A process for producing a high strength UNS N07718 alloy bar of 140 ksi grade

Abstract

The present application belongs to the technical field of metal material processing, and discloses a preparation process of 140ksi steel grade high-strength UNS N07718 alloy bar, which comprises the following steps: alloy smelting, homogenization treatment, billet sheath assembly, billet heating, billet forging, peeling off the skin, solid solution treatment, straightening, aging treatment and pickling; when the sheath is assembled, a layer of lubricating glass cotton is wrapped outside the ingot, a stainless steel sleeve is arranged on the lubricating glass cotton sleeve, and the stainless steel sleeve completely encloses the ingot; by arranging the sheath, low-temperature forging is realized, and the problem of rapid temperature drop in low-temperature forging is solved. The present application has high yield, good straightness, high grain size, few cracks, high strength and toughness, high corrosion resistance and low production cost.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of metal material processing, and particularly relates to a preparation process of alloy bar, in particular to a preparation process of 140 ksi steel grade high-strength UNS N07718 alloy bar. BACKGROUND

[0002] UNS N07718 alloy is a Fe-Ni-Cr-based wrought superalloy, which is a key material for aero-engine components such as turbine disc and compressor disc. In recent years, with the increase of the thrust ratio of civil engines, the size of UNS N07718 turbine disc in the low-pressure turbine part of the engine also gradually increases, and the processing difficulty increases. UNS N07718 alloy is composed of a matrix γ phase and a precipitated phase, and excellent high-temperature strength and stability mainly depend on the strengthening phase γ″ (Ni3AlTi) phase and the auxiliary strengthening phase γ' (Ni3Nb) phase. During heat treatment and deformation, δ (Ni3Nb) phase will also be precipitated. The δ phase is a stable phase of γ″, which not only promotes the nucleation of dynamic recrystallization, but also has the functions of pinning grain boundaries to inhibit grain growth and improving fatigue life. Appropriate δ phase can reduce notch sensitivity, but excessive δ phase will reduce the use strength of the alloy, promote crack initiation and propagation, etc. Therefore, it is necessary to reasonably control the content of δ phase. However, the precipitation temperature of γ″ phase is 600-900 ℃, and the precipitation temperature of δ phase is 750-1020 ℃. During heat treatment and deformation of the alloy, γ″ phase will be converted to δ phase which is more stable at high temperature. However, the number, morphology and distribution of δ phase have a great influence on the deformation behavior and mechanical properties of the alloy. Therefore, how to control the precipitation amount of δ phase has become a technical difficulty.

[0003] In the prior art, the forming methods of UNS N07718 bar mainly include forging and hot extrusion, but both have certain shortcomings. The shortcomings of high-temperature forging are that the cast ingot is directly heated to 1140-1150 ℃ for forging, and it is difficult to control the organization under high temperature conditions, and too much δ phase is precipitated, which affects the mechanical properties of the bar. The shortcomings of low-temperature forging are that the temperature drops quickly, the forging window is narrow, the material deformation resistance is large, the tonnage requirement of the forging machine equipment is high, and cracks are prone to occur. The shortcomings of extrusion process are that the equipment investment is large, the direct extrusion of the cast blank is easy to cause uneven organization, the cost is high after the bar is forged and is extruded at low temperature, the extrusion force is high, and the vehicle is prone to be jammed. SUMMARY

[0004] The purpose of the present application is to provide a preparation process of 140 ksi steel grade high-strength UNS N07718 alloy bar, so as to achieve good heat preservation effect in the forging process, reduce the forging difficulty, and make the bar have high grain size, few cracks and stable mechanical properties.

