High-casting-temperature as-cast high-elongation nodular cast iron process

Abstract

The invention provides a high-pouring-temperature as-cast high-elongation nodular cast iron process, and belongs to the technical field of nodular cast iron production processes. A pretreatment agent adopted in the process comprises a large-particle pretreatment agent with the particle size of 1-10 mm and a small-particle pretreatment agent with the particle size of 0.2-0.8 mm; according to the process, 0.15% of high-barium inoculant is adopted during tapping inoculation; according to the process, 0.1% silicon iron is adopted for stream during stream inoculation. Wherein the adding time of the large-particle pretreating agent is at the time midpoint of the smelting process, and the adding amount is 1%. The adding time of the small-particle pretreating agent is 3-5 minutes before discharging each time, and the adding amount is 0.15%. The nodular cast iron which is smelted at the high temperature of 1620 DEG C or above and is discharged for 40 minutes or above is produced through the method, the quality is more stable, the mechanical performance far exceeds the national standard and can reach the QT500-15 mark, a solid foundation is laid for producing higher-end and stable nodular cast iron castings through lost foam products, and the market competitiveness is improved.

Description

Technical Field

[0001] The invention belongs to the technical field of ductile iron production technology, in particular to a high-pouring-temperature cast-state high-elongation ductile iron process. Background Art

[0002] Ductile iron castings produced by lost foam, grades QT500-7, QT450-12, QT400-15, QT400-18, in actual production, the pouring temperature of the lost foam reaches 1460℃, and the furnace temperature reaches 1620℃. Some production sites may be limited by the site and distance and may be higher than this temperature, which is fatal to ductile iron. At the same time, castings are basically scrapped after the pouring time is extended to 12-15 minutes. High elongation castings often have unqualified elongation (elongation is between 8-10), unqualified low-temperature impact performance (8-11 / J at -40℃), and even lower performance, which cannot meet the process and customer requirements. Measures such as increasing the inoculation amount, increasing the proportion of spheroidizing agent, and appropriately increasing Sb to increase the inoculation particles and spheroidization rate have little effect on the elongation of the castings. The graphite balls are still not round and the spheroidization grade is low. The following Table 1 and Figure 1 The performance test indicators and metallographic diagrams of typical products are shown respectively.

[0003] Table 1 Performance test indicators of typical products

[0004] The conventional process takes into account the effect of high temperature on the burning loss of molten iron, and deliberately adds 1% silicon carbide as a pretreatment and carbon and silicon increase effect. At the same time, the inoculation of molten iron before feeding wire is deliberately increased, including 0.2% tapping inoculation, but the effect during the process implementation is not ideal, the spheroidization rate is less than 80%, and even 30 minutes after tapping, the remaining molten iron has poor spheroidization and creep scrap. This shows that long-term high temperature has caused serious burning loss of molten iron particles. At the same time, the heterogeneous particle nucleation of sulfides and oxides formed by the inoculant alone cannot meet the conditions for producing qualified ductile iron with high-temperature molten iron, and the stability is poor.

[0005] The traditional lost foam process has a pouring temperature of 1455℃, a furnace temperature of 1625℃, and a pouring time of more than 15 minutes. For ductile iron, the long-term heat preservation of the molten iron causes serious burning of the nucleation particles in the molten iron (SiO2+2C=Si+2CO, etc.), which seriously affects the nucleation quality and spheroidization quality. In addition, a large amount of spheroidizing agent is added in the spheroidization process, and the molten iron is severely deoxidized and decarburized, resulting in a decrease in the concentration of S and O required for nucleation (forming MgS, Mgo, CeS, and CeO consumes S / O), which increases the difficulty of subsequent inoculation treatment. Even if the inoculation amount reaches 1%, there is no effect, and the spheroidization rate is less than 80%. Summary of the invention

[0006] The present invention aims to provide a high pouring temperature as-cast high elongation ductile iron process to address the technical defects of the prior art, so as to solve the technical problem that the conventional process has a high rate of failure in terms of elongation, low temperature impact performance, spheroidization grade, etc.

[0007] In order to achieve the above technical objectives, the present invention adopts the following technical solutions: A high pouring temperature as-cast high elongation ductile iron process, the pretreatment agent used in the process includes a large particle pretreatment agent with a particle size of 1-10 mm and a small particle pretreatment agent with a particle size of 0.2-0.8 mm; the process uses a 0.15% high-barium inoculant during iron tapping inoculation; and the process uses 0.1% ferrosilicon in the flow during inoculation.

[0008] Preferably, the raw material ratio of the process is: 80% scrap steel, 20% Q12 pig iron.

[0009] Preferably, the large particle pretreatment agent is added at the midpoint of the smelting process, and the amount added is 1%.

[0010] Preferably, the small particle pretreatment agent is added 3-5 minutes before each exit from the furnace, and the added amount is 0.15%.

