Method for forming AL203 passive film around graphite in grey cast iron

Abstract

According to the method for forming the AL203 passive film around the graphite in the grey cast iron, in the production process, the grey cast iron with the carbon equivalent being 3.8-4.2% and the aluminum content being 1-5% is heated to 750-850 DEG C in a heating furnace in an oxidizing atmosphere, heat preservation is conducted for 8-12 hours, under the condition, the oxygen element enters the inside through a gap between the graphite and a matrix interface, and the AL203 passive film is formed around the graphite in the grey cast iron. According to the present invention, the aluminum oxide reacts with the aluminum in the matrix around the graphite to form the Al2O3, the continuous Al2O3 passivation film is gradually formed around the graphite by using the segregation phenomenon of the aluminum towards the matrix around the graphite, and the continuous Al2O3 passivation film can be formed on the cast iron surface so as to complete the comprehensive protection of the cast iron;

Description

Technical Field

[0001] The invention relates to the technical field of grey cast iron protection, in particular to a method for forming an AL203 passivation film around graphite in grey cast iron. Background Art

[0002] The main technical route to improve the corrosion resistance and heat resistance of gray cast iron is to add alloy elements, use the alloy elements to form a continuous passivation film to isolate the gray cast iron from the environment or medium, so as to prevent the gray cast iron matrix from being oxidized or corroded by the medium, and use the alloy elements to increase the electrode potential of the matrix to improve the ability to prevent electrochemical corrosion. Usually, the heat resistance and corrosion resistance of gray cast iron are improved by increasing or adding elements such as silicon, chromium, and aluminum.

[0003] When the silicon content of gray cast iron is increased to more than 5%, a dense SiO2 oxide film is formed on the surface of the cast iron, which has a protective effect on the gray cast iron. Due to the excessively high silicon content, the brittleness of the ferrite increases. At the same time, due to the large thermal expansion coefficient of cast iron, it is easy to crack under conditions of rapid heating and cooling. If the silicon content is low, a continuous SiO2 oxide film cannot be formed on the surface of the cast iron, and the protective effect on the gray cast iron is limited.

[0004] After adding chromium, a dense Cr2O3 passivation film is formed on the surface of cast iron, which can better protect the cast iron. At the same time, carbides are easily formed in the cast iron, so the method of adding chromium is not suitable for the protection of gray cast iron.

[0005] After adding aluminum, a dense Al2O3 passivation film is formed on the surface of the cast iron, which can also protect the cast iron well. If the amount of aluminum added is insufficient, a continuous Al2O3 passivation film cannot be formed and the protective effect is limited. If the amount of aluminum added is too high, the brittleness of the cast iron increases, and the smelting and pouring of the casting are difficult.

[0006] The method of increasing the content of elements that can form a dense passive film to protect gray cast iron always has a negative impact. At the same time, the passive film formed is on the surface of the cast iron. For elements that can enter the cast iron along the interface between the flake graphite and the matrix and can interact with the matrix, it is impossible to protect the matrix inside the cast iron.

[0007] Therefore, in view of the shortcomings of the prior art, it is necessary to provide a method for forming an AL203 passivation film around graphite in gray cast iron to solve the shortcomings of the prior art. Summary of the invention

[0008] The purpose of the present invention is to avoid the shortcomings of the prior art and provide a method for forming an Al2O3 passivation film around graphite in gray cast iron. The gray cast iron with a carbon equivalent of 3.8-4.2% and an aluminum content of 1-5% is heated to 750°C-850°C in a heating furnace in an oxidizing atmosphere and kept warm for 8-12 hours. Under this condition, oxygen enters the interior through the gap between the graphite and the matrix interface and reacts with aluminum in the matrix around the graphite to form Al2O3. The phenomenon that aluminum can segregate to the matrix around the graphite is utilized to gradually form a continuous Al2O3 passivation film around the graphite. At the same time, a continuous Al2O3 passivation film can also be formed on the surface of the cast iron, thereby completing comprehensive protection of the cast iron.

[0009] The above-mentioned purpose of the present invention is achieved through the following technical means.

