P92 low-s low-p steel ingot and forged piece, and preparation method and application thereof

Abstract

This invention provides a P92 series low-S, low-P steel ingot and forgings, as well as their preparation method and applications, belonging to the field of metallic materials technology. The preparation method of the P92 series low-S, low-P steel ingot provided by this invention includes the following steps: sequentially smelting, refining, casting, and annealing the raw materials for the P92 series low-S, low-P steel ingot to obtain the P92 series low-S, low-P steel ingot; wherein, by mass fraction, S ≤ 0.005% and P ≤ 0.015% in the P92 series low-S, low-P steel ingot. This invention controls specific smelting and refining conditions to obtain the P92 series low-S, low-P steel ingot, and the forgings prepared using it have excellent high-temperature mechanical properties.

Description

Technical Field

[0001] This invention relates to the field of metallic materials technology, and in particular to a P92 series low-S, low-P steel ingot and forging, as well as its preparation method and application. Background Technology

[0002] P92 steel is a martensitic heat-resistant stainless steel, conforming to the standard SA-335 / SA-335M. P92 steel is based on P91 steel with a reduced molybdenum content (Mo 0.30~0.60wt%), while adding a certain amount of tungsten (W 1.50~2.00wt%) and trace amounts of boron (B 0.001~0.006wt%).

[0003] P92 steel possesses excellent wear resistance, corrosion resistance, and weldability, and has been widely used in thermal power plants in recent years. However, the high-temperature mechanical properties of forgings made from P92 steel still need improvement. Summary of the Invention

[0004] The purpose of this invention is to provide a P92 series low-S, low-P steel ingot and forging, as well as a preparation method and application. Forgings prepared using the P92 series low-S, low-P steel ingot provided by this invention have excellent high-temperature mechanical properties.

[0005] To achieve the above-mentioned objectives, the present invention provides the following technical solution: This invention provides a method for preparing P92 series low-S, low-P steel ingots, comprising the following steps: The raw materials for preparing the P92 series low S and low P steel ingot are smelted, refined, cast and annealed in sequence to obtain the P92 series low S and low P steel ingot. The elemental composition of the P92 series low-S, low-P steel ingot, by mass fraction, includes C 0.07~0.13%, Si 0.20~0.40%, Mn 0.30~0.50%, P≤0.015%, S≤0.005%, Cr 8.50~9.10%, Ni 0.10~0.18%, Mo 0.30~0.50%, Nb 0.04~0.09%, N 0.04~0.07%, V 0.15~0.25%, Al≤0.015%, Cu≤0.20%, W 1.55~1.75%, B 0.001~0.006%, Ti≤0.008%, Zr≤0.008%, with the balance being Fe; The smelting process includes a melting stage, an oxidation stage, and a reduction stage in sequence. The conditions for the melting stage include: a molten pool temperature of 1550~1570℃; the addition of FeO, the mass of which is 2~4% of the mass of the molten steel; co-injection of carbon and oxygen, with an injection amount of 4~6 kg / t and a foam slag retention time of 8~10 min; The conditions for the oxidation stage include: oxygen blowing pressure of 1.3~1.7 MPa; molten pool temperature of 1650~1670℃; boiling time of molten steel of 5~7 min; and addition of Mn, wherein the mass of Mn is 0.1~0.3% of the mass of molten steel. The conditions for the reduction stage include: after slag discharge, adding thin slag material, adjusting the C mass content to 0.8~1.1%, then adding silicon-manganese alloy, ferromanganese alloy, ferrochrome alloy and nickel plate to make thin slag, and then adding reducing agent to make white slag; The refining process includes sequentially performing the VOD stage, VCD stage, VOH stage, and VD stage. The conditions for the VOD stage include: a vacuum of 80-120 mbar and an oxygen blowing rate of 450-650 m³ / h. 3 / h, Ar flow rate is 3~6m 3 / h; The conditions for the VCD stage include: a vacuum level of 1-5 mbar, a vacuuming time of 8-10 min, and an Ar flow rate of 3-6 m³ / min. 3 / h, temperature is 1620~1650℃, slag and reducing agent are added; The conditions for the VOH stage include: a vacuum of 350-450 mbar and an oxygen flow rate of 450-550 m³ / h. 3 / h, Ar flow rate is 3~6m 3 / h; The conditions for the VD stage include: vacuum degree ≤ 2.0 mbar, evacuation time 8~10 min, and Ar flow rate 4.5~6 m³ / min. 3 / h.

[0006] Preferably, the casting conditions include: molten steel calming time of 6-7 min, argon blowing rate of 5-10 L / min, casting temperature of 1540-1560℃, and casting flow rate of 1-2 t / min.

[0007] Preferably, the annealing temperature is 850~870℃ and the holding time is 0.8~1min / mm.

[0008] The present invention provides a P92 series low S and low P steel ingot prepared by the preparation method described in the above technical solution.

[0009] This invention provides a forging prepared from the P92 series low-S, low-P steel ingot described in the above technical solution.

[0010] Preferably, the forging is a tubular forging.

[0011] This invention provides a method for preparing the forging described in the above technical solution, comprising the following steps: The P92 series low S and low P steel ingots are sequentially forged, annealed, normalized and tempered, and quenched and tempered to obtain the forgings.

[0012] Preferably, the forging conditions include: initial forging temperature of 1170~1190℃, final forging temperature ≥850℃, forging ratio ≥3.0, elongation ratio ≥2.0, and total forging ratio ≥4.0.

[0013] Preferably, the normalizing and tempering treatment is further divided into quenching and tempering treatment.

