Forging method for improving impact toughness of H13 type round steel

Abstract

The invention relates to a forging method for improving impact toughness of H13 type round steel, which is characterized in that a special heating standard is used for heating, and a special forging mode of axial upsetting, radial large rolling reduction forging, square flattening, high-temperature diffusion, axial upsetting, radial large rolling reduction forging, square forming and octagonal forming and precision forging machine forming is adopted for forging. According to the process, after each axial upsetting, one-pass radial pressing, 90-degree overturning and one-pass radial pressing are carried out on a lower platform of an upper flat plate, the pressing amount each time is 45%-50% and is equivalent to the axial upsetting deformation amount, the core of the forge piece can be fully compacted, the forge piece grains are refined, the structure is homogenized, the anisotropy of the forge piece can be reduced, the transverse performance of the forge piece can be improved, and the yield of the forge piece is improved. According to the method, the blank drawn to be flat and square is subjected to high-temperature diffusion, sufficient heat preservation is conducted at 1250 + / -10 DEG C to 1280 + / -10 DEG C, the excellent effect is achieved, then grown grains are refined through sufficient deformation, and finally the unnotched impact toughness can reach the industry leading level.

Description

Technical Field

[0001] The invention belongs to the technical field of steel material equipment manufacturing process control, and relates to a forging method for improving the impact toughness of H13 type round steel, which can effectively improve the impact toughness of H13 type round steel. Background Art

[0002] H13 is a common hot working die steel, widely used in high temperature processing industries such as die casting, forging and extrusion. It is a chromium-molybdenum-vanadium series heat-resistant die steel with excellent high temperature strength, toughness and good heat treatment performance.

[0003] In the process of use, in order to ensure that the mold is not easy to crack and thus increase its service life, impact toughness becomes a very critical indicator. The higher the impact toughness, the less likely the mold is to crack and the longer its service life.

[0004] Impact toughness is affected by many factors, such as raw material quality, forging method, heat treatment system, etc. Due to the many influencing factors, it is not easy to improve impact toughness. At present, the unnotched impact toughness of H13 round steel on the market reaches 300J / cm 2 It is already at a relatively high level. As customers have higher and higher requirements on the service life of molds, improving the impact toughness of H13 round steel is becoming more and more important. Summary of the invention

[0005] The purpose of the present invention is to overcome the shortcomings of the prior art and provide a forging method for greatly improving the unnotched impact toughness of H13 round steel by heating the steel ingot using a special heating specification and forging it through a special forging method.

[0006] The present invention is realized by the following scheme: a forging method for improving the impact toughness of H13 round steel, steel ingot heating → upsetting + radial large reduction forging + flattening → high temperature diffusion → upsetting + radial large reduction forging + four-square and eight-square → precision forging machine forming → post-forging heat treatment, the specific forging steps are as follows:

[0007] Step 1) is carried out according to the special heating specification: the steel ingot is kept at 450±10℃, then heated to 850±10℃ at ≤60℃ / h, then heated to 1250±10℃ at ≤120℃ / h, then cooled to 1230±10℃ and taken out of the furnace;

[0008] Step 2), after being taken out of the furnace, the steel ingot is axially upset on the hydraulic press, with an upset reduction of 50%. During the upsetting process, it is paused once every 300mm of upsetting; after upsetting, it is radially pressed down once on the upper flat plate and the lower platform, turned 90°, and radially pressed down once again, with a reduction of 45%-50%; then the shape of the blank is stretched to a flat square on the upper and lower flat anvils, and the size requirements are: width: thickness = 1.3-1.4, length: thickness = 2.5-3.0;

[0009] Step 3), the flat square billet is returned to the furnace for high temperature diffusion, the furnace temperature is heated to 1250±10℃~1280±10℃, after the insulation is completed, the temperature is lowered to 1230±10℃ and taken out of the furnace;

[0010] Step 4), after being taken out of the furnace, the billet is axially upset again on the hydraulic press, with an upset reduction of 50%. During the upsetting process, it is paused once every 300mm of upsetting; after upsetting, it is radially pressed down once on the lower platform of the upper plate, turned 90°, and radially pressed down once again, with a reduction of 45%-50%; then it is stretched to four sides and inverted on the upper and lower flat anvils, and the size needs to meet the feed size of the precision forging machine;

[0011] Step 5) Forming on a precision forging machine has the advantages of fast speed and good surface quality;

[0012] Step 6), heat treatment after forging.

