Wear-resistant steel-based mold material for plastic magnetic injection molding and preparation method of wear-resistant steel-based mold material

Abstract

The invention discloses a wear-resistant steel-based mold material for plastic magnetic injection molding and a preparation method of the wear-resistant steel-based mold material, and relates to the technical field of mold steel materials. When the steel-based mold material is prepared, metal chromium, titanium powder, ferromolybdenum, graphite, ferroboron, lanthanum iron and electrolytic iron are weighed according to a specific proportion, and a cast ingot is obtained through vacuum induction melting and argon protection pouring; a calcium fluoride-aluminum oxide-calcium oxide mixed slag system serves as a remelting medium, electroslag remelting, homogenization treatment and oil quenching are conducted on the cast ingot, and a steel ingot is obtained; the steel ingot is subjected to multidirectional forging and temperature-controlled cooling, and forged die steel is obtained; and finally, the forging die steel is subjected to gas nitriding subzero treatment and multi-stage tempering, gradient titanium nitride and chromium nitride metal ceramic layers are induced to be formed on the surface, and the wear-resistant steel-based die material for plastic magnetic injection molding is prepared. The prepared steel-based mold material has high hardness, high wear resistance and corrosion resistance.

Description

Technical Field

[0001] This invention relates to the field of mold steel materials technology, specifically to a wear-resistant steel-based mold material for plastic magnetic injection molding and its preparation method. Background Technology

[0002] Injection molding of plastic magnetic components is a key process for manufacturing high-precision, complex-shaped plastic magnetic components. During this process, the molten plastic is typically filled with hard magnetic powder, and may release trace amounts of corrosive substances, causing severe abrasive wear and corrosion on the mold cavity surface. This necessitates mold materials with extremely high hardness, excellent wear resistance, good corrosion resistance, and sufficient strength and toughness. Currently, commonly used mold steels often fail to meet these demanding conditions due to insufficient surface wear and corrosion resistance, inadequate core toughness, or poor overall performance matching. This leads to premature wear, corrosion pitting, and even cracking of the mold, significantly shortening its service life and affecting the dimensional accuracy and surface quality of the final plastic magnetic parts. Developing a dedicated mold material that combines excellent surface hardness, high wear resistance, good corrosion resistance, and a high strength-toughness ratio is crucial for improving mold life, ensuring product consistency, and reducing maintenance costs. Therefore, preparing steel-based mold materials capable of simultaneously addressing wear and corrosion challenges through matrix reinforcement combined with microstructure control and surface functionalization has become an urgent and important technological development direction. Summary of the Invention

[0003] The purpose of this invention is to provide a wear-resistant steel-based mold material for plastic magnetic injection molding and its preparation method, so as to solve the problems existing in the prior art.

[0004] To solve the above-mentioned technical problems, the present invention provides the following technical solution:

[0005] A method for preparing a wear-resistant steel-based mold material for plastic magnetic injection molding includes the following steps:

[0006] (1) Weigh the raw materials by mass percentage: 14%~15% metallic chromium, 0.2%~0.4% titanium powder, 0.8%~1.2% ferromolybdenum, 0.2%~0.4% graphite, 0.002%~0.01% ferroboron, 0.001%~0.005% ferrolanthanum, with the balance being electrolytic iron; perform vacuum induction melting, and then cast the ingots.

[0007] (2) Prepare a remelting slag system, use the ingot obtained in step (1) as a consumable electrode for electroslag remelting, and obtain a remelted ingot; homogenize the remelted ingot and oil quench it to obtain a steel ingot;

[0008] (3) The steel ingot is subjected to multi-directional forging and temperature-controlled cooling to obtain forging die steel;

[0009] (4) The forging die steel is subjected to surface polishing, gas nitriding, deep cryogenic treatment, and finally gradient tempering to obtain the wear-resistant steel-based die material.

[0010] As an optimization, the specific process of vacuum induction melting in step (1) is as follows: weighed electrolytic iron, metallic chromium, ferromolybdenum, ferrolanthanum and ferroboron are loaded into a crucible, vacuumed until the pressure inside the furnace is lower than 5 Pa, and then high-purity argon is introduced to 0.03~0.07 MPa; the temperature is increased at a rate of 10~20 kW every 3~5 min until all the furnace materials are completely melted, and stirred at 1600~1650℃ for 5~7 min; then the temperature is decreased at a rate of 5~10 kW every 3~5 min to 1550~1600℃, titanium powder and graphite are added, and stirred for 1~3 min to obtain a melt; the melt is poured into a preheated cylindrical steel mold and cooled to 25~30℃ under argon protection to obtain an ingot.

[0011] As an optimization, the method for preparing the remelting slag system in step (2) is as follows: calcium fluoride, alumina and calcium oxide are mixed in a mass ratio of (60~70):(15~20):(15~20), dried and calcined at 550~600℃ for 0.5~1.5h, and then cooled to 180~220℃ and held for 3~4h to obtain the slag system.

[0012] As an optimization, the electroslag remelting in step (2) is carried out under nitrogen protection, using an alternating current of 500~700A and 50~55Hz, under a magnetic field of 45~60mT, and the melting rate is controlled at 2~3g / min, with the cooling water pressure of the crystallizer being 0.3MPa.

[0013] As an optimization, in step (2), the homogenization process is as follows: the remelted ingot is kept at 1050~1150℃ for 1.5~2.5h, and then oil quenched.

[0014] As an optimization, the specific process of multi-directional forging and temperature-controlled cooling in step (3) is as follows: heat the steel ingot to 1100~1200℃ and hold it for 1.5~2.5h, and perform multi-directional forging at an initial forging temperature of 1050~1150℃ for 7~9h; after forging, furnace cool it to 450~550℃ at a rate of 15~20℃ / h, hold it for 0.5~1.5h, and then air cool it to 25~30℃.

