Method for improving toughness of high-Si ferrite / martensitic steel through dispersed forging

Abstract

The invention provides a method for improving the toughness of high-Si ferrite / martensitic steel through dispersed forging, and relates to the technical field of ferrite / martensitic steel. The method comprises the steps of first-time upsetting and drawing-out, second-time upsetting and drawing-out, third-time upsetting and drawing-out, fourth-time upsetting and drawing-out, plate forging and heat treatment after forging which are conducted in sequence, and finally the finished high-Si ferrite / martensite steel plate is obtained. The tissue structure of the finished high-Si ferrite / martensite steel plate is bamboo-like delta ferrite and martensite. According to the method, the content of delta ferrite is reduced in a manner of combining circulating forging and heat treatment; and on the basis that the corrosion resistance is kept, the strength and toughness of the high-Si ferrite / martensitic steel in the room temperature environment and the high temperature environment can be cooperatively improved, and industrial large-scale production and popularization are facilitated.

Description

Technical Field

[0001] The invention relates to the technical field of ferrite / martensitic steel, in particular to a method for improving the toughness of high-Si ferrite / martensitic steel by dispersed forging. Background Art

[0002] Ferrite / martensitic steel has excellent high temperature mechanical properties and radiation resistance, and is a candidate core structural material for lead-cooled fast reactors, but its corrosion resistance is relatively weak. Although its corrosion resistance can be improved by increasing the Si content, it will also promote the increase of delta ferrite content, thereby deteriorating the toughness of ferrite / martensitic steel. Therefore, reducing delta ferrite is very important for the performance of ferrite / martensitic steel, and there is currently little research on this type of process.

[0003] The main matrix of ferrite / martensitic steel is martensite, with only a small amount of delta ferrite at the grain boundary, where martensite is transformed from austenite. During the solidification process of molten steel, ferrite / martensitic steel usually goes through the stages of molten steel-delta ferrite-austenite-martensite. If the transformation of delta ferrite to austenite is incomplete, it will remain in the matrix. Therefore, the essence of reducing delta ferrite is to promote the transformation of delta ferrite to austenite.

[0004] Generally, the transformation of delta ferrite to austenite is promoted by long-term heat preservation at a certain temperature. The toughness of duplex steel can also be improved by changing the composition and / or organizational structure.

[0005] For example: Chinese patent CN110396583A discloses a high-strength martensite / ferrite dual-phase steel strengthening and toughening treatment process and dual-phase steel. This method ultimately obtains a dual-phase steel with a two-phase structure of "lamellar ferrite + lamellar lath martensite" with fine grains; the tensile strength of the prepared martensite / ferrite dual-phase steel can be increased by more than 60%, and the plasticity can be increased by more than 70%; but the improvement of impact toughness is not achieved.

[0006] Chinese patent CN117925965A discloses a heat treatment method for improving the strength of ferrite martensitic steel. The method uses austenitization + quenching + tempering process to improve strength and plasticity. Although the tensile strength is improved, the impact toughness is not enhanced.

[0007] Chinese patent CN117431370A discloses a high-temperature, high-strength, plastic ferrite martensitic steel and a preparation method thereof, which requires firstly heat treatment to obtain the original ferrite martensitic steel, then cold plastic deformation to obtain nanocrystalline or ultrafine-grained ferrite martensitic steel, and finally annealing to obtain the steel; obviously, the content of high-cost elements is relatively high, the process of obtaining the original ferrite martensitic steel is complicated, the operation is difficult, and the equal channel angular extrusion process is difficult to use for processing larger samples; although the room temperature tensile strength is improved, the elongation is reduced.

[0008] Chinese patent CN115354227A discloses a ferritic martensitic steel for reactor fuel cladding material and its heat treatment process, which not only requires the addition of high-cost alloying elements to the material composition, but also requires multiple brine quenching and heat preservation tempering treatments, has strict requirements on the temperature control range, a long process, and low efficiency, and the room temperature and high temperature impact toughness of the steel finally obtained is not improved. Summary of the invention

[0009] In order to solve the problem that the room temperature impact toughness and high temperature impact toughness of high Si ferrite / martensitic steel, which is a candidate core structural material for lead-cooled fast reactors in the prior art, are reduced in order to improve the corrosion resistance, and although there are many technical solutions to improve the toughness of ferrite / martensitic steel, they are mainly improved from the composition and organizational structure, among which there are not many technical solutions to reduce delta ferrite, and there are technical problems such as high-cost alloy element addition and complex heat treatment process cycle control; therefore, the embodiment of the present invention provides a method for improving the toughness of high Si ferrite / martensitic steel by dispersed forging, which can synergistically improve strength and toughness (especially). The technical solution is as follows:

[0010] A method for improving the toughness of high Si ferrite / martensitic steel by dispersed forging, the method for improving the toughness of high Si ferrite / martensitic steel by dispersed forging comprises the following steps:

[0011] S1. Upsetting and drawing once: heating and keeping the high Si ferrite / martensitic steel ingot, upsetting and drawing once, and obtaining a forging billet after heating and keeping the heat;

[0012] S2, secondary upsetting and drawing: the first forging billet of S1 is upset and drawn once, and then heated and kept warm to obtain the second forging billet;

[0013] S3, three times of upsetting and drawing: the second forging billet of S2 is upset and drawn once, and then heated and kept warm to obtain the third forging billet;

[0014] S4, four times upsetting and drawing: the three forging billets of S3 are upsetting and drawing once, and then heated and kept warm to obtain four forging billets;

[0015] S5, forging plate: forging the four forging billets of S4, keeping them warm and air cooling them to room temperature to obtain forging plates;

[0016] S6. Post-forging heat treatment: The forged plate of S5 is heated and kept warm, water quenched to room temperature, and then heated and kept warm, and air-cooled to room temperature to obtain a finished high-Si ferrite / martensitic steel plate.

[0017] Preferably, the composition of the ingot of high Si ferrite / martensitic steel in S1 is 0.9-1.2wt.% Si, 10-11wt.% Cr, 0.1-0.2wt.% C, 0.03-0.05wt.% N, 0.75-1.25wt.% Mn, 1.5-1.8wt.% W, 0.25-0.3wt.% V, 0.01-0.02wt.% Ti, 0.1-0.15wt.% Y, 0.25-0.3wt.% Nb.

