1. The white molten iron is characterized in that the white molten iron contains 92-95 wt% of iron, 2.75-3.15 wt% of carbon, 1.25-1.65 wt% of silicon, 0.35-0.65 wt% of manganese, less than 0.2 wt% of sulfur and less than 0.1 wt% of phosphorus.

2. The white molten iron of claim 1, wherein the white molten iron has an iron content of 93-94%, a carbon content of 2.85-3.00%, a silicon content of 1.3-1.45%, a manganese content of 0.35-0.55%, a sulfur content of less than 0.15%, and a phosphorus content of less than 0.08%, by weight;

preferably, the molten white iron contains 93.5-94% of iron, 2.85-2.95% of carbon, 1.3-1.4% of silicon, 0.4-0.5% of manganese, less than 0.08% of sulfur and less than 0.05% of phosphorus; the balance being impurities.

3. The method of manufacturing molten white iron according to claim 1 or 2, comprising the steps of:

the method comprises the following steps: adding raw materials into a furnace for melting to obtain base iron water;

step two: detecting the weight percentage of carbon and silicon elements in the molten iron by using the molten iron obtained in the step one;

step three: and adding ferrosilicon alloy into the molten iron in the furnace, and mixing to obtain the white molten iron.

4. The production method according to claim 3, wherein the raw material is one or more of scrap steel, pig iron, scrap returns, ferrosilicon and ferromanganese.

5. The production method according to claim 3 or 4, wherein the raw material in the first step contains the following elements of 92 to 95% of iron, 2.75 to 3.15% of carbon, 0.9 to 1.35% of silicon, 0.35 to 0.65% of manganese, less than 0.2% of sulfur and less than 0.1% of phosphorus, with the balance being impurities.

6. The production method according to claim 4 or 5, wherein in the raw materials in the first step, the scrap steel accounts for 5-55 wt%, the pig iron accounts for 5-60 wt%, the scrap returns account for 25-80 wt%, the ferrosilicon alloy accounts for 0.01-0.6 wt%, and the ferromanganese alloy accounts for 0.01-0.6 wt%;

preferably, the scrap steel accounts for 10-45%, the pig iron accounts for 5-50%, the foundry returns 35-70%, the ferrosilicon alloy accounts for 0.03-0.5%, and the ferromanganese alloy accounts for 0.03-0.5%.

7. The production method according to any one of claims 3 to 6, wherein the furnace in the first step is an electric furnace; the melting time in the first step is 55-80 min; the melting temperature is 1500-; preferably, the melting temperature in the first step is 1530-1600 ℃.

8. The method according to any one of claims 3-7, wherein the step two further comprises measuring the white spot width with a triangular test strip after detecting the element content.

9. The manufacturing method according to any one of claims 3 to 8, wherein the third step further comprises a step of pouring the molten base iron obtained in the first step into a ladle, wherein ferrosilicon is previously added to the ladle.

10. A production method according to any one of claims 3 to 9, wherein the ferrosilicon alloy is added in the third step in an amount of 0.01 to 0.8 wt%, preferably 0.2 to 0.6 wt%, more preferably 0.3 to 0.45 wt% of the base iron.

11. A production method according to any one of claims 3 to 10, wherein the silicon content of the silicon-iron alloy added in the third step is 0.65 to 0.75 wt%, and the particle size of the silicon-iron alloy is 5 to 15 mm.

12. A white body obtained by casting the molten white iron according to any one of claims 1 to 11.

13. The white blank according to claim 14, wherein the casting temperature is 1350-; preferably, the casting temperature is 1420-.

14. The white blank according to claim 12 or 13, wherein the embedded nuclei, which are graphitized embedded nuclei, are observable at a magnification of > 200 times of an electron microscope SEM.

15. A brown compact obtained by annealing the white compact according to any one of claims 12 to 14.

16. The cooked blank according to claim 15, wherein the temperature of the first annealing treatment is 955-975 ℃ and the first annealing time is 5-7h, preferably, the second annealing temperature is 720-740 ℃ and the second annealing time is 8-10 h.

17. The cooked blank according to claim 15 or 16, further comprising performing tests on the annealed blank, wherein the tests include appearance tests, tensile strength tests, elongation tests, and flattening tests; preferably, the tensile strength is 305-350kg/mm²The elongation is 6.6-10.2%, and the flattening rate is 10.3-20.3%.

18. A brown compact according to any one of claims 15-17, wherein the brown compact has an iron content of 93-94%, a carbon content of 2.5-2.9%, a silicon content of 1.25-1.65%, a manganese content of 0.35-0.65%, a sulphur content of less than 0.2% and a phosphorus content of less than 0.1%, the remainder being impurities, in weight%.

19. Use of the molten white iron according to any one of claims 1 to 11 or the green white body according to any one of claims 12 to 14 or the wrought body according to any one of claims 15 to 18 in the field of black-heart malleable cast iron materials, preferably in the field of materials for the production of pipe connectors, plumbing connectors, line fittings, construction fasteners and valve body members.

Background

Malleable cast iron, commonly known as malleable iron or galvanized iron, is cast from molten iron of a certain chemical composition into a blank and then annealed to form cast iron, which is a metal material with high strength, plasticity and toughness. China is the country which uses the malleable cast iron the earliest, and as early as the war of China, the brittleness of white iron is eliminated by a melting process, and the white malleable cast iron is researched and invented in 1722 France. The components of the castings with different purposes are slightly different, molten iron with certain chemical components is smelted according to different requirements of different castings, and the molten iron is poured into a white blank; then, the white blank is annealed to obtain a high-strength and high-toughness malleable cast iron product.

In the early casting field, molten irons for producing malleable cast irons were generally melted using a cupola furnace. The energy consumption of the cupola furnace is low, the equipment cost is low, the molten iron can be continuously discharged, but because a large amount of dust, sulfur dioxide, nitrogen oxide and other waste gases are discharged in the smelting process, the environment is seriously polluted, and the smelting technology of the cupola furnace is difficult to master and control, so the use of the cupola furnace is gradually reduced.