[0013] In step 1), heating is performed according to a special heating specification: the steel ingot is kept at 450±10℃ for 3 to 6 hours, and then the temperature is increased at ≤60℃ / h to minimize the temperature stress caused by the internal and external temperature difference; the temperature is increased to 850±10℃ for 4 to 7 hours to minimize the organizational stress caused by phase change; the temperature is then increased to 1250±10℃ at ≤120℃ / h for 6 to 10 hours to fully and evenly heat the steel ingot; the temperature is then reduced to 1230±10℃ and taken out of the furnace. Cooling is beneficial to preventing coarse grains.

[0014] In steps 2) and 4), the forging process is paused every 300 mm, and each pause time is 15 to 20 seconds to avoid excessive temperature rise in the center of the forging due to too fast deformation speed, resulting in local overheating and overburning, which will seriously affect the performance of the forging.

[0015] In steps 2) and 4), after each axial upsetting, the upper plate and lower platform are radially pressed once, turned 90°, and radially pressed once again, with each pressing amount of 45%-50%. This pressing amount is close to the pressing amount during upsetting, which is equivalent to performing upsetting once in two radial directions at an angle of 90° after each axial upsetting; this can not only fully compact the core of the forging, refine the grains of the forging, and homogenize the structure, but also reduce the anisotropy of the forging and improve its lateral performance.

[0016] In step 3), the heating furnace temperature is 1250±10℃~1280±10℃, and the holding time is d×(2.5h~3h) / 100mm, where d is the equivalent diameter of the flat square billet, and d=2*thickness*width / (thickness+width), which can obtain excellent high-temperature diffusion effect.

[0017] After high-temperature diffusion in step 3), steps 4) and 5) are followed, i.e. the forging process of "axial upsetting + radial large reduction forging + four-way and eight-way forging → precision forging machine forming". The reserved forging ratio is very sufficient, which varies according to the specifications of the finished product and can generally reach more than 7. In this way, the grains grown after high-temperature diffusion can be refined through sufficient deformation, thereby improving the performance of the forging.

[0018] During the entire forging process, the hydraulic press forging controls the initial forging temperature to be 900-1180°C, and the final forging temperature to be ≥850°C. The precision forging machine forging controls the initial forging temperature to be 850-1050°C, and the final forging temperature to be ≥800°C.

[0019] The present invention has the following beneficial effects:

[0020] The present invention utilizes a special heating specification to heat the steel ingot, and adopts a special forging method of "axial upsetting + radial large reduction forging + flattening → high temperature diffusion → axial upsetting + radial large reduction forging + four-square and eight-square → precision forging machine forming" for forging. Compared with the traditional forging process of multiple upsetting and stretching, this forging process presses radially on the upper flat plate and lower platform once after each axial upsetting, turns 90°, and presses radially again once, with a reduction of 45%-50% each time. This reduction is close to the reduction during upsetting, which is equivalent to upsetting in two radial directions at an angle of 90° after each axial upsetting. It can not only fully compact the core of the forging, refine the grains of the forging, and homogenize the structure, but also reduce the anisotropy of the forging and improve its lateral performance. Compared with the traditional high-temperature diffusion method of steel ingots, the high-temperature diffusion is carried out by drawing the billet into a flat square, and the thickness of the flat square becomes smaller. In the same time, the high-temperature diffusion can achieve better results. In addition, sufficient heat preservation at 1250±10℃~1280±10℃ further enhances the effect of high-temperature diffusion, which can reduce component segregation and make the organization more uniform. After high-temperature diffusion, the grown grains are refined through sufficient deformation, thereby improving the performance of forgings. Finally, the unnotched impact toughness of H13 round steel is greatly improved, and the unnotched impact toughness can reach the industry-leading level. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 This is the heating specification diagram of H13 round steel before forging of the present invention.

