Preparation method of as-cast qt700-10 nodular cast iron material

Abstract

The application provides a preparation method of a QT700-10 as-cast ductile iron material, and comprises the following steps: S1, preparing materials; S2, smelting molten iron; S3, putting low-magnesium and low-rare earth nodulizer at the bottom of a nodulizing ladle, covering 0.4-0.6wt% of silicon-barium-calcium inoculant in the total amount of molten iron in the nodulizing ladle on the low-magnesium and low-rare earth nodulizer; pouring the molten iron, stopping tapping when the amount of molten iron in the nodulizing ladle reaches 1 / 3, adding 0.2-0.4wt% of silicon-barium-calcium inoculant in the total amount of molten iron in the nodulizing ladle into the nodulizing ladle, and continuously pouring the molten iron to perform secondary inoculation treatment; stopping tapping when the amount of molten iron in the nodulizing ladle reaches 2 / 3, adding 0.2-0.4wt% of silicon-barium-calcium inoculant in the total amount of molten iron in the nodulizing ladle into the nodulizing ladle, and then continuously pouring the molten iron into the nodulizing ladle to perform nodulization and in-ladle inoculation treatment, and controlling the nodulization treatment temperature to be 1470-1500 DEG C; and S4, pouring. The application has the advantages that it helps to stabilize the production of QT700-10 castings, significantly improves the elongation, and is more beneficial to accelerate the popularization and application of high-performance ductile iron materials in safety components.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of cast iron materials, and particularly relates to a preparation method of as-cast QT700-10 nodular cast iron material. BACKGROUND

[0002] How to develop as-cast nodular cast iron material with high strength and high toughness is an important research topic in the current industrial field. The nodular cast iron material with excellent comprehensive performance has a strength of generally greater than or equal to 600 MPa, and the corresponding nodular cast iron grades are QT600-10, QT700-10 and QT800-5.

[0003] Advanced foundry enterprises abroad have stably realized the industrialization of as-cast QT700-10 and QT800-5 nodular cast iron parts. According to the existing nodular cast iron technology retrieval, SiboDur nodular cast iron is a kind of high-strength and high-toughness nodular cast iron suitable for the automobile industry. According to the analysis of the chemical composition and mechanical properties, SiboDur nodular cast iron takes silicon (Si) and boron (B) as alloying elements, and the comprehensive mechanical properties are much higher than those of traditional pearlite-ferrite nodular cast iron. Although the corresponding technical information has not been reported, it can be expected that the matrix structure is still a composite matrix structure of pearlite and ferrite mainly composed of pearlite. In order to obtain as-cast QT700-10 nodular cast iron material with excellent comprehensive mechanical properties, the optimization design of alloy composition and reasonable preparation technology need to be considered.

[0004] The alloy element range disclosed in the Chinese invention patent application with the publication number CN109536824A, "Low-cost high-strength and high-toughness as-cast QT700-10 and preparation method thereof", is difficult to explore whether the metallographic structure and mechanical properties meet the standard requirements, and the secondary inoculation and alloying treatment in the spheroidizing and inoculation process have safety hazards, which is not conducive to safety and batch production.

[0005] The Chinese invention patent with the publication number CN106811676B, "High-strength and high-toughness as-cast QT700-10 and production method thereof", adopts high-purity pig iron and high-quality non-rust low-carbon steel, which has a high cost of raw materials, and adopts the reverse ladling method for secondary inoculation treatment in the molten iron spheroidizing and inoculation process. The process is long and the operation is complicated.

[0006] The article "Preliminary Study on As-cast QT700-10 Technology" discusses the feasibility of developing as-cast QT700-10 process. The Ni element content range is 0.6-0.7%, which is not conducive to reducing production cost. Although the above alloying and molten iron treatment processes can also obtain nodular cast iron materials meeting the requirements, the preparation method of the nodular cast iron material still needs to be further improved. SUMMARY

[0007] In view of the above defects, the present application aims to provide a preparation method of as-cast QT700-10 nodular cast iron material, so as to obtain a nodular cast iron material with high toughness and high strength.