[0018] Preferably, the size of the ingot of high Si ferrite / martensitic steel in S1 is 55-60×75-80×85-90mm, the size of a forged billet is 30-32×105-115×120-127mm, the deformation is 50-60%, and the size after drawing is 55-60×75-80×85-90mm, and the deformation is 50-60%.

[0019] Preferably, the insulation temperature of the heating and insulation in S1 is 1150-1200° C., and the insulation time is 30-60 min.

[0020] Preferably, the size of the second forging billet in S2 is 55-60×75-80×85-90mm, the deformation is 50-60%, the size after drawing is 30-32×105-115×120-127mm, the deformation is 50-60%; the insulation temperature is 1150-1200℃, and the insulation time is 30-60min.

[0021] Preferably, the size of the three forging billets in S3 is 55-60×75-80×85-90mm, the deformation is 50-60%, the size after drawing is 30-32×105-115×120-127mm, the deformation is 50-60%; the insulation temperature is 1150-1200℃, and the insulation time is 30-60min.

[0022] Preferably, the size of the four forging billets in S4 is 55-60×75-80×85-90mm, the deformation is 50-60%, the size after drawing is 30-32×105-115×120-127mm, the deformation is 50-60%; the insulation temperature is 1150-1200℃, and the insulation time is 30-60min.

[0023] Preferably, the forging method in S5 is to forge the sample into a plate shape, the forging temperature is 1200-1000° C., and the size of the forged plate is 30-32×105-115×120-127 mm.

[0024] Preferably, in S6, the insulation temperature of the forged plate in S5 is 1000-1050°C for 60-90 min, and the subsequent insulation temperature is 700-750°C for 90-120 min; the microstructure of the finished high Si ferrite / martensite steel plate is 4.0-4.5% by volume of bamboo-shaped delta ferrite and 95.5-96.0% by volume of martensite.

[0025] Preferably, the room temperature properties of the finished high Si ferrite / martensitic steel plate in S6 are: tensile strength of 732-747 MPa, yield strength of 560-579 MPa, yield strength ratio of 0.76-0.78, elongation of 23.0-26.5%, strength-plastic product of 16.8-19.8 GPa·%, and V-notch Charpy impact energy of 28-31 J; high temperature performance at 650°C: tensile strength of 251-261 MPa, yield strength of 160-240 MPa, yield strength ratio of 0.61-0.96, elongation of 35.0-41.0%, and strength-plastic product of 8.8-10.7 GPa·%.

[0026] Compared with the prior art, the above technical solution has at least the following beneficial effects:

[0027] The above scheme, the present invention proposes a method for improving the toughness of high Si ferrite / martensitic steel by dispersed forging, which can solve the technical defect that the strength and toughness of high Si ferrite / martensitic steel cannot be synergistically improved at room temperature and high temperature, thereby reducing production costs and improving economic benefits.

[0028] The present invention reduces the content of delta ferrite by combining cyclic forging and heat treatment without adding any high-cost alloy elements and rare earth elements, so that the strength and toughness can be synergistically improved while maintaining corrosion resistance. The process flow is short, the efficiency is high, the organizational structure is easy to control, and the cost advantage of industrialization is very obvious.

[0029] In the cyclic forging process of the present invention, the deformation temperature is in the temperature range of the transformation from delta ferrite to austenite, and it can be ensured that no cracking occurs during the forging process; the key point is that only a small deformation amount of forging is performed, and only a short period of heat preservation is performed after forging; therefore, the cyclic forging is simple and easy to operate.

[0030] In the cyclic forging process of the present invention, the small deformation and short-time heat preservation are cyclically performed for an unlimited number of times, the more the better, and the plate is finally forged to facilitate the subsequent rolling process, so the size can be suitable for various product requirements and has a wide range of applications.

[0031] The room temperature properties of the finished high-Si ferrite / martensite steel plate of the present invention are as follows: the tensile strength is 732-747MPa, the yield strength is 560-579MPa, the yield strength ratio is 0.76-0.78, the elongation is 23.0-26.5%, the strength-ductility product is 16.8-19.8GPa·%, and the V-notch Charpy impact energy is 28-31J; the high temperature properties at 650°C are as follows: the tensile strength is 251-261MPa, the yield strength is 160-240MPa, the yield strength ratio is 0.61-0.96, the elongation is 35.0-41.0%, and the strength-ductility product is 8.8-10.7GPa·%.

[0032] In summary, compared with other traditional methods, the method of the present invention reduces the content of delta ferrite by combining cyclic forging and heat treatment; it is possible to synergistically improve the strength and toughness of high Si ferrite / martensitic steel at room temperature and high temperature while maintaining corrosion resistance, which is conducive to large-scale industrial production and promotion. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following briefly introduces the drawings required for use in the description of the embodiments. 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 creative work.

[0034] Figure 1 The present invention is a process flow chart of a method for improving the toughness of high-Si ferrite / martensitic steel by dispersed forging. DETAILED DESCRIPTION

[0035] The technical solution of the present invention is described below in conjunction with the accompanying drawings.

[0036] In the embodiments of the present invention, words such as "exemplarily" and "for example" are used to indicate examples, illustrations or explanations. Any embodiment or design described as "example" in the present invention should not be interpreted as being more preferred or more advantageous than other embodiments or designs. Specifically, the use of the word "example" is intended to present the concept in a specific way. In addition, in the embodiments of the present invention, the meaning expressed by "and / or" can be both, or it can be either of the two.

[0037] In the embodiments of the present invention, "image" and "picture" can sometimes be used interchangeably. It should be noted that when the difference between them is not emphasized, the meanings they want to express are the same. "of", "corresponding" and "corresponding" can sometimes be used interchangeably. It should be noted that when the difference between them is not emphasized, the meanings they want to express are the same.

[0038] In the embodiments of the present invention, sometimes a subscript such as W1 may be written as a non-subscript such as W1. When the difference is not emphasized, the meanings to be expressed are the same.

[0039] In order to make the technical problems, technical solutions and advantages to be solved by the present invention more clear, a detailed description will be given below with reference to the accompanying drawings and specific embodiments.

