High-vermicular-rate cast iron material and preparation method thereof

Abstract

The invention discloses a high-vermicular-rate cast iron material and a preparation method thereof, and belongs to the field of casting processes. By accurately controlling the components of all the materials and optimizing the smelting, vermicularizing and inoculation treatment processes, the problems that in the prior art, the stability of the vermicularizing rate is poor, the number of casting defects is large, and operation is complex are solved. The method comprises the specific steps that raw materials such as waste steel and high-purity pig iron are smelted according to the proportion at the temperature of 1500-1550 DEG C to obtain basic molten iron, after dross is removed, copper and tin raw materials are added, wire feeding treatment is conducted through a vermicularizing cored wire, and finally a high-rare-earth nucleating agent is added into a tundish and pouring is conducted at the temperature of 1420-1440 DEG C. The high-vermicularizing-rate cast iron material casting prepared through the method has the advantages that the vermicularizing rate of the edge part is larger than 60%, the vermicularizing rate of the center position is larger than 70%, the casting does not have the defects of shrinkage cavities, shrinkage porosity and the like, the tensile strength reaches 450 MPa or above, and the casting has excellent high-temperature performance and mechanical performance and can be widely applied to the fields of automobiles, aerospace, mechanical manufacturing and the like; the practical value and the market prospect are relatively high.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of casting process, more particularly to a high vermicular rate cast iron material and its preparation method. BACKGROUND

[0002] Vermicular graphite cast iron is a kind of cast iron material with graphite distributed in the ferrite matrix in the form of vermicules. It has been widely used in many fields such as automobiles, aerospace, mechanical manufacturing, etc. due to its excellent high-temperature strength, oxidation resistance and heat fatigue resistance. High vermicular rate material refers to the material with high vermicular rate under certain temperature and stress conditions. The parts made of high vermicular rate vermicular graphite cast iron material have higher heat resistance and creep resistance, and can better adapt to various harsh working environments.

[0003] The existing high vermicular rate material preparation mainly adopts wire feeding method, that is, using vermicular cored wire as wire feeding material to treat molten iron, and then adding inoculant in the pouring ladle for pouring. This method can improve the vermicular rate to a certain extent, but there are many problems in actual application.

[0004] Firstly, the existing wire feeding method can easily reduce the vermicular rate to below 60% when producing cast iron products with high vermicular rate, resulting in castings being scrapped and seriously affecting production efficiency and product quality. This is because in the production process, slight changes in various factors such as temperature, time, raw material ratio, etc. can have a significant impact on the vermicular rate, and the existing technology is difficult to accurately control these factors, resulting in poor stability of the vermicular rate.

[0005] Secondly, the inoculant used in the wire feeding method has high cost and short vermicular recession time, which greatly increases the production cost. Inoculant is one of the key raw materials to ensure the performance of cast iron material, and its high price directly leads to the increase of total production cost. At the same time, the short vermicular recession time means that the vermicular agent and inoculant need to be added frequently during production, which not only increases the consumption of raw materials, but also prolongs the production cycle and reduces the production efficiency.

[0006] Thirdly, the existing casting process is prone to produce shrinkage holes, shrinkage porosity and other defects, which will seriously affect the mechanical properties and service life of the castings. Shrinkage holes and shrinkage porosity are caused by insufficient feeding of molten iron during solidification process. The existing process has deficiencies in controlling the temperature distribution and flow state of molten iron during solidification process, resulting in the presence of cavities and porosity in the castings.

[0007] Finally, the existing casting process is complex and requires high experience and skills of the operators, which is easy to cause the castings to be scrapped due to operation errors. The complex operation process increases the uncertainty in the production process, which is not conducive to the standardization and automation of the production process, and also restricts the further improvement of production efficiency.

[0008] In summary, the existing high vermicularity cast iron material preparation technology has a series of problems, as follows:

[0009] The problem of difficult to control the stability of vermicularity: in the prior art, due to the lack of accurate control of various factors affecting the vermicularity, the vermicularity fluctuates greatly, often below 60%, which seriously affects the quality of the castings.

[0010] The problem of more casting defects: the existing casting process is prone to shrinkage, shrinkage and other defects, which affects the mechanical properties and service life of the castings. SUMMARY

[0011] 1. The technical problem to be solved by the invention

[0012] In view of the above problems existing in the prior art of vermicular graphite cast iron castings, the present invention provides a high vermicularity cast iron material and its preparation method, by accurately controlling the content and proportion of each element, and optimizing the production process parameters, the vermicularity is stably controlled in the range of >60%, the stability of high vermicularity material is improved.

