High-phosphorus wear-resistant gray cast iron and production method thereof

Abstract

The invention provides high-phosphorus wear-resistant gray cast iron and a production method thereof, and belongs to the technical field of high-phosphorus wear-resistant gray cast irons.The production method comprises the following steps that raw materials are inspected; smelting is conducted, specifically, waste steel, gray iron foundry returns, pig iron, a carburant and ferrophosphorus are sequentially put into an electric furnace to be melted; nickel, chromium and copper are sequentially added into the electric furnace, and the molten iron is quenched and tempered, so that the final components of the molten iron meet the requirements; molding: preparing a casting mold; a casting ladle is preheated, meanwhile, an inoculant is placed at the bottom of the casting ladle, then molten iron is poured into the casting ladle, and the inoculant is added along with flow in the process that the casting ladle conducts casting into the mold; box opening: the box is opened after the temperature is reduced, and the formed high-phosphorus wear-resistant gray cast iron is obtained; and performing heat treatment: performing high-temperature annealing on the high-phosphorus wear-resistant gray cast iron, and inspecting the casting to obtain a final finished product. According to the technical scheme, the purpose of improving the abrasion resistance and the mechanical performance of the gray cast iron is achieved.

Description

Technical Field

[0001] This invention relates to the field of high-phosphorus wear-resistant gray cast iron technology, specifically to a high-phosphorus wear-resistant gray cast iron and its production method. Background Technology

[0002] In numerous fields such as machinery manufacturing, automotive, aerospace, and metallurgy, there are extremely high requirements for the wear resistance and hardness of materials. For example, in the manufacture of key components such as machine tool guideways, piston rings, cylinder liners, sliding bearings, and camshafts, materials must withstand friction, wear, and heavy loads for extended periods. Under these conditions, traditional materials often struggle to meet the ever-increasing performance demands, resulting in shorter service lives. Frequent component replacements not only increase maintenance costs but also disrupt normal equipment operation, leading to decreased production efficiency.

[0003] Among various cast iron materials, gray cast iron is a relatively common basic material. Ferrite in gray cast iron forms the soft matrix, cementite the hard component, and flake graphite provides a certain degree of lubrication; the pits formed after flaking can also retain oil, thus meeting some general wear resistance requirements to a certain extent. However, when faced with more demanding working conditions, its insufficient wear resistance and hardness become apparent.

[0004] Chinese invention patent document CN104498816A, entitled "Gray Cast Iron with Excellent Machining Performance and its Production Method," discloses a production process including primary melting, secondary melting, refining, inoculation, and casting. In this method, the raw material is melted twice, ensuring sufficient melting and high absorption rate. Controlling the carbon equivalent range guarantees excellent mechanical properties of the cast iron parts. A large amount of scrap steel is added to the batching, achieving the goal of turning waste into treasure and reducing costs. The addition of ferrous sulfate and ferrophosphate improves the inoculation effect, increases the fluidity of the molten iron, reduces porosity and scrap rate of the castings, and improves the wear resistance and machinability of the castings. However, the hardness of the gray cast iron product obtained by the above technical solution is still relatively low. Summary of the Invention

[0005] In view of this, the present invention provides a high-phosphorus wear-resistant gray cast iron and its production method, thereby improving the wear resistance and mechanical properties of gray cast iron in the prior art.

[0006] To achieve the above objectives, the present invention provides a method for producing high-phosphorus wear-resistant gray cast iron, comprising the following steps: Step 1: Raw material inspection; Step 2: Smelting: Scrap steel, gray iron remelting material, pig iron, carbon raiser, and ferrophosphate are sequentially added to the electric furnace for smelting; Step 3: Add nickel, chromium, and copper sequentially to the electric furnace to temper the molten iron, so that the final composition of the molten iron meets the requirements; Step 4: Molding: Preparing the mold; Step 5: Pouring: Preheat the ladle, and place an inoculant at the bottom of the ladle. Then pour molten iron into the ladle. During the pouring process, add more inoculant along with the flow. Step Six: Unpacking: After lowering the temperature, unpack the box to obtain the formed high-phosphorus wear-resistant gray cast iron; Step 7: Heat treatment: High-temperature annealing of high-phosphorus wear-resistant gray cast iron, followed by inspection of the castings to obtain the final product; In step three, the weight percentages of each component that make the final composition of the molten iron meet the requirements are as follows: carbon 3.35-3.5%, silicon 1.15-1.25%, manganese 0.6-0.9%, phosphorus 1.7-1.9%, sulfur 0.04-0.08%, chromium 0.5-1.0%, nickel 1.7-1.9%, copper 0.3-0.45%, with the remainder being trace elements and iron.

