P92-series low-S and low-P steel ingot and forge piece as well as preparation method and application

Abstract

The invention provides a P92-series low-S and low-P steel ingot and forge piece and a preparation method and application thereof, and belongs to the technical field of metal materials. The preparation method of the P92-series low-S and low-P steel ingot comprises the following steps that raw materials for preparing the P92-series low-S and low-P steel ingot are sequentially smelted, refined, cast and annealed, and the P92-series low-S and low-P steel ingot is obtained; wherein in the P92-series low-S and low-P steel ingot, the S content is less than or equal to 0.005%, and the P content is less than or equal to 0.015% by mass. According to the method, the P92-series low-S and low-P steel ingot is obtained by controlling specific smelting and refining conditions, and the forged piece prepared from the P92-series low-S and low-P steel ingot has excellent high-temperature mechanical property.

Description

Technical Field

[0001] The present invention relates to the technical field of metal materials, and in particular to a P92 series low-S and low-P steel ingot and forging, and a preparation method and application thereof. Background Art

[0002] P92 steel is a martensitic heat-resistant stainless steel, and its implementation standard is SA-335 / SA-335M. P92 steel is made by appropriately reducing the content of molybdenum (Mo 0.30~0.60wt%) on the basis of P91 steel, and adding a certain amount of tungsten (W 1.50~2.00wt%) and a trace amount of boron (B 0.001~0.006wt%).

[0003] P92 steel has good 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 to be improved. Summary of the invention

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

[0005] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions: The present invention provides a method for preparing a P92 series low-S and low-P steel ingot, comprising the following steps: The raw materials for preparing the P92 series low-S and low-P steel ingot are sequentially smelted, refined, cast and annealed to obtain the P92 series low-S and low-P steel ingot; The element composition of the P92 series low S and low P steel ingot includes, by mass fraction, 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%, and the balance is Fe; The smelting includes a melting stage, an oxidation stage and a reduction stage in sequence; The conditions of the melting stage include: the molten pool temperature is 1550-1570°C; FeO is added, the mass of FeO is 2-4% of the mass of the molten steel; carbon and oxygen are co-sprayed, the powder spraying amount is 4-6kg / t, and the foam slag is maintained for 8-10min; The conditions of the oxidation stage include: oxygen blowing pressure of 1.3-1.7 MPa; molten pool temperature of 1650-1670°C; molten steel boiling time of 5-7 min; adding Mn, the mass of Mn is 0.1-0.3% of the mass of molten steel; The conditions of the reduction stage include: adding thin slag material after slag discharge, adjusting the C mass content to 0.8-1.1%, 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 includes sequentially performing a VOD stage, a VCD stage, a VOH stage and a VD stage; The conditions of the VOD stage include: vacuum degree of 80-120 mbar, oxygen blowing volume of 450-650 m 3 / h, Ar flow rate is 3~6m 3 / h; The conditions of the VCD stage include: vacuum degree of 1-5 mbar, vacuum pumping time of 8-10 min, Ar flow rate of 3-6 m 3 / h, the temperature is 1620~1650℃, adding slag and reducing agent; The conditions of the VOH stage include: vacuum degree of 350-450 mbar, oxygen flow rate of 450-550 mbar 3 / h, Ar flow rate is 3~6m 3 / h; The conditions of the VD stage include: vacuum degree ≤ 2.0 mbar, vacuum pumping time 8-10 min, Ar flow rate 4.5-6 m 3 / h.

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

[0007] Preferably, the annealing temperature is 850-870° C., and the holding time is 0.8-1 min / 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] The present invention provides a forging, which is prepared from the P92 series low-S and low-P steel ingot described in the above technical solution.

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

[0011] The present 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 ingot is subjected to forging, annealing, normalizing and tempering treatments and quenching and tempering treatments in sequence to obtain the forging.

[0012] Preferably, the forging conditions include: initial forging temperature of 1170-1190°C, final forging temperature ≥850°C, forging ratio ≥3.0, extension ratio ≥2.0, and total forging ratio ≥4.0.

[0013] Preferably, a quenching and tempering treatment is further included between the normalizing and tempering treatment and the quenching and tempering treatment.

