Production and manufacturing process of ten-ton 17-4PH precipitation-hardening martensitic stainless steel

Abstract

The invention belongs to the field of ultra-large 17-4PH forge piece manufacturing, and discloses a production and manufacturing process of ten-ton 17-4PH precipitation hardening martensitic stainless steel, which comprises the following steps: preparing raw materials according to electrode material chemical components and a slag system of the ten-ton 17-4PH precipitation hardening martensitic stainless steel, and sequentially carrying out electroslag remelting, forging and heat treatment to obtain the ten-ton 17-4PH precipitation hardening martensitic stainless steel. And finally, the ten-ton 17-4PH precipitation hardening martensitic stainless steel is obtained. According to the ten-ton 17-4PH precipitation-hardening martensitic stainless steel produced through the method, the volume fractions of retained austenite, a copper-rich phase and a dispersed precipitation phase in a product are successfully controlled, the controllable matrix grain size is achieved, precipitation of an unfavorable phase is effectively restrained, the internal stress and the cracking risk of a workpiece are remarkably reduced, and the ten-ton 17-4PH precipitation-hardening martensitic stainless steel is excellent in mechanical property and good in mechanical property. And the grain size of the product is 2-3 grades, and the high-strength and high-toughness alloy can be suitable for the fields of aerospace, petrifaction, ocean engineering, mold manufacturing, pressure containers and the like.

Description

Technical Field

[0001] The present invention belongs to the field of manufacturing super-large 17-4PH forgings, and particularly relates to a production and manufacturing process for a ten-ton 17-4PH precipitation-hardening martensitic stainless steel. Background Art

[0002] Disclosing the information of this background art section is only intended to increase the understanding of the overall background of the present invention, and it is not necessarily regarded as an admission or an implication in any form that this information constitutes the prior art already known to those of ordinary skill in the art.

[0003] 17-4PH is a typical martensitic precipitation-hardening stainless steel, which has good mechanical properties, machining properties and corrosion resistance, and is usually widely used in the fields of aerospace, petrochemical, ocean engineering, die manufacturing and pressure vessels, etc.

[0004] For a production and manufacturing process of a ten-ton 17-4PH precipitation-hardening martensitic stainless steel, the main technical difficulties at the present stage include:

[0005] (1) In the aspect of electroslag remelting: The main chemical elements of 17-4PH include alloy elements such as C, Cr, Cu, Ni, Nb, etc., where the C content is ≤0.07%, the Cr content is 15.00% - 17.50%, the Ni content is 3.00% - 5.00%, and the Nb content is 0.15% - 0.45%. Due to the presence of multiple alloy elements such as Cu and Nb, its melting point is relatively low, being 1399°C, and the melting point of the slag system used in the previous smelting is about 1340°C, with a small melting point difference; when smelting in a three-phase electroslag furnace, using a diameter crystallizer for smelting, due to the large ingot size of the electroslag ingot and the small filling ratio, it is extremely difficult to control the temperature during the feeding process, and it is very easy to cause the shrinkage cavity and steel slag to be indistinguishable. Especially when smelting in a three-phase furnace, feeding is very difficult. And the steel ingot is prone to cracking during both the smelting and annealing processes;

[0006] (2) In the aspect of forging: Due to the large ingot size of the product, when producing with a three-phase electroslag ingot, the shrinkage cavity at the arc extinguishing end is serious; containing multiple alloy elements such as Cu and Nb, it is extremely easy to generate cracks or even cracking during the forging process, and the forming difficulty is large; the forging temperature range of 17-4PH stainless steel is narrow, only 200°C, and it is very easy to generate cracks when the temperature is lower than the final forging temperature or with a large deformation amount, and it is difficult to control the grain size;

[0007] (3) In the aspect of heat treatment: Due to the large cross-sectional size of the product, rapid solution quenching will cause excessive stress in the core of the workpiece, bringing a risk of cracking, and reducing the solution cooling rate will cause an increase in retained austenite. At the same time, a large amount of copper-rich phases will precipitate during the slow cooling process, resulting in a reduction in the dispersed precipitated phases during subsequent aging, affecting the performance of the product.

[0008] Therefore, it is an urgent problem to propose a ten-ton precipitation hardening martensitic stainless steel 17-4PH production and manufacturing process to effectively solve the various technical difficulties in the process of ultra-large 17-4PH forgings from electroslag remelting to obtaining finished products, ensure the quality of the products, and effectively promote the successful research and development and promotion of ten-ton ultra-large 17-4PH forgings. Summary of the invention

[0009] In order to solve the above problems, the present invention provides a production process for 10-ton 17-4PH precipitation hardening martensitic stainless steel, which aims to effectively control the grain size of the product matrix, inhibit the precipitation of unfavorable phases, and significantly reduce the internal stress of the workpiece and the risk of product cracking. The products manufactured by the method of the present invention have excellent mechanical properties and a long service life, and effectively solve many technical problems in the production process of super-large 17-4PH forgings.

