Application of Austempered Ductile Iron (ADI) in Engineering Machinery and Agricultural Machinery Castings

Abstract

An application method of austempered ductile iron (ADI) in castings for construction machinery and agricultural machinery, the steps include: 1) Selection and composition control of raw materials: The main raw material is high-purity pig iron, and other chemical components are: w Si <0.4%, w Mn <0.2%, w P <0.03%, w S <0.02%; The scrap steel is carbon steel scrap; 2) Production process control: For a 500 kg nodulizing ladle, the nodulizing temperature is controlled at 1500 - 1530 °C; The molten iron is pretreated with 0.15% of the pretreatment agent; The nodulizer is selected with an addition amount of 1.1 - 1.2%, and the nodulizing time is 60 - 90 seconds; After nodulizing is completed, 0.4% of the inoculant is added by transferring the ladle for the first inoculation; The molten iron is inoculated during pouring with an inoculant having a particle size of 0.2 - 0.5 mm and an inoculation amount of 0.1% for the first inoculation; The pouring temperature is 1420 ± 20 °C; 3) Requirements for ADI austempering of ductile iron: Austenitization: 820 - 930 °C, for 1.5 - 3 hours; Quenching: Quenching is stopped between 230 - 390 °C; Quenching time: The time is at least 1 hour, preferably 1.5 hours.

Description

Technical Field

[0001] The technical solution belongs to the field of casting technology, and specifically is an application method of ADI in engineering machinery and agricultural machinery. Technical Background

[0002] With the rapid development of the equipment manufacturing industry, the requirements for castings are becoming higher and higher. In the field of cast iron, many cast irons with high standards and high requirements have appeared. Austempered ductile iron ADI and austempered ductile iron CADI are among them.

[0003] There are many factors that affect the production process of isothermal annealing ductile iron CADI parts. The size and distribution of spheroidal graphite in the cast structure have a great influence on the isothermal transformation and mechanical properties of austenite. Small, large and evenly distributed graphite balls will accelerate the transformation of acicular ferrite, make the quenched structure finer, and have better fatigue strength and impact toughness. Therefore, the casting should be free of non-metallic inclusions, carbides, shrinkage and slag. Proper storage and use of furnace charges can reduce the probability of carbide and gas defects. Proper molding control can minimize the surface and subcutaneous defects of castings. The casting gating system should be properly designed, and stable and effective spheroidization and inoculation technology should be used during the casting process to obtain castings without shrinkage. Any inconsistency with the above will reduce the "quality" of ADI parts. Summary of the invention

[0004] The present invention proposes a method for applying austempered ductile iron (ADI) to engineering machinery and agricultural machinery castings, the steps comprising:

[0005] 1) Raw material selection and composition control:

[0006] 1.1) The main raw material is high-purity pig iron, and the other chemical components are (mass fraction): w Si <0.4﹪、w Mn <0.2﹪、w P <0.03﹪、w S <0.02﹪, the mass fraction of the total amount of other harmful elements does not exceed 0.2﹪;

[0007] The scrap steel is carbon scrap steel; the recarburizer is a recarburizer with a particle size of 0.5-mm;

[0008] 1.2) Chemical composition control

[0009] Carbon equivalent CE = %C + 1 / 3 (%Si), carbon equivalent should be controlled according to the following parameters:

[0010] Diagonal size of casting section Carbon equivalent range 0-13mm 4.4–4.6 13-51mm 4.3–4.6 More than 51mm 4.3–4.5

[0011] 2) Production process control

[0012] 2.1) Spheroidization inoculation treatment 500kg spheroidization bag, spheroidization temperature controlled at 1500 ~ 1530 ℃, sandwich injection method;

[0013] 2.2) Use 0.15% pretreatment agent to pretreat the molten iron;

[0014] 2.3) The dosage of spheroidizing agent is 1.1-1.2%, and the spheroidizing time is 60-90 seconds;

[0015] 2.4) Covering the spheroidizing agent with carbon scrap steel;

[0016] 2.5) After spheroidization is completed, add 0.4% inoculant with a particle size of 0.7-3mm for the first inoculation;

