CN110714157B

CN110714157B - Corrosion-resistant cast iron alloy and preparation method thereof

Info

Publication number: CN110714157B
Application number: CN201911048049.3A
Authority: CN
Inventors: 徐流杰; 魏世忠; 路富刚; 王方方; 周玉成; 潘昆明; 李秀青; 李继文; 毛丰; 王晓东; 陈冲; 司岸恒; 熊美; 张国赏; 张程; 靳东亮; 任永鹏
Original assignee: Henan University of Science and Technology
Current assignee: Henan University of Science and Technology
Priority date: 2019-10-30
Filing date: 2019-10-30
Publication date: 2021-12-03
Anticipated expiration: 2039-10-30
Also published as: CN110714157A

Abstract

The invention relates to a corrosion-resistant cast iron alloy and a preparation method thereof, belonging to the field of cast iron alloys. The corrosion-resistant cast iron alloy consists of the following elements in percentage by mass: n: 0.2-0.6%, C: 2.1-2.5%, Cr: 23-28%, Mo: 0.5-0.8%, Si: 0.9-1.2%, Mn: 0.5-0.8%, Al: 1.0-1.4%, P is less than or equal to 0.01%, S is less than or equal to 0.01%, rare earth elements: 0.1-0.3%, and the balance of iron and inevitable impurities. The corrosion-resistant cast iron alloy provided by the invention contains elements such as chromium, nitrogen and aluminum, and nitrogen can be enriched on the interface of metal and an oxide film and the active surface of the metal to slow down electrochemical corrosion; aluminum can form and expand a ferrite phase region, promote the formation of an alpha-Fe single phase and improve the corrosion resistance of a matrix; the combination of all elements obviously slows down the corrosion of the material and improves the corrosion resistance.

Description

Corrosion-resistant cast iron alloy and preparation method thereof

Technical Field

The invention belongs to the field of cast iron alloy, and particularly relates to a corrosion-resistant cast iron alloy and a preparation method thereof.

Background

At present, in mechanical equipment in the industries of petrochemical industry, aerospace industry, water conservancy and electric power industry and the like, various iron castings such as pump bodies, valves, pipelines, wing wheels of hydroelectric generators and the like are often out of work due to corrosion in the service process because the iron castings are often operated in working conditions such as seawater, corrosive media, atmosphere and the like.

At present, the widely used corrosion-resistant cast iron material is mainly high-chromium cast iron. However, Cr white cast iron has serious interphase corrosion, the weight loss caused by the interphase corrosion accounts for a higher proportion in the total weight loss, the driving force of the interphase corrosion is the difference between the electric potentials of a matrix phase and a carbide interphase, and in the corrosion process, the carbide is protected as a cathode, and the matrix is accelerated to corrode as an anode. This makes ordinary high-chromium cast iron unsuitable for use in more corrosive media.

Disclosure of Invention

The invention aims to provide a corrosion-resistant cast iron alloy to solve the problem of poor corrosion resistance of the existing cast iron alloy.

The second purpose of the invention is to provide a preparation method of the corrosion-resistant cast iron alloy.

In order to achieve the purpose, the technical scheme of the corrosion-resistant cast iron alloy is as follows:

the corrosion-resistant cast iron alloy consists of the following elements in percentage by mass: n: 0.2-0.6%, C: 2.1-2.5%, Cr: 23-28%, Mo: 0.5-0.8%, Si: 0.9-1.2%, Mn: 0.5-0.8%, Al: 1.0-1.4%, P is less than or equal to 0.01%, S is less than or equal to 0.01%, rare earth elements: 0.1-0.3%, and the balance of iron and inevitable impurities.

The corrosion-resistant cast iron alloy provided by the invention contains elements such as chromium, nitrogen and aluminum, and nitrogen can be enriched on the interface of metal and an oxide film and the active surface of the metal to slow down electrochemical corrosion; aluminum can form and expand a ferrite phase region, promote the formation of an a-Fe single phase and improve the corrosion resistance of a matrix; the combination of all elements obviously slows down the corrosion of the material and improves the corrosion resistance.

The rare earth element is a very strong purifying agent for molten steel and an effective alterant for cleaning steel inclusion. Preferably, the rare earth element is cerium (Ce).