[0014] This invention provides applications of the P92 series low-S, low-P steel ingots described in the above technical solutions, the forgings described in the above technical solutions, or the forgings prepared by the preparation methods described in the above technical solutions in ultra-supercritical boilers, compressed air energy storage power stations, or aerospace rockets.

[0015] Beneficial Effects: Compared with AS-335 / AS-335M P92 steel, by controlling specific smelting and refining conditions, this invention optimizes the S content from ≤0.010wt% to ≤0.005wt%, which helps reduce sulfide banding segregation, improves the purity of the steel ingot, and thus improves the grain size grade, high-temperature creep strength, operational safety, and service life of the forging products. This invention optimizes the P content from ≤0.020wt% to ≤0.015wt%, which helps reduce P segregation, ensures weld quality, and ensures the quality and service life of high-temperature equipment components. AS-335 / AS-335M P92 steel does not require testing for Ni and Cu; this invention limits the Ni content to 0.10~0.18wt% and the Cu content to ≤0.20wt%. Ni helps strengthen ferrite and refine pearlite, improving strength, while trace amounts of Cu can increase corrosion resistance and extend service life. Furthermore, this invention performs annealing after casting, which can prevent product cracking and improve product quality.

[0016] The P92 series low-S, low-P steel ingots and forgings provided by this invention belong to martensitic heat-resistant stainless steel. Forgings prepared using these P92 series low-S, low-P steel ingots possess excellent high-temperature mechanical properties, making them suitable for high-end equipment such as key components of ultra-supercritical boilers (e.g., main steam chamber pipes, reheat steam chamber pipes, flanges), key components of compressed air storage power stations (e.g., ultra-high pressure high-temperature air pipes, high-pressure main valves and regulating valves, high-temperature valve discs, valve stems), and key components of aerospace rockets (e.g., high-temperature nozzle components). They have broad application prospects in aerospace, ship propulsion, and thermal power generation. Furthermore, the P92 series low-S, low-P steel ingots and forgings provided by this invention also possess excellent corrosion resistance, high hardness, and good weldability. Detailed Implementation

[0017] This invention provides a method for preparing P92 series low-S, low-P steel ingots, comprising the following steps: The raw materials for preparing the P92 series low S and low P steel ingot are smelted, refined, cast and annealed in sequence to obtain the P92 series low S and low P steel ingot. The elemental composition of the P92 series low-S, low-P steel ingot, by mass fraction, includes C 0.07~0.13%, Si 0.20~0.40%, Mn 0.30~0.50%, P≤0.015%, S≤0.005%, Cr 8.50~9.10%, Ni 0.10~0.18%, Mo 0.30~0.50%, Nb 0.04~0.09%, N 0.04~0.07%, V 0.15~0.25%, Al≤0.015%, Cu≤0.20%, W 1.55~1.75%, B 0.001~0.006%, Ti≤0.008%, Zr≤0.008%, with the balance being Fe; The smelting process includes a melting stage, an oxidation stage, and a reduction stage in sequence. The conditions for the melting stage include: a molten pool temperature of 1550~1570℃; the addition of FeO, the mass of which is 2~4% of the mass of the molten steel; co-injection of carbon and oxygen, with an injection amount of 4~6 kg / t and a foam slag retention time of 8~10 min; The conditions for the oxidation stage include: oxygen blowing pressure of 1.3~1.7 MPa; molten pool temperature of 1650~1670℃; boiling time of molten steel of 5~7 min; and addition of Mn, wherein the mass of Mn is 0.1~0.3% of the mass of molten steel. The conditions for the reduction stage include: after slag discharge, adding thin slag material, adjusting the C mass content to 0.8~1.1%, then adding silicon-manganese alloy, ferromanganese alloy, ferrochrome alloy and nickel plate to make thin slag, and then adding reducing agent to make white slag; The refining process includes sequentially performing the VOD stage, VCD stage, VOH stage, and VD stage. The conditions for the VOD stage include: a vacuum of 80-120 mbar and an oxygen blowing rate of 450-650 m³ / h. 3 / h, Ar flow rate is 3~6m 3 / h; The conditions for the VCD stage include: a vacuum level of 1-5 mbar, a vacuuming time of 8-10 min, and an Ar flow rate of 3-6 m³ / min. 3 / h, temperature is 1620~1650℃, slag and reducing agent are added; The conditions for the VOH stage include: a vacuum of 350-450 mbar and an oxygen flow rate of 450-550 m³ / h. 3 / h, Ar flow rate is 3~6m 3 / h; The conditions for the VD stage include: vacuum degree ≤ 2.0 mbar, evacuation time 8~10 min, and Ar flow rate 4.5~6 m³ / min. 3 / h.

[0018] The present invention first describes the elemental composition of the P92 series low S and low P steel ingot.

[0019] In this invention, the elemental composition of the P92 series low S and low P steel ingot, by mass fraction, includes 0.07~0.13% C, specifically 0.07%, 0.08%, 0.09%, 0.10%, 0.11%, 0.12% or 0.13%.

[0020] In this invention, the elemental composition of the P92 series low S and low P steel ingot, by mass fraction, includes 0.20~0.40% Si, specifically 0.20%, 0.24%, 0.27%, 0.29%, 0.32%, 0.34%, 0.37% or 0.40%.

[0021] In this invention, the elemental composition of the P92 series low S and low P steel ingot, by mass fraction, includes 0.30~0.50% Mn, specifically 0.30%, 0.35%, 0.38%, 0.41%, 0.43%, 0.45%, 0.48% or 0.50%.