[0017] 2.6) Use inoculant to inoculate the molten iron with the inoculant particle size of 0.2-0.5mm and the inoculation amount of 0.1% for the first inoculation;

[0018] 2.7) The pouring temperature is 1420±20℃;

[0019] 3) Molding process control

[0020] Requirements for ADI austempering of ductile iron:

[0021] Austenitizing: 820-930°C, 1.5-3 hours;

[0022] Quenching: Stop quenching at 230-390℃;

[0023] Quenching time: at least 1 hour, preferably 1.5 hours. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 It is a top view schematic diagram of the primary and secondary molten iron flow channels of the double inoculation device of the present invention;

[0025] Figure 2 This is the first top view of the molten iron flow path (inside the sand box);

[0026] Figure 3 This is the first longitudinal cross-sectional diagram of the molten iron flow path (inside the sand box);

[0027] Figure 4 It is a schematic diagram of the longitudinal section of the secondary molten iron flow channel (inside the sand box).

[0028] In the figure: the first molten iron flow channel 1, the sand box 2, the casting sand 3, the branch channel 4, the vertical channel 5, the pouring cup 6, the molten iron outlet 7, the parting surface 8, the secondary molten iron flow channel 9, the delivery port 10, the filler 11, and the block inoculant 12. DETAILED DESCRIPTION

[0029] The method is described below in conjunction with embodiments:

[0030] The method of this example is to use austempered ductile iron (ADI) to manufacture agricultural machinery opener castings, and the steps include:

[0031] 1) Raw material selection and composition control:

[0032] 1.1) The raw material is high-purity pig iron, and its chemical composition is (mass fraction): w Si <0.4﹪、w Mn <0.2﹪、w P <0.03﹪、w S <0.02﹪, the mass fraction of the total amount of other harmful elements does not exceed 0.2﹪, including spheroidization interference elements (Ti, As, V, Sb, Bi);

[0033] The scrap steel is high-quality carbon scrap steel (mainly leftover briquettes from the stamping of iron parts);

[0034] The recarburizer is a 0.5-5mm particle size recarburizer produced by Elkem Elgraph.

[0035] 1.2) Chemical composition control

[0036] Carbon equivalent CE = %C + 1 / 3 (%Si), carbon equivalent should be controlled according to the following parameters:

[0037] Diagonal size of casting section Carbon equivalent range 0-13mm 4.4–4.6 13-51mm 4.3–4.6 More than 51mm 4.3–4.5

[0038] The ingredients are controlled as follows:

[0039]

[0040]

[0041] 2) Production process control

[0042] Key points of ADI production:

[0043] 2.1) High spheroidization rate and graphite nodule number so that carbon can easily diffuse throughout the matrix.

[0044] 2.2) If the as-cast structure is defective, heat treatment cannot solve the problem and usually makes it worse.

[0045] Tests show that the production of ADI requires a high spheroidization rate and a high number of graphite nodules. This requires that the molten iron can form nuclei well and have a suitable magnesium content so that the ideal metallographic structure can be obtained after adding the inoculant.

[0046] Practice has proved that two inoculation processes can make the casting have a very good metallographic structure, which is convenient for subsequent heat treatment and thus produces ADI that meets performance requirements.

[0047] As we all know, to produce a good cast matrix structure, correct inoculation is a basic requirement. ADI or CADI contains high Mn and Mo or Cr. These elements tend to segregate seriously at the grain boundaries. Good inoculation can suppress this defect. Low segregation means better mechanical properties and processability.

[0048] 2.3) Pretreatment agent - The quality of raw materials of the charge has a direct impact on the number of graphite nodules and the spheroidization rate.

[0049] It has been found in ADI production practice that the selection of appropriate pretreatment agents can ensure the potential core number of the original molten iron, thereby producing ductile iron that meets performance requirements.

