Large-thickness 4Cr5MoSiV1 hot-working die steel plate and preparation method thereof

Abstract

The invention relates to a large-thickness 4Cr5MoSiV1 hot-working die steel plate and a preparation method thereof, and belongs to the field of metallurgy. Comprising the following steps: smelting and continuous casting: controlling a secondary cooling area to be weak cooling, controlling the total water quantity of secondary cooling to be 860-980L / min, and controlling the surface temperature of a blank in a straightening area to be 900-1000 DEG C; casting blank slow cooling: slowly cooling the continuous casting blank in a slow cooling cover, opening the cover when the surface temperature of the blank is more than or equal to 200 DEG C, and heating in a heating furnace; heating and rolling: charging a casting blank into a furnace at the surface temperature of more than or equal to 150 DEG C and the furnace temperature of more than or equal to 200 DEG C, raising the temperature to 1200-1280 DEG C, and keeping the temperature for 10-12 hours; rolling is started at the temperature of 1050-1150 DEG C, the reduction rate of the first two passes is controlled to be 10%-12%, the reduction rate of the first two passes in the finish rolling stage is controlled to be 11%-13%, the finish rolling temperature is 850-930 DEG C, cooling is conducted to the temperature larger than or equal to 300 DEG C, and the steel plate is loaded into a heat treatment furnace; homogenizing, wherein the preset temperature of the heat treatment furnace is 1020-1080 DEG C, and the preset heat preservation time is 5-7 h; and annealing: performing spheroidizing annealing on the homogenized steel plate. And finally, the homogeneity of the 4Cr5MoSiV1 hot-working die steel plate is less than or equal to 2HRC, and the transverse impact performance reaches 9.0-18J.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of metallurgy, and particularly relates to a die steel plate and a preparation method thereof. BACKGROUND

[0002] 4Cr5MoSiV1 has high thermal strength and hardness, is a widely used hot work die steel, has good hardenability, strength, toughness, thermal stability, wear resistance and cold and hot fatigue resistance, is widely used in the industrial field, and is mainly widely used in aluminum alloy profile extrusion dies. However, in a harsh service environment of high pressure, high temperature and high stress, the surface of the 4Cr5MoSiV1 steel die is failed due to wear and tear and thermal fatigue and the like. To increase the service life of the 4Cr5MoSiV1 steel die, improving the surface performance is the key. However, since the 4Cr5MoSiV1 steel contains a high content of alloying elements, the solid-liquid two-phase region is wide, and during the solidification process of the molten steel, composition segregation is easily generated due to solute redistribution, which significantly reduces the mechanical properties and service life of the material. Improving the composition uniformity, reducing the content of harmful elements, reducing and refining non-metallic inclusions, and improving the morphology and distribution of carbides can improve the service life. Since the deformation resistance of the 4Cr5MoSiV1 steel is large at a high temperature stage, the steel is sensitive to temperature and strain rate, and the rolling process is prone to cracking.

[0003] Compared with die casting, since the solidification characteristics of continuous casting are good, the composition segregation, composition uniformity and quality stability are good, and the cost is also low. However, since the 4Cr5MoSiV1 steel contains a high content of alloying elements, the high-temperature surface reduction rate is 17.69% at 800 DEG C, 31.69% at 850 DEG C, 39.87% at 900 DEG C, and 52.91% at 950 DEG C, so that the continuous casting is difficult, and if the operation is improper, the continuous casting equipment is damaged. At present, only square and round billets are reported to be produced, and there is no public production of slab continuous casting process.

[0004] Chinese patent publication No. CN116574962A discloses a low-titanium H13 hot work die steel and a preparation method thereof, relates to the technical field of metal metallurgy, and the method comprises the following steps: blending raw materials, EBT electric arc furnace smelting, LF furnace smelting and VD furnace smelting to obtain alloy liquid; and the alloy liquid is subjected to die casting to obtain a steel ingot.

[0005] Chinese patent publication No. CN115896594A discloses a high-strength and high-toughness H13 die steel for aluminum extrusion and a preparation method thereof, which also adopts die casting of a steel ingot. SUMMARY

[0006] The present application provides a large thickness 4Cr5MoSiV1 hot work die steel plate and a preparation method thereof, which overcomes the problem of high temperature surface shrinkage sensitivity of the steel plate, and finally realizes continuous casting and rolling process production, reduces composition segregation, improves carbide morphology and distribution, and further improves the service life.

