High-corrosion-resistance plastic die steel and preparation method thereof

Abstract

The invention relates to the technical field of steel and iron materials, in particular to high-corrosion-resistance plastic die steel and a preparation method thereof.The high-corrosion-resistance plastic die steel is prepared by combining V-N microalloying and heat treatment, adding a certain amount of V and N elements into traditional plastic die steel and combining an improved heat treatment technology. The self-corrosion potential of the high-corrosion-resistance plastic die steel is larger than or equal to-320 mV, the self-corrosion current density is smaller than or equal to 1.6 * 10 <-7 > A / cm < 2 >, the pitting potential is larger than or equal to 230 mV, and the corrosion rate is smaller than or equal to 0.035 g / m < 2 > / h. The prepared plastic die steel has excellent corrosion resistance, and guidance is provided for alloy design and process optimization of plastic die steel products.

Description

Technical Field

[0001] The present invention relates to the technical field of steel materials, and particularly to a high-corrosion-resistant plastic mold steel and a preparation method thereof. Background Art

[0002] As an important high-end material in the field of mold steel, plastic mold steel is mainly used in the fields of special engineering plastics with higher molding temperatures and plastic products containing flame retardants due to its excellent strength and corrosion resistance. However, these plastics will release gases such as hydrogen chloride, hydrogen fluoride, and sulfur dioxide in the molten state, and these gases will corrode the mold cavity, resulting in a reduction in the service life of the mold. Therefore, corrosion-resistant plastic mold steel should be selected for mold forming parts. At present, the commonly used mold materials in China are traditional steel grades such as 20Cr13, 30Cr13, and 40Cr13. These steel grades have problems such as serious carbide segregation, poor tissue uniformity, and insufficient corrosion resistance, which affect their performance in high-temperature forming environments. Therefore, developing a new type of high-corrosion-resistant plastic mold steel and significantly improving its corrosion resistance have important engineering application value and potential economic benefits. Summary of the Invention

[0003] In view of the technical problems existing in the prior art, the present invention provides a high-corrosion-resistant plastic mold steel and a preparation method thereof.

[0004] According to one aspect of the present invention, the present invention provides the following technical solution: A preparation method of a high-corrosion-resistant plastic mold steel, comprising the following steps: S1. Smelting and casting in a vacuum induction furnace to obtain an ingot; S2. Heating and insulating the ingot and then forging it into a billet; S3. Performing hot rolling treatment on the billet to obtain a hot-rolled sheet; S4. Performing annealing treatment on the hot-rolled sheet; S5. Performing cold rolling on the annealed hot-rolled sheet to obtain a cold-rolled sheet; S6. Performing quenching-tempering treatment on the cold-rolled sheet, wherein the quenching austenitizing temperature is 980 - 1130 °C, and the holding time is 30 - 60 min; the tempering temperature is 200 - 300 °C, and the holding time is 60 - 120 min; to obtain the high-corrosion-resistant plastic mold steel, and the mass percentage of V in the high-corrosion-resistant plastic mold steel is 0.1 - 0.3%, and the mass percentage of N is 0.05 - 0.2%.

[0005] According to another aspect of the present invention, the present invention provides the following technical solution: A high corrosion-resistant plastic mold steel is prepared by using the above-mentioned preparation method of high corrosion-resistant plastic mold steel. The self-corrosion potential of the high corrosion-resistant plastic mold steel is ≥ -320 mV, and the self-corrosion current density is ≤ 1.6×10 -7 A / cm 2 , the pitting potential is ≥ 230 mV, and the corrosion rate is ≤ 0.035 g / m 2 / h.

[0006] The beneficial effects of the present invention are as follows: The present invention provides a high corrosion-resistant plastic mold steel and a preparation method thereof. By combining V-N microalloying with heat treatment, a certain amount of V and N elements are added to the traditional plastic mold steel, and at the same time, an improved heat treatment process is combined to prepare the plastic mold steel. The self-corrosion potential of the high corrosion-resistant plastic mold steel is ≥ -320 mV, and the self-corrosion current density is ≤ 1.6×10 -7 A / cm 2 , the pitting potential is ≥ 230 mV, and the corrosion rate is ≤ 0.035 g / m 2 / h. The plastic mold steel prepared by the present invention has excellent corrosion resistance, which provides guidance for the alloy design and process optimization of plastic mold steel products. BRIEF DESCRIPTION OF THE DRAWINGS

[0007] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the following drawings are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained based on the structures shown in these drawings.