[0013] 2. Technical scheme

[0014] In order to achieve the above purpose, the technical scheme provided by the present invention is:

[0015] Accurate control of material composition: by accurately controlling the addition content and proportion of carbon, silicon, copper, tin, rare earth and other materials, the vermicularity is stably controlled in the range of >60%, and the stability of high vermicularity material is enhanced. These elements play different roles in the formation process of cast iron material, for example, carbon and silicon are the key elements to form graphite and matrix organization, their content directly affects the strength and toughness of cast iron; rare earth elements are the core elements of vermiculation treatment, which can promote the distribution of graphite in the form of vermicules.

[0016] Optimization of smelting process: after smelting scrap steel, high-purity pig iron, vermicular iron return material and silicon iron into molten iron, add carbon additive and silicon carbide to balance the carbon and silicon content, then add deslagging agent to remove dross, add copper and tin raw materials after smelting, and obtain tundish molten iron. This process can effectively remove impurities in the molten iron, ensure the purity and uniformity of the molten iron, and lay a good foundation for subsequent vermiculation treatment and inoculation treatment.

[0017] Optimization of inoculation treatment: inoculant is added in the tundish, and the molten iron is fed with vermicular cored wire. The mass percentage of each component of high-rare earth inoculant is 70-76% of silicon, 0.75-1.25% of calcium, 0.75-1.25% of aluminum, 1.5-2.0% of cerium, and the balance of iron, which can promote the nucleation and growth of graphite, improve the vermicular rate, refine the grain, improve the mechanical properties of the material, and improve the structure and performance of the cast iron; the vermicular alloy powder in the vermicular cored wire can react with the molten iron, so that the graphite is distributed in the form of vermicules, thereby obtaining high vermicular rate RuT450 material, and further improving the mechanical properties and service life of the castings.

[0018] 3. Beneficial effects

[0019] Compared with the prior art, the technical scheme provided by the present application has the following beneficial effects:

[0020] (1) The high vermicular rate cast iron material and its preparation method can stably control the vermicular rate in the range of >60%, so that the high vermicular rate material of the present application has higher stability and reliability in actual application, avoids the quality problems of castings caused by the fluctuation of vermicular rate, and improves the qualified rate of products;

[0021] (2) The high vermicular rate cast iron material and its preparation method can make the tensile strength and pearlite content of the castings reach the technical requirements, ensuring the stability and reliability of the castings under high pressure and high temperature environment. This makes the high vermicular rate material of the present application have higher durability and anti-vermiculation ability under harsh environment, which can meet the demand of high performance application and expand its application field;

[0022] (3) The high vermicular rate cast iron material and its preparation method can reduce the defects of castings: effectively reduces the generation of defects such as shrinkage and shrinkage hole, and improves the forming quality of castings. This not only improves the mechanical properties and service life of the castings, but also reduces the product scrap caused by defects, reduces the production cost and maintenance cost;

[0023] (4) The high vermicular rate cast iron material and its preparation method can reduce the consumption and cost of inoculant and other raw materials by optimizing the vermicular process, and significantly prolong the vermicular recession time. This makes the high vermicular rate material of the present application have higher economic benefit in the production process, and improves the competitiveness of enterprises. DETAILED DESCRIPTION

[0024] In order to further understand the content of the present application, the application will be described in detail in combination with examples.

[0025] Example 1

[0026] The preparation method of the high vermicular rate cast iron material of the present embodiment comprises the following steps:

[0027] Step one: smelting. Scrap, high-purity pig iron, vermicular iron re-melted material, silicon iron, carbon additive and silicon carbide are smelted to obtain base molten iron material. The scrap is added in an amount of 600 kg, the high-purity pig iron has a mass of 50 kg, the vermicular iron re-melted material has a mass of 350 kg, the silicon iron has a mass of 2 kg, the carbon additive has a mass of 17 kg, and the silicon carbide has a mass of 7 kg. The addition amount of each material is accurately controlled. The smelting temperature is 1520°C, and the time is 1 hour.

[0028] Step two: removing dross. A dross removal agent is used to treat the molten iron to remove the dross in the molten iron, ensuring that the molten iron is pure.

