A method for preparing gradient-structured hypereutectic high-chromium cast iron based on pulsed current

Abstract

This invention relates to a method for preparing gradient-structured hypereutectic high-chromium cast iron based on pulsed current, belonging to the field of metal wear-resistant material processing technology. The method, tailored to the specific requirements of the casting, involves placing electrodes with a depth of at least 5 mm into the mold cavity on the surface requiring a wear-resistant layer. This allows for the formation of a wear-resistant layer containing coarse carbides on the suitable casting surface, and a toughening structure containing fine carbides in the core. Ultimately, a gradient microstructure is formed, with coarse carbides on the surface and fine carbides in the core. Alternatively, electrodes with a depth of less than 5 mm into the mold cavity can be placed on the surface where a wear-resistant layer is not needed, enabling the formation of a microstructure containing fine carbides in both the surface and core of that area, thus improving the toughness of the casting. The preparation method also features simple production process, low cost, long service life under impact and wear conditions, and high service safety.

Description

TECHNICAL FIELD

[0001] The application relates to a method for preparing gradient structure hypereutectic high-chromium cast iron based on pulse current, and belongs to the technical field of metal wear-resistant material processing. BACKGROUND

[0002] In the steel, metallurgy, coal, building material and electric power industries, material crushing and grinding are very common. Hypereutectic high-chromium cast iron has great application potential in the field of wear-resistant materials. Coarse primary carbide is beneficial to improving the hardness and wear resistance of high-chromium cast iron material, but is not conducive to the toughness. Single coarse carbide structure makes it difficult for high-chromium cast iron to be applied in high-impact working conditions, and the service safety is poor. Traditional inoculation and modification treatment can reduce the size of carbide and improve the toughness of hypereutectic high-chromium cast iron, but single fine carbide structure reduces the wear resistance of the material and shortens the service life. Preparing gradient structure hypereutectic high-chromium cast iron with coarse carbide in the surface layer and fine carbide in the core becomes an important technology for improving the service safety and life of hypereutectic high-chromium cast iron in impact working conditions. However, due to the limitation of the process mode, the surface layer of the traditional casting is often obtained with fine carbide structure due to rapid cooling, and the core is obtained with coarse carbide structure due to slow cooling, which seriously weakens the wear resistance and toughness of the hypereutectic high-chromium cast iron.

[0003] It has been reported in the prior art that gradient materials are prepared by using laser or electron beam local melting additive technology, but the high-hardness layer on the surface of the obtained gradient material is often realized by refining the grains, which is contrary to the mechanism of improving the wear resistance of hypereutectic high-chromium cast iron by using coarse carbide, and the process is complex, the equipment cost is high, and it is not suitable for preparing thick and hardened layer. Since the primary carbide and eutectic carbide in the hypereutectic high-chromium cast iron have good stability, it is difficult to change the size and morphology of the carbide by using local heat treatment technology or surface heat treatment technology. SUMMARY

[0004] In view of the defects and deficiencies of the prior art, the application provides a method for preparing gradient structure hypereutectic high-chromium cast iron based on pulse current. In the method, pulse current is applied to a specific position in the mold cavity during the cooling and solidification of the melt, and the free energy effect and electromagnetic stirring effect of the pulse current are used to realize inoculation and broken refinement of the carbide in the core region. The region close to the surface layer of the mold cavity which is not subjected to pulse current treatment is solidified from the high-temperature melt to obtain coarse carbide. Finally, the gradient structure hypereutectic high-chromium cast iron part with coarse carbide grains in the surface layer and fine carbide grains in the core is obtained.

