LU502566B1 - Method for increasing number of graphite balls and improving roundness of graphite balls in nodular cast iron - Google Patents
Method for increasing number of graphite balls and improving roundness of graphite balls in nodular cast iron Download PDFInfo
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- LU502566B1 LU502566B1 LU502566A LU502566A LU502566B1 LU 502566 B1 LU502566 B1 LU 502566B1 LU 502566 A LU502566 A LU 502566A LU 502566 A LU502566 A LU 502566A LU 502566 B1 LU502566 B1 LU 502566B1
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- molten iron
- rare earth
- graphite
- iron
- graphite balls
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- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 title claims abstract description 86
- 229910002804 graphite Inorganic materials 0.000 title claims abstract description 67
- 239000010439 graphite Substances 0.000 title claims abstract description 67
- 229910001141 Ductile iron Inorganic materials 0.000 title claims abstract description 52
- 238000000034 method Methods 0.000 title claims abstract description 45
- XEEYBQQBJWHFJM-UHFFFAOYSA-N Iron Chemical compound [Fe] XEEYBQQBJWHFJM-UHFFFAOYSA-N 0.000 claims abstract description 198
- 229910052742 iron Inorganic materials 0.000 claims abstract description 99
- NINIDFKCEFEMDL-UHFFFAOYSA-N Sulfur Chemical compound [S] NINIDFKCEFEMDL-UHFFFAOYSA-N 0.000 claims abstract description 51
- 229910052717 sulfur Inorganic materials 0.000 claims abstract description 45
- 239000011593 sulfur Substances 0.000 claims abstract description 45
- 229910052761 rare earth metal Inorganic materials 0.000 claims abstract description 37
- 150000002910 rare earth metals Chemical class 0.000 claims abstract description 27
- 229910000616 Ferromanganese Inorganic materials 0.000 claims abstract description 19
- DALUDRGQOYMVLD-UHFFFAOYSA-N iron manganese Chemical compound [Mn].[Fe] DALUDRGQOYMVLD-UHFFFAOYSA-N 0.000 claims abstract description 19
- -1 rare earth sulfide Chemical class 0.000 claims abstract description 10
- 239000002245 particle Substances 0.000 claims abstract description 8
- 238000002425 crystallisation Methods 0.000 claims abstract description 5
- 230000008025 crystallization Effects 0.000 claims abstract description 5
- 229910000831 Steel Inorganic materials 0.000 claims description 41
- 239000010959 steel Substances 0.000 claims description 41
- 239000002994 raw material Substances 0.000 claims description 30
- 229910000519 Ferrosilicon Inorganic materials 0.000 claims description 23
- XUIMIQQOPSSXEZ-UHFFFAOYSA-N Silicon Chemical compound [Si] XUIMIQQOPSSXEZ-UHFFFAOYSA-N 0.000 claims description 19
- 229910052799 carbon Inorganic materials 0.000 claims description 19
- 229910052710 silicon Inorganic materials 0.000 claims description 19
- 239000010703 silicon Substances 0.000 claims description 19
- PWHULOQIROXLJO-UHFFFAOYSA-N Manganese Chemical compound [Mn] PWHULOQIROXLJO-UHFFFAOYSA-N 0.000 claims description 16
- 229910052748 manganese Inorganic materials 0.000 claims description 16
- 239000011572 manganese Substances 0.000 claims description 16
- 229910052684 Cerium Inorganic materials 0.000 claims description 12
- GWXLDORMOJMVQZ-UHFFFAOYSA-N cerium Chemical compound [Ce] GWXLDORMOJMVQZ-UHFFFAOYSA-N 0.000 claims description 12
- 229910000636 Ce alloy Inorganic materials 0.000 claims description 10
- WMOHXRDWCVHXGS-UHFFFAOYSA-N [La].[Ce] Chemical compound [La].[Ce] WMOHXRDWCVHXGS-UHFFFAOYSA-N 0.000 claims description 10
- 229910000975 Carbon steel Inorganic materials 0.000 claims description 6
- 239000010962 carbon steel Substances 0.000 claims description 6
- 229910000640 Fe alloy Inorganic materials 0.000 claims description 4
- GSVIBLVMWGSPRZ-UHFFFAOYSA-N cerium iron Chemical compound [Fe].[Fe].[Fe].[Fe].[Fe].[Fe].[Fe].[Fe].[Fe].[Fe].[Fe].[Fe].[Fe].[Fe].[Fe].[Fe].[Fe].[Ce].[Ce] GSVIBLVMWGSPRZ-UHFFFAOYSA-N 0.000 claims description 4