[0007] The beneficial effect is that by precisely controlling the proportion of each element and utilizing the synergistic effect between the elements, the wear resistance and hardness of the material can be directly improved.

[0008] Optionally, the smelting includes the following raw materials by weight percentage: 20-30% scrap steel, 50-65% gray iron remelting material, 5-30% pig iron, 4-5% ferrophosphorus, and 1-1.5% carbon raiser; the smelting involves sequentially adding scrap steel, gray iron remelting material, pig iron, and carbon raiser into an electric furnace to melt and obtain molten iron, and adding ferrophosphorus in stages when the molten iron reaches 1490-1510℃.

[0009] Optionally, the addition in stages may be done in two separate steps.

[0010] The beneficial effect is that by adding ferrophosphorus in stages within a specific temperature range, the dissolution, distribution and morphology of phosphorus eutectic are precisely controlled. This ensures that the phosphorus content meets the standards while avoiding phosphorus segregation or the formation of a continuous network, which would lead to excessive brittleness. Ultimately, this balances the wear resistance and mechanical properties of gray cast iron.

[0011] Optionally, the mold is made of resin sand.

[0012] Optionally, the mold includes a gating system consisting of a flaming bar and a runner, and a mold plate; the flaming bar and runner guide the molten metal into the mold plate; the mold plate includes a flaming plate, a riser, and a casting mold; the molten metal passes through the runner and the flaming plate into the riser, and the two sides of the riser are casting molds, and the molten metal passes through the riser and enters the two casting molds respectively to obtain the casting.

[0013] Optionally, the preheating temperature of the ladle during casting is greater than or equal to 900°C; the temperature of the molten iron when it is poured into the ladle is 1520~1540°C.

[0014] The beneficial effect is that when the ladle is preheated to above 900°C, the temperature difference between it and the molten iron is greatly reduced, which can significantly slow down the cooling rate of the molten iron, ensure that the molten iron maintains sufficient fluidity and temperature stability during the pouring process, ensure that the alloying elements are evenly distributed, and lay the foundation for the subsequent formation of uniform phosphorus eutectic and pearlite structures.

[0015] Optionally, the mass of the inoculant placed at the bottom of the ladle is 0.2-0.4% of the mass of the molten iron, and the particle size of the inoculant is 1mm-3mm.

[0016] Optionally, the mass of the inoculant added during the flow is 0.5-0.15% of the mass of the molten iron, and the particle size of the inoculant is 0.2mm-0.8mm.

[0017] Optionally, during the pouring process, the initial pouring temperature is 1400~1420℃, the final pouring temperature is 1360~1380℃, and the pouring time is 15~17s.

[0018] Beneficial effects: The fluidity of molten iron decreases as the temperature decreases. In the initial pouring stage, the temperature is 1400~1420℃. At this time, the temperature of molten iron is relatively high and the fluidity is sufficient. It can quickly fill the complex cavity of the mold and avoid defects caused by insufficient fluidity. In the final pouring stage, the temperature is 1360~1380℃. The temperature is about 40℃ lower than that at the beginning of pouring, but it still maintains sufficient fluidity. This can ensure that the last part is fully filled to compensate for shrinkage and avoid shrinkage cavities and porosity.

[0019] Optionally, the cast iron surface is cooled to 720~500℃ during unpacking.

[0020] The beneficial effect is that when the casting is opened at 720℃~500℃, most of the phosphorus eutectic has been precipitated through the slow cooling of the mold. After opening the mold, the medium-speed cooling in the air can further refine the incompletely precipitated phosphorus eutectic, while avoiding the formation of continuous network, and finally keeping the phosphorus eutectic in a fine, discontinuous and uniform ideal shape.

[0021] Optionally, the high-temperature annealing includes the following steps: Loading into the furnace: The product is loaded into the heat treatment furnace at room temperature; Heating: Heat the product to 920-1050℃ at a heating rate of 70-100℃ / hour; Insulation: Insulate at 920–1050℃ for 1–1.5 hours; Cooling: The furnace temperature is lowered to 600℃, then cooled to 300℃ at a rate of 50-100℃ / h, and finally air-cooled after being removed from the furnace to obtain high-phosphorus wear-resistant gray cast iron.