[0040] A method for improving the toughness of high Si ferrite / martensitic steel by dispersed forging, the method for improving the toughness of high Si ferrite / martensitic steel by dispersed forging comprises the following steps:

[0041] S1. Upsetting and drawing once: heating and keeping the high Si ferrite / martensitic steel ingot, upsetting and drawing once, and obtaining a forging billet after heating and keeping the heat;

[0042] S2, secondary upsetting and drawing: heating and keeping the first forged billet of S1, performing upsetting and drawing once, and obtaining the second forged billet after heating and keeping the temperature;

[0043] S3, three times of upsetting and drawing: the second forging billet of S2 is heated and kept warm, and upsetting and drawing is performed once, and the third forging billet is obtained after heating and keeping warm;

[0044] S4, four times upsetting and drawing: the three forged billets of S3 are heated and kept warm, and upsetting and drawing are performed once, and four forged billets are obtained after heating and keeping warm;

[0045] S5, forging plate: forging the four forging billets of S4, keeping them warm and air cooling them to room temperature to obtain forging plates;

[0046] S6. Post-forging heat treatment: The forged plate of S5 is heated and kept warm, water quenched to room temperature, and then heated and kept warm, and air-cooled to room temperature to obtain a finished high-Si ferrite / martensitic steel plate.

[0047] In particular, the composition of the ingot of high Si ferrite / martensitic steel in S1 is 0.9-1.2wt.% Si, 10-11wt.% Cr, 0.1-0.2wt.% C, 0.03-0.05wt.% N, 0.75-1.25wt.% Mn, 1.5-1.8wt.% W, 0.25-0.3wt.% V, 0.01-0.02wt.% Ti, 0.1-0.15wt.% Y, 0.25-0.3wt.% Nb.

[0048] In particular, the size of the ingot of S1 medium-high Si ferrite / martensitic steel is 55-60×75-80×85-90mm, the size of a forged billet is 30-32×105-115×120-127mm, the deformation is 50-60%, and the size after drawing is 55-60×75-80×85-90mm, the deformation is 50-60%.

[0049] In particular, the insulation temperature of the heating and insulation in S1 is 1150-1200° C., and the insulation time is 30-60 min.

[0050] In particular, the size of the second forging billet in S2 is 55-60×75-80×85-90mm, the deformation is 50-60%, the size after drawing is 30-32×105-115×120-127mm, the deformation is 50-60%; the holding temperature is 1150-1200℃, and the holding time is 30-60min.

[0051] In particular, the size of the three forging billets in S3 is 55-60×75-80×85-90mm, the deformation is 50-60%, and the size after drawing is 30-32×105-115×120-127mm, the deformation is 50-60%; the holding temperature is 1150-1200℃, and the holding time is 30-60min.

[0052] In particular, the size of the four forging billets in S4 is 55-60×75-80×85-90mm, the deformation is 50-60%, the size after drawing is 30-32×105-115×120-127mm, the deformation is 50-60%; the holding temperature is 1150-1200℃, and the holding time is 30-60min.

[0053] In particular, the forging method in S5 is to forge the sample into a plate shape, the forging temperature is 1200-1000°C, and the size of the forged plate is 30-32×105-115×120-127mm.

[0054] In particular, in S6, the holding temperature of the forged plate of S5 is 1000-1050°C for 60-90 min, and the subsequent holding temperature is 700-750°C for 90-120 min; the microstructure of the finished high Si ferrite / martensite steel plate is bamboo-shaped delta ferrite with a volume fraction of 4.0-4.5% and martensite with a volume fraction of 95.5-96.0%.

[0055] In particular, the room temperature properties of the finished high Si ferrite / martensitic steel plate in S6 are: tensile strength of 732-747MPa, yield strength of 560-579MPa, yield strength ratio of 0.76-0.78, elongation of 23.0-26.5%, strength-ductility product of 16.8-19.8GPa·%, and V-notch Charpy impact energy of 28-31J; high temperature performance at 650℃: tensile strength of 251-261MPa, yield strength of 160-240MPa, yield strength ratio of 0.61-0.96, elongation of 35.0-41.0%, and strength-ductility product of 8.8-10.7GPa·%.

[0056] Example 1

[0057] A method for improving the toughness of high Si ferrite / martensitic steel by dispersed forging, the method for improving the toughness of high Si ferrite / martensitic steel by dispersed forging comprises the following steps:

[0058] S1. Upsetting and drawing once: a 60×80×90mm high Si ferrite / martensitic steel ingot is heated and kept warm, and upsetting and drawing is performed once. The size of a forged billet is 32×115×127mm, the deformation is 50%, and the size after drawing is 60×80×90mm, and the deformation is 50%; wherein: the composition of the high Si ferrite / martensitic steel ingot is 1wt.%Si, 10wt.%Cr, 0.1wt.%C, 0.03wt.%N, 1wt.%Mn, 1.5wt.%W, 0.25wt.%V, 0.02wt.%Ti, 0.01wt.%Y, 0.22wt.%Nb; the holding temperature is 1200℃, and the holding time is 120min;

[0059] S2, secondary upsetting and drawing: the first forging billet of S1 is heated and kept warm, and upsetting and drawing is performed once. The size of the second forging billet after upsetting is 32×115×127mm, the deformation is 50%, and the size after drawing is 60×80×90mm, the deformation is 50%; the holding temperature is 1200℃, and the holding time is 60min;

[0060] S3, three times upsetting and drawing: the second forging billet of S2 is heated and kept warm, and upsetting and drawing is performed once. The size of the three-forging billet after upsetting is 32×115×127mm, the deformation is 50%, and the size after drawing is 60×80×90mm, the deformation is 50%; the holding temperature is 1200℃, and the holding time is 60min;

[0061] S4, four times upsetting and drawing: the three forging billets of S3 are heated and kept warm, and upsetting and drawing are performed once. The size of the four forging billets after upsetting is 32×115×127mm, the deformation is 50%, and the size after drawing is 60×80×90mm, the deformation is 50%; the holding temperature is 1200℃, and the holding time is 60min;

[0062] S5, forged plates: the four forged billets of S4 were forged in the following manner: the samples were forged into plates at a forging temperature of 1200°C, kept warm and air-cooled to room temperature, and forged plates of 32×115×127 mm were obtained;

[0063] S6, post-forging heat treatment: the forged plate of S5 is heated and kept warm, water quenched to room temperature, and then heated and kept warm and air-cooled to room temperature; the holding temperature is 1050°C, the holding time is 90 minutes, and then the holding temperature is 750°C, and the holding time is 120 minutes; the finished high Si ferrite / martensitic steel plate is obtained.

