An abrasion-resistant and corrosion-resistant white cast iron for marine engineering dredging pumps and its preparation method

Abstract

The present invention discloses an abrasion-resistant and corrosion-resistant white cast iron for marine engineering dredging pumps and a preparation method thereof, which relates to the field of casting technology. The abrasion-resistant and corrosion-resistant white cast iron for marine engineering dredging pumps comprises the following components in mass percentage: Cr 23-28%, C 2.5-3.5%, Mn ≤ 1.5%, Si ≤ 1.0%, Ni ≤ 1.0%, Mo ≤ 1.0%, Cu 0.7-1.0%, Nb ≤ 0.5%, V ≤ 0.5%, and the balance is Fe. The white cast iron obtained by using the preparation method provided by the present invention has strong abrasion resistance and corrosion resistance, can also improve the casting quality while reducing energy consumption, reduce the scrap rate of castings, meet the requirements of marine engineering dredging pumps for the wear resistance and corrosion resistance of processing materials, and effectively extend the service life of dredging pumps.

Description

Technical Field:

[0001] The present invention relates to the field of casting technology, and particularly relates to an abrasion-resistant and corrosion-resistant white cast iron for marine engineering dredging pumps and a preparation method thereof. Background Art:

[0002] The rapid economic development of eastern coastal cities in China is inseparable from the development of ports. Ports serve the cities, and cities thrive with the development of ports. The expansion of urban land and the enlargement of port scale require river port dredging, reclamation, and island building, resulting in a large amount of fill soil. At the same time, the large-scale of ships will inevitably bring about the deepening of waterways. Dredging is a necessary way to solve the safe navigation of ships and the infrastructure construction of ports and waterways. At present, the urgent problem faced by dredging is the too low service life of dredging pumps, and the reason is the poor abrasion resistance and corrosion resistance of materials.

[0003] High-chromium white cast iron has the following advantages: 1) It can be cast in one molding, and the overall quality is good. Compared with welded parts, the production process is greatly reduced. 2) It has excellent abrasion resistance and good erosion resistance to media containing impurities, and is particularly suitable for the production of flow-through components of dredging pumps. 3) It has good corrosion resistance to the atmospheric environment. 4) It can be mass-produced. As long as the process is reasonable, high-quality castings can be mass-produced.

[0004] However, for large marine engineering dredging pumps, ordinary high-chromium white cast iron still has the following problems: 1) The as-cast hardness is relatively low, affecting the abrasion resistance, and the alloy composition does not consider the corrosiveness of seawater. 2) For large shells, high-chromium white cast iron is particularly prone to cracking during heat treatment. Summary of the Invention:

[0005] The technical problem to be solved by the present invention is to provide an abrasion-resistant and corrosion-resistant white cast iron for marine engineering dredging pumps and a preparation method thereof. By optimizing the component formulation and modification treatment, the abrasion resistance and corrosion resistance of white cast iron are substantially improved, thereby prolonging the service life of dredging pumps and enabling dredging pumps to be better applied to large marine engineering.

[0006] The technical problem to be solved by the present invention is achieved by adopting the following technical solutions:

[0007] One of the purposes of the present invention is to provide an abrasion-resistant and corrosion-resistant white cast iron for marine engineering dredging pumps, including the following components by mass percentage:

[0008] Cr 23 - 28%, C 2.5 - 3.5%, Mn ≤ 1.5%, Ni ≤ 1.5%, Si ≤ 1.0%, Mo ≤ 1.0%, Cu 0.7 - 1.0%, Nb ≤ 0.5%, and the balance is Fe.

[0009] Preferably, the hardness HRC of the abrasion-resistant and corrosion-resistant white cast iron is greater than 55.

[0010] The second object of the present invention is to provide a preparation method of the wear-resistant and corrosion-resistant white cast iron for marine engineering dredging pumps as described above, including the following preparation steps:

[0011] (1) Heat scrap steel, pig iron, high-carbon ferrochromium, nickel plates, ferromolybdenum and waste brass in an intermediate frequency induction furnace until melting. After the molten iron is melted and clarified, add ferrosilicon, ferromanganese, ferroniobium and ferrovanadium, and further clarify;

[0012] (2) When the melting temperature rises to 1550 - 1600 °C, add aluminum for deoxidation;

[0013] (3) When the temperature of the molten iron drops to 1350 - 1450 °C, pour the molten iron into the sand mold to obtain white cast iron parts;

[0014] (4) Heat-treat the white cast iron parts.

