High-alloy heat-resistant steel and method for producing the same

Abstract

The application provides a high-alloy heat-resistant steel and a preparation method thereof. The high-alloy heat-resistant steel comprises the following chemical components in percentage by mass: C: 0.07% to 0.13%, Si: 0.20% to 0.50%, Mn: 0.30% to 0.60%, S: 0 to 0.005%, P: 0 to 0.018%, Nb: 0.040% to 0.090%, Ti: 0 to 0.01%, Cr: 8.5% to 9.5%, Mo: 0.30% to 0.60%, W: 1.50 to 2.00%, V: 0.18% to 0.25%, Al: 0 to 0.02%, N: 0.03% to 0.07%, H: 0 to 0.0015%, and the rest is Fe and inevitable impurity elements. The application reasonably selects the chemical component composition and content, so that the high-alloy heat-resistant steel can meet the use requirements of high hardness and high toughness, and has good yield.

Description

Technical Field

[0001] This application relates to the field of metallurgy, and in particular to a high-alloy heat-resistant steel and its preparation method. Background Technology

[0002] High-alloy heat-resistant steel, such as grade P92, is a type of heat-resistant steel widely used in high-temperature pressure-bearing components of ultra-supercritical thermal power generating units, such as boiler headers, main steam pipes, and reheaters, due to its excellent high-temperature strength, creep resistance, and oxidation resistance. As energy equipment develops towards higher parameters and higher efficiency, the comprehensive performance requirements for high-alloy heat-resistant steels like P92 steel plates are becoming increasingly stringent. They must not only meet the requirements for high strength and high toughness at both room and high temperatures, but also possess structural stability under long-term service conditions.

[0003] However, in the actual production process of P92 medium and heavy steel plates, there has long been a technical bottleneck that makes it difficult to simultaneously achieve both mechanical properties and yield. Therefore, improvements are urgently needed. Summary of the Invention

[0004] In view of the above problems, this application provides a high-alloy heat-resistant steel and its preparation method to solve the problem that steel plates in related technologies cannot simultaneously meet the requirements of high hardness, tensile strength and high toughness, while also taking into account the yield of high-alloy heat-resistant steel.

[0005] In a first aspect, embodiments of this application provide a high-alloy heat-resistant steel comprising the following chemical composition by mass percentage: C: 0.07%~0.13%, Si: 0.20%~0.50%, Mn: 0.30%~0.60%, S: 0~0.005%, P: 0~0.018%, Nb: 0.040%~0.090%; Ti: 0~0.01%, Cr: 8.5%~9.5%, Mo: 0.30%~0.60%, W: 1.50-2.00%; V: 0.18%~0.25%, Al: 0~0.02%, N: 0.03%~0.07%, H: 0~0.0015%, with the remainder being Fe and unavoidable impurity elements.

[0006] In some embodiments, the high-alloy heat-resistant steel comprises the following chemical composition by mass percentage: C: 0.08%~0.12%, Si: 0.20%~0.50%, Mn: 0.30%~0.60%, S: 0~0.005%, P: 0~0.018%, Nb: 0.045%~0.090%; Ti: 0~0.01%, Cr: 9.0%~9.5%, Mo: 0.30%~0.60%, W: 1.80-2.00%; V: 0.2%~0.25%, Al: 0~0.02%, N: 0.03%~0.07%, H: 0~0.0015%, with the remainder being Fe and impurity elements remaining from the smelting process.

[0007] In some embodiments, the microstructure of the high-alloy heat-resistant steel is tempered sorbite, and the grain size of the high-alloy heat-resistant steel is less than or equal to grade 7-9 according to GB / T 6394-2017.

[0008] In some embodiments, the high-alloy heat-resistant steel meets at least one of the following conditions: yield strength not less than 440 MPa; tensile strength of 620~840 MPa; elongation A50 greater than 20%; and thickness of 6~25.4 mm.

[0009] Secondly, embodiments of this application also provide a method for preparing high-alloy heat-resistant steel, which includes the following steps: Slabs are obtained by continuous casting of refined molten steel. Hot-rolled steel is obtained by hot rolling slabs. Hot-rolled steel is coiled to obtain steel coils; High-alloy heat-resistant steel is obtained by leveling and heat treatment of steel coils; The composition is as follows: C: 0.07%~0.13%, Si: 0.20%~0.50%, Mn: 0.30%~0.60%, S: 0~0.005%, P: 0~0.018%, Nb: 0.040%~0.090%; Ti: 0~0.01%, Cr: 8.5%~9.5%, Mo: 0.30%~0.60%, W: 1.50-2.00%; V: 0.18%~0.25%, Al: 0~0.02%, N: 0.03%~0.07%, H: 0~0.0015%, with the remainder being Fe and unavoidable impurity elements.