[0015] As an optimization, the surface polishing in step (4) requires a surface roughness Ra of 0.7~0.9μm; the gas nitriding is carried out in an ammonia atmosphere of 450mL / min, heated to 1000~1100℃ at 8~12℃ / min and held for 1.5~2.5h, then cooled to 850~900℃ and held for 1~2h, and then quenched to 25~30℃ with high-pressure nitrogen gas of 0.6MPa.

[0016] As an optimization, the cryogenic treatment in step (4) involves immersing the workpiece, which has been quenched by high-pressure nitrogen, in liquid nitrogen for 7 to 9 hours.

[0017] As an optimization, in step (4), the gradient tempering process includes: first, heating the cryogenically treated workpiece to 500~600℃ in an air furnace, holding it at that temperature for 4~6h, and then air-cooling it to 25~30℃; then continuing to heat it to 240~260℃, holding it at that temperature for 1.5~2.5h, and then air-cooling it to 25~30℃.

[0018] Compared with the prior art, the beneficial effects achieved by the present invention are:

[0019] This invention, in preparing wear-resistant steel-based mold materials for plastic magnetic injection molding, utilizes a specific alloy composition design, combined with vacuum induction melting, magnetically controlled electroslag remelting, multi-directional forging, and composite heat treatment processes to ultimately obtain high-performance mold materials. Firstly, in the alloy design, 14%–15% chromium, 0.2%–0.4% titanium, and trace amounts of boron and lanthanum are introduced through vacuum melting. Chromium provides an excellent corrosion-resistant substrate, while the combination of titanium and nitrogen creates conditions for the formation of a core reinforcing phase. The addition of trace amounts of boron and lanthanum effectively purifies the molten steel, refines the grains, and strengthens the grain boundaries, thereby improving the material's strength and toughness while enhancing its resistance to crack propagation.

[0020] Secondly, magnetron sputtering remelting under nitrogen protection effectively controls the flow and morphology of the molten metal pool by applying an axial static magnetic field. This results in a shallow, flat pool with a uniform temperature field, significantly refining the dendritic structure, reducing elemental segregation, and laying the foundation for the uniform distribution of the subsequent reinforcing phase. During this process, titanium reacts in situ with nitrogen to generate high-hardness nanoscale TiN particles, which are uniformly dispersed in the matrix. In the subsequent solidification process, controlled cooling induces self-propagating synthesis reactions in local micro-regions, promoting the formation of a "core-shell" reinforcing phase with TiN as the core and a (Cr,Fe)₂N shell. This unique multiphase reinforcing structure is firmly bonded to the matrix and effectively hinders the cutting and ploughing action of abrasive grains, which is the fundamental reason for the material's excellent wear resistance.

[0021] Finally, the combination of high-temperature nitriding and high-pressure nitrogen quenching forms a high-nitrogen supersaturated hardened layer on the material surface. Subsequent cryogenic treatment promotes the transformation of retained austenite and enriches solute atoms at defect sites. Through gradient tempering within a specific temperature range, an in-situ self-generated cermet gradient layer, primarily composed of Cr2N and TiN, is induced to form on the surface, exhibiting metallurgical bonding with the matrix. This gradient layer possesses extremely high hardness, wear and corrosion resistance, and seamlessly transitions with the robust matrix at the core. Consequently, the material ultimately combines extremely high surface hardness and wear resistance, excellent corrosion resistance, and good overall strength and toughness, significantly extending its service life under harsh plastic injection molding conditions. Detailed Implementation

[0022] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0023] To more clearly illustrate the method provided by the present invention, the following embodiments will be described in detail.

[0024] Example 1:

[0025] A method for preparing a wear-resistant steel-based mold material for plastic magnetic injection molding includes the following preparation steps:

[0026] (1) Weigh the raw materials according to the following target composition mass percentages: 14% metallic chromium, 0.2% titanium powder, 0.8% ferromolybdenum, 0.2% graphite, 0.002% ferroboron, 0.001% ferrolanthanum, and the balance is electrolytic iron; put the crucible into the vacuum induction melting furnace, add electrolytic iron, metallic chromium, ferromolybdenum, ferrolanthanum and ferroboron to the crucible in sequence, evacuate the furnace until the pressure inside the furnace is lower than 5Pa, fill with high-purity argon to 0.03MPa, increase the power by 10kW every 3min until all furnace materials are completely melted, maintain the temperature at 1600℃, stir for 5min, decrease the power by 5kW every 3min, control the temperature at 1550℃, add titanium powder and graphite, stir for 1min to obtain the melt; pour the melt into a preheated cylindrical steel mold, cool to 25℃ under argon protection to obtain the ingot;

[0027] (2) Calcium fluoride, alumina and calcium oxide are mixed in a mass ratio of 60:20:20, dried and calcined at 550℃ for 0.5h, cooled to 180℃ and held for 3h to obtain a remelting slag system; the remelting slag system is placed in a crystallizer, the ingot is used as a consumable electrode, and electroslag remelting is carried out under nitrogen protection with an alternating current of 600A and 50Hz and a magnetic field of 50mT, the melting rate is controlled at 2g / min and the cooling water pressure is 0.3MPa to obtain a remelted ingot; the remelted ingot is held at 1050℃ for 1.5h to homogenize, and then oil quenched to obtain a steel ingot;

[0028] (3) Heat the steel ingot to 1100℃ and hold for 1.5h, and perform multi-directional forging at an initial forging temperature of 1050℃ for 7h; after forging, furnace cool to 450℃ at a rate of 15℃ / h, hold for 0.5h, and then air cool to 25℃ to obtain forging die steel.

