阅读说明：本技术 一种硅固溶强化铁素体球墨铸铁及其制备方法 (Silicon solid solution reinforced ferrite nodular cast iron and preparation method thereof ) 是由 王小磊 程淦昌 陈思 杨正银 贺献峰 于 2018-07-26 设计创作，主要内容包括：一种硅固溶强化铁素体球墨铸铁,其组成质量百分比为：C含量为3.3～3.7％,Si含量为3.5～4.2％,Mn含量≤0.25％,Mg含量为0.04～0.06％,P含量≤0.035％,S含量≤0.015％,Ce含量为0.042～0.058％,Sb含量为0.008～0.012％,Bi含量为0.012～0.016％,Ca含量≤0.05％,其余为铁。本发明通过Bi的添加,降低了石墨球的尺寸,通过Ce、Sb和Bi元素的加入及加入比例的控制,提高了石墨的球化率、减少碎块状石墨现象,并且通过高硅固溶强化铁素体球墨铸铁,实现大断面铸件的高强度、高延伸率和良好抗冲击性能；本发明的技术方案生产工艺简单、成本低、易于实现工业化生产。(The silicon solid solution reinforced ferrite nodular cast iron comprises the following components in percentage by mass: 3.3 to 3.7 percent of C, 3.5 to 4.2 percent of Si, less than or equal to 0.25 percent of Mn, 0.04 to 0.06 percent of Mg, less than or equal to 0.035 percent of P, less than or equal to 0.015 percent of S, 0.042 to 0.058 percent of Ce, 0.008 to 0.012 percent of Sb, 0.012 to 0.016 percent of Bi, less than or equal to 0.05 percent of Ca and the balance of Fe. According to the invention, the size of graphite nodules is reduced by adding Bi, the nodularity of graphite is improved and the phenomenon of broken graphite is reduced by adding Ce, Sb and Bi elements and controlling the adding proportion, and the high strength, high elongation and good impact resistance of a large-section casting are realized by high-silicon solid solution strengthening of ferrite nodular cast iron; the technical scheme of the invention has the advantages of simple production process, low cost and easy realization of industrial production.)

1. The silicon solid solution strengthened ferritic nodular cast iron is characterized in that the silicon solid solution strengthened ferritic nodular cast iron comprises the following element components in percentage by mass: 3.3 to 3.7 percent of C, 3.5 to 4.2 percent of Si, less than or equal to 0.25 percent of Mn, 0.04 to 0.06 percent of Mg, less than or equal to 0.035 percent of P, less than or equal to 0.015 percent of S, 0.042 to 0.058 percent of Ce, 0.008 to 0.012 percent of Sb, 0.012 to 0.016 percent of Bi, less than or equal to 0.05 percent of Ca and the balance of Fe.

2. A preparation method of silicon solid solution reinforced ferritic nodular cast iron is characterized by comprising the following steps:

(1) adding pig iron and scrap steel into a medium-frequency induction furnace, heating to 1420-1480 ℃ for melting, detecting the content of carbon in the molten iron after all the molten iron is melted, and adjusting the content of C to 3.3-3.7% to form original molten iron;

(2) spheroidizing the molten iron by using a flushing method, wherein the adding amount of a spheroidizing agent is 1.0-2.0% of the weight of the original molten iron, when the spheroidizing agent is tight during preparation of a spheroidizing bag, 75 ferrosilicon with the weight of 0.3-0.4% of the weight of the original molten iron and an inoculant a with the particle size of 3-8 mm are uniformly covered above the spheroidizing agent, and elements Ce and Sb are added during spheroidizing, so that the content of Ce after spheroidizing is 0.042-0.058%, the content of Sb is 0.008-0.012%, and the adding amount of the inoculant a is 0.5-0.8% of the weight of the original molten iron;

(3) stream inoculation is carried out during pouring, the adding amount of a stream inoculant b is 0.25-0.30 percent of the weight of the original molten iron, and the pouring temperature of the molten iron is 1360-1380 ℃;

(4) and cooling the molten iron to obtain the silicon solid solution strengthened ferrite nodular cast iron.

