A cast iron mold hardfacing flux-cored electrode and a method for manufacturing the same

Abstract

The application discloses a cast iron mold surfacing flux-cored electrode and a preparation method thereof, and relates to the technical field of electric welding materials. The cast iron mold surfacing flux-cored electrode comprises a tube body, a flux core filled in the tube body and a coating wrapping the tube body. The components of the flux core and the coating are selected, so that a surfacing weld with good crack resistance, brittleness resistance and strong impact wear resistance performance can be formed on an FC300 imported automobile cast iron mold, the hardness of the welding layer meets the use requirement, and the mold after surfacing repair by using the electric welding strip has a longer service life.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of electric welding material, in particular to a cast iron mold surfacing flux-cored electrode and a preparation method thereof. BACKGROUND

[0002] In various vehicle manufacturing, cast iron molds are widely used to produce various parts. These molds are subjected to strong impact, drawing, extrusion, thermal fatigue and other effects in use, resulting in various problems such as wear, scratches, and broken edges, which affect the quality of the workpieces, and even cause them to be scrapped, resulting in huge losses. Therefore, various surfacing and repair work needs to be carried out on these molds during production or after use. The cast iron materials used for these molds are various, and commonly used are Japanese imported mold gray iron materials FC300 and the like. The material is similar to the domestic gray iron HT-300 material, both of which have a high carbon content (more than 3.5%) and high surface hardness, and have poor weldability. Among them, HT-300 has a higher phosphorus and silicon content, and has even poorer weldability. When surfacing the above-mentioned materials, the welds at the welding sites are prone to white structure and brittle martensite structure, and the welds have high hardness and high brittleness, which causes the welds and their periphery to be prone to cracking, and even peeling.

[0003] In order to solve the above technical problems, the commonly used means at present is to use high nickel, nickel-copper, nickel-iron alloy and the like to prepare a nickel-based series surfacing electrode in the electrode manufacturing material, so as to form a non-cast iron structure weld; or to add strong oxidizing agents such as marble powder, iron oxide powder and the like to the coating of the electrode to reduce the carbon content of the weld in the form of burning loss and chemical reaction, and to reduce the white area of the weld.

[0004] However, the above-mentioned schemes have some drawbacks to a greater or lesser extent, for example: the weld of the pure nickel solid core electrode has too low hardness, poor wear resistance, resulting in a very short service life of the surfacing workpiece, and high production cost; if the coating contains strong oxidizing agents or a large amount of iron powder, the effect on reducing the white area of the weld is limited. SUMMARY

[0005] The present application aims to overcome the shortcomings of the prior art and provide a cast iron mold surfacing flux-cored electrode and a preparation method thereof. The weld after surfacing using the electrode has good impact and wear resistance, and the weld has an attractive appearance. The electrode is easy to operate and is suitable for welding imported molds such as FC300.

[0006] To achieve the above-mentioned purpose, the technical scheme adopted by the present application is as follows:

[0007] A cast iron mold surfacing flux-cored electrode, comprising a tube body, a flux core filled in the tube body, and a coating wrapping the tube body.

[0008] The core comprises the following components: iron powder, manganese powder, ferrosilicon powder and mixed powder; the mass ratio of the iron powder, manganese powder, ferrosilicon powder, mixed powder is (60-68):(10.4-11):(11.5-12.5):(12-14); the mixed powder is a mixture of nickel powder, copper powder and cobalt powder;

[0009] The coating comprises the following components: marble powder, fluorite powder, graphite powder, titanium white powder, ilmenite powder, zircon powder, iron powder, ferrosilicon powder and manganese powder; the mass ratio of the marble powder, fluorite powder, graphite powder, titanium white powder, ilmenite powder, zircon powder, iron powder, ferrosilicon powder and manganese powder is (50-55):(8-12):(1-1.5):(1-4):(6-8):(10-14):(4-10):(2-5):(3-5).

[0010] A series of liquid phase physical and metallurgical chemical reactions occur during the welding process, and under the action of arc blowing force, electromagnetic force and the like, the liquid phase is instantaneously sprayed to the surface of the base material to form a molten pool. As the welding continues, the droplets polymerize and increase, thereby forming small fluid and flowing to the molten pool; the powder materials with different distances from the arc end are different in heating condition, and once the welding is stopped, sintering, calcination and the like occur at the arc end. Under the action of the welding arc, obvious cathode spots are prone to occur at the arc starting end of the thin tube wall, and the current density is very high, so that the cross-sectional area of the tube skin (i.e. the tube body) is much smaller than that of the solid core welding wire, resulting in that the heating efficiency of the tube skin is very high.

[0011] It is found by experiments that the core formed by injecting the above alloying substances into the tube skin is better than adding these alloying substances in the coating, the temperature in the tube skin is low, the burn loss is small when the alloying substances are transferred to the weld, the welding spatter is small, and thus the transition efficiency is higher. In addition, the required hardening alloy components do not need to be added in the coating, and thus a larger percentage of the weight is left, which can better adjust the proportion of components that are helpful for reducing carbon, crack resistance, pore resistance, forming and the like, and further improve the welding process of the electrode. That is, the core is used to realize weld alloying and hardening, the coating is used to improve the welding process, crack resistance, pore resistance and the like, so that the electrode with the above structure has the respective advantages of the solid core electrode and the flux-cored wire, and better comprehensive performance.

[0012] The present application finds that the melting point of the core is moderate, which can accelerate the melting speed during welding by studying the components of the core and the coating; the melting point of the coating is slightly higher than that of the core, which can form a sleeve of a certain length at the droplet part of the electrode, and the transition of the droplet is changed from the short circuit form to the slag wall or the spraying form to the welding pool. This transition also helps to prevent the perforation and powder leakage problems at the end of the droplet, and reduces the red phenomenon of the electrode tube coating and the coating. The components of the core and the coating in the present application are specially selected based on the base material cast iron, which is affected by the welding object, and there is a big difference in the components of different welding layers. For example, in the first layer, the carbon and other harmful elements in the base material are easy to diffuse, so the carbon content of this layer is high, even reaching the level of high carbon steel, which leads to the phenomena of white mouth, brittle and hard cracking, porosity sensitivity, etc. The components of the second layer and above are less affected by the base material, and the components of the third layer welding seam are close to the pure welding seam level, and the welding seam structure and performance are also changed accordingly. Therefore, the formula design must take into account the characteristics of the components, structure and performance of the first, third and above welding seams.

