Method for manufacturing a plastic mold flat steel and plastic mold flat steel manufactured thereby

Abstract

This invention discloses a preparation method, particularly a method for preparing and manufacturing plastic mold flat steel, belonging to the field of mold steel production technology. It provides a method for preparing and manufacturing plastic mold flat steel that can effectively improve the flaw detection pass rate, enhance the anisotropy and mechanical properties of the finished product. The preparation method first obtains a pre-rolled billet with uniform internal heating temperature and balanced stress in the alloy element enrichment region and related regions through gradient heating. Then, a uniform deformation rolling process is used to obtain a finished rolled billet with uniform deformation in the alloy element enrichment zone and the depletion zone. Finally, temperature-controlled cooling is used to obtain a finished plastic mold flat steel with the required stress in the alloy element enrichment region and good internal welding. The plastic mold flat steel is a 4Cr13 series plastic mold flat steel.

Description

Technical Field

[0001] This invention relates to a preparation method, and more particularly to a method for preparing flat steel for plastic molds, belonging to the technical field of mold steel production processes. This invention also relates to a plastic mold flat steel manufactured using the aforementioned method for preparing plastic mold flat steel. Background Technology

[0002] Plastic mold flat steel is a high-quality steel material specifically used for manufacturing plastic molds. It is usually produced by hot rolling. Due to its high strength, hardness, toughness, good corrosion resistance and wear resistance, it is often used to manufacture key components of plastic molds such as templates, guide pillars, and guide sleeves.

[0003] Hot-rolled production of flat steel for plastic molds offers advantages such as high production efficiency, low energy consumption, good dimensional and performance stability, and high material utilization. However, the uniformity of mechanical properties in hot-rolled products has always been a focus of industry attention. During the rolling process, the metal extends along the rolling direction, resulting in alternating banded segregation or phase distribution (such as ferrite and pearlite bands) within the metal material. For conventional steel grades, the presence of this banded structure leads to anisotropy, significantly affecting the material's mechanical and processing properties. For 4Cr13 type rolled flat steel, the impact of banded structure is even more severe. Due to its high alloy content, the presence of banded structure exacerbates the uneven deformation during rolling, causing internal defects to occur along grain boundaries in the relatively hard alloy-rich bands, ultimately leading to non-compliance in flaw detection.

[0004] Currently, solutions to banding in hot-rolled products are mainly based on their different causes. For example, optimizing smelting and casting processes can reduce banding caused by component segregation. For banding generated during rolling, measures such as increasing rolling temperature, increasing reduction, slow cooling after rolling, annealing, and normalizing are used to mitigate or eliminate it. These solutions are applicable to most steel grades. However, for 4Cr13 series plastic mold flat steel, which often requires online pre-hardening, this method is not only ineffective but also cannot be followed by annealing and normalizing. Therefore, to address the problem of internal defects caused by cracking along segregation bands during the rolling process of 4Cr13 series plastic mold flat steel, leading to non-compliance in flaw detection, there is an urgent need for a rolling method for plastic mold flat steel. This method should be applied to the rolling of 4Cr13 series flat steel to reduce or eliminate banding, prevent internal defects and non-compliance in flaw detection, improve the anisotropy of the steel, enhance product quality, and extend the service life of the mold. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide a method for preparing flat steel for plastic molds that can effectively improve the pass rate of flaw detection, improve the anisotropy and mechanical properties of finished products. The present invention also provides a flat steel for plastic molds manufactured by the above-mentioned method for preparing flat steel for plastic molds.

[0006] The technical solution adopted to solve the above-mentioned technical problems is: a method for preparing flat steel for plastic molds. The preparation method first obtains a pre-heated billet with uniform internal heating temperature and balanced stress in the alloy element enrichment area and related areas through gradient heating. Then, a uniform deformation rolling process is used to obtain a finished rolled billet with uniform deformation in the alloy element enrichment zone and the depletion zone. Finally, temperature-controlled cooling is used to obtain a finished plastic mold flat steel with the required structural stress in the alloy element enrichment area and good internal welding.

[0007] Furthermore, the strip structure of the finished plastic mold flat steel is controlled within the range of 0-2.

[0008] The preferred method of the above scheme is to use red die casting ingots as billets and carry out gradient heating in a heating furnace with an initial furnace temperature of not less than 850°C. After the red die casting ingots are loaded into the heating furnace, the furnace temperature is kept at a stable temperature for at least 2 hours before the temperature is increased for heating.