[0015] Preferably, the heat treatment includes quenching and tempering, and the specific conditions are: first heat up to 1000 - 1050 °C and hold for 3 - 8 h, then take out of the furnace and air-cool to 450 - 500 °C and transfer to a tempering furnace, hold at 450 - 500 °C for 5 - 10 h, and take out of the furnace and air-cool to room temperature.

[0016] Preferably, the heating rate of the heat treatment is 20 - 50 °C / min.

[0017] Preferably, the addition amount of aluminum is 0.1 - 0.3% of the mass of the white cast iron parts.

[0018] Adding Cu element can partly prevent the high-chromium cast iron from interphase corrosion. The distribution state of copper in the matrix is different from that of chromium in the matrix. The copper content is higher around the carbides, while the chromium content is lower around the carbides; since Cu is dissolved in the matrix, its electrode potential is increased. In this way, the corrosion resistance reduced due to the reduction of chromium around the carbides can be increased to a certain extent by the Cu enriched around the carbides, thereby hindering the occurrence of interphase corrosion to a certain extent. The matrix tissue corrosion potential of the high-chromium cast iron with added copper is significantly higher than the matrix potential of the high-chromium cast iron without added copper. Therefore, the role of copper is to promote the passivation of the matrix, make the passivation film more stable, at the same time increase the corrosion potential of the matrix and reduce the corrosion rate.

[0019] The third object of the present invention is to provide a wear-resistant and corrosion-resistant white cast iron for marine engineering dredging pumps, including the following components by mass percentage:

[0020] Cr 23 - 28%, C 2.5 - 3.5%, Mn ≤ 1.5%, Ni ≤ 1.5%, Si ≤ 1.0%, composite modifier 0.5 - 1.0%, Mo ≤ 1.0%, Cu 0.7 - 1.0%, Nb ≤ 0.5%, and the balance is Fe.

[0021] Modification treatment makes the primary austenite grains of high chromium cast iron refined and transforms from columnar crystals to equiaxed crystals. After modification treatment, the martensite content in the structure increases, and the eutectic carbide is refined. Moreover, the continuous and thick network is locally disconnected, and the eutectic carbide tends to transform into isolated strip and short rod shapes. Therefore, the hardness of the material is significantly improved.

[0022] Preferably, the composite modifier is Re-B-V-Ti, where Re is 5-10%, B is 1-3%, V is 2-5%, and the balance is Ti, by mass percentage.

[0023] Re and B have the effect of promoting martensite transformation. Modification treatment increases the proportion of martensite and decreases the proportion of retained austenite in the structure. The increase in martensite structure is not conducive to the improvement of toughness, but modification treatment refines the grains, especially the breaking of the eutectic carbide network at the grain boundaries plays a dominant role in the improvement of toughness. Therefore, the comprehensive effect of modification treatment is to improve toughness.

[0024] Both V and Ti can combine with C to form carbides, which act as foreign cores during crystallization, control the growth of grains and the movement of carbide grain boundaries, refine the structure, and improve the distribution of carbides; the high-hardness VC and TiC can also improve the wear resistance of the material.

[0025] Preferably, the composite modifier is CaC2.

[0026] The addition of CaC2 can provide heterogeneous cores for austenite, resulting in an increase in the number of carbide nucleations, while hindering the growth of carbides, refining the carbides, and making the carbide distribution more uniform.

[0027] Preferably, the hardness HRC of the wear-resistant and corrosion-resistant white cast iron is greater than 60.

[0028] The fourth object of the present invention is to provide a wear-resistant and corrosion-resistant white cast iron for a marine engineering dredging pump as described above, including the following preparation steps:

[0029] (1) Heat scrap steel, pig iron, high-carbon ferrochromium, nickel plate, ferromolybdenum, and waste brass in an intermediate frequency induction furnace until melted. After the molten iron is melted and clarified, add ferrosilicon, ferromanganese, ferrocolumbium, and ferrovanadium, and further clarify.

