the heat generated by the air heat exchange is recovered through a heat recovery preheating device for preheating the ductile iron male mold casting. A certain amount of cleaning liquid is sprayed on the outer surface of the heat-treated ductile iron male mold casting, and the ductile iron male mold casting is brushed through a brushing device, and then dried. After drying, a layer of protective oil is evenly applied on the outer surface of the ductile iron male mold casting.

[0023] In this embodiment, the ductile iron male mold casting is tempered so that the original matrix is ​​converted into tempered martensite and residual austenite structure, the original spheroidal graphite morphology remains unchanged, the treated casting has high hardness and certain toughness, the lubricating properties of graphite are retained, and the wear resistance is enhanced. Through the coordination of multiple heat treatment processes, the treated ductile iron male mold casting has high strength, high toughness and good comprehensive mechanical properties.

[0024] Step 4: Clean and dry: The ductile iron male mold casting after heat treatment still needs to be cleaned to remove the impurities carried on the outer surface of the ductile iron male mold casting during the heat treatment process. The impurities attached to the outer surface of the ductile iron male mold casting during the treatment process are removed by cleaning and drying. Then, a layer of protective oil is applied on its outer surface to isolate the ductile iron male mold casting from the air, slow down the oxidation process of the ductile iron male mold casting, and ensure the stability of various properties of the ductile iron male mold casting after heat treatment.

[0025] The cleaning liquid is an aqueous solution in which the metal cleaning agent plays a major role. A mixed liquid can be used in which the metal cleaning agent accounts for 4% to 6% and the rest is water. The metal cleaning agent is mainly a non-ionic surfactant, which has strong cleaning power, simple application process, can be used in a variety of cleaning methods, and has good stability, corrosion inhibition, non-toxicity, non-flammability, safe use, low cost and other characteristics.

[0026] The protective oil may be common machine oil with a density of 0.8 g / cm³ to 0.96 g / cm³.

Claims

1. A heat treatment process for ductile iron male die casting, characterized in that: The method comprises the following steps, and the following steps are performed in sequence: Step 1: Pretreatment of castings; The casting pretreatment includes cleaning and preheating of the outer surface of the ductile iron male mold casting; the preheating treatment includes preliminary preheating treatment and active preheating treatment; The preliminary preheating treatment uses a heat recovery preheating device, which recovers the waste heat generated during quenching and tempering to preheat and keep the ductile iron male mold casting warm; In the active preheating treatment, an active preheating device is used to preheat the ductile iron male mold casting after preliminary preheating and keep it warm, so that the temperature of the ductile iron male mold casting reaches 440 to 480 degrees Celsius; Step 2: quenching treatment; The preheated ductile iron male mold casting is heated to between 865 and 898 degrees Celsius by a heating device and kept warm for 30 to 35 minutes, and then the heated ductile iron male mold casting is quickly placed in quenching oil for 50 to 75 seconds to reduce the temperature of the ductile iron male mold casting to 360 to 420 degrees Celsius, and the original matrix is ​​converted into tempered martensite and residual austenite by quenching; Step 3: Tempering treatment; The quenched ductile iron male mold casting is placed in a tempering device, the ductile iron male mold casting is heated to 480-500 degrees Celsius, and kept warm for 50-60 minutes, and then the temperature of the ductile iron male mold casting is lowered to room temperature through an air cooling device; and the heat generated by the air heat exchange is recovered through a heat recovery preheating device; Step 4: Clean and dry.

2. The heat treatment process for a ductile iron male die casting according to claim 1, characterized in that: In the step 1, the temperature of the ductile iron male mold casting reaches 230 to 260 degrees Celsius after preliminary preheating treatment, and the insulation time is 15 to 17 minutes.

3. The heat treatment process for a ductile iron male die casting according to claim 1, characterized in that: In the step 1, the heat preservation time of the ductile iron male mold casting after preheating treatment is 20 to 23 minutes.

4. The heat treatment process for a ductile iron male die casting according to claim 1, characterized in that: The components of the quenching oil in step 2 are: No. 10 machine oil, EPDM copolymer, high temperature amine antioxidant and fatty acid glyceride, wherein the mass ratio of each component is: 100 parts of No. 10 machine oil, 8 parts of EPDM copolymer, 5 parts of high temperature amine antioxidant and 6 parts of fatty acid glyceride.

5. The heat treatment process for a ductile iron male die casting according to claim 1, characterized in that: In the step 2, the initial temperature of the quenching oil is 60 to 75 degrees Celsius. After the quenching treatment, the heat generated by the heat exchange of the quenching oil is recovered by the heat recovery preheating device to restore the temperature to 60 to 75 degrees Celsius. In the step 3, the heat generated by the air heat exchange in the air cooling device is recovered by the heat recovery preheating device.

6. The heat treatment process for a ductile iron male die casting according to claim 1, characterized in that: The cleaning and drying in step 4 is specifically as follows: spraying cleaning liquid on the outer surface of the ductile iron male mold casting after tempering, brushing the ductile iron male mold casting with a brushing device, drying it, and then evenly applying a layer of protective oil on the outer surface of the ductile iron male mold casting to isolate the air and prevent oxidation.