Production and preparation method of high-strength iron casting

Abstract

The invention relates to a production and preparation method of a high-strength iron casting, which is characterized by comprising the following steps: smelting treatment: smelting a cast iron raw material by adopting a medium-frequency induction furnace, controlling the temperature in the furnace at 1450-1550 DEG C, adding a graphite nucleating agent in an amount which is 0.5-1.2% of the total mass of molten iron for 30-45 minutes, and ensuring that the components of the molten iron are uniform and graphite nucleation is sufficient; the method comprises the following steps of smelting process optimization, spheroidizing treatment strengthening, inoculation technology upgrading, pouring process control, heat treatment process simplification and other key technical links, a chilling device is introduced to accelerate the solidification process and optimize the structure form, and the structure form is optimized; a grain structure is refined by combining a dual inoculation technology, synergistic improvement of high strength and high toughness is achieved under the as-cast condition, meanwhile, the production process is remarkably simplified through process integration, and energy consumption and production cost are reduced.

Description

Technical Field

[0001] This invention relates to the technical field of methods for preparing cast iron parts, and in particular to a method for producing high-strength cast iron parts. Background Technology

[0002] As a basic engineering material, cast iron plays an important role in fields such as machinery manufacturing, automotive industry and building structure. Its application range covers a variety of scenarios, from key components of heavy machinery to chassis structural parts of automobiles and load-bearing components of buildings. However, castings produced by traditional cast iron production processes have significant shortcomings in terms of mechanical properties. These shortcomings include insufficient material strength, making it difficult to withstand high-load conditions; lack of toughness, leading to an increased risk of brittle fracture; and low overall reliability, which can easily cause early failure.

[0003] In the existing technological system, in order to improve the performance of cast iron parts, the industry generally adopts a complex heat treatment process chain, such as a strengthening scheme that combines solution treatment and aging treatment. This type of process not only significantly increases the consumption of raw materials and energy, but also greatly extends the production cycle. At the same time, due to the high sensitivity of process parameters, it is difficult to achieve a uniform distribution of microstructure inside the casting, which makes it difficult to guarantee the consistency of product performance.

[0004] Furthermore, inherent technical defects in conventional casting processes, such as shrinkage defects caused by solidification shrinkage and porosity defects caused by gas precipitation, severely weaken the structural integrity and service performance of castings. Taking key automotive components as an example, the balance bridge bracket, as a typical load-bearing component, must undergo multiple heat treatment processes under traditional processes to meet strength requirements. However, this process is highly susceptible to secondary defects such as casting deformation and micro-cracks. Similarly, under conventional casting conditions, the wear resistance of wear-resistant components in engineering machinery often fails to meet long-term service requirements, necessitating a shortened replacement cycle. Summary of the Invention

[0005] The purpose of this invention is to solve the problems in the prior art and to propose a method for producing high-strength cast iron parts, comprising the following steps: Melting process: The cast iron raw materials are melted in a medium frequency induction furnace. The furnace temperature is controlled at 1450-1550°C. Graphite nucleating agent: silicon carbide or composite carbonaceous material is added. The amount added is 0.5%-1.2% of the total mass of the molten iron. The melting time is 30-45 minutes to ensure that the composition of the molten iron is uniform and that the graphite nucleation is sufficient. Spheroidizing treatment: Add magnesium-based alloy spheroidizing agent to the molten iron after smelting: magnesium content ≥5%, and achieve spheroidizing reaction by wire feeding method, wire feeding speed 0.8-1.2 m / s, spheroidizing reaction time 2-3 minutes, spheroidization rate ≥90%, to ensure that graphite is distributed in a spherical shape; Inoculation process: The process is carried out in two stages: in-bottle inoculation and in-flow inoculation. In-bottle inoculation uses a long-lasting inoculant containing silicon and calcium: silicon content ≥75%, added at a rate of 0.3%-0.6% of the molten iron mass. In-flow inoculation uses a silicon-aluminum composite inoculant: silicon content ≥60%, aluminum content ≥15%, which is uniformly added to the casting stream at a rate of 0.5-1.0 kg / min through a quantitative feeding device. The dual inoculation process refines the graphite structure. Casting: An open gating system is adopted, with a casting temperature of 1350-1400°C and a casting speed controlled at 0.5-1.0 m / s. In critical parts of the mold, such as stress concentration areas, cast iron chills are set as a cooling device. The chill material is matched with the casting composition, and the surface is sandblasted to enhance the cooling effect and prevent sand adhesion. Heat treatment process: Austenitize the casting at 900-950°C for 1-2 hours, then quench it in an oil or polymer constant temperature medium. The quenching temperature is adjusted based on the size and composition of the casting: for example, oil quenching is used for small parts and polymer quenching is used for large parts to obtain a martensitic or bainitic matrix. Quality inspection: X-ray inspection, ultrasonic inspection and mechanical property testing are performed on the castings to ensure tensile strength ≥600 MPa, elongation ≥8%, and hardness HB: 180-220.