[0029] Step three: adding copper and tin raw materials. Copper and tin are added to the purified molten iron, with the copper added in an amount of 3 kg and the tin added in an amount of 0.5 kg. After adding, stir evenly to make the copper and tin completely dissolved in the molten iron.

[0030] Step four: vermiculation treatment. The molten iron is treated with vermiculation cored wire to obtain pouring molten iron. The addition amount of the vermiculation cored wire is 7 meters, and the feeding speed is 21 m / min. The material of the vermiculation cored wire is a cold-rolled steel strip wrapped around vermiculation alloy powder.

[0031] Step five: inoculation treatment. High-rare earth inoculant is added to the molten iron in the tundish and poured to obtain high- vermiculation rate RuT450 material. The mass percentage of each component in the high-rare earth inoculant is silicon 70%, calcium 1.25%, aluminum 0.75%, cerium 2.0%, and the balance is pure iron; the addition amount is 1 kg, the pouring temperature is 1430°C, and the pouring speed is 14 s per type.

[0032] The above method is used to cast a casting with a thin-walled edge disc, with a disc diameter of 140-260 mm, an edge wall thickness of about 10 mm, and a center thickness of about 60-80 mm. The casting is detected, and the results are as follows: the casting has no shrinkage cavity or shrinkage porosity, the edge portion has a vermiculation rate > 60%, the center portion has a vermiculation rate > 70%, the tensile strength reaches more than 450 MPa, and the pearlite content meets the technical requirements.

[0033] Example 2

[0034] The high- vermiculation rate cast iron material and the preparation method thereof of the present embodiment comprise the following steps:

[0035] Step one: smelting. Waste steel, high-purity pig iron, vermicular iron re-melted material, ferrosilicon, carbon additive and silicon carbide are smelted to obtain base molten iron material. The waste steel is added in an amount of 550 kg, the high-purity pig iron has a mass of 40 kg, the vermicular iron re-melted material has a mass of 300 kg, the ferrosilicon has a mass of 1 kg, the carbon additive has a mass of 15 kg, and the silicon carbide has a mass of 5 kg. The smelting temperature is 1500 °C, and the time is 0.8 hours.

[0036] Step two: removing scum. The same deslagging agent and method as in Example 1 are used to remove scum.

[0037] Step three: adding copper and tin raw materials. Copper and tin are added to the purified molten iron, wherein the copper is added in an amount of 0.5 kg, and the tin is added in an amount of 0.1 kg. After adding, uniform stirring is performed to ensure that the copper and tin are completely dissolved in the molten iron.

[0038] Step four: vermiculation treatment. The molten iron is treated by feeding vermiculation cored wire to obtain pouring molten iron. The vermiculation cored wire is added in an amount of 5 meters, and the feeding speed is 20 m / min. The material of the vermiculation cored wire is a cold-rolled steel strip wrapped around vermicular alloy powder.

[0039] Step five: inoculation treatment. High-rare earth inoculant is added to the molten iron in the tundish and poured to obtain high- vermiculation rate RuT450 material. The mass percentage of each component in the high-rare earth inoculant is silicon 73%, calcium 1.0%, aluminum 1.0%, cerium 1.8%, and the balance is pure iron; the addition amount is 0.8 kg, the pouring temperature is 1420 °C, and the pouring speed is 13 s per type.

[0040] The same thin-walled disc castings as in Example 1 are cast using the above method. The detection results show that the castings have no obvious shrinkage holes and shrinkage porosity, the edge portion vermiculation rate is 62%, the center position vermiculation rate is 71%, the tensile strength is 455 MPa, and the pearlite content meets the technical requirements.

[0041] Example 3

[0042] The high- vermiculation rate cast iron material and the preparation method thereof of the present embodiment comprise the following steps:

[0043] Step one: smelting. Waste steel, high-purity pig iron, vermicular iron re-melted material, ferrosilicon, carbon additive and silicon carbide are smelted to obtain base molten iron material. The waste steel is added in an amount of 650 kg, the high-purity pig iron has a mass of 60 kg, the vermicular iron re-melted material has a mass of 400 kg, the ferrosilicon has a mass of 3 kg, the carbon additive has a mass of 19 kg, and the silicon carbide has a mass of 9 kg. The smelting temperature is 1550 °C, and the time is 1.2 hours.

[0044] Step two: removing scum. The same deslagging agent and method as in Example 1 are used to remove scum.