[0013] As mentioned above, when the general welding material is used for surfacing cast iron, the average carbon content of the first layer welding seam can reach 0.7%-1.0%(even up to 2.0% near the fusion zone), which is the main reason for the cracking of the welding seam. The present application first solves the problems of high carbon content, easy cracking and porosity in the first layer welding seam. A large number of experiments show that the addition of the following substances in the coating can achieve the purpose of reducing carbon, anti-cracking and anti-porosity to a certain extent:

[0014] Marble powder decomposes at high temperature during welding droplet and pool stage. Marble powder can be decomposed into calcium oxide and CO2 gas. The former is a high alkalinity and high oxidizing substance, which reacts with the high concentration of carbon components in the first layer welding seam diffused from the base material, greatly reducing the free carbon content and producing CO2 gas, and improving the basicity of the molten pool. At the same time, this substance is also beneficial to improve the fluidity of the molten pool stage, and helps to remove the slag and make the gas in the molten pool float up, purifying the welding seam and improving the anti-porosity. CO2 gas can also prevent the surrounding of the molten pool from being affected by air, thereby improving the anti-porosity. Experiments show that if too much marble powder is added, the welding spatter increases, the alloy loss is large, and the components of the third layer and above are not beneficial; if too little marble powder is added, the arc atmosphere is weak, which is not conducive to the gas protection effect, the basicity of the molten pool is small, and the anti-cracking property is weak.

[0015] Fluorite powder. The present application finds through experiments that the addition of a certain proportion of fluorite powder in the coating helps to improve the fluidity of the liquid metal in the welding cast iron molten pool stage, solve the problems of slag inclusion and porosity caused by the limited floating ability of impurities in the slag, and improve the welding seam forming, further enhance the basicity of the liquid metal, and improve the toughness and anti-cracking property of the welding seam. However, too much fluorite powder will reduce the stability of the arc and make the slag removal worse; and because of its low melting point, it is not conducive to the formation of a suitable sleeve for the coating, and is not conducive to improving the transition form of the droplet.

[0016] Graphite powder, adding a certain amount of graphite powder in the coating can improve the smoothness of the electrode surface, and can improve the welding performance, but the addition of too much graphite powder is easy to produce cracks.

[0017] Titanium dioxide, adding a certain amount of titanium dioxide can improve the adhesion of the coating, improve the production performance of the electrode, and make the electrode surface more smooth, but too much will affect the welding process, such as weld slag, porosity, etc.

[0018] Ilmenite powder, adding ilmenite powder can further reduce carbon in the first layer of weld, and produce CO2 protective gas, improve the stability of the welding arc, which is beneficial to the extrusion production of the electrode coating, and can cooperate with marble powder to better achieve the purpose of reducing carbon and resisting porosity. Adding too much will cause the welding spatter to increase.

[0019] Zircon powder, adding zircon powder can help to improve the melting point of the coating, reduce the droplet temperature, lengthen the coating sleeve, improve the droplet transition form, reduce the loss of alloy elements in the droplet and molten pool stages. If the amount is too small, the improvement effect is not obvious, and if the amount is too large, the coating may fall off.

[0020] Adding appropriate amount of iron powder, ferrosilicon powder and manganese powder in the coating and core can further enhance the deoxidation ability of the molten pool and droplet stage, and assist to improve the toughness of the weld. Manganese can react with sulfur in cast iron to form manganese sulfide into the slag and be removed, reducing the harmful effects of impurity sulfur, but too much manganese will affect the hardness, wear resistance of the weld and the welding process. Silicon can significantly reduce the solubility of carbon in austenite and promote carbon desorption, increasing the tendency of carbide precipitation, and inhibiting the formation of manganese carbide, but it is harmful to crack resistance and reduces the hardenability, which is not conducive to martensite transformation, so the amount of silicon should not be too much. Adding manganese and silicon in the core is mainly to meet the strength requirements of the weld, and adding them in the coating can further improve the welding process such as deoxidation and auxiliary alloying.

[0021] Adding nickel powder in the core can better dissolve carbon and reduce the free carbon content in the weld. Nickel, copper and cobalt are good austenite and non-carbide forming elements, which are less affected by the oxidation-reduction reaction of the coating strong oxidizer in the welding arc and molten pool stage, resulting in less loss of alloy content in the weld. In addition, the three have high hardenability and good solid solution strengthening. Nickel and copper can be infinitely soluble in the welding droplet and molten pool stage. The present invention found through experiments that adding a small amount of mixed powder of nickel powder, copper powder and cobalt powder in the core can effectively improve the strength and hardness of the weld, reduce the width of the white spot, refine the grain, promote the formation of tough martensite, and improve the resistance to thermal cracking, thereby achieving relatively good comprehensive performance.

[0022] The present application can contain a sheath sleeve formed during the welding process, and can not cause powder leakage, improve the welding public welfare, and improve the appearance of the weld. At the same time, the components can promote each other and improve the hardness and wear resistance of the weld, and improve the service life of the welding object.

[0023] Preferably, the mass ratio of nickel powder, copper powder and cobalt powder in the mixed powder is (1.4-1.6):(2.4-2.6):(5.9-6.1). Controlling the ratio of the three powders in the above range can significantly improve the hardness, thermal fatigue resistance, red hardness and tempering stability of the weld.

[0024] Preferably, the pipe body is a carbon steel H08A hollow pipe; the wall thickness of the pipe body is 0.3-0.5mm, the diameter (outer diameter) of the pipe body is Φ3.98-4.02mm, and the length is 395-400mm; the outer diameter of the electrode is Φ6.2-6.6mm. There is a certain chemical reaction relationship between the components in the core and the sheath. The design of the powder component and the structure of the electrode can prevent the electrode and the pipe skin from red and the molten droplet stage from powder leakage, which can cause the chemical components of the weld to be uneven, the welding process to be poor, and the comprehensive performance of the weld to be affected. The outer diameter of the sheath and the length of the sleeve are appropriate, the blowing force of the arc atmosphere is moderate, the penetration is small, the influence of the high carbon content of the base material on the first layer of the weld is avoided, and at the same time, the thickness of the sheath is controlled, that is, the inner diameter of the pipe body and the outer diameter of the electrode are in the above range, which can stabilize the arc, reduce spatter and slag, and improve the appearance of the weld. The electrode is too long, and the sheath is easy to red and even melt during the welding process; the electrode is too short, the welding production efficiency is low, and it is not conducive to practical application. It has been proved that 395-400mm is the best.

[0025] Preferably, the iron powder is atomized iron powder; the manganese powder is electrolytic manganese powder; and the ferrosilicon powder is atomized ferrosilicon powder. The use of atomized process to treat iron powder and ferrosilicon powder can prevent the sheath from bubbling during the production of the electrode and prevent oxidation during the production of the electrode, and can improve the bulk density and flowability of the alloy powder. The electrolytic manganese powder has less impurities, and is good for welding process and weld crack resistance.

