阅读说明：本技术 一种高强度低应力汽车压盘灰铸铁件的孕育处理方法 (Inoculation treatment method for high-strength low-stress automobile pressure plate gray iron casting ) 是由 周飞 洪军 黄克俊 陈翌庆 袁建伟 方晓刚 于 2021-01-18 设计创作，主要内容包括：本发明公开了一种高强度低应力汽车压盘灰铸铁件的孕育处理方法,是将粒度分级后的硅钡孕育剂分两次加入到铁液中,一次为包内孕育、一次为随流孕育。本发明采用分级筛选获得合适粒度的硅钡孕育剂,通过两次孕育处理得到所需的压盘铸件,其抗拉强度和硬度分别可以稳定达到300MPa以上、230HB以上,从而可满足高强度低应力汽车压盘灰铸铁件的使用需求和规模化生产需求。(The invention discloses a method for inoculating and treating high-strength low-stress automobile platen gray iron castings. The invention obtains the silicon-barium inoculant with proper granularity by screening in grades, obtains the required platen casting by two inoculation treatments, and can respectively stably reach the tensile strength and the hardness of more than 300MPa and more than 230HB, thereby meeting the use requirements and the large-scale production requirements of the high-strength low-stress automobile platen gray iron casting.)

1. A inoculation treatment method for a high-strength low-stress automobile pressure plate gray iron casting is characterized by comprising the following steps:

step 1, inoculant particle size classification

Screening the silicon-barium inoculant by using a grading sieve to respectively obtain a primary inoculant with the granularity of 1.5-2.5 mm and a secondary inoculant with the granularity of 0.3-0.4 mm;

step 2, melting

Melting the raw materials into molten iron in a smelting furnace;

step 3, primary inoculation

Pouring the iron liquid obtained in the step (2) into a pouring ladle, when 10-20% of the total mass of the iron liquid in the pouring ladle is poured into the pouring ladle, uniformly dispersing a primary inoculant preheated to 400 ℃ into the pouring ladle for primary ladle inoculation, and then pouring the residual iron liquid into the pouring ladle;

step 4, secondary inoculation

Pouring molten iron into a sand mold along with an inclined pouring ladle, and blowing a secondary inoculant preheated to 400 ℃ into flowing molten iron by using nitrogen for secondary stream inoculation;

step 5, demoulding

And after the injection is finished, naturally cooling and demolding to obtain the gray iron casting of the automobile pressure plate.

2. The inoculation process according to claim 1, characterized in that: in step 1, the screening method comprises the following steps:

firstly, enabling the silicon-barium inoculant with the granularity of 1-3 mm to pass through a classifying screen with the aperture of 2.5mm, and then passing through a classifying screen with the aperture of 1.5mm to obtain a primary inoculant with the granularity of 1.5-2.5 mm;

the silicon-barium inoculant with the granularity of 0.2-0.5 mm firstly passes through a classifying screen with the aperture of 0.4mm, and then passes through a classifying screen with the aperture of 0.3mm, so that the secondary inoculant with the granularity of 0.3-0.4 mm is obtained.

3. The inoculation process according to claim 1, characterized in that: the silicon-barium inoculant comprises the following components in percentage by mass: more than 60% of Si, 1.0-7.0% of Ba and the balance of Fe.

4. The inoculation process according to claim 1, characterized in that: in step 2, the raw materials comprise: pig iron: 4% -6%, scrap steel: 45-55% of residual materials, namely, recycled iron;

5. the inoculation process according to claim 1, characterized in that: in the step 3, the dosage of the primary inoculant accounts for 0.35-0.45% of the total mass of the molten iron in the ladle.

6. The inoculation process according to claim 1, characterized in that: in the step 4, the dosage of the secondary inoculant accounts for 0.15-0.20% of the total mass of the molten iron in the sand mold.

7. The inoculation process according to claim 1, characterized in that: in the step 3, the primary inoculant is heated to an inoculation temperature of 1440-1460 ℃ along with the molten iron in the pouring ladle; in the step 4, the temperature of the secondary inoculant is raised to an inoculation temperature of 1390-1440 ℃ along with the molten iron.

8. The inoculation process according to claim 1, characterized in that: in the step 3 and the step 4, the total time from the addition of the primary inoculant to the pouring ladle to the completion of the pouring of the molten iron into the sand mold die along with the inclined pouring ladle is 7-8 minutes.

