Corrosion-resistant plastic die steel material

Abstract

The invention discloses a corrosion-resistant plastic die steel material. The die steel material comprises the following components in percentage by mass: 0.40%-0.48% of C, 12.00%-12.90% of Cr, 0.50%-0.60% of Mn, 0.35%-0.40% of Si, 1.10%-1.20% of Mo, 0.25%-0.30% of V, 0.35%-0.38% of Ni, 0.15%-0.20% of N, less than or equal to 0.03% of P, less than or equal to 0.03% of S and the balance of Fe. The corrosion-resistant plastic die steel material has good mechanical properties and corrosion resistance, and the corrosion rate of electrochemical corrosion in a 3.5 wt.% NaCl solution is smaller than or equal to 0.01 mm / a while the mechanical properties that the hardness is 50 HRC and the tensile strength is 1700 MPa or above are kept.

Description

Technical Field

[0001] The present invention belongs to the technical field of alloy steel materials, and particularly relates to a corrosion-resistant plastic mold steel material. Background Art

[0002] With the development of technology, especially in the fields of information and electronics, the performance and variety of plastics have been continuously improved and perfected, and the demand has been increasing day by day. This has directly led to the rapid development of the plastic mold industry, and the status of plastic mold steel in mold steel has been rising day by day. Every year, a large amount of special scrap steel is scrapped in various mold manufacturing plants and machinery manufacturing plants. As a strategic resource that can be recycled almost infinitely, scrap steel plays an important role in the production of the steel industry. According to statistics, using one more ton of scrap steel can reduce 1.65 tons of iron ore concentrate, and at the same time can save the use of coal, reduce carbon dioxide emissions and solid waste emissions. Therefore, the scrap steel industry is a rising sun industry with emerging strategies and has great development prospects.

[0003] Although the output of plastic mold steel in China is huge and the production technology level is constantly improving, the same as the overall status of the mold steel industry in China, there is an oversupply of plastic mold steel with low technical content, while medium and high-grade plastic molds still cannot meet the demand and are basically dependent on imports, which further increases the production cost. Due to the harsh working environment of plastic molds, they not only have to bear a certain mechanical load and serve in a working environment with repeated temperature alternation for a long time, but also some corrosive gases will be generated during the forming process of certain plastic materials, which will cause corrosion to the mold cavity and the humid air passage to form halogen ions and hydrogen ions, resulting in mold scrapping. Therefore, it is particularly important to develop a plastic mold steel with excellent mechanical properties and corrosion resistance.

[0004] Generally speaking, the methods to improve the strength, toughness and corrosion resistance of plastic mold steel in industrial production mainly include composition optimization and preparation process design, etc. As an important part of the preparation process design, the influence of heat treatment process design on the structure, mechanical properties and corrosion resistance of plastic mold steel is of great significance for the development and improvement of the life of the mold. Summary of the Invention

[0005] Aiming at the deficiencies of the prior art, the purpose of the present invention is to provide a corrosion-resistant plastic mold steel material. Through the regulation and optimization of Mo element and N element, combined with this heat treatment process, the corrosion-resistant plastic mold steel material can adjust the organizational structure, improve the carbide distribution and its uniformity, and make it have excellent mechanical properties and corrosion resistance.

[0006] To achieve the above purpose, the present invention is realized through the following technical solutions:

[0007] A corrosion-resistant plastic mold steel material, comprising components in the following mass percentages: C 0.40%-0.48%, Cr 12.00%-12.90%, Mn 0.50%-0.60%, Si 0.35%-0.40%, Mo 1.10%-1.20%, V 0.25-0.30%, Ni 0.35%-0.38%, N 0.15%-0.20%, P≤0.03%, S≤0.03%, and the balance being Fe.

[0008] Preferably, the corrosion-resistant plastic mold steel material comprises raw materials in the following mass percentages: C 0.45%, Cr 12.82%, Mn 0.52%, Si 0.39%, Mo 1.12%, V 0.26%, Ni 0.35%, N 0.17%, P 0.001%, S 0.001%, and the balance being Fe.

[0009] Preferably, the corrosion-resistant plastic mold steel material comprises raw materials in the following mass percentages: C 0.44%, Cr 12.89%, Mn 0.58%, Si 0.35%, Mo 1.12%, V 0.25%, Ni 0.36%, N 0.16%, P 0.003%, S 0.002%, and the balance being Fe.

