CN114592152A

CN114592152A - Preparation method of pearlite nodular cast iron and nodular cast iron prepared by adopting method

Info

Publication number: CN114592152A
Application number: CN202210244394.XA
Authority: CN
Inventors: 赵兰英
Original assignee: CHANGSHU JINGGONG MOULD MANUFACTURING CO LTD
Current assignee: CHANGSHU JINGGONG MOULD MANUFACTURING CO LTD
Priority date: 2022-03-14
Filing date: 2022-03-14
Publication date: 2022-06-07
Anticipated expiration: 2042-03-14
Also published as: CN114592152B

Abstract

The application relates to the field of cast iron, and particularly discloses a preparation method of pearlite nodular cast iron and the nodular cast iron prepared by the method. The preparation method of the pearlite nodular cast iron comprises the steps of proportioning, smelting, ladle casting, pouring, annealing, cooling and the like; wherein: adding a nodulizer and an inoculant during ladle casting; the inoculant comprises the following components: 45-55wt% of Si, 15-20wt% of Ba, 8-12wt% of Ca, 3-6wt% of Cu, 1-3wt% of Al, 1-3wt% of W, and the balance of Fe and inevitable impurities. The nodular cast iron is prepared by the preparation method of the pearlite nodular cast iron. The obtained pearlite nodular cast iron has Brinell hardness (HBW10/3000) not less than 220 and shows higher hardness. The hardness of the nodular cast iron is improved by introducing tungsten into the inoculant and utilizing the synergistic cooperation of the tungsten, carbon, iron and other components.

Description

Preparation method of pearlite nodular cast iron and nodular cast iron prepared by adopting method

Technical Field

The application relates to the field of cast iron, in particular to a preparation method of pearlite nodular cast iron and the nodular cast iron prepared by the method.

Background

The nodular cast iron is a cast iron material obtained after spheroidizing and inoculation, has the advantages of high strength, good toughness and good wear resistance, and is widely applied to casting parts with higher requirements on strength, toughness and wear resistance or complicated stress. The preparation process of the nodular cast iron mainly comprises the following steps: smelting raw materials, casting ladles, pouring, annealing and cooling. Wherein, the casting ladle is an important step; adding a nodulizer and an inoculant into molten iron during ladle casting; the former is favorable to making graphite in cast iron crystallize into spherical shape, and the latter is favorable to improving graphite form and distribution, and can increase graphitized core and refine matrix structure.

At present, more and more attempts are made to replace steel with nodular cast iron, which also puts higher demands on the nodular cast iron and requires higher hardness. Therefore, how to improve the hardness of the nodular cast iron becomes an important research subject.

Disclosure of Invention

In order to effectively improve the hardness of the nodular cast iron, the application provides a preparation method of pearlite nodular cast iron and the nodular cast iron prepared by the method.

In a first aspect, a preparation method of pearlite nodular cast iron is provided, and the following technical scheme is adopted:

the preparation method of the pearlite nodular cast iron comprises the following steps:

the formula comprises the following components in percentage by weight: 3.5 to 3.7 weight percent of C, 2.1 to 2.5 weight percent of Si, less than 0.3 weight percent of Mn, less than 0.1 weight percent of S, less than 0.06 weight percent of P, 0.1 to 0.2 weight percent of Cr, less than 0.1 weight percent of Ni, 0.3 to 0.4 weight percent of Mo, less than 0.05 weight percent of V, less than 0.08 weight percent of Ti, 0.3 to 0.4 weight percent of Cu, and the balance of Fe and inevitable impurities, and weighing the raw materials;

smelting the raw materials into molten iron;

pouring the molten iron into a ladle, and adding a nodulizer and an inoculant during pouring; the inoculant comprises the following components: 45-55wt% of Si, 15-20wt% of Ba, 8-12wt% of Ca, 3-6wt% of Cu, 1-3wt% of Al, 1-3wt% of W, and the balance of Fe and inevitable impurities;

casting, annealing and cooling.

