A forging and rolling method for improving hot-rolled edge cracking of extra-super ferritic stainless steel

Abstract

The present invention relates to the technical field of super-super ferritic stainless steel, and specifically to a forging and rolling method for improving the hot-rolled edge cracking of super-super ferritic stainless steel. In order to solve the problem that hot-rolled edge cracking is prone to occur during the rolling process of super-super ferritic stainless steel, a new forging and rolling method for improving the hot-rolled edge cracking of super-super ferritic stainless steel is provided, including melting, casting, three-stage heating of the cast billet, two rounds of forging with intermediate heating, rough rolling, heating after rough rolling, and finish rolling. The present invention is improved from two aspects of composition control and preparation process, reduces the precipitation of alumina particles, avoids the clustering of TiN and Nb(C, N) particles around the alumina particles, simultaneously inhibits the precipitation of brittle phases such as σ phase, refines the grains, improves the plasticity and toughness of the steel plate, improves the rolling performance, and the prepared hot-rolled plate of super-super ferritic stainless steel has no edge cracking phenomenon.

Description

Technical Field

[0001] The present invention relates to the technical field of super ferritic stainless steel, and specifically provides a forging and rolling method for improving the hot rolling edge cracking of super ferritic stainless steel. Background Art

[0002] Super ferritic stainless steel is a high-chromium, high-molybdenum, aluminum-containing ferritic stainless steel. Its relatively high Cr and Mo contents are the key to high corrosion resistance. The low Ni content reduces the material cost. At the same time, by adding a certain amount of Al content, the precipitation of σ and χ phases is inhibited, and the precipitation of nano-scale Laves phases is promoted to pin the grain boundaries and refine the grains. It has good corrosion resistance, mechanical properties, and thermal conductivity, and is usually used as a low-cost heat exchange material in corrosive environments, such as the super ferritic stainless steel described in the patent with publication number 115652224 B and patent name "A Super Ferritic Stainless Steel and Its Preparation Method". Although a certain amount of Al element is added to super ferritic stainless steel to reduce the σ-phase precipitation kinetics, the added Al element is likely to change the lattice constant, increase the dislocation resistance, reduce the plasticity, and at the same time, it is easy to combine with O during the melting process to precipitate alumina particles. And the alumina particles provide nucleation sites for TiN and Nb(C, N), promoting the precipitation and clustering of TiN and Nb(C, N) particles as Figure 1 shown, and during the rolling process, large particles of alumina, TiN, and Nb(C, N) will be crushed to generate microcracks, pores and other micro-defects as Figure 2 shown, and the phenomenon of hot rolling edge cracking is likely to occur as Figure 3 shown. Therefore, how to reduce the precipitation of alumina particles in the preparation process, avoid the clustering of TiN and Nb(C, N) particles around the alumina particles, inhibit the precipitation of brittle phases and refine the grains, and improve the plastic toughness of the steel plate is the key to improving the hot rolling edge cracking of super ferritic stainless steel.

[0003] Chinese Patent CN114990417A discloses a smelting method for realizing the purification and grain refinement of super ferritic stainless steel. By adding rare earth ferrosilicon manganese alloy, the purity of the molten steel is improved, the alumina inclusions are reduced, and the tendency of hot rolling cracking is reduced. However, the Al content in the steel is relatively low and only used as a deoxidizing element, and this method cannot be applied to super ferritic stainless steel. Summary of the Invention

[0004] In order to solve the problem that super ferritic stainless steel is prone to hot rolling edge cracking during the rolling process, the present invention provides a new forging and rolling method for improving the hot rolling edge cracking of super ferritic stainless steel.

