Vermicularizing treatment method of RuT500 vermicular graphite cast iron

Abstract

The invention discloses a vermicularizing treatment method of RuT500 vermicular graphite cast iron. According to the method, the antimony alloy is put into a treatment ladle after tapping and before vermicularizing treatment, the proportion of the magnesium cored wire is controlled, the required wire feeding amount is simply and conveniently calculated according to an obtained magnesium cored wire adding amount formula, meanwhile, the content of each alloy is controlled according to a pearlite amount empirical formula, and the obtained casting is excellent in metallographic structure and mechanical performance. The production method is easy and convenient to operate, high in applicability and capable of being widely applied to the production process of various castings.

Description

Technical Field

[0001] This invention relates to the field of cast iron processing technology, specifically to a method for vermicularization treatment of RuT500 vermicular graphite cast iron. Background Technology

[0002] The casting industry is a foundational industry of national manufacturing, and castings are widely used in equipment manufacturing, serving as core components. With the continuous development of these industries, the quality requirements for castings are becoming increasingly stringent. This is especially true for engine castings, and with rising environmental protection standards, the demands on castings are also increasing.

[0003] Vermicular graphite cast iron is a type of cast iron material between ductile iron and gray cast iron. Its production process has a smaller window of opportunity, making its production significantly more difficult than that of ductile iron and gray cast iron. Currently, vermicular graphite cast iron is generally produced using a wire feeding method for vermicularization treatment of molten iron. This method allows for precise control of the wire feeding amount and stable control of various elements. Furthermore, it results in less cooling of the molten iron, a high degree of automation, and a favorable operating environment. Due to differences in production conditions, such as the source and quality of furnace charge, production equipment, and process flow, the vermicularization treatment processes for vermicular graphite cast iron vary among manufacturers. However, they generally suffer from a short usable time for the molten iron after vermicularization, subsequent degradation of the molten iron, and failure to meet requirements in terms of mechanical properties and microstructure. To ensure the mechanical properties of the castings, currently, increasing the amount of magnesium-coated wire added is commonly used to improve mechanical properties. However, this method does not fundamentally solve the problem and may even lead to a higher spheroidization rate in the molten iron, resulting in a greater tendency for shrinkage porosity in the final casting, and the microstructure still failing to meet standard requirements.

[0004] Currently, the following are examples of reports on the vermicularization treatment of vermicular graphite cast iron: CN 108060284 A discloses a method for vermicularization treatment of vermicular graphite cast iron. The problem it solves is to provide a method that can stably control the vermicularization rate of vermicular graphite cast iron using a common vermicularization treatment package and a chemical composition analyzer. The technical solution adopted is that the weight percentage of the added vermicularizing agent is determined by the content of element S in the original molten iron, and the specific added value is increased by an order of magnitude, thereby solving the problem of vermicularization qualification rate. CN105624375A discloses a vermicularization process for ductile iron, characterized by the following steps: (1) adding a vermicularizing agent directly into the furnace for treatment, adding 3-5% magnesium and 2-4% zinc by weight to the rare earth ferrosilicon alloy, vaporizing and boiling the iron, and controlling the stirring time to 2.5-3.5 minutes; (2) mixing the molten iron with the vermicularizing agent in the intermediate ladle before it flows into the ladle, so as to strengthen the stirring of the molten iron and the vermicularizing agent to carry out the vermicularization reaction; (3) crushing the rare earth alloy into particles smaller than 7mm, and adding them to the tapping trough during the tapping process. Adding high-temperature resistant elements such as chromium, nickel, and titanium, which can form a protective film, to the steel improves the high-temperature resistance of bearing steel, reduces production costs, and extends service life. The vermicularization treatment mentioned above improves certain properties of ductile iron, but it does not solve the problem of molten iron decay or high spheroidization rate leading to microstructure that does not meet the standard requirements. It is still necessary to develop a simpler and better vermicularization treatment process for ductile iron to obtain castings with excellent microstructure and mechanical properties. Summary of the Invention

