Corrosion-resistant iron-based materials for aluminum alloy die casting molds and their strengthening and toughening heat treatment methods

Abstract

This invention discloses an anti-erosion iron-based material for aluminum alloy die-casting molds, composed of the following raw material components by mass percentage: C 3.5%, Si 1.5%, Ni 1.6%, Cr 0.4%, Mo 1.1%, V 0.6%, Al 0.2%, other alloying elements ≤1.0%, and the balance being Fe. The total content of all the above components should be 100%. This invention also discloses a strengthening and toughening heat treatment method for this material: Step 1, the material is heated and held at a specific temperature in a protective atmosphere furnace using a staged heating method, followed by staged cooling, and then air-cooled to obtain a first metal; Step 2, the first metal is heated and held at a specific temperature, and then quenched in preheated oil to obtain a second metal; Step 3, the second metal is heated and held at a specific temperature to obtain the final product. The anti-erosion iron-based material for aluminum alloy die-casting molds, after undergoing the strengthening and toughening heat treatment method of this invention, significantly improves the material's strength and toughness properties, extending its service life in aluminum alloy die-casting molds.

Description

Technical Field

[0001] This invention belongs to the technical field of aluminum alloy die casting mold materials, specifically relating to erosion-resistant iron-based materials for aluminum alloy die casting molds. This invention also relates to a strengthening and toughening heat treatment method for erosion-resistant iron-based materials for aluminum alloy die casting molds. Background Technology

[0002] Currently, aluminum alloy die casting molds mostly use medium carbon Cr5Mo2V1 series hot work die steels such as H13, DAC, DH31, and Dievar, which are developed by hot forging of steel parts. Although these steels have excellent high-temperature strength and impact toughness, the Fe, Cr and other metal elements and their oxides in their matrix can all undergo an exothermic "aluminothermic reaction" with the Al element in the high-temperature aluminum melt. As a result, each die casting mold worth hundreds of thousands or millions of dollars often fails prematurely due to the aluminum melt corroding the mold cavity surface.

[0003] Studies have found that ductile iron with appropriate amounts of Ni, Cr, Mo, and V can still maintain a hardness of no less than 45 HRC after tempering at 600℃ for 2 hours. However, the presence of Ni, Cr, Mo, and V in ductile iron results in a large number of primary carbides. The presence of these coarse primary carbides significantly reduces the amount of chromium, molybdenum, and vanadium dissolved in the iron matrix, thereby weakening the dispersion strengthening effect after high-temperature tempering. In addition, these coarse carbides also make ductile iron extremely tough. As a result, although the material exhibits good high-temperature structural stability, it still exhibits poor thermal fatigue performance.

[0004] To improve the thermal fatigue properties of Ni, Cr, Mo, and V alloyed ductile iron, it is necessary to eliminate the coarse primary carbides. In addition, because graphite can provide a continuous supply of carbon atoms, ductile iron forms high-carbon austenite during high-temperature austenitization and obtains a high-carbon matrix structure after heat treatment, which is not conducive to improving toughness. Summary of the Invention

[0005] The purpose of this invention is to provide an anti-erosion iron-based material for aluminum alloy die-casting molds, which solves the problem of poor strength and toughness of ductile iron containing Ni, Cr, Mo and V in the prior art.

[0006] Another object of the present invention is to provide a method for strengthening and toughening heat treatment of erosion-resistant iron-based materials for aluminum alloy die-casting molds.

[0007] The technical solution adopted in this invention is that the anti-corrosion iron-based material for aluminum alloy die casting molds is composed of the following raw material components by mass percentage: C 3.5%, Si 1.5%, Ni 1.6%, Cr 0.4%, Mo 1.1%, V 0.6%, Al 0.2%, other alloying elements ≤1.0%, and the balance being Fe. The total content of the above components should be 100%.