[0005] To achieve the above object, the technical scheme adopted by the present application is as follows:

[0006] A preparation process of 140ksi steel grade high-strength UNS N07718 alloy bar, comprising the following steps:

[0007] S1, alloy smelting: according to the component element ratio, blanking is carried out, and a cylindrical ingot is smelted by a vacuum induction melting + electroslag remelting + vacuum consumable process;

[0008] S2, homogenization treatment: the ingot is heated to 1180-1190 DEG C, and then 1150-1160 DEG C for 45-50 h, and then water cooled;

[0009] S3, blank package assembly: a layer of lubricating glass wool is wrapped outside the ingot obtained in S2, and a stainless steel sleeve is provided on the lubricating glass wool sleeve, so that the stainless steel sleeve completely encloses the ingot;

[0010] S4, blank heating: the blank assembled in S3 is placed into a heating furnace below 500 DEG C, and then heated to 1030 DEG C at a speed of 160-250 DEG C / h, and then kept for 2-3.5 h;

[0011] S5, blank forging: the blank heated in S4 is forged on a forging machine, the downward displacement of each pass is 5-35 mm, the feed displacement is 30-80 mm, the final forging temperature is 950 DEG C, the forging ratio of the blank is 4.5-25, and the blank is cooled in water after forging;

[0012] S6, peeling: the blank forged in S5 is sawn into segments, and the stainless steel sleeve and the lubricating glass wool on the surface are removed by machining to obtain the UNS N07718 alloy bar;

[0013] S7, solid solution treatment: heating by a trolley furnace, entering the furnace below 350 DEG C, then heating to 950-1020 DEG C at a speed of 160-300 DEG C / h, keeping for 1.0-2.0 h, and then transferring into water within 70 s to rapidly cool to below 50 DEG C;

[0014] S8, straightening: straightening the UNS N07718 alloy bar after solid solution treatment;

[0015] S9, aging treatment: heating by a trolley furnace, entering the furnace below 350 DEG C, then heating to 710-730 DEG C at a speed of 160-300 DEG C / h, keeping for more than 8 h, furnace cooling to 610-630 DEG C at a speed of 30-60 DEG C / h, keeping for 16 h, and then air cooling after exiting the furnace;

[0016] S10, pickling: removing the surface oxide skin and oil stains of the UNS N07718 alloy bar after aging treatment in mixed acid to obtain the final product.

[0017] As a limitation of the present application, the composition of the alloy bar is as follows in mass percentage: C: 0.01-0.08%, Nb: 4.90-5.55%, Ni: 50.3-55.0%, Mo: 2.5-3.3%, Al: 0.15-0.65%, Cr: 17.6-20.5%, Co: 0.20-0.60%, Ti: 0.75-1.10%, B: ≤0.005%, Si: ≤0.30%, P: ≤0.014%, S: ≤0.008%, Mn: ≤0.35%, Cu: ≤0.30%, Mg: ≤0.03%, W: ≤0.3%, and the rest is Fe and inevitable impurities.

[0018] As a further limitation of the present application, the diameter of the finished UNS N07718 alloy bar ranges from 50 to 160 mm, and the properties at room temperature are as follows: tensile strength Rm≥1150 MPa, yield strength Rp0.2≥965 MPa, elongation A%≥15%, reduction of area Z%≥30%, grain size finer than 3.0, transverse impact energy at 0℃≥35 J, and corrosion rate in ASTM A262 C method is less than 0.12 mm / month.

[0019] As another limitation of the present application, in S1, the electroslag remelting process controls the smelting current and voltage, and the control range is: voltage 50-80 V, current 7000-13000 A; the outlet water temperature of the crystallizer cooling water in the electroslag remelting process is: 35-70℃; the electroslag remelting slag system uses a CaF2, CaO, Al2O3, MgO2, TiO2 five-element slag system, wherein the CaF2 content is 60%-70%, the CaO content is 10%-20%, and argon protection is used in the whole electroslag remelting process.

[0020] As a limitation of the present application, in S1, the surface of the electrode blank of the electroslag remelting is treated by shot blasting, and vacuum consumable is performed after cleaning the iron oxide scale.

[0021] As a further limitation of the present application, in S3, the thickness of the lubricating glass wool is 2 mm, the thinnest part of the stainless steel sleeve wall is greater than 10 mm, and the gap between the stainless steel sleeve and the UNS N07718 ingot is 3 mm.

