A mold steel with high uniformity and high mirror polishing performance and preparation method thereof

Abstract

The invention discloses a high-uniform high-mirror-polishing performance mold steel and a preparation method thereof, which belongs to the technical field of tool and die steel, and solves the problems of serious carbide segregation and poor organizational uniformity in the prior art plastic mold steel. The components of the high-uniform high-mirror-polishing performance mold steel include, by mass percentage: C: 0.10% to 0.30%, Si: ≤1%, Mn: ≤1%, Cr: 10.0% to 14.0%, Ni: 0.2% to 2.0%, Mo: 0.5% to 1.0%, V: 0.005% to 1.00%, N: 0.15% to 0.50%, and the remainder is Fe and unavoidable impurities. The high-uniform high-mirror-polishing performance mold steel of the invention has good uniformity, excellent cutting performance, and excellent corrosion resistance.

Description

Technical Field

[0001] The invention relates to the technical field of tool steel, and in particular to a tool steel with high uniformity and high mirror polishing performance and a preparation method thereof. Background Art

[0002] As a high-end product among mold steels, corrosion-resistant plastic mold steel is mainly used for special engineering plastics with high forming temperatures and plastics containing flame retardants. This raw material will decompose in a molten state to produce a large amount of corrosive gases, such as hydrogen chloride, hydrogen fluoride and sulfur dioxide, which will corrode the plastic mold cavity used, resulting in a reduction in the service life of the mold. Therefore, this type of mold should have certain corrosion resistance. Currently, the commonly used corrosion-resistant plastic mold steels are 4Cr13, 9Cr18, etc., which belong to martensitic stainless steel. However, this type of steel still has problems such as severe carbide segregation, poor organizational uniformity, and insufficient corrosion resistance. It is difficult to meet the requirements of ultra-high precision plastic products for high polishing performance and corrosion resistance, which restricts the quality stabilization and high-end market of this type of steel, and its performance needs to be further improved. Summary of the invention

[0003] In view of the above situation, the present invention aims to provide a high-uniformity and high-mirror polishing performance mold steel and a preparation method thereof, which are used to solve the problems of severe carbide segregation and poor organizational uniformity in the existing high-nitrogen corrosion-resistant plastic mold steel; and the inability to take into account hardness, corrosion resistance and wear resistance at the same time.

[0004] The purpose of the present invention is mainly achieved through the following technical solutions:

[0005] The invention provides a high-uniform and high-mirror-polishing performance mold steel. The components of the high-uniform and high-mirror-polishing performance mold steel include, by mass percentage: C: 0.10%-0.30%, Si: ≤1%, Mn: ≤1%, Cr: 10.0%-14.0%, Ni: 0.2%-2.0%, Mo: 0.5%-1.0%, V: 0.005%-1.00%, N: 0.15%-0.50%, and the balance is Fe and inevitable impurities.

[0006] Furthermore, the components of the mold steel with high uniformity and high mirror polishing performance are further added with one or more of the following elements, in percentage by mass: Cu≤0.5%, Nb≤0.05%, Co≤0.5%, and rare earth elements≤0.05%.

[0007] Furthermore, the components of the high-uniform and high-mirror-polishing performance mold steel include, by mass percentage: C: 0.11% to 0.30%, Si: 0.20% to 0.80%, Mn: 0.20% to 0.80%, Cr: 10.2% to 13.7%, Ni: 0.2% to 1.9%, Mo: 0.5% to 1.0%, V: 0.005% to 0.95%, N: 0.15% to 0.50%, and the remainder is Fe and unavoidable impurities.