[0008] Another technical solution adopted in this invention is a heat treatment method for strengthening and toughening erosion-resistant iron-based materials for aluminum alloy die-casting molds, which is implemented according to the following steps:

[0009] Step 1: The material is heated and held at a temperature in a protective atmosphere furnace using a staged heating method. After holding at a temperature, it is cooled in stages and then removed and air-cooled to obtain the first metal.

[0010] Step 2: Heat and hold the first metal at that temperature, then quench it in preheated oil to obtain the second metal;

[0011] Step 3: Heat and hold the second metal at that temperature to obtain the final product.

[0012] Another feature of the technical solution of the present invention is that:

[0013] The protective atmosphere in the atmosphere protection furnace in step 1 adopts one of the following two protective atmospheres: The first protective atmosphere is an R atmosphere composed of 19%–20% CO, 40%–41% H2 and 38%–39% N2. X An endothermic atmosphere is used as a dilution protective atmosphere, and CH4 and air are introduced through a carbon control system to control and adjust the amount of CH4 and air introduced so that the carbon potential CP value in the furnace is within the set carbon potential CP range; the second protective atmosphere consists of nitrogen and propane gas with a purity of 99.99%, and the ratio of nitrogen to propane gas is 20 to 30:1.

[0014] The specific steps of the graded heating in step 1 are as follows: Under the first protective atmosphere, the material is heated to 750℃ and held for 1 hour at a carbon potential CP of 0.75% to 0.85%. Then, the temperature is raised to 850℃ and held for 1 hour at a carbon potential CP of 1.00% to 1.10%. The temperature is then raised to 920℃ and held for 1 hour at a carbon potential CP of 1.30% to 1.40%. Finally, the temperature is raised to 940℃-1100℃ and held for 1-5 hours at a carbon potential CP of 1.55% to 1.65%.

[0015] The specific steps of cooling in step 1 are as follows: at a rate of 20℃ / h-60℃ / h, the temperature is gradually reduced to 950℃ and held for 1h-2h at a carbon potential CP of 1.30%-1.40%. Then, the temperature is further reduced to 850℃ and held for 1h-2h at a carbon potential CP of 1.00%-1.10%. Then, the temperature is further reduced to 700℃ and held for 0.5h-1h at a carbon potential CP of 0.65%-0.75%. Finally, the temperature is further reduced to 650℃ and held for 1h under nitrogen protection with a purity of 99.99%. After that, the temperature is removed and air-cooled to room temperature.

[0016] The flow rate of the protective atmosphere gas in step 1 is 8m³. 3 / h.

[0017] In step 2, the first metal is heated to an austenitizing temperature of 850℃-950℃, held for 5min-10min, and the temperature of the quenching medium oil is 100℃-200℃.

[0018] In step 2, the interval between removing the item from the atmosphere furnace and quenching it in oil should not exceed 60 seconds.

[0019] The heating temperature in step 3 is 300℃-600℃, and the holding time is 0.5h-3h.

[0020] The beneficial effects of this invention are:

[0021] (1) The aluminum alloy die-casting mold uses iron-based metal material with a small amount of Al replacing Si, so that the Si content is no more than 2%, which reduces the brittleness of the material; (2) The high spheroid number in the iron-based metal can reduce the wetting of the material with the aluminum liquid and improve the corrosion resistance of the material; (3) The low carbon martensite of the iron-based metal and the fine dispersed Cr, Mo, V and other carbides thereon ensure the strength and toughness of the material and thus improve the thermal fatigue performance; (4) The high solid solution temperature in step 1 of the toughening heat treatment method of the present invention can make the solidified dendrite segregated chromium, molybdenum and vanadium uniformly distributed in the austenite. The ferrite matrix is ​​subjected to graded slow cooling to ensure that the graphite (carbon atoms) generated from the decomposition of a small amount of chromium, molybdenum and vanadium primary carbides that are unavoidable during solidification are diffused and aggregated into graphite spheres to avoid the formation of secondary carbides, thus obtaining a full ferrite matrix; (5) In step 2 of the toughening heat treatment method of the present invention, the rapid heating and short-time heat treatment controls the total amount of internal carburization of graphite into austenite, so that low-carbon martensite is obtained by quenching; (6) In step 3 of the toughening heat treatment method of the present invention, high-temperature tempering promotes the precipitation of fine and dispersed Cr, Mo and V carbides, ensuring the high strength of the material. Attached Figure Description