9. An automobile platen gray iron casting obtained by the inoculation method as claimed in any one of claims 1 to 8.

10. The automotive platen gray iron casting of claim 9, wherein the composition in weight percent is:

3.10-3.20% of C, 1.79-1.83% of Si, 0.65-0.67% of Mn, 0.014-0.015% of P, 0.069-0.083% of S, less than or equal to 0.001% of Mg, 0.15-0.16% of Cr, 0.011-0.014% of Ni, 0.001-0.010% of Mo, 0.55-0.57% of Cu, 0.003-0.005% of Al, 0.011-0.012% of Ti, 0.002-0.004% of Sb, 0.08-0.09% of Sn, 0.84-0.86% of Sc, less than or equal to 0.001% of Pb, less than or equal to 0.001% of Zn, less than or equal to 0.001% of Ce, less than or equal to 0.001% of La and the balance of Fe.

Technical Field

The invention belongs to the technical field of processes in the casting process of automobile parts, and particularly relates to a method for inoculating a high-strength low-stress automobile platen gray iron casting.

Background

Gray cast iron is one of the most widely used metallic materials in industry and is an important foundation for the mechanical manufacturing industry. Gray cast iron has high mechanical properties, low cost, good castability, and unique advantages in terms of shock absorption, friction reduction, and notch sensitivity. Meanwhile, compared with other alloys, the gray cast iron also has the advantages of low melting point, good processability, good filling property and simple production facilities and forming process. At present, the automobile clutch in China mainly adopts a gray cast iron pressure plate casting, most of the material of the pressure plate casting is HT250, after the pressure plate casting is used for a period of time, the phenomena of pressure plate deformation, ablation, cracking and the like often occur, so that the clutch fails in advance, and the strength, hardness and surface characteristics of the clutch pressure plate directly influence the service performance and service life of the automobile clutch.

The inoculation treatment is an indispensable link in the production process of the gray cast iron, and aims to promote graphite nucleation, reduce chilling tendency, promote graphite growth, improve graphite morphology and distribution, refine eutectic clusters, refine matrix tissues, reduce section sensitivity and have important influence on the properties of materials such as strength and the like. In practical production application, the gray cast iron is generally applied to 75SiFe inoculant, the inoculation effect is poor, other materials are often required to be added to prepare the composite inoculant, and the cost of the inoculant is greatly increased.

Disclosure of Invention

The invention aims to provide a method for inoculating and treating high-strength low-stress automobile platen gray iron castings, which overcomes the defect of poor inoculating effect of the existing inoculating and treating mode by screening inoculant in a grading manner, improves the strength of the inoculated automobile platen gray iron castings and obtains the automobile platen gray iron castings meeting production and use requirements.

A inoculation treatment method of a high-strength low-stress automobile pressure plate gray iron casting comprises the following steps:

step 1, inoculant particle size classification

Screening the silicon-barium inoculant by using a grading sieve to respectively obtain a primary inoculant with the granularity of 1.5-2.5 mm and a secondary inoculant with the granularity of 0.3-0.4 mm;

step 2, melting

Melting the raw materials into molten iron in a smelting furnace;

step 3, primary inoculation

Pouring the iron liquid obtained in the step (2) into a pouring ladle, when 10-20% of the total mass of the iron liquid in the pouring ladle is poured into the pouring ladle, uniformly dispersing a primary inoculant preheated to 400 ℃ into the pouring ladle for primary ladle inoculation, and then pouring the residual iron liquid into the pouring ladle;

step 4, secondary inoculation

Pouring molten iron into a sand mold along with an inclined pouring ladle, and blowing a secondary inoculant preheated to 400 ℃ into flowing molten iron by using nitrogen for secondary stream inoculation;

step 5, demoulding

And after the injection is finished, naturally cooling and demolding to obtain the gray iron casting of the automobile pressure plate.

Further, in step 1, the screening method comprises: firstly, enabling the silicon-barium inoculant with the granularity of 1-3 mm to pass through a classifying screen with the aperture of 2.5mm, and then passing through a classifying screen with the aperture of 1.5mm to obtain a primary inoculant with the granularity of 1.5-2.5 mm; the silicon-barium inoculant with the granularity of 0.2-0.5 mm firstly passes through a classifying screen with the aperture of 0.4mm, and then passes through a classifying screen with the aperture of 0.3mm, so that the secondary inoculant with the granularity of 0.3-0.4 mm is obtained.

Further, the silicon-barium inoculant comprises the following components in percentage by mass: more than 60% of Si, 1.0-7.0% of Ba and the balance of Fe.

Further, in step 2, the raw materials comprise: pig iron: 4% -6%, scrap steel: 45-55% of residual materials, namely, recycled iron;

further, in the step 3, the dosage of the primary inoculant accounts for 0.35-0.45% of the total mass of the molten iron in the ladle.

Further, in the step 4, the dosage of the secondary inoculant accounts for 0.15-0.20% of the total mass of the molten iron in the sand mold.

