A method for preparing gradient laminated dual-phase multi-level heterogeneous steel plates by folding forging

Abstract

The present invention discloses a method for preparing a gradient laminated dual-phase multi-level heterogeneous steel plate by folding forging, comprising the following steps: (1) plate pretreatment; (2) forging and combining dissimilar steel plates; (3) repeated filling and folding forging; (4) rolling and refinement; (5) isomerization heat treatment; the gradient laminated dual-phase multi-level heterogeneous steel plate obtained by the above steps has multiple heterogeneous characteristics such as dual-phase lamellar layers, gradient structure, and non-uniform grain structure, which can give full play to the advantages of heterogeneous materials, has excellent comprehensive mechanical properties, has a simple process flow, and has good interface bonding of the formed heterogeneous materials.

Description

Technical Field

[0001] The invention relates to the field of material preparation, and in particular to a method for preparing a gradient laminated dual-phase multi-level heterogeneous steel plate by folding and forging. Background Art

[0002] Human beings have a long history of using and researching steel. Since the invention of the Bain steelmaking process in the 19th century, the cost of making steel has been greatly reduced. Nowadays, steel has become one of the most widely used materials in daily life due to its low price and high strength. However, the increase in material strength is often accompanied by a decrease in plasticity. Therefore, how to simultaneously improve the strength and plasticity of steel materials has become one of the hot topics in the field of steel material research.

[0003] After searching the prior art, it was found that in the "Heat Treatment Method for High-Toughness and High-Strength Steel Plate" disclosed in Chinese invention patent CN201110029418.1, by heating the steel plate, water quenching and then tempering, a steel plate with high strength and toughness is finally obtained, which has a structure of carbon-poor martensite, bainite, a small amount of residual austenite and finely dispersed carbonitrides on the martensite or bainite matrix. The characteristics of this technology are: (1) the heat treatment production efficiency is improved, and the total energy consumption is reduced compared with offline heat treatment; (2) the obtained plate has improved plasticity and toughness while ensuring strength. However, this technology also has the following problems: (1) the improvement of toughness is relatively limited; (2) it is difficult to accurately control the mechanical properties required by the product.

[0004] Further searching of the prior art revealed that in order to alleviate the contradictory relationship between the strength and plasticity of metal materials, some scholars proposed the concept of "heterogeneous" metals, designed metal materials containing components with different properties at the microscopic scale, and used the coordinated deformation between the soft and hard components and the resulting deformation-induced strain hardening to make the material have both high strength and high plasticity. Li et al. (Superior strength and ductility of 316L stainless steel with heterogeneous lamella structure, J Mater Sci, (2018) 53: 10442-10456) prepared 316L austenitic stainless steel with a heterogeneous layered structure formed by ultrafine grain / nanocrystalline layer wrapped in coarse crystalline layer by cold rolling with large deformation and combined with incomplete recrystallization annealing, which has excellent comprehensive mechanical properties. The characteristics of this technology are: (1) simple process and low equipment requirements; (2) heterogeneous layered structure has both strength and plasticity. This technology also has the following problems: (1) It requires cold rolling with a large deformation amount, and large-size samples will place higher requirements on equipment; (2) Incomplete recrystallization annealing makes it difficult to accurately control the thickness of the heterogeneous layer, making it difficult to accurately control the mechanical properties of the material.

[0005] Further search revealed that Ma et al. published an article titled “Mechanical properties of copper / bronze laminates: Role of interfaces” in Acta Materialia, 2016, 116: 43-52, which introduced a method for preparing laminated heterogeneous copper alloy sheets composed of multiple layers of coarse-grained copper and fine-grained brass alternating by cumulative rolling and heat treatment. The characteristics of this technology are as follows: (1) As the number of layers increases, the strength and tensile plasticity of the material increase simultaneously; (2) The obtained laminated Cu alloy sheet has excellent mechanical properties. While maintaining the high strength of nanocrystalline Cu, the material also has super strong strain hardening ability, and to a certain extent maintains the uniform elongation of coarse-grained Cu. However, this technology has the following problems: (1) The thickness of each metal layer obtained is the same, and the thickness of the soft and hard components cannot be flexibly changed; (2) It is difficult to ensure interface bonding by room temperature cumulative rolling.

