阅读说明：本技术 一种改善高硅固溶厚大断面风电球墨铸铁件金相组织的工艺 (Process for improving metallographic structure of high-silicon solid solution thick large-section wind power nodular iron casting ) 是由 王美喜 占进 余帆 史学涌 季虎 邵悦翔 于 2021-07-13 设计创作，主要内容包括：本发明公开了一种改善高硅固溶厚大断面风电球墨铸铁件金相组织的工艺,具体涉及铸铁材料技术领域。本发明选用微量元素低,尤其是Ti含量低的高纯生铁、优质废钢片和不使用回炉,以及使用稀土元素RE低的球化剂和Al、Ba和Ca低的孕育剂以及硫氧含Zr的随流孕育剂这种熔炼工艺,第一可以保证铁水足够纯净,尽可能的控制有害元素如：Ti、V、W等微量元素；第二可以获得足够多的石墨核心；本发明的效果和优点：完全消除高硅球墨铸铁附铸试块和本体套样金相组织中的钉状石墨缺陷,而且,该生产工艺不需进行任何热处理,也不进行合金化,工艺简单,生产成本低,产品完全符合客户的要求。(The invention discloses a process for improving the metallographic structure of a high-silicon solid solution thick large-section wind power nodular iron casting, and particularly relates to the technical field of cast iron materials. The invention selects the smelting process of high-purity pig iron with low trace elements, particularly low Ti content, high-quality waste steel sheets, no need of furnace return, nodulizer with low rare earth element RE, inoculant with low Al, Ba and Ca and stream-following inoculant with sulfur and oxygen containing Zr, and the invention can ensure that the molten iron is pure enough, and control harmful elements as far as possible as: trace elements such as Ti, V, W, etc.; secondly, enough graphite cores can be obtained; the invention has the advantages that: the nail-shaped graphite defects in the metallographic structure of the high-silicon nodular cast iron casting block and the body sleeve sample are completely eliminated, the production process does not need any heat treatment and alloying, the process is simple, the production cost is low, and the product completely meets the requirements of customers.)

1. A process for improving the metallographic structure of a high-silicon solid solution thick large-section wind power nodular iron casting is characterized by comprising the following steps of: the preparation method comprises the following specific steps:

the method comprises the following steps: material preparation and molten iron smelting: the proportion of ingredients is as follows: 40-60% of pig iron and 40-60% of scrap steel;

wherein the content of the trace element components in the pig iron is as follows: 4.0 to 4.5 weight percent of C, 0.40 to 0.60 weight percent of Si, less than or equal to 0.10 weight percent of Mn, less than or equal to 0.03 weight percent of P, less than or equal to 0.01 weight percent of S, less than 0.010 weight percent of Ti, and the content of trace element components in the scrap steel is as follows: less than or equal to 0.15 wt% of C, less than or equal to 0.40 wt% of Si, less than or equal to 0.30 wt% of Mn, less than or equal to 0.02 wt% of P, less than or equal to 0.03 wt% of S, less than or equal to 0.06 wt% of Cr, and less than 0.001 wt% of Ti;

step two: molten iron and component adjustment: adding pig iron and scrap steel into a medium-frequency induction furnace for melting, sampling after molten iron is melted, carrying out spectral analysis and thermal analysis, and then carrying out molten iron component adjustment, including desulfurization and adjustment of C amount and Si amount of the molten iron; after the components are adjusted, the contents of the trace element components in the molten iron are as follows: c: 3.40-3.50 wt%; si: 2.60-2.80 wt%; mn is less than or equal to 0.15 wt%; p is less than or equal to 0.035 wt%; s is less than or equal to 0.012 wt%;

step three: spheroidizing inoculation: placing a nodulizer, a covering agent and alloy Sb at the bottom of a casting ladle in advance, then pouring molten iron in an electric furnace into the casting ladle, and simultaneously adding a primary inoculant when the molten iron is discharged from 2/3 to perform nodulizing and primary inoculation reaction on the molten iron;

step four: pouring treatment: after molten iron is spheroidized, scattering a molten iron deslagging agent on the surface of the molten iron for slagging-off treatment, then pouring the molten iron in a casting ladle into a casting mold, and adding a stream-following inoculant during pouring, wherein the pouring temperature is 1340-1360 ℃;

step five: cleaning the casting: after the pouring is finished, the casting is slowly cooled to below 400 ℃ in a sand mold, and the casting is cleaned from the casting mold.

2. The process for improving the metallographic structure of the high-silicon solid solution thick large-section wind power nodular iron casting according to claim 1, wherein the metallographic structure of the high-silicon solid solution thick large-section wind power nodular iron casting is as follows: in the second step, the components of the desulfurizer adopted for desulfurization are CaO and CaC₂The granularity is less than 10 mm; adjusting the C amount by adopting a carburant, wherein the fixed carbon is more than or equal to 99 percent, and the particle size is 0.5-5 mm; the Si content is adjusted by using 75-ferrosilicon, the silicon content in the 75-ferrosilicon is 72-80%, the balance is Mn, Cr, P, S, Al and Ca, and the granularity is 5-100 mm.

3. The process for improving the metallographic structure of the high-silicon solid solution thick large-section wind power nodular iron casting according to claim 1, wherein the metallographic structure of the high-silicon solid solution thick large-section wind power nodular iron casting is as follows: in step three, the nodularizer: selecting a rare earth silicon magnesium nodulizer, wherein the components comprise 5.5-6.0 wt% of Mg, 0.15-0.30 wt% of Ce, 40-50 wt% of Si and the balance of iron; the nodulizer is 1.0-1.2 wt% and has a particle size of 4-32 mm.