[0010] In order to achieve the above object, the present invention adopts the following technical solution:

[0011] The first aspect of the present invention provides a production process for 10-ton 17-4PH precipitation hardening martensitic stainless steel, comprising:

[0012] According to the chemical composition of the electrode material of 10-ton 17-4PH precipitation hardening martensitic stainless steel and the raw materials of the slag system, electroslag remelting, forging and heat treatment are carried out in sequence to obtain;

[0013] Among them, the ten-ton grade 17-4PH precipitation hardening martensitic stainless steel is composed of the following chemical components in weight percentage: C: 0.03-0.05%, Si: ≤0.40%, Mn: 0.70-0.80%, P≤0.03%, S≤0.008%, Cr: 15.00-15.50%, Ni: 4.50-5.00%, Nb: 0.20-0.30%, Cu: 3.00-3.50%, and the balance is Fe.

[0014] The slag system is composed of CaF2, Al2O3 and MgO, and the mass ratio of CaF2, Al2O3 and MgO is (65±2):(30±2):(5±0.5).

[0015] The present invention adjusts the slag components to reduce the melting point of the slag from about 1340°C to about 1290°C, thereby increasing the melting point difference between steel (melting point is 1399°C) and slag, while improving the fluidity of the slag system, reducing energy consumption, and avoiding the incompatibility of steel and slag as much as possible.

[0016] In some embodiments, the specific steps of slag making include: igniting the consumable electrode, starting the arc with 17-4PH steel chips, the starting arc voltage being 62.5-63V, adding all the slag materials when the voltage is 65-67.5V, raising one gear every 20-25 minutes (2.5V / gear), and controlling the current at 6-12KA;

[0017] In some embodiments, the specific steps of remelting include: for the first group, the maximum melting speed in the early stage is controlled at 1600-1650 kg / h, the voltage is 70-72.5V, reducing one gear after 1-1.5h, and then reducing one gear every 0.5-0.8h until the melting speed is controlled at 1400-1500 kg / h; for the second group, the melting speed is controlled at 1250-1350 kg / h, the voltage is 57.5-67.5V, and reducing one gear of voltage when the melting speed exceeds this range; for the third group, the melting speed is controlled at 1150-1250 kg / h, the voltage is 55-67.5V, and reducing one gear of voltage when the melting speed exceeds this range; for the fourth group, the melting speed is controlled at 1100-1200 kg / h, the voltage is 52.5-65V, and reducing one gear of voltage when the melting speed exceeds this range; adjusting the voltage and current according to the melting speed, with the current fluctuation ≤1000A; controlling the argon gas flow rate ≥50 Nm 3 / h; adding aluminum powder at a uniform rate of 70-75 g / 5 min for deoxidation in this stage;

[0018] In some embodiments, the specific steps of feeding include: injecting the feeding material at a height of 390-400 mm from the ingot height, feeding when the difference from the planned ingot height is 340-350 mm, and gradually reducing the power during feeding; controlling the melting speed at 1050-1060 kg / h after the feeding material enters, at a height of 180-260 mm from the ingot height, controlling the melting speed at 950-960 kg / h; at a height of 80-180 mm from the ingot height, controlling the melting speed at 900-910 kg / h; at a height of 30-80 mm from the ingot height, controlling the melting speed at 800-810 kg / h; at a height of 0-30 mm from the ingot height, gradually reducing the melting speed from 700-710 kg / h to 280 kg / h; the feeding voltage is between 50-65V, reducing one gear at a height of 20-25 mm from the ingot height, and the entire feeding stage is controlled within 3.5-3.6h; adjusting the voltage and current according to the melting speed, controlling the current fluctuation within ≤1000A, controlling the argon gas flow rate ≥50 Nm 3 / h, and the deoxidizer during feeding is aluminum powder at 50-55 g / 5 min; finally, after the electroslag ingot mold is cooled for 4-4.5h, it is demolded and loaded into the furnace for stress relief annealing treatment.

[0019] The present invention reduces the melting speed, thereby ensuring the feeding quality. In addition, the demolding time of the electroslag ingot is adjusted, the loading speed after demolding is accelerated, the annealing temperature is increased, and at the same time, the cooling speed is slowed down, effectively reducing the risk of cracking of the steel ingot after annealing.

[0020] In some embodiments, the specific steps of forging include:

[0021] Before forging, cut off the arc-retracting end shrinkage cavity and the arc-striking end iron plate and slag inclusion at both ends of the electroslag ingot, peel the ingot body of the electroslag ingot, remove the ingot body scab and molten steel flow, and preheat the tooling to ≥450°C; at the same time, strictly control the forging temperature. When cracks appear during forging, they should be cleaned up in time. When the forging ratio is insufficient, attention should be paid to cooling.

[0022] Preferably, the arc-striking end is sawed 100 - 120 mm long, and the arc-retracting end is 180 - 200 mm long.

