Hot work die steel and manufacturing method for improving structure performance of hot work die steel at low cost

Abstract

The invention discloses hot work die steel and a low-cost manufacturing method for improving the structure performance of the hot work die steel. Chemical components are proportioned, and molten steel is obtained through electric furnace smelting, LF smelting and VD smelting; forming a cast ingot from the molten steel through a die casting process; the cast ingot is put into a furnace to be subjected to segmented heating treatment, and then forging and annealing treatment are conducted in sequence; in the die casting process, the superheat degree is maintained at 29.5-30.5 DEG C in the pouring period. An electroslag remelting process is replaced by a die casting process, so that the production cost is effectively reduced; and the superheat degree of the molten steel in the pouring process is reduced, and the corresponding pouring speed is matched, so that the effect of reducing the banded structure grade incompatibility caused by segregation of elements in the solidification process can be effectively achieved. According to the die ingot casting, the process of steel ingot homogenization, fast forging and precision forging is adopted, the traditional forging mode of steel ingot homogenization, fast forging, blank homogenization and precision forging is replaced, the production scheduling efficiency of the forging process can be improved, and energy loss caused by the fact that the blank needs to be returned to a furnace to be heated is reduced.

Description

Technical Field

[0001] The invention relates to the technical field of iron and steel metallurgy, and in particular to a hot working die steel and a manufacturing method for improving the structure and performance of the hot working die steel at a low cost. Background Art

[0002] As one of the widely used mold materials, hot working die steel is mainly used for pressing and forming high-temperature solid metal or liquid metal. Its service characteristics are: high working temperature, harsh thermal cycle, large mechanical stress and thermal stress. This puts higher requirements on the comprehensive performance of die steel, such as high strength and toughness, high thermal stability and wear resistance. In recent years, the most widely used hot working die steel H13 and its improved steel grades in industrial production have two major performance defects (poor isotropy and low high-temperature thermal strength), which are closely related to the uniformity of the organization and the precipitation evolution of carbides. Researchers have sorted out the causes of liquid carbides and adopted various means to control the generation of liquid carbides in steel.

[0003] Based on this, the existing technology still needs to be improved. Summary of the invention

[0004] In order to solve the above technical problems, an embodiment of the present invention provides a hot working die steel and a low-cost manufacturing method for improving its microstructure and performance.

[0005] In order to solve the above technical problems, on the one hand, some embodiments of the present invention disclose a low-cost manufacturing method for improving the microstructure and properties of hot working die steel, comprising: According to the chemical composition, the steel is prepared by smelting in an electric furnace, LF, or VD process. Forming the molten steel into an ingot through a die casting process; After the ingot is put into the furnace for staged heating treatment, forging and annealing treatment are carried out in sequence; Among them, in the die casting process, the superheat during the pouring period is maintained at 29.5℃-30.5℃, and the pouring speed is 420-430s for the ingot body and 340-350s for the riser. In some embodiments, the chemical components are mixed in the following ratios: C 0.40%-0.50%, Si 0.6%-1.2%, Mn 0.37%-0.42%, Cr 5.0%-5.3%, Mo 1.3%-1.5%, V0.9%-1%, W 0.05%, and the balance is iron and inevitable impurities.

[0006] In some embodiments, placing the ingot into the furnace for staged heating treatment includes: ensuring that the temperature of the heating furnace before forging the die-cast ingot is no greater than 650°C.

[0007] In some embodiments, placing the ingot into the furnace for staged heating treatment further comprises: Keeping the temperature at a first temperature for a first predetermined time; Raising the temperature to a second temperature and keeping the temperature for a second predetermined time; Raising the temperature to a third temperature and keeping it warm for a third predetermined time; The temperature is lowered to a fourth temperature and kept warm for a fourth predetermined time.

[0008] In some embodiments, the first temperature is 850±10°C; the second temperature is 1150±10°C; the third temperature is 1280±10°C; the fourth temperature is 1180±10°C; The first scheduled time is 110-130 minutes; the second scheduled time is 350-370 minutes; the third scheduled time is 350-370 minutes; the fourth scheduled time is not less than 60 minutes; Furthermore, the cooling time from the third temperature to the fourth temperature is 55-65 minutes.

[0009] In some embodiments, the first temperature is 650±10°C; the second temperature is 850±10°C; the third temperature is 1280±10°C; the fourth temperature is 1180±10°C; The first scheduled time is 350-370 minutes; the second scheduled time is 110-130 minutes; the third scheduled time is 350-370 minutes; the fourth scheduled time is not less than 60 minutes; Furthermore, the cooling time from the third temperature to the fourth temperature is 55-65 minutes.

[0010] In some embodiments, the superheat is maintained at 30°C during the pouring period.

[0011] In some embodiments, the forging adopts a process of steel ingot homogenization + rapid forging + fine forging.