4. The process for improving the metallographic structure of the high-silicon solid solution thick large-section wind power nodular iron casting according to claim 3, wherein the metallographic structure of the high-silicon solid solution thick large-section wind power nodular iron casting is as follows: in the third step, both the covering agent and the primary inoculant are low-silicon inoculants, the components comprise 40-50 wt% of Si, 1.8-2.2 wt% of Ba, 0.4-0.6 wt% of Ca, 0.4-1.0 wt% of Al, 0.05-0.15 wt% of Gd and the balance of iron, and the particle size is 0.5-6 mm; according to the weight percentage of the poured molten iron, the dosage of the covering agent is 0.4-0.6 wt%, and the dosage of the primary inoculant is 0.4-0.8 wt%.

5. The process for improving the metallographic structure of the high-silicon solid solution thick large-section wind power nodular iron casting according to claim 1, wherein the metallographic structure of the high-silicon solid solution thick large-section wind power nodular iron casting is as follows: in step three, the alloy Sb: the use amount of the alloy Sb is 0.003-0.005 wt% in terms of the weight percentage of the cast molten iron.

6. The process for improving the metallographic structure of the high-silicon solid solution thick large-section wind power nodular iron casting according to claim 4, wherein the metallographic structure of the high-silicon solid solution thick large-section wind power nodular iron casting is as follows: in the fourth step, the stream-following inoculant is a sulfur-oxygen-containing Zr inoculant which comprises 73-76 wt% of Si, 2.0-2.5 wt% of Ca, 1.3-1.8 wt% of Zr, 0.05-0.15 wt% of Mo, 0.32-0.36 wt% of S, 0.32-0.36 wt% of O and the balance of iron, and the particle size is 0.2-0.7 mm; the amount of the stream-following inoculant is 0.10-0.30 wt% in percentage by weight of the poured molten iron.

7. The process for improving the metallographic structure of the high-silicon solid solution thick large-section wind power nodular iron casting according to claim 1, wherein the metallographic structure of the high-silicon solid solution thick large-section wind power nodular iron casting is as follows: in the fourth step, the slag removing agent is perlite and SiO in the perlite₂Not less than 72 percent and the granularity is 1-3 mm.

8. The process for improving the metallographic structure of the high-silicon solid solution thick large-section wind power nodular iron casting according to claim 6, wherein the metallographic structure of the high-silicon solid solution thick large-section wind power nodular iron casting is as follows: in step three, the nodularizer: selecting a rare earth silicon magnesium nodulizer, wherein the components comprise 5.5 wt% of Mg, 0.15 wt% of Ce, 40 wt% of Si and the balance of iron; according to the weight percentage of the poured molten iron, the using amount of the nodulizer is 1.0 wt%, and the granularity is 4 mm; the covering agent and the primary inoculant are both low-silicon inoculants, and the components comprise 40 wt% of Si, 1.8 wt% of Ba, 0.4 wt% of Ca, 0.4 wt% of Al, 0.05 wt% of Gd and the balance of iron, and the granularity is 0.5 mm; according to the weight percentage of the poured molten iron, the using amount of the covering agent is 0.4 wt%, and the using amount of the primary inoculant is 0.4 wt%; in the fourth step, the stream inoculant is a sulfur-oxygen-containing Zr inoculant which comprises 73 wt% of Si, 2.0 wt% of Ca, 1.3 wt% of Zr, 0.05 wt% of Mo, 0.32 wt% of S, 0.32 wt% of O and the balance of iron, and the granularity is 0.2 mm; the amount of the stream-following inoculant is 0.10 wt% in percentage by weight of the poured molten iron.

9. The process for improving the metallographic structure of the high-silicon solid solution thick large-section wind power nodular iron casting according to claim 6, wherein the metallographic structure of the high-silicon solid solution thick large-section wind power nodular iron casting is as follows: in step three, the nodularizer: selecting a rare earth silicon magnesium nodulizer, wherein the components comprise 6.0 wt% of Mg, 0.30 wt% of Ce, 50 wt% of Si and the balance of iron; according to the weight percentage of the poured molten iron, the using amount of the nodulizer is 1.2 wt%, and the granularity is 32 mm; the covering agent and the primary inoculant are both low-silicon inoculants, the components comprise 50 wt% of Si, 2.2 wt% of Ba, 0.6 wt% of Ca, 1.0 wt% of Al, 0.15 wt% of Gd and the balance of iron, and the particle size is 6 mm; according to the weight percentage of the poured molten iron, the using amount of the covering agent is 0.6 wt%, and the using amount of the primary inoculant is 0.8 wt%; in the fourth step, the stream inoculant is a sulfur-oxygen-containing Zr inoculant which comprises 76 wt% of Si, 2.5 wt% of Ca, 1.8 wt% of Zr, 0.15 wt% of Mo, 0.36 wt% of S, 0.36 wt% of O and the balance of iron, and the granularity is 0.7 mm; the amount of the stream-following inoculant is 0.30 wt% in percentage by weight of the poured molten iron.