[0030] (2) When the melting temperature rises to 1550-1600 °C, add aluminum for deoxidation, and then pour the molten iron into a ladle. The composite modifier is pre-added to the ladle.

[0031] (3) When the temperature of the molten iron in the ladle drops to 1350-1450 °C, pour the molten iron into a sand mold to obtain a white cast iron part.

[0032] (4) Perform heat treatment on the white cast iron part.

[0033] Preferably, the heat treatment includes quenching and tempering, and the specific conditions are as follows: first, heat up to 1000 - 1050 °C and hold for 3 - 8 h, then take it out of the furnace and air-cool to 450 - 500 °C, transfer it to a tempering furnace, hold at 450 - 500 °C for 5 - 10 h, and then take it out of the furnace and air-cool to room temperature.

[0034] Preferably, the addition amount of aluminum is 0.1 - 0.3% of the mass of the white cast iron parts.

[0035] The beneficial effects of the present invention are as follows:

[0036] 1. The hardness of traditional white cast materials is only about HRC45. To achieve high abrasion resistance, its Rockwell hardness should be greater than HRC55, and generally heat treatment is required, but the crack tendency is serious; at the same time, the heating rate during heat treatment is low, the equipment utilization rate is low, and due to the high heating and holding temperatures, the energy waste is serious; and during the heating and air-cooling processes, large parts are extremely prone to cracking and scrapping. The white cast iron prepared by the present invention has strong abrasion resistance, can meet the requirements of the wear resistance of the processing materials for the marine engineering dredging pump, can also shorten the heat treatment time, significantly improve the casting quality while reducing energy consumption, and reduce the casting scrap rate.

[0037] 2. The present invention improves the corrosion resistance by adding a small amount of Cu to the white cast iron, so that the prepared white cast iron can meet the requirements of the corrosion resistance of the processing materials for the marine engineering dredging pump, and effectively extends the service life of the dredging pump. Specific embodiments:

[0038] In order to make the technical means, creative features, achieved purposes and effects of the present invention easy to understand, the present invention will be further described below in conjunction with specific embodiments.

[0039] Example 1

[0040] The white cast iron includes the following components in mass percentage:

[0041] Cr 23%, C 3%, Mn 1.2%, Ni 1.25%, Si 0.8%, Mo 1.0%, Cu 0.85%, Nb 0.34%, and the balance is Fe.

[0042] The preparation method of the white cast iron includes the following preparation steps:

[0043] (1) According to the above composition ratio, scrap steel, pig iron, high-carbon ferrochrome, nickel plate, ferromolybdenum and waste brass are heated to melting in an intermediate frequency induction furnace. After the molten iron is melted and clarified, ferrosilicon, ferromanganese, ferroniobium and ferrovanadium are added to further clarify it.

[0044] (2) When the melting temperature rises to 1580 °C, add aluminum for deoxidation, and the addition amount of aluminum is 0.2% of the mass of the white cast iron part.

[0045] (3) When the temperature of the molten iron drops to 1420 °C, pour the molten iron into the sand mold to obtain a white cast iron part.

[0046] (4) Heat-treat the white cast iron part, and the specific conditions are: first raise the temperature to 1020 °C at a heating rate of 30 °C / min and hold for 5 h, then take it out of the furnace and air-cool it to 500 °C and transfer it to a tempering furnace, hold at 500 °C for 8 h, and then take it out of the furnace and air-cool it to room temperature.

[0047] Example 2

[0048] The white cast iron includes the following components by mass percentage:

[0049] Cr 24%, C 2.5%, Mn 1.3%, Ni 1.5%, Si 0.7%, Mo 1.0%, Cu 0.8%, Nb 0.29%, and the balance is Fe.

[0050] The preparation method of the white cast iron includes the following preparation steps:

[0051] (1) According to the above component ratio, heat scrap steel, pig iron, high-carbon ferrochrome, nickel plate, ferromolybdenum, and waste brass in an intermediate frequency induction furnace until melted. After the molten iron is melted and clarified, add ferrosilicon, ferromanganese, ferrocolumbium, and ferrovanadium to further clarify it.

