Preparation method of cast steel

Abstract

The invention discloses a preparation method of cast steel, and relates to the technical field of vehicles. The alloy comprises the following raw materials in percentage by mass: 0.15%-0.20% of C, 0.7%-0.9% of Mn, 0.2%-0.4% of Si, 0.5%-1.5% of Cr and the balance of Fe and inevitable impurities. P is less than or equal to 0.02%, S is less than or equal to 0.02%, and the balance is Fe and unavoidable impurities. Comprising the following steps that raw materials of low-carbon low-alloy cast steel are smelted, deoxidized and deslagged, and alloy melt is obtained; the alloy melt is subjected to casting mold forming, and an alloy casting is obtained; and normalizing the alloy casting at 850-900 DEG C, and cooling to obtain the cast steel part. In order to improve the strength and plasticity of the cast steel, slag and oxygen are removed through smelting, normalizing treatment is carried out, the temperature of normalizing treatment is 850-900 DEG C, and a normal-temperature pearlite and ferrite double-phase structure is obtained. And slag is removed in the smelting process, so that the melt cleanliness is ensured, and the inclusion content in the casting is reduced. And through the normalizing treatment process, the structure of the cast steel is more uniform and refined, so that the strength and comprehensive performance of the cast steel are improved.

Description

Technical Field

[0001] The present application relates to the field of automobile technology, and in particular to a method for preparing cast steel. Background Art

[0002] As global attention to energy consumption and environmental protection increases, the automotive industry faces increasingly stringent fuel economy standards. Reducing the weight of a car is one of the effective ways to improve fuel efficiency. Low-carbon, low-alloy, high-strength steel has high strength, which can reduce the use of steel while ensuring the structural strength and safety of the car, thereby reducing the weight of the car body and reducing fuel consumption. For example, automotive parts made of low-carbon, low-alloy, high-strength steel, such as body structural parts, engine brackets, chassis parts, etc., can be 10%-30% lighter than traditional steel parts without reducing performance. In addition, the design of modern cars pays more and more attention to the structural strength of the car body to improve the handling and stability of the car. Low-carbon, low-alloy, high-strength steel can meet the strength requirements of the car body structure, making the car body more solid and reliable.

[0003] The pursuit of high strength is an important goal of low-carbon low-alloy high-strength steel, but while increasing strength, it often leads to a decrease in plasticity. After the strength reaches the requirement, the plasticity index is not ideal, which makes the steel prone to cracking, deformation and other problems during the processing and forming process, affecting its actual application range. Summary of the invention

[0004] The present application provides a method for preparing cast steel to solve the problem that the existing plasticity index is not ideal, which makes the steel prone to cracking and deformation during the processing and forming process.

[0005] In a first aspect, the present application provides a method for preparing cast steel, comprising the following raw material compositions by mass fraction:

[0006] C: 0.15-0.20%, Mn: 0.7-0.9%, Si: 0.2-0.4%, Cr: 0.5-1.5%; P≤0.02%, S≤0.02%, the balance is Fe and unavoidable impurities;

[0007] The following steps are involved:

[0008] The raw materials of low-carbon low-alloy cast steel are melted, deoxidized and slag removed to obtain alloy melt;

[0009] Casting the alloy melt into a mold to obtain an alloy casting;

[0010] The alloy casting is normalized at 850-900°C and cooled to obtain cast steel parts.

[0011] In the present application, by reducing the content of Si, Mn, P, and S elements in the traditional low-carbon steel cast steel grades, the carbon content in the cast steel is not only low, but also the content of alloy elements is low, thereby reducing the cost of the cast steel. Among them, Mn has an obvious solid solution strengthening effect on ferrite, which can not only improve the strength of the steel, but also reduce the cold brittle transition temperature of the steel, and increase the amount of pearlite in the steel, further improving the strength. At the same time, in order to improve the strength and plasticity of the cast steel, the slag removal, deoxidation, and normalizing treatment are carried out by smelting, wherein the temperature of the normalizing treatment is 850 to 900°C, and a two-phase structure of pearlite and ferrite at room temperature is obtained. Slag removal during the smelting process ensures the cleanliness of the melt and reduces the inclusion content in the casting. The normalizing treatment process makes the structure of the cast steel more uniform and refined, the pearlite lamellar spacing is reduced, and the strength of the pearlite is related to the lamellar spacing. The smaller the lamellar spacing, the higher the strength. At the same time, normalizing can also eliminate some casting defects in the cast steel, such as Widmanstatten structure, thereby improving the strength and comprehensive performance of the cast steel. The mold forming process can be used to form parts with complex structures, reducing the cracking problem caused by the stamping process on cast steel. The present application can reduce the alloy content while ensuring the strength and elongation of cast steel parts, thereby reducing the cost of raw materials.