By adopting the technical scheme, the pearlite nodular cast iron is successfully prepared by the steps of proportioning, smelting, casting, pouring, annealing, cooling and the like. Wherein: during casting, a tungsten-containing inoculant is adopted, and the synergistic cooperation of tungsten, carbon, iron and other components is beneficial to forming high-hardness alloy; these alloys participate in the formation of the nodular structure of the nodular cast iron and contribute to the hardness of the nodular cast iron obtained.

In a specific implementation scheme, the temperature for smelting the raw materials into the molten iron is 1580-1600 ℃.

By adopting the technical scheme, the smelting temperature is optimized, and the graphite cast iron with better performance is obtained.

In a specific possible embodiment, the nodulizer is a magnesium-silicon-iron alloy nodulizer, and the addition amount of the nodulizer is 1-1.2wt% of the molten iron.

By adopting the technical scheme, the type and the adding amount of the nodulizer are optimized, and the method has positive significance for improving the performance of the obtained graphite cast iron.

In a specific embodiment, the inoculant is added in an amount of 0.3-0.5wt% of the molten iron.

By adopting the technical scheme, the addition amount of the inoculant is optimized, the addition of a proper amount of the inoculant is favorable for better improving the graphite form and distribution condition, and the obtained graphite cast iron has higher hardness.

In a specific possible embodiment, a covering agent is further added during the casting of the molten iron; the covering agent comprises the following components: 15-33wt% of vermiculite, 30-50wt% of expanded perlite, 10-15wt% of microcapsule carbonate, 8-12wt% of zeolite, 5-10wt% of calcium oxide and 5-10wt% of aluminum oxide.

By adopting the technical scheme, the covering agent can be added to prolong the solidification time of molten iron, and the preparation method is favorable for obtaining the nodular cast iron with better hardness. Meanwhile, the carbonate can be subjected to phase change at high temperature to form a molten state, and when the temperature is reduced, the carbonate can be subjected to phase change again and release a large amount of heat, so that the heat preservation effect on the molten iron is achieved; therefore, the microcapsule carbonate is introduced into the covering agent, so that the solidification time of molten iron can be further prolonged, and the hardness of the nodular cast iron is improved. In addition, the microcapsule is adopted to encapsulate the carbonate, so that the leakage of the carbonate in a molten state can be reduced, and the heat preservation effect of the carbonate is improved.

In a specific possible embodiment, the microcapsule carbonate is prepared by the following method:

mixing carbonate, water, an organic solvent and alkali to form a water-in-oil system;

and (3) adding tetraethyl orthosilicate dropwise into the water-in-oil system to obtain the microcapsule carbonate.

By adopting the technical scheme, the wall material of the microcapsule carbonate adopts silicon dioxide, which is beneficial to better protecting the carbonate.

In a specific possible embodiment, the covering agent is added in an amount of 0.5 to 1wt% of the molten iron.

By adopting the technical scheme, the addition amount of the covering agent is optimized.

In a specific possible embodiment, the molten iron is cast in a spheroidizing ladle;

and a dam is arranged at the bottom of the spheroidizing bag, and a plurality of liquid passing holes which can enable molten iron to flow through the dam are formed in the dam.

By adopting the technical scheme, the liquid passing port is formed in the dam, so that part of molten iron passes through the liquid passing port, the amount of the molten iron passing over from the dam can be reduced, the hedging of the poured molten iron on a nodulizer and the like can be further reduced, the nodulizing and inoculating time is further prolonged, and the graphite cast iron with better hardness can be obtained.

In a specific embodiment, a closing member is further arranged on the dam, and the closing member closes the liquid through hole.

By adopting the technical scheme, the closing piece can control the opening and closing of the liquid passing hole, so that the proportion of the molten iron passing through the liquid passing hole and the molten iron passing over the dam can be adjusted, the impact of the poured molten iron on a nodulizer and the like can be adjusted, and the control of the time of nodulizing the molten iron is facilitated.

In a second aspect, the invention provides nodular cast iron, which adopts the following technical scheme:

the nodular cast iron is prepared by the preparation method of the pearlite nodular cast iron.

By adopting the technical scheme, the content of pearlite in the obtained nodular cast iron reaches 65%, and the nodular cast iron has high hardness.