[0014] The present invention provides the use of the P92 series low-S and low-P steel ingots described in the above technical scheme, the forgings described in the above technical scheme, or the forgings prepared by the preparation method described in the above technical scheme 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, the present invention optimizes the S content from ≤0.010wt% to ≤0.005wt%, which is beneficial to reducing sulfide band segregation, improving the purity of the steel ingot, and thus improving the grain size grade, high temperature resistant lasting strength, operation safety and service life of the forging products; the present invention optimizes the P content from ≤0.020wt% to ≤0.015wt%, which is beneficial to reducing P segregation, ensuring the quality of the weld, and ensuring the quality and service life of high temperature resistant equipment parts; AS-335 / AS-335M P92 steel does not assess Ni and Cu, and the present invention limits the Ni content to 0.10~0.18wt% and the Cu content to ≤0.20wt%. The Ni element is beneficial to strengthening ferrite and refining pearlite, improving strength, and trace Cu can increase corrosion resistance and extend service life. At the same time, the present invention performs annealing after casting, which can avoid product cracking and improve product quality.

[0016] The P92 series low S and low P steel ingots and forgings provided by the present invention belong to martensitic heat-resistant stainless steel. The forgings prepared by using the P92 series low S and low P steel ingots have excellent high-temperature mechanical properties, and are suitable for high-end equipment such as ultra-supercritical boiler key components (such as main steam chamber pipelines, reheat steam chamber pipelines, flanges), compressed air energy storage power station key components (such as ultra-high pressure and high temperature resistant air pipelines, high pressure main air valves and regulating valves, high temperature resistant door valve discs, valve stems) and aerospace rocket key components (such as high temperature resistant nozzle components), and have broad application prospects in the fields of aerospace, ship power and thermal power generation. In addition, the P92 series low S and low P steel ingots and forgings provided by the present invention also have excellent corrosion resistance, high hardness and good welding performance. DETAILED DESCRIPTION

[0017] The present invention provides a method for preparing a P92 series low-S and low-P steel ingot, comprising the following steps: The raw materials for preparing the P92 series low-S and low-P steel ingot are sequentially smelted, refined, cast and annealed to obtain the P92 series low-S and low-P steel ingot; The element composition of the P92 series low S and low P steel ingot includes, by mass fraction, 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%, and the balance is Fe; The smelting includes a melting stage, an oxidation stage and a reduction stage in sequence; The conditions of the melting stage include: the molten pool temperature is 1550-1570°C; FeO is added, the mass of FeO is 2-4% of the mass of the molten steel; carbon and oxygen are co-sprayed, the powder spraying amount is 4-6kg / t, and the foam slag is maintained for 8-10min; The conditions of the oxidation stage include: oxygen blowing pressure of 1.3-1.7 MPa; molten pool temperature of 1650-1670°C; molten steel boiling time of 5-7 min; adding Mn, the mass of Mn is 0.1-0.3% of the mass of molten steel; The conditions of the reduction stage include: adding thin slag material after slag discharge, adjusting the C mass content to 0.8-1.1%, 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 includes sequentially performing a VOD stage, a VCD stage, a VOH stage and a VD stage; The conditions of the VOD stage include: vacuum degree of 80-120 mbar, oxygen blowing volume of 450-650 m 3 / h, Ar flow rate is 3~6m 3 / h; The conditions of the VCD stage include: vacuum degree of 1-5 mbar, vacuum pumping time of 8-10 min, Ar flow rate of 3-6 m 3 / h, the temperature is 1620~1650℃, adding slag and reducing agent; The conditions of the VOH stage include: vacuum degree of 350-450 mbar, oxygen flow rate of 450-550 mbar 3 / h, Ar flow rate is 3~6m 3 / h; The conditions of the VD stage include: vacuum degree ≤ 2.0 mbar, vacuum pumping time 8-10 min, Ar flow rate 4.5-6 m 3 / h.

[0018] The present invention firstly describes the element composition of the P92 series low-S and low-P steel ingot.

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

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

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

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

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

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

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

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

[0027] In the present invention, the element composition of the P92 series low S and low P steel ingot 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%, by mass fraction.

[0028] In the present invention, the element composition of the P92 series low S and low P steel ingot includes N 0.04-0.07% by mass, and specifically can be 0.04%, 0.045%, 0.05%, 0.055%, 0.06% or 0.07%.