[0023] Preferably, the starting forging temperature of the first heat is 1180 - 1190°C, keep warm for 20 - 24 h, the finishing forging temperature is 1000 - 1010°C, and then roll the electroslag ingot horizontally, with the single-side reduction amount of 30 - 35 mm;

[0024] Preferably, the starting forging temperature of the second heat is 1200 - 1210°C, keep warm for 4 - 5 h, the finishing forging temperature is 1000 - 1010°C, and perform one-time upsetting on the extra-large 17 - 4PH forging until When upsetting, it is carried out in multiple times, with the single-time reduction amount ≤100 mm, and then roll it round;

[0025] Preferably, the starting forging temperature of the third heat is 1200 - 1210°C, keep warm for 4 - 5 h, the finishing forging temperature is 1000 - 1010°C, and perform flat anvil drawing on the extra-large 17 - 4PH forging, turn it 45° in sequence, draw it to 1260 - 1270 mm in octagon shape, and the reduction amount is 5 - 10%;

[0026] Preferably, the starting forging temperature of the fourth heat is 1200 - 1210°C, keep warm for 4 - 5 h, the finishing forging temperature is 1000 - 1010°C, and perform secondary upsetting on the extra-large 17 - 4PH forging until When upsetting, it is carried out in multiple times, with the single-time reduction amount ≤100 mm, and roll it round;

[0027] Preferably, the starting forging temperature of the fifth heat is 1200 - 1210°C, keep warm for 3 - 4 h, the finishing forging temperature is 1000 - 1010°C, and perform flat anvil drawing on the extra-large 17 - 4PH forging, turn it 45° in sequence, draw it to 1260 - 1270 mm in octagon shape, and the reduction amount is 5 - 10%;

[0028] Preferably, the starting forging temperature of the sixth heat is 1180 - 1190°C, keep warm for 2 - 3 h, the finishing forging temperature is 1000 - 1010°C, place the arc-retracting end of the extra-large 17 - 4PH forging upward, and perform three-time upsetting with a concave panel until Upsetting is carried out in multiple times, with the single pass reduction ≤ 100 mm, then spin - pressed to size, rolled round, finished, and the finished product is obtained.

[0029] In the present invention, the shrinkage cavity, inclusion, etc. are removed by sawing, reducing the crack risk caused by the shrinkage cavity and slag inclusion at the end of the electroslag ingot, ensuring the quality of the outer diameter of the ingot. At the same time, the grain size and flaw detection requirements can be effectively guaranteed by forging in multiple times.

[0030] In some embodiments, the heat treatment includes: solution treatment and a three - step heating, holding, and aging process.

[0031] Preferably, the specific steps of the solution treatment include: heating from an initial temperature ≤ 150 °C at a heating rate ≤ 30 °C / h to 400 ± 30 °C and holding for 8.5 - 9 h, then heating at a heating rate ≤ 30 °C / h to 640 ± 15 °C and holding for 8.5 - 9 h, heating at a heating rate ≤ 60 °C / h to 850 ± 10 °C and holding for 5.5 - 6 h, continuing to heat to 1040 ± 10 °C and holding for 17 - 18 h. After the holding is completed, first air - cool and then air - cool to room temperature for the first aging treatment.

[0032] Preferably, for the first aging treatment of the super - large 17 - 4PH forging: heating from an initial temperature ≤ 150 °C at a heating rate ≤ 30 °C / h to 200 ± 30 °C and holding for 10.5 - 11 h, then heating at a heating rate ≤ 30 °C / h to 520 ± 10 °C and holding for 37 - 38 h. After the holding is completed, air - cool the product to ≤ 32 °C.

[0033] Preferably, for the second aging treatment of the super - large 17 - 4PH forging: heating from an initial temperature ≤ 150 °C at a heating rate ≤ 30 °C / h to 300 ± 30 °C and holding for 10.5 - 11 h, then heating at a heating rate ≤ 30 °C / h to 520 ± 10 °C and holding for 37 - 38 h. After the holding is completed, air - cool the product to ≤ 32 °C.

[0034] Preferably, for the third aging treatment of the super - large 17 - 4PH forging: heating from an initial temperature ≤ 150 °C at a heating rate ≤ 30 °C / h to 300 ± 30 °C and holding for 10.5 - 11 h, then heating at a heating rate ≤ 30 °C / h to 510 ± 10 °C and holding for 37 - 38 h. After the holding is completed, air - cool the product.

[0035] The present invention conducts solution treatment and a three - step heating, holding, and aging treatment on the super - large 17 - 4PH forging. While effectively reducing the volume fractions of retained austenite, copper - rich phase, and dispersed precipitation phase at room temperature, it maximally reduces the internal stress of the workpiece, realizes controllable matrix grain size, ensures the strength, plasticity, and toughness of the product, and improves the service life of the product.

[0036] In the second aspect of the present invention, there is provided a ten-ton 17-4PH precipitation-hardening martensitic stainless steel prepared by the above method, all of which meet the standard requirements, the grain size is 2-3 grades, and the mechanical properties meet the standard requirements.

[0037] In the third aspect of the present invention, there is provided the application of the above-mentioned ten-ton 17-4PH precipitation-hardening martensitic stainless steel in aerospace, petrochemical, offshore engineering, die manufacturing and pressure vessels.

[0038] Advantages of the present invention

[0039] (1) The ten-ton 17-4PH precipitation-hardening martensitic stainless steel of the present invention performs a tensile test in accordance with the GB / T 228.1 standard, and an impact test is carried out in accordance with the GB / T 229 test method for Charpy pendulum impact test of metallic materials. After testing, the mechanical property indexes of the ten-ton 17-4PH precipitation-hardening martensitic stainless steel produced and manufactured according to the present invention are shown in Table 1. Ultrasonic flaw detection is carried out in accordance with the Class B standard of the GJB1580A-2019 standard, wherein all of which meet the standard requirements, and at the same time, the grain size of the product is detected to be 2-3 grades.