[0011] Preferably, the method for adding the small particle pretreatment agent is: adding 0.15% silicon carbide to the surface of the molten iron 3-5 minutes before it is taken out of the furnace, and then taking it out of the furnace.

[0012] Preferably, the particle size of the ferrosilicon is 0.2-0.8 mm.

[0013] Preferably, during the wire feeding process, the wire feeding amount is added at 0.75% and the residual magnesium is controlled between 0.04% and 0.045%.

[0014] Preferably, the inoculation is carried out to the ladle opening on the surface of the molten iron ladle during the inoculation.

[0015] In the present invention, the pouring temperature is the pouring temperature, which is specially explained.

[0016] Compared with the prior art, the innovations of the present invention mainly include the following aspects: 1. Pretreatment: The selection of pretreatment agents for gray iron and ductile iron is based on completely different theories. Gray iron is only used to increase the graphite core, while ductile iron must also ensure sufficient inoculation effect of the inoculant and cannot excessively consume the S / O content in the original molten iron.

[0017] 2. Increase the particle size of the pretreatment agent: adjust the particle size of the pretreatment agent from 1-5mm to 1-10mm, extend the melting time of the pretreatment agent, and reduce the amount of burning.

[0018] 3. Delayed pretreatment: The original process of adding pretreatment agent after 1 / 3 of the molten iron is adjusted to adding pretreatment agent after 1 / 2 of the molten iron to extend the action time.

[0019] 4. Instantaneous pretreatment: In order to reduce the reduction and burning of SiO2 caused by the high temperature (1620℃) molten iron, add 0.2-0.8mm fine-grained pretreatment agent 3-5 minutes before each furnace discharge to instantly increase the SiO2 particles burned in the molten iron (there is a layer of SiO2 protective film on the surface of silicon carbide, which can increase the particles in the molten iron by decomposition, fast and stable), and at the same time increase the dissolution of SiC in the molten iron to achieve the effect of activating the pretreated molten iron.

[0020] 5. Principle of heterogeneous nucleation before spheroidization: The present invention finds that calcium and barium have much greater affinity with oxygen and sulfur than magnesium. If they are added to the cast iron melt together with magnesium, first of all, they are deoxidized and desulfurized, thereby effectively protecting magnesium and creating better metamorphic conditions for magnesium, increasing the residual amount of magnesium, preventing and slowing down the decline of spheroidization, and at the same time, the generated sulfide becomes the core of graphite crystallization, increasing and refining graphite balls, improving their shape and distribution, and reducing the probability of graphite distortion. In addition, calcium and rare earth work together to further increase the number of graphite balls, and barium can make the metamorphic effect of calcium more sufficient and longer-lasting. Therefore, the inoculation treatment of deoxidation and desulfurization before spheroidization is very necessary for ductile iron, especially molten iron with a high S content in the molten iron.

[0021] High-barium inoculant for tapping: Add 0.15% of tapping inoculant, use conventional high-barium inoculant, consume excess O and S in the molten iron, ensure the accumulation of some Bao and BaS particles in the molten iron, and further stabilize the quality of spheroidization treatment, while reducing the amount of wire fed, ensure the wire feeding quality and reduce the tendency of shrinkage.

[0022] 6. Instantaneous inoculation with the flow: add 0.1% of ferrosilicon with a particle size of 0.2-0.8 for inoculation with the flow (inoculate to the ladle mouth but not on the molten iron flow, make full use of the low density of ferrosilicon, and form SiO2 particles on the surface of the molten iron through instant oxidation with air to achieve instantaneous inoculation effect), while avoiding the inoculation decay caused by long-term pouring. At the same time, the use of ferrosilicon inoculation can reduce the generation of instantaneous oxidation slag, improve the purity of molten iron, and thus improve the performance of castings.

[0023] The present invention is used to produce ductile iron with high-temperature melting of more than 1620°C and a furnace-out time of more than 40 minutes, with more stable quality and mechanical properties far exceeding national standards, which can reach QT500-15 grade, laying a solid foundation for the production of more high-end and stable ductile iron castings for lost foam products and improving market competitiveness. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1It is the metallographic structure of products produced by conventional technology.

[0025] Figure 2 This is an example of a product produced by the present invention, spheroidized metallographic phase before corrosion.

[0026] Figure 3 This is an example of a product produced by the present invention, and the metallographic structure of the substrate after corrosion.

[0027] Figure 4 This is another example of the product produced by the present invention, the spheroidized metallographic phase before corrosion.

[0028] Figure 5 This is another example of the product produced by the present invention, the metallographic structure of the substrate after corrosion.

[0029] Figure 6 It is a physical picture of the bracket (load-bearing member) produced by the present invention.

[0030] Figure 7 It is a physical picture of the box produced by the present invention.