[0010] Preferably, the corrosion-resistant plastic mold steel material comprises raw materials in the following mass percentages: C 0.42%, Cr 12.76%, Mn 0.51%, Si 0.37%, Mo 1.16%, V 0.27%, Ni 0.37%, N 0.15%, P 0.005%, S 0.002%, and the balance being Fe.

[0011] Preferably, the hardness of the corrosion-resistant plastic mold steel material is >50HRC, the tensile strength is ≥1700MPa, and the corrosion rate of electrochemical corrosion in 3.5wt.% NaCl solution is ≤0.01mm / a.

[0012] Preferably, the heat treatment process of the corrosion-resistant plastic mold steel material comprises the following steps

[0013] (1) Pretreatment: The furnace charge raw materials adopt high-purity cutting scrap steel, and the steel ingot primary product is prepared through the technological processes of arc melting, refining outside the furnace, electroslag remelting, and forging.

[0014] (2) Diffusion annealing: The steel ingot primary product obtained in step (1) is placed in a high-temperature annealing furnace and heated to 1150°C-1300°C, and kept warm for 4-8h until the primary carbides and banded structure in the steel ingot primary product disappear, then taken out of the furnace and air-cooled to room temperature to prepare the steel ingot.

[0015] (3) Normalizing: Heat the steel ingot obtained in step (2) to 860°C - 890°C, hold for 0.5 - 1 h, and then air cool to room temperature after taking it out of the furnace;

[0016] (4) Spheroidizing annealing: Heat the steel ingot material obtained in step (3) to 810°C - 830°C and hold for 1 - 3 h, then cool at a rate of 110°C / h - 130°C / h to 670°C - 690°C and hold for 4 - 6 h, and then cool to below 450°C, and air cool to room temperature after taking it out of the furnace to prepare the initial product of the corrosion-resistant plastic mold steel material;

[0017] (5) Quenching and tempering process: Heat the material obtained in step (4) to 1060°C - 1080°C, hold for 0.5 - 1 h, quench in oil, and immediately perform two temperings after cooling to room temperature. The tempering temperature is 250°C - 300°C, hold for 2 - 4 h, and air cool to room temperature after taking it out of the furnace to prepare the corrosion-resistant plastic mold steel material.

[0018] Preferably, in the electric arc melting process in step (1), the tapping temperature is 1550°C - 1600°C, and the pouring temperature is 1480°C - 1520°C.

[0019] Preferably, the secondary refining process in step (1) is to carry out alloying treatment and temperature control operation on the ingot smelted in the electric furnace, and take it out of the furnace at a temperature of 1550°C - 1600°C to obtain the refined mold steel ingot.

[0020] Among them, the electroslag remelting process in step (1) is to reduce the influence of harmful elements and inclusions in the steel, improve the ingot structure, and improve the purity and performance of the metal material;

[0021] Preferably, in the forging process in step (1), the initial forging temperature is 1080°C - 1120°C, and the final forging temperature is ≥850°C.

[0022] In order to obtain a corrosion-resistant plastic mold steel material with excellent mechanical properties and corrosion resistance, the present invention makes the following controls:

[0023] Carbon (C) is an important element to ensure the quenching hardness and hardenability. It improves the strength of the steel through solid solution strengthening and precipitation strengthening. Therefore, the content of C largely determines the strength of the steel. At the same time, under appropriate processes, an appropriate amount of C content can form carbides with Cr and Mo, and the fine carbides are beneficial to improving the hardness and corrosion resistance of the steel. However, too high C content will cause carbide segregation and growth, reducing the corrosion resistance of the steel. Therefore, the C content range of the present invention is 0.40% - 0.48%.

[0024] Chromium (Cr) is an important element to ensure excellent corrosion resistance of plastic mold steel. The corrosion potential of Cr is more negative than that of iron, and its passivation ability is stronger than that of iron. In the iron-chromium alloy, the increase of Cr content will cause the corrosion potential of the alloy to shift towards the negative potential direction, and the corrosion current gradually decreases, indicating that the higher the Cr content in the alloy, the easier it is to passivate. Therefore, the Cr content range in the present invention is 13.00% - 13.90%.

[0025] Silicon (Si) is a strong deoxidizing element. Adding an appropriate amount of Si can improve the oxidation resistance and sulfidation resistance of plastic mold steel. However, Si is prone to segregation at the austenite grain boundaries. Therefore, too high Si content will promote segregation, form banded structure, and deteriorate the hot working performance of plastic mold steel. Therefore, the Si content in the present invention is controlled within 0.30% - 0.40%.