10. The process for improving the metallographic structure of the high-silicon solid solution thick large-section wind power nodular iron casting according to claim 6, wherein the metallographic structure of the high-silicon solid solution thick large-section wind power nodular iron casting is as follows: in step three, the nodularizer: selecting a rare earth silicon magnesium nodulizer, wherein the components comprise 5.75 wt% of Mg, 0.225 wt% of Ce, 45 wt% of Si and the balance of iron; according to the weight percentage of the poured molten iron, the using amount of the nodulizer is 1.1 wt%, and the granularity is 18 mm; the covering agent and the primary inoculant are both low-silicon inoculants, the components of the low-silicon inoculants comprise 45 wt% of Si, 2.0 wt% of Ba, 0.5 wt% of Ca, 0.7 wt% of Al, 0.10 wt% of Gd and the balance of iron, and the particle size is 3.2 mm; according to the weight percentage of the poured molten iron, the using amount of the covering agent is 0.5 wt%, and the using amount of the primary inoculant is 0.6 wt%; in the fourth step, the stream inoculant is a sulfur-oxygen-containing Zr inoculant which comprises 74.5 wt% of Si, 2.25 wt% of Ca, 1.55 wt% of Zr, 0.10 wt% of Mo, 0.34 wt% of S, 0.34 wt% of O and the balance of iron, and the granularity is 0.45 mm; the amount of the stream-following inoculant is 0.20 wt% in percentage by weight of the poured molten iron.

Technical Field

The invention relates to the technical field of cast iron materials, in particular to a process for improving the metallographic structure of a high-silicon solid solution thick large-section wind power nodular iron casting.

Background

With the rapid development of the wind power industry, the demand of wind power nodular cast iron accessories is rapidly increased, the nodular cast iron for wind power is rapidly developed, the nodular cast iron is widely applied at home and abroad due to low cost and high toughness, but has higher requirements on the quality and the performance of wind power castings compared with common nodular cast iron, because the wind power generator set has a severe working environment and is difficult to maintain, the requirements on the quality and the service performance of the wind power castings are higher; the tonnage of a wind power casting of more than 5MW is heavy, the material cost and the installation cost are very high, and the application of a new silicon solid solution strengthening material such as QT 600-10 and QT 500-14 with high strength and high toughness on the wind power casting is particularly necessary for realizing cost reduction and efficiency improvement and realizing the maximum light weight of the casting. The material wind power casting belongs to the brand new field in China, the smelting process and the casting process are not mature from other common materials, and experience and data which can refer to the problems are relatively less.

At present, in the process of producing high-silicon solid-solution nodular iron castings, the high-silicon castings are found to be easy to generate special-shaped graphite such as spiky graphite and the like compared with common material castings, the mechanical properties of the castings are seriously influenced, and particularly the high-silicon solid-solution nodular iron castings are reflected obviously in the detection of sleeve samples.

Disclosure of Invention

In order to overcome the defects in the prior art, the embodiment of the invention provides a process for improving the metallographic structure of a high-silicon solid solution thick large-section wind power nodular iron casting.

A process for improving the metallographic structure of a high-silicon solid solution thick large-section wind power nodular iron casting comprises the following specific preparation steps:

the method comprises the following steps: material preparation and molten iron smelting: the proportion of ingredients is as follows: 40-60% of pig iron and 40-60% of scrap steel;

wherein the content of the trace element components in the pig iron is as follows: 4.0 to 4.5 weight percent of C, 0.40 to 0.60 weight percent of Si, less than or equal to 0.10 weight percent of Mn, less than or equal to 0.03 weight percent of P, less than or equal to 0.01 weight percent of S, less than 0.010 weight percent of Ti, and the content of trace element components in the scrap steel is as follows: less than or equal to 0.15 wt% of C, less than or equal to 0.40 wt% of Si, less than or equal to 0.30 wt% of Mn, less than or equal to 0.02 wt% of P, less than or equal to 0.03 wt% of S, less than or equal to 0.06 wt% of Cr, and less than 0.001 wt% of Ti;

step two: molten iron and component adjustment: adding pig iron and scrap steel into a medium-frequency induction furnace for melting, sampling after molten iron is melted, carrying out spectral analysis and thermal analysis, and then carrying out molten iron component adjustment, including desulfurization and adjustment of C amount and Si amount of the molten iron; after the components are adjusted, the contents of the trace element components in the molten iron are as follows: c: 3.40-3.50 wt%; si: 2.60-2.80 wt%; mn is less than or equal to 0.15 wt%; p is less than or equal to 0.035 wt%; s is less than or equal to 0.012 wt%;

step three: spheroidizing inoculation: placing a nodulizer, a covering agent and alloy Sb at the bottom of a casting ladle in advance, then pouring molten iron in an electric furnace into the casting ladle, and simultaneously adding a primary inoculant when the molten iron is discharged from 2/3 to perform nodulizing and primary inoculation reaction on the molten iron;

step four: pouring treatment: after molten iron is spheroidized, scattering a molten iron deslagging agent on the surface of the molten iron for slagging-off treatment, then pouring the molten iron in a casting ladle into a casting mold, and adding a stream-following inoculant during pouring, wherein the pouring temperature is 1340-1360 ℃;

step five: cleaning the casting: after the pouring is finished, the casting is slowly cooled to below 400 ℃ in a sand mold, and the casting is cleaned from the casting mold.

Further, in the second step, the components of the desulfurizer adopted for desulfurization are CaO and CaC₂The granularity is less than 10 mm; adjusting the C amount by adopting a carburant, wherein the fixed carbon is more than or equal to 99 percent, and the particle size is 0.5-5 mm; the Si content is adjusted by using 75-ferrosilicon, the silicon content in the 75-ferrosilicon is 72-80%, the balance is Mn, Cr, P, S, Al and Ca, and the granularity is 5-100 mm.