[0012] In some embodiments, the raw material of low-carbon low-alloy cast steel is melted, deoxidized and slag removed to obtain the alloy melt: the melting temperature is 1560-1600° C. Within this melting temperature range, the alloy elements can be fully dissolved and evenly distributed, avoiding the problems of element burning and increased steel liquid aspiration caused by too high temperature, and poor steel liquid fluidity and uneven chemical composition caused by too low temperature.

[0013] In some embodiments, the raw material of low-carbon low-alloy cast steel is melted, deoxidized and slag removed to obtain the alloy melt: the slag removal method includes slag making and slag pushing using a slag making agent. Slag making and slag pushing using a slag making agent can ensure the cleanliness of the melt, reduce the inclusion content in the casting, and improve the strength of the cast steel.

[0014] In some embodiments, the slag-forming agent slags and pushes 3 to 5 times. The slag-forming agent slags and pushes 3 to 5 times within the above range, which can further ensure the cleanliness of the melt, reduce the inclusion content in the casting, and improve the strength of the cast steel.

[0015] In some embodiments, the raw material of low-carbon low-alloy cast steel is melted, deoxidized and slag removed to obtain a molten alloy: the deoxidation method includes adding pure aluminum to the molten alloy for deoxidation. Adding pure aluminum to the molten alloy for deoxidation can reduce the probability of molten steel oxidation, improve the strength of cast steel, and reduce oxide impurities.

[0016] In some embodiments, the alloy melt is molded to obtain an alloy casting:

[0017] The pouring temperature of the mold is 1540-1580°C. Within this range, the fluidity of the molten steel can be ensured, and the chemical composition of the molten steel can be uniform, without insufficient pouring, thermal cracking, shrinkage cavities or shrinkage defects; and / or,

[0018] The pouring time of the mold is 8 to 10 minutes. When the pouring time of the mold is within this range, the molding can be smooth, the casting structure is uniform, and the dimensional accuracy is high, while the production efficiency is improved and the production cost is reduced.

[0019] In some embodiments, the alloy casting is normalized at 850-900°C and cooled to obtain a cast steel part: the holding time of the normalizing treatment is 2-4 hours. The holding time of the normalizing treatment within this range can make the structure of the cast steel more uniform and refined, the pearlite lamellar spacing smaller, and improve the strength of the cast steel.

[0020] In some embodiments, the alloy casting is normalized at 850-900° C. and cooled to obtain a cast steel part, which comprises:

[0021] The alloy casting surface is coated with high aluminum powder for hardening, and then normalized at 850-900°C and cooled to obtain cast steel parts.

[0022] By coating the surface of the alloy casting with high aluminum powder, hardening and drying it, and then normalizing it, a room temperature pearlite and ferrite dual phase structure can be obtained, which inhibits grain growth and makes the material still have high strength and toughness under the premise of low carbon and low alloying.

[0023] In some embodiments, the alloy casting is coated with high aluminum powder on the surface for hardening, and then normalized at 850-900° C. and cooled to obtain a cast steel part:

[0024] The coating thickness of high aluminum powder is 8 to 10 mm. The coating thickness of high aluminum powder is within this range, which can prevent oxidation of castings, reduce decarburization, control and adjust the cooling speed, and achieve uniform cooling.

[0025] In some embodiments, the alloy casting is coated with high aluminum powder on the surface for hardening, and then normalized at 850-900° C. and cooled to obtain a cast steel part:

[0026] The cooling method includes air cooling and spray cooling. The use of air cooling and spray cooling can reduce the problem of surface roughness caused by excessive surface oxidation and the problem of partially coarse crystal particles caused by uneven cooling. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the drawings required for use in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0028] Figure 1 This is a metallographic microstructure diagram of a cast steel part produced by the cast steel production method of Example 1 of the present application. DETAILED DESCRIPTION