[0040] (2) The present invention performs solution treatment and three-step step-by-step heating and holding aging process on ultra-large 17-4PH forgings, successfully controls the volume fractions of retained austenite, copper-rich phase and dispersed precipitation phase in the product, achieves a controllable matrix grain size, effectively inhibits the precipitation of adverse phases, and at the same time significantly reduces the internal stress of the workpiece and significantly reduces the cracking risk of the product.

[0041] (3) Through the present invention, not only the mechanical properties of the product are ensured, but also its service life is significantly extended, and a number of technical problems in this field are effectively solved.

[0042] Table 1 Product mechanical property indexes

[0043] Brief description of the drawings

[0044] The specification drawings constituting a part of the present invention are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention.

[0045] Figure 1 It is an optical microscope metallographic diagram of the ten-ton 17-4PH precipitation-hardening martensitic stainless steel provided in Embodiment 1 of the present invention. Detailed implementation manners

[0046] It should be noted that the following detailed description is exemplary and is intended to provide further illustration of the present invention. Unless otherwise specified, all technical and scientific terms used in the present invention have the same meaning as commonly understood by those of ordinary skill in the technical field to which the present invention pertains.

[0047] The present invention will be further described in detail below in conjunction with specific embodiments. It should be noted that the specific embodiments are interpretations rather than limitations of the present invention.

[0048] Embodiment 1:

[0049] The chemical composition and weight percentage of the 17-4PH electrode material are as follows: C: 0.044%, Si: 0.20%, Mn: 0.74%, P: 0.017%, S: 0.002%, Cr: 15.15%, Ni: 4.67%, Nb: 0.26%, Cu: 3.20%, and the balance is Fe. The actual composition of the slag system used is a pre-melted slag with CaF2:Al2O3:MgO = 64.5:30.7:4.8, and the slag amount is 950 kg. The consumable electrode needs to be ground by a grinding machine before use to remove the surface scale. During use, no welding slag or scale is allowed, and the surface and end face of the electrode blank need to be cleaned in advance.

[0050] Slag making: Ignite the consumable electrode of the metal, start the arc through 17-4PH steel chips, the voltage is 62.5 V, add the slag material when the voltage reaches 65 V, raise one gear every 20 minutes, and the current is 10 KA.

[0051] Remelting: For the first group, the maximum melting rate in the early stage is controlled at 1650 kg / h, the voltage is 72.5 V, lower one gear after 1 h, and then lower one gear every half hour, and the melting rate is controlled at 1450 kg / h; for the second group, the melting rate is controlled at 1300 kg / h, the voltage is 65 V, and lower one gear of voltage if the melting rate exceeds this range; for the third group, the melting rate is controlled at 1250 kg / h, the voltage is 62.5 V, and lower one gear of voltage if the melting rate exceeds this range; for the fourth group, the melting rate is controlled at 1150 kg / h, the voltage is 60 V, and lower one gear of voltage if the melting rate exceeds this range. Adjust the voltage and current according to the melting rate, and the current fluctuation ≤ 1000 A. The current needs to match the voltage, and ensure that the electrode burial depth cannot be too deep throughout the process. When the remaining material enters again, the deoxidizer dosage is doubled for the first three times to prevent element burning loss, control the argon flow rate at 53 Nm 3 / h, and seal the furnace mouth well. During this stage, add aluminum powder at 70 g / 5 min evenly for deoxidation.

[0052] Feeding: Feed the feeding material at a height of 400 mm from the ingot bottom, and start feeding when the height difference from the planned ingot height is 350 mm. During feeding, the current gradually decreases. Calculate the thickness of the slag mass as 230 mm. After the feeding material enters, control the melting rate at 1060 kg / h; at a height of 260 mm from the ingot bottom, control the melting rate at 960 kg / h; at a height of 180 mm from the ingot bottom, control the melting rate at 910 kg / h; at a height of 80 mm from the ingot bottom, control the melting rate at 810 kg / h; at a height of 30 mm from the ingot bottom, the melting rate is 710 kg / h and then gradually decreases to 280 kg / h. The feeding voltage is 55 - 65 V, and it is reduced by one level at a height of 25 mm from the ingot bottom until the end of smelting. The feeding stage is controlled within 3.5 h. Adjust the voltage and current according to the melting rate, and the current fluctuation ≤ 1000 A. The current needs to match the voltage, and ensure that the electrode immersion depth is not too deep throughout the process. Control the argon flow rate at 53 Nm 3 / h, and seal the furnace mouth well. Add aluminum powder evenly at a rate of 50 g / 5 min during this stage. Finally, after the electroslag ingot is cooled in the mold for 4 h, demold it and load it into an annealing furnace for stress relief annealing treatment.

[0053] Among them, during the electroslag remelting process, when exchanging electrodes, it should be done quickly and in a timely manner. Control the electrode exchange time within 200 s. The three electrodes should be centered with the mold. Bake and preheat them for a long time in advance before screwing them in to ensure that the melting rate can be quickly increased after electrode exchange and avoid the appearance of slag channels.

[0054] Forging: After the electroslag ingot is annealed, saw off 100 mm long at the arc starting end and 180 mm long at the arc ending end, and clean the surface slag channels.