[0008] The present invention also provides a method for preparing a mold steel with high uniformity and high mirror polishing performance, which is used to prepare the above-mentioned mold steel with high uniformity and high mirror polishing performance, comprising:

[0009] Step 1, smelting and casting to obtain an electrode blank, and subjecting the electrode blank to slow cooling or heat preservation annealing treatment;

[0010] Step 2, remelting the electrode blank in a pressurized electroslag furnace, casting it into a steel ingot, and subjecting the steel ingot to slow cooling or heat preservation annealing treatment;

[0011] Step 3, forging the steel ingot to obtain a forging blank;

[0012] Step 4, dispersing the forging blank;

[0013] Step 5, annealing the steel after dispersion treatment;

[0014] Step 6: quench the annealed steel and then perform tempering; or quench the annealed steel, perform deep cooling, and then perform tempering.

[0015] Furthermore, in step 3, forging includes: fully heating the steel ingot and keeping it warm before forging; the heating temperature is controlled at 1160-1200° C. and the keeping time is 10-15 hours.

[0016] Furthermore, in step 3, the initial forging temperature is 1160-1200°C, and the final forging temperature is 830-860°C.

[0017] Furthermore, in step 4, the dispersion treatment includes: heating the forging blank to a first holding temperature of 980-1020°C for 1-2 hours, and then water cooling to room temperature; then holding at a second holding temperature of 630-670°C for 2-4 hours, and air cooling to room temperature.

[0018] Furthermore, in step 5, the annealing treatment includes: heating the steel after dispersion treatment to 850±10°C and keeping it warm for 1 to 2 hours; furnace cooling to 650±10°C and keeping it warm for 1 to 2 hours, and then furnace cooling to below 400°C and taking it out of the furnace.

[0019] Furthermore, in step 6, the tempering treatment is performed at 150-520°C.

[0020] Furthermore, in step 6, the microstructure of the steel after tempering is martensite + fine dispersed carbide and carbonitride precipitation phases, the martensite laths are uniform, and no obvious network segregation and strip segregation are observed.

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

[0022] a) The high uniformity and high mirror polishing performance mold steel of the present invention adopts low C, adds appropriate amounts of Cr, Mo, V and N elements, reduces carbide and tissue segregation, and obtains a structure of martensite + fine dispersed carbide and carbonitride precipitation phase under appropriate dispersion treatment and quenching + tempering process. The martensite laths are uniform without obvious network segregation and strip segregation, thereby obtaining a mold steel with high uniformity, high mirror polishing performance and excellent corrosion resistance.

[0023] b) The high uniformity and high mirror polishing performance mold steel prepared by the composition and method of the present invention has good comprehensive mechanical properties, good uniformity of the steel after annealing, and excellent cutting performance. The structure of the steel after tempering is uniform, and the steel after tempering has high tempering hardness, high impact toughness and low roughness, meets the mirror polishing performance requirements, and has excellent corrosion resistance.

[0024] Other features and advantages of the present invention will be described in the following description, and part of them will become obvious from the description, or will be understood by practicing the present invention. The purpose and other advantages of the present invention can be realized and obtained by the structures particularly pointed out in the written description, claims, and drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] The drawings are only for the purpose of illustrating particular embodiments and are not to be considered limiting of the present invention. Like reference symbols denote like components throughout the drawings.

[0026] Figure 1 The tempered structure is 50× of Example 2;

[0027] Figure 2 The tempered structure is 100× of Comparative Example 1;

[0028] Figure 3 The tempered structure of the steel in Example 1 after tempering at 240°C is 500×;

[0029] Figure 4 The tempered structure of the steel of comparative example 1 after tempering at 240°C is 500×;

[0030] Figure 5 The tempered structure of the steel in Example 1 after tempering at 500°C is 500×;

[0031] Figure 6 This is the tempered structure 500× of the steel in Comparative Example 1 after tempering at 500°C. DETAILED DESCRIPTION

[0032] Preferred embodiments of the present invention will be described in detail below in conjunction with the accompanying drawings, wherein the accompanying drawings constitute a part of the present invention and are used to explain the principles of the present invention together with the embodiments of the present invention.