Further, in step three, the ratio of the nodulizer: selecting a rare earth silicon magnesium nodulizer, wherein the components comprise 5.5-6.0 wt% of Mg, 0.15-0.30 wt% of Ce, 40-50 wt% of Si and the balance of iron; the nodulizer is 1.0-1.2 wt% and has a particle size of 4-32 mm.

Further, in the third step, both the covering agent and the primary inoculant are low-silicon inoculants, the components comprise 40-50 wt% of Si, 1.8-2.2 wt% of Ba, 0.4-0.6 wt% of Ca, 0.4-1.0 wt% of Al, 0.05-0.15 wt% of Gd and the balance of iron, and the particle size is 0.5-6 mm; according to the weight percentage of the poured molten iron, the dosage of the covering agent is 0.4-0.6 wt%, and the dosage of the primary inoculant is 0.4-0.8 wt%.

Further, in step three, the alloy Sb: the use amount of the alloy Sb is 0.003-0.005 wt% in terms of the weight percentage of the cast molten iron.

Furthermore, in the fourth step, the stream-following inoculant is a sulfur-oxygen-containing Zr inoculant which comprises 73-76 wt% of Si, 2.0-2.5 wt% of Ca, 1.3-1.8 wt% of Zr, 0.05-0.15 wt% of Mo, 0.32-0.36 wt% of S, 0.32-0.36 wt% of O and the balance of iron, and the particle size is 0.2-0.7 mm; the amount of the stream-following inoculant is 0.10-0.30 wt% in percentage by weight of the poured molten iron.

Further, in the fourth step, the slag removing agent is perlite, SiO in the perlite₂Not less than 72 percent and the granularity is 1-3 mm.

Further, in step three, the ratio of the nodulizer: selecting a rare earth silicon magnesium nodulizer, wherein the components comprise 5.5 wt% of Mg, 0.15 wt% of Ce, 40 wt% of Si and the balance of iron; according to the weight percentage of the poured molten iron, the using amount of the nodulizer is 1.0 wt%, and the granularity is 4 mm; the covering agent and the primary inoculant are both low-silicon inoculants, and the components comprise 40 wt% of Si, 1.8 wt% of Ba, 0.4 wt% of Ca, 0.4 wt% of Al, 0.05 wt% of Gd and the balance of iron, and the granularity is 0.5 mm; according to the weight percentage of the poured molten iron, the using amount of the covering agent is 0.4 wt%, and the using amount of the primary inoculant is 0.4 wt%; in the fourth step, the stream inoculant is a sulfur-oxygen-containing Zr inoculant which comprises 73 wt% of Si, 2.0 wt% of Ca, 1.3 wt% of Zr, 0.05 wt% of Mo, 0.32 wt% of S, 0.32 wt% of O and the balance of iron, and the granularity is 0.2 mm; the amount of the stream-following inoculant is 0.10 wt% in percentage by weight of the poured molten iron.

Further, in step three, the ratio of the nodulizer: selecting a rare earth silicon magnesium nodulizer, wherein the components comprise 6.0 wt% of Mg, 0.30 wt% of Ce, 50 wt% of Si and the balance of iron; according to the weight percentage of the poured molten iron, the using amount of the nodulizer is 1.2 wt%, and the granularity is 32 mm; the covering agent and the primary inoculant are both low-silicon inoculants, the components comprise 50 wt% of Si, 2.2 wt% of Ba, 0.6 wt% of Ca, 1.0 wt% of Al, 0.15 wt% of Gd and the balance of iron, and the particle size is 6 mm; according to the weight percentage of the poured molten iron, the using amount of the covering agent is 0.6 wt%, and the using amount of the primary inoculant is 0.8 wt%; in the fourth step, the stream inoculant is a sulfur-oxygen-containing Zr inoculant which comprises 76 wt% of Si, 2.5 wt% of Ca, 1.8 wt% of Zr, 0.15 wt% of Mo, 0.36 wt% of S, 0.36 wt% of O and the balance of iron, and the granularity is 0.7 mm; the amount of the stream-following inoculant is 0.30 wt% in percentage by weight of the poured molten iron.

Further, in step three, the ratio of the nodulizer: selecting a rare earth silicon magnesium nodulizer, wherein the components comprise 5.75 wt% of Mg, 0.225 wt% of Ce, 45 wt% of Si and the balance of iron; according to the weight percentage of the poured molten iron, the using amount of the nodulizer is 1.1 wt%, and the granularity is 18 mm; the covering agent and the primary inoculant are both low-silicon inoculants, the components of the low-silicon inoculants comprise 45 wt% of Si, 2.0 wt% of Ba, 0.5 wt% of Ca, 0.7 wt% of Al, 0.10 wt% of Gd and the balance of iron, and the particle size is 3.2 mm; according to the weight percentage of the poured molten iron, the using amount of the covering agent is 0.5 wt%, and the using amount of the primary inoculant is 0.6 wt%; in the fourth step, the stream inoculant is a sulfur-oxygen-containing Zr inoculant which comprises 74.5 wt% of Si, 2.25 wt% of Ca, 1.55 wt% of Zr, 0.10 wt% of Mo, 0.34 wt% of S, 0.34 wt% of O and the balance of iron, and the granularity is 0.45 mm; the amount of the stream-following inoculant is 0.20 wt% in percentage by weight of the poured molten iron.