[0005] To address the problem of molten iron degradation or high nodularity in existing vermicularization processes, which leads to substandard microstructure, this invention provides a vermicularization treatment method for RuT500 vermicular graphite cast iron. This method involves adding an antimony alloy to the treatment ladle after tapping and before vermicularization, and controlling the magnesium cored wire ratio. The required wire feeding amount is easily calculated using a formula for the amount of magnesium cored wire added. Simultaneously, the content of each alloy is controlled based on an empirical formula for pearlite content, resulting in castings with excellent microstructure and mechanical properties. This production method is simple and convenient to operate, highly applicable, and can be widely used in the production of various castings.

[0006] Currently, vermicularizing agents for molten iron are mainly classified into magnesium-based, rare-earth-based, and calcium-based vermicularizing agents. Known magnesium-based vermicularizing agents include magnesium alloy powder, pure magnesium powder, or mixtures of magnesium with other silicon-based alloy powders. Because these types of vermicularizing agents contain a high magnesium content, when they "dissolve" in molten iron, they react with the iron to form a large amount of magnesium vapor, resulting in violent turbulence and a deterioration of the production environment. In production, the specific circumstances of each unit vary greatly. The amount of alloying elements and magnesium cored wire used in vermicular graphite cast iron should be comprehensively considered based on the condition of the furnace charge used by each foundry and the quality of the castings. The optimal amount needs to be gradually optimized during actual application.

[0007] To address the problems inherent in conventional vermicularization processes, this invention provides a vermicularization treatment method for RuT500 vermicular graphite cast iron. The method involves adding magnesium cored wire, inoculated cored wire, and other alloys to the original molten iron for smelting to obtain the final molten iron. This molten iron is then rapidly poured into a mold to obtain qualified castings. The method is characterized by... (1) Magnesium-coated wire Magnesium-coated wire undergoes vermicomposting inoculation treatment using an in-coat feeding method. Each meter of magnesium-coated wire contains the following raw materials by weight: 45-48g magnesium, 110-130g silicon, 10-18g rare earth elements, 10-15g calcium, with the balance being iron; the total weight of the core per meter is 220g-330g. The magnesium and other element ratios are reasonable, the reaction is stable, and the resulting molten iron has a uniform and stable composition.

[0008] The amount of magnesium-coated wire added per ton of molten iron is calculated based on the sulfur content and trace interfering element content of the original molten iron, according to the following formula: The amount of magnesium-coated wire added per ton of molten iron (meters / ton) = β × (sulfur content of the original molten iron % + content of trace interfering elements %) × 1000, where β is a variable factor.

[0009] (2) Timing of adding antimony as an alloying element Antimony, an alloying element, is added separately to the treatment package one minute before the magnesium-coated wire is added. Adding antimony before the magnesium-coated wire allows the boiling effect of magnesium to be fully utilized, resulting in a more uniform composition of the molten iron after the reaction.

[0010] (3) Control the content of each alloy to obtain an empirical formula for the pearlite content and the content of each alloy, wherein the pearlite content is controlled at ≥95%; Pearlite content = 1 - (1.7 × Mn% + 2.5 × Cu% + 0.05 × Sn% + 0.7 × Sb% + 1.7 × Cr%).

[0011] Furthermore, the rare earth elements, by mass ratio, are: lanthanum 28%~39%, cerium 61%~71%, praseodymium 0%~1.5%, neodymium 0%~0.8%, and scandium 0%~0.6%.

[0012] Furthermore, the magnesium-coated wire has a diameter of 13mm, which ensures a suitable processing time. The amount of magnesium-coated wire added is 3.4~5.5 meters per ton of molten iron.