[0022] The beneficial effect is that high-temperature annealing can effectively decompose free cementite in castings and refine pearlite, thereby improving the toughness and plasticity of cast iron.

[0023] To achieve the above objectives, the present invention also provides a method for producing high-phosphorus wear-resistant gray cast iron.

[0024] The above-described technical solution of the present invention has at least the following beneficial effects: The high-phosphorus wear-resistant gray cast iron prepared by the technical solution provided by this invention has strong mechanical properties and excellent wear resistance. Attached Figure Description

[0025] Figure 1 This is a process flow diagram of the present invention; Figure 2 This is a schematic diagram of the high-temperature annealing temperature of the present invention; Figure 3 This is a schematic diagram of the mold for this invention; Figure 4 This is a microscopic characterization diagram of the high-phosphorus wear-resistant gray cast iron in Example 1 of the present invention; Figure 5 This is a microscopic characterization diagram of the high-phosphorus wear-resistant gray cast iron in Example 2 of the present invention. Detailed Implementation

[0026] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the following will be described in conjunction with the accompanying drawings of the embodiments of the present invention. Figures 1-5 The technical solutions of the embodiments of the present invention will be clearly and completely described herein. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. All other embodiments obtained by those skilled in the art based on the described embodiments of the present invention are within the scope of protection of the present invention.

[0027] This invention provides a method for producing high-phosphorus wear-resistant gray cast iron, comprising the following steps: Step 1: Raw material inspection.

[0028] Step 2: Smelting: Weigh out 20-30% scrap steel, 50-65% gray iron remelting material, 5-30% pig iron, 4-5% ferrophosphate, and 1% carbon raiser by weight, and put them into the electric furnace for smelting.

[0029] Step 3: Add nickel, chromium, and copper to the electric furnace.

[0030] Nickel can lower the eutectoid transformation temperature, refine pearlite, and improve the strength and hardness of castings, while also enhancing their wear resistance and corrosion resistance. Chromium can control grain size during crystallization and refine graphite, thereby significantly reducing the cutting effect of graphite on castings and improving their strength and wear resistance. Copper can increase and stabilize pearlite and offset the adverse effect of chromium on increasing white iron content. Molten iron is poured into a rapidly cooling model of a spectral test block in an electric furnace. The elemental composition of the test block is detected using a rapid direct-reading spectrometer. Based on the spectral analysis, the final composition of the molten iron is fine-tuned to meet the requirements, and the composition is calculated as a mass percentage.

[0031] Step 4: Molding: A resin sand casting mold is used. The mold includes a gating system consisting of a sprue and a runner, and a mold plate. The sprue and runner guide the molten metal into the mold plate. The mold plate includes a sprue, a riser, and a casting mold. The molten metal passes through the runner and the sprue into the riser. The two sides of the riser are the casting molds. The molten metal passes through the riser and enters the two side casting molds to obtain the casting.

[0032] Resin sand molds have good rigidity and high strength, which is beneficial for the graphitization expansion during the solidification process of the casting, effectively offsetting shrinkage cavities and porosity defects, and achieving a defect-free casting. At the same time, a good casting process is also required to complete the casting. A good casting process should have the following characteristics: 1. It facilitates the smooth filling of the mold with molten metal, reduces metal oxidation, prevents sand erosion, and reduces turbulence and gas entrapment; 2. It facilitates the discharge of gas from the mold cavity; 3. It can effectively prevent slag from entering the mold cavity; 4. It allows for the reasonable determination of the pouring time.

[0033] Step 5: Pouring: Preheat the ladle, and place an inoculant at the bottom of the ladle. Then pour molten iron into the ladle. During the pouring process, add more inoculant along with the flow.

[0034] Step Six: Unpacking: After lowering the temperature, unpack the box to obtain the formed high-phosphorus wear-resistant gray cast iron.

[0035] Step 7: Heat treatment: High-temperature annealing of high-phosphorus wear-resistant gray cast iron, followed by inspection of the casting to obtain the final product.

[0036] The final composition by weight of molten iron that meets the requirements is: carbon 3.35-3.5%, silicon 1.15-1.25%, manganese 0.6-0.9%, phosphorus 1.7-1.9%, sulfur 0.04-0.08%, chromium 0.5-1.0%, nickel 1.7-1.9%, copper 0.3-0.45%, with the remainder being iron.