[0008] The present application provides a preparation method of as-cast QT700-10 nodular cast iron material, comprising the following steps:

[0009] S1, preparing raw materials: preparing raw materials according to the following mass percentages: pig iron: 40-60%, scrap steel: 25-40%, nodular iron return material: 5-20%, carbon additive: 1-1.5%, electrolytic copper plate: 0.3-0.4%, pure nickel plate: 0.1-0.2%, manganese iron: 0.2-0.3%;

[0010] S2, molten iron smelting: adding scrap steel, pig iron, carbon additive and nodular iron return material, after the scrap steel, pig iron and return material are completely melted, adding electrolytic copper plate, pure nickel plate and manganese iron, detecting by direct-reading spectroscopy, and adjusting the adding amount of electrolytic copper plate, pure nickel plate and manganese iron before the molten iron is discharged, and making component analysis before the molten iron is discharged; controlling the melting temperature to be 1350-1390℃, and controlling the molten iron discharge temperature to be 1470-1500℃;

[0011] S3, molten iron treatment in spheroidizing ladle: placing low-magnesium and low-rare earth spheroidizing agent at the bottom of the spheroidizing ladle, covering 0.4-0.6wt% of silicon barium calcium inoculant in the total amount of molten iron in the spheroidizing ladle on the low-magnesium and low-rare earth spheroidizing agent; pouring the molten iron, stopping the molten iron discharge when the amount of molten iron in the spheroidizing ladle reaches 1 / 3, adding 0.2-0.4wt% of silicon barium calcium inoculant in the total amount of molten iron in the spheroidizing ladle into the spheroidizing ladle, continuing to pour the molten iron for secondary inoculation treatment; stopping the molten iron discharge when the amount of molten iron in the spheroidizing ladle reaches 2 / 3, adding 0.2-0.4wt% of silicon barium calcium inoculant in the total amount of molten iron in the spheroidizing ladle into the spheroidizing ladle, and then continuing to pour the molten iron into the spheroidizing ladle for spheroidizing and inoculation treatment, and controlling the spheroidizing treatment temperature to be 1470-1500℃;

[0012] S4, pouring: transferring the spheroidizing treated molten iron ladle to the pouring site for pouring, controlling the molten iron pouring temperature to be 1400-1430℃, and adding strontium silicon inoculant with the molten iron above the pouring cup during pouring.

[0013] Preferably, in the step S1, the pig iron comprises the following mass percentages of components: C: 4.3-4.5%, Si: 0.8-0.9%, Mn: <0.1%, P: <0.04%, S: <0.02%; the scrap steel comprises the following mass percentages of components: C: 0.1-0.15%, Si: 0.2-0.4%, Mn: 1-1.3%, P: <0.03%, S: <0.02%.

[0014] Preferably, in the step S3, the particle size of the silicon-barium-calcium inoculant is 3-10mm, and the inoculant comprises the following components by mass percentage: Ca: 0.5-2.5%, Si: 65-72%, Al: <1.5%, and Ba: 4.0-6.0%.

[0015] Preferably, in the step S3, the spheroidizing package is a dam-type package, and the low-magnesium and low-rare earth spheroidizing agent is selected from FeSiMg5RE1 type spheroidizing agent with a particle size of 10-30mm.

[0016] Preferably, the FeSiMg5RE1 type spheroidizing agent comprises the following components by mass percentage: RE: 0.8-1.2%, Mg: 5.0-5.5%, Si: 39-43%, Al: <1%, and Ca: 2.0-3.0%.

[0017] Preferably, in the step S3, after the spheroidizing reaction is completed, sampling and detection are performed to control the molten iron after spheroidizing to comprise the following components by mass percentage: C: 3.5-3.7%, Si: 2.6-2.8%, Mn: 0.4-0.5%, Cu: 0.4-0.5%, Ni: 0.1-0.3%, P: <0.02%, S: <0.02%, Mg: 0.04-0.05%, RE: 0.01-0.02%, and the balance being Fe and inevitable impurities.

[0018] Preferably, in the step S4, the particle size of the strontium silicon inoculant is 0.2-0.8mm.

[0019] Preferably, the method further comprises the following steps:

[0020] S5, filtering: filtering the molten iron by using a foamed ceramic filter;

[0021] S6, sand mold heat preservation: after heat preservation for 12 hours, the sand mold is knocked out and opened.

[0022] Preferably, in the step S5, the material of the foamed ceramic filter comprises any one or more of ZrO2, SiC, and Al2O3.

[0023] Preferably, in the step S5, the foamed ceramic filter is placed on both sides of the cross gate.