[0022] As a further limitation of the present application, in S7, when water cooling, ice cubes are put into the water, the cooling water circulates and flows, and at the same time, the UNS N07718 alloy bar is rotated.

[0023] As a third limitation of the present application, in S10, the mixing ratio of the mixed acid is HF: 2-5%, HNO3: 15-22%, and the rest is water, and the temperature of the acid solution is 40℃-60℃.

[0024] Compared with the prior art, the application has the following technical progress:

[0025] (1) The final forging temperature of the application is 950 DEG C, compared with the traditional technology of high temperature forging of 1140-1150 DEG C, low temperature forging is adopted, because the surface heat dissipation of low temperature forging is faster, the UNS N07718 alloy bar which is difficult to deform is placed in the inside of the package, and the outside is packaged with ordinary 304 stainless steel, which can not only hinder the heat dissipation of the UNS N07718 alloy bar, but also make the UNS N07718 alloy bar in the required forging temperature range, reduce the friction, realize isothermal forging at low temperature, obtain complete fine organization of streamline, improve the grain size, and the material is not easy to crack; because the temperature is relatively constant, the deformation resistance is reduced, the tonnage requirement of the production equipment is reduced, and the manufacturing cost is reduced;

[0026] (2) The application adopts low temperature forging, which can reduce the transformation of gamma '' phase to delta phase, enough gamma '' can maintain the mechanical stability of the bar, and show excellent high temperature strength, and appropriate delta phase not only can promote dynamic recrystallization nucleation, but also has the function of pinning grain boundary to inhibit grain growth, so that the grain is finer, and at the same time, the notch sensitivity can be reduced, the crack generation can be reduced, and the service life can be prolonged;

[0027] (3) The application adopts the three combined smelting mode of vacuum induction melting + electroslag remelting + vacuum consumable, improves the purity of smelting, reduces the interference of impurities, ensures the uniformity of composition through homogenization treatment, and makes the mechanical properties of finished bar more excellent.

[0028] In summary, the application has high material yield, good straightness, high grain size, few cracks, high strength and toughness, and high corrosion resistance, and the production cost is reduced. BRIEF DESCRIPTION OF DRAWINGS

[0029] Figure 1 It is the production process flow chart of embodiment 1 of the application;

[0030] Figure 2 It is the schematic diagram of the blank package assembly structure of embodiment 1 of the application;

[0031] Figure 3 It is the structure schematic diagram of the cooling device in the solid solution treatment stage of embodiment 1 of the application;

[0032] Figure 4 It is the microstructure diagram of embodiment 1 of the application after solid solution + aging treatment, which is enlarged 100 times;

[0033] Figure 5 It is the microstructure diagram of embodiment 1 of the application after solid solution + aging treatment, which is enlarged 500 times;

[0034] Figure 6This is a magnified 100x microstructure image of the tissue after solution treatment and aging treatment in Example 2 of the present invention.

[0035] Figure 7 This is a microstructure image magnified 500 times after solution treatment and aging treatment in Example 2 of the present invention.

[0036] In the diagram: 1. Stainless steel sleeve; 2. Lubricating glass wool; 3. UNS N07718 ingot; 4. Stop block; 5. Drag wheel; 6. UNSN07718 alloy bar. Detailed Implementation

[0037] The present invention will now be described in detail with reference to the embodiments and accompanying drawings. The scope of protection of the present invention is not limited to the embodiments, and any modifications made by those skilled in the art within the scope defined by the claims also fall within the scope of protection of the present invention.

[0038] Example 1

[0039] This embodiment describes the preparation process of a φ50mm 140ksi high-strength UNS N07718 alloy bar, the chemical composition of which is shown in Table 1:

[0040] Table 1 Chemical composition (mass percentage) of φ50mm UNS N07718 alloy bar

[0041]

[0042] The remainder consists of Fe and unavoidable impurities.

[0043] like Figure 1 As shown, the preparation process of φ50mm 140ksi grade high-strength UNS N07718 alloy bar is carried out according to the following steps.