As cupola furnaces are gradually eliminated, electric furnaces become new equipment for smelting malleable cast iron and molten iron. The electric furnace occupies small area, the temperature and the components of the molten iron are relatively uniform, and the generated dust and waste gas are relatively less, thereby being more beneficial to environmental protection. However, it has been found that many unfavorable factors of the electric furnace melting of the white iron, such as easy oxidation of the molten iron and easy oxygen absorption during the melting process, also, scrap is frequently used in the production of the white iron, the oxidation of the molten iron is aggravated by severe corrosion of the material, and also, the oxidation of the molten iron is also caused by the requirement of low carbon for the white iron, and thus, various factors cause the oxidation of the molten iron during the melting of the white iron, and the phenomenon of poor fluidity of the molten iron. Especially, in a large furnace, molten iron in one furnace cannot be discharged at one time, and the residual molten iron is easier to oxidize.

The existing treatment method for smelting white molten iron by using an electric furnace generally comprises the steps of adding bismuth iron into base molten iron, wherein the bismuth iron is an iron alloy consisting of bismuth and iron; bismuth element can increase the chilling tendency; or ferrosilicon in the raw materials is added, but because of the particularity of the white iron, the content of carbon and silicon elements in the furnace is too high, so that the cast white blank is easy to generate an ash hole, and the ash hole is changed into a waste product.

Disclosure of Invention

Therefore, the problems to be solved by the present invention are: although the molten iron obtained by the conventional treatment method can be poured into the white blank, in the actual production, the quality of the poured white blank is unstable, partial blanks are often accompanied by the problems of large internal stress, easy occurrence of dominant or even invisible cracks and the like, the tensile strength is low, the elongation rate is low, the flattening rate is low, the embrittlement phenomenon of the white blank is very serious, and the blanks can be cracked due to slight collision in the processes of tamping, inspecting, transporting and the like of the blanks before annealing treatment, so that the subsequent annealing treatment cannot be performed. The problems not only greatly increase the rejection rate of the white blank, reduce the qualification rate of the malleable cast iron, increase the production cost of enterprises, but also ensure the quality of the product.

After the inventors of the present invention have made extensive studies, the quality of a cast product is directly affected by the composition of molten iron, and thus the melting process of molten iron is very important. In order to ensure the performance of the malleable cast iron product, the contents of the respective components in the molten iron must be controlled within a prescribed range, particularly the contents of five main elements of carbon (C), silicon (Si), manganese (Mn), sulfur (S), and phosphorus (P).

Carbon (C) is a strong element for promoting graphitization, and when the content of the carbon (C) in molten iron is too high, the amount of flocculent graphite in the malleable cast iron is too large, and the mechanical properties of the product, such as tensile strength, elongation, flattening rate and the like, are reduced; when the content of carbon (C) is too low, the number of crystal nuclei in the product becomes too small, which makes annealing of the product difficult and greatly prolongs the annealing time.

Silicon (Si) is also a strong graphitization promotion element, and increasing the content of silicon can improve the mechanical properties of the malleable cast iron, such as tensile strength, elongation, flattening ratio and the like.

Sulfur (S) is a harmful element that hinders the graphitization process, and decreases the fluidity of molten iron, increases the tendency to crack, and decreases the toughness of a casting, so the lower the content of sulfur in molten iron, the better.

During the casting process of manganese (Mn), part of manganese (Mn) reacts with sulfur (S) to generate manganese sulfide (MnS), the manganese sulfide can be discharged along with slag of molten iron, and part of manganese can be left in a product and serves as a non-spontaneous core for graphitization to neutralize the harm caused by sulfur elements; however, when the manganese content is too high, the graphitization process is strongly hindered. Therefore, the content of manganese should be controlled to be 2.5-3.2 times of the content of sulfur.

Phosphorus (P) has little influence on the graphitization process of malleable cast iron, but too high a phosphorus content may reduce the toughness of the casting, resulting in brittle and brittle products.

The inventor finds that the technology of adding the ferrosilicon alloy into the furnace outer package strictly controls the silicon content in the base iron, and the technology of adding the specific silicon content into the furnace outer package is a core technology for improving the strength, toughness and plasticity of the white-mouth green compact. The addition of rare and expensive bismuth iron is reduced, the pollution of bismuth iron to the environment is reduced, and the cost is saved.

Specifically, the invention provides the following technical scheme:

the invention provides white molten iron which is characterized in that the white molten iron contains 92-95 wt% of iron, 2.75-3.15 wt% of carbon, 1.25-1.65 wt% of silicon, 0.35-0.65 wt% of manganese, less than 0.2 wt% of sulfur and less than 0.1 wt% of phosphorus.

Preferably, the molten white iron contains 93-94% of iron, 2.85-3.00% of carbon, 1.3-1.45% of silicon, 0.35-0.55% of manganese, less than 0.15% of sulfur and less than 0.08% of phosphorus by weight percent;

preferably, the molten white iron contains 93.5-94% of iron, 2.85-2.95% of carbon, 1.3-1.4% of silicon, 0.4-0.5% of manganese, less than 0.08% of sulfur and less than 0.05% of phosphorus; the balance being impurities.

The invention also provides a preparation method of the white molten iron, which is characterized by comprising the following steps:

the method comprises the following steps: adding raw materials into a furnace for melting to obtain base iron water;

step two: detecting the weight percentage of carbon and silicon elements in the molten iron by using the molten iron obtained in the step one;

step three: and adding ferrosilicon alloy into the molten iron in the furnace, and mixing to obtain the white molten iron.

Preferably, the raw materials are one or more than two of scrap steel, pig iron, foundry returns, ferrosilicon and ferromanganese.

Preferably, in the first step, the raw material contains 92-95% of iron, 2.75-3.15% of carbon, 0.9-1.35% of silicon, 0.35-0.65% of manganese, less than 0.2% of sulfur and less than 0.1% of phosphorus, and the balance of impurities.

Preferably, in the raw materials in the first step, the scrap steel accounts for 5-55 wt%, the pig iron accounts for 5-60 wt%, the foundry returns 25-80 wt%, the ferrosilicon alloy accounts for 0.01-0.6 wt%, and the ferromanganese alloy accounts for 0.01-0.6 wt%;

preferably, the scrap steel accounts for 10-45%, the pig iron accounts for 5-50%, the foundry returns 35-70%, the ferrosilicon alloy accounts for 0.03-0.5%, and the ferromanganese alloy accounts for 0.03-0.5%.

Preferably, the furnace in the first step is an electric furnace; the melting time in the first step is 55-80 min; the melting temperature is 1500-; preferably, the melting temperature in the first step is 1530-1600 ℃.