[0029] In the present invention, the element composition of the P92 series low S and low P steel ingot includes V 0.15-0.25% by mass, and specifically can be 0.15%, 0.18%, 0.20%, 0.22%, 0.23% or 0.25%.

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

[0031] In the present invention, the element composition of the P92 series low S and low P steel ingot includes Cu≤0.20%, by mass fraction, and can be 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 the present invention, the element composition of the P92 series low S and low P steel ingot includes W 1.55-1.75% by mass, and specifically can be 1.55%, 1.57%, 1.59%, 1.63%, 1.67%, 1.71%, 1.73% or 1.75%.

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

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

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

[0036] In the present invention, the element composition of the P92 series low S and low P steel ingot includes the balance Fe by mass fraction.

[0037] The preparation method of the P92 series low S and low P steel ingot of the present invention is described in detail below. In the present invention, unless otherwise specified, the raw materials and reagents used are commercially available products well known to those skilled in the art.

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

[0039] In the present invention, the conditions of the melting stage include: the molten pool temperature is 1550-1570°C, preferably 1560°C; FeO is added, the mass of the FeO is 2-4% of the mass of the molten steel, preferably 3%; carbon and oxygen are preferably co-sprayed at the end of the melting stage, the spraying amount is 4-6kg / t, preferably 5kg / t, and the foam slag is kept for 8-10min (more preferably 9min) to make the P content ≤0.008wt%, and enter the oxidation stage. The present invention preferably controls the amount of FeO added within the above range, which is conducive to ensuring high oxygen potential.

[0040] In the present invention, the conditions of the oxidation stage include: oxygen blowing pressure of 1.3-1.7 MPa, preferably 1.5 MPa; molten pool temperature of 1650-1670°C, preferably 1660°C; carbon removal is preferably ≥40%, and sampling analysis satisfies the C content ≤1.0wt%, P content ≤0.010wt%, and S content ≤0.020wt%; Mn is added after the molten steel is boiled for 5-7 minutes (preferably 6 minutes), and the mass of Mn is 0.1-0.3% of the mass of the molten steel, preferably 0.2%; when the C content is 0.80-1.0wt%, the P content is ≤0.010wt%, the S content is ≤0.020wt% and the molten steel temperature is 1670-1720°C (preferably 1700°C), the reduction stage is entered.

[0041] In the present invention, the conditions of the reduction stage include: adding thin slag material after removing the slag produced in the oxidation stage, adjusting the C content to 0.8-1.1wt% (preferably 1.0wt%); then adding silicon manganese alloy, ferromanganese alloy, ferrochrome alloy and nickel plate, adding reducing agent to make white slag after the thin slag is made; the white slag is preferably kept for 18-23min (more preferably 20min), and the molten steel temperature is preferably 1670-1720℃ (more preferably 1700℃) when it is transferred into the ladle, and the slag in the ladle is preferably ≤1.5kg / t when the residue amount is preferably 1630-1680℃ (more preferably 1650℃) when the molten steel temperature is preferably 1630-1680℃ (more preferably 1650℃) and the material is discharged for subsequent processes. In the present 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 the present invention, the addition amount of the silicon manganese alloy is preferably 4~6kg / t, more preferably 5kg / t; the addition amount of the manganese iron alloy is preferably 4~6kg / t, more preferably 5kg / t; the addition amount of the chromium iron alloy is preferably based on ensuring that the Cr content is 12~14wt% (more preferably 13wt%); the addition amount of the nickel plate is preferably based on ensuring that the Ni content is 4.5~5.5wt% (more preferably 5wt%). In the present invention, the reducing agent preferably includes a first reducing agent and a second reducing agent. In the present invention, the first reducing agent preferably includes ferrosilicon powder or calcium carbide; the amount of the ferrosilicon powder is preferably 4~7kg / t, more preferably 5kg / t; the amount of the calcium carbide is preferably 2~3kg / t, more preferably 2.5kg / t. In the present invention, the second reducing agent preferably includes carbon powder or AD powder; the amount of the carbon powder is preferably 0.8-1.5 kg / t, more preferably 1 kg / t; the amount of the AD powder is preferably 5-8 kg / t, more preferably 6.6 kg / t.

