Preparation process of 140ksi steel grade high-strength UNS N07718 alloy bar

Abstract

The invention belongs to the technical field of metal material processing, and discloses a preparation process of a 140ksi steel-grade high-strength UNS N07718 alloy bar, which comprises the following steps: alloy smelting, homogenization treatment, blank sheathing and assembling, blank heating, blank forging, outer skin stripping, solution treatment, straightening, aging treatment and acid pickling, during sheathing and assembling, a layer of lubricating glass wool is wrapped outside a cast ingot, and the cast ingot is subjected to heat treatment and heat treatment to obtain the 140ksi steel-grade high-strength UNS N07718 alloy bar. The stainless steel sleeve is sleeved outside the lubricating glass wool, so that the cast ingot is completely sealed by the stainless steel sleeve, low-temperature forging is realized by arranging the sheath, and the problem of fast temperature drop in low-temperature forging is solved. The aluminum alloy has the advantages of high yield, good straightness, high grain size, few cracks, high obdurability and 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 defects. The defects of high-temperature forging are that: after the ingot is smelted, it is directly heated to 1140-1150 ℃ for forging. Under high-temperature conditions, it is difficult to control the organization, and too much δ phase is precipitated, which affects the mechanical properties of the bar. The defects 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 defects of extrusion process are that: the equipment investment is large, the direct extrusion of the casting blank is easy to cause uneven organization, the cost of low-temperature extrusion after forging breakdown is high, the extrusion force is high, and the vehicle is prone to be smothered. 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: A preparation process of 140 ksi steel grade high-strength UNS N07718 alloy bar, comprising the following steps: 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; 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; 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 outside the lubricating glass wool, 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 heated to 1030 DEG C at a speed of 160-250 DEG C / h, and then kept for 2-3.5 h; 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; 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; 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, transferring to water within 70 s, and rapidly cooling to below 50 DEG C; S8, straightening: the UNS N07718 alloy bar after solid solution treatment is straightened; 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 air cooling after exiting the furnace; S10, pickling: the UNS N07718 alloy bar after aging treatment is removed from the surface of the oxide skin and oil stains in mixed acid to obtain the final product.

[0006] 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.

[0007] 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.

[0008] 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.

[0009] 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.

[0010] 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.

[0011] 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.

[0012] 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℃.

[0013] Compared with the prior art, the present application has the following technical progress: (1) The final forging temperature of the present 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 inside the package, and the outer package is ordinary 304 stainless steel, which can not only hinder the heat dissipation of the UNS N07718 alloy bar inside, 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; (2) The present 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, 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 is reduced, the crack is reduced, and the service life is prolonged; (3) The present 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.

[0014] In summary, the present application has high material yield, good straightness, high grain size and less cracks, has high strength and toughness and corrosion resistance, and reduces the production cost. BRIEF DESCRIPTION OF DRAWINGS

[0015] Figure 1 The production process flow chart of the embodiment 1 of the present application is shown in the figure; Figure 2 The blank package assembly structure schematic diagram of the embodiment 1 of the present application is shown in the figure; Figure 3 The structure schematic diagram of the cooling device in the solid solution treatment stage of the embodiment 1 of the present application is shown in the figure; Figure 4 The microstructure diagram of the embodiment 1 of the present application after solid solution + aging treatment is shown in the figure, which is enlarged 100 times; Figure 5 The microstructure diagram of the embodiment 1 of the present application after solid solution + aging treatment is shown in the figure, which is enlarged 500 times; Figure 6 The microstructure diagram of the embodiment 2 of the present application after solid solution + aging treatment is shown in the figure, which is enlarged 100 times; Figure 7 The microstructure diagram of the embodiment 2 of the present application after solid solution + aging treatment is shown in the figure, which is enlarged 500 times.

[0016] Figure: 1, stainless steel sleeve; 2, lubricating glass wool; 3, UNS N07718 ingot; 4, stop block; 5, tow rope; 6, UNS N07718 alloy bar. DETAILED DESCRIPTION

[0017] The present application will be described in detail below with reference to examples and drawings. The scope of protection of the present application is not limited to the examples, and any modification made by those skilled in the art within the scope defined by the claims is also within the scope of protection of the present application.

[0018] Example 1

[0019] This example is a preparation process of φ50mm 140ksi steel grade high-strength UNS N07718 alloy bar, and the chemical composition is shown in Table 1: Table 1 Chemical composition of φ50mm UNS N07718 alloy bar (% by mass)

[0020] The rest is Fe and unavoidable impurities.