The invention has the technical effects and advantages that:

1. by adopting the process for improving the metallographic structure of the high-silicon solid-solution thick and large-section wind power nodular iron casting, the smelting process of high-purity pig iron with low trace elements, particularly low Ti content, high-quality waste steel sheets, no scrap returns, nodulizer with low rare earth element RE, inoculant with low Al, Ba and Ca and flow-following inoculant containing Zr in sulfur and oxygen is adopted, so that the first step can ensure that molten iron is pure enough, and harmful elements such as: trace elements such as Ti, V, W, etc.; secondly, enough graphite cores can be obtained; therefore, the nail-shaped graphite defect in the metallographic structure of the high-silicon solid solution nodular iron casting can be eliminated, and the requirements of customers on various aspects of quality can be well met;

2. by adopting the process for improving the metallographic structure of the high-silicon solid-solution thick and large-section wind power nodular iron casting, trace Ce is used in a nodulizer, Gd is added into a covering agent and a primary inoculant, Mo is added into a stream inoculant, and the three are matched to inhibit a graphite abnormal-shape generation mechanism in a grading manner, so that the uniformity and the stability of the nodular graphite distribution can be sequentially ensured; the invention has the advantages that: the nail-shaped graphite defects in the metallographic structure of the high-silicon nodular cast iron casting block and the body jacket sample are completely eliminated, and the performance of the casting block can be stabilized as follows: the tensile strength is more than or equal to 530MPa, the yield strength is more than or equal to 400MPa, the elongation is more than or equal to 12.5 percent, the unnotched impact at the temperature of 20 ℃ below zero is more than or equal to 7J, and the sample nesting performance of the body is stable as follows: the tensile strength is more than or equal to 500MPa, the yield strength is more than or equal to 400MPa, and the elongation is more than or equal to 10 percent; moreover, the production process does not need any heat treatment or alloying, has simple process and low production cost, and the product completely meets the requirements of customers.

Drawings

The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and together with the description serve to explain the principles of the invention and not to limit the invention. In the drawings:

FIG. 1 is a graph of spiked graphite after scanning under SEM, a scanning electron microscope, and compositional analysis by its own spectrometer;

FIG. 2 is a metallographic structure of a body in example 1 of the present invention;

FIG. 3 is the metallographic structure of the body in example 2 of the present invention;

FIG. 4 shows the metallographic structure of the body in example 3 of the present invention.

Detailed Description

The technical solutions in the embodiments of the present invention will be described clearly and completely with reference to the accompanying drawings, and it is to be understood that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

Referring to the attached drawings 1-4 of the specification:

example 1:

the invention provides a process for improving the metallographic structure of a high-silicon solid solution thick large-section wind power nodular iron casting, which comprises the following specific preparation steps of:

the method comprises the following steps: material preparation and molten iron smelting: the proportion of ingredients is as follows: 40-60% of pig iron and 40-60% of scrap steel, wherein the content of trace element components in the pig iron is as follows: 4.0 to 4.5 weight percent of C, 0.40 to 0.60 weight percent of Si, less than or equal to 0.10 weight percent of Mn, less than or equal to 0.03 weight percent of P, less than or equal to 0.01 weight percent of S, less than 0.010 weight percent of Ti, and the content of trace element components in the scrap steel is as follows: less than or equal to 0.15 wt% of C, less than or equal to 0.40 wt% of Si, less than or equal to 0.30 wt% of Mn, less than or equal to 0.02 wt% of P, less than or equal to 0.03 wt% of S, less than or equal to 0.06 wt% of Cr, and less than 0.001 wt% of Ti;

step two: molten iron and component adjustment: adding pig iron and scrap steel into a medium-frequency induction furnace for melting, sampling after molten iron is melted, carrying out spectral analysis and thermal analysis, and then carrying out molten iron component adjustment, including desulfurization and adjustment of C amount and Si amount of the molten iron; the components of the desulfurizer adopted for desulfurization are CaO and CaC₂The granularity is less than 10 mm; adjusting the C amount by adopting a carburant, wherein the fixed carbon is more than or equal to 99 percent, and the particle size is 0.5-5 mm; adjusting the Si content by using 75-ferrosilicon, wherein the silicon content in the 75-ferrosilicon is 72-80%, the balance is Mn, Cr, P, S, Al and Ca, and the granularity is 5-100 mm; after the components are adjusted, the contents of the trace element components in the molten iron are as follows: c: 3.40-3.50 wt%; si: 2.60-2.80 wt%; mn is less than or equal to 0.15 wt%; p is less than or equal to 0.035 wt%; s is less than or equal to 0.012 wt%;

step three: spheroidizing inoculation: placing a nodulizer, a covering agent and alloy Sb at the bottom of a casting ladle in advance, then pouring molten iron in an electric furnace into the casting ladle, and simultaneously adding a primary inoculant when the molten iron is discharged from 2/3 to perform nodulizing and primary inoculation reaction on the molten iron.