Preferably, the second step of detecting the element content further comprises measuring the white spot width with a triangular test strip.

Preferably, the third step further comprises a step of pouring the base iron obtained in the first step into a ladle, wherein the ferrosilicon alloy is added into the ladle in advance.

Preferably, the ferrosilicon alloy is added in the third step in an amount of 0.01 to 0.8 wt%, preferably 0.2 to 0.6 wt%, and more preferably 0.3 to 0.45 wt% of the base iron;

preferably, the silicon content of the silicon-iron alloy added in the third step is 0.65-0.75 wt%, and the particle size of the silicon-iron alloy is 5-15 mm.

The invention also provides a white cast iron green body which is characterized in that the white cast iron green body is cast by the white cast iron.

Preferably, wherein the casting temperature is 1350-; preferably, the casting temperature is 1420-.

Preferably, the white blank can observe pre-buried crystal nuclei under the magnification of more than 200 times of an electron microscope SEM, and the pre-buried crystal nuclei are graphitized pre-buried crystal nuclei.

The invention also provides a cooked blank, which is characterized in that the cooked blank is obtained by annealing the white blank.

Preferably, wherein the temperature of the first annealing treatment is 955-,

preferably, the second annealing temperature is 720-740 ℃, and the second annealing time is 8-10 h.

Preferably, the method further comprises the step of detecting the annealed blank, wherein the detection comprises appearance detection, tensile strength detection, elongation and flattening rate detection;

preferably, the tensile strength is 305-350kg/mm²The elongation is 6.6-10.2%, and the flattening rate is 10.3-20.3%.

Preferably, the content of iron in the cooked blank is 93-94%, the content of carbon is 2.5-2.9%, the content of silicon is 1.25-1.65%, the content of manganese is 0.35-0.65%, the content of sulfur is less than 0.2%, the content of phosphorus is less than 0.1%, and the balance is impurities.

The invention also provides the application of the white molten iron or the white green compact or the cooked compact in the field of black-heart malleable cast iron materials, preferably in the field of producing pipe connectors, water-heating connectors, line fittings, building fasteners and valve body materials.

The beneficial effects of the invention include: according to the white iron and the preparation method of the white iron, the addition of rare and expensive bismuth iron is reduced, the pollution of the bismuth iron to the environment is reduced, the addition of ferrosilicon in the raw materials is reduced, the production raw materials are saved, the production cost is reduced, the toughness, the strength and the plasticity of the cast white green compact are improved, the problems that the white green compact is brittle and easy to break are solved, and the quality and the production yield of the white green compact are greatly improved. And the process operation is simple, and the components are easy to control.

Drawings

FIG. 1 is a triangular test piece test chart obtained by taking out molten iron in the second step of example 1.

FIG. 2 is a diagram showing pre-buried nuclei observed in the white bar obtained in the fourth step of example 1.

Detailed Description

As described above, the present invention is intended to solve the problems that molten iron obtained by the conventional treatment method can be poured into a white blank, but in actual production, the quality of the poured white blank is unstable, some blanks are often accompanied by problems of large internal stress, easy generation of invisible cracks, etc., the tensile strength is low, the elongation rate is low, the flattening rate is low, and the brittleness of the blank is very serious, and the blank is cracked due to slight collision during the processes of tamping, inspecting, transporting, etc. of the blank before annealing treatment, so that subsequent annealing treatment cannot be performed. The problems not only greatly increase the rejection rate of the white blank, reduce the qualification rate of the malleable cast iron and increase the production cost of enterprises, but also can not ensure the quality of the product and seriously affect the reputation of the enterprises.

The invention provides white molten iron which is characterized in that the white molten iron contains 92-95 wt% of iron, 2.75-3.15 wt% of carbon, 1.25-1.65 wt% of silicon, 0.35-0.65 wt% of manganese, less than 0.2 wt% of sulfur and less than 0.1 wt% of phosphorus.

In a preferred embodiment of the present invention, wherein the molten white iron contains, by weight, 93 to 94% of iron, 2.85 to 3.00% of carbon, 1.3 to 1.45% of silicon, 0.35 to 0.55% of manganese, less than 0.15% of sulfur, and less than 0.08% of phosphorus;

in a preferred embodiment of the present invention, the molten white iron has an iron content of 93.5 to 94%, a carbon content of 2.85 to 2.95%, a silicon content of 1.3 to 1.4%, a manganese content of 0.4 to 0.5%, a sulfur content of less than 0.08% and a phosphorus content of less than 0.05%; the balance being impurities.

The invention also provides a preparation method of the white molten iron, which is characterized by comprising the following steps:

the method comprises the following steps: adding raw materials into a furnace for melting to obtain base iron water;

step two: detecting the weight percentage of carbon and silicon elements in the molten iron by using the molten iron obtained in the step one;

step three: and adding ferrosilicon alloy into the molten iron in the furnace, and mixing to obtain the white molten iron.

Preferably, the raw materials are one or more than two of scrap steel, pig iron, foundry returns, ferrosilicon and ferromanganese.

In a preferred embodiment of the present invention, in the first step, the raw material contains the following elements of 92 to 95% of iron, 2.75 to 3.15% of carbon, 0.9 to 1.35% of silicon, 0.35 to 0.65% of manganese, less than 0.2% of sulfur and less than 0.1% of phosphorus, with the balance being impurities.

In a preferred embodiment of the invention, in the raw materials in the first step, the scrap steel accounts for 5-55 wt%, the pig iron accounts for 5-60 wt%, the foundry returns 25-80 wt%, the ferrosilicon alloy accounts for 0.01-0.6 wt%, and the ferromanganese alloy accounts for 0.01-0.6 wt%;

in a preferred embodiment of the invention, scrap steel is 10-45%, pig iron is 5-50%, foundry returns are 35-70%, ferrosilicon is 0.03-0.5%, and ferromanganese is 0.03-0.5%.

In a preferred embodiment of the present invention, wherein the furnace in the first step is an electric furnace; the melting time in the first step is 55-80 min; the melting temperature is 1500-; preferably, the melting temperature in the first step is 1530-1600 ℃.

Preferably, the second step of detecting the element content further comprises measuring the white spot width with a triangular test strip.

Preferably, the third step further comprises a step of pouring the base iron obtained in the first step into a ladle, wherein the ferrosilicon alloy is added into the ladle in advance.