[0033] The invention provides a high-uniform and high-mirror-polishing performance mold steel. The components of the high-uniform and high-mirror-polishing performance mold steel include, by mass percentage: C: 0.10%-0.30%, Si: ≤1%, Mn: ≤1%, Cr: 10.0%-14.0%, Ni: 0.2%-2.0%, Mo: 0.5%-1.0%, V: 0.005%-1.00%, N: 0.15%-0.50%, and the balance is Fe and inevitable impurities.

[0034] The following is a detailed description of the effects and dosage of the components in the present invention:

[0035] C: The carbon content in steel determines the matrix hardness of the steel. For tool steel, part of the carbon dissolves into the matrix to play a role in solid solution strengthening, and the other part of the carbon combines with strong carbide forming elements to form alloy carbides. C forms alloy carbides with some alloy elements to improve the hardness and wear resistance of the steel, and the uniformly dispersed alloy carbides and tempered martensite structure affect the corrosion resistance of the steel. In order to obtain higher hardness, wear resistance and corrosion resistance, the carbon content is controlled at 0.10% to 0.30% in the present invention.

[0036] Si: Silicon is added as a reducing agent and deoxidizer in the steelmaking process, and has a significant effect on improving corrosion resistance. However, too high Si content will not only lead to a decrease in the toughness of the steel, but also promote the formation of segregation. Therefore, the silicon content is generally controlled below 1%.

[0037] Mn: Manganese is an element that improves the hardenability of steel, so that the core can also achieve the desired mechanical properties. An appropriate amount of manganese can also effectively improve the strength, hardness and toughness of steel, eliminate the harmful effects of sulfur and oxygen on steel, improve the hot working performance of steel, and improve the cold brittle tendency of steel. However, too high a manganese content is prone to segregation, so the Mn content in the present invention is controlled to be below 1.0%.

[0038] Ni: Nickel is an important element for improving hardenability. In some steels, it can improve the strength and toughness of steel. The addition of Ni can improve the passivation tendency of Fe-Cr alloys, and can not only improve the corrosion resistance of steel in acid and alkali media, but also have corrosion resistance to air and salt. The Ni content in the steel of the present invention is determined to be 0.2% to 2.0%.

[0039] Cr: As the main component of corrosion-resistant steel, chromium can not only improve the hardenability of Fe-Cr alloy, but also guarantee the corrosion resistance and rust-proofness of steel. However, too high Cr content will promote the formation of high-temperature ferrite and network carbide, affecting the performance of steel. Therefore, the present invention controls the Cr content to 10.0% to 14.0%.

[0040] Mo: Molybdenum in steel can improve the hardenability of steel. At the same time, Mo combines with C and N elements to produce carbides and carbonitrides, which improve the secondary hardening ability and tempering stability of steel. Mo is also a main element for improving corrosion resistance, but too high Mo content will promote the formation of ferrite and reduce the strength and toughness of steel. The present invention further improves the corrosion resistance of steel through Mo-Ni composite, and controls the Mo content to 0.5% to 1.0%.

[0041] V: Vanadium can reduce the overheat sensitivity of steel. A small amount of V element can refine the grains and promote the dispersion and precipitation of carbides through proper heat treatment, which plays a role in strengthening secondary hardening. However, too high a V content will increase the probability of primary carbide formation in the steel and affect the toughness of the steel. The present invention controls the V content to 0.005% to 1.00%.

[0042] N: Nitrogen is an interstitial solid solution element that can produce a significant solid solution strengthening effect and can also improve the corrosion resistance of steel. The present invention replaces part of C with N to reduce the coarse carbides formed by excessive C content combined with Cr, which is detrimental to the uniformity of the structure and polishing performance. High hardness is obtained by N alloying to improve the polishing performance. At the same time, a small amount of N combines with Cr and V to precipitate fine and dispersed Cr2N and NV carbides during the tempering process, which has a precipitation strengthening effect, so that the steel obtains high hardness, thereby improving the polishing performance and the wear resistance of the steel. The present invention uses the concept of distributed strengthening of nitrogen to control N at 0.15% to 0.50%.