[0010] In some embodiments, hot rolling includes the following steps: Heating the slab; The heated slab is subjected to multiple passes of rough rolling and multiple passes of finish rolling. The slab heating must meet the following conditions: heating temperature is 1230℃~1270℃, heating time is 150min~250min, and solution treatment time is 28min~32min. The roughing rolling temperature is 1170~1220℃, the finishing rolling temperature is 1020~1070℃, the finishing rolling temperature is 890~950℃, and the finishing rolling thickness is 6~25.4mm.

[0011] In some embodiments, the winding temperature of the winding process is 780°C to 850°C.

[0012] In some embodiments, continuous casting is performed using peritectic steel protective slag.

[0013] In some embodiments, during continuous casting, the tundish superheat is 10~25°C.

[0014] In some embodiments, during continuous casting, the slab casting speed is 0.9~1.1 m / min.

[0015] In some embodiments, the continuous casting process is carried out at a casting rejection temperature of 30~38°C.

[0016] In some embodiments, heat treatment includes the following steps: The steel coil is cut horizontally and flat into individual steel sheets; High-alloy heat-resistant steel is obtained by normalizing and tempering a single steel plate. The normalizing treatment meets the following conditions: heating temperature is 1050℃~1070℃; holding time is 60min~80min.

[0017] In some embodiments, the tempering process meets the following conditions: the heating temperature is 760°C to 780°C; the holding time is 60 min to 80 min.

[0018] In some embodiments, prior to the step of continuously casting the refined molten steel to obtain a slab, the process further includes smelting the refined molten steel to obtain the refined molten steel, which includes the following steps: Desulfurized molten iron is obtained by desulfurization treatment of molten iron; Primary steel molten steel is obtained by smelting desulfurized hot iron in a converter. LF refining treatment is performed on primary molten steel to obtain LF refined molten steel; Refined steel liquid is obtained by subjecting LF refined steel liquid to RH vacuum treatment.

[0019] In some embodiments, the refined steel obtained by smelting satisfies at least one of the following conditions: The sulfur content of the desulfurized molten iron, expressed as a percentage by mass, shall not exceed 0.010%. The temperature at the converter argon station is greater than 1522℃; The LF refining process should take no less than 45 minutes, and the outlet temperature after LF refining should be 1595~1640℃. Calcium wire should not be fed during LF refining, and the soft blowing time should be no less than 6 minutes. The RH vacuum treatment time is 25~35min, the vacuum degree of RH vacuum treatment is no greater than 133Mpa, and the lifting gas of RH vacuum treatment is nitrogen.

[0020] The above description is only an overview of the technical solution of this application. In order to better understand the technical means of this application and to implement it in accordance with the contents of the specification, and to make the above and other objects, features and advantages of this application more obvious and understandable, the following are specific embodiments of this application. Attached Figure Description

[0021] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with this application and, together with the description, serve to explain the principles of this application.

[0022] Figure 1 Metallographic microstructure of high alloy heat-resistant steel provided in some embodiments of this application, magnified 500 times under a metallographic microscope; Figure 2 The images show the appearance of high-alloy heat-resistant steel provided in some embodiments of this application.

[0023] The accompanying drawings illustrate specific embodiments of this application, which will be described in more detail below. These drawings and descriptions are not intended to limit the scope of the concept in any way, but rather to illustrate the concept of this application to those skilled in the art through reference to particular embodiments. Detailed Implementation

[0024] To make the inventive objectives, technical solutions, and beneficial effects of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the embodiments described in this specification are merely illustrative of the invention and are not intended to limit the invention.

[0025] For simplicity, this paper only explicitly discloses some numerical ranges. However, any lower limit can be combined with any upper limit to form an undefined range; and any lower limit can be combined with other lower limits to form an undefined range, just as any upper limit can be combined with any other upper limit to form an undefined range. Furthermore, although not explicitly stated, every point or individual value between the endpoints of a range is included within that range. Therefore, each point or individual value can serve as its own lower or upper limit and be combined with any other point or individual value, or with other lower or upper limits, to form an undefined range.

[0026] In this description, it should be noted that, unless otherwise stated, "above" and "below" include the stated number, "multiple" in "one or more" means two or more, and "more than" in "one or more" means two or more.

[0027] The above description of the invention is not intended to describe every disclosed embodiment or implementation of the invention. Instead, the following description provides more specific examples of exemplary embodiments. Throughout this application, guidance is provided through a series of embodiments that can be used in various combinations. The examples listed are representative only and should not be construed as exhaustive.

[0028] In this application, "multiple" means two or more (including two).

[0029] High-alloy heat-resistant steel, represented by grade P92, has poor thermoplasticity, high deformation resistance, and an extremely narrow hot working window due to its high Cr, Mo, V, and Nb alloy content. If a lower final rolling temperature or a large reduction is used to ensure mechanical properties, it is very easy to cause edge cracks, surface cracks, or even internal delamination, significantly reducing the yield. For example, the yield of some production lines is less than 70%. Conversely, if the rolling temperature is relaxed or the reduction is reduced to improve the yield, it will lead to grain coarsening and uneven distribution of precipitates, resulting in unqualified room temperature impact toughness (such as below 68J) or unqualified high temperature creep strength.