[0022] In this invention, the elemental composition of the P92 series low S and low P steel ingot, by mass fraction, includes P ≤ 0.015%, specifically 0.008%, 0.010%, 0.011%, 0.012%, 0.013%, 0.014% or 0.015%.

[0023] In this invention, the elemental composition of the P92 series low S and low P steel ingot, by mass fraction, includes S ≤ 0.005%, specifically 0.001%, 0.002%, 0.003%, 0.004% or 0.005%.

[0024] In this invention, the elemental composition of the P92 series low S and low P steel ingot, by mass fraction, includes 8.50~9.10% Cr, specifically 8.50%, 8.60%, 8.70%, 8.75%, 8.80%, 8.83%, 8.85%, 8.90%, 9.00% or 9.10%.

[0025] In this invention, the elemental composition of the P92 series low S and low P steel ingot, by mass fraction, includes 0.10~0.18% Ni, specifically 0.10%, 0.12%, 0.14%, 0.15%, 0.16%, 0.17% or 0.18%.

[0026] In this invention, the elemental composition of the P92 series low S and low P steel ingot, by mass fraction, includes 0.30~0.50% Mo, specifically 0.30%, 0.34%, 0.37%, 0.40%, 0.43%, 0.46% or 0.50%.

[0027] In this invention, the elemental composition of the P92 series low S and low P steel ingot, by mass fraction, includes Nb 0.04~0.09%, specifically 0.04%, 0.05%, 0.06%, 0.068%, 0.071%, 0.075%, 0.078%, 0.08% or 0.09%.

[0028] In this invention, the elemental composition of the P92 series low S and low P steel ingot, by mass fraction, includes N 0.04~0.07%, specifically 0.04%, 0.045%, 0.05%, 0.055%, 0.06% or 0.07%.

[0029] In this invention, the elemental composition of the P92 series low S and low P steel ingot, by mass fraction, includes V 0.15~0.25%, specifically 0.15%, 0.18%, 0.20%, 0.22%, 0.23% or 0.25%.

[0030] In this invention, the elemental composition of the P92 series low S and low P steel ingot, by mass fraction, includes Al ≤ 0.015%, specifically 0.005%, 0.008%, 0.010%, 0.011%, 0.012%, 0.013%, 0.014% or 0.015%.

[0031] In this invention, the elemental composition of the P92 series low-S low-P steel ingot, by mass fraction, includes Cu ≤ 0.20%, specifically 0.03%, 0.04%, 0.043%, 0.046%, 0.048%, 0.052%, 0.055%, 0.06%, 0.08%, 0.10%, 0.15%, or 0.20%.

[0032] In this invention, the elemental composition of the P92 series low S and low P steel ingot, by mass fraction, includes W 1.55~1.75%, specifically 1.55%, 1.57%, 1.59%, 1.63%, 1.67%, 1.71%, 1.73% or 1.75%.

[0033] In this invention, the elemental composition of the P92 series low-S low-P steel ingot, by mass fraction, includes 0.001~0.006% B, specifically 0.001%, 0.0015%, 0.002%, 0.0025%, 0.0028%, 0.0031%, 0.0035%, 0.004%, 0.005%, or 0.006%.

[0034] In this invention, the elemental composition of the P92 series low S and low P steel ingot, by mass fraction, includes Ti ≤ 0.008%, specifically 0.001%, 0.002%, 0.003%, 0.004%, 0.005%, 0.006%, 0.007%, or 0.008%.

[0035] In this invention, the elemental composition of the P92 series low S and low P steel ingot, by mass fraction, includes Zr ≤ 0.008%, specifically 0.001%, 0.002%, 0.003%, 0.004%, 0.005%, 0.006%, 0.007%, or 0.008%.

[0036] In this invention, the elemental composition of the P92 series low-S, low-P steel ingot, by mass fraction, includes the balance Fe.

[0037] The preparation method of the P92 series low-S, low-P steel ingot described in this invention will be described in detail below. Unless otherwise specified, all raw materials and reagents used in this invention are commercially available products well-known to those skilled in the art.

[0038] This invention involves smelting the raw materials for preparing P92 series low-S, low-P steel ingots. In this invention, the raw materials preferably include scrap steel and alloy raw materials; the scrap steel is preferably pure scrap steel with a S mass fraction ≤ 0.020% and a P mass fraction ≤ 0.020%; the type of alloy raw material is preferably selected according to the elemental composition of the P92 series low-S, low-P steel ingot, such as ferrochrome alloy, ferromanganese alloy, ferrosilicon alloy, ferronickel alloy, ferroniobium alloy, and ferromolybdenum alloy, etc.; in an embodiment of this invention, specifically, pure scrap steel with an S content ≤ 0.020 wt% and a P content ≤ 0.020 wt% and alloy raw materials are placed in an electric arc furnace (EAF) for smelting. In this invention, the smelting includes a melting stage, an oxidation stage, and a reduction stage in sequence.

[0039] In this invention, the conditions for the melting stage include: a molten pool temperature of 1550~1570℃, preferably 1560℃; the addition of FeO, wherein the mass of FeO is 2~4% of the mass of the molten steel, preferably 3%; and, preferably, carbon and oxygen co-injection at the end of the melting stage, with an injection amount of 4~6 kg / t, preferably 5 kg / t, and a foam slag holding time of 8~10 min (more preferably 9 min) to ensure that the P content is ≤0.008wt%, thus entering the oxidation stage. This invention preferably controls the amount of FeO added within the above range, which is beneficial for ensuring a high oxygen potential.

