Inoculating agent and preparation method thereof, free-cutting gray cast iron and application of gray cast iron

Abstract

The invention discloses a nucleating agent, a preparation method of the nucleating agent, free-cutting gray cast iron and application of the free-cutting gray cast iron, and belongs to the technical field of casting. The nucleating agent used in gray cast iron casting comprises, by mass, 40%-70% of Si, 1%-5% of Ca and 1%-5% of Mg. The gray cast iron comprises the following components in percentage by mass: 0.5-3% of Mg, 0.5-3% of Al and the balance of Fe and incidental impurities in a conventional amount, and the elements Mg and Al can be uniformly distributed in a gray cast iron matrix in the form of oxides and / or sulfides. According to the inoculant, magnesium and aluminum elements are added and exist in a gray cast iron matrix in the form of oxides or sulfides, when a tool cuts gray cast iron at a high speed, heat is generated through friction, the oxides or sulfides in the gray cast iron matrix can form a layer of protective film on the surface of the tool, and the wear resistance of the tool is improved; and the service life of the cutter is effectively prolonged.

Description

Technical Field

[0001] The invention belongs to the technical field of casting, and more specifically, relates to an inoculant and a preparation method thereof, free-cutting grey cast iron and applications of the grey cast iron. Background Art

[0002] Gray cast iron (abbreviated as gray cast iron or gray iron) parts are important parts in the field of engineering machinery. Commonly used gray cast iron products are often produced by sand casting, and their surface accuracy does not meet the use grade requirements. Therefore, cutting the machined surface of gray cast iron parts is an important production link. In order to make gray cast iron materials have good cutting performance, the first thing to do is to improve the poor heredity of molten iron. The ways include changing the charge, using a variety of charges, overheating the molten iron, etc. Among them, increasing the overheating temperature of the molten iron is a simple and effective measure; the second is inoculation treatment. The inoculant is dissolved in the molten iron to promote the formation of graphite cores and improve the graphitization ability of the molten iron. This treatment process can minimize the white cast tendency of thin-walled parts, improve the microstructure of gray castings and refine the grains, so that the graphite obtained in the gray cast iron is small and small, curved and evenly distributed, which greatly improves the cutting performance of gray cast iron. Figure 1 Graphite length fraction shown.

[0003] In order to solve the above problems, the prior art discloses that the machinability of gray cast iron can be further improved by improving the components of the inoculant. After searching, in the prior art, for example, patent application number CN87100402.X discloses a ferrosilicon inoculant for gray cast iron, which contains 0.1 to 10% (by weight) strontium, less than 0.35% (by weight) calcium and 0.1 to 15% (by weight) zirconium, 0.1 to 20% (by weight) titanium, or a mixture of zirconium, iron and the strontium. Patent application number CN202210105407.5 discloses a vanadium-manganese-chromium inoculant containing scandium and yttrium, which can promote the formation of curved, fine and passivated A-type graphite; increase the content of pearlite, reduce the pearlite lamellar spacing and optimize the eutectic cell structure, improve the strength and stiffness of gray cast iron, and improve the machinability of castings. Patent application number CN201610479585.9 discloses a silicon-zirconium inoculant, which replaces the traditional medium-frequency induction furnace that requires the addition of alloying elements such as copper or tin when smelting high-grade gray cast iron parts, reducing manufacturing costs and facilitating the management of recycled materials. Patent application number CN202210180630 discloses an inoculant for improving the machinability of high-strength gray cast iron. When the carbon equivalent is as high as 3.8%, the inoculant can obtain fine and uniformly distributed type A graphite. Patent application number CN201310285504.8 discloses a high-strength, low-alloy high-strength gray cast iron with a metallographic structure dominated by type A graphite, low production cost, and good cutting performance, as well as a preparation method for the low-alloy high-strength gray cast iron.

[0004] However, as machining becomes increasingly efficient, thermal wear between tools and materials intensifies, resulting in extremely low tool life. Low tool life not only leads to poor machining shape and increased tool costs, but also reduces production efficiency due to frequent tool replacement. Summary of the invention

[0005] 1. Problem to be solved

[0006] In view of the problem of low cutting efficiency of grey cast iron in the prior art, the present invention provides an inoculant which can evenly distribute oxides and / or sulfides in a grey cast iron matrix, thereby improving the cutting performance of the grey cast iron.

[0007] Another object of the present invention is to provide a method for preparing a grey cast iron inoculant, wherein the steps are connected in an orderly manner.

[0008] Another object of the present invention is to provide a free-cutting grey cast iron prepared by using the above-mentioned inoculant, wherein oxides and / or sulfides of Mg and Al elements are uniformly distributed in the grey cast iron matrix.

[0009] Another object of the present invention is to provide an application of free-cutting gray cast iron, for example, for use in automobile parts such as brake discs, brake drums, flywheels, as well as motor housings (bases), motor end covers in the motor industry; air conditioning compressor parts; and in the cutting processing of automobile gearboxes, cylinder blocks, and machine tool guide rails.