[0022] FIG. 2 is a schematic diagram of the forging deformation of the H13 round steel oil press of the present invention.

[0023] Figure 2a ) is a schematic diagram of the structure of the steel ingot before upsetting.

[0024] Figure 2b ) is a schematic diagram of the structure of the steel ingot after upsetting.

[0025] Figure 2c ) is a schematic diagram of the steel ingot being radially pressed down once on the upper flat plate and the lower platform after being upset.

[0026] Figure 2d ) is a schematic diagram of the subsequent flipping 90° and radial pressing once more.

[0027] Figure 2e ) is a schematic diagram of stretching the blank into a flat square on upper and lower flat anvils.

[0028] Figure 2f ) is a schematic diagram of the structure of the blank before upsetting.

[0029] Figure 2g ) is a schematic diagram of the structure of the blank after upsetting.

[0030] Figure 2h ) is a schematic diagram of the blank being radially pressed down once on the upper flat plate and the lower platform after being upset.

[0031] Figure 2i ) is a schematic diagram of the subsequent flipping 90° and radial pressing once more.

[0032] Figure 2j ) is a schematic diagram of the blank being stretched to a certain size on the upper and lower flat anvils and then inverted into eight sides in preparation for forging on the precision forging machine.

[0033] Figure 2k ) is a schematic diagram of the finished forging. DETAILED DESCRIPTION

[0034] As shown in FIG. 2 , in the schematic diagram of forging deformation of the hydraulic press of the present invention, the section line portion of the blank 3 represents the riser end, and the same is true for the following diagrams.

[0035] The implementation of the technical solution of the present invention mainly utilizes special heating specifications to heat the steel ingot, adopts a special forging method to forge it after heating, and performs post-forging annealing, surface and dimensional inspection, ultrasonic flaw detection, sawing and cutting, physical and chemical testing, etc. after forging.

[0036] The specific production process of a forging method for improving the impact toughness of H13 round steel is as follows: steel ingot → heating → axial upsetting + radial large reduction forging + flattening → high temperature diffusion → axial upsetting + radial large reduction forging + four-square and eight-square → precision forging machine forming → annealing → surface and size inspection → ultrasonic flaw detection → sawing and cutting → physical and chemical testing → delivery.

[0037] Forging example: Take the H13 round steel of Φ450 specification forged from steel ingot as an example, as shown in Figure 2. The steel ingot in this example is an electroslag ingot, weighing 7.5 tons and with a diameter of Φ800mm.

[0038] The specific forging steps are as follows:

[0039] Step 1), heating in the heating furnace, heating specifications are as follows Figure 1 As shown, the electroslag ingot is first kept at 450±10℃ for 4h, and then heated at ≤60℃ / h to minimize the temperature stress caused by the internal and external temperature difference; heated to 850±10℃ for 5h to minimize the organizational stress caused by phase change; then heated to 1250±10℃ for 9h at ≤120℃ / h to make the ingot fully and evenly heated; then cooled to 1230±10℃ and taken out of the furnace, cooling is beneficial to prevent coarse grains;

[0040] Step 2), after being taken out of the furnace, the electroslag ingot (also called blank, serial number 3) is upset to a height of 800 mm using an upper plate (serial number 1) and a lower platform (serial number 2) on a hydraulic press. Figure 2b ), during the upsetting process, the material is paused once every 300 mm, and each pause time is 15 to 20 seconds; after upsetting, the blank (serial number 3) is radially pressed down to 650 mm on the upper plate (serial number 1) and the lower platform (serial number 2), as shown in FIG. Figure 2c ), then turn 90° and press radially down to 750mm, as shown in Figure 2d ) as shown; then on the 700 upper and lower flat anvils (No. 4 and 5), the shape is stretched to a flat square with dimensions of: width 900mm, thickness 650mm, and about 1640mm long. Figure 2e )