[0029] As global attention to energy consumption and environmental protection increases, the automotive industry faces increasingly stringent fuel economy standards. Reducing the weight of a car is one of the effective ways to improve fuel efficiency. Low-carbon, low-alloy, high-strength steel has high strength, which can reduce the use of steel while ensuring the structural strength and safety of the car, thereby reducing the weight of the car body and reducing fuel consumption. For example, automotive parts made of low-carbon, low-alloy, high-strength steel, such as body structural parts, engine brackets, chassis parts, etc., can reduce weight by 10%-30% compared with traditional steel parts without reducing performance. In addition, the design of modern cars pays more and more attention to the structural strength of the car body to improve the handling and stability of the car. Low-carbon, low-alloy, high-strength steel can meet the strength requirements of the car body structure and make the car body more solid and reliable. For example, the car body frame made of low-carbon, low-alloy, high-strength steel can improve the overall strength and rigidity of the car body and reduce the vibration and noise of the car body during driving. Although the production process of low-carbon, low-alloy, high-strength steel is relatively complex, its alloy element content is relatively low, and some cheap alloy elements, such as manganese and silicon, can be used to improve the strength of the steel. Therefore, compared with other high-strength materials, the material cost of low-carbon low-alloy high-strength steel is relatively low. In the case of large-scale production, the production cost of automobiles can be reduced.

[0030] The pursuit of high strength is an important goal of low-carbon, low-alloy, high-strength steel, but while increasing strength, it often leads to a decrease in plasticity. After the strength reaches the requirement, the plasticity index is not ideal, which makes the steel prone to cracking, deformation and other problems during the processing and forming process, affecting its actual application range. At the same time, in order to obtain specific properties, more alloy elements such as nickel, molybdenum, and chromium are added. The prices of these alloy elements are relatively high, which leads to an increase in the production cost of steel. For example, some high-strength low-carbon, low-alloy, high-strength steels, in order to improve hardenability and strength, add a large amount of molybdenum, which greatly increases the cost of the steel and limits its application in some cost-sensitive fields.

[0031] In view of this, the present application provides a method for preparing cast steel to solve the problem that the existing plasticity index is not ideal, which makes the steel prone to cracking and deformation during the processing and forming process.

[0032] In a first aspect, the present application provides a method for preparing cast steel, comprising the following raw material compositions by mass fraction:

[0033] C: 0.15-0.20%, Mn: 0.7-0.9%, Si: 0.2-0.4%, Cr: 0.5-1.5%; P≤0.02%, S≤0.02%, the balance is Fe and unavoidable impurities;

[0034] The following steps are involved:

[0035] The raw materials of low-carbon low-alloy cast steel are melted, deoxidized and slag removed to obtain alloy melt;

[0036] Casting the alloy melt into a mold to obtain an alloy casting;

[0037] The alloy casting is normalized at 850-900°C and cooled to obtain cast steel parts.

[0038] In the present application, by reducing the content of Si, Mn, P, and S elements in the traditional low-carbon steel cast steel grades, the carbon content in the cast steel is not only low, but also the content of alloy elements is low, thereby reducing the cost of the cast steel. Among them, Mn has an obvious solid solution strengthening effect on ferrite, which can not only improve the strength of the steel, but also reduce the cold brittle transition temperature of the steel, and increase the amount of pearlite in the steel, further improving the strength. At the same time, in order to improve the strength and plasticity of the cast steel, the slag removal, deoxidation, and normalizing treatment are carried out by smelting, wherein the temperature of the normalizing treatment is 850 to 900°C, and a two-phase structure of pearlite and ferrite at room temperature is obtained. Slag removal during the smelting process ensures the cleanliness of the melt and reduces the inclusion content in the casting. The normalizing treatment process makes the structure of the cast steel more uniform and refined, the pearlite lamellar spacing is reduced, and the strength of the pearlite is related to the lamellar spacing. The smaller the lamellar spacing, the higher the strength. At the same time, normalizing can also eliminate some casting defects in the cast steel, such as Widmanstatten structure, thereby improving the strength and comprehensive performance of the cast steel. The mold forming process can be used to form parts with complex structures, reducing the cracking problem caused by the stamping process on cast steel. This application can reduce the alloy content while ensuring the strength and elongation of cast steel parts, reducing the cost of raw materials. At the same time, the preparation process is simple and does not require rolling. It can be used to manufacture complex-shaped automotive structural castings.

[0039] The temperature of the normalizing treatment includes, but is not limited to, 850°C, 860°C, 870°C, 880°C, 890°C or 900°C.

[0040] In combination with the first aspect, in some embodiments provided in the present application, the raw material of the low-carbon low-alloy cast steel is melted, deoxidized and slag-removed to obtain an alloy melt: the melting temperature is 1560-1600°C. The melting temperature within this range can achieve full dissolution and uniform distribution of alloy elements, avoid element burnout and increased steel liquid aspiration caused by excessively high temperature, and avoid problems such as poor fluidity and uneven chemical composition of the steel liquid caused by excessively low temperature. The melting temperature includes but is not limited to 1560°C, 1570°C, 1580°C, 1590°C or 1600°C.

