Method for casting thick-wall nodular cast iron KPF material for low-speed diesel engine cylinder block of ship

Abstract

The invention discloses a casting method of a thick-wall nodular cast iron KPF material for a low-speed diesel engine cylinder block of a ship. The material comprises the following components in percentage by mass: 3.4-3.7% of C; 2.2%-2.6% of Si; mn is less than 0.5%; less than or equal to 0.05% of P; s is less than or equal to 0.02%; 0.25 to 0.5 percent of Cu; 0.003% to 0.01% of Sb; 0.03 to 0.06 percent of Mg; 0.01 to 0.03 percent of sigma Re; the maximum casting wall thickness of the thick-wall nodular cast iron KPF material cylinder block is larger than or equal to 300 MM, body sampling is conducted at the position with the wall thickness of 200 mm, the tensile strength Rm is larger than or equal to 400 MPa, the elongation A% is larger than or equal to 5, and the brinell hardness is larger than or equal to 140 HB. The tensile strength and the ductility of the material are improved by pretreating SiC, adding Cu to refine the structure, improving the pearlite content of a casting body and adding trace alloy Sb to improve the graphite form.

Description

Technical Field

[0001] The invention relates to the field of casting, and in particular to a casting method of thick-wall ductile iron KPF material for a cylinder body of a low-speed ship diesel engine. Background Art

[0002] KPF material is a kind of cylinder block material for low-speed marine diesel engines, used for ductile iron cylinder blocks with a cylinder diameter of 350mm or more, and a maximum casting wall thickness of 300MM or more. The tensile strength of the body specimen at the 200mm wall thickness position is required to be Rm ≥ 400MPa, the elongation A% ≥ 5, and the Brinell hardness requirement is ≥ 140 HB.

[0003] At present, the Cu addition amount of KPF material cylinder body produced by conventional ductile iron production method reaches 0.6-0.8%, which has high production cost. Summary of the invention

[0004] In order to solve the above problems, the present invention provides a casting method of thick-wall ductile iron KPF material for a cylinder body of a low-speed diesel engine for ships.

[0005] The solution of the present invention: A thick-walled ductile iron KPF material for a cylinder block of a low-speed marine diesel engine, the material comprising the following components by mass ratio: C 3.4~3.7%; Si 2.2~2.6%; Mn <0.5%; P ≤0.05%; S ≤0.02%; Cu 0.25~0.5%; Sb 0.003~0.01%; Mg 0.03~0.06%; ΣRe 0.01~0.03%; The maximum casting wall thickness of thick-walled ductile iron KPF material cylinder body is ≥300MM, the tensile strength of the body specimen at the wall thickness of 200mm is Rm≥400MPa, the elongation A%≥5, and the Brinell hardness is required to be ≥140 HB.

[0006] A casting method of thick-walled ductile iron KPF material for a cylinder block of a low-speed diesel engine for a ship, the method comprising the following steps: S1: During smelting, pig iron, ductile iron waste and scrap steel are added into the furnace in order. When the molten iron temperature reaches 1420±10℃, samples are taken for spectral analysis to adjust the chemical composition of the molten iron in the furnace; S2: After the composition is qualified, the molten iron continues to heat up and then keeps warm, and cools down by pouring. SiC is added into the furnace during the pouring process. The furnace temperature is 1410-1450°C. The inoculation method before the furnace is discharged adopts the spheroidization inoculation method + flow inoculation treatment. During the spheroidization of the molten iron, 0.05-0.15% Cu and 0.004-006% Sb are added according to the weight of the molten iron. The molten iron is spheroidized by a composite spheroidizer and inoculated by a BaSi / CaBaSi composite inoculant. After the spheroidization is completed, the slag removal operation is carried out. During the slag removal process, a slag remover is added according to the slag on the surface of the molten iron, and pouring is prepared after there is no obvious blocky slag on the surface; S3: Add the flow inoculant into the ladle, confirm that there is no abnormality in the sealing of the plug, and then pour. Pour the molten iron obtained in step S2, let it stand, pick out the surface slag, and then pick up the plug and pour until the pouring is completed. Preferably, the step S1 comprises: 50±5% scrap steel, 10±5% old ductile iron, 40±5% pig iron, 0.2% FeSi75, 1.53% recarburizer, 0.25% Cu and 0.1% SiC.