[0052] (2) When the melting temperature rises to 1585 °C, add aluminum for deoxidation, and the addition amount of aluminum is 0.3% of the mass of the white cast iron part.

[0053] (3) When the temperature of the molten iron drops to 1430 °C, pour the molten iron into the sand mold to obtain a white cast iron part.

[0054] (4) Heat-treat the white cast iron part, and the specific conditions are: first raise the temperature to 1050 °C at a heating rate of 35 °C / min and hold for 5 h, then take it out of the furnace and air-cool it to 450 °C and transfer it to a tempering furnace, hold at 450 °C for 10 h, and then take it out of the furnace and air-cool it to room temperature.

[0055] Example 3

[0056] The white cast iron includes the following components by mass percentage:

[0057] Cr 25%, C 2.8%, Mn 1.25%, Ni 1.5%, Si 0.6%, Mo 0.8%, Cu 0.9%, Nb 0.28%, and the balance is Fe.

[0058] The preparation method of the white cast iron includes the following preparation steps:

[0059] (1) According to the above component ratio, scrap steel, pig iron, high-carbon ferrochromium, nickel plate, ferromolybdenum, and scrap brass are heated to melting in an intermediate frequency induction furnace. After the molten iron is melted and clarified, ferrosilicon, ferromanganese, ferroniobium, and ferrovanadium are added for further clarification.

[0060] (2) When the melting temperature rises to 1600 °C, aluminum is added for deoxidation, and the addition amount of aluminum is 0.15% of the mass of the white cast iron part.

[0061] (3) When the temperature of the molten iron drops to 1400 °C, the molten iron is poured into the sand mold to obtain a white cast iron part.

[0062] (4) The white cast iron part is heat-treated. The specific conditions are as follows: First, it is heated to 1030 °C at a heating rate of 40 °C / min and held for 6 h, then taken out of the furnace and air-cooled to 480 °C and transferred to a tempering furnace, held at 480 °C for 8 h, and then taken out of the furnace and air-cooled to room temperature.

[0063] Example 4

[0064] The white cast iron includes the following components by mass percentage:

[0065] Cr 26%, C 3.2%, Mn 1.0%, Ni 1.35%, Si 0.9%, Mo 0.85%, Cu 1.0%, Nb 0.25%, and the balance is Fe.

[0066] The preparation method of the white cast iron includes the following preparation steps:

[0067] (1) According to the above component ratio, scrap steel, pig iron, high-carbon ferrochromium, nickel plate, ferromolybdenum, and scrap brass are heated to melting in an intermediate frequency induction furnace. After the molten iron is melted and clarified, ferrosilicon, ferromanganese, ferroniobium, and ferrovanadium are added for further clarification.

[0068] (2) When the melting temperature rises to 1550 °C, aluminum is added for deoxidation, and the addition amount of aluminum is 0.25% of the mass of the white cast iron part.

[0069] (3) When the temperature of the molten iron drops to 1390 °C, the molten iron is poured into the sand mold to obtain a white cast iron part.

[0070] (4) The white cast iron part is heat-treated. The specific conditions are as follows: First, it is heated to 1000 °C at a heating rate of 50 °C / min and held for 6 h, then taken out of the furnace and air-cooled to 500 °C and transferred to a tempering furnace, held at 500 °C for 10 h, and then taken out of the furnace and air-cooled to room temperature.

[0071] Example 5

[0072] The white cast iron includes the following components by mass percentage:

[0073] Cr 28%, C 3.5%, Mn 1.1%, Ni 1.2%, Si 0.7%, Mo 0.8%, Cu 1.0%, Nb 0.18%, the balance being Fe.

[0074] The preparation method of white cast iron comprises the following preparation steps:

[0075] (1) According to the above component ratio, scrap steel, pig iron, high-carbon ferrochrome, nickel plate, ferromolybdenum and waste brass are heated to melting in an intermediate frequency induction furnace. After the molten iron is melted clear, ferrosilicon, ferromanganese, ferrocolumbium and ferrovanadium are added and further melted clear.

