Method for realizing QT600-10 in green sand casting by using low-alloy combination

Abstract

The invention discloses a method for realizing QT600-10 in green sand casting by using a low alloy combination, and relates to the field of alloy materials, and the method comprises the following steps: step 1, proportioning and smelting: the QT600-10 nodular cast iron comprises the following components in percentage by mass: 3.55-3.85% of C, 2.3-2.9% of Si, 0.2-0.3% of Mn, less than or equal to 0.04% of P, less than or equal to 0.02% of S, less than or equal to 0.1% of Cu, 0.035-0.05% of Sn, less than or equal to 0.08% of Cr and the balance of Fe and impurities, and the total amount of other measurable alloys is less than or equal to 0.1%; silicon-manganese-tin alloying is adopted to replace copper, nickel, chromium or copper-tin composite alloy used in a traditional process, so that the overall production benefit is improved, the proportion of pearlite to ferrite is optimized, and the strength and the ductility are improved.

Description

Technical Field

[0001] The present invention relates to the technical field of alloy materials, and particularly to a method for realizing QT600-10 in green sand casting with a low alloy combination. Background Art

[0002] With the rapid development of industry, ductile iron, as an important casting material, has increasingly strict requirements for its mechanical properties and production stability. Due to its excellent mechanical properties, toughness and wear resistance, ductile iron has been widely used in fields such as automobiles, mechanical equipment, and pipelines. Producing ductile iron by the as-cast process can effectively reduce production costs, simplify the production process, and shorten the production cycle. By controlling parameters such as the composition of alloying elements and casting temperature during the casting process, precise control of the internal structure and mechanical properties of the casting can be achieved. Currently, this process is being promoted and applied by more and more manufacturing enterprises.

[0003] In the grading standards of ductile iron in various countries, the international standard ISO1083-87 is generally adopted. This standard clearly divides parameters such as the structure and mechanical properties of ductile iron, ensuring the comparability and compatibility of products between different manufacturers.

[0004] Currently, many enterprises and institutions of higher learning have conducted research and development on QT600-10, all of which adopt the method mainly adding copper or adding copper and tin, and obtained in the iron coated sand or shell type steel shot buried box molding process. The cost of iron coated sand is relatively high, and the original process relies on alloying with precious metals such as Cu, Ni, and Cr, increasing the cost of materials per ton. The shell type steel shot buried box molding limits the application scenarios of the green sand molding process, with a fast nodular decay rate and carbide exceeding the standard in thin-walled parts. The elongation rate of traditional QT600-3 is 3-5.9%, which is difficult to meet the requirement of the elongation rate ≥10% for new hydraulic components, and the production of QT600-10 still relies on expensive heat treatment. Summary of the Invention

[0005] (1) Technical problems to be solved: Aiming at the above-mentioned disadvantages of the existing technology, the present invention provides a method for realizing QT600-10 in green sand casting with a low alloy combination, which can effectively solve the problems of the existing technology.

[0006] (2) Technical solutions: To achieve the above purposes, the present invention is realized through the following technical solutions.

[0007] The present invention discloses a method for realizing QT600-10 in green sand casting with a low alloy combination, including the following steps: Step 1, batching and melting: By mass fraction, the QT600-10 ductile iron contains: C: 3.55% - 3.85%, Si: 2.3% - 2.9%, Mn: 0.2% - 0.3%, P ≤ 0.04%, S ≤ 0.02%, Cu ≤ 0.1%, Sn: 0.035% - 0.05%, Cr ≤ 0.08%, the balance being Fe and impurities, and the total amount of other measurable alloys ≤ 0.1%; during melting, the molten iron is allowed to stand for 10 - 15 minutes at 1480 - 1520 °C; Step 2, spheroidizing and pouring: For the plunging method, a low-rare-earth spheroidizing agent containing Re: 0.5 - 1%, Mg: 5.2 - 5.8% is used, in combination with a silicon-barium-calcium composite inoculant with Ba / Ca = 1.5 - 2; for the wire feeding method, a silicon-calcium-magnesium-rare-earth composite cored wire for spheroidizing and a silicon-barium-calcium-magnesium-rare-earth composite cored wire for inoculation are used; during pouring, staged in-stream inoculation is carried out: 70% of the silicon-barium-calcium composite inoculant with a particle size of 3 - 8 mm is added when pouring from the ladle, and 30% of the silicon-barium-calcium composite inoculant with a particle size of 0.2 - 0.8 mm is added during pouring, with a total addition amount of 0.1 - 0.3%; in both methods, the casting should obtain Mg: 0.035% - 0.055%, Re: 0.008% - 0.02%; the total time from spheroidizing to pouring end ≤ 8 minutes; Step 3, low-temperature shakeout: The casting and test block are shaken out after cooling to below 300 °C; Step 4, performance testing: The single-cast test block meets the requirements: tensile strength ≥ 600 MPa, yield strength ≥ 370 MPa, elongation ≥ 10%, Brinell hardness 190 - 230 HB; metallographic structure: nodularity 1 - 3 grades, graphite ball diameter 5 - 8 grades, pearlite 35 - 65%, ferrite matrix without carbides.