[0005] The present invention is implemented by adopting the following technical solutions:

[0006] A forging and rolling method for improving the hot rolling edge cracking of super ferritic stainless steel, comprising the following steps:

[0007] 1) Melting: The weight percentages of each element in the melting raw materials are as follows: 25% ≤ Cr ≤ 30.0%, 1.5% ≤ Mo ≤ 5.5%, 1.0% ≤ Ni ≤ 4.0%, C ≤ 0.015%, N ≤ 0.015%, 0.5% ≤ Al ≤ 5.0%, 0.10% ≤ Nb ≤ 0.60%, 0.10% ≤ Ti ≤ 0.30%, Mn ≤ 0.4%, Si ≤ 0.6%, S ≤ 0.005%, P ≤ 0.005%, O ≤ 0.004%, and it satisfies Cr + 3.3×Mo ≥ 35%. The rest are Fe and inevitable impurities. After preparing the raw materials according to the above element ratios, melting is carried out to obtain molten steel; (In order to reduce the purification cost, a certain content of C and N elements is retained in the raw materials. By adding Nb and Ti elements, fine and dispersed Nb(C, N) and TiN compounds are formed to stabilize C and N elements. In order to avoid forming too many and too large Nb(C, N) and TiN compounds, C ≤ 0.015% and N ≤ 0.015% are controlled in the raw materials. In order to reduce the precipitation of alumina particles, O ≤ 0.004% is controlled)

[0008] 2) Casting: The molten steel obtained in step 1) is cast into a billet under argon protection and cooled at a cooling rate of 10 - 50 °C / min to 600 - 800 °C, and then air-cooled to room temperature; (During the casting process, argon protection is used to prevent the molten steel from reacting with elements such as O and N in the air, inhibiting the formation of alumina particles. At the same time, it is cooled to 600 - 800 °C at a relatively fast cooling rate to avoid the precipitation and cluster distribution of TiN and Nb(C, N) particles around the alumina particles)

[0009] 3) Multi-stage heating of the billet:

[0010] The first-stage heating: The billet obtained in step 2) is heated to 400 - 650 °C at a heating rate of 0.5 - 10 °C / min, and the holding time is 60 - 90 min; (In the first-stage heating, the temperature is raised slowly to ensure uniform heating of the whole billet)

[0011] The second-stage heating: The billet is heated to 1000 - 1100 °C at a heating rate ≥ 25 °C / min and held for 60 - 90 min; (In the second-stage heating, the heating temperature is raised to 1000 - 1100 °C and rapidly heated at a rate ≥ 25 °C / min to avoid the precipitation temperature range of σ and χ phases)

[0012] The third-stage heating: The billet is heated to 1180 - 1250 °C at a heating rate of 0.5 - 10 °C / min, and the holding time is 30 - 120 min; (In the third-stage heating, the heating temperature is 1180 - 1250 °C to eliminate the segregation of alloy elements such as Cr, Mo, Nb, and Al during the casting process, make the alloy elements fully dissolve and evenly distribute, and at the same time eliminate the casting stress);

[0013] 4) Forging

[0014] The heated billet obtained in step 3) is forged in multiple rounds.

[0015] The first round of forging: The starting forging temperature is 1150 - 1200 °C, and the final forging temperature is ≥1000 °C; (If the forging temperature is too high, it will cause coarse grains. If the forging temperature is too low, the deformation resistance of the forgings is too large, the plasticity is poor, and the forging is difficult).

[0016] Intermediate heating: Heat the forgings in the first round to 1100 - 1200 °C and hold for 15 - 120 min; (Intermediate heating obtains a microstructure with fine grains through recrystallization, improving the plasticity and toughness of the forgings).

[0017] The second round of forging: The starting forging temperature is 1050 - 1150 °C, the final forging temperature is ≥950 °C, and the forgings are air-cooled after forging; (If the final forging temperature is too low, the deformation resistance of the forgings is too large, and cracks are likely to appear. Air cooling slowly reduces the temperature to ensure the uniformization of the forging structure, reduces residual stress, and prevents edge cracking during subsequent hot rolling).

[0018] 5) Rough rolling

[0019] Heat the forgings obtained in step 4) to 1100 - 1200 °C, with a heating rate of ≥25 °C / min, hold for 0.5 - 3 h, and perform multi-pass rough rolling. The starting rolling temperature is 1080 - 1180 °C, the final rolling temperature is 950 - 1000 °C, the reduction rate per pass is ≥15%, and the total reduction rate is ≥50% to obtain rough rolled plates; (During the second round of forging, it is inevitable to cause segregation of interface elements and even the precipitation of intermediate phases. Therefore, during rough rolling, the forgings are first heated to dissolve the segregated Cr, Mo, Nb, Al and other elements at the interface, avoiding the precipitation of brittle phases such as Cr23C6, σ phase, χ phase, etc. At the same time, high-temperature heating enables the deformed structure formed by forging to complete recrystallization, reduces the rolling deformation resistance, improves the plasticity and toughness of the steel plate, and prevents rough rolling edge cracking; at the same time, a large number of deformation microstructures such as deformation bands and shear bands are formed through rough rolling with a large reduction rate, and the deformation energy storage is increased, providing nucleation sites and driving force for recrystallization after reheating after rough rolling).