[0029] (4) Grind the surface of the forging die steel to Ra0.7μm, put it into a tube furnace, introduce ammonia gas at 450mL / min, heat it to 1000℃ at 8℃ / min, hold it for 1.5h, cool it down to 850℃, hold it for 1h, quench it with 0.6MPa high-pressure nitrogen gas, cool it to 25℃, and then soak it in liquid nitrogen for 7h to obtain a cryogenic workpiece; put the cryogenic workpiece into an air furnace, heat it to 500℃, hold it for 4h and then air cool it to 25℃; then continue to heat it to 240℃, hold it for 1.5h and then air cool it to 25℃ to obtain a wear-resistant steel-based mold material for plastic magnetic injection molding.

[0030] Example 2:

[0031] A method for preparing a wear-resistant steel-based mold material for plastic magnetic injection molding includes the following preparation steps:

[0032] (1) Weigh the raw materials according to the following target composition mass percentages: 14.5% metallic chromium, 0.3% titanium powder, 1% ferromolybdenum, 0.3% graphite, 0.006% ferroboron, 0.003% ferrolanthanum, and the balance is electrolytic iron; put the crucible into the vacuum induction melting furnace, add electrolytic iron, metallic chromium, ferromolybdenum, ferrolanthanum and ferroboron to the crucible in sequence, evacuate the furnace until the pressure inside the furnace is lower than 5Pa, fill with high-purity argon to 0.05MPa, increase the power by 15kW every 4min until all the furnace materials are completely melted, maintain the temperature at 1625℃, stir for 6min, decrease the power by 8kW every 4min, control the temperature at 1575℃, add titanium powder and graphite, stir for 2min to obtain the melt; pour the melt into a preheated cylindrical steel mold, cool to 27℃ under argon protection to obtain the ingot;

[0033] (2) Calcium fluoride, alumina and calcium oxide are mixed in a mass ratio of 65:15:20, dried and calcined at 570℃ for 1h, cooled to 200℃ and held for 3.5h to obtain a remelting slag system; the remelting slag system is placed in a crystallizer, the ingot is used as a consumable electrode, and electroslag remelting is carried out under nitrogen protection with an alternating current of 600A and 53Hz and a magnetic field of 50mT, the melting rate is controlled at 2.5g / min and the cooling water pressure is 0.3MPa to obtain a remelted ingot; the remelted ingot is held at 1100℃ for 2h to homogenize, and then oil quenched to obtain a steel ingot;

[0034] (3) Heat the steel ingot to 1150℃ and hold for 2 hours, and perform multi-directional forging at an initial forging temperature of 1100℃ for 8 hours; after forging, furnace cool to 500℃ at a rate of 17℃ / h, hold for 1 hour, and then air cool to 27℃ to obtain forging die steel.

[0035] (4) Grind the surface of the forging die steel to Ra0.8μm, put it into a tube furnace, introduce 450mL / min of ammonia, heat it to 1050℃ at 10℃ / min, hold it for 2h, cool it down to 870℃, hold it for 1.5h, quench it with 0.6MPa high-pressure nitrogen, cool it to 27℃, and then soak it in liquid nitrogen for 8h to obtain a cryogenic workpiece; put the cryogenic workpiece into an air furnace, heat it to 550℃, hold it for 5h and then air cool it to 27℃; then continue to heat it to 250℃, hold it for 2h and then air cool it to 27℃ to obtain a wear-resistant steel-based mold material for plastic magnetic injection molding.

[0036] Example 3:

[0037] A method for preparing a wear-resistant steel-based mold material for plastic magnetic injection molding includes the following preparation steps:

[0038] (1) Weigh the raw materials according to the following target composition mass percentages: 15% metallic chromium, 0.4% titanium powder, 1.2% ferromolybdenum, 0.4% graphite, 0.01% ferroboron, 0.005% ferrolanthanum, and the balance is electrolytic iron; put the crucible into the vacuum induction melting furnace, add electrolytic iron, metallic chromium, ferromolybdenum, ferrolanthanum and ferroboron to the crucible in sequence, evacuate the furnace until the pressure inside the furnace is lower than 5Pa, fill with high-purity argon to 0.07MPa, increase the power by 20kW every 5min until all the furnace materials are completely melted, maintain the temperature at 1650℃, stir for 7min, decrease the power by 10kW every 5min, control the temperature at 1600℃, add titanium powder and graphite, stir for 3min to obtain the melt; pour the melt into a preheated cylindrical steel mold, cool to 30℃ under argon protection to obtain the ingot;

[0039] (2) Calcium fluoride, alumina and calcium oxide are mixed in a mass ratio of 70:15:15, dried and calcined at 600℃ for 1.5h, cooled to 220℃ and held for 4h to obtain a remelting slag system; the remelting slag system is placed in a crystallizer, the ingot is used as a consumable electrode, and electroslag remelting is carried out under nitrogen protection with an alternating current of 600A and 55Hz and a magnetic field of 50mT, the melting rate is controlled at 3g / min and the cooling water pressure is 0.3MPa to obtain a remelted ingot; the remelted ingot is held at 1150℃ for 2.5h to homogenize, and then oil quenched to obtain a steel ingot;

[0040] (3) Heat the steel ingot to 1200℃ and hold for 2.5h, and perform multi-directional forging at an initial forging temperature of 1150℃ for 9h; after forging, furnace cool to 550℃ at a rate of 20℃ / h, hold for 1.5h, and then air cool to 30℃ to obtain forging die steel.