[0026] Preferably, the particle size of the nickel powder is 60-120 mesh, the particle size of the copper powder is 150-200 mesh, and the particle size of the cobalt powder is 50-80 mesh; the particle size of the ferrosilicon powder, iron powder, manganese powder, ilmenite powder, zircon powder and graphite powder is 40-150 mesh, the particle size of the marble powder and fluorite powder is 100-250 mesh, and the particle size of the titanium dioxide powder is 250-325 mesh. The above limitation on the particle size of the powder can improve the welding process of the electrode, prevent the pipe skin and the sheath from red, and prevent powder leakage.

[0027] Preferably, the cobalt powder is mechanically broken and ground from cobalt block, the copper powder is electrolytic copper powder, and the nickel powder is atomized nickel powder.

[0028] Preferably, the mass ratio of marble powder, fluorite powder, graphite powder, titanium white powder, ilmenite powder, zircon powder, iron powder, ferrosilicon powder and manganese powder in the coating is 53:10:1.3:4:8:12:4.7:3:4.

[0029] Preferably, the mass ratio of marble powder, fluorite powder, graphite powder, titanium white powder, ilmenite powder, zircon powder, iron powder, ferrosilicon powder and manganese powder in the coating is 50:10:1.5:3.5:8:12:5:5:5.

[0030] Preferably, the mass ratio of marble powder, fluorite powder, graphite powder, titanium white powder, ilmenite powder, zircon powder, iron powder, ferrosilicon powder and manganese powder in the coating is 55:10:1.5:1:6:12:4.5:5:5.

[0031] Preferably, the mass ratio of marble powder, fluorite powder, graphite powder, titanium white powder, ilmenite powder, zircon powder, iron powder, ferrosilicon powder and manganese powder in the coating is 55:10:1.5:1:8:12:7.5:2:3.

[0032] Preferably, the mass ratio of marble powder, fluorite powder, graphite powder, titanium white powder, ilmenite powder, zircon powder, iron powder, ferrosilicon powder and manganese powder in the coating is 53.5:10:1.5:3:6:12:4:5:5.

[0033] The coating prepared by using the above preferred formula has higher wear resistance of the surfacing weld layer and better processability of the electrode.

[0034] In addition, the application also provides a preparation method of the cast iron mold surfacing flux-cored electrode, and the preparation method comprises the following steps:

[0035] (1) The components of the flux are weighed according to the proportion, mixed uniformly, and filled into a carbon steel H08A hollow tube;

[0036] (2) The components of the coating are weighed according to the proportion, stirred uniformly in a stirrer, added with a binder, wet-stirred again, put into a briquetting machine to be pressed into a cylindrical briquette, extruded on the outer surface of the tube body and the two ports of the tube body by a pressure coating machine, and formed into a wet electrode, and then dried in an oven, so that the cast iron mold surfacing flux-cored electrode is obtained.

[0037] Preferably, in step (2), the temperature of the drying is 280-300 DEG C.

[0038] Preferably, the binder is liquid potassium-sodium water glass with a modulus of 2.9-3.1 and a concentration of 38-45°Bé, and is used in an amount of 10%-15% by weight of the coating powder. The molar ratio of sodium atoms to potassium atoms in the potassium-sodium water glass is 1:3. This binder prevents foaming of the coating, provides excellent results, and does not adversely affect welding rod production.

[0039] Preferably, in step (2), the coating can be applied on an existing coating machine dedicated to producing welding rods, and the coating can be coated on the outer surface of the tube body and the two ends of the tube body.

[0040] The present invention also discloses a method for using the flux-cored welding rod for cladding cast iron molds, which comprises welding using an AC or DC welding power source at a welding current of 100-140A. Welding under these conditions can reduce phenomena such as reddening of the flux coating and powder leakage during the electrode droplet stage. Using the flux-cored welding rod for cladding cast iron molds according to the present invention can reduce the welding current by more than 20% compared to solid steel welding rods, resulting in shallower base metal penetration, a narrower heat-affected zone, and a reduced white cast metal width. This also reduces the diffusion of base metal carbon into the first weld layer, thereby reducing its carbon content. Furthermore, the high welding airflow of the flux-cored welding rod reduces weld temperature, thereby reducing welding stress and crack susceptibility.

[0041] Compared with the prior art, the present invention has the following beneficial effects:

[0042] (1) The present invention uses a flux core to achieve weld metallurgy and strong hardening, and uses a flux coating to improve welding process, crack resistance, porosity resistance, and electrode pressure coating. By screening the components of the flux core and the flux coating and designing the structure of the electrode, imported automotive molds such as FC300 can be repaired.

[0043] (2) When welding with the welding rod of the present invention, the welding current is only 100-140A, which is more than 20% less than that of solid welding rod. Moreover, the welding deposition efficiency is about 20% higher than that of flux-cored wire.

[0044] (3) The coating has a reasonable composition and size, which can make the transition of the molten droplet change from short-circuit transition to slag-wall transition, fine particle transition, and spray transition, thereby ensuring the stability of the electric arc, reducing the burning loss of alloying elements, and improving the transition coefficient of the alloying elements. For example, the coating contains a large amount of strong oxidizing agent, high-basicity marble powder, and fluorite powder, and the welding current can be smaller, so that the carbon content in the first weld layer formed by the surfacing can be greatly reduced, thereby effectively reducing the white structure and brittle-hard structure of the weld, and effectively improving the resistance to pores and cracks of the weld; the weld contains a proper amount of austenite-promoting elements such as manganese, nickel, copper, and cobalt, which have solid solution strengthening, good red hardness, wear resistance, and impact resistance, thereby improving the hardenability of the weld structure, the hardness of the first weld layer is higher than HRC50, and when multiple layers are used, the hardness of the weld slightly decreases after welding due to the decrease in the carbon content, the change in the weld structure, and the preheating effect of the residual temperature of the previous weld layer, but the hardness is still greater than HRC45, and under the action of strong hammering and extrusion, the hardness of the weld is further improved due to the certain work hardening performance, so that the purpose of good strength and toughness and good crack resistance under the condition of strong impact is better achieved, the wear resistance of the weld is effectively improved, and the service life of the welding object is effectively improved; in addition, these strengthening elements are non-carbide-forming elements, which can strongly delay the formation and growth of cementite nuclei, improve the strength and hardness of the weld at a higher temperature, and especially the cobalt and nickel elements have strong resistance to high-temperature oxidation and softening, thereby solving the problems of good resistance to thermal fatigue, good red hardness, and good tempering stability of the weld. Practice shows that the service life of the workpiece surfacing by the welding rod is basically close to or exceeds that of the workpiece surfacing by the imported welding wire in the case of normal and high-temperature use. In summary, the welding rod is especially suitable for surfacing and repairing workpieces such as imported mold FC300, which requires high hardness, strong impact resistance, good red hardness, and good wear resistance. DETAILED DESCRIPTION

[0045] In order to better illustrate the purpose, technical scheme and advantages of the present application, the present application will be further described below in combination with specific examples.