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

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

[0044] In the present invention, the conditions of the VCD stage include: vacuum degree of 1-5 mbar, preferably 3-4 mbar; vacuum pumping time of 8-10 min, preferably 9 min; Ar flow rate of 3-6 mbar; 3 / h, preferably 4.5m 3 / h; the temperature is 1620~1650℃, preferably 1635℃; add slag and reducing agent; 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 optional type and amount of the reducing agent are preferably consistent with the above technical solution, which will not be repeated here. In an embodiment 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, and Al is added according to the temperature increase of 250℃ for every 1wt% of Al added, so as to further perform slag making and deoxidation work.

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

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

[0047] After the VD stage is completed, the present invention preferably passes Ar through the bottom of the tundish to exhaust the air in the tundish, and discharges the material in the Ar protective atmosphere for subsequent processes. The present invention discharges the material in the Ar protective atmosphere to prevent secondary oxidation.

[0048] After the refining is completed, the present invention casts the obtained molten steel. The casting of the present invention is preferably carried out in an argon protective atmosphere. Before the casting, the present invention preferably pre-checks the casting system and the steel mold to ensure that they are dry, moisture-free, clean and pollution-free. In the present invention, the casting conditions include: the molten steel calming time is preferably 6~7min; the argon blowing amount is preferably 5~10L / min, more preferably 8L / min; the casting temperature is preferably 1540~1560℃, more preferably 1550℃; the casting flow rate is preferably 1~2t / min, more preferably 1.5t / min. The present invention casts in an Ar protective atmosphere to prevent secondary oxidation. In the present invention, after the casting is completed, it is preferably cooled in the mold, and the cooling time in the mold is preferably according to the formula T (h) = 35R 2 (m) × 1.2, where R is the radius of the steel mold, and the mold is demoulded after the cooling in the mold is completed.

[0049] After the casting is completed, the present invention anneals the obtained steel ingot to obtain the P92 series low S and low P steel ingot. In the present invention, the annealing temperature is preferably 850-870°C, more preferably 860°C; the holding time is preferably determined according to the thickness of the steel ingot, and specifically, the holding time is preferably 0.8-1min / mm, more preferably 0.9min / mm. The present invention preferably anneals the steel ingot obtained after demoulding quickly to prevent the temperature of the steel ingot from dropping excessively. In an embodiment of the present invention, in the process of heating to the required temperature for annealing, the heating rate is not particularly limited when the furnace temperature is below 400°C. The furnace temperature is preferably heated to the annealing temperature at a heating rate of ≤100°C / h (the heating rate is more preferably 80°C / h) from 400°C, and then annealed under the insulation condition; after the insulation is completed, the furnace is preferably cooled to ≤450°C, and then air-cooled out of the furnace.

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

[0051] 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. In an embodiment of the present invention, the P92 series low S and low P steel ingot can be specifically an octagonal steel ingot.

[0052] The present invention provides a forging, which is prepared from the P92 series low-S and low-P steel ingot described in the above technical solution. In the present invention, the forging is preferably a tube forging.

[0053] The present 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 ingot is subjected to forging, annealing, normalizing and tempering treatments and quenching and tempering treatments in sequence to obtain the forging.

[0054] In the present invention, the P92 series low S and low P steel ingot is preferably subjected to blanking and heat treatment in sequence before forging; in the embodiment of the present invention, the P92 series low S and low P steel ingot is blanked, then subjected to heat treatment, and forged after the heat treatment is completed. In the present invention, the temperature of the heat treatment is preferably 1170-1190°C, more preferably 1180°C; the holding time is preferably 8-10h, more preferably 9h.

[0055] In the present 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℃ and air cooling after exiting the furnace; the forging ratio is preferably ≥3.0, specifically 3.0; the extension ratio is preferably ≥2.0, more preferably 2.2~2.5; the total forging ratio is preferably ≥4.0, specifically 4.0.

[0056] After forging, the present invention anneals the workpiece. In the present invention, the annealing temperature is preferably 820-850°C, more preferably 830°C; the holding time is preferably 8-10h, more preferably 9h; the heating rate to the annealing temperature is preferably 70-90°C / h, more preferably 80°C / h; after the holding is completed, the workpiece is preferably cooled to ≤200°C in the furnace and then air-cooled out of the furnace.