[0005] The application aims to realize the following technical scheme:

[0006] A method for preparing a gradient structure hypereutectic high-chromium cast iron based on pulse current, the method comprising the following steps:

[0007] (1) Melting the hypereutectic high-chromium cast iron and holding at a temperature higher than the liquidus temperature T l of the hypereutectic high-chromium cast iron to obtain a hypereutectic high-chromium cast iron superheated melt;

[0008] (2) Preparing a pretest mold according to the structure of the castings, pouring the hypereutectic high-chromium cast iron superheated melt into the cavity of the pretest mold, and measuring the time t required for the hypereutectic high-chromium cast iron superheated melt at the center of the cavity of the pretest mold to cool to the solidus temperature T s of the hypereutectic high-chromium cast iron;

[0009] (3) Preparing a mold according to the structure of the castings, fixing an electrode in the mold and deep into the cavity of the mold, pouring the hypereutectic high-chromium cast iron superheated melt into the cavity of the mold, and after pouring is completed, passing a pulse current to the center of the melt through the electrode, and the duration of the pulse current passing is t;

[0010] (4) Naturally cooling the melt after solidification to obtain a gradient structure hypereutectic high-chromium cast iron part with coarse carbide grains on the surface and fine carbide grains in the center.

[0011] According to the embodiments of the present application, in step (1), the hypereutectic high-chromium cast iron is any one of the hypereutectic high-chromium cast irons known in the art and purchased through commercial channels or prepared by the methods known in the art. Exemplarily, the hypereutectic high-chromium cast iron comprises the following components in mass fraction: Cr element with a content of 12% or more, C element with a content of 3.6% or more, and the rest is Fe element. For example, the hypereutectic high-chromium cast iron comprises the following components in mass fraction: Cr element with a content of 12%-22%, C element with a content of 3.6%-4.5%, and the rest is Fe element. For example, the hypereutectic high-chromium cast iron comprises the following components in mass fraction: 20% of Cr element, 4% of C element, and the rest is Fe element.

[0012] According to the embodiments of the present application, in step (1), the liquidus temperature T l of the hypereutectic high-chromium cast iron is tested by differential thermal analysis. Preferably, the liquidus temperature T l of the hypereutectic high-chromium cast iron is tested by a differential thermal tester. Exemplarily, the liquidus temperature T l of the hypereutectic high-chromium cast iron during heating is tested by the differential thermal tester with a heating rate of 10 ℃ / min continuously to 1400 ℃.

[0013] According to an embodiment of the present invention, in step (1), the holding time is not specifically defined, but only until the hypereutectic high-chromium cast iron is completely melted and the melt temperature is uniform; the holding temperature is higher than the liquidus temperature T of the hypereutectic high-chromium cast iron. l 100~400℃, for example 100℃, 150℃, 200℃, 250℃, 300℃, 350℃ or 400℃.

[0014] According to an embodiment of the present invention, in step (2), the solidus temperature T of the hypereutectic high-chromium cast iron is tested using differential thermal analysis. s Preferably, the solidus temperature T of the hypereutectic high-chromium cast iron is measured using a differential thermal analyzer. s For example, using a differential thermal analyzer, the temperature was continuously increased to 1400°C at a heating rate of 10°C / min and held for 5 min, then continuously decreased to 200°C at a cooling rate of 10°C / min. The solidus temperature T of the hypereutectic high-chromium cast iron during the cooling process was measured. s .

[0015] According to an embodiment of the present invention, in step (2), the hypereutectic high-chromium cast iron superheated melt is cooled to the solidus temperature T at the center of the pre-test mold cavity. s The time t required is determined by factors such as the cooling conditions of the mold and the size of the casting. For example, the time t required will vary with the size of the casting. Larger castings cool more slowly and require a larger t, while smaller castings cool more quickly and require a smaller t.

[0016] According to an embodiment of the present invention, in step (2), the pouring temperature is higher than the liquidus temperature T of hypereutectic high-chromium cast iron. l 100~400℃, for example 100℃, 150℃, 200℃, 250℃, 300℃, 350℃ or 400℃.

[0017] According to an embodiment of the present invention, the pre-test mold in step (2) has the same structure as the mold in step (3), the only difference being that the pre-test mold in step (2) does not have electrodes, which are only for testing the cooling of the hypereutectic high-chromium cast iron superheated melt to the solidus temperature T of the hypereutectic high-chromium cast iron at the center of the cavity of the pre-test mold. s The time t required.