[0008] Figure 1 It is the microstructure diagram of the high corrosion-resistant plastic mold steel prepared in Example 1.

[0009] The realization of the object, functional features and advantages of the present invention will be further described in conjunction with the embodiments and with reference to the drawings. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0010] The following will clearly and completely describe the technical solutions in the embodiments. Obviously, the described embodiments are only some of the embodiments of the present invention, rather than all of them. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the scope of protection of the present invention.

[0011] The present invention provides a high corrosion-resistant plastic mold steel and a preparation method thereof. By adjusting the composition and strictly controlling the heat treatment process, a uniform structure is obtained, and thus excellent corrosion resistance is obtained.

[0012] According to one aspect of the present invention, the present invention provides the following technical solutions: A preparation method of a high corrosion-resistant plastic mold steel, comprising the following steps: S1. Smelt and cast in a vacuum induction furnace to obtain an ingot; S2. Heat and hold the ingot and then forge it into a billet; S3. Perform hot rolling treatment on the billet to obtain a hot-rolled plate; S4. Perform annealing treatment on the hot-rolled plate; S5. Perform cold rolling on the annealed hot-rolled plate to obtain a cold-rolled plate; S6. Perform quenching-tempering treatment on the cold-rolled plate, wherein the quenching austenitizing temperature is 980-1130°C and the holding time is 30-60 min; the tempering temperature is 200-300°C and the holding time is 60-120 min; to obtain the high corrosion-resistant plastic mold steel.

[0013] Preferably, in the step S2, the heating temperature of the ingot is 1140-1220°C and the holding time is 1-3 h; the forging temperature is 980-1170°C. Specifically, the heating temperature can be, for example, any one of 1140°C, 1160°C, 1180°C, 1200°C, 1220°C or the range between any two of them; the holding time can be, for example, any one of 1 h, 1.5 h, 2 h, 2.5 h, 3 h or the range between any two of them; the forging temperature can be, for example, any one of 980°C, 1000°C, 1020°C, 1050°C, 1080°C, 1100°C, 1030°C, 1150°C, 1170°C or the range between any two of them.

[0014] Preferably, in the step S3, the billet is heated, hot-rolled and pickled to obtain a hot-rolled plate, the heating temperature is 1140-1220°C, hot-rolled in the austenitizing temperature range, the rolling start temperature is 1100-1150°C, the number of hot-rolling passes is 5-7 passes, and after hot-rolling, it is air-cooled to room temperature. Specifically, the heating temperature can be, for example, any one of 1140°C, 1160°C, 1180°C, 1200°C, 1220°C or the range between any two of them; the rolling start temperature can be, for example, any one of 1100°C, 1110°C, 1120°C, 1130°C, 1140°C, 1150°C or the range between any two of them; the number of hot-rolling passes can be, for example, any one of 5 passes, 6 passes, 7 passes or the range between any two of them.

[0015] Preferably, in the step S4, the annealing process is as follows: first, keep the temperature at 790 - 830 °C for 8 - 10 h, then cool it to 400 °C at a cooling rate of ≤30 °C / h, and subsequently air-cool it to room temperature. Specifically, the holding temperature can be any one of, for example, 790 °C, 800 °C, 810 °C, 820 °C, 830 °C or the range between any two of them; the cooling rate can be any one of, for example, 15 °C / h, 20 °C / h, 25 °C / h, 30 °C / h or the range between any two of them.

[0016] Preferably, in the step S5, the total cold rolling reduction is 60 - 70%. Specifically, the total cold rolling reduction can be any one of, for example, 60%, 62.5%, 65%, 67.5%, 70% or the range between any two of them.