In summary, the present application has at least one of the following beneficial technical effects:

1. the obtained pearlite nodular cast iron has the Brinell hardness (HBW10/3000) not less than 220 and shows higher hardness.

2. According to the method, tungsten is introduced into the inoculant, and the synergistic cooperation of the tungsten, carbon, iron and other components is utilized, so that high-hardness alloys can be formed, and the alloys enter the nodular cast iron to improve the hardness of the nodular cast iron.

3. Microcapsule carbonate is introduced into the covering agent, and the phase change heat release of the covering agent during cooling can be utilized to play a heat preservation role in molten iron, so that the solidification time of the molten iron is further prolonged, and the hardness of the nodular cast iron is improved.

4. The liquid passing port is formed in the dam in the spheroidizing ladle, so that the counter impact of poured molten iron on a spheroidizing agent and the like is further reduced, and the positive significance is achieved for prolonging the spheroidizing and inoculating time and further obtaining graphite cast iron with better hardness.

5. According to the method, the closing of the closing piece is controlled, and the spheroidization time of the molten iron can be adjusted.

Drawings

Fig. 1 is an external view schematically showing a spheroidized bag according to example 18 of the present application.

Fig. 2 is a schematic cross-sectional view of a spheroidizing bag according to example 18 of the present application.

Fig. 3 is an external view of a bank in example 18 of this application.

Fig. 4 is an optical micrograph (after polishing) of the pearlitic spheroidal graphite cast iron of example 1 of the present application.

Fig. 5 is an optical microscope photograph (after polishing and nital etching) of the pearlitic spheroidal graphite cast iron of example 1 of the present application.

Description of the reference numerals: 1. a dam; 11. a liquid passing port; 12. a closure; 2. a balling barrel.

Detailed Description

The present application will be described in further detail with reference to the following drawings and examples.

Preparation example 1

The preparation example discloses a preparation method of microcapsule carbonate, which comprises the following steps:

p1, taking 100g of sodium carbonate and crushing the sodium carbonate into 300 meshes; then, sodium carbonate was dissolved in 50mL of distilled water at 35 ℃ to prepare a mixed solution, and the pH of the mixed solution was adjusted to 8.0 with aqueous ammonia.

P2, 5g of sodium dodecyl sulfate is dissolved in 500mL of cyclohexane; then, the mixture was added to cyclohexane at 35 ℃ and stirred at 1000rpm for 20min to form a water-in-oil system.

P3, keeping the temperature and the stirring speed of the system, dropwise adding 100g of tetraethyl orthosilicate into the water-in-oil system, and controlling the completion of dropping for 5 min; stirring was then continued for 5 h.

P4, centrifuging at 3000rpm for 2min, and collecting solid product; then the solid product is placed in an oven at 100 ℃ for drying; at this time, sodium carbonate is wrapped by a silicon dioxide layer formed by tetraethyl orthosilicate to form a microcapsule structure, and the particle size of the obtained microcapsule carbonate is 30-40 μm.

Preparation example 2

p1, taking 200g of potassium carbonate and crushing to 300 meshes; then, potassium carbonate was dissolved in 80mL of distilled water at 38 ℃ to prepare a mixture, and the pH of the mixture was adjusted to 7.5 with aqueous ammonia.

P2, taking 7g of sodium dodecyl benzene sulfonate to dissolve in 800mL of cyclohexane; then, the mixture was added to cyclohexane at 38 ℃ and stirred at 1200rpm for 15min to form a water-in-oil system.

P3, keeping the temperature and the stirring speed of the system, dropwise adding 400g of tetraethyl orthosilicate into the water-in-oil system, and controlling the dropwise adding to be finished within 10 min; stirring was then continued for 7 h.

P4, centrifuging at 3500rpm for 1min, and collecting solid product; the solid product was then dried in an oven at 105 ℃.

Preparation example 3

p1, mixing 25g of potassium carbonate and 25g of sodium carbonate, heating at the speed of 5 ℃/min until the potassium carbonate and the sodium carbonate are completely melted, and cooling to the normal temperature at the speed of 10 ℃/min to obtain potassium carbonate-sodium carbonate eutectic salt; pulverizing the eutectic salt to 300 meshes; then, the eutectic salt was dissolved in 40mL of distilled water at 40 ℃ to prepare a mixed solution, and the pH of the mixed solution was adjusted to 8.5 with aqueous ammonia.