[0041] Step 3), the flat square billet (serial number 3) is returned to the chamber furnace for high temperature diffusion, the furnace temperature is heated to 1270±10℃, the insulation time is 21h, after the insulation is completed, the temperature is lowered to 1230±10℃ and taken out of the furnace;

[0042] Step 4) After the flat square billet (No. 3) is taken out of the furnace, it is upset again using the upper plate (No. 1) and the lower platform (No. 2) on the hydraulic press. Figure 2g ), upsetting to a height of 800mm, during the upsetting process, pause once every 300mm, each pause time is 15 to 20 seconds. After upsetting, the blank (serial number 3) is radially pressed down to 700mm on the upper plate (serial number 1) and the lower platform (serial number 2), as shown in FIG. Figure 2h ), then turn 90° and press radially down to 700mm, as shown in Figure 2i Then, it is stretched to 530 square and 550 square on the 700 upper and lower flat anvils (numbers 4 and 5), as shown in FIG. Figure 2j ) as shown.

[0043] Step 5) Forge on a precision forging machine to the finished product size of hot Φ460, such as Figure 2k ) as shown.

[0044] Step 6), heat treatment after forging.

[0045] After that, surface and dimension inspection, ultrasonic flaw detection, sawing and cutting, and physical and chemical testing are carried out.

[0046] In steps 2) and 4), the forging process is paused every 300 mm, and each pause time is 15 to 20 seconds. This can prevent the deformation speed from being too fast, which may cause the center of the forging to heat up too high, resulting in local overheating and overburning, which will seriously affect the performance of the forging.

[0047] In steps 2) and 4), after each axial upsetting, the upper plate and lower platform are radially pressed once, turned 90°, and radially pressed once again, with each pressing amount of 45%-50%, which is close to the pressing amount during upsetting, equivalent to upsetting once in two radial directions at an angle of 90° after each axial upsetting. This can not only fully compact the core of the forging, refine the grains of the forging, and homogenize the structure, but also reduce the anisotropy of the forging and improve its lateral performance.

[0048] In step 2), the shape of the billet is stretched to a flat square, which not only makes its deformation more sufficient and uniform, but also improves the compaction effect of the core of the forging, and the thickness of the flat square becomes smaller. Compared with the original steel ingot, under the same time, high-temperature diffusion can achieve better results, reduce component segregation, make the organization more uniform, and thus improve the performance of the forging.

[0049] In step 3), the heating furnace temperature is 1250±10℃~1280±10℃, and the holding time is d×(2.5h~3h) / 100mm, where d is the equivalent diameter of the flat square billet, and d=2*thickness*width / (thickness+width), so that an excellent high-temperature diffusion effect can be obtained.

[0050] After high temperature diffusion in step 3), steps 4) and 5) are followed, i.e. the forging process of "axial upsetting + radial large reduction forging + four-way and eight-way forging → finishing forging machine forming". The reserved forging ratio is very sufficient, which varies according to the specifications of the finished product and can generally reach more than 7. In this way, the grains grown after high temperature diffusion can be refined through sufficient deformation, thereby improving the performance of the forging.

[0051] During the entire forging process, the hydraulic press forging controls the initial forging temperature to be 900-1180°C, and the final forging temperature to be ≥850°C. The precision forging machine forging controls the initial forging temperature to be 850-1050°C, and the final forging temperature to be ≥800°C.

[0052] By adopting the above forging methods and strictly controlling the forging parameters of each process, the physical and chemical testing shows that the impact toughness without notch is extremely high, with an average of 400.6J / cm 2 , reaching the industry leading level. The other low magnification, annealing structure and flaw detection results are all excellent, without coarse grains.