Nodulizing agent: selecting a rare earth silicon magnesium nodulizer, wherein the components comprise 5.5 wt% of Mg, 0.15 wt% of Ce, 40 wt% of Si and the balance of iron; according to the weight percentage of the poured molten iron, the using amount of the nodulizer is 1.0 wt%, and the granularity is 4 mm; the covering agent and the primary inoculant are both low-silicon inoculants, and the components comprise 40 wt% of Si, 1.8 wt% of Ba, 0.4 wt% of Ca, 0.4 wt% of Al, 0.05 wt% of Gd and the balance of iron, and the granularity is 0.5 mm; according to the weight percentage of the poured molten iron, the using amount of the covering agent is 0.4 wt%, and the using amount of the primary inoculant is 0.4 wt%;

step four: pouring treatment: spreading molten iron deslagging agent on the surface of molten iron after molten iron spheroidization for deslagging treatment, wherein the deslagging agent is perlite, and SiO in the perlite₂Not less than 72 percent and the granularity is 1-3 mm; then, pouring molten iron in a casting ladle into the casting mold, and adding a stream-following inoculant in the pouring process, wherein the preferable pouring temperature is 1340-1360 ℃;

the stream inoculant is a sulfur-oxygen Zr-containing inoculant which comprises 73 wt% of Si, 2.0 wt% of Ca, 1.3 wt% of Zr, 0.05 wt% of Mo, 0.32 wt% of S, 0.32 wt% of O and the balance of iron, and the particle size is 0.2 mm; the amount of the stream-following inoculant is 0.10 wt% in percentage by weight of the poured molten iron

Step five: cleaning the casting: after the pouring is finished, the casting is slowly cooled to below 400 ℃ in a sand mold, and the casting is cleaned from the casting mold.

Example 2:

the invention provides a process for improving the metallographic structure of a high-silicon solid solution thick large-section wind power nodular iron casting, which comprises the following specific preparation steps of:

the method comprises the following steps: material preparation and molten iron smelting: the proportion of ingredients is as follows: 40-60% of pig iron, 10-20% of foundry returns and 10-30% of scrap steel, wherein the pig iron is cast by using ductile iron Q10, and the trace element content of the pig iron is as follows: 4.0 to 4.5 weight percent of C, 0.50 to 0.90 weight percent of Si, less than or equal to 0.15 weight percent of Mn, less than or equal to 0.04 weight percent of P, less than or equal to 0.02 weight percent of S and less than 0.04 weight percent of Ti, wherein the steel scrap adopts common steel scrap slices with the following trace element components: less than or equal to 0.15 wt% of C, less than or equal to 0.40 wt% of Si, less than or equal to 0.40 wt% of Mn, less than or equal to 0.03 wt% of P, less than or equal to 0.03 wt% of S, less than or equal to 0.06 wt% of Cr, less than 0.03 wt% of Ti, and the foundry returns refer to ferritic nodular cast iron foundry returns;

step two: molten iron and component adjustment: adding pig iron, scrap steel and a foundry returns into a medium-frequency induction furnace for melting, sampling after molten iron is melted, carrying out spectral analysis and thermal analysis, and then carrying out molten iron component adjustment, including desulfurization and adjustment of C amount and Si amount of the molten iron; the components of the desulfurizer adopted for desulfurization are CaO and CaC₂The granularity is less than 10 mm; the amount of C is adjusted by adopting carburant, and the fixed carbon is more than or equal to 99 percentThe granularity is 0.5-5 mm; adjusting the Si content by using 75-ferrosilicon, wherein the silicon content in the 75-ferrosilicon is 72-80%, the balance is Mn, Cr, P, S, Al and Ca, and the granularity is 5-100 mm; after the components are adjusted, the contents of the trace element components in the molten iron are as follows: c: 3.40-3.50 wt%; si: 2.60-2.80 wt%; mn is less than or equal to 0.15 wt%; p is less than or equal to 0.035 wt%; s is less than or equal to 0.012 wt%;

step three: spheroidizing inoculation: placing a nodulizer, a covering agent and alloy Sb at the bottom of a casting ladle in advance, then pouring molten iron in an electric furnace into the casting ladle, and simultaneously adding a primary inoculant when the molten iron is discharged from 2/3 to perform nodulizing and primary inoculation reaction on the molten iron;

nodulizing agent: selecting a rare earth silicon magnesium nodulizer, wherein the components comprise 5.5-6.0 wt% of Mg, 0.15-0.30 wt% of RE, 40-50 wt% of Si and the balance of iron; according to the weight percentage of the poured molten iron, the using amount of the nodulizer is 1.0-1.2 wt%, and the granularity is 4-32 mm;

inoculant: the inoculant comprises a covering agent, a primary inoculant and a stream inoculant, wherein the covering agent and the primary inoculant are low-silicon inoculants, and the ingredients comprise 40-50 wt% of Si, 1.8-2.2 wt% of Ba, 0.4-0.6 wt% of Ca, 0.4-1.0 wt% of Al and the balance of iron, and the granularity is 0.5-6 mm; the stream inoculant is a sulfur-oxygen Zr-containing inoculant which comprises 73-76 wt% of Si, 2.0-2.5 wt% of Ca, 1.3-1.8 wt% of Zr and the balance of iron, and the particle size is 0.2-0.7 mm; according to the weight percentage of the poured molten iron, the using amount of the covering agent is 0.4-0.6 wt%, and the using amount of the primary inoculant is 0.4-0.8 wt%; the dosage of the stream inoculant is 0.10-0.30 wt%;

alloy Sb: the use amount of the alloy Sb is 0.003-0.005 wt% in terms of the weight percentage of the cast molten iron.

Nodulizing agent: selecting a rare earth silicon magnesium nodulizer, wherein the components comprise 5.5 wt% of Mg, 0.15 wt% of Ce, 40 wt% of Si and the balance of iron; according to the weight percentage of the poured molten iron, the using amount of the nodulizer is 1.0 wt%, and the granularity is 4 mm; the covering agent and the primary inoculant are both low-silicon inoculants, and the components comprise 40 wt% of Si, 1.8 wt% of Ba, 0.4 wt% of Ca, 0.4 wt% of Al, 0.15 wt% of Gd and the balance of iron, and the granularity is 0.5 mm; according to the weight percentage of the poured molten iron, the using amount of the covering agent is 0.4 wt%, and the using amount of the primary inoculant is 0.4 wt%;

step four: pouringPerforming injection treatment: spreading molten iron deslagging agent on the surface of molten iron after molten iron spheroidization for deslagging treatment, wherein the deslagging agent is perlite, and SiO in the perlite₂Not less than 72 percent and the granularity is 1-3 mm; then, pouring molten iron in a casting ladle into the casting mold, and adding a stream-following inoculant in the pouring process, wherein the preferable pouring temperature is 1340-1360 ℃;

step five: after the pouring is finished, the casting is slowly cooled to below 400 ℃ in a sand mold, and the casting is cleaned from the casting mold.