In a preferred embodiment of the present invention, the ferrosilicon alloy is added in the third step in an amount of 0.01 to 0.8 wt%, preferably 0.2 to 0.6 wt%, and more preferably 0.3 to 0.45 wt% of the base iron;

in a preferred embodiment of the present invention, wherein the silicon content of the ferrosilicon alloy added in the third step is 0.65 to 0.75 wt%, and the grain size of the ferrosilicon alloy is 5 to 15 mm.

The invention also provides a white cast iron green body which is characterized in that the white cast iron green body is cast by the white cast iron.

In a preferred embodiment of the present invention, wherein the casting temperature is 1350-; preferably, the casting temperature is 1420-.

In a preferred embodiment of the present invention, the white blank can observe pre-buried crystal nuclei under an electron microscope SEM with a magnification of more than 200 times, wherein the pre-buried crystal nuclei are graphitized pre-buried crystal nuclei.

The invention also provides a cooked blank, which is characterized in that the cooked blank is obtained by annealing the white blank.

In a preferred embodiment of the present invention, wherein the temperature of the first annealing treatment is 955-.

In a preferred embodiment of the invention, the method further comprises the steps of detecting the annealed blank, wherein the detection comprises appearance detection, tensile strength detection, elongation detection and flattening detection;

in a preferred embodiment of the present invention, the tensile strength is 305-350kg/mm²The elongation is 6.6-10.2%, and the flattening rate is 10.3-20.3%.

In a preferred embodiment of the present invention, wherein the content of iron in the clinker is 93-94%, the content of carbon is 2.5-2.9%, the content of silicon is 1.25-1.65%, the content of manganese is 0.35-0.65%, the content of sulfur is less than 0.2%, the content of phosphorus is less than 0.1%, and the balance is impurities.

The invention also provides the application of the white molten iron or the white green compact or the cooked compact in the field of black-heart malleable cast iron materials, preferably in the field of producing pipe connectors, water-heating connectors, line fittings, building fasteners and valve body materials.

The detection method of the triangular test piece comprises the following steps: and casting the molten white iron in the second step into a sand mold with the height of 11.5cm, the upper width of 4.0cm and the included angle downward of 15 degrees, casting into a triangular test piece, measuring the width of a white opening of the triangular test piece on the cross section, wherein the width of the white opening is the starting width of the white opening, comparing the vertical distance from the wide part of the triangular test piece to a test line with the white opening of the triangular test piece in the figure 1 with L1, and the width of the position where the test line is located is the width of the white opening. The width of the white opening is equal to or slightly larger than the maximum wall thickness required by the casting, and the casting is qualified.

The method for detecting the tensile strength comprises the following steps: and casting the molten white iron in the step two into a test bar, pressurizing by using a tensile machine until the test bar is broken, wherein the area of the cross section of the tensile force/test bar when the test bar is broken is the tensile strength. (load per unit area: kg/mm)²)

The elongation (ratio of maximum length at the time of failure to elongation) was measured by the following method: and casting the molten white iron in the step two into a test bar, and pressurizing by using a tensile machine until the test bar is broken, (the elongated length of the test bar-the original length of the test bar)/the original length of the test bar is the elongation.

The detection method of the flattening rate (the ratio of the diameter after flattening to the diameter before flattening) comprises the following steps: and pressing the obtained black-core malleable cast iron material by using a press machine, and applying pressure until fine cracks appear, (the diameter after flattening-the diameter before flattening)/the diameter before flattening is the flattening rate.

The invention is described in detail below with reference to the figures and specific embodiments. The following is a description of the manufacturers of the raw materials and equipment used in the present example, and the equipment and analysis method used for product analysis.

TABLE 1 information on materials and instruments used in the present invention

Example (b): method for preparing white molten iron, white green compact, cooked compact and black core malleable cast iron

Example 1

Preparing white molten iron:

the method comprises the following steps: adding raw materials into an electric furnace, wherein the raw materials comprise 20% of scrap steel, 40% of pig iron and 40% of foundry returns, and the total amount of the raw materials is 3000 kg;

wherein the raw material comprises 93.15% of iron, 2.94% of carbon, 1.144% of silicon, 0.35% of manganese, 0.079% of sulfur and 0.0428% of phosphorus; the melting time was 55 minutes and the melting temperature was 1600 ℃.

Step two: taking out a small amount of the base iron obtained in the first step, and detecting the weight percentages of carbon and silicon elements in the molten iron by using a stokehole thermal analyzer, wherein the weight percentages of the carbon and the silicon elements are respectively 2.92% of the carbon content and 1.18% of the silicon content; taking out molten iron at 1600 ℃, taking a small amount of molten iron for triangular test piece testing, pouring the small amount of molten iron into a sand mold of the triangular test piece, and cooling and forming to test the width of a white notch to be 16 mm.

Step three: and (2) adding the molten iron in the second step into a ladle, wherein 8.8Kg of ferrosilicon alloy with the silicon content of 75% is added into the ladle, the granularity of the ferrosilicon alloy is 5mm, and the ferrosilicon alloy accounts for 0.29 wt% of the raw materials by mass, so that the white molten iron is obtained. And (3) carrying out element component analysis on the molten white iron obtained in the third step, wherein an instrument for carrying out element component analysis is a direct-reading spectrometer. The iron content was 93.14%, the carbon content was 2.95%, the silicon content was 1.40%, the manganese content was 0.35%, the sulphur content was 0.074% and the phosphorus content was 0.041%.

The preparation method of the white blank comprises the following steps:

step four: and (4) casting the white molten iron obtained in the third step in a three-way pipe sand mould with the pipe wall thickness of 8 mm at the casting temperature of 1380 ℃ to obtain a white green compact of the three-way pipe.

The obtained white blank can observe pre-buried crystal nuclei which are graphitized pre-buried crystal nuclei under the magnification of 200 times by using an SEM microscope.

The preparation method of the cooked blank comprises the following steps:

step five: and fourthly, annealing the white blank obtained in the fourth step, wherein the annealing temperature is 960 ℃, preserving heat for 6 hours, cooling to 720 ℃, and preserving heat for 8 hours to obtain the black core malleable cast iron of the three-way pipe. The instrument for analyzing element components is a carbon-sulfur analyzer and a microcomputer multi-element analyzer. Wherein the element composition is 93.15% iron, 2.66% carbon, 1.41% silicon, 0.36% manganese, 0.078% sulphur and 0.042% phosphorus.