[0041] (4) Grind the surface of the forging die steel to Ra0.9μm, put it into a tube furnace, introduce 450mL / min of ammonia, heat it to 1100℃ at 12℃ / min, hold it for 2.5h, cool it down to 900℃, hold it for 2h, quench it with 0.6MPa high-pressure nitrogen, cool it to 30℃, and then immerse it in liquid nitrogen for 9h to obtain a cryogenic workpiece; put the cryogenic workpiece into an air furnace, heat it to 600℃, hold it for 6h and then air cool it to 30℃; then continue to heat it to 260℃, hold it for 2.5h and then air cool it to 30℃ to obtain a wear-resistant steel-based mold material for plastic magnetic injection molding.

[0042] Comparative Example 1:

[0043] The difference from Example 2 is only in step (2). The phrase "Place the remelting slag system in the crystallizer, use the ingot as the consumable electrode, and electroslag remelt under nitrogen protection with an alternating current of 600A and 53Hz and a magnetic field of 50mT, control the melting rate at 2.5g / min, and the cooling water pressure at 0.3MPa to obtain the remelted ingot" is changed to "Place the remelting slag system in the crystallizer, use the ingot as the consumable electrode, and electroslag remelt under nitrogen protection with an alternating current of 400A and 53Hz and a magnetic field of 50mT, control the melting rate at 2.5g / min, and the cooling water pressure at 0.3MPa to obtain the remelted ingot".

[0044] Comparative Example 2:

[0045] The difference from Example 2 is only in step (2). The phrase "Place the remelted slag system in the crystallizer, use the ingot as the consumable electrode, and electroslag remelt under nitrogen protection with an alternating current of 600A and 53Hz and a magnetic field of 50mT, control the melting rate at 2.5g / min, and the cooling water pressure at 0.3MPa to obtain the remelted ingot" is changed to "Place the remelted slag system in the crystallizer, use the ingot as the consumable electrode, and electroslag remelt under nitrogen protection with an alternating current of 500A and 53Hz and a magnetic field of 50mT, control the melting rate at 2.5g / min, and the cooling water pressure at 0.3MPa to obtain the remelted ingot".

[0046] Comparative Example 3:

[0047] The difference from Example 2 is only in step (2). The phrase "Place the remelted slag system in the crystallizer, use the ingot as the consumable electrode, and electroslag remelt under nitrogen protection with an alternating current of 600A and 53Hz and a magnetic field of 50mT, control the melting rate at 2.5g / min, and the cooling water pressure at 0.3MPa to obtain the remelted ingot" is changed to "Place the remelted slag system in the crystallizer, use the ingot as the consumable electrode, and electroslag remelt under nitrogen protection with an alternating current of 700A and 53Hz and a magnetic field of 50mT, control the melting rate at 2.5g / min, and the cooling water pressure at 0.3MPa to obtain the remelted ingot".

[0048] Comparative Example 4:

[0049] The difference from Example 2 is only in step (2). The phrase "Place the remelting slag system in the crystallizer, use the ingot as the consumable electrode, and electroslag remelt under nitrogen protection with an alternating current of 600A and 53Hz and a magnetic field of 50mT, control the melting rate at 2.5g / min, and the cooling water pressure at 0.3MPa to obtain the remelted ingot" is changed to "Place the remelting slag system in the crystallizer, use the ingot as the consumable electrode, and electroslag remelt under nitrogen protection with an alternating current of 800A and 53Hz and a magnetic field of 50mT, control the melting rate at 2.5g / min, and the cooling water pressure at 0.3MPa to obtain the remelted ingot".

[0050] Comparative Example 5:

[0051] The difference from Example 2 is only in step (2). The phrase "Place the remelted slag system in the crystallizer, use the ingot as the consumable electrode, and electroslag remelt under nitrogen protection with an alternating current of 600A and 53Hz and a magnetic field of 50mT, control the melting rate at 2.5g / min, and the cooling water pressure at 0.3MPa to obtain the remelted ingot" is changed to "Place the remelted slag system in the crystallizer, use the ingot as the consumable electrode, and electroslag remelt under nitrogen protection with an alternating current of 600A and 53Hz and a magnetic field of 40mT, control the melting rate at 2.5g / min, and the cooling water pressure at 0.3MPa to obtain the remelted ingot".

[0052] Comparative Example 6:

[0053] The difference from Example 2 is only in step (2). The phrase "Place the remelting slag system in the crystallizer, use the ingot as the consumable electrode, and electroslag remelt under nitrogen protection with an alternating current of 600A and 53Hz and a magnetic field of 50mT, control the melting rate at 2.5g / min, and the cooling water pressure at 0.3MPa to obtain the remelted ingot" is changed to "Place the remelting slag system in the crystallizer, use the ingot as the consumable electrode, and electroslag remelt under nitrogen protection with an alternating current of 600A and 53Hz and a magnetic field of 45mT, control the melting rate at 2.5g / min, and the cooling water pressure at 0.3MPa to obtain the remelted ingot".

[0054] Comparative Example 7:

[0055] The difference from Example 2 is only in step (2). The phrase "Place the remelting slag system in the crystallizer, use the ingot as the consumable electrode, and electroslag remelt under nitrogen protection with an alternating current of 600A and 53Hz and a magnetic field of 50mT, control the melting rate at 2.5g / min, and the cooling water pressure at 0.3MPa to obtain the remelted ingot" is changed to "Place the remelting slag system in the crystallizer, use the ingot as the consumable electrode, and electroslag remelt under nitrogen protection with an alternating current of 600A and 53Hz and a magnetic field of 55mT, control the melting rate at 2.5g / min, and the cooling water pressure at 0.3MPa to obtain the remelted ingot".

