High-toughness ultrafine pearlite steel plate and method for manufacturing the same

Abstract

The application discloses a high-toughness superfine pearlite steel plate and a preparation method thereof. The application takes common 65# steel as a raw material, relies on a carbide-assisted ferrite structure refining rule, designs a new carbide / ferrite system, fully prolongs a pearlite phase change incubation period, and avoids phase change of metastable austenite in a large deformation warm rolling process. A large-size alloy steel plate with a superfine metastable austenite structure is prepared by adopting a high-temperature hot rolling, large deformation synchronous warm rolling and relaxation treatment process, and then a large-size pearlite steel plate with a uniform and fine granular carbide / ferrite complex phase structure is directly prepared by adopting a long-time pearlite heat treatment process.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of alloy material preparation, and particularly relates to a high-strength and high-toughness ultra-fine pearlite steel plate and a preparation method thereof. BACKGROUND

[0002] The information disclosed in this Background section is for the purpose of generally presenting the context of the application. The information disclosed in this Background section is not to be taken as an admission that it is prior art to the present application, nor necessarily essential to the practice of the application.

[0003] Pearlite is generally composed of mechanical mixture of ferrite and cementite, and under different multi-phase systems, the microstructure of pearlite includes lamellar, globular and other irregular shapes. Among them, lamellar pearlite steel is widely used in suspension bridge cables, steel cord for tires and springs, etc. which require high strength, while tool steel and medium carbon steel are generally used for cutting and cold heading with granular pearlite structure. Generally, lamellar pearlite has higher strength, and granular pearlite has better plasticity. Pearlitic steel has excellent wear resistance, fatigue resistance, high temperature creep resistance, good thermal conductivity and other properties, and is one of the common processing materials for steel rails, turbine blades or pressure vessels, etc.

[0004] Fine-grain strengthening is a very effective way to optimize the comprehensive mechanical properties of steel materials, and can generally improve the strength and toughness of steel materials. With the help of fine-grain strengthening mechanism, the preparation of ultra-high strength steel can reduce the addition of a large amount of alloying elements, and has a good development prospect with high cost performance. The preparation of ultra-high strength steel by fine-grain strengthening is suitable for most types of steel with different microstructures, especially lamellar pearlite steel and granular carbide / ferrite steel with complex microstructure. As a typical cementite / ferrite complex microstructure, the related deformation law of pearlite under plastic strain has great reference significance for the deformation of complex microstructure.

[0005] Intermediate temperature thermomechanical treatment is a very effective method of grain refinement, through the combination of phase transformation and deformation, refining the parent phase austenite grain, inhibiting its recovery and recrystallization, preparing ultra-high strength and toughness ultra-fine martensitic steel, related studies show that the ultra-fine heterogeneous lamellar martensite plate consisting of lath and twin can be prepared by large deformation warm rolling of metastable austenite, the martensitic steel of this structure shows excellent mechanical properties, the tensile strength is not less than 2.5 GPa, and the total elongation is not less than 5.0%. In the preparation of ultra-fine grain pearlitic steel plate, intermediate temperature thermomechanical treatment is less used. If the parent phase austenite can be refined by large deformation warm rolling before obtaining pearlite structure, can high strength and toughness ultra-fine grain pearlite structure be further prepared? Especially, can the ultra-fine metastable austenite structure be treated by eutectoid transformation to obtain ultra-fine lamellar or granular pearlite structure? There is no definite conclusion at present. Therefore, from the perspective of refining the parent phase austenite, the research on the transformation of ultra-fine grain austenite to pearlite is very worth paying attention to. SUMMARY

[0006] In order to overcome the above problems, the present application provides a high strength and toughness ultra-fine pearlitic steel plate and a preparation method thereof. The present application takes ordinary 65# steel as raw material, relies on the carbide assisted ferrite structure refinement rule, designs a new carbide / ferrite system, fully extends the incubation period of pearlite phase transformation, and avoids the phase transformation of metastable austenite in the process of large deformation warm rolling. A large size alloy steel plate with ultra-fine metastable austenite structure is prepared by adopting high temperature hot rolling, large deformation synchronous warm rolling and relaxation treatment process, and then a large size pearlitic steel plate with uniform and fine granular carbide / ferrite complex structure is prepared by directly adopting long time pearlite heat treatment process.