Example 2

Preparing white molten iron:

the method comprises the following steps: adding raw materials into an electric furnace, wherein the raw materials comprise 15% of scrap steel, 50% of pig iron and 35% of foundry returns, and the total amount of the raw materials is 3000 kg; then 2.5kg of ferromanganese alloy is added.

Wherein the raw material comprises 93.05% of iron, 3.07% of carbon, 1.094% of silicon, 0.38% of manganese, 0.087% of sulfur and 0.044% of phosphorus; the melting time was 70 minutes and the melting temperature was 1550 ℃.

Step two: taking out a small amount of the base iron obtained in the first step, and detecting the weight percentages of carbon and silicon elements in the molten iron by using a stokehole thermal analyzer, wherein the weight percentages of the carbon and the silicon elements are respectively 3.02% of the carbon content and 1.1% of the silicon content; taking out the molten iron, wherein the temperature of the molten iron is 1500 ℃, then taking a small amount of molten iron to carry out a triangular test piece test, pouring a small amount of molten iron into a sand mold of the triangular test piece, and after cooling and forming, testing the width of a white notch to be 18 mm.

Step three: and (2) adding the molten iron in the second step into a ladle, wherein 8.0Kg of ferrosilicon alloy with the silicon content of 75% is added into the ladle, the particle size of the ferrosilicon alloy is 10mm, and the ferrosilicon alloy accounts for 0.266 wt% of the raw materials by mass, so that the white molten iron is obtained. And (3) carrying out element component analysis on the molten white iron obtained in the third step, wherein an instrument for carrying out element component analysis is a direct-reading spectrometer. The iron content was 93.01%, the carbon content was 3.05%, the silicon content was 1.31%, the manganese content was 0.383%, the sulphur content was 0.082% and the phosphorus content was 0.047%.

The preparation method of the white blank comprises the following steps:

step four: and (4) casting the white molten iron obtained in the third step in a three-way pipe sand mold with the pipe wall thickness of 8 mm at the casting temperature of 1530 ℃, thus obtaining a white green compact of the three-way pipe.

The obtained white blank can observe pre-buried crystal nuclei which are graphitized pre-buried crystal nuclei under the magnification of 200 times by using an SEM microscope.

The preparation method of the cooked blank comprises the following steps:

step five: and fourthly, annealing the white blank obtained in the fourth step, wherein the annealing temperature is 970 ℃, preserving heat for 6 hours, cooling to 730 ℃, and preserving heat for 8 hours to obtain the black-core malleable cast iron of the three-way pipe. Wherein the element composition is 93.15% iron, 2.73% carbon, 1.32% silicon, 0.389% manganese, 0.083% sulphur and 0.048% phosphorus.

Example 3

Preparing white molten iron:

the method comprises the following steps: adding raw materials into an electric furnace, wherein the raw materials comprise 15% of scrap steel, 45% of pig iron and 40% of foundry returns, and the total amount of the raw materials is 3000 kg; 0.825kg of ferromanganese alloy is added.

Wherein the raw material comprises 92.85% of iron, 3.02% of carbon, 1.194% of silicon, 0.36% of manganese, 0.084% of sulfur and 0.023% of phosphorus; the melting time was 80 minutes and the melting temperature was 1500 ℃.

Step two: taking out a small amount of the base iron obtained in the first step, and detecting the weight percentages of carbon and silicon elements in the molten iron by using a stokehole thermal analyzer, wherein the carbon content is 3.04 percent and the silicon content is 1.18 percent respectively; taking out the molten iron, wherein the temperature of the molten iron is 1500 ℃, then taking a small amount of molten iron to carry out a triangular test piece test, pouring a small amount of molten iron into a sand mold of the triangular test piece, and after cooling and forming, testing the width of a white notch to be 14 mm.

Step three: and (2) adding the molten iron in the second step into a foundry ladle, wherein 9.04Kg of ferrosilicon alloy is added into the foundry ladle, the silicon content is 75%, the granularity of the ferroalloy is 15mm, and the ferrosilicon alloy accounts for 0.3 wt% of the raw materials by mass, so that the white molten iron is obtained. And (3) carrying out element component analysis on the molten white iron obtained in the third step, wherein an instrument for carrying out element component analysis is a carbon direct-reading spectrometer. The iron content was 92.83%, the carbon content was 3.01%, the silicon content was 1.4%, the manganese content was 0.361%, the sulfur content was 0.081% and the phosphorus content was 0.03%.

The preparation method of the white blank comprises the following steps:

step four: and (4) casting the white molten iron obtained in the third step in an elbow pipe sand mold with the pipe wall thickness of 8 mm at the casting temperature of 1480 ℃ to obtain a white green body of the elbow pipe.

The obtained white blank can observe pre-buried crystal nuclei which are graphitized pre-buried crystal nuclei under the magnification of 200 times by using an SEM microscope.

The preparation method of the cooked blank comprises the following steps:

step five: and annealing the white blank obtained in the fourth step at 965 ℃, preserving heat for 6 hours, cooling to 730 ℃, and preserving heat for 8 hours to obtain the black-core malleable cast iron of the elbow pipe. Wherein the element composition is iron content 92.84%, carbon content 2.71%, silicon content 1.42%, manganese content 0.36%, sulfur content 0.082% and phosphorus content 0.034%.

Example 4

Preparing white molten iron:

the method comprises the following steps: raw materials are added into an electric furnace, wherein the raw materials comprise 5% of scrap steel, 25% of pig iron and 70% of foundry returns, and the total amount of the raw materials is 3000 kg.

Wherein the raw material comprises 92.97% of iron, 3.01% of carbon, 1.33% of silicon, 0.408% of manganese, 0.079% of sulfur and 0.043% of phosphorus; the melting time was 70 minutes and the melting temperature was 1570 ℃.

Step two: taking out a small amount of the base iron obtained in the first step, and detecting the weight percentages of carbon and silicon elements in the molten iron by using a stokehole thermal analyzer, wherein the carbon content is 3.04 percent and the silicon content is 1.35 percent respectively; taking out the molten iron at 1560 ℃, then taking a small amount of molten iron to perform a triangular test piece test, pouring a small amount of molten iron into a sand mold of the triangular test piece, and cooling and forming to obtain a test blank with the width of 9 mm.