[0030] Furthermore, high-alloy heat-resistant steels like P92 are extremely sensitive to compositional segregation. Segregation at the center of the continuously cast billet easily induces uneven microstructure, further exacerbating the risk of rolling cracking. There is also a process conflict between slow cooling for hydrogen removal after rolling and rapid cooling to suppress δ-ferrite. Existing technologies mostly alleviate these contradictions by optimizing continuous casting with light reduction, employing controlled rolling and controlled cooling (TMCP), or strengthening surface grinding, but they cannot fundamentally overcome the core challenge of "high performance versus low yield" that restricts the large-scale, low-cost manufacturing of P92 steel plates.

[0031] Therefore, there is an urgent need to develop a new method that can synergistically regulate the solidification structure, hot deformation behavior and phase transformation process of P92 steel plates, so as to significantly improve the hot rolling yield and product qualification rate while ensuring that it has good mechanical properties and microstructure requirements.

[0032] Based on this, the inventors conducted extensive research in order to provide a high-alloy heat-resistant steel that combines good mechanical properties with high yield.

[0033] The high-alloy heat-resistant steels of this application include, but are not limited to, applications in boilers, power generation, and other fields.

[0034] High-alloy heat-resistant steel In a first aspect, some embodiments of this application provide a high-alloy heat-resistant steel comprising the following chemical composition by mass percentage: C: 0.07%~0.13%, Si: 0.20%~0.50%, Mn: 0.30%~0.60%, S: 0~0.005%, P: 0~0.018%, Nb: 0.040%~0.090%; Ti: 0~0.01%, Cr: 8.5%~9.5%, Mo: 0.30%~0.60%, W: 1.50-2.00%; V: 0.18%~0.25%, Al: 0~0.02%, N: 0.03%~0.07%, H: 0~0.0015%, with the remainder being Fe and unavoidable impurity elements.

[0035] The chemical composition and content of the technical solution in this application are described in detail below.

[0036] Carbon (0.07%~0.13%): Carbon also significantly affects the microstructure of steel. When the carbon content in steel does not exceed 0.31%, lath martensite is obtained after normalizing. For steel, wear resistance is related to hardness and toughness. The hardest martensite structure has the best wear resistance. Among them, lath martensite has better strength and toughness, and also better wear resistance than plate martensite. It can balance the strength and weldability of high-alloy heat-resistant steel. Carbon content largely determines the hardness and strength of steel plates, and is also a key element determining the toughness and hardenability of steel.

[0037] If the carbon content is too high, the steel plate will have high hardness but low toughness, which is detrimental to wear resistance; if the carbon content is too low, the steel plate will have insufficient hardenability, low hardness, and insufficient wear resistance.

[0038] For example, the content of C can be 0.08%, 0.09%, 0.10%, 0.11%, 0.12%, or 0.13%.

[0039] Mn (0.3-0.6%) and Si (0.2-0.5%): Mn and Si are elements with a strong tendency to segregate. Controlling them at low levels can significantly reduce center segregation, thereby alleviating banded structure and local property inhomogeneity caused by segregation and reducing the tendency for rolling cracks.

[0040] For example, the content of Mn can be 0.30%, 0.35%, 0.40%, 0.45%, 0.50%, 0.55%, or 0.60%.

[0041] For example, the Si content can be 0.20%, 0.25%, 0.30%, 0.35%, 0.40%, 0.45%, or 0.50%.

[0042] Mo (0.30-0.60%) and W (1.50-2.00%): While ensuring high-temperature strength, the total amount of the elements with the strongest solid solution strengthening is reduced, which helps to reduce the resistance to high-temperature deformation and improve the thermal stability of modified high-alloy heat-resistant steel.

[0043] For example, the content of Mo can be 0.30%, 0.40%, 0.50%, or 0.60%.

[0044] For example, the content of W can be 1.50%, 1.80%, or 2.00%.

[0045] S (≤0.005%) and P (≤0.018%): Minimize the formation of low-melting-point brittle phases such as MnS and Fe3P at grain boundaries, avoid hot brittle cracks at grain boundaries during rolling, reduce head and tail losses, and increase yield.

[0046] For example, the content of P can be 0%, 0.005%, 0.010%, 0.015%, or 0.018%; the content of Nb can be 0.060%, 0.065%, 0.070%, 0.075%, 0.080%, 0.085%, 0.090%, 0.095%, or 0.100%.

[0047] For example, the content of S can be 0%, 0.001%, 0.002%, 0.003%, 0.004% or 0.005%.

[0048] The precise matching of Nb (0.04-0.09%) and V (0.18-0.25%), combined with N (0.03-0.07%), aims to promote the precipitation of fine, dispersed MX phases (Nb,V)(C,N) during rolling and heat treatment, rather than the premature precipitation of coarse primary phases during solidification. This helps mitigate the harmful effects of solidification segregation.