[0010] 2. Technical solution

[0011] In order to solve the above problems, the technical solution adopted by the present invention is as follows:

[0012] The first aspect of the present invention provides an inoculant, which contains 40-70% by mass of Si, 1-5% by mass of Ca, 1-5% by mass of Mg, 0.5-3% by mass of Al, and the rest is Fe and conventional amounts of incidental impurities, wherein the Mg and Al elements can be uniformly distributed in the form of oxides and / or sulfides in a gray cast iron matrix prepared by inoculation with the inoculant, and the oxides and / or sulfides are at least partially exposed on the surface, thereby improving the cutting performance of the gray cast iron.

[0013] In addition, the inoculant utilizes the inoculating ability and synergistic effect of each element to reduce the cross-section sensitivity and chilling tendency of gray cast iron, and obtain graphite with a small and curved shape and the most uniform distribution. The length of the graphite becomes significantly smaller than that of traditional graphite.

[0014] Furthermore, the mass percentages of Al, Ca, and Mg satisfy the relationship: 5.5%≤Al+Ca+Mg≤13.0%, and by adding magnesium and aluminum elements to the inoculant, the mass percentages of Mg and Al satisfy: 3.0≥[Mg] / [Al]≥1.5, [Mg] and [Al] are the mass percentages of Mg and Al, respectively, and magnesium and aluminum elements can be uniformly distributed in the gray cast iron matrix in the form of oxides or sulfides; when the tool cuts the gray cast iron matrix at high speed, friction generates heat, so that the oxides (mainly MgO / Al2O3) or sulfides (mainly MgS) exposed on the surface of the gray cast iron matrix will adhere to the surface of the tool to form a protective film, which improves the wear resistance of the tool, thereby effectively improving the service life of the tool.

[0015] According to any embodiment of the first aspect of the present invention, the inoculant contains other trace elements Ba, and the mass percentage of Ba element is 3-8%. Ba can inhibit the decay of inoculation, and it is still effective even when inoculated at a high temperature of 1480°C.

[0016] According to any embodiment of the first aspect of the present invention, the inoculant contains 3-5% by mass of Mg and 1.5-2.5% by mass of Al.

[0017] The second aspect of the present invention provides a method for preparing the gray cast iron inoculant described in the first aspect, comprising the following steps:

[0018] S1. Raw material preparation: weigh the raw materials of the inoculant according to the elemental composition, and weigh the raw materials of the inoculant, namely ferrosilicon, calcium silicon, calcium barium, magnesium and metallic silicon, by weight for use.

[0019] The raw materials of the inoculant are ferrosilicon, calcium silicon, barium calcium, metallic magnesium and metallic silicon, and the added proportions are 50% ferrosilicon, 5% calcium silicon, 15% barium calcium, 2% metallic magnesium, 20% metallic silicon and 8% scrap steel.

[0020] The raw materials of the inoculant, ferrosilicon, calcium silicon, barium calcium, magnesium and metal silicon, are subjected to surface pretreatment. The specific process of surface pretreatment is: the surfaces of ferrosilicon, calcium silicon, barium calcium, magnesium and metal silicon are polished with sandpaper, and then cleaned with acetone to remove oil and impurities on the surfaces of aluminum ingots, zinc ingots and magnesium ingots.

[0021] S2. Smelting: Smelting the weighed raw materials at a temperature of 1300°C-1400°C to obtain molten iron.

[0022] Furthermore, in step S2, a medium frequency induction furnace is used to melt the raw materials.

[0023] After the charge is completely melted, the molten iron is inspected and taken for spectral experiment. The molten iron is discharged after passing the inspection. If it is unqualified, the composition of the molten iron is adjusted until it passes. The qualified composition of the molten iron is Si 40%-70%, Ca 1~5%, Mg1~5%, Al0.5~3%.

[0024] S3, casting: pouring the smelted inoculant into a mold and cooling it;

[0025] After the melt in S3 is cooled, it is cast into an ingot, the oxide scale on the surface of the ingot is removed, and then a homogenization treatment is performed. The specific operation process is: after the melt is cast into an ingot, the oxide scale on the surface of the ingot is removed, and then the ingot is placed in a heat treatment furnace for homogenization treatment. The temperature of the homogenization treatment is 450°C and the time of the homogenization treatment is 24 hours.

[0026] S4. Crushing and screening: The cooled inoculant is crushed and screened into particles ≤10mm, and then weighed and packaged.

[0027] The third aspect of the present invention provides a gray cast iron prepared by the gray cast iron inoculant described in the first aspect, wherein the gray cast iron matrix has oxides and / or sulfides of Mg and Al elements at least partially exposed on the surface evenly distributed.

[0028] The third aspect of the present invention provides a gray cast iron, which contains the inoculant described in the first aspect, which accounts for 0.35-0.45% of the total mass of the molten iron, and the inoculant contains 40-70% by mass of Si, 1-5% by mass of Ca, 1-5% by mass of Mg; 0.5-3% by mass of Al, and the rest is Fe and a conventional amount of incidental impurities, wherein the Mg and Al elements can be uniformly distributed in the gray cast iron matrix in the form of oxides and / or sulfides, and the oxides and / or sulfides are at least partially exposed on the surface, thereby improving the cutting performance of the gray cast iron.