[0012] In some embodiments, the heat preservation system for homogenizing the steel ingot is 1270° C.-1290° C. for 11.5-12.5 hours.

[0013] On the other hand, an embodiment of the present invention further discloses a hot working die steel, which is manufactured by the aforementioned low-cost manufacturing method for improving the microstructure and properties of hot working die steel.

[0014] By adopting the above technical solution, the present invention has at least the following beneficial effects: The present invention provides a hot working die steel and a low-cost manufacturing method for improving its structural properties, which can simplify the production process, improve its metallurgical quality and reduce costs. The die casting process is used to replace the electroslag remelting process to effectively reduce its production cost; reducing the superheat of the molten steel during the casting process and matching the corresponding casting speed can effectively reduce the banded structural grade incompatibility caused by the segregation of elements during the solidification process. The die casting ingot adopts the process of ingot homogenization + fast forging + fine forging, replacing the traditional forging method of ingot homogenization + fast forging + billet homogenization + fine forging, which can improve the production efficiency of the forging process and reduce the energy loss caused by the billet needing to be returned to the furnace for heating. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] 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.

[0016] Figure 1 A diagram of the pre-forging temperature rise system for a low-cost manufacturing method for improving the microstructure and properties of hot-working die steel disclosed in some embodiments of the present invention; Figure 2 A diagram of the pre-forging temperature rise system for a low-cost manufacturing method for improving the microstructure and properties of hot-working die steel disclosed in some embodiments of the present invention; Figure 3 This is the product organization diagram of the hot working die steel obtained in Comparative Example 1; Figure 4 This is the product organization diagram of the hot working die steel obtained in Example 1; Figure 5 This is the product organization diagram of the hot working die steel obtained in Example 2. DETAILED DESCRIPTION

[0017] 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.

[0018] 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.

[0019] 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.

[0020] 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.

[0021] 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.

[0022] 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.

[0023] 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.

[0024] like Figure 1 As shown, some embodiments of the present invention disclose a low-cost manufacturing method for improving the microstructure and properties of hot working die steel, which can simplify the production process, improve its metallurgical quality, and reduce costs. In order to achieve the above technical effects, the present invention is specifically implemented through the following technical solutions: Calculated by mass percentage, smelting is carried out according to the following chemical composition: C 0.40-0.50%, Si 0.6-1.2%, Mn 0.37-0.42%, Cr 5.0-5.3%, Mo 1.3-1.5%, V 0.9-1%, W 0.05%, and the balance is iron and inevitable impurities.

[0025] After molten steel is smelted by the electric furnace + LF + VD process, the ingot is directly formed by the die casting process. Compared with the traditional electroslag remelting process, it has achieved the effect of effectively reducing its production cost; At the same time, during the die casting process, the pouring temperature is lowered (the superheat during the pouring period is controlled at about 30°C), which can reduce the segregation of elements during the solidification process and effectively avoid the resulting unqualified banded structure grade.

[0026] In addition, when the temperature of the heating furnace before forging the die-cast ingot is guaranteed to be ≥650°C, the ingot is put into the furnace for staged heating. Preferably, the heating system can be as follows: Figure 2 shown.

[0027] Forging: The die-cast ingot is processed by the process of ingot homogenization + fast forging + fine forging. Compared with the traditional forging method of ingot homogenization + fast forging + billet homogenization + fine forging, it can effectively improve the production efficiency of the forging process and reduce the energy loss caused by the billet needing to be returned to the furnace for heating. The ingot homogenization insulation system should generally be controlled to be around 1280℃ for 12 hours.

[0028] Annealing: After fine forging, the steel is placed in an annealing furnace for annealing and stress relief treatment.

[0029] Comparative Example 1 Calculated by mass percentage, smelting is carried out according to the following chemical composition: C 0.4%, Si 1.0%, Mn 0.4%, Cr 5%, Mo 1.4%, V 1.0%, W 0.05%, and the balance is iron and inevitable impurities.

[0030] The configured raw materials are smelted into molten steel through the electric furnace + LF + VD process, and then formed into a mold-cast ingot through a pouring process, wherein the pouring molten steel has a superheat of 50°C, a pouring speed of 430s for the mold-cast ingot body, and 350s for the riser, and the resulting ingot size is a rectangular mold-cast ingot of 3.7t.

[0031] When the temperature of the heating furnace before forging is ≤650℃, the ingot is put into the furnace and heated up in stages. The heating system is as follows: Figure 1 As shown, keep the temperature at 650℃ for 2 hours; heat to 850℃ and keep it for 2 hours; heat to 1280℃ and keep it for 6 hours; then cool down to 1180℃ for 1 hour and keep it warm. The warming time should be no less than one hour before starting forging.