[0009] Furthermore, the heating rate of the gradient heating is controlled at 100℃ / h until the heating temperature reaches 1260℃, then it is held at that temperature for at least 5 hours, and then cooled down to 1150℃ in the furnace and held for 2 hours before being taken out of the furnace for rolling.

[0010] The preferred method of the above scheme is that the uniform rolling process includes the front rolling and the rear rolling, with the reduction reaching 50% as the dividing line. In the front rolling, the reduction of each rolling pass is controlled to not exceed 25%, and the reduction rate is not greater than 1.0 s. -1 Control measures are in place; the reduction amount in each rolling pass during the subsequent rolling process shall not exceed 15%, and the reduction rate shall not exceed 0.5 seconds. -1 control.

[0011] Furthermore, the uniform rolling is carried out on the 1350 rolling mill. After the ingot is reduced by 50% in the first stage of rolling, before entering the second stage of rolling, the process billet is first placed on the rolling mill roller table for 3-5 minutes before the second stage of rolling.

[0012] The preferred method of the above scheme is to carry out temperature-controlled cooling on a stepping cooling bed equipped with a windproof cover, and control the cooling rate of the cooling bed at ≤10℃ / min until the billet temperature drops to room temperature.

[0013] The plastic mold flat steel manufactured using the aforementioned method for preparing plastic mold flat steel is a 4Cr13 series plastic mold flat steel.

[0014] Furthermore, the 4Cr13 series of plastic mold flat steel includes 40Cr13, 40Cr13H, 40Cr13HL and 40Cr13HH.

[0015] The preferred embodiment of the above scheme is that the chemical composition of the 4Cr13 series flat steel is C 0.36%~0.45%; Si≤0.40%; Mn≤0.60%; Cr 12.00%~14.00%; Ni≤0.60%; P≤0.030%; S≤0.025%; with the balance being Fe and unavoidable impurities.

[0016] The beneficial effects of this invention are as follows: The preparation method provided in this application first obtains a pre-rolled billet with uniform internal heating temperature and balanced stress between the alloy element enrichment region and related regions through gradient heating. Then, a uniform deformation rolling process is used to obtain a finished rolled billet with uniform deformation between the alloy element enrichment zone and the depletion zone. Finally, temperature-controlled cooling is used to obtain a finished plastic mold flat steel with the required structural stress in the alloy element enrichment region and good internal welding. Since each step of the preparation method in this application is performed on the alloy element concentration region inside the billet, the alloy element enrichment region inside the plastic mold flat steel is well welded along the crystal orientation, the alloy element enrichment zone and the depletion zone are uniformly deformed, and the structural stress performance and welding performance between the structures in the alloy element enrichment region are effectively improved. This achieves the purpose of effectively improving the flaw detection pass rate, improving the anisotropy and mechanical properties of the finished product. Attached Figure Description

[0017] Figure 1 (a, b) are grade 5 banded microstructure and microstructure with intergranular boundary cracking defects of 40Cr13 steel produced by conventional rolling method in Comparative Example 1, respectively. Figure 2 (a) and (b) represent grade 0 strip tissue produced in Example 3 and grade 1 strip tissue produced in Example 1, respectively. Detailed Implementation

[0018] like Figure 1 , Figure 2This invention illustrates a method for preparing flat steel for plastic molds that effectively improves the pass rate of flaw detection, enhances the anisotropy and mechanical properties of finished products, and a method for manufacturing flat steel for plastic molds using the aforementioned method. The preparation method first obtains a pre-rolled billet with uniform internal heating temperature and balanced stress in the alloy element enrichment region and related regions through gradient heating. Then, a uniform deformation rolling process is used to obtain a finished rolled billet with uniform deformation in the alloy element enrichment zone and depletion zone. Finally, controlled-temperature cooling is used to obtain a finished plastic mold flat steel with the required structural stress in the alloy element enrichment region and good internal welding. The preparation method provided in this application first obtains a pre-rolled billet with uniform internal heating temperature and balanced stress in the alloy element enrichment region and related regions through gradient heating. Then, a uniform deformation rolling process is used to obtain a finished rolled billet with uniform deformation in the alloy element enrichment zone and depletion zone. Finally, controlled-temperature cooling is used to obtain a finished plastic mold flat steel with the required structural stress in the alloy element enrichment region and good internal welding. Since each step of the preparation method in this application is carried out on the alloy element concentration area inside the steel billet, the alloy element enrichment area inside the plastic mold flat steel is well welded along the crystal direction, the alloy element enrichment zone and the depletion zone are deformed uniformly, and the structural stress properties and welding performance between the structures in the alloy element enrichment area are effectively improved, thereby achieving the purpose of effectively improving the flaw detection pass rate, improving the anisotropy and mechanical properties of the finished product.