[0024] The method has the following advantages:

[0025] 1. The as-cast QT700-10 ductile iron prepared by the method has a tensile strength Rm of ≥700 MPa, a yield strength Rp0.2 of ≥450 MPa, an elongation A of ≥10%, a pearlite content in the matrix structure in the range of 45-60%, a ferrite content in the range of 35-50%, a spheroidization grade of 1-2, and a graphite ball size of 6-7, and a spheroidization rate of the graphite ball of ≥90%. The application helps to stably produce QT700-10 castings, and significantly improves the elongation compared with the national standard QT700-2, and is more beneficial to the popularization and application of high-performance ductile iron materials in safety components.

[0026] 2. The main alloying element range of the application is the first key technology of the application: the Si content is controlled in the range of 2.6-2.8%, the C content is controlled in the range of 3.5-3.7%, the Cu content is controlled in the range of 0.4-0.5%, the Ni content is controlled in the range of 0.1-0.3%, and the Mn content is controlled in the range of 0.4-0.5%. Through the component optimization design and reasonable trace alloy element control, the ratio of pearlite and ferrite in the ductile iron is adjusted, so that the elongation and tensile strength of the ductile iron are improved.

[0027] 3. The multi-stage inoculant treatment technology of the application is the second key technology of the application: through the hierarchical inoculation effect strengthening, the silicon barium calcium inoculant is put into the spheroidizing package, the silicon barium calcium inoculant is intermittently added in the spheroidizing package, and the strontium silicon inoculant is applied during pouring, so that many micro-concentration fluctuations and temperature fluctuations are generated in the molten iron, and then many graphite cores are generated, the number of graphite balls is increased, and the graphitization is promoted. At the same time, the inoculation recession is effectively prevented, the recession time is prolonged, the graphite ball size grade is significantly improved, the solidification structure of the castings is improved, and the comprehensive performance of the as-cast ductile iron is improved. BRIEF DESCRIPTION OF DRAWINGS

[0028] Figure 1 The as-cast matrix structure and the etched metallographic photos (100 times) of Example 1 of the application are shown in the figure;

[0029] Figure 2 The as-cast matrix structure and the etched metallographic photos (100 times) of Comparative Example 1 of the application are shown in the figure;

[0030] Figure 3 The as-cast matrix structure and the etched metallographic photos (100 times) of Comparative Example 2 of the application are shown in the figure;

[0031] Figure 4 The as-cast matrix structure and the etched metallographic photos (100 times) of Comparative Example 3 of the application are shown in the figure;

[0032] Figure 5 The as-cast matrix structure and the etched metallographic photos (100 times) of Comparative Example 4 of the application are shown in the figure;

[0033] Figure 6 Casting state base material structure and corrosion state metallographic photo (100 times) of the present application comparative example 5;

[0034] Figure 7 Casting state base material structure and corrosion state metallographic photo (100 times) of the present application comparative example 6;

[0035] Figure 8 Casting state base material structure and corrosion state metallographic photo (100 times) of the present application comparative example 7;

[0036] Figure 9 Casting state base material structure and corrosion state metallographic photo (100 times) of the present application comparative example 8;

[0037] Figure 10 Casting state base material structure and corrosion state metallographic photo (100 times) of the present application comparative example 9;

[0038] Figure 11 Casting state base material structure and corrosion state metallographic photo (100 times) of the present application comparative example 10;

[0039] Figure 12 Casting state base material structure and corrosion state metallographic photo (100 times) of the present application comparative example 11. DETAILED DESCRIPTION

[0040] In order to make the objects, technical solutions and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be described below in connection with the data in the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative work fall within the protection scope of the present application.

[0041] Embodiment 1

[0042] The embodiment provides a preparation method of a casting state QT700-10 ductile iron material, and comprises the following steps:

[0043] S1, preparation: prepare each raw material according to the following mass percentage, pig iron: 40-60%, scrap steel: 25-40%, nodular iron return material: 5-20%, carburant: 1-1.5%, electrolytic copper plate: 0.3-0.4%, pure nickel plate: 0.1-0.2%, manganese iron 0.2-0.3%. Specifically, the pig iron used is Q10 pig iron for nodular iron, including the following mass percentage of components: C: 4.3-4.5%, Si: 0.8-0.9%, Mn <0.1%, P <0.04%, S <0.02%. The scrap steel is high-quality carbon scrap steel, including the following mass percentage of components: C: 0.1-0.15%, Si: 0.2-0.4%, Mn: 1-1.3%, P <0.03%, S <0.02%. The pig iron and scrap steel need to be treated by shot blasting before use to remove surface rust and other impurities.