[0020] 6) Heating after rough rolling

[0021] Heat the rough rolled plates obtained in step 5) to 1050 - 1150 °C; (Heating after rough rolling refines the grains of the rough rolling deformed structure through recrystallization, further improving the plasticity and toughness of the steel plate).

[0022] 7) Finish rolling

[0023] The rough-rolled plate after heating in step 6) is subjected to multi-pass finish rolling. The starting rolling temperature is 1000 - 1100 °C, the finishing rolling temperature is 650 - 850 °C, and the finishing rolling reduction rate is 15 - 50%. (Since the Al element inhibits the precipitation of σ and χ phases, low-temperature finish rolling can be adopted on the premise of preventing hot-rolled edge cracking. Low-temperature finish rolling forms a large-deformation structure, increases the stored energy of deformation, and refines the grains. In addition, the finish rolling temperature range is the easy precipitation range of the Laves phase. While avoiding the precipitation of Nb(C, N) particles, the excess Nb element in the steel is transformed into a beneficial nano-scale Laves phase, and then the nano-scale Laves phase is used to pin the grain boundaries to refine the grains.)

[0024] Further, in step 1), the aluminum added to the melting raw materials is granular aluminum with a particle size ≤ 5 mm. During melting, the raw materials other than the granular aluminum are first placed in the crucible of the medium-frequency induction vacuum furnace for melting at a temperature of 1600 - 1680 °C, and then cooled to 1500 - 1580 °C before adding the granular aluminum for refining to obtain the molten steel, so as to ensure the full dissolution and uniform distribution of the Al element.

[0025] Further, in step 4), the forging ratio of the first-round forging is 3 - 8 to ensure the deformation effect of the first-round forging.

[0026] The present invention controls the melting with low contents of C, N, and O impurity elements, reduces the precipitation of alumina particles, avoids the clustered precipitation of TiN and Nb(C, N) particles around the alumina particles, and makes the TiN and Nb(C, N) particles small and dispersed; in step 2), casting is carried out under argon protection to avoid the contact reaction of the molten steel with elements such as O and N in the air, inhibit the generation of alumina particles, and at the same time quickly cool to 600 - 800 °C at a faster cooling rate to avoid the precipitation and clustered distribution of TiN and Nb(C, N) particles around the alumina particles; the cast billet is heated in multiple stages in step 3) to ensure the overall uniform heating of the cast billet, and at the same time avoid the precipitation temperature range of σ and χ phases, eliminate the segregation of elements such as Cr, Mo, Nb, and Al during the casting process, and make the alloying elements fully dissolve and uniformly distribute; after heating, the cast billet is subjected to multiple rounds of forging in step 4), the forging temperature is controlled, the deformation resistance of the forgings is reduced, forging cracks are prevented, the forging efficiency is improved, after the first-round forging, secondary heating is carried out to obtain a recrystallized fine structure, the plasticity and toughness are improved, then the second-round forging is carried out, and air-cooled to room temperature to make the structure of the forgings uniform, reduce the residual stress, and prevent subsequent hot-rolled edge cracking; the forgings are heated in step 5) to dissolve the elements such as Cr, Mo, Nb, and Al that cause interface segregation due to the second-round forging, and avoid Cr 23The precipitation of brittle phases such as C6, σ-phase, and χ-phase improves the plasticity and toughness of the steel plate, prevents edge cracking during rough rolling. At the same time, a large number of deformation microstructures such as deformation bands and shear bands are formed through rough rolling with a large reduction ratio, increasing the stored energy of deformation. Then, step 6) heating after rough rolling is carried out to refine the grains of the deformed structure after rough rolling by recrystallization, further improving the plasticity and toughness of the steel plate. At the same time, the finishing rolling temperature is controlled to avoid cracking during the finishing rolling process. Finally, the rough rolled plate after heating is subjected to step 7) multi-pass finishing rolling, with low-temperature finishing rolling to form a large number of deformation structures such as shear bands and deformation bands, increasing the stored energy of deformation. Moreover, the finishing rolling temperature range is the interval where the Laves phase is prone to precipitate. While avoiding the precipitation of Nb(C, N) particles, the excess Nb element is transformed into beneficial nano-scale Laves phase.