[0043] P: Phosphorus forms microscopic segregation when the molten steel solidifies, and then segregates at the grain boundary when heated to the austenitizing temperature, which significantly increases the brittleness of the steel. The present invention controls the P content to be below 0.030%, and the lower the content, the better.

[0044] S: Sulfur is an inevitable impurity, forming FeS, which brings hot brittleness to the steel. The present invention controls the S content to be below 0.030%, and the lower the content, the better.

[0045] In order to further improve the comprehensive performance of the above-mentioned high-uniform and high-mirror-polishing performance mold steel, the components of the above-mentioned high-uniform and high-mirror-polishing performance mold steel can also be added with one or more of the following elements, in terms of mass percentage, including: Cu≤0.5%, Nb≤0.05%, Co≤0.5%, rare earth elements≤0.05%.

[0046] The functions and proportions of the above elements are as follows:

[0047] Cu: Copper is an austenite-forming element that can improve corrosion resistance and cause a secondary hardening effect. However, if the copper content is too high, it will be sensitive to overheating. In the present invention, the copper content is controlled to be ≤0.5%.

[0048] Nb: Niobium can refine grains, increase grain coarsening temperature, reduce overheat sensitivity and temper brittleness of steel, and improve strength and toughness of steel under certain conditions. In the present invention, ≤0.05% niobium is added.

[0049] Co: Cobalt is an austenite-forming element that improves tempering stability. Cobalt can improve the strength of steel by solid solution strengthening, and can also promote the second phase dispersion precipitation strengthening effect to obtain ultra-high strength and good comprehensive mechanical properties. The present invention controls the cobalt content to ≤0.5%.

[0050] Rare earth elements: Rare earth elements can refine the cast structure of steel. For large-sized steel, large ingot steel ingots are required for smelting. If necessary, a small amount of rare earth elements can be added to reduce the segregation of the cast structure and obtain a uniform solidified structure. At the same time, rare earth elements can improve the plasticity and impact toughness of steel, further strengthen the beneficial effects of silicon and manganese, and enhance the oxidation resistance of the alloy. In the present invention, ≤0.05% of rare earth elements are added.

[0051] In order to further improve the comprehensive performance of the above-mentioned high-uniform and high-mirror-polishing performance mold steel, the components of the above-mentioned high-uniform and high-mirror-polishing performance mold steel may include, by mass percentage: C: 0.11%~0.30%, Si: 0.20%~0.80%, Mn: 0.20%~0.80%, Cr: 10.2%~13.7%, Ni: 0.2%~1.9%, Mo: 0.5%~1.0%, V: 0.005%~0.95%, N: 0.15%~0.50%, and the balance is Fe and unavoidable impurities.

[0052] The present invention also provides a method for preparing the above-mentioned mold steel with high uniformity and high mirror polishing performance, comprising:

[0053] Step 1, smelting and casting to obtain an electrode blank, and subjecting the electrode blank to slow cooling or annealing at 800-900° C.;

[0054] Step 2, remelting the electrode blank in a pressurized electroslag furnace, casting it into a steel ingot, and subjecting the steel ingot to slow cooling or annealing at 800-900°C;

[0055] Step 3, forging the steel ingot to obtain a forging blank;

[0056] Step 4, dispersing the forging blank;

[0057] Step 5, annealing the steel after dispersion treatment;

[0058] Step 6: quench the annealed steel and then perform tempering; or quench the annealed steel, perform deep cooling, and then perform tempering.

[0059] Specifically, in the above step 1, the smelting can be carried out by a converter, an electric furnace, an induction furnace + refining outside the furnace.

[0060] Specifically, in the above step 3, forging includes: fully heating the steel ingot and keeping it warm before forging. Considering that too high a heating temperature or too long a holding time will cause the steel ingot to be overburned and abnormal structure will affect the subsequent processing and performance of the steel, and too high a heating temperature and too long a holding time will waste energy; too low a heating temperature or too short a holding time will not achieve the effect of homogenizing the structure and carbide, therefore, the heating temperature is controlled to 1160-1200°C and the holding time is 10-15h.