[0050] Therefore, in order to ensure the production of good ADI, it is necessary to ensure the production of good cast ductile iron first. Therefore, the following pretreatment agents, spheroidizing agents, inoculants, carburizers and process methods are selected;

[0051] The following are the mass percentages of the molten iron mass:

[0052] Spheroidization inoculation treatment 500kg spheroidization bag, spheroidization temperature controlled at 1500-1530℃, sandwich injection method;

[0053] Use 0.15% of EIkem Preseed pretreatment agent to pretreat the molten iron;

[0054] The spheroidizer is EIkem LAMET5922, the addition amount is 1.1-1.2%, and the spheroidization time is 60-90 seconds;

[0055] Cover the spheroidizer with high-quality carbon scrap steel (which can be 5mm thin steel sheets);

[0056] After spheroidization is completed, 0.4﹪Elkem Ressed inoculant is added to the subcontractor with a particle size of 0.7-3mm;

[0057] The Elkem SMZ inoculant was used to inoculate the molten iron with a particle size of 0.2-0.5 mm and an inoculation amount of 0.1%.

[0058] The temperature of molten iron is strictly controlled; the pouring temperature is 1420±20℃.

[0059] Modeling process

[0060] Horizontal cladding process, open pouring system.

[0061] Process requirements for ADI isothermal quenching of ductile iron:

[0062] ADI has both good ductility and high hardness, which seems contradictory, but this can be explained by its organization.

[0063] Since the ADI matrix consists of two different tissues:

[0064] --40% retained austenite (stably controlled by precise carbon content) ensures ductility.

[0065] --60% acicular ferrite ensures strength.

[0066] Austenitization: 820-930℃, 1.5-3 hours, uniform diffusion of fully austenitized carbon in the matrix. Carbon diffusion is very important, which ensures the stability of the retained austenite. Incompletely stable austenite has a tendency to turn into martensite.

[0067] Quenching: To get a good ADI, we need the right cooling rate and stop quenching between 230-390°C. To do this, the ideal quenching medium is molten salt. Cooling too slowly will enter the pearlite range. Cooling too quickly will produce martensite.

[0068] Hardenability: For large castings, the surface and the core cool at different rates, and the core will be all pearlite. By adding Cu, Ni and Mo, the Bain curve can be correctly shifted to the correct position, giving more space for quenching large castings.

[0069] Austempering time: The casting must be kept at austenitizing temperature for a sufficient time to obtain the desired structure. This time is at least 1 hour, and the optimal time is 1.5 hours. If the holding time is too long, it will enter the bainite range.

[0070] Chemical composition: The basic composition of ADI is not much different from that of normal ductile iron. For example (mass percentage):

[0071] C Si Mn P S 3.6-3.8 1.8-2.2 0.3Max 0.06Max 0.015Max

[0072] The main difference is the addition of specific alloy elements, such as Cu, Cr, Mo, Ni, etc.

[0073] The casting product obtained by the method has the following performance tests:

[0074]

[0075] Casting appearance and internal defect requirements

[0076] (1) The casting surface is smooth and has no damaging pores, sand holes, burrs or cracks;

[0077] (2) Remove burrs and blunt sharp corners; cut the casting to find no pores or shrinkage, and use a coloring flaw detector to check for internal defects;

[0078] (3) The sample parts need to be X-rayed and the test report must be attached;

[0079] (4) After metallographic testing and ultrasonic thickness gauge testing:

[0080] Spheroidization rate: ≥90%;

[0081] Graphite ball size: ≥6 levels

[0082] Number of graphite balls: ≥200mm 2

[0083] Matrix metallographic structure: spheroidal graphite + carbon-rich austenitized ferrite (acicular ferrite + carbon-rich austenite)

[0084] Carbide: 15%.

[0085] In order to make the existing production line suitable for the double inoculation requirements of small castings and large-scale production of ADI engineering and agricultural machinery castings, a double inoculation production auxiliary device suitable for the above production is proposed. Figures 1 to 4 The two-time inoculation device includes a first inoculation time control device and a second inoculation time control device;

[0086] The first inoculation time control device comprises a first molten iron flow channel, which is formed by casting sand molding; the first molten iron flow channel is formed by connecting multiple identical branch flow channels end to end in sequence; the horizontal height of each branch flow channel decreases in sequence from 1 to n; n is a natural number; it also comprises multiple vertical channels, each vertical channel passes through the end of the previous branch flow channel from top to bottom to reach the head end of the next branch flow channel; the head end of the first branch flow channel is connected to the bottom of a separate vertical channel; the top of the vertical channel is located on the top surface of the casting sand; the top of each vertical channel is connected to a pouring cup;

