阅读说明：本技术 一种高强度灰铸铁件的生产方法 (Production method of high-strength gray iron casting ) 是由 陈孝先 苏少静 宋亮 韩军 戚梦林 于 2021-08-26 设计创作，主要内容包括：本发明属于铸造技术领域,主要涉及一种高强度灰铸铁件的生产方法,包括以下步骤：熔炼,称取60％～65％废钢、30％～35％回炉铁、5％～10％生铁加入电炉中,加热升温至全部加入料熔化；调整铁水化学成分；调整完成后进行铁水过热处理；一次孕育,过热处理后的铁水中加入孕育剂,铁水与孕育剂反应,进行一次孕育；二次孕育,一次孕育后的铁水中加入球化剂,铁水与球化剂反应,进行二次孕育；浇注,二次孕育后的铁水进行拔渣、浇注,得到灰铸铁件。本发明通过两次孕育配合、合理的化学成分控制,使得所述灰铸铁件不经过锰、铬、锑等元素的合金强化就能达到高强度要求,避免灰铸铁件热节处的缩松、缩孔缺陷。(The invention belongs to the technical field of casting, and mainly relates to a production method of a high-strength gray iron casting, which comprises the following steps: smelting, namely weighing 60-65% of scrap steel, 30-35% of returning iron and 5-10% of pig iron, adding into an electric furnace, heating and raising the temperature until all the added materials are melted; adjusting the chemical components of molten iron; carrying out molten iron overheating treatment after the adjustment is finished; performing primary inoculation, namely adding an inoculant into the overheated molten iron, reacting the molten iron with the inoculant, and performing primary inoculation; secondary inoculation, namely adding a nodulizer into the molten iron subjected to the primary inoculation, and reacting the molten iron with the nodulizer to perform secondary inoculation; and (4) pouring, wherein slag is pulled out from the molten iron after secondary inoculation, and pouring is carried out to obtain the gray iron casting. According to the invention, through two-time inoculation matching and reasonable chemical component control, the gray iron casting can meet the high strength requirement without alloy reinforcement of elements such as manganese, chromium, antimony and the like, and the defects of shrinkage porosity and shrinkage cavity at the hot spot of the gray iron casting are avoided.)

1. The production method of the high-strength gray iron casting is characterized by comprising the following steps of:

smelting, namely weighing 60-65% of scrap steel, 30-35% of return iron and 5-10% of pig iron, adding into an electric furnace, heating and raising the temperature until all the added materials are melted; adjusting the chemical components of the molten iron; carrying out molten iron overheating treatment after the adjustment is finished;

performing primary inoculation, namely adding an inoculant into the overheated molten iron, reacting the molten iron with the inoculant, and performing primary inoculation;

secondary inoculation, namely adding a nodulizer into the molten iron subjected to the primary inoculation, and reacting the molten iron with the nodulizer to perform secondary inoculation;

and (4) pouring, wherein slag is pulled out from the molten iron after secondary inoculation, and pouring is carried out to obtain the high-strength gray iron casting.

2. The method for producing high-strength gray iron castings according to claim 1, wherein the scrap, the return iron, and the pig iron are added to an electric furnace in the order of scrap, return iron, and pig iron.

3. The method for producing high-strength gray iron castings according to claim 1, wherein the inoculant is previously put into an inoculating hopper provided in an inoculating tank before the primary inoculation; transferring the molten iron after the overheating treatment to the inoculation groove, opening the inoculation hopper when the molten iron enters the inoculation groove, and adding the inoculant into the molten iron.

4. The method for manufacturing high-strength gray iron castings according to claim 1, wherein said nodulizing agent is embedded in the bottom of a ladle in advance before said secondary inoculation, and the primarily inoculated molten iron is transferred to a ladle to be brought into contact with the nodulizing agent embedded in the bottom of the ladle.

5. The method for producing high-strength gray iron castings according to claim 1, wherein the chemical composition of the high-strength gray iron castings comprises, by mass, 3.3-3.5% of C, 1.8-2.0% of Si, 0.6-0.9% of Mn, 0.07-0.12% of S, 0.03% or less of P, 0.5-0.6% of Cu, 0.011% or less of Mg, and the balance of Fe and impurity elements.