Step three: and (2) adding the molten iron in the second step into a foundry ladle, wherein 2.8Kg of ferrosilicon alloy with the silicon content of 75% is added into the foundry ladle, the granularity of the ferrosilicon alloy is 11mm, and the ferrosilicon alloy accounts for 0.09 wt% of the raw materials by mass, so that the white molten iron is obtained. And (3) carrying out element component analysis on the molten white iron obtained in the third step, wherein an instrument for carrying out element component analysis is a direct-reading spectrometer. The iron content was 92.96%, the carbon content was 2.98%, the silicon content was 1.39%, the manganese content was 0.401%, the sulphur content was 0.072% and the phosphorus content was 0.044%.

The preparation method of the white blank comprises the following steps:

step four: and (4) casting the white molten iron obtained in the third step in an elbow pipe sand mold with the pipe wall thickness of 8 mm at the casting temperature of 1510 ℃, thus obtaining a white green compact of the elbow pipe.

The obtained white blank can observe pre-buried crystal nuclei which are graphitized pre-buried crystal nuclei under the magnification of 200 times by using an SEM microscope.

The preparation method of the cooked blank comprises the following steps:

step five: and annealing the white blank obtained in the fourth step at 965 ℃, preserving heat for 6 hours, cooling to 730 ℃, and preserving heat for 8 hours to obtain the black-core malleable cast iron of the elbow pipe. Wherein the element composition is 92.96% iron, 2.69% carbon, 1.38% silicon, 0.406% manganese, 0.082% sulphur and 0.045% phosphorus.

Example 5

Preparing white molten iron:

the method comprises the following steps: raw materials are added into an electric furnace, wherein the raw materials comprise 10% of scrap steel, 20% of pig iron and 70% of foundry returns, and the total amount of the raw materials is 3000 kg.

Wherein the raw materials comprise 93.27 percent of iron, 2.82 percent of carbon, 1.28 percent of silicon, 0.415 percent of manganese, 0.074 percent of sulfur and 0.034 percent of phosphorus; the melting time was 75 minutes and the melting temperature was 1550 ℃.

Step two: taking out a small amount of the base iron obtained in the first step, and detecting the weight percentages of carbon and silicon elements in the molten iron by using a stokehole thermal analyzer, wherein the weight percentages of the carbon and the silicon elements are respectively 2.8 percent of the carbon content and 1.27 percent of the silicon content; taking out the molten iron at 1550 ℃, taking a small amount of molten iron to perform a triangular test piece test, pouring the small amount of molten iron into a sand mold of the triangular test piece, and cooling and forming to obtain a test white notch with the width of 17 mm.

Step three: and (2) adding the molten iron in the second step into a foundry ladle, wherein 9.2Kg of ferrosilicon alloy with the silicon content of 75% is added into the foundry ladle, the granularity of the ferrosilicon alloy is 12mm, and the ferrosilicon alloy accounts for 0.31 wt% of the raw materials by mass, so that the white molten iron is obtained. And (3) carrying out element component analysis on the molten white iron obtained in the third step, wherein an instrument for carrying out element component analysis is a direct-reading spectrometer. The iron content was 93.26%, the carbon content was 2.88%, the silicon content was 1.48%, the manganese content was 0.421%, the sulphur content was 0.081% and the phosphorus content was 0.042%.

The preparation method of the white blank comprises the following steps:

step four: and casting the white molten iron obtained in the third step in a pipe hoop sand mold with the pipe wall thickness of 8 mm at the casting temperature of 1520 ℃ to obtain a white green body of the pipe hoop.

The obtained white blank can observe pre-buried crystal nuclei which are graphitized pre-buried crystal nuclei under the magnification of 200 times by using an SEM microscope.

The preparation method of the cooked blank comprises the following steps:

step five: and annealing the white green compact obtained in the fourth step at 965 ℃, preserving heat for 6 hours, cooling to 730 ℃, and preserving heat for 8 hours to obtain the black-core malleable cast iron of the pipe hoop. Wherein the element composition is 93.26% of iron, 2.51% of carbon, 1.46% of silicon, 0.408% of manganese, 0.071% of sulfur and 0.035% of phosphorus.

Example 6

Preparing white molten iron:

the method comprises the following steps: raw materials are added into an electric furnace, wherein the raw materials comprise 10 percent of scrap steel, 45 percent of pig iron, 45 percent of foundry returns, 3000kg of total, and 7.5kg of ferromanganese.

Wherein the raw material comprises 92.67 percent of iron, 3.14 percent of carbon, 1.25 percent of silicon, 0.35 percent of manganese, 0.087 percent of sulfur and 0.044 percent of phosphorus; the melting time was 75 minutes and the melting temperature was 1550 ℃.

Step two: taking out a small amount of the base iron obtained in the first step, and detecting the weight percentages of carbon and silicon elements in the molten iron by using a stokehole thermal analyzer, wherein the carbon content is 3.08 percent and the silicon content is 1.23 percent respectively; taking out the molten iron at 1550 ℃, taking a small amount of molten iron to perform a triangular test piece test, pouring the small amount of molten iron into a sand mold of the triangular test piece, and cooling and forming to obtain a test white notch with the width of 10 mm.

Step three: and (2) adding the molten iron in the second step into a foundry ladle, wherein 4.81Kg of ferrosilicon alloy is added into the foundry ladle, the silicon content is 75%, the granularity of the ferrosilicon alloy is 10mm, and the ferrosilicon alloy accounts for 0.16 wt% of the raw materials by mass, so that the white molten iron is obtained. And (3) carrying out element component analysis on the molten white iron obtained in the third step, wherein an instrument for carrying out element component analysis is a direct-reading spectrometer. The iron content was 92.66%, the carbon content was 3.09%, the silicon content was 1.36%, the manganese content was 0.502%, the sulfur content was 0.088% and the phosphorus content was 0.042%.

The preparation method of the white blank comprises the following steps:

step four: and (4) casting the white molten iron obtained in the third step in a pipe clamp sand mold with the pipe wall thickness of 8 mm at the casting temperature of 1490 ℃ to obtain a white green body of the pipe clamp.

The obtained white blank can observe pre-buried crystal nuclei which are graphitized pre-buried crystal nuclei under the magnification of 200 times by using an SEM microscope.