[0044] S2, molten iron smelting: first add scrap steel, pig iron, carburant and nodular iron return material into the melting ladle, after the scrap steel, pig iron and return material are completely melted, add electrolytic copper plate, pure nickel plate and manganese iron, detect by direct-reading spectroscopy, and adjust the amount of electrolytic copper plate, pure nickel plate and manganese iron before the furnace is discharged, and make component analysis before discharge; control the melting temperature to be 1350-1390℃, and control the molten iron discharge temperature to be 1470-1500℃.

[0045] S3, molten iron treatment in nodularizing ladle: the in-ladle nodularizing method uses the impingement method, FeSiMg5RE1 low-magnesium low-rare earth nodularizing agent is placed at the bottom of one side of the nodularizing ladle, then CBSALLOY type silicon barium calcium inoculant is placed on the upper part of the low-magnesium low-rare earth nodularizing agent, the molten iron is discharged into the nodularizing ladle, and in-ladle nodularizing and hierarchical inoculation treatment are carried out, and the nodularizing treatment temperature is controlled to be 1470-1500℃.

[0046] The nodularizing ladle used in this embodiment is a dam type treatment ladle, and the total amount of molten iron in the nodularizing ladle is N kg, and the nodularizing reaction time is controlled to be 20-30 seconds. The particle size of the low-magnesium low-rare earth nodularizing agent is 10-30 mm, and includes the following mass percentage of components: RE: 0.8-1.2%, Mg: 5.0-5.5%, Si: 39-43%, Al: <1%, Ca: 2.0-3.0%.

[0047] 0.4-0.6% N CBSALLOY type silicon barium calcium inoculant is uniformly covered on the metal particles of the low-magnesium low-rare earth nodularizing agent, the particles in the nodularizing ladle are tamped, and then nodular iron sheet is used to cover it to prevent the nodularizing agent from reacting violently.

[0048] In the hierarchical inoculation process, first pour 1 / 3N molten iron, stop tapping, add 0.2-0.4% N silicon barium calcium inoculant to the spheroidizing ladle, continue to pour molten iron for secondary inoculation treatment; when the molten iron in the spheroidizing ladle reaches 2 / 3N, stop tapping, add 0.2-0.4% N silicon barium calcium inoculant to the spheroidizing ladle, and then continue to pour molten iron into the spheroidizing ladle. After the spheroidization reaction is completed, sampling is detected, and the molten iron after spheroidization includes the following mass percentages: C: 3.5-3.7%, Si: 2.6-2.8%, Mn: 0.4-0.5%, Cu: 0.4-0.5%, Ni: 0.1-0.3%, P < 0.02%, S < 0.02%, Mg: 0.04-0.05%, RE: 0.01-0.02%, and the balance is Fe and unavoidable impurities. After the reaction is completed, the molten iron in the spheroidizing ladle is sprinkled with a slag remover to quickly remove slag, and the surface of the molten iron is pulled clean of slag.

[0049] The particle size of the silicon barium calcium inoculant used is 3-10 mm, and it includes the following mass percentages: Ca: 0.5-2.5%, Si: 65-72%, Al: <1.5%, and Ba: 4.0-6.0%.

[0050] S4, pouring: the molten iron after spheroidization is transferred to the pouring site for pouring, and the pouring temperature of the molten iron is controlled at 1400-1430°C. When pouring, 0.05-0.15wt% strontium silicon inoculant is added to the molten iron above the sprue cup, and the particle size of the strontium silicon inoculant is 0.2-0.8mm. The time from the end of spheroidization to the completion of pouring is controlled within 8 minutes.

[0051] S5, filtering: a foam ceramic filter is used to filter the molten iron. The material of the foam ceramic filter includes any one or more of ZrO2, SiC, and Al2O3. A specific material includes: 80-65wt% ZrO2, 10-25wt% SiC, and 10-25% Al2O3. The pore size of the foam ceramic filter is 5-30 ppi, and specifically 10 ppi, and the size is 80mm x 80mm x 30mm. The foam ceramic filter is placed on both sides of the cross gate.

[0052] S6, sand mold heat preservation: after 12 hours of heat preservation, the sand mold is knocked out and the box is opened.

[0053] Between steps S5 and S6, a step of single-casting Y-shaped test block is also included. The size of the Y-shaped test block is in accordance with the relevant provisions of GB / T 1348-2009 Nodular Iron Castings. The single-cast Y-shaped test block is dissected, and the core position is processed into a tensile test bar, a metallographic sample, and a component analysis sample for chemical composition, metallographic structure, and mechanical property testing.

