Patent Application
20240035126
The present invention relates to the technical field of metallurgy and cast iron alloys, and particularly to a method for increasing the quality of graphite balls.
Nodular cast iron is widely used, and the roundness and size of the graphite balls in nodular cast iron are critical factors affecting its performance. It is well known that sulfur is a main factor causing poor nodularization of graphite, and the molten iron is required to have a sulfur content that is as low as possible to obtain round graphite balls. Where fine graphite balls are desired, ferrosilicon is required for inoculation. The nodularization allows graphite to grow spherically, and the inoculation increases the nucleation rate of graphite, ensuring the number and roundness of graphite balls. Therefore, the traditional nodularization technology includes desulfurization, and then nodularization and inoculation. For nodular cast iron with a thick and large cross-section, due to the long solidification time of molten iron after inoculation, the inoculation effect is gradually deteriorated, as shown by a decrease in the number of graphite balls per unit area of cast iron, the size of graphite balls is increased, and the degree of nodularization becomes worse, affecting the mechanical performances of castings.
Therefore, for nodular cast iron with a thick and large cross-section, to increase the number of graphite balls and improve the roundness of graphite balls, generally a multi-stage inoculation technology including ladle inoculation, ladle-to-ladle inoculation, in-stream inoculation, and in-mould inoculation is employed. The process is cumbersome, and difficult to control, and the nodularization effect is unstable.
Therefore, a method for producing nodular cast iron is desired, to solve the above problems.
To solve the above technical problems, the present invention provides a method for increasing the quality of graphite balls. In the method of the present invention, sulfur and rare earth are added in molten iron in advance, to produce a large amount of rare earth sulfide that forms a large number of nuclei of graphite crystallization, and then nodularization is performed, to extend the time of inoculation fade, and allow nodular cast iron with a thick and large cross-section to have good nodularization effect.
An object of the present invention is to provide a method for increasing the quality of graphite balls. The method specifically comprises the following steps: increasing the sulfur content in base molten iron in advance, and adding rare earth to a nodularizing unit previously, so that dispersed rare earth sulfide particles are formed during the nodularization process, wherein the rare earth sulfide particles serve as the nuclei of graphite crystallization to increase the number of graphite balls, and improve the roundness of graphite balls.
In an embodiment of the present invention, the nodularizing unit is a nodularizing ladle.
In an embodiment of the present invention, the rare earth is selected from the group consisting of cerium, a lanthanum-cerium alloy and a cerium-iron alloy and any combination thereof.
In an embodiment of the present invention, the rare earth is added to the nodularizing unit previously, and the molten iron is poured into the nodularizing unit and nodularized, wherein the rare earth covers the surface of a nodularizer.
In an embodiment of the present invention, the temperature change in the nodularization process is such that the molten iron is heated to 1500° C., held for 4 min, and then cooled to 1450° C. at which the molten iron is poured into the nodularizing ladle and nodularized.
In an embodiment of the present invention, the sulfur content is increased by adding sulfur or ferric sulfide.
In an embodiment of the present invention, the rare earth accounts for 0.01-0.08 wt % of the molten iron.
In an embodiment of the present invention, the sulfur content in the sulfur-increased molten iron is 0.03-0.07 wt %.
In an embodiment of the present invention, the raw material of the base molten iron is selected from steel scrap and recycled scrap; the steel scrap is selected from carbon steel and/or alloy steel. The sources of steel scrap include, but are not limited to, scraps of stamping parts, for example, scraps of automobile stamping parts. The use of steel scraps as a raw material can avoid the hereditary effects of pig iron as a raw material.
In an embodiment of the present invention, the steel scrap in the raw material accounts for 50-100 wt %, and the recycled scrap accounts for 0-50 wt %.
In an embodiment of the present invention, the method further comprises adding ferrosilicon, and a recarburizer to the base molten iron, to give a carbon content of 3.6-4.0 wt % and a silicon content of 1.8-2.1 wt % in the molten iron.
In an embodiment of the present invention, the method further comprises adding ferromanganese to the molten iron after nodularization, wherein the ferromanganese has a particle size of 5 to 15 mm.
In an embodiment of the present invention, the manganese content in the molten iron is 0.4-0.6 wt %.
In an embodiment of the present invention, the method for increasing number of graphite balls and improving the roundness of graphite balls in nodular cast iron comprises the following operations:
Steel scrap and recycled scrap are used as main raw materials and melted to produce nodular cast iron in During melting, an electric furnace. Ferrosilicon, a recarburizer, sulfur powder (or ferric sulfide), and rare earth are added, where the molten iron is controlled to have a carbon content of 3.6-4.0 wt %, a silicon content of 1.8-2.1 wt %, a sulfur content of 0.03-0.07 wt %, and a rare earth content of 0.01 wt %-0.08 wt %. The method comprises specifically the following steps:
Compared with the prior art, the technical solution of the present invention has the following advantages:
In view of the problems of reduced number of graphite balls and poor roundness of graphite balls, caused by inoculation fade during the nodularization of nodular iron castings with a thick and large cross-section, the traditional ideal of desulfurization and then nodularization and inoculation in the production of nodular cast iron is overturned in the present invention. Instead, sulfur and rare earth are added in molten iron in advance, to produce a large amount of rare earth sulfide that forms a large number of nuclei of graphite crystallization, and then nodularization is performed, to extend the time of inoculation fade, and allow nodular cast iron with a thick and large cross-section to have good nodularization effect.