[0064] The microstructure of the finished high-Si ferrite / martensite steel plate of this embodiment is bamboo-shaped delta-ferrite with a volume fraction of 4.3% and martensite with a volume fraction of 95.7%.

[0065] The room temperature properties of the finished high-Si ferrite / martensite steel plate of this embodiment are as follows: tensile strength is 747 MPa, yield strength is 579 MPa, yield strength ratio is 0.78, elongation is 26.5%, strength-ductility product is 19.8 GPa·%, and V-notch Charpy impact energy is 31 J; high temperature properties at 650°C are as follows: tensile strength is 261 MPa, yield strength is 240 MPa, yield strength ratio is 0.96, elongation is 41.0%, and strength-ductility product is 10.7 GPa·%.

[0066] Example 2

[0067] A method for improving the toughness of high Si ferrite / martensitic steel by dispersed forging, the method for improving the toughness of high Si ferrite / martensitic steel by dispersed forging comprises the following steps:

[0068] S1. Upsetting and drawing once: a 55×75×85mm high Si ferrite / martensitic steel ingot is heated and kept warm, and upsetting and drawing is performed once. The size of a forged billet is 30×105×120mm, the deformation is 50%, and the size after drawing is 55×75×85mm, and the deformation is 50%. The composition of the high Si ferrite / martensitic steel ingot is 0.9wt.%Si, 10wt.%Cr, 0.1wt.%C, 0.03wt.%N, 0.75wt.%Mn, 1.5wt.%W, 0.25wt.%V, 0.01wt.%Ti, 0.01wt.%Y, 0.25wt.%Nb; the holding temperature is 1150℃, and the holding time is 30min;

[0069] S2, secondary upsetting and drawing: heat and keep the first forged billet of S1, and perform upsetting and drawing once. The size of the second forged billet is 30×105×120mm, the deformation is 50%, and the size after drawing is 55×75×85mm, the deformation is 50%; the holding temperature is 1150℃, and the holding time is 30min;

[0070] S3, three times upsetting and drawing: the second forging billet of S2 is heated and kept warm, and upsetting and drawing is performed once. The size of the three-forging billet is 30×105×120mm, the deformation is 50%, and the size after drawing is 55×75×85mm, the deformation is 50%; the holding temperature is 1150℃, and the holding time is 30min;

[0071] S4, four times upsetting and drawing: the three forging billets of S3 are heated and kept warm, and upsetting and drawing are performed once. The size of the four forging billets after upsetting is 30×105×120mm, the deformation is 50%, and the size after drawing is 55×75×85mm, the deformation is 50%; the holding temperature is 1150℃, and the holding time is 30min;

[0072] S5, forged plates: the four forged billets of S4 were forged in the following manner: the samples were forged into plates at a forging temperature of 1100°C and air-cooled to room temperature to obtain forged plates of 30×105×120 mm;

[0073] S6, post-forging heat treatment: the forged plate of S5 is heated and kept warm, water quenched to room temperature, and then heated and kept warm and air-cooled to room temperature; the holding temperature is 1000°C, the holding time is 60 minutes, and then the holding temperature is 700°C, and the holding time is 90 minutes; the finished high-Si ferrite / martensitic steel plate is obtained.

[0074] The microstructure of the finished high-Si ferrite / martensite steel plate of this embodiment is bamboo-shaped delta-ferrite with a volume fraction of 4.1% and martensite with a volume fraction of 95.9%.

[0075] The room temperature properties of the finished high-Si ferrite / martensitic steel plate of this embodiment are as follows: tensile strength is 732 MPa, yield strength is 560 MPa, yield strength ratio is 0.77, elongation is 23.0%, strength-ductility product is 16.8 GPa·%, and V-notch Charpy impact energy is 28 J; high temperature properties at 650°C are as follows: tensile strength is 251 MPa, yield strength is 160 MPa, yield strength ratio is 0.64, elongation is 35.0%, and strength-ductility product is 8.8 GPa·%.

[0076] Example 3

[0077] A method for improving the toughness of high Si ferrite / martensitic steel by dispersed forging, the method for improving the toughness of high Si ferrite / martensitic steel by dispersed forging comprises the following steps:

[0078] S1. Upsetting and drawing once: a 58×79×86mm high Si ferrite / martensitic steel ingot is heated and kept warm, and upsetting and drawing is performed once. The size of a forged billet after upsetting is 31×106×125mm, the deformation is 60%, and the size after upsetting is 58×79×86mm, and the deformation is 60%. The composition of the high Si ferrite / martensitic steel ingot is 1.2wt.%Si, 11wt.%Cr, 0.2wt.%C, 0.05wt.%N, 1.25wt.%Mn, 1.8wt.%W, 0.3wt.%V, 0.02wt.%Ti, 0.15wt.%Y, 0.3wt.%Nb; the holding temperature is 1150°C, and the holding time is 30min;

[0079] S2, secondary upsetting and drawing: the first forging billet of S1 is heated and kept warm, and upsetting and drawing is performed once. The size of the second forging billet after upsetting is 31×106×125mm, the deformation is 60%, and the size after drawing is 58×79×86mm, the deformation is 60%; the holding temperature is 1180℃, and the holding time is 50min;

[0080] S3, three times upsetting and drawing: the second forging billet of S2 is heated and kept warm, and upsetting and drawing is performed once. The size of the three-forging billet is 31×106×125mm, the deformation is 60%, and the size after drawing is 58×79×86mm, the deformation is 60%; the holding temperature is 1180℃, and the holding time is 50min;

[0081] S4, four times upsetting and drawing: the three forging billets of S3 are heated and kept warm, and upsetting and drawing are performed once. The size of the four forging billets after upsetting is 31×106×125mm, the deformation is 60%, and the size after drawing is 58×79×86mm, the deformation is 60%; the holding temperature is 1180℃, and the holding time is 50min;

[0082] S5, forged plate: the four forged billets of S4 were forged in the following manner: the samples were forged into plates at a forging temperature of 1180°C and air-cooled to room temperature to obtain forged plates of 31×106×125 mm;

[0083] S6, post-forging heat treatment: the forged plate of S5 is heated and kept warm, water quenched to room temperature, and then heated and kept warm and air-cooled to room temperature; the holding temperature is 1030°C, the holding time is 80 minutes, and then the holding temperature is 730°C, and the holding time is 100 minutes; the finished high Si ferrite / martensite steel plate is obtained.