[0040] In this invention, the conditions for the oxidation stage include: an oxygen blowing pressure of 1.3~1.7 MPa, preferably 1.5 MPa; a molten pool temperature of 1650~1670℃, preferably 1660℃; a carbon removal rate preferably ≥40%; and sampling analysis satisfying a C content ≤1.0 wt%, a P content ≤0.010 wt%, and a S content ≤0.020 wt%. Mn is added after the molten steel has boiled for 5~7 min (preferably 6 min), with the mass of Mn being 0.1~0.3% of the molten steel mass, preferably 0.2%. The reduction stage begins when the C content is 0.80~1.0 wt%, the P content ≤0.010 wt%, the S content ≤0.020 wt%, and the molten steel temperature is 1670~1720℃ (preferably 1700℃).

[0041] In this invention, the conditions for the reduction stage include: after removing the slag produced in the oxidation stage, adding thin slag material and adjusting the C content to 0.8~1.1wt% (preferably 1.0wt%); then adding silicon-manganese alloy, ferromanganese alloy, ferrochrome alloy, and nickel plate; after the thin slag is formed, adding a reducing agent to form white slag; the white slag is preferably maintained for 18~23 min (more preferably 20 min), and the molten steel temperature is preferably 1670~1720℃ (more preferably 1700℃) before being transferred to the ladle; slag is skimmed from the ladle until the residual slag amount is preferably ≤1.5kg / t, and the molten steel temperature is preferably 1630~1680℃ (more preferably 1650℃) before being discharged for subsequent processes. In this invention, the thin slag material is preferably lime and fluorite; the amount of lime added is preferably 180~220kg / t, more preferably 200kg / t; the amount of fluorite added is preferably 60~80kg / t, more preferably 70kg / t. In this invention, the preferred amount of silicon-manganese alloy added is 4-6 kg / t, more preferably 5 kg / t; the preferred amount of manganese-iron alloy added is 4-6 kg / t, more preferably 5 kg / t; the preferred amount of chromium-iron alloy added is based on ensuring a Cr content of 12-14 wt% (more preferably 13 wt%); the preferred amount of nickel plate added is based on ensuring a Ni content of 4.5-5.5 wt% (more preferably 5 wt%). In this invention, the reducing agent preferably includes a first reducing agent and a second reducing agent. In this invention, the first reducing agent preferably includes ferrosilicon powder or calcium carbide; the preferred amount of ferrosilicon powder is 4-7 kg / t, more preferably 5 kg / t; the preferred amount of calcium carbide is 2-3 kg / t, more preferably 2.5 kg / t. In this invention, the second reducing agent preferably includes carbon powder or AD powder; the amount of carbon powder is preferably 0.8~1.5 kg / t, more preferably 1 kg / t; the amount of AD powder is preferably 5~8 kg / t, more preferably 6.6 kg / t.

[0042] After smelting, the molten steel obtained in this invention is refined. In an embodiment of this invention, the molten steel obtained after smelting is specifically transferred to a vacuum refining furnace (VODC) for refining. In this invention, the refining includes sequentially performing a VOD stage, a VCD stage, a VOH stage, and a VD stage.

[0043] In this invention, the conditions for the VOD stage include: a vacuum degree of 80-120 mbar, preferably 100 mbar; and an oxygen blowing rate of 450-650 m³ / h. 3 / h, preferably 550m 3 / h; Ar flow rate is 3~6m 3 / h, preferably 4~5m 3 / h.

[0044] In this invention, the conditions for the VCD stage include: a vacuum level of 1-5 mbar, preferably 3-4 mbar; a vacuuming time of 8-10 min, preferably 9 min; and an Ar flow rate of 3-6 m³ / min. 3 / h, preferably 4.5m 3 / h; temperature is 1620~1650℃, preferably 1635℃; slag and reducing agent are added; the slag is preferably lime and fluorite; the amount of lime added is preferably 18~23kg / t, more preferably 20kg / t; the amount of fluorite added is preferably 2~4kg / t, more preferably 3kg / t; the types and amounts of the reducing agent are preferably consistent with the above technical solution, and will not be repeated here. In the embodiments of the present invention, during actual operation, after adding slag and reducing agent, the present invention preferably determines whether to perform VOD stage operation again according to actual needs. If the O content in the molten steel is high, VOD stage operation is performed again. Al is added based on the calculation that each 1wt% Al added can increase the temperature by 250℃, in order to further carry out slag formation and deoxidation.

[0045] In this invention, the conditions for the VOH stage include: a vacuum degree of 350-450 mbar, preferably 400 mbar; and an oxygen flow rate of 450-550 m³ / h. 3 / h, preferably 500m 3 / h; Ar flow rate is 3~6m 3 / h, preferably 4~5m 3 / h.

[0046] In this invention, the conditions for the VD stage include: vacuum degree ≤ 2.0 mbar, preferably 1.5~1.8 mbar; evacuation time 8~10 min, preferably 9 min; Ar flow rate 4.5~6 m³ / min. 3 / h, preferably 5.5m 3 / h.

[0047] After the VD stage is completed, the present invention preferably introduces Ar into the bottom of the intermediate bale to expel air from the bale, and discharges the material in an Ar protective atmosphere for subsequent processes. Discharging the material in an Ar protective atmosphere prevents secondary oxidation.