6. The method for producing a high-strength gray iron casting according to claim 1, wherein the temperature of the hot metal is 1490 ℃ to 1510 ℃ and the holding time is 3 to 5 minutes.

7. The method for producing high-strength gray iron castings according to claim 1, wherein the nodulizer is a rare earth nodulizer; the chemical components of the rare earth nodulizer comprise 44-48% of Si, less than 0.4% of Mn, less than 0.5% of Ti, 7-9% of Mg, less than 1.0% of MgO, 3.5-4.5% of RE, and the balance of Fe and impurity elements.

8. The method for producing high-strength gray iron castings according to claim 7, wherein the weight of the rare earth nodulizer is 0.15-0.2% of the amount of iron tapped from molten iron after melting.

9. The method of producing high strength gray iron castings according to claim 1, wherein said inoculant is a silicon-barium inoculant; the chemical components of the silicon-barium inoculant comprise 66-72% of Si, 4-6% of Ba, less than 1.5% of Ca, less than 1.5% of Al and the balance of Fe and impurity elements.

10. The method for producing high-strength gray iron castings according to claim 9, wherein the weight of the silicon-barium inoculant is 0.4-0.5% of the iron yield of the molten iron after smelting.

Technical Field

The invention belongs to the technical field of casting, and mainly relates to a production method of a high-strength gray iron casting.

Background

The gray cast iron is widely applied to the aspects of machinery, metallurgy and the like by virtue of the unique metallographic structure and performance characteristics. The method is particularly applied to key parts of heavy engineering machinery, the heavy engineering machinery has higher requirements on properties such as strength, hardness and the like of the gray iron castings, but the gray iron castings have the defects of heavy tonnage, large section thickness, low cooling speed, large and thick graphite, substandard performance and the like. When producing gray iron castings, ferrosilicon or silicon barium inoculants are generally adopted, and the gray iron is inoculated by methods such as a punching method and a secondary inoculation groove. For high-strength gray iron castings, the strength requirement is met by alloy strengthening through elements such as manganese, chromium and antimony, but the alloy strengthening mode has a series of defects of increasing shrinkage of the gray iron castings, increasing cost and the like, and even the defects of shrinkage porosity, shrinkage cavity and the like at the heat joint of the thick-wall iron castings.

Disclosure of Invention

The invention aims to solve the technical problems and provides a production method of high-strength gray iron castings, so that the high-strength gray iron castings can be produced without alloy strengthening of elements such as manganese, chromium, antimony and the like, the defects of shrinkage porosity, shrinkage cavity and the like at the hot junctions of the high-strength gray iron castings are avoided, and the casting cost is saved.

In order to achieve the purpose, the technical scheme of the invention is as follows:

a production method of high-strength gray iron castings comprises the following steps:

the method comprises the following steps: smelting, namely weighing 60-65% of scrap steel, 30-35% of returning iron and 5-10% of pig iron, adding into an electric furnace, heating and raising the temperature until all the added materials are melted; adjusting the chemical components of molten iron; carrying out molten iron overheating treatment after the adjustment is finished;

step two: performing primary inoculation, namely adding an inoculant into the overheated molten iron, reacting the molten iron with the inoculant, and performing primary inoculation;

step three: secondary inoculation, namely adding a nodulizer into the molten iron subjected to the primary inoculation, and reacting the molten iron with the nodulizer to perform secondary inoculation;

step four: and (4) pouring, wherein slag is pulled out from the molten iron after secondary inoculation, and pouring is carried out to obtain the high-strength gray iron casting.

Specifically, the pig iron is added into the electric furnace in the step one to increase the purity and nucleation capability of molten iron, and the recycled iron is added into the electric furnace to save the production cost.