[0018] According to an embodiment of the present application, the temperature of pouring in step (2) is the same as the temperature of pouring in step (3). The cooling condition of the hypereutectic high chromium cast iron superheated melt in step (2) is the same as the cooling condition of the hypereutectic high chromium cast iron superheated melt in step (3). The cavity structure in step (2) is the same as the cavity structure in step (3), except that there is an electrode in the cavity in step (3). In other words, the preparation of the pretest cast in step (2) should be consistent with the preparation process of the cast in step (3), and the difference is only that the pulse current is passed to the core of the melt through the electrode after the hypereutectic high chromium cast iron superheated melt in step (3) is poured into the cavity of the casting mold.

[0019] According to an embodiment of the present application, in step (2), the hypereutectic high chromium cast iron superheated melt at the center of the cavity of the pretest casting mold is cooled to the solidus temperature T s of the hypereutectic high chromium cast iron, and the time t required is the time required for the hypereutectic high chromium cast iron superheated melt at the center of the cavity of the pretest casting mold to be cooled from the pouring temperature to the solidus temperature T s of the hypereutectic high chromium cast iron in the casting mold. Research experiments show that when the hypereutectic high chromium cast iron superheated melt at the center of the cavity is cooled to the solidus temperature T s of the hypereutectic high chromium cast iron, and the pulse current is passed, there is no effect on the size of the carbide. When the composition of the hypereutectic high chromium cast iron is different or the size of the cast to be prepared is different, the time t required for the hypereutectic high chromium cast iron superheated melt at the center of the cavity to be cooled to the temperature T s of the hypereutectic high chromium cast iron is different, that is, the lower the solidus temperature T l of the cast, the larger the size of the cast, and the longer the time t required.

[0020] According to an embodiment of the present application, in step (2), the cavity of the pretest casting mold is a cavity formed by a non-conductive casting mold, such as a sand mold or a ceramic mold.

[0021] According to an embodiment of the present application, in step (3), the temperature of pouring is higher than the liquidus temperature T l 100-400°C, for example, 100°C, 150°C, 200°C, 250°C, 300°C, 350°C, or 400°C; research has found that by adjusting the superheat of the hypereutectic high chromium cast iron superheated melt, the size of the surface layer carbide of the cast can be effectively adjusted, and its wear resistance can be improved. Selecting this pouring temperature can also heat the casting mold and the electrode during pouring of the hypereutectic high chromium cast iron superheated melt, reduce the cooling rate of the surface melt, make the surface layer of the cast obtain coarse carbide structure, and by adjusting the temperature of pouring, the size of the surface layer carbide of the cast can be adjusted. For example, the higher the temperature of pouring, the larger the size of the surface layer carbide of the cast obtained.

[0022] According to the embodiment of the present application, in step (3), the length L of the electrode penetrating into the cavity of the mold can be selected according to the thickness of the designed wear-resistant layer of the surface of the casting, i.e. changing the length L of the electrode penetrating into the cavity of the mold can change the thickness of the wear-resistant layer of the surface of the casting; preferably, the length L of the electrode penetrating into the cavity of the mold is equal to the thickness of the wear-resistant layer of the surface of the casting. Exemplarily, the length L of the electrode penetrating into the cavity is 0-100 mm, such as 0-5 mm or 5-100 mm; such as 0 mm, 5 mm, 10 mm, 15 mm, 20 mm, 25 mm, 30 mm, 35 mm, 40 mm, 45 mm, 50 mm, 60 mm, 70 mm, 80 mm, 90 mm or 100 mm; it is found that by adjusting the length L of the electrode penetrating into the cavity of the mold, the thickness of the coarse carbide structure of the surface layer of the casting can be controlled, and a wear-resistant layer can be obtained on the surface layer of the casting, which is beneficial to improve the wear resistance of the surface layer of the casting and improve the service life of the casting.