[0029] As we all know, the mechanical properties of gray cast iron are determined by its matrix structure and the distribution of flake graphite: 1) In order to obtain high strength, gray cast iron hopes that the matrix structure is mainly pearlite and the ferrite content is minimized; if the amount of ferrite is too much, it will not only lead to low strength of cast iron, but also cause overheating of the tool during processing, significantly reducing the life of the tool; unlike ductile iron, it is impossible to have ductility and toughness requirements for gray cast iron, only its strength is required, so generally a high pearlite content is better; 2) The graphite flakes in gray cast iron have the effect of cutting the metal matrix, destroying its continuity and reducing its strength. From the perspective of strength, long and thin graphite flakes and thick graphite flakes should be avoided, and graphite flakes with obvious directionality have a particularly large impact.

[0030] Based on the above factors, in the prior art: Si is the main element of the inoculant, which can increase the activity of carbon in the molten iron, promote graphitization, and can also interact with other elements to enhance the effect, such as the effect is doubled when used with Ca. Ca: The Ca content cannot be too low. The relevant US standards stipulate that the calcium content is 0.5-1.5%; my country's standard GB / T2272 has 75 ferrosilicon grades with different aluminum contents, and the upper limit of the calcium content is 1.0%. Al: The aluminum content cannot be too high, generally not exceeding 1.5%, otherwise it may cause subcutaneous pores (pinholes) in gray cast iron castings. The relevant US standards stipulate that the aluminum content is 0.75-1.75%. Mg: Use rusty furnace charge or molten iron for oxidation (molten iron is not allowed to be severely oxidized), use an inoculant with strong deoxidation ability (such as RE, Mg), and the upper limit of the magnesium content is 1.0%.

[0031] In this regard, the gray cast iron of the present invention adopts a high content of magnesium and aluminum elements (1-5% Mg, 0.5-3% Al), and the magnesium and aluminum elements can be evenly distributed in the gray cast iron matrix in the form of oxides and / or sulfides; when the tool cuts the gray cast iron matrix at high speed, friction generates heat, so that the oxides (mainly MgO / Al2O3) or sulfides (mainly MgS) exposed on the surface of the gray cast iron matrix are heated and adhere to the surface of the tool to form a protective film, which improves the wear resistance of the tool, thereby effectively improving the service life of the tool.

[0032] It should be noted that the main function of the inoculant of the present invention is to prevent carbide formation by introducing graphite nucleation sites. In addition to introducing nucleation sites, the ductile iron inoculation also converts these inclusions into nucleation sites by adding a layer (containing Ca, Ba or Sr) on the inclusions such as MgO and MgS formed during the spheroidizing process. However, the inoculant of the present invention can be uniformly distributed in the gray cast iron matrix in the form of oxides and / or sulfides, and the oxides and / or sulfides are at least partially exposed. Here, at least partially exposed means that at least 50% of the surface of the inclusions such as MgO and MgS is not covered.

[0033] Analysis shows that the possible reasons are: the increase in aluminum content causes the generated Al2O3 to directly react with substances containing Ca, Ba or Sr to form solid solutions. These solid solutions directly wrap MgO and MgS, rather than substances containing Ca, Ba or Sr connected to MgO and MgS. These solid solutions are easily broken during cutting, thus exposing MgO and MgS.

[0034] Meanwhile, when the Si content exceeds 70%, the protective film is not formed sufficiently because the addition amount of Al and Ca becomes too small. If the addition amount of Al and Ca is within this range, it is difficult to form a protective film, and if the addition amount is too large within this range, CaO is connected to Al2O3, and the heat generated by cutting cannot react with oxides (mainly MgO / Al2O3) or sulfides (mainly MgS).

[0035] The fourth aspect of the present invention provides a gray cast iron as described in the third aspect. The gray cast iron obtained by the above method can be used to produce automobile parts such as brake discs, brake drums, flywheels, as well as motor casings (bases) and motor end covers in the motor industry; air-conditioning compressor parts; and automobile gearboxes, cylinder blocks, and machine tool guide rails in cutting processing.

[0036] 3. Beneficial effects

[0037] Compared with the prior art, the present invention has the following beneficial effects:

[0038] (1) The gray cast iron inoculant of the present invention adds magnesium and aluminum elements, and the magnesium and aluminum elements exist in the gray cast iron matrix in the form of oxides or sulfides. When the tool cuts the gray cast iron at high speed, friction heat is generated, so that the oxides or sulfides in the gray cast iron matrix form a protective film on the surface of the tool, thereby improving the wear resistance of the tool, thereby effectively improving the tool life;

[0039] (2) The gray cast iron inoculant of the present invention promotes graphitization of carbon in the gray cast iron matrix by adding aluminum, calcium and barium elements, reduces the tendency of the gray cast iron matrix to white cast iron, and achieves a good inoculation effect. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] The technical solution of the present invention will be further described in detail below in conjunction with the accompanying drawings and embodiments, but it should be understood that these drawings are designed only for explanation purposes and are not intended to limit the scope of the present invention. In addition, unless otherwise specified, these drawings are intended only to conceptually illustrate the structural configurations described herein and are not necessarily drawn to scale.