Further, the scrap steel, the recycled iron and the pig iron are added into the electric furnace in sequence; the recycled iron and the pig iron contain graphite, and the pig iron contains the largest amount of graphite in the three materials; the scrap steel, the recycled iron and the pig iron are sequentially added into the electric furnace, so that the purity of molten iron can be guaranteed, the nucleation capability of the molten iron can be improved by graphite in the recycled iron and the pig iron, the quality of the molten iron is improved, and high-strength gray iron castings with excellent quality can be finally obtained by pouring.

Further, before the primary inoculation, the inoculant is put into an inoculation hopper arranged in an inoculation groove in advance; transferring the molten iron after the overheating treatment to the inoculation groove, opening the inoculation hopper when the molten iron enters the inoculation groove, and adding the inoculant into the molten iron; the inoculant reacts with molten iron to perform primary inoculation.

Further, before the secondary inoculation, the nodulizer is embedded at the bottom of a casting ladle in advance, the molten iron after the primary inoculation is transferred to the casting ladle and is contacted with the nodulizer embedded at the bottom of the casting ladle for secondary inoculation.

Furthermore, the melting temperature of scrap steel, return iron and pig iron is less than 1380 ℃.

Further, the sampling temperature for the chemical composition detection sample is 1470 ℃ to 1490 ℃.

Furthermore, the chemical components of the high-strength gray iron casting comprise, by mass, 3.3% -3.5% of C, 1.8% -2.0% of Si, 0.6% -0.9% of Mn, 0.07% -0.12% of S, less than or equal to 0.03% of P, 0.5% -0.6% of Cu, less than or equal to 0.011% of Mg, and the balance of Fe and impurity elements.

Specifically, if the detection result of the chemical components of the molten iron does not meet 3.3-3.5% of C, 1.8-2.0% of Si, 0.6-0.9% of Mn, 0.07-0.12% of S, less than or equal to 0.03% of P, 0.5-0.6% of Cu, less than or equal to 0.011% of Mg, and the balance of Fe and impurity elements; adjustment should be made until the chemical composition of the molten iron meets the requirements.

Further, the temperature of the molten iron overheating treatment is 1490-1510 ℃, and the heat preservation time is 3-5 minutes.

Further, the nodulizer is a rare earth nodulizer; the chemical components of the rare earth nodulizer comprise 44-48% of Si, less than 0.4% of Mn, less than 0.5% of Ti, 7-9% of Mg, less than 1.0% of MgO, 3.5-4.5% of RE, and the balance of Fe and impurity elements.

Further, the weight of the rare earth nodulizer is 0.15-0.2% of the iron yield of molten iron after smelting.

Further, the inoculant is a silicon-barium inoculant; the chemical components of the silicon-barium inoculant comprise 66-72% of Si, 4-6% of Ba, less than 1.5% of Ca, less than 1.5% of Al and the balance of Fe and impurity elements.

Further, the weight of the silicon-barium inoculant is 0.4-0.5% of the iron yield of molten iron after smelting.

Further, the pouring time of the high-strength gray iron casting is within 10 minutes so as to avoid inoculation fade.

According to the technical scheme, the invention has the advantages and positive effects that:

according to the invention, the nodulizer is pre-embedded at the bottom of the ladle, the molten iron after primary inoculation is transferred to the ladle and reacts with the nodulizer at the bottom of the ladle for secondary inoculation, so that the inoculation effect is further enhanced, and inoculation recession is effectively prevented. In the secondary inoculation process, a small amount of magnesium element contained in the nodulizer is gasified, and the gasification promotes the rolling of molten iron, so that the secondary inoculation is uniform, and the inoculation effect is enhanced.

According to the invention, through reasonable chemical component control, the interaction among all elements is fully exerted, so that the intensity performance of the cast gray iron casting is excellent, the hardness drop is small, the stability is high, the gray iron casting produced by adopting the technical scheme of the invention is sampled and detected at the wall thickness of 50-60 mm, and the tensile strength is more than or equal to 320 MPa.

Drawings

FIG. 1 is a metallographic structure picture of an unetched state of a gray iron casting produced using only a silicon-barium inoculant;

FIG. 2 is a metallographic structure picture of etched state of a gray iron casting produced by using only a silicon-barium inoculant;

FIG. 3 is a metallographic structure picture of an unetched state of a gray iron casting, which is subjected to primary inoculation and secondary inoculation by using a silicon-barium inoculant and a rare earth nodulizer respectively;

FIG. 4 is a metallographic structure picture of an etched state of a gray iron casting, which is subjected to primary inoculation and secondary inoculation by using a silicon-barium inoculant and a rare earth nodulizer respectively.