[0056] Comparative Example 8:

[0057] The difference from Example 2 is only in step (2). The phrase "Place the remelting slag system in the crystallizer, use the ingot as the consumable electrode, and electroslag remelt under nitrogen protection with an alternating current of 600A and 53Hz and a magnetic field of 50mT, control the melting rate at 2.5g / min, and the cooling water pressure at 0.3MPa to obtain the remelted ingot" is changed to "Place the remelting slag system in the crystallizer, use the ingot as the consumable electrode, and electroslag remelt under nitrogen protection with an alternating current of 600A and 53Hz and a magnetic field of 60mT, control the melting rate at 2.5g / min, and the cooling water pressure at 0.3MPa to obtain the remelted ingot".

[0058] Comparative Example 9:

[0059] A method for preparing a wear-resistant steel-based mold material for plastic magnetic injection molding includes the following preparation steps:

[0060] (1) Weigh the raw materials according to the following target composition mass percentages: 14.5% metallic chromium, 0.3% titanium powder, 1% ferromolybdenum, 0.3% graphite, and the balance is electrolytic iron; put the crucible into the vacuum induction melting furnace, add electrolytic iron, metallic chromium and ferromolybdenum to the crucible in sequence, evacuate the furnace until the pressure inside the furnace is lower than 5Pa, fill with high-purity argon to 0.05MPa, increase the power by 15kW every 4min until all the furnace materials are completely melted, maintain the temperature at 1625℃, stir for 6min, decrease the power by 8kW every 4min, control the temperature at 1575℃, add titanium powder and graphite, stir for 2min to obtain the melt; pour the melt into a preheated cylindrical steel mold, cool to 27℃ under argon protection to obtain the ingot;

[0061] (2) Calcium fluoride, alumina and calcium oxide are mixed in a mass ratio of 65:15:20, dried and calcined at 570℃ for 1h, cooled to 200℃ and held for 3.5h to obtain a remelting slag system; the remelting slag system is placed in a crystallizer, the ingot is used as a consumable electrode, and electroslag remelting is carried out under nitrogen protection with an alternating current of 600A and 53Hz and a magnetic field of 50mT, the melting rate is controlled at 2.5g / min and the cooling water pressure is 0.3MPa to obtain a remelted ingot; the remelted ingot is held at 1100℃ for 2h to homogenize, and then oil quenched to obtain a steel ingot;

[0062] (3) Heat the steel ingot to 1150℃ and hold for 2 hours, and perform multi-directional forging at an initial forging temperature of 1100℃ for 8 hours; after forging, furnace cool to 500℃ at a rate of 17℃ / h, hold for 1 hour, and then air cool to 27℃ to obtain forging die steel.

[0063] (4) Grind the surface of the forging die steel to Ra0.8μm, put it into a tube furnace, introduce 450mL / min of ammonia, heat it to 1050℃ at 10℃ / min, hold it for 2h, cool it down to 870℃, hold it for 1.5h, quench it with 0.6MPa high-pressure nitrogen, cool it to 27℃, and then soak it in liquid nitrogen for 8h to obtain a cryogenic workpiece; put the cryogenic workpiece into an air furnace, heat it to 550℃, hold it for 5h and then air cool it to 27℃; then continue to heat it to 250℃, hold it for 2h and then air cool it to 27℃ to obtain a wear-resistant steel-based mold material for plastic magnetic injection molding.

[0064] Comparative Example 10:

[0065] A method for preparing a wear-resistant steel-based mold material for plastic magnetic injection molding includes the following preparation steps:

[0066] (1) Weigh the raw materials according to the following target composition mass percentages: 14.5% metallic chromium, 0.3% titanium powder, 1% ferromolybdenum, 0.3% graphite, 0.006% ferroboron, 0.003% ferrolanthanum, and the balance is electrolytic iron; put the crucible into the vacuum induction melting furnace, add electrolytic iron, metallic chromium, ferromolybdenum, ferrolanthanum and ferroboron to the crucible in sequence, evacuate the furnace until the pressure inside the furnace is lower than 5Pa, fill with high-purity argon to 0.05MPa, increase the power by 15kW every 4min until all the furnace materials are completely melted, maintain the temperature at 1625℃, stir for 6min, decrease the power by 8kW every 4min, control the temperature at 1575℃, add titanium powder and graphite, stir for 2min to obtain the melt; pour the melt into a preheated cylindrical steel mold, cool to 27℃ under argon protection to obtain the ingot;

[0067] (2) Heat the ingot to 1150℃ and hold for 2 hours, and perform multi-directional forging at an initial forging temperature of 1100℃ for 8 hours; after forging, furnace cool to 500℃ at a rate of 17℃ / h, hold for 1 hour, and then air cool to 27℃ to obtain forging die steel.

[0068] (3) The forging die steel is placed in a tube furnace and heated to 1050°C at 10°C / min. It is held for 2 hours and then oil-quenched to 27°C to obtain a homogenized workpiece. The homogenized workpiece is placed in an air furnace, heated to 550°C, held for 5 hours and then air-cooled to 27°C. Then it is heated to 250°C, held for 2 hours and then air-cooled to 27°C to obtain a wear-resistant steel-based mold material for plastic magnetic injection molding.