[0041] Figure 1 It is the length standard of graphite in grey cast iron in the prior art;

[0042] Figure 2 The process flow chart of the preparation method of the gray cast iron inoculant of the present invention is as follows;

[0043] Figure 3 This is a SEM image of the gray cast iron prepared using the gray cast iron inoculant described in Example 1 of the present invention. DETAILED DESCRIPTION

[0044] The following detailed description of exemplary embodiments of the present invention refers to the accompanying drawings, which form a part of the description, and in which exemplary embodiments of the present invention that can be implemented are shown as examples. Although these exemplary embodiments are described in sufficient detail to enable those skilled in the art to implement the present invention, it should be understood that other embodiments can be implemented and various changes can be made to the present invention without departing from the spirit and scope of the present invention. The following more detailed description of the embodiments of the present invention is not intended to limit the scope of the claimed invention, but is only for the purpose of illustrating and not limiting the description of the characteristics and features of the present invention, so as to propose the best mode for performing the present invention and to enable those skilled in the art to implement the present invention. Therefore, the scope of the present invention is limited only by the appended claims.

[0045] It should be emphasized that the purpose of inoculation treatment of gray cast iron is to promote graphitization, reduce the tendency of chilling, reduce cross-section sensitivity, control graphite morphology, eliminate supercooled graphite, appropriately increase the number of eutectic clusters and promote the formation of fine pearlite; compared with ductile iron, the purpose of inoculation is to eliminate supercooling tendency, promote graphite spheroidization and reduce intergranular segregation.

[0046] There are a lot of flake graphite in gray cast iron, which is equivalent to a lot of gaps inside, thus reducing the sensitivity of mechanical properties to external gaps. Similarly, a lot of flake graphite splits the matrix, organizes the propagation of vibration, and can be converted into heat energy and dissipated, so it has good shock absorption. The structure of ductile iron is a metal matrix and small round graphite. The graphite has no destructive effect on the metal matrix, so it is more notch-sensitive than gray cast iron and has poorer shock absorption.

[0047] The inoculant of the present invention contains 40-70% by mass of Si, 1-5% by mass of Ca, 1-5% by mass of Mg, 0.5-3% by mass of Al, and the rest is Fe and conventional amounts of incidental impurities, wherein the Mg and Al elements can be uniformly distributed in the gray cast iron matrix prepared by inoculation with the inoculant in the form of oxides and / or sulfides, and the oxides and / or sulfides are at least partially exposed on the surface, thereby improving the cutting performance of the gray cast iron.

[0048] It should be noted that the main function of the inoculant of the present invention is to prevent the formation of carbides by introducing graphite nucleation sites. The present invention does not need to convert the inclusions such as MgO and MgS formed during the inoculation process into nucleation sites by adding a layer (containing Ca, Ba or Sr). The inoculant of the present invention can be evenly distributed in the gray cast iron matrix in the form of oxides and / or sulfides, and the oxides and / or sulfides are at least partially exposed on the surface. Here, at least partially exposed on the surface means that at least 50% of the surface of the inclusions such as MgO and MgS is not covered.

[0049] Furthermore, the mass percentages of Al, Ca, and Mg satisfy the relationship: 5.5%≤Al+Ca+Mg≤13.0%, and by adding magnesium and aluminum elements to the inoculant, the mass percentages of Mg and Al satisfy: 3.0≥[Mg] / [Al]≥1.5, [Mg] and [Al] are the mass percentages of Mg and Al, respectively, and magnesium and aluminum elements can be uniformly distributed in the gray cast iron matrix in the form of oxides or sulfides; when the tool cuts the gray cast iron matrix at high speed, friction generates heat, so that the oxides (mainly MgO / Al2O3) or sulfides (mainly MgS) partially exposed on the surface of the gray cast iron matrix contact and react with the substances on the surface of the tool at high temperature, thereby adhering to the surface of the tool to form a protective film, which improves the wear resistance of the tool, thereby effectively improving the service life of the tool.

[0050] Furthermore, the inoculant utilizes the inoculating ability and synergistic effect of each element to reduce the cross-section sensitivity and chilling tendency of the gray cast iron, and obtain graphite with a fine and curved shape and the most uniform distribution.

[0051] Furthermore, the inoculant contains other trace elements Ba, and the mass percentage of Ba element is 3-8%. Ba can inhibit the decay of inoculation, and it is still effective even when inoculated at a high temperature of 1480°C.

[0052] The second aspect of the present invention provides a method for preparing the grey cast iron inoculant, comprising the following steps:

[0053] S1. Raw material preparation: weigh the raw materials of the inoculant according to the elemental composition, and weigh the raw materials of the inoculant, namely ferrosilicon, calcium silicon, calcium barium, magnesium and metallic silicon, by weight for use.

[0054] The raw materials of the inoculant are ferrosilicon, silicon calcium, barium calcium, metal magnesium and metal silicon, and the mass ratio of the ferrosilicon, silicon calcium, barium calcium, metal magnesium and metal silicon is: the added proportion is 50% ferrosilicon, 5% silicon calcium, 15% barium calcium, 2% metal magnesium, 20% metal silicon and 8% scrap steel;

[0055] The raw materials of the inoculant, ferrosilicon, calcium silicon, barium calcium, magnesium and metal silicon, are subjected to surface pretreatment. The specific process of surface pretreatment is: the surfaces of ferrosilicon, calcium silicon, barium calcium, magnesium and metal silicon are polished with sandpaper, and then cleaned with acetone to remove oil and impurities on the surfaces of aluminum ingots, zinc ingots and magnesium ingots.