Example 3:

the invention provides a process for improving the metallographic structure of a high-silicon solid solution thick large-section wind power nodular iron casting, which comprises the following specific preparation steps of:

the method comprises the following steps: material preparation and molten iron smelting: the proportion of ingredients is as follows: 40-60% of pig iron and 40-60% of scrap steel, wherein the pig iron is cast by ductile iron and comprises the following trace element components in percentage by weight: 4.0 to 4.5 weight percent of C, 0.40 to 0.60 weight percent of Si, less than or equal to 0.10 weight percent of Mn, less than or equal to 0.03 weight percent of P, less than or equal to 0.01 weight percent of S and less than 0.010 weight percent of Ti, wherein the scrap steel adopts high-quality scrap steel sheets with the following trace element components: less than or equal to 0.15 wt% of C, less than or equal to 0.40 wt% of Si, less than or equal to 0.30 wt% of Mn, less than or equal to 0.02 wt% of P, less than or equal to 0.03 wt% of S, less than or equal to 0.06 wt% of Cr, and less than 0.001 wt% of Ti;

step two: molten iron and component adjustment: adding pig iron and scrap steel into a medium-frequency induction furnace for melting, sampling after molten iron is melted, carrying out spectral analysis and thermal analysis, and then carrying out molten iron component adjustment, including desulfurization and adjustment of C amount and Si amount of the molten iron; the components of the desulfurizer adopted for desulfurization are CaO and CaC₂The granularity is less than 10 mm; adjusting the C amount by adopting a carburant, wherein the fixed carbon is more than or equal to 99 percent, and the particle size is 0.5-5 mm; adjusting the Si content by using 75-ferrosilicon, wherein the silicon content in the 75-ferrosilicon is 72-80%, the balance is Mn, Cr, P, S, Al and Ca, and the granularity is 5-100 mm; after the components are adjusted, the contents of the trace element components in the molten iron are as follows: c: 3.40-3.50 wt%; si: 2.60-2.80 wt%; mn is less than or equal to 0.15 wt%; p is less than or equal to 0.035 wt%; s is less than or equal to

0.012wt％；

Step three: spheroidizing inoculation: placing a nodulizer, a covering agent and alloy Sb at the bottom of a casting ladle in advance, then pouring molten iron in an electric furnace into the casting ladle, and simultaneously adding a primary inoculant when the molten iron is discharged from 2/3 to perform nodulizing and primary inoculation reaction on the molten iron;

nodulizing agent: selecting a rare earth silicon magnesium nodulizer, wherein the components comprise 5.0-7.0 wt% of Mg, 0.40-0.60 wt% of RE, 40-50 wt% of Si and the balance of iron; the amount of the nodulizer is 1.0-1.2 wt% in terms of the weight percentage of the poured molten iron;

inoculant: the inoculant comprises a covering agent, a primary inoculant and a stream inoculant, wherein the covering agent is silicon 75 aluminum, and the ingredients of the covering agent comprise 72-80 wt% of Si, 1.5-2.0 wt% of Ba, 1.0-1.5 wt% of Ca and the balance of iron; the primary inoculant is a silicon-calcium-barium inoculant which comprises 72-78 wt% of Si, 2.0-3.0 wt% of Ba, 1.0-2.0 wt% of Ca and the balance of iron; selecting a sulfur-oxygen inoculant as a stream inoculant, wherein the components comprise 65-80 wt% of Si, 0.5-1.5 wt% of Ca and the balance of iron; according to the weight percentage of the poured molten iron, the using amount of the covering agent is 0.3-0.5 wt%, and the using amount of the primary inoculant is 0.4-0.8 wt%; the dosage of the stream inoculant is 0.10-0.30 wt%;

alloy Sb: the usage amount of the alloy Sb is 0.003-0.005 wt% in terms of the weight percentage of the casting molten iron;

step four: pouring treatment: spreading molten iron deslagging agent on the surface of molten iron after molten iron spheroidization for deslagging treatment, wherein the deslagging agent is perlite, and SiO in the perlite₂Not less than 72 percent and the granularity is 1-3 mm; then pouring molten iron in a pouring ladle into the casting mold, adding a stream-following inoculant during pouring, wherein the pouring temperature is 1340-1360 DEG C

Step five: cleaning the casting: after the pouring is finished, the casting is slowly cooled to below 400 ℃ in a sand mold, and the casting is cleaned from the casting mold.

The cast castings of the embodiments 1 to 3 are bases of certain wind power 4.XMW, the casting weight is 28.5T, the wall thickness is 100 to 400mm, the chemical components of key elements are shown in table 1, the detection results of the mechanical properties of the attached casting test blocks and the body sleeve sample are shown in tables 2 and 3, and the specification of the attached casting test blocks is 70 x 170 mm. FIGS. 2 to 4 show the metallographic structure of the body shell samples in examples 1 to 3.