P2, 3g of sodium dodecyl sulfate is dissolved in 400mL of cyclohexane; then, the mixture was added to cyclohexane at 40 ℃ and stirred at 800rpm for 30min to form a water-in-oil system.

P3, keeping the temperature and the stirring speed of the system, dropwise adding 200g of tetraethyl orthosilicate into the water-in-oil system, and controlling the completion of dropping for 8 min; stirring was then continued for 10 h.

P4, centrifuging for 5min at the rotating speed of 2500rpm, and collecting a solid product; the solid product was then dried in an oven at 100 ℃.

Example 1

The embodiment discloses a preparation method of pearlite nodular cast iron, which comprises the following steps:

s1, blending: taking pig iron, scrap steel, foundry returns, ferromanganese, ferrosilicon, ferrochromium, ferromolybdenum and pure copper as raw materials; each raw material was weighed in a mass ratio of 3.5wt% of C, 2.1wt% of Si, 0.2wt% of Mn, 0.08wt% of S, 0.05wt% of P, 0.1wt% of Cr, 0.08wt% of Ni, 0.3wt% of Mo, 0.04wt% of V, 0.07wt% of Ti, 0.3wt% of Cu, and 93.18wt% of Fe (including unavoidable impurities) in the total raw materials.

S2, smelting: firstly, mixing pig iron, scrap steel and foundry returns, then placing the mixture into a smelting furnace, and heating the mixture to 1400 ℃; and then adding ferromanganese, ferrosilicon, ferrochromium, ferromolybdenum and pure copper into the smelting furnace, heating to 1580 ℃ for smelting, and controlling the smelting time to be 20min to obtain molten iron.

S3, casting ladle: pouring 1000g of molten iron obtained in the step S2 into a balling ladle (the balling ladle is a conventional structure with a dam at the bottom), and paving 10g of nodulizer and 3g of inoculant on one side of the dam at the bottom of the balling ladle from bottom to top in sequence; after molten iron enters the spheroidizing ladle, the molten iron firstly falls to one side of the dam, which is far away from the spheroidizing agent, and then crosses the dam to contact with the spheroidizing agent and the inoculant for spheroidizing for 3 min.

Wherein: the nodulizer is a magnesium-silicon-iron alloy nodulizer, and comprises the following components: 40wt% of Si, 5.5wt% of Mg, 1wt% of Ca, 0.15wt% of Al, 0.5wt% of La and 52.85wt% of Fe (including unavoidable impurities); the nodulizer is prepared from scrap steel, silicon wafer cutting powder, pure magnesium, pure calcium and lanthanide rare earth by smelting at 1300 ℃ and pouring at 1200 ℃, and the particle size of the nodulizer is 5-20 mm. The inoculant comprises the following components: 45wt% of Si, 20wt% of Ba, 12wt% of Ca, 3wt% of Cu, 1wt% of Al, 1wt% of W and 18wt% of Fe (containing unavoidable impurities); the inoculant is prepared from ferrosilicon, silicon-barium, silicon-calcium, pure copper, pure aluminum and ferrotungsten by smelting (1500 ℃), pouring (1300 ℃) and ball milling, and the particle size is 1-3 mm.

S4, pouring: injecting molten iron subjected to spheroidizing inoculation of S3 into a mold, and cooling the molten iron to obtain a blank piece; the casting temperature was controlled at 1430 ℃.

S5, annealing: and (4) taking the blank obtained in the step S4 out of the die, putting the blank into an annealing furnace, heating to 900 ℃, and then preserving heat for 2 h.

S6, cooling: and cooling the blank obtained in the step S5 to 800 ℃ along with the furnace, discharging from the furnace, and air-cooling to obtain the pearlite nodular iron casting.

The embodiment also discloses a pearlite nodular iron casting obtained by the preparation method; the ductile iron casting has a pearlite content of 65% and a Brinell hardness (HBW10/3000) of 220.