[0037] This embodiment directly improves the wear resistance and hardness of cast iron by precisely controlling the proportion of each element and utilizing the synergistic effect between them.

[0038] In this embodiment, phosphorus is the key element for improving wear resistance. During the solidification process of cast iron, phosphorus forms a phosphorus eutectic structure with iron, which has extremely high hardness. The phosphorus eutectic is distributed in the casting in a network or discontinuous network pattern. When the casting is subjected to friction, the hard particles of the phosphorus eutectic can resist the cutting and extrusion of abrasive grains, reducing the wear of the casting. Controlling the phosphorus content to 1.7%~1.9% ensures a sufficient amount of phosphorus eutectic while avoiding excessive phosphorus content, which would cause the phosphorus eutectic to form a continuous network distribution, leading to brittleness.

[0039] Chromium combines with carbon to form chromium carbides, which have high hardness and further increase the number of hard particles. At the same time, chromium can refine grains, promote pearlite formation, and improve hardness and strength.

[0040] Nickel is an austenite stabilizing element that can expand the austenite region, making the graphite finer and more evenly distributed, thus reducing the cutting effect of graphite on castings. At the same time, nickel can improve the toughness and hardenability of castings, and work synergistically with chromium to promote the formation of a uniform pearlite structure, avoiding premature wear in local soft areas.

[0041] Copper can significantly promote pearlite formation and increase the proportion of pearlite in castings. At the same time, copper can refine graphite and grains, making the microstructure more uniform, reducing local wear differences caused by component segregation, and indirectly improving overall wear resistance.

[0042] A medium to high carbon content (3.35~3.5%) ensures sufficient carbon for the formation of pearlite and an appropriate amount of flake graphite. If the carbon content is too low, there will be insufficient pearlite, resulting in a soft casting; if it is too high, the graphite will be coarse, causing severe cracking of the casting.

[0043] Low silicon content (1.15~1.25%) can inhibit excessive graphite growth, ensure fine and uniform graphite, and reduce cracking of castings. At the same time, silicon can strengthen ferrite through solid solution, thereby improving the strength of castings.

[0044] Manganese combines with sulfur to form high-melting-point MnS, preventing sulfur from forming low-melting-point FeS with iron. Manganese is an anti-graphitizing element, which can stabilize the pearlite structure and ensure the high hardness of the casting.

[0045] Sulfur is a harmful element. If its content is too high, it will form low-melting-point sulfides with iron and manganese, which are prone to precipitate along grain boundaries during the casting process, leading to hot brittleness of the casting. Controlling the sulfur content to ≤0.08% and forming high-melting-point MnS through the combination of manganese can prevent grain boundary embrittlement, ensure the structural integrity of the casting during friction, and indirectly improve wear resistance.

[0046] In this embodiment, an inoculant is placed at the bottom of the ladle, and then added with the flow. This makes the flake graphite smaller, shorter, and blunter, reducing the cutting effect of graphite on the casting. The inoculation treatment also promotes the uniform formation of pearlite, avoids local ferrite aggregation, and makes the overall hardness of the casting more uniform and the wear more consistent.

[0047] High-temperature annealing after casting can eliminate casting stress, preventing deformation or cracking caused by stress release during use. At the same time, annealing can adjust the phosphorus eutectic and the microstructure stability of the casting, avoiding localized hardness reduction due to microstructure instability and ensuring wear resistance during long-term use.

[0048] In step two, scrap steel, recycled gray iron, pig iron, and carburizing agent are first added to the electric furnace in sequence to melt into molten iron. Then, when the molten iron reaches 1500℃, ferrophosphorus is added in two batches. Ferrophosphorus exists in cast iron in the form of phosphorus eutectic, which is distributed in a discontinuous or continuous network at the grain boundaries. Its microhardness is 750-950 HV, so phosphorus can improve the wear resistance of gray cast iron.

[0049] In this embodiment, the phosphorus iron is added twice at 1500°C. This is achieved by precisely controlling the dissolution, distribution, and morphology of phosphorus eutectic, ensuring that the phosphorus content meets the standard while avoiding phosphorus segregation or the formation of a continuous network, which would lead to excessive brittleness. Ultimately, this balances the wear resistance and mechanical properties of gray cast iron.