- KAEAMHPPLLJBKF-UHFFFAOYSA-N iron(3+) sulfide Chemical compound [S-2].[S-2].[S-2].[Fe+3].[Fe+3] KAEAMHPPLLJBKF-UHFFFAOYSA-N 0.000 claims description 4
- 229910000851 Alloy steel Inorganic materials 0.000 claims description 3
- 238000010309 melting process Methods 0.000 abstract description 12
- 238000002844 melting Methods 0.000 abstract description 5
- 230000008018 melting Effects 0.000 abstract description 5
- 229910001018 Cast iron Inorganic materials 0.000 abstract description 3
- 229910045601 alloy Inorganic materials 0.000 abstract description 3
- 239000000956 alloy Substances 0.000 abstract description 3
- 238000005272 metallurgy Methods 0.000 abstract description 2
- 239000000463 material Substances 0.000 description 36
- 239000002699 waste material Substances 0.000 description 23
- 230000000052 comparative effect Effects 0.000 description 18
- 238000011081 inoculation Methods 0.000 description 18
- 238000005266 casting Methods 0.000 description 11
- 230000000694 effects Effects 0.000 description 9
- 238000005303 weighing Methods 0.000 description 9
- 229910000805 Pig iron Inorganic materials 0.000 description 5
- ACXGJHCPFCFILV-UHFFFAOYSA-M sodium;2-(4-chloro-2-methylphenoxy)acetate;3,6-dichloro-2-methoxybenzoic acid Chemical compound [Na+].COC1=C(Cl)C=CC(Cl)=C1C(O)=O.CC1=CC(Cl)=CC=C1OCC([O-])=O ACXGJHCPFCFILV-UHFFFAOYSA-M 0.000 description 5
- 241001280078 Nodula Species 0.000 description 4
- 238000005516 engineering process Methods 0.000 description 4
- WPBNNNQJVZRUHP-UHFFFAOYSA-L manganese(2+);methyl n-[[2-(methoxycarbonylcarbamothioylamino)phenyl]carbamothioyl]carbamate;n-[2-(sulfidocarbothioylamino)ethyl]carbamodithioate Chemical compound [Mn+2].[S-]C(=S)NCCNC([S-])=S.COC(=O)NC(=S)NC1=CC=CC=C1NC(=S)NC(=O)OC WPBNNNQJVZRUHP-UHFFFAOYSA-L 0.000 description 4
- CADICXFYUNYKGD-UHFFFAOYSA-N sulfanylidenemanganese Chemical compound [Mn]=S CADICXFYUNYKGD-UHFFFAOYSA-N 0.000 description 3
- 238000006477 desulfuration reaction Methods 0.000 description 2
- 230000023556 desulfurization Effects 0.000 description 2
- 238000004519 manufacturing process Methods 0.000 description 2
- 230000006911 nucleation Effects 0.000 description 2
- 238000010899 nucleation Methods 0.000 description 2
- HMDDXIMCDZRSNE-UHFFFAOYSA-N [C].[Si] Chemical compound [C].[Si] HMDDXIMCDZRSNE-UHFFFAOYSA-N 0.000 description 1
- 230000015572 biosynthetic process Effects 0.000 description 1
- 238000010191 image analysis Methods 0.000 description 1
- 239000000203 mixture Substances 0.000 description 1
- 101150103670 ple2 gene Proteins 0.000 description 1
- 101150039516 ple3 gene Proteins 0.000 description 1
- 238000005070 sampling Methods 0.000 description 1
- 238000007711 solidification Methods 0.000 description 1
- 230000008023 solidification Effects 0.000 description 1
Classifications
-
- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C33/00—Making ferrous alloys
- C22C33/08—Making cast-iron alloys
-
- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21C—PROCESSING OF PIG-IRON, e.g. REFINING, MANUFACTURE OF WROUGHT-IRON OR STEEL; TREATMENT IN MOLTEN STATE OF FERROUS ALLOYS
- C21C1/00—Refining of pig-iron; Cast iron
- C21C1/10—Making spheroidal graphite cast-iron
- C21C1/105—Nodularising additive agents
-
- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21B—MANUFACTURE OF IRON OR STEEL
- C21B3/00—General features in the manufacture of pig-iron
- C21B3/02—General features in the manufacture of pig-iron by applying additives, e.g. fluxing agents
-
- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21C—PROCESSING OF PIG-IRON, e.g. REFINING, MANUFACTURE OF WROUGHT-IRON OR STEEL; TREATMENT IN MOLTEN STATE OF FERROUS ALLOYS
- C21C1/00—Refining of pig-iron; Cast iron
- C21C1/10—Making spheroidal graphite cast-iron