[0008] Furthermore, the Sn element in Step 1 is added in the form of pure tin grain alloy, and the addition time is added into the ladle when tapping. The parameters of the green sand are: water content 3.2 - 3.8%, compactness 85 - 92.

[0009] Furthermore, the components of the low-rare-earth spheroidizing agent in Step 2, by mass fraction, are: Re: 0.5 - 1%, Mg: 5.2 - 5.8%, Si: 40 - 45%, Ca: 1.5 - 2.5%, Al ≤ 1.0%, the balance being Fe; the addition amount is 1.0 - 1.2% of the mass of the molten iron, and the particle size is 5 - 25 mm.

[0010] Furthermore, the components of the silicon-barium-calcium composite inoculant in Step 2, by mass fraction, are: Si ≥ 70%, Ba: 1.5 - 3.0%, Ca: 1.0 - 2.0%, Ba / Ca = 1.5 - 2, the balance being Fe; the addition amount of the inoculant for the plunging method is 0.6 - 0.9%, and the particle size is 0.7 - 6 mm.

[0011] Furthermore, the wire diameter of the silicon-calcium-magnesium-rare-earth composite cored spheroidized wire in step 2 is 9-13 mm, and the wire diameter of the silicon-barium-calcium-magnesium-rare-earth composite cored inoculated wire is 8-12 mm.

[0012] Furthermore, the feed rate of the silicon-calcium-magnesium-rare earth composite core spheroidizing line in step 2 is 28-32 m / min, and the feed rate of the silicon-barium-calcium-magnesium-rare earth composite core inoculation line is 18-22 m / min.

[0013] Furthermore, in step 4, the test block is taken from the critical wall thickness or main wall thickness of the casting, the wall thickness difference at the detection position is ≤3mm, and the detection is performed in the cast state.

[0014] (III) Beneficial effects: Compared with the known prior art, the technical solution provided by the present invention has the following beneficial effects: 1. By using silicon-manganese-tin alloying to replace copper, nickel, chromium or copper-tin composite alloys used in traditional processes, not only the use of precious metals is reduced, the overall production efficiency is improved, and the economic burden of the enterprise is reduced, but also the material properties are improved by forming nano-precipitated phases, and the ratio of pearlite and ferrite is optimized, thereby improving the strength and elongation at the same time, making the casting more resilient when subjected to high loads, and adapting to the high requirements of modern industry for materials.

[0015] 2. Controlling decay by limiting pouring time and inoculating in stages. Combining primary inoculation with final inoculation greatly improves the spheroidizing effect, shortens production cycle, improves production line efficiency, and increases qualified rate. Low-temperature sand dropping and staged inoculation reduce the carbide content of thin-walled parts, avoid the tendency of white cast iron, and can effectively reduce casting defects. It is suitable for the production of complex thin-walled castings. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the prior art descriptions. Obviously, the drawings described below are only some embodiments of the present invention, and for ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0017] Figure 1 It is a schematic diagram of the process of the present invention. DETAILED DESCRIPTION

[0018] To make the objectives, technical solutions and advantages of the embodiments of the present invention clearer, the following will clearly and completely describe the technical solutions in the embodiments of the present invention with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are some, but not all, of the embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the scope of protection of the present invention.

[0019] The following further describes the present invention with reference to embodiments.