[0044] S1. Alloy Smelting: Materials are prepared according to the elemental composition ratio. Cylindrical ingots are smelted using a combination of vacuum induction melting, electroslag remelting, and vacuum arc remelting processes, with dimensions of φ240mm (diameter) × 1000mm (length). The electroslag remelting process controls the smelting current and voltage, with a control range of 50–60 V for voltage and 7000–9000 A for current. The cooling water outlet temperature of the crystallizer during electroslag remelting is 50℃. The electroslag remelting slag system uses a five-element slag system of CaF2, CaO, Al2O3, MgO2, and TiO2, with CaF2 content of 60%–70% and CaO content of 10%–20%. Argon gas protection is used throughout the electroslag remelting process to ensure the alloy liquid is always protected by an inert gas, effectively preventing secondary oxidation of the alloy liquid. The electrode billet surface of the electroslag remelted material is shot-blasted to remove iron oxide scale before vacuum arc remelting.

[0045] S2, homogenization treatment: the ingot is heated to 1180-1190 °C, and held for 67 h, then 1150-1160 °C for 45 h, and water cooled.

[0046] S3, blank cladding assembly: a layer of lubricating glass wool 2 is wrapped around the ingot obtained in S2, and a stainless steel sleeve 1 is wrapped outside the lubricating glass wool sleeve, so that the stainless steel sleeve 1 completely encloses the UNS N07718 ingot 3. In this embodiment, the thickness of the lubricating glass wool 2 is 2 mm. When making the stainless steel sleeve 1, the size of the ingot is calculated according to the size of the finished rod and the deformation amount, and then the size of the stainless steel sleeve 1 is designed according to the size of the ingot. The thinnest part of the wall thickness of the stainless steel sleeve 1 is greater than 10 mm, and the gap between the stainless steel sleeve 1 and the UNS N07718 ingot 3 is 3 mm. A part of the stainless steel sleeve 1 is in a barrel structure, and the opening end is welded and sealed by a stop block 4 to completely enclose the ingot in the stainless steel sleeve 1. The material of the stainless steel sleeve 1 is 304L material.

[0047] S4, blank heating: the blank after S3 assembly is placed into a heating furnace below 500 °C, and then heated to 1030 °C at a speed of 160-250 °C / h, and held for 3 h.

[0048] S5, blank forging: the blank after S4 heating is forged on a forging machine, with a downward displacement of 5-35 mm per pass, a feed amount of 30-80 mm, a final forging temperature of 950 °C, and a blank forging ratio of 4.5-25. After forging, the blank is cooled in water.

[0049] S6, peeling off the skin: the blank after S5 forging is sawn into segments, and the stainless steel sleeve 1 and the lubricating glass wool 2 on the surface are removed by machining to obtain UNS N07718 alloy rod.

[0050] S7, solution treatment: heating with a trolley furnace, entering the furnace below 350 °C, then heating to 950-960 °C at a speed of 160-300 °C / h, holding for 1.5 h, and transferring the UNS N07718 alloy rod obtained in S6 to water within 70 s, and placing it on a tow wheel 5. During the cooling process, the tow wheel 5 rotates to drive the UNS N07718 alloy rod 6 to rotate. Ice blocks are put into the water, and the cooling water circulates to quickly cool the rod to below 50 °C, greatly reducing the degree of bending after cooling.

[0051] S8, straightening: the UNS N07718 alloy rod after solution treatment is straightened by applying pressure to one point with two-point support.

[0052] S9, aging treatment: heating with a trolley furnace, entering the furnace below 350 °C, then heating to 710-730 °C at a speed of 160-300 °C / h, holding for 9 h or more, furnace cooling at 30-60 °C / h to 610-630 °C, holding for 16 h, and air cooling after exiting the furnace.

[0053] S10, pickling: the UNS N07718 alloy bar after aging is removed from the surface of the oxide and oil in the mixed acid to obtain the final product, the mixed acid ratio is HF: 2%, HNO3: 22%, the rest is water, the temperature of the acid solution is 60℃.