[0007] The technical scheme adopted by the present application to solve the above problems is as follows: raw materials are prepared, melted in a converter, refined in an LF furnace, and vacuum degassed in an (RH furnace) to obtain an alloy liquid, the alloy liquid is continuously cast to obtain a continuously cast thick slab; the continuously cast slab is slowly cooled and then sent to a heating furnace for heating and rolling to obtain a steel plate; the steel plate is homogenized at a predetermined temperature and for a predetermined time to dissolve the carbides contained in the steel plate, thereby obtaining a homogenized steel plate; and the homogenized steel plate is spheroidized to obtain a 4Cr5MoSiV1 hot work die steel plate.

[0008] The preparation method of the large thickness 4Cr5MoSiV1 hot work die steel plate of the present application is as follows: The total water quantity is 860-980 L / min. The superheat degree of the continuously cast molten steel is controlled to be 20-50℃. The surface temperature of the slab in the straightening area is controlled to be 900℃-1000℃.

[0009] The reasons are as follows: The high temperature surface shrinkage rate of 4Cr5MoSiV1 is very low at ≤900℃, as shown in the following table High temperature surface shrinkage rate of Cr5MoSiV1 (%)

[0010] For the continuously cast slabs of other alloy steels, the surface temperature of the slab in the straightening area is controlled to be 800-900℃, and if it is >900℃, the continuous casting cannot be normally carried out.

[0011] However, according to the data of the high temperature surface shrinkage rate of the 4Cr5MoSiV1 hot work die steel plate of the present application in the above table, if the surface temperature of the slab in the straightening area is <900℃, the plasticity of the slab is poor, the slab is difficult to straighten, the continuous casting machine equipment is easily damaged, and the slab is easily cracked during straightening. Therefore, the surface temperature of the slab in the continuous casting straightening area of the 4Cr5MoSiV1 hot work die steel plate of the present application is controlled to be 900℃-1000℃.

[0012] The continuously cast slab is slowly cooled: after the continuously cast slab is discharged, it is immediately put into a slow cooling cover for slow cooling for ≥48 hours, and the surface temperature of the slab is ≥200℃, and then the slab is sent to a heating furnace for heating and rolling.

[0013] Casting slab warm charging furnace rolling: the surface temperature of the casting slab is greater than or equal to 150 DEG C, the furnace temperature is greater than or equal to 200 DEG C, charging is carried out, the temperature is raised to 1200 DEG C-1280 DEG C, and the temperature is kept for 10-12 hours, and the rolling is started at 1050 DEG C-1150 DEG C, the reduction of the first two passes in the starting rolling stage is 10-12%, the reduction of the first two passes in the finishing rolling stage is 11%-13%, the final rolling temperature in the finishing rolling stage is 850 DEG C-930 DEG C, the finished steel plate with a thickness of 150-200 mm is obtained, the final rolling temperature is close to the AC3 temperature, the segregation can be reduced or the probability of segregation can be reduced, and then the steel plate is cooled to greater than or equal to 300 DEG C and is charged into a heat treatment furnace; the production efficiency can be improved, energy can be saved, and the consumption of coal gas can be reduced. In the cooling process of the steel plate cooled to 300 DEG C, the cooling speed is 8-10 DEG C / min.

[0014] Steel plate homogenization: the rolled steel plate is homogenized to dissolve internal carbides; in the process of heating the steel plate, according to the principle of atomic diffusion, the carbides contained in the steel plate can be dissolved, so that the ductility and toughness of the steel plate are ensured, and then the phenomenon that the 4Cr5MoSiV1 hot work die steel processed is prone to cracking or early cracking can be avoided.

[0015] The specific homogenization process is that the steel plate is kept at a predetermined temperature for a predetermined time, the predetermined temperature is 1020 DEG C-1080 DEG C, the predetermined time is 5h-7h, and the steel plate is cooled to 300 DEG C after keeping warm and is discharged from the furnace.

[0016] Steel plate annealing: the homogenized steel plate is cooled to greater than or equal to 150 DEG C and is charged into a heat treatment furnace for annealing. The annealing process is that the heating speed is less than or equal to 80 DEG C / h. The first stage of keeping warm temperature is 960 DEG C±10 DEG C, and the keeping warm time is 3min / mm. The cooling speed is less than or equal to 30 DEG C / h, and the cooling is carried out to 870 DEG C±10 DEG C, and the keeping warm time is 5min / mm. The cooling speed is less than or equal to 30 DEG C / h, and the cooling is carried out to 500 DEG C, and then the furnace cooling is carried out, and the furnace cooling is carried out to 300 DEG C, and the steel plate is discharged from the furnace.