[0048] After refining, the resulting molten steel is cast. Casting is preferably performed in an argon-protected atmosphere. Before casting, the casting system and mold are preferably inspected to ensure they are dry, free of moisture, and clean. The casting conditions include: a preferred molten steel settling time of 6-7 minutes; a preferred argon blowing rate of 5-10 L / min, more preferably 8 L / min; a preferred casting temperature of 1540-1560℃, more preferably 1550℃; and a preferred casting flow rate of 1-2 t / min, more preferably 1.5 t / min. Casting in an Ar protective atmosphere prevents secondary oxidation. After casting, in-mold cooling is preferably performed, with the in-mold cooling time preferably calculated using the formula T(h) = 35R. 2 The calculation is (m) × 1.2, where R is the radius of the steel mold, and the mold is demolded after the in-mold cooling is completed.

[0049] After casting, the resulting steel ingot is annealed to obtain the P92 series low-S, low-P steel ingot. In this invention, the annealing temperature is preferably 850~870℃, more preferably 860℃; the holding time is preferably determined according to the ingot thickness, specifically, the holding time is preferably 0.8~1 min / mm, more preferably 0.9 min / mm. This invention preferably anneals the steel ingot quickly after demolding to prevent excessive temperature drop. In embodiments of this invention, during the process of heating to the required annealing temperature, the heating rate is not particularly limited when the furnace temperature is below 400℃. Starting from 400℃, the furnace temperature is preferably heated at a rate of ≤100℃ / h (more preferably 80℃ / h) to the annealing temperature, and then annealed under holding conditions; after holding, the furnace temperature is preferably cooled to ≤450℃, and then removed from the furnace and air-cooled.

[0050] After annealing, the present invention preferably performs surface inspection and composition analysis on the obtained steel ingot to obtain a qualified product.

[0051] This invention provides a P92 series low-S, low-P steel ingot prepared by the preparation method described in the above technical solution. In the embodiments of this invention, the P92 series low-S, low-P steel ingot can specifically be an octagonal steel ingot.

[0052] This invention provides a forging prepared from the P92 series low-S, low-P steel ingot described in the above technical solution. In this invention, the forging is preferably a tubular forging.

[0053] This invention provides a method for preparing the forging described in the above technical solution, comprising the following steps: The P92 series low S and low P steel ingots are sequentially forged, annealed, normalized and tempered, and quenched and tempered to obtain the forgings.

[0054] In this invention, the P92 series low-S, low-P steel ingot is preferably subjected to blanking and heat treatment sequentially before forging. Specifically, in an embodiment of this invention, the P92 series low-S, low-P steel ingot is blanked, then heat-treated, and finally forged. In this invention, the heat treatment temperature is preferably 1170~1190℃, more preferably 1180℃; the holding time is preferably 8~10h, more preferably 9h.

[0055] In this invention, the forging conditions include: the initial forging temperature is preferably 1170~1190℃, more preferably 1180℃; the final forging temperature is preferably ≥850℃, more preferably 860℃; the cooling method is preferably furnace cooling to ≤200℃ followed by air cooling; the forging ratio is preferably ≥3.0, specifically 3.0; the elongation ratio is preferably ≥2.0, more preferably 2.2~2.5; and the total forging ratio is preferably ≥4.0, specifically 4.0.

[0056] After forging, the resulting workpiece is annealed. In this invention, the annealing temperature is preferably 820~850℃, more preferably 830℃; the holding time is preferably 8~10h, more preferably 9h; the heating rate to the annealing temperature is preferably 70~90℃ / h, more preferably 80℃ / h; after holding, it is preferably furnace cooled to ≤200℃ and then air-cooled.

[0057] After annealing, the present invention preferably performs rough machining on the resulting workpiece and uses ultrasonic testing for flaw detection, followed by normalizing and tempering treatment. In an embodiment of the present invention, after rough machining and ultrasonic testing, a workpiece (specifically a seamless steel pipe) that has passed the ultrasonic testing is obtained.

[0058] In this invention, the normalizing and tempering treatment preferably includes performing normalizing and tempering treatments sequentially. In this invention, the normalizing temperature is preferably 1040~1080℃, more preferably 1060℃. Taking the preparation of a tube forging as an example, the holding time (h) of the normalizing treatment is preferably calculated as 1h + 2h for a thickness of 25mm, specifically calculated using the following formula: t = 2 + (workpiece wall thickness / 25), where the workpiece wall thickness is in mm. Taking a workpiece wall thickness of 100mm as an example, the holding time of the normalizing treatment is specifically 6h. In this invention, the tempering temperature is preferably 760~790℃, more preferably 775℃; the holding time of the tempering treatment is preferably calculated as 1h + 2h for a thickness of 25mm (i.e., the holding time calculation method is consistent with the normalizing holding time calculation method).

[0059] In this invention, when the workpiece wall thickness is >70mm, after the normalizing and tempering treatment, a quenching and tempering treatment is preferably performed. The quenching and tempering treatment preferably includes sequential quenching and tempering. The quenching temperature is preferably 1030~1050℃, more preferably 1040℃, and the holding time is preferably 1 hour + 2 hours for every 25mm of thickness. The tempering temperature is preferably 760~790℃, more preferably 775℃, and the holding time is preferably 1 hour + 2 hours for every 25mm of thickness. In this invention, when the workpiece wall thickness is ≤70mm, after the normalizing and tempering treatment, no quenching and tempering treatment is performed; subsequent quenching and tempering treatment is performed directly.

[0060] In this invention, the conditioning process preferably includes performing a first conditioning process and a second conditioning process in sequence; the conditions for the first conditioning process include: a temperature preferably of 1040~1080℃, more preferably 1060℃, a holding time preferably of 1h + 2h based on a thickness of 25mm, and air cooling or wind cooling after the holding time is completed; the conditions for the second conditioning process include: a temperature preferably of 730~780℃, more preferably 750℃, a holding time preferably of 1h + 2h based on a thickness of 25mm, and air cooling after the holding time is completed.