[0054] The obtained final product is detected, wherein nondestructive testing is carried out by ultrasonic flaw detection and color penetration detection, and physical and chemical testing of composition, mechanical properties, microstructure and corrosion performance is carried out.

[0055] As shown in Figure 4 , Figure 5 , the bar after forging is treated by solid solution aging, a metallographic sample is prepared and the surface is polished, a corrosion solution (a mixture of 4g potassium permanganate, 10ml sulfuric acid and 95ml distilled water) is configured, the sample is placed in the corrosion solution heated to a slightly boiling state and boiled for 10-15min, and then observed under a metallographic microscope. The grain size is uniform, the matrix structure is austenite, and the precipitated phase is mainly the compound of Nb and Ti. The difference in the structure of the whole cross section of the sample is not large. The structure of the NbC phase is irregularly oval, and the TiN phase is regularly angular. NbC and TiN are formed during smelting, pouring and solidification, and are not easy to dissolve. They are isolated intergranular precipitates and do not have other harmful precipitates. The grain boundary of the austenite is clean, the grain size is 5.5 according to the detection of GB / T 6394-2017 Metal Average Grain Size Determination Method, the grain is relatively uniform, there is no mixed crystal, and there is no needle-like precipitate. The good microstructure provides a good organizational basis for high strength and high toughness stability, and the metallographic structure meets the requirements of API STD 6A CRA-2015 Aging Hardened Nickel-Based Alloy for Oil and Gas Drilling and Production Equipment.

[0056] Three final products of UNS N07718 alloy bars are randomly selected in this embodiment, numbered 1#, 2# and 3#, and the detection results at room temperature are shown in Table 2:

[0057] Table 2 Properties of UNS N07718 alloy bar products with a diameter of 50mm

[0058]

[0059] As shown in Table 2, the tensile strength Rm is ≥1150MPa, the yield strength Rp0.2 is ≥965MPa, the elongation A% after fracture is ≥15%, the reduction of area Z% is ≥30%, the grain size is finer than 3.0, the transverse impact energy at 0℃ is ≥35J, and the corrosion rate is less than 0.12mm / month.

[0060] The embodiment is widely applied in aerospace, nuclear energy, petroleum chemical industry and the like. The alloy bar is a raw material for producing key components such as rotating parts and turbine discs of a space engine, and the cast ingot prepared through vacuum induction melting and electroslag remelting has very coarse grains after homogenization heat treatment, and the grain size is controlled to be above grade 3 after package forging, and the alloy bar of the embodiment is an iron-nickel-based high-temperature alloy strengthened by body-centered cubic Ni3Nb and face-centered cubic Ni3 (Al, Ti), and has high oxidation resistance, high strength, good corrosion resistance and the like at 650 DEG C.

[0061] Embodiment 2

[0062] The embodiment is a preparation process of a φ160mm 140ksi steel grade high-strength UNS N07718 alloy bar, and the chemical components are shown in Table 3.

[0063] Table 3 Chemical components of the φ160mm UNS N07718 alloy bar (% by mass)

[0064]

[0065] The rest is Fe and inevitable impurities.

[0066] The preparation process of the φ160mm 140ksi steel grade high-strength UNS N07718 alloy bar is carried out according to the following steps.

[0067] S1, alloy smelting: according to the component element ratio, the alloy is smelted into a cylindrical ingot with a specification of φ550mm (diameter) x 1200mm (length) through vacuum induction melting + electroslag remelting + vacuum consumable process; the smelting current and voltage are controlled in the electroslag remelting process, and the control range is: voltage 60-80 V, current 9000-13000 A; the crystallizer cooling water outlet temperature in the electroslag remelting process is 70 DEG C; the electroslag remelting slag system adopts a CaF2, CaO, Al2O3, MgO2 and TiO2 five-element slag system, wherein the CaF2 content is 60%-70%, and the CaO content is 10%-20%; argon gas protection is adopted in the whole electroslag remelting process, so that the alloy liquid is always protected by inert gas in the smelting process, and the secondary oxidation of the alloy liquid is effectively prevented. The surface of the electrode blank of the electroslag remelting is treated by shot blasting, and then the vacuum consumable process is carried out after the iron oxide skin is cleaned.