[0055] The initial forging temperature of the first fire is 1180 °C (holding for 20 h), and the final forging temperature is 1000 °C. Then roll the electroslag ingot horizontally, with a single-side reduction of 30 mm. During this period, strictly control the reduction and surface quality, without obvious indentations and slag channels.

[0056] The initial forging temperature of the second fire is 1200 °C (holding for 4.5 h), and the final forging temperature is 1000 °C. Upset the super-large 17-4PH forging once, and upset it to The upsetting is carried out in multiple times, with a single-side reduction ≤ 100 mm each time, and then roll it round; the initial forging temperature of the third fire is 1200 °C (holding for 4.5 h), and the final forging temperature is 1000 °C. Stretch the super-large 17-4PH forging with an 850 flat anvil, turn it 45° in sequence, and stretch it to an octagon with a side length of 1260 mm, with a reduction of 8%; the initial forging temperature of the fourth fire is 1200 °C (holding for 4.5 h), and the final forging temperature is 1000 °C. Upset the super-large 17-4PH forging twice to The upsetting is carried out in multiple times, with a single-side reduction ≤ 100 mm each time, and roll it round; the initial forging temperature of the fifth fire is 1200 °C (holding for 3.5 h), and the final forging temperature is 1000 °C. Stretch the super-large 17-4PH forging with an 850 flat anvil, turn it 45° in sequence, and stretch it to an octagon with a side length of 1260 mm, with a reduction of 8%.

[0057] The sixth starting forging temperature is 1180 °C (holding for 2.5 h), and the final forging temperature is 1000 °C. For the ultra-large 17-4PH forgings, with the arc-extinguishing end upward, the concave panel is upset three times to The upsetting is carried out in multiple times, with the single reduction amount ≤ 100 mm, then spun to the size, rolled round, finished, and the finished product is obtained.

[0058] Heat treatment: First, solution treatment is carried out on the ultra-large 17-4PH forgings. When the initial temperature ≤ 150 °C, it is heated to 420 °C at a heating rate of 25 °C / h and held for 8.5 h, then heated to 640 °C at a heating rate of 25 °C / h and held for 8.5 h, heated to 850 °C at a heating rate of 55 °C / h and held for 5.5 h, and continuously heated to 1040 °C and held for 17 h. After the holding is completed, the product is lifted and placed on the padding iron for air cooling first and then air cooling. The temperature is measured every 1 h during air cooling and every 2 h during air cooling. The temperature measurement is carried out at the central position and recorded. It is air-cooled to 327 °C, and then air-cooled to room temperature and then the first aging treatment is carried out.

[0059] The first aging treatment is carried out on the ultra-large 17-4PH forgings. The specific first aging process is to heat to 210 °C at a heating rate of 20 °C / h when the initial temperature ≤ 150 °C and hold for 10.5 h, then heat to 525 °C at a heating rate of 25 °C / h and hold for 37 h. After the holding is completed, the product is air-cooled to ≤ 32 °C.

[0060] The second aging treatment is carried out on the ultra-large 17-4PH forgings: The specific second aging process is to heat to 320 °C at a heating rate of 20 °C / h when the initial temperature ≤ 150 °C and hold for 10.5 h, then heat to 520 °C at a heating rate of 25 °C / h and hold for 37 h. After the holding is completed, the product is air-cooled to ≤ 32 °C.

[0061] The third aging treatment is carried out on the ultra-large 17-4PH forgings: The specific third aging process is to heat to 310 °C at a heating rate of 20 °C / h when the initial temperature ≤ 150 °C and hold for 10.5 h, then heat to 515 °C at a heating rate of 25 °C / h and hold for 37 h. After the holding is completed, the product is air-cooled.

[0062] The mass of the ten-ton 17-4PH precipitation-hardening martensitic stainless steel obtained is 18480 kg. Tensile tests are carried out in accordance with the GB / T 228.1 standard and Charpy pendulum impact test methods for metallic materials are carried out in accordance with the GB / T 229 standard for testing. The mechanical properties are excellent, and the measured values of the mechanical properties are shown in Tables 2 and 3. Ultrasonic flaw detection is carried out in accordance with the Class B standard of the GJB 1580A-2019 standard for testing. In the matrix All meet the standard requirements. At the same time, the grain size of the product is detected to be 2-3 levels.

[0063] Example 2

[0064] The difference from Example 1 is as follows:

[0065] Slag making: Ignite the consumable metal electrode, strike an arc through 17-4PH steel chips, with a voltage of 63V, add slag materials when the voltage reaches 67.5V, increase one gear every 25 minutes, and control the current at 9KA.

[0066] Remelting: For the first group, the maximum melting speed in the early stage is controlled at 1600 kg / h, with a voltage of 70V. After 1 hour, reduce one gear, and then reduce one gear every half hour, with the melting speed controlled at 1400 kg / h; for the second group, the melting speed is controlled at 1300 kg / h, with a voltage of 62.5V. If the melting speed exceeds this range, reduce one gear of voltage; for the third group, the melting speed is controlled at 1150 kg / h, with a voltage of 60V. If the melting speed exceeds this range, reduce one gear of voltage; for the fourth group, the melting speed is controlled at 1100 kg / h with a voltage of 57.5V. If the melting speed exceeds this range, reduce one gear of voltage.