[0050] The solubility of phosphorus in molten iron decreases with decreasing temperature. The solubility is highest at 1500℃, but drops rapidly below this temperature. If a large amount of ferrophosphorus is added at once, the phosphorus concentration may become excessively high in some areas, exceeding the solubility at that temperature. During cooling, this phosphorus may rapidly precipitate and aggregate, forming coarse, continuous network-like phosphorus eutectic. While this morphology offers high hardness, it significantly increases the brittleness of the casting.

[0051] When added in two stages, the first addition allows phosphorus to fully dissolve and diffuse in the high-temperature molten iron, avoiding local concentration peaks. The second addition replenishes the phosphorus content based on the first dissolution. At this time, the temperature of the molten iron is still relatively high, and the phosphorus can continue to diffuse evenly. The phosphorus eutectic that precipitates during solidification tends to be discontinuous network or diffuse distribution, which ensures the wear resistance of hard particles and reduces the risk of brittleness.

[0052] The first addition serves as a baseline. The amount of phosphorus to be added is estimated based on the volume of molten iron and the initial phosphorus content. Most of the phosphorus and iron is added initially, such as 60-70%. After complete dissolution, the actual phosphorus content in the molten iron is tested using a rapid sampling method. The second addition precisely replenishes the remaining phosphorus and iron, such as 30-40%, based on the test results. This ensures that the final phosphorus content is strictly controlled within the target range of 1.7-1.9%, avoiding excessive or insufficient phosphorus content due to estimation errors from a single addition, and significantly reducing the risk of compositional fluctuations.

[0053] Ferrophosphorus has a melting point of approximately 1100-1200℃, which is lower than the molten iron temperature of 1500℃. However, adding a large amount of ferrophosphorus at once can cause a sudden drop in local temperature due to the absorption of heat from the molten iron by the low-temperature ferrophosphorus, potentially leading to a decrease in the fluidity of the molten iron in certain areas. This can result in the aggregation of undissolved ferrophosphorus particles or impurities, forming casting defects. Furthermore, excessive temperature fluctuations may affect the uniformity of dissolution of other alloying elements. Adding ferrophosphorus in two stages, with each addition being a smaller amount, results in limited heat absorption, avoiding significant temperature fluctuations in the molten iron. This ensures that the molten iron remains at a high fluidity of around 1500℃, providing stable conditions for subsequent alloying element addition, tempering, and casting, and reducing structural defects caused by temperature fluctuations.

[0054] In step five, the ladle is preheated to above 900°C. When the temperature of the molten iron in the electric furnace rises to 1530°C, the molten iron in the electric furnace is poured into the ladle. By preheating the ladle to above 900°C, the temperature of the molten iron can be stabilized, compositional fluctuations can be reduced, casting defects can be avoided, and the hardness and wear resistance of the casting can be indirectly enhanced.

[0055] Before pouring, the molten iron for high-phosphorus gray cast iron must be kept at a sufficient temperature to ensure its fluidity, facilitate filling the mold cavity, and ensure uniform distribution of alloying elements. If the ladle is not preheated or is insufficiently preheated, the temperature of the molten iron will drop sharply after being poured in due to heat absorption by the inner wall of the ladle. This will cause the molten iron to become too cold, resulting in increased viscosity, poor fluidity, and inability to completely fill the complex mold cavity, leading to pouring defects. At the same time, the sudden temperature drop will prevent elements such as phosphorus and chromium from diffusing evenly, causing them to precipitate rapidly in localized areas. This results in phosphorus eutectics concentrating in the low-temperature region to form a coarse network, leading to uneven composition in the casting. This can cause some areas to be excessively hard and brittle, while other areas may lack sufficient hardness.

[0056] In this embodiment, when the ladle is preheated to above 900°C, the temperature difference between it and the molten iron is greatly reduced, which can significantly slow down the cooling rate of the molten iron, ensure that the molten iron maintains sufficient fluidity and temperature stability during the pouring process, and ensure that the alloying elements are evenly distributed, laying the foundation for the subsequent formation of uniform phosphorus eutectic and pearlite structures.

[0057] Ladles are typically made of cast iron or heat-resistant steel. If subjected to rapid heating and cooling of molten iron over a prolonged period, the resulting thermal expansion and contraction will generate significant thermal stress, leading to cracking and spalling of the ladle's inner wall. Preheating to above 900℃ allows the ladle's inner wall to expand prematurely, reducing thermal stress upon contact with the molten iron, lowering the risk of cracking, extending the ladle's service life, and preventing impurities from contaminating the ladle due to damage, thus indirectly ensuring the quality of the castings.