Sulfur in molten iron can react with rare earth to form rare earth sulfide and also react with manganese to form manganese sulfide; and large manganese sulfide is difficult to be used as the nuclei of graphite nucleation, and reduces the mechanical performances of the material. Therefore, in the present invention, sulfur and rare earth are added before nodularization, to form fine rare earth sulfide acting as the nuclei of graphite balls. After nodularization, ferromanganese is added, to reduce the formation of manganese sulfide inclusions.
By using the method for increasing the quality of graphite balls according to the present invention, the obtained thick and large castings of 200 mm×200 mm×200 mm have a nodularization rate of graphite balls increased by 20% or more at the surface and in the core, a diameter of graphite balls increased by 1 grade, and a number of graphite balls per unit area increased by 50% or more.
To make the disclosure of the present invention more comprehensible, the present invention will be further described in detail by way of specific embodiments of the present invention with reference the accompanying drawings, in which:
The present invention will be further described below with reference to the accompanying drawings and specific examples, so that those skilled in the art can better understand and implement the present invention; however, the present invention is not limited thereto.
The materials such as ferrosilicon, the recarburizer, ferrosulfur, the rare earth alloy, and the nodularizer etc. used in the present invention are all commercially available.
To enhance the effect of nodularization and inoculation of nodular cast iron, the present invention provides a method for increasing the quality of graphite balls. The method comprises the following steps.
Steel scrap and recycled scrap are used as raw materials and melted to produce nodular cast iron. The sources of steel scrap include, but are not limited to, scraps of stamping parts, for example, scraps of automobile stamping parts. The steel scrap may be carbon steel, alloy steel or a mixture of thereof. The use of steel scraps as a raw material can avoid the hereditary effects of pig iron as a raw material.
After the steel scrap and recycled scrap are melted, ferrosilicon and a recarburizer are added to adjust the components in molten iron, and the sulfur content in the base molten iron in the electric furnace is increased to adjust the sulfur content in the base molten iron to 0.03%-0.07%. Rare earth is added before nodularization, to allow the molten iron to have a cerium content reaching 0.01%-0.08%, and a manganese content of 0.4-0.6 wt %. After nodularization, ferromanganese is added to the molten iron, and then a casting is formed by casting according to a conventional procedure.
This example provides a method for increasing the quality of graphite balls. The method comprises the following steps:
This example provides a method for increasing the quality of graphite balls. The method comprises the following steps:
This example provides a method for increasing the quality of graphite balls. The method comprises the following steps:
This example provides a method for increasing the quality of graphite balls. The method comprises the following steps:
This example provides a method for increasing the quality of graphite balls. The method comprises the following steps:
(1) In the comparative example, nodular cast iron is produced according to an existing conventional technology. That is, pig iron, steel scrap, and recycled scrap are used as raw materials, and the sulfur content is controlled to be low. Ferrosilicon is added during the melting process for inoculation, followed by nodularization and casting of a nodular cast iron specimen of 200 mm×200 mm×200 mm. The carbon content, silicon content, and manganese content are controlled according to the ranges in the examples; and the sulfur content is ≤0.03 wt %.
(2) The comparative example differs from the examples mainly in that the molten iron is subjected to sulfur-increasing treatment in the electric furnace in the examples, rare earth is added to molten iron before nodularization, and ferromanganese is added to molten iron after nodularization. In the comparative example, the sulfur content is controlled to be low, and no rare earth is added before nodularization.
(3) In the comparative example, pig iron, steel scrap and recycled scrap are used as raw materials specific proportion of the raw materials is 50 wt % pig iron+30 wt % carbon steel scrap+20 wt % recycled scrap. A material list is formulated, and entered into an automatic material weighing system; and the materials are automatically weighed, added to an electric furnace, and melted.
(4) Ferrosilicon, ferromanganese, and a recarburizer are added during the melting process of molten iron. After melting, a sample is taken and analyzed, and the components in molten iron are adjusted to have a carbon content of 3.6 wt %, a silicon content of 2.1 wt %, and a manganese content of 0.4 wt %; and the sulfur content in molten iron is detected to be 0.02 wt %.
(5) The molten iron is heated to 1500° C., held for 4 min, and then cooled to 1450° C. at which the molten iron is poured into the nodularizing ladle previously added with the nodularizer and nodularized.
(6) After nodularization, the molten iron is casted to form a nodular cast iron specimen of 200 mm×200 mm×200 mm.