[0056] S2. Smelting: Smelting the weighed raw materials at a temperature of 1500°C to 1600°C to obtain molten iron.

[0057] Furthermore, in step S2, a medium frequency induction furnace is used to melt the raw materials.

[0058] After the charge is completely melted, the molten iron is inspected and taken for spectral experiment. The molten iron is discharged after passing the inspection. If it is unqualified, the composition of the molten iron is adjusted until it passes. The qualified composition of the molten iron is Si 40%-70%, Ca 1~5%, Mg1~5%, Al0.5~3%.

[0059] S3, casting: pouring the smelted inoculant into a mold and cooling it;

[0060] After the melt in S3 is cooled, it is cast into an ingot, the oxide scale on the surface of the ingot is removed, and then a homogenization treatment is performed. The specific operation process is: after the melt is cast into an ingot, the oxide scale on the surface of the ingot is removed, and then the ingot is placed in a heat treatment furnace for homogenization treatment. The temperature of the homogenization treatment is 450°C and the time of the homogenization treatment is 24 hours.

[0061] S4. Crushing and screening: The cooled inoculant is crushed and screened into particles ≤10mm, and then weighed and packaged.

[0062] The third aspect of the present invention provides a gray cast iron, which contains the inoculant described in the first aspect, which accounts for 0.35-0.45% of the total mass of the molten iron, and the inoculant contains 40-70% by mass of Si, 1-5% by mass of Ca, 1-5% by mass of Mg; 0.5-3% by mass of Al, and the rest is Fe and a conventional amount of incidental impurities, wherein the Mg and Al elements can be uniformly distributed in the gray cast iron matrix in the form of oxides and / or sulfides, and the oxides and / or sulfides are at least partially exposed on the surface, thereby improving the cutting performance of the gray cast iron.

[0063] The gray cast iron obtained by the above method can be used to produce automobile parts such as brake discs, brake drums, flywheels, as well as motor housings (bases) and motor end covers in the motor industry; air conditioning compressor parts; and cutting processing of automobile gearboxes, cylinder blocks, and machine tool guide rails.

[0064] Example 1

[0065] As shown in Table 1, the gray cast iron inoculant of this embodiment includes Mg with a mass percentage of 1%, Si with a mass percentage of 40%, Ca with a mass percentage of 1%, Al with a mass percentage of 0.5%, Ba with a mass percentage of 3%, and the rest is iron Fe. The preparation method of the gray cast iron inoculant includes the following steps:

[0066] S1. Raw material preparation: weigh the raw materials of the inoculant, ferrosilicon, calcium silicon, barium calcium, magnesium and metallic silicon by weight for later use; the addition ratio is 50% ferrosilicon, 5% calcium silicon, 15% barium calcium, 2% metallic magnesium, 20% metallic silicon and 8% scrap steel;

[0067] S2, smelting: the weighed raw materials are placed in a medium frequency induction furnace for smelting, the smelting temperature is controlled at 1500 ° C, after the charge is completely melted, the molten iron is taken for spectrum experiment, and the molten iron is discharged after the inspection is qualified. If it is unqualified, the composition of the molten iron is adjusted until it is qualified; the composition of the qualified molten iron is 1% by mass of Mg, 40% by mass of Si, 1% by mass of Ca, 0.5% by mass of Al, 3% by mass of Ba, and the rest is iron Fe;

[0068] S3, casting: pour the smelted inoculant into the mold to cool; after the melt is cooled, cast it into an ingot, remove the oxide scale on the surface of the ingot, and then perform homogenization. During the homogenization process: after the melt is cast into an ingot, remove the oxide scale on the surface of the ingot, and then place it in a heat treatment furnace for homogenization. The homogenization temperature is 450°C and the homogenization time is 24 hours;

[0069] S4. Crushing and screening: The cooled inoculant is crushed and screened into 5 mm particles according to the particle size, and then weighed and packaged.

[0070] The inoculant obtained above is used to produce compressor housing cast iron. The gray cast iron contains the inoculant accounting for 0.45% of the total mass of the molten iron. The compressor housing cast iron is cut using tools made of WC-Co alloy, TiC-Ni and other hard alloys, Mo-based metal ceramics and other metal ceramics, ceramics, etc., and the tool life reaches 210 pieces.

[0071] Example 2

[0072] The gray cast iron inoculant of this embodiment includes 3% by mass of Mg, 55% by mass of Si, 3% by mass of Ca, 2% by mass of Al, 5% by mass of Ba, and the rest is iron Fe. The preparation method of the gray cast iron inoculant includes the following steps:

[0073] S1. Raw material preparation: weigh the raw materials of the inoculant, ferrosilicon, calcium silicon, barium calcium, magnesium and metallic silicon by weight for later use; the addition ratio is 50% ferrosilicon, 5% calcium silicon, 15% barium calcium, 2% metallic magnesium, 20% metallic silicon and 8% scrap steel;