[0026] Manganese (Mn) is an austenite stabilizing element that can significantly improve the hardenability of steel. The combination of Mn and S can prevent the hot brittleness caused by S. However, too high Mn content will cause grain coarsening in the steel and increase the temper brittleness of the steel. Therefore, the Mn content range in the present invention is 0.50% - 0.60%.

[0027] Molybdenum (Mo) can promote the precipitation of precipitation phases to play a secondary hardening role and enhance the temper stability. In addition, Mo can replace part of Cr to form carbides and nitrides, thereby increasing the Cr content of the matrix and improving the corrosion resistance. Because Mo is a strong ferrite stabilizing element, excessive Mo will cause δ-ferrite to exist in the quenched structure, thereby deteriorating the mechanical properties and corrosion resistance of plastic mold steel. Therefore, the Mo content range in the present invention is 1.10% - 1.20%.

[0028] Vanadium (V) can reduce the overheating sensitivity of steel. A small amount of V can refine the grains and promote the uniform and dispersed precipitation of carbides after appropriate heat treatment. However, too high V content will increase the formation probability of primary carbides in the steel and affect the toughness of the steel. Therefore, the V content range in the present invention is 0.25% - 0.30%.

[0029] Nickel (Ni) can improve the toughness of plastic mold steel, reduce the cracking tendency of the steel, and at the same time Ni can increase the passivation tendency of the iron-chromium alloy and improve the corrosion resistance of the steel. Therefore, the Ni content range in the present invention is 0.35% - 0.40%.

[0030] Nitrogen (N) is a stronger precipitation-phase forming element than C, forming fine nitrides. The increase in these nitrides may lead to an increase in the brittleness of the material, affecting the strength of the steel. Secondly, N can increase the corrosion resistance of the passive film. In addition, when N and Mo elements coexist, Mo generates hydrogen nuclei, which will move into the solution under the repulsive force of the passive film, thereby further strengthening the role of N in improving the local corrosion environment. Therefore, the N content range in the present invention is 0.05% - 0.20%.

[0031] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0032] (1) The corrosion-resistant plastic mold steel material provided by the present invention controls the chemical composition and dosage in the steel, and improves the type, quantity and distribution law of the precipitated phases in the steel through a cooperative heat treatment process, so that while its mechanical properties meet the requirements of plastic mold steel, the corrosion resistance of the plastic mold steel is improved. High proportions of scrap steel are utilized as raw materials, greatly promoting the recycling of scrap steel and reducing production costs;

[0033] (2) The present invention successively undergoes processes such as electric furnace smelting, ladle furnace refining, electroslag remelting, forging, high-temperature homogenization annealing, normalizing, spheroidizing annealing, quenching and secondary tempering, so that the prepared corrosion-resistant plastic mold steel material has mechanical properties of hardness > 50 HRC and tensile strength ≥ 1700 MPa, and at the same time, the corrosion rate of electrochemical corrosion in 3.5 wt.% NaCl solution ≤ 0.01 mm / a. Description of the Drawings

[0034] Figure 1 It is the SEM microstructure diagram after tempering of the corrosion-resistant plastic mold steel material in Example 1;

[0035] Figure 2 It is the morphology of the scanning electron microscope (5000×) after electrochemical corrosion of Example 1 in 3.5 wt.% NaCl solution;

[0036] Figure 3 It is the morphology of the scanning electron microscope (20000×) after electrochemical corrosion of Example 1 in 3.5 wt.% NaCl solution;

[0037] Figure 4 It is the energy spectrum analysis result of the Cr-rich precipitation phase in the pitting corrosion pit on the corrosion surface of Example 1 ( Figure 3 )

[0038] Figure 5 It is the microstructure diagrams after quenching of Comparative Example 1 ( Figure 5 (a)) and Example 1 ( Figure 5 (b)). Detailed Embodiments

[0039] The present invention will be further described in detail below in conjunction with embodiments and the accompanying drawings. It should be noted that from the perspective of raw material cost and abundant and easily available sources, 4Cr13, Cr12Mo1V1 cutting scrap steel and various intermediate alloys are used as examples for the furnace charge. However, in fact, various metal raw materials are not limited thereto, as long as it is ensured that the raw materials meet the requirements for the mass composition of various elements in die steel.