The preparation method of the cooked blank comprises the following steps:

step five: and annealing the white green compact obtained in the fourth step at 965 ℃, preserving heat for 7 hours, cooling to 730 ℃, and preserving heat for 10 hours to obtain the black-core malleable cast iron of the pipe hoop. Wherein the element composition is 92.66% of iron, 2.79% of carbon, 1.37% of silicon, 0.498% of manganese, 0.082% of sulfur and 0.041% of phosphorus.

Example 7

Preparing white molten iron:

the method comprises the following steps: raw materials are added into an electric furnace, wherein the raw materials comprise 15% of scrap steel, 30% of pig iron and 55% of foundry returns, and the total amount of the raw materials is 3000 kg.

Wherein the raw material comprises 93.21% of iron, 2.83% of carbon, 1.21% of silicon, 0.383% of manganese, 0.076% of sulfur and 0.043% of phosphorus; the melting time was 80 minutes and the melting temperature was 1500 ℃.

Step two: taking out a small amount of the base iron obtained in the first step, and detecting the weight percentages of carbon and silicon elements in the molten iron by using a stokehole thermal analyzer, wherein the weight percentages of the carbon and the silicon elements are respectively 2.85% of the carbon content and 1.22% of the silicon content; taking out the molten iron at 1500 ℃, taking a small amount of molten iron to perform a triangular test piece test, pouring a small amount of molten iron into a sand mold of the triangular test piece, and cooling and forming to test the width of a white notch to be 18 mm.

Step three: and (2) adding the molten iron in the second step into a foundry ladle, wherein 9.6Kg of ferrosilicon alloy with the silicon content of 75% is added into the foundry ladle, the granularity of the ferrosilicon alloy is 12mm, and the ferrosilicon alloy accounts for 0.32 wt% of the raw materials by mass, so that the white molten iron is obtained. And (3) carrying out element component analysis on the molten white iron obtained in the third step, wherein an instrument for carrying out element component analysis is a direct-reading spectrometer. The obtained product had an iron content of 93.2%, a carbon content of 2.88%, a silicon content of 1.43%, a manganese content of 0.386%, a sulphur content of 0.072% and a phosphorus content of 0.048%.

The preparation method of the white blank comprises the following steps:

step four: and casting the white molten iron obtained in the third step in a pipe hoop sand mold with the pipe wall thickness of 8 mm at the casting temperature of 1450 ℃, thus obtaining a white green compact of the four-way pipe.

The obtained white blank can observe pre-buried crystal nuclei which are graphitized pre-buried crystal nuclei under the magnification of 200 times by using an SEM microscope.

The preparation method of the cooked blank comprises the following steps:

step five: and annealing the white blank obtained in the fourth step at 955 ℃, preserving the heat for 7 hours, cooling to 740 ℃, and preserving the heat for 10 hours to obtain the black-core malleable cast iron of the four-way pipe. Wherein, the instrument for analyzing the element components is a carbon-sulfur analyzer and a microcomputer multi-element analyzer, and the element components comprise 93.22 percent of iron, 2.51 percent of carbon, 1.42 percent of silicon, 0.378 percent of manganese, 0.074 percent of sulfur and 0.045 percent of phosphorus.

Example 8

Preparing white molten iron:

the method comprises the following steps: raw materials comprising 18 percent of scrap steel, 38 percent of pig iron and 44 percent of foundry returns are added into the electric furnace, and the total amount of the raw materials is 3000 kg.

Wherein the element composition of the raw material comprises 93.13 percent of iron, 2.85 percent of carbon, 1.17 percent of silicon, 0.358 percent of manganese, 0.079 percent of sulfur and 0.043 percent of phosphorus; the melting time was 80 minutes and the melting temperature was 1500 ℃.

Step two: taking out a small amount of the base iron obtained in the first step, and detecting the weight percentages of carbon and silicon elements in the molten iron by using a stokehole thermal analyzer, wherein the weight percentages of the carbon and the silicon elements are respectively 2.88% of the carbon content and 1.2% of the silicon content; taking out the molten iron at 1500 ℃, taking a small amount of molten iron to perform a triangular test piece test, pouring a small amount of molten iron into a sand mold of the triangular test piece, and cooling and forming to test the width of a white notch to be 18 mm.

Step three: and (2) adding the molten iron in the second step into a foundry ladle, wherein 18Kg of ferrosilicon alloy with the silicon content of 75% is added into the foundry ladle, the particle size of the ferrosilicon alloy is 10mm, and the ferrosilicon alloy accounts for 0.6 wt% of the raw materials by mass, so that the white molten iron is obtained. And (3) carrying out element component analysis on the molten white iron obtained in the third step, wherein an instrument for carrying out element component analysis is a direct-reading spectrometer. The iron content was 93.12%, the carbon content was 2.86%, the silicon content was 1.64%, the manganese content was 0.361%, the sulphur content was 0.08% and the phosphorus content was 0.045%.

The preparation method of the white blank comprises the following steps:

step four: and casting the white molten iron obtained in the third step in a pipe hoop sand mold with the pipe wall thickness of 8 mm at the casting temperature of 1450 ℃, thus obtaining a white green compact of the four-way pipe.

The obtained white blank can observe pre-buried crystal nuclei which are graphitized pre-buried crystal nuclei under the magnification of 200 times by using an SEM microscope.

The preparation method of the cooked blank comprises the following steps:

step five: and annealing the white blank obtained in the fourth step at 955 ℃, preserving the heat for 7 hours, cooling to 740 ℃, and preserving the heat for 10 hours to obtain the black-core malleable cast iron of the four-way pipe. Wherein the element composition is 93.12% iron, 2.53% carbon, 1.62% silicon, 0.364% manganese, 0.072% sulfur and 0.046% phosphorus.

Comparative example

Comparative example 1

The same raw materials as those used in example 1, except that 8.8kg of ferrosilicon alloy was not added in step three, and the white molten iron was obtained. And (3) carrying out element component analysis on the molten white iron obtained in the third step, wherein an instrument for carrying out element component analysis is a direct-reading spectrometer. The iron content was 93.12%, the carbon content was 2.98%, the silicon content was 1.17%, the manganese content was 0.36%, the sulphur content was 0.076% and the phosphorus content was 0.044%.

The preparation method of the white blank comprises the following steps:

step four: and (4) casting the white molten iron obtained in the third step in a three-way pipe sand mould with the pipe wall thickness of 8 mm at the casting temperature of 1380 ℃ to obtain a white green compact of the three-way pipe.

The obtained white compact was observed to have no embedded nuclei at a magnification of 200 times using an SEM microscope.