[0045] Step three: adding copper and tin raw materials. Copper and tin are added into the purified molten iron, wherein the added amount of copper is 5 kg and the added amount of tin is 1.0 kg. After adding, the molten iron is stirred uniformly to make the copper and tin completely dissolved in the molten iron.

[0046] Step four: vermicularizing treatment. The molten iron is treated by feeding vermicularizing cored wire to obtain the pouring molten iron. The added amount of the vermicularizing cored wire is 9 meters and the feeding speed is 22 m / min. The material of the vermicularizing cored wire is a cold-rolled steel belt wrapped vermicularizing alloy powder.

[0047] Step five: inoculation treatment. High rare earth inoculant is added into the molten iron in the tundish and poured to obtain the high vermicularization rate RuT450 material. The mass percentage of each component in the high rare earth inoculant is: silicon 76%, calcium 0.75%, aluminum 1.25%, cerium 1.5%, and the balance is pure iron; the added amount is 1.2 kg, the pouring temperature is 1440°C, and the pouring speed is 15 seconds per type.

[0048] The same specification thin-walled disc castings as in Example 1 are cast by the above method. The detection results show that the castings have no shrinkage holes and shrinkage porosities, the vermicularization rate at the edge position is 63%, the vermicularization rate at the center position is 72%, the tensile strength is 455 MPa, and the pearlite content meets the technical standard.

[0049] Comparative Example 1

[0050] This comparative example omits step three in Example 1, and the remaining steps and parameters are the same as in Example 1.

[0051] The same specification thin-walled disc castings as in Example 1 are cast by this method. The detection shows that the castings have a small amount of shrinkage holes and shrinkage porosities, the vermicularization rate at the edge position is <55%, the vermicularization rate at the center position is <65%, the tensile strength is 300-400 MPa, and the pearlite content does not meet the technical requirements.

[0052] Comparative Example 2

[0053] This comparative example uses the existing silicon-barium inoculant to replace the high rare earth inoculant in Example 1, and the remaining steps and parameters are the same as in Example 1.

[0054] After casting the same specification thin-walled disc castings, the detection shows that the castings have a small amount of shrinkage porosities, the vermicularization rate at the edge position is <45%, the vermicularization rate at the center position is <55%, and both the tensile strength and the pearlite content do not meet the technical requirements.

[0055] Comparative analysis, Comparative Examples 1-3 and Comparative Examples 1 and 2:

[0056] Category Defect condition of castings Edge vermicularity rate Center vermicularity rate Tensile strength Example 1 No shrinkage, porosity 68 77 450 MPa or more Example 2 No shrinkage, porosity 62 71 450 MPa or more Example 3 No shrinkage, porosity 63 72 450 MPa or more Comparative Example 1 Small amount of shrinkage, porosity 54 60 300-400 MPa Comparative Example 2 Small amount of porosity 44 50 300-400 MPa

[0057] Through the comparison of the data in the table, it is shown that:

[0058] 1. Improvement of stability of vermicularity

[0059] In the examples, the vermicularity of the edge part of the castings of the three examples is stably >60%, and the vermicularity of the center part is >70% without obvious fluctuation, which shows that the present technical solution effectively solves the problem of poor stability of vermicularity in the prior art by precisely controlling the material composition (such as the addition of copper and tin) and process parameters (such as melting temperature and wire feeding speed), and realizes stable control of high vermicularity.

[0060] In Comparative Example 1, the edge and center vermicularity is reduced to <55% and <65% respectively due to the omission of the copper and tin addition step; in Comparative Example 2, the vermicularity is further reduced to <45% and <55% due to the replacement of the inoculant type, and it can be seen from the comparison that the addition of copper and tin and the use of high rare earth inoculant are the key to ensuring high vermicularity and directly affect the stability of the vermicularity effect.

[0061] 2. Reduction of casting defects

[0062] The castings of the three examples are free of shrinkage holes and shrinkage porosities, which shows that the present technical solution effectively controls the problem of insufficient feeding during the solidification process of the casting by optimizing the melting process (such as slag removal treatment), inoculation treatment (intermediate ladle inoculation) and pouring parameters (temperature and speed control), and significantly improves the forming quality of the casting.

[0063] In Comparative Example 1, a small amount of shrinkage holes and shrinkage porosities appear due to the lack of the adjusting effect of copper and tin elements; in Comparative Example 2, a small amount of shrinkage porosities exist due to the unsuitable type of inoculant, and the comparison shows that the process steps and material selection of the present solution can effectively reduce defects and ensure the integrity of the casting.