[0007] In order to achieve the above technical purposes, the present application adopts the following technical scheme:

[0008] In a first aspect of the present application, a preparation method of a high strength and toughness ultra-fine pearlitic steel plate is provided, and the preparation method comprises:

[0009] S1, alloy smelting: the composition of the high strength and toughness ultra-fine pearlitic steel plate is as follows in terms of mass percentage of each component: C: 0.6-0.7%, Si: 0.9-1.2%, Mn: 0.5-1.0%, Cr: 2.0-3.0%, Ni: 1.3-1.5%, Mo: 0.5-0.7%, and the rest is Fe and inevitable impurities; ingredients are prepared according to the mass percentage, and smelting is carried out by using a vacuum induction furnace, and a steel ingot is cast;

[0010] S2, cogging forging: the steel ingot cast in step S1 is subjected to cogging at a temperature of 1200-1250℃ for 1.0-2.0h, and then is subjected to hot forging treatment at 1150-1200℃;

[0011] S3, solid solution treatment: the ingot prepared in step S2 is subjected to high-temperature solid solution treatment under an atmosphere of inert gas, the temperature of the solid solution treatment is 1150-1250 DEG C, the time is 4.0-5.0 h, and then air cooling to room temperature;

[0012] S4, high-temperature hot rolling treatment: the ingot prepared in step S3 is reheated to 1000-1050 DEG C, and kept for 0.5-1.0 h, and then subjected to continuous three-pass large deformation synchronous hot rolling treatment after discharging, the final rolling temperature is not lower than 950 DEG C, and then water cooling to room temperature;

[0013] S5, austenitizing treatment: the cuboid ingot prepared in S4 is subjected to austenitizing treatment under an atmosphere of inert gas, the austenitizing temperature is 930-960 DEG C, and the holding time is 1.0-1.5 h;

[0014] S6, large deformation synchronous warm rolling and relaxation treatment: the cuboid ingot prepared in S5 is air cooled to 680-690 DEG C, and then subjected to three-pass large deformation synchronous warm rolling, the cumulative reduction is 85-95%, and short-time relaxation treatment is adopted between the warm rolling passes, and the total warm rolling time is controlled within 30 s;

[0015] S7, pearlitizing treatment: the steel plate prepared by warm rolling in S6 is subjected to pearlitizing treatment under an atmosphere of inert gas, the temperature of the pearlitizing treatment is 680 DEG C, the holding time is 3.0-4.0 h, and then air cooling to room temperature, thereby obtaining a high-strength and high-toughness ultrafine pearlitic steel plate.

[0016] In a second aspect, the application provides a high-strength and high-toughness ultrafine pearlitic steel plate prepared by the above preparation method.

[0017] Compared with the prior art, the application has the following advantages:

[0018] (1) The application considers the pearlite phase change as a diffusion type phase change, and comprehensively analyzes the influence of different alloy elements (C, Si, Mn, Cr, Ni, Mo) on eutectoid phase change and carbide precipitation from the aspects of environmental protection, cost and performance, and develops and prepares a new type of pearlitic alloy steel based on ordinary 65# steel. Compared with the existing high-strength and high-toughness pearlitic steel, the new type of high-strength and high-toughness pearlitic steel prepared by the application has a room temperature yield strength of 1791 MPa and a tensile strength of 2612 MPa, and a room temperature total elongation of 5.6%, and has ultra-high strength and excellent toughness and plasticity, and shows good comprehensive mechanical properties.

[0019] (2) Compared with the prior art for preparing high strength and toughness ultrafine pearlite steel, the present application has the characteristics of long incubation period of pearlite phase transformation, and innovatively uses large deformation warm rolling technology to prepare ultrafine metastable austenite structure, and then directly prepares ultrafine pearlite steel at the pearlite eutectoid time through long-time holding. The present application introduces short-time relaxation treatment in the process of large deformation warm rolling, which on the one hand realizes the static recovery and recrystallization of the metastable austenite phase in the rolled state, and on the other hand fully releases the internal stress of the material, so as to realize the ultrafining of the structure.

[0020] (3) The pearlite steel prepared by the present application is prepared by fine tuning on the basis of 65# steel, and has the characteristics of low cost and high performance. Moreover, the preparation method of the present application is simple and easy to operate, and has low requirements on the performance of the equipment, so it is suitable for the development of large plate wire high strength steel, so that the pearlite alloy steel has high performance price ratio and market application prospect. BRIEF DESCRIPTION OF DRAWINGS

[0021] The accompanying drawings, which form a part of this specification, are included to provide a further understanding of the application and are incorporated herein for explanation.

[0022] Figure 1 The undercooled austenite continuous cooling transformation (CCT) curve of the new alloy steel in Example 1 is shown in the figure.

[0023] Figure 2 The martensite microstructure morphology of the new alloy steel after hot rolling and water cooling in Example 1 is shown in the figure.

[0024] Figure 3 The granular carbide / ferrite complex phase scanning microstructure morphology of the high strength and toughness ultrafine pearlite steel plate prepared in Example 1 is shown in the figure.

[0025] Figure 4 The granular carbide / ferrite complex phase transmission microstructure morphology of the high strength and toughness ultrafine pearlite steel plate prepared in Example 1 is shown in the figure.

[0026] Figure 5 The room temperature tensile mechanical property curve of the high strength and toughness ultrafine pearlite steel plate prepared in Example 1 is shown in the figure. DETAILED DESCRIPTION

[0027] It should be noted that the following detailed description is exemplary and is intended to provide further explanation of the present application. Unless otherwise specified, all technical and scientific terms used in the present application have the same meaning as generally understood by those skilled in the art to which the present application belongs.