[0074] S2, smelting: the weighed raw materials are placed in a medium frequency induction furnace for smelting, the smelting temperature is controlled at 1550 ° C, after the charge is completely melted, the molten iron is taken for spectrum experiment, and the molten iron is discharged after the inspection is qualified. If it is unqualified, the composition of the molten iron is adjusted until it is qualified; the composition of the qualified molten iron is 3% by mass of Mg, 55% by mass of Si, 3% by mass of Ca, 2% by mass of Al, 5% by mass of Ba, and the rest is iron Fe;

[0075] S3, casting: pour the smelted inoculant into the mold to cool; after the melt is cooled, cast it into an ingot, remove the oxide scale on the surface of the ingot, and then perform homogenization. During the homogenization process: after the melt is cast into an ingot, remove the oxide scale on the surface of the ingot, and then place it in a heat treatment furnace for homogenization. The homogenization temperature is 450°C and the homogenization time is 24 hours;

[0076] S4. Crushing and screening: The cooled inoculant is crushed and screened into 8 mm particles according to the particle size, and then weighed and packaged.

[0077] The inoculant obtained above is used to produce compressor housing cast iron. The gray cast iron contains the inoculant accounting for 0.4% of the total mass of the molten iron. The compressor housing cast iron is cut using tools made of WC-Co alloy, TiC-Ni and other hard alloys, Mo-based metal ceramics and other metal ceramics, ceramics, etc., and the tool life is 206 pieces.

[0078] Example 3

[0079] The gray cast iron inoculant of this embodiment includes Mg with a mass percentage of 5%, Si with a mass percentage of 70%, Ca with a mass percentage of 5%, Al with a mass percentage of 3%, Ba with a mass percentage of 8%, and the rest is iron Fe. The preparation method of the gray cast iron inoculant includes the following steps:

[0080] S1. Raw material preparation: weigh the raw materials of the inoculant, ferrosilicon, calcium silicon, barium calcium, magnesium and metallic silicon by weight for later use; the addition ratio is 50% ferrosilicon, 5% calcium silicon, 15% barium calcium, 2% metallic magnesium, 20% metallic silicon and 8% scrap steel;

[0081] S2, smelting: the weighed raw materials are placed in a medium frequency induction furnace for smelting, the smelting temperature is controlled at 1600 ° C, after the charge is completely melted, the molten iron is taken for spectrum experiment, and the molten iron is discharged after the inspection is qualified. If it is unqualified, the composition of the molten iron is adjusted until it is qualified; the mass percentage of Mg is 5%, the mass percentage of Si is 70%, the mass percentage of Ca is 5%, the mass percentage of Al is 3%, the mass percentage of Ba is 8%, and the rest is iron Fe;

[0082] S3, casting: pouring the smelted inoculant into a mold to cool; after the melt is cooled, casting it into an ingot, removing the oxide scale on the surface of the ingot, and then homogenizing it. During the homogenizing process, after the melt is cast into an ingot, the oxide scale on the surface of the ingot is removed, and then placing it in a heat treatment furnace for homogenizing, the temperature of the homogenizing treatment is 450°C, and the time of the homogenizing treatment is 24 hours;

[0083] S4. Crushing and screening: The cooled inoculant is crushed and screened into particles ≤10mm, and then weighed and packaged.

[0084] The inoculant obtained above is used to produce compressor housing cast iron. The gray cast iron contains the inoculant accounting for 0.35% of the total mass of the molten iron. The compressor housing cast iron is cut using tools made of WC-Co alloy, TiC-Ni and other hard alloys, Mo-based metal ceramics and other metal ceramics, ceramics, etc., and the tool life is 214 pieces.

[0085] Example 4

[0086] The gray cast iron inoculant of this embodiment includes Mg with a mass percentage of 3.2%, Si with a mass percentage of 51.9%, Ca with a mass percentage of 2.25%, Al with a mass percentage of 1.9%, Ba with a mass percentage of 3%, and the rest is iron Fe. The preparation method of the gray cast iron inoculant includes the following steps:

[0087] S1. Raw material preparation: weigh the raw materials of the inoculant, ferrosilicon, calcium silicon, barium calcium, magnesium and metallic silicon by weight for later use; the addition ratio is 50% ferrosilicon, 5% calcium silicon, 15% barium calcium, 2% metallic magnesium, 20% metallic silicon and 8% scrap steel;

[0088] S2, smelting: the weighed raw materials are placed in a medium frequency induction furnace for smelting, the smelting temperature is controlled at 1500 ° C, after the charge is completely melted, the molten iron is taken for spectrum experiment, and the molten iron is discharged after the inspection is qualified. If it is unqualified, the composition of the molten iron is adjusted until it is qualified; the composition of the qualified molten iron is 3.2% by mass of Mg, 51.9% by mass of Si, 2.25% by mass of Ca, 1.9% by mass of Al, 3% by mass of Ba, and the rest is iron Fe;

[0089] S3, casting: pour the smelted inoculant into the mold to cool; after the melt is cooled, cast it into an ingot, remove the oxide scale on the surface of the ingot, and then perform homogenization. During the homogenization process: after the melt is cast into an ingot, remove the oxide scale on the surface of the ingot, and then place it in a heat treatment furnace for homogenization. The homogenization temperature is 450°C and the homogenization time is 24 hours;

[0090] S4. Crushing and screening: The cooled inoculant is crushed and screened into 5 mm particles according to the particle size, and then weighed and packaged.