[0046] The materials used in the examples and comparative examples are commercially available unless otherwise specified.

[0047] Cobalt powder: purity ≥ 99.0%, 50-80 mesh;

[0048] Copper powder: purity ≥ 99.0%, 150-200 mesh;

[0049] Nickel powder: purity ≥ 99.0%, 60-120 mesh;

[0050] Atomized ferrosilicon powder: 45# ferrosilicon powder (mass fraction of Si ≥ 43.5%), 40-150 mesh;

[0051] Atomized iron powder: Fe mass fraction ≥ 99.0%, 40-150 mesh;

[0052] Electrolytic manganese metal powder: Mn mass fraction ≥ 99.5%, 40-150 mesh;

[0053] Zircon powder: mass fraction of Zr(Hf)O2 ≥ 63%, 40-150 mesh;

[0054] Ilmenite powder: TiO2 mass fraction ≥ 52%, FeO mass fraction ≥ 47%, 40-150 mesh;

[0055] Graphite powder: C mass fraction ≥ 95%, 40-150 mesh;

[0056] Titanium dioxide: TiO2 mass fraction ≥ 99%, 250-325 mesh;

[0057] The above powders were purchased from Jiangsu Haimen Jinyi Welding Materials Co., Ltd.

[0058] Marble powder: CaCO3 mass fraction ≥ 96%, 100-250 mesh;

[0059] Fluorite powder: CaF2 mass fraction ≥ 96%, 100-250 mesh;

[0060] High potassium feldspar powder: mass fraction of SiO2 ≥ 60%, mass fraction of K2O + Na2O ≥ 15%, 80-200 mesh.

[0061] The above three powders were purchased from Datuo Mine in Changsha, Hunan Province.

[0062] Binder: Liquid potassium sodium water glass, modulus 3.0, concentration 40-43°Bé, purchased from Huzhou Hongsheng Material Technology Co., Ltd., Zhejiang Province.

[0063] The tube diameter, wall thickness and outer diameter of the welding rods in the following Examples 1 to 6, Examples 9 to 10, Comparative Example 2, and Comparative Examples 4 to 9 are all the same, that is, the diameter (outer diameter) of the tube is Φ4.0 mm, the wall thickness is 0.3-0.5 mm, and the length is 400 mm; the outer diameter of the welding rod is Φ6.4 mm.

[0064] The solid core diameter and the outer diameter of the solid coated electrode in Comparative Example 1 are the same as those in Example 1. The chemical components of the welding base materials HT-300 and FC300 except Fe are shown in Table 1.

[0065] Table 1

[0066]

[0067] Example 1

[0068] An embodiment of the cast iron mold surfacing flux-cored electrode according to the present application includes a tube, a flux core filled in the tube, and a coating covering the tube.

[0069] The ratio of the components in the flux core is atomized iron powder: electrolytic manganese powder: atomized ferrosilicon powder: mixed powder (mass ratio of atomized nickel powder, electrolytic copper powder, and mechanically ground cobalt powder is 1.5:2.5:6) = 64.5:10.4:12:13.1.

[0070] The ratio of the components in the coating is marble powder: fluorite powder: graphite powder: titanium white powder: ilmenite powder: zircon powder: atomized iron powder: atomized ferrosilicon powder: electrolytic manganese powder = 53:10:1.3:4:8:12:4.7:3:4.

[0071] The preparation method of the cast iron mold surfacing flux-cored electrode according to the embodiment includes the following steps:

[0072] (1) A carbon steel H08A steel strip is used to prepare a tube of a required specification through rolling and coiling processes;

[0073] (2) The components of the flux core are weighed according to the ratio, mixed uniformly, and filled in the tube;

[0074] (3) The components of the coating are weighed according to the ratio, stirred uniformly in a stirrer, and then wet-stirred after adding a binder (an amount of 10% of the weight of the coating powder); the mixture is then put into a briquetting machine to be pressed into a cylindrical briquette, extruded onto the outer surface of the tube and the two ends of the tube by a special coating extruder for welding rods, and then dried in an oven at about 280-300°C to obtain the cast iron mold surfacing flux-cored electrode.

[0075] Comparative Example 1

[0076] A cast iron mold solid core surfacing electrode. The welding core is a solid core rod drawn from a H08A electrode high-quality steel disc; the coating components are marble powder, fluorite powder, electrolytic manganese powder, graphite powder, mixed powder (mass ratio of nickel powder, copper powder, and cobalt powder is 1.5:2.5:6), atomized ferrosilicon powder, titanium white powder, ilmenite powder, and zircon powder; and the ratio of the components is marble powder: fluorite powder: electrolytic manganese powder: graphite powder: mixed powder: atomized ferrosilicon powder: titanium white powder: ilmenite powder: zircon powder = 50:10:7.5:1.3:13.1:6:1:6:5.1.

[0077] First, the performance of the electrodes according to Example 1 and Comparative Example 1 is compared.

[0078] Test 1: The ZX7-400 manual arc welding machine was used for welding, and the welding current of the welding rod of Example 1 and Comparative Example 1 was 130 A and 170 A, respectively (as the welding current of the two groups of welding rods was better in this value range). According to the A-grade low-carbon steel (specification: 100 mm x 50 mm x 16 mm) specified in GB / T 700-2006, three layers were stacked on the A-grade low-carbon steel, and the hardness of the three layers after welding and after the butt weld was hammered for fifty times was detected. The hardness of the weld was measured by using a desktop HR150-A Rockwell hardness tester. And according to GB / T 984-2001, the carbon content of the three layers of the weld was tested, and the test results are shown in Table 2.

[0079] Table 2

[0080]

[0081] Note: Hammering test method: On the above-mentioned A-grade low-carbon steel (specification: 100 mm x 50 mm x 16 mm) test block, three layers of the same size were continuously stacked, and after cooling, a 10 kg hammer was used to continuously strike fifty times, and the hardness was detected as a reference for the work hardening effect of the weld.

[0082] As can be seen from Table 2, the hardness of the weld of the two groups of welding rods is somewhat different: whether the three layers after welding and subsequent work hardening, the hardness of Example 1 is lower than that of Comparative Example 1, which is related to the slightly lower carbon content of the weld. This shows that the carbon content of the multi-layer weld of the flux-cored welding rod is greatly affected by its structure, and the welding rod prepared by using the structure described in the application can make the carbon content in the weld less.

[0083] Test 2: The carbon content, hardness, and cracking of the weld after one layer of welding on the HT-300 gray iron test block with a size of 60*45*25 mm were investigated. The welding method, current, and hardness determination method were the same as in Test 1. The results are shown in Table 3.

