CN112210709B

CN112210709B - Light-weight product nodular cast iron and preparation method thereof

Info

Publication number: CN112210709B
Application number: CN202011020260.7A
Authority: CN
Inventors: 罗铖; 冀元贵; 何家元; 刘仁峰
Original assignee: Hubei Xingyuan Science And Technology Co ltd
Current assignee: Hubei Xingyuan Science And Technology Co ltd
Priority date: 2020-09-24
Filing date: 2020-09-24
Publication date: 2022-09-27
Anticipated expiration: 2040-09-24
Also published as: CN112210709A

Abstract

The invention relates to nodular cast iron and a preparation method thereof, wherein the nodular cast iron comprises the following elements C in percentage by mass: 3.7% -3.85%, Si: 2.7% -2.9%, Mn: 0.2-0.35%, P is less than or equal to 0.05%, S: less than or equal to 0.03 percent, Mg: 0.035-0.055%, Cu: 0.5-0.65%, Sn: 0.005% -0.020%, RE: 0.01-0.015%, Al: less than or equal to 0.001%, Ca: less than or equal to 0.0025%, Ba: less than or equal to 0.005 percent and Cr: the ductile iron comprises, by mass, not more than 0.03%, and the balance of Fe and unavoidable impurities, the total being 100%, a matrix structure of the ductile iron comprises pearlite and ferrite, the pearlite accounts for 55% -75% of the matrix structure, and the balance of the ferrite, the total being 100%. Compared with the prior art, the invention has the beneficial effects that: the nodular cast iron provided by the invention meets the requirements of light weight at the same time on the basis of meeting the requirements of high strength and high toughness.

Description

Light-weight product nodular cast iron and preparation method thereof

Technical Field

The invention belongs to the field of cast iron smelting, and particularly relates to a light-weight product nodular cast iron and a preparation method thereof.

Background

The ductile iron is a high-strength cast iron material developed in the 20 th century and the fifties, the comprehensive performance of the ductile iron is close to that of steel, and the ductile iron is successfully used for casting parts which are complex in stress and high in requirements on strength, toughness and wear resistance based on the excellent performance of the ductile iron. Nodular cast iron has rapidly evolved to a very widely used cast iron material second only to gray cast iron. The term "steel is replaced by iron" is mainly used for nodular cast iron.

The nodular cast iron is spheroidized and inoculated to obtain spheroidal graphite, so that the mechanical properties of the cast iron are effectively improved, and particularly, the plasticity and toughness are improved, so that the strength of the cast iron is higher than that of carbon steel.

With the development of lightweight products, the demand of spheroidal graphite cast iron for high strength and high toughness from the traditional demand of spheroidal graphite cast iron for lightweight is a trend of current research in many fields, so that the development of spheroidal graphite cast iron which has high strength and high toughness and meets the requirement of current lightweight is very important.

Disclosure of Invention

In order to solve the technical problems, the invention provides a light-weight product nodular cast iron and a preparation method thereof.

The specific technical scheme is as follows:

nodular cast iron is characterized in that the nodular cast iron comprises the following elements in percentage by mass:

c: 3.7% -3.85%, Si: 2.7% -2.9%, Mn: 0.2-0.35%, P is less than or equal to 0.05%, S: less than or equal to 0.03 percent, Mg: 0.035-0.055%, Cu: 0.5-0.65%, Sn: 0.005% -0.020%, RE: 0.01-0.015%, Al: less than or equal to 0.001%, Ca: less than or equal to 0.0025 percent, Ba: less than or equal to 0.005 percent and Cr: less than or equal to 0.03 percent, and the balance of Fe and inevitable impurities, accounting for 100 percent;

the matrix structure of the nodular cast iron comprises pearlite and ferrite, wherein the pearlite accounts for 55-75% of the matrix structure by mass, and the balance is the ferrite, and the total amount is 100%.

Further, the nodular cast iron comprises the following elements in percentage by mass:

further, the spheroidization rate of the matrix structure of the nodular cast iron is over 80 percent, the graphite grade reaches 6-7 grades, and the spheroidization grade is 2-3 grades.

Furthermore, the pearlite accounts for 60-75% of the matrix structure by mass, the balance is ferrite, the total is 100%, and the spheroidization rate of the matrix structure of the nodular cast iron is more than 86%.