[0067] Feeding: Inject feeding materials at a height of 390 mm from the ingot height, and conduct feeding when the difference from the planned ingot height is 340 mm. During feeding, the current gradually decreases. Calculate the slag lump thickness according to 230 mm. After the feeding materials enter, control the melting speed at 1050 kg / h; at a height of 200 mm from the ingot height, control the melting speed at 950 kg / h; at a height of 120 mm from the ingot height, control the melting speed at 900 kg / h; at a height of 50 mm from the ingot height, control the melting speed at 800 kg / h; at a height of 25 mm from the ingot height, gradually reduce the melting speed from 700 kg / h to 280 kg / h. The feeding voltage is 50 - 60V. Reduce one gear at a height of 20 mm from the ingot height until the smelting ends. The feeding stage is controlled within 3.6h.

[0068] Forging: The starting forging temperature of the second heat is 1200 °C (holding for 4h), and the final forging temperature is 1000 °C. For extra-large 17-4PH forgings, perform upsetting once until The upsetting is carried out in multiple times, with the single reduction amount ≤ 100 mm, and then roll it round; the starting forging temperature of the third heat is 1200 °C (holding for 4h), and the final forging temperature is 1000 °C. For extra-large 17-4PH forgings, perform drawing out with an 850 flat anvil, turn it 45° in sequence, and draw it out to an octagon with a side length of 1260 mm, with a reduction amount of 5%; the starting forging temperature of the fourth heat is 1200 °C (holding for 4h), and the final forging temperature is 1000 °C. For extra-large 17-4PH forgings, perform upsetting twice until The upsetting is carried out in multiple times, with the single reduction amount ≤ 100 mm, and roll it round; the starting forging temperature of the fifth heat is 1200 °C (holding for 3h), and the final forging temperature is 1000 °C. For extra-large 17-4PH forgings, perform drawing out with an 850 flat anvil, turn it 45° in sequence, and draw it out to an octagon with a side length of 1260 mm, with a reduction amount of 5%.

[0069] The starting forging temperature of the sixth heat is 1180 °C (holding for 2 h), and the finishing forging temperature is 1000 °C. For the extra-large 17-4PH forgings, with the arc-termination end upward, the concave panel is upset three times to The upsetting is carried out in multiple steps, with the single-pass reduction amount ≤ 100 mm. It is spun to the size, rolled round, finished, and the finished product is obtained.

[0070] Example 3

[0071] The difference from Example 1 is as follows:

[0072] Slag making: Ignite the consumable metal electrode, strike an arc with 17-4PH steel chips, the voltage is 62.5 V, add the slag material when the voltage reaches 65 V, increase one gear every 20 min, and control the current at 11 KA.

[0073] Remelting: For the first group, the maximum melting rate in the early stage is controlled at 1600 kg / h, the voltage is 70 V, reduce one gear after 1 h, and then reduce one gear every half hour, with the melting rate controlled at 1500 kg / h; for the second group, the melting rate is controlled at 1350 kg / h, the voltage is 65 V, and reduce one gear of voltage when the melting rate exceeds this range; for the third group, the melting rate is controlled at 1250 kg / h, the voltage is 62.5 V, and reduce one gear of voltage when the melting rate exceeds this range; for the fourth group, the melting rate is controlled at 1200 kg / h, the voltage is 60 V, and reduce one gear of voltage when the melting rate exceeds this range.

[0074] Feeding: Inject the feeding material at 400 mm from the ingot height, carry out feeding when the difference from the planned ingot height is 340 mm, and the current gradually decreases during feeding. The thickness of the slag lump is calculated as 230 mm. After the feeding material enters, the melting rate is controlled at 1060 kg / h; at 220 mm from the ingot height, the melting rate is controlled at 960 kg / h; at 150 mm from the ingot height, the melting rate is controlled at 910 kg / h; at 60 mm from the ingot height, the melting rate is controlled at 810 kg / h; at 30 mm from the ingot height, the melting rate is 710 kg / h, and then gradually decreases to 280 kg / h until the end of smelting. The feeding voltage is 52.5 - 62.5 V, reduce one gear at 20 mm from the ingot height until the end of smelting, and the feeding stage is controlled at 3.5 h.

[0075] Forging: The starting forging temperature of the second heat is 1200 °C (holding for 5 h), and the finishing forging temperature is 1000 °C. Carry out one upsetting on the extra-large 17-4PH forgings, and upset to Upsetting is carried out in multiple times, with the single-pass reduction ≤ 100 mm, and then it is rolled round; the starting forging temperature of the third heating is 1200 °C (holding for 5 h), and the finishing forging temperature is 1000 °C. Forging elongation of the super-large 17-4PH forging is carried out with an 850 flat anvil, turning 45° in sequence, elongating to an octagon with a side length of 1260 mm, and the reduction is 5-10%; the starting forging temperature of the fourth heating is 1200 °C (holding for 5 h), and the finishing forging temperature is 1000 °C. The super-large 17-4PH forging is upset twice to Upsetting is carried out in multiple times, with the single-pass reduction ≤ 100 mm, and it is rolled round; the starting forging temperature of the fifth heating is 1200 °C (holding for 3-4 h), and the finishing forging temperature is 1000 °C. Forging elongation of the super-large 17-4PH forging is carried out with an 850 flat anvil, turning 45° in sequence, elongating to an octagon with a side length of 1260 mm, and the reduction is 10%.