[0084] The microstructure of the finished high-Si ferrite / martensite steel plate of this embodiment is bamboo-shaped delta-ferrite with a volume fraction of 4.2% and martensite with a volume fraction of 95.8%.

[0085] The room temperature properties of the finished high-Si ferrite / martensite steel plate of this embodiment are as follows: tensile strength is 740 MPa, yield strength is 570 MPa, yield strength ratio is 0.77, elongation is 26.0%, strength-ductility product is 38.5 GPa·%, and V-notch Charpy impact energy is 30 J; high temperature properties at 650°C are as follows: tensile strength is 255 MPa, yield strength is 200 MPa, yield strength ratio is 0.78, elongation is 40.0%, and strength-ductility product is 10.2 GPa·%.

[0086] Example 4

[0087] A method for improving the toughness of high Si ferrite / martensitic steel by dispersed forging, the method for improving the toughness of high Si ferrite / martensitic steel by dispersed forging comprises the following steps:

[0088] S1. Upsetting and drawing once: a 56×76×86mm high Si ferrite / martensitic steel ingot is heated and kept warm, and upsetting and drawing is performed once. The size of a forged billet after upsetting is 31×106×126mm, the deformation is 60%, and the size after upsetting is 56×76×86mm, and the deformation is 60%. The composition of the high Si ferrite / martensitic steel ingot is 1.1wt.%Si, 10.5wt.%Cr, 0.15wt.%C, 0.035wt.%N, 1wt.%Mn, 1.6wt.%W, 0.26wt.%V, 0.015wt.%Ti, 0.11wt.%Y, 0.26wt.%Nb; the holding temperature is 1160°C, and the holding time is 40min;

[0089] S2, secondary upsetting and drawing: the first forging billet of S1 is heated and kept warm, and upsetting and drawing is performed once. The size of the second forging billet after upsetting is 31×106×126mm, the deformation is 60%, and the size after drawing is 56×76×86mm, the deformation is 60%; the holding temperature is 1160℃, and the holding time is 40min;

[0090] S3, three times upsetting and drawing: the second forging billet of S2 is heated and kept warm, and upsetting and drawing is performed once. The size of the three-forging billet after upsetting is 31×106×126mm, the deformation is 60%, and the size after drawing is 56×76×86mm, the deformation is 60%; the holding temperature is 1160℃, and the holding time is 40min;

[0091] S4, four times upsetting and drawing: the three forging billets of S3 are heated and kept warm, and upsetting and drawing are performed once. The size of the four forging billets after upsetting is 31×106×126mm, the deformation is 60%, and the size after drawing is 56×76×86mm, the deformation is 60%; the holding temperature is 1160℃, and the holding time is 40min;

[0092] S5, forged plate: the four forged billets of S4 were forged in the following manner: the samples were forged into plates at a forging temperature of 1160°C and air-cooled to room temperature to obtain forged plates of 31×106×126 mm;

[0093] S6, post-forging heat treatment: the forged plate of S5 is heated and kept warm, water quenched to room temperature, and then heated and kept warm and air-cooled to room temperature; the holding temperature is 1010°C, the holding time is 70min, and then the holding temperature is 710°C, and the holding time is 110min; the finished high Si ferrite / martensite steel plate is obtained.

[0094] The microstructure of the finished high-Si ferrite / martensite steel plate of this embodiment is bamboo-shaped delta-ferrite with a volume fraction of 4.4% and martensite with a volume fraction of 95.6%.

[0095] The room temperature properties of the finished high Si ferrite / martensite steel plate of this embodiment are as follows: tensile strength is 745 MPa, yield strength is 565 MPa, yield strength ratio is 0.76, elongation is 24.0%, strength-ductility product is 17.9 GPa·%, and V-notch Charpy impact energy is 29 J; high temperature properties at 650°C are as follows: tensile strength is 256 MPa, yield strength is 210 MPa, yield strength ratio is 0.82, elongation is 36.0%, and strength-ductility product is 9.2 GPa·%.

[0096] Example 5

[0097] A method for improving the toughness of high Si ferrite / martensitic steel by dispersed forging, the method for improving the toughness of high Si ferrite / martensitic steel by dispersed forging comprises the following steps:

[0098] S1. Upsetting and drawing once: a 57×77×87mm high Si ferrite / martensitic steel ingot is heated and kept warm, and upsetting and drawing is performed once. The size of a forged billet is 30×107×122mm, the deformation is 55%, and the size after drawing is 57×77×87mm, and the deformation is 55%. Among them, the composition of the high Si ferrite / martensitic steel ingot is 1.15wt.%Si, 10wt.%Cr, 0.18wt.%C, 0.04wt.%N, 1wt.%Mn, 1.7wt.%W, 0.29wt.%V, 0.02wt.%Ti, 0.12wt.%Y, 0.33wt.%Nb; the holding temperature is 1170℃, and the holding time is 45min;

[0099] S2, secondary upsetting and drawing: the first forging billet of S1 is heated and kept warm, and upsetting and drawing is performed once. The size of the second forging billet after upsetting is 30×107×122mm, the deformation is 55%, and the size after drawing is 57×77×87mm, the deformation is 55%; the holding temperature is 1170℃, and the holding time is 45min;

[0100] S3, three times of upsetting and drawing: the second forging billet of S2 is heated and kept warm, and upsetting and drawing is performed once. The size of the three-forging billet is 30×107×122mm, the deformation is 55%, and the size after upsetting is 57×77×87mm, the deformation is 55%; the holding temperature is 1170℃, and the holding time is 45min;

[0101] S4, four times upsetting and drawing: the three forging billets of S3 are heated and kept warm, and upsetting and drawing are performed once. The size of the four forging billets after upsetting is 30×107×122mm, the deformation is 55%, and the size after drawing is 57×77×87mm, the deformation is 55%; the holding temperature is 1170℃, and the holding time is 45min;

[0102] S5, forged plate: the four forged billets of S4 were forged in the following manner: the samples were forged into plates at a forging temperature of 1170°C and air-cooled to room temperature to obtain forged plates of 30×107×122 mm;

[0103] S6, post-forging heat treatment: the forged plate of S5 is heated and kept warm, water quenched to room temperature, and then heated and kept warm and air-cooled to room temperature; the holding temperature is 1020°C, the holding time is 70 minutes, and then the holding temperature is 720°C, and the holding time is 95 minutes; the finished high Si ferrite / martensitic steel plate is obtained.