[0032] Quick forging: After the first homogenization, the steel ingot is upset to a height of 1000mm, stretched to 750±10mm rough square (light chamfer), returned to the furnace for homogenization at 1280℃ for 6h, then cooled to 1180℃ and kept warm for 1h; upset to a height of 700mm, stretched to 400±5mm octagonal (the furnace temperature for each fire during the stretching process is 1180±10℃, and the holding time is 2~4h), the cap is cut off, and then fine forging is performed; Precision forging: The quick forging billet is placed in the furnace and kept at 1150±10℃ for ≥2.5h before forging begins. The size is controlled to be Φ280±10mm, and any defects at both ends must be cut off.

[0033] Annealing: After fine forging, the product is put into the annealing furnace for annealing and stress relief treatment. Figure 3 The carbide size and impact toughness test results are shown in Table 1.

[0034] Example 1 Calculated by mass percentage, smelting is carried out according to the following chemical composition: C 0.4%, Si 1.0%, Mn 0.4%, Cr 5%, Mo 1.4%, V 1.0%, W 0.05%, and the balance is iron and inevitable impurities.

[0035] The configured raw materials are smelted into molten steel through the electric furnace + LF + VD process, and then formed into a mold-cast ingot through a pouring process, wherein the pouring molten steel is superheated at 30°C, the pouring speed is 400s for the mold-cast ingot body, and 330s for the riser, and the formed ingot size is a rectangular mold-cast ingot of 3.7t.

[0036] When the temperature of the heating furnace before forging is ≤650℃, the ingot is put into the furnace and heated up in stages. The heating system is as follows: Figure 1 As shown, keep the temperature at 650℃ for 2 hours; heat to 850℃ and keep it for 2 hours; heat to 1280℃ and keep it for 6 hours; then cool down to 1180℃ for 1 hour and keep it warm. The warming time should be no less than one hour before starting forging.

[0037] Quick forging: After the first homogenization, the steel ingot (ingot) is upset to a height of 1000mm, stretched to 750±10mm rough square (light chamfer), returned to the furnace for homogenization at 1280℃ for 6h, then cooled to 1180℃ and kept warm for 1h; upset to a height of 700mm, stretched to 400±5mm octagonal (the furnace temperature for each fire during the stretching process is 1180±10℃, and the holding time is 2~4h), the cap is cut off, and then fine forging is performed; Precision forging: The quick forging billet is placed in the furnace and kept at 1150±10℃ for ≥2.5h before forging begins. The size is controlled to be Φ280±10mm, and any defects at both ends must be cut off.

[0038] Annealing: After fine forging, the product is put into the annealing furnace for annealing and stress relief treatment. Figure 4 shown.

[0039] Compared with the comparative example, the superheat of the poured molten steel is improved, so that the carbide size in the obtained product structure is reduced from 15-28 microns to 10-14 microns, and the impact toughness result is also much better than that of comparative example 1. The results are shown in Table 1.

[0040] Example 2 Calculated by mass percentage, smelting is carried out according to the following chemical composition: C 0.4%, Si 1.0%, Mn 0.4%, Cr 5%, Mo 1.4%, V 1.0%, W 0.05%, and the balance is iron and inevitable impurities.

[0041] The configured raw materials are smelted into molten steel through the electric furnace + LF + VD process, and then formed into a mold-cast ingot through a pouring process, wherein the pouring molten steel is superheated at 30°C, the pouring speed is 400s for the mold-cast ingot body, and 330s for the riser, and the formed ingot size is a rectangular mold-cast ingot of 3.7t.

[0042] Ensure the timing of hot delivery of mold casting ingots, make the measured temperature of the heating furnace before forging the steel ingot ≥ 650℃, put the ingot into the furnace and heat it up in stages. The heating system is as follows: Figure 2 As shown, keep the temperature at 850℃ for 2 hours; heat to 1150℃ and keep it for 6 hours; heat to 1280℃ and keep it for 6 hours; then cool to 1180℃ for 1 hour and keep it warm. The warming time should not exceed one hour before starting forging.

[0043] Quick forging: After the first homogenization, the steel ingot (ingot) is upset to a height of 1000mm, and stretched to 750±10mm square (light chamfer); upset to a height of 700mm, and stretched to 400±5mm octagonal (the temperature of each fire during the stretching process is 1180±10℃, and the holding time is 2~4h), the cap is cut off, and then fine forging is performed; Precision forging: The quick forging billet is placed in the furnace and kept at 1150±10℃ for ≥2.5h before forging begins. The size is controlled to be Φ280±10mm, and any defects at both ends must be cut off.

[0044] Annealing: After fine forging, the product is put into the annealing furnace for annealing and stress relief treatment. Figure 5 The carbide size and impact toughness test results are shown in Table 1. Compared with Comparative Example 1 and the embodiment, this embodiment ensures the timing of hot delivery of the mold casting ingot, the cast mold casting ingot can be delivered to the heating furnace in time, the 650 temperature section is omitted in the heating system, and the energy consumption is effectively reduced.