[0010] A method for forming an AL203 passivation film around graphite in grey cast iron is provided, comprising the following steps:

[0011] Step S1: When preparing the Al2O3 passivation film, the carbon equivalent of grey cast iron is calculated using the following formula:

[0012] CE=w C +0.31w Si -0.3w Al -0.027w Mn +0.33w P +0.4w S (Al≤2%)

[0013] CE=w C +0.31w Si -0.13w Al -0.027w Mn +0.33w P +0.4w S (Al≤5%);

[0014] Step S2: Calculate the gray cast iron with a carbon equivalent of 3.8-4.2%, and control the aluminum content range of the gray cast iron;

[0015] Step S3: heating the gray cast iron to 750°C-850°C in a heating furnace in an oxidizing atmosphere, keeping the temperature for 8-12 hours for protection treatment, and then performing normalizing treatment. Under this condition, oxygen enters the interior through the gap between the graphite and the matrix interface, and reacts with aluminum in the matrix around the graphite to form Al2O3;

[0016] Step S4: Experimental data detection.

[0017] Specifically, in step S2, the aluminum content of the grey cast iron is controlled within a range of 1-5%.

[0018] Specifically, in step S3, the gray cast iron is normalized by heating it to 850° in a heating furnace and keeping the temperature for 2 hours.

[0019] The invention heats gray cast iron with a carbon equivalent of 3.8-4.2% and an aluminum content of 1-5% to 750°C-850°C in a heating furnace in an oxidizing atmosphere during production, and keeps the temperature for 8-12 hours. Under this condition, oxygen enters the interior through the gap between the graphite and the matrix interface, reacts with aluminum in the matrix around the graphite to form Al2O3, and utilizes the phenomenon that aluminum can segregate to the matrix around the graphite to gradually form a continuous Al2O3 passivation film around the graphite. At the same time, a continuous Al2O3 passivation film can also be formed on the surface of the cast iron, thereby achieving comprehensive protection of the cast iron. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] The present invention is further described with reference to the accompanying drawings, but the contents in the accompanying drawings do not constitute any limitation to the present invention.

[0021] Figure 1 This is a scanning electron microscope result view of a gray cast iron with a carbon equivalent of 3.8 and Al: 1wt% in a new gray cast iron preparation method resistant to aluminum liquid corrosion of the present invention.

[0022] Figure 2 This is a scanning electron microscope result view of a gray cast iron with a carbon equivalent of 3.8 and Al: 2wt% in a new gray cast iron preparation method resistant to aluminum liquid corrosion of the present invention.

[0023] Figure 3 This is a scanning electron microscope result view of a gray cast iron with a carbon equivalent of 3.8 and Al: 3wt% in a new gray cast iron preparation method resistant to aluminum liquid corrosion of the present invention.

[0024] Figure 4 This is a scanning electron microscope result view of a gray cast iron with a carbon equivalent of 3.8 and Al: 4wt% in a new gray cast iron preparation method resistant to aluminum liquid corrosion of the present invention.

[0025] Figure 5 This is a scanning electron microscope result view of a gray cast iron with a carbon equivalent of 3.8 and Al: 5wt% in a new gray cast iron preparation method resistant to aluminum liquid corrosion of the present invention.

[0026] Figure 6 This is a scanning electron microscope result view of a gray cast iron with a carbon equivalent of 4.2, Al: 2wt% and 750°C in a new gray cast iron preparation method resistant to aluminum liquid corrosion of the present invention.

[0027] Figure 7 This is a scanning electron microscope result view of a gray cast iron with a carbon equivalent of 4.2, Al: 2wt% and 800°C in a new gray cast iron preparation method resistant to aluminum liquid corrosion of the present invention.

[0028] Figure 8 This is a scanning electron microscope result view of gray cast iron with a carbon equivalent of 4.2, Al: 2wt% and 850°C in a new gray cast iron preparation method resistant to aluminum liquid corrosion of the present invention.

[0029] Fig. 9 This is a scanning electron microscope result view of a gray cast iron with a carbon equivalent of 4.2 and Al: 2wt% at 800°C for 10 hours in a new gray cast iron preparation method resistant to aluminum liquid corrosion of the present invention.

[0030] Fig.10 This is a scanning electron microscope result view of a gray cast iron with a carbon equivalent of 4.2 and Al: 2wt% at 800°C for 12 hours in a new gray cast iron preparation method resistant to aluminum liquid corrosion of the present invention.