[0040] The heat treatment method of the corrosion-resistant plastic mold steel material described in this embodiment includes the following steps:

[0041] (1) Prepare the initial product of the steel ingot by subjecting the metal raw materials (waste steel materials) to electric furnace smelting - secondary refining - electroslag remelting - forging - heat treatment.

[0042] (2) High-temperature diffusion annealing: Place the initial product of the steel ingot in a high-temperature annealing furnace, heat it from room temperature to 1150°C - 1300°C and hold for 4 - 8 hours to make the primary carbides and banded structure disappear, and prepare the steel ingot.

[0043] (3) Normalizing: Raise the temperature to 860°C - 890°C, hold for 0.5 - 1 h, and then air-cool to room temperature after discharging from the furnace.

[0044] (4) Spheroidizing annealing: Raise the temperature to 810°C - 830°C and hold for 1 - 3 h, then cool to 680°C - 720°C and hold for 4 - 6 h, and then cool to below 500°C, and air-cool to room temperature after discharging from the furnace to prepare the initial product of the corrosion-resistant plastic mold steel material.

[0045] (5) Quenching: Raise the temperature to 1020°C - 1080°C and hold for 0.5 - 1 h, and quench in oil.

[0046] (6) Tempering: Immediately perform tempering after quenching. The tempering temperature is 180°C - 220°C, hold for 2 - 4 h, and air-cool to room temperature after discharging from the furnace. Temper twice to prepare the corrosion-resistant plastic mold steel material.

[0047] The melting compositions of the materials prepared in Examples 1 to 3 and Comparative Example 2 of the present invention are shown in Table 1, and the physical property test results of Examples 1 to 3 and Comparative Example 2 of the present invention are shown in Table 2. Comparative Example 1 of the present invention is the same as Example 1, and the difference is that the normalizing treatment is not adopted in the heat treatment process of Comparative Example 1.

[0048] The room temperature tensile test measures the room temperature tensile properties of the material according to GB / T 228.1-2010 "Metallic materials - Tensile testing - Part 1: Method of test at room temperature".

[0049] The Rockwell hardness test measures the Rockwell hardness of the material according to GB / T 230.1-2018 "Metallic materials - Rockwell hardness test - Part 1: Test method".

[0050] The corrosion resistance test was performed by using a Zahner electrochemical workstation to conduct electrochemical corrosion experiments on each embodiment. The corrosion solution was a 3.5 wt. % NaCl solution, and the test was performed at room temperature.

[0051] See also Figures 1 - 3 . Figure 1 is a SEM image of the corrosion-resistant plastic mold steel material after tempering in Example 1 of the present invention. Figure 1 It can be seen that the tempered carbides are evenly distributed. Figures 2 - 4 This is the SEM image of Example 1 of the present invention in 3.5wt.% NaCl solution and the energy spectrum analysis result of the Cr-rich precipitate phase on the corrosion surface. It can be seen that the pitting pits on the corrosion surface are small, the corrosion surface is relatively smooth as a whole, and pitting occurs preferentially near the larger precipitate phase. Figure 5 Comparative Example 1 of the present invention ( Figure 5 (a)) and Example 1 ( Figure 5 (b)) The microstructure after quenching. Figure 5 It can be seen that there is a network of proeutectoid cementite in the quenched structure of Comparative Example 1. The presence of this phase makes the steel brittle and often serves as a crack initiation point. This phase is eliminated in Example 1.

[0052] Table 1 shows the composition (wt.%) of the new plastic mold steel material prepared in Examples 1 to 3

[0053] Number C Cr Mn Si Mo V Ni N P S Example 1 0.45 12.82 0.52 0.39 1.12 0.26 0.35 0.17 0.001 0.001 Example 2 0.44 12.89 0.58 0.35 1.12 0.25 0.36 0.16 0.003 0.002 Example 3 0.42 12.76 0.51 0.37 1.16 0.27 0.37 0.15 0.005 0.002 Comparative Example 2 0.44 12.83 0.57 0.35 1.14 0.28 0.38 0.16 0.005 0.005

[0054] Table 2 is the test results of the new plastic mold steel materials prepared in Examples 1 to 3

[0055]

[0056] By comparing Comparative Example 2 with Examples 1-3, it can be found that after adding N element and performing N alloying, the tensile strength of the experimental steel is lost and the corrosion resistance is significantly improved.

[0057] The above embodiments are preferred implementation modes of the present invention, but the implementation modes of the present invention are not limited to the above embodiments. Any other changes, modifications, substitutions, combinations, and simplifications made without departing from the spirit and principles of the present invention shall be equivalent replacement methods and shall be included in the protection scope of the present invention.