[0049] With Cr (8.5-9.5%) at the lower end of the range, and utilizing N as a strong austenite-forming element, Cr is controlled at the lower end of the nominal content of 9%, and the full utilization of N (a strong austenite stabilizer) helps to obtain a single martensitic structure, which is then tempered sorbite after tempering. This resolves the process conflict between "rapid cooling after rolling to suppress δ-ferrite" and "slow cooling to remove hydrogen".

[0050] Nb and V carbonitrides effectively pin grain boundaries during high-temperature rolling: even at relatively high final rolling temperatures, undissolved fine Nb(C,N) particles can inhibit austenite grain growth, creating conditions for obtaining fine grains (≥7 grade). This makes it possible to "appropriately relax the rolling temperature to improve yield" without causing excessive grain coarsening.

[0051] Precise C, N, V, Nb ratio: This aims to ensure that C and N combine with strong carbonitride forming elements V and Nb as much as possible to form a stable tempered sorbite phase, reducing the consumption of dissolved Cr. This can delay grain coarsening and improve microstructure stability.

[0052] For example, the content of V can be 0.18%, 0.19%, 0.20%, 0.21%, 0.22%, 0.23%, 0.24%, or 0.25%.

[0053] For example, the content of N can be 0.030%, 0.035%, 0.040%, 0.045%, 0.050%, 0.055%, 0.060%, 0.065%, or 0.070%.

[0054] For example, the Nb content can be 0.060%, 0.065%, 0.070%, 0.075%, 0.080%, 0.085%, or 0.090%.

[0055] Al (≤0.02%) and Ti (≤0.01%): These two elements are strong nitride-forming elements. Strict control over them is to protect the valuable nitrogen element for the formation of beneficial and thermally more stable (V,Nb)(C,N), rather than for the formation of coarse AlN or TiN, which improves mechanical properties while maintaining thermal stability.

[0056] For example, the Al content can be 0%, 0.005%, 0.010%, 0.015% or 0.020%.

[0057] For example, the content of Ti can be 0%, 0.002%, 0.005%, 0.008%, or 0.010%. For example, the content of Cr can be 8.0%, 8.2%, 8.5%, 8.8%, 9.0%, 9.2%, or 9.5%.

[0058] H (≤1.5 ppm): Strictly controlling the hydrogen content is the fundamental measure to prevent "hydrogen-induced cracking" and "white spots," directly reducing the risk of internal cracking, avoiding cracking caused by subsequent processes such as rolling, and improving the yield. For example, the H content can be 0%, 0.0003%, 0.0005%, 0.0008%, 0.0010%, 0.0012%, or 0.0015%. Of course, the content of each of the above elements can also be any range of values ​​within their respective ranges.

[0059] Because the carbon content is within the aforementioned range, uneven shrinkage and stress concentration during continuous casting can cause longitudinal depressions on the billet surface. In severe cases, longitudinal cracks may appear at the bottom of these depressions. If these cracks cannot be welded together during subsequent rolling, they will become internal defects in the product. Adding alloying elements to change the phase diagram: Adding austenite stabilizing elements such as Ni, Mn, and N can expand the austenite region, reduce or even eliminate the peritectic reaction zone, improve defects such as cracking, and increase the yield of high-alloy heat-resistant steel.

[0060] In some embodiments, the high-alloy heat-resistant steel comprises the following chemical composition by mass percentage: C: 0.08%~0.12%, Si: 0.20%~0.50%, Mn: 0.30%~0.60%, S: 0~0.005%, P: 0~0.018%, Nb: 0.045%~0.090%; Ti: 0~0.01%, Cr: 9.0%~9.5%, Mo: 0.30%~0.60%, W: 1.80-2.00%; V: 0.2%~0.25%, Al: 0~0.02%, N: 0.03%~0.07%, H: 0~0.0015%, with the remainder being Fe and impurity elements remaining from the smelting process. In some embodiments, the high-alloy heat-resistant steel meets the following conditions: yield strength of not less than 440 MPa, tensile strength of 620~840 MPa, elongation A50 greater than 20%, and thickness of 6~25.4 mm.

[0061] Among them, elongation A50 is specified by gauge length L0 of 50 mm. In tensile testing, gauge length L0 refers to the initial length specified on the specimen for measuring elongation deformation.