[0054] The chemical analysis results of the single cast test block prepared above are shown in Table 1, the as-cast metallographic structure test results are shown in Table 2, and the as-cast matrix structure and the etched metallographic photos are shown in Figs. 1 and 2. Figure 1 The spheroidization grade of the nodular cast iron prepared in this embodiment is 1-2 grade, the graphite ball size is 6-7 grade, the spheroidization rate is ≥90%, the pearlite content of the matrix structure is in the range of 45-60%, and the ferrite content is in the range of 35-50%. The performance test of the as-cast high-strength and high-toughness QT700-10 nodular cast iron prepared in this embodiment is shown in Table 3. The test results show that the mechanical properties of the single cast test block of this embodiment reach Rm≥700 MPa, Rp0.2≥450 MPa, and A≥10%. The various performances meet the design requirements.

[0055] Comparative Example 1

[0056] The difference between this comparative example and Example 1 is that the mass percentage of C element in the molten iron after spheroidization is 3.2-3.5%.

[0057] The chemical analysis results of the single cast test block of Comparative Example 1 are shown in Table 1, the as-cast metallographic structure test is shown in Table 2, and the as-cast matrix structure and the etched metallographic photos are shown in Figs. 1 and 2. Figure 2 The spheroidization grade is 2 grade, the graphite ball size is 5-6 grade, the spheroidization rate is ≥90%, the pearlite content of the matrix structure is in the range of 45-60%, and the ferrite content is in the range of 35-50%. The performance test is shown in Table 3. The test results show that when the mass percentage of C element is controlled in the range of 3.2-3.5%, the tensile strength and the yield strength of the mechanical properties of the single cast test block meet the design requirements, and the elongation is <10%.

[0058] Comparative Example 2

[0059] The difference between this comparative example and Example 1 is that the mass percentage of C element in the molten iron after spheroidization is 3.8-4.0%.

[0060] The chemical analysis results of the single cast test block of Comparative Example 2 are shown in Table 1, the as-cast metallographic structure test is shown in Table 2, and the as-cast matrix structure and the etched metallographic photos are shown in Figs. 1 and 2. Figure 3 The spheroidization grade is 2-3 grade, the graphite ball size is 5-6 grade, the spheroidization rate is ≥90%, the pearlite content of the matrix structure is in the range of 45-60%, and the ferrite content is in the range of 35-50%. The performance test is shown in Table 3. The test results show that when the mass percentage of C element is controlled in the range of 3.8-4.0%, the yield strength and the elongation of the mechanical properties of the single cast test block do not meet the design requirements, and the metallographic structure also does not meet the design requirements.

[0061] Comparative Example 3

[0062] The difference between this comparative example and Example 1 is that the mass percentage of Si element in the molten iron after spheroidization is 2.3-2.5%.

[0063] The chemical analysis results of the single casting test block of Comparative Example 3 are shown in Table 1, the as-cast metallographic structure test is shown in Table 2, and the as-cast matrix structure and the etched metallographic photos are shown in Figure 4 The spheroidization level is 2-3, the graphite ball size is 5-6, the spheroidization rate is ≥90%, the pearlite content of the matrix structure is in the range of 55-65%, and the ferrite content is in the range of 30-45%. The performance test is shown in Table 3, and the test results show that when the mass percentage of Si element is controlled in 2.3-2.5%, the yield strength and the elongation of the single casting test block do not meet the design requirements, and the metallographic structure does not meet the design requirements.

[0064] Comparative Example 4

[0065] The difference between this comparative example and Example 1 is that the mass percentage of Si element in the spheroidized molten iron is 2.9-3.0%.

[0066] The chemical analysis results of the single casting test block of Comparative Example 4 are shown in Table 1, the as-cast metallographic structure test is shown in Table 2, and the as-cast matrix structure and the etched metallographic photos are shown in Figure 5 The spheroidization level is 1-2, the graphite ball size is 6-7, the spheroidization rate is ≥90%, the pearlite content of the matrix structure is in the range of 35-45%, and the ferrite content is in the range of 50-65%. The performance test is shown in Table 3, and the test results show that when the mass percentage of Si element is controlled in 2.9-3.0%, the elongation of the single casting test block is slightly lower than the design requirement.

[0067] Comparative Example 5

[0068] The difference between this comparative example and Example 1 is that the mass percentage of Mn element in the spheroidized molten iron is 0.75-0.85%.

