High-strength and high-toughness aluminum profile hot extrusion die steel and manufacturing method thereof

Abstract

The invention discloses high-strength and high-toughness aluminum profile hot extrusion die steel and a manufacturing method thereof. The die steel is composed of the following elements in percentage by mass: 0.30-0.45% of C; 0.20% to 0.50% of Si; 0.30% to 0.60% of Mn; 1.0% to 2.0% of Cr; 1.0% to 2.0% of Mo; 0.20% to 0.50% V; 1.5% to 2.5% of Ni; 0.07% to 0.11% of La; 0.001% to 0.003% of B; and the balance of Fe and inevitable impurities. The manufacturing method comprises the following steps: smelting and casting waste steel into round ingots, remelting electroslag to generate electroslag ingots, heating and forging to generate round steel, annealing to obtain the die steel and the like. The die steel has the advantages that high hardness and high toughness are achieved, a high-strength aluminum alloy profile hot extrusion die manufactured by adopting the steel type solves the problems that a high-strength aluminum alloy profile extruded by the die is not wear-resistant and easy to crack, and the service life of the die is greatly prolonged.

Description

Technical Field

[0001] The invention belongs to the field of steel material die steel, and in particular relates to a high-strength and toughness aluminum profile hot extrusion die steel and a manufacturing method thereof. Background Art

[0002] Aluminum alloys are widely used in architecture, transportation, automotive, and other fields. Aluminum alloy profiles are formed using hot extrusion. Due to the complex cross-sectional shapes and numerous sharp corners of aluminum alloy profiles, the mold cavity surface is prone to wear and cracking during the extrusion process. This is especially true when extruding high-strength aluminum alloy profiles, where the mold is subjected to significant deformation resistance, which can easily lead to wear and cracking of the mold cavity surface.

[0003] Currently, H13 steel is the primary material used for hot extrusion dies for aluminum alloy profiles. H13 steel excels in extruding 6063-type aluminum alloy profiles, offering a long die life due to its 100% extrudability and low resistance to deformation during extrusion. However, H13 steel is susceptible to wear and cracking when used to extrude 7005-type aluminum alloys, as the deformation resistance of 7005-type aluminum alloys increases significantly during hot extrusion. Therefore, H13 steel is no longer suitable for hot extrusion dies for these types of aluminum alloy profiles. While some improved H13 steel grades have been tested in hot extrusion dies for 7005-type aluminum alloy profiles, the results have been unsatisfactory. For example, reducing the V content of H13 steel to around 0.5% improves toughness compared to H13 steel, but it also leads to premature die wear. Another approach is to add 1-2% W and 1-3% Co to the H13 steel chemical composition, which improves wear resistance but lacks toughness and can lead to die cracking during hot extrusion. For example, patent publication CN116555679A discloses a hot extrusion die steel with a composition of 0.17-0.24% C, 0.10-0.45% Si, 0.20-0.45% Mn, 7-9.5% Cr, 0.8-1.25% W, 0.2-0.4% V, and 0.004-0.009% B. This steel has a high Cr content and incorporates W to improve its red hardness. However, the addition of W reduces toughness, making the die prone to cracking when extruding aluminum alloys with high deformation resistance. Therefore, to further extend the service life of hot extrusion dies for high-strength aluminum alloy profiles, it is necessary to improve both the high-temperature strength and toughness of the die. Summary of the Invention

[0004] The present invention provides a high-strength and toughness aluminum profile hot extrusion die steel and a manufacturing method thereof, aiming to overcome the shortcomings of the existing high-strength aluminum alloy profile hot extrusion die in the prior art, such as poor durability and short service life (the cavity of the existing aluminum profile hot extrusion die is prone to wear and cracking when hot extruding high-strength aluminum alloy profiles).

[0005] The technical scheme for solving the above technical problems is as follows: a high-toughness aluminum profile hot extrusion die steel is composed of the following elements in percentage by mass: 0.30-0.45% C; 0.20-0.50% Si; 0.30-0.60% Mn; 1.0-2.0% Cr; 1.0-2.0% Mo; 0.20-0.50% V; 1.5-2.5% Ni; 0.07-0.11% La; 0.001-0.003% B; and the balance of Fe and inevitable impurities.

[0006] Based on the above technical scheme, the application can further have the following further specific selection or more optimal selection.

[0007] Specifically, the percentage content of the elements La and B is limited to %La=(%B*20)+0.05.