[0031] Fig.11 This is a scanning electron microscope result view of a gray cast iron with a carbon equivalent of 4.2 and Al: 1wt% in a new gray cast iron preparation method resistant to aluminum liquid corrosion of the present invention.

[0032] Fig.12 This is a scanning electron microscope result view of a gray cast iron with a carbon equivalent of 4.2 and Al: 3wt% in a new gray cast iron preparation method resistant to aluminum liquid corrosion of the present invention.

[0033] Fig.13 This is a scanning electron microscope result view of a gray cast iron with a carbon equivalent of 4.2 and Al: 4wt% in a new gray cast iron preparation method resistant to aluminum liquid corrosion of the present invention.

[0034] Fig.14 This is a scanning electron microscope result view of a gray cast iron with a carbon equivalent of 4.2 and Al: 4wt% in a new gray cast iron preparation method resistant to aluminum liquid corrosion of the present invention. DETAILED DESCRIPTION

[0035] The present invention is further described in conjunction with the following examples.

[0036] Embodiment 1:

[0037] A method for forming an AL203 passivation film around graphite in grey cast iron comprises the following steps:

[0038] Step S1: When preparing the Al2O3 passivation film, the carbon equivalent of grey cast iron is calculated using the following formula:

[0039] CE=w C +0.31w Si -0.3w Al -0.027w Mn +0.33w P +0.4w S (Al≤2%)

[0040] CE=w C +0.31w Si -0.13w Al -0.027w Mn +0.33w P +0.4w S (Al≤5%);

[0041] Step S2: Calculate the gray cast iron with a carbon equivalent of 3.8-4.2%, and control the aluminum content of the gray cast iron to be within the range of 1-5%;

[0042] Step S3: heating the gray cast iron to 750°C-850°C in a heating furnace in an oxidizing atmosphere, keeping the temperature for 8-12 hours for protection treatment, and then normalizing the gray cast iron to 850°C in a heating furnace for 2 hours. Under this condition, oxygen enters the interior through the gap between the graphite and the matrix interface, and reacts with aluminum in the matrix around the graphite to form Al2O3;

[0043] Step S4: Experimental data detection.

[0044] Embodiment 2:

[0045] The other steps in this embodiment are the same as those in embodiment 1, except that: CE=w C +0.31w Si -0.3w Al -0.027w Mn +0.33w P +0.4w S (Al≤2%) Calculate the carbon equivalent of cast iron. When the carbon equivalent is 3.8, the aluminum content is 1wt%, and it is heated to 800℃ and kept warm for 8 hours for protection treatment. The Al2O3 passivation film around the flake graphite of gray cast iron is as follows: Figure 1 shown.

[0046] Embodiment 3:

[0047] The other steps in this embodiment are the same as those in embodiment 1, except that: CE=w C +0.31w Si -0.3w Al -0.027w Mn +0.33w P +0.4w S (Al≤2%) Calculate the carbon equivalent of cast iron. When the carbon equivalent is 3.8, the aluminum content is 2wt%, and it is heated to 800℃ and kept warm for 8 hours for protection treatment. The Al2O3 passivation film around the flake graphite of gray cast iron is as follows: Figure 2 shown.

[0048] Embodiment 4:

[0049] The other steps in this embodiment are the same as those in embodiment 1, except that: CE=w C +0.31w Si -0.3w Al -0.027w Mn +0.33w P +0.4w S (Al≤2%) Calculate the carbon equivalent of cast iron. When the carbon equivalent is 3.8, the aluminum content is 3wt% and heated to 800℃. Keep warm for 8 hours for protective treatment. The Al2O3 passivation film around the flake graphite of gray cast iron is as follows: Figure 3 shown.

[0050] Embodiment 5:

[0051] The other steps in this embodiment are the same as those in embodiment 1, except that: CE=w C +0.31w Si -0.3w Al -0.027w Mn +0.33w P +0.4w S (Al≤2%) Calculate the carbon equivalent of cast iron. When the carbon equivalent is 3.8, the aluminum content is 4wt% and heated to 800℃, kept warm for 8 hours for protection treatment. The Al2O3 passivation film around the flake graphite of gray cast iron is as follows: Figure 4 shown.