[0041] In combination with the first aspect, in some embodiments provided in the present application, the raw material of low-carbon low-alloy cast steel is melted, deoxidized and slag removed to obtain the alloy melt: the slag removal method includes slag making and slag pushing using a slag making agent. Slag making and slag pushing using a slag making agent can ensure the cleanliness of the melt, reduce the inclusion content in the casting, and improve the strength of the cast steel.

[0042] In combination with the first aspect, in some embodiments provided in the present application, the slag-making agent slags and pushes the slag 3 to 5 times. The slag-making agent slags and pushes the slag 3 to 5 times within the above range, which can further ensure the cleanliness of the melt, reduce the inclusion content in the casting, and improve the strength of the cast steel.

[0043] In combination with the first aspect, in some embodiments provided in the present application, the raw material of the low-carbon low-alloy cast steel is melted, deoxidized and slag removed to obtain an alloy melt: the deoxidation method includes adding pure aluminum to the alloy melt for deoxidation. Adding pure aluminum to the alloy melt for deoxidation can reduce the probability of molten steel oxidation, improve the strength of the cast steel, and reduce oxide impurities.

[0044] In combination with the first aspect, in some embodiments provided in the present application, the alloy molten metal is molded to obtain an alloy casting: the pouring temperature of the mold is 1540-1580°C. The pouring temperature of the mold within this range can ensure the fluidity of the molten steel and the uniform chemical composition of the molten steel, without insufficient pouring, thermal cracking, shrinkage cavities and shrinkage defects. The pouring temperature of the mold includes but is not limited to 1540°C, 1550°C, 1560°C, 1570°C or 1580°C.

[0045] In combination with the first aspect, in some embodiments provided in the present application, the alloy molten metal is molded to obtain an alloy casting: the pouring time of the mold is 8 to 10 minutes. The pouring time of the mold within this range can make the molding smooth, the casting structure uniform, and the dimensional accuracy high, while improving production efficiency and reducing production costs. The pouring time of the mold includes but is not limited to 8 minutes, 8.5 minutes, 9 minutes, 9.5 minutes or 10 minutes.

[0046] In combination with the first aspect, in some embodiments provided in the present application, the alloy casting is normalized at 850-900°C and cooled to obtain a cast steel part: the holding time of the normalizing treatment is 2-4 hours. The holding time of the normalizing treatment within this range can make the structure of the cast steel more uniform and refined, the pearlite lamellar spacing smaller, and improve the strength of the cast steel. The holding time of the normalizing treatment includes but is not limited to 2 hours, 2.5 hours, 3 hours, 3.5 hours or 4 hours.

[0047] In combination with the first aspect, in some embodiments provided in the present application, the alloy casting is normalized at 850-900° C. and cooled to obtain a cast steel part, comprising:

[0048] The alloy casting surface is coated with high aluminum powder for hardening, and then normalized at 850-900°C and cooled to obtain cast steel parts.

[0049] By coating the surface of the alloy casting with high aluminum powder, hardening and drying it, and then normalizing it, a room temperature pearlite and ferrite dual phase structure can be obtained, which inhibits grain growth and makes the material still have high strength and toughness under the premise of low carbon and low alloying.

[0050] It should be noted that high alumina powder refers to a powder material with alumina as the main component. You can choose the high alumina powder product with a powder particle size of 180 mesh produced by Lushan County Xingjiao Rongtong Refractory Material Processing Plant.

[0051] In combination with the first aspect, in some embodiments provided in the present application, the alloy casting surface is coated with high aluminum powder and hardened, and then normalized and cooled at 850-900°C to obtain a cast steel part: the coating thickness of the high aluminum powder is 8-10 mm. Within this range, the coating thickness of the high aluminum powder can prevent oxidation of the casting, reduce decarburization, control and adjust the cooling rate, and achieve uniform cooling. The coating thickness of the high aluminum powder includes but is not limited to 8 mm, 8.5 mm, 9 mm, 9.5 mm or 10 mm.

[0052] In combination with the first aspect, in some embodiments provided in the present application, the alloy casting surface is coated with high aluminum powder for hardening, and then normalized at 850-900°C and cooled to obtain a cast steel part: the cooling method includes air cooling and spray cooling. The use of air cooling and spray cooling can reduce the problem of surface roughness caused by excessive surface oxidation and partial coarseness of crystal particles caused by uneven cooling.