[0061] Specifically, in the above step 3, considering that too high initial forging temperature may cause overburning and overheating, too low initial forging temperature will shorten the forging operation time, narrow the forging temperature range, and cause forging difficulties; if the final forging temperature is too high, the grains will grow rapidly at high temperature after forging, resulting in coarse grains of the forgings and reduced mechanical properties of the forgings, while if the final forging temperature is too low, the forgings will have poor plasticity, difficult deformation, increased internal stress, and cracks in the forgings. Therefore, the initial forging temperature is controlled to be 1160-1200°C and the final forging temperature is 830-860°C.

[0062] Specifically, in the above step 4, the dispersion treatment includes: heating the forging blank to a first holding temperature of 980-1020°C for 1-2 hours, and then water cooling to room temperature; then keeping it at a second holding temperature of 630-670°C for 2-4 hours, and air cooling to room temperature.

[0063] Specifically, in the above step 4, the purpose of the first insulation is to make the steel reach the austenitizing temperature, so that the carbides are dissolved and refined. Considering that the first insulation temperature is too high and the insulation time is too long, the structure and grains will be coarsened; the insulation temperature is too low and the insulation time is too short, it is difficult to achieve the effect of carbide dissolution and refinement. Therefore, the first insulation temperature is controlled to 980-1020°C and the insulation time is 1-2h.

[0064] Specifically, in the above step 4, the purpose of the second heat preservation is to obtain a granular pearlite structure with ferrite as the matrix and granular carbides uniformly dispersed. Considering that the second heat preservation temperature is too high or too low, it will exceed the pearlite formation temperature range, and the heat preservation time is too long to cause the structure to be coarse, and the time is too short to achieve the effect of pearlite dispersion distribution, therefore, the second heat preservation temperature is controlled to be 630-670°C, and the heat preservation is 2-4h.

[0065] Specifically, in the above step 5, the role of annealing is to reduce the hardness of steel, improve cutting performance and process performance, eliminate or reduce internal stress to prevent deformation and cracking during processing, and refine the grains to make the chemical composition and structure uniform. The annealing process includes: heating the steel after dispersion treatment to 850±10℃, keeping it warm for 1 to 2 hours; furnace cooling to 650±10℃, keeping it warm for 1 to 2 hours, and then furnace cooling to below 400℃. Granular pearlite is the most ideal annealing structure state, which can ensure the uniformity of the structure and has a lower hardness, which is convenient for subsequent cutting. According to the characteristics of steel structure transformation and phase change, it is necessary to carry out specific austenitization of the steel at 850±10℃. In this temperature range, some undissolved carbides are retained as non-spontaneous nucleation points for the decomposition of supercooled austenite to form pearlite nuclei. Subsequently, the supercooled austenite is decomposed in the temperature range of 650±10℃ to obtain a granular pearlite structure with ferrite as the matrix and granular carbides evenly dispersed. The pearlite transformation is completed and stabilized when cooled to 400℃, and then the steel is taken out of the furnace.

[0066] Specifically, in the above step 6, the quenching treatment includes: keeping the temperature at 950-1050° C. for 0.5-2 h, and cooling the product to room temperature by water or oil after it is taken out of the furnace.

[0067] Specifically, in the above step 6, the cryogenic treatment is to reduce the residual austenite content in the steel after quenching and improve the strength and hardness of the steel. The cryogenic treatment includes: keeping warm at -73°C to -84°C for 0.5 to 2h.

[0068] Specifically, in the above step 6, the tempering treatment can be performed at 150-520°C.

[0069] Specifically, in the above step 5, the uniformity of the steel after annealing is good, and the hardness difference at different positions is small, for example, the hardness difference at different positions is within 7 HB.

[0070] Specifically, in the above step 5, the hardness of the steel after annealing is ≤185HB, and the cutting performance is excellent.