[0062] Method for producing a high-alloy heat-resistant steel Secondly, embodiments of this application provide a method for preparing the above-mentioned high-alloy heat-resistant steel, comprising the following steps: Slabs are obtained by continuous casting of refined molten steel. Hot-rolled steel is obtained by hot rolling slabs. Hot-rolled steel is coiled to obtain steel coils; High-alloy heat-resistant steel is obtained by heat treatment of steel coils; The composition is as follows: C: 0.07%~0.13%, Si: 0.20%~0.50%, Mn: 0.30%~0.60%, S: 0~0.005%, P: 0~0.018%, Nb: 0.040%~0.090%; Ti: 0~0.01%, Cr: 8.5%~9.5%, Mo: 0.30%~0.60%, W: 1.50-2.00%; V: 0.18%~0.25%, Al: 0~0.02%, N: 0.03%~0.07%, H: 0~0.0015%, with the remainder being Fe and unavoidable impurity elements.

[0063] In the technical solution of this application, the manufacturing method is simple, and the high alloy heat-resistant steel produced by using refined steel liquid with specific chemical composition and content has the advantage of high heat resistance.

[0064] In some embodiments, a low-frequency pulsed current or alternating magnetic field is applied during heating or rolling. This promotes atomic diffusion, accelerates Nb / V element homogenization, reduces the need for high-temperature diffusion annealing, improves thermal conductivity, reduces the temperature difference between the inside and outside of the slab, lowers the risk of surface overheating and core underheating, and improves microstructure uniformity, thereby increasing yield.

[0065] In some embodiments, hot rolling includes the following steps: Heating the slab; The heated slab is subjected to multiple passes of rough rolling and multiple passes of finish rolling. The slab heating must meet the following conditions: heating temperature is 1230℃~1270℃, heating time is 150min~250min, and solution treatment time is 28min~32min. The roughing rolling temperature is 1170~1220℃, the finishing rolling temperature is 1020~1070℃, the finishing rolling temperature is 890~950℃, and the finishing rolling thickness is 6~25.4mm.

[0066] For example, the heating temperature for slab heating can be 1230℃, 1233℃, 1235℃, 1237℃, 1241℃, 1245℃, 1247℃, 1250℃, 1252℃, 1255℃, 1257℃, 1260℃, 1263℃, 1265℃, 1268℃, or 1270℃. Of course, the heating temperature for slab heating can also be any combination of the above values.

[0067] For example, the heating time for slab heating can be 150 min, 155 min, 160 min, 165 min, 170 min, 175 min, 180 min, 185 min, 190 min, 195 min, 200 min, 205 min, 210 min, 215 min, 220 min, 225 min, 230 min, 235 min, 240 min, 245 min, or 250 min. Of course, the heating time for slab heating can also be any combination of the above values.

[0068] For example, the roughing rolling start temperature can be 1170℃, 1175℃, 1180℃, 1185℃, 1190℃, 1195℃, 1200℃, 1205℃, 1210℃, 1215℃, or 1220℃. Of course, the roughing rolling start temperature can also be any combination of the above values.

[0069] For example, the finishing rolling start temperature can be 1020℃, 1025℃, 1030℃, 1035℃, 1040℃, 1045℃, 1050℃, 1055℃, 1060℃, 1065℃, or 1070℃. Of course, the finishing rolling start temperature can also be any combination of the above values.

[0070] For example, the final rolling temperature can be 890℃, 895℃, 900℃, 905℃, 910℃, 915℃, 920℃, 925℃, 930℃, 935℃, 940℃, 945℃, or 950℃. Of course, the final rolling temperature can also be any combination of the above values.

[0071] For example, the final rolled thickness can be 6 mm, 7 mm, 8 mm, 9 mm, 10 mm, 11 mm, 12 mm, 13 mm, 14 mm, 15 mm, 16 mm, 17 mm, 18 mm, 19 mm, 20 mm, 21 mm, 22 mm, 23 mm, 24 mm, 25 mm, or 25.4 mm. Of course, the final rolled thickness can also be any combination of the above values.

[0072] In some embodiments, the winding temperature of the winding process is 780°C to 850°C.

[0073] According to some embodiments of this application, the winding temperature is 780~850°C.

[0074] For example, the winding temperature can be 780°C, 785°C, 790°C, 795°C, 800°C, 805°C, 810°C, 815°C, 820°C, 825°C, 830°C, 835°C, 840°C, 845°C, or 850°C. Of course, the winding temperature can also be any combination of the above values.

[0075] In some embodiments, the continuous casting process meets the following conditions: peritectic steel protective slag is used; the tundish superheat is 10~25℃; the slab casting speed is 0.9~1.1m / min; and the rejection temperature is 30~38℃, optionally 35℃.

[0076] For example, the superheat of the tundish can be 10℃, 11℃, 12℃, 13℃, 14℃, 15℃, 16℃, 17℃, 18℃, 19℃, 20℃, 21℃, 22℃, 23℃, 24℃ or 55℃. Of course, the superheat of the tundish can also be any combination of the above values.

[0077] Using low superheat casting can reduce the tendency for center segregation and cracking. At the same time, using high-performance mold mold protectant slag can form a uniform glassy or crystalline slag film on the mold wall, stabilize heat flow, reduce friction, and help the billet shell descend smoothly.