[0076] (2) When the melting temperature rises to 1590 °C, aluminum is added for deoxidation, and the addition amount of aluminum is 0.2% of the mass of the white cast iron parts.

[0077] (3) When the temperature of the molten iron drops to 1440 °C, the molten iron is poured into the sand mold to obtain white cast iron parts.

[0078] (4) Heat treatment is carried out on the white cast iron parts. The specific conditions are as follows: First, it is heated to 1050 °C at a heating rate of 30 °C / min and held for 5 h, then taken out of the furnace and air-cooled to 470 °C and transferred to a tempering furnace, held at 470 °C for 5 h, and then taken out of the furnace and air-cooled to room temperature.

[0079] Example 6

[0080] The white cast iron comprises the following components by mass percentage:

[0081] Cr 26%, C 3.2%, Mn 1.0%, Ni 1.35%, Si 0.9%, complex modifier 1.0%, Mo 0.85%, Cu 1.0%, Nb 0.25%, the balance being Fe.

[0082] The preparation method of white cast iron comprises the following preparation steps:

[0083] (1) According to the above component ratio, scrap steel, pig iron, high-carbon ferrochrome, nickel plate, ferromolybdenum and waste brass are heated to melting in an intermediate frequency induction furnace. After the molten iron is melted clear, ferrosilicon, ferromanganese, ferrocolumbium and ferrovanadium are added and further melted clear.

[0084] (2) When the melting temperature rises to 1550 °C, aluminum is added for deoxidation, and the addition amount of aluminum is 0.25% of the mass of the white cast iron parts; then the molten iron is taken out of the furnace and put into a ladle, and a complex modifier Re-B-V-Ti is pre-added to the ladle, where Re is 8%, B is 3%, V is 4%, and the balance is Ti, by mass percentage.

[0085] (3) When the temperature of the molten iron in the ladle drops to 1390 °C, the molten iron is poured into the sand mold to obtain white cast iron parts.

[0086] (4) Heat-treat the white cast iron parts, with the specific conditions being: first, raise the temperature to 1000°C at a heating rate of 50°C / min and hold for 3 h, then take out of the furnace and air-cool to 500°C, transfer to a tempering furnace, hold at 500°C for 5 h, and then take out of the furnace and air-cool to room temperature.

[0087] Example 7

[0088] The white cast iron includes the following components by mass percentage:

[0089] Cr 26%, C 3.2%, Mn 1.0%, Ni 1.35%, Si 0.9%, complex modifier 1%, Mo 0.85%, Cu 1.0%, Nb 0.25%, and the balance is Fe.

[0090] The preparation method of the white cast iron includes the following preparation steps:

[0091] (1) According to the above component ratio, heat scrap steel, pig iron, high-carbon ferrochrome, nickel plate, ferromolybdenum, and waste brass in an intermediate frequency induction furnace until melted. After the molten iron is completely melted, add ferrosilicon, ferromanganese, ferroniobium, and ferrovanadium, and further melt until clear.

[0092] (2) When the melting temperature rises to 1550°C, add aluminum for deoxidation, and the addition amount of aluminum is 0.25% of the mass of the white cast iron parts; then pour the molten iron out of the furnace into a ladle, and pre-add a complex modifier Re-B-V-Ti in the ladle, where Re is 10%, B is 3%, V is 5%, and the balance is Ti, by mass percentage.

[0093] (3) When the temperature of the molten iron in the ladle drops to 1390°C, pour the molten iron into the sand mold to obtain white cast iron parts.

[0094] (4) Heat-treat the white cast iron parts, with the specific conditions being: first, raise the temperature to 1000°C at a heating rate of 50°C / min and hold for 3 h, then take out of the furnace and air-cool to 500°C, transfer to a tempering furnace, hold at 500°C for 5 h, and then take out of the furnace and air-cool to room temperature.

[0095] Example 8

[0096] Replace the complex modifier in Example 6 with CaC2, and the other conditions are exactly the same as those in Example 6.

[0097] Example 9

[0098] Replace the complex modifier in Example 7 with CaC2, and the other conditions are exactly the same as those in Example 6.

