Flat steel for plastic mold and rolling method of flat steel

Abstract

According to the flat steel for the plastic mold and the rolling method of the flat steel, in the rolling process, stepped rolling reduction is adopted for rolling a steel ingot, only taper grinding treatment is conducted on the steel ingot in the first pass, the second pass and the third pass, and the rolling reduction is not set; from the fourth pass to the ninth pass, rolling is conducted under the first rolling reduction; the tenth pass to the thirteenth pass are rolled under the second rolling reduction; after the fourteenth pass until rolling is completed, rolling is conducted under the first rolling reduction; in addition, in the first pass to the thirteenth pass, the steel ingot is subjected to steel overturning and leveling treatment after two passes of pressing are completed every time; the first rolling reduction is smaller than or equal to 15%, and the second rolling reduction is larger than 35%. According to the method, the product with the required shape and size can be obtained, the thick as-cast structure in the steel ingot can be fully crushed, internal defects can be fully welded, and the problem that flaw detection is unqualified due to the core part and even head-tail through loose defects occurring during flat steel rolling is solved.

Description

Technical Field

[0001] The invention relates to the technical field of steel rolling forming, in particular to a flat steel for plastic moulds and a rolling method thereof. Background Art

[0002] Flat steel for plastic molds is a high-quality steel specially used for manufacturing plastic molds. It is mainly made of medium-carbon alloy structural steel and has high hardness and strength. In mold manufacturing, it is often used to make support structures and stress-bearing parts of high-precision, wear-resistant and long-life molds, such as templates, guide pillars, guide sleeves, etc., to ensure the stability and precision of the mold. Due to its excellent performance and wide range of applications, it plays a vital role in the plastic mold manufacturing industry, and has won the favor and trust of the majority of users with its stable quality, excellent processing performance and long service life.

[0003] In order to improve the yield rate of flat steel for plastic molds, reduce production costs, and improve market competitiveness, various manufacturers are currently competing to develop large ingot direct rolling technology to produce flat steel. Compared with the previous forging and finishing rolling process, although the direct rolling process can directly reduce production costs, it still needs to be matched with a reasonable process to ensure product quality. For example, most rolled flat steels have loose defects in the core or even the head and tail, which cannot be pressed together, and ultimately lead to unqualified flaw detection. To solve this problem, the present invention provides a flat steel for plastic molds and a rolling method thereof.

[0004] Based on this, the existing technology still needs to be improved. Summary of the invention

[0005] In order to solve the above technical problems, an embodiment of the present invention proposes a flat steel for plastic molds and a rolling method thereof, so as to solve the problem of unqualified flaw detection caused by loose defects in the core or even the head and tail when flat steel is produced by large ingot direct rolling process in industrial production.

[0006] In order to solve the above technical problems, some embodiments of the present invention disclose a flat steel for plastic mold and a rolling method thereof, comprising: during the rolling process, the steel ingot is rolled with a stepped reduction, wherein: In the first pass, the second pass and the third pass, the steel ingot is only subjected to taper grinding without setting a reduction amount; The fourth to ninth passes are rolled at the first reduction; The tenth to thirteenth passes are rolled at the second reduction; After the fourteenth pass until the rolling is completed, rolling is performed at the first reduction; Furthermore, from the first pass to the thirteenth pass, the steel ingot is turned over and leveled after every two passes of pressing; The first pressing amount is a pressing amount ≤ 15%, and the second pressing amount is a pressing amount > 35%.

[0007] Furthermore, it also includes: heating the steel ingot before rolling, the heating treatment including: sending the steel ingot to a heating furnace, keeping it at 600℃±10℃ for 2h~5h, then heating it to 850℃±10℃ at a heating rate of ≤100℃ / h and keeping it for 2h~5h, and then heating it to 1210℃±10℃ at a heating rate of ≤100℃ / h and keeping it for 10h~15h.

[0008] Furthermore, during the rolling process, the steel ingot is unidirectionally rolled with the nozzle end facing forward.