[0061] After the heat treatment, the present invention preferably performs physical and chemical property testing and dimensional testing on the obtained workpiece to obtain a qualified product.

[0062] This invention provides applications of the P92 series low-S, low-P steel ingots, forgings, or forgings prepared by the methods described above in ultra-supercritical boilers, compressed air storage power stations, or aerospace rockets. Specifically, the P92 series low-S, low-P steel ingots and forgings described in this invention can be used as high-temperature resistant core forgings and fittings in ultra-supercritical boilers, compressed air storage power stations, or aerospace rockets. In this invention, the ultra-supercritical boiler is preferably a 660-1350MW ultra-supercritical boiler, specifically a large-scale clean coal-fired 660-1350MW ultra-supercritical boiler; the P92 series low-S, low-P steel ingots or forgings described in this invention are preferably used in key components of the ultra-supercritical boiler, and these key components preferably include main steam chamber pipes, reheat steam chamber pipes, or flanges. In this invention, the compressed air energy storage power station is preferably a 300-350MW compressed air energy storage power station; the P92 series low-S, low-P steel ingots or forgings of this invention are preferably used for key components of the compressed air energy storage power station, and the key components preferably include ultra-high pressure and high-temperature resistant air pipes, high-pressure main valves and regulating valves, and high-temperature resistant valve discs or valve stems. In this invention, the P92 series low-S, low-P steel ingots or forgings are preferably used for key components of aerospace rockets, and the key components preferably include high-temperature resistant nozzle components. In this invention, the operating temperature of the forgings is preferably no more than 620℃, specifically 610-620℃.

[0063] The technical solutions of this invention will be clearly and completely described below with reference to the embodiments thereof. Obviously, the described embodiments are only a part of the embodiments of this invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0064] The testing methods used in the following experiments include: GB / 222 for permissible deviations in the chemical composition of finished steel products; GB / T223 for chemical composition analysis methods of steel and alloys; GB / T226 for acid etching inspection of low-magnification microstructure and defects of steel; GB / T2975 for sampling location and sample preparation of mechanical property test specimens of steel and steel products; GB / 16394 for testing the average grain size of metals; GB / T10561 for the standard rating chart microscopic inspection method for determining the content of non-metallic inclusions in steel; and GB / T11170 for the spark atomic emission spectrometry (conventional method) for measuring the multi-element content of stainless steel.

[0065] The mechanical property testing methods in the following experimental process include: The room temperature tensile test method follows GB / T228.1, specifically using a Φ5mm standard specimen, a WE-300 tensile testing machine, and a test temperature of 25℃ to determine the tensile strength Rm and yield strength R of the material.P0.2 The four indicators are elongation at break (A) and reduction of area (Z); the impact performance is tested according to the Charpy pendulum impact test method for metallic materials in GB / T 229-2020; the high-temperature mechanical properties of the forgings are tested for compressive strength and creep strength (MPa) according to GB / T8732-2014 standard, the grading method for strength grades QT1 and QT2 is adopted according to EN10269-2006, and the high-temperature performance data are from EN10269-2006 and DIN17240-1976.

[0066] Comparative Example 1 The chemical composition of the SA-335 / SA-335M P92 steel ingot (denoted as P92 steel ingot) is shown in Table 1.