[0013] Furthermore, the β variable factor is selected based on the sulfur content and trace interfering element content of the original molten iron, generally ranging from 4 to 19. Common trace interfering elements include Ti, As, Sb, N, Pb, Zr, Zn, and Bi. When the total amount of trace interfering elements is <0.06%, β is selected within the range of 10 to 19; when the total amount of trace interfering elements is between 0.06 and 0.09%, β is selected within the range of 4 to 9. Based on the detected composition of the original molten iron, this treatment method is applied by first adding the alloying element antimony, then treating it with magnesium cored wire, inoculated cored wire, and other alloying materials. After treatment, casting is performed, and the molten iron is gradually cooled in a sand box to obtain the casting.

[0014] The RuT500 vermicular graphite cast iron castings prepared by the above vermicularization treatment method have a pearlite content of ≥95% and a tensile strength of ≥500MPa.

[0015] The technical advantages of this invention are as follows: The vermicularization treatment method of this invention can solve the problem of "iron fading or high spheroidization rate leading to substandard metallographic structure," thus improving the metallurgical state of the molten iron. Castings made from molten iron treated in this way can achieve a metallographic structure with good vermicularization and a reasonable pearlite content, thereby giving the castings good tensile strength and enabling them to meet the application conditions of engines. This vermicular graphite cast iron treatment method can be widely used in the production of various castings; it is simple, convenient, and highly applicable. Attached Figure Description Figure 1 The image shows the creep rate of the casting body in Example 1, where the left and right images are two randomly selected sample castings. Figure 2 The image shows a pearlitic metallographic image of the casting body of Example 1, where the left and right images are two randomly selected sample castings. Detailed Implementation

[0016] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are some embodiments of the present invention, but not all embodiments.

[0017] An embodiment of the present invention discloses a method for producing RuT500 vermicular graphite cast iron, comprising: smelting pig iron, scrap steel, carbon raiser, ferrosilicon, etc., to prepare molten iron, wherein the mass percentage of the components in the prepared molten iron is: C 3.5~3.9%, Si 2.2~2.5%, P ≤0.03%, S 0.005~0.017%, Mn 0.2~0.3%, Cu 0.3~0.5%, Sn 0.02~0.05%; the balance being iron. Then, when the temperature of the molten iron is 1420~1455℃, ferromanganese alloy, No. 1 standard copper, and metallic tin are added to obtain secondary molten iron. Then, when the temperature of the secondary molten iron reaches 1470~1520℃, magnesium cored wire, inoculated cored wire, and other alloys are added and smelted to obtain final molten iron; this molten iron is then rapidly poured into a mold to obtain qualified castings. In embodiments of the present invention, the content per meter of magnesium-cored wire is: magnesium 45-48g, silicon 110-130g, rare earth elements 10-18g, calcium 10-15g, with the balance being iron. The amount of magnesium-cored wire added per ton of molten iron can be 3.4-5.5 meters, and the specific amount added can be selected according to the actual content of each relevant element in the molten iron.

[0018] Antimony, an alloying element, can be added to molten iron before magnesium cored wire, effectively ensuring the uniformity of its composition in the molten iron. In embodiments of the present invention, in order to obtain a good pearlitic structure in the casting, an empirical formula was summarized for controlling the content of manganese, copper-tin, antimony, and chromium.

[0019] Example 1 A method for producing RuT500 vermicular graphite cast iron, comprising the following steps: (1) The added iron materials were smelted to prepare the first iron liquid Y1. The mass percentage of the components in the prepared iron liquid was: C 3.5~3.9%, Si 2.2~2.5%, P ≤0.03%, S 0.005~0.017%, Mn 0.2~0.3%, Cu 0.3~0.5%, Sn 0.02~0.05%; the balance was iron.