-
- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C33/00—Making ferrous alloys
- C22C33/04—Making ferrous alloys by melting
-
- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C37/00—Cast-iron alloys
- C22C37/04—Cast-iron alloys containing spheroidal graphite
Landscapes
- Chemical & Material Sciences (AREA)
- Engineering & Computer Science (AREA)
- Materials Engineering (AREA)
- Metallurgy (AREA)
- Organic Chemistry (AREA)
- Mechanical Engineering (AREA)
- Manufacturing & Machinery (AREA)
- Refinement Of Pig-Iron, Manufacture Of Cast Iron, And Steel Manufacture Other Than In Revolving Furnaces (AREA)
Abstract
The present invention relates to the technical field of metallurgy and cast iron alloys, and provides a method for increasing the number of graphite balls and improving the roundness of graphite balls in nodular cast iron. The method for increasing the number of graphite balls and improving the roundness of graphite balls in nodular cast iron comprises melting molten iron in an electric furnace, increasing the sulfur content in the molten iron during the melting process, and adding rare earth in the electric furnace or in a nodularizing ladle; after the molten iron is completely melted, pouring the molten iron into the nodularizing ladle and nodularizing; and after nodularization, adding ferromanganese to a transfer ladle. In the present invention, sulfur is added to molten iron in advance, and rare earth is added to a nodularizing ladle previously, so that a large number of dispersed rare earth sulfide particles are formed in the molten iron during the nodularization process. 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.
Description
Method for increasing number of graphite balls and improving roundness of graphite balls in nodular cast iron
FIELD OF THE INVENTION The present invention relates to the technical field of metallurgy and cast iron alloys, and particularly to a method for increasing the number of graphite balls and improving the roundness of graphite balls in nodular cast iron.
DESCRIPTION OF THE RELATED ART 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.
SUMMARY OF THE INVENTION To solve the above technical problems, the present invention provides a method for increasing the number of graphite balls and improving the roundness of graphite balls in nodular cast iron. 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 number of graphite balls and improving the roundness of graphite balls in nodular cast iron. 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 one or more selected from cerium, a lanthanum-cerium alloy and a cerium-iron alloys. 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 is covered on 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, arecarburizer, 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 0.01wt%-0.08wt%. The method comprises specifically the following steps: (1) Waste steel tube is used as raw material; a material list is formulated, and entered into an automatic material weighing system; and the materials are automatically weighed.
(2) Waste steel tube is added to an electric furnace, then ferrosilicon and a recarburizer are added to the base molten iron, and the sulfur content in the base molten iron in the electric furnace is increased by adding a sulfur increasing material selected from sulfur power (or ferric sulfide). After the molten iron is melted, a sample is taken to analyze the contents of various elements. The contents of various auxiliary materials are adjusted to allow the molten iron to have a carbon silicon, manganese, and sulfur content reaching the above contents.
(3) 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 a nodularizing ladle previously added with a nodularizer and nodularized, where rare earth is added to the nodularizing ladle previously.