[0023] Exemplarily, when there is no wear-resistant requirement on the surface of the casting, the length L of the electrode penetrating into the cavity is preferably 0-5 mm, at this time, a hypereutectic high-chromium cast iron with fine carbides in the surface layer and the core can be obtained; when there is a wear-resistant requirement on the surface of the casting, the length of the electrode penetrating into the cavity is equal to the thickness of the wear-resistant layer, and is preferably 5-100 mm, at this time, a gradient-structured hypereutectic high-chromium cast iron with coarse carbides in the surface layer and fine carbides in the core can be obtained, and a wear-resistant layer of coarse carbide structure can be obtained on the surface layer of the casting.

[0024] According to the embodiment of the present application, in step (3), when the pulse current is passed for a duration t, at this time the casting has been completely solidified, the pulse current needs to be cut off, and then the casting can be naturally cooled.

[0025] According to the embodiment of the present application, in step (3), the cavity of the mold is a cavity formed by a non-conductive mold, such as a sand mold or a ceramic mold.

[0026] According to the embodiment of the present application, in step (3), the melting point of the material forming the electrode is higher than the melting point of the hypereutectic high-chromium cast iron material, for example, a low-carbon high-chromium cast iron or a low-carbon steel material is selected as the electrode. When a low-carbon high-chromium cast iron or a low-carbon steel material is selected as the electrode, on the one hand, its composition is similar to that of the hypereutectic high-chromium cast iron and will not contaminate the high-chromium cast iron; on the other hand, after the hypereutectic high-chromium cast iron overheated melt is solidified, the low-carbon high-chromium cast iron and the low-carbon steel and the casting are metallurgically combined into one body, which can improve the toughness of the surface layer.

[0027] According to an embodiment of the present application, in step (3), the electrodes include a positive electrode and a negative electrode, and a current channel is formed between the positive electrode and the negative electrode, and the melt in the cavity between the positive electrode and the negative electrode is refined in size under the action of the pulse current. Preferably, the electrodes include at least one positive electrode and at least one negative electrode. If there are at least two positive electrodes, the distance between adjacent positive electrodes is 50-200 mm; if there are at least two negative electrodes, the distance between adjacent negative electrodes is 50-200 mm. The number of electrodes can also be optimized according to the size of the casting to ensure that the melt can be refined and broken in the core region under the free energy effect and electromagnetic stirring effect of the pulse current.

[0028] According to an embodiment of the present application, in step (3), the size of the electrode is adjusted according to the size of the casting, and a small size electrode is selected for a small casting and a large size electrode is selected for a large casting, for example, the size of the electrode is 5-30 mm.

[0029] According to an embodiment of the present application, in step (3), the positive electrode and the negative electrode are respectively arranged at both ends of the casting in the horizontal direction or in the vertical direction, or on two nearly parallel surfaces of the casting, to ensure that the melt between the positive electrode and the negative electrode in the casting can be refined under the action of the pulse current.

[0030] According to an embodiment of the present application, in step (3), the waveform of the pulse current can be any waveform such as a sharp wave, a rectangular wave, a sine wave, etc. The pulse current can introduce varying current and magnetic field into the hypereutectic high-chromium cast iron melt, which can produce electromagnetic stirring effect; at the same time, the current can cause the free change of liquid and solid phases, increase the free energy difference between the liquid and solid phases, promote the rapid nucleation of carbides in the melt, increase the number of carbide grains, and further refine the size of the carbides.

[0031] According to an embodiment of the present application, in step (3), the density of the pulse current is 10-1000 A / cm 2 , for example, 10 A / cm 2 , 20 A / cm 2 , 50 A / cm 2 , 80 A / cm 2 , 100 A / cm 2 , 150 A / cm 2 , 200 A / cm 2 , 300 A / cm 2 , 400 A / cm 2 , 500 A / cm 2 , 600 A / cm 2 , 700 A / cm 2 , 800 A / cm2 , 900 A / cm 2 or 1000 A / cm 2 ; the size of the central carbide grains can be changed by changing the density of the pulse current, effectively refining the size of the central region carbide, improving the toughness of the hypereutectic high chromium cast iron and the service safety. For example, increasing the density of the pulse current can reduce the size of the central carbide grains.