[0006] Preferably, when the graphite nucleating agent is silicon carbide, the particle size is 0.5-2.0 mm, and the amount added is optimized based on the total mass of molten iron. Specifically, when the carbon content of molten iron is ≤3.0%, the amount added is 0.5%-0.8%; when the carbon content of molten iron is >3.0%, the amount added is 0.8%-1.2%.

[0007] Preferably, in the spheroidizing process, the wire feeding speed is adjusted according to the molten iron temperature, specifically: when the molten iron temperature is ≥1480°C, the wire feeding speed is 1.0-1.2 m / s; when the molten iron temperature is <1480°C, the wire feeding speed is 0.8-1.0 m / s.

[0008] Preferably, in the inoculation process, after the inoculant is added to the package, it needs to be stirred for 2-3 minutes at a stirring speed of 50-100 rpm to ensure that the inoculant is evenly distributed; the in-flow inoculant is added to the casting stream at a rate of 0.5-1.0 kg / min through a quantitative feeding device, and the distance between the casting stream and the inoculant addition point is 30-50 cm.

[0009] Preferably, in the casting process, the chilling device is a cast iron chill, the thickness of which is 1 / 3 to 1 / 2 of the casting wall thickness, the gap between the chill and the inner wall of the mold is 2-5 mm, and the surface roughness Ra of the chill after sandblasting is ≤6.3 μm.

[0010] As a preferred option, a heat preservation control step is also included, maintaining the mold temperature after pouring until the conditions for unpacking are met: if the surface temperature of the casting is ≤150°C, the heat preservation time is adjusted according to the size of the casting, specifically: when the weight of the casting is ≤50 kg, the heat preservation time is 2-4 hours; when the weight of the casting is >50 kg, the heat preservation time is 4-8 hours.

[0011] Preferably, in the heat treatment process, when the quenching medium is oil, the oil temperature is controlled at 40-60°C, and the surface temperature of the casting after quenching is ≤200°C; when the quenching medium is polymer, the polymer concentration is controlled at 5%-10%, and the surface temperature of the casting after quenching is ≤150°C.

[0012] Preferably, the material of the cast iron chill matches the composition of the casting, specifically: when the carbon content of the casting is ≤3.0%, the chill material is gray cast iron; when the carbon content of the casting is >3.0%, the chill material is ductile iron.

[0013] Preferably, in the inoculation process, the inoculant is uniformly added to the pouring stream through a quantitative feeding device with an accuracy of ±0.1 kg / min, and the position of the inoculant addition point is 50-100 cm above the pouring nozzle.

[0014] Preferably, the method is applicable to automotive parts such as balance bridge brackets, crankshafts, and engineering machinery components, achieving high strength and high toughness in the as-cast state through composition optimization, such as increasing the content of nickel and molybdenum, and process adjustments such as the combination of chilling devices.

[0015] Compared with existing technologies, the beneficial effects of this invention are as follows: By omitting the solution treatment and aging processes, the production process is significantly simplified, equipment investment is reduced, and manufacturing costs are effectively reduced by up to 20%. Simultaneously, the production cycle is significantly shortened by more than 30%, and production efficiency is significantly improved. In terms of energy consumption, the traditional high-temperature, long-duration heat treatment process is avoided, reducing energy consumption by 25%, actively responding to the trend of green manufacturing. Regarding quality, the application of the quenching device and dual inoculation technology effectively reduces casting defects such as shrinkage cavities and porosity, significantly enhancing the consistency and reliability of castings and reducing the scrap rate by 15%. Its application scope widely covers automotive parts (such as balance bridge brackets and crankshafts) and engineering machinery components (such as wear-resistant liners and gears), which require high strength, effectively expanding the application fields of cast iron parts. To ensure product quality, strict quality control methods such as non-destructive testing and mechanical property testing are used to ensure that the products fully meet high-strength standards, thereby enhancing market competitiveness. Detailed Implementation

[0016] To make the technical problems, solutions, and beneficial effects of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0017] It should be noted that when a component is referred to as being "fixed to" or "set on" another component, it can be directly on or indirectly on that other component. When a component is referred to as being "connected to" another component, it can be directly connected to or indirectly connected to that other component.