[0027] The beneficial effects of the present invention are as follows: By controlling the impurity elements of C, N, and O, and adopting the preparation processes of melting, casting with rapid cooling afterwards, three-stage billet heating, two-round forging with intermediate heating, rough rolling, heating after rough rolling, and finishing rolling, the precipitation of alumina particles is reduced, the clustering of TiN and Nb(C, N) particles around the alumina particles is avoided, and at the same time, the precipitation of brittle phases such as σ-phase is inhibited, the grains are refined, the plasticity and toughness of the steel plate are improved, and the rolling performance is improved. The prepared hot-rolled plate of super-ferritic stainless steel has no edge cracking phenomenon, and no brittle phases such as σ-phase and χ-phase and alumina particles are observed in the steel. Only a small amount of TiN and Nb(C, N) particles are dispersed, and a large number of nano-scale Laves phases are present. Brief Description of the Drawings

[0028] The accompanying drawings here are incorporated into the specification and form a part of this specification, showing the embodiments in line with the present invention, and are used together with the specification to explain the principles of the present invention.

[0029] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the accompanying drawings required for the description of the embodiments or the prior art. Obviously, for those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0030] Figure 1 It shows the clustering phenomenon of TiN and Nb(C, N) particles in the hot-rolled plate of the existing process;

[0031] Figure 2 It shows the microcracks caused by the clustering of TiN and Nb(C, N) particles in the hot-rolled plate of the existing process;

[0032] Figure 3 It shows the physical picture of the edge cracking of the hot-rolled plate prepared by the existing process;

[0033] Figure 4 It shows the microscopic structure of the forging of the present invention;

[0034] Figure 5 The microstructure of the hot-rolled sheet of the present invention is the microstructure of hot rolling. The white phase is the nano-scale Laves phase;

[0035] Figure 6 This is the phenomenon of the dispersion distribution of TiN and Nb(C, N) particles in the hot-rolled sheet of the present invention. The black particles are TiN, and the white phase around TiN is Nb(C, N);

[0036] Figure 7 This is the physical drawing of the hot-rolled sheet prepared by the process of the present invention. Detailed implementation manners

[0037] In order to more clearly understand the above-mentioned objects, features and advantages of the present invention, the solution of the present invention will be further described below. It should be noted that, without conflict, the embodiments of the present invention and the features in the embodiments can be combined with each other.

[0038] In the description, it should be noted that the terms "first" and "second" are only used for descriptive purposes and cannot be understood as indicating or implying relative importance. It should be noted that unless otherwise clearly defined and limited, the terms "installed", "connected" and "connected" should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection or an integral connection; it can be a mechanical connection or an electrical connection; it can be directly connected or indirectly connected through an intermediate medium, and it can be the communication inside two elements. For those of ordinary skill in the art, the specific meanings of the above terms can be understood according to specific situations.

[0039] Many specific details are set forth in the following description in order to fully understand the present invention, but the present invention can also be implemented in other ways different from those described herein; obviously, the embodiments in the specification are only a part of the embodiments of the present invention, rather than all the embodiments.

[0040] The specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings. Embodiment 1

[0041] A forging and rolling method for improving the hot-rolled edge cracking of super-super ferritic stainless steel includes the following steps:

[0042] 1) Melting: The weight percentages of the elements in the melting raw materials are as follows: 30.0% Cr, 1.7% Mo, 1.0% Ni, 0.015% C, 0.015% N, 5.0% Al, 0.10% Nb, 0.30% Ti, 0.4% Mn, 0.6% Si, 0.005% S, 0.005% P, 0.004% O, and the rest are Fe and inevitable impurities. After preparing the raw materials according to the above element ratios, melting is carried out to obtain molten steel. Among them, the aluminum added in the melting raw materials is granular aluminum with a particle size ≤ 5 mm. During melting, the raw materials other than granular aluminum are first placed in the crucible of an intermediate frequency induction vacuum furnace for melting at a melting temperature of 1680 °C, then cooled to 1580 °C and then granular aluminum is added for refining to obtain molten steel to ensure that the Al element is fully dissolved and evenly distributed;