[0032] According to the embodiment of the present application, in step (4), the high chromium cast iron piece is a high-toughness high-wear-resistance cast piece.

[0033] The present application has the following beneficial effects:

[0034] The method can obtain a hypereutectic high chromium cast iron with a gradient structure of coarse carbides on the surface and fine carbides in the center. The hypereutectic high chromium cast iron manufactured by the method has high surface hardness, good wear resistance, high toughness in the center, and good impact resistance. The size of the coarse carbides on the surface and the size of the fine carbides in the center can be adjusted. The method is flexible and has the characteristics of adjustable wear-resistant surface thickness. Specifically, electrodes with a length of 5mm or more inside the deep cavity can be arranged on the surface of the cast piece where wear-resistant layers are needed, so that a wear-resistant layer with a specific thickness containing coarse carbide structure can be formed on the surface of the specific cast piece, and a toughness structure containing fine carbides in the center can be obtained by pulse current treatment, thereby comprehensively forming a gradient structure of coarse carbide structure on the surface and fine carbide structure in the center. Electrodes with a length of less than 5mm inside the deep cavity can be arranged on the surface where wear-resistant layers are not needed, so that a structure containing fine carbides can be formed on the surface and in the center of the region, thereby improving the toughness of the cast piece. The preparation method also has the characteristics of simple production process, low cost, long service life under impact and wear conditions, and high service safety. BRIEF DESCRIPTION OF DRAWINGS

[0035] Figure 1 A schematic structural diagram (cross-sectional view) of the gradient structure of the crusher hammer head of Example 1 is shown.

[0036] Figure 2 A schematic structural diagram (cross-sectional view) of the gradient structure of the ball mill liner of Example 4 is shown.

[0037] Figure 3 A photograph showing the hypereutectic high chromium cast iron structure of the lower surface of the gradient structure of the crusher hammer head of Example 1 is shown.

[0038] Figure 4 A photograph showing the hypereutectic high chromium cast iron structure of the center of the gradient structure of the crusher hammer head of Example 1 is shown.

[0039] The drawings show that: 1 is the negative electrode, 2 is the positive electrode, 3 is the mold, and 4 is the cavity. Detailed Implementation

[0040] The preparation method of the present invention will be further described in detail below with reference to specific embodiments. It should be understood that the following embodiments are merely illustrative and explanatory of the present invention and should not be construed as limiting the scope of protection of the present invention. All technologies implemented based on the above content of the present invention are covered within the scope of protection intended by the present invention.

[0041] Unless otherwise specified, the experimental methods used in the following examples are conventional methods; unless otherwise specified, the reagents and materials used in the following examples are commercially available.

[0042] The hypereutectic high-chromium cast iron used in the following examples has a composition of 20% Cr, 4% C, and the remainder Fe.

[0043] The liquidus temperature T of the hypereutectic high-chromium cast iron used in the following examples l and solidus temperature T s The liquidus temperature T of the eutectic high-chromium cast iron was obtained through differential thermal analysis and continuous heating testing. l The solidus temperature T of eutectic high-chromium cast iron during cooling was tested by continuous cooling. s Specifically, using a differential thermal analyzer, the temperature was continuously increased to 1400℃ at a heating rate of 10℃ / min and held for 5 minutes, then continuously decreased to 200℃ at a cooling rate of 10℃ / min. The liquidus temperature T of the hypereutectic high-chromium cast iron during the heating process was measured. l The solidus temperature T of eutectic high-chromium cast iron during cooling was tested. s .

[0044] Test results show that the liquidus temperature T l The solidus temperature is 1327℃, and the solidus temperature T is... s It is 1219℃.

[0045] Example 1

[0046] (1) Melt hypereutectic high-chromium cast iron and hold it at 1500℃ for 10 min to make the melt temperature uniform, and obtain hypereutectic high-chromium cast iron superheated melt.