[0017] Preferably, in the step S6, specifically, the quenching austenitizing temperature can be any one of, for example, 980 °C, 1000 °C, 1030 °C, 1050 °C, 1080 °C, 1100 °C, 1130 °C or the range between any two of them, and the tempering temperature can be any one of, for example, 200 °C, 220 °C, 240 °C, 260 °C, 280 °C, 300 °C or the range between any two of them.

[0018] According to another aspect of the present invention, the present invention provides the following technical solution: A high corrosion-resistant plastic mold steel is prepared by using the preparation method of the above-mentioned high corrosion-resistant plastic mold steel. The mass percentage of V in the high corrosion-resistant plastic mold steel is 0.1 - 0.3%, and the mass percentage of N is 0.05 - 0.2%.

[0019] Preferably, the high corrosion-resistant plastic mold steel, by mass percentage, comprises C: 0.35 - 0.45%, Cr: 12.0 - 14.0%, Mn: 0.3 - 0.6%, Si: 0.3 - 0.6%, Mo: 0.03 - 0.06%, V: 0.1 - 0.3%, N: 0.05 - 0.2%, Ni: 0.2 - 0.8%, P < 0.01%, S < 0.01%, and the balance is Fe and inevitable impurity elements.

[0020] C: Carbon is the main austenitizing element and the main element to improve the hardness and strength of the steel, with a strong solid solution strengthening effect. However, too high a C content in the steel will not only affect the impact toughness of the material but also cause the precipitation of a large amount of carbides, resulting in chromium depletion in the matrix and reducing the corrosion resistance of the steel. In the present invention, the C content is controlled at 0.35 - 0.45%.

[0021] Cr: Chromium is the main component element of steel. It can not only improve the hardenability of Fe-Cr alloys, but also form an oxide film on the surface of steel, effectively improving the corrosion resistance of the material. However, too high a Cr content will promote the formation of high-temperature ferrite and network carbide, affecting the service performance of the steel. In the present invention, the Cr content is controlled at 12.0 - 14.0%.

[0022] Mn: Manganese is an element that improves the hardenability of steel and can lower the martensite transformation temperature. Appropriate Mn can also effectively improve the strength, hardness and toughness of steel, eliminating the hot brittleness effects of sulfur and oxygen on steel. At the same time, controlling the Mn content at a relatively low level can prevent grain coarsening and prevent the corrosion resistance of stainless steel from decreasing. In the present invention, the Mn content is controlled at 0.3 - 0.6%.

[0023] Si: Silicon is a strong deoxidizing element and has an obvious effect on improving corrosion resistance. However, too high a content will not only lead to poor ductility of the steel, but also promote the occurrence of segregation. In the present invention, the Si content is controlled at 0.3 - 0.6%.

[0024] Mo: Molybdenum element can improve the corrosion resistance of the material and at the same time can improve the hardenability of steel. However, too much Mo content in steel will promote the formation of ferrite, reducing the strength and toughness of steel. In the present invention, the Mo content is controlled at 0.03 - 0.06%.

[0025] V: Vanadium is a strong carbide-forming element. When it reaches more than 0.1%, it can refine the grain size of the structure and improve the corrosion resistance of steel. However, too high a V content will increase the probability of the formation of primary carbides in steel, having an adverse effect on corrosion resistance. In the present invention, the V content is controlled at 0.1 - 0.3%; specifically, the V content can be any one of, for example, 0.1%, 0.15%, 0.2%, 0.25%, 0.3% or the range between any two of them.

[0026] N: Nitrogen is an excellent austenite stabilizing element and can improve the corrosion resistance of steel. The addition of N will not only not affect other properties of stainless steel, but also can partially replace expensive Ni and other elements to provide the corrosion resistance of steel. N will combine with V to form V-N microalloying, promoting the precipitation of V(C,N), and enhancing strength and hardness to achieve the purpose of improving wear resistance. However, too much N content will cause it to exist as interstitial atoms in steel, significantly increasing the brittleness of steel and damaging the welding ability of steel. In the present invention, the N content is controlled at 0.05 - 0.2%; specifically, the N content can be any one of, for example, 0.05%, 0.1%, 0.15%, 0.2% or the range between any two of them.