[0068] S2, homogenization treatment: the ingot is heated to 1180-1190 DEG C, and then kept at 1150-1160 DEG C for 50h, and then water-cooled.

[0069] S3, blank package assembly: the ingot obtained in S2 is wrapped with a layer of lubricating glass wool 2, and a stainless steel sleeve 1 is sleeved outside the lubricating glass wool 2, so that the stainless steel sleeve 1 completely encloses the ingot. In the embodiment, the thickness of the lubricating glass wool 2 is 2 mm. When the stainless steel sleeve 1 is made, the size of the ingot is calculated according to the size of the finished rod and the deformation amount, and then the size of the stainless steel sleeve 1 is designed according to the size of the ingot. The thinnest part of the wall thickness of the stainless steel sleeve 1 is greater than 10 mm, and the gap between the stainless steel sleeve 1 and the UNS N07718 ingot 3 is 3 mm. A part of the stainless steel sleeve 1 is in a barrel structure, and the opening end is welded and sealed by a stop block 4. The material of the stainless steel sleeve 1 is 304L material.

[0070] S4, blank heating: the blank assembled in S3 is placed into a heating furnace below 500°C, and then heated to 1030°C at a speed of 160-250°C / h, and kept for 2 h.

[0071] S5, blank forging: the blank heated in S4 is forged on a forging machine, the downward pressing amount of each pass is 5-35 mm, the feed amount is 30-80 mm, the final forging temperature is 950°C, the forging ratio of the blank is 4.5-25, and the blank is cooled in water after forging.

[0072] S6, peeling off the skin: the blank after forging in S5 is sawn and segmented, and the stainless steel sleeve 1 and the lubricating glass wool 2 on the surface are removed by machining to obtain the UNS N07718 alloy rod.

[0073] S7, solution treatment: heating with a trolley furnace, entering the furnace below 350°C, then heating to 990-1020°C at a speed of 160-300°C / h, keeping for 1.0 h, and transferring the UNS N07718 alloy rod obtained in S6 to water within 70S, and placing it on a tow wheel 5 horizontally. During the cooling process, the tow wheel 5 rotates to drive the UNS N07718 alloy rod 6 to rotate. Ice blocks are put into the water, and the cooling water circulates to quickly cool the rod to below 50°C, greatly reducing the bending degree after cooling.

[0074] S8, straightening: the UNS N07718 alloy rod after solution treatment is straightened by the method of two-point support and one-point pressure application.

[0075] S9, aging treatment: heating with a trolley furnace, entering the furnace below 350°C, then heating to 710-730°C at a speed of 160-300°C / h, keeping for 10 h or more, furnace cooling to 610-630°C at a speed of 30-60°C / h, keeping for 16 h, and air cooling after exiting the furnace.

[0076] S10. Pickling: After aging, the UNS N07718 alloy bars are pickled in a mixed acid solution to remove surface oxide scale and oil stains, and the final product is obtained. The ratio of the mixed acid solution is HF: 5%, HNO3: 15%, and the remainder is water. The temperature of the acid solution is 50℃.

[0077] The final product is tested, including non-destructive testing using ultrasonic testing and dye penetrant testing, as well as physicochemical testing for composition, mechanical properties, microstructure, and corrosion resistance.