[0021] As shown in the table, the preparation process of φ50mm 140ksi steel grade high-strength UNS N07718 alloy bar is carried out according to the following steps. Figure 1

[0022] S1, alloy smelting: according to the proportioning of component elements, the cylindrical ingot is smelted by vacuum induction smelting + electroslag remelting + vacuum consumable process, with a specification of φ240mm (diameter) x 1000mm (length); the smelting current and voltage are controlled during electroslag remelting process, with a control range of 50-60V for voltage and 7000-9000A for current; the crystallizer cooling water outlet temperature in the electroslag remelting process is 50℃; the electroslag remelting slag system adopts CaF2, CaO, Al2O3, MgO2 and TiO2 five-element slag system, with a CaF2 content of 60%-70% and a CaO content of 10%-20%; argon gas protection is adopted during the whole electroslag remelting process, so that the alloy liquid is always protected by inert gas during the smelting process, effectively preventing secondary oxidation of the alloy liquid. 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 cleaning the iron oxide scale.

[0023] S2, homogenization treatment: heat the ingot to 1180-1190℃, keep for 67h, then keep at 1150-1160℃ for 45h, and water cool.

[0024] ​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 arranged on 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 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 to completely enclose the ingot in the stainless steel sleeve 1. The material of the stainless steel sleeve 1 is 304L material.

[0025] S4, blank heating: the blank assembled in S3 is placed into a heating furnace below 500℃, and then heated to 1030℃ at a speed of 160-250℃ / h, and kept for 3h.

[0026] S5, blank forging: the blank heated in S4 is forged on a forging machine, the downward pressing amount of each pass is 5-35mm, the feed amount is 30-80mm, the final forging temperature is 950℃, the forging ratio of the blank is 4.5-25, and the blank is cooled in water after forging.

[0027] S6, peeling off the skin: the blank after 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.

[0028] S7, solution treatment: heating with a trolley furnace, entering the furnace below 350℃, then heating to 950-960℃ at a speed of 160-300℃ / h, keeping for 1.5h, 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, the cooling water circulates, the rod is quickly cooled to below 50℃, and the degree of bending after cooling is greatly reduced.

[0029] S8, straightening: the UNS N07718 alloy rod after solution treatment is straightened by the method of two-point support and one-point pressure.

[0030] S9, aging treatment: heating with a trolley furnace, entering the furnace below 350℃, then heating to 710-730℃ at a speed of 160-300℃ / h, keeping for 9h or more, furnace cooling at a speed of 30-60℃ / h to 610-630℃, keeping for 16h, and air cooling after taking out of the furnace.

[0031] S10, pickling: the UNS N07718 alloy bar after aging is removed from the surface of the oxide and oil stains 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℃.

[0032] The obtained final product is detected, wherein nondestructive testing is carried out by using ultrasonic flaw detection and coloring penetration detection method, and physical and chemical detection of composition, mechanical property, microstructure and corrosion performance is carried out.

[0033] 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 put into 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, the precipitated phase is mainly the compound of Nb and Ti, and 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, which are isolated intergranular precipitated phases without other harmful precipitated phases. The grain boundary of the austenite is clean, the grain size is detected as 5.5 level according to GB / T 6394-2017 Metal Average Grain Size Determination Method, the grain is relatively uniform, there is no mixed crystal and no needle-shaped precipitated phase. The good microstructure provides a good microstructure 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 Petroleum and Natural Gas Drilling and Production Equipment.

[0034] Three final products of UNS N07718 alloy bars are randomly selected in this embodiment, numbered as 1#, 2# and 3#, and the detection results at room temperature are shown in Table 2. Table 2 Properties of UNS N07718 alloy bar products with a diameter of 50mm

[0035] As shown in Table 2, the tensile strength Rm is greater than or equal to 1150MPa, the yield strength Rp0.2 is greater than or equal to 965MPa, the elongation A% after fracture is greater than or equal to 15%, the reduction of area Z% is greater than or equal to 30%, the grain size is finer than 3.0 level, the transverse impact energy at 0℃ is greater than or equal to 35J, and the corrosion rate is less than 0.12mm / month.

[0036] The embodiment is widely applied in aerospace, nuclear energy, petroleum chemical industry and other fields. The alloy bar is a raw material for producing key components such as rotating parts and turbine discs of aerospace engines, and the grain is very coarse after homogenization heat treatment of the ingot prepared by vacuum induction melting and electroslag remelting, and the grain size is controlled to be above 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 other excellent properties at 650 DEG C.

[0037] Embodiment 2

[0038] The embodiment is a preparation process of a φ160mm 140ksi steel grade high-strength UNS N07718 alloy bar, and the chemical composition is shown in Table 3: Table 3 Chemical composition of φ160mm UNS N07718 alloy bar (% by mass)

[0039] The rest is Fe and inevitable impurities.

[0040] The preparation process of the φ160mm 140ksi steel grade high-strength UNS N07718 alloy bar is carried out according to the following steps.