[0064] 3. Improvement of mechanical properties of the casting

[0065] The tensile strength of the castings of the examples reaches 450 MPa or more, and the pearlite content meets the technical requirements, which shows that the material has good mechanical properties and can meet the use requirements in high pressure and high temperature environments.

[0066] The tensile strength of Comparative Example 1 is only 300-400 MPa, and the tensile strength of Comparative Example 2 does not meet the technical requirements, which further proves that the synergistic effect of various elements (such as copper and tin to enhance the strength of the matrix) and process optimization (such as vermicularity treatment to promote the vermicular distribution of graphite) in the present solution significantly improves the mechanical properties of the casting.

[0067] 4. Verification of process reliability

[0068] The consistency data (defects, vermicularity and strength) of the examples show that after simplifying the process in the present technical solution, the operation stability is high and quality fluctuation is not easy to occur due to operation differences, which solves the problem of complex operation and easy to produce waste products in the prior art, and is more conducive to realizing mechanized and automated production.

[0069] The comparative example proves that the overall process design of the technical solution is reasonable and reliable, and the synergy between the steps and the selection of the materials ensures the high performance of the final product.

[0070] In summary, the data comparison of the examples and the comparative example fully proves the significant effect of the technical solution in improving the stability of the vermiculation rate, reducing casting defects, enhancing the mechanical properties and improving the process reliability.

[0071] The high vermiculation rate cast iron material prepared by the application can be widely used in the industrial fields of automobile manufacturing, aerospace, mechanical manufacturing, etc. In the automobile industry, it can be used to manufacture key components such as engine cylinder body, cylinder cover, crankshaft, etc., which can withstand high temperature, high pressure and alternating load during engine operation, improve the reliability and durability of the engine, and at the same time, it is beneficial to improve the fuel economy. In the field of aerospace, it is suitable for high-temperature components such as turbine blades and combustion chambers in aero-engines, which can maintain good mechanical properties and dimensional stability under high-temperature environment, help to improve the efficiency and reliability of the engine, reduce the weight, and have important significance for improving the performance and fuel efficiency of the aircraft. In the field of mechanical manufacturing, it can be applied to hydraulic pumps, compressors, hoisting arms of large cranes and machine bodies of large presses.

Claims

1. A method for preparing a high creep rate cast iron material, characterized in that: The following steps are involved: 590-710 kg of iron, 300-400 kg of vermicular iron scrap, 1-3 kg of ferrosilicon, 15-19 kg of recarburizer and 5-9 kg of silicon carbide are smelted to obtain a basic molten iron material at a temperature of 1500-1550° C. for 0.8-1.2 hours; Add 0.5-5kg of copper and 0.1-1.0kg of tin to the basic molten iron material to completely dissolve the copper and tin in the molten iron; Use creeping cored wire to feed molten iron to obtain tundish iron liquid. The amount of creeping cored wire added is 5-9 meters, and the feeding speed is 20-22m / min. The material of the creeping cored wire is creeping alloy powder wrapped with cold-rolled steel strip; Add high rare earth inoculant to the tundish iron liquid and pour it. The amount of inoculant added is 0.8-1.2kg, the pouring temperature is 1420-1440℃, and the pouring speed is 13s-15s per mold.

2. The preparation method according to claim 1, wherein: Of the 590-710 kg of iron, the amount of scrap steel added is 550-650 kg, and the mass of high-purity pig iron is 40-60 kg.

3. The preparation method according to claim 1, wherein: The mass percentages of the components in the high rare earth inoculant are silicon 70-76%, calcium 0.75-1.25%, aluminum 0.75-1.25%, cerium 1.5-2.0%, and the balance iron.

4. The preparation method according to claim 1, wherein: The basic molten iron material is subjected to a slag removal treatment.

5. A high creep rate cast iron material prepared according to the method according to any one of claims 1 to 4, characterized in that: It is made of RuT450 material with high creep rate, the creep rate of the edge is greater than 60%, and the creep rate of the center is greater than 70%.

6. The high creep rate cast iron material according to claim 5, characterized in that: It is used in automobile engine cylinder blocks, cylinder heads and crankshaft castings, aircraft engine turbine blades and combustion chamber castings, as well as hydraulic pumps, compressors, large crane booms and large press fuselage castings in mechanical manufacturing.