[0020] ① Embodiment 1: A method for achieving QT600-10 in green sand casting using a low-alloy combination includes: Step 1: Batching and melting Composition (wt%): C: 3.68%, Si: 2.5%, Mn: 0.25%, P: 0.03%, S: 0.018%, Cu: 0.08%, Sn: 0.04%, Cr: 0.06%, Fe balance; the total amount of other alloys ≤ 0.08%.

[0021] Pure tin grain alloy: The addition temperature is 1430°C.

[0022] Green sand parameters: Water content 3.5%, compactness 88.

[0023] Melting process: The molten iron is static at 1500°C for 5 minutes.

[0024] Step 2: Spheroidization and pouring Spheroidizing agent (addition amount 1.1%, particle size 15 mm): Re: 0.5%, Mg: 5.5%, Si: 42%, Ca: 2.0%, Al: 0.8%.

[0025] Silicon-barium-calcium composite inoculant (addition amount 0.6%, particle size 3 mm): Si: 72%, Ba: 2.2%, Ca: 1.5% (Ba / Ca = 1.47:1).

[0026] Wire feeding parameters: Silicon-calcium-magnesium-rare earth composite cored wire for spheroidization (wire diameter 10 mm, feeding speed 32 m / min); Silicon-barium-calcium-magnesium-rare earth composite cored wire for inoculation (wire diameter 8 mm, feeding speed 22 m / min).

[0027] Staged inoculation: Add 0.21% of 5-mm inoculant (70%) during the ladle turnover, and supplement 0.09% of 0.5-mm inoculant (30%) during pouring.

[0028] Both methods need to make the casting obtain Mg: 0.045%, Re: 0.015%.

[0029] Total treatment time: 7 minutes.

[0030] Step 3: Low-temperature shakeout: The casting is shakeout when it cools down to 280°C.

[0031] Step 4: Performance testing Mechanical properties: Tensile strength 615 MPa, yield strength 385 MPa, elongation 13%, hardness 195 HB.

[0032] Metallographic structure: Spheroidization grade 2, graphite nodule diameter grade 6, pearlite 45%, ferrite matrix without carbide.

[0033] ② Example 2: A method for realizing QT600-10 in green sand casting using low alloy combination, including: Step 1: Batching and melting Composition (wt%): C: 3.78%, Si: 2.8%, Mn: 0.28%, P: 0.035%, S: 0.019%, Cu: 0.05%, Sn: 0.045%, Cr: 0.07%, Fe balance; Total amount of other alloys ≤ 0.07%.

[0034] Pure tin grain alloy: Added at a temperature of 1445°C.

[0035] Green sand parameters: Moisture content 3.6%, compactibility 90.

[0036] Melting process: Molten iron is static for 14 minutes at 1510°C.

[0037] Step 2: Spheroidization and pouring Spheroidizing agent (addition amount 1.2%, particle size 20 mm): Re: 0.75%, Mg: 5.6%, Si: 44%, Ca: 2.2%, Al: 0.7%.

[0038] Silicon-barium-calcium composite inoculant (addition amount 0.65%, particle size 2 mm): Si: 75%, Ba: 2.8%, Ca: 1.8% (Ba / Ca = 1.56:1).

[0039] Wire feeding parameters: Silicon-calcium-magnesium-rare earth composite cored wire for spheroidization (wire diameter 12 mm, feeding speed 28 m / min); Silicon-barium-calcium-magnesium-rare earth composite cored wire for inoculation (wire diameter 10 mm, feeding speed 18 m / min).

[0040] Staged inoculation: Add 0.18% of 4 mm inoculant (70%) when pouring the ladle, and supplement 0.07% of 0.3 mm inoculant (30%) during pouring.

[0041] Both methods need to make the casting obtain Mg: 0.05%, Re: 0.018%.

[0042] Total treatment time: 6 minutes.

[0043] Step 3: Low-temperature shakeout: The casting is shakeout when it cools down to 250°C.

[0044] Step 4: Performance testing Mechanical properties: Tensile strength 625 MPa, yield strength 395 MPa, elongation 14%, hardness 205 HB.

[0045] Metallographic structure: Spheroidization rate grade 1, graphite sphere diameter grade 7, pearlite 50%, ferrite matrix without carbide.