[0067] Example 1 The chemical composition of the steel ingot in this embodiment is shown in Table 1, and the specific preparation method is as follows: (1) Pure scrap steel and alloy raw materials (such as ferrochrome alloy, ferromanganese alloy, ferrosilicon alloy, ferronickel alloy, ferroniobium alloy, ferromolybdenum alloy, etc.) with S content ≤ 0.020wt% and P content ≤ 0.020wt% are placed in an electric arc furnace (EAF) for smelting, the smelting including the melting stage, oxidation stage and reduction stage in sequence; The conditions for the melting stage include: a molten pool temperature of 1560℃; the addition of FeO, the mass of which is 3% of the mass of the molten steel; and the implementation of carbon and oxygen co-injection at the end of the melting stage, with an injection rate of 5 kg / t, and maintaining the foamy slag for 9 minutes to ensure that the P content is ≤0.008 wt%, before entering the oxidation stage. The conditions for the oxidation stage include: oxygen blowing pressure of 1.5 MPa, molten pool temperature of 1660℃, carbon removal ≥40%, and sampling analysis meeting the following requirements: C content ≤1.0 wt%, P content ≤0.010 wt%, and S content ≤0.020 wt%. Mn is added after the molten steel boils for 6 minutes, and the mass of Mn is 0.2% of the molten steel mass. When the C content is 0.80~1.0 wt%, P content ≤0.010 wt%, S content ≤0.020 wt%, and the molten steel temperature is 1700℃, the reduction stage begins. The conditions for the reduction stage include: after removing the slag produced in the oxidation stage, adding thin slag material (specifically 200 kg / t of lime and 70 kg / t of fluorite), adjusting the C content to 1.0 wt%, then adding 5 kg / t of ferromanganese alloy, 5 kg / t of ferromanganese alloy, ferrochrome alloy (the amount added is based on ensuring a Cr content of 13 wt%) and nickel plate (the amount added is based on ensuring a Ni content of 5 wt%). After the thin slag is formed, adding a reducing agent (specifically 5 kg / t of ferrosilicon powder and 1 kg / t of carbon powder) to form white slag, maintaining the white slag for 20 minutes, transferring it to the ladle when the molten steel temperature is 1700℃, removing slag from the ladle until the residual slag amount is ≤1.5 kg / t, and discharging the material when the molten steel temperature is 1650℃. (2) The molten steel obtained after smelting at a temperature of 1650°C is transferred into a vacuum refining furnace (VODC) for refining, wherein the refining includes sequentially performing the VOD stage, VCD stage, VOH stage and VD stage; The conditions for the VOD stage include: a vacuum of 100 mbar and an oxygen blowing rate of 550 m³ / h. 3 / h, Ar flow rate is 4m 3 / h; The conditions for the VCD stage include: a vacuum level of 3 mbar, a vacuuming time of 9 min, and an Ar flow rate of 4.5 m³ / min. 3 / h; then take samples to measure the temperature. When the temperature of the molten steel is 1635℃, add slag (specifically 20kg / t of lime and 3kg / t of fluorite) and reducing agent (specifically 5kg / t of ferrosilicon powder and 1kg / t of carbon powder). The conditions for the VOH stage include: a vacuum of 400 mbar and an oxygen flow rate of 500 m³ / h. 3 / h, Ar flow rate is 4m 3 / h; The conditions for the VD stage include: a vacuum level of 1.5 mbar, a evacuation time of 9 min, and an Ar flow rate of 5.5 m³ / min. 3 / h; After the VD stage is completed, Ar is introduced through the bottom of the intermediate ladle to expel the air inside the ladle, and the material is discharged in an Ar protective atmosphere to prevent secondary oxidation. (3) Before casting, check the casting system and steel mold to ensure they are dry, free of moisture, clean, and free of contamination. Cast the refined molten steel. The casting conditions include: molten steel calming time of 6 min, argon blowing rate of 8 L / min, casting temperature of 1550℃, and casting flow rate of 1.5 t / min. After casting, perform in-mold cooling. The in-mold cooling time is calculated according to the formula T(h) = 35R. 2 Calculate using (m) × 1.2, where R is the radius of the steel mold, and the mold is demolded after cooling inside the mold. (4) Anneal the steel ingot obtained after demolding. The annealing conditions include: the furnace temperature is below 400℃ and the heating rate is not specifically limited. The furnace temperature starts from 400℃ and is heated to 860℃ at a heating rate of 80℃ / h. The holding time is 0.9min / mm (the specific time is determined according to the thickness of the steel ingot). After the holding time is completed, the furnace is cooled to ≤450℃ and then air-cooled to obtain the steel ingot.

[0068] Example 2 The chemical composition of the steel ingot in this embodiment is shown in Table 1, and the specific preparation method is as described in Example 1.

[0069] Example 3 The chemical composition of the steel ingot in this embodiment is shown in Table 1, and the specific preparation method is as described in Example 1.

[0070] Table 1 Chemical composition of steel ingots in Examples 1-3 and Comparative Example 1

[0071] Example 4 The tube forgings were prepared using the steel ingot from Example 1, and the specific preparation method is as follows: (1) The steel ingot is blanked and then heated to 1180°C and held for 9 hours. Then it is forged (expanded). The forging conditions include: initial forging temperature of 1180°C, final forging temperature of 860°C, cooling method of furnace cooling to ≤200°C and air cooling after exiting the furnace, forging ratio of 3.0, elongation ratio of 2.5, and total forging ratio of 4.0. (2) Anneal the workpiece obtained after forging. The annealing conditions include: heating from room temperature to 830°C at a heating rate of 80°C / h and holding for 9 hours; after holding, furnace cooling to ≤200°C and air cooling. (3) The workpiece obtained after annealing is rough machined and then tested by ultrasonic testing; (4) The workpiece that has passed the ultrasonic flaw detection shall be subjected to normalizing and tempering treatment. The normalizing and tempering treatment includes normalizing and tempering treatment in sequence. The normalizing temperature is 1060℃ and the holding time is 1h + 2h for a thickness of 25mm. The tempering temperature is 775℃ and the holding time is 1h + 2h for a thickness of 25mm. When the workpiece wall thickness is >70mm, after the normalizing and tempering treatment, a quenching and tempering treatment is performed. The quenching and tempering treatment includes quenching and tempering treatment sequentially. The quenching temperature is 1040℃, and the holding time is 1 hour for every 25mm of thickness plus 2 hours. The tempering temperature is 775℃, and the holding time is 1 hour for every 25mm of thickness plus 2 hours. When the workpiece wall thickness is ≤70mm, after the normalizing and tempering treatment is completed, no quenching and tempering treatment is performed, and the subsequent processes are carried out directly. (5) The workpiece obtained in step (4) is subjected to quenching and tempering treatment, which includes performing a first quenching and tempering treatment and a second quenching and tempering treatment in sequence. The conditions for the first quenching and tempering treatment include: a temperature of 1060℃, a holding time of 1h plus 2h for a thickness of 25mm, and air cooling after the holding time. The conditions for the second quenching and tempering treatment include: a temperature of 750℃, a holding time of 1h plus 2h for a thickness of 25mm, and air cooling after the holding time, to obtain the tube forging.

[0072] Example 5 The steel ingots in Example 2 were used to prepare the tube forgings, and the specific preparation method is the same as in Example 4.

[0073] Example 6 The steel ingots in Example 3 were used to prepare the tube forgings, and the specific preparation method is the same as in Example 4.

[0074] Test Example 1 The room temperature mechanical properties of the steel ingots in Comparative Example 1 and Examples 1-3 were tested, and the specific results are shown in Table 2.