[0006] Therefore, there is an urgent need for a method for preparing gradient laminated two-phase multi-level heterogeneous steel plates by folding forging, which can solve the problem that the existing technology is difficult to prepare steel materials with good strength and plasticity at the same time. Summary of the invention

[0007] The purpose of the present invention is to provide a method for preparing gradient laminated two-phase multi-level heterogeneous steel plates by folding forging, so as to solve the problem that the above-mentioned prior art is difficult to prepare steel materials with good strength and plasticity at the same time.

[0008] To achieve the above object, the present invention provides the following solutions:

[0009] The present invention provides a method for preparing a gradient laminated dual-phase multi-level heterogeneous steel plate by folding forging, comprising the following steps:

[0010] S1. Plate pretreatment: Use electric spark wire cutting to process low carbon steel plates and austenitic steel plates, and then use a grinding wheel to clean the surface of the plates to remove surface oil and impurities;

[0011] S2. Forging and pressing of dissimilar steel plates: the folded low-carbon steel plate is filled with an austenitic steel plate, the stacked plates are placed in a heat treatment furnace for heating, and after heat preservation, the two plates are taken out and combined together by a forging press to form a laminated plate of low-carbon steel wrapped with austenitic steel;

[0012] S3. Repeated filling, folding and forging: The laminated sheet obtained in step S2 is divided and folded from the middle by wire electric discharge cutting, and then austenitic steel plates are filled between the folded sheets. The folded sheets are placed in a heat treatment furnace for heating, taken out after heat preservation, and hot forged. The above operation is repeated several times to obtain a gradient laminated sheet;

[0013] S4. Rolling refinement: rolling the gradient laminated sheet obtained in step S3 to improve the surface flatness of the sheet and refine the grains;

[0014] S5. Isomerization heat treatment: Perform isomerization heat treatment on the gradient laminated plate after rolling in step S4, so that the austenite lamellae form non-uniformly distributed austenite grains and the low-carbon steel lamellae form fine martensite grains, thereby obtaining a gradient laminated dual-phase multi-level isomerized steel plate.

[0015] Preferably, in step S1, the low carbon steel plate has a thickness of 1-10 mm, a length of 30-150 mm, and a width of 30-150 mm. The austenitic steel plate has the same thickness and width as the low carbon steel plate, and the length of the low carbon steel plate is equal to twice the length of the austenitic steel plate plus its thickness.

[0016] Preferably, in step S1, the carbon content of the low carbon steel plate is 0.03-0.25wt.%; the austenitic steel plate includes 3 series austenitic stainless steel and medium / high manganese steel with a Mn element content of more than 4wt.%.

[0017] Preferably, in step S2, the heating temperature is controlled to be 1000-1200°C, the holding time is 20-60 min, the final forging temperature is 900-1000°C, and the forging reduction is 50%.

[0018] Preferably, in step S3, the heating temperature is controlled to be 1000-1200°C, the holding time is 20-60 min, the final forging temperature is 900-1000°C, and the forging reduction is 50%.

[0019] Preferably, in step S4, the cumulative pressing amount of rolling deformation is 50-90%, and the deformation temperature is room temperature to 400°C.

[0020] Preferably, step S5 is specifically as follows: heating the obtained gradient laminated plate to 750-950°C, keeping warm for 1-60 minutes, quenching the plate, the quenching medium is water or quenching oil, the volume fraction of martensite in the low carbon steel layer accounts for more than 80% of the layer, the fine grain size in the austenite layer is 100-1000nm, and the size of the coarse grain is above 1μm.

[0021] Compared with the prior art, the present invention has achieved the following beneficial technical effects:

[0022] 1. The present invention provides a method for preparing gradient laminated dual-phase multi-level heterogeneous steel plates by folding and forging. Austenitic steel plates and low-carbon steel plates are stacked to form an integral plate by simple folding and high-temperature forging. Some defects generated by the metal during the smelting process can also be appropriately eliminated. The interface bonding effect is better than low-temperature mechanical alloying.