In order to further optimize the corrosion resistance of the cast iron alloy, preferably, the corrosion-resistant cast iron alloy consists of the following elements in percentage by mass: n: 0.43-0.47%, C: 2.403-2.482%, Cr: 24.78-26.31%, Mo: 0.7206-0.7672%, Si: 0.985-1.137%, Mn: 0.6613-0.6753%, Al: 1.075-1.176%, P is less than or equal to 0.01%, S is less than or equal to 0.01%, rare earth element Ce: 0.25-0.3%, and the balance of iron and inevitable impurities.

The nitrogen-containing cast iron can be prepared by hot isostatic pressing smelting, pressurized plasma arc smelting and other methods.

The pressure in the hot isostatic pressing smelting furnace is maximum, so that higher pressure can be achieved, and the prepared high-nitrogen cast iron can reach higher nitrogen content, but nitride precipitates are easily formed in a matrix. The pressurized plasma arc melting has fluctuation of temperature in the molten pool, thereby causing poor nitrogen homogenization effect in the molten pool.

Compared with the smelting method, the invention also provides a vacuum induction positive pressure smelting method.

A preparation method of the corrosion-resistant cast iron alloy comprises the following steps: taking raw materials according to the proportion, smelting, and solidifying and forming the obtained smelting liquid to obtain an as-cast alloy; sequentially quenching and tempering the as-cast alloy to obtain a martensite phase and an M phase₇C₃Corrosion resistant cast iron alloy of carbide.

Vacuum induction positive pressure smelting is adopted, the melt is evenly smelted under the action of electromagnetic induction, and the diffusion of nitrogen in the melt is accelerated, so that the time for the nitrogen in the melt to reach balance under specific pressure is shortened, and the uniformity of ingot casting tissues is improved.

To obtain conveniently martensite and M phase composition₇C₃The temperature of the quenching treatment is 850-1050 ℃, and the temperature of the tempering treatment is 270-300 ℃ preferably.

Further improving the efficiency of heat treatment, promoting the formation of a uniform crystal structure and improving the quality stability of the batch of products, preferably, the quenching treatment comprises firstly heating to 850 ℃, preserving heat for 1h, then heating to 1000-1050 ℃, preserving heat for 2-4h, and air cooling to room temperature; the tempering treatment is to keep the temperature at 270-300 ℃ for 2-2.5h and then air-cool to the room temperature.

In order to reduce the precipitation of nitrogen during the solidification process, preferably, the solidification molding is performed under a nitrogen atmosphere, and the pressure of nitrogen is more than 0.1 MPa. Generally speaking, when the smelting liquid of the conventional nitrogen-containing cast iron is solidified, a higher positive pressure nitrogen environment is needed to prevent the precipitation of nitrogen, and the cast iron alloy can achieve a good effect under a lower nitrogen pressure, so that the reasonability of the composition of the alloy is further proved. On the basis of ensuring that nitrogen is not precipitated, in order to further reduce the difficulty of the smelting process, the pressure of the nitrogen is preferably 0.4-0.8 MPa.

In order to better remove water and oxygen during smelting, preferably, the smelting is vacuum smelting, and the vacuum degree of the vacuum smelting is 20-40 Pa.

Smelting raw materials can be selected correspondingly according to the composition of the cast iron alloy, such as simple substances, corresponding alloys and the like. In order to further reduce the smelting loss and facilitate the uniform mixing of all elements, the raw materials are preferably Fe, Mn, Cr, Si, C, chromium iron nitride, Al and rare earth ferrosilicon alloy, and the rare earth ferrosilicon alloy comprises the following components in percentage by mass: ce39-42%, Si not more than 37%, Mn not more than 2.0%, and the balance of iron and inevitable impurities.

Drawings

FIG. 1 is an XRD pattern of a corrosion-resistant cast iron alloy of example 1 of the present invention;

FIG. 2 is an SEM photograph of a corrosion-resistant cast iron alloy according to example 1 of the present invention;

FIG. 3 is a graph comparing the corrosion resistance of corrosion-resistant cast iron alloys of examples 1 to 5 of the present invention and a comparative example.