[0078] For example, the slab drawing speed can be 0.9 m / min, 0.91 m / min, 0.92 m / min, 0.93 m / min, 0.94 m / min, 0.95 m / min, 0.96 m / min, 0.97 m / min, 0.98 m / min, 0.99 m / min, 1.0 m / min, 1.01 m / min, 1.02 m / min, 1.03 m / min, 1.04 m / min, 1.05 m / min, 1.06 m / min, 1.07 m / min, 1.08 m / min, 1.09 m / min, or 1.1 m / min. Of course, the slab drawing speed can also be any combination of the above values.

[0079] By controlling the overheating within the aforementioned range and combining it with the appropriate pulling speed, compositional segregation can be reduced, avoiding localized Cr / Mo enrichment and thus relaxing the requirements for high-temperature diffusion annealing. Rough rolling is completed at the aforementioned temperature to prevent excessive grain growth caused by excessive temperatures. Tempering temperature is within the aforementioned range, with a slightly shorter time, controlled within a suitable range to promote atomic diffusion, accelerate Nb / V element homogenization, reduce the need for high-temperature diffusion annealing, improve thermal conductivity, reduce the temperature difference between the inside and outside of the slab, and lower the risk of surface overheating and core underheating.

[0080] In some embodiments, heat treatment includes the following steps: The steel coil is cut horizontally and flat into individual steel sheets; High-alloy heat-resistant steel is obtained by normalizing and tempering a single steel plate.

[0081] In some embodiments, the heating temperature for normalizing is 1050℃~1070℃; the holding time for normalizing is 60min~80min; the heating temperature for tempering is 760℃~780℃; and the holding time for tempering is 60min~80min.

[0082] According to some embodiments of this application, normalizing treatment ensures the formation of martensite, and tempering treatment produces tempered sorbite, resulting in a coarse microstructure and ensuring the high-temperature performance of the steel.

[0083] In some embodiments, prior to the step of continuously casting the refined molten steel to obtain a slab, the process further includes smelting the refined molten steel to obtain the refined molten steel, which includes the following steps: Desulfurized molten iron is obtained by desulfurization treatment of molten iron; Primary steel molten steel is obtained by smelting desulfurized hot iron in a converter. LF refining treatment is performed on primary molten steel to obtain LF refined molten steel; Refined steel liquid is obtained by subjecting LF refined steel liquid to RH vacuum treatment.

[0084] In some embodiments, the refined molten steel obtained by smelting meets the following conditions: the S content of the desulfurized hot metal is not greater than 0.010% by mass percentage; the temperature of the converter argon station is greater than 1522°C; the LF refining treatment time is not less than 45 min, and the outlet temperature after LF refining treatment is 1595~1640°C; no calcium wire is fed during LF refining treatment, and the soft blowing time is not less than 6 min; the RH vacuum treatment time is 25~35 min, the vacuum degree of RH vacuum treatment is not greater than 133 MPa, and the lifting gas for RH vacuum treatment is nitrogen.

[0085] Example The following embodiments describe the disclosure of this application in more detail. These embodiments are merely illustrative, as various modifications and variations will be apparent to those skilled in the art within the scope of the disclosure of this application. Unless otherwise stated, all parts, percentages, and ratios reported in the following embodiments are based on weight, and all reagents used in the embodiments are commercially available or synthesized by conventional methods and can be used directly without further processing, and the instruments used in the embodiments are commercially available.

[0086] Examples and Comparative Examples This embodiment or comparative example provides a high-alloy heat-resistant steel P92 with the following chemical composition by mass percentage: C: 0.07%~0.13%, Si: 0.20%~0.50%, Mn: 0.30%~0.60%, S: 0~0.005%, P: 0~0.018%, Nb: 0.040%~0.090%; Ti: 0~0.01%, Cr: 8.5%~9.5%, Mo: 0.30%~0.60%, W: 1.50-2.00%; V: 0.18%~0.25%, Al: 0~0.02%, N: 0.03%~0.07%, H: 0~0.0015%, with the remainder being Fe and unavoidable impurity elements. The steel plate has a tempered sorbite microstructure and a thickness of 6-25.4 mm.

[0087] The preparation method includes processes such as smelting, refining, continuous casting, rolling, controlled cooling, coiling, leveling, and heat treatment. The key control points are: KR desulfurization: The sulfur content must be reduced to below 0.010% before molten iron can be fed into the furnace.

[0088] Converter smelting: After converter smelting, the steel ladle is blown with argon, and the final temperature of the argon station is controlled to be greater than 1522℃.

[0089] LF refining: LF outlet temperature 1595-1640℃, refining time ≥ 45 minutes. Alloying: Add micro-chromium and vanadium-nitrogen alloy in batches. Observe the slag surface condition after adding the alloy to ensure melting. LF does not feed calcium wire, soft blowing time ≥ 6 minutes, and can only be discharged after the composition and temperature are qualified.