[0087] The secondary inoculation time control device comprises a secondary molten iron flow channel, which is formed by a foundry sand mold; the head end of the secondary molten iron flow channel is connected to the end of the nth branch flow channel; a plurality of inoculant delivery ports are provided on the secondary molten iron flow channel, each delivery port reaches the top surface of the foundry sand through a pipeline penetrating the foundry sand, and a filler is detachably placed in each pipeline; each delivery port is arranged in sequence along the axial direction of the secondary molten iron flow channel;

[0088] The inner wall of the primary molten iron flow channel and the inner wall of the secondary molten iron flow channel are coated with a casting refractory coating.

[0089] During implementation, for the first molten iron flow channel, the foundry sand is divided into multiple layers from top to bottom, and the adjacent layers of sand form a branch flow channel, and the axis of this branch flow channel is on the parting surface of the two layers of foundry sand. For the secondary molten iron flow channel, the foundry sand is divided into left and right sides, and the axis of the secondary molten iron flow channel is on the parting surface of the foundry sand on both sides. When this device is used, it can be made with a standard sand box and fixed to the production line.

[0090] During the first inoculation, molten iron can be poured from different pouring cups according to the inoculation time requirements of different batches of products. Due to the different lengths of the molten iron process, the inoculation time is different. The inoculated molten iron flows into the next process from the end of the nth branch channel. In this process, the temperature of the molten iron is fully insulated by the molding sand. During the second inoculation, inoculants are added at different injection ports to control the time of the second inoculation.

[0091] The manufacturing method of this device can be compared with ordinary casting products. First, the mold is pressed in the sand box to obtain the cavity (i.e., the molten iron flow channel), and then the mold is taken out of the box and then the box is closed. It can also be made by foam lost mold, etc. The manufacturing method of the cavity is selected according to the complexity of the cavity. The manufacturing materials used in this device are all from the casting site, such as molding sand, sand box, refractory coating, etc.

[0092] In this example, there are 3 tributaries in total.

[0093] The end of the third branch channel is the outlet of the primary molten iron flow channel. The inlet at the head end of the secondary molten iron flow channel is connected to the upper surface of the casting sand through a vertical channel, and the opening position of this vertical channel is connected to a pouring cup. The outlet of the primary molten iron flow channel is within the top opening range of this pouring cup, and the molten iron flowing out of the primary molten iron flow channel directly falls into the secondary molten iron flow channel.

[0094] The molten iron outlet of the secondary molten iron flow channel is above the sand box assembly line with the casting cavity. The assembly line transfers the sand box with the corresponding casting cavity to the bottom of the molten iron outlet of the secondary molten iron flow channel, and is aligned by the pouring cup. At this time, the molten iron is poured from the corresponding pouring cup of the primary molten iron flow channel into the primary molten iron flow channel by the ladle. After one inoculation, the molten iron flows into the secondary molten iron flow channel, and the inoculant for the secondary inoculation is added at the corresponding delivery port, and inoculated in the secondary molten iron flow channel, and finally flows into the casting cavity. A round of casting operation is completed.

[0095] All surfaces in contact with molten iron (pouring cup, molten iron runner, etc.) can be coated with casting refractory coating.

[0096] In this example:

[0097] In the first molten iron runner, the axes of the three branch runners are parallel to the horizontal plane. In the horizontal plane projection, the axes of the branch runners are three S-shaped ones connected end to end. The foundry sand is divided into four layers from top to bottom, and the adjacent layers of sand form a branch runner. The axis of this branch runner is on the parting surface of the two layers of foundry sand, respectively in four sand boxes; the axis of each branch runner corresponds to the parting surface of the four parts of foundry sand.

[0098] In the secondary molten iron runner, the casting sand is divided into left and right sides, and the axis of the secondary molten iron runner is on the parting surface of the casting sand on both sides. The secondary molten iron runner is a straight line.

[0099] Different castings have different requirements for the physical form of the inoculant.

[0100] For the powdered inoculant, a storage hopper for the powdered inoculant is connected above the delivery port through a chute, and a door that can be opened and closed is connected to the outlet at the bottom of the storage hopper. This method is similar to the existing method of delivering the powdered inoculant. The processing method of this example is the powdered inoculant.