Detailed Description

The following further describes embodiments of the present invention with reference to the drawings.

First, specific examples of the corrosion-resistant cast iron alloy of the present invention

Example 1

The corrosion-resistant cast iron alloy of the embodiment comprises the following elements in percentage by mass: c: 2.167%, Cr: 27.38%, Mo: 0.6387%, Si: 0.9637%, Mn: 0.7628%, N: 0.58%, Al: 1.368%, P is less than or equal to 0.01%, S is less than or equal to 0.01%, rare earth element Ce: 0.1% and the balance of iron and inevitable impurities.

Example 2

The corrosion-resistant cast iron alloy of the embodiment comprises the following elements in percentage by mass: c: 2.241%, Cr: 26.53%, Mo: 0.7521%, Si: 1.036%, Mn: 0.6853%, N: 0.52%, Al: 1.246%, P is less than or equal to 0.01%, S is less than or equal to 0.01%, rare earth element Ce: 0.15%, and the balance of iron and inevitable impurities.

Example 3

The corrosion-resistant cast iron alloy of the embodiment comprises the following elements in percentage by mass: c: 2.347%, Cr: 25.07%, Mo: 0.6871%, Si: 1.047%, Mn: 0.5946%, N: 0.46%, Al: 1.179%, P is less than or equal to 0.01%, S is less than or equal to 0.01%, rare earth element Ce: 0.20%, and the balance of iron and inevitable impurities.

Example 4

The corrosion-resistant cast iron alloy of the embodiment comprises the following elements in percentage by mass: c: 2.482%, Cr: 24.78%, Mo: 0.7672%, Si: 0.985%, Mn: 0.6613%, N: 0.43%, Al: 1.176%, P is less than or equal to 0.01%, S is less than or equal to 0.01%, rare earth element Ce: 0.30% and the balance of iron and inevitable impurities.

Example 5

The corrosion-resistant cast iron alloy of the embodiment comprises the following elements in percentage by mass: c: 2.403%, Cr: 26.31%, Mo: 0.7206%, Si: 1.137%, Mn: 0.6753%, N: 0.47%, Al: 1.075%, P less than or equal to 0.01%, S less than or equal to 0.01%, rare earth element Ce: 0.25%, and the balance of iron and inevitable impurities.

Second, specific examples of the method for producing the corrosion-resistant cast iron alloy of the present invention

Example 6

The preparation method of the corrosion-resistant cast iron alloy of the embodiment explains the preparation of the corrosion-resistant cast iron alloy of the embodiment 1, and concretely comprises the following steps:

1) in a vacuum induction positive pressure smelting furnace of 20kg, firstly, proportioned Fe raw materials, Mn raw materials and Cr raw materials are put into a crucible of a smelting chamber in the furnace, then, proportioned Si raw materials, C raw materials, granular ferrochromium nitride, Al raw materials and rare earth ferrosilicon are added into a main feeding chamber and an alloy material chamber, a vacuum cover is covered tightly, and a vacuum pump is started to enable the vacuum degree (namely absolute pressure) in the smelting chamber to reach 20 Pa.

Then heating, melting and refining the raw materials in the crucible, and controlling the temperature at 1500 ℃ to obtain molten metal.

2) Adding Si raw material, C raw material, granular ferrochromium nitride and Al raw material into molten metal in sequence, carrying out melting alloying treatment, keeping the temperature of the molten metal at 1500 ℃ by utilizing medium-high frequency induction heating, sampling and testing, and adjusting the content of corresponding elements to meet the requirements if the content of each element does not meet the composition requirements.

3) Adding rare earth ferrosilicon alloy into a casting ladle, then pouring the smelting liquid in the crucible into the casting ladle by using a hydraulic system, and then solidifying and forming the smelting liquid to obtain the cast ingot. The solidification molding was carried out in a nitrogen atmosphere under a nitrogen pressure of 0.8 MPa. The rare earth silicon-iron alloy comprises the following components in percentage by weight: ce 39%, Si 30%, Mn 1.3%, the balance being iron and unavoidable impurities.