[0027] Ni: As an austenite-forming element, the addition of nickel to steel will increase the hardenability of the steel, thereby ensuring uniform hardness of the steel. The addition of Ni can increase the passivation tendency of the Fe-Cr alloy and improve the corrosion resistance of the steel. In the present invention, the Ni content is controlled at 0.2-0.8%; P, S: Phosphorus and sulfur elements are prone to segregation at grain boundaries, reducing the hot workability of the material. Therefore, the lower the content, the better.

[0028] Preferably, the structure of the high-corrosion-resistant plastic mold steel is tempered martensite + fine and dispersed carbides and carbonitrides.

[0029] Preferably, the self-corrosion potential of the high-corrosion-resistant plastic mold steel is ≥ -320 mV, and the self-corrosion current density is ≤ 1.6×10 -7 A / cm 2 , the pitting potential is ≥ 230 mV, and the corrosion rate is ≤ 0.035 g / m 2 / h.

[0030] The technical solution of the present invention will be further described below in conjunction with specific embodiments.

[0031] Example 1 A preparation method of a high-corrosion-resistant plastic mold steel includes the following steps: S1. Smelt and cast in a vacuum induction furnace to obtain an ingot; S2. After heating and holding the ingot, forge it into a billet in the temperature range of 980 °C - 1170 °C; the heating temperature is 1180 °C, and the holding time is 2 h; S3. Heat, hot-roll and pickle the billet to obtain a hot-rolled sheet. The heating temperature is 1180 °C. Hot-roll in the austenitizing temperature range, the starting rolling temperature is 1140 °C, the number of hot-rolling passes is 6 passes, and air-cool to room temperature after hot-rolling; S4. Anneal the hot-rolled sheet; the annealing process is: first hold at 820 °C for 8 h, then cool at a cooling rate of 20 °C / h to 400 °C, and then air-cool to room temperature; S5. Cold-roll the annealed hot-rolled sheet to obtain a cold-rolled sheet; the total cold-rolling reduction is 65%; S6. Quench and temper the cold-rolled sheet. The quenching austenitizing temperature is 1080 °C, and the holding time is 60 min; the quenching method is oil cooling; the tempering temperature is 240 °C, and the holding time is 120 min; to obtain the high-corrosion-resistant plastic mold steel. The microstructure diagram of the high-corrosion-resistant plastic mold steel prepared in this example is as Figure 1 shown, by Figure 1It can be seen that the structure of the high corrosion-resistant plastic mold steel in Embodiment 1 of the present invention is tempered martensite + fine and dispersed carbides and carbonitrides. The martensite laths are uniform, and no obvious network segregation and band segregation are observed, and the structure is more uniform. The addition of N and V elements can reduce the precipitation amount of M 23 C6, reduce the generation of chromium-depleted zones, and improve the corrosion resistance; the composition of the high corrosion-resistant plastic mold steel is shown in Table 1.

[0032] Table 1 Composition of the high corrosion-resistant plastic mold steel in Embodiment 1 (mass percentage, %) Embodiment 2 The difference from Embodiment 1 is that in step S6, the quenching austenitizing temperature is 1130 °C.

[0033] Comparative Example 1 The difference from Embodiment 1 is that a commercial 40Cr13 cold-rolled plate is used.

[0034] Comparative Example 2 The difference from Embodiment 2 is that a commercial 40Cr13 cold-rolled plate is used.

[0035] Comparative Example 3 The difference from Embodiment 1 is that in step S6, the quenching austenitizing temperature is 1150 °C.

[0036] Comparative Example 4 The difference from Embodiment 1 is that in step S6, the tempering temperature is 400 °C.

[0037] Comparative Example 5 The difference from Embodiment 1 is that in step S4, it is held at 860 °C for 10 h.

[0038] Comparative Example 6 The difference from Embodiment 1 is that the mass percentage of N is 0.4%.

[0039] Comparative Example 7 The difference from Embodiment 1 is that the mass percentage of V is 0.5%.

[0040] Comparative Example 8 The difference from Embodiment 1 is that N and V elements are not contained.