[0076] The starting forging temperature of the sixth heating is 1180 °C (holding for 3 h), and the finishing forging temperature is 1000 °C. For the super-large 17-4PH forging, with the arc end facing up, it is upset three times with a concave panel to Upsetting is carried out in multiple times, with the single-pass reduction ≤ 100 mm, spun to size, rolled round, finished, and the finished product is obtained.

[0077] Comparative Example 1

[0078] The difference from Example 1 is that the traditional 17-4PH chemical composition and weight percentages are: C: 0.058%, Si: 0.19%, Mn: 0.68%, P: 0.020%, S: 0.005%, Cr: 16.10%, Ni: 4.10%, Nb: 0.21%, Cu: 3.10%, and the balance is Fe.

[0079] Comparative Example 2

[0080] The difference from Example 1 is that the traditional heat treatment method is adopted: air cooling is used during the solution treatment cooling and a single heating and holding aging process, that is: holding at 1040 °C for 18 h, after the holding is completed, air cooling to room temperature and then carrying out a single 520 °C holding for 38 h aging treatment.

[0081] Table 2 Measured tensile values of examples and comparative examples

[0082]

[0083]

[0084] Table 3 Measured impact values of examples and comparative examples

[0085]

[0086] From the comparison between Example 1 and Comparative Example 1, it can be seen that by adopting the alloy formula of the present invention, while maintaining excellent mechanical properties, the impact resistance is significantly improved.

[0087] From the comparison between Example 1 and Comparative Example 2, it can be seen that compared with the traditional method, adopting the heat treatment process of the present invention can obtain better mechanical properties, and at the same time, the impact resistance is significantly improved.

[0088] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, the present invention can have various changes and modifications. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A production process for 10-ton 17-4PH precipitation hardening martensitic stainless steel, characterized in that: include: According to the chemical composition of the electrode material of 10-ton 17-4PH precipitation hardening martensitic stainless steel and the raw materials of the slag system, electroslag remelting, forging and heat treatment are carried out in sequence to obtain; Wherein, the ten-ton grade 17-4PH precipitation hardening martensitic stainless steel is composed of the following chemical components in weight percentage: C: 0.03-0.05%, Si: ≤0.40%, Mn: 0.70-0.80%, P≤0.03%, S≤0.008%, Cr: 15.00-15.50%, Ni: 4.50-5.00%, Nb: 0.20-0.30%, Cu: 3.00-3.50%, and the balance is Fe; The slag system is composed of CaF2, Al2O3 and MgO, and the mass ratio of CaF2, Al2O3 and MgO is (65±2):(30±2):(5±0.5).

2. The manufacturing process for the ten-ton 17-4PH precipitation hardening martensitic stainless steel according to claim 1, characterized in that: The specific steps of slag making include: ignition of consumable electrode, arc starting through 17-4PH steel scraps, arc starting voltage of 62.5-63V, adding slag when the voltage is 65-67.5V, raising the voltage by one level every 20-25min, and controlling the current at 6-12KA; Or, the specific steps of remelting include: in the first group, the maximum melting rate is controlled at 1600-1650kg / h in the early stage, the voltage is 70-72.5V, and it is reduced by one level after 1-1.5h, and then reduced by one level every 0.5-0.8h until the melting rate is controlled at 1400-1500kg / h; in the second group, the melting rate is controlled at 1250-1350kg / h, the voltage is 57.5-67.5V, and the voltage is reduced by one level when the melting rate exceeds this range; in the third group, the melting rate is controlled at 1150-1250kg / h, the voltage is 55-67.5V, and the voltage is reduced by one level when the melting rate exceeds this range; in the fourth group, the melting rate is controlled at 1100-1200kg / h, the voltage is 52.5-65V, and the voltage is reduced by one level when the melting rate exceeds this range; adjust the voltage and current according to the melting rate, and the current fluctuation is ≤1000A; control the argon gas flow rate ≥50Nm 3 / h; During this stage, 70-75g / 5min of aluminum powder is evenly added for deoxidation; Or, the specific steps of feeding include: injecting the feeding material at a distance of 390-400mm from the ingot height, feeding at a distance of 340-350mm from the planned ingot height difference, and gradually reducing the power during the feeding period; after the feeding material enters, the melting rate is controlled at 1050-1060kg / h, and the melting rate is controlled at 950-960kg / h at a distance of 180-260mm from the ingot height; the melting rate is controlled at 900-910kg / h at a distance of 80-180mm from the ingot height; When the ingot height is 30-80mm, the melting rate is controlled at 800-810kg / h; when the ingot height is 0-30mm, the melting rate is gradually reduced from 700-710kg / h to 280kg / h; the feeding voltage is between 50 and 65V, and it is reduced by one level when the ingot height is 20-25mm. The whole feeding stage is controlled at 3.5-3.6h; the voltage and current are adjusted according to the melting rate, the current fluctuation is controlled at ≤1000A, and the argon flow rate is controlled at ≥50Nm 3 / h, the deoxidizer during the shrinkage period is 50-55g / 5min of aluminum powder; finally, the electroslag ingot mold is cooled for 4-4.5h and then demolded and loaded into the furnace for stress relief annealing treatment.