Further: in the step 3, the primary inoculant is heated to an inoculation temperature of 1440-1460 ℃ along with the molten iron in the pouring ladle; in the step 4, the temperature of the secondary inoculant is raised to an inoculation temperature of 1390-1440 ℃ along with the molten iron.

Further, in the step 3 and the step 4, the inoculation is declined due to overlong primary inoculation time from the beginning of adding the primary inoculant into the pouring ladle to the end of pouring the molten iron into the sand mold die along with the inclined pouring ladle, and the inoculation effect is reduced.

The gray iron casting for the automobile pressure plate comprises the following components in percentage by weight: 3.10-3.20% of C, 1.79-1.83% of Si, 0.65-0.67% of Mn, 0.014-0.015% of P, 0.069-0.083% of S, less than or equal to 0.001% of Mg, 0.15-0.16% of Cr, 0.011-0.014% of Ni, 0.001-0.010% of Mo, 0.55-0.57% of Cu, 0.003-0.005% of Al, 0.011-0.012% of Ti, 0.002-0.004% of Sb, 0.08-0.09% of Sn, 0.84-0.86% of Sc, less than or equal to 0.001% of Pb, less than or equal to 0.001% of Zn, less than or equal to 0.001% of Ce, less than or equal to 0.001% of La and the balance of Fe.

Compared with the prior art, the invention has the beneficial effects that:

1. the invention adopts the silicon-barium inoculant with proper granularity, obtains the required platen casting through two inoculation treatments, and the tensile strength and the hardness of the platen casting can stably reach more than 300MPa and more than 230HB respectively, thereby meeting the use requirements and the large-scale production requirements of the high-strength low-stress automobile platen gray iron casting.

2. The required casting is obtained through two inoculation treatments, and the inoculants are silicon-barium inoculants. After inoculation, the silicon enables the iron liquid to generate concentration fluctuation, generates a large amount of crystal cores, carries barium into the iron liquid, and the barium is also a nucleation element, has large specific gravity and small vapor pressure, is not easy to lose before the iron liquid is solidified, so that the inoculated iron liquid has strong anti-fading capability. The silicon-barium inoculant enables graphite to be distributed in an A shape, eutectic clusters are refined, and the spacing between pearlite pieces is reduced.

3. The invention adopts a secondary grading sieve to sieve the inoculant, so that the granularity is accurate in a certain range, and the following problems are effectively avoided: when the inoculant particle size is too small, the inoculant particles can be agglomerated and oxidized; when the particle size of the inoculant is too large, the inoculant cannot be dissolved and absorbed, unnecessary impurities can be caused, and the performance of the pressing plate piece is low.

4. The particle size of the inoculant used in the primary inoculation is within the range of 1.5-2.5 mm, the inoculation temperature is 1440-1460 ℃, so that the particle size of graphite precipitated during the temperature and concentration fluctuation in the inoculation process is large enough to possibly survive and become a graphite core which is continuously cooled, and the inoculation recession is reduced.

5. The granularity of the inoculant used in secondary stream inoculation is 0.3-0.4 mm, the inoculation temperature is 1390-1440 ℃, the lower inoculation temperature increases A-type graphite and reduces D-type graphite, the graphite length is shorter, and the smaller inoculation granularity ensures the inoculant to be dissolved and absorbed.

Drawings

FIG. 1 is a schematic view of a gray iron casting for an automobile platen according to example 1 of the present invention;

FIG. 2 is a 500-fold metallographic structure of an automotive platen gray iron casting obtained in example 1 of the present invention;

FIG. 3 is an SEM image of gray iron castings of automotive platens obtained in example 1 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 following embodiments of the present invention, and it is obvious 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.

Example 1

In the embodiment, the gray iron casting of the automobile pressure plate is obtained by the following inoculation method:

step 1, inoculant particle size classification

Firstly, passing a silicon-barium inoculant (comprising components of Si: 68.81%, Ba: 2.84% and the balance Fe) with the particle size of 1-3 mm through a classifying screen with the aperture of 2.5mm, and then passing through a classifying screen with the aperture of 1.5mm to obtain a primary inoculant with the particle size of 1.5-2.5 mm;

the silicon-barium inoculant (the components are Si: 68.88%, Ba: 2.86% and the balance Fe) with the granularity of 0.2-0.5 mm firstly passes through a classifying screen with the aperture of 0.4mm, and then passes through a classifying screen with the aperture of 0.3mm, so that the secondary inoculant with the granularity of 0.3-0.4 mm is obtained.

Step 2, melting

Raw materials (5% of pig iron, 52% of scrap steel and the balance of return iron) are melted into molten iron in a melting furnace.