[0007] Preferably, in step S1, the pig iron is Q10 pig iron; the scrap material is ductile iron scrap; the scrap steel is ordinary carbon steel scrap; and the recarburizer is a low-nitrogen recarburizer.

[0008] Preferably, in step S1, the composition in the furnace is controlled to include the following components by mass fraction: C 3.50-3.60%; Si 1.1-1.3%; Mn <0.5%; P ≤0.05%; S ≤0.02%; Cu 0.25-0.4%.

[0009] Preferably, in step S2, after the composition is qualified, the molten iron continues to be heated to 1510±5°C and kept warm for 10±5 minutes, and then cooled by inverting. 0.1% SiC is added into the furnace during the inverting process, and the furnace outlet temperature is 1410-1450°C.

[0010] Preferably, in step S2: in the composition of the composite spheroidizer, the mass ratio of Si:Mg:Re is (40-45):(5-7):1, and the amount of the composite spheroidizer added is 1.3-1.5% of the weight of the molten iron; in the composition of the composite inoculant BaSi / CaBaSi, the mass ratio of Si:Ba:Ca is (64-66):(3-5):1, and the amount of the composite inoculant added is 0.8-1.2% of the weight of the molten iron; Further preferably, 0.1% Cu and 0.005% Sb are added to the molten iron during spheroidization, the amount of composite spheroidizing agent added is 1.35% of the weight of the molten iron, and the amount of composite inoculant added is 1% of the weight of the molten iron.

[0011] Preferably, in step S2: the deslagging agent contains SiO 2 :Al2 O 3 :K 2 The mass ratio of O is (20-22):(3-5):1), and the amount of slag remover added is 0.0015-0.0025% of the weight of molten iron.

[0012] Preferably, in the composition of the in-flow inoculant in step S3, the mass ratio of Si:Ba is (10-15):1, and the amount of the in-flow inoculant added is 0.1-0.2% of the weight of the molten iron; preferably, the amount of the in-flow inoculant added is 0.15% of the weight of the molten iron.

[0013] Beneficial effects of the present invention: The maximum casting wall thickness of the KPF material cylinder body produced by this method is ≥300mm, the tensile strength of the body specimen at the wall thickness of 200mm is Rm≥400MPa, the elongation A%≥5, and the Brinell hardness is ≥140 HB.

[0014] 1. The present invention adopts induction furnace smelting, and effectively improves the purity of the original iron liquid through high-temperature overheating and a slag remover with a specific ratio. Metal elements such as Cu and Sb that promote the formation of pearlite are added to the iron liquid. Cu is an element that promotes the formation of pearlite, promotes graphitization during the eutectic period, reduces the critical temperature of austenite transformation, and increases the pearlite content; Sb in the present invention is a pearlite promoting element, which can refine graphite, improve the roundness of graphite balls, and prevent graphite distortion; through reasonable ratios and dosages and synergistic effects between each other, the problems of poor graphite morphology and coarse matrix structure in thick-walled parts are overcome, so that the mechanical properties of the body test block in the thick-walled part of the casting meet the performance requirements of KPF materials.

[0015] 2. The present invention adopts the punching method for spheroidization and inoculation, the mass ratio of the spheroidizing agent component Si:Mg:Re is (40-45): (5-7): 1, the spheroidization reaction time of the molten iron is completed within 120, the amount of the spheroidizing agent added is controlled between 1.3-1.5%, the desulfurization effect is enhanced, the residual rare earth content is controlled at 0.01-0.03%, and the residual magnesium content is 0.03-0.06%; the mass ratio of Si:Ba:Ca in the composition of the composite inoculant BaSi / CaBaSi is (64-66): (3-5): 1, and the amount of the composite inoculant added is 0.8-1.2% of the weight of the molten iron. Through the joint action of Si, Ba, and Ca, the molten iron is purified, the anti-degradation ability of the molten iron is improved, the nucleation is promoted to improve the graphite morphology, thereby achieving the effect of improving the metallographic structure and refining the grains. Through this method, while purifying the molten iron and refining the grains, the formation of pearlite is promoted and the pearlite structure is refined, achieving ideal material mechanical properties.