[0022] Figure 1 This is a microscopic photograph of the distribution state of ductile iron in the iron-based metal material in Embodiment 1 of the present invention;

[0023] Figure 2This is a micrograph of the all-ferrite matrix obtained by graded heating and cooling of the iron-based metal material in Embodiment 2 of the present invention;

[0024] Figure 3 This is a microstructure diagram of the iron-based metal material obtained after high-temperature tempering in Example 3 of the present invention, which contains a large amount of dispersed second phase. Detailed Implementation

[0025] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments.

[0026] The erosion-resistant iron-based material for aluminum alloy die-casting molds is composed of the following raw material components by mass percentage: C 3.5%, Si 1.5%, Ni 1.6%, Cr 0.4%, Mo 1.1%, V 0.6%, Al 0.2%, other alloying elements ≤1.0%, and the balance being Fe. The total content of the above components should be 100%.

[0027] The heat treatment method for strengthening and toughening erosion-resistant iron-based materials used in aluminum alloy die-casting molds is implemented according to the following steps:

[0028] Step 1: The material is heated and held at a temperature in a protective atmosphere furnace using a staged heating method. After holding at a temperature, it is cooled in stages and then removed and air-cooled to obtain the first metal.

[0029] The protective atmosphere in the atmosphere protection furnace in step 1 adopts one of the following two protective atmospheres: The first protective atmosphere is an R atmosphere composed of 19%–20% CO, 40%–41% H2 and 38%–39% N2. X An endothermic atmosphere is used as a dilution protective atmosphere. CH4 gas, which can increase the CP value, and air, which can decrease the CP value, are automatically introduced through the carbon control system. The amount of CH4 and air introduced is controlled and adjusted so that the carbon potential CP value in the furnace is within the set carbon potential CP range. The second protective atmosphere consists of nitrogen gas and propane gas with a purity of 99.99%, and the ratio of nitrogen gas to propane gas is 20 to 30:1. The propane gas introduced into the furnace will decompose into carbon and hydrogen at high temperature. The carbon and hydrogen will consume the oxidizing elements CO2, H2O and O2 in the furnace to prevent the material from being oxidized and decarburized at high temperature.

[0030] The specific steps of the graded heating in step 1 are as follows: when the material is in the first protective atmosphere, it is heated to 750℃ and held for 1 hour under a carbon potential CP of 0.75% to 0.85%, then heated to 850℃ and held for 1 hour under a carbon potential CP of 1.00% to 1.10%, then heated to 920℃ and held for 1 hour under a carbon potential CP of 1.30% to 1.40%, and then heated to 940℃-1100℃ and held for 1-5 hours under a carbon potential CP of 1.55% to 1.65%.

[0031] The specific steps of cooling in step 1 are as follows: at a rate of 20℃ / h-60℃ / h, the temperature is gradually reduced to 950℃ and held for 1h-2h at a carbon potential CP of 1.30%-1.40%. Then, the temperature is further reduced to 850℃ and held for 1h-2h at a carbon potential CP of 1.00%-1.10%. Then, the temperature is further reduced to 700℃ and held for 0.5h-1h at a carbon potential CP of 0.65%-0.75%. Finally, the temperature is further reduced to 650℃ and held for 1h under nitrogen protection with a purity of 99.99%. The temperature is then removed and air-cooled to room temperature.