[0084] Table 3

[0085] Name Carbon content of one layer (%) Rockwell hardness value (HRC) Cracking degree of one layer weld Example 1 One layer 0.85 55-58 Microcracks at arc collection Comparative Example 1 One layer 1.04 58-61 More cracks at arc collection

[0086] As can be seen from Table 3, after one layer of welding on the cast iron test block, the carbon content of the weld of Example 1 was significantly lower than that of Comparative Example 1, the weld hardness was also lower, and the cracks were fewer.

[0087] Test three: to investigate the carbon content of one layer of welds of two groups of electrodes on FC300 imported automobile cast iron molds and the crack resistance, pore resistance, forming, deslagging and Rockwell hardness of the welds. The hardness test of the welds and the carbon content and other alloy component tests of the welds use the base metal, which is an imported FC300 mold workpiece provided by an automobile mold factory, and the workpiece number is 62-071-OP315-2010. The welding currents of Example 1 and Comparative Example 1 are 130 A and 170 A, respectively, and one layer and three layers of welds are deposited on the working surface of the mold, and a type AH150 portable Rockwell hardness tester is used to measure the hardness of the welds, respectively. Subsequently, the work hardening treatment is performed on the one layer and three layers of welds by using the hammering method of Test One, and the hardness is measured again.

[0088] The chemical components of one layer of welds of two groups of electrodes are the diffusion, melting and metallurgical chemical reaction of the base metal components and the weld pool metal of the two groups of electrodes, and the components of three layers and more of welds are gradually weakened by the base metal and are basically pure weld components. Therefore, the sampling and sampling method of the carbon content test sample of one layer and three layers of welds is different from that of Test One, and the specific method is as follows: one layer and three layers of 70 mm long welds are deposited on the working surface of the mold, and after the welds are cooled, a 30 mm long sample is cut in the middle section of the weld by wire cutting, and the carbon content of one layer and three layers is analyzed, respectively. In addition, the welding process performance of two groups of electrodes is also investigated. The results of the above tests are shown in Table 4.

[0089] Table 4

[0090]

[0091]

[0092] *Note: The carbon content of the three layers of welds of Comparative Example 1 is not detected because the hardness of the three layers of welds is not ideal.

[0093] From Table 4, it can be seen that the carbon content of one layer of welds deposited on FC300 is greatly different between two groups of electrodes, and the carbon content of Example 1 is significantly lower than that of Comparative Example 1, and has been significantly decreased to the level of medium-low carbon steel, while the carbon content of Comparative Example 1 is still in the range of medium carbon steel, therefore, the weldability of Example is significantly better than that of Comparative Example. However, from the perspective of crack generation, there is no crack phenomenon in one layer and three layers of two groups.

[0094] The reason for the different performance of the crack resistance in Tables 3 and 4 should be that the size of the HT-300 test piece is much smaller than that of the FC300 mold, the workpiece is slow in heat dissipation when the two groups of welding rods are surfacing, the molten pool exists for a longer time, the penetration is large, the carbon in the base material diffuses into the weld more seriously, so the carbon content of the one layer weld of the two groups of welding rods has reached the level of high carbon steel; in addition, the HT-300 itself contains high silicon and phosphorus, so it is inevitable that the weld cracks. The FC300 mold workpiece is large, fast in heat dissipation, shallow in penetration, the first layer is weak in the diffusion of high carbon components from the base material, and the carbon content of the first layer is low, the carbon content of the one layer weld of the two groups of welding rods can be reduced to the level of medium and low carbon steel; the content of other components such as silicon and phosphorus is also very low; in addition, the structure of the mold itself is dense and is subjected to strengthening and toughening heat treatment, so that the welds of the two groups of welding rods have good crack resistance. Especially in Example 1, because the welding current is smaller, the welding penetration is shallower, and the welding rod droplet transfer is changed from short circuit transfer to slag wall transfer, fine particle transfer, and spray transfer, the carbon content of the one layer weld is reduced more, and the carbon content of the three layer weld is even reduced to the level of the three layer surfacing on the A-grade carbon steel test block, and the welding process of Comparative Example 1 is poor under the same small current condition as Example 1, and cannot be effectively welded. Thus, the weld of the example has lower crack sensitivity.

[0095] The surface hardness of the one layer weld on the mold is high (greater than HRC 50), the hardness of the three layer weld is reduced a lot, but is improved after work hardening, and Example 1 is more obvious than Comparative Example 1. It is shown that the carbon content of the three layer weld is low and contains manganese, nickel, copper, cobalt and other elements that promote the formation of austenite, so the hardness is reduced, but these elements play a strong solid solution strengthening role in the weld structure, so the weld hardness still remains at a certain level, especially after being subjected to strong impact and hammering, the weld hardness is further hardened, thereby improving the impact and wear resistance of the weld. The one layer weld contains carbon and other components diffused from the base material, and under the condition of fast welding cooling speed, low carbon martensite is more likely to appear, and under the joint action of the above-mentioned solid solution strengthening elements, the hardness of the one layer weld is effectively improved. In addition, it is found through experiments that adding an appropriate amount of mixed powder in the flux core also helps to improve the red hardness of the weld, so that the weld has the effects of resisting thermal fatigue oxidation and preventing softening, thereby achieving the goal of the weld metal having good wear resistance, impact resistance, thermal fatigue resistance and softening resistance.

[0096] Example 2

[0097] An embodiment of the cast iron mold surfacing flux-cored electrode according to the present application is different from Example 1 in that the formula of the coating is different, and the ratio of the components in the coating of the present embodiment is marble powder: fluorite powder: graphite powder: titanium white powder: ilmenite powder: zircon powder: atomized iron powder: atomized silicon-iron powder: electrolytic manganese powder = 50:10:1.5:3.5:8:12:5:5:5.

[0098] Example 3

[0099] An embodiment of the cast iron mold hardfacing flux-cored electrode according to the present application differs from the embodiment 1 only in the composition of the coating, wherein the ratio of the components in the coating of the embodiment is marble powder: fluorite powder: graphite powder: titanium white powder: ilmenite powder: zircon powder: atomized iron powder: atomized ferrosilicon powder: electrolytic manganese powder = 50:10:1:4:8:12:10:2:3.

[0100] Embodiment 4

[0101] An embodiment of the cast iron mold hardfacing flux-cored electrode according to the present application differs from the embodiment 1 only in the composition of the coating, wherein the ratio of the components in the coating of the embodiment is marble powder: fluorite powder: graphite powder: titanium white powder: ilmenite powder: zircon powder: atomized iron powder: atomized ferrosilicon powder: electrolytic manganese powder = 55:10:1.5:1:6:12:4.5:5:5.