[0053] The technical solution provided by the present application is described in detail below in conjunction with the embodiments and drawings. The modeling of this embodiment adopts investment molding. The die is designed and manufactured according to the shape and size of the casting, and the molten wax is pressed into the die. The wax solidifies and forms, and then is taken out of the die. The wax mold is immersed in a coating of refractory materials, and refractory materials such as coarse quartz sand are sprinkled on the wax mold group after the coating is dipped. The refractory material in the shell is solidified by a chemical hardening method to form a solid shell. The wax mold group that has completed the shell is heated to melt the internal wax mold and flow out of the shell. The dewaxed shell is placed in a roasting furnace for high-temperature roasting.

[0054] Example 1

[0055] Example 1 of the present application provides a method for preparing cast steel.

[0056] The raw materials include, by mass fraction, C: 0.17%; Si: 0.30%; Mn: 0.80%; Cr: 0.50%; P: 0.01%; S: 0.01%, and the balance is Fe and unavoidable impurity elements;

[0057] The method for preparing cast steel comprises the following steps:

[0058] Add scrap steel, ferromanganese, ferrosilicon and other raw materials into a medium frequency induction furnace, gradually increase the temperature slowly at first and then quickly, so that the charge is melted at an appropriate speed. After the charge is melted, scrape off the slag and use a slag-making agent to make new slag. Push the slag for deoxidation, and then prepare a test sample of the molten steel. After sampling, slag is made again, and the molten steel is covered with a slag-making agent to prevent oxidation of the molten steel and maintain the temperature of the molten steel at 1580°C. After the molten steel is tested, weigh the weight of various required alloys and add them to the furnace. Slag is made again, and 0.03% pure aluminum (mass proportion of the molten steel) is added to the furnace for pre-deoxidation. When the composition meets the expected settings and deoxidation is completed, steel tapping begins. When tapping, 0.01% pure aluminum (mass proportion of the molten steel) is added to the ladle for final deoxidation;

[0059] The steel is tapped at 1550°C, and the alloy melt is poured into the mold shell for 10 minutes. The casting is then air-cooled to room temperature to obtain a casting.

[0060] The poured ingot is normalized. During the heat treatment, the surface is coated with 9mm thick high aluminum powder, hardened and dried, and then put into the normalizing furnace. The normalizing temperature is set to 880℃, the holding time is set to 3 hours, the cooling time is 1 hour, and after being taken out of the furnace, it is air-cooled and spray-cooled to obtain cast steel parts.

[0061] Example 2

[0062] Example 2 of the present application provides a method for preparing cast steel.

[0063] The raw materials include, by mass fraction, C: 0.15%; Si: 0.20%; Mn: 0.70%; Cr: 1.00%; P: 0.015%; S: 0.015%, and the balance is Fe and unavoidable impurity elements;

[0064] The method for preparing cast steel comprises the following steps:

[0065] Add scrap steel, ferromanganese, ferrosilicon and other raw materials into a medium frequency induction furnace, gradually increase the temperature slowly at first and then quickly, so that the charge is melted at an appropriate speed. After the charge is melted, scrape off the slag and use a slag-making agent to make new slag. Push the slag for deoxidation, and then prepare a test sample of the molten steel. After sampling, slag is made again, and the molten steel is covered with a slag-making agent to prevent oxidation of the molten steel and maintain the temperature of the molten steel at 1560°C. After the molten steel is tested, weigh the weight of various required alloys and add them to the furnace. Slag is made again, and 0.03% pure aluminum (mass proportion of the molten steel) is added to the furnace for pre-deoxidation. When the composition meets the expected settings and deoxidation is completed, steel tapping begins. When tapping, 0.01% pure aluminum (mass proportion of the molten steel) is added to the ladle for final deoxidation;

[0066] The steel is tapped at 1540°C, and the alloy melt is poured into the mold shell for 10 minutes, and the casting is obtained after air cooling to room temperature;

[0067] The poured ingot is normalized, the normalizing temperature is set to 850℃, the holding time is set to 4 hours, and the cooling time is 2 hours. During the heat treatment, the surface is coated with 8mm thick high-aluminum powder, hardened and dried, and then put into the normalizing furnace. The normalizing temperature remains unchanged, and the holding time is extended for 30 minutes. After being taken out of the furnace, it is air-cooled and spray-cooled to obtain cast steel parts.

[0068] Example 3

[0069] Example 3 of the present application provides a method for preparing cast steel and a processing method thereof.