[0057] After annealing, the present invention preferably performs rough machining on the obtained workpiece, and uses ultrasonic flaw detection, and then performs normalizing and tempering. In an embodiment of the present invention, after rough machining and ultrasonic flaw detection, a workpiece (specifically a seamless steel pipe) that passes the ultrasonic flaw detection is obtained.

[0058] In the present invention, the normalizing and tempering treatment preferably includes normalizing treatment and tempering treatment in sequence. In the present invention, the temperature of the normalizing treatment is preferably 1040~1080℃, more preferably 1060℃; taking the preparation of pipe forgings as an example, the holding time (h) of the normalizing treatment is preferably 1h cumulatively + 2h with a thickness of 25mm, which can be specifically calculated according to the following formula: t=2+(workpiece wall thickness / 25), the unit of the workpiece wall thickness is mm; taking the workpiece wall thickness of 100mm as an example, the holding time of the normalizing treatment is specifically 6h. In the present invention, the temperature of the tempering treatment is preferably 760~790℃, more preferably 775℃; the holding time of the tempering treatment is preferably 1h cumulatively + 2h with a thickness of 25mm (that is, the calculation method of the holding time is consistent with the calculation method of the holding time of the normalizing treatment).

[0059] In the present invention, when the wall thickness of the workpiece is >70mm, quenching and tempering treatment is preferably performed after the normalizing and tempering treatment is completed, and the quenching and tempering treatment preferably includes quenching treatment and tempering treatment in sequence; the temperature of the quenching treatment is preferably 1030~1050℃, more preferably 1040℃, and the holding time is preferably 1h cumulatively +2h based on the thickness of 25mm; the temperature of the tempering treatment is preferably 760~790℃, more preferably 775℃, and the holding time is preferably 1h cumulatively +2h based on the thickness of 25mm. In the present invention, when the wall thickness of the workpiece is ≤70mm, quenching and tempering treatment is not performed after the normalizing and tempering treatment is completed, and subsequent quenching and tempering treatment is directly performed.

[0060] In the present invention, the tempering treatment preferably includes a first tempering treatment and a second tempering treatment in sequence; the conditions of the first tempering treatment include: the temperature is preferably 1040-1080°C, more preferably 1060°C, the insulation time is preferably 1h cumulatively + 2h with a thickness of 25mm, and air cooling or wind cooling is preferably performed after the insulation is completed; the conditions of the second tempering treatment include: the temperature is preferably 730-780°C, more preferably 750°C, the insulation time is preferably 1h cumulatively + 2h with a thickness of 25mm, and air cooling is preferably performed after the insulation is completed.

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

[0062] The present invention provides the use of the P92 series low S and low P steel ingots described in the above technical solution, the forgings described in the above technical solution, or the forgings prepared by the preparation method described in the above technical solution in ultra-supercritical boilers, compressed air energy storage power stations, or aerospace rockets. The P92 series low S and low P steel ingots and forgings described in the present invention can be specifically used for high-temperature resistant core forgings and pipe fittings in ultra-supercritical boilers, compressed air energy storage power stations, or aerospace rockets. In the present invention, the ultra-supercritical boiler is preferably a 660~1350MW ultra-supercritical boiler, specifically an ultra-large clean coal-fired 660~1350MW ultra-supercritical boiler; the P92 series low S and low P steel ingots or forgings described in the present invention can preferably be used for key components of the ultra-supercritical boiler, and the key components preferably include main steam chamber pipelines, reheat steam chamber pipelines or flanges. In the present invention, the compressed air energy storage power station is preferably a 300~350MW compressed air energy storage power station; the P92 series low S and low P steel ingots or forgings of the present invention can be preferably used for key components of compressed air energy storage power stations, and the key components preferably include ultra-high pressure and high temperature resistant air pipes, high pressure main air valves and regulating valves, and high temperature resistant valve discs or valve stems. In the present invention, the P92 series low S and low P steel ingots or forgings can be preferably used for key components of aerospace rockets, and the key components preferably include high temperature resistant nozzle components. In the present invention, the working temperature of the forging is preferably not more than 620°C, and can specifically be 610~620°C.