[0043] 2) Casting: The molten steel obtained in step 1) is cast into a billet under argon protection and cooled to 800 °C at a cooling rate of 10 °C / min, and then air-cooled to room temperature;

[0044] 3) Multi-stage heating of the billet:

[0045] First-stage heating: The billet obtained in step 2) is heated to 650 °C at a heating rate of 10 °C / min and held for 90 min;

[0046] Second-stage heating: The billet is heated to 1100 °C at a heating rate of 40 °C / min and held for 90 min;

[0047] Third-stage heating: The billet is heated to 1250 °C at a heating rate of 10 °C / min and held for 120 min;

[0048] 4) Forging

[0049] The heated billet obtained in step 3) is forged in multiple rounds;

[0050] First-round forging: The starting forging temperature is 1200 °C, the final forging temperature is 1050 °C, and the first-round forging ratio is 3; Intermediate heating: The first-round forgings are heated to 1200 °C and held for 120 min;

[0051] Second-round forging: The starting forging temperature is 1150 °C, the final forging temperature is 1000 °C, and the thickness is forged to 50 mm, and the forgings are air-cooled after forging to obtain forgings;

[0052] 5) Rough rolling

[0053] The forgings obtained in step 4) are heated to 1200 °C at a heating rate of 40 °C / min and held for 3 h, and multi-pass rough rolling is carried out. The starting rolling temperature is 1180 °C, the final rolling temperature is 1000 °C, the single-pass reduction rate is 15%, and the total reduction rate is 50% to obtain rough rolled plates;

[0054] 6) Post-rough rolling heating

[0055] Heat the rough rolled plate obtained in step 5) to 1150 °C;

[0056] 7) Finish rolling

[0057] Perform multi-pass finish rolling on the rough rolled plate heated in step 6), with the starting rolling temperature of 1100 °C, the final rolling temperature of 850 °C, and the final rolling reduction ratio of 50%. Example 2

[0058] A forging and rolling method for improving hot rolling edge cracking of super super ferritic stainless steel, comprising the following steps:

[0059] 1) Melting: The weight percentages of the elements in the melting raw materials are as follows: 25.0% Cr, 5.5% Mo, 4.0% Ni, 0.015% C, 0.015% N, 0.5% Al, 0.60% Nb, 0.10% Ti, 0.3% Mn, 0.5% Si, 0.005% S, 0.005% P, 0.003% O, and the rest are Fe and inevitable impurities. After preparing the raw materials according to the above element ratios, perform melting to obtain molten steel. Among them, the aluminum added in the melting raw materials is granular aluminum with a particle size ≤ 5 mm. During melting, the raw materials other than granular aluminum are first placed in the crucible of an intermediate frequency induction vacuum furnace for melting at a melting temperature of 1600 °C, and then cooled to 1500 °C and then granular aluminum is added for refining to obtain molten steel to ensure that the Al element is fully dissolved and evenly distributed;

[0060] 2) Casting: Cast the molten steel obtained in step 1) into a casting blank under argon protection, cool it at a cooling rate of 50 °C / min to 600 °C, and then air-cool it to room temperature;

[0061] 3) Multi-stage heating of the casting blank:

[0062] First-stage heating: Heat the casting blank obtained in step 2) to 400 °C at a heating rate of 0.5 °C / min and hold for 60 min;

[0063] Second-stage heating: Heat the casting blank to 1000 °C at a heating rate of 25 °C / min and hold for 60 min;

[0064] Third-stage heating: Heat the casting blank to 1180 °C at a heating rate of 0.5 °C / min and hold for 30 min;

[0065] 4) Forging

[0066] Perform multi-round forging on the heated casting blank obtained in step 3);

[0067] The first round of forging: The starting forging temperature is 1150 °C, the final forging temperature is 1000 °C, and the forging ratio in the first round is 8; Intermediate heating: Heat the forgings from the first round to 1100 °C and hold for 15 min;