[0102] Embodiment 5

[0103] An embodiment of the cast iron mold hardfacing flux-cored electrode according to the present application differs from the embodiment 1 only in the composition of the coating, wherein the ratio of the components in the coating of the embodiment is marble powder: fluorite powder: graphite powder: titanium white powder: ilmenite powder: zircon powder: atomized iron powder: atomized ferrosilicon powder: electrolytic manganese powder = 55:10:1.5:1:8:12:7.5:2:3.

[0104] Embodiment 6

[0105] An embodiment of the cast iron mold hardfacing flux-cored electrode according to the present application differs from the embodiment 1 only in the composition of the coating, wherein the ratio of the components in the coating of the embodiment is marble powder: fluorite powder: graphite powder: titanium white powder: ilmenite powder: zircon powder: atomized iron powder: atomized ferrosilicon powder: electrolytic manganese powder = 53.5:10:1.5:3:6:12:4:5:5.

[0106] Embodiments 7-8

[0107] An embodiment of the cast iron mold hardfacing flux-cored electrode according to the present application differs from the embodiment 1 only in the diameter of the electrode, which is Φ5.7mm and Φ7.1mm, respectively.

[0108] Embodiments 9-10

[0109] An embodiment of the cast iron mold hardfacing flux-cored electrode according to the present application differs from the embodiment 1 only in the composition of the mixed powder in the core, wherein the mass ratio of the atomized nickel powder, electrolytic copper powder and mechanically ground cobalt powder in the mixed powder of the embodiments 9 and 10 is 3:2.5:4.5 and 1:2:7, respectively.

[0110] Comparative Example 2

[0111] An electrode, which is distinguished from Comparative Example 1 as follows: the core is made of 100% iron powder filled in a carbon steel H08A hollow tube, and the coating composition and electrode size are the same as those of Comparative Example 1.

[0112] Comparative Example 3

[0113] A FC300 mold overlay repair special-purpose carbon dioxide gas shielded flux-cored wire widely used in the automotive mold industry, with an outer diameter of Φ1.2 mm. The wire is produced by Donghai Rongcai Co., Ltd.

[0114] Comparative Example 4

[0115] An electrode, which is distinguished from Example 1 in that no graphite powder is added to the coating, and the coating is composed of the following components in mass ratio: marble powder: fluorite powder: titanium white powder: ilmenite powder: zircon powder: atomized iron powder: atomized silicon-iron powder: electrolytic manganese powder = 55:10:1:6:12:6:5:5.

[0116] Comparative Example 5

[0117] An electrode, which is distinguished from Example 1 in that the components of the coating are different, and the coating is composed of the following components in mass ratio: marble powder: fluorite powder: graphite powder: titanium white powder: ilmenite powder: atomized iron powder, atomized silicon-iron powder, electrolytic manganese powder, high-potassium feldspar powder = 55:10:1.5:3:8:7.5:2:3:10.

[0118] Comparative Example 6

[0119] An electrode, which is distinguished from Example 1 in that the components of the coating are different, and the coating is composed of the following components in mass ratio: marble powder: fluorite powder: graphite powder: titanium white powder: ilmenite powder: atomized iron powder: atomized silicon-iron powder: electrolytic manganese powder = 55:10:1.5:3:8:17.5:2:3.

[0120] Comparative Example 7

[0121] An electrode, which is distinguished from Example 1 in that the components of the coating are different, and the coating is composed of the following components in mass ratio: marble powder: fluorite powder: graphite powder: titanium white powder: ilmenite powder: atomized iron powder: high-potassium feldspar powder: atomized silicon-iron powder: electrolytic manganese powder = 55:10:1.5:1:8:13.5:6:2:3.

[0122] Comparative Example 8

[0123] A cast iron mold hardfacing flux-cored electrode differs from Example 1 only in the composition of the coating, the ratio of the components in the coating being marble powder: fluorite powder: graphite powder: titanium white powder: ilmenite powder: zircon powder: atomized iron powder: atomized ferrosilicon powder: electrolytic manganese powder = 46: 14: 1.5: 3.5: 8: 12: 5: 5: 5.

[0124] Comparative Example 9

[0125] A cast iron mold hardfacing flux-cored electrode differs from Example 1 only in the composition of the coating, the ratio of the components in the coating being marble powder: fluorite powder: graphite powder: titanium white powder: ilmenite powder: zircon powder: atomized iron powder: atomized ferrosilicon powder: electrolytic manganese powder = 60: 10: 1.5: 3.5: 3: 10: 2: 5: 5.

[0126] Test Four: Investigation of the hardfacing of Comparative Example 2 on FC300 molds: welding process, weld crack resistance, porosity, carbon content of the first layer, hardness of the first and third layers, and forming.

[0127] The welding method and welding current of Example 1 in Test One were used to hardface the working surface of FC300 molds with a first and third layer of weld, the hardness of the weld was measured, and the sample taking method for the carbon content of the first layer of weld was the same as in Test Three. The test results are shown in Table 5.

[0128] Table 5

[0129]

[0130]

[0131] As can be seen from Table 5, although Comparative Example 2 has the same coating composition as Comparative Example 1, the difference in the core and solid core structure results in a difference in the carbon content of the first layer of weld: higher than Example 1, but similar to Comparative Example 1. Moreover, there is a powder leakage phenomenon at the tail of the welding electrode, and it cannot be welded again. Therefore, the effect of using 100% iron powder as the core, and transferring the alloy to the weld through the coating rather than the core, is poor.

[0132] Test Five: Comparative Example 2 and Comparative Example 3 were selected for comparison, the welding method and current of Example 2 were the same as those of Example 1 in Test One; Comparative Example 3 was welded using a model NB-500E carbon dioxide gas shielded welding machine, with a welding current of 200 A. The following tests were conducted on the two groups of welding materials: hardfacing process, hardness testing, and sampling for carbon content analysis of the weld, etc. The methods were the same as in Test Three:

[0133] 1. The carbon content of the third layer of weld of the two groups of welding materials on the aforementioned A-grade carbon steel test piece was detected. The test results are shown in Table 6.

[0134] Table 6

[0135] Name Carbon content of one layer (%) Example 2 0.22 Comparative Example 3 0.21

[0136] 2. The carbon content of the first and third layers of the welds of the two groups of welding materials on the FC300 mold workpieces was detected. The test results are shown in Table 7.

[0137] Table 7

[0138] Name Carbon content of one layer (%) Carbon content of three layers (%) Example 2 0.37 0.24 Comparative Example 3 0.43 0.28

[0139] 3. The welding process performance and hardness of the first and third layers of the two groups of welding materials on the aforementioned FC300 mold (workpiece number is the same as above) and the aforementioned A-grade carbon steel test piece were tested.

[0140] 4. The hardness of the welds of the third test after work hardening was tested by hammering the welds of the third test fifty times by the aforementioned hammering method.