[0075] Table 2. Room temperature mechanical property test results of steel ingots in Comparative Example 1 and Examples 1-3

[0076] Test Example 2 The high-temperature mechanical properties of the tube forgings in Examples 4-6 were tested, and the specific results are shown in Table 3.

[0077] Table 3. High-temperature mechanical property test results of tube forgings in Examples 4-6

[0078] The test results above show that the P92 series low-S, low-P steel ingot provided by this invention, compared with the original P92 steel ingot, has an optimized S content from ≤0.010% to ≤0.005%, which can reduce sulfide inclusions and eliminate sulfide banding segregation; the P content is optimized from ≤0.020% to ≤0.015%, which can reduce phosphorus segregation and improve impact toughness; the room temperature impact absorption energy AKV2 (J) is increased from the original longitudinal AKV2 (J) ≥40 to AKV2 (J) ≥50, and from the original transverse AKV2 (J) ≥27 to AKV2 (J) ≥35. Furthermore, testing shows that the grain size grade of forgings prepared using the P92 series low-S, low-P steel ingot of this invention is 1-2 grades higher than the standard AS-335 / AS-335M requirements; the improvement in high-temperature mechanical properties, specifically the creep strength, is detailed in Table 3. This invention employs an EAF (electric arc furnace) + VODC (vacuum refining furnace) + argon-protected casting process, which can minimize non-metallic inclusions, improve the purity of molten steel and the quality of steel, and ensure that the forgings have excellent high-temperature mechanical properties.

[0079] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing P92 series low-S, low-P steel ingots, characterized in that, Includes the following steps: The raw materials for preparing the P92 series low S and low P steel ingot are smelted, refined, cast and annealed in sequence to obtain the P92 series low S and low P steel ingot. The elemental composition of the P92 series low-S, low-P steel ingot, by mass fraction, includes C 0.07~0.13%, Si 0.20~0.40%, Mn 0.30~0.50%, P≤0.015%, S≤0.005%, Cr 8.50~9.10%, Ni 0.10~0.18%, Mo 0.30~0.50%, Nb 0.04~0.09%, N 0.04~0.07%, V 0.15~0.25%, Al≤0.015%, Cu≤0.20%, W 1.55~1.75%, B 0.001~0.006%, Ti≤0.008%, Zr≤0.008%, with the balance being Fe; The smelting process includes a melting stage, an oxidation stage, and a reduction stage in sequence. The conditions for the melting stage include: a molten pool temperature of 1550~1570℃; the addition of FeO, the mass of which is 2~4% of the mass of the molten steel; co-injection of carbon and oxygen, with an injection amount of 4~6 kg / t and a foam slag retention time of 8~10 min; The conditions for the oxidation stage include: oxygen blowing pressure of 1.3~1.7 MPa; molten pool temperature of 1650~1670℃; boiling time of molten steel of 5~7 min; and addition of Mn, wherein the mass of Mn is 0.1~0.3% of the mass of molten steel. The conditions for the reduction stage include: after slag discharge, adding thin slag material, adjusting the C mass content to 0.8~1.1%, then adding silicon-manganese alloy, ferromanganese alloy, ferrochrome alloy and nickel plate to make thin slag, and then adding reducing agent to make white slag; The refining process includes sequentially performing the VOD stage, VCD stage, VOH stage, and VD stage. The conditions for the VOD stage include: a vacuum of 80-120 mbar and an oxygen blowing rate of 450-650 m³ / h. 3 / h, Ar flow rate is 3~6m 3 / h; The conditions for the VCD stage include: a vacuum level of 1-5 mbar, a vacuuming time of 8-10 min, and an Ar flow rate of 3-6 m³ / min. 3 / h, temperature is 1620~1650℃, slag and reducing agent are added; The conditions for the VOH stage include: a vacuum of 350-450 mbar and an oxygen flow rate of 450-550 m³ / h. 3 / h, Ar flow rate is 3~6m 3 / h; The conditions for the VD stage include: vacuum degree ≤ 2.0 mbar, evacuation time 8~10 min, and Ar flow rate 4.5~6 m³ / min. 3 / h; The annealing temperature is 850~870℃, and the holding time is 0.8~1min / mm.

2. The preparation method according to claim 1, characterized in that, The casting conditions include: molten steel calming time of 6-7 min, argon blowing rate of 5-10 L / min, casting temperature of 1540-1560℃, and casting flow rate of 1-2 t / min.

3. The P92 series low S and low P steel ingot prepared by the preparation method according to claim 1 or 2.

4. A forging, characterized in that, It is prepared from the P92 series low-S and low-P steel ingot described in claim 3.

5. The forging according to claim 4, characterized in that, The forging is a tube forging.

6. The method for preparing the forging according to claim 4 or 5, characterized in that, Includes the following steps: The P92 series low S and low P steel ingots are subjected to forging, annealing, normalizing and tempering treatment and quenching and tempering treatment in sequence to obtain the forgings; The annealing temperature is 820~850℃, and the holding time is 8~10h.

7. The preparation method according to claim 6, characterized in that, The forging conditions include: initial forging temperature of 1170~1190℃, final forging temperature ≥850℃, forging ratio ≥3.0, elongation ratio ≥2.0, and total forging ratio ≥4.

0.

8. The preparation method according to claim 6 or 7, characterized in that, The normalizing and tempering treatment is followed by the quenching and tempering treatment.

9. The application of the P92 series low S and low P steel ingot of claim 3, the forging of claim 4 or 5, or the forging prepared by the preparation method of any one of claims 6 to 8 in ultra-supercritical boilers, compressed air energy storage power stations, or aerospace rockets.

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