Detailed Description

To facilitate an understanding of the invention, the invention will now be described more fully with reference to the accompanying drawings. Preferred embodiments of the present invention are shown in the drawings. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete.

For further explanation of the principles and construction of the present invention, reference will now be made in detail to the preferred embodiments of the present invention, which are illustrated in the accompanying drawings.

The invention provides a comparative example, as shown in figure 1-2, in the prior art, only a silicon-barium inoculant is used for inoculation to produce a gray iron casting with a material of HT350, a casting body is sampled, metallographic detection shows that A-type graphite is not uniformly distributed, the graphite is longer, and after being etched by 4% nitric acid alcoholic solution, a matrix structure not only contains pearlite, but also contains a small amount of white ferrite.

The invention provides a comparative example, which is used for a gray iron casting of an engine product accessory, wherein a sample is taken at a position with the wall thickness of 50-60 mm, and the tensile strength is required to be more than or equal to 300 MPa. The wall thickness of the HT350 material iron casting is regulated to be 40-80 mm in the GB/T9439-. Therefore, the gray iron castings used for engine product accessories belong to the super-specification high-strength iron castings. And the gray iron casting used for the engine product fittings requires nondestructive testing, and shrinkage porosity and shrinkage cavity defects are not allowed. The requirement that the tensile strength is more than or equal to 300MPa at the position with the wall thickness of 50-60 mm can be met by adding alloy and/or reducing the carbon equivalent, but shrinkage porosity defects exist at the hot spot of a gray iron casting used for engine product accessories, so that batch scrap is caused.

The embodiment of the invention discloses a production method of a high-strength gray iron casting, which comprises the following specific steps:

the method comprises the following steps: raw materials, 1851kg of scrap steel, 942kg of return iron and 172kg of grey pig iron were weighed.

Step two: 1851kg of scrap steel, 942kg of return iron and 172kg of gray pig iron are sequentially and rapidly added into a 3T medium frequency electric furnace continuously for smelting, and the last addition of the gray pig iron is to ensure the core of molten iron after smelting. The temperature in the melting process is less than 1380 ℃, the temperature is raised to 1475 ℃ after the melting is finished, samples are taken from the molten iron for chemical component detection, and the detection result is 3.36 percent of C and 1.41 percent of Si; 0.87% Mn; 0.0285% P; 0.11% S; 0.014% Cu; mg is less than 0.0010 percent, the content of C, Mn, P, S and Mg in the chemical composition detection result meet the process requirements, 2kg of 75# ferrosilicon and 16kg of copper are added for chemical composition adjustment, the chemical composition of the adjusted molten iron meets 3.3 to 3.5 percent of C, 1.8 to 2.0 percent of Si, 0.6 to 0.9 percent of Mn, 0.07 to 0.12 percent of S, less than or equal to 0.03 percent of P, 0.5 to 0.6 percent of Cu, less than or equal to 0.011 percent of Mg, and the balance of Fe and impurity elements. And (4) after the chemical components of the molten iron are detected to be qualified, carrying out molten iron overheating treatment, heating the molten iron to 1504 ℃, and preserving the heat for 3 minutes.

Step three: tapping after the molten iron is subjected to overheating treatment, wherein the tapping amount is 1500 kg;

step four: weighing 3kg of rare earth nodulizer and 7kg of silicon-barium inoculant; 7.5kg of silicon-barium inoculant is placed in advance in an inoculation hopper arranged in an inoculation groove, and 3kg of rare earth inoculant is buried in advance in the bottom of a ladle.

Step five: transferring the molten iron to an inoculation groove, opening an inoculation hopper when the molten iron enters the inoculation groove, and reacting the molten iron with a silicon-barium inoculant which is put into the inoculation hopper in advance to perform primary inoculation on the molten iron.