[0047] (2) According to Figure 1 The crusher hammer shown is used to prepare a casting sand mold, but no electrodes are placed inside the mold; the superheated melt of hypereutectic high-chromium cast iron is poured into the cavity of the casting sand mold, and the temperature T of the superheated melt of hypereutectic high-chromium cast iron at the center of the cavity of the pre-test mold is measured when it cools to the solidus temperature T of the hypereutectic high-chromium cast iron. sThe required time t is 1.5 min; after the melt solidifies, it cools naturally to obtain a conventionally cast hammerhead.

[0048] (3) According to Figure 1 The crusher hammer shown is prepared using a sand casting mold, and low-carbon steel electrodes are fixed within the mold. Several negative electrodes are first arranged on the lower surface (plane) of the hammer, which requires a gradient microstructure, while several positive electrodes are arranged on the surface of the central hole. The negative electrodes on the lower surface of the hammer, the positive electrodes in the central hole, and the melt between them form a current channel to refine the carbide grains in the region between the lower surface of the hammer and the central hole. Several negative electrodes are arranged on the upper surface of the hammer (the upper arc), forming a current channel with the positive electrodes at the central hole, further refining the carbide grains in the region between the upper surface of the hammer and the central hole. According to the design requirements, the lower surface of the hammerhead has wear resistance requirements, and the wear-resistant layer is designed to be 40mm thick. Therefore, the length of the negative electrodes arranged on the lower surface of the hammerhead extending into the cavity is 40mm. The upper surface of the hammerhead and the central hole of the hammerhead do not have wear resistance requirements. Therefore, the length of the negative electrodes arranged on the upper surface of the hammerhead extending into the cavity is 0-5mm. The length of the positive electrodes arranged in the central hole of the hammerhead extending into the cavity is 0-5mm.

[0049] (4) The above-mentioned hypereutectic high-chromium cast iron superheated melt is poured into the cavity of the casting sand mold. After pouring, a spike pulse current is passed into the core of the melt through an electrode. The peak current density of the pulse current is 200 A / cm. 2 The pulsed current was applied for 1.5 minutes. After the melt solidified, it cooled naturally, resulting in a surface layer (lower surface of the hammerhead) with coarse carbide grains, averaging 50 μm in width; and a core layer with fine carbide grains, averaging 30 μm in diameter. This resulted in a hypereutectic high-chromium cast iron hammerhead with a gradient structure of coarse outer layer and fine inner layer. In contrast, conventionally cast hammerheads prepared in the above manner tend to have a faster cooling rate on the surface in contact with the mold cavity, leading to the formation of fine carbides on the surface and coarse carbides inside the hammerhead due to slower cooling. Consequently, the hypereutectic high-chromium cast iron hammerhead structure with a gradient structure of coarse outer layer and fine inner layer cannot be obtained.

[0050] Example 2

[0051] (1) The hypereutectic high-chromium cast iron was melted and held at 1600℃ for 10 min to make the temperature of the melt uniform, thus obtaining the hypereutectic high-chromium cast iron superheated melt.

[0052] (2) According to Figure 1 The crusher hammer shown is used to prepare a casting sand mold, but no electrodes are placed inside the mold; the superheated melt of hypereutectic high-chromium cast iron is poured into the cavity of the casting sand mold, and the temperature T of the superheated melt of hypereutectic high-chromium cast iron at the center of the cavity of the pre-test mold is measured when it cools to the solidus temperature T of the hypereutectic high-chromium cast iron. sThe required time t is 2 minutes; after the melt solidifies, it cools naturally to obtain a conventionally cast hammerhead;

[0053] (3) Same as Example 1;

[0054] (4) The above-mentioned hypereutectic high-chromium cast iron superheated melt is poured into the cavity of the casting sand mold. After pouring, a spike pulse current is passed into the core of the melt through an electrode. The peak current density of the pulse current is 200 A / cm. 2 The pulsed current was applied for 2 minutes. After the melt solidified, it cooled naturally, resulting in a surface layer (lower surface of the hammerhead) with coarse carbide grains and an average width of 55 μm. The core layer had fine carbide grains with an average carbide diameter of 30 μm. The hammerhead was a hypereutectic high-chromium cast iron with a gradient structure of coarse outer layer and fine inner layer.