[0101] For the block inoculant, the cross-sectional shape of the delivery port corresponds to the shape of the block inoculant. When implementing, the block inoculant is directly placed in the required delivery port. As the molten iron is flushed, the block inoculant in the secondary molten iron flow channel gradually disappears, and the unflushed part falls into the secondary molten iron flow channel by its own gravity. Figure 4 Shown is the block inoculant method.

[0102] The temporarily unused delivery port is filled with fillers. The shape of the filler corresponds to the inner cavity of the pipe above the delivery port. The filler can be pressed with foundry sand (the edge of the filler is made into a step shape so that the filler will not fall into the secondary molten iron flow channel), or it can be made of cast iron plates, etc., to seal the pipe port and isolate the molten iron from the external space.

[0103] The secondary molten iron flow channel can be horizontal or high in front and low in the back. The secondary molten iron flow channel is in a straight line shape. The horizontal shape makes it easier to control the time of the secondary incubation. The inclined shape requires the secondary incubation time corresponding to the different positions of the inlet to be tested in advance according to factors such as different molten iron and its flow rate.

Claims

1. A method for applying austempered ductile iron (ADI) to engineering machinery and agricultural machinery castings, characterized in that the steps include: 1) Raw material selection and composition control: 1.1) The main raw material is high-purity pig iron, and its chemical composition is (mass fraction): WSi<0.4﹪, WMn<0.2﹪, WP<0.03﹪, WS<0.02﹪, and the total mass fraction of other harmful elements does not exceed 0.2﹪; The scrap steel is carbon scrap steel; the recarburizer is a recarburizer with a particle size of 0.5-5 mm; 1.2) Chemical composition control Carbon equivalent CE = %C + 1 / 3 (%Si), carbon equivalent should be controlled according to the following parameters: ； 2) Production process control 2.1) Spheroidization inoculation treatment 500kg spheroidization bag, spheroidization temperature controlled at 1500 ~ 1530 ℃, sandwich injection method; 2.2) Use 0.15% pretreatment agent to pretreat the molten iron; 2.3) The dosage of spheroidizing agent is 1.1-1.2%, and the spheroidizing time is 60-90 seconds; 2.4) Covering the spheroidizing agent with carbon scrap steel; 2.5) After spheroidization is completed, add 0.4% inoculant with a particle size of 0.7-3mm for the first inoculation; 2.6) Carry out in-stream inoculation of molten iron, the particle size of in-stream inoculant is 0.2-0.5mm, and the inoculation amount is 0.1%; 2.7) The pouring temperature is 1420±20℃; 3) Molding process control Requirements for ADI austempering of ductile iron: Austenitizing: 820-930°C, 1.5-3 hours; Quenching: Stop quenching at 230-390℃; Quenching time: 1-1.5 hours; The two inoculations in steps 2.5) and 2.6) are completed with the assistance of two inoculation devices, and the two inoculation devices include a first inoculation time control device and a second inoculation time control device; The first inoculation time control device comprises a first molten iron flow channel, which is formed by casting sand molding; the first molten iron flow channel is formed by connecting multiple identical branch flow channels end to end in sequence; the horizontal height of each branch flow channel decreases in sequence from 1 to n; n is a natural number; it also comprises multiple vertical channels, each vertical channel passes through the end of the previous branch flow channel from top to bottom to reach the head end of the next branch flow channel; the head end of the first branch flow channel is connected to the bottom of a separate vertical channel; the top of the vertical channel is located on the top surface of the casting sand; the top of each vertical channel is connected to a pouring cup; The secondary inoculation time control device comprises a secondary molten iron flow channel, which is formed by a foundry sand mold; the head end of the secondary molten iron flow channel is connected to the end of the nth branch flow channel; a plurality of inoculant delivery ports are provided on the secondary molten iron flow channel, each delivery port reaches the top surface of the foundry sand through a pipeline penetrating the foundry sand, and a filler is detachably placed in each pipeline; each delivery port is arranged in sequence along the axial direction of the secondary molten iron flow channel; The inner wall of the primary molten iron flow channel and the inner wall of the secondary molten iron flow channel are coated with a casting refractory coating.

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