[0070] The raw materials include, by mass fraction, C: 0.20%; Si: 0.40%; Mn: 0.90%; Cr: 1.5%; P: 0.005%; S: 0.005%, and the balance is Fe and unavoidable impurity elements;

[0071] The method for preparing cast steel comprises the following steps:

[0072] Add scrap steel, ferromanganese, ferrosilicon and other raw materials into the medium frequency induction furnace, gradually increase the temperature slowly at first and then quickly, so that the charge is melted at an appropriate speed. After the charge is melted, scrape off the slag and use a slag-making agent to make new slag. Push the slag for deoxidation, and then prepare the test sample of the molten steel. After sampling, slag is made again, and the molten steel is covered with a slag-making agent to prevent oxidation of the molten steel and maintain the temperature of the molten steel at 1600°C. After the molten steel is tested, weigh the weight of various required alloys and add them to the furnace. Slag is made again, and 0.03% pure aluminum (mass proportion of the molten steel) is added to the furnace for pre-deoxidation. When the composition meets the expected settings and deoxidation is completed, steelmaking begins. When steelmaking is completed, 0.01% (mass proportion of the molten steel) pure aluminum is added to the ladle for final deoxidation;

[0073] The steel is tapped at 1560°C, and the alloy melt is poured into the mold shell for 10 minutes, and the casting is obtained after air cooling to room temperature;

[0074] The poured ingot is normalized, the normalizing temperature is set to 900℃, the holding time is set to 2 hours, and the cooling time is 1 hour. During the heat treatment, a 10mm thick high-aluminum powder is coated on the surface, hardened and dried, and then put into the normalizing furnace. The normalizing temperature remains unchanged, and the holding time is extended for 60 minutes. After being taken out of the furnace, it is air-cooled and spray-cooled to obtain cast steel parts.

[0075] Example 4

[0076] Example 4 of the present application provides a method for preparing cast steel.

[0077] The raw materials include, by mass fraction, C: 0.16%; Si: 0.25%; Cr: 0.75%; Mn: 0.85%; P: 0.01%; S: 0.01%, and the balance is Fe and unavoidable impurity elements;

[0078] The method for preparing cast steel comprises the following steps:

[0079] Add scrap steel, ferromanganese, ferrosilicon and other raw materials into the medium frequency induction furnace, gradually increase the temperature slowly at first and then quickly, so that the charge is melted at an appropriate speed. After the charge is melted, scrape off the slag and use a slag-making agent to make new slag. Push the slag for deoxidation, and then prepare the test sample of molten steel. After sampling, cover the molten steel with a slag-making agent to prevent oxidation of the molten steel and maintain the temperature of the molten steel at 1580°C. After the molten steel is tested, weigh the weight of various required alloys and add them to the furnace. Add 0.03% pure aluminum (mass proportion of molten steel) into the furnace for pre-deoxidation. When the temperature of the molten steel reaches 1590°C and the composition meets the expected setting, steel tapping begins after deoxidation is completed. When tapping, add 0.01% pure aluminum (mass proportion of molten steel) into the ladle for final deoxidation;

[0080] The steel is tapped at 1560°C, and the alloy melt is poured into the mold shell for 10 minutes, and the casting is obtained after air cooling to room temperature;

[0081] The cast ingot is normalized with the normalizing temperature set at 870°C, the holding time set at 2.5 hours, the cooling time set at 1.5 hours, and the ingot is air-cooled and spray-cooled after being taken out of the furnace to obtain cast steel parts.

[0082] Example 5

[0083] Example 5 of the present application provides a method for preparing cast steel.

[0084] The raw materials include, by mass fraction, C: 0.18%; Si: 0.35%; Cr: 1.25%; Mn: 0.75%; P: 0.01%; S: 0.01%, and the balance is Fe and unavoidable impurity elements;

[0085] The method for preparing cast steel comprises the following steps:

[0086] Add scrap steel, ferromanganese, ferrosilicon and other raw materials into a medium frequency induction furnace, gradually increase the temperature slowly at first and then quickly, so that the charge is melted at an appropriate speed. After the charge is melted, scrape off the slag and use a slag-making agent to make new slag. Push the slag for deoxidation, and then prepare a test sample of the molten steel. After sampling, keep the molten steel temperature at 1570°C. After the molten steel is tested, weigh the weight of various required alloys and add them to the furnace. When the molten steel temperature reaches 1570°C and the composition meets the expected settings, tapping begins after deoxidation is completed. When tapping, add 0.01% pure aluminum (as a percentage of the mass of the molten steel) to the ladle for final deoxidation;

[0087] The steel was tapped at 1540°C, and the alloy melt was poured into the mold shell for 9 minutes. The casting was obtained after air cooling to room temperature.