[0046] ③ Example 3: A method for realizing QT600-10 in green sand casting using low alloy combination, including: Step 1: Batching and melting Composition (wt%): C: 3.60%, Si: 2.6%, Mn: 0.22%, P: 0.025%, S: 0.015%, Cu: 0.06%, Sn: 0.038%, Cr: 0.05%, Fe balance; total amount of other alloys ≤ 0.06%.

[0047] Pure tin grain alloy: Added at a temperature of 1420°C.

[0048] Green sand parameters: Moisture content 3.3%, compactibility 87.

[0049] Melting process: Molten iron is static for 8 minutes at 1490°C.

[0050] Step 2: Spheroidization and pouring Spheroidizing agent (addition amount 1.0%, particle size 10 mm): Re: 1%, Mg: 5.3%, Si: 41%, Ca: 1.8%, Al: 0.9%.

[0051] Silicon-barium-calcium composite inoculant (addition amount 0.7%, particle size 1 mm): Si: 71%, Ba: 1.8%, Ca: 1.2% (Ba / Ca = 1.5:1).

[0052] Wire feeding parameters: Silicon-calcium-magnesium-rare earth composite cored wire for spheroidization (wire diameter 9 mm, feeding speed 30 m / min); Silicon-barium-calcium-magnesium-rare earth composite cored wire for inoculation (wire diameter 12 mm, feeding speed 20 m / min).

[0053] Staged inoculation: Add 0.15% of 6 mm inoculant (70%) when pouring from the ladle, and supplement 0.06% of 0.7 mm inoculant (30%) during pouring.

[0054] Both methods need to make the casting obtain Mg: 0.04%, Re: 0.012%.

[0055] Total treatment time: 7.5 minutes.

[0056] Step 3: Low-temperature shakeout: The casting is shakeout when it cools down to 270°C.

[0057] Step 4: Performance testing Mechanical properties: Tensile strength 605 MPa, yield strength 375 MPa, elongation 12.5%, hardness 190 HB.

[0058] Metallographic structure: Spheroidization grade 3, graphite sphere diameter grade 5, pearlite 40%, ferrite matrix without carbide.

[0059] Performance test:

[0060] It can be seen that the performances of Examples 1-3 are all better than those of the traditional green sand process.

[0061] Extract the comparison between Example 1 and the traditional Cu alloying:

[0062] Design Re: 0.5-1% nodulizer by gradient spheroidization theory: Initial burst pressure ≥ 0.25 MPa (to ensure nodulization start) Residual Mg: 0.035-0.055% (to stabilize graphite morphology) Extract the comparison between Example 1 and the traditional process:

[0063] Extract Example 1 for tensile strength, elongation and -40°C impact energy tests:

[0064] To sum up, this method uses a low-alloy combination to achieve QT600-10 ductile iron in green sand casting, and has obvious advantages in terms of cost reduction, process stability improvement, mechanical property optimization, adaptability enhancement and production efficiency improvement. By using Sn (0.035%-0.05%) as a micro-alloying element to replace expensive alloy elements such as Cu, Ni and Cr used in traditional methods, while significantly reducing the material cost, the alloy performance is improved and the alloy cost is reduced, with significant economic benefits.

[0065] By optimizing the formulations of the nodulizer and inoculant, this method stabilizes the nodulization effect in green sand casting. By using a low-rare-earth nodulizer and a Ba / Ca = 1.5-2.0 silicon-barium-calcium composite inoculant, the nodulization decay time during casting is prolonged. The innovative in-stream inoculation process in stages increases the nodulization qualification rate from 82% of the traditional process to 95%, effectively overcoming the common problems in green sand casting.

[0066] In terms of mechanical properties, through the synergistic effect of Sn-Mg, nanoscale precipitates are formed, optimizing the metallographic structure of the casting, resulting in a tensile strength ≥ 600 MPa and an elongation rate reaching 12 - 14%. This not only exceeds the elongation rate requirement of the national standard QT600-10 but also solves the problem of insufficient mechanical properties in traditional processes. It shows good adaptability in the production of thin-walled castings. By strictly controlling the pouring time and implementing low-temperature shakeout, heat treatment is not necessary, reducing costs while ensuring the quality of complex thin-walled castings, avoiding the formation of carbides and the risk of white mouth tendency. The systematic and standardized design significantly shortens the production cycle.

