Sulfur-fixing multi-element composite free-machining titanium alloys and their preparation methods

Abstract

This invention discloses a sulfur-fixed multi-element composite free-machining titanium alloy and its preparation method, belonging to the field of non-ferrous metal materials. The sulfur-fixed multi-element composite free-machining titanium alloy comprises a matrix composition group and a sulfur-fixing composition group; the matrix composition group includes Ti, S, O, Al, Fe, Sn, C, and N; the sulfur-fixing composition group includes Cr, Cu, Mn, Mo, and V; wherein the S component, by mass percentage, is 0.06–0.12%. This invention also discloses a method for preparing the sulfur-fixed multi-element composite free-machining titanium alloy. The sulfur-fixed multi-element composite free-machining titanium alloy of this invention improves the stability of sulfides through multi-element alloying. The titanium alloy contains a layered structure of Ti-Cr-Cu-Mn-Mo-S sulfur compounds, and the uniformly distributed titanium-sulfur compounds improve chip breaking and tool tip lubrication.

Description

Technical Field

[0001] This invention relates to the field of non-ferrous metal materials, and in particular to a sulfur-fixing multi-element composite free-machining titanium alloy and its preparation method. Background Technology

[0002] Multi-element alloys have become indispensable basic materials in precision manufacturing due to their unique advantages in high-performance functional materials and engineering materials. In high-end applications such as digital 3C products, medical devices, and aerospace, the requirements for the machinability, surface quality, and lightweighting of alloy materials are increasingly stringent. Free-machining alloys, by introducing specific additive phases to improve machinability, are of great significance for reducing processing costs and improving product precision.

[0003] Existing mechanisms for improving the machinability of free-machining alloys mainly fall into two categories: The first involves introducing low-melting-point softening phases (such as lead-tin, lead-bismuth, indium-bismuth, etc.) into the matrix. During cutting, frictional heat generation causes these softening phases to melt or soften, promoting chip fracture and improving chip removal performance. The second involves adding high-melting-point hardening phases (such as boron, carbon, oxides, nitrides, etc.), utilizing the difference in fluidity between the matrix and the hardening phase to form a discontinuous structure, thereby controlling fracture during the cutting process. However, alloy systems based on low-melting-point phases (such as lead-containing alloys like 6012 and 6262) are gradually being restricted due to the biotoxicity and environmental hazards of lead, necessitating a shift towards lead-free technologies.

[0004] Titanium alloys, as typical high-strength and lightweight materials, continue to see increasing demand in fields such as biomedicine and consumer electronics. Sulfur (S) has been proven to significantly improve the machinability of titanium alloys, through the formation of titanium-sulfur compounds as a free-machining phase. However, in traditional smelting processes, liquid sulfur easily separates from the molten titanium, leading to uneven compound distribution; furthermore, as the sulfur content increases, the hot working properties of titanium materials decline sharply, and the risk of surface cracking increases significantly. Existing technologies aim to fix sulfur by introducing rare earth elements, but the presence of rare earth elements may cause contact allergies or poisoning in humans.

[0005] Therefore, developing novel free-machining titanium alloys and their preparation methods that address both the issues of uniform sulfur distribution and the safety of rare earth elements are of significant practical importance. Summary of the Invention

[0006] Based on this, and to address the shortcomings of the existing technology, a multi-element composite free-cutting titanium alloy with sulfur fixation and its preparation method are provided. The aim is to solve the problem of uniform distribution and fixation of sulfur and the safety issues of rare earth elements through multi-element composite design, and to provide an innovative solution for the industrial application of lead-free free-cutting titanium alloys.

[0007] To achieve the above objectives, the following technical solution is adopted:

[0008] This invention provides a sulfur-fixing multi-element composite free-machining titanium alloy, comprising a matrix composition group and a sulfur-fixing composition group;

[0009] The matrix composition group includes Ti, S, O, Al, Fe, Sn, C, and N;

[0010] The sulfur-fixing components include Cr, Cu, Mn, Mo, and V;

[0011] The component S, by mass percentage, is 0.06–0.12%.

[0012] In some embodiments, the mass fraction ratio of Cr:Cu:Mn:Mo:V:S is (15~20):(6~8):(4~6):(5~8):(6~10):1.

[0013] In some embodiments, the remaining components of the sulfur-fixing multi-element composite free-machining titanium alloy, by mass percentage, are: O: 0.1-0.2%; Al: 2.00-3.00%; Fe: 0.05-0.15%; Sn: 0.05-0.15%; C≤0.03%; N≤0.03%, with the balance being titanium and unavoidable impurities.

[0014] This invention also provides a method for preparing the sulfur-fixed multi-element composite free-machining titanium alloy as described above, comprising:

[0015] S101. Raw material preparation: Titanium source, aluminum source, chromium source, copper source, molybdenum source, sulfur source, manganese source, vanadium source, iron source, and tin source are pressed into electrode blocks and welded to form consumable electrodes.