[0023] 2. The present invention provides a method for preparing gradient laminated two-phase multi-level heterogeneous steel plates by folding forging. The thickness of the sheet layer is accurately controllable. The downward pressure of each folding forging is controlled to be 50%. The thickness of the low carbon steel layer obtained after n times of folding forging is h / 2n, and the thickness of the austenitic steel layer has a gradient distribution characteristic from the surface to the core.

[0024] 3. The present invention provides a method for preparing gradient laminated two-phase multi-level heterogeneous steel plates by folding forging. The finally obtained heterogeneous plates have multiple heterogeneous characteristics such as two-phase lamellar layers, gradient structure, non-uniform grain structure, etc., which can give full play to the advantages of heterogeneous materials and have excellent comprehensive mechanical properties.

[0025] 4. The present invention provides a method for preparing gradient laminated dual-phase multi-level heterogeneous steel plates by folding forging, which has a simple process flow, common production equipment and low operating difficulty. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] 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 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 labor.

[0027] Figure 1 A flow chart of forging and combining heterogeneous steel plates in the method for preparing gradient laminated dual-phase multi-level heterogeneous steel plates by folding forging provided by the present invention;

[0028] Figure 2 A flow chart of repeated filling and folding forging in the method for preparing gradient laminated dual-phase multi-level heterogeneous steel plates by folding forging provided by the present invention;

[0029] Figure 3 A flow chart of rolling refinement and isomerization heat treatment in the method for preparing gradient laminated dual-phase multi-level isomerized steel plates by folding forging provided by the present invention;

[0030] Figure 4 A schematic diagram of the microstructure of a gradient laminated plate before and after quenching in the method for preparing a gradient laminated dual-phase multi-level heterogeneous steel plate by folding forging provided by the present invention;

[0031] Figure 5A distribution law diagram of the gradient laminated structure of the gradient laminated dual-phase multi-level heterogeneous steel plate prepared by the method for preparing the gradient laminated dual-phase multi-level heterogeneous steel plate by folding forging provided by the present invention;

[0032] In the figure: 1-austenitic steel plate, 2-low carbon steel plate, 3-heat treatment furnace, 4-upper anvil of forging equipment, 5-lower anvil of forging equipment, 6-gradient laminated plate, 7-upper roller, 8-lower roller, 9-quenching liquid. DETAILED DESCRIPTION

[0033] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0034] The purpose of the present invention is to provide a method for preparing gradient laminated dual-phase multi-level heterogeneous steel plates by folding forging, so as to solve the problem that it is difficult to prepare steel materials with good strength and plasticity in the prior art.

[0035] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

[0036] The invention provides a method for preparing a gradient laminated dual-phase multi-level heterogeneous steel plate by folding forging, such as Figure 1-5 As shown, it includes the following steps:

[0037] The first step is plate pretreatment: use electric spark wire cutting to process low carbon steel plate 2 and austenitic steel plate 1 of a certain size, and then use a grinding wheel to clean the surface of the plate to remove surface oil and impurities. The thickness of the low carbon steel plate 2 is 1-10mm, the length is 30-150mm, and the width is 30-150mm. The thickness and width of the low carbon steel plate 2 and the austenitic steel plate 1 are the same. The length of the low carbon steel plate 2 is equal to twice the length of the austenitic steel plate 1 plus the thickness of the austenitic steel plate 1, to ensure that the low carbon steel plate 2 can cover the austenitic steel plate 1 on the upper and lower surfaces during folding forging.

[0038] The second step is to combine the dissimilar steel plates by forging: fill the folded low-carbon steel plate 2 with the austenitic steel plate 1, put the stacked plates into the heat treatment furnace 3 for heating, take them out after keeping them warm for a period of time, and combine the two plates together through a forging machine to form a laminated structure of low-carbon steel wrapped with austenitic steel. The heating temperature is 1000-1200℃, the insulation time is 20-60min, the final forging temperature is 900-1000℃, and the forging reduction is 50%.