[0063] The technical solutions in the present invention will be described clearly and completely below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0064] The detection methods in the following experimental process include: the allowable deviation of the chemical composition of the finished steel product adopts GB / 222, the chemical composition analysis method of steel and alloy adopts GB / T223, the macrostructure and defect acid etching test method of steel adopts GB / T226, the sampling location and sample preparation of mechanical properties of steel and steel products adopt GB / T2975, the metal average grain size test method adopts GB / 16394, the standard rating chart microscopic inspection method for the determination of non-metallic inclusion content in steel adopts GB / T10561, and the spark atomic emission spectrometry (conventional method) for measuring the multi-element content of stainless steel adopts GB / T11170.

[0065] The mechanical properties test methods in the following experimental process include: room temperature tensile test method adopts GB / T228.1, specifically using Φ5mm standard specimens, using WE-300 tensile testing machine, the test temperature is 25℃, and the tensile strength Rm and yield strength RP0.2 , elongation after fracture A and cross-sectional shrinkage rate Z; the impact performance adopts the Charpy pendulum impact test method for metal materials in accordance with GB / T 229-2020; the high-temperature mechanical properties, compressive strength and endurance strength MPa of the forgings are tested using GB / T8732-2014 standard, the grading method for strength grades QT1 and QT2 adopts EN10269-2006, and the high-temperature performance data are cited 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) placing pure scrap steel and alloy raw materials (such as ferrochrome, ferromanganese, ferrosilicon, ferronickel, ferroniobium, ferromolybdenum, etc.) with a S content of ≤0.020wt% and a P content of ≤0.020wt% in an electric arc furnace (EAF) for smelting, wherein the smelting includes a melting stage, an oxidation stage and a reduction stage in sequence; The conditions of the melting stage include: the molten pool temperature is 1560°C; FeO is added, and the mass of the FeO is 3% of the mass of the molten steel; carbon and oxygen are co-sprayed at the end of the melting stage, the spraying amount is 5kg / t, and the foamed slag is maintained for 9 minutes to make the P content ≤0.008wt% and enter the oxidation stage; The conditions of the oxidation stage include: oxygen blowing pressure of 1.5MPa, molten pool temperature of 1660°C, C removal of ≥40%, sampling analysis of C content ≤1.0wt%, P content ≤0.010wt%, S content ≤0.020wt%; Mn is added after the molten steel is boiled for 6 minutes, and the mass of Mn is 0.2% of the mass of the molten steel. When the C content is 0.80-1.0wt%, the P content is ≤0.010wt%, the S content is ≤0.020wt% and the molten steel temperature is 1700°C, the reduction stage is entered; The conditions of the reduction stage include: after removing the slag produced in the oxidation stage, adding thin slag material (specifically 200kg / t of lime and 70kg / t of fluorite), adjusting the C content to 1.0wt%, then adding 5kg / t of silicon manganese alloy, 5kg / t of ferromanganese alloy, ferrochrome alloy (the amount added is based on ensuring that the Cr content is 13wt%) and nickel plate (the amount added is based on ensuring that the Ni content is 5wt%), adding a reducing agent (specifically 5kg / t of ferrosilicon powder and 1kg / t of carbon powder) to make white slag after the thin slag is made, keeping the white slag for 20 minutes, transferring the molten steel into a ladle when the temperature of the molten steel is 1700°C, skimming the slag in the ladle until the residual amount is ≤1.5kg / t, and discharging the material when the temperature of the molten steel is 1650°C; (2) transferring the molten steel having a temperature of 1650° C. obtained after smelting into a vacuum refining furnace (VODC) for refining, wherein the refining includes sequentially performing a VOD stage, a VCD stage, a VOH stage and a VD stage; The conditions of the VOD stage include: vacuum degree of 100 mbar, oxygen blowing volume of 550 m 3 / h, Ar flow rate is 4m 3 / h; The conditions of the VCD stage include: vacuum degree of 3 mbar, vacuum pumping time of 9 min, Ar flow rate of 4.5 m 3 / h; then take samples to measure the temperature, and when the temperature of the molten steel reaches 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 of the VOH stage include: vacuum degree of 400 mbar, oxygen flow rate of 500 m 3 / h, Ar flow rate is 4m 3 / h; The conditions of the VD stage include: vacuum degree of 1.5 mbar, vacuum pumping time of 9 min, Ar flow rate of 5.5 m 3 / h; After the VD stage is completed, Ar is passed through the bottom of the tundish to exhaust the air inside the tundish, and the material is discharged in an Ar protective atmosphere to prevent secondary oxidation; (3) Pre-check the casting system and steel mold to ensure that they are dry, free of moisture, clean and free of pollution, and cast the molten steel obtained after refining. The casting conditions include: molten steel calming time of 6 minutes, argon blowing volume of 8L / min, casting temperature of 1550℃, and casting flow rate of 1.5t / min; after casting, the mold is cooled, and the cooling time in the mold is calculated according to the formula T (h) = 35R 2 (m) × 1.2, where R is the radius of the steel mold, and the mold is demoulded after the cooling in the mold is completed; (4) annealing the steel ingot obtained after demolding, wherein the annealing conditions include: the heating rate is not particularly limited when the furnace temperature is below 400°C, the furnace temperature is increased from 400°C to 860°C at a heating rate of 80°C / h, and the holding time is 0.9 min / mm (determined according to the thickness of the steel ingot); after the holding time is completed, the furnace is cooled to ≤450°C and then air-cooled to obtain the steel ingot.