TABLE 1 key elemental chemistry for examples 1-3

Chemical composition/%)	C	Si	Mn	P	S	Mg	Ti
								Example 1	3.45	3.81	0.151	0.022	0.006	0.040	0.010
Example 2	3.46	3.82	0.154	0.023	0.006	0.039	0.023
								Example 3	3.45	3.81	0.150	0.022	0.007	0.041	0.013

Table 2 examples 1-3 mechanical properties of cast test blocks

TABLE 3 examples 1-3 mechanical properties of body set samples

Mechanical properties	Tensile strength Rm/MPa	Yield strength Rp0.2/MPa	Elongation/percent
				Example 1	536	422	15.6
Example 2	505	404	7.5
				Example 3	513	408	9.3

As can be seen from the data in tables 1 to 3 and FIGS. 1 to 4: scanning the spiky graphite under a scanning electron microscope, and performing component analysis through an energy spectrometer carried by the spiky graphite to obtain the spiky graphite, wherein the main components around the spiky graphite are carbides of trace elements such as Ti, V, Nb, W and the like, and TiC is mainly used; the method is characterized in that high-purity pig iron, high-quality waste steel sheets and no scrap returns are selected to reduce trace elements such as Ti, V, W and the like in molten iron, particularly Ti elements, and research shows that carbides of the elements are main elements causing nail-shaped graphite defects in the metallographic structure of high-silicon solid-solution nodular cast iron; because the content of Si in the high-silicon solid-solution nodular iron castings is continuously increased, if the content of the rare earth elements in the low-Si nodular iron castings is still kept, the graphite variation is easy to occur in the process of graphite formation and growth, and the low-rare earth element nodulizer is selected for consideration; meanwhile, the inoculant with low Al, Ca and Ba contents can be better matched with the low rare earth nodulizer, and the high-silicon solid-solution nodular cast iron with good graphite form can be obtained; unlike the traditional sulfur-containing inoculant, the sulfur-containing Zr-containing stream inoculant has the advantages that the availability of S and O is limited, the addition of the inoculant can possibly reach the performance limit, and in the condition, the effectiveness of the inoculant is limited by the number of potential cores formed, so that a small amount of Zr and Ca elements added into the Zr-containing stream inoculant can intentionally generate the number of cores with higher density and improve the nucleation state through the equilibrium reaction between metal and nonmetal components, thereby better improving the metallographic structure of a casting; example 1, which selects high-purity pig iron, high-quality scrap steel sheets, and a nodulizer without using a scrap and using a rare earth element with low RE, an inoculant with low content of Al, Ba and Ca, and a flow-following inoculant containing Zr and sulfur, is the best in view of the properties of the casting block and the body set sample, and has no nail-like graphite defect in the body set sample; the casting test block and the body case sample performance of the example 2 which uses a nodulizer with low RE, a nucleating agent with low Al, Ba and Ca and a stream inoculant containing Zr and sulfur, but does not select high-purity pig iron high-quality waste steel sheet and returns the raw material, and the example 3 which uses high-purity pig iron, high-quality waste steel sheet and returns the raw material, but does not use the nodulizer with low RE, the nucleating agent with low Al, Ba and Ca and the stream inoculant containing Zr and sulfur are poor, and nail-shaped graphite defects exist; chemical examination revealed that example 1 had a Ti content of 0.010%, and examples 2 and 3% were 0.023% and 0.013%, respectively; the following conclusions can be drawn: the smelting process of selecting high-purity pig iron with low trace elements, particularly low Ti content, high-quality waste steel sheets and no scrap returns, and using a nodulizer with low rare earth elements RE, an inoculant with low Al, Ba and Ca and a stream-following inoculant containing Zr in sulfur and oxygen is characterized in that firstly, the molten iron is ensured to be pure enough, and harmful elements such as: trace elements such as Ti, V, W, etc.; secondly, enough graphite cores can be obtained; therefore, the nail-shaped graphite defect in the metallographic structure of the high-silicon solid solution nodular iron casting can be eliminated, and the requirements of customers on various aspects of quality can be well met; trace Ce is used in a nodulizer, Gd is added into a covering agent and a primary inoculant, Mo is added into a stream inoculant, and the three are matched to inhibit a graphite abnormal-shape generation mechanism in a grading manner, so that the uniformity and the stability of the nodular graphite distribution can be sequentially ensured; the invention has the advantages that: the nail-shaped graphite defects in the metallographic structure of the high-silicon nodular cast iron casting block and the body jacket sample are completely eliminated, and the performance of the casting block can be stabilized as follows: the tensile strength is more than or equal to 530MPa, the yield strength is more than or equal to 400MPa, the elongation is more than or equal to 12.5 percent, the unnotched impact at the temperature of 20 ℃ below zero is more than or equal to 7J, and the sample nesting performance of the body is stable as follows: the tensile strength is more than or equal to 500MPa, the yield strength is more than or equal to 400MPa, and the elongation is more than or equal to 10 percent; moreover, the production process does not need any heat treatment or alloying, has simple process and low production cost, and the product completely meets the requirements of customers.

It is noted that, herein, relational terms such as first and second, and the like may be used solely to distinguish one entity or action from another entity or action without necessarily requiring or implying any actual such relationship or order between such entities or actions. Also, the terms "comprises," "comprising," or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus.

Finally, it should be noted that: although the present invention has been described in detail with reference to the foregoing embodiments, it will be apparent to those skilled in the art that changes may be made in the embodiments and/or equivalents thereof without departing from the spirit and scope of the invention. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.