[0090] RH vacuum treatment: Vacuum level requirement ≤133MPa. Nitrogen gas is used throughout the RH boosting process. After the main valve is opened, the first-stage pump is started at the fastest speed. After circulating for 2 minutes, the circulation flow rate is increased to the maximum. After circulating for 10 minutes, the flow rate is reduced to the fourth-stage pump. The RH treatment time is 20-30 minutes.

[0091] Continuous casting: A conventional continuous casting machine is used, with a special peritectic steel protective slag. The casting speed is controlled at 0.9-1.1 m / min. The target superheat of the tundish is controlled between 10 and 25℃, and the rejection temperature is 35℃.

[0092] The slab is stacked and cooled to the slab warehouse, then slowly cooled to room temperature before being heated. It undergoes five roughing passes followed by seven finishing passes on a laminar flow cooling section without water cooling. After the steel coils come off the production line, they are placed in the coil warehouse for stacking and cooling.

[0093] The slab is heated to 1230-1270℃, with a heating time of 150-250 min and a solution treatment time of 30 min.

[0094] The thermomechanical controlled rolling and cooling process is as follows: the roughing rolling temperature is 1170-1220℃, the finishing rolling temperature is 1020-1070℃, the final rolling temperature is 890-950℃, the hot-rolled thickness is 6-25.4mm, and after the finishing rolling, laminar flow cooling is performed without water, and the final cooling temperature is 780-850℃ before coiling.

[0095] Heat treatment process: The steel plate is subjected to normalizing and tempering heat treatment. Normalizing temperature: 1060±10℃, holding time: 60-80min. After cooling to room temperature on the cooling bed, it is tempered at 770±10℃ and held for 60-80min. After cooling to room temperature, it is taken off the production line.

[0096] The chemical composition of the examples and comparative examples is shown in Table 1 below.

[0097] The main process parameters for the examples and comparative examples are shown in Table 2 below. Table 1 shows the mass percentage of the chemical composition of the high-alloy heat-resistant steels in each embodiment and comparative example.

[0098] Table 2 shows the main process parameters for the preparation methods of high-alloy heat-resistant steels in each embodiment and comparative example.

[0099] Test section The high-alloy heat-resistant steels prepared in the examples and comparative examples were tested. The chemical composition of the continuously cast billets prepared in the examples and comparative examples was tested according to the method of GB / T 20066-2006.

[0100] 1. Testing of the mechanical properties of high-alloy heat-resistant steel: The high-alloy heat-resistant steel prepared in the examples was tested according to GB / T228.1-2010 "Metallic materials - Tensile testing - Part 1 - Room temperature test method". Tensile tests were conducted using a German Zwick tensile testing machine with a load range of 50 to 1500 kN and a displacement speed of 2 mm / min. The tensile strength, yield strength, elongation, and other test data of the materials were obtained by computer-generated graphs. The test results are shown in Table 3.

[0101] 2. The impact energy of high alloy heat-resistant steel shall be tested in accordance with GB / T 229-2020 "Metallic Materials Charpy Pendulum Impact Test Method".

[0102] 3. Steel plates with unqualified performance or defects such as cracks at the head and tail are removed. The remaining yield is calculated as follows: 1 - (mass of steel plates with unqualified performance or defects such as cracks at the head and tail) / (total mass of steel plates produced).

[0103] The performance test results of the steel plates obtained in the examples and comparative examples are shown in Table 3 below.

[0104] Table 3 shows the performance test results of the products made from high-alloy heat-resistant steel in each embodiment and comparative example.

[0105] As can be seen from Table 3 above, the high-alloy heat-resistant steel of the embodiments of this application has both good mechanical properties and yield.

[0106] Figure 1 The image shows the metallographic structure of the high-alloy heat-resistant steel provided in some embodiments of this application, magnified 500 times under a metallographic microscope. The metallographic structure should be uniform and fine tempered sorbite, with fine and uniform grains, which is beneficial to balancing the high strength and high toughness of the high-alloy heat-resistant steel.

[0107] Figure 2 The images show the appearance of the high-alloy heat-resistant steel provided in some embodiments of this application. In the images, the steel plate has a smooth surface, no cracks, intact edges, and a regular shape, solving the problems of poor thermoplasticity, easy cracking, and low yield.

[0108] It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other.

[0109] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of this application, and they should all be covered within the scope of the claims and specification of this application.

Claims

1. A high-alloy heat-resistant steel, characterized in that, The high-alloy heat-resistant steel comprises the following chemical composition by mass percentage: C: 0.07%~0.13%, Si: 0.20%~0.50%, Mn: 0.30%~0.60%, S: 0~0.005%, P: 0~0.018%, Nb: 0.040%~0.090%; Ti: 0~0.01%, Cr: 8.5%~9.5%, Mo: 0.30%~0.60%, W: 1.50-2.00%; V: 0.18%~0.25%, Al: 0~0.02%, N: 0.03%~0.07%, H: 0~0.0015%, with the remainder being Fe and unavoidable impurity elements.