[0068] Example 2 The chemical composition of the steel ingot in this example is shown in Table 1. The specific preparation method is shown in Example 1.

[0069] Example 3 The chemical composition of the steel ingot in this example is shown in Table 1. The specific preparation method is shown in Example 1.

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

[0071] Example 4 The steel ingot in Example 1 is used to prepare a pipe forging, and the specific preparation method is as follows: (1) blanking the steel ingot, heating it to 1180° C., keeping it at that temperature for 9 hours, and then forging (expanding the roundness), wherein the forging conditions include: the initial forging temperature is 1180° C., the final forging temperature is 860° C., the cooling method is furnace cooling to ≤200° C. and air cooling after exiting the furnace, the forging ratio is 3.0, the extension ratio is 2.5, and the total forging ratio is 4.0; (2) annealing the workpiece obtained after forging, wherein the annealing conditions include: heating from room temperature to 830°C at a heating rate of 80°C / h, and keeping the temperature for 9 hours; cooling the furnace to ≤200°C after the end of the heat preservation, and then cooling in air out of the furnace; (3) Rough machining the workpiece obtained after annealing and inspecting it using ultrasonic flaw detection; (4) The workpieces that have passed the ultrasonic flaw detection are subjected to normalizing and tempering treatment, wherein the normalizing and tempering treatment includes normalizing treatment and tempering treatment in sequence; the temperature of the normalizing treatment is 1060°C, and the holding time is 1 hour for a thickness of 25 mm + 2 hours; the temperature of the tempering treatment is 775°C, and the holding time is 1 hour for a thickness of 25 mm + 2 hours; Wherein, when the wall thickness of the workpiece is greater than 70mm, the quenching and tempering treatment is performed after the normalizing and tempering treatment is completed, and the quenching and tempering treatment includes sequentially performing quenching treatment and tempering treatment; the temperature of the quenching treatment is 1040°C, and the holding time is 1h for a thickness of 25mm plus 2h; the temperature of the tempering treatment is 775°C, and the holding time is 1h for a thickness of 25mm plus 2h; When the wall thickness of the workpiece is ≤70mm, the quenching and tempering treatment is not performed after the normalizing and tempering treatment, and the subsequent process is directly performed; (5) The workpiece obtained in step (4) is subjected to a tempering treatment, wherein the tempering treatment includes sequentially performing a first tempering treatment and a second tempering treatment; the conditions of the first tempering treatment include: a temperature of 1060° C., a holding time of 1 hour plus 2 hours based on a thickness of 25 mm, and air cooling after the end of the holding period; the conditions of the second tempering treatment include: a temperature of 750° C., a holding time of 1 hour plus 2 hours based on a thickness of 25 mm, and air cooling after the end of the holding period, to obtain the pipe forging.

[0072] Example 5 The steel ingot in Example 2 was used to prepare the tube forging. The specific preparation method is as shown in Example 4.

[0073] Example 6 The steel ingot in Example 3 was used to prepare the tube forging. The specific preparation method is as shown in Example 4.

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

[0075] Table 2 Room temperature mechanical properties test results of the steel ingots in Comparative Example 1 and Examples 1 to 3

[0076] Test Example 2 The pipe forgings in Examples 4 to 6 were subjected to high temperature mechanical property tests, and the specific results are shown in Table 3.