[0028] It is to be understood that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of example embodiments in accordance with the present application. As used herein, the singular forms "a", "an" and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms "comprises" and / or "comprising," when used in this specification, specify the presence of stated features, steps, operations, elements, components, and / or groups thereof, but do not preclude the presence or addition of one or more other features, steps, operations, elements, components, and / or groups thereof.

[0029] In a first exemplary embodiment of the present application, a method for preparing a high-toughness ultra-fine pearlite steel plate includes:

[0030] S1, alloy smelting: the composition of the high-toughness ultra-fine pearlite steel plate is as follows in terms of mass percentage: C: 0.6-0.7%, Si: 0.9-1.2%, Mn: 0.5-1.0%, Cr: 2.0-3.0%, Ni: 1.3-1.5%, Mo: 0.5-0.7%, and the rest is Fe and inevitable impurities; ingredients are prepared according to the mass percentage, and a vacuum induction melting furnace is used for smelting to cast a steel ingot;

[0031] S2, cogging forging: the steel ingot cast in step S1 is subjected to cogging at a temperature of 1200-1250°C for 1.0-2.0h, and then is subjected to hot forging at 1150-1200°C;

[0032] S3, solid solution treatment: the steel ingot prepared in step S2 is subjected to high-temperature solid solution treatment in an inert gas atmosphere at a temperature of 1150-1250°C for 4.0-5.0h, and then is air-cooled to room temperature;

[0033] S4, high-temperature hot rolling: the steel ingot prepared in step S3 is reheated to 1000-1050°C for 0.5-1.0h, and then is subjected to continuous 3-pass large deformation synchronous hot rolling after being discharged, with a final rolling temperature not lower than 950°C, and then is water-cooled to room temperature;

[0034] S5, austenitizing treatment: the cuboid steel ingot prepared in S4 is subjected to austenitizing treatment in an inert gas atmosphere at a temperature of 930-960°C for 1.0-1.5h;

[0035] S6, large deformation synchronous warm rolling and relaxation treatment: the cuboid steel ingot prepared in S5 is air-cooled to 680-690°C, and then is subjected to 3-pass large deformation synchronous warm rolling with a cumulative reduction of 85-95%, and short-time relaxation treatment is applied between the warm rolling passes, with the total warm rolling time controlled within 30s;

[0036] S7. Pearlitization treatment: The steel plate prepared by S6 medium-temperature rolling is pearlitized in an inert gas atmosphere at a temperature of 680° C. for 3.0 to 4.0 hours, and then air-cooled to room temperature to obtain a high-strength and tough ultrafine pearlite steel plate.

[0037] In one or more embodiments, in S1, the raw material is placed in a vacuum greater than 1×10 -3 MPa in a vacuum arc furnace and repeatedly melted 5 to 7 times, and stirred by electromagnetic vibration in the vacuum arc furnace chamber to eliminate the component segregation of the alloy steel ingot and make its structure fully uniform. After the melting is completed, it is cast into a rectangular ingot.

[0038] In one or more embodiments, in S2, the hot forging treatment is a multi-directional forging treatment, and the final forging temperature is not less than 1150° C. There is no need to limit the deformation amount during the hot forging treatment.

[0039] In one or more embodiments, after the solution treatment, the steel ingot needs to be subjected to a wire cutting process, and is cut into a rectangular blank with a length×width×height of 300 mm×50 mm×50 mm by a wire electric discharge machine.

[0040] In one or more embodiments, in S4, during the hot rolling process, the hot rolling start temperature is 1000-1050°C, the final rolling temperature is 950-980°C; the deformation amount of the first hot rolling pass is 30-40%, the deformation amount of the second hot rolling pass is 50-60%, and the deformation amount of the third hot rolling pass is 65-70%, and the structure after water cooling is martensite.

[0041] In one or more embodiments, in S4, after the high-temperature hot rolling treatment, the final rolling thickness of the steel ingot is 20 to 30 mm.

[0042] In one or more embodiments, in S6, the first pass of warm rolling starts at 680-690°C and ends at 650-660°C, with a deformation of 50-55%; after relaxation for 5s, the second pass starts at 640-650°C and ends at 580-590°C, with a deformation of 70-80%; after the second relaxation for 5s, the third pass of warm rolling starts at 510-520°C and ends at 460-470°C, with a deformation of 85-95%, and the metastable austenite structure is fully refined by large deformation warm rolling.

[0043] In one or more embodiments, in S6, after large deformation synchronous warm rolling and relaxation treatment, the thickness of the steel plate is controlled to be 1.0 to 2.0 mm.

[0044] In one or more embodiments, in S6, an infrared temperature measuring gun is used to synchronously detect the temperature change of the steel plate during the large deformation synchronous warm rolling process.