[0016] 3. The present invention adopts secondary inoculation technology. When tapping iron, a specific proportion of inoculant is used for primary inoculation with a particle size of 3-8mm, and the added amount is 0.8-1.2% of the weight of the molten iron. Before pouring, a silicon rare earth inoculant of 0.2-0.7mm is used for secondary inoculation, and the added amount is 0.1-0.2% of the weight of the molten iron to solve the problems of poor graphite morphology and spheroidization decline. DETAILED DESCRIPTION

[0017] The present invention is described in further detail below in conjunction with examples, but embodiments of the present invention are not limited thereto. Unless otherwise specified, the reagents, methods and equipment used in the present invention are conventional reagents, methods and equipment in the art. The test methods for which specific experimental conditions are not specified in the following examples are usually carried out according to conventional experimental conditions or according to the experimental conditions recommended by the manufacturer. Unless otherwise specified, reagents and raw materials used in the present invention can be obtained by commercial means or conventional methods.

[0018] Example 1 A thick-walled ductile iron KPF material for a cylinder block of a low-speed marine diesel engine, the material comprising the following components by mass ratio: C 3.55%; Si 2.3%; Mn 0.4%; P 0.044%; S 0.015%; Cu 0.35%; Sb 0.005%; Mg0.04%; ΣRe 0.02%; The pouring weight of thick-walled ductile iron KPF material cylinder body is 32 tons, the maximum casting wall thickness is ≥300MM, the tensile strength of the body specimen at the wall thickness of 200mm is Rm≥400MPa, the elongation A%≥5, and the Brinell hardness requirement is ≥140 HB.

[0019] A casting method of thick-walled ductile iron KPF material for a cylinder block of a low-speed diesel engine for a ship, the method comprising the following steps: S1: During smelting, pig iron, ductile iron waste and scrap steel are added into the furnace in order. When the molten iron temperature reaches 1420±10℃, samples are taken for spectral analysis to adjust the chemical composition of the molten iron in the furnace; S2: After the composition is qualified, the molten iron continues to heat up and then keeps warm, and the temperature is lowered by pouring. SiC is added into the furnace during the pouring process. The furnace temperature is 1420°C. The inoculation method before the furnace is discharged adopts the spheroidization inoculation method + flow inoculation treatment. During the spheroidization of the molten iron, 32kgCu and 1.6kgSb are added. The molten iron is spheroidized by a composite spheroidizer and inoculated by a BaSi / CaBaSi composite inoculant. After the spheroidization is completed, the slag removal operation is carried out. During the slag removal process, a slag removal agent is added according to the slag on the surface of the molten iron, and pouring is prepared after there is no obvious blocky slag on the surface; S3: Add the flow inoculant into the ladle, confirm that there is no abnormality in the sealing of the plug, and then pour. Pour the molten iron obtained in step S2, let it stand, pick out the surface slag, and then pick up the plug and pour until the pouring is completed.

[0020] Preferably, in step S1: 16000 kg (50%) of scrap steel, 3200 kg (40%) of old ductile iron, 12800 kg (40%) of pig iron, 92.8 kg (0.29%) of FeSi75, 489.6 kg (1.53%) of carburizer, 80 kg (0.25%) of Cu, and 32 kg (0.1%) of SiC. Preferably, in step S1, the pig iron is Q10 pig iron; the scrap material is ductile iron scrap; the scrap steel is ordinary carbon steel scrap; and the recarburizer is a low-nitrogen recarburizer.

[0021] Preferably, in step S1, the composition in the furnace is controlled to include the following components by mass fraction: C 3.55%; Si 1.2%; Mn 0.4%; P 0.044%; S 0.015%; and Cu 0.25%. Preferably, in step S2, after the composition is qualified, the molten iron continues to be heated to 1510±5°C and kept warm for 10±5 minutes, and then cooled by inverting. During the inverting process, 0.1% SiC is added into the furnace, and the furnace outlet temperature is 1420°C.

[0022] Preferably, in step S2, the mass ratio of Si:Mg:Re in the composite spheroidizer is 42:6:1; the mass ratio of Si:Ba:Ca in the BaSi / CaBaSi composite inoculant is 63:4:1. The amount of the composite spheroidizer added is 1.35% of the weight of the molten iron, and the amount of the composite inoculant added is 1% of the weight of the molten iron.