Compared with the prior art, the invention has the beneficial effects that: the ductile iron is suitable in proportion, and is matched with a reasonable process to form an excellent metallographic structure and a spheroidized structure, so that the requirements of light weight at present are met on the basis of meeting high strength and high toughness.

c: 3.78%, Si: 2.78%, Mn: 0.258%, P is less than or equal to 0.025%, S is less than or equal to 0.0096%, Mg: 0.037%, Cu: 0.520%, Sn: 0.008%, RE: 0.013%, Al: <0.001%, Ca: 0.0022%, Ba is less than or equal to 0.005%, and Cr: 0.023 percent, and the balance of Fe and inevitable impurities, accounting for 100 percent.

The preparation method of the nodular cast iron is characterized by comprising the following steps:

step S1: smelting raw materials, namely selecting pig iron and scrap steel, adding a carburant, a pretreating agent, ferrosilicon and ferromanganese to melt into first molten iron;

step S2, spheroidizing and primary inoculation, namely, preparing alloy cored wires from silicon-containing rare earth magnesium alloy by adopting wire feeding spheroidization, and adding the alloy cored wires into the molten iron prepared in the step S1 to obtain second molten iron;

step S3: performing second inoculation, namely inoculating a second inoculant into the second molten iron to obtain third molten iron;

step S4: pouring and inoculating for the third time, pouring the third molten iron into a mold, and simultaneously adding a following agent, wherein the proportion of all elements is adjusted to obtain fourth molten iron;

step S5: and cooling after pouring, and taking out the die.

Compared with the prior art, the nodular cast iron prepared by the preparation method through a three-time inoculation process and a proportioning process can improve the spheroidization effect, and specifically, the spheroidization rate is improved, the number of graphite, the spheroidization grade and the graphite grade are increased, and the metallographic structure of ferrite and pearlite is prepared.

Further, the first molten iron comprises the following elements in percentage by mass: c: 3.6% -3.9%, Si: 1.3% -1.6%, Mn: 0.2-0.35%, P is less than or equal to 0.05%, and S: less than or equal to 0.03 percent.

Further, in the step S2, the temperature of the molten iron during the spheroidization and the first inoculation is 1470 ℃ to 1500 ℃ and the processing time is 45S.

Further, in the step S2, a single wire is adopted for wire feeding and spheroidizing, the weight of the alloy core-spun yarn powder core is 230-250 g/m, and after the alloy core-spun yarn is added, the content of silicon is increased by 0.5-1%;

further, in the step S2, the alloy cored wire includes the following elements RE by mass ratio: 2.85 percent; si: 45.93 percent; mg: 29.32 percent.

The further technical scheme has the advantages that the single-wire feeding spheroidizing core-spun wire is inserted at a certain speed, so that the whole process can be automated, the feeding speed and the adding amount can be controlled, and the proportioning operation is convenient.

Further, in the step S3, in the third molten iron, the addition amount of the second inoculant is 1.5% -2.0% of that of the third molten iron, copper is added and the content of copper is adjusted, and the addition amount of copper is 0.5% -0.8% of that of the third molten iron.

The beneficial effects of adopting the further technical scheme are that: copper adds an expandable pearlite formation zone at this step, promotes pearlite formation and refinement of the structure, and reinforces ferrite.

Further, in the step S3, silicon carbide is added for grain adjustment, and the addition amount of the silicon carbide is 0.2% to 0.4% of the third molten iron by mass.

Further, in the step S4, the addition amount of the flow-accompanying agent is 0.1% to 0.2% of the mass of the fourth molten iron.

Furthermore, the particle size of the flow-following inoculant is 0.3-1 mm, and the adding flow of the flow-following inoculant is about 8-11 g/s.

Further, in the step S4, the casting temperature is 1400 ℃ to 1450 ℃, and the casting time is 8 minutes to 10 minutes.

Drawings

FIG. 1 is a test picture of graphite for nodular cast iron prepared in example 1;

FIG. 2 is a photograph of the metallographic structure of spheroidal graphite cast iron prepared in example 1;

FIG. 3 is a test picture of graphite for nodular cast iron prepared in example 2;

FIG. 4 is a metallographic structure photograph of spheroidal graphite cast iron prepared in example 2;

FIG. 5 is a test picture of graphite for nodular cast iron prepared in example 3;

FIG. 6 is a metallographic structure photograph of spheroidal graphite cast iron prepared in example 3;

fig. 7 is a picture of a graphite test of spheroidal graphite cast iron of comparative example 2;

FIG. 8 is a photograph of the metallographic structure of spheroidal graphite cast iron of comparative example 2;

FIG. 9 is a schematic view of a counterbalancing suspension mount.