[0088] The poured ingot is normalized, the normalizing temperature is set to 890℃, the holding time is set to 3.5 hours, and the cooling time is 2 hours. During the heat treatment, the surface is coated with 8mm thick high-aluminum powder, hardened and dried, and then put into the normalizing furnace. The normalizing temperature remains unchanged, and the holding time is extended for 60 minutes. After being taken out of the furnace, it is air-cooled and spray-cooled to obtain cast steel parts.

[0089] Comparative Example 1

[0090] Comparative Example 1 of the present application provides a method for preparing cast steel. Comparative Example 1 is similar to Example 3, except that the normalizing temperature of Comparative Example 1 is 920°C.

[0091] Comparative Example 2

[0092] Comparative Example 2 of the present application provides a method for preparing cast steel. Comparative Example 2 is similar to Example 3, except that the normalizing temperature of Comparative Example 1 is 830°C.

[0093] Comparative Example 3

[0094] Comparative Example 3 of the present application provides a method for preparing cast steel. Comparative Example 3 is similar to Example 3, except that Comparative Example 3 does not undergo deoxidation and slag removal.

[0095] Performance Testing

[0096] The tensile strength, yield strength and elongation after fracture of the cast steel parts prepared in Examples 1 to 5 and Comparative Examples 1 to 3 were tested by quasi-static tensile testing after sampling the casting body. The measurement results are shown in Table 1. The cost reduction rate is compared with ZG310-570 grade cast steel with similar mechanical properties.

[0097] Table 1 Performance of cast steel parts obtained in Examples 1 to 5 and Comparative Examples 1 to 3

[0098] Tensile strength MPa Yield strength MPa Elongation after break % Cost reduction % Example 1 583 322 25 20 Example 2 552 308 23 14 Example 3 561 325 20 10 Example 4 573 311 21 17 Example 5 512 281 10 12 Comparative Example 1 424 202 14 20 Comparative Example 2 508 243 17 20 Comparative Example 3 320 140 6 20

[0099] Figure 1 The metallographic structure diagram of the cast steel part obtained in Example 1 is as follows: Figure 1 It can be seen that the pearlite of cast steel parts is uniform and the interlamellar spacing is small.

[0100] As can be seen from Table 1, the cast steel parts obtained in Examples 1 to 5 have a tensile strength of more than 550 MPa, a yield strength of more than 300 MPa, and an elongation after fracture of more than 20%. High-strength and tough low-carbon low-alloy steel is obtained, and no subsequent forging, rolling and other processes are required. It can be used to manufacture automotive parts with complex structures. The intermediate alloys required for smelting are widely available, the process is simple and easy to operate, and it has high strength and toughness and low cost.

[0101] In Comparative Example 1, due to the excessively high normalizing temperature, the room temperature microstructure of the alloy is coarse, the bulk tensile strength is only 424 MPa, the yield strength is 202 MPa, and the elongation after fracture is 14%.

[0102] In Comparative Example 2, due to the low normalizing temperature, the microstructure refinement effect is poor and the residual stress is not sufficiently eliminated. The tensile strength of the body is only 508 MPa, the yield strength is 243 MPa, and the elongation after fracture is 17%.

[0103] In Comparative Example 3, since deoxidation and slag removal were not performed, coarse and irregular slag inclusions existed in the room temperature microstructure of the alloy, the tensile strength of the alloy was only 320 MPa, the yield strength was 140 MPa, and the elongation after fracture was 6%.

[0104] In summary, by reducing the content of Si, Mn, P, and S elements in traditional low-carbon steel casting grades, the carbon content in the cast steel is not only low, but also the content of alloy elements is low, which reduces the cost of cast steel. Among them, Mn has an obvious solid solution strengthening effect on ferrite, which can not only improve the strength of steel, but also reduce the cold brittle transition temperature of steel, and increase the amount of pearlite in the steel, further improving the strength. At the same time, in order to improve the strength and plasticity of cast steel, smelting, deslagging, deoxidation, and normalizing treatment are carried out, and the temperature of normalizing treatment is 850-900℃ to obtain a two-phase structure of pearlite and ferrite at room temperature. Slag removal during the smelting process ensures the cleanliness of the melt and reduces the inclusion content in the casting. The normalizing process makes the structure of the cast steel more uniform and refined, and the pearlite lamellar spacing is reduced. The strength of pearlite is related to the lamellar spacing. The smaller the lamellar spacing, the higher the strength. At the same time, normalizing can also eliminate some casting defects in cast steel, such as Widmanstatten structure, thereby improving the strength and comprehensive performance of cast steel. The mold forming process can be used to form parts with complex structures, reducing the cracking problem caused by the stamping process on cast steel. The present application can reduce the alloy content while ensuring the strength and elongation of cast steel parts, thereby reducing the cost of raw materials.