(4) After nodularization, FeMn68 ferromanganese is added to a transfer ladle, where the manganese content is controlled to 0.4-0.6%. Then, a nodular cast 5 iron specimen of 200 mm x 200 mm x 200 mm is casted.
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 number of graphite balls and improving the roundness of graphite balls in nodular cast iron according to the present invention, the obtained thick and large castings of 200 mm x 200 mm x 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.
BRIEF DESCRIPTION OF THE DRAWINGS 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: FIG. 1 schematically shows a sampling position in Comparative Example 3 of the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 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 number of graphite balls and improving the roundness of graphite balls in nodular cast iron. 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.
Example 1 This example provides a method for increasing the number of graphite balls and improving the roundness of graphite balls in nodular cast iron. The method comprises the following steps: (1) Waste steel tube and recycled scrap of nodular cast iron are used as main raw materials and melted in an electric furnace, where the waste steel tube and recycled scrap each account for 50 wt%. Ferrosilicon, a recarburizer, and ferrosulphur are added during the melting process, where the molten iron is controlled to have a carbon content of 3.6 wt%, a silicon content of 2.1 wt%, and a sulfur content of 0.03 wt%.
(2) In this example, waste steel tube and recycled scrap of nodular cast iron are used as raw materials, a material list is formulated, and entered into an automatic material weighing system; and the materials are automatically weighed.
(3) The waste steel tube and recycled scrap of nodular cast iron are added to the electric furnace at a ratio of waste steel tube to recycled scrap of nodular cast iron of 1:1. Then, FeS175 ferrosilicon, the recarburizer, and FeS40 ferrosulphur are added. After the molten iron is melted, a sample is taken to analyze the contents of various elements. The contents of various auxiliary materials are adjusted to allow the molten iron to have a carbon, silicon, and sulfur content reaching the above contents. (4) À nodularizer is added to a nodularizing ladle, and Ce is covered on the nodularizer, where the amount of cerium added is calculated according to a content of 0.02 wt% in the molten iron.
(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 and nodularized. (6) After nodularization, FeMn68 ferromanganese is added to a transfer ladle, where the manganese content is controlled to 0.4 wt%. Then, a nodular cast iron specimen of 200 mm x 200 mm x 200 mm is casted.
Example 2 This example provides a method for increasing the number of graphite balls and improving the roundness of graphite balls in nodular cast iron. The method comprises the following steps: (1) Waste steel tube and recycled scrap of nodular cast iron are used as main raw materials and melted in an electric furnace, where the weight ratio of the waste steel tube and the recycled scrap is 7:3. Ferrosilicon, a recarburizer, and ferrosulphur are added during the melting process, where the molten iron is controlled to have a carbon content of 4.0 wt%, a silicon content of 1.8 wt%, and a sulfur content of 0.07 wt%.
(2) In this example, waste steel tube and recycled scrap of nodular cast iron are used as raw materials, a material list is formulated, and entered into an automatic material weighing system; and the materials are automatically weighed.
(3) The waste steel tube and recycled scrap of nodular cast iron are added to the electric furnace, where the weight ratio of the waste steel tube and the recycled scrap is 7:3. Then, FeSi75 ferrosilicon, the recarburizer, and FeS40 ferrosulphur are added. After the molten iron is melted, a sample is taken to analyze the contents of various elements. The contents of various auxiliary materials are adjusted to allow the molten iron to have a carbon, silicon, and sulfur content reaching the above contents. (4) A nodularizer is added to a nodularizing ladle, and a lanthanum-cerium alloy is covered on the nodularizer, where the amount of the lanthanum-cerium alloy added 1s calculated according to a content of 0.08 wt% in the molten iron.
(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 and nodularized. (6) After nodularization, FeMn68 ferromanganese 1s added to a transfer ladle, where the manganese content is controlled to 0.4 wt%. Then, a nodular cast iron specimen of 200 mm x 200 mm x 200 mm is casted.