[0099] Comparative Example 1

[0100] Replace the composite modifier in Example 6 with Re-V-Ti, where Re is 8%, V is 4%, and the balance is Ti, by mass percentage, and the other conditions are exactly the same as those in Example 6.

[0101] Comparative Example 2

[0102] Replace the composite modifier in Example 6 with B-V-Ti, where B is 3%, V is 4%, and the balance is Ti, by mass percentage, and the other conditions are exactly the same as those in Example 6.

[0103] Comparative Example 3

[0104] Replace the composite modifier in Example 8 with CaO, and the other conditions are exactly the same as those in Example 8.

[0105] Cut the white cast iron parts prepared in Examples 1-9 and Comparative Examples 1-3 into specimens of 20mm×20mm×20mm, and test the hardness HRC with a Rockwell hardness tester. Test 5 times in parallel and take the average value.

[0106] Cut the white cast iron parts prepared in Examples 1-9 and Comparative Examples 1-3 into unnotched specimens of 20mm×20mm×110mm, and test the impact toughness with a JB-300B semi-automatic impact testing machine. Test 5 times in parallel and take the average value.

[0107] The test results are shown in Table 1.

[0108] Table 1 Hardness and impact toughness of white cast iron parts prepared in Examples 1-9 and Comparative Examples 1-3

[0109]

[0110]

[0111] It can be seen from Table 1 that through the modification treatment of the present invention, the hardness and impact toughness of white cast iron parts can be significantly improved.

[0112] The above shows and describes the basic principles, main features and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited by the above embodiments. What is described in the above embodiments and the specification only illustrates the principle of the present invention. Without departing from the spirit and scope of the present invention, the present invention will have various changes and improvements, and these changes and improvements all fall within the scope of the present invention claimed. The scope of protection claimed by the present invention is defined by the appended claims and their equivalents.

Claims

1. An abrasion-resistant and corrosion-resistant white cast iron for marine engineering dredging pumps, characterized in that: Comprising components with the following mass percentages: Cr 23 - 28%, C 2.5 - 3.5%, Mn 1.0 - 1.5%, Ni 1.2 - 1.5%, Si 0.6 - 1.0%, composite modifier 0.5 - 1.0%, Mo 0.8 - 1.0%, Cu 0.7 - 1.0%, Nb 0.18 - 0.5%, the balance being Fe; The composite modifier is Re - B - V - Ti, wherein Re is 5 - 10%, B is 1 - 3%, V is 2 - 5%, and the balance is Ti, by mass percentage.

2. The abrasion-resistant and corrosion-resistant white cast iron for marine engineering dredging pumps according to claim 1, wherein: The hardness HRC of the wear - resistant and corrosion - resistant white cast iron is greater than 60.

3. The preparation method of the wear-resistant and corrosion-resistant white cast iron for the ocean engineering dredging pump according to claim 1, characterized in that: Including the following preparation steps: (1) Heat scrap steel, pig iron, high - carbon ferrochrome, nickel plate, ferromolybdenum, and waste brass in an intermediate - frequency induction furnace until melted. After the molten iron is melted clear, add ferrosilicon, ferromanganese, ferroniobium, and ferrovanadium to further melt clear. (2) When the melting temperature rises to 1550 - 1600 °C, add aluminum for deoxidation, then pour the molten iron into a ladle, and pre - add the composite modifier into the ladle. (3) When the temperature of the molten iron in the ladle drops to 1350 - 1450 °C, pour the molten iron into a sand mold to obtain a white cast iron part. (4) Conduct heat treatment on the white cast iron part.

4. The preparation method according to claim 3, characterized in that: The heat treatment includes quenching and tempering, and the specific conditions are: first heat up to 1000 - 1050 °C and hold for 3 - 8 h, then take it out of the furnace and air - cool to 450 - 500 °C and transfer it to a tempering furnace, hold at 450 - 500 °C for 5 - 10 h, and take it out of the furnace and air - cool to room temperature.

5. The preparation method according to claim 3, characterized in that: The addition amount of aluminum is 0.1 - 0.3% of the mass of the white cast iron part.

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