[0019] Accordingly, in order to obtain finished plastic mold flat steel with a banded structure in the range of 0-2, and to maximize the quality of the finished product, the gradient heating of this application uses red-die casting ingots as billets, and is carried out in a heating furnace with an initial furnace temperature of not less than 850°C. After the red-die casting ingots are loaded into the heating furnace, they are held at the furnace temperature for at least 2 hours after the furnace temperature stabilizes before the temperature is increased. The uniform rolling of this application includes the front rolling and the back rolling, with the reduction reaching 50% as the dividing line. In the front rolling, the reduction of each rolling pass is controlled to not exceed 25%, and the reduction rate is not greater than 1.0 s. -1 Control measures are in place; the reduction amount in each rolling pass during the subsequent rolling process shall not exceed 15%, and the reduction rate shall not exceed 0.5 seconds. -1 Temperature control. The temperature-controlled cooling of this application is carried out on a walking cooling bed equipped with a windproof cover. The cooling rate of the cooling bed is controlled at ≤10℃ / min until the billet temperature drops to room temperature.

[0020] More specifically, in this application, the gradient heating rate is controlled at 100℃ / h until the heating temperature reaches 1260℃, then held at that temperature for at least 5 hours, and then cooled in the furnace to 1150℃ and held for 2 hours before being rolled out. The uniform rolling in this application is carried out on a 1350 rolling mill. After the ingot has undergone 50% reduction in the initial rolling stage, before entering the subsequent rolling stage, the process billet is first placed idle on the mill roller table for 3-5 minutes before proceeding with the subsequent rolling.

[0021] At this point, the plastic mold flat steel prepared using the method of this application is preferably 4Cr13 series plastic mold flat steel. More specifically, the 4Cr13 series plastic mold flat steel includes at least several components such as 40Cr13, 40Cr13H, 40Cr13HL, and 40Cr13HH. Its specific chemical composition is: C 0.36%~0.45%; Si≤0.40%; Mn≤0.60%; Cr 12.00%~14.00%; Ni≤0.60%; P≤0.030%; S≤0.025%; the balance being Fe and unavoidable impurities.

[0022] In summary, the technical solution provided in this application also has the following advantages: This invention provides a method for effectively controlling the banded structure and resulting defects within 40Cr13 series plastic mold flat steel. This method improves the quality of rolled 40Cr13 series plastic mold flat steel products and increases the product flaw detection pass rate. When using 3-6 ton ingots to roll flat steel products with cross-sectional dimensions of (50-200 mm) × (400-600 mm), according to the banded structure evaluation method of series E in GB / T34474.1-2017, the banded structure can be controlled within the range of 0-2, and the flaw detection pass rate can be improved by 3-5%.

[0023] The technical solution of this application will be further described below through specific embodiments: The purpose of this invention is to provide a rolling method for plastic mold flat steel, so as to solve the problem that the 40Cr13 series plastic mold flat steel produced by the existing rolling method will have internal defects caused by the formation of banded structure, which will eventually lead to failure of flaw detection.

[0024] The technical solution of this invention is: A rolling method for flat steel for plastic molds includes three steps: gradient heating, uniform deformation, and controlled cooling.

[0025] The method for rolling flat steel for plastic molds includes 40Cr13 series plastic mold steels, such as 40Cr13, 40Cr13H, 40Cr13HL, 40Cr13HH, etc., with the following chemical composition by weight percentage: C: 0.36%~0.45%; Si: ≤0.40%; Mn: ≤0.60%; Cr: 12.00%~14.00%; Ni: ≤0.60%; P: ≤0.030%; S: ≤0.025%; the balance being Fe and unavoidable impurities.

[0026] Step 1: Gradient heating The gradient heating process involves sending the hot ingot from the mold to a high-temperature heating furnace, setting the initial temperature of the furnace to 850°C. After the ingot is loaded into the furnace and the temperature stabilizes, it is held at that temperature for 2 hours. Then, it is heated to 1260°C at a heating rate of 100°C / h and held at that temperature for 5 hours. Finally, it is cooled down to 1150°C in the furnace and held at that temperature for 2 hours before being taken out of the furnace and rolled.