[0008] Preferably, the application is composed of the following elements in percentage by mass: 0.30-0.40% C; 0.38-0.50% Si; 0.49-0.60% Mn; 1.6-2.0% Cr; 1.5-2.0% Mo; 0.32-0.50% V; 1.9-2.5% Ni; 0.07-0.09% La; 0.001-0.002% B; and the balance of Fe and inevitable impurities.

[0009] The application also provides a manufacturing method of the high-toughness aluminum profile hot extrusion die steel, which comprises the following steps:

[0010] S1. Scrap smelting and casting into round ingot: melting scrap in an electric arc furnace, then placing the molten steel into a refining furnace to adjust the mass percentage of each element in the molten steel to the corresponding numerical range described above, then transferring the ladle on the refining furnace base into a vacuum furnace for vacuum degassing treatment, then casting when the temperature of the molten steel reaches the process requirement, and casting into a round ingot, and then demolding after mold cooling;

[0011] S2. Electroslag remelting to generate electroslag ingot: transferring the round ingot obtained after demolding in S1 to an electroslag remelting station for electroslag remelting, using a slag system of CaF2:Al2O3:SiO2:CaO=60:20:5:15, and after remelting, demolding after mold cooling to obtain an electroslag ingot;

[0012] S3. Heating and forging to generate round steel: transferring the electroslag ingot obtained in S2 to a heating furnace in a forging station for heating, heating to a set temperature, and then taking out the furnace for forging after sufficient heat preservation treatment, and forging into a round steel;

[0013] S4. Annealing treatment to obtain a die steel: annealing the round steel forged in S3, and obtaining the high-toughness aluminum profile hot extrusion die steel.

[0014] On the basis of the above technical solutions, the present invention may further have the following specific options or more preferred options.

[0015] Specifically, the electric arc furnace used in S1 is a 20-ton EAF electric arc furnace, the refining furnace used is a 20-ton LF refining furnace, and the vacuum furnace used is a 20-ton VD vacuum furnace.

[0016] Specifically, the process in S1 requires that the temperature of the molten steel be 1550-1560°C, the specification of the round ingot be Φ900mm, and the mold be cooled for 48 hours after casting before demolding.

[0017] Specifically, after the remelting in S2 is completed, the mold is cooled for 150 minutes and then demolded. The specifications of the electroslag ingot obtained by demolding are Φ1200×2200 mm.

[0018] Specifically, the temperature is set at 1220-1240° C. in S3, and the insulation treatment time is 30 hours.

[0019] Specifically, the specification of the round steel forged in S3 is Φ950mm.

[0020] Specifically, during the annealing treatment in S4, the annealing temperature is 820° C., and the annealing holding time is 25 hours.

[0021] Compared with the prior art, the present invention has the following beneficial effects:

[0022] The mold steel provided by the present invention has appropriate proportions of Cr, Ni, La and B in its constituent elements. Their synergistic combination can effectively inhibit bainite phase transformation and improve hardenability, so that the mold steel has good toughness and hardness. In particular, the amounts of La and B meet a specific ratio, which can enable La to be preferentially enriched at the grain boundaries, while B and other impurity elements are not enriched at the grain boundaries, which can significantly improve the toughness of the mold steel.

[0023] The high-strength aluminum alloy profile hot extrusion die manufactured using the die steel provided by the present invention has higher wear resistance and is not easy to crack. The die heat treatment hardness reaches 52-55HRC, and the impact energy of a 7×10×55mm unnotched specimen is 340-360J, achieving both high hardness and high toughness. The high-strength aluminum alloy profile hot extrusion die manufactured using the steel grade provided by the present invention solves the problem that the high-strength aluminum alloy profile extruded by the die is not wear-resistant and is easy to crack, and the die life is greatly improved. DETAILED DESCRIPTION

[0024] The technical solutions provided by the present invention are described clearly and completely below with reference to specific embodiments. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. All other embodiments derived by persons of ordinary skill in the art based on the embodiments of the present invention without creative effort are also within the scope of protection of the present invention.

[0025] To avoid redundancy, the devices used in the following embodiments are all conventional devices in the art unless otherwise specified, and the methods used are all conventional methods in the art unless otherwise specified.