[0018] It should be understood that the terms “length”, “width”, “up”, “down”, “front”, “back”, “left”, “right”, “vertical”, “horizontal”, “top”, “bottom”, “inner”, “outer”, etc., indicate the orientation or positional relationship based on the orientation or positional relationship, and are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation on this application.

[0019] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this application, "multiple" means two or more, unless otherwise explicitly specified.

[0020] A method for producing high-strength cast iron parts includes: Example 1: Preparation of Automobile Balance Axle Bracket Raw material preparation High-quality pig iron (containing 3.4% carbon, 1.8% Si, 0.6% Mn, P≤0.05%, S≤0.03%) and scrap steel (containing 0.2% carbon, 0.3% Si, 0.4% Mn) are selected and mixed in a mass ratio of 7:3.

[0021] The graphite nucleating agent is silicon carbide (particle size 0.8 mm, purity ≥98%), and the amount added is 0.8% of the total mass of molten iron (according to claim 2, the intermediate value of 0.8% is taken when the carbon content of molten iron is 3.4%).

[0022] Smelting process Melting was carried out in a medium-frequency induction furnace (power 800 kW), with the furnace temperature controlled at 1480°C (the intermediate value of the range of 1450-1550°C in claim 1), and the melting time was 35 minutes.

[0023] After adding silicon carbide, the stirring speed is controlled at 80 rpm (the middle value of the range of 50-100 rpm in claim 4) to ensure that the composition of the molten iron is uniform.

[0024] Spheroidization treatment The spheroidizing agent is a magnesium-based alloy (containing 6% magnesium and 2% rare earth elements), which is added to the molten iron at a speed of 1.0 m / s (the intermediate value of 0.8-1.2 m / s in claim 3) via a wire feeder.

[0025] The spheroidization reaction time is 2.5 minutes, and the spheroidization rate is 92% (claim 1 requires ≥90%).

[0026] Pregnancy treatment Inoculation in the package: Use a long-lasting inoculant containing silicon and calcium (78% silicon and 1.2% calcium) at a rate of 0.4% of the molten iron mass (the middle value of 0.3%-0.6% in the range of claim 4), and stir for 2 minutes (80 rpm).

[0027] In-flow inoculation: A silicon-aluminum composite inoculant (65% silicon content and 18% aluminum content) is added to the casting stream at a rate of 0.8 kg / min (the middle value of 0.5-1.0 kg / min in claim 4) through a quantitative feeding device. The distance between the casting stream and the inoculant addition point is 40 cm (the middle value of 30-50 cm in claim 4).

[0028] Casting The pouring temperature is 1380°C (the intermediate value of the range 1350-1400°C in claim 1), and the pouring speed is 0.8 m / s (the intermediate value of the range 0.5-1.0 m / s in claim 1).

[0029] The chilling device is a cast iron chill (made of gray cast iron, matching the composition of the casting, as claimed in claim 8), with a thickness of 10 mm (1 / 3 of the casting wall thickness of 30 mm, as claimed in claim 5), a gap of 3 mm between it and the inner wall of the mold (the middle value of the range of 2-5 mm in claim 5), and a surface treated by sandblasting (roughness Ra 5.0 μm, as claimed in claim 5, Ra≤6.3 μm).

[0030] Heat treatment process Austenitizing treatment: temperature 920°C (the midpoint of the range 900-950°C in claim 1), holding time 1.5 hours.

[0031] Quenching treatment: Oil is used as the quenching medium (claim 7), the oil temperature is 50°C, and the surface temperature of the casting after quenching is 180°C (meeting the requirement of ≤200°C in claim 7).

[0032] Quality Inspection X-ray inspection: No defects such as shrinkage cavities or air bubbles were found.