[0032] The flow rate of the protective atmosphere gas in step 1 is 8m³. 3 / h;

[0033] The high solution temperature is to ensure that the chromium, molybdenum, and vanadium segregated by the solidification dendrites are uniformly distributed in the austenitic matrix. The staged slow cooling ensures that the small amount of graphite (carbon atoms) that inevitably forms primary chromium, molybdenum, and vanadium carbides during solidification diffuses and aggregates into existing graphite spheres, preventing the formation of secondary carbides and resulting in a fully ferrite matrix. The CH4 protective atmosphere is used to prevent decarburization of the sample during heat treatment.

[0034] Step 2: Rapidly heat the first metal to the austenitizing temperature and hold it at that temperature, then quench it in preheated oil to obtain the second metal;

[0035] In step 2, the first metal is heated to the austenitizing temperature of 850℃-950℃, and the holding time is 5min-10min. The temperature of the quenching medium oil is 100℃-200℃.

[0036] Rapid heating to the austenitizing temperature and holding for a short time is to control the total amount of carburization of graphite into the austenite. After quenching, low-carbon martensite is obtained to ensure the toughness of the material.

[0037] In step 2, the interval between removing the item from the atmosphere furnace and quenching it in oil should not exceed 60 seconds.

[0038] Step 3: Heat and hold the second metal to obtain an iron-based metal material for die casting aluminum alloys that has both high strength and toughness and is resistant to corrosion.

[0039] The heating temperature in step 3 is 300℃-600℃, and the holding time is 0.5h-3h. This is to precipitate dispersed Cr, Mo, and V carbides in the low-carbon martensitic matrix to improve its strength.

[0040] Example 1

[0041] The heat treatment method for strengthening and toughening erosion-resistant iron-based materials used in aluminum alloy die-casting molds is implemented according to the following steps:

[0042] Step 1: Add material at a flow rate of 8m³ / min 3 / h of R XIn an atmosphere-protected furnace, the temperature was first raised to 750℃ and held for 1 hour under CP 0.8%, then raised to 850℃ and held for 1 hour under CP 1.05%, then raised to 920℃ and held for 1 hour under CP 1.35%, then raised to 1000℃ and held for 2 hours under CP 1.6%. The temperature was then reduced in stages at a rate of 20℃ / h. The temperature was lowered to 950℃ under CP 1.35% and held for 2 hours, then lowered to 850℃ under CP 1.05% and held for 1 hour, then lowered to 700℃ under CP 0.7% and held for 0.5 hours, and then lowered to 650℃ under nitrogen protection and held for 1 hour. The furnace was then removed and air-cooled to room temperature.

[0043] Step 2: Rapidly heat the first metal obtained in Step 1 to 850°C and hold for 10 minutes, then quickly quench it in oil at 200°C to obtain the second metal.

[0044] Step 3: Heat the second metal obtained in Step 2 to 600℃ and hold for 2 hours to obtain an iron-based metal material for die casting aluminum alloys that combines high strength, toughness, and corrosion resistance. Figure 1 As shown.

[0045] Example 2

[0046] The heat treatment method for strengthening and toughening erosion-resistant iron-based materials used in aluminum alloy die-casting molds is implemented according to the following steps:

[0047] Step 1: Add material at a flow rate of 8m³ / min 3 / h of R X In an atmosphere-protected furnace, the temperature was first raised to 750℃ and held for 1 hour under CP 0.8%, then raised to 850℃ and held for 1 hour under CP 1.05%, then raised to 920℃ and held for 1 hour under CP 1.35%, then raised to 1000℃ and held for 2 hours under CP 1.6%, and then cooled in stages at a rate of 40℃ / h. The temperature was lowered to 950℃ under CP 1.35% and held for 2 hours, then lowered to 850℃ and held for 1 hour under CP 1.05%, then lowered to 700℃ and held for 0.5 hours under CP 0.7%, and then lowered to 650℃ and held for 1 hour under nitrogen protection. The furnace was then removed and air-cooled to room temperature.

[0048] Step 2: Rapidly heat the first metal obtained in Step 1 to 950°C and hold for 5 minutes, then quickly quench it in oil at 200°C to obtain the second metal.