[0104] The microstructure of the finished high-Si ferrite / martensite steel plate of this embodiment is bamboo-shaped delta-ferrite with a volume fraction of 4.5% and martensite with a volume fraction of 95.5%.

[0105] The room temperature properties of the finished high-Si ferrite / martensite steel plate of this embodiment are as follows: tensile strength is 737 MPa, yield strength is 567 MPa, yield strength ratio is 0.77, elongation is 23.7%, strength-ductility product is 17.5 GPa·%, and V-notch Charpy impact energy is 28.7 J; high temperature properties at 650°C are as follows: tensile strength is 257 MPa, yield strength is 220 MPa, yield strength ratio is 0.86, elongation is 37.0%, and strength-ductility product is 9.5 GPa·%.

[0106] Example 6

[0107] A method for improving the toughness of high Si ferrite / martensitic steel by dispersed forging, the method for improving the toughness of high Si ferrite / martensitic steel by dispersed forging comprises the following steps:

[0108] S1. Upsetting and drawing once: a 59×79×89mm high Si ferrite / martensitic steel ingot is heated and kept warm, and upsetting and drawing is performed once. The size of a forged billet after upsetting is 30×109×124mm, the deformation is 55%, and the size after upsetting is 59×79×89mm, and the deformation is 55%. The composition of the high Si ferrite / martensitic steel ingot is 1wt.%Si, 10wt.%Cr, 0.1wt.%C, 0.03wt.%N, 1wt.%Mn, 1.8wt.%W, 0.25wt.%V, 0.02wt.%Ti, 0.1wt.%Y, 0.25wt.%Nb; the holding temperature is 1190°C, and the holding time is 55min;

[0109] S2, secondary upsetting and drawing: the first forging billet of S1 is heated and kept warm, and upsetting and drawing is performed once. The size of the second forging billet after upsetting is 30×109×124mm, the deformation is 55%, and the size after drawing is 59×79×89mm, the deformation is 55%; the holding temperature is 1190℃, and the holding time is 55min;

[0110] S3, three times upsetting and drawing: the second forging billet of S2 is heated and kept warm, and upsetting and drawing is performed once. The size of the three-forging billet is 30×109×124mm, the deformation is 55%, and the size after drawing is 59×79×89mm, the deformation is 55%; the holding temperature is 1190℃, and the holding time is 55min;

[0111] S4, four times upsetting and drawing: the three forging billets of S3 are heated and kept warm, and upsetting and drawing are performed once. The size of the four forging billets after upsetting is 30×109×124mm, the deformation is 55%, and the size after drawing is 59×79×89mm, the deformation is 55%; the holding temperature is 1190℃, and the holding time is 55min;

[0112] S5, forged plate: the four forged billets of S4 were forged in the following manner: the samples were forged into plates at a forging temperature of 1190°C and air-cooled to room temperature to obtain forged plates of 30×109×124 mm;

[0113] S6, post-forging heat treatment: the forged plate of S5 is heated and kept warm, water quenched to room temperature, and then heated and kept warm and air-cooled to room temperature; the holding temperature is 1040°C, the holding time is 80 minutes, and then the holding temperature is 745°C, and the holding time is 115 minutes; the finished high-Si ferrite / martensitic steel plate is obtained.

[0114] The microstructure of the finished high-Si ferrite / martensite steel plate of this embodiment is 4.0% by volume of bamboo-shaped delta-ferrite and 96.0% by volume of martensite.

[0115] The room temperature properties of the finished high Si ferrite / martensite steel plate of this embodiment are as follows: tensile strength is 744 MPa, yield strength is 577 MPa, yield strength ratio is 0.78, elongation is 25.0%, strength-ductility product is 18.6 GPa·%, and V-notch Charpy impact energy is 29.5 J; high temperature properties at 650°C are as follows: tensile strength is 255 MPa, yield strength is 235 MPa, yield strength ratio is 0.92, elongation is 39.0%, and strength-ductility product is 9.9 GPa·%.

[0116] Comparative Example 1

[0117] S1. Upsetting and drawing once: a 60×80×90 mm high Si ferrite / martensitic steel ingot is heated and kept warm at a temperature of 1200°C for 120 min; upsetting and drawing are performed once, and the size of a forged billet is 30×105×120 mm, and the size after drawing is 60×80×90 mm; wherein: the composition of the high Si ferrite / martensitic steel ingot is 1wt.%Si, 10wt.%Cr, 0.1wt.%C, 0.03wt.%N, 1wt.%Mn, 1wt.%W, 0.25wt.%V, 0.02wt.%Ti, 0.0059wt.%Y, 0.22wt.%Nb;

[0118] S2, secondary upsetting and drawing: the first forging billet of S1 is upset and drawn once, the size of the second forging billet is 30×105×120mm, and the size after drawing is 60×80×90mm;

[0119] S3, three times upsetting and drawing: the second forging billet of S2 is upset and drawn once, the size of the three forging billet is 30×105×120mm, and the size after drawing is 60×80×90mm;

[0120] S4, four times upsetting and drawing: the three-forged billet of S3 is upset and drawn once, the size of the four-forged billet after upsetting is 30×105×120mm, and the size after drawing is 60×80×90mm;

[0121] S5, forging plate: the four forging billets of S4 were forged, the forging method was to forge the sample into a plate shape, the total deformation of the forging was 50%, the forging temperature was 1200℃, and a forging plate of 30×105×120mm was obtained, which was kept warm and air-cooled to room temperature, the holding temperature was 1200℃, and the holding time was 180min;

[0122] S6. Post-forging heat treatment: the forged plate of S5 is heated and kept warm, and water quenched to room temperature, the holding temperature is 1050° C., the holding time is 90 min, and then the holding temperature is 750° C., the holding time is 120 min; and the finished high-Si ferrite / martensitic steel plate is obtained.