[0023] Preferably, in step S2: the deslagging agent contains SiO 2 :Al 2 O 3 :K 2 The mass ratio of O is 21:4:1, and the amount of slag remover added is 0.0016% of the weight of molten iron.

[0024] Preferably, in the composition of the in-stream inoculant in step S3, the mass ratio of Si:Ba is 13:1. The amount of the in-stream inoculant added is 0.15% of the weight of the molten iron.

[0025] Table 1

[0026] Example 2 Example 2-1 is based on Example 1, except that the composition of the inoculant in step S2 is changed, and the rest is the same as Example 1. The mass ratio of Si:Mg:Re in the composite spheroidizing agent is 42:6:0; the mass ratio of Si:Ba:Ca in the BaSi / CaBaSi composition is 63:4:0.

[0027] Example 2-2 is based on Example 1, except that the composition of the inoculant in step S2 is changed, and the rest is the same as Example 1.

[0028] In the step S2, the mass ratio of Si:Mg:Re in the composite spheroidizing agent is 42:10:1; the mass ratio of Si:Ba:Ca in the BaSi / CaBaSi is 63:4:3.

[0029] Table 2

[0030] As shown in Table 2, rare earth elements have the function of promoting graphite spheroidization and refining graphite, stabilizing pearlite and refining ferrite, thereby improving the tensile strength and elongation of ductile iron, and play an indispensable role in the production of ductile iron. Ca can react with impurity elements such as sulfur and oxygen in molten iron to form high-melting point compounds and float up, thereby having the ability to purify molten iron. At the same time, it can be used as an effective nucleating agent to increase the number of graphite nucleation cores, which helps to refine the graphite structure, improve the density of the structure, and improve the mechanical properties. Excessive calcium content will deteriorate the graphite morphology and affect the mechanical properties of the material. Magnesium is an important spheroidizing element in ductile iron, but excessive content can easily lead to poor graphite spheroidization, abnormal graphite morphology, destroy the continuity of the metal matrix, and reduce the mechanical properties of cast iron.

[0031] Example 3 Example 3-1 is based on Example 1, except that the composition of the inoculant in step S2 is changed, and the rest is the same as Example 1. In the composition of the inoculant, the mass ratio of Si:Ba is 18:1.

[0032] Example 3-2 is based on Example 1, except that the composition of the inoculant in step S2 is changed, and the rest is the same as Example 1. In the composition of the inoculant, the mass ratio of Si:Ba is 13:0.

[0033] Table 3

[0034] Example 4 Example 4-1: Based on Example 1, in step S2, SiC is not added into the furnace during the inverted packaging process; Example 4-2: Based on Example 1, in step S2, no Cu is added during the spheroidization of molten iron; Example 4-3: Based on Example 1, in step S2, no Sb is added during the spheroidization of molten iron.

[0035] Table 4

[0036] The technical solution of the present invention is explained through the above embodiments, but the present invention is not limited to the above embodiments, that is, it does not mean that the present invention must rely on the above specific embodiments to be implemented. Any improvements made by technicians in the relevant field based on the present invention, or equivalent replacement of the materials selected by the present invention, etc., fall within the scope of protection of the patent.

Claims

1. A thick-walled ductile iron KPF material for a low-speed marine diesel engine cylinder block, characterized in that: The material comprises the following components by mass ratio: C 3.4~3.7%; Si 2.2~2.6%; Mn <0.5%; P ≤0.05%; S ≤0.02%; Cu 0.25~0.5%; Sb0.003~0.01%; Mg 0.03~0.06%; ΣRe0.01~0.03%; The maximum casting wall thickness of thick-walled ductile iron KPF material cylinder body is ≥300MM. The body is sampled at the wall thickness of 200mm. The tensile strength Rm is required to be ≥400MPa, the elongation A% is ≥5, and the Brinell hardness is required to be ≥140 HB.