3. The method of claim 2, wherein the pig iron has a P content of 0.03% or less, an S content of 0.015% or less, a P content of scrap iron of 0.035% or less, an S content of 0.015% or less, and an Mn content of 0.25% or less.

4. The method of claim 2, wherein the ratio of pig iron to scrap added is (6-7) to (3-4).

5. The method for preparing the silicon solid solution reinforced ferritic nodular cast iron as claimed in claim 2, wherein the nodulizer comprises 0.3-0.5% of Ce, 2.5-4.0% of Mg, 40.0-45.0% of Si, 0.5-0.8% of Ca, and the balance of Fe.

6. The method for preparing the silicon solid solution reinforced ferritic spheroidal graphite cast iron according to claim 2, characterized in that the inoculant a contains 65.0-75.0% of Si, 0.3-0.5% of Bi, and the balance of Fe; the content of Si in the inoculant b is 65.0-75.0%, the content of Bi is 0.3-0.5%, the balance is iron, and the particle size of the inoculant b is 1-2 mm.

Technical Field

The invention relates to the field of preparation of ferritic nodular cast iron, in particular to silicon solid solution strengthened ferritic nodular cast iron and a preparation method thereof.

Background

Due to the development of wind power technology, wind power generation projects are supported greatly all over the world. With the development of wind turbine projects around the world, the geographical conditions selected as wind farms become increasingly severe. As a core component in wind power projects: the parts such as the hub, the base, the shaft and the like are made of ferrite nodular cast iron materials which are selected along with the severe geographical conditions, and the performance requirements are higher.

Many wind power ferrite nodular cast iron parts are large in section (the wall thickness is larger than 60mm), however, due to slow cooling speed and long eutectic solidification time, the large-section nodular cast iron is easy to generate broken block-shaped graphite in the cooling process, which is shown in the fact that macroscopic gray spot fractures appear at the center of a thick-wall nodular iron part, the microstructure of the large-section nodular cast iron is the broken block-shaped graphite and a ferrite matrix, and the microstructure can obviously reduce the performances of the nodular iron such as tensile strength, elongation and impact power.

The invention patent CN 103710612A discloses a production method of an as-cast ferrite-based nodular cast iron QT600-10, and the invention patent CN104120332A discloses a high-strength high-toughness nodular cast iron 600-10 and a production process thereof, the elongation of the nodular cast iron produced by the technical schemes of the two patents is low, and the technical scheme does not provide a solution aiming at the strength and the elongation of a large-section casting.

Disclosure of Invention

Aiming at the problems in the prior art, the invention aims to provide the silicon solid solution strengthened ferritic nodular cast iron and the preparation method thereof, so that the strength and the elongation of the prepared large-section ferritic nodular cast iron are improved, and the large-section ferritic nodular cast iron has good impact resistance.

In order to achieve the purpose, the invention is realized by the following technical scheme:

the silicon solid solution strengthening ferritic nodular cast iron comprises the following elements in percentage by mass: 3.3 to 3.7 percent of C, 3.5 to 4.2 percent of Si, less than or equal to 0.25 percent of Mn, 0.04 to 0.06 percent of Mg, less than or equal to 0.035 percent of P, less than or equal to 0.015 percent of S, 0.042 to 0.058 percent of Ce, 0.008 to 0.012 percent of Sb, 0.012 to 0.016 percent of Bi, less than or equal to 0.05 percent of Ca and the balance of Fe.