[0078] like Figure 6 , Figure 7 As shown, after forging, the bar stock underwent solution aging treatment. Metallographic samples were prepared and polished. A etching solution (a mixture of 4g potassium permanganate, 10ml sulfuric acid, and 95ml distilled water) was prepared. The samples were placed in the etching solution heated to a slight boiling state for 10-15 minutes and then observed under a metallographic microscope. The grain size was uniform, the matrix was austenite, and the precipitates were mainly compounds of Nb and Ti. The microstructure of the entire cross-section of the sample was not significantly different. The NbC phase had an irregular elliptical shape, while the TiN phase had a regular angular shape. Both NbC and TiN were formed during smelting, casting, and solidification, and were not easily dissolved. They were isolated intergranular precipitates without other harmful precipitates. The austenite grain boundaries were clean, and the grain size was grade 4 according to GB / T 6394-2017 "Method for Determination of Average Grain Size of Metals". The grains were relatively uniform, without mixed crystals or needle-like precipitates. It provides a good microstructure for high strength and high toughness stability, and the metallographic structure meets the requirements of the API STD 6A CRA-2015 standard for age-hardening nickel-based alloys for oil and gas drilling and production equipment.

[0079] In this embodiment, three final products of UNS N07718 alloy bars were randomly selected and numbered 4#, 5#, and 6# respectively. The test results at room temperature are shown in Table 4:

[0080] Table 4. Properties of finished UNS N07718 alloy bars with a diameter of 160 mm

[0081]

[0082] As shown in Table 4, the tensile strength Rm≥1150MPa, yield strength Rp0.2≥965MPa, elongation after fracture A%≥15%, reduction of area Z%≥30%, grain size finer than grade 3.0, transverse impact energy at 0℃≥35J, and corrosion rate less than 0.12mm / month.

[0083] Comparative Example 1

[0084] Take one φ50mm 140ksi steel grade high strength UNS N07718 alloy bar made by using the prior art preparation process, numbered a.

[0085] Product mechanical property detection: 1#, 2#, 3# of example 1 and the same specification ordinary alloy bar of comparative example 1 are compared, and detailed comparison is shown in table 5.

[0086] Table 5 mechanical property comparison of alloy bar of example 1 and comparative example 1

[0087]

[0088] As shown in table 5, among the same specification alloy bars, the bar produced after wrapping the stainless steel sleeve 1 in the embodiment has high strength, high yield strength, improved elongation after fracture and area reduction, high impact, fine grain size and less cracks.

[0089] Comparative example 2

[0090] Take one φ160mm 140ksi steel grade high strength UNS N07718 alloy bar made by using the prior art preparation process, numbered b.

[0091] Product mechanical property detection: 4#, 5#, 6# of example 2 and the same specification b ordinary alloy bar of comparative example are compared, and detailed comparison is shown in table 6.

[0092] Table 6 mechanical property comparison of alloy bar of example 2 and comparative example 2

[0093]

[0094] As shown in table 6, among the same specification alloy bars, the bar produced after wrapping the stainless steel sleeve 1 in the embodiment has high strength, high yield strength, improved elongation after fracture and area reduction, high impact, fine grain size and less cracks.

[0095] It should be noted that the above only describes the preferred embodiments of the present application and is not intended to limit the present application. Although the present application has been described in detail with reference to the above embodiments, those skilled in the art can still modify the technical solutions described in the above embodiments or make equivalent replacements to some technical features. Any modification, equivalent replacement, improvement, etc. made within the spirit and principles of the present application shall be included in the protection scope of the present application.