[0039] The third step is repeated filling, folding and forging: the laminated plate obtained in the second step is divided and folded from the middle by electric spark wire cutting, and then the austenitic steel plate 1 is filled between the folded plates, and the folded and bonded plates are placed in a heat treatment furnace 3 for heating, and taken out after keeping warm for a period of time, and placed between the upper anvil 4 and the lower anvil 5 of the forging equipment, and hot forged. The above steps are repeated for many times to obtain a gradient laminated plate 6, the heating temperature is controlled at 1000-1200℃, the insulation time is 20-60min, the final forging temperature is 900-1000℃, and the forging reduction is 50%.

[0040] The fourth step is rolling refinement: the gradient laminated plate 6 obtained by repeated folding and forging is placed between the upper roller 7 and the lower roller 8 for rolling, with the cumulative pressing amount being 50-90% and the deformation temperature being room temperature to 400°C.

[0041] The fifth step is isomerization heat treatment: the rolled gradient laminated plate 6 is heated to 750-950°C, kept warm for 1-60 minutes, and then the plate is quenched in a quenching liquid 9. The quenching medium is water or quenching oil. The volume fraction of martensite obtained in the low-carbon steel layer accounts for more than 80% of the layer, and a gradient laminated dual-phase multi-level isomerized steel plate is obtained.

[0042] The method for preparing a gradient laminated dual-phase multi-level heterogeneous steel plate by folding forging provided by the present invention comprises the following steps: firstly, a low carbon steel plate (A) and an austenitic steel plate (B) are folded and forged. Figure 1 The dissimilar steel plates shown are folded and forged to achieve metallurgical bonding to obtain a three-layer laminated plate (ABA), in which the low-carbon steel plate and the austenitic steel plate have the same thickness and width, and the length of the low-carbon steel plate is equal to twice the length of the austenitic steel plate plus the thickness, to ensure that the low-carbon steel plate can cover the austenitic steel plate on the upper and lower surfaces during folding and forging. Then, a block of austenitic stainless steel is placed on the above-mentioned laminated plate, and folding and high-temperature hot forging are continued to obtain a seven-layer laminated plate (ABABABA). The above folding and forging operations are repeated many times, with the downward pressure of each forging being 50% of the total thickness, to obtain a laminated plate with alternating distribution of low-carbon steel and austenitic steel. The layer distribution of the laminated plate obtained by repeated folding and forging has the following rules: (1) After n times of folding and forging, the total number of layers is 2 (n+1) -1; (2) The initial thickness of both steel plates is h, and after n times of folding and forging, the thickness of the low carbon steel layer is h / 2 n ; (3) The austenitic steel layer has the characteristics of gradient distribution, such as Figure 5 As shown in the figure, after n times of folding and forging, the thickness of the austenite layer closest to the surface of the laminated sheet is h / 2 n From the surface to the core of the plate, it can be found that the thickness of the austenite layer is h / 2 nThe gradient distribution of the steel sheet varies from h / 2 to h / 2. In addition, there are two types of steel sheets alternately stacked in the middle of these gradient austenite layers. (4) Due to the characteristics of repeated folding and forging, the number of layers between adjacent gradient austenite layers also presents the characteristics of gradient distribution, increasing from 1 layer near the surface to 3, 7, ..., 2. n-1 -1 layer. Then, the laminated structure after folding and forging is subjected to rolling deformation treatment to improve the surface flatness of the plate and refine the grain size. Finally, the laminated structure after rolling is subjected to heterogeneous heat treatment to transform the low-carbon steel lamellae into a structure dominated by martensite, and the austenite lamellae are an austenite structure with non-uniform distribution of grain size. The martensite structure can be used as a hard component in heterogeneous materials, and the austenite grains are used as soft components in heterogeneous materials. There are various forms of heterogeneous structures in the laminated plate obtained after heterogeneous heat treatment. First, a two-phase lamella isomerism is formed between the martensite lamellae and the austenite lamellae; secondly, the thickness of the austenite lamellae presents a gradient distribution characteristic from the surface to the core; then, a non-uniform structure of grain size can also be formed inside the austenite lamellae. Finally, this multi-level heterogeneous steel plate composed of multiple heterogeneous forms can give full play to the advantages of heterogeneous materials and has excellent comprehensive mechanical properties.