[0069] Comparative Example 11:

[0070] A method for preparing a wear-resistant steel-based mold material for plastic magnetic injection molding includes the following preparation steps:

[0071] (1) Weigh the raw materials according to the following target composition mass percentages: 14.5% metallic chromium, 0.3% titanium powder, 1% ferromolybdenum, 0.3% graphite, 0.006% ferroboron, 0.003% ferrolanthanum, and the balance is electrolytic iron; put the crucible into the vacuum induction melting furnace, add electrolytic iron, metallic chromium, ferromolybdenum, ferrolanthanum and ferroboron to the crucible in sequence, evacuate the furnace until the pressure inside the furnace is lower than 5Pa, fill with high-purity argon to 0.05MPa, increase the power by 15kW every 4min until all the furnace materials are completely melted, maintain the temperature at 1625℃, stir for 6min, decrease the power by 8kW every 4min, control the temperature at 1575℃, add titanium powder and graphite, stir for 2min to obtain the melt; pour the melt into a preheated cylindrical steel mold, cool to 27℃ under argon protection to obtain the ingot;

[0072] (2) Calcium fluoride, alumina and calcium oxide are mixed in a mass ratio of 65:15:20, dried and calcined at 570℃ for 1h, cooled to 200℃ and held for 3.5h to obtain a remelting slag system; the remelting slag system is placed in a crystallizer, the ingot is used as a consumable electrode, and electroslag remelting is carried out under nitrogen protection with an alternating current of 600A and 53Hz and a magnetic field of 50mT, the melting rate is controlled at 2.5g / min and the cooling water pressure is 0.3MPa to obtain a remelted ingot; the remelted ingot is held at 1100℃ for 2h to homogenize, and then oil quenched to obtain a steel ingot;

[0073] (3) Heat the steel ingot to 1150℃ and hold for 2 hours, and perform multi-directional forging at an initial forging temperature of 1100℃ for 8 hours; after forging, furnace cool to 500℃ at a rate of 17℃ / h, hold for 1 hour, and then air cool to 27℃ to obtain forging die steel.

[0074] (4) The forging die steel is placed in a tube furnace and heated to 1050°C at 10°C / min. It is held for 2 hours and then oil-quenched to 27°C to obtain a homogenized workpiece. The homogenized workpiece is placed in an air furnace, heated to 550°C, held for 5 hours and then air-cooled to 27°C. Then it is heated to 250°C, held for 2 hours and then air-cooled to 27°C to obtain a wear-resistant steel-based mold material for plastic magnetic injection molding.

[0075] Comparative Example 12:

[0076] A method for preparing a wear-resistant steel-based mold material for plastic magnetic injection molding includes the following preparation steps:

[0077] (1) Weigh the raw materials according to the following target composition mass percentages: 14.5% metallic chromium, 1% ferromolybdenum, 0.3% graphite, 0.006% ferroboron, 0.003% ferrolanthanum, and the balance is electrolytic iron; put the crucible into the vacuum induction melting furnace, add electrolytic iron, metallic chromium, ferromolybdenum, ferrolanthanum and ferroboron to the crucible in sequence, evacuate the furnace until the pressure inside the furnace is lower than 5Pa, fill with high-purity argon to 0.05MPa, increase the power by 15kW every 4min until all the furnace materials are completely melted, maintain the temperature at 1625℃, stir for 6min, decrease the power by 8kW every 4min, control the temperature at 1575℃, add graphite, stir for 2min to obtain the melt; pour the melt into a preheated cylindrical steel mold, cool to 27℃ under argon protection to obtain the ingot;

[0078] (2) Calcium fluoride, alumina and calcium oxide are mixed in a mass ratio of 65:15:20, dried and calcined at 570℃ for 1h, cooled to 200℃ and held for 3.5h to obtain a remelting slag system; the remelting slag system is placed in a crystallizer, the ingot is used as a consumable electrode, and electroslag remelting is carried out under argon protection with an alternating current of 600A and 53Hz and a magnetic field of 50mT, the melting rate is controlled at 2.5g / min and the cooling water pressure is 0.3MPa to obtain a remelted ingot; the remelted ingot is held at 1100℃ for 2h to homogenize, and then oil quenched to obtain a steel ingot;

[0079] (3) Heat the steel ingot to 1150℃ and hold for 2 hours, and perform multi-directional forging at an initial forging temperature of 1100℃ for 8 hours; after forging, furnace cool to 500℃ at a rate of 17℃ / h, hold for 1 hour, and then air cool to 27℃ to obtain forging die steel.

[0080] (4) Grind the surface of the forging die steel to Ra0.8μm, put it into a tube furnace, introduce 450mL / min of ammonia, heat it to 1050℃ at 10℃ / min, hold it for 2h, cool it down to 870℃, hold it for 1.5h, quench it with 0.6MPa high-pressure nitrogen, cool it to 27℃, and then soak it in liquid nitrogen for 8h to obtain a cryogenic workpiece; put the cryogenic workpiece into an air furnace, heat it to 550℃, hold it for 5h and then air cool it to 27℃; then continue to heat it to 250℃, hold it for 2h and then air cool it to 27℃ to obtain a wear-resistant steel-based mold material for plastic magnetic injection molding.

[0081] Experimental Example 1:

[0082] Determination of optimal reaction conditions for magnetron electroslag remelting (alternating current, magnetic field conditions)

[0083] Test method: Determined through friction loss testing. Friction and wear testing was conducted at room temperature using a pin-disc wear testing machine. The wear-resistant steel-based mold material used for plastic magnetic injection molding was machined into a regular block with dimensions of 45mm × 15mm. Test conditions were: load 100N, rotation speed 100r / min, duration 15min. The average coefficient of friction was recorded during the test, and the sample was weighed before and after the test to obtain the wear loss weight.

[0084] The results are shown in Table 1.