Claims

1. A corrosion-resistant plastic mold steel material, characterized in that: The steel comprises the following components in mass percentage: C 0.40%-0.48%, Cr 12.00%-12.90%, Mn 0.50%-0.60%, Si 0.35%-0.40%, Mo 1.10%-1.20%, V 0.25-0.30%, Ni 0.35%-0.38%, N 0.15%-0.20%, P≤0.03%, S≤0.03%, and the balance is Fe.

2. The corrosion-resistant plastic mold steel material according to claim 1, characterized in that: The corrosion-resistant plastic mold steel material comprises the following raw materials in percentage by mass: C 0.45%, Cr 12.82%, Mn 0.52%, Si 0.39%, Mo 1.12%, V 0.26%, Ni 0.35%, N 0.17%, P 0.001%, S 0.001%, and the balance Fe.

3. The corrosion-resistant plastic mold steel material according to claim 1, characterized in that: The corrosion-resistant plastic mold steel material comprises the following raw materials in percentage by mass: C 0.44%, Cr 12.89%, Mn 0.58%, Si 0.35%, Mo 1.12%, V 0.25%, Ni 0.36%, N 0.16%, P 0.003%, S 0.002%, and the balance Fe.

4. The corrosion-resistant plastic mold steel material according to claim 1, characterized in that: The corrosion-resistant plastic mold steel material comprises the following raw materials in percentage by mass: C 0.42%, Cr 12.76%, Mn 0.51%, Si 0.37%, Mo 1.16%, V 0.27%, Ni 0.37%, N 0.15%, P 0.005%, S 0.002%, and the balance Fe.

5. The corrosion-resistant plastic mold steel material according to claim 1, characterized in that: The corrosion-resistant plastic mold steel material has a hardness greater than 50HRC, a tensile strength greater than or equal to 1700MPa, and an electrochemical corrosion rate less than or equal to 0.01mm / a in a 3.5wt.% NaCl solution.

6. The corrosion-resistant plastic mold steel material according to any one of claims 1 to 5, characterized in that: The heat treatment process of the corrosion-resistant plastic mold steel material comprises the following steps: (1) Pretreatment: The raw materials for the furnace charge are high-purity scrap steel, which is prepared into the primary steel ingot product through arc melting, refining outside the furnace, electroslag remelting and forging process; (2) Diffusion annealing: placing the steel ingot product obtained in step (1) in a high temperature annealing furnace and heating it to 1150° C.-1300° C., keeping the temperature for 4-8 hours until the primary carbides and banded structures in the steel ingot product disappear, and then taking it out of the furnace and air cooling it to room temperature to obtain a steel ingot; (3) Normalizing: The steel ingot obtained in step (2) is heated to 860°C-890°C, kept at this temperature for 0.5-1h, and then air-cooled to room temperature after being taken out of the furnace; (4) spheroidizing annealing: the steel ingot material obtained in step (3) is heated to 810°C-830°C and kept at this temperature for 1-3 hours, then cooled to 670°C-690°C at a rate of 110°C / h-130°C / h and kept at this temperature for 4-6 hours, then cooled to below 450°C, taken out of the furnace and air-cooled to room temperature, thereby preparing a primary product of corrosion-resistant plastic mold steel material; (5) Quenching and tempering process: the material obtained in step (4) is heated to 1060°C-1080°C, kept at this temperature for 0.5-1h, oil quenched, and immediately tempered twice after cooling to room temperature, the tempering temperature is 250°C-300°C, kept at this temperature for 2-4h, and then taken out of the furnace and air-cooled to room temperature to prepare a corrosion-resistant plastic mold steel material.

7. The corrosion-resistant plastic mold steel material according to claim 6, characterized in that: In the arc melting process in step (1), the steel tapping temperature is 1550°C-1600°C, and the pouring temperature is 1480°C-1520°C.

8. The corrosion-resistant plastic mold steel material according to claim 6, characterized in that: The out-of-furnace refining process in step (1) is to subject the ingot smelted in the electric furnace to alloying treatment and temperature control operation, and to take it out of the furnace at a temperature of 1550°C-1600°C to obtain a refined mold steel ingot.

9. The corrosion-resistant plastic mold steel material according to claim 6, characterized in that: In the forging process of step (1), the initial forging temperature is 1080°C-1120°C, and the final forging temperature is ≥850°C.

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