[0053] Table 1. Unnotched impact toughness

[0054]

[0055] Table 2, low magnification

[0056]

[0057] Table 3, Annealed structure

[0058] Ingot No. Forging specifications Tail Center Center Testing standards 9A24164 φ450mm AS5 AS5 NADCA#207

[0059] Table 4, flaw detection

[0060] Ingot No. Forging specifications Detection results Testing standards 9A24164 φ450mm qualified GB / T6402-2008 Level 3

Claims

1. A forging method for improving the impact toughness of H13 round steel, characterized in that: Ingot heating → upsetting + radial large reduction forging + flattening → high temperature diffusion → upsetting + radial large reduction forging + four-square and eight-square pouring → finishing forging → heat treatment after forging. The specific forging steps are as follows: Step 1) is carried out according to the special heating specification: the steel ingot is kept at 450±10℃, then heated to 850±10℃ at ≤60℃ / h, then heated to 1250±10℃ at ≤120℃ / h, then cooled to 1230±10℃ and taken out of the furnace; Step 2), after being taken out of the furnace, the steel ingot is axially upset on the hydraulic press, with an upset reduction of 50%. During the upsetting process, it is paused once every 300mm of upsetting; after upsetting, it is radially pressed down once on the upper flat plate and the lower platform, turned 90°, and radially pressed down once again, with a reduction of 45%-50%; then the billet shape is stretched to a flat square on the upper and lower flat anvils, and the size requirements are: width: thickness = 1.3~1.4, length: thickness = 2.5~3.0; Step 3), the flat square billet is returned to the furnace for high temperature diffusion, the furnace temperature is heated to 1250±10℃~1280±10℃, after the insulation is completed, the temperature is lowered to 1230±10℃ and then taken out of the furnace; Step 4), after being taken out of the furnace, the billet is axially upset again on the hydraulic press, with an upset reduction of 50%. During the upsetting process, it is paused once every 300mm of upsetting; after upsetting, it is radially pressed down once on the lower platform of the upper plate, turned 90°, and radially pressed down once again, with a reduction of 45%-50%; then it is stretched to four sides and inverted on the upper and lower flat anvils, and the size needs to meet the feed size of the precision forging machine; Step 5) Forming on a precision forging machine has the advantages of fast speed and good surface quality; Step 6), heat treatment after forging.

2. A forging method for improving the impact toughness of H13 round steel according to claim 1, characterized in that: In step 1), heating is performed according to special heating specifications: the steel ingot is kept at 450±10℃ for 3 to 6 hours, and then heated at ≤60℃ / h to minimize the temperature stress caused by the internal and external temperature difference; the temperature is raised to 850±10℃ for 4 to 7 hours to minimize the organizational stress caused by phase transformation; the temperature is then raised to 1250±10℃ at ≤120℃ / h for 6 to 10 hours to fully and evenly heat the steel ingot; the temperature is then lowered to 1230±10℃ and taken out of the furnace. Cooling is beneficial to prevent coarse grains.

3. A forging method for improving the impact toughness of H13 round steel according to claim 1, characterized in that: In steps 2) and 4), the forging process is paused every 300 mm, and each pause time is 15 to 20 seconds to avoid excessive temperature rise in the center of the forging due to too fast deformation speed, resulting in local overheating and overburning, which will seriously affect the performance of the forging.

4. A forging method for improving the impact toughness of H13 round steel according to claim 1, characterized in that: In steps 2) and 4), after each axial upsetting, radial pressing is performed on the lower platform of the upper plate, turned 90°, and radial pressing is performed again, with each pressing amount of 45%-50%. This pressing amount is close to the pressing amount during upsetting, which is equivalent to performing upsetting in two radial directions at an angle of 90° after each axial upsetting; this can not only fully compact the core of the forging, refine the grains of the forging, and homogenize the structure, but also reduce the anisotropy of the forging and improve its lateral performance.

5. A forging method for improving the impact toughness of H13 round steel according to claim 1, characterized in that: In step 3), the heating furnace temperature is 1250±10℃~1280±10℃, and the holding time is d×(2.5h~3h) / 100mm, where d is the equivalent diameter of the flat square billet, d=2*thickness*width / (thickness+width), to obtain an excellent high-temperature diffusion effect.

6. A forging method for improving the impact toughness of H13 round steel according to claim 1, characterized in that: During the entire forging process, the hydraulic press forging controls the initial forging temperature to be 900-1180°C, and the final forging temperature to be ≥850°C. The precision forging machine forging controls the initial forging temperature to be 850-1050°C, and the final forging temperature to be ≥800°C.

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