[0045] Table 1

[0046] In the above embodiment, the existing homogenization system is 1280℃ insulation for 6h of ingot casting + 6h of billet casting, which is optimized to 1280℃ insulation for 12h of ingot casting in embodiment 1, and optimized to 1150℃ insulation for 6h of ingot casting + 1280℃ insulation for 6h of ingot casting in embodiment 2. The optimization method of embodiment 2 can not only further reduce energy consumption by reducing the insulation time at 1280℃, but also avoid the phenomenon of grain overburning caused by long-term exposure to 1280℃ in the internal structure of the material, which is more helpful to ensure the uniformity of the material structure.

[0047] In summary, the embodiment of the present invention discloses a low-cost manufacturing method for improving the microstructure and properties of hot working die steel. By controlling the superheat during the casting period, controlling the temperature of the heating furnace before forging, performing staged temperature increase treatment, and combining the forging process optimization with the default sequential homogenization of the billet, the degree of microstructure segregation is changed, and even hot working die steel with no detected carbides is obtained. In addition, various microstructure and properties such as impact properties are also greatly improved. The production process is simplified, the metallurgical quality is improved, and the cost is reduced.

[0048] 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.

[0049] 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 low-cost manufacturing method for improving the microstructure and properties of hot working die steel, characterized in that: include: According to the chemical composition, the steel is prepared by smelting in an electric furnace, LF, or VD process. Forming the molten steel into an ingot through a die casting process; After the ingot is put into the furnace for staged heating treatment, forging and annealing treatment are carried out in sequence; Among them, in the die casting process, the superheat during the pouring period is maintained at 29.5℃-30.5℃, and the pouring speed is 420-430s for the ingot body and 340-350s for the riser.

2. The low-cost manufacturing method for improving the microstructure and properties of hot working die steel according to claim 1 is characterized in that: The chemical components are mixed in the following proportions: C 0.40%-0.50%, Si 0.6%-1.2%, Mn 0.37%-0.42%, Cr 5.0%-5.3%, Mo 1.3%-1.5%, V0.9%-1%, W 0.05%, and the balance is iron and inevitable impurities.

3. The low-cost manufacturing method for improving the microstructure and properties of hot working die steel according to claim 1 is characterized in that: The ingot is placed in the furnace for staged heating treatment, including: ensuring that the temperature of the heating furnace before forging the die-cast ingot is not greater than 650°C.

4. The low-cost manufacturing method for improving the microstructure and properties of hot working die steel according to claim 3 is characterized in that: The stepwise heating treatment of the ingot into the furnace also includes: Keeping the temperature at a first temperature for a first predetermined time; Raising the temperature to a second temperature and keeping the temperature for a second predetermined time; Raising the temperature to a third temperature and keeping it warm for a third predetermined time; The temperature is lowered to a fourth temperature and kept warm for a fourth predetermined time.

5. The low-cost manufacturing method for improving the microstructure and properties of hot working die steel according to claim 4 is characterized in that: The first temperature is 850±10°C; the second temperature is 1150±10°C; the third temperature is 1280±10°C; the fourth temperature is 1180±10°C; The first scheduled time is 110-130 minutes; the second scheduled time is 350-370 minutes; the third scheduled time is 350-370 minutes; the fourth scheduled time is not less than 60 minutes; Furthermore, the cooling time from the third temperature to the fourth temperature is 55-65 minutes.

6. The low-cost manufacturing method for improving the microstructure and properties of hot working die steel according to claim 4 is characterized in that: The first temperature is 650±10°C; the second temperature is 850±10°C; the third temperature is 1280±10°C; the fourth temperature is 1180±10°C; The first scheduled time is 350-370 minutes; the second scheduled time is 110-130 minutes; the third scheduled time is 350-370 minutes; the fourth scheduled time is not less than 60 minutes; Furthermore, the cooling time from the third temperature to the fourth temperature is 55-65 minutes.

7. The low-cost manufacturing method for improving the microstructure and properties of hot working die steel according to claim 1 is characterized in that: The superheat was maintained at 30°C during pouring.

8. The low-cost manufacturing method for improving the microstructure and properties of hot working die steel according to claim 1 is characterized in that: The forging adopts the process of steel ingot homogenization + fast forging + fine forging.

9. The low-cost manufacturing method for improving the microstructure and properties of hot working die steel according to claim 8, characterized in that: The heat preservation system for homogenizing the steel ingot is 1270° C.-1290° C. for 11.5-12.5 hours.

10. A hot working die steel, characterized in that: The hot working die steel is manufactured by adopting the low-cost manufacturing method for improving the microstructure and properties of hot working die steel as described in any one of claims 1 to 9.

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