[0052] Embodiment 6:

[0053] The other steps in this embodiment are the same as those in embodiment 1, except that: CE=w C +0.31w Si -0.3w Al -0.027w Mn +0.33w P +0.4w S (Al≤2%) Calculate the carbon equivalent of cast iron. When the carbon equivalent is 3.8, the aluminum content is 5wt% and heated to 800℃. Keep warm for 8 hours for protective treatment. The Al2O3 passivation film around the flake graphite of gray cast iron is as follows: Figure 5 shown.

[0054] Embodiment 7:

[0055] The other steps in this embodiment are the same as those in embodiment 1, except that: CE=w C +0.31w Si -0.3w Al-0.027w Mn +0.33w P +0.4w S (Al≤2%) Calculate the carbon equivalent of cast iron. When the carbon equivalent is 4.2, the aluminum content is 2wt%, and it is heated to 750℃ and kept warm for 8 hours for protection treatment. The Al2O3 passivation film around the flake graphite of gray cast iron is as follows Figure 6 shown.

[0056] Embodiment 8:

[0057] The other steps in this embodiment are the same as those in embodiment 1, except that: CE=w C +0.31w Si -0.3w Al -0.027w Mn +0.33w P +0.4w S (Al≤2%) Calculate the carbon equivalent of cast iron. When the carbon equivalent is 4.2, the aluminum content is 2wt%, and it is heated to 800℃ and kept warm for 8 hours for protection treatment. The Al2O3 passivation film around the flake graphite of gray cast iron is as follows: Figure 7 shown.

[0058] Embodiment 9:

[0059] The other steps in this embodiment are the same as those in embodiment 1, except that: CE=w C +0.31w Si -0.3w Al -0.027w Mn +0.33w P +0.4w S (Al≤2%) Calculate the carbon equivalent of cast iron. When the carbon equivalent is 4.2, the aluminum content is 2wt%, and it is heated to 850℃ and kept warm for 8 hours for protection treatment. The Al2O3 passivation film around the flake graphite of gray cast iron is as follows Figure 8 shown.

[0060] Embodiment 10:

[0061] The other steps in this embodiment are the same as those in embodiment 1, except that: CE=w C +0.31w Si -0.3w Al -0.027w Mn +0.33w P +0.4w S (Al≤2%) Calculate the carbon equivalent of cast iron. When the carbon equivalent is 4.2, the aluminum content is 2wt% and heated to 800℃. Keep warm for 10 hours for protective treatment. The Al2O3 passivation film around the flake graphite of gray cast iron is as follows: Fig. 9 shown.

[0062] Embodiment 11:

[0063] The other steps in this embodiment are the same as those in embodiment 1, except that: CE=w C +0.31w Si -0.3w Al -0.027w Mn +0.33w P +0.4w S (Al≤2%) Calculate the carbon equivalent of cast iron. When the carbon equivalent is 4.2, the aluminum content is 2wt%, and it is heated to 800℃ and kept warm for 12 hours for protection treatment. The Al2O3 passivation film around the flake graphite of gray cast iron is as follows: Fig.10 shown.

[0064] Embodiment 12:

[0065] The other steps in this embodiment are the same as those in embodiment 1, except that: CE=w C +0.31w Si -0.3w Al -0.027w Mn +0.33w P +0.4w S (Al≤2%) Calculate the carbon equivalent of cast iron. When the carbon equivalent is 4.2, the aluminum content is 1wt%, and it is heated to 800℃ and kept warm for 8 hours for protection treatment. The Al2O3 passivation film around the flake graphite of gray cast iron is as follows: Fig.11 shown.

[0066] Embodiment 13:

[0067] The other steps in this embodiment are the same as those in embodiment 1, except that: CE=w C +0.31w Si -0.13w Al -0.027w Mn +0.33w P +0.4w S (Al≤5%) Calculate the carbon equivalent of cast iron. When the carbon equivalent is 4.2, the aluminum content is 3wt%, and it is heated to 800℃ and kept warm for 8 hours for protection treatment. The Al2O3 passivation film around the flake graphite of gray cast iron is as follows: Fig.12 shown.

[0068] Embodiment 14:

[0069] The other steps in this embodiment are the same as those in embodiment 1, except that: CE=w C +0.31wSi -0.13w Al -0.027w Mn +0.33w P +0.4w S (Al≤5%) Calculate the carbon equivalent of cast iron. When the carbon equivalent is 4.2, the aluminum content is 4wt% and heated to 800℃. Keep warm for 8 hours for protective treatment. The Al2O3 passivation film around the flake graphite of gray cast iron is as follows: Fig.13 shown.