[0020] (2) Then, when the temperature of the molten iron is 1420~1455℃, ferromanganese alloy, No. 1 standard copper, and metallic tin are added (based on the mass of the first molten iron Y1, the amount of ferromanganese alloy is 0.36%, the amount of No. 1 standard copper is generally 0.55%, and the amount of metallic tin is generally 0.6%) to obtain secondary molten iron Y2; the ferromanganese alloy is FeMn68C7.0, the copper content of No. 1 standard copper is ≥99.9%, and the tin content of metallic tin is ≥99.9%; then the temperature of the secondary molten iron is adjusted to 1470~1520℃, and then the secondary molten iron Y2 is subsequently subjected to vermicomposting inoculation treatment in separate packages; (3) Add magnesium cored wire to the secondary molten iron Y2. The magnesium cored wire is subjected to vermicomposting treatment by the in-bundle feeding method. Add the magnesium cored wire in the middle of the bundle, and then add the inoculated cored wire (addition amount 0.6 m / ton). Add antimony metal block (addition amount 150 g / ton) before adding the cored wire. That is, add it separately to the treatment bundle within 1 minute before adding the magnesium cored wire. The vermicomposting rate is ≥85%.

[0021] The composition per meter of magnesium-core wire is as follows: magnesium 46.5g, silicon 118.3g, rare earth elements (lanthanum 32.5%, cerium 66%, praseodymium 0.8%, neodymium 0.4%, scandium 0.3%) 15.2g, calcium 12.1g, with the balance being iron. The weight of the core in the magnesium-core wire is 263.2g. The diameter of the magnesium-core wire is 13mm.

[0022] The amount of magnesium-cored wire added is calculated based on the following formula: (Number of magnesium-cored wire added per ton of molten iron (meters / ton)) = β × (Sulfur content of the original molten iron % + Trace interfering element content %) × 1000. β is a variable factor (selected based on the sulfur content and trace interfering element content of the original molten iron, generally ranging from 4 to 19. Common trace interfering elements are Ti, As, Sb, N, Pb, Zr, Zn, and Bi. When the total trace interfering element content is <0.06%, β is selected within the range of 10 to 19; when the total trace interfering element content is between 0.06% and 0.09%, β is selected within the range of 4 to 9). In this embodiment, the β variable factor is selected as 14 based on the sulfur content and trace interference element content in the original molten iron Y2, thus obtaining a magnesium cored wire addition amount of 3.36 meters / ton (14×(0.009%+0.015%)×1000).

[0023] (4) The content of manganese, copper, tin, antimony and chromium elements in the pearlite structure is controlled according to empirical formulas, and the pearlite content needs to be controlled at ≥95%; Pearlite content = 1 - (1.7 × Mn% + 2.5 × Cu% + 0.05 × Sn% + 0.7 × Sb% + 1.7 × Cr%). According to this embodiment, when the manganese content is 0.55%, the copper content is 0.9%, the tin content is 0.09%, the antimony content is 0.006%, and the chromium content is 0.05%, the pearlite content obtained by the above formula is 96.72%.

[0024] After the molten iron reaches a temperature of 1470-1520℃, it is transferred to a processing ladle. Magnesium cored wire, inoculated cored wire, and other alloys are then added for vermicularization treatment to obtain the final molten iron. This molten iron is then rapidly poured into a mold to obtain a qualified casting. The metallographic image of the vermicularization rate of the obtained casting is shown below. Figure 1 As shown, the pearlitic metallographic image of the casting body is as follows: Figure 2 As shown.

[0025] Comparative Example 1 The difference between Comparative Example 1 and Example 1 is that the content of magnesium, silicon, rare earth elements and calcium per meter of magnesium cored wire is changed to: magnesium 50g, silicon 105g, rare earth elements 8.9g, calcium 17.3g, and the balance is iron.

[0026] Comparative Example 2 The difference between Comparative Example 2 and Example 1 is that the diameter of the magnesium cored wire is 9mm, and the content per meter is changed to: magnesium 40g, silicon 85g, rare earth elements 6.5g, calcium 10.2g, with the balance being iron.

[0027] Comparative Example 3 The difference between Comparative Example 3 and Example 1 is that the alloying element antimony was added to the treatment package after the vermicularization treatment.