[0045] In one or more embodiments, in S7, the steel plate after the large deformation and synchronous warm rolling in S6 is directly subjected to the pearlitization treatment in S7 without cooling.

[0046] In one or more embodiments, in S7, the microstructure of the high strength and toughness ultra-fine pearlite steel plate is a uniform and fine granular carbide / ferrite complex phase structure, the average grain size of the ferrite structure is 330-390 nm, and the granular carbide is uniformly and dispersedly distributed on the ferrite matrix and the grain boundary; the room temperature yield strength and the tensile strength are respectively 1791 MPa and 2612 MPa, and the room temperature total elongation is 5.6%.

[0047] In one or more embodiments, in S3, S5 and S7, the atmosphere of the inert gas is an argon protective atmosphere.

[0048] The second typical embodiment of the present application provides a high strength and toughness ultra-fine pearlite steel plate prepared by the above preparation method.

[0049] In order to enable those skilled in the art to more clearly understand the technical solutions of the present application, the technical solutions of the present application will be described in detail below in combination with specific examples.

[0050] Example 1

[0051] Preparation of a high strength and toughness ultra-fine pearlite steel plate:

[0052] S1, alloy smelting: the composition of the high strength and toughness ultra-fine pearlite steel plate is as follows in terms of mass percentage: C: 0.6-0.7%, Si: 0.9-1.2%, Mn: 0.5-1.0%, Cr: 2.0-3.0%, Ni: 1.3-1.5%, Mo: 0.5-0.7%, and the rest is Fe and inevitable impurities; the new alloy steel has a long incubation period of pearlite phase change (CCT curve is shown in Figure 1 ), which provides a large processing window for obtaining ultra-fine metastable austenite through large deformation warm rolling; the raw materials are repeatedly smelted 5-7 times in a vacuum arc furnace with a vacuum degree greater than 1×10 -3 MPa, and are stirred by electromagnetic vibration in the vacuum arc furnace cavity to eliminate the composition segregation of the alloy steel ingot and fully homogenize the structure; after the smelting is completed, the alloy steel ingot is poured into an ingot.

[0053] S2, cogging forging: the cuboid ingot poured in S1 is subjected to cogging at a temperature of 1230°C for 1.5 h, and then is subjected to multi-directional forging at a temperature of 1180°C, and the final forging temperature is not lower than 1150°C.

[0054] S3, solution treatment: the steel ingot prepared in step S2 is subjected to high-temperature solution treatment under an argon protective atmosphere, the temperature of the solution treatment is 1200 °C, the time is 4.5 h, and then air cooling to room temperature. After the solution treatment, the steel ingot is subjected to billet wire cutting treatment, and is cut into a cuboid billet by using an electric spark wire cutting machine, the size of the cuboid billet is 300 mm x 50 mm x 50 mm.

[0055] S4, high-temperature hot rolling treatment: the steel ingot prepared in step S3 is reheated to 1030 °C, and is kept for 1.0 h, and then is subjected to continuous three-pass large deformation synchronous hot rolling treatment, in the process of the hot rolling treatment, the hot rolling starting temperature is 1030 °C, and the final rolling temperature is 960 °C; the deformation amount of the first-pass hot rolling is 35%, the deformation amount of the second-pass hot rolling is 55%, the deformation amount of the third-pass hot rolling is 70%, and the final rolling thickness of the steel ingot is 25 mm, and then is water cooled to room temperature, and the martensite structure after water cooling is shown in Figure 2 .

[0056] S5, austenitizing treatment: the cuboid steel ingot prepared in S4 is subjected to austenitizing treatment under an inert gas atmosphere, the austenitizing temperature is 950 °C, and the holding time is 1.5 h;

[0057] S6, large deformation synchronous warm rolling and relaxation treatment: the cuboid steel ingot prepared in S5 is air cooled to 690 °C, and then is subjected to three-pass large deformation synchronous warm rolling, the first-pass warm rolling starts at 690 °C and ends at 660 °C, and the deformation amount is 55%; after 5 s of relaxation, the second-pass warm rolling starts at 650 °C and ends at 590 °C, and the deformation amount is 75%; after 5 s of second relaxation, the third-pass warm rolling starts at 520 °C and ends at 460 °C, and the deformation amount is 95%, and the metastable austenite structure is fully refined by the large deformation warm rolling. The total time of the warm rolling is controlled within 30 s, and the thickness of the steel plate after the warm rolling is controlled to be 1.0-2.0 mm.

[0058] S7, pearlitizing treatment: the steel plate prepared by the warm rolling in S6 is subjected to pearlitizing treatment under an inert gas atmosphere, the temperature of the pearlitizing treatment is 680 °C, the holding time is 3.0 h, and then air cooling to room temperature, and a high-strength and high-toughness ultrafine pearlitic steel plate material is obtained.