[0027] The purpose of this is to heat the ingot at high temperature until it is fully heated through, and then cool it down and heat it for a period of time. At this time, the ingot is fully heated but the core temperature is relatively low, which can provide favorable conditions for subsequent rolling deformation. Under the action of deformation heat, the core temperature rise is not so large, which can avoid the core rich alloy element strips from being too hot due to excessive temperature rise, resulting in poor plasticity and intergranular cracking.

[0028] Step 2: Uniform Deformation The rolling deformation is carried out on the 1350 unit reciprocating rolling mill. The uniform deformation is achieved by equal rolling force rolling. The reduction per pass in the initial rolling process is ≤25%, and the reduction rate per pass is ≤1.0 s. -1 After the reduction reaches 50%, the billet is left idle on the rolling mill roller table for 3-5 minutes, followed by reductions of ≤15% per pass and a reduction rate of ≤0.5 seconds per pass. -1 The subsequent rolling process continues until the finished product size is achieved, resulting in a rolled billet.

[0029] The purpose of this is to make the alloy element enrichment zone and depletion zone deform uniformly, thereby reducing or eliminating the banded structure.

[0030] Step 3: Controlling Cooling The controlled cooling involves feeding the rolled billet to a cooling bed equipped with a windproof cover, thus avoiding the rapid air cooling zone formed by the natural air duct effect at both ends of the cooling bed. Simultaneously, the cooling bed stepping speed is adjusted to control the cooling rate of the flat steel within the range of ≤10℃ / min until room temperature is reached.

[0031] The purpose of this is to avoid excessively rapid cooling, which could cause an increase in internal stress in the flat steel (especially in areas where alloying elements are relatively concentrated), leading to internal stress cracking.

[0032] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. 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 skilled in the art without creative effort are within the scope of protection of the present invention.

[0033] Furthermore, the terms "first," "second," etc., used in the specification, claims, and accompanying drawings of this application are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such data can be interchanged where appropriate so that the embodiments of this application described herein can be implemented, for example, in orders other than those illustrated or described herein.

[0034] Furthermore, the terms “comprising” and “having”, and any variations thereof, are intended to cover non-exclusive inclusion, such that a process, method, system, product, or device that includes a series of steps or sub-modules is not necessarily limited to those steps or sub-modules that are explicitly listed, but may include other steps or sub-modules that are not explicitly listed or that are inherent to such process, method, product, or device.

[0035] The present invention will now be described in detail: Table 1 is a list of steel grades and chemical composition values ​​for each embodiment and comparative example of the present invention; Table 2 is a list of the main process values ​​for each embodiment and comparative example of the present invention; Table 3 shows the banded tissue level and the percentage improvement in flaw detection pass rate for each embodiment and comparative example of the present invention; A rolling method for flat steel for plastic molds includes three steps: gradient heating, uniform deformation, and controlled cooling.

[0036] The method for rolling flat steel for plastic molds includes 40Cr13 series plastic mold steels, such as 40Cr13, 40Cr13H, 40Cr13HL, 40Cr13HH, etc., with the following chemical composition by weight percentage: C: 0.36%~0.45%; Si: ≤0.40%; Mn: ≤0.60%; Cr: 12.00%~14.00%; Ni: ≤0.60%; P: ≤0.030%; S: ≤0.025%; the balance being Fe and unavoidable impurities.

[0037] Step 1: Gradient heating The gradient heating process involves sending the hot ingot from the mold to a high-temperature heating furnace, setting the initial temperature of the furnace to 850°C. After the ingot is loaded into the furnace and the temperature stabilizes, it is held at that temperature for 2 hours. Then, it is heated to 1260°C at a heating rate of 100°C / h and held at that temperature for 5 hours. Finally, it is cooled down to 1150°C in the furnace and held at that temperature for 2 hours before being taken out of the furnace and rolled.

[0038] Step 2: Uniform Deformation The rolling deformation is carried out on the 1350 unit reciprocating rolling mill. The uniform deformation is achieved by equal rolling force rolling. The reduction per pass in the initial rolling process is ≤25%, and the reduction rate per pass is ≤1.0 s. -1After the reduction reaches 50%, the billet is left idle on the rolling mill roller table for 3-5 minutes, followed by reductions of ≤15% per pass and a reduction rate of ≤0.5 seconds per pass. -1 The subsequent rolling process continues until the finished product size is achieved, resulting in a rolled billet.

[0039] Step 3: Controlling Cooling The controlled cooling involves feeding the rolled billet to a cooling bed equipped with a windproof cover, thus avoiding the rapid air cooling zone formed by the natural air duct effect at both ends of the cooling bed. Simultaneously, the cooling bed stepping speed is adjusted to control the cooling rate of the flat steel within the range of ≤10℃ / min until room temperature is reached.