Example 3 This example provides a method for increasing the number of graphite balls and improving the roundness of graphite balls in nodular cast iron. The method comprises the following steps: (1) Waste steel tube is used as main raw material and melted in an electric furnace, where no recycled scrap is added. Ferrosilicon, a recarburizer, sulfur powder, and a lanthanum-cerium alloy are added during the melting process, where the molten iron is controlled to have a carbon content of 3.8wt%, a silicon content of 2.0 wt%, a sulfur content of 0.03 wt%, and a cerium content of 0.01 wt%.
(2) In this example, waste steel tube is used as raw material; a material list is formulated, and entered into an automatic material weighing system; and the materials are automatically weighed.
(3) The waste steel tube is added to the electric furnace. Then, FeSi75 ferrosilicon, the recarburizer, sulfur powder, and the lanthanum-cerium alloy are added. After the molten iron is melted, a sample is taken to analyze the contents of various elements. The contents of various auxiliary materials are adjusted to allow the molten iron to have a carbon, silicon, manganese, sulfur, and cerium content reaching the above contents. (4) A nodularizer is added to a nodularizing ladle, and a lanthanum-cerium alloy is covered on the nodularizer, where the amount of the lanthanum-cerium alloy added is calculated according to a content of 0.01 wt% in the molten iron.
(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, FeMn68 ferromanganese is added to a transfer ladle, where the manganese content is controlled to 0.6 wt%. Then, a nodular cast iron specimen of 200 mm x 200 mm x 200 mm is casted.
Example 4 This example provides a method for increasing the number of graphite balls and improving the roundness of graphite balls in nodular cast iron. The method comprises the following steps: (1) Waste steel tube is used as main raw material and melted in an electric furnace, where no recycled scrap is added. Ferrosilicon, a recarburizer, sulfur powder, and cerium are added during the melting process, where the molten iron is controlled to have a carbon content of 3.9 wt%, a silicon content of 1.9 wt%, a sulfur content of
0.07 wt%, and a cerium content of 0.08 wt%.
(2) In this example, waste steel tube is used as raw material, a material list is formulated, and entered into an automatic material weighing system; and the materials are automatically weighed.
(3) The waste steel tube is added to the electric furnace. Then, FeSi75 ferrosilicon, the recarburizer, sulfur powder, and a lanthanum-cerium alloy are added. After the molten iron is melted, a sample is taken to analyze the contents of various elements.
The contents of various auxiliary materials are adjusted to allow the molten iron to have a carbon, silicon, manganese, sulfur, and cerium content reaching the above contents. (4) A nodularizer is added to a nodularizing ladle, and a lanthanum-cerium alloy is covered on the nodularizer.
(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, FeMn68 ferromanganese is added to a transfer ladle, where the manganese content is controlled to 0.5 wt%. Then, a nodular cast iron specimen of 200 mm x 200 mm x 200 mm is casted.
Example 5 This example provides a method for increasing the number of graphite balls and improving the roundness of graphite balls in nodular cast iron. The method comprises the following steps: (1) Waste steel tube is used as main raw material and melted in an electric furnace, where no recycled scrap is added. Ferrosilicon, a recarburizer, ferrosulfur, and cerium are added during the melting process, where the molten iron is controlled to have a carbon content of 3.8 wt%, a silicon content of 2.1 wt%, a sulfur content of
0.05 wt%, and a cerium content of 0.08 wt%.
(2) In this example, waste steel tube is used as raw material, a material list is formulated, and entered into an automatic material weighing system; and the materials are automatically weighed.
(3) The waste steel tube is added to the electric furnace. Then, FeSi75 ferrosilicon, the recarburizer, sulfur powder, and a cerium-iron alloy are added. After the molten iron is melted, a sample is taken to analyze the contents of various elements. The contents of various auxiliary materials are adjusted to allow the molten iron to have a carbon, silicon, manganese, sulfur, and cerium content reaching the above contents. (4) A nodularizer is added to a nodularizing ladle, and a cerium-iron alloy is covered on the nodularizer. (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, FeMn68 ferromanganese is added to a transfer ladle, where the manganese content is controlled to 0.5 wt%. Then, a nodular cast iron specimen of 200 mm x 200 mm x 200 mm is casted.
Comparative Example 1 (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 x 200 mm x 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 1s 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 x 200 mm x 200 mm.