(1) In the comparative example, nodular cast iron is produced according to an existing conventional technology. Steel scrap, and recycled scrap are used as raw materials, and the sulfur content is controlled to be low. Ferrosilicon is added during the melting process for inoculation, followed by nodularization and casting of a nodular cast iron specimen of 200 mm×200 mm×200 mm. The carbon content, silicon content, and manganese content are controlled according to the ranges in the examples; and the sulfur content is ≤0.02 wt %.
(2) The comparative example differs from the examples mainly in that the molten iron is subjected to sulfur-increasing treatment in the electric furnace in the examples, rare earth is added to molten iron before nodularization, and ferromanganese is added to molten iron after nodularization. In the comparative example, the sulfur content is controlled to be low, and no rare earth is added before nodularization.
(3) In the comparative example, steel scrap and recycled scrap are used as raw materials, and specific proportion of the raw materials is 70 wt % carbon steel scrap+30 wt % recycled scrap. A material list is formulated, and entered into an automatic material weighing system; and the materials are automatically weighed, added to an electric furnace, and melted.
(4) Ferrosilicon, ferromanganese, and a recarburizer are added during the melting process of molten iron. After melting, a sample is taken and analyzed, and the components in molten iron are adjusted to have a carbon content of 4.0 wt %, a silicon content of 1.8 wt %, and a manganese content of 0.6 wt %; and the sulfur content in molten iron is detected to be 0.015 wt %.
(5) The molten iron is heated to 1500° C., held for 4 min, and then cooled to 1450° C. at which the molten iron is poured into the nodularizing ladle previously added with the nodularizer and nodularized.
(6) After nodularization, the molten iron is casted to form a nodular cast iron specimen of 200 mm×200 mm×200 mm.
(1) In this comparative example, waste steel alone is used as raw material, and the sulfur content is controlled to be extremely low. Ferrosilicon is added during the melting process for inoculation, followed by nodularization and casting of a nodular cast iron specimen of 200 mm×200 mm×200 mm. The carbon content, silicon content, and manganese content are controlled according to the ranges in the examples; and the sulfur content is ≤0.01 wt %.
(2) The comparative example differs from the examples mainly in that the molten iron is subjected to sulfur-increasing treatment in the electric furnace in the examples, rare earth is added to molten iron before nodularization, and ferromanganese is added to molten iron after nodularization. In the comparative example, the sulfur content is controlled to be extremely low, and no rare earth is added before nodularization.
(3) In the comparative example, waste steel alone is used as raw material, and specific proportion of the raw material is 100 wt % carbon steel scrap. A material list is formulated, and entered into an automatic material weighing system; and the materials are automatically weighed, added to an electric furnace, and melted.
(4) Ferrosilicon, ferromanganese, and a recarburizer are added during the melting process of molten iron. After melting, a sample is taken and analyzed, and the components in molten iron are adjusted to have a carbon content of 3.8 wt %, a silicon content of 2.0 wt %, a manganese content of 0.5 wt %; and the sulfur content in molten iron is detected to be 0.008 wt %.
(5) The molten iron is heated to 1500° C., held for 4 min, and then cooled to 1450° C. at which the molten iron is poured into the nodularizing ladle previously added with the nodularizer and nodularized.
(6) After nodularization, the molten iron is casted to form a nodular cast iron specimen of 200 mm×200 mm×200 mm.
The nodularization effects of graphite in each part of the nodular iron castings of 200 mm×200 mm×200 mm obtained in the above examples and comparative examples are shown in Table 1.
The test samples are taken from 4 surface positions and a central part of a cubic nodular iron casting of 200 mm×200 mm×200 mm, respectively. The 4 surface samples are numbered 1, 2, 3, and 4, and the central sample is numbered 5, as shown in Table 1 below.
According to GB/T9441 “Metallographic Test for Spheroidal Graphite Cast Iron” in connection with image analysis, the nodularization rate, the ball diameter and the number density of graphite in the sample are determined.
In the above table 1, E1 refers to Example 1, E2 refers to Example 2, E3 refers to Example 3, E4 refers to Example 4, and Average refers to the average of Examples 1-4; CE1 refers to Comparative Example 1, CE2 refers to Comparative Example 2, CE3 refers to Comparative Example 3, and Average′ refers to the average of Comparative Examples 1-3. As can be seen from Table 1, the method for increasing the quality of graphite balls has a nodularization effect that is obviously better than the existing common methods. For a thick and large casting, the nodularization rate is increased by 20% or more, the diameter is increased by 1 grade, and the number density of graphite is increased by 50% or more.
Apparently, the above-described embodiments are merely examples provided for clarity of description, and are not intended to limit the implementations of the present invention. Other variations or changes can be made by those skilled in the art based on the above description. The embodiments are not exhaustive herein. Obvious variations or changes derived therefrom also fall within the protection scope of the present invention.
| Number | Date | Country | Kind |
|---|---|---|---|
| 502566 | Jul 2022 | LU | national |