[0028] Comparative Example 4 The difference between Comparative Example 4 and Example 1 is that the alloying elements manganese, copper, tin, antimony, and chromium were not added according to empirical formulas, and the pearlite content was 90%, which is lower than 95%. The samples from the above-mentioned examples (8 samples) and comparative examples (2 samples for each comparative example) were tested, and the specific test results are shown in Table 1 below. The tensile strength, elongation, vermicularization rate, and pearlite content were tested according to GB / T26655 "Vermicular Graphite Cast Iron" and GB / T26656 "Metallographic Examination of Vermicular Graphite Cast Iron", respectively.

[0029] Table 1 Product performance test indicators of the examples and comparative examples

[0030] As can be seen from Table 1, the tensile strength and elongation are significantly improved by using the vermicomposting treatment method of the present invention.

Claims

1. A method for vermicularization treatment of RuT500 vermicular graphite cast iron, comprising adding magnesium cored wire, inoculated cored wire and other alloys to the original molten iron for smelting to obtain the final molten iron; the molten iron is then rapidly poured into a mold to obtain qualified castings, characterized in that, (1) Magnesium-coated wire The core of each meter of magnesium-coated wire includes the following raw materials by weight: 45-48g magnesium, 110-130g silicon, 10-18g rare earth elements, 10-15g calcium, and the balance is iron. The amount of magnesium-coated wire added per ton of molten iron is calculated based on the sulfur content and trace interfering element content of the original molten iron, according to the following formula: The amount of magnesium-coated wire added per ton of molten iron (meters / ton) = β × (sulfur content of the original molten iron % + content of trace interfering elements %) × 1000, where β is a variable factor; (2) Timing of adding antimony as an alloying element The alloying element antimony is added separately to the treatment package within one minute before the magnesium cored wire is added. (3) Control the content of each alloy to obtain an empirical formula for the pearlite content and the content of each alloy, wherein the pearlite content is controlled at ≥95%; Pearlite content = 1 - (1.7 × Mn% + 2.5 × Cu% + 0.05 × Sn% + 0.7 × Sb% + 1.7 × Cr%).

2. The vermicularization treatment method for RuT500 vermicular graphite cast iron as described in claim 1, characterized in that, The trace interfering elements are Ti, As, Sb, N, Pb, Zr, Zn and Bi.

3. The vermicularization treatment method for RuT500 vermicular graphite cast iron as described in claim 2, characterized in that, The β variable factor is selected from 4 to 19 based on the sulfur content and trace interference element content of the original molten iron.

4. The vermicularization treatment method for RuT500 vermicular graphite cast iron as described in claim 3, characterized in that, When the total amount of trace interfering elements is less than 0.06%, β is selected within the range of 10 to 19.

5. The vermicularization treatment method for RuT500 vermicular graphite cast iron as described in claim 3, characterized in that, When the total amount of trace interfering elements is between 0.06% and 0.09%, β should be selected between 4 and 9.

6. The vermicularization treatment method for RuT500 vermicular graphite cast iron as described in claim 1, characterized in that, The rare earth elements, by mass ratio, are: lanthanum 28%~39%, cerium 61%~71%, praseodymium 0%~1.5%, neodymium 0%~0.8%, and scandium 0%~0.6%.

7. The vermicularization treatment method for RuT500 vermicular graphite cast iron as described in claim 1, characterized in that, The magnesium-clad wire is subjected to vermicomposting treatment using an in-clad feeding method.

8. The vermicularization treatment method for RuT500 vermicular graphite cast iron as described in claim 1, characterized in that, The diameter of the magnesium-coated wire is 13 mm.

9. The vermicularization treatment method for RuT500 vermicular graphite cast iron as described in claim 1, characterized in that, The amount of magnesium-coated wire added is 3.4 to 5.5 meters per ton of molten iron.

10. The RuT500 vermicular graphite cast iron casting prepared by the vermicularization treatment method according to any one of claims 1-9 has a pearlite content controlled at ≥95% and a tensile strength ≥500MPa.

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