[0058] The inoculant placed at the bottom of the ladle has a mass percentage of 0.3% and a particle size of 1mm to 3mm. Pouring then proceeds, with the initial pouring temperature at 1410℃ and the final pouring temperature at 1370℃, and the pouring time at 16 seconds. The inoculant added during the pouring process has a mass percentage of 0.1% and a particle size of 0.2mm to 0.8mm.

[0059] The fluidity of molten iron decreases as the temperature decreases. The initial pouring temperature is 1410℃, at which point the molten iron is hot enough and fluid enough to quickly fill the complex cavities of the mold, avoiding defects caused by insufficient fluidity. The final pouring temperature is 1370℃, 40℃ lower than the initial pouring temperature, but still maintains sufficient fluidity to ensure adequate shrinkage compensation in the final filling areas, preventing shrinkage cavities and porosity.

[0060] The role of inoculants: They help to increase and refine eutectic clusters, and at the same time increase the quantity of phosphorus eutectic and refine and uniformly distribute it. Phosphorus eutectic with fine eutectic clusters and discontinuous network and uniform distribution has better wear resistance. Therefore, high phosphorus cast iron must undergo effective inoculation treatment.

[0061] In step six, the casting is opened from the mold when its surface has cooled to below the eutectoid temperature of 720°C, with a minimum opening temperature of 500°C. After solidification, gray cast iron undergoes a eutectoid transformation at approximately 727°C, where austenite transforms into pearlite during cooling. If the cooling rate is too rapid or the temperature does not reach the eutectoid point, it may transform into ferrite or bainite. Opening the mold below 720°C ensures that the casting has cooled below the eutectoid temperature, and the eutectoid transformation is essentially complete. This guarantees that the casting is primarily composed of pearlite, avoiding the formation of free ferrite or martensite due to incomplete transformation. Pearlite effectively supports hard particles such as phosphine eutectic, ensuring the overall hardness of the casting and laying the foundation for wear resistance.

[0062] The design has a heat-insulating effect. When the casting is opened at a temperature above 500°C, it is still at a relatively high temperature. After being opened, it is slowly cooled in the air, which allows the internal stress to be released gradually rather than concentrated, further reducing the risk of cracking.

[0063] The morphology of phosphorus eutectic is closely related to the cooling rate. If the mold opening temperature is too high, the casting cools rapidly outside the mold, causing phosphorus to accumulate rapidly at the grain boundaries, forming a continuous network of phosphorus eutectic. This continuous network of phosphorus eutectic is brittle and easily fractures along the grain boundaries. If the mold opening temperature is too low, the casting cools too slowly inside the mold, causing the phosphorus eutectic to coarsen and become unevenly distributed.

[0064] When the casting is opened at 720℃~500℃, most of the phosphorus eutectic has precipitated through the slow cooling of the mold. After opening the mold, the medium-speed cooling in the air can further refine the incompletely precipitated phosphorus eutectic, while avoiding the formation of continuous network, so that the phosphorus eutectic can maintain the ideal shape of small, discontinuous and uniform.

[0065] In step seven, high-temperature annealing can effectively decompose free cementite in the casting and refine pearlite, thereby improving the toughness and plasticity of cast iron. For example... Figure 2 As shown, the heat treatment steps for high-temperature annealing are as follows: Loading into the furnace: The product is loaded into the heat treatment furnace at room temperature; Heating: Heat the product to 920-1050℃ at a heating rate of 70-100℃ / hour; Insulation: Insulate at 920–1050℃ for 1 hour; Cooling: The furnace temperature is lowered to 600℃, then cooled to 300℃ at a rate of 50-100℃ / hour, and finally removed from the furnace and air-cooled to obtain the final product.

[0066] In step seven, the casting inspection process involves examining the surface hardness and metallographic structure of the casting.

[0067] Example 1 The production method of high-phosphorus wear-resistant gray cast iron includes the following steps: Step 1: Raw material inspection.

[0068] Step 2: Smelting: Weigh out 20% scrap steel, 65% gray iron remelting material, 10% pig iron, 4% ferrophosphate, and 1% carbon raiser by weight in sequence. First, add the scrap steel, gray iron remelting material, pig iron, and carbon raiser to the electric furnace in sequence to melt into molten iron. Then, when the molten iron is at 1500℃, add the ferrophosphate in two batches.