2. A casting method of thick-walled ductile iron KPF material for a low-speed marine diesel engine cylinder block, characterized in that: The method comprises the following steps: S1: During smelting, pig iron, ductile iron waste and scrap steel are added into the furnace in order. When the molten iron temperature reaches 1420±10℃, samples are taken for spectral analysis to adjust the chemical composition of the molten iron in the furnace; S2: After the composition is qualified, the molten iron continues to heat up and then keeps warm, and cools down by pouring. SiC is added into the furnace during the pouring process. The furnace temperature is 1410-1450°C. The inoculation method before the furnace is discharged adopts the spheroidization inoculation method + flow inoculation treatment. During the spheroidization of the molten iron, 0.05-0.15% Cu and 0.004-006% Sb are added according to the weight of the molten iron. The molten iron is spheroidized by a composite spheroidizer and inoculated by a BaSi / CaBaSi composite inoculant. After the spheroidization is completed, the slag removal operation is carried out. During the slag removal process, a slag remover is added according to the slag on the surface of the molten iron, and pouring is prepared after there is no obvious blocky slag on the surface; S3: Add the flow inoculant into the ladle, confirm that there is no abnormality in the sealing of the plug, and then pour. Pour the molten iron obtained in step S2, let it stand, pick out the surface slag, and then pick up the plug and pour until the pouring is completed.

3. The casting method of thick-walled ductile iron KPF material for a cylinder block of a low-speed marine diesel engine according to claim 2, characterized in that: The step S1: scrap steel 50±5%, ductile iron waste 10±5%, pig iron 40±5%, FeSi75 0.2%, recarburizer 1.53%, Cu 0.2%, SiC 0.1%.

4. According to the casting method of thick-walled ductile iron KPF material for a cylinder block of a low-speed diesel engine for ships as described in claim 2, the step S1: the pig iron is Q10 pig iron; the old material is ductile iron old material; the scrap steel is ordinary carbon steel scraps; and the recarburizer is a low-nitrogen recarburizer.

5. The casting method of thick-walled ductile iron KPF material for a cylinder block of a low-speed marine diesel engine according to claim 2, characterized in that: The step S1: the composition in the furnace is controlled to include the following components by mass fraction: C 3.50-3.60%; Si 1.1-1.3%; Mn <0.5; P ≤0.05%; S ≤0.02%; Cu 0.25-0.4%.

6. The casting method of thick-walled ductile iron KPF material for a cylinder block of a low-speed marine diesel engine according to claim 2, characterized in that: The step S2: after the composition is qualified, the molten iron is further heated to 1510±5°C and kept warm for 10±5 minutes, and then cooled by pouring. 0.1% SiC is added into the furnace during the pouring process, and the furnace temperature is 1410-1450°C.

7. The casting method of thick-walled ductile iron KPF material for a low-speed marine diesel engine cylinder block according to claim 2, characterized in that: Step S2: In the composition of the composite spheroidizer, the mass ratio of Si:Mg:Re is (40-45):(5-7):1, and the amount of the composite spheroidizer added is 1.3-1.5% of the weight of the molten iron; in the composition of the composite inoculant BaSi / CaBaSi, the mass ratio of Si:Ba:Ca is (64-66):(3-5):1, and the amount of the composite inoculant added is 0.8-1.2% of the weight of the molten iron; Preferably, 0.1% Cu and 0.005% Sb are added during spheroidization of molten iron, the amount of composite spheroidizing agent added is 1.35% of the weight of molten iron, and the amount of composite inoculant added is 1% of the weight of molten iron.

8. The casting method of thick-walled ductile iron KPF material for a cylinder block of a low-speed marine diesel engine according to claim 2, characterized in that: The step S2: the mass ratio of SiO2:Al2O3:K2O in the components of the slag remover is (20-22):(3-5):1), and the amount of the slag remover added is 0.0015-0.0025% of the weight of the molten iron.

9. The casting method of thick-walled ductile iron KPF material for a low-speed marine diesel engine cylinder block according to claim 2, characterized in that: In the composition of the in-flow inoculant in step S3, the mass ratio of Si:Ba is (10-15):1, and the amount of the in-flow inoculant added is 0.1-0.2% of the weight of the molten iron; preferably, the amount of the in-flow inoculant added is 0.15% of the weight of the molten iron.

10. The casting method of thick-walled ductile iron KPF material for a low-speed marine diesel engine cylinder block according to claim 2, characterized in that: The pouring temperature in step S3 is 1320-1350°C.

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