4) Quenching the ingot obtained in the step 3) and then tempering. During quenching treatment, the temperature is firstly increased to 850 ℃ and is kept for 1h, then the temperature is increased to 1000 ℃ and is kept for 2h, and air cooling is carried out to the room temperature. The tempering treatment is that the temperature is kept at 270 ℃ for 2.5h, and then the air cooling is carried out to the room temperature, thus obtaining the product.

Example 7

The method for producing a corrosion-resistant cast iron alloy of the present example is described with reference to example 2, and differs from example 6 only in that:

in step 1), the vacuum degree was kept at 25 Pa.

In step 2), sampling and checking at 1520 ℃.

In the step 3), the nitrogen pressure during solidification molding is 0.75 MPa.

In the step 4), the quenching treatment is to heat up to 850 ℃ and preserve heat for 1h, then heat up to 1000 ℃ and preserve heat for 3h, and air-cool to room temperature. The tempering treatment is that the temperature is kept for 2 hours at 300 ℃, and then the air cooling is carried out to the room temperature.

Example 8

The method for producing a corrosion-resistant cast iron alloy of the present example is described with reference to example 3, and differs from example 6 only in that:

in step 1), the vacuum degree was maintained at 30 Pa.

In step 2), sampling and checking at 1550 ℃.

In the step 3), the nitrogen pressure during solidification molding is 0.6 MPa.

In the step 4), the quenching treatment is to heat up to 850 ℃ and preserve heat for 1h, then heat up to 1000 ℃ and preserve heat for 4h, and air-cool to room temperature. The tempering treatment is that the temperature is kept for 2 hours at 300 ℃, and then the air cooling is carried out to the room temperature.

Example 9

The method for producing a corrosion-resistant cast iron alloy according to the present example is described with reference to example 4, and differs from example 6 only in that:

in step 1), the vacuum degree was maintained at 35 Pa.

In step 2), sampling and checking at 1550 ℃.

In the step 3), the nitrogen pressure during solidification molding is 0.4 MPa.

In the step 4), the quenching treatment is to heat up to 850 ℃ and preserve heat for 1h, then heat up to 1050 ℃ and preserve heat for 3h, and air-cool to room temperature. The tempering treatment is that the temperature is kept for 2 hours at 300 ℃, and then the air cooling is carried out to the room temperature.

Example 10

The method for producing a corrosion-resistant cast iron alloy of the present example is described below with reference to example 5, and differs from example 6 only in that:

in step 1), the vacuum degree was maintained at 40 Pa.

In step 2), sampling and checking at 1550 ℃.

In the step 3), the nitrogen pressure during solidification molding is 0.5 MPa.

In the step 4), the quenching treatment is to heat up to 850 ℃ and preserve heat for 1h, then heat up to 1050 ℃ and preserve heat for 2h, and air-cool to room temperature. The tempering treatment is that the temperature is kept for 2 hours at 300 ℃, and then the air cooling is carried out to the room temperature.

Third, comparative example

The ordinary high-chromium cast iron of the comparative example consists of the following elements in mass percent: c: 3.2%, Cr: 23.7%, Mo: 0.45%, Mn: 1.23%, Si: 0.52%, Ni: 0.42%, Cu: 0.18 percent, less than or equal to 0.01 percent of P, less than or equal to 0.01 percent of S, and the balance of iron and inevitable impurities. The concrete preparation method thereof corresponds to example 6.

Fourth, example of experiment

Experimental example 1

In this experimental example, a typical region of the material of experimental example 1 was ground and polished with sandpaper, phase structure analysis was performed on an X-ray diffractometer, and the results of texture morphology analysis using a scanning electron microscope were shown in fig. 1 and 2, respectively.

As can be seen from FIG. 1, the phase composition of the material of example 1 is martensite and M₇C₃Carbide and the matrix phase are alpha-Fe single phase, and no gamma-Fe exists, so the corrosion resistance is high.

As can be seen from FIG. 2, M in the corrosion-resistant cast iron alloy prepared in example₇C₃The carbide is mainly polygonal eutectic with a cavity in the center and is secondly linear secondary precipitates with different lengths, the content of the secondary precipitates is less, the corresponding electrochemical corrosion tendency with a matrix is less, and the corrosion resistance of the material is improvedAnd (6) benefiting.