Examples 2 to 7

Examples 2-7 are essentially the same as example 1, except that: the inoculant was different in composition.

In particular, the method comprises the following steps of,

in example 2: the inoculant comprises the following components: 45wt% of Si, 20wt% of Ba, 12wt% of Ca, 3wt% of Cu, 1wt% of Al, 1.5wt% of W and 17.5wt% of Fe (containing unavoidable impurities).

In example 3: the inoculant comprises the following components: 45wt% of Si, 20wt% of Ba, 12wt% of Ca, 3wt% of Cu, 1wt% of Al, 2wt% of W and 17wt% of Fe (containing unavoidable impurities).

In example 4: the inoculant comprises the following components: 45wt% of Si, 20wt% of Ba, 12wt% of Ca, 3wt% of Cu, 1wt% of Al, 2.5wt% of W and 16.5wt% of Fe (containing inevitable impurities).

In example 5: the inoculant comprises the following components: 45wt% of Si, 20wt% of Ba, 12wt% of Ca, 3wt% of Cu, 1wt% of Al, 3wt% of W and 16wt% of Fe (containing unavoidable impurities).

In example 6: the inoculant comprises the following components: 50wt% of Si, 18wt% of Ba, 10wt% of Ca, 5wt% of Cu, 2wt% of Al, 2.5wt% of W and 12.5wt% of Fe (containing unavoidable impurities).

In example 7: the inoculant comprises the following components: 55wt% of Si, 15wt% of Ba, 8wt% of Ca, 6wt% of Cu, 3wt% of Al, 2.5wt% of W and 10.5wt% of Fe (containing inevitable impurities).

Examples 8 to 9

Examples 8-9 are essentially the same as example 6, except that: the addition amount of the inoculant is different.

In particular, the method comprises the following steps of,

in example 8: the addition amount of the inoculant was 4 g.

In example 9: the addition amount of the inoculant is 5 g.

Examples 10 to 14

Examples 10-14 are essentially the same as example 8, except that: when the molten iron is poured into the ladle, 5g of covering agent is also added, and the covering agent is positioned on one side of the dam at the bottom of the spheroidizing ladle and between the spheroidizing agent and the inoculant.

In particular, the method comprises the following steps of,

in example 10: the covering agent is prepared by mixing the following raw materials: 20% by weight of vermiculite, 50% by weight of expanded perlite, 10% by weight of microcapsule carbonate, 8% by weight of zeolite, 5% by weight of calcium oxide and 7% by weight of alumina. Among them, microcapsule carbonate was prepared by preparation example 1.

In example 11: the covering agent is prepared by mixing the following raw materials: 15wt% vermiculite, 41wt% expanded perlite, 12wt% microcapsule carbonate, 12wt% zeolite, 10wt% calcium oxide and 10wt% alumina. Among them, microcapsule carbonate was prepared by preparation example 1.

In example 12: the covering agent is prepared by mixing the following raw materials: 33% by weight of vermiculite, 30% by weight of expanded perlite, 15% by weight of microcapsule carbonate, 10% by weight of zeolite, 7% by weight of calcium oxide and 5% by weight of alumina. Among them, microcapsule carbonate was prepared by preparation example 1.

In example 13: the covering agent is prepared by mixing the following raw materials: 15wt% vermiculite, 41wt% expanded perlite, 12wt% microcapsule carbonate, 12wt% zeolite, 10wt% calcium oxide and 10wt% alumina. Among them, microcapsule carbonate was prepared by preparation example 2.

In example 14: the covering agent is prepared by mixing the following raw materials: 15wt% vermiculite, 41wt% expanded perlite, 12wt% microcapsule carbonate, 12wt% zeolite, 10wt% calcium oxide and 10wt% alumina. Among them, microcapsule carbonate was prepared by preparation example 3.

Examples 15 to 16

Examples 15-16 are essentially the same as example 11, except that: the amount of the covering agent added varies.

In particular, the method comprises the following steps of,

in example 15: the amount of the covering agent added was 8 g.

In example 16: the amount of the covering agent added was 10 g.

Example 17

This example is substantially the same as example 15 except that: the preparation method has different proportions of the nodular cast iron raw materials, compositions and dosage of the nodulizer and process parameters.