[0009] Furthermore, the taper flattening process includes: In the first pass, the rolling mill pass height is set to be 2 mm to 5 mm smaller than the maximum height of the ingot riser end; In the second pass, the rolling mill pass height is set to the height of the middle part of the steel ingot in the axial direction; In the third pass, the rolling mill pass height is set to be the height of the middle part of the ingot in the axial direction.

[0010] Furthermore, the steel turning and leveling process includes: turning the steel ingot 90 degrees in the axial direction for rolling.

[0011] Further, the pressing amount setting includes: When the weight of the steel ingot is 3.75t to 5t and the thickness of the finished product is 55mm to 195mm, the reduction from the fourth to ninth passes is 8% to 14%, the reduction from the tenth to thirteenth passes is 50% to 60%, and the reduction from the fourteenth pass to the completion of rolling is 6% to 10%.

[0012] Furthermore, an embodiment of the present invention also discloses a flat steel for plastic molds, which is rolled according to the above-mentioned rolling method of the flat steel for plastic molds.

[0013] Furthermore, the chemical composition of the flat steel is as follows in percentage by weight: C=0.35%-0.45%, Si≤0.60%, Mn≤0.80%, Cr=12.00%-14.00%, Ni≤0.60%, and the remainder is Fe and unavoidable impurities.

[0014] Furthermore, the unavoidable impurities include P and S, and in terms of mass percentage, P≤0.025%, S≤0.020%.

[0015] Furthermore, the flat steel has a B-level flaw detection pass rate of ≥98%.

[0016] By adopting the above technical solution, the present invention has at least the following beneficial effects: The present invention provides a flat steel for plastic molds and a rolling method thereof. During the rolling process, the steel ingot is rolled with a stepped reduction amount to ensure that a product of a desired shape and size can be obtained, and the coarse cast structure inside the steel ingot can be fully crushed, and internal defects can be fully welded, so as to finally obtain a product with good internal quality. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0018] Figure 1 A rolling flow chart of flat steel for plastic moulds disclosed in some embodiments of the present invention. DETAILED DESCRIPTION

[0019] The following is a further detailed description of the embodiments of the present disclosure in conjunction with the accompanying drawings and examples. The detailed description of the following embodiments and the accompanying drawings are used to exemplarily illustrate the principles of the present disclosure, but cannot be used to limit the scope of the present disclosure. The present disclosure can be implemented in many different forms and is not limited to the specific embodiments disclosed herein, but includes all technical solutions that fall within the scope of the claims.

[0020] The present disclosure provides these embodiments to make the present disclosure thorough and complete, and to fully express the scope of the present disclosure to those skilled in the art. It should be noted that unless otherwise specifically stated, the relative arrangement of the parts and steps, the composition of the materials, the numerical expressions and the numerical values ​​set forth in these embodiments should be interpreted as being merely exemplary, and not as limiting.

[0021] It should be noted that, in the description of the present disclosure, unless otherwise specified, the meaning of "multiple" is greater than or equal to two; the terms "upper", "lower", "left", "right", "inner", "outer", etc., indicating the orientation or positional relationship, are only for the convenience of describing the present disclosure and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation of the present disclosure. When the absolute position of the object being described changes, the relative positional relationship may also change accordingly.

[0022] In addition, the words "first", "second" and similar words used in the present disclosure do not indicate any order, quantity or importance, but are only used to distinguish different parts. "Vertical" does not mean vertical in the strict sense, but is within the tolerance range. "Parallel" does not mean parallel in the strict sense, but is within the tolerance range. "Include" or "comprising" and similar words mean that the elements before the word include the elements listed after the word, and do not exclude the possibility of including other elements.

[0023] It should also be noted that in the description of the present disclosure, unless otherwise clearly specified and limited, the terms "installed", "connected", and "connected" should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral connection; it can be directly connected or indirectly connected through an intermediate medium. For ordinary technicians in this field, the specific meanings of the above terms in the present disclosure can be understood according to the specific circumstances. When a specific device is described as being located between a first device and a second device, there may or may not be an intermediate device between the specific device and the first device or the second device.