[0068] The second round of forging: The starting forging temperature is 1050 °C, the final forging temperature is 950 °C, forge the thickness to 20 mm, and obtain the forgings by air cooling after forging;

[0069] 5) Rough rolling

[0070] Heat the forgings obtained in step 4) to 1100 °C at a heating rate of 25 °C / min, hold for 0.5 h, perform multi-pass rough rolling, the starting rolling temperature is 1080 °C, the final rolling temperature is 950 °C, the reduction rate per pass is 15%, and the total reduction rate is 70% to obtain rough rolled plates;

[0071] 6) Heating after rough rolling

[0072] Heat the rough rolled plates obtained in step 5) to 1050 °C;

[0073] 7) Finish rolling

[0074] Perform multi-pass finish rolling on the rough rolled plates heated in step 6), the starting rolling temperature is 1000 °C, the final rolling temperature is 650 °C, and the final rolling reduction rate is 15%. Example 3

[0075] A forging and rolling method for improving the hot rolling edge cracking of super super ferritic stainless steel, comprising the following steps:

[0076] 1) Melting: The weight percentages of the elements in the melting raw materials are: 27.5% Cr, 3.5% Mo, 2.5% Ni, 0.01% C, 0.01% N, 1.5% Al, 0.40% Nb, 0.20% Ti, 0.3% Mn, 0.5% Si, 0.005% S, 0.005% P, 0.004% O, and the rest are Fe and unavoidable impurities. After preparing the raw materials according to the above element ratios, perform melting to obtain molten steel. Among them, the aluminum added in the melting raw materials is granular aluminum with a particle size ≤ 5 mm. During melting, the raw materials other than granular aluminum are first placed in the crucible of an intermediate frequency induction vacuum furnace for melting at a melting temperature of 1650 °C, then cooled to 1550 °C and then granular aluminum is added for refining to obtain molten steel to ensure that the Al element is fully dissolved and evenly distributed;

[0077] 2) Casting: Pour the molten steel obtained in step 1) into a cast billet under argon protection, cool it to 700 °C at a cooling rate of 30 °C / min, and then air cool it to room temperature;

[0078] 3) Multi-stage heating of the cast billet

[0079] First-stage heating: Heat the billet obtained in step 2) to 500 °C at a heating rate of 2.5 °C / min and hold for 60 min;

[0080] Second-stage heating: Heat the billet to 1050 °C at a heating rate of 30 °C / min and hold for 90 min;

[0081] Third-stage heating: Heat the billet to 1200 °C at a heating rate of 5 °C / min and hold for 60 min;

[0082] 4) Forging

[0083] Perform multi-pass forging on the heated billet obtained in step 3);

[0084] First-pass forging: The starting forging temperature is 1170 °C, the final forging temperature is 1020 °C, and the forging ratio of the first pass is 4.5; Intermediate heating: Heat the first-pass forgings to 1150 °C and hold for 30 min;

[0085] Second-pass forging: The starting forging temperature is 1100 °C, the final forging temperature is 970 °C, forge to a thickness of 30 mm, and obtain forgings by air cooling after forging;

[0086] 5) Rough rolling

[0087] Heat the forgings obtained in step 4) to 1150 °C at a heating rate of 30 °C / min and hold for 2 h. Perform multi-pass rough rolling. The starting rolling temperature is 1130 °C, the final rolling temperature is 950 °C, the single-pass reduction rate is 20%, and the total reduction rate is 75% to obtain rough-rolled plates;

[0088] 6) Heating after rough rolling

[0089] Heat the rough-rolled plates obtained in step 5) to 1100 °C;

[0090] 7) Finish rolling

[0091] Perform multi-pass finish rolling on the rough-rolled plates heated in step 6). The starting rolling temperature is 1050 °C, the final rolling temperature is 700 °C, and the final rolling reduction rate is 20%.