[0071] Specifically, in the above step 6, the structure of the steel after tempering is martensite + fine dispersed carbide and carbonitride precipitation phases, the martensite laths are uniform, no obvious network segregation and strip segregation are observed, the structure is more uniform, the carbides and carbonitrides are less than 1 μm in size, and are more finely dispersed in the matrix structure. The uniformity of the structure is beneficial to the improvement of various performance properties of the steel.

[0072] Specifically, in the above step 6, the steel after tempering has a higher tempering hardness. For example, when tempered at 150°C, the hardness reaches 54HRC or above (for example, 54.8-57.5HRC); when tempered at 200°C, the hardness reaches 55.5HRC or above (for example, 55.7-58.5HRC); when tempered at 300°C, the hardness reaches 53HRC or above (for example, 53.4-57HRC); when tempered at 350°C, the hardness reaches 53HRC or above (for example, 53.2-55.5HRC); when tempered at 400°C, the hardness reaches 54.5HRC or above (for example, 54.5-56.5HRC); when tempered at 450°C, the hardness reaches 55HRC or above (for example, 55-58HRC); when tempered at 500°C, the hardness reaches 56.5HRC or above (for example, 56.5-60HRC).

[0073] Specifically, in the above step 6, the steel after tempering has higher impact toughness, for example, the impact toughness Aku≥25J (for example, 25.1~32J) after quenching at 1030℃ and tempering at 240℃, and the impact toughness Aku≥9.5J (for example, 9.6~12J) after quenching at 1030℃ and tempering at 500℃.

[0074] Specifically, in the above step 6, the roughness of the steel after tempering is low, and a polishing performance of Ra 0.01 μm can be obtained, achieving the mirror polishing performance requirement.

[0075] Specifically, in step 6 above, the tempered steel is subjected to a 120-hour salt spray corrosion test using a 5% NaCl solution, and has a lower corrosion rate and corrosion weight loss, and has excellent corrosion resistance. For example, the corrosion rate is 0.009 g / m 2 ·h or less, and the annual corrosion depth is less than 0.0095mm / a.

[0076] Compared with the prior art, the high-uniform and high-mirror-polishing-performance mold steel of the present invention adopts low C, adds appropriate amounts of Cr, Mo, V and N elements, reduces carbide and tissue segregation, and obtains a structure of martensite + fine dispersed carbide and carbonitride precipitation phases under appropriate dispersion treatment and quenching + tempering process. The martensite laths are uniform, and no obvious network segregation and strip segregation are observed, thereby obtaining a mold steel with high uniformity, high mirror-polishing performance and excellent corrosion resistance.

[0077] The high-uniform and high-mirror-polishing die steel prepared by the composition and method of the present invention has good comprehensive mechanical properties, good uniformity of the steel after annealing, and excellent cutting performance. The structure of the steel after tempering is uniform, and the steel after tempering has high tempering hardness, high impact toughness and low roughness, meets the requirements of mirror-polishing performance, and has excellent corrosion resistance.

[0078] Examples 1-6

[0079] Embodiments 1-6 of the present invention provide a high-uniformity and high-mirror-polishing performance mold steel and a preparation method thereof. The components of the steel in Embodiments 1-4 include, by mass percentage: C: 0.10% to 0.30%, Si: ≤1%, Mn: ≤1%, Cr: 10.0% to 14.0%, Ni: 0.2% to 2.0%, Mo: 0.5% to 1.0%, V: 0.005% to 1.00%, N: 0.15% to 0.50%, and the remainder is Fe and unavoidable impurities.

[0080] Specifically, one or more of the following elements may be added to the steel of Examples 5-6, in percentage by mass: Cu≤0.5%, Nb≤0.05%, Co≤0.5%, and rare earth elements≤0.05%.

[0081] The compositions of the steels of Examples 1-6 are shown in Table 1 below.