A preparation method of pearlite nodular cast iron comprises the following steps:

s1, batching: taking pig iron, scrap steel, foundry returns, ferromanganese, ferrosilicon, ferrochromium, ferromolybdenum and pure copper as raw materials; each raw material was weighed in a mass ratio of 3.7wt% of C, 2.5wt% of Si, 0.23 wt% of Mn, 0.02wt% of S, 0.04wt% of P, 0.2wt% of Cr, 0.01wt% of Ni, 0.4wt% of Mo, 0.02wt% of V, 0.05wt% of Ti, 0.4wt% of Cu, and 92.43wt% of Fe (including unavoidable impurities) in the total raw materials.

S2, smelting: firstly, mixing pig iron, scrap steel and foundry returns, then placing the mixture into a smelting furnace, and heating the mixture to 1450 ℃; and then adding ferromanganese, ferrosilicon, ferrochromium, ferromolybdenum and pure copper into the smelting furnace, heating to 1600 ℃ for smelting, and controlling the smelting time to be 15min to obtain molten iron.

S3, casting ladle: pouring 1000g of molten iron obtained in the step S2 into a balling ladle (the balling ladle is a conventional structure with a bottom at the bottom), and sequentially paving 12g of nodulizer, 8g of covering agent and 4g of inoculant on one side of a dam at the bottom of the balling ladle from bottom to top; after molten iron enters the spheroidizing ladle, the molten iron firstly falls to one side of the dam, which is far away from the spheroidizing agent, and then crosses the dam to contact with the spheroidizing agent and the inoculant for spheroidizing for 3 min.

Wherein: the nodulizer is a magnesium-silicon-iron alloy nodulizer, and comprises the following components: 35wt% of Si, 7.5wt% of Mg, 2wt% of Ca, 0.25wt% of Al, 0.8wt% of La and 54.45 wt% of Fe (containing inevitable impurities); the nodulizer is prepared from scrap steel, silicon wafer cutting powder, pure magnesium, pure calcium and rare earth by smelting (1300 ℃) and pouring (1200 ℃), and the particle size of the nodulizer is 5-20 mm. The inoculant comprises the following components: 50wt% of Si, 18wt% of Ba, 10wt% of Ca, 5wt% of Cu, 2wt% of Al, 2.5wt% of W, and 12.5wt% of Fe (containing unavoidable impurities); the inoculant is prepared from ferrosilicon, silicon-barium, silicon-calcium, pure copper, pure aluminum and ferrotungsten by smelting (1500 ℃), pouring (1300 ℃) and ball milling, and the particle size is 1-3 mm. The covering agent is prepared by mixing the following raw materials: 15wt% of vermiculite, 41wt% of expanded perlite, 12wt% of microcapsule carbonate, 12wt% of zeolite, 10wt% of calcium oxide and 10wt% of alumina; among them, microcapsule carbonate was prepared by preparation example 1.

S4, pouring: injecting molten iron subjected to spheroidizing inoculation of S3 into a mold, and cooling the molten iron to obtain a blank piece; the casting temperature was controlled to 1480 ℃.

S5, annealing: and (4) taking the blank obtained in the step S4 out of the die, putting the blank into an annealing furnace, heating to 1000 ℃, and then preserving heat for 3 hours.

S6, cooling: and cooling the blank obtained in the step S5 to 700 ℃ along with a furnace, discharging from the furnace, and carrying out air cooling to obtain the pearlite nodular iron casting.

Example 18

This example is substantially the same as example 17 except that: the spheroidized bags have different structures.

The method specifically comprises the following steps: referring to fig. 1 and 2, the spheroidization bag includes a spheroidization barrel 2 and a dam 1. The top of the balling barrel 2 is opened; the dike 1 is located in the spheroidizing barrel 2 and is fixedly connected to the inner bottom wall of the spheroidizing barrel 2, and the dike 1 divides the bottom of the inner space of the spheroidizing barrel 2 into two parts.

Referring to fig. 3, the dam 1 is provided with a plurality of liquid passing holes 11 penetrating the dam 1 in the width direction thereof; the plurality of liquid passing holes 11 are arranged at equal intervals along the longitudinal direction of the bank 1.