[0092] In the above embodiments, no brittle phases such as σ and χ and alumina particles were observed in the forgings and hot-rolled plates, as shown in Figure 4 、 5 、6 (the phenomena in the three embodiments are basically the same, so a set of figures are given in this application to illustrate the experimental phenomena). Only a small amount of TiN and Nb(C, N) particles are dispersed and a large number of nano-scale Laves phases (ultra-super ferritic stainless steel uses Al element to promote the precipitation of nano-scale Laves phases to pin grain boundaries and refine grains) are present. At the same time, no hot-rolled edge cracking phenomenon occurred during the hot-rolling process, as shown in Figure 7 shown.

[0093] The above are only specific embodiments of the present invention, enabling those skilled in the art to understand or implement the present invention. Although the foregoing embodiments have been described in detail, those of ordinary skill in the art should understand that they can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements for some or all of the technical features; and these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the foregoing embodiments, and they should all be covered by the protection scope of the claims.

Claims

1. A forging and rolling method for improving hot-rolled edge cracking of super-super ferritic stainless steel, characterized in that, It includes the following steps: 1) Melting: The weight percentages of the elements in the melting raw materials are as follows: 25% ≤ Cr ≤ 30.0%, 1.5% ≤ Mo ≤ 5.5%, 1.0% ≤ Ni ≤ 4.0%, C ≤ 0.015%, N ≤ 0.015%, 0.5% ≤ Al ≤ 5.0%, 0.10% ≤ Nb ≤ 0.60%, 0.10% ≤ Ti ≤ 0.30%, Mn ≤ 0.4%, Si ≤ 0.6%, S ≤ 0.005%, P ≤ 0.005%, O ≤ 0.004%, and it satisfies Cr + 3.3×Mo ≥ 35%. The rest are Fe and inevitable impurities. After preparing the raw materials according to the above element ratios, melting is carried out to obtain molten steel. 2) Casting: The molten steel obtained in step 1) is cast into a billet under argon protection and cooled at a cooling rate of 10 - 50°C / min to 600 - 800°C, and then air-cooled to room temperature. 3) Multi-stage heating of the billet: The first-stage heating: The billet obtained in step 2) is heated to 400 - 650°C, the heating rate is 0.5 - 10°C / min, and the holding time is 60 - 90 min. The second-stage heating: The billet is heated to 1000 - 1100°C, the heating rate ≥ 25°C / min, and it is held for 60 - 90 min. The third-stage heating: The billet is heated to 1180 - 1250°C, the heating rate is 0.5 - 10°C / min, and the holding time is 30 - 120 min. 4) Forging: The heated billet obtained in step 3) is forged in multiple rounds. The first-round forging: The starting forging temperature is 1150 - 1200°C, and the final forging temperature ≥ 1000°C; Intermediate heating: The first-round forgings are heated to 1100 - 1200°C and held for 15 - 120 min. The second-round forging: The starting forging temperature is 1050 - 1150°C, the final forging temperature ≥ 950°C, and the forgings are air-cooled after forging to obtain forgings. 5) Rough rolling The forgings obtained in step 4) are heated to 1100 - 1200°C, the heating rate ≥ 25°C / min, and held for 0.5 - 3 h. Multi-pass rough rolling is adopted, the starting rolling temperature is 1080 - 1180°C, the final rolling temperature is 950 - 1000°C, the single-pass reduction rate ≥ 15%, and the total reduction rate ≥ 50% to obtain rough-rolled plates. 6) Heating after rough rolling The rough-rolled plates obtained in step 5) are heated to 1050 - 1150°C. 7) Finish rolling The rough-rolled plates heated in step 6) are subjected to multi-pass finish rolling, the starting rolling temperature is 1000 - 1100°C, the final rolling temperature is 650 - 850°C, and the final rolling reduction rate is 15 - 50%.

2. A forging and rolling method for improving hot-rolled edge cracking of super-super ferritic stainless steel according to claim 1, characterized in that, In step 1), the aluminum added to the melting raw materials is granular aluminum with a particle size ≤ 5 mm. During melting, the raw materials other than granular aluminum are first placed in the crucible of an intermediate-frequency induction vacuum furnace for melting at a melting temperature of 1600 - 1680°C, and then cooled to 1500 - 1580°C and then granular aluminum is added for refining to obtain molten steel.

3. A forging and rolling method for improving hot-rolled edge cracking of super-super ferritic stainless steel according to claim 2, characterized in that, In step 4), the forging ratio of the first-round forging is 3 - 8.

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