[0024] All terms used in the present disclosure have the same meanings as those understood by those of ordinary skill in the art to which the present disclosure belongs, unless otherwise specifically defined. It should also be understood that terms defined in general dictionaries, for example, should be interpreted as having meanings consistent with their meanings in the context of the relevant technology, and should not be interpreted in an idealized or extremely formal sense, unless explicitly defined as such herein.

[0025] Technologies, methods, and equipment known to ordinary technicians in the relevant art may not be discussed in detail, but where appropriate, the technologies, methods, and equipment should be considered part of the specification.

[0026] like Figure 1 As shown, some embodiments of the present invention disclose a rolling method for flat steel for plastic molds, including: during the rolling process, the steel ingot is rolled with a stepped reduction, wherein, in the first, second and third passes, only the steel ingot is taper-ground without setting the reduction; during the rolling process from the fourth to the ninth passes, the reduction is ≤15%; during the rolling process from the tenth to the thirteenth passes, the reduction is >35%; after the fourteenth pass until the rolling is completed, the reduction is ≤15%; and, during the rolling process from the first to the thirteenth passes, the steel ingot is turned over and flattened after every two passes of reduction, and after the fourteenth pass, the turning over and flattening may not be performed according to the finished product size and actual demand.

[0027] By adopting the above rolling method, steel ingots weighing 3.75t to 5t can be rolled into finished flat steel with a thickness of 50mm to 200mm and a width of 350mm to 650mm under the corresponding reduction amount. Specifically, the corresponding reduction amount can be allocated for rolling according to parameters such as the incoming ingot shape and material, and the finished product specifications to obtain finished flat steel of corresponding size.

[0028] It can be seen that the use of the above-mentioned stepped reduction amount to roll the steel ingot can not only ensure that the product of the required shape and size is obtained, but also enable the coarse cast structure inside the steel ingot to be fully crushed, so that the internal defects can be fully welded, and finally a product with good internal quality is obtained.

[0029] Some embodiments of the present invention disclose a method for rolling flat steel for plastic molds. On the basis of the above embodiments, the method further includes: heating the steel ingot before rolling. Specifically, the steel ingot can be first sent to a heating furnace, kept at 600℃±10℃ for 2h~5h to make the temperature of the steel ingot uniform, and ensure that the temperature of the steel ingot is uniform throughout the subsequent heating process. Then, the steel ingot is heated to 850℃±10℃ at a heating rate of ≤100℃ / h and kept for 2h~5h to further make the temperature of the phase change zone uniform, avoid cracking caused by uneven stress of the surface and core tissues after austenitization, and then heated to 1210℃±10℃ at a heating rate of ≤100℃ / h and kept for 10h~15h to fully diffuse the alloy elements and improve the inhomogeneity of the cast tissue. The heating treatment can destroy the casting structure of the steel ingot, refine the grains of the steel ingot, eliminate microstructure defects, make the steel ingot dense, and the heated steel ingot has better plasticity and toughness, so that the rolling process is smoother and the processing efficiency is improved.

[0030] Some embodiments of the present invention disclose a method for rolling flat steel for plastic molds. On the basis of the above embodiments, during the rolling process, the steel ingot is unidirectionally rolled with the water nozzle end facing forward, so that the riser end with relatively weak casting quality will not be cracked due to the tensile stress in the rolling mill biting process, causing the coarse cast structure in the core to be torn. At the same time, it can avoid the riser position being torn due to the tensile stress in the core when the rolling mill bites back, causing the core to be affected by the tensile stress, resulting in the enlargement of the defects in the core.