[0049] Step 3: Heat the second metal obtained in Step 2 to 600℃ and hold for 2 hours to obtain an iron-based metal material for die casting aluminum alloys that combines high strength, toughness, and corrosion resistance. Figure 2 As shown.

[0050] Example 3

[0051] The heat treatment method for strengthening and toughening erosion-resistant iron-based materials used in aluminum alloy die-casting molds is implemented according to the following steps:

[0052] Step 1: Add material at a flow rate of 8m³ / min 3 / h of R X In an atmosphere-protected furnace, the temperature was first raised to 750℃ and held for 1 hour under CP 0.8%, then raised to 850℃ and held for 1 hour under CP 1.05%, then raised to 920℃ and held for 1 hour under CP 1.35%, then raised to 1000℃ and held for 2 hours under CP 1.6%, and then cooled in stages at a rate of 30℃ / h. The temperature was lowered to 950℃ under CP 1.35% and held for 2 hours, then lowered to 850℃ and held for 1 hour under CP 1.05%, then lowered to 700℃ and held for 0.5 hours under CP 0.7%, and then lowered to 650℃ and held for 1 hour under nitrogen protection. The furnace was then removed and air-cooled to room temperature.

[0053] Step 2: The first metal obtained in Step 1 is rapidly heated to 850°C and held at that temperature for 8 minutes, then quickly quenched in oil at 200°C to obtain the second metal.

[0054] Step 3: Heat the second metal obtained in Step 2 to 600℃ and hold for 2 hours to obtain an iron-based metal material for die casting aluminum alloys that combines high strength, toughness, and corrosion resistance. Figure 3 As shown.

[0055] Example 4

[0056] The heat treatment method for strengthening and toughening erosion-resistant iron-based materials used in aluminum alloy die-casting molds is implemented according to the following steps:

[0057] Step 1: Add material at a flow rate of 8m³ / min 3 / h of R X In an atmosphere-protected furnace, the temperature was first raised to 750℃ and held for 1 hour under CP 0.8%, then raised to 850℃ and held for 1 hour under CP 1.05%, then raised to 920℃ and held for 1 hour under CP 1.35%, then raised to 1000℃ and held for 2 hours under CP 1.6%. The temperature was then reduced in stages at a rate of 50℃ / h. The temperature was lowered to 950℃ under CP 1.35% and held for 2 hours, then lowered to 850℃ under CP 1.05% and held for 1 hour, then lowered to 700℃ under CP 0.7% and held for 0.5 hours, and then lowered to 650℃ under nitrogen protection and held for 1 hour. The furnace was then removed and air-cooled to room temperature.

[0058] Step 2: The first metal obtained in Step 1 is rapidly heated to 900°C and held at that temperature for 8 minutes, then quickly quenched in oil at 200°C to obtain the second metal.

[0059] Step 3: Heat the second metal obtained in Step 2 to 400℃ and hold for 3 hours to obtain an iron-based metal material for die casting of aluminum alloy that has both high strength and toughness and corrosion resistance.

[0060] Example 5

[0061] The heat treatment method for strengthening and toughening erosion-resistant iron-based materials used in aluminum alloy die-casting molds is implemented according to the following steps:

[0062] Step 1: Add material at a flow rate of 8m³ / min 3 / h of R X In an atmosphere-protected furnace, the temperature was first raised to 750℃ and held for 1 hour under CP 0.8%, then raised to 850℃ and held for 1 hour under CP 1.05%, then raised to 920℃ and held for 1 hour under CP 1.35%, then raised to 1000℃ and held for 2 hours under CP 1.6%, and then cooled in stages at a rate of 60℃ / h. The temperature was lowered to 950℃ under CP 1.35% and held for 2 hours, then lowered to 850℃ and held for 1 hour under CP 1.05%, then lowered to 700℃ and held for 0.5 hours under CP 0.7%, and then lowered to 650℃ and held for 1 hour under nitrogen protection. The furnace was then removed and air-cooled to room temperature.