[0069] Step 3: Add nickel, chromium, and copper to the electric furnace. The final weight ratio of the molten iron that meets the requirements is: carbon 3.35%, silicon 1.15%, manganese 0.6%, phosphorus 1.7%, sulfur 0.04%, chromium 0.5%, nickel 1.7%, copper 0.3%, and the remainder is iron.

[0070] Step 4: Pour molten iron from the electric furnace into the rapid cooling model of the spectral test block, and use a rapid direct-reading spectrometer to detect the elemental composition of the test block. Based on the elemental composition detected by the spectrum, fine-tune the final composition of the molten iron to meet the requirements, and calculate it as a percentage by mass.

[0071] Step 5: Molding: Resin sand molding is used. Resin sand molds have good rigidity and high strength, which is conducive to the graphitization expansion during the solidification process of the casting, effectively offsetting shrinkage cavities and porosity defects, and achieving a defect-free casting.

[0072] Step Six: Pouring: Preheat the ladle to above 900℃, and place an inoculant at the bottom of the ladle. When the temperature of the molten iron in the electric furnace reaches 1530℃, pour the molten iron into the ladle. During the pouring process into the mold, add more inoculant along with the flow. The inoculant at the bottom of the ladle has a mass percentage of 0.3% and a particle size of 1mm to 3mm. The initial pouring temperature is 1410℃, the final pouring temperature is 1370℃, and the pouring time is 16 seconds. The inoculant added along with the flow has a mass percentage of 0.1% and a particle size of 0.2mm to 0.8mm.

[0073] Step 7: Unpacking: Unpack the casting when the surface has cooled to below the eutectoid temperature of 720°C. The minimum temperature for unpacking is 500°C.

[0074] Step 8: Heat treatment: High-temperature annealing of high-phosphorus wear-resistant gray cast iron, followed by inspection of the casting to obtain the final product.

[0075] The heat treatment steps for high-temperature annealing are as follows: Loading into the furnace: The product is loaded into the heat treatment furnace at room temperature; Heating: Heat the product to 920℃ at a heating rate of 70℃ / hour; Insulation: Insulate at 920℃ for 1 hour; Cooling: The furnace temperature is lowered to 600℃, then cooled to 300℃ at a rate of 50℃ / hour, and finally removed from the furnace and air-cooled to obtain the final product.

[0076] Example 2 The difference between this embodiment and embodiment 1 is that in step two of this embodiment, 30% scrap steel, 50% gray iron remelting material, 14% pig iron, 5% ferrophosphate, and 1.5% carbon raiser are weighed in sequence by weight.

[0077] The final composition of the molten iron that meets the requirements is as follows by weight: 3.5% carbon, 1.25% silicon, 0.9% manganese, 1.9% phosphorus, 0.08% sulfur, 1.0% chromium, 1.9% nickel, 0.45% copper, and the remainder is iron.

[0078] The heat treatment steps for high-temperature annealing are as follows: Loading into the furnace: The product is loaded into the heat treatment furnace at room temperature; Heating: Heat the product to 1050℃ at a heating rate of 100℃ / hour; Insulation: Insulate at 1050℃ for 1 hour; Cooling: The furnace temperature is lowered to 600℃, then cooled to 300℃ at a rate of 100℃ / hour, and finally removed from the furnace and air-cooled to obtain the final product.

[0079] Example 3 The difference between this embodiment and embodiment 1 is that in step two of this embodiment, 25% scrap steel, 55% gray iron remelting material, 15% pig iron, 4% ferrophosphate, and 1% carbon raiser are weighed in sequence by weight.

[0080] The final composition of the molten iron that meets the requirements is as follows by weight: 3.4% carbon, 1.2% silicon, 0.7% manganese, 1.8% phosphorus, 0.06% sulfur, 0.8% chromium, 1.8% nickel, 0.4% copper, and the remainder is iron.

[0081] The heat treatment steps for high-temperature annealing are as follows: Loading into the furnace: The product is loaded into the heat treatment furnace at room temperature; Heating: Heat the product to 1000℃ at a heating rate of 85℃ / hour; Insulation: Insulate at 1000℃ for 1 hour; Cooling: The furnace temperature is lowered to 600℃, then cooled to 300℃ at a rate of 80℃ / hour, and finally removed from the furnace and air-cooled to obtain the final product.

[0082] The high-phosphorus wear-resistant gray cast iron prepared in Examples 1 and 2 was used for metallographic-phosphorus eutectic quantity classification of gray cast iron, and the results were obtained respectively. Figure 3 , Figure 4 According to the technical conditions of the Railway Industry Standard of the People's Republic of China (TB / T3104.3-2017), the test results of the amount of phosphorus eutectic meet the standard value requirements.