[0031] Some embodiments of the present invention disclose a method for rolling flat steel for plastic molds. On the basis of the above embodiments, the taper grinding process includes: in the first pass, setting the rolling mill hole height to be 2mm to 5mm smaller than the maximum height of the riser end of the steel ingot, so that after the steel ingot passes through the rolling mill, its nozzle end is subjected to slight pressure and shakes, which can cause the iron oxide scale on the ingot body to fall off, thereby preventing the surface iron oxide scale from being pressed into the steel surface during the subsequent rolling process; in the second and third passes, setting the rolling mill hole height to the height of the middle part of the steel ingot in the axial direction under the rolling state, preferably the height at about one-half of the axial direction of the steel ingot, so that after the steel ingot passes through the rolling mill, its section close to the riser can be flattened.

[0032] Some embodiments of the present invention disclose a method for rolling flat steel for plastic molds. On the basis of the above embodiments, the steel ingot can be flipped 90° in the axial direction for rolling by steel flipping and leveling. The flipping and rolling facilitates the control of the shape and size of the steel, and avoids the phenomenon that one side is rolled well due to non-flipping, while the corresponding side has angular protrusions and the side core is concave due to metal flow during the rolling process, resulting in uncontrolled shape and size of the finished product. In addition, flipping facilitates the control of the internal quality of the steel, and avoids the phenomenon that the internal structure is not sufficiently deformed under the action of the unidirectional rolling force due to non-flipping, such as insufficient carbide crushing, uneven recrystallized grains, coarse core structure and other quality defects.

[0033] Some embodiments of the present invention disclose a method for rolling flat steel for plastic molds. Based on the above embodiments, the steel ingot is preferably a die-cast flat ingot.

[0034] Some embodiments of the present invention also disclose a flat steel for plastic molds, whose chemical composition by mass percentage is: C=0.35%~0.45%, Si≤0.60%, Mn≤0.80%, Cr=12.00%~14.00%, Ni≤0.60%, and the remainder is Fe and inevitable impurities, wherein the inevitable impurities include P and S, and the mass percentage of P and S is: P≤0.025%, S≤0.020%.

[0035] The following is a description of the specific embodiments and comparative examples. Table 1 shows the ingot shape and finished product thickness of embodiments 1-5 and comparative examples 1 and 2, as well as the rolling parameter control. Table 2 shows the chemical composition mass percentages of embodiments 1-5 and comparative examples 1 and 2 of the present invention.

[0036] Table 1 shows the main process values ​​of various embodiments and comparative examples of the present invention.

[0037] Table 2 shows the chemical composition weight percentages of the embodiments and comparative examples of the present invention. Serial number C Si Mn Cr Ni P S 1 0.39 0.41 0.61 13.12 0.14 0.02 0.02 2 0.36 0.43 0.54 13.07 0.23 0.01 0.015 3 0.42 0.32 0.58 12.89 0.18 0.02 0.02 4 0.45 0.29 0.60 13.76 0.20 0.01 0.015 5 0.37 0.40 0.57 12.78 0.19 0.02 0.02 Comparative Example 1 0.36 0.31 0.54 12.49 0.23 0.01 0.015 Comparative Example 2 0.43 0.34 0.55 13.81 0.17 0.02 0.02 The chemical composition and process parameters of the above-mentioned embodiments 1-5 and comparative examples 1 and 2 were used for rolling, and the flaw detection grade B pass rate of the finished flat steels rolled was shown in Table 3. It can be seen that the flaw detection grade B pass rate of the flat steels obtained by the rolling method of the present invention is ≥98%, which is a great improvement over comparative examples 1 and 2.

[0038] Table 3 is a list of the first pass rates of flaw detection level B of various embodiments of the present invention and comparative examples Serial number NDT Grade B pass rate / % 1 98.5% 2 99.1% 3 99.4% 4 98.7% 5 98.3% Comparative Example 1 84.1% Comparative Example 2 86.6% In summary, the flat steel for plastic molds and the rolling method thereof disclosed in the present invention adopt a stepped reduction amount to roll the steel ingot. During the rolling process, the steel billet is only pressed down by compressive stress, which can not only obtain products of required shape and size, but also enable the coarse cast structure inside the steel ingot to be fully crushed, and the internal defects can be fully welded, thereby solving the problem of unqualified flaw detection caused by loose defects in the core or even the head and tail when rolling flat steel.