[0082] The method for preparing the steel of Examples 1-6 comprises:

[0083] (1) casting molten steel into ingots;

[0084] (2) The ingot is heated to 1160-1200°C, kept at this temperature for 10-15 hours, and then forged into bars of Φ130 mm and Φ170 mm; the initial forging temperature is 1160-1200°C, and the final forging temperature is 830-860°C;

[0085] (3) Dispersion treatment of the rod: heating to the first holding temperature of 980-1020°C for 1-2 hours, then water cooling to room temperature; then keeping at the second holding temperature of 630-670°C for 2-4 hours, and air cooling to room temperature;

[0086] (4) Then annealing treatment: heat the steel after dispersion treatment to 850±10℃ and keep it for 1~2h, slowly cool it to 650±10℃ and keep it, furnace cool it to below 400℃ and take it out of the furnace; process it into samples, and carry out quenching, deep cooling and tempering treatment. Among them, quenching at 950~1050℃ and tempering at 150~520℃. Its properties are shown in Tables 2~7.

[0087] It can be seen from Tables 2 to 7 that the steel of the present invention has excellent structural uniformity, and also has good polishability, toughness and corrosion resistance.

[0088] Specifically, as shown in Table 2, after the steel is forged and annealed, the edge, one-quarter and center of the comparative steels of Examples 1-6 are selected for annealing hardness testing. Compared with the comparative steel, the steel of the present invention has an annealing hardness of ≤185HB after annealing, and the difference in annealing hardness at each position is small (the hardness difference at different positions is within 7HB), and has excellent cutting performance and good uniformity.

[0089] Specifically, after quenching at the same temperature and tempering at different temperatures, the tempered structures of the comparative steels of Examples 1-6 are all martensite + carbonitride. Figure 1 The tempered structure of Example 2 is 50×, Figure 2 The tempered structure is 100× that of comparative example 1. The comparative steel has macroscopic structural segregation and obvious large-particle carbides. Compared with the comparative steel, the steel of the present invention has no structural segregation, and the carbide and carbonitride precipitation phases are fine and evenly distributed, with a more uniform structure. Figure 3 The tempered structure of the steel in Example 1 after tempering at 240°C is 500×, Figure 4 The tempered structure of the steel of comparative example 1 after tempering at 240°C is 500×; Figure 5 The tempered structure of the steel in Example 1 after tempering at 500°C is 500×, Figure 6 This is the tempered structure 500× of the steel in Comparative Example 1 after tempering at 500°C.

[0090] Specifically, as shown in Table 3 and Table 4, after quenching at the same temperature and tempering at different temperatures, the steel of the present invention has a higher tempering hardness than the comparative steel when tempered at above 150°C.

[0091] Specifically, as shown in Table 5, after quenching at the same temperature and tempering at different temperatures, the steel of the present invention has higher impact toughness than the comparative steel, and can better meet the requirement of high toughness.

[0092] Specifically, as shown in Table 6, after quenching at the same temperature and tempering at 240°C, the surface roughness tester is used to test the surface roughness. The steel of the present invention has lower roughness than the comparative steel, and can obtain a polishing performance of Ra 0.01 μm, achieving the mirror polishing performance requirements.

[0093] Specifically, as shown in Table 7, after quenching at the same temperature, tempering at 240°C, and conducting a 120h salt spray corrosion test using a 5% NaCl solution, the steel of the present invention has a lower corrosion rate and corrosion weight loss than the comparative steel, and has better corrosion resistance, which can meet the requirements of corrosion resistance.

[0094] Table 1 Chemical composition (%)

[0095]

[0096] Table 2 Annealing hardness of the embodiment and the comparative steel

[0097]

[0098]

[0099] Table 3 Hardness values ​​of the embodiment and the comparative steel after quenching at 1030℃ and deep cooling at 73℃ and tempering at different temperatures

[0100]

[0101] Table 4 Hardness values ​​of the embodiment and the comparative steel after quenching at 1050℃ and deep cooling at 73℃ and tempering at different temperatures

[0102]

[0103] Table 5 Impact toughness of the embodiment and the comparative steel after quenching at 1030℃ and tempering at different temperatures

[0104]

[0105] Table 6 Polishing performance of the embodiments and comparative examples after quenching at 1030°C and tempering at 240°C

[0106]

[0107] Table 7 Corrosion resistance of the example and comparative steel after quenching at 1030℃ and tempering at 240℃

[0108]

[0109] The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by any technician familiar with the technical field within the technical scope disclosed by the present invention should be covered within the protection scope of the present invention.