[0123] The microstructure of the high Si ferrite / martensite steel plate of this comparative example is 6.1% by volume of bamboo-shaped delta-ferrite and 93.9% by volume of martensite.

[0124] The room temperature properties of the finished high Si ferrite / martensite steel plate of this embodiment are as follows: tensile strength is 729 MPa, yield strength is 561 MPa, yield strength ratio is 0.77, elongation is 23.5%, strength-ductility product is 17.1 GPa·%, and V-notch Charpy impact energy is 14 J; high temperature properties at 650°C are as follows: tensile strength is 254 MPa, yield strength is 218 MPa, yield strength ratio is 0.86, elongation is 34.5%, and strength-ductility product is 8.8 GPa·%.

[0125] Comparative Example 2

[0126] S1. Upsetting and drawing once: a 60×80×90 mm high Si ferrite / martensitic steel ingot is heated and kept warm at a temperature of 1200°C for 120 min; upsetting and drawing are performed once, and the size of a forged billet is 30×105×120 mm, and the size after drawing is 60×80×90 mm; wherein: the composition of the high Si ferrite / martensitic steel ingot is 1wt.%Si, 10wt.%Cr, 0.1wt.%C, 0.03wt.%N, 1wt.%Mn, 1wt.%W, 0.25wt.%V, 0.02wt.%Ti, 0.0059wt.%Y, 0.22wt.%Nb;

[0127] S2, secondary upsetting and drawing: the first forging billet of S1 is upset and drawn once, the size of the second forging billet is 30×105×120mm, and the size after drawing is 60×80×90mm;

[0128] S3, three times upsetting and drawing: the second forging billet of S2 is upset and drawn once, the size of the three forging billet is 30×105×120mm, and the size after drawing is 60×80×90mm;

[0129] S4, four times upsetting and drawing: the three-forged billet of S3 is upset and drawn once, the size of the four-forged billet after upsetting is 30×105×120mm, and the size after drawing is 60×80×90mm;

[0130] S5, five times upsetting and drawing: the four forging billets of S4 are upset and drawn once, the size of the five forging billets after upsetting is 30×105×120mm, and the size after drawing is 60×80×90mm;

[0131] S6, six times upsetting and drawing: the five forging billets of S5 are upset and drawn once, the size of the six forging billets after upsetting is 30×105×120mm, and the size after drawing is 60×80×90mm;

[0132] S7, seven times of upsetting and drawing: the six forging billets of S6 are upset and drawn once, the size of the seven forging billets after upsetting is 30×105×120mm, and the size after drawing is 60×80×90mm;

[0133] S8, eight times of upsetting and drawing: the seven forging billets of S7 are upset and drawn once, the size of the eight forging billets after upsetting is 30×105×120mm, and the size after drawing is 60×80×90mm;

[0134] S9, forging plate: the eight forging billets of S8 were forged, the forging method was to forge the sample into a plate shape, the total forging deformation was 50%, the forging temperature was 1200°C, and a forging plate of 30×105×120mm was obtained, which was kept warm and air-cooled to room temperature, the holding temperature was 1200°C, and the holding time was 180min;

[0135] S10, post-forging heat treatment: the forged plate of S9 is heated and kept warm, and water quenched to room temperature, the holding temperature is 1050° C., the holding time is 90 min, and then the holding temperature is 750° C., the holding time is 120 min; and the finished high Si ferrite / martensitic steel plate is obtained.

[0136] The microstructure of the high Si ferrite / martensite steel plate of this comparative example is 6.5% by volume of massive delta-ferrite and 93.5% by volume of martensite.

[0137] The room temperature properties of the finished high Si ferrite / martensite steel plate of this embodiment are as follows: tensile strength is 732 MPa, yield strength is 558 MPa, yield strength ratio is 0.76, elongation is 22.0%, strength-ductility product is 16.1 GPa·%, and V-notch Charpy impact energy is 19 J; high temperature properties at 650°C are as follows: tensile strength is 252 MPa, yield strength is 214 MPa, yield strength ratio is 0.85, elongation is 55.0%, and strength-ductility product is 13.9 GPa·%.

[0138] In summary, the embodiments of the present invention have the advantage over the control examples that, when the total insulation time and the total deformation are the same, or even when the total deformation is only half of that of the control group, the impact energy of the samples treated by the present invention is twice that of the control samples without sacrificing strength.

[0139] The above scheme, the present invention proposes a method for improving the toughness of high Si ferrite / martensitic steel by dispersed forging, which can solve the technical defect that the strength and toughness of high Si ferrite / martensitic steel cannot be synergistically improved at room temperature and high temperature, thereby reducing production costs and improving economic benefits.

[0140] The present invention reduces the content of delta ferrite by combining cyclic forging and heat treatment without adding any high-cost alloy elements and rare earth elements, so that the strength and toughness can be synergistically improved while maintaining corrosion resistance. The process flow is short, the efficiency is high, the organizational structure is easy to control, and the cost advantage of industrialization is very obvious.

[0141] In the cyclic forging process of the present invention, the deformation temperature is in the temperature range of the transformation from delta ferrite to austenite, and it can be ensured that no cracking occurs during the forging process; the key point is that only a small deformation amount of forging is performed, and only a short period of heat preservation is performed after forging; therefore, the cyclic forging is simple and easy to operate.

[0142] In the cyclic forging process of the present invention, the small deformation and short-time heat preservation are cyclically performed for an unlimited number of times, the more the better, and the plate is finally forged to facilitate the subsequent rolling process, so the size can be suitable for various product requirements and has a wide range of applications.

[0143] The room temperature properties of the finished high-Si ferrite / martensite steel plate of the present invention are as follows: the tensile strength is 732-747MPa, the yield strength is 560-579MPa, the yield strength ratio is 0.76-0.78, the elongation is 23.0-26.5%, the strength-ductility product is 16.8-19.8GPa·%, and the V-notch Charpy impact energy is 28-31J; the high temperature properties at 650°C are as follows: the tensile strength is 251-261MPa, the yield strength is 160-240MPa, the yield strength ratio is 0.61-0.96, the elongation is 35.0-41.0%, and the strength-ductility product is 8.8-10.7GPa·%.