[0091] The inoculant obtained above is used to produce compressor housing cast iron. The gray cast iron contains the inoculant accounting for 0.45% of the total mass of the molten iron. The compressor housing cast iron is cut using tools made of WC-Co alloy, TiC-Ni and other hard alloys, Mo-based metal ceramics and other metal ceramics, ceramics, etc., and the tool life is 207 pieces.

[0092] Example 5

[0093] The gray cast iron inoculant of this embodiment includes Mg in a mass percentage of 3.5%, Si in a mass percentage of 53.5%, Ca in a mass percentage of 4.02%, Al in a mass percentage of 2.1%, Ba in a mass percentage of 5%, and the rest is iron Fe. The preparation method of the gray cast iron inoculant includes the following steps:

[0094] S1. Raw material preparation: weigh the raw materials of the inoculant, ferrosilicon, calcium silicon, barium calcium, magnesium and metallic silicon by weight for later use; the addition ratio is 50% ferrosilicon, 5% calcium silicon, 15% barium calcium, 2% metallic magnesium, 20% metallic silicon and 8% scrap steel;

[0095] S2, smelting: the weighed raw materials are placed in a medium frequency induction furnace for smelting, the smelting temperature is controlled at 1600 ° C, after the charge is completely melted, the molten iron is taken for spectrum experiment, and the molten iron is discharged after the inspection is qualified. If it is unqualified, the composition of the molten iron is adjusted until it is qualified; the mass percentage of Mg is 3.5%, the mass percentage of Si is 53.5%, the mass percentage of Ca is 4.02%, the mass percentage of Al is 2.1%, the mass percentage of Ba is 5%, and the rest is iron Fe;

[0096] S3, casting: pouring the smelted inoculant into a mold to cool; after the melt is cooled, casting it into an ingot, removing the oxide scale on the surface of the ingot, and then homogenizing it. During the homogenizing process, after the melt is cast into an ingot, the oxide scale on the surface of the ingot is removed, and then placing it in a heat treatment furnace for homogenizing, the temperature of the homogenizing treatment is 450°C, and the time of the homogenizing treatment is 24 hours;

[0097] S4. Crushing and screening: The cooled inoculant is crushed and screened into particles ≤10mm, and then weighed and packaged.

[0098] The inoculant obtained above is used to produce compressor housing cast iron. The gray cast iron contains the inoculant accounting for 0.35% of the total mass of the molten iron. The compressor housing cast iron is cut using tools made of WC-Co alloy, TiC-Ni and other hard alloys, Mo-based metal ceramics and other metal ceramics, ceramics, etc., and the tool life is 209 pieces.

[0099] Comparative Example 1

[0100] The gray cast iron inoculant of this comparative example includes Mg with a mass percentage of 0.22%, Si with a mass percentage of 51.9%, Ca with a mass percentage of 2.25%, Al with a mass percentage of 1.61%, Ba with a mass percentage of 3%, and the rest is iron Fe. The preparation method of the gray cast iron inoculant includes the following steps:

[0101] S1. Raw material preparation: weigh the raw materials of the inoculant, ferrosilicon, calcium silicon, barium calcium, magnesium and metallic silicon by weight for later use; the addition ratio is 50% ferrosilicon, 5% calcium silicon, 15% barium calcium, 2% metallic magnesium, 20% metallic silicon and 8% scrap steel;

[0102] S2, smelting: the weighed raw materials are placed in a medium frequency induction furnace for smelting, the smelting temperature is controlled at 1500 ° C, after the charge is completely melted, the molten iron is taken for spectrum experiment, and the molten iron is discharged after the inspection is qualified. If it is unqualified, the composition of the molten iron is adjusted until it is qualified; the composition of the qualified molten iron is 3.2% by mass of Mg, 51.9% by mass of Si, 2.25% by mass of Ca, 1.9% by mass of Al, 3% by mass of Ba, and the rest is iron Fe;

[0103] S3, casting: pour the smelted inoculant into the mold to cool; after the melt is cooled, cast it into an ingot, remove the oxide scale on the surface of the ingot, and then perform homogenization. During the homogenization process: after the melt is cast into an ingot, remove the oxide scale on the surface of the ingot, and then place it in a heat treatment furnace for homogenization. The homogenization temperature is 450°C and the homogenization time is 24 hours;

[0104] S4. Crushing and screening: The cooled inoculant is crushed and screened into 5 mm particles according to the particle size, and then weighed and packaged.

[0105] The inoculant obtained above is used to produce compressor housing cast iron. The gray cast iron contains the inoculant accounting for 0.45% of the total mass of the molten iron. The compressor housing cast iron is cut using tools made of WC-Co alloy, TiC-Ni and other hard alloys, Mo-based metal ceramics and other metal ceramics, ceramics, etc., and the tool life is 98 pieces.