[0017] The beneficial effects of the present application are that the preparation method of the present application makes the homogeneity of the 4Cr5MoSiV1 hot work die steel plate reach less than or equal to 2HRC, the transverse impact performance reaches 9.0-18J, and the thickness of the produced steel plate is 150-200mm. BRIEF DESCRIPTION OF DRAWINGS

[0018] Figure 1 It is a preparation method flow chart of the 4Cr5MoSiV1 hot work die steel of the embodiment 1 of the present application; Figure 2 It is a flow chart of the specific operation of the step 101 in the embodiment 1 of the present application; Figure 3 It is a flow chart of the specific operation of the step 103 in the embodiment 1 of the present application. DETAILED DESCRIPTION

[0019] The application will be further described in conjunction with the following examples which are illustrative and are intended to explain but not to limit the application.

[0020] In the embodiment of the application, an implementation method of 4Cr5MoSiV1 hot work die steel is provided, and a step flowchart is as follows Figure 1 .

[0021] Step 101: processing raw materials to obtain a continuous casting slab: In step 101, the raw materials are processed through a series of processes to obtain a slab. Specifically, the raw materials can be high-quality molten iron from a large blast furnace and scrap steel materials. In addition, in this step, attention should be paid to controlling the content range of various elements in the raw materials during the smelting process, especially the content range of copper elements.

[0022] The chemical composition of the steel of examples 1-3 is shown in Table 1.

[0023] Table 1 Composition of 4Cr5MoSiV1 hot work die steel of the embodiment of the application (wt%)

[0024] The control of the secondary cooling water volume of continuous casting is shown in Table 2. Table 2 Secondary cooling water volume, L / min

[0025] The control of the straightening area reduction of continuous casting is shown in Table 3.

[0026] Table 3 Parameter selection of heavy reduction of the embodiment

[0027] Step 102: slow cooling the continuous casting slab to obtain a slow-cooled slab.

[0028] In step 102 of the embodiment: the thick slab slow cooling process parameters are shown in Table 4.

[0029] Table 4 Slow cooling process parameters of continuous casting thick slab

[0030] Step 103: rolling the slow-cooled slab, homogenizing, and annealing to obtain 4Cr5MoSiV1 hot work die steel.

[0031] Specifically, in order to ensure the performance requirements, the process of the operation should be controlled. Then the hardness of the 4Cr5MoSiV1 hot work die steel plate is less than 270 HBW.

[0032] Preferably, in step 103 of the embodiment, the specific step flowchart can include Figure 3: Step 301: the slow-cooled plate blank is rolled to obtain a steel plate Coarse rolling: the initial rolling temperature of the rolling process is 1050-1150℃. The reduction rate of the first two passes before the opening rolling stage is 10-12%.

[0033] The heating temperature and temperature equalization time in the rolling process of the embodiment are shown in Table 5 below Table 5 Parameter selection in the rolling process of the embodiment

[0034] Finish rolling: the finish rolling temperature of the finish rolling stage is 850-930℃, and the reduction rate of the first two passes before the finish rolling stage is 11%-13%; then the steel plate is cooled to ≥300℃ and loaded into a heat treatment furnace; preferably, the cooling process can be performed according to the following operation: In the step of cooling to ≥300℃, the cooling speed is 8-10℃ / min.

[0035] Step 302: the rolled steel plate is homogenized to obtain a homogenized steel plate.

[0036] Homogenization operation: after obtaining the steel plate, the obtained steel plate is heated for a predetermined time to dissolve the carbides inside, thereby obtaining a homogenized steel plate. After homogenization of the steel plate, most of the carbides contained therein will disappear.

[0037] Specifically, the homogenization treatment can be carried out in a controllable atmosphere furnace or an inert gas protection furnace, and the time and temperature of the homogenization treatment can be specifically set according to the weight of the steel plate by referring to Table 6.