[0031] Figure 8 It is a physical picture of the bracket (load-bearing member) produced by the present invention.

[0032] Fig. 9 This is a physical picture of the swing frame produced by the present invention (the working conditions have high requirements for anti-impact performance). DETAILED DESCRIPTION

[0033] The specific embodiments of the present invention will be described in detail below. In order to avoid too much unnecessary details, the well-known structures or functions will not be described in detail in the following examples. The approximate language used in the following examples can be used for quantitative expression, indicating that the quantity can be allowed to have a certain change without changing the basic function. Unless otherwise defined, the technical and scientific terms used in the following examples have the same meaning as those generally understood by those skilled in the art to which the present invention belongs.

[0034] The invention discloses a high pouring temperature as-cast high elongation ductile iron process.

[0035] The following process is used to produce lost foam ductile iron (melting temperature above 1620℃, furnace time above 40 minutes): 1. Charge ratio: 80% scrap steel + 20% Q12 pig iron.

[0036] 2. Melting pretreatment: In order to ensure the activity of molten iron and sufficient graphite core, considering the working principle of the pretreatment agent, a pretreatment agent with larger particles (particle size 1-10mm) is used, which has a longer action time and a more obvious pretreatment effect. Therefore, the addition amount of the pretreatment agent (particle size 1-10mm) is 1%, and the addition time is 1 / 2 of the smelting time. It is not allowed to add it too early or too late. (Increasing silicon, increasing carbon, and slight inoculation effect) 3. Iron pretreatment: 0.15% small particle pretreatment agent (particle size 0.2-0.8mm) (addition method: add 0.15% silicon carbide to the surface of molten iron 3-5 minutes before the furnace is discharged, and then discharge) 4. Iron inoculation: 0.15% high barium inoculant (iron inoculation) 5. Wire feeding: add 0.75% wire feeding amount. Control the residual magnesium between 0.04-0.045%.

[0037] 6. Flow inoculation: Flow inoculation uses large-pore flow 0.1% (ordinary ferrosilicon flow). (To ensure sufficient inoculation points) Based on the above process scheme, the experimental data obtained are shown in Table 2 below; the metallographic structure of the obtained product is as follows Figure 2~Figure 5 As shown; the physical picture of the obtained product is as shown Figure 6~Figure 9 shown.

[0038] Table 2 Performance test indicators

[0039] In summary, the present invention adopts 1-10mm large particle pretreatment agent and 0.2-0.8mm small particle pretreatment agent; 0.15% high barium inoculant is used for furnace discharge; and 0.1% ferrosilicon is used in the flow (inoculated to the ladle surface at the ladle mouth).

[0040] The above process produces ductile iron with high-temperature melting above 1620℃ and furnace-out time of more than 40 minutes. The quality is more stable and the mechanical properties far exceed the national standards. It can reach QT500-15 grade, laying a solid foundation for the production of more high-end and stable ductile iron castings for lost foam products and improving market competitiveness.

[0041] The embodiments of the present invention are described in detail above, but the contents are only preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the scope of the present invention shall be included in the protection scope of the present invention.

Claims

1. A high pouring temperature as-cast high elongation ductile iron process, characterized in that: The pretreatment agents used in this process include large-particle pretreatment agents with a particle size of 1~10mm and small-particle pretreatment agents with a particle size of 0.2~0.8mm; this process uses 0.15% high-barium inoculant during iron-out inoculation; this process uses 0.1% ferrosilicon in the flow during inoculation.

2. A high pouring temperature as-cast high elongation ductile iron process according to claim 1, characterized in that: The raw material ratio of this process is: 80% scrap steel, 20% Q12 pig iron.

3. A high pouring temperature as-cast high elongation ductile iron process according to claim 1, characterized in that: The large particle pretreatment agent is added at the midpoint of the smelting process, and the amount added is 1%.

4. A high pouring temperature as-cast high elongation ductile iron process according to claim 1, characterized in that: The small particle pretreatment agent is added 3-5 minutes before each out-of-furnace release, and the added amount is 0.15%.

5. A high pouring temperature as-cast high elongation ductile iron process according to claim 1, characterized in that: The method for adding the small particle pretreatment agent is as follows: 0.15% silicon carbide is added to the surface of the molten iron 3-5 minutes before it is taken out of the furnace, and then taken out of the furnace.

6. A high pouring temperature as-cast high elongation ductile iron process according to claim 1, characterized in that: The particle size of the ferrosilicon is 0.2-0.8 mm.

7. A high pouring temperature as-cast high elongation ductile iron process according to claim 1, characterized in that: During the wire feeding process of this process, the wire feeding amount is added at 0.75% and the residual magnesium is controlled between 0.04% and 0.045%.

8. A high pouring temperature as-cast high elongation ductile iron process according to claim 1, characterized in that: During the inoculation process, it is inoculated to the surface of the ladle.

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