[0085] Table 1

[0086]

[0087] Through comparisons of Example 2 and Comparisons 1-4, it can be found that a current value of 600A achieves an optimal balance between heat input and solidification structure during electroslag remelting. If the current is too low, the heat input will be insufficient, which may lead to uneven slag pool temperature and incomplete metallurgical reaction; while if the current is too high, although it can provide sufficient heat, it will cause the molten metal pool to deepen significantly and the local solidification time to be prolonged. This will promote the increase of the secondary dendrite arm spacing and the more severe segregation of carbide forming elements between dendrites, creating conditions for the precipitation of coarse, network-like primary carbides. These coarse hard phases are prone to becoming crack sources during service, impairing the strength, toughness and wear resistance of the material.

[0088] Through comparisons of Examples 2 and Comparisons 1-4, it can be observed that the electromagnetic force generated by applying a 50mT axial static magnetic field plays a crucial "active control" role. When the magnetic field is too low, the electromagnetic force may be insufficient, resulting in inadequate droplet refinement and insufficient stirring intensity in the molten pool, thus limiting the effects of microstructure refinement and impurity removal. Conversely, if the magnetic field is too high, excessive electromagnetic stirring may cause the molten pool to flow too violently, interfering with stable directional solidification and even re-entraining already floated inclusions, which is detrimental to performance improvement. Therefore, the 50mT magnetic field used can generate sufficient electromagnetic force to effectively break up molten droplets, homogenize the composition and temperature of the molten pool, while avoiding the negative effects of excessive stirring, thereby achieving the optimal balance between purifying the molten steel and refining the microstructure.

[0089] Experimental Example 2:

[0090] This example tests the performance of the wear-resistant steel-based mold materials for plastic magnetic injection molding obtained in Examples 1-3 and Comparative Examples 9-12. The specific test items and methods are as follows:

[0091] Wear resistance testing method: Friction and wear tests were conducted at room temperature using a pin-disc wear testing machine. The wear-resistant steel-based mold materials for plastic magnetic injection molding obtained in each embodiment, along with the materials from Comparative Examples 9-12, were processed into regular blocks with dimensions of 45mm × 15mm × 4mm. The test conditions were: load 100N, rotation speed 100r / min, and duration 15min. The average coefficient of friction was recorded during the test, and the samples were weighed before and after the test to obtain the wear loss weight.

[0092] Hardness testing method: The hardness of the wear-resistant steel-based mold materials used for plastic magnetic injection molding in each embodiment and the materials of comparative examples 9-12 were measured using a microhardness tester (FM-ARS900). The load was 0.2N and the holding time was 15s.

[0093] Corrosion resistance test method: The wear-resistant steel-based mold material for plastic magnetic injection molding obtained in each embodiment and the material of comparative examples 9 to 12 were processed into samples with a size of 60mm×40mm×4mm according to standard TB / T2375-93. Then, they were polished and ground to a surface roughness Ra≤0.8. The test solution was prepared with sodium bisulfite solution that meets the requirements of HG3-1291 standard. The cyclic immersion equipment was a calibrated high-throughput integrated test chamber with a temperature of 45℃ and 70%RH. Each cycle was 60min and the immersion time was 12min.

[0094] The results are shown in Table 2.

[0095] Table 2

[0096]

[0097] By comparing Examples 1-3 with Comparative Example 9, it can be found that adding trace amounts of boron and lanthanum elements during the preparation of wear-resistant steel-based mold materials for plastic magnetic injection molding can improve the wear resistance of the material by allowing boron to segregate at grain boundaries and lanthanum to refine grains and purify molten steel. Furthermore, the synergistic effect of the two elements can improve the corrosion resistance of the material by reducing the number of harmful inclusions and improving their morphology.

[0098] A comparison of Examples 1-3 with Comparative Example 10 reveals that the composite process of "in-situ synthesis of TiN via magnetron electroslag remelting" and "nitriding heat treatment" in the material preparation process allows titanium and nitrogen to react in the molten steel during electroslag remelting, generating dispersed nano-TiN particles in situ within the matrix. This significantly enhances the material's resistance to plastic deformation and micro-cutting, thereby improving overall wear resistance. Furthermore, in the subsequent nitriding heat treatment, chromium and titanium on the matrix surface react with the infiltrated nitrogen in the solid state, generating a gradient cermet layer dominated by high-hardness Cr2N and TiN in situ. This reaction directly forms a high-hardness nitride reinforcement layer on the material surface, resulting in a significant increase in surface Vickers hardness. Simultaneously, this continuous and dense chromium-rich nitride surface layer acts as a stable chemical barrier, effectively preventing the intrusion of corrosive media and enhancing passivation capabilities, thus greatly improving the material's corrosion resistance.

[0099] By comparing Examples 1-3 with Comparative Example 11, it can be found that when the "nitriding" process is omitted during heat treatment, the substrate surface cannot generate a high-hardness gradient ceramic layer in situ through the solid-state reaction of chromium, titanium and nitrogen. Therefore, the surface Vickers hardness of the material cannot be further improved. At the same time, due to the lack of a chemical barrier composed of dense chromium-rich nitrides on the surface, corrosive media can penetrate more easily, thus limiting the further improvement of the material's corrosion resistance.

[0100] A comparison of Examples 1-3 with Comparative Example 12 reveals that in the material preparation process, only a single process of "heat treatment-induced surface gradient ceramic layer" is used. In the subsequent nitriding heat treatment, the chromium and titanium on the substrate surface react with the diffused nitrogen in the solid state to generate a gradient metal-ceramic layer mainly composed of high-hardness Cr2N and TiN in situ. This reaction directly forms a high-hardness nitride reinforcement layer on the material surface, thereby significantly improving the surface Vickers hardness. At the same time, this continuous and dense chromium-rich nitride surface layer acts as a stable chemical barrier, effectively preventing the intrusion of corrosive media, thus improving the corrosion resistance of the material. However, since the preceding electroslag remelting process is carried out under argon protection, no in-situ reaction between titanium and nitrogen occurs, and the substrate lacks dispersed nano-TiN particle reinforcement. Therefore, the overall wear resistance of the material cannot be further improved, and its wear performance mainly depends on the surface ceramic layer.