[0055] Example 3

[0056] (1) Same as Example 1;

[0057] (2) Same as Example 1;

[0058] (3) Same as Example 1;

[0059] (4) The above-mentioned hypereutectic high-chromium cast iron superheated melt is poured into the cavity of the casting sand mold. After pouring, a rectangular wave pulse current is passed into the core of the melt through an electrode. The peak current density of the pulse current is 500 A / cm. 2 The pulsed current was applied for 1.5 minutes. After the melt solidified, it cooled naturally, resulting in a surface layer (lower surface of the hammerhead) with coarse carbide grains and an average width of 52 μm; a core layer with fine carbide grains and an average carbide diameter of 31 μm; and a hypereutectic high-chromium cast iron hammerhead with a gradient structure of coarse outer layer and fine inner layer.

[0060] Example 4

[0061] (1) Melt hypereutectic high-chromium cast iron and hold it at 1700℃ for 10 min to make the melt temperature uniform, and obtain hypereutectic high-chromium cast iron superheated melt.

[0062] (2) According to Figure 2 The ball mill liner shown is used to prepare a ceramic casting mold, but no electrodes are placed inside the mold. The superheated melt of hypereutectic high-chromium cast iron is poured into the cavity of the ceramic casting mold, and the temperature T of the superheated melt of hypereutectic high-chromium cast iron at the center of the cavity of the pre-test mold is measured when it cools to the solidus temperature T of the hypereutectic high-chromium cast iron. s The required time t is 1.3 min; after the melt solidifies, it cools naturally to obtain a conventionally cast ball mill liner.

[0063] (3) According to Figure 2The ball mill liner shown, a cast ceramic mold is prepared, and low carbon steel electrodes are fixed in the ceramic mold. A plurality of positive electrodes are arranged on the upper surface of the ball mill liner, and a plurality of negative electrodes are arranged on the lower surface of the ball mill liner. The positive electrodes on the upper surface of the ball mill liner and the negative electrodes on the lower surface of the ball mill liner and the molten metal therebetween form a current channel, and the carbide grains in the region between the upper surface of the ball mill liner and the lower surface of the ball mill liner.

[0064] The upper surface of the ball mill liner has wear resistance requirements. The wear-resistant layer of the upper surface of the ball mill liner is designed to be 15 mm, so the length of the positive electrode of the upper surface of the ball mill liner into the cavity is 15 mm. The lower surface of the ball mill liner has no wear resistance requirements, and the length of the negative electrode of the lower surface of the ball mill liner into the cavity is 0-5 mm.

[0065] (4) Pouring the hypereutectic high chromium cast iron superheated melt into the cavity of the cast ceramic mold, and after pouring is completed, a sinusoidal pulse current is passed to the core of the melt through the electrodes, the peak current density of the pulse current is 800 A / cm 2 , the duration of the pulse current is 1.3 min; the melt is naturally cooled after solidification, and a ball mill liner of hypereutectic high chromium cast iron with a gradient structure of coarse carbide grains on the outer layer and fine carbide grains on the inner layer is obtained, the average width of the coarse carbide grains on the upper surface is 63 μm, and the average diameter of the fine carbide grains on the core and the lower surface is 28 μm. The conventional cast ball mill liner prepared by the above method cannot obtain the structure of the ball mill liner of hypereutectic high chromium cast iron with a gradient structure of coarse carbide grains on the outer layer and fine carbide grains on the inner layer, because the surface in contact with the cavity cools quickly, the surface layer is prone to form fine carbide grains, and the inner part cools slowly, which is prone to form coarse carbide grains.

[0066] As can be seen from the above examples, if no pulse current is passed during the cooling and solidification of the casting, the cooling rate of the core is lower than that of the surface layer, resulting in coarse carbide grains in the core and poor toughness of the casting. Gradient structure can be obtained by conventional casting, but the gradient structure is that the carbide grains on the outer layer are fine and the carbide grains on the inner layer are coarse, and both the wear resistance of the surface layer and the toughness of the core are poor. Using ordinary high superheating pouring method, the carbide grains on the surface layer are coarse, the carbide grains on the core are even coarser, and the toughness of the casting is very poor. On the basis of superheating pouring, after the pulse current is passed to the core, the reverse conventional gradient of coarse carbide grains on the surface layer and fine carbide grains on the core can be realized, which is beneficial to improving the wear resistance of the surface layer and the toughness of the core of the cast iron casting and prolonging the service life of the casting.