[0063] Step 2: The first metal obtained in Step 1 is rapidly heated to 900°C and held at that temperature for 8 minutes, then quickly quenched in oil at 200°C to obtain the second metal.

[0064] Step 3: Heat the second metal obtained in Step 2 to 400℃ and hold for 3 hours to obtain an iron-based metal material for die casting of aluminum alloy that has both high strength and toughness and corrosion resistance.

[0065] The erosion-resistant iron-based material for aluminum alloy die-casting molds, after undergoing a toughening heat treatment method, significantly improves the material's strength and toughness, extending its service life for use in aluminum alloy die-casting molds.

Claims

1. An anti-erosion iron-based material for aluminum alloy die-casting molds, characterized in that, The composition by mass percentage is as follows: C 3.5%, Si 1.5%, Ni 1.6%, Cr 0.4%, Mo 1.1%, V 0.6%, Al 0.2%, other alloying elements ≤1.0%, balance Fe, and the total content of all the above components shall be 100%. The heat treatment method for strengthening and toughening erosion-resistant iron-based materials used in aluminum alloy die-casting molds is implemented according to the following steps: Step 1: The material is heated and held at a temperature in a protective atmosphere furnace using a staged heating method. After holding at a temperature, it is cooled in stages and then removed and air-cooled to obtain the first metal. Step 2: Heat and hold the first metal at that temperature, then quench it in preheated oil to obtain the second metal; Step 3: Heat and hold the second metal at that temperature to obtain the final product; The graded heating in step 1 is as follows: when the material is in the first protective atmosphere, it is heated to 750℃ and held for 1 hour under a carbon potential CP of 0.75%~0.85%, then heated to 850℃ and held for 1 hour under a carbon potential CP of 1.00%~1.10%, then heated to 920℃ and held for 1 hour under a carbon potential CP of 1.30~1.40%, and then heated to 1000℃-1100℃ and held for 1-5 hours under a carbon potential CP of 1.55%~1.65%. The step 1 cooling process specifically involves: cooling down to 950℃ at a rate of 20℃ / h - 60℃ / h under a carbon potential CP of 1.30%~1.40% and holding for 1h-2h; cooling down to 850℃ at a carbon potential CP of 1.00%~1.10% and holding for 1h-2h; cooling down to 700℃ at a carbon potential CP of 0.65%~0.75% and holding for 0.5h-1h; and then cooling down to 650℃ under nitrogen protection with a purity of 99.99% and holding for 1h. Finally, the sample is removed and air-cooled to room temperature. In step 2, the first metal is heated to an austenitizing temperature of 850℃-950℃, and the holding time is 5min-10min. The temperature of the quenching medium oil is 100℃-200℃. The heating temperature in step 3 is 300℃-600℃, and the holding time is 0.5h-3h.

2. The anti-erosion iron-based material for aluminum alloy die-casting molds according to claim 1, characterized in that, The protective atmosphere in the atmosphere protection furnace in step 1 adopts one of the following two protective atmospheres: The first protective atmosphere is an R atmosphere composed of 19%~20% CO, 40%~41% H2 and 38%~39% N2. X An endothermic atmosphere is used as a dilution protective atmosphere, and CH4 and air are introduced through a carbon control system to control and adjust the amount of CH4 and air introduced so that the carbon potential CP value in the furnace is within the set carbon potential CP range; the second protective atmosphere consists of nitrogen and propane gas with a purity of 99.99%, and the ratio of nitrogen to propane gas is 20~30:

1.

3. The anti-erosion iron-based material for aluminum alloy die-casting molds according to claim 1, characterized in that, The flow rate of the protective atmosphere gas in step 1 is 8 m³ / s. 3 / h.

4. The anti-erosion iron-based material for aluminum alloy die-casting molds according to claim 1, characterized in that, In step 2, the interval between removing the item from the atmosphere furnace and quenching it in oil should not exceed 60 seconds.

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