[0059] The microstructure of the high-strength and high-toughness ultrafine pearlitic steel plate material prepared in this embodiment is a uniform and fine granular carbide / ferrite complex phase structure (the scanning structure is shown in Figure 3 , and the transmission structure is shown in Figure 4 ), the average grain size of the ferrite structure is 360 nm, the granular carbide is uniformly and dispersedly distributed on the ferrite matrix and the grain boundary; the room temperature yield strength and the tensile strength are respectively 1791 MPa and 2612 MPa, and the room temperature total elongation is 5.6% (see Figure 5 ).

[0060] Example 2

[0061] Preparation of high-toughness superfine pearlite steel plate:

[0062] S1, alloy smelting: the composition of the high-toughness superfine pearlite steel plate is as follows in terms of mass percentage of each component: C: 0.6-0.7%, Si: 0.9-1.2%, Mn: 0.5-1.0%, Cr: 2.0-3.0%, Ni: 1.3-1.5%, Mo: 0.5-0.7%, and the rest is Fe and inevitable impurities; the raw materials are placed in a vacuum arc furnace with a vacuum degree greater than 1×10 -3 MPa for repeated smelting 5-7 times, and stirring is performed by using electromagnetic vibration in the vacuum arc furnace cavity to eliminate composition segregation of the alloy steel ingot and fully homogenize the structure, and after the smelting is completed, the ingot is poured.

[0063] S2, cogging forging: the cuboid ingot poured in step S1 is subjected to cogging at a temperature of 1200℃ for 1h, and then subjected to multi-directional forging at a temperature of 1150℃, with a final forging temperature not lower than 1150℃.

[0064] S3, solid solution treatment: the steel ingot prepared in step S2 is subjected to high-temperature solid solution treatment under an argon protective atmosphere, with a solid solution treatment temperature of 1250℃ and a time of 5h, and then air-cooled to room temperature. After the solid solution treatment, the steel ingot is subjected to billet wire cutting treatment, and cut into a cuboid billet by using an electric spark wire cutting machine, with the dimensions of length, width and height being 300mm×50mm×50mm.

[0065] S4, high-temperature hot rolling treatment: the steel ingot prepared in step S3 is reheated to 1050℃ and kept for 1.0h, and then subjected to continuous three-pass large deformation synchronous hot rolling treatment after being discharged, with a hot rolling opening temperature of 1030℃ and a final rolling temperature of 960℃; the deformation amount of the first hot rolling pass is 35%, the deformation amount of the second hot rolling pass is 55%, and the deformation amount of the third hot rolling pass is 70%, with a final rolling thickness of the steel ingot being 25mm, and then water-cooled to room temperature, with the structure after water cooling being martensite structure.

[0066] S5, austenitizing treatment: the cuboid steel ingot prepared in S4 is subjected to austenitizing treatment in an inert gas atmosphere, with an austenitizing temperature of 940℃ and a holding time of 1.5h;

[0067] S6, large deformation synchronous warm rolling and relaxation treatment: the rectangular steel ingot prepared in S5 is air-cooled to 690°C, and then 3 passes of large deformation synchronous warm rolling are performed, the first pass of warm rolling starts at 690°C and ends at 660°C, the deformation is 55%; after 5s of relaxation, the second pass starts at 650°C and ends at 590°C, the deformation is 75%; after 5s of second relaxation, the third pass of warm rolling starts at 520°C and ends at 460°C, the deformation is 95%, and the metastable austenite structure is fully refined by large deformation warm rolling. The total warm rolling time is controlled within 30s, and the thickness of the steel plate after warm rolling is controlled at 1.0-2.0mm.

[0068] S7, pearlitization treatment: the steel plate prepared by warm rolling in S6 is subjected to pearlitization treatment in an inert gas atmosphere, the temperature of the pearlitization treatment is 680°C, the holding time is 4.0h, and then air-cooled to room temperature, to obtain a high strength and toughness ultrafine pearlitic steel plate.

[0069] The microstructure of the high strength and toughness ultrafine pearlitic steel plate prepared in this embodiment is a uniform and fine granular carbide / ferrite complex phase structure, the average grain size of the ferrite structure is 380nm, and the granular carbide is uniformly dispersed on the ferrite matrix and the grain boundary; the room temperature yield strength and tensile strength are 1745MPa and 2590MPa respectively, and the room temperature total elongation is 5.0%.

[0070] Example 3

[0071] Preparation of a high strength and toughness ultrafine pearlitic steel plate:

[0072] S1, alloy smelting: the composition of the high strength and toughness ultrafine pearlitic steel plate is as follows in terms of mass percentage: C: 0.6-0.7%, Si: 0.9-1.2%, Mn: 0.5-1.0%, Cr: 2.0-3.0%, Ni: 1.3-1.5%, Mo: 0.5-0.7%, and the rest is Fe and unavoidable impurities; the raw materials are placed in a vacuum arc furnace with a vacuum degree greater than 1x10 -3 MPa and subjected to repeated smelting for 5-7 times, and stirred by electromagnetic vibration in the vacuum arc furnace cavity to eliminate the composition segregation of the alloy steel ingot and fully homogenize the structure. After smelting, the ingot is poured.