[0069] The chemical analysis results of the single casting test block of Comparative Example 5 are shown in Table 1, the as-cast metallographic structure test is shown in Table 2, and the as-cast matrix structure and the etched metallographic photos are shown in Figure 6 The spheroidization level is 1-2, the graphite ball size is 6-7, the spheroidization rate is ≥90%, the pearlite content of the matrix structure is in the range of 45-55%, and the ferrite content is in the range of 40-55%. The performance test is shown in Table 3, and the test results show that when the mass percentage of Mn element is controlled in 0.75-0.85%, the tensile strength and the yield strength of the single casting test block are higher than the design requirements, and the elongation is lower than the design requirements.

[0070] Comparative Example 6

[0071] The difference between this comparative example and Example 1 is that the mass percentage of Mn element in the spheroidized molten iron is 0.35-0.4%.

[0072] The chemical analysis results of the single cast test block of Comparative Example 6 are shown in Table 1, the as-cast metallographic structure test is shown in Table 2, and the as-cast matrix structure and the etched metallographic photos are shown in Figure 7 The spheroidization level is 1-2 grade, the graphite ball size is 6-7 grade, the spheroidization rate is ≥90%, the pearlite content of the matrix structure is in the range of 30-40%, and the ferrite content is in the range of 55-70%. The performance test results are shown in Table 3. The test results show that when the mass percentage of Mn element is controlled in the range of 0.35-0.4%, the mechanical properties of the single cast test block do not meet the design requirements.

[0073] Comparative Example 7

[0074] The difference between this comparative example and Example 1 is that no Ni element is added in Comparative Example 7.

[0075] The chemical analysis results of the single cast test block of Comparative Example 7 are shown in Table 1, the as-cast metallographic structure test is shown in Table 2, and the as-cast matrix structure and the etched metallographic photos are shown in Figure 8 The spheroidization level is 1-2 grade, the graphite ball size is 6-7 grade, the spheroidization rate is ≥90%, the pearlite content of the matrix structure is in the range of 45-60%, and the ferrite content is in the range of 35-50%. The performance test results are shown in Table 3. The test results show that without adding Ni element, the tensile strength and the yield strength of the single cast test block are slightly lower than the design requirements, and the elongation meets the design requirements.

[0076] Comparative Example 8

[0077] The difference between this comparative example and Example 1 is that the mass percentage of Ni element in the molten iron after spheroidization is 0.35-0.45%.

[0078] The chemical analysis results of the single cast test block of Comparative Example 8 are shown in Table 1, the as-cast metallographic structure test is shown in Table 2, and the as-cast matrix structure and the etched metallographic photos are shown in Figure 9 The spheroidization level is 1-2 grade, the graphite ball size is 6-7 grade, the spheroidization rate is ≥90%, the pearlite content of the matrix structure is in the range of 45-60%, and the ferrite content is in the range of 35-50%. The performance test results are shown in Table 3. The test results show that when the mass percentage of Ni element is controlled in the range of 0.35-0.45%, the tensile strength and the yield strength of the single cast test block meet the design requirements, and the elongation is far lower than the design requirements.

[0079] Comparative Example 9

[0080] The difference between this comparative example and Example 1 is that the mass percentage of Cu element in the molten iron after spheroidization is 0.3-0.4%.

[0081] The chemical analysis results of the single cast test block of Comparative Example 9 are shown in Table 1, the as-cast metallographic structure test is shown in Table 2, and the as-cast matrix structure and the etched metallographic photos are shown in Figure 10The spheroidization level is 1-2, the graphite ball size is 6-7, the spheroidization rate is ≥90%, the pearlite content of the matrix structure is in the range of 40-55%, and the ferrite content is in the range of 40-55%. The performance test is shown in Table 3. The test results show that when the mass percentage of Cu element is controlled to be 0.3-0.4%, the mechanical properties of the single-cast test block are far lower than the design requirements.

[0082] Comparative Example 10

[0083] The difference between the present comparative example and Example 1 is that the mass percentage of Cu element in the spheroidized molten iron is 0.55-0.7%.

[0084] The chemical analysis results of the single-cast test block of Comparative Example 10 are shown in Table 1, the as-cast metallographic structure test is shown in Table 2, and the as-cast matrix structure and the etched metallographic photos are shown in Figure 11 The spheroidization level is 1-2, the graphite ball size is 6-7, the spheroidization rate is ≥90%, the pearlite content of the matrix structure is in the range of 55-70%, and the ferrite content is in the range of 25-40%. The performance test is shown in Table 3. The test results show that when the mass percentage of Cu element is controlled to be 0.55-0.7%, the elongation of the single-cast test block is far lower than the design requirements.