[0144] In summary, compared with other traditional methods, the method of the present invention reduces the content of delta ferrite by combining cyclic forging and heat treatment; it is possible to synergistically improve the strength and toughness of high Si ferrite / martensitic steel at room temperature and high temperature while maintaining corrosion resistance, which is conducive to large-scale industrial production and promotion.

[0145] It should be understood that the term "and / or" in this article is only a description of the association relationship of associated objects, indicating that there can be three relationships. For example, A and / or B can represent: A exists alone, A and B exist at the same time, and B exists alone. A and B can be singular or plural. In addition, the character " / " in this article generally indicates that the associated objects before and after are in an "or" relationship, but it may also indicate an "and / or" relationship. Please refer to the context for specific understanding.

[0146] In the present invention, "at least one" means one or more, and "plurality" means two or more. "At least one of the following" or similar expressions refers to any combination of these items, including any combination of single items or plural items. For example, at least one of a, b, or c can be represented by: a, b, c, ab, ac, bc, or abc, where a, b, and c can be single or multiple.

[0147] It should be understood that in various embodiments of the present invention, the size of the serial numbers of the above-mentioned processes does not mean the order of execution. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of the present invention.

[0148] The above is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any person skilled in the art can easily think of changes or substitutions within the technical scope disclosed by the present invention, which should be included in the protection scope of the present invention. Therefore, the protection scope of the present invention should be based on the protection scope of the claims.

Claims

1. A method for improving the toughness of high Si ferrite / martensitic steel by dispersed forging, characterized in that: The method for improving the toughness of high Si ferrite / martensitic steel by dispersed forging is as follows: S1. Upsetting and drawing once: heating and keeping the high Si ferrite / martensitic steel ingot, upsetting and drawing once, and obtaining a forging billet after heating and keeping the heat; S2, secondary upsetting and drawing: the first forging billet of S1 is upset and drawn once, and then heated and kept warm to obtain the second forging billet; S3, three times of upsetting and drawing: the second forging billet of S2 is upset and drawn once, and then heated and kept warm to obtain the third forging billet; S4, four times upsetting and drawing: the three forging billets of S3 are upsetting and drawing once, and then heated and kept warm to obtain four forging billets; S5, forging plate: forging the four forging billets of S4, keeping them warm and air cooling them to room temperature to obtain forging plates; S6. Post-forging heat treatment: The forged plate of S5 is heated and kept warm, water quenched to room temperature, and then heated and kept warm, and air-cooled to room temperature to obtain a finished high-Si ferrite / martensitic steel plate.

2. The method for improving the toughness of high Si ferrite / martensitic steel by dispersed forging according to claim 1, characterized in that: The composition of the ingot of S1 medium-high Si ferrite / martensitic steel is 0.9-1.2wt.% Si, 10-11wt.% Cr, 0.1-0.2wt.% C, 0.03-0.05wt.% N, 0.75-1.25wt.% Mn, 1.5-1.8wt.% W, 0.25-0.3wt.% V, 0.01-0.02wt.% Ti, 0.1-0.15wt.% Y, 0.25-0.3wt.% Nb.

3. The method for improving the toughness of high Si ferrite / martensite steel by dispersed forging according to claim 1, characterized in that: The size of the ingot of S1 medium-high Si ferrite / martensitic steel is 55-60×75-80×85-90mm, the size of a forged billet is 30-32×105-115×120-127mm, the deformation is 50-60%, and the size after drawing is 55-60×75-80×85-90mm, the deformation is 50-60%.

4. The method for improving the toughness of high Si ferrite / martensitic steel by dispersed forging according to claim 1, characterized in that: The insulation temperature of the heating and insulation in S1 is 1150-1200°C, and the insulation time is 30-60min.

5. The method for improving the toughness of high Si ferrite / martensite steel by dispersed forging according to claim 1, characterized in that: The size of the S2 forging billet is 55-60×75-80×85-90mm, the deformation is 50-60%, the size after drawing is 30-32×105-115×120-127mm, the deformation is 50-60%; the holding temperature is 1150-1200℃, and the holding time is 30-60min.

6. The method for improving the toughness of high Si ferrite / martensite steel by dispersed forging according to claim 1, characterized in that: The size of the S3 forging billet is 55-60×75-80×85-90mm, the deformation is 50-60%, the size after drawing is 30-32×105-115×120-127mm, the deformation is 50-60%; the holding temperature is 1150-1200℃, and the holding time is 30-60min.

7. The method for improving the toughness of high Si ferrite / martensite steel by dispersed forging according to claim 1, characterized in that: The size of the S4 forging billet is 55-60×75-80×85-90mm, the deformation is 50-60%, the size after drawing is 30-32×105-115×120-127mm, the deformation is 50-60%; the holding temperature is 1150-1200℃, and the holding time is 30-60min.

8. The method for improving the toughness of high Si ferrite / martensite steel by dispersed forging according to claim 1, characterized in that: The forging method in S5 is to forge the sample into a plate shape, the forging temperature is 1200-1000°C, and the size of the forged plate is 30-32×105-115×120-127mm.

9. The method for improving the toughness of high Si ferrite / martensite steel by dispersed forging according to claim 1, characterized in that: In S6, the insulation temperature of the forged plate of S5 is 1000-1050℃, the insulation time is 60-90min, and the subsequent insulation temperature is 700-750℃, and the insulation time is 90-120min; the microstructure of the finished high Si ferrite / martensite steel plate is bamboo-shaped δ-ferrite with a volume fraction of 4.0-4.5% and martensite with a volume fraction of 95.5-96.0%.

10. The method for improving the toughness of high Si ferrite / martensite steel by dispersed forging according to claim 1, characterized in that: The room temperature properties of S6 finished high Si ferrite / martensite steel plates are as follows: tensile strength is 732-747MPa, yield strength is 560-579MPa, yield strength ratio is 0.76-0.78, elongation is 23.0-26.5%, strength-ductility product is 16.8-19.8GPa·%, and V-notch Charpy impact energy is 28-31J; high temperature performance at 650℃: tensile strength is 251-261MPa, yield strength is 160-240MPa, yield strength ratio is 0.61-0.96, elongation is 35.0-41.0%, and strength-ductility product is 8.8-10.7GPa·%.

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