The implementation principle of the spheroidizing bag is as follows: nodulizing agent, covering agent and inoculant are paved on one side of the dam 1, and molten iron is poured from the other side of the dam 1; then, a part of molten iron is contacted with the nodulizer, the covering agent and the inoculant through the liquid passing hole 11, and the other part of molten iron is contacted with the nodulizer, the covering agent and the inoculant after passing through the dam 1. Through the arrangement of the liquid passing holes 11, the counter flushing of the poured molten iron to nodulizers and the like can be further reduced, so that the nodulizing and inoculating time is prolonged, and the graphite cast iron with better performance can be obtained.

In some embodiments, with reference to fig. 3, an openable and closable closing element 12 is also provided on the dike 1; the closing element 12 is embodied as a plug which is plugged into the liquid passage opening 11 (of course, it can also be a lid which is hinged to the dam 1 and covers the liquid passage opening 11). By providing the closing member 12, the molten iron passing holes 11 of the corresponding number are opened and closed according to the requirement of the molten iron spheroidizing time, so that the ratio of the molten iron which passes through the liquid passing holes 11 and comes into contact with the spheroidizing agent or the like to the molten iron which passes over the dam 1 and comes into contact with the spheroidizing agent or the like is adjusted, and further, the impact of the poured molten iron on the spheroidizing agent or the like is adjusted, which is advantageous in controlling the time of the molten iron spheroidizing.

Comparative example 1

The main differences between this comparative example and example 1 are: the inoculant was different in composition.

The inoculant comprises the following components: 45wt% of Si, 20wt% of Ba, 12wt% of Ca, 3wt% of Cu, 1wt% of Al and 19wt% of Fe (containing unavoidable impurities).

Comparative example 2

The main differences between this comparative example and example 1 are: the inoculant compositions are different.

The inoculant comprises the following components: 45wt% of Si, 20wt% of Ba, 12wt% of Ca, 3wt% of Cu, 1wt% of Al, 4wt% of W and 15wt% of Fe (containing unavoidable impurities).

Performance detection

First, hardness testing

The ball-milled cast irons obtained in examples 1 to 18 and comparative examples 1 to 2 are tested for Brinell hardness by referring to the detection method of GB/T231-: the diameter of the hard alloy ball is 10mm, and the test force is 29420N; the results of the tests are shown in Table 1.

TABLE 1 Brinell hardness of the nodular cast irons obtained in examples 1 to 18 and comparative examples 1 to 2

Item	Brinell hardness (HBW10/3000)
		Example 1	220
Example 2	225
		Example 3	231
Example 4	232
		Example 5	227
Example 6	235
		Example 7	233
Example 8	240
		Example 9	239
Example 10	247
		Example 11	253
Example 12	252
		Example 13	250
Example 14	255
		Example 15	257
Example 16	258
		Example 17	255
Example 18	261
		Comparative example 1	212
Comparative example 2	217

Referring to Table 1, it can be seen from the results of the tests of examples 1 to 18 that: the ball-milling cast iron obtained in each example of the application has the Brinell hardness (HBW10/3000) of no less than 220, and shows higher hardness.

From the test results of example 1 and comparative example 1, it can be found that: the Brinell hardness (HBW10/3000) of the resulting nodular cast iron was significantly improved when tungsten (W) was incorporated into the inoculant. The inventor thinks that: this is because tungsten, carbon, iron, etc. can form high strength alloys which eventually enter the nodular cast iron, contributing to its increased hardness. Meanwhile, from the test results of examples 1 to 5 and comparative example 2, it can be found that: with the increase of the tungsten content in the inoculant, the Brinell hardness (HBW10/3000) of the obtained nodular cast iron is increased and then decreased; shows that: an appropriate amount of tungsten is advantageous for improving the hardness of the nodular cast iron, but when excessive amount of tungsten is used, the hardness of the nodular cast iron may be lowered because the overall structure of the nodular cast iron may be adversely affected.

From the test results of examples 6, 8 to 9, it was found that: the proper amount of inoculant is beneficial to obtaining the nodular cast iron with more ideal hardness.