[0073] S2, cogging forging: the rectangular cast ingot poured in step S1 is subjected to cogging at a temperature of 1250°C for 2h, and then subjected to multi-directional forging at a temperature of 1180°C, and the final forging temperature is not lower than 1150°C.

[0074] S3, solution treatment: the steel ingot prepared in step S2 is subjected to high-temperature solution treatment under an argon protective atmosphere, the temperature of the solution treatment is 1200 °C, the time is 4.0 h, and then air cooling to room temperature. After the solution treatment, the steel ingot is subjected to billet wire cutting treatment, and is cut into a cuboid billet by using an electric spark wire cutting machine, the size of the cuboid billet is 300 mm x 50 mm x 50 mm.

[0075] S4, high-temperature hot rolling treatment: the steel ingot prepared in step S3 is reheated to 1050 °C, and is kept for 1.0 h, and then is subjected to continuous three-pass large deformation synchronous hot rolling treatment, in the process of the hot rolling treatment, the hot rolling starting temperature is 1030 °C, the final rolling temperature is 960 °C, the deformation amount of the first-pass hot rolling is 35%, the deformation amount of the second-pass hot rolling is 55%, the deformation amount of the third-pass hot rolling is 70%, the final rolling thickness of the steel ingot is 25 mm, and then is water cooled to room temperature, and the microstructure after the water cooling is a martensite microstructure.

[0076] S5, austenitizing treatment: the cuboid steel ingot prepared in S4 is subjected to austenitizing treatment under an inert gas atmosphere, the austenitizing temperature is 960 °C, and the keeping time is 1.5 h;

[0077] S6, large deformation synchronous warm rolling and relaxation treatment: the cuboid steel ingot prepared in S5 is air cooled to 690 °C, and then is subjected to three-pass large deformation synchronous warm rolling, the first-pass warm rolling starts at 690 °C and ends at 660 °C, and the deformation amount is 55%; after 5 s of relaxation, the second-pass warm rolling starts at 650 °C and ends at 590 °C, and the deformation amount is 75%; after 5 s of second relaxation, the third-pass warm rolling starts at 520 °C and ends at 460 °C, and the deformation amount is 95%, and the metastable austenite microstructure is fully refined through the large deformation warm rolling. The total time of the warm rolling is controlled within 30 s, and the thickness of the steel plate after the warm rolling is controlled to be 1.0-2.0 mm.

[0078] S7, pearlitizing treatment: the steel plate prepared by the warm rolling in S6 is subjected to pearlitizing treatment under an inert gas atmosphere, the temperature of the pearlitizing treatment is 680 °C, the keeping time is 4.0 h, and then air cooling to room temperature, and a high-strength and high-toughness ultrafine pearlite steel plate material is obtained.

[0079] The microstructure of the high-strength and high-toughness ultrafine pearlite steel plate material prepared in the embodiment is a uniform and fine granular carbide / ferrite complex microstructure, the average grain size of the ferrite microstructure is 390 nm, and the granular carbide is uniformly and dispersedly distributed on the ferrite matrix and the grain boundaries; the room-temperature yield strength and the tensile strength are respectively 1680 MPa and 2550 MPa, and the room-temperature total elongation is 4.8%.

[0080] Comparative Example 1

[0081] A high-strength and high-toughness ultrafine pearlite steel plate material and a preparation method thereof

[0082] S1, alloy smelting is same as example 1.

[0083] S2, open forging: the cuboid ingot cast in step S1, the open forging temperature is 1230℃, the holding time is 1.5h; then high temperature hot rolling is carried out at 1180℃ for 3-5 passes, the final rolling temperature is not lower than 1150℃, the high temperature hot rolling treatment is single in deformation direction, so that the grain orientation of the plate is obvious.

[0084] S3 solid solution treatment, S4 high temperature hot rolling treatment, S5 austenitizing treatment, S6 large deformation synchronous warm rolling and relaxation treatment and S7 pearlitizing treatment are same as example 1.

[0085] The microstructure of the high strength and toughness ultra-fine pearlitic steel plate prepared in the example is uniform and fine granular carbide / ferrite complex phase structure, the average grain size of the ferrite structure is about 390nm, the granular carbide is uniformly and dispersedly distributed on the ferrite matrix and the grain boundary; the room temperature yield strength and tensile strength are respectively 1650MPa and 2460MPa, and the room temperature total elongation is 4.3%.

[0086] Comparative example 2

[0087] A high strength and toughness ultra-fine pearlitic steel plate and a preparation method thereof:

[0088] S1 alloy smelting, S2 open forging and S3 solid solution treatment are same as example 1.