[0083] The hardness of the surface of the high-phosphorus wear-resistant gray cast iron prepared in Example 1 was tested, and the results are shown in Table 1.

[0084] Table 1. Test results of surface hardness of high-phosphorus wear-resistant gray cast iron

[0085] It can be seen that the surface hardness of the castings obtained by the preparation method provided by the present invention meets the requirements.

[0086] The above are preferred embodiments of the present invention. It should be noted that, for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for producing a high phosphorus wear resistant gray cast iron, characterized in that, The method comprises the following steps: Step one: raw material inspection; Step two: smelting: sequentially adding scrap steel, gray iron return material, pig iron, carbon additive and phosphorus iron into the electric furnace for melting; Step three: sequentially adding nickel, chromium and copper into the electric furnace for adjusting the quality of the molten iron, so that the final composition of the molten iron meets the requirements; Step four: molding: preparing a casting mold; Step five: pouring: preheating a pouring ladle, placing inoculants at the bottom of the pouring ladle, then pouring the molten iron into the pouring ladle, and adding the inoculants along with the flow during the pouring process; Step six: opening the box: opening the box after the temperature is lowered, and obtaining the formed high-phosphorus wear-resistant gray cast iron; Step seven: Heat treatment: high-temperature annealing the high-phosphorus wear-resistant gray cast iron, then inspecting the castings, and obtaining the final product; In step three, the weight percentage of each component in the final composition of the molten iron that meets the requirements is as follows: carbon 3.35-3.5%, silicon 1.15-1.25%, manganese 0.6-0.9%, phosphorus 1.7-1.9%, sulfur 0.04-0.08%, chromium 0.5-1.0%, nickel 1.7-1.9%, copper 0.3-0.45%, and the rest is trace elements and iron.

2. The production method of high phosphorus wear-resistant gray cast iron according to claim 1, characterized in that, The smelting comprises the following raw materials in percentage by weight: scrap steel 20-30%, gray iron return material 50-65%, pig iron 5-30%, phosphorus iron 4-5%, and carbon additive 1-1.5%; the smelting is sequentially adding scrap steel, gray iron return material, pig iron and carbon additive into the electric furnace for melting to obtain the molten iron, and adding the phosphorus iron in batches when the molten iron reaches 1490-1510℃.

3. The production method of high phosphorus wear resistant gray cast iron according to claim 1, characterized in that, The material of the casting mold is resin sand.

4. The production method of high phosphorus wear resistant gray cast iron according to claim 1, characterized in that, The preheating temperature of the pouring ladle is greater than or equal to 900℃; the temperature of the molten iron poured into the pouring ladle is 1520-1540℃.

5. The production method of high phosphorus wear resistant gray cast iron according to claim 1, characterized in that, The mass of the inoculants placed at the bottom of the pouring ladle is 0.2-0.4% of the mass of the molten iron, and the particle size of the inoculants is 1-3mm.

6. The production method of high phosphorus wear resistant gray cast iron according to claim 1, characterized in that, The mass of the inoculants added along with the flow is 0.5-0.15% of the mass of the molten iron, and the particle size of the inoculants is 0.2-0.8mm.

7. The production method of high phosphorus wear resistant gray cast iron according to claim 1, characterized in that, During the pouring, the pouring temperature is 1400-1420℃, the end pouring temperature is 1360-1380℃, and the pouring time is 15-17s.

8. The production method of high phosphorus wear resistant gray cast iron according to claim 1, characterized in that, During the opening of the box, the surface of the cast iron is cooled to 720-500℃.

9. The production method of high phosphorus wear resistant gray cast iron according to claim 1, characterized in that, The high-temperature annealing comprises the following steps: Furnace loading: loading the product into the heat treatment furnace at room temperature; Heating: heating the product to 920-1050℃ at a heating rate of 70-100℃ / h; Soaking: soaking at 920-1050℃ for 1-1.5h; Cooling: furnace cooling to 600℃, then cooling to 300℃ at a rate of 50-100℃ / h, and finally furnace-outlet air cooling to obtain the high-phosphorus wear-resistant gray cast iron.

10. A high-phosphorus wear-resistant gray cast iron produced by the production method of the high-phosphorus wear-resistant gray cast iron according to any one of claims 1-9.

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