[0141] The hardness test results of the aforementioned 3 and 4 are shown in Table 8.

[0142] Table 8

[0143]

[0144] As can be seen from Tables 6 and 7, the carbon content of the three layers of the two groups of welding materials on the A-grade carbon steel test piece is basically close. When the first layer is welded on the FC300 mold, the carbon content of Example 2 is lower than that of Comparative Example 3, and even has been reduced to the level of medium and low carbon steel. The above results show that the flux-cored electrode utilizes a high proportion of strong oxidizing agents, alkalinity substances such as marble powder and fluorite powder in the coating, and the advantages of the flux-cored electrode itself (extremely small welding current, shallow penetration, and less diffusion of the base material composition, etc.), so that the carbon content of the first layer of the weld on the mold is reduced more than that of the flux-cored wire. This makes the crack resistance of the weld of the example better than that of Comparative Example 3.

[0145] As can be seen from Table 8, the hardness change of the two groups of welding materials after welding the first and third layers on the mold and after work hardening is not large when the first layer is welded, and the welds have a certain work hardening effect when the third layer is welded. Thus, the impact and grinding resistance of the welds is improved, which helps to improve the service life of the workpiece.

[0146] In addition, it should be pointed out that the welds of the two groups of welding materials do not have crack defects after work hardening treatment, which shows that the plasticity and toughness of the welds when subjected to strong impact are good.

[0147] As can be seen from the results of the aforementioned test five, the flux-cored electrode for surfacing cast iron molds according to the present application can replace the currently commonly used imported product Comparative Example 3.

[0148] Test six: The anti-crack, anti-porosity, forming, deslagging and Rockwell hardness of the three groups of electrodes of Example 3, 4 and Comparative Example 4 were investigated when they were used to build up a layer of weld on FC300 die. The welding method and welding current were the same as those of Example 1. The test results are shown in Table 9.

[0149] Table 9

[0150]

[0151]

[0152] As shown in Table 9, the addition of graphite powder in the coating of the electrode has little effect on the hardness of the electrode weld, but is unfavorable for the arc starting, arc stabilizing and electrode press-coating production. Therefore, a small amount of graphite powder should be added to the coating to facilitate the arc starting and the press-coating production. However, too much graphite powder should not be added, otherwise cracks will be produced.

[0153] Test seven: The occurrence of the powder leakage of the five groups of electrodes of Example 5, 6 and Comparative Examples 5, 6 and 7 was investigated under the same welding current. The welding method and welding current were the same as those of Example 1. The test results show that the electrode of Comparative Example 5 containing a large amount of high-potassium feldspar powder in the coating has a fast coating melting speed and a short coating sleeve, and thus the powder leakage of the tube core powder due to the perforation of the arc end portion is easily produced, which results in the failure of the continuous welding. The electrode of Comparative Example 6 containing a large amount of iron powder in the coating has the powder leakage during the welding, which results in the failure of the continuous welding. The electrode of Comparative Example 7 containing a large amount of iron powder and additional high-potassium feldspar powder in the coating also has the above-mentioned problems. Therefore, the addition of such substances to the coating of the electrode should be avoided.

[0154] As shown in Test seven, when the coating contains a substance which can greatly increase the coating melting speed and thus greatly shorten the coating sleeve, the powder leakage of the tube core powder due to the perforation of the arc end portion is easily produced, which results in the failure of the continuous welding. Therefore, too much of such substances should not be added to the coating of the electrode to avoid the powder leakage.

[0155] Test eight: The welding method and current of Example 7-8 were the same as those of Example 1 in Test one, and the welding was carried out on the plane of FC300 die to investigate the hardness of the one layer of the weld and the welding process and the anti-crack property of the weld. The test results are shown in Table 10.

[0156] Table 10

[0157]

[0158] As shown in the table, the outer diameter of the electrode affects the hardness of the weld to some extent. When the outer diameter of the electrode is Φ6.4 mm, the hardness of the one layer of the weld is the highest.

[0159] In addition, from the view of the weld formation, the outer diameter of the electrode is Φ5.7 and Φ7.1, the fluidity of the molten pool stage metal is not ideal, which affects the formability; only when the outer diameter of the electrode is Φ6.4, the formability is the best.

[0160] In consideration of the above, it is meaningful to select the outer diameter of the electrode as Φ6.4 mm as one of the process parameters of the electrode pressure coating.

[0161] Test nine: the welding method and current of examples 9-10 and example 1 are the same as those of test one, and the welding is performed on the above-mentioned FC300 die plane, and the deslagging, formability, crack resistance, pore resistance and one layer Rockwell hardness of the weld after welding are investigated. The experimental results are shown in Table 11.

[0162] Table 11

[0163]

[0164] As shown in Table 11, when the mass ratio of the nickel powder, copper powder and cobalt powder in the mixed powder in the flux is (1.4-1.6):(2.4-2.6):(5.9-6.1), the welding process and the weld crack resistance are both better.

[0165] Test ten: the welding method and current of comparative examples 8 and 9 and example 1 are the same as those of test one, and the welding is performed on the above-mentioned FC300 die plane, and the deslagging, formability, molten pool metal fluidity, crack resistance, pore resistance and one layer Rockwell hardness of the weld after welding are investigated. The experimental results are shown in Table 12.

[0166] Table 12

[0167]

[0168] As shown in Table 12, when the ratio of the components in the flux is not within the range defined in the present application, the welding process and / or the weld crack resistance are both significantly worse.

[0169] Test eleven: the welding method and current of example 2 and comparative example 3 are the same as those of test five, and the welding is performed on a FCD550 cast iron die workpiece provided by a certain automobile die factory, the workpiece number is B13B-743F4-6XJOF-PD-02, and the chemical components of the die except Fe are shown in Table 13.

[0170] Table 13 (mass fraction: %)

[0171] C Mn Si S P Cr Cu Mg 3.72 0.53 2.48 0.02 0.07 0.36 0.64 0.02

[0172] Compared with FC300, the FCD550 mold composition increases the contents of silicon, magnesium, copper, and reduces the content of manganese. Among them, magnesium is added as a spheroidizing modifier, and a small amount of magnesium can make the base material obtain complete spherical graphite and the structure more compact; the content of manganese less than 0.6% makes the plasticity of the ductile iron base material better; the content of silicon is significantly increased to make the graphite structure better and the effect of inoculation treatment better; a small amount of copper is added to stabilize and refine the pearlite structure, better casting performance, thermal fatigue resistance and shock absorption level. Such composition ensures that the workpiece has good comprehensive mechanical properties, such as high strength, impact resistance, high temperature oxidation resistance, etc. However, it is known from the welding theory and practical experience that the weldability of the mold composition is worse than that of FC300, and cracks are easily generated during surfacing.