[0043] Example 1

[0044] (1) Plate pretreatment:

[0045] 316L austenitic stainless steel plates with a length, width and thickness of 50mm, 40mm and 5mm respectively and Q235 with a length, width and thickness of 105mm, 40mm and 5mm respectively were processed by electric spark cutting, and then the surface of the plates was cleaned with a grinding wheel to remove surface oil and impurities.

[0046] (2) Forging and pressing of dissimilar steel plates:

[0047] The folded low-carbon steel is filled with austenitic steel, the stacked plates are placed in a heat treatment furnace and heated to 1100°C for 30 minutes before being taken out, and the two plates are combined together by a forging press. The final forging temperature is 900-950°C, and the reduction is 50%, forming a laminated structure of low-carbon steel wrapped in austenitic steel.

[0048] (3) Repeated filling and folding forging:

[0049] The laminated sheet obtained in the second step is split and folded from the middle by electric spark wire cutting, and then austenitic steel plates are filled between the folded sheets. The folded sheets are placed in a heat treatment furnace and heated to 1100°C. After keeping the temperature for 30 minutes, they are taken out and hot forged. The final forging temperature is 900-950°C and the forging pressure is 50%. The above steps are repeated many times to obtain a gradient laminated sheet.

[0050] (4) Rolling refinement:

[0051] The gradient laminated plate obtained by repeated folding and forging is rolled, with a cumulative pressing amount of 50% and a deformation temperature of room temperature.

[0052] (5) Isomerization heat treatment:

[0053] The rolled laminated plate is heated to 800°C and kept warm for 10 minutes, and then the plate is quenched with the quenching medium being water or quenching oil to obtain a gradient laminated dual-phase multi-level heterogeneous steel plate.

[0054] Example 2

[0055] (1) Plate pretreatment:

[0056] 316L austenitic stainless steel plates with a length, width and thickness of 50mm, 40mm and 5mm respectively and Q235 with a length, width and thickness of 105mm, 40mm and 5mm respectively were processed by electric spark cutting, and then the surface of the plates was cleaned with a grinding wheel to remove surface oil and impurities.

[0057] (2) Forging and pressing of dissimilar steel plates:

[0058] The folded low-carbon steel is filled with austenitic steel, the stacked plates are placed in a heat treatment furnace and heated to 1100°C for 30 minutes before being taken out, and the two plates are combined together by a forging press. The final forging temperature is 900-950°C, and the reduction is 50%, forming a laminated structure of low-carbon steel wrapped in austenitic steel.

[0059] (3) Repeated filling and folding forging:

[0060] The laminated sheet obtained in the second step is split and folded from the middle by electric spark wire cutting, and then austenitic steel plates are filled between the folded sheets. The folded sheets are placed in a heat treatment furnace and heated to 1100°C. After keeping the temperature for 30 minutes, they are taken out and hot forged. The final forging temperature is 900-950°C and the forging pressure is 50%. The above steps are repeated many times to obtain a gradient laminated sheet.

[0061] (4) Rolling refinement:

[0062] The gradient laminated plate obtained by repeated folding and forging is rolled, with a cumulative reduction amount of 90% and a deformation temperature of 300°C.

[0063] (5) Isomerization heat treatment:

[0064] The rolled laminated plate is heated to 820°C, kept warm for 8 minutes, and then quenched with water or quenching oil as the quenching medium to obtain a gradient laminated dual-phase multi-level heterogeneous steel plate.

[0065] Example 3

[0066] (1) Plate pretreatment:

[0067] 316L austenitic stainless steel plates with a length, width and thickness of 50mm, 40mm and 5mm respectively and Q195 with a length, width and thickness of 105mm, 40mm and 5mm respectively were processed by electric spark cutting, and then the surface of the plates was cleaned with a grinding wheel to remove surface oil and impurities.

[0068] (2) Forging and pressing of dissimilar steel plates:

[0069] The folded low-carbon steel is filled with austenitic steel, the stacked plates are placed in a heat treatment furnace and heated to 1100°C for 30 minutes before being taken out, and the two plates are combined together by a forging press. The final forging temperature is 900-950°C, and the reduction is 50%, forming a laminated structure of low-carbon steel wrapped in austenitic steel.