[0041] The potentiodynamic polarization curve tests were respectively carried out on the plastic mold steel specimens prepared in Examples 1-2 and Comparative Examples 1-8. And the corrosion rates of the specimens were compared according to the method in GB / T 17897-2016 "Corrosion of metals and alloys - Pitting corrosion test for stainless steels in ferric chloride solution", and the results are shown in Table 2 and Table 3. It can be seen that the embodiments of the present invention have better corrosion resistance than the comparative examples.

[0042] Table 2 Potentiodynamic polarization curve test data of specimens in each example and comparative example Table 3 Comparison of corrosion rates of specimens in each example and comparative example The above are only the preferred embodiments of the present invention, and do not limit the patent scope of the present invention. Any equivalent structural transformation made by using the content of the specification of the present invention under the inventive concept of the present invention, or direct / indirect application in other related technical fields are all included in the patent protection scope of the present invention.

Claims

1. A preparation method of a high corrosion-resistant plastic mold steel, characterized in that, It includes the following steps: S1. Smelt and cast in a vacuum induction furnace to obtain an ingot; S2. Heat and hold the ingot and then forge it into a billet; S3. Perform hot rolling on the billet to obtain a hot-rolled sheet; S4. Perform annealing heat treatment on the hot-rolled sheet; S5. Perform cold rolling on the annealed hot-rolled sheet to obtain a cold-rolled sheet; S6. Perform quenching-tempering treatment on the cold-rolled sheet, wherein the quenching austenitizing temperature is 980 - 1130 °C and the holding time is 30 - 60 min; the tempering temperature is 200 - 300 °C and the holding time is 60 - 120 min; to obtain the high corrosion-resistant plastic mold steel, and the mass percentage of V in the high corrosion-resistant plastic mold steel is 0.1 - 0.3%, and the mass percentage of N is 0.05 - 0.2%.

2. The preparation method of the highly corrosion-resistant plastic mold steel according to claim 1, characterized in that, In step S2, the ingot heating temperature is 1140 - 1220 °C, the holding time is 1 - 3 h; the forging temperature is 980 - 1170 °C.

3. The preparation method of the highly corrosion-resistant plastic mold steel according to claim 1, characterized in that, In step S3, heat, hot roll and pickling are performed on the billet to obtain a hot-rolled sheet, the heating temperature is 1140 - 1220 °C, hot rolling is performed in the austenitizing temperature range, the rolling start temperature is 1100 - 1150 °C, the number of hot rolling passes is 5 - 7 passes, and after hot rolling, it is air-cooled to room temperature.

4. The preparation method of the high corrosion-resistant plastic mold steel according to claim 1, characterized in that, In step S4, the annealing process is: first hold at 790 - 830 °C for 8 - 10 h, then cool at a cooling rate of ≤30 °C / h to 400 °C, and then air-cool to room temperature.

5. The preparation method of the highly corrosion-resistant plastic mold steel according to claim 1, characterized in that, In step S5, the total cold rolling reduction is 60 - 70%.

6. A high corrosion-resistant plastic mold steel, characterized in that, It is prepared by using the preparation method of the high corrosion-resistant plastic mold steel according to any one of claims 1 - 5.

7. The highly corrosion-resistant plastic mold steel according to claim 6, characterized in that, By mass percentage, its composition includes, C: 0.35 - 0.45%, Cr: 12.0 - 14.0%, Mn: 0.3 - 0.6%, Si: 0.3 - 0.6%, Mo: 0.03 - 0.06%, V: 0.1 - 0.3%, N: 0.05 - 0.2%, Ni: 0.2 - 0.8%, P < 0.01%, S < 0.01%, and the balance is Fe and inevitable impurity elements.

8. The highly corrosion-resistant plastic mold steel according to claim 6, characterized in that, The structure of the high corrosion-resistant plastic mold steel is tempered martensite + fine and dispersed carbides and carbonitrides.

9. The highly corrosion-resistant plastic mold steel according to claim 6, wherein The self-corrosion potential of the high corrosion-resistant plastic mold steel is ≥ -320 mV, and the self-corrosion current density is ≤ 1.6×10 -7 A / cm 2 , the pitting potential is ≥ 230 mV, and the corrosion rate is ≤ 0.035 g / m 2 / h.

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