[0039] So far, various embodiments of the present disclosure have been described in detail. In order to avoid obscuring the concept of the present disclosure, some details known in the art are not described. Based on the above description, those skilled in the art can fully understand how to implement the technical solution disclosed here.

[0040] Although some specific embodiments of the present disclosure have been described in detail by way of examples, it should be understood by those skilled in the art that the above examples are for illustration only and are not intended to limit the scope of the present disclosure. It should be understood by those skilled in the art that the above embodiments may be modified or some technical features may be replaced by equivalents without departing from the scope and spirit of the present disclosure. In particular, the various technical features mentioned in the various embodiments may be combined in any manner as long as there is no structural conflict.

Claims

1. A method for rolling flat steel for plastic molds, characterized in that: include: During the rolling process, the steel ingot is rolled with a stepped reduction, In the first pass, the second pass and the third pass, the steel ingot is only subjected to taper grinding without setting a reduction amount; The fourth to ninth passes are rolled at the first reduction; The tenth to thirteenth passes are rolled at the second reduction; After the fourteenth pass until the rolling is completed, rolling is performed at the first reduction; Furthermore, from the first pass to the thirteenth pass, the steel ingot is turned over and leveled after every two passes of pressing; The first pressing amount is a pressing amount ≤ 15%, and the second pressing amount is a pressing amount > 35%.

2. The method for rolling flat steel for plastic molds according to claim 1, characterized in that: Also includes: The steel ingot is subjected to a heating treatment before rolling, and the heating treatment includes: The steel ingot is red sent to a heating furnace, kept at 600℃±10℃ for 2h~5h, then heated to 850℃±10℃ at a heating rate of ≤100℃ / h and kept for 2h~5h, and then heated to 1210℃±10℃ at a heating rate of ≤100℃ / h and kept for 10h~15h.

3. The method for rolling flat steel for plastic molds according to claim 1, characterized in that: During the rolling process, the steel ingot is unidirectionally rolled with the water inlet end facing forward.

4. The method for rolling flat steel for plastic molds according to claim 1, characterized in that: During the first rolling, the rolling mill pass height is set to be 2 mm to 5 mm smaller than the maximum height of the riser end of the steel ingot; During the second rolling, the rolling mill pass height is set to be the height of the middle part of the steel ingot in the axial direction; During the third rolling pass, the rolling mill pass height is set to be the height of the middle part of the steel ingot in the axial direction.

5. The method for rolling flat steel for plastic molds according to claim 1, characterized in that: The steel turning and leveling process includes: turning the steel ingot 90 degrees in the axial direction for rolling.

6. The method for rolling flat steel for plastic molds according to claim 1, characterized in that: The pressing amount setting includes: When the weight of the steel ingot is 3.75t to 5t and the thickness of the finished product is 55mm to 195mm, the reduction from the fourth to ninth passes is 8% to 14%, the reduction from the tenth to thirteenth passes is 50% to 60%, and the reduction from the fourteenth pass to the completion of rolling is 6% to 10%.

7. A flat steel for plastic mold, characterized in that: The plastic mold according to any one of claims 1 to 6 is made by rolling flat steel.

8. The flat steel for plastic mold according to claim 7, characterized in that: The chemical composition of the flat steel is as follows: C=0.35%-0.45%, Si≤0.60%, Mn≤0.80%, Cr=12.00%-14.00%, Ni≤0.60%, and the remainder is Fe and unavoidable impurities.

9. The flat steel for plastic mold according to claim 8, characterized in that: The unavoidable impurities include P and S, and in terms of mass percentage, P≤0.025%, S≤0.020%.

10. The flat steel for plastic mold according to claim 7, characterized in that: The flat steel has a B-level flaw detection pass rate of ≥98%.

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