[0070] (3) Repeated filling and folding forging:

[0071] The laminated sheet obtained in the second step is split and folded from the middle by electric spark wire cutting, and then austenitic steel plates are filled between the folded sheets. The folded sheets are placed in a heat treatment furnace and heated to 1100°C. After keeping the temperature for 30 minutes, they are taken out and hot forged. The final forging temperature is 900-950°C and the forging pressure is 50%. The above steps are repeated many times to obtain a gradient laminated sheet.

[0072] (4) Rolling refinement:

[0073] The gradient laminated plate obtained by repeated folding and forging is rolled, with a cumulative reduction of 70% and a deformation temperature of 300°C.

[0074] (5) Isomerization heat treatment:

[0075] The rolled laminated plate is heated to 750°C and kept warm for 15 minutes, and then the plate is quenched with water or quenching oil as the quenching medium to obtain a gradient laminated dual-phase multi-level heterogeneous steel plate.

[0076] The present invention uses specific examples to illustrate the principles and implementation methods of the present invention. The above examples are only used to help understand the method and core ideas of the present invention. At the same time, for those skilled in the art, according to the ideas of the present invention, there will be changes in the specific implementation methods and application scopes. In summary, the content of this specification should not be understood as limiting the present invention.

Claims

1. A method for preparing a gradient laminated dual-phase multi-level heterogeneous steel plate by folding forging, characterized in that: The following steps are involved: S1. Plate pretreatment: Use electric spark wire cutting to process low carbon steel plates and austenitic steel plates, and then use a grinding wheel to clean the plate surface to remove surface oil and impurities; the thickness of the low carbon steel plate is 1-10mm, the length is 30-150mm, and the width is 30-150mm. The thickness and width of the austenitic steel plate are the same as those of the low carbon steel plate. The length of the low carbon steel plate is equal to twice the length of the austenitic steel plate plus its thickness; the carbon content of the low carbon steel plate is 0.03-0.25wt.%; the austenitic steel plate includes 3 series of austenitic stainless steel and medium / high manganese steel with a Mn element content of more than 4wt.%; S2. Forging and pressing of dissimilar steel plates: filling the folded low-carbon steel plate with an austenitic steel plate, placing the stacked plates in a heat treatment furnace for heating, taking them out after heat preservation, and combining the two plates together through a forging press to form a laminated plate of low-carbon steel wrapped with austenitic steel; the heating temperature is controlled at 1000-1200°C, the holding time is 20-60min, the final forging temperature is 900-1000°C, and the forging reduction is 50%; S3. Repeated filling, folding and forging: The laminated sheet obtained in step S2 is divided and folded from the middle by wire electric discharge cutting, and then austenitic steel plates are filled between the folded sheets. The folded sheets are placed in a heat treatment furnace for heating, taken out after heat preservation, and hot forged. The above operation is repeated several times to obtain a gradient laminated sheet; the heating temperature is controlled to be 1000-1200°C, the heat preservation time is 20-60min, the final forging temperature is 900-1000°C, and the forging reduction is 50%; S4. Rolling refinement: rolling the gradient laminated sheet obtained in step S3 to improve the surface flatness of the sheet and refine the grains; S5. Isomerization heat treatment: isomerization heat treatment is performed on the gradient laminated plate after rolling in step S4, so that the austenite lamellae form non-uniformly distributed austenite grains, and the low carbon steel lamellae form fine martensite grains, so as to obtain a gradient laminated dual-phase multi-level isomerized steel plate; specifically: the obtained gradient laminated plate is heated to 750-950°C, kept warm for 1-60min, and the plate is quenched, the quenching medium is water or quenching oil, the volume fraction of martensite in the low carbon steel lamellae accounts for more than 80% of the lamellae, the fine grain size in the austenite lamellae is 100-1000nm, and the size of the coarse grain is above 1μm.

2. The method for preparing gradient laminated dual-phase multi-level heterogeneous steel sheet by folding forging according to claim 1, characterized in that: In step S4, the cumulative rolling deformation is 50-90%, and the deformation temperature is room temperature to 400°C.

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