Specifically, when the molten iron is fully contacted with the silicon-barium inoculant put into the inoculation hopper in advance, Si, Ba, Al and Ca elements in the silicon-barium inoculant react with O, S elements in the molten iron to form sulfides and oxides, and the sulfides and oxides of the Si, Ba, Al and Ca elements can be used as the cores of the graphite. The mechanical properties of the high-strength gray iron casting described in this example are largely dependent on its microstructure; the adding amount of the silicon-barium inoculant used in the primary inoculation treatment is only 0.46 percent of the iron yield, the influence on the chemical components of the high-strength gray iron casting is small, but the influence on the microstructure of the high-strength gray iron casting is large, the graphite form of the high-strength gray iron casting is A-type graphite, the eutectic cell nucleation is facilitated, and the number of eutectic cells is increased.

Step six: and transferring the molten iron after the primary inoculation to a casting ladle, reacting with a rare earth nodulizer embedded into the bottom of the casting ladle in advance, and performing secondary inoculation.

Specifically, the addition amount of the rare earth nodulizer used for secondary inoculation is 0.2 percent of the iron yield of molten iron after smelting, has little influence on the chemical components of the high-strength gray iron casting, but has great influence on the microstructure of the high-strength gray iron casting; the rare earth elements in the rare earth nodulizer have the functions of passivating graphite and forming a rare earth compound to serve as a graphite core in the secondary inoculation process, so that the inoculation effect is enhanced; a small amount of Mg element contained in the rare earth nodulizer is gasified, and the gasification promotes the rolling of molten iron, so that the secondary inoculation is uniform, and the inoculation effect is further enhanced; after the Mg element in the rare earth nodulizer is gasified, the residual Mg element is not enough to vermiculize the flake graphite, and only the effects of trace amount of curling and flake graphite thinning are achieved, so that the graphite form of the high-strength gray iron casting is fine and uniformly distributed a-type graphite.

Step seven: and after the secondary inoculation is finished, drawing slag from molten iron, pouring a casting, wherein the pouring time is 8 minutes after the secondary inoculation is finished.

The embodiment of the invention discloses a production method of a high-strength gray iron casting, wherein the chemical composition percentage content of the produced high-strength gray iron casting comprises 3.32% of C, 1.97% of Si, 0.86% of Mn, 0.0285% of P, 0.10% of S, 0.53% of Cu, 0.0039% of Mg, and the balance of Fe and impurity elements. Sampling is carried out at the position of 50-60 mm of the wall thickness of the high-strength gray iron casting, and a tensile test is carried out, wherein the detection result of the tensile strength is 328 MPa. As shown in fig. 3-4, samples were taken at the positions of 50-60 mm of the high-strength gray iron casting in the embodiment, and metallographic examination was performed, the a-type graphite was uniformly distributed, the graphite length was significantly shorter than that of the gray iron casting produced only with the silicon barium inoculant in fig. 1, after etching with 4% nital solution, the matrix structure was 100% pearlite, no ferrite, no carbide, and uniform pearlite lamellar spacing distribution. The difference of the Brinell hardness between the thin wall and the thick wall of the high-strength gray iron casting is less than 20 HB. The high-strength gray iron casting is subjected to nondestructive testing, and shrinkage porosity and shrinkage cavity defects are not found. The high-strength gray iron casting has small hardness fall and high performance stability while ensuring high strength, and has no shrinkage porosity and shrinkage cavity defects in nondestructive testing.

The embodiment of the invention discloses a production method of high-strength gray iron castings, wherein 5000 more high-strength gray iron castings are produced by using the method, nondestructive testing of the castings is carried out, mechanical property detection and metallographic detection of the thick walls of the castings are carried out, and the qualification rate is up to more than 90%.

The above-mentioned embodiments only express the specific embodiments of the present invention, and the description thereof is more specific and detailed, but not construed as limiting the scope of the invention. It should be noted that, for a person skilled in the art, several variations and modifications can be made without departing from the inventive concept, which falls within the scope of the present invention. Therefore, the protection scope of the present patent shall be subject to the appended claims.