Detailed Description

The principles and features of this invention are described below in conjunction with the following drawings, which are set forth by way of illustration only and are not intended to limit the scope of the invention.

In the examples and comparative examples of the present invention, the raw materials involved are as follows:

scrap steel: low carbon low alloy (carbon 0.03-0.06 wt%, silicon 0.16 wt%, manganese 0.38 wt%, S not more than 0.02 wt%, P not more than 0.03 wt%);

the pig iron is high-quality casting pig iron of Longfengshan or adopts low-phosphorus (P is less than or equal to 0.03), low-sulfur (S is less than or equal to 0.02) and rust-free pig iron;

carburant: (carbon ≧ 98.5%, sulfur ≦ 0.1%, nitrogen ≦ 300ppm, water ≦ 0.5%, volatile ≦ 0.5%, ash ≦ 0.5%, particle size 0-5mm)

A pretreating agent: (SiC ≧ 98%; F.C ≦ 0.5%; Fe ₂ O ₃ 0.5% or less; the water content is less than or equal to 0.5%; granularity is 1 mm-5 mm)

Molten iron purifying agent: (active content)>97％；CaO：45％～75％；Al ₂ O ₃ 10 to 30 percent; water content less than or equal to 0.25%)

Silicon iron: 75 silicon iron

Ferromanganese: 65 ferromanganese

Copper electrolysis: the copper content is more than or equal to 99.9 percent

A second inoculant: silicon: 65 to 70 percent; aluminum is less than or equal to 1.5%; barium: 3% -6%; calcium: 1% -3%; granularity: 3 mm-8 mm.

Silicon carbide: grade a silicon carbide.

The used mold: preparing a sand box with an adjustable temperature control film coating as a mold;

returning materials: refers to a raw material that is reused as a residue produced by the present invention.

A culture medium following the culture: (68% -75% of silicon, 4% -6% of barium, 1% -3% of calcium and 0.2-0.8 mm of granularity)

Example 1

The following method is adopted to manufacture the nodular cast iron

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

step S1, smelting raw materials: the method comprises the steps of selecting pig iron, waste steel and foundry returns, adding a carburant, a pretreating agent, ferrosilicon and ferromanganese to melt into first molten iron, wherein the adding sequence is carburant → waste steel, ferromanganese → foundry returns → pig iron, the pretreating agent is added when materials are melted to 2/3, and the ferrosilicon is added after the other materials are completely dissolved, in the step, an OBLF photoelectric direct-reading spectrometer is used for measuring chemical components of the materials, and the batching is controlled, wherein the results are shown in Table 1.

Step S2, spheroidizing and first inoculating: according to the test result of S1, the single-wire feeding spheroidizing is adopted to make the silicon-containing rare earth magnesium alloy into the alloy core-spun wire, the alloy core-spun wire is added into the molten iron prepared in the step S1, and the diameter of the alloy core-spun wire

The weight of the powder core is 235g/m, and the alloy cored wire comprises RE: 2.85 percent; si: 45.93 percent; mg: 29.32 percent of element, the content of the added silicon is increased by 0.71 percent to obtain second molten iron, the temperature of the molten iron at the stage is 1470-1500 ℃, and the processing time is 45 s.

Step S3, second inoculation: according to the test result of the step S2, adding the second inoculant, copper and silicon carbide, wherein the adding amount of the second inoculant is 1.65% of the mass of the third molten iron, the adding amount of the copper is 0.62% of the mass of the third molten iron, and the adding amount of the silicon carbide is 0.3% of the mass of the third molten iron; the chemical components of the materials were measured by an OBLF photoelectric direct-reading spectrometer, and the ingredients were controlled, with the results shown in Table 1.

Step S4, pouring and third inoculation: pouring the third molten iron into a model, and simultaneously adding a flow-following agent, wherein the flow-following agent with the granularity of 0.3-1 mm is added on the surface of the molten iron during pouring, the pouring temperature is 1421 ℃, the pouring temperature is 1357 ℃ after pouring, and the pouring time is 8-10 minutes; the flow rate of the stream inoculant is about 9g/s, the fourth molten iron is obtained after the adjustment of the proportion of all elements is finished, and the stream inoculant accounts for 0.15 percent of the mass of the fourth molten iron;

and step S5, cooling after pouring, taking out of the mold after 35min, and measuring the chemical components of the material by using an OBLF photoelectric direct-reading spectrometer, wherein the results are shown in Table 1.