[0089] S4, high temperature hot rolling treatment: the ingot prepared in step S3 is reheated to 1030℃ and held for 1.0h, then continuous 3-pass large deformation synchronous hot rolling treatment is carried out after discharging, in the hot rolling treatment process, the hot rolling initial rolling temperature is 1030℃ and the final rolling temperature is 960℃; the first-pass hot rolling deformation is 45%, the second-pass hot rolling deformation is 65%, the third-pass hot rolling deformation is 80%, the final rolling thickness of the ingot is 15mm, then water cooling to room temperature, the structure after water cooling is martensite, which improves the high temperature hot rolling deformation and is beneficial to further refining the structure, but reduces the overall plate yield.

[0090] S5 austenitizing treatment, S6 large deformation synchronous warm rolling and relaxation treatment and S7 pearlitizing treatment are same as example 1.

[0091] The microstructure of the high strength and toughness ultra-fine pearlitic steel plate prepared in the example is uniform and fine granular carbide / ferrite complex phase structure, the average grain size of the ferrite structure is about 410nm, the granular carbide is uniformly and dispersedly distributed on the ferrite matrix and the grain boundary; the room temperature yield strength and tensile strength are respectively 1580MPa and 2410MPa, and the room temperature total elongation is 4.0%.

[0092] Comparative example 3

[0093] A high-toughness ultrafine pearlitic steel plate and a preparation method thereof

[0094] S1 alloy smelting, S2 cogging forging, S3 solid solution treatment, S4 high-temperature hot rolling treatment, and S5 austenitizing treatment are the same as in Example 1.

[0095] S6, large deformation synchronous warm rolling plus relaxation treatment: the cuboid steel ingot prepared in S5 is air-cooled to 690°C, and then 3 passes of large deformation asynchronous warm rolling are performed, the first pass of warm rolling starts at 690°C and ends at 660°C, the deformation amount is 55%; after 5s of relaxation, the second pass starts at 650°C and ends at 590°C, the deformation amount is 75%; after 5s of second relaxation, the third pass of warm rolling starts at 520°C and ends at 460°C, the deformation amount is 95%, and the metastable austenite structure is fully refined through large deformation warm rolling. The total warm rolling time is controlled within 30s, and the thickness of the steel plate after warm rolling is controlled at 1.0-2.0mm. The large deformation synchronous warm rolling is changed to large deformation asynchronous warm rolling, compared with large deformation synchronous rolling, the asynchronous rolling increases the deformation amount to some extent, which increases the strength of the plate, but the increase of the deformation amount leads to the introduction of a large number of defects, which is not conducive to the improvement of the plasticity of the deformed plate.

[0096] S7, pearlitizing treatment is the same as in Example 1.

[0097] The high-toughness ultrafine pearlitic steel plate prepared in the present example has a uniform and fine granular carbide / ferrite complex phase microstructure, the average grain size of the ferrite structure is about 320nm, and the granular carbide is uniformly and dispersedly distributed on the ferrite matrix and the grain boundary; the room temperature yield strength and tensile strength reach 1750MPa and 2660MPa respectively, and the room temperature total elongation reaches 2.1%.

[0098] Comparative Example 4

[0099] A high-toughness ultrafine pearlitic steel plate and a preparation method thereof

[0100] S1 alloy smelting, S2 cogging forging, S3 solid solution treatment, S4 high-temperature hot rolling treatment, S5 austenitizing treatment, and S6 large deformation synchronous warm rolling plus relaxation treatment are the same as in Example 1.

[0101] S7, pearlitizing treatment: the steel plate prepared by warm rolling in S6 is subjected to pearlitizing treatment in an inert gas atmosphere, the temperature of the pearlitizing treatment is 680°C, the holding time is 6.0h, and then air-cooling to room temperature is performed, to obtain a high-toughness ultrafine pearlitic steel plate. The extension of the pearlitizing treatment time leads to the growth of the pearlitic cluster grains, which improves the plasticity of the pearlitic steel plate, but rapidly decreases the yield and tensile strengths thereof.

[0102] The microstructure of the high strength and toughness ultrafine pearlite steel plate prepared in the example is a uniform and fine granular carbide / ferrite complex phase structure, the average grain size of the ferrite structure is about 450 nm, and the granular carbide is uniformly and dispersedly distributed on the ferrite matrix and the grain boundary; the room temperature yield strength and the tensile strength are respectively 1510 MPa and 1980 MPa, and the room temperature total elongation is 8.5%.