[0106] Comparative Example 2

[0107] The gray cast iron inoculant of this comparative example includes 0.33% by mass of Mg, 53.5% by mass of Si, 4.02% by mass of Ca, 1.84% by mass of Al, 5% by mass of Ba, and the rest is iron Fe. The preparation method of the gray cast iron inoculant includes the following steps:

[0108] S1. Raw material preparation: weigh the raw materials of the inoculant, ferrosilicon, calcium silicon, calcium barium, magnesium and metallic silicon according to weight and set aside;

[0109] S2, smelting: the weighed raw materials are placed in a medium frequency induction furnace for smelting, the smelting temperature is controlled at 1600 ° C, after the charge is completely melted, the molten iron is taken for spectrum experiment, and the molten iron is discharged after the inspection is qualified. If it is unqualified, the composition of the molten iron is adjusted until it is qualified; the mass percentage of Mg is 3.5%, the mass percentage of Si is 53.5%, the mass percentage of Ca is 4.02%, the mass percentage of Al is 2.1%, the mass percentage of Ba is 5%, and the rest is iron Fe;

[0110] S3, casting: pouring the smelted inoculant into a mold to cool; after the melt is cooled, casting it into an ingot, removing the oxide scale on the surface of the ingot, and then homogenizing it. During the homogenizing process, after the melt is cast into an ingot, the oxide scale on the surface of the ingot is removed, and then placing it in a heat treatment furnace for homogenizing, the temperature of the homogenizing treatment is 450°C, and the time of the homogenizing treatment is 24 hours;

[0111] S4. Crushing and screening: The cooled inoculant is crushed and screened into particles ≤10mm, and then weighed and packaged.

[0112] The inoculant obtained above is used to produce compressor housing cast iron. The gray cast iron contains the inoculant accounting for 0.35% of the total mass of the molten iron. The compressor housing cast iron is cut using tools made of WC-Co alloy, TiC-Ni and other hard alloys, Mo-based metal ceramics and other metal ceramics, ceramics, etc., and the tool life is 101 pieces.

[0113] Table 1 Parameters of each embodiment and comparative example

[0114]

[0115]

[0116] Combination Figure 3 As shown, the graphite in the gray cast iron obtained by the present invention meets the requirements of the prior art, the length and distribution of the graphite are basically not affected, and the graphitization of carbon in the gray cast iron matrix is ​​promoted by adding aluminum, calcium and barium elements, the white cast iron matrix tendency is reduced, and a good inoculation effect is achieved.

[0117] In addition, combined with the data in Table 1 and Figure 3 It can be seen from the content that the surface part of the oxide or sulfide in the gray cast iron matrix is ​​not wrapped, and when magnified 200 times, the length of the graphite is obviously smaller than that of the traditional graphite. The inoculant utilizes the inoculation ability and synergistic effect of each element to reduce the cross-section sensitivity and white cast iron tendency of the gray cast iron, and obtains graphite with a small, curved shape and the most uniform distribution. Therefore, compared with the gray cast iron obtained by the existing technology, the gray cast iron of the present invention has a tool life increased by at least 100%, thereby effectively improving the tool life.

Claims

1. An inoculant for use in grey cast iron casting, characterized in that: The inoculant contains 40-70% by mass of Si, 1-5% by mass of Ca, 1-5% by mass of Mg, 0.5-3% by mass of Al, and the remainder is Fe and conventional amounts of incidental impurities, wherein the Mg and Al elements can be uniformly distributed in the form of oxides and / or sulfides in the gray cast iron matrix prepared by inoculation with the inoculant.

2. The inoculant according to claim 1, characterized in that The inoculant further comprises Ba, and the mass percentage of Ba is 3% to 8%.

3. The inoculant according to claim 1, characterized in that The inoculant contains 3-5% by mass of Mg and 1.5-2.5% by mass of Al.

4. A method for preparing the inoculant according to any one of claims 2 to 3, characterized in that: The following steps are involved: S1. Material preparation: weigh the raw materials of the inoculant according to the elemental composition; S2, smelting: smelting the weighed raw materials, controlling the smelting temperature at 1500°C to 1600°C to obtain molten iron; S3, casting: pouring the smelted inoculant into a mold and cooling it; S4. Crushing and screening: The cooled inoculant is crushed and screened into particles ≤10 mm.

5. The preparation method according to claim 4, characterized in that: The surfaces of the tools used in the operation process of steps S1 and S2 are coated with a zinc oxide layer.

6. The preparation method according to claim 4, characterized in that: The raw materials of the inoculant are subjected to surface pretreatment, and the specific process is: the surfaces of ferrosilicon, calcium silicon, barium calcium, magnesium and metallic silicon are polished with sandpaper and then cleaned with acetone.

7. The preparation method according to claim 4, characterized in that: After the solution is cast into an ingot in step S3, the oxide scale on the surface of the ingot is removed, and then the ingot is placed in a heat treatment furnace for homogenization treatment. The temperature of the homogenization treatment is 450° C. and the time of the homogenization treatment is 24 hours.

8. A free-cutting grey cast iron, characterized in that: The raw material is free-cutting grey cast iron prepared by inoculation with the inoculant described in any one of claims 1 to 3, and the grey cast iron matrix is ​​uniformly distributed with oxides and / or sulfides of Mg and Al elements at least partially exposed on the surface.

9. Use of the free-cutting grey cast iron according to claim 8 in the preparation of grey cast iron products.

10. The use according to claim 9, characterized in that: The gray cast iron products include brake discs, brake drums, flywheels, motor housings, motor end covers, air-conditioning compressors, automobile gearboxes, cylinder blocks, and machine tool guide rails.

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