[0016] S102. Perform two vacuum consumable electrode melting processes:

[0017] First melting: The consumable electrode is placed in a water-cooled copper crucible. The vacuum degree of the first melting is controlled at 0.1~1.0 Pa to ensure that the electrolyte impurities (mainly magnesium chloride MgCl2) in the sponge titanium are effectively removed and to prevent the formation of large powdery inclusions.

[0018] Secondary melting: The ingot after primary melting is placed into a secondary water-cooled copper crucible; H2S gas is introduced to adjust the vacuum degree of secondary melting to 1~2.5Pa; after melting, it is cooled by low-temperature cooling water, wherein the inlet temperature of the cooling water is controlled at ≤5℃ and the outlet temperature of the cooling water is controlled at ≤15℃. A faster cooling rate can refine the liquid-precipitated free-machining phase.

[0019] S103. Ingot forming: After the surface peeling treatment of the ingot after secondary melting, the square billet is obtained by radial forging in the temperature range of 1050~1100℃.

[0020] S104. Hot rolling: The billet is heated to 920~940℃ and then hot rolled to obtain a free-cutting disc.

[0021] In some embodiments, the diameter of the primary water-cooled copper crucible is ≤340mm; the diameter of the secondary water-cooled copper crucible is ≤400mm.

[0022] In some embodiments, the outlet water temperature of the vacuum consumable melting cooling water is below 15°C.

[0023] In some embodiments, the melting voltage for the two vacuum self-consumption melting processes is 28–32 V, and the melting current is 2–6 kA.

[0024] In some embodiments, the secondary melting vacuum control method is as follows: after the ingot is loaded into the furnace and the electrodes are welded, the vacuum is evacuated to below 0.5 Pa, the vacuum pump is kept at a stable 0.5 ± 0.1 Pa, the gas charging valve is opened and H2S gas is charged to 1.5 Pa. During the melting process, the H2S charging flow rate is adjusted to ensure that the secondary melting vacuum is between 1 and 2.5 Pa.

[0025] In some embodiments, the billet cross-sectional dimensions are 140~155mm×140~155mm, and the billet length is between 4.5m and 5.8m.

[0026] In some embodiments, during the hot rolling process in step S104, when the cross-sectional diameter of the free-cutting disc is ≤17mm and the rolling speed is greater than 10m / s, the surface of the free-cutting disc is heated, and the surface temperature after heating is between 900~930℃.

[0027] In some embodiments, a high-frequency induction heating device is used to compensate for the surface temperature of the easily cut disc, and the power of the high-frequency induction heating device is 450~600kW.

[0028] The present invention has the following beneficial technical effects:

[0029] The sulfur-fixing multi-element composite free-cutting titanium alloy of the present invention improves the stability of sulfides through multi-element alloying. The titanium alloy contains a layered structure of Ti-Cr-Cu-Mn-Mo-S sulfur compounds. The uniformly distributed titanium-sulfur compounds have the effect of improving chip breaking and improving tool tip lubrication conditions.

[0030] The method for preparing the sulfur-fixing multi-element composite free-machining titanium alloy of the present invention introduces a trace amount of hydrogen sulfide gas during the secondary melting process, which helps to improve the yield of sulfur and the uniform distribution of sulfur in the ingot. Attached Figure Description

[0031] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0032] Figure 1 This is a flowchart of the method for preparing a sulfur-fixed multi-element composite free-machining titanium alloy according to the present invention.

[0033] Figure 2 This is a 50x metallographic image of the sulfur-fixing multi-element composite free-machining titanium alloy of Embodiment 1 of the present invention.

[0034] Figure 3 This is a 500x metallographic image of the sulfur-fixing multi-element composite free-machining titanium alloy of Example 1 of the present invention.

[0035] Figure 4 The above is the EDS energy spectrum of the sulfur-fixing multi-element composite free-machining titanium alloy of Example 1 of the present invention.

[0036] Figure 5 The image shows a metallographic diagram of a titanium alloy material for comparison. Detailed Implementation

[0037] To make the objectives, technical solutions, and advantages of the present invention clearer, the embodiments of the present invention will be further described in detail below with reference to specific examples and the accompanying drawings.

[0038] It should be understood that the embodiments of the invention shown in the exemplary embodiments are merely illustrative. Although only a few embodiments have been described in detail in this invention, those skilled in the art will readily recognize that various modifications are possible without substantially departing from the teachings of the invention. Accordingly, all such modifications should be included within the scope of the invention. Other substitutions, modifications, variations, and deletions can be made to the design, operating conditions, and parameters of the following exemplary embodiments without departing from the spirit of the invention.

[0039] Based on the above objectives, a first aspect of the embodiments of the present invention proposes a sulfur-fixed multi-element composite free-machining titanium alloy, comprising a matrix composition group and a sulfur-fixing composition group.