[0070] Embodiment 15:

[0071] The other steps in this embodiment are the same as those in embodiment 1, except that: CE=w C +0.31w Si -0.13w Al -0.027w Mn +0.33w P +0.4w S (Al≤5%) Calculate the carbon equivalent of cast iron. When the carbon equivalent is 4.2, the aluminum content is 5wt% and heated to 800℃. Keep warm for 8 hours for protective treatment. The Al2O3 passivation film around the flake graphite of gray cast iron is as follows: Fig.14 shown.

[0072] In the production process, gray cast iron with a carbon equivalent of 3.8-4.2% and an aluminum content of 1-5% is heated to 750°C-850°C in a heating furnace in an oxidizing atmosphere and kept warm for 8-12 hours. Under this condition, oxygen enters the interior through the gap between the graphite and the matrix interface, reacts with the aluminum in the matrix around the graphite to form Al2O3, and utilizes the phenomenon that aluminum can segregate to the matrix around the graphite to gradually form a continuous Al2O3 passivation film around the graphite. At the same time, a continuous Al2O3 passivation film can also be formed on the surface of the cast iron, thereby completing comprehensive protection of the cast iron.

[0073] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solution of the present invention can be modified or replaced by equivalents without departing from the essence and scope of the technical solution of the present invention.

Claims

1. A method for forming an AL203 passivation film around graphite in grey cast iron, characterized in that: The following steps are included Step S1: When preparing the Al2O3 passivation film, the carbon equivalent of grey cast iron is calculated using the following formula: <h2 style=";text-align:left;direction:ltr">CE=w<h2 style=";text-align:left;direction:ltr"> C <h2 style=";text-align:left;direction:ltr"> +0.31w<h2 style=";text-align:left;direction:ltr"> Si <h2 style=";text-align:left;direction:ltr"> -0.3w<h2 style=";text-align:left;direction:ltr"> Al <h2 style=";text-align:left;direction:ltr"> -0.027w<h2 style=";text-align:left;direction:ltr"> Mn <h2 style=";text-align:left;direction:ltr"> +0.33w<h2 style=";text-align:left;direction:ltr"> P <h2 style=";text-align:left;direction:ltr"> +0.4w<h2 style=";text-align:left;direction:ltr"> S <h2 style=";text-align:left;direction:ltr"> (Al≤2%) <h2 style=";text-align:left;direction:ltr">CE=w<h2 style=";text-align:left;direction:ltr"> C <h2 style=";text-align:left;direction:ltr"> +0.31w<h2 style=";text-align:left;direction:ltr"> Si <h2 style=";text-align:left;direction:ltr"> -0.13w<h2 style=";text-align:left;direction:ltr"> Al <h2 style=";text-align:left;direction:ltr"> -0.027w<h2 style=";text-align:left;direction:ltr"> Mn <h2 style=";text-align:left;direction:ltr"> +0.33w<h2 style=";text-align:left;direction:ltr"> P <h2 style=";text-align:left;direction:ltr"> +0.4w<h2 style=";text-align:left;direction:ltr"> S <h2 style=";text-align:left;direction:ltr"> (Al≤5%); Step S2: calculating the gray cast iron with a carbon equivalent of 3.8-4.2%, and controlling the aluminum content range of the gray cast iron; Step S3: heating the grey cast iron to 750° C.-850° C. in a heating furnace in an oxidizing atmosphere, keeping the temperature for 8-12 hours for protection treatment, and then performing normalizing treatment. Under this condition, oxygen enters the interior through the gap between the graphite and the matrix interface, and reacts with aluminum in the matrix around the graphite to form Al2O3; Step S4: Experimental data detection.

2. The method for forming an AL203 passivation film around graphite in a gray cast iron according to claim 1, characterized in that: In step S2, the aluminum content of the grey cast iron is controlled within a range of 1-5%.

3. The method for forming an AL203 passivation film around graphite in a gray cast iron according to claim 2, characterized in that: In step S3, the gray cast iron is normalized by heating it to 850° in a heating furnace for 2 hours.

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