Claims

1. A method for preparing mold steel with high uniformity and high mirror polishing performance, characterized in that: The components of the high-uniform and high-mirror-polishing performance mold steel include, by mass percentage: C: 0.10% to 0.30%, Si: ≤1%, Mn: ≤1%, Cr: 10.0% to 14.0%, Ni: 0.2% to 2.0%, Mo: 0.5% to 1.0%, V: 0.005% to 1.00%, N: 0.15% to 0.50%, and the balance is Fe and unavoidable impurities; The preparation method comprises: Step 1, smelting and casting to obtain an electrode blank, and subjecting the electrode blank to slow cooling or heat preservation annealing treatment; Step 2, remelting the electrode blank in a pressurized electroslag furnace, casting it into a steel ingot, and subjecting the steel ingot to slow cooling or heat preservation annealing treatment; Step 3, forging the steel ingot to obtain a forging blank; Step 4, dispersing the forging blank; Step 5, annealing the steel after dispersion treatment; Step 6: quenching the annealed steel and then tempering it; or quenching the annealed steel, subzero treatment, and then tempering it; In step 4, the dispersion treatment includes: heating the forging blank to a first holding temperature of 980-1020° C. for 1-2 hours, and then water cooling to room temperature; then holding the blank at a second holding temperature of 630-670° C. for 2-4 hours, and air cooling to room temperature; In step 5, the annealing treatment includes: heating the steel after dispersion treatment to 850±10°C, keeping the temperature for 1 to 2 hours; cooling the steel to 650±10°C, keeping the temperature for 1 to 2 hours, and then cooling the steel to below 400°C before taking it out of the furnace; In step 6, the quenching treatment includes: keeping at 950-1050°C for 0.5-2h, and cooling to room temperature with water or oil after being taken out of the furnace; the cryogenic treatment includes: keeping at -73°C to -84°C for 0.5-2h; and the tempering treatment is performed at 150-520°C.

2. The preparation method according to claim 1, characterized in that: In the step 3, the forging includes: fully heating the steel ingot and keeping it warm before forging; the heating temperature is controlled to be 1160-1200° C. and the keeping time is 10-15 hours.

3. The preparation method according to claim 1, characterized in that: In the step 3, the initial forging temperature is 1160-1200°C, and the final forging temperature is 830-860°C.

4. A mold steel with high uniformity and high mirror polishing performance, characterized in that: The high-uniformity and high-mirror-polishing performance mold steel is prepared by the preparation method described in any one of claims 1 to 3. The structure of the steel after tempering is martensite + fine dispersed carbide and carbonitride precipitation phases, the martensite laths are uniform, and no obvious network segregation and strip segregation are observed.

5. The mold steel with high uniformity and high mirror polishing performance according to claim 4, characterized in that: The components of the high uniformity and high mirror polishing performance mold steel are further added with one or more selected from the following elements, which are included in mass percentage: Cu≤0.5%, Nb≤0.05%, Co≤0.5%, and rare earth elements≤0.05%.

6. The mold steel with high uniformity and high mirror polishing performance according to claim 4, characterized in that: The components of the high-uniform and high-mirror-polishing performance mold steel include, by mass percentage, C: 0.11% to 0.30%, Si: 0.20% to 0.80%, Mn: 0.20% to 0.80%, Cr: 10.2% to 13.7%, Ni: 0.2% to 1.9%, Mo: 0.5% to 1.0%, V: 0.005% to 0.95%, N: 0.15% to 0.50%, and the remainder is Fe and unavoidable impurities.

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