Experimental example 2

The cast iron alloys of examples 1 to 5 and comparative example were taken and tested for H at different mass fractions₂SO₄Amount of corrosion weight loss in solution. The size of the sample used for the corrosion test is 30mm × 15mm × 2mm, and the sample is polished with metallographic abrasive paper before the test, ultrasonically washed in an acetone solution, dried and weighed. The samples were placed in sulfuric acid of different mass fractions, soaked for 4 hours at room temperature, taken out, ultrasonically cleaned and dried with alcohol, weighed before and after corrosion using an analytical balance with a precision of 0.1g, and the loss of the material was used to characterize the corrosion resistance, the results are shown in fig. 3.

As can be seen from FIG. 3, the cast iron alloys of examples are significantly superior in corrosion resistance to the conventional high-chromium cast iron of comparative example, and H₂SO₄The higher the concentration of the solution, the more remarkable the improvement in corrosion resistance of the cast iron alloy of the example. The corrosion resistance of the cast iron product of the embodiment in a strong corrosion medium is improved, and the service life of corresponding iron castings such as a pump body, a valve, a pipeline and the like is prolonged.

Claims

1. The corrosion-resistant cast iron alloy is characterized by comprising the following elements in percentage by mass: n: 0.2-0.6%, C: 2.1-2.5%, Cr: 23-28%, Mo: 0.5-0.8%, Si: 0.9-1.2%, Mn: 0.5-0.8%, Al: 1.0-1.4%, P is less than or equal to 0.01%, S is less than or equal to 0.01%, rare earth elements: 0.1-0.3%, the balance being iron and unavoidable impurities; the rare earth element is cerium;

the preparation method of the corrosion-resistant cast iron alloy comprises the following steps: taking raw materials according to the proportion, smelting, and solidifying and forming the obtained smelting liquid to obtain an as-cast alloy; sequentially quenching and tempering the as-cast alloy to obtain a martensite phase and an M phase₇C₃Corrosion resistant cast iron alloys of carbide; the temperature of the quenching treatment is 850-1050 ℃, and the temperature of the tempering treatment is 270-300 ℃; the solidification molding is carried out in a nitrogen atmosphere, and the pressure of nitrogen is 0.4-0.8 MPa.

2. The corrosion-resistant cast iron alloy according to claim 1, consisting of, in mass percent: n: 0.43-0.47%, C: 2.403-2.482%, Cr: 24.78-26.31%, Mo: 0.7206-0.7672%, Si: 0.985-1.137%, Mn: 0.6613-0.6753%, Al: 1.075-1.176%, P is less than or equal to 0.01%, S is less than or equal to 0.01%, rare earth element Ce: 0.25-0.3%, and the balance of iron and inevitable impurities.

3. A method for preparing a corrosion-resistant cast iron alloy according to claim 1, comprising the steps of: taking raw materials according to the proportion, smelting, and solidifying and forming the obtained smelting liquid to obtain an as-cast alloy; sequentially quenching and tempering the as-cast alloy to obtain a martensite phase and an M phase₇C₃Corrosion resistant cast iron alloys of carbide;

the temperature of the quenching treatment is 850-1050 ℃, and the temperature of the tempering treatment is 270-300 ℃; the solidification molding is carried out in a nitrogen atmosphere, and the pressure of nitrogen is 0.4-0.8 MPa.

4. The method for preparing a corrosion-resistant cast iron alloy according to claim 3, wherein the quenching treatment comprises heating to 850 ℃ and maintaining the temperature for 1 hour, then heating to 1000-; the tempering treatment is to keep the temperature at 270-300 ℃ for 2-2.5h and then air-cool to the room temperature.

5. The method of manufacturing a corrosion-resistant cast iron alloy according to claim 3, wherein the melting is vacuum melting, and a degree of vacuum of the vacuum melting is 20 to 40 Pa.

6. The method of producing a corrosion-resistant cast iron alloy according to any one of claims 3 to 5, wherein the raw materials are Fe, Mn, Cr, Si, C, ferrochromium nitride, Al, and a rare-earth ferrosilicon alloy consisting of the following components in mass percent: ce39-42%, Si not more than 37%, Mn not more than 2.0%, and the balance of iron and inevitable impurities.