2. The high-alloy heat-resistant steel according to claim 1, characterized in that, The high-alloy heat-resistant steel comprises the following chemical composition by mass percentage: C: 0.08%~0.12%, Si: 0.20%~0.50%, Mn: 0.30%~0.60%, S: 0~0.005%, P: 0~0.018%, Nb: 0.045%~0.090%; Ti: 0~0.01%, Cr: 9.0%~9.5%, Mo: 0.30%~0.60%, W: 1.80-2.00%; V: 0.2%~0.25%, Al: 0~0.02%, N: 0.03%~0.07%, H: 0~0.0015%, with the remainder being Fe and impurity elements remaining from the smelting process.

3. The high-alloy heat-resistant steel according to claim 1, characterized in that, The microstructure of the high-alloy heat-resistant steel is tempered sorbite, and the grain size of the high-alloy heat-resistant steel is grade 7 to 9 according to GB / T 6394-2017.

4. The high-alloy heat-resistant steel according to claim 1, characterized in that, The high-alloy heat-resistant steel meets the following requirements: yield strength ≥ 440 MPa; tensile strength 620~840 MPa; elongation A50 greater than 20%; thickness 6~25.4 mm.

5. A method for preparing high-alloy heat-resistant steel, characterized in that, Includes the following steps: Slabs are obtained by continuous casting of refined molten steel. Hot-rolled steel is obtained by hot rolling slabs. Hot-rolled steel is coiled to obtain steel coils; High-alloy heat-resistant steel is obtained by leveling and heat treatment of steel coils; The high-alloy heat-resistant steel comprises the following components by mass percentage: C: 0.07%~0.13%, Si: 0.20%~0.50%, Mn: 0.30%~0.60%, S: 0~0.005%, P: 0~0.018%, Nb: 0.040%~0.090%; Ti: 0~0.01%, Cr: 8.5%~9.5%, Mo: 0.30%~0.60%, W: 1.50-2.00%; V: 0.18%~0.25%, Al: 0~0.02%, N: 0.03%~0.07%, H: 0~0.0015%, with the remainder being Fe and unavoidable impurity elements.

6. The method for preparing high-alloy heat-resistant steel according to claim 5, characterized in that, Hot rolling includes the following steps: Heating the slab; The heated slab is subjected to multiple passes of rough rolling and multiple passes of finish rolling. The slab heating must meet the following conditions: heating temperature is 1230℃~1270℃, heating time is 150min~250min, and solution treatment time is 28min~32min. The roughing rolling temperature is 1170~1220℃, the finishing rolling temperature is 1020~1070℃, the finishing rolling temperature is 890~950℃, and the finishing rolling thickness is 6~25.4mm.

7. The method for preparing high-alloy heat-resistant steel according to claim 5, characterized in that, Continuous casting processes must meet at least one of the following conditions: (1) Peritectic steel protective slag is used in the crystallizer during continuous casting; (2) Control the superheat of the tundish to be 10~25℃; (3) Control the slab drawing speed to be 0.9~1.1m / min; (4) The temperature for refusing to pour water is 30~38℃.

8. The method for preparing high-alloy heat-resistant steel according to claim 5, characterized in that, Heat treatment includes the following steps: The steel coil is cut horizontally and flat into individual steel sheets; High-alloy heat-resistant steel is obtained by normalizing and tempering a single steel plate. The normalizing treatment meets the following conditions: heating temperature is 1050℃~1070℃; holding time is 60min~80min; the tempering treatment meets the following conditions: heating temperature is 760℃~780℃; holding time is 60min~80min.

9. The method for preparing high-alloy heat-resistant steel according to claim 5, characterized in that, Before the step of continuously casting the refined molten steel to obtain a slab, the process also includes smelting to obtain refined molten steel, which includes the following steps: Desulfurized molten iron is obtained by desulfurization treatment of molten iron; Primary steel molten steel is obtained by smelting desulfurized hot iron in a converter. LF refining treatment is performed on primary molten steel to obtain LF refined molten steel; Refined steel liquid is obtained by subjecting LF refined steel liquid to RH vacuum treatment.

10. The method for preparing high-alloy heat-resistant steel according to claim 9, characterized in that, The smelting process yields refined molten steel that satisfies at least one of the following conditions: (1) The sulfur content of the desulfurized molten iron, expressed as a percentage by mass, shall not exceed 0.010%; (2) The temperature of the converter argon station is greater than 1522℃; (3) The LF refining treatment time shall not be less than 45 min, and the outlet temperature after LF refining treatment shall be 1595~1640℃. Calcium wire shall not be fed during LF refining treatment, and the soft blowing time shall not be less than 6 min. (4) The RH vacuum treatment time is 25~35min, the vacuum degree of RH vacuum treatment is no more than 133Mpa, and the lifting gas of RH vacuum treatment is nitrogen.

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