The results of the tests of analytical examples 10 to 12 were as follows: the increased amount of microcapsule carbonate in the capping agent helps to increase the brinell hardness (HBW10/3000) of the resulting nodular cast iron. The inventor thinks that: the carbonate can be subjected to phase change at high temperature to form a molten state and absorb heat; after the temperature is reduced, the carbonate can generate phase change again and emit a large amount of heat, and the heat plays a heat preservation role in the molten iron, so that the solidification time of the molten iron is further prolonged, and the method is favorable for obtaining the ball-milling cast iron with a better organization structure and more ideal performance.

The results of the assays of analytical examples 11, 15 to 16 gave: the proper amount of inoculant has positive significance for obtaining the nodular cast iron with better hardness.

The results of the tests of analytical examples 15 and 18 were obtained as follows: the liquid passing port 11 is arranged on the dam 1 in the spheroidizing ladle, so that the counter-impact of poured molten iron on a spheroidizing agent and the like can be further reduced, the spheroidizing and inoculating time is prolonged, and the obtained graphite cast iron can obtain better tissue structure and hardness.

Second, microstructure

The nodular cast iron obtained in example 1 was sampled and polished with reference to GB/T9441-. From FIG. 4 in combination with GB/T9441-2009: in the microstructure of the spheroidal graphite cast iron obtained in example 1, the graphite is spherical, the graphite grade is grade 2, and the graphite length is 6-8 mm.

The nodular cast iron obtained in example 1 was sampled, and after a metallographic sample was taken with reference to GB/T9441-. From FIG. 5 in combination with GB/T9441-2009: the microstructure of the spheroidal graphite cast iron obtained in example 1 exceeded 65% of pearlite.

The present embodiment is only for explaining the present application, and it is not limited to the present application, and those skilled in the art can make modifications of the present embodiment without inventive contribution as needed after reading the present specification, but all of them are protected by patent law within the scope of the claims of the present application.

Claims

1. The preparation method of the pearlite nodular cast iron is characterized by comprising the following steps: the method comprises the following steps:

smelting the raw materials into molten iron;

casting, annealing and cooling.

2. The method of preparing pearlitic spheroidal graphite cast iron according to claim 1, characterized in that: the temperature for smelting the raw materials into molten iron is 1580-1600 ℃.

3. The method of preparing pearlitic spheroidal graphite cast iron according to claim 1, characterized in that: the nodulizer is a magnesium-silicon-iron alloy nodulizer, and the addition amount of the nodulizer is 1-1.2wt% of molten iron.

4. The method of preparing pearlitic spheroidal graphite cast iron according to claim 1, characterized in that: the addition amount of the inoculant is 0.3-0.5wt% of the molten iron.

5. The method of preparing pearlitic spheroidal graphite cast iron according to claim 1, characterized in that: during the molten iron casting, a covering agent is also added; the covering agent comprises the following components: 15-33wt% of vermiculite, 30-50wt% of expanded perlite, 10-15wt% of microcapsule carbonate, 8-12wt% of zeolite, 5-10wt% of calcium oxide and 5-10wt% of aluminum oxide.

6. The method of preparing pearlitic spheroidal graphite cast iron according to claim 5, characterized in that: the microcapsule carbonate is prepared by the following method:

7. The method of preparing pearlitic spheroidal graphite cast iron according to claim 6, characterized in that: the addition amount of the covering agent is 0.5-1wt% of the molten iron.

8. The method of producing pearlitic spheroidal graphite cast iron according to claim 1, wherein: the molten iron is cast in a spheroidizing ladle;

a dam (1) is arranged at the bottom of the spheroidizing bag, and a plurality of liquid passing holes (11) which can enable molten iron to flow through the dam (1) are formed in the dam (1).

9. The method of preparing pearlitic spheroidal graphite cast iron according to claim 8, wherein: the dam (1) is also provided with a sealing element (12), and the sealing element (12) seals the liquid passing hole (11).

10. The nodular cast iron is characterized in that: the pearlitic spheroidal graphite cast iron produced by the method according to any one of claims 1 to 9.