Claims

1. A method for preparing high-strength and tough ultrafine pearlite steel plate, characterized in that: The preparation method comprises: S1, alloy smelting: the composition of the high strength and toughness ultrafine pearlitic steel plate is as follows in terms of mass percentage: C: 0.6-0.7%, Si: 0.9-1.2%, Mn: 0.5-1.0%, Cr: 2.0-3.0%, Ni: 1.3-1.5%, Mo: 0.5-0.7%, and the rest is Fe and inevitable impurities; ingredients are prepared according to the mass percentage, a vacuum induction melting furnace is used for smelting, and a steel ingot is cast; S2, cogging forging: the steel ingot cast in step S1 is subjected to cogging at a temperature of 1200-1250 DEG C for 1.0-2.0 h, and then subjected to hot forging treatment at 1150-1200 DEG C; S3, solid solution treatment: the steel ingot prepared in step S2 is subjected to high-temperature solid solution treatment in an inert gas atmosphere, the temperature of the solid solution treatment is 1150-1250 DEG C, and the time is 4.0-5.0 h, and then air-cooled to room temperature; S4, high-temperature hot rolling treatment: the steel ingot prepared in step S3 is reheated to 1000-1050 DEG C, and kept for 0.5-1.0 h, and then subjected to continuous three-pass large deformation synchronous hot rolling treatment after being discharged, the final rolling temperature is not lower than 950 DEG C, and then water-cooled to room temperature; the deformation of the first pass of hot rolling is 30-40%, the deformation of the second pass of hot rolling is 50-60%, and the deformation of the third pass of hot rolling is 65-70%; S5, austenitizing treatment: the rectangular steel ingot prepared in S4 is subjected to austenitizing treatment in an inert gas atmosphere, the austenitizing temperature is 930-960 DEG C, and the holding time is 1.0-1.5 h; S6, large deformation synchronous warm rolling and relaxation treatment: the rectangular steel ingot prepared in S5 is air-cooled to 680-690 DEG C, and then subjected to three-pass large deformation synchronous warm rolling, the cumulative reduction is 85-95%, short-time relaxation treatment is adopted between the warm rolling passes, and the total warm rolling time is controlled within 30 s; the first pass of warm rolling starts at 680-690 DEG C and ends at 650-660 DEG C, with a deformation of 50-55%; after 5 s of relaxation, the second pass starts at 640-650 DEG C and ends at 580-590 DEG C, with a deformation of 70-80%; after 5 s of second relaxation, the third pass of warm rolling starts at 510-520 DEG C and ends at 460-470 DEG C, with a deformation of 85-95%; S7, pearlitizing treatment: the steel plate prepared by warm rolling in S6 is subjected to pearlitizing treatment in an inert gas atmosphere, the temperature of the pearlitizing treatment is 680 DEG C, the holding time is 3.0-4.0 h, and then air-cooled to room temperature, thereby obtaining a high strength and toughness ultrafine pearlitic steel plate.

2. The production method according to claim 1, wherein In the S1, the raw material is repeatedly melted 5 to 7 times in a vacuum arc furnace with a vacuum degree greater than 1 x 10 -3 MPa, and stirring is performed using electromagnetic vibration in the vacuum arc furnace chamber to eliminate composition segregation of the alloy steel ingot and fully homogenize the structure. After the melting is completed, the alloy steel ingot is poured into a cuboid ingot.

3. The production method according to claim 1, wherein In S2, the hot forging treatment is multi-directional forging treatment, and the final forging temperature is not lower than 1150 DEG C.

4. The production method according to claim 1, wherein After the solid solution treatment, the steel ingot needs to be subjected to billet wire cutting treatment, and is cut into a rectangular billet by using an electric spark wire cutting machine, with a size of 300 mm*50 mm*50 mm. In S2, the hot forging treatment is multi-directional forging treatment, and the final forging temperature is not lower than 1150 DEG C. After the solid solution treatment, the steel ingot needs to be subjected to billet wire cutting treatment, and is cut into a rectangular billet by using an electric spark wire cutting machine, with a size of 300 mm*50 mm*50 mm.

5. The production method according to claim 1, wherein In the S4, the hot rolling process is performed at a hot rolling starting temperature of 1000-1050 DEG C and a finish rolling temperature of 950-980 DEG C, and the microstructure after water cooling is martensite.

6. The production method according to claim 4, wherein In the S4, the finish rolling thickness of the ingot after high temperature hot rolling is 20-30 mm.

7. The production method according to claim 1, wherein In the S6, the metastable austenite structure is sufficiently refined by the large deformation warm rolling.

8. The production method according to claim 1, wherein In the S6, the thickness of the steel plate after the large deformation synchronous warm rolling and relaxation treatment is controlled to be 1.0-2.0 mm. In the S6, the temperature change of the steel plate during the large deformation synchronous warm rolling is detected by using an infrared temperature gun. In the S7, the steel plate after the large deformation synchronous warm rolling in the S6 is directly subjected to the pearlitization treatment without cooling.

9. The production method according to claim 1, wherein In the S7, the microstructure of the high strength and toughness ultrafine pearlitic steel plate is a uniform and fine granular carbide / ferrite composite structure, the average grain size of the ferrite structure is 330-390 nm, and the granular carbide is uniformly and dispersedly distributed on the ferrite matrix and the grain boundary; the room temperature yield strength and tensile strength are respectively 1791 MPa and 2612 MPa, and the room temperature total elongation is 5.6%.

10. The high strength and toughness ultrafine pearlitic steel plate prepared by the preparation method in any one of claims 1-9.

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