Comparative Example 2 (1) In the comparative example, nodular cast iron 1s 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 x 200 mm x 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 0.015wt%. (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 x 200 mm x 200 mm.
Comparative Example 3 (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 x 200 mm x 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 x 200 mm x 200 mm.
The nodularization effects of graphite in each part of the nodular iron castings of 200 mm x 200 mm x 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 x 200 mm x 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.
Table 1. Comparison of nodularization rate and number density of graphite of Examples 1-4 and Comparative Examples 1-3 Test Exa | Embo | Fxa | Fxa | Ave | Comp | Comp | Comp | Avera Ko item mpl | dimen | mpl | mpl | rage | arativ | arativ | arativ | ge of el |t2 e3 |e4 |of e e e comp exa | Exam | Exam | Exam | arativ mpl |plel |ple2 |ple3 |e es exam ples Nodula rizatio
86.5 | 87.2 83.1 | 88.5 | 86.3 | 71.3 66.2 69.1 68.9 n rate (%) Ball diamet 5 5 5 5 4 4 4 4 er Sa (grade) mp Numbe le 1 r density of 163. 159 | 172 152 | 169 97 116 103.7 graphit 0 e (balls/ mm?) Nodula rizatio Sa 86.3 | 85.4 82.7 85.9 | 66.7 67.3 70.1 68.0 n rate mp (%) le 2 Ball 5 5 5 5 5 4 4 4 4 diamet er (grade) Numbe r density of 184. 200 | 185 163 | 190 88 106 91 95.0 graphit 5 e (balls/ mm?) Nodula rizatio
84.7 | 80.9 83.2 | 85.5 | 83.6 | 68.3 65.8 65.6 n rate (%) Ball diamet 5 5 5 5 4 4 4 4 er Sa (grade) mp Numbe le 3 r density of 167. 175 | 162 155 | 176 103 112 104.7 graphit 0 e (balls/ mm?)
mp | rizatio le 4 |n rate (%) Ball diamet 5 5 5 5 4 4 4 4 er (grade) Numbe r density of 167. 147 | 163 181 | 177 117 109 108.0 graphit 0 e (balls/ mm?) Nodula rizatio
84.3 | 81.3 80.8 | 84.6 | 82.8 | 64.5 62.1 64.4 n rate (%) Ball Sa diamet mp 5 5 5 5 5 4 4 4 4 er le 5 (grade) Numbe r 174. 181 | 166 172 | 178 131 105 111 115.7 density 3 of graphit e (balls/ mm?) As can be seen from Table 1, the method for increasing the number of graphite balls and improving the roundness of graphite balls in nodular cast iron 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.
Claims (11)
1. A method for increasing the number of graphite balls and improving the roundness of graphite balls in nodular cast iron, comprising 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.
2. The method according to claim 1, wherein the rare earth is one or more selected from cerium, a lanthanum-cerium alloy and a cerium-iron alloys.
3. The method according to claim 1, wherein the sulfur content is increased by adding sulfur or ferric sulfide.
4. The method according to claim 1, wherein the rare earth accounts for 0.01%-0.08% by weight of the base molten iron.
5. The method according to claim 1, wherein the sulfur content in the sulfur-increased molten iron is 0.03-0.07 wt%.
6. The method according to claim 1, wherein 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 is covered on the surface of a nodularizer.
7. The method according to claim 1, wherein the raw material of the base molten iron is selected from steel scrap and recycled scrap; and the steel scrap is selected from carbon steel and/or alloy steel.
8. The method according to claim 7, wherein the steel scrap in the raw material accounts for 50-100 wt%, and the recycled scrap accounts for 0-50 wt%.
9. The method according to claim 1, further comprising 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.
10. The method according to claim 1, further comprising adding ferromanganese to the molten iron after nodularization, and the ferromanganese has a particle size of 5 to 15 mm.
11. The method according to claim 10, wherein the manganese content in the molten iron is 0.4-0.6 wt%.
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| US18/125,093 US20240035126A1 (en) | 2022-07-26 | 2023-03-22 | Method for increasing the quality of graphite balls |
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