[0040] The differences in preparation methods for the comparative example: Compared with the method of this invention, the comparative example uses a conventional method, with the main differences being: 1. The conventional method uses direct heating in a single stage instead of gradient heating. Specifically, the ingot is sent to a high-temperature heating furnace, the initial temperature of which is set to 850°C. After the ingot is loaded into the furnace and the temperature stabilizes, it is held at that temperature for 2 hours. Then, it is heated to 1260°C at a heating rate of 100°C / h and held at that temperature for 8 hours before being rolled out. 2. The conventional method does not have detailed control over the reduction amount and reduction rate per pass, and it does not include a 3-5 minute cooling process on the rolling mill roller table during the intermediate rolling process. 3. Regarding the cooling process, the conventional method sends the rolled billet directly to the cooling bed without effectively controlling whether there is a windproof cover and the stepping speed of the cooling bed, resulting in excessively rapid and uneven cooling of the flat steel.

[0041] Table 1. List of steel grades and chemical composition values ​​(mass percentage) for each embodiment and comparative example of the present invention. Table 2. Main process values ​​for each embodiment and comparative example Table 3 shows the banded tissue level and the percentage improvement in flaw detection pass rate for each embodiment and comparative example. Finally, it should be noted that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing flat steel for plastic molds, characterized in that: The preparation method first obtains a pre-rolled billet with uniform internal heating temperature and balanced stress in the alloy element enrichment area and related areas through gradient heating. Then, a uniform deformation rolling process is used to obtain a finished rolled billet with uniform deformation in the alloy element enrichment zone and the depletion zone. Finally, temperature-controlled cooling is used to obtain a finished plastic mold flat steel with the required structural stress in the alloy element enrichment area and good internal fusion.

2. The method for preparing flat steel for plastic molds according to claim 1, characterized in that: The strip structure of the flat steel used to prepare qualified finished plastic molds should be controlled within the range of 0-2.

3. The method for preparing flat steel for plastic molds according to claim 1 or 2, characterized in that: Gradient heating uses red die casting ingots as billets and is carried out in a heating furnace with an initial furnace temperature of not less than 850°C. After the red die casting ingots are loaded into the heating furnace, the furnace temperature is kept at a stable temperature for at least 2 hours before the temperature is increased for heating.

4. The method for preparing flat steel for plastic molds according to claim 3, characterized in that: The heating rate of gradient heating is controlled at 100℃ / h until the heating temperature reaches 1260℃, then it is held at that temperature for at least 5 hours, and then cooled down to 1150℃ in the furnace and held for 2 hours before being taken out of the furnace for rolling.

5. The method for preparing flat steel for plastic molds according to claim 4, characterized in that: The uniform rolling process is divided into front-end rolling and back-end rolling, with a reduction of 50% as the dividing line. In the front-end rolling, the reduction of each rolling pass is controlled to not exceed 25%, and the reduction rate is not greater than 1.0 s. -1 Control measures are in place; the reduction amount in each rolling pass during the subsequent rolling process shall not exceed 15%, and the reduction rate shall not exceed 0.5 seconds. -1 control.

6. The method for preparing flat steel for plastic molds according to claim 5, characterized in that: The uniform rolling is carried out on the 1350 rolling mill. After the ingot is reduced by 50% in the first stage of rolling, before entering the second stage of rolling, the process billet is first placed on the rolling mill roller table for 3-5 minutes before the second stage of rolling.

7. The method for preparing flat steel for plastic molds according to claim 6, characterized in that: Temperature-controlled cooling is carried out on a walking cooling bed equipped with a windproof cover. The cooling rate of the cooling bed is controlled at ≤10℃ / min until the billet temperature drops to room temperature.

8. A plastic mold flat steel manufactured using the method for preparing plastic mold flat steel according to claim 7, characterized in that: The plastic mold flat steel mentioned is 4Cr13 series plastic mold flat steel.

9. The plastic mold flat steel according to claim 8, characterized in that: The 4Cr13 series of plastic mold flat steel includes 40Cr13, 40Cr13H, 40Cr13HL and 40Cr13HH.

10. The plastic mold flat steel according to claim 9, characterized in that: The chemical composition of 4Cr13 series flat steel is: C 0.36%~0.45%; Si≤0.40%; Mn≤0.60%; Cr 12.00%~14.00%; Ni≤0.60%; P≤0.030%; S≤0.025%; the balance is Fe and unavoidable impurities.

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