[0173] The surfaces of the worn parts (in the following two cases) in the mold were surfaced by using the welding materials of Example 2 and Comparative Example 3, respectively.

[0174] 1. The wear of the working surface of the mold itself after use, which has not been subjected to any process treatment in advance, is surfaced with one layer, three layers, and the surfacing thickness is 3-6mm, and the surfacing thickness of the two groups of welding materials is the same.

[0175] 2. The wear of the wear surface after other treatments is formed after use (see Table 14 for the composition, and the rest of the composition is Fe), and one layer is surfaced to test the weldability, and if cracks occur, it is not repaired by surfacing.

[0176] Table 14 (mass fraction: %)

[0177] C Mn Si S P Cr Ni Mg Cu 3.60 0.80 2.30 0.01 0.06 3.33 0.71 0.04 0.45

[0178] The results of the above surfacing repair are as follows:

[0179] In the first case, the two groups of welding materials have stable welding arc, easy deslagging, good molten pool fluidity, and good appearance without pores. It is found that the spatter of the welding rod of Example 2 is less than that of the welding wire of Comparative Example 3. After welding, one layer of the two groups of welds is subjected to various mechanical and physical inspections, and it is found that the welds surfaced by the welding wire of Comparative Example 3 have obvious cracking at the arc receiving position, while the welding rod of Example 2 does not have such phenomenon. It can be seen that the weldability of the mold is obviously worse than that of the FC300 mold, and the surfacing effect of the imported welding wire is not as good as the product of the present application.

[0180] The hardness of the first and third layers of the above welds and the hardness after work hardening treatment of the welds according to the above hammering method are measured by using a type AH150 portable Leed hardness tester, and the results are shown in Table 15.

[0181] Table 15

[0182]

[0183] As shown in Table 15, the weld hardness and work hardening effect of the two groups of welding materials are not much different, but unlike the FC300 surfacing, the hardness of the first, third layer welds is not much different and the work hardening effect is general.

[0184] The workpieces repaired by the welding rod are processed and then used in an automobile factory. The results show that the multi-layer surfacing welds of the welding rod have good resistance to hammer forging impact, high temperature oxidation and thermal fatigue, and no cracking phenomenon.

[0185] In the second case, it is found that the welds of the two groups of welding materials all have different degrees of cracking phenomenon. The reason is that the surface composition contains a large amount of chromium, as described above, which is not conducive to the surfacing of the mold and is easy to cause cracking.

[0186] In summary, the flux-cored welding rod is suitable for surfacing repair of the working surface of FC300, FCD550 and other molds without chromium process treatment, and it is feasible to replace the imported welding wire.

[0187] In addition, the HT-300 test block and FC300 are welded by the welding rod described in Example 1, and the welding current is 100A, 130A, 140A, 170A and 210A, respectively, to investigate the welding process and crack resistance. The results show that when the welding current is 100-140A, the weld has the most beautiful appearance, stable hardness, good red resistance, good deslagging and no air hole, but when the current increases to 170A, the welding rod starts to red, and the number of weld cracks increases. The above results show that the welding rod described in the application is suitable for welding current range of 100-140A.

[0188] Finally, it should be noted that the above examples are only used to illustrate the technical solutions of the present application and not to limit the protection scope of the present application. Although the present application has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present application can be modified or replaced by equivalents without departing from the essence and scope of the technical solutions of the present application.

Claims

1. A flux-cored welding electrode for cast iron mold surfacing, characterized in that: It comprises a tube body, a medicine core filled in the tube body and a medicine coating wrapping the tube body; The core comprises the following components: iron powder, manganese powder, ferrosilicon powder and mixed powder; the mass ratio of the iron powder, manganese powder, ferrosilicon powder and mixed powder is (60-68): (10.4-11): (11.5-12.5): (12-14); the mixed powder is a mixture of nickel powder, copper powder and cobalt powder; The coating comprises the following components: marble powder, fluorite powder, graphite powder, titanium dioxide, ilmenite powder, zircon powder, iron powder, ferrosilicon powder, and manganese powder; the mass ratio of the marble powder, fluorite powder, graphite powder, titanium dioxide, ilmenite powder, zircon powder, iron powder, ferrosilicon powder, and manganese powder is (50-55): (8-12): (1-1.5): (1-4): (6-8): (10-14): (4-10): (2-5): (3-5).

2. The flux-cored welding electrode for cast iron mold surfacing according to claim 1, characterized in that: The mass ratio of nickel powder, copper powder and cobalt powder in the mixed powder is (1.4-1.6):(2.4-2.6):(5.9-6.1).

3. The flux-cored welding electrode for cast iron mold surfacing according to claim 1, characterized in that: The tube body is a carbon steel hollow tube.

4. The flux-cored welding electrode for cast iron mold surfacing according to claim 1, characterized in that: The iron powder is atomized iron powder, the manganese powder is electrolytic manganese powder, and the ferrosilicon powder is atomized ferrosilicon powder.

5. The flux-cored welding electrode for cast iron mold surfacing according to claim 1, characterized in that: The particle size of the nickel powder is 60-120 mesh, the particle size of the copper powder is 150-200 mesh, and the particle size of the cobalt powder is 50-80 mesh; the particle size of the ferrosilicon powder, iron powder, manganese powder, ilmenite powder, zircon powder, and graphite powder is 40-150 mesh, the particle size of the marble powder and fluorite powder is 100-250 mesh, and the particle size of the titanium dioxide is 250-325 mesh.

6. The flux-cored welding electrode for cast iron mold surfacing according to claim 1, characterized in that: The cobalt powder is made from cobalt blocks through mechanical crushing and grinding, the copper powder is electrolytic copper powder, and the nickel powder is atomized nickel powder.

7. The flux-cored welding electrode for cast iron mold surfacing according to claim 1, characterized in that: The wall thickness of the tube body is 0.3-0.5 mm, the diameter of the tube body is Φ3.98-4.02 mm, and the length is 395-400 mm; the outer diameter of the welding rod is Φ6.2-6.6 mm.

8. A method for preparing a flux-cored welding electrode for cast iron mold surfacing according to any one of claims 1 to 7, characterized in that: The steps include: (1) Weighing the components of the drug core according to the ratio, mixing them evenly, and filling them into the tube body; (2) Weigh the components of the coating according to the proportion, stir them evenly, add a binder, continue stirring, and then squeeze it onto the outer surface of the tube body and the two ends of the tube body to form a wet welding rod, dry it, and obtain the cast iron mold surfacing flux-cored welding rod.

9. A method for using the flux-cored welding electrode for surfacing cast iron molds according to any one of claims 1 to 7, characterized in that: Use AC or DC welding power source for welding; the welding current is 100-140A.

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