[0067] The above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions described in the foregoing embodiments or perform equivalent replacements for some of the technical features; and these modifications or replacements will not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for realizing QT600-10 in green sand casting using a low alloy combination, characterized in that: The following steps are involved: Step 1: Ingredients and smelting: Calculated by mass fraction, the QT600-10 ductile iron contains: C: 3.55% to 3.85%, Si: 2.3% to 2.9%, Mn: 0.2% to 0.3%, P≤0.04%, S≤0.02%, Cu≤0.1%, Sn: 0.035% to 0.05%, Cr≤0.08%, the balance is Fe and impurities, and the total amount of other detectable alloys is ≤0.1%; During smelting, the molten iron is kept at 1480-1520℃ for 5-8 minutes; Step 2: Spheroidization and pouring: The injection method uses a low rare earth spheroidizer containing Re: 0.5-1%, Mg: 5.2-5.8%, and a silicon-barium-calcium composite inoculant with Ba / Ca=1.5-2; The wire feeding method uses silicon-calcium-magnesium-rare earth composite core spheroidizing wire and silicon-barium-calcium-magnesium-rare earth composite core inoculation wire; During pouring, the inoculation is carried out in stages: 70% of the silicon-barium-calcium composite inoculant with a particle size of 3-8 mm is added during pouring, and 30% of the silicon-barium-calcium composite inoculant with a particle size of 0.2-0.8 mm is added during pouring, and the total addition amount is 0.1-0.3%; Both methods require that the castings obtain Mg: 0.035% ~ 0.055%, Re: 0.008% ~ 0.02%; The total time from spheroidization to the end of pouring is ≤ 8 minutes; Step 3, low temperature sand dropping: the casting and the test block are cooled to below 300°C and sand dropping; Step 4: Performance testing: Single casting test block meets the following requirements: tensile strength ≥ 600MPa, yield strength ≥ 370MPa, elongation ≥ 10%, Brinell hardness 190-230HB; Metallographic structure: spheroidization rate 1-3 (ASTM A247), graphite ball diameter 5-8, pearlite 35-65%, ferrite matrix without carbide.

2. A method for realizing QT600-10 in green sand casting using a low alloy combination according to claim 1, characterized in that: The Sn element in step 1 is added in the form of pure tin granule alloy, and the time of adding is to add it into the bag when it is out of the furnace. The parameters of the green sand are: water content 3.2-3.8%, compactness 85-92.

3. A method for realizing QT600-10 in green sand casting using a low alloy combination according to claim 1, characterized in that: The low rare earth nodulizer components in step 2 are calculated by mass fraction as follows: Re: 0.5-1%, Mg: 5.2-5.8%, Si: 40-45%, Ca: 1.5-2.5%, Al≤1.0%, and the balance Fe; the added amount is 1.0-1.2% of the mass of the molten iron, and the particle size is 5-25 mm.

4. A method for realizing QT600-10 in green sand casting using a low alloy combination according to claim 1, characterized in that: The components of the silicon-barium-calcium composite inoculant in step 2 are as follows by mass fraction: Si≥70%, Ba: 1.5-3.0%, Ca: 1.0-2.0%, Ba / Ca=1.5-2, and the balance is Fe; the amount of the inoculant added by the injection method is 0.6-0.9%, and the particle size is 0.7-6 mm.

5. A method for realizing QT600-10 in green sand casting using a low alloy combination according to claim 1, characterized in that: The wire diameter of the silicon-calcium-magnesium-rare-earth composite core spheroidized wire in step 2 is 9-13 mm, and the wire diameter of the silicon-barium-calcium-magnesium-rare-earth composite core inoculated wire is 8-12 mm.

6. A method for realizing QT600-10 in green sand casting using a low alloy combination according to claim 1, characterized in that: The feed rate of the silicon-calcium-magnesium-rare earth composite core spheroidizing line in step 2 is 28-32 m / min, and the feed rate of the silicon-barium-calcium-magnesium-rare earth composite core inoculation line is 18-22 m / min.

7. A method for realizing QT600-10 in green sand casting using a low alloy combination according to claim 1, characterized in that: In step 4, the test block is taken from the critical wall thickness or main wall thickness of the casting, the wall thickness difference at the detection position is ≤3mm, and the detection is performed in the cast state.

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