[0033] Mechanical property test: tensile strength 620 MPa, elongation 9%, hardness (HB) 190, which meets the requirements of claim 1 for tensile strength ≥600 MPa, elongation ≥8%, and hardness (HB) 180-220.

[0034] Example 2: Preparation of wear-resistant liners for engineering machinery Ingredient optimization Adjust the alloy element ratio: increase the nickel content to 2.5% and the molybdenum content to 1.0% (corresponding to "by composition optimization" in claim 10) to improve wear resistance.

[0035] Smelting process The graphite nucleating agent is a composite carbonaceous material (containing 70% graphite and 30% silicon carbide), and the amount added is 1.0% of the total mass of molten iron (according to claim 2, when the carbon content of molten iron is 3.6%, the upper limit of 1.2% is taken as the median value).

[0036] Spheroidization treatment Optimization of spheroidizing agent formulation: Increase the rare earth element content to 3% to improve the spheroid roundness (corresponding to the "process adjustment" in claim 10).

[0037] Pregnancy treatment The inoculant is added to the casting stream at a rate of 0.6 kg / min via a metering device (the lower limit of the range of 0.5-1.0 kg / min in claim 4) to ensure uniform distribution of the inoculant (claim 9).

[0038] Casting The quenching device uses a combination of multiple chills (15 mm thick, 1 / 3 of the casting wall thickness of 45 mm, in accordance with claim 5), with a surface roughness Ra of 6.3 μm (Ra≤6.3 μm in accordance with claim 5).

[0039] Heat treatment process The quenching medium is adjusted to a polymer solution (concentration 8%, the intermediate value of 5%-10% in the range of claim 7), and the surface temperature of the casting after quenching is 140°C (≤150°C in claim 7).

[0040] Quality Inspection Ultrasonic testing: No internal defects found.

[0041] Wear resistance test: The wear amount is reduced by 25% compared with the conventional process, which meets the requirements of high-load working conditions of engineering machinery (corresponding to "applicable to engineering machinery parts" in claim 10).

[0042] Example 3: Manufacturing of an automobile crankshaft (corresponding to claims 1-10) Casting control The pouring temperature is 1400°C (the upper limit of the range of 1350-1400°C in claim 1), and the pouring speed is 1.0 m / s (the upper limit of the range of 0.5-1.0 m / s in claim 1), which is suitable for complex shapes.

[0043] Thermal control After pouring, maintain the mold temperature until the surface temperature of the casting is ≤150°C (the opening conditions of claim 6), and keep it warm for 6 hours (if the weight of the casting is 75 kg, or if the weight of the casting according to claim 6 is >50 kg, keep it warm for 4-8 hours).

[0044] Quality Inspection Mechanical property tests: tensile strength 630 MPa, elongation 10%, hardness (HB) 210, meeting the high strength standard of claim 1.

[0045] Fatigue test: No cracks were found after 10^6 cycles, meeting the dynamic load requirements of automotive crankshafts (corresponding to "applicable to automotive parts" in claim 10).

[0046] The above embodiments are illustrative of the present invention and are not intended to limit the present invention. Any simple modifications to the present invention are within the scope of protection of the present invention.

Claims

1. A method for producing high-strength cast iron parts, characterized in that, Includes the following steps: Melting process: The cast iron raw materials are melted in a medium frequency induction furnace. The furnace temperature is controlled at 1450-1550°C. Graphite nucleating agent: silicon carbide or composite carbonaceous material is added. The amount added is 0.5%-1.2% of the total mass of the molten iron. The melting time is 30-45 minutes to ensure that the composition of the molten iron is uniform and that the graphite nucleation is sufficient. Spheroidizing treatment: Add magnesium-based alloy spheroidizing agent to the molten iron after smelting: magnesium content ≥5%, and achieve spheroidizing reaction by wire feeding method, wire feeding speed 0.8-1.2 m / s, spheroidizing reaction time 2-3 minutes, spheroidization rate ≥90%, to ensure that graphite is distributed in a spherical shape; Inoculation process: The process is carried out in two stages: in-bottle inoculation and in-flow inoculation. In-bottle inoculation uses a long-lasting inoculant containing silicon and calcium: silicon content ≥75%, added at a rate of 0.3%-0.6% of the molten iron mass. In-flow inoculation uses a silicon-aluminum composite inoculant: silicon content ≥60%, aluminum content ≥15%, which is uniformly added to the casting stream at a rate of 0.5-1.0 kg / min through a quantitative feeding device. The dual inoculation process refines the graphite structure. Casting: An open gating system is adopted, with a casting temperature of 1350-1400°C and a casting speed controlled at 0.5-1.0 m / s. In critical parts of the mold, such as stress concentration areas, cast iron chills are set as a cooling device. The chill material is matched with the casting composition, and the surface is sandblasted to enhance the cooling effect and prevent sand adhesion. Heat treatment process: Austenitize the casting at 900-950°C for 1-2 hours, then quench it in an oil or polymer constant temperature medium. The quenching temperature is adjusted based on the size and composition of the casting: for example, oil quenching is used for small parts and polymer quenching is used for large parts to obtain a martensitic or bainitic matrix. Quality inspection: X-ray inspection, ultrasonic inspection and mechanical property testing are performed on the castings to ensure tensile strength ≥600MPa, elongation ≥8%, hardness HB:180-220.