The preparation method of the cooked blank comprises the following steps:

step five: and fourthly, annealing the white blank obtained in the fourth step, wherein the annealing temperature is 960 ℃, preserving heat for 6 hours, cooling to 720 ℃, and preserving heat for 8 hours to obtain the black core malleable cast iron of the three-way pipe. Wherein the element composition is 93.13% iron, 2.62% carbon, 1.17% silicon, 0.36% manganese, 0.078% sulphur and 0.042% phosphorus.

Comparative example 2

The same raw materials as those used in the first step of example 4, except that 2.8Kg of ferrosilicon alloy is not added in the third step, and the white molten iron is obtained. And (3) carrying out element component analysis on the molten white iron obtained in the third step, wherein an instrument for carrying out element component analysis is a direct-reading spectrometer. The iron content was 92.95%, the carbon content was 2.98%, the silicon content was 1.30%, the manganese content was 0.412%, the sulfur content was 0.071% and the phosphorus content was 0.047%.

The preparation method of the white blank comprises the following steps:

step four: and casting the white molten iron obtained in the third step in an elbow pipe sand mold with the pipe wall thickness of 8 mm at the casting temperature of 1500 ℃ to obtain a white green body of the elbow pipe.

The obtained white compact was observed to have no embedded nuclei at a magnification of 200 times using an SEM microscope.

The preparation method of the cooked blank comprises the following steps:

step five: and annealing the white blank obtained in the fourth step at 965 ℃, preserving heat for 6 hours, cooling to 730 ℃, and preserving heat for 8 hours to obtain the black-core malleable cast iron of the elbow pipe. Wherein the element composition is 92.96% of iron, 2.78% of carbon, 1.29% of silicon, 0.398% of manganese, 0.081% of sulfur and 0.042% of phosphorus.

Comparative example 3

The same starting material as used in step one of example 1, except that in step three: and (2) adding the molten iron in the second step into a ladle, wherein 34.3Kg of ferrosilicon alloy is added into the ladle, and the silicon content is 75%, namely the ferrosilicon alloy accounts for 1.13 wt% of the raw materials, and the granularity of the ferroalloy is 5mm, so that the white molten iron is obtained. And (3) carrying out element component analysis on the molten white iron obtained in the third step, wherein an instrument for carrying out element component analysis is a direct-reading spectrometer. The iron content was 93.14%, the carbon content was 2.93%, the silicon content was 2.08%, the manganese content was 0.354%, the sulphur content was 0.078% and the phosphorus content was 0.044%.

Step four: and (4) casting the white molten iron obtained in the third step in a three-way pipe sand mould with the pipe wall thickness of 8 mm at the casting temperature of 1380 ℃ to obtain the grey cast blank of the three-way pipe.

The preparation method of the cooked blank comprises the following steps:

step five: and annealing the grey blank obtained in the fourth step, wherein the annealing temperature is 960 ℃, keeping the temperature for 6 hours, cooling to 720 ℃, and keeping the temperature for 8 hours to obtain the black-core malleable cast iron for the three-way pipe. Wherein the element composition is 93.14% iron, 2.54% carbon, 2.06% silicon, 0.359% manganese, 0.076% sulphur and 0.045% phosphorus.

Comparative example 4

The same raw materials as used in the first step of example 2 were used, except that the molten white iron was prepared in the following steps:

the melting time of the first step was 70 minutes, and the melting temperature was 1300 ℃.

And in the second step, the temperature of the molten iron taken out is 1300 ℃, and in the second step, a small amount of molten iron is taken out to be subjected to a triangular test piece test, and the width of a test white notch is 3 mm.

And step four, the casting temperature is 1250 ℃, and then the white-mouth green body of the three-way pipe is obtained.

The obtained white compact was observed to have no embedded nuclei at a magnification of 200 times using an SEM microscope.

The preparation method of the cooked blank comprises the following steps:

step five: and fourthly, annealing the white blank obtained in the fourth step, wherein the annealing temperature is 970 ℃, preserving heat for 6 hours, cooling to 730 ℃, and preserving heat for 8 hours to obtain the black-core malleable cast iron of the three-way pipe. Wherein the element composition is 93.19% of iron, 2.78% of carbon, 1.33% of silicon, 0.38% of manganese, 0.085% of sulfur and 0.050% of phosphorus.

Comparative example 5

The same raw materials as used in the first step of example 8, except that 18Kg of ferrosilicon alloy was not added in the third step, and the white hot metal was obtained. And (3) carrying out element component analysis on the molten white iron obtained in the third step, wherein an instrument for carrying out element component analysis is a direct-reading spectrometer. The iron content was 93.12%, the carbon content was 2.79%, the silicon content was 1.18%, the manganese content was 0.362%, the sulphur content was 0.081% and the phosphorus content was 0.041%.

The preparation method of the white blank comprises the following steps:

step four: and casting the white molten iron obtained in the third step in a pipe hoop sand mold with the pipe wall thickness of 8 mm at the casting temperature of 1450 ℃, thus obtaining a white green compact of the four-way pipe.

The obtained white compact was observed to have no embedded nuclei at a magnification of 200 times using an SEM microscope.

The preparation method of the cooked blank comprises the following steps:

step five: and annealing the white blank obtained in the fourth step at 955 ℃, preserving the heat for 7 hours, cooling to 740 ℃, and preserving the heat for 10 hours to obtain the black-core malleable cast iron of the four-way pipe. Wherein the element composition is 93.11% iron, 2.79% carbon, 1.2% silicon, 0.364% manganese, 0.072% sulphur and 0.045% phosphorus.

Application example Performance detection

The different types of black heart malleable cast irons obtained in the examples and comparative examples were examined using a hydraulic testing machine, and the examination included appearance examination, tensile strength, elongation, and flattening examination. The results of the data are shown in Table 2 below.

TABLE 2 test results table

As seen from the above table, the different types of black heart malleable cast iron prepared in the examples were intact in appearance and had tensile strengths of 305-350kg/mm²The elongation is 6.6-10.2%, and the flattening rate is 10.3-20.3%. The toughness, strength and plasticity of the blank are improved, the tensile strength is increased, the elongation is increased and the flattening rate is improved.

The foregoing is considered as illustrative and not restrictive in character, and that various modifications, equivalents, and improvements made within the spirit and principles of the invention are intended to be included within the scope of the invention.