[0105] In the description of this specification, the description with reference to the terms "one embodiment / method", "some embodiments / methods", "example", "specific example" or "some examples" etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment / method or example are included in at least one embodiment / method or example of the present application. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment / method or example. Moreover, the specific features, structures, materials or characteristics described may be combined in a suitable manner in any one or more embodiments / methods or examples. In addition, those skilled in the art may combine and combine the different embodiments / methods or examples described in this specification and the features of the different embodiments / methods or examples, unless they are contradictory.

[0106] It should be noted that, in the present application, relational terms such as "first" and "second" are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply that there is any such actual relationship or order between these entities or operations. Moreover, the terms "include", "comprise" or any other variants thereof are intended to cover non-exclusive inclusion, so that the process, method, article or equipment including a series of elements includes not only those elements, but also includes other elements not explicitly listed, or also includes elements inherent to such process, method, article or equipment. In the absence of more restrictions, the elements defined by the sentence "comprise one..." do not exclude the existence of other identical elements in the process, method, article or equipment including the elements. In the present application, the meaning of "multiple" is at least two, such as two, three, etc., unless otherwise clearly and specifically stipulated.

[0107] The above description is only a specific implementation of the present application, so that those skilled in the art can understand or implement the present application. Various modifications to these embodiments will be apparent to those skilled in the art, and the general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present application. Therefore, the present application will not be limited to the embodiments shown herein, but will conform to the widest range consistent with the principles and novel features applied for herein.

Claims

1. A method for preparing cast steel, characterized in that: The raw materials include the following by mass fraction: C: 0.15-0.20%, Mn: 0.7-0.9%, Si: 0.2-0.4%, Cr: 0.5-1.5%; P≤0.02%, S≤0.02%, the balance is Fe and unavoidable impurities; The following steps are involved: The raw materials of low-carbon low-alloy cast steel are melted, deoxidized and slag removed to obtain alloy melt; Casting the alloy melt into a mold to obtain an alloy casting; The alloy casting is normalized at 850-900°C and cooled to obtain cast steel parts.

2. The method for preparing cast steel according to claim 1, characterized in that: The raw materials of low-carbon low-alloy cast steel are melted, deoxidized and slag removed to obtain alloy melt: The smelting temperature is 1560~1600℃.

3. The method for preparing cast steel according to claim 1, characterized in that: The raw materials of low-carbon low-alloy cast steel are melted, deoxidized and slag removed to obtain alloy melt: The methods for removing slag include slag forming using slag forming agents and slag pushing.

4. The method for preparing cast steel according to claim 3, characterized in that: The slag-forming agent slags and pushes the slag 3 to 5 times.

5. The method for preparing cast steel according to claim 1, characterized in that: The raw materials of low-carbon low-alloy cast steel are melted, deoxidized and slag removed to obtain alloy melt: The deoxidation method includes adding pure aluminum to the alloy melt for deoxidation.

6. The method for preparing cast steel according to claim 1, characterized in that: The alloy melt is molded to obtain an alloy casting: The pouring temperature of the mold is 1540-1580°C; and / or, The pouring time of the mold is 8 to 10 minutes.

7. The method for preparing cast steel according to claim 1, characterized in that: The alloy casting is normalized at 850-900°C and cooled to obtain the cast steel parts: The holding time of normalizing treatment is 2 to 4 hours.

8. The method for preparing cast steel according to claim 1, characterized in that: The alloy casting is normalized at 850-900° C. and cooled to obtain a cast steel part, which comprises: The alloy casting surface is coated with high aluminum powder for hardening, and then normalized at 850-900°C and cooled to obtain cast steel parts.

9. The method for preparing cast steel according to claim 8, characterized in that: The alloy casting is coated with high aluminum powder on the surface for hardening, and then normalized at 850-900° C. and cooled to obtain the cast steel parts: The coating thickness of high alumina powder is 8 to 10 mm.

10. The method for preparing cast steel according to claim 8, characterized in that: The alloy casting is coated with high aluminum powder on the surface for hardening, and then normalized at 850-900° C. and cooled to obtain the cast steel parts: Cooling methods include air cooling and spray cooling.

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