[0026] The present invention provides a high-strength and toughness aluminum profile hot extrusion die steel, comprising the following elements in percentage by mass: 0.30-0.45% C; 0.20-0.50% Si; 0.30-0.60% Mn; 1.0-2.0% Cr; 1.0-2.0% Mo; 0.20-0.50% V; 1.5-2.5% Ni; 0.07-0.11% La; 0.001-0.003% B; the balance being Fe and unavoidable impurities. The percentage of La and B is defined as %La = (%B × 20) + 0.05.

[0027] It should be noted that the addition of 0.30~0.45% C element is to ensure that the service hardness of the mold reaches above 50HRC; the addition of 0.20~0.50% Si can inhibit the precipitation and aggregation of carbides during tempering, thereby improving the thermal stability of the mold; the addition of 0.30~0.6% Mn can inhibit the pearlite phase transformation during the quenching cooling process, thereby improving the hardenability of the mold; the addition of 1.0~2.0% Cr can inhibit the bainite phase transformation and improve the hardenability; the addition of 1.5~2.0% 5% Ni inhibits bainite phase transformation and improves hardenability; the addition of 1.80~2.0% Mo improves hardenability and thermal stability; the addition of 0.20~0.50% V precipitates high-hardness MC-type carbides during tempering treatment and improves the wear resistance of the mold; the addition of 0.07~0.11% La inhibits the enrichment of impurity elements at the grain boundaries and improves toughness; the addition of 0.001~0.003% B inhibits bainite phase transformation and improves hardenability.

[0028] Among them, the relationship between the percentage limits of La and B is limited to %La=(%B×20)+0.05. The purpose of this limitation is to allow La to be enriched preferentially at the grain boundaries and prevent B and other impurity elements from being enriched along the grain boundaries, thereby achieving the purpose of significantly improving toughness. In addition, Cr, Ni, B and La all have a certain ability to inhibit bainite phase transformation. If only one or two of these alloying elements are used and the content is increased, adverse effects will occur. For example, if only Cr is added and the Cr content is increased, such as adding 3~8% Cr, not only is the effect of inhibiting the transformation of bainite structure not significant, but the amount of carbides will be increased and the toughness will be reduced; if only Ni is added and the Ni content is increased, such as adding 3~5% Ni, although the effect of inhibiting the transformation of bainite structure is significant, the hardenability is reduced and the risk of cracking after forging annealing is increased; if only B is added and the B content is increased, such as adding 0.005~0.01% B, the effect of inhibiting the transformation of bainite structure is not significantly improved, and the toughness is reduced. Therefore, the present invention uses the above four elements simultaneously and controls their appropriate proportions, and the synergistic combination can effectively improve the hardenability, thereby ensuring that the obtained die steel has both good toughness and hardness.

[0029] Specifically, the mass percentages of the elements in the mold steels provided in Examples 1 to 5 and the comparative example are shown in the following table:

[0030]

[0031] The mold steels provided in the above embodiments and comparative examples are all manufactured by the following method:

[0032] A 20-ton EAF electric arc furnace was used to melt the scrap steel, and then the molten steel was dropped into a 20-ton LF refining furnace. The composition of each element was adjusted in the LF furnace according to the above chemical composition range to reach the range required by each embodiment and comparative example. The ladle on the LF furnace base was then transferred to a 20-ton VD vacuum furnace for vacuum degassing. When the molten steel temperature was 1550-1560°C, a Φ900 round ingot was cast. The mold was demoulded after cooling for 48 hours, and the Φ900 round ingot was transferred to the electroslag remelting station for electroslag remelting. The remelting is carried out using a slag system of CaF2:Al2O3:SiO2:CaO=60:20:5:15. After the remelting is completed, the mold is cooled for 150 minutes and then demolded. The specification of the electroslag ingot is Φ1200×2200mm. The electroslag ingot is transferred to the heating furnace of the forging station for heating at a heating temperature of 1220~1240℃ and then kept warm for 30 hours before being taken out of the furnace for forging to forge into Φ950mm round steel. It is then annealed at a temperature of 820℃ and a holding time of 25h.

[0033] Using the mold steel prepared by the above method and having the elemental composition required in each embodiment and comparative example as the material, a high-strength and toughness aluminum profile hot extrusion mold was processed, and then the corresponding mold was subjected to performance testing. The test results are shown in the following table:

[0034]

[0035] Comparative Example 1 is the chemical composition of H13 steel. As can be seen from the above table, the molds prepared with the mold steel corresponding to each embodiment of the present invention show significantly better toughness and better hardness retention ability under continuous high temperature compared with the comparative example. The molds prepared in each embodiment have good durability and longer service life.