[0085] Comparative Example 11

[0086] The difference between the present comparative example and Example 1 is that the conventional method of pouring into the spheroidizing ladle is used for the melt spheroidization and inoculation treatment, instead of the hierarchical inoculation treatment method.

[0087] The chemical analysis results of the single-cast test block of Comparative Example 11 are shown in Table 1, the as-cast metallographic structure test is shown in Table 2, and the as-cast matrix structure and the etched metallographic photos are shown in Figure 12 The spheroidization level is 1-2, the graphite ball size is 6-7, the spheroidization rate is ≥90%, the pearlite content of the matrix structure is in the range of 45-60%, and the ferrite content is in the range of 35-50%. The performance test is shown in Table 3. The test results show that when the conventional method of pouring into the spheroidizing ladle is used for the melt spheroidization and inoculation treatment, the mechanical properties of the single-cast test block are all slightly lower than the design requirements, the number of graphite balls per unit area is significantly reduced, the inoculation effect is not good, and it is not conducive to the improvement of the comprehensive mechanical properties.

[0088] Table 1: Alloy element composition table after furnace of QT700-10

[0089]

[0090] Table 2: As-cast matrix metallographic structure test results

[0091] Item Spheroidization level Graphite ball size level Spheroidization rate Matrix structure Example 1-2 level 6-7 level ≥90％ 45-60% pearlite, 35-50% ferrite Comparative Example 1 2 level 5-6 level ≥90％ 45-60% pearlite, 35-50% ferrite Comparative Example 2 2-3 level 5-6 level ≥90％ 45-60% pearlite, 35-50% ferrite Comparative Example 3 2-3 level 5-6 level ≥90％ 55-65% pearlite, 30-45% ferrite Comparative Example 4 1-2 level 6-7 level ≥90％ 35-45% pearlite, 50-65% ferrite Comparative Example 5 1-2 level 6-7 level ≥90％ 45-55% pearlite, 40-55% ferrite Comparative Example 6 1-2 level 6-7 level ≥90％ 30-40% pearlite, 55-70% ferrite Comparative Example 7 1-2 level 6-7 level ≥90％ 45-60% pearlite, 35-50% ferrite Comparative Example 8 1-2 level 6-7 level ≥90％ 45-60% pearlite, 35-50% ferrite Comparative Example 9 1-2 level 6-7 level ≥90％ 40-55% pearlite, 40-55% ferrite Comparative Example 10 1-2 level 6-7 level ≥90％ 55-70% pearlite, 25-40% ferrite Comparative Example 11 1-2 level 6-7 level ≥90％ 45-60% pearlite, 35-50% ferrite

[0092] Table 3: Mechanical property test results of as-cast QT700-10

[0093] Item Tensile strength MPa Yield strength MPa Elongation % Hardness HB Example 735 / 705 / 705 470 / 455 / 450 11.5 / 10.5 / 10.5 201 Comparative Example 1 710 / 790 / 750 465 / 490 / 470 11 / 7.0 / 7.0 210 Comparative Example 2 760 / 775 / 720 435 / 410 / 440 8.5 / 10 / 9.5 204 Comparative Example 3 710 / 705 / 700 430 / 430 / 435 5.5 / 6.0 / 5.5 195 Comparative Example 4 770 / 770 / 770 475 / 475 / 475 7.0 / 7.0 / 8 212 Comparative Example 5 760 / 775 / 790 470 / 465 / 480 6.5 / 8 / 5.5 220 Comparative Example 6 685 / 720 / 685 425 / 445 / 425 10 / 7 / 7 198 Comparative Example 7 695 / 680 / 670 430 / 425 / 415 10 / 10.5 / 11.5 190 Comparative Example 8 700 / 760 / 740 445 / 465 / 465 5.5 / 7.5 / 8.5 205 Comparative Example 9 690 / 775 / 720 405 / 465 / 415 11 / 10 / 9.5 208 Comparative Example 10 740 / 750 / 755 440 / 470 / 485 6.0 / 7.0 / 8.5 211 Comparative Example 11 690 / 685 / 705 430 / 420 / 435 6.5 / 7.5 / 8.0 205

[0094] The above merely describes the preferred embodiments of the present application. It should be noted that those skilled in the art can make several improvements and replacements without departing from the technical principles of the present application, and these improvements and replacements should also be considered as the protection scope of the present application.