Table 1 example 1 preparation procedure element mass percent test results

	Step S1	Step S3	Step S5
				C(％)	3.9	3.80	3.78
Si(％)	1.3	2.01	2.78
				Mn(％)	0.248	0.257	0.258
P(％)	0.023	0.024	0.025
				S(％)	0.0131	0.0096	0.0096
Mg(％)	<0.001	0.045	0.037
				Cu(％)	0.072	0.518	0.520
Sn(％)	0.008	0.008	0.008
				Cr(％)	0.017	0.023	0.023
RE(％)	Is free of	0.015	0.013
				Ba(％)	<0.001	0.0043	0.0042
Ca(％)	<0.0001	0.0027	0.0020
				Al(％)	<0.001	<0.001	<0.001

In table 1, Fe and inevitable impurities are included in addition to the above elements, and the total amount is 100%.

Example 2

Nodular cast iron was prepared by the method of example 1, but the steps involved in the preparation process were completed with the material parameters adjusted and controlled according to the element mass ratios shown in table 2.

Table 2 example 2 preparation procedure element mass percent test results

	Step S1	Step S3	Step S5
				C(％)	3.9	3.77	3.72
Si(％)	1.3	1.99	2.72
				Mn(％)	0.246	0.242	0.242
P(％)	0.022	0.025	0.025
				S(％)	0.0141	0.0099	0.0093
Mg(％)	<0.001	0.048	0.038
				Cu(％)	0.054	0.632	0.630
Sn(％)	0.007	0.01	0.011
				Cr(％)	0.017	0.024	0.023
RE(％)	Is free of	0.014	0.012
				Ba(％)	<0.001	0.0041	0.0040
Ca(％)	<0.0001	0.0022	0.002
				Al(％)	<0.001	<0.001	<0.001

In table 2, Fe and inevitable impurities are included in addition to the above elements, and the total amount is 100%.

Example 3

Nodular cast iron was prepared by the method of example 1, but the steps involved in the preparation were completed with the material parameters adjusted and controlled according to the element mass ratios shown in table 3.

Table 3 example 3 element mass percent test results of preparation procedure

	Step S1	Step S3	Step S5
				C(％)	3.85	3.83	3.84
Si(％)	1.31	2.29	2.87
				Mn(％)	0.235	0.247	0.244
P(％)	0.021	0.023	0.022
				S(％)	0.012	0.0102	0.01
Mg(％)	<0.001	0.044	0.035
				Cu(％)	0.112	0.577	0.578
Sn(％)	0.004	0.014	0.009
				Cr(％)	0.021	0.017	0.015
RE(％)	Is free of	0.014	0.012
				Ba(％)	<0.001	0.0041	0.0040
Ca(％)	<0.0001	0.0021	0.0021
				Al(％)	<0.001	<0.001	<0.001

In table 3, Fe and inevitable impurities are included in addition to the above elements, and the total amount is 100%.

Example 4

The method of example 1 was used to prepare spheroidal graphite cast iron, but in the preparation method, in step S2, the proportioning of copper was completed; that is, in step S3, no copper was added, and the remaining steps involved material parameter adjustment and control were completed according to the element mass ratios shown in Table 4.

Table 4 example 4 element mass percent test results of preparation procedure

	Step S1	Step S3	Step S5
				C(％)	3.85	3.78	3.75
Si(％)	1.31	2.05	2.77
				Mn(％)	0.235	0.245	0.245
P(％)	0.021	0.02	0.019
				S(％)	0.012	0.011	0.012
Mg(％)	<0.001	0.045	0.037
				Cu(％)	0.047	0.572	0.570
Sn(％)	0.003	0.012	0.011
				Cr(％)	0.02	0.019	0.02
RE(％)	Is composed of	0.014	0.012
				Ba(％)	<0.001	0.0041	0.0040
Ca(％)	<0.0001	0.0019	0.0017
				Al(％)	<0.001	<0.001	<0.001

In table 4, Fe and inevitable impurities are included in addition to the above elements, and the total is 100%.

Example 5

Nodular cast iron was prepared by the method of example 1, except that in the preparation method, the material parameter adjustment and control were performed in accordance with the element mass ratio shown in table 3 and in step S3, silicon carbide was not added.