3. The manufacturing process of the ten-ton 17-4PH precipitation hardening martensitic stainless steel according to claim 1, characterized in that: The specific steps of forging include: Before forging, the shrinkage holes at the arc closing end and the iron plates and slag inclusions at the arc striking end are sawed off at both ends of the electroslag ingot, the electroslag ingot body is peeled, the ingot body scars and steel flow are removed, and the tooling is preheated to ≥450℃; Or, the arc-starting end of the saw is 100-120mm long, and the arc-ending end is 180-200mm long; Or, the first forging temperature is 1180-1190℃, kept at this temperature for 20-24h, and the final forging temperature is 1000-1010℃, then the electroslag ingot is rolled horizontally, with a single-side reduction of 30-35mm; Or, the second fire forging temperature is 1200-1210℃, keep warm for 4-5h, and the final forging temperature is 1000-1010℃. The super large 17-4PH forgings are upset once, upsetting to The upsetting is carried out in multiple times, with a single pressing amount of ≤100mm, and then rounding; Or, the third fire forging temperature is 1200-1210℃, kept at temperature for 4-5h, the final forging temperature is 1000-1010℃, the super large 17-4PH forgings are stretched flat anvil, turned 45-46° in sequence, stretched to 1260-1270mm in all directions, and the reduction is 5-10%; Or, the fourth fire starts at 1200-1210℃, keeps warm for 4-5h, and the final forging temperature is 1000-1010℃. The super large 17-4PH forgings are subjected to secondary upsetting to The upsetting is carried out in multiple times, with a single pressing amount of ≤100mm, and rounding; Or, the fifth fire starts with a forging temperature of 1200-1210°C, which is kept for 3-4 hours, and the final forging temperature is 1000-1010°C. The super-large 17-4PH forgings are stretched flat on anvil, turned 45° in sequence, stretched to 1260-1270mm in all directions, and the reduction is 5-10%; Or, the sixth fire forging temperature is 1180-1190℃, keep warm for 2-3h, and the final forging temperature is 1000-1010℃. For the super large 17-4PH forging, the arc end is upward and the concave panel is upset three times to The upsetting is carried out in multiple times, with the single pressing amount ≤100mm. It is spun to size, rounded, and finished.

4. The manufacturing process for the ten-ton 17-4PH precipitation hardening martensitic stainless steel according to claim 1, characterized in that: The heat treatment includes: solution treatment and three-step heating and heat preservation aging processes.

5. The manufacturing process for the ten-ton 17-4PH precipitation hardening martensitic stainless steel according to claim 4, characterized in that: The specific steps of the solution treatment include: when the initial temperature is ≤150°C, heating the temperature to 400±30°C at a heating rate of ≤30°C / h and keeping the temperature for 8.5-9h, then heating the temperature to 640±15°C at a heating rate of ≤30°C / h and keeping the temperature for 8.5-9h, heating the temperature to 850±10°C at a heating rate of ≤60°C / h and keeping the temperature for 5.5-6h, and then heating the temperature to 1040±10°C and keeping the temperature for 17-18h. After the insulation is completed, firstly air-cooling and then air-cooling are performed to 300-400°C, and then air-cooling to room temperature before the first aging treatment.

6. The manufacturing process for the ten-ton 17-4PH precipitation hardening martensitic stainless steel according to claim 4, characterized in that: The first aging treatment of the super-large 17-4PH forgings is performed as follows: when the initial temperature is ≤150°C, the temperature is increased to 200±30°C at a heating rate of ≤30°C / h and kept warm for 10.5-11h, and then the temperature is increased to 520±10°C at a heating rate of ≤30°C / h and kept warm for 37-38h. After the insulation is completed, the product is air-cooled to ≤32°C.

7. The manufacturing process for the ten-ton 17-4PH precipitation hardening martensitic stainless steel according to claim 4, characterized in that: The second aging treatment is carried out on the super-large 17-4PH forgings: when the initial temperature is ≤150℃, the temperature is increased to 300±30℃ at a heating rate of ≤30℃ / h and kept warm for 10.5-11h, and then the temperature is increased to 520±10℃ at a heating rate of ≤30℃ / h and kept warm for 37-38h. After the insulation is completed, the product is air-cooled to ≤32℃.

8. The manufacturing process for the ten-ton 17-4PH precipitation hardening martensitic stainless steel according to claim 4, characterized in that: The third aging treatment is carried out on the super-large 17-4PH forgings: when the initial temperature is ≤150℃, the temperature is increased to 300±30℃ at a heating rate of ≤30℃ / h and kept at a temperature for 10.5-11h, and then the temperature is increased to 510±10℃ at a heating rate of ≤30℃ / h and kept at a temperature for 37-38h. After the insulation is completed, the product is air-cooled.

9. A 10-ton grade 17-4PH precipitation hardening martensitic stainless steel prepared by the method according to any one of claims 1 to 8, characterized in that: All meet the standard requirements, the grain size is level 2-3, and the mechanical properties meet the standard requirements.

10. Application of the ten-ton 17-4PH precipitation hardening martensitic stainless steel according to claim 9 in aerospace, petrochemical, marine engineering, mold manufacturing and pressure vessels.

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