[0036] According to actual measurements, the mold steel prepared in each embodiment, after being processed into a mold for hot extrusion of 7005 aluminum alloy profiles, has both high hardness and high toughness, good wear resistance and is not easy to crack. Its service life is an average of 1.2 to 1.5 times longer than that of the mold processed in the comparative example (H13).

[0037] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A high-strength and toughness aluminum profile hot extrusion die steel, characterized in that: It is composed of the following elements in the following mass percentages: 0.30~0.45% C; 0.20~0.50% Si; 0.30~0.60% Mn; 1.0~2.0% Cr; 1.0~2.0% Mo; 0.20~0.50% V; 1.5~2.5% Ni; 0.07~0.11% La; 0.001~0.003% B; the balance is Fe and unavoidable impurities.

2. The high-strength and toughness aluminum profile hot extrusion die steel according to claim 1, characterized in that: The percentage content of elements La and B is limited to %La=(%B×20)+0.

05.

3. The high-strength and toughness aluminum profile hot extrusion die steel according to claim 1 or 2, characterized in that: It is composed of the following elements in the following mass percentages: 0.30~0.40% C; 0.38~0.50% Si; 0.49~0.60% Mn; 1.6~2.0% Cr; 1.5~2.0% Mo; 0.32~0.50% V; 1.9~2.5% Ni; 0.07~0.09% La; 0.001~0.002% B; the balance is Fe and unavoidable impurities.

4. A method for manufacturing high-strength and high-toughness aluminum profile hot extrusion die steel, characterized in that: The steps include: S1. Melting and Casting Scrap into Ingots: Melting scrap steel in an electric arc furnace, then placing the molten steel into a refining furnace, adjusting the mass percentages of various elements in the molten steel to fall within the numerical ranges described in any one of claims 1 to 3, then transferring the ladle from the refining furnace to a vacuum furnace for vacuum degassing, and then casting the molten steel into ingots when the temperature reaches the process requirements. The ingots are then cooled and demolded for later use. S2. Electroslag remelting to generate electroslag ingots: The round ingot obtained after demolding S1 is transferred to the electroslag remelting station for electroslag remelting. The electroslag remelting uses a slag system of CaF2:Al2O3:SiO2:CaO = 60:20:5:

15. After the remelting is completed, the mold is cooled and demolded to obtain an electroslag ingot. S3 heating forging to generate round steel: The electroslag ingot obtained in S2 is transferred to the heating furnace for forging station for heating, heating to the set temperature and then fully heat-insulating treatment after forging, forging into round steel; S4. Annealing to obtain die steel: The round steel forged in S3 is annealed to obtain the high-strength and toughness aluminum profile hot extrusion die steel.

5. The method for manufacturing a high-strength and toughness aluminum profile hot extrusion die steel according to claim 4, characterized in that: The electric arc furnace used in S1 is a 20-ton EAF electric arc furnace, the refining furnace used is a 20-ton LF refining furnace, and the vacuum furnace used is a 20-ton VD vacuum furnace.

6. The method for manufacturing a high-strength and toughness aluminum profile hot extrusion die steel according to claim 4, characterized in that: The process in S1 requires that the temperature of the molten steel is 1550~1560℃, the specification of the round ingot is Φ900mm, and the mold is cooled for 48 hours after casting before demolding.

7. The method for manufacturing a high-strength and toughness aluminum profile hot extrusion die steel according to claim 4, characterized in that: After the remelting in S2 is completed, the mold is cooled for 150 minutes and then demolded. The specifications of the electroslag ingot obtained by demolding are Φ1200×2200mm.

8. The method for manufacturing a high-strength and toughness aluminum profile hot extrusion die steel according to claim 4, characterized in that: The temperature in S3 is set to 1220~1240℃, and the insulation treatment time is 30h.

9. The method for manufacturing a high-strength and toughness aluminum profile hot extrusion die steel according to claim 4, characterized in that: The specification of round steel forged in S3 is Φ950mm.

10. The method for manufacturing a high-strength and toughness aluminum profile hot extrusion die steel according to any one of claims 4 to 9, characterized in that: During the annealing treatment in S4, the annealing temperature is 820° C. and the annealing holding time is 25 h.

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