Step 3, primary inoculation

Pouring the iron liquid obtained in the step (2) into a pouring ladle, when 10-20% of the total mass of the iron liquid in the pouring ladle is poured into the pouring ladle, uniformly dispersing a primary inoculant preheated to 400 ℃ into the pouring ladle for primary ladle inoculation, and then pouring the residual iron liquid into the pouring ladle; wherein: the total mass of the iron liquid in the first ladle is 700kg, the dosage of the primary inoculant accounts for 0.4 percent of the total mass of the iron liquid in the first ladle, and the primary inoculant is heated to the inoculation temperature of 1440-1460 ℃ along with the iron liquid in the first ladle.

Step 4, secondary inoculation

Pouring molten iron into a sand mold along with an inclined pouring ladle, and blowing a secondary inoculant preheated to 400 ℃ into flowing molten iron by using nitrogen for secondary stream inoculation; wherein: the total mass of the iron liquid in the sand mold is 16kg, the dosage of the secondary inoculant accounts for 0.18 percent of the total mass of the iron liquid in the sand mold, and the secondary inoculant is heated to an inoculation temperature of 1390-1440 ℃ along with the iron liquid.

Step 5, demoulding

And after the injection is finished, naturally cooling the casting in a sand mold for 50 minutes, and then separating the sand mold from the casting in a roller to obtain the gray iron casting for the automobile pressure plate.

Through detection, the gray iron casting for the automobile pressure plate comprises the following components in percentage by weight: 3.15 percent of C, 1.82 percent of Si, 0.66 percent of Mn, 0.014 percent of P, 0.076 percent of S, 0.001 percent of Mg, 0.15 percent of Cr, 0.012 percent of Ni, 0.007 percent of Mo, 0.556 percent of Cu, 0.004 percent of Al, 0.011 percent of Ti, 0.003 percent of Sb, 0.087 percent of Sn, 0.85 percent of Sc, 0.001 percent of Pb, 0.001 percent of Zn, 0.001 percent of Ce, 0.001 percent of La and the balance of Fe.

Fig. 1 is a schematic diagram of the gray iron casting for the automobile platen obtained in this embodiment, and fig. 2 is a 500-fold metallographic structure diagram of the gray iron casting for the automobile platen obtained in this embodiment. Fig. 3 is an SEM image of the gray iron casting for the automobile platen obtained in this example. As can be seen from fig. 2, the metallographic structure of the gray iron casting for the automobile platen is composed of a metal matrix and graphite, wherein the graphite is a type a graphite, i.e., uniformly distributed flake graphite, and the matrix mainly contains pearlite and a small amount of ferrite. As can be seen from fig. 3, the pearlite layer has a small lamellar spacing and a pearlite volume fraction of 95% or more.

The automobile pressure plate gray iron casting sample of the embodiment is subjected to a tensile test and a hardness test, and the obtained tensile strength is 335MPa, and the hardness is 246 HB.

Comparative example 1

In this example, the same inoculation procedure as in example 1 was used to obtain grey iron castings for automotive platens, with the only difference that: the granularity of the silicon-barium inoculant used in the primary inoculation process is 1-3 mm, and the granularity of the silicon-barium inoculant used in the secondary inoculation process is 0.2-0.5 mm.

The test shows that the tensile strength of the gray iron casting for the automobile pressure plate is 309MPa, and the hardness of the gray iron casting is 230 HB.

Example 3

In this example, the same inoculation procedure as in example 1 was used to obtain grey iron castings for automotive platens, with the only difference that: in the step 3, the dosage of the primary inoculant accounts for 0.35 percent of the total mass of the molten iron in the ladle; in the step 4, the dosage of the secondary inoculant accounts for 0.15 percent of the total mass of the iron liquid in the sand mold.

The test shows that the tensile strength of the gray iron casting for the automobile pressure plate is 325MPa, and the hardness of the gray iron casting is 239 HB.

Example 4

In this example, the same inoculation procedure as in example 1 was used to obtain grey iron castings for automotive platens, with the only difference that: : in the step 3, the dosage of the primary inoculant accounts for 0.45 percent of the total mass of the molten iron in the ladle; in the step 4, the dosage of the secondary inoculant accounts for 0.20 percent of the total mass of the iron liquid in the sand mold.

The test shows that the tensile strength of the gray iron casting for the automobile pressure plate is 327MPa, and the hardness is 240 HB.

The preferred embodiments of the invention disclosed above are intended to be illustrative only. The preferred embodiments are not intended to be exhaustive or to limit the invention to the precise embodiments disclosed. Obviously, many modifications and variations are possible in light of the above teaching. The embodiments were chosen and described in order to best explain the principles of the invention and the practical application, to thereby enable others skilled in the art to best utilize the invention. The invention is limited only by the claims and their full scope and equivalents.