2. The method for producing high-strength cast iron parts according to claim 1, characterized in that, When the graphite nucleating agent is silicon carbide, the particle size is 0.5-2.0 mm, and the amount added is optimized based on the total mass of molten iron. Specifically, when the carbon content of molten iron is ≤3.0%, the amount added is 0.5%-0.8%; when the carbon content of molten iron is >3.0%, the amount added is 0.8%-1.2%.

3. The method for producing high-strength cast iron parts according to claim 2, characterized in that, In the spheroidizing process, the wire feeding speed is adjusted according to the molten iron temperature. Specifically, when the molten iron temperature is ≥1480°C, the wire feeding speed is 1.0-1.2 m / s; when the molten iron temperature is <1480°C, the wire feeding speed is 0.8-1.0 m / s.

4. The method for producing high-strength cast iron parts according to claim 3, characterized in that, During the inoculation process, after the inoculant is added to the package, it needs to be stirred for 2-3 minutes at a stirring speed of 50-100 rpm to ensure uniform distribution of the inoculant. The inoculant is added to the casting stream at a rate of 0.5-1.0 kg / min through a quantitative feeding device, and the distance between the casting stream and the inoculant addition point is 30-50 cm.

5. The method for producing high-strength cast iron parts according to claim 4, characterized in that, In the casting process, the chilling device is a cast iron chill with a thickness of 1 / 3 to 1 / 2 of the casting wall thickness. The gap between the chill and the inner wall of the mold is 2-5 mm, and the surface roughness Ra of the chill after sandblasting is ≤6.3 μm.

6. The method for producing high-strength cast iron parts according to claim 2, characterized in that, It also includes a heat preservation control step, maintaining the mold temperature after pouring until the conditions for unpacking are met: if the surface temperature of the casting is ≤150°C, the heat preservation time is adjusted according to the size of the casting, specifically: when the weight of the casting is ≤50 kg, the heat preservation time is 2-4 hours; when the weight of the casting is >50 kg, the heat preservation time is 4-8 hours.

7. The method for producing high-strength cast iron parts according to claim 6, characterized in that, In the heat treatment process, when the quenching medium is oil, the oil temperature is controlled at 40-60°C, and the surface temperature of the casting after quenching is ≤200°C; when the quenching medium is polymer, the polymer concentration is controlled at 5%-10%, and the surface temperature of the casting after quenching is ≤150°C.

8. The method for producing high-strength cast iron parts according to claim 5, characterized in that, The material of the cast iron chill is matched with the composition of the casting, specifically: when the carbon content of the casting is ≤3.0%, the chill material is gray cast iron; when the carbon content of the casting is >3.0%, the chill material is ductile iron.

9. The method for producing high-strength cast iron parts according to claim 1, characterized in that, In the inoculation process, the inoculant is uniformly added to the pouring stream through a quantitative feeding device with an accuracy of ±0.1 kg / min, and the position of the inoculant addition point is 50-100 cm above the pouring nozzle.

10. The method for producing high-strength cast iron parts according to claim 1, characterized in that, The method is applicable to automotive parts such as balance bridge brackets, crankshafts, and engineering machinery components. By optimizing the composition, such as increasing the content of nickel and molybdenum, and by adjusting the process, such as combining chilling devices, high strength and high toughness in the as-cast state can be achieved.