Table 5 example 5 element mass percent test results of preparation procedure

In table 5, Fe and inevitable impurities are included in addition to the above elements, and the total amount is 100%.

The proportions of the spheroidal graphite cast irons prepared in the respective examples are summarized in Table 6:

TABLE 6 composition of nodular cast iron of each example in terms of percentage by mass of elements

	Example 1	Example 2	Example 3	Example 4	Example 5
						C(％)	3.78	3.72	3.84	3.75	3.76
Si(％)	2.78	2.72	2.87	2.77	2.74
						Mn(％)	0.258	0.242	0.244	0.245	0.248
P(％)	0.025	0.025	0.022	0.019	0.019
						S(％)	0.0096	0.0093	0.01	0.012	0.012
Mg(％)	0.037	0.038	0.035	0.037	0.038
						Cu(％)	0.520	0.630	0.578	0.570	0.572
Sn(％)	0.008	0.011	0.009	0.011	0.011
						Cr(％)	0.023	0.023	0.015	0.02	0.020
RE(％)	0.013	0.012	0.012	0.012	0.013
						Ba(％)	0.0042	0.0040	0.0040	0.0040	0.0041
Ca(％)	0.0020	0.002	0.0021	0.0017	0.0025
						Al(％)	<0.001	<0.001	<0.001	<0.001	<0.001

In table 6, Fe and inevitable impurities are included in addition to the above elements, and the total is 100%.

Comparative example 1

The method of example 1 was used to prepare spheroidal graphite cast iron, the proportions of the respective contents of which are shown in table 7.

TABLE 7 composition of nodular cast iron of comparative example 1 in terms of percentage by mass of elements

In table 7, Fe and inevitable impurities are included in addition to the above elements, and the total is 100%.

Comparative example 2

The following method is adopted to manufacture the nodular cast iron

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

step S1, smelting raw materials: the method comprises the steps of selecting pig iron, waste steel and foundry returns, adding a carburant, a pretreating agent, ferrosilicon and ferromanganese to melt into first molten iron, wherein the adding sequence is carburant → waste steel, ferromanganese → foundry returns → pig iron, the pretreating agent is added when materials are molten to 2/3, and the ferrosilicon is added after other materials are completely dissolved.

Step S3, second inoculation: adding the second inoculant, copper and silicon carbide according to the test result of the step S2, and adjusting all elements;

and step S4, cooling after pouring, wherein the pouring temperature is 1421 ℃, the pouring temperature is 1357 ℃, the die is taken out after 35min, and the chemical components of the material are measured by using an OBLF photoelectric direct-reading spectrometer, and the results are shown in Table 1.

The final composition of each content in the spheroidal graphite cast iron is shown in table 8.

Table 8 composition of nodular cast iron of comparative example 2 in terms of percentage by mass of elements

	Comparative example 2
		C(％)	3.78
Si(％)	2.81
		Mn(％)	0.260
P(％)	0.0263
		S(％)	0.0096
Mg(％)	0.038
		Cu(％)	0.518
Sn(％)	0.008
		Cr(％)	0.024
RE(％)	0.013
		Ba(％)	0.004
Ca(％)	0.002
		Al(％)	<0.01

Example 6

The examples, comparative examples and commercial QT550-7 products were tested.

6.1

And (3) carrying out detection on the metallographic phase, the nodularity grade and the graphite grade according to GB/T1348-2019, wherein the detection results are shown in a table 9.

TABLE 96.1 test results

	The spheroidization rate%	Number of graphite	Grade of spheroidisation	Graphite grade	Pearlite%	Ferrite%
							Example 1	94.7	287	2	7	68.9	31.1
Example 2	89.3	267	3	7	71.1	28.9
							Example 3	92.1	400	2	6	73	27
Example 4	88.1	224	3	6	68	32
							Example 5	88.6	245	3	6	62	38
Comparative example 1	86.4	192	3	5	52	48
							Comparative example 2	87	185	3	7	35	65

6.2

And (3) carrying out mechanical property detection according to GB/T1348-2019, wherein the detection results are shown in Table 10.

TABLE 106.2 test results

6.3A balance bracket (for automobile) made of the nodular cast iron prepared in example 1 and QT550-7 is used, as shown in FIG. 9.

The two were identically dimensioned, but the gimbal fabricated using the ductile iron of example 1 weighed 50.5kg, and the gimbal fabricated using QT550-7 weighed 63.57 kg.