Claims

1. A process for producing a high strength UNS N07718 alloy bar in the 140 ksi grade, characterized by, The method comprises the following steps: S1, alloy smelting: according to the component element proportion, blanking is carried out, and a cylindrical ingot is smelted by a vacuum induction smelting + electroslag remelting + vacuum consumable process; S2, homogenization treatment: the ingot is heated to 1180-1190 DEG C, and then is kept for 67-72 h, and then is kept for 45-50 h at 1150-1160 DEG C, and is water-cooled; S3, blank package assembly: a layer of lubricating glass cotton is wrapped outside the ingot obtained in S2, and a stainless steel sleeve is sleeved outside the lubricating glass cotton, so that the stainless steel sleeve completely encloses the ingot; S4, blank heating: the blank assembled in S3 is placed into a heating furnace below 500 DEG C, and then is heated to 1030 DEG C at a speed of 160-250 DEG C / h, and is kept for 2-3.5 h; S5, blank forging: the blank heated in S4 is forged on a forging machine, the downward pressing amount of each pass is 5-35 mm, the feeding amount is 30-80 mm, the final forging temperature is 950 DEG C, and the blank forging ratio is 4.5-25, and the blank is cooled in water after forging; S6, peeling off the outer skin: the blank forged in S5 is sawed into segments, and the stainless steel sleeve and the lubricating glass cotton on the surface are removed by machining, so that the UNS N07718 alloy rod is obtained; S7, solid solution treatment: heating is carried out by using a trolley furnace, the blank is put into the furnace below 350 DEG C, and then is heated to 950-1020 DEG C at a speed of 160-300 DEG C / h, and is kept for 1.0-2.0 h, and is transferred into water within 70 s, and is rapidly cooled to below 50 DEG C; S8, straightening: the UNS N07718 alloy rod after the solid solution treatment is straightened; S9, aging treatment: heating is carried out by using a trolley furnace, the blank is put into the furnace below 350 DEG C, and then is heated to 710-730 DEG C at a speed of 160-300 DEG C / h, and is kept for more than 8 h, and is furnace-cooled to 610-630 DEG C at a speed of 30-60 DEG C / h, and is kept for 16 h, and is taken out of the furnace and air-cooled; S10, pickling: the UNS N07718 alloy rod after the aging treatment is removed from the surface oxide skin and oil stains in mixed acid, so that the final product is obtained; The components of the alloy rod are as follows in percentage by mass: C: 0.01-0.08%, Nb: 4.90-5.55%, Ni: 50.3-55.0%, Mo: 2.5-3.3%, Al: 0.15-0.65%, Cr: 17.6-20.5%, Co: 0.20-0.60%, Ti: 0.75-1.10%, B: ≤0.005%, Si: ≤0.30%, P: ≤0.014%, S: ≤0.008%, Mn: ≤0.35%, Cu: ≤0.30%, Mg: ≤0.03%, W: ≤0.3%, and the rest is Fe and inevitable impurities; UNS N07718 alloy bar finished product diameter range is 50-160 mm, room temperature performance: tensile strength R m ≥ 1150 MPa, yield strength R p0.2 ≥ 965 MPa, elongation A% ≥ 15%, reduction of area Z% ≥ 30%, grain size is finer than 3.0 level, 0℃ transverse impact energy ≥ 35 J; ASTM A262 C method of corrosion performance: corrosion rate is less than 0.12 mm / month; In S3, the thickness of the lubricating glass cotton is 2 mm, the thinnest part of the stainless steel sleeve has a thickness greater than 10 mm, and the gap between the stainless steel sleeve and the UNS N07718 ingot is 3 mm.

2. A process for producing a 140 ksi grade high strength UNS N07718 alloy bar as claimed in claim 1, wherein, In S1, the electroslag remelting process controls the smelting current and voltage, the control range: voltage 50-80 V, current 7000-13000 A; the water outlet temperature of the crystallizer cooling water in the electroslag remelting process is: 35-70 ℃; the electroslag remelting slag system adopts CaF2, CaO, Al2O3, MgO2, TiO2 five-element slag system, wherein the CaF2 content is 60%-70%, the CaO content is 10%-20%, and argon protection is adopted in the whole electroslag remelting process.

3. A process for producing a 140 ksi grade high strength UNS N07718 alloy bar as claimed in claim 2, wherein, In S1, the surface of the electrode blank of the electroslag remelting is treated by shot blasting, and vacuum consumable is carried out after cleaning the iron oxide scale.

4. A process for producing a 140 ksi grade high strength UNS N07718 alloy bar as claimed in claim 3, wherein, In S7, when water cooling, ice blocks are put into the water, the cooling water circulates and flows, and the UNS N07718 alloy bar is rotated at the same time.

5. A process for producing a 140 ksi grade high strength UNS N07718 alloy bar according to any one of claims 1-4, characterized in that, In S10, the mixing ratio of the mixed acid is HF: 2-5%, HNO3: 15-22%, and the rest is water, and the temperature of the acid liquid is 40-60 ℃.

Images