[0041] S1, alloy smelting: according to the component element ratio, the cylindrical ingot is smelted by vacuum induction melting + electroslag remelting + vacuum consumable process, and the specification is φ550mm (diameter) x1200mm (length); the smelting current and voltage are controlled in the electroslag remelting process, and the control range is: voltage 60-80V, current 9000-13000A; the crystallizer cooling water outlet temperature in the electroslag remelting process is 70 DEG C; the electroslag remelting slag system adopts CaF2, CaO, Al2O3, MgO2 and TiO2 five-element slag system, wherein the content of CaF2 is 60%-70%, the content of CaO is 10%-20%, and argon protection is adopted in the whole process of electroslag remelting, 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 is carried out after cleaning the iron oxide skin.

[0042] S2, homogenization treatment: heat the ingot to 1180-1190 DEG C, and keep for 70h, then keep at 1150-1160 DEG C for 50h, and water cool.

[0043] 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.

[0044] 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 2h.

[0045] 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.

[0046] 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.

[0047] 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 1.0h, 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.

[0048] S8, straightening: the UNS N07718 alloy rod after solution treatment is straightened by adopting the mode of two-point support and one-point pressure application.

[0049] 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 10h or more, furnace cooling to 610-630°C at a speed of 30-60°C / h, keeping for 16h, and air cooling after exiting the furnace.

[0050] 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℃.

[0051] 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.

[0052] 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.

[0053] 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: Table 4. Properties of finished UNS N07718 alloy bars with a diameter of 160 mm

[0054] 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.

[0055] Comparative Example 1

[0056] Choose any one of the existing manufacturing processes to produce a φ50mm high-strength UNS N07718 alloy bar of steel grade 140ksi, designated as a.

[0057] Product mechanical property detection: 1#, 2# and 3# of example 1 are compared with the ordinary alloy bar of the same specification of comparative example 1, and the detailed comparison is shown in table 5.

[0058] Table 5 comparison of mechanical properties of alloy bars of example 1 and comparative example 1

[0059] As shown in table 5, among the alloy bars of the same specification, 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 few cracks.

[0060] Comparative example 2

[0061] Take one φ160mm 140ksi steel grade high strength UNS N07718 alloy bar made by the preparation process of the prior art, numbered b.

[0062] Product mechanical property detection: 4#, 5# and 6# of example 2 are compared with the ordinary alloy bar of the same specification b of comparative example, and the detailed comparison is shown in table 6.

[0063] Table 6 comparison of mechanical properties of alloy bars of example 2 and comparative example 2

[0064] As shown in table 6, among the alloy bars of the same specification, 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 few cracks.

[0065] 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 above 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. 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 wool is wrapped outside the ingot obtained in S2, and a stainless steel sleeve is sleeved outside the lubricating glass wool, 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, 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, the stainless steel sleeve and the lubricating glass wool on the surface are removed by machining, and 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 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 air-cooled after being taken out of the furnace; S10, pickling: the UNS N07718 alloy rod after aging treatment is subjected to pickling in mixed acid to remove the surface oxide skin and oil stains, and the final product is obtained.

2. A process for producing a 140 ksi grade high strength UNS N07718 alloy bar as claimed in claim 1, wherein, 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.

3. A process for producing a 140 ksi grade high strength UNS N07718 alloy bar as claimed in claim 2, wherein, The diameter of the finished UNS N07718 alloy rod ranges from 50 mm to 160 mm, and the performance at room temperature is as follows: the tensile strength Rm is greater than or equal to 1150 MPa, the yield strength Rp0.2 is greater than or equal to 965 MPa, the elongation A% after fracture is greater than or equal to 15%, the reduction of area Z% is greater than or equal to 30%, the grain is finer than 3.0 grade, the transverse impact energy at 0 DEG C is greater than or equal to 35 J, the corrosion performance of ASTM A262 C method is that the corrosion rate is less than 0.12 mm / month.

4. A process for producing a 140 ksi grade high strength UNS N07718 alloy bar according to any one of claims 1-3, characterized in that, In S1, the electroslag remelting process controls the smelting current and voltage, the control range: 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 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.

5. A process for making a 140 ksi grade high strength UNS N07718 alloy bar as claimed in claim 4, 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.

6. A process for producing a 140 ksi grade high strength UNS N07718 alloy bar as claimed in claim 5, wherein, In S3, the thickness of the lubricated glass cotton 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.

7. A process for producing a 140 ksi grade high strength UNS N07718 alloy bar as claimed in claim 6, wherein, 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.

8. A process for producing a 140 ksi grade high strength UNS N07718 alloy bar according to any one of claims 1-3, 5-7, characterized in that, In S10, the mixing acid is mixed in a ratio of HF: 2-5%, HNO3: 15-22%, and the rest is water, and the temperature of the acid solution is 40-60 ℃.

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