[0077] Table 3 High temperature mechanical properties test results of pipe forgings in Examples 4 to 6

[0078] It can be seen from the above test results that the P92 low S and low P steel ingot provided by the present invention has an S content optimized from ≤0.010% to ≤0.005% compared with the original P92 steel ingot, which can reduce sulfide inclusions and eliminate sulfide band 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. In addition, it has been tested that the grain size grade of the forgings prepared by the P92 low S and low P steel ingot of the present invention is 1~2 grades higher than the standard AS-335 / AS-335M requirements; the degree of improvement of the endurance strength of high temperature mechanical properties is shown in Table 3. The present invention adopts EAF (electric arc furnace) + VODC (vacuum refining furnace) + argon protection casting process, which can reduce non-metallic inclusions to the maximum extent, is beneficial to improving the purity of molten steel and the quality of steel, and ensures that the forgings have excellent high-temperature mechanical properties.

[0079] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A method for preparing a P92 series low S and low P steel ingot, It is characterized in that The following steps are involved: The raw materials for preparing the P92 series low-S and low-P steel ingot are sequentially smelted, refined, cast and annealed to obtain the P92 series low-S and low-P steel ingot; The element composition of the P92 series low S and low P steel ingot includes, by mass fraction, 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%, B0.001-0.006%, Ti≤0.008%, Zr≤0.008%, and the balance is Fe; The smelting includes a melting stage, an oxidation stage and a reduction stage in sequence; The conditions of the melting stage include: the molten pool temperature is 1550-1570°C; FeO is added, the mass of FeO is 2-4% of the mass of the molten steel; carbon and oxygen are co-sprayed, the powder spraying amount is 4-6kg / t, and the foam slag is maintained for 8-10min; The conditions of the oxidation stage include: oxygen blowing pressure of 1.3-1.7 MPa; molten pool temperature of 1650-1670°C; molten steel boiling time of 5-7 min; adding Mn, the mass of Mn is 0.1-0.3% of the mass of molten steel; The conditions of the reduction stage include: adding thin slag material after slag discharge, adjusting the C mass content to 0.8-1.1%, 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 includes sequentially performing a VOD stage, a VCD stage, a VOH stage and a VD stage; The conditions of the VOD stage include: vacuum degree of 80-120 mbar, oxygen blowing volume of 450-650 m 3 / h, Ar flow rate is 3~6m 3 / h; The conditions of the VCD stage include: vacuum degree of 1-5 mbar, vacuum pumping time of 8-10 min, Ar flow rate of 3-6 m 3 / h, the temperature is 1620~1650℃, adding slag and reducing agent; The conditions of the VOH stage include: vacuum degree of 350-450 mbar, oxygen flow rate of 450-550 mbar, 3 / h, Ar flow rate is 3~6m 3 / h; The conditions of the VD stage include: vacuum degree ≤ 2.0 mbar, vacuum pumping time 8-10 min, Ar flow rate 4.5-6 m 3 / h.

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

3. The preparation method according to claim 1 or 2, It is characterized in that The annealing temperature is 850-870° C., and the holding time is 0.8-1 min / mm.

4. The P92 series low S and low P steel ingot prepared by the preparation method according to any one of claims 1 to 3.

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

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

7. A method for preparing a forging according to claim 5 or 6, It is characterized in that The following steps are involved: The P92 series low-S and low-P steel ingot is subjected to forging, annealing, normalizing and tempering treatments and quenching and tempering treatments in sequence to obtain the forging.

8. The preparation method according to claim 7, It is characterized in that The forging conditions include: initial forging temperature of 1170-1190° C., final forging temperature ≥850° C., forging ratio ≥3.0, extension ratio ≥2.0, and total forging ratio ≥4.

0.

9. The preparation method according to claim 7 or 8, It is characterized in that The normalizing and tempering treatment and the quenching and tempering treatment also include a quenching and tempering treatment.

10. Use of the P92 low-S and low-P steel ingot according to claim 4, the forging according to claim 5 or 6, or the forging prepared by the preparation method according to any one of claims 7 to 9 in ultra-supercritical boilers, compressed air energy storage power stations or aerospace rockets.

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