[0101] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from its spirit or essential characteristics. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, all variations falling within the meaning and scope of equivalents of the claims are intended to be included within the present invention. No markings in the claims should be construed as limiting the scope of the claims.

Claims

1. A method for preparing a wear-resistant steel-based mold material for plastic magnetic injection molding, characterized in that, Includes the following steps: (1) Weigh the raw materials by mass percentage: 14%~15% metallic chromium, 0.2%~0.4% titanium powder, 0.8%~1.2% ferromolybdenum, 0.2%~0.4% graphite, 0.002%~0.01% ferroboron, 0.001%~0.005% ferrolanthanum, with the balance being electrolytic iron; perform vacuum induction melting, and then cast the ingots. (2) Prepare a remelting slag system, use the ingot obtained in step (1) as a consumable electrode for electroslag remelting, and obtain a remelted ingot; homogenize the remelted ingot and oil quench it to obtain a steel ingot; (3) The steel ingot is subjected to multi-directional forging and temperature-controlled cooling to obtain forging die steel; (4) The forging die steel is subjected to surface polishing, gas nitriding, high-pressure nitrogen quenching, deep cryogenic treatment, and finally gradient tempering to obtain the wear-resistant steel-based die material.

2. The method for preparing a wear-resistant steel-based mold material for plastic magnetic injection molding according to claim 1, characterized in that, The titanium powder in step (1) has a purity of >99.5% and a particle size of <45μm.

3. The method for preparing a wear-resistant steel-based mold material for plastic magnetic injection molding according to claim 1, characterized in that, The specific process of vacuum induction melting in step (1) is as follows: Weighed electrolytic iron, metallic chromium, ferromolybdenum, ferrolanthanum and ferroboron are loaded into a crucible, and a vacuum is drawn until the pressure inside the furnace is lower than 5 Pa. Then, high-purity argon gas is introduced to 0.03~0.07 MPa. The temperature is increased at a rate of 10~20 kW every 3~5 min until all the furnace materials are completely melted. The mixture is stirred at 1600~1650℃ for 5~7 min. Then, the temperature is decreased at a rate of 5~10 kW every 3~5 min to 1550~1600℃. Titanium powder and graphite are added and stirred for 1~3 min to obtain a melt. The melt is poured into a preheated cylindrical steel mold and cooled to 25~30℃ under argon protection to obtain an ingot.

4. The method for preparing a wear-resistant steel-based mold material for plastic magnetic injection molding according to claim 1, characterized in that, The method for preparing the remelting slag system in step (2) is as follows: calcium fluoride, alumina and calcium oxide are mixed in a mass ratio of (60~70):(15~20):(15~20), dried and calcined at 550~600℃ for 0.5~1.5h, and then cooled to 180~220℃ and kept at 3~4h to obtain the slag system.

5. The method for preparing a wear-resistant steel-based mold material for plastic magnetic injection molding according to claim 1, characterized in that, The electroslag remelting in step (2) is carried out under nitrogen protection, using an alternating current of 500~700A and 50~55Hz, under a magnetic field of 45~60mT, with the melting rate controlled at 2~3g / min, and the cooling water pressure of the crystallizer at 0.3MPa.

6. The method for preparing a wear-resistant steel-based mold material for plastic magnetic injection molding according to claim 1, characterized in that, In step (2), the homogenization process is as follows: the remelted ingot is kept at 1050~1150℃ for 1.5~2.5h, and then oil quenched.

7. The method for preparing a wear-resistant steel-based mold material for plastic magnetic injection molding according to claim 1, characterized in that, The specific process of multi-directional forging and temperature-controlled cooling in step (3) is as follows: heat the steel ingot to 1100~1200℃ and hold it for 1.5~2.5h, and perform multi-directional forging at an initial forging temperature of 1050~1150℃ for 7~9h; after forging, furnace cool it to 450~550℃ at a rate of 15~20℃ / h, hold it for 0.5~1.5h, and then air cool it to 25~30℃.

8. The method for preparing a wear-resistant steel-based mold material for plastic magnetic injection molding according to claim 1, characterized in that, The surface polishing in step (4) requires a surface roughness Ra of 0.7~0.9μm; the gas nitriding is carried out in an ammonia atmosphere of 450mL / min, heated to 1000~1100℃ at 8~12℃ / min and held for 1.5~2.5h, then cooled to 850~900℃ and held for 1~2h, and then quenched to 25~30℃ with high-pressure nitrogen gas of 0.6MPa.

9. A method for preparing a wear-resistant steel-based mold material for plastic magnetic injection molding according to claim 1 or 8, characterized in that, The cryogenic treatment in step (4) involves immersing the workpiece, which has been quenched by high-pressure nitrogen, in liquid nitrogen for 7 to 9 hours.

10. A method for preparing a wear-resistant steel-based mold material for plastic magnetic injection molding according to claim 1, characterized in that, In step (4), the gradient tempering process includes: first, heating the cryogenically treated workpiece to 500~600℃ in an air furnace, holding it at that temperature for 4~6h, and then air cooling it to 25~30℃; then continuing to heat it to 240~260℃, holding it at that temperature for 1.5~2.5h, and then air cooling it to 25~30℃.

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