[0067] The above describes the embodiments of the present application. However, the present application is not limited to the above embodiments. Any modification, equivalent replacement, improvement, etc. made within the spirit and principles of the present application shall be included in the protection scope of the present application.

Claims

1. A method for preparing gradient structure hypereutectic high chromium cast iron based on pulse current, the method comprising the following steps: (1) melt the hypereutectic high-chromium cast iron and keep it at a temperature higher than the liquidus temperature T of the hypereutectic high-chromium cast iron to obtain a hypereutectic high-chromium cast iron superheated melt; l (1) melt the hypereutectic high-chromium cast iron and keep it at a temperature higher than the liquidus temperature T of the hypereutectic high-chromium cast iron to obtain a hypereutectic high-chromium cast iron superheated melt; (2) A pretest mold is prepared according to the structure of the casting, and the hypereutectic high-chromium cast iron superheated melt is poured into the cavity of the pretest mold, and the time t required for the hypereutectic high-chromium cast iron superheated melt at the center of the cavity of the pretest mold to cool to the solidus temperature T s of the hypereutectic high-chromium cast iron is measured. (3) preparing a mold according to the structure of the castings, fixing electrodes in the mold and deep into the cavity of the mold, pouring a hypereutectic high chromium cast iron superheated melt into the cavity of the mold, and after the pouring is completed, passing a pulse current to the heart of the melt through the electrodes, the duration of the pulse current passing being t; (4) naturally cooling the melt after solidification to obtain a gradient structure hypereutectic high chromium cast iron part with coarse carbide grains on the surface and fine carbide grains in the heart; In step (1), the temperature of the holding is higher than the liquidus temperature T of the hypereutectic high-chromium cast iron l 100~400°C; the pretest mold in step (2) is the same in structure as the mold in step (3); the pouring temperature in step (2) is the same as the pouring temperature in step (3); the cooling condition of the hypereutectic high-chromium cast iron superheated melt in step (2) is the same as the cooling condition of the hypereutectic high-chromium cast iron superheated melt in step (3); in step (2), the pouring temperature is higher than the liquidus temperature T of the hypereutectic high-chromium cast iron l 100~400°C; in step (3), the pouring temperature is higher than the liquidus temperature T of the hypereutectic high-chromium cast iron l 100~400°C; in step (3), when there is no wear resistance requirement on the surface of the casting, the length L of the electrode penetrating into the inside of the cavity is 0~5mm, and when there is wear resistance requirement on the surface of the casting, the length of the electrode penetrating into the inside of the cavity is equal to the thickness of the wear-resistant layer, being 5~100mm; in step (3), low-carbon high-chromium cast iron or low-carbon steel material is selected as the electrode.

2. The method of claim 1, wherein, In step (1), the hypereutectic high chromium cast iron comprises the following components by mass fraction: Cr element with a content ratio of 12% or more, C element with a content ratio of 3.6% or more, and the rest being Fe element.

3. The method according to claim 1 or 2, characterized in that, In step (3), the melting point of the material forming the electrode is higher than the melting point of the hypereutectic high chromium cast iron material.

4. The method according to claim 1 or 2, characterized in that, In step (3), the electrode comprises at least one positive electrode and at least one negative electrode; if there are at least two positive electrodes, the distance between adjacent positive electrodes is 50-200 mm; If there are at least two negative electrodes, the distance between adjacent negative electrodes is 50-200 mm.

5. The method according to claim 1 or 2, characterized in that, In step (3), the waveform of the pulse current is a sharp wave, a rectangular wave or a sine wave. And / or, in step (3), the density of the pulse current is 10-1000 A / cm 2 .

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