[0038] Table 6 Temperature and time of homogenization treatment of 4Cr5MoSiV1 in the embodiment

[0039] Main process parameters of the homogenization of the plate blank in the embodiment of the application are shown in Table 7 Table 7 Main process parameters of the homogenization of the plate blank in the embodiment of the application

[0040] Step 303: the homogenized steel plate is spheroidized annealed to obtain a 4Cr5MoSiV1 hot work die steel: In step 303, the spheroidizing annealing specific steps can be performed according to the following operation: Specific operation: the homogenized steel plate is cooled to ≥150℃ and loaded into a heat treatment furnace for annealing.

[0041] Ramp to ≤ 80°C / h. First stage: 960 ± 10°C, dwell time 3 min / mm, then cool to 870 ± 10°C at ≤ 30°C / h, dwell time 5 min / mm. Cool to 500°C at ≤ 30°C / h, then furnace cool to 300°C, discharge.

[0042] Table 8 Main parameters of spheroidizing annealing of slab of inventive example

[0043] Table 9 Impact properties of inventive example

[0044] The above only describes the preferred embodiments of the present application and is not intended to limit the present application. The present application can have various modifications and changes for those skilled in the art. Any modification, equivalent replacement, improvement, etc. within the spirit and principles of the present application shall be included in the protection scope of the present application.

Claims

1. A method of manufacturing a large thickness 4Cr5MoSiVl hot work die steel sheet, characterized in that: Comprising, Smelting: ingredient, converter smelting, secondary refining and vacuum degassing, obtaining alloy liquid; Continuous casting: control the weak cooling of the secondary cooling zone, the total water quantity of the secondary cooling zone is 860-980 L / min, and the surface temperature of the straightening zone billet is 900-1000℃; Slow cooling of the casting blank: the continuous casting blank is slowly cooled in the slow cooling cover, and the billet surface temperature is ≥200℃ after the cover is opened, and then it is sent to the heating furnace for heating; Heating and rolling: the billet is put into the furnace when the surface temperature of the billet is ≥150℃ and the furnace temperature is ≥200℃, the temperature is raised to 1200-1280℃, and the temperature is kept for 10-12 hours; the rolling is started at 1050-1150℃, the reduction rate of the first two passes is controlled to be 10-12%, the reduction rate of the first two passes in the finishing rolling stage is controlled to be 11-13%, and the final rolling temperature is 850-930℃, which is close to the AC3 temperature; the cooling speed of the steel plate after controlled rolling is 8-10℃ / min, and the steel plate is cooled to ≥300℃ and then put into the heat treatment furnace; Homogenization: the pre-set temperature of the heat treatment furnace is 1020-1080℃, the pre-set holding time is 5-7h, and the steel plate is cooled to 300℃ after holding and then taken out of the furnace; Annealing: the steel plate after homogenization is cooled to ≥150℃ and then put into the heat treatment furnace for spheroidizing annealing.

2. The method of claim 1, wherein: In the annealing step, the heating rate of the heat treatment furnace is ≤80℃ / h, the first stage holding temperature is 960±10℃, the holding time is 3min / mm, the cooling rate is ≤30℃ / h to 870±10℃, the holding time is 5min / mm*the thickness of the steel plate, and the cooling rate is ≤30℃ / h to 500℃, then the furnace is cooled to 300℃ and the steel plate is taken out of the furnace.

3. The method of claim 1, wherein: The production thickness of the steel plate is 150-200mm.

4. The method of claim 1, wherein: The superheat degree of the continuous casting liquid steel is controlled to be 20-50℃.

5. The method of claim 1, wherein: The composition of the steel plate is as follows in terms of percentage by weight: C: 0.32-0.38%, Si: 0.80-1.20%, Mn: 0.20-0.50%, P≤0.015%, S≤0.005%, Cr: 4.75-5.50%, Mo: 1.10-1.50%, V: 0.80-1.20%, and the balance is Fe and unavoidable impurities.

6. The method of claim 1, wherein: The water quantity of the secondary cooling zone of the continuous casting is set as follows: full roll: 320-360L / min, 1st stage: 48-56L / min, 2nd stage: 78-90L / min, 3rd stage: 78-90L / min, 4th stage: 54-62L / min, 5th stage: 54-62L / min, 6th stage: 28-32L / min, and 7th stage: 28-32L / min.

7. The method of claim 1, wherein: The reduction amount of the straightening zone of the continuous casting is set according to the length of the casting blank: 15.8-19m: 2mm, 19-22m: 3.5mm, 22-25m: 4mm, 25-28m: 4mm, 28-31m: 3.5mm, and 31-35m: 3.5mm.

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