As can be seen from the test results of the embodiment and the comparative example 1, the nodular cast iron prepared by adopting the element proportion range of the invention has more excellent performance;

from the test results of the example and the comparative example 2, the nodular cast iron prepared by the method of the invention can prepare a pearlite and ferrite composite metallographic structure with excellent proportion;

as can be seen from the examples and the test results of a commercial product QT550-7, the mechanical properties of the nodular cast iron prepared by the invention are superior to those of the commercial product, and the lightweight can be realized.

Moreover, the inventor research team also finds that whether Cu is added or not in the second inoculation stage has an influence on the metallographic structure of the nodular cast iron, for example, after Cu is added in the second inoculation stage, the metallographic structure of the nodular cast iron is higher in pearlite content and finer in structure.

Secondly, in the second inoculation stage, silicon carbide is added, so that the grain structure can be further refined.

It should be noted that, in the present invention, the proportion adjustment is adjusted according to theory and test, but in the casting stage, element floating occurs, the element proportion of the finally prepared product is accurate to the element test proportion after the preparation, and the test data adopts an OBLF photoelectric direct-reading spectrometer.

The above description is only for the purpose of illustrating the preferred embodiments of the present invention and should not be taken as limiting the scope of the present invention, which is intended to cover any modifications, equivalents, improvements, etc. within the spirit and scope of the present invention.

Claims

1. Nodular cast iron, characterized in that it comprises the following elements in mass percent:

c: 3.7% -3.85%, Si: 2.7% -2.9%, Mn: 0.2-0.35%, P is less than or equal to 0.05%, S: less than or equal to 0.03 percent, Mg: 0.035% -0.055%, Cu: 0.5% -0.65%, Sn: 0.005% -0.020%, RE: 0.01% -0.015%, Al: less than or equal to 0.001%, Ca: less than or equal to 0.0025 percent, Ba: less than or equal to 0.005 percent and Cr: less than or equal to 0.03 percent, and the balance of Fe and inevitable impurities, accounting for 100 percent;

the matrix structure of the nodular cast iron comprises pearlite and ferrite;

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

step S2, spheroidizing and primary inoculation, namely, preparing alloy cored wires from silicon-containing rare earth magnesium alloy by adopting wire feeding and spheroidizing, and adding the alloy cored wires into the molten iron prepared in the step S1 to obtain second molten iron;

step S3: second inoculation, namely adding a second inoculant into the second molten iron for inoculation to obtain third molten iron;

step S4: pouring and third inoculation, namely pouring the third molten iron into a mold, and simultaneously adding a stream inoculant to obtain fourth molten iron after the proportion of all elements is adjusted;

step S5: cooling after pouring, and taking out the die;

in the step S3, the second inoculant and copper are added, wherein the adding amount of the second inoculant in the third molten iron is 1.5-2.0% of the mass of the third molten iron, and the adding amount of the copper is 0.5-0.8% of the mass of the third molten iron; in step S3, adding silicon carbide for grain adjustment, wherein the adding amount of the silicon carbide is 0.2-0.4% of the mass of the third molten iron.

2. The nodular cast iron of claim 1, wherein the nodular cast iron comprises the following elements in mass percent:

3. The nodular cast iron according to claim 1 or 2, wherein the spheroidization rate of the matrix structure of the nodular cast iron is 80% or more, the graphite grade is 6-7 grade, and the spheroidization grade is 2-3 grade.

4. The ductile iron of claim 1, wherein the first molten iron comprises the following elements in mass percent: c: 3.6% -3.9%, Si: 1.3% -1.6%, Mn: 0.2-0.35%, P is less than or equal to 0.05%, and S: less than or equal to 0.03 percent.

5. The nodular cast iron according to claim 1, wherein in the step S2, the nodular cast iron is fed by single wire, the weight of the powder core of the alloy cored wire is 230g/m to 250g/m, and the mass of silicon in the molten iron is increased by 0.5% to 1% after the alloy cored wire is added.

6. The nodular cast iron according to claim 1, wherein the particle size of the stream inoculant is 0.3-1 mm, and the addition flow rate of the stream inoculant is 8-11 g/s.

7. The nodular cast iron according to claim 1, wherein in the step S4, the pouring temperature is 1400 ℃ to 1450 ℃, and the pouring time is 8 minutes to 10 minutes.