A preparation method of silicon solid solution reinforced ferritic nodular cast iron comprises the following steps:

(1) adding pig iron and scrap steel into a medium-frequency induction furnace, heating to 1420-1480 ℃ for melting, detecting the content of carbon in the molten iron after all the molten iron is melted, and adjusting the content of C to 3.3-3.7% to form original molten iron;

(2) spheroidizing the molten iron by using a flushing method, wherein the adding amount of a spheroidizing agent is 1.0-2.0% of the weight of the original molten iron, when the spheroidizing agent is tight during preparation of a spheroidizing bag, 75 ferrosilicon with the weight of 0.3-0.4% of the weight of the original molten iron and an inoculant a with the particle size of 3-8 mm are uniformly covered above the spheroidizing agent, and elements Ce and Sb are added during spheroidizing, so that the content of Ce after spheroidizing is 0.042-0.058%, the content of Sb is 0.008-0.012%, and the adding amount of the inoculant a is 0.5-0.8% of the weight of the original molten iron;

(3) stream inoculation is carried out during pouring, the adding amount of a stream inoculant b is 0.25-0.30 percent of the weight of the original molten iron, and the pouring temperature of the molten iron is 1360-1380 ℃;

(4) and cooling the molten iron to obtain the silicon solid solution strengthened ferrite nodular cast iron.

Furthermore, the P content of the pig iron is less than or equal to 0.03%, the S content is less than or equal to 0.015%, the P content of the waste iron is less than or equal to 0.035%, the S content is less than or equal to 0.015%, and the Mn content is less than or equal to 0.25%.

Further, the adding ratio of the pig iron to the scrap steel is (6-7) to (3-4).

Further, the nodulizer comprises 0.3-0.5% of Ce, 2.5-4.0% of Mg, 40.0-45.0% of Si, 0.5-0.8% of Ca and the balance of Fe.

Further, the inoculant a contains 65.0-75.0% of Si, 0.3-0.5% of Bi and the balance of iron; the content of Si in the inoculant b is 65.0-75.0%, the content of Bi is 0.3-0.5%, the balance is iron, and the particle size of the inoculant b is 1-2 mm.

Si is an element promoting graphite spheroidization, the content of silicon is increased in a proper range, and the silicon is dissolved in ferrite lattices in a solid mode, so that the tensile strength and the hardness of the nodular cast iron are effectively improved, and the toughness of the nodular cast iron is reduced, the content of Si is controlled to be 3.5-4.2% in the technical scheme, and the elongation, the strength and the impact resistance are favorably improved; the use of trace elements such as Cu, Ni, Sn, Mo, Cr and the like is reduced by high-silicon solid solution strengthening.

In order to inhibit the formation of the blocky graphite, Ce and Sb elements are added during spheroidization in the technical scheme, Sb is rare earth which interferes with the spheroidization of the graphite, and when magnesium alloy is selected as a spheroidizing agent, the content of Sb is 0.008-0.012%, the spheroidization effect is realized on a large-section casting instead, so that the number of graphite balls is increased. In addition, Sb and added Ce are easy to form a high-melting-point stable compound and further serve as a heterogeneous core of the nodular graphite, the number of graphite spheres is increased, and when the Sb content is higher than 0.012%, the phenomenon of broken graphite is increased and is increased along with the increase of the Sb content.

Magnesium is a nodulizer with good nodulizing effect, but the magnesium explosion phenomenon is easy to occur when a single magnesium nodulizer is used for nodulizing, particularly when a large-section casting is prepared. In order to protect the lasting spheroidization effect of the magnesium element in the spheroidization process, the Ce element is added when the spheroidizing agent is added, but the content of the Ce is not easy to be too high. In order to reduce the magnesium explosion phenomenon, an inoculant containing Bi is adopted to reduce the magnesium explosion problem by reducing the size of graphite nodules and promoting the formation of ferrite.

The beneficial effects of the invention include:

according to the invention, the size of graphite nodules is reduced by adding Bi, the nodularity of graphite is improved and the phenomenon of broken graphite is reduced by adding Ce, Sb and Bi elements and controlling the adding proportion, and the high strength, high elongation and good impact resistance of a large-section casting are realized by high-silicon solid solution strengthening ferrite nodular cast iron; the technical scheme of the invention has the advantages of simple production process, low cost and easy realization of industrial production.

Detailed Description

The present invention will be further described with reference to examples, but the present invention is not limited to these examples.