Claims

1. A method for preparing as-cast QT700-10 ductile iron material, characterized in that: The following steps are involved: S1. Material preparation: Prepare the raw materials according to the following mass percentages: pig iron: 40-60%, scrap steel: 25-40%, ductile iron return material: 5-20%, recarburizer: 1-1.5%, electrolytic copper plate: 0.3-0.4%, pure nickel plate: 0.1-0.2%, ferromanganese 0.2-0.3%; S2. Hot metal smelting: adding scrap steel, pig iron, recarburizer and ductile iron return charge. After the scrap steel, pig iron and return charge are all melted, adding electrolytic copper plate, pure nickel plate and ferromanganese. Direct reading spectrum detection is used. The amount of electrolytic copper plate, pure nickel plate and ferromanganese added is adjusted before being discharged from the furnace. The composition analysis is performed before being discharged from the furnace. The melting temperature is controlled at 1350-1390°C and the hot metal discharge temperature is controlled at 1470-1500°C. S3, spheroidizing ladle molten iron treatment: low magnesium and low rare earth spheroidizing agent is placed on one side of the bottom of the spheroidizing ladle, and silicon barium calcium inoculant accounting for 0.4-0.6wt% of the total amount of molten iron in the spheroidizing ladle is covered on the low magnesium and low rare earth spheroidizing agent; pouring molten iron, when the amount of molten iron in the spheroidizing ladle reaches 1 / 3, stopping tapping, adding silicon barium calcium inoculant accounting for 0.2-0.4wt% of the total amount of molten iron in the spheroidizing ladle, and continuing to pour molten iron for secondary inoculation treatment; when the amount of molten iron in the spheroidizing ladle reaches 2 / 3, stopping tapping, adding silicon barium calcium inoculant accounting for 0.2-0.4wt% of the total amount of molten iron in the spheroidizing ladle , then continue to pour molten iron into the spheroidizing ladle for spheroidization and ladle inoculation treatment, and control the spheroidizing treatment temperature to be 1470-1500°C; after the spheroidizing reaction is completed, sampling and testing are performed, and the molten iron after spheroidization is controlled to include the following components in mass percentage: C: 3.5-3.7%, Si: 2.6-2.8%, Mn: 0.4-0.5%, Cu: 0.4-0.5%, Ni: 0.1-0.3%, P < 0.02%, S < 0.02%, Mg: 0.04-0.05%, RE: 0.01-0.02%, and the balance is Fe and unavoidable impurities; S4. Pouring: The spheroidized molten iron ladle is transferred to the pouring site for pouring. The pouring temperature of the molten iron is controlled at 1400-1430°C. During pouring, strontium silicon inoculant is added along with the molten iron above the pouring cup.

2. The preparation method according to claim 1, characterized in that In step S1, the pig iron includes the following components in mass percentage: C: 4.3-4.5%, Si: 0.8-0.9%, Mn < 0.1%, P < 0.04%, S < 0.02%; the scrap steel includes the following components in mass percentage: C: 0.1-0.15%, Si: 0.2-0.4%, Mn: 1-1.3%, P < 0.03%, S < 0.02%.

3. The preparation method according to claim 1, characterized in that In step S3, the silicon-barium-calcium inoculant has a particle size of 3 to 10 mm and includes the following components in mass percentage: Ca: 0.5 to 2.5%, Si: 65 to 72%, Al: <1.5%, and Ba: 4.0 to 6.0%.

4. The preparation method according to claim 1, characterized in that In step S3, the spheroidizing bag is a dam-type processing bag, and the low-magnesium and low-rare-earth spheroidizing agent is a FeSiMg5RE1 type spheroidizing agent with a particle size of 10 to 30 mm.

5. The preparation method according to claim 4, characterized in that The FeSiMg5RE1 type spheroidizer includes the following components in mass percentage: RE: 0.8-1.2%, Mg: 5.0-5.5%, Si: 39-43%, Al: <1%, and Ca: 2.0-3.0%.

6. The preparation method according to claim 1, characterized in that In the step S4, the particle size of the strontium silicon inoculant is 0.2-0.8 mm.

7. The preparation method according to claim 1, characterized in that The following steps are also included: S5. Filtration: Filter the molten iron using a ceramic foam filter; S6. Sand mold insulation: After 12 hours of insulation, the sand is removed and unpacked.

8. The preparation method according to claim 7, characterized in that In the step S5, the material of the foam ceramic filter includes any one or more of ZrO2, SiC, and Al2O3.

9. The preparation method according to claim 7, characterized in that In step S5, the ceramic foam filters are placed on both sides of the runner.

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