[0040] The matrix composition group includes Ti, S, O, Al, Fe, Sn, C, and N;

[0041] The sulfur-fixing components include Cr, Cu, Mn, Mo, and V;

[0042] The component S, by mass percentage, is 0.06–0.12%.

[0043] The mass fraction ratio of Cr:Cu:Mn:Mo:V:S is (15~20):(6~8):(4~6):(5~8):(6~10):1.

[0044] The mass percentages of Cr, Cu, Mn, Mo, and V are multiples of S. The mass percentage of S is 0.06% to 0.12%.

[0045] The remaining components of the sulfur-fixing multi-element composite free-machining titanium alloy, by mass percentage, are: O: 0.1–0.2%; Al: 2.00–3.00%; Fe: 0.05–0.15%; Sn: 0.05–0.15%; C ≤ 0.03%; N ≤ 0.03%, with the balance being titanium and unavoidable impurities. The content of any single unavoidable impurity must be ≤ 0.05%, and the sum of the contents of all unavoidable impurities must be ≤ 0.1%.

[0046] The above element ratio ensures that Cu can form a series of compounds such as CuTi2 and Cu2S with Ti and S elements in the material.

[0047] By using a multi-element composite design (matrix composition group + sulfur-fixing composition group), sulfur (S) is effectively fixed in titanium alloys, avoiding the problem of stratification between liquid sulfur and titanium melt in traditional smelting, ensuring uniform distribution of titanium-sulfur compounds, thereby improving machinability; at the same time, S, as a free-machining element, forms titanium-sulfur compounds, reducing cutting resistance and improving chip removal performance.

[0048] By optimizing the mass ratio of sulfur-fixing components (Cr, Cu, Mn, Mo, V) to sulfur, the sulfur-fixing effect is synergistically enhanced, ensuring the stable presence of sulfur in the alloy. At the same time, the multi-element composite can balance the mechanical properties (such as strength and hardness) and machinability of the alloy, avoiding performance imbalances caused by a single sulfur-fixing element.

[0049] A second aspect of the present invention provides a method for preparing the sulfur-fixed multi-element composite free-machining titanium alloy as described above. Figure 1 The diagram shown is a schematic flowchart of the method.

[0050] like Figure 1 As shown, the preparation may include the following steps:

[0051] S101. Raw material preparation: Titanium source, aluminum source, chromium source, copper source, molybdenum source, sulfur source, manganese source, vanadium source, iron source and tin source are pressed into electrode blocks and welded to form consumable electrodes;

[0052] S102. Perform two vacuum consumable electrode melting processes:

[0053] First melting: The consumable electrode is placed in a water-cooled copper crucible, and the vacuum degree of the first melting is controlled at 0.1~1.0 Pa;

[0054] Secondary melting: The ingot after primary melting is placed into a secondary water-cooled copper crucible; H2S gas is introduced to adjust the vacuum degree of secondary melting to 1~2.5Pa; after melting, it is cooled with low-temperature cooling water, wherein the inlet temperature of the cooling water is controlled at ≤5℃ and the outlet temperature of the cooling water is controlled at ≤15℃.

[0055] S103. Ingot forming: After the surface peeling treatment of the ingot after secondary melting, the square billet is obtained by radial forging in the temperature range of 1050~1100℃.

[0056] S104. Hot rolling: The billet is heated to 920~940℃ and then hot rolled to obtain a free-cutting disc.

[0057] Titanium, aluminum, chromium, copper, molybdenum, sulfur, manganese, vanadium, iron, and tin sources include 0A grade sponge titanium (chemical formula Ti, particle size ≤24.5mm), aluminum granules (chemical formula Al, particle size ≤15mm), chromium granules (chemical formula Cr, particle size ≤5mm), or aluminum-chromium master alloys (such as Al). 70 Cr (particle size ≤ 5 mm), copper strips (chemical formula Cu, diameter ≤ 2 mm, length ≤ 15 mm), titanium dioxide (chemical formula TiO2, particle size ≤ 58 μm or 250 mesh), titanium-silicon alloy (chemical formula Ti... 50 Si (particle size ≤ 6 mm) or aluminum-silicon alloys (such as Al) 40 Si, particle size ≤6mm), titanium-molybdenum alloy (chemical formula Ti) 32 Mo (particle size ≤ 8 mm), manganese sulfide (MnS, particle size ≤ 160 μm or 90 mesh), aluminum-vanadium alloy (chemical formula Al) 55 V, particle size ≤8mm), titanium-iron alloy (Ti32Fe, particle size ≤6mm), titanium-tin alloy (Ti 80 Sn, particle size ≤ 6 mm.

[0058] By combining two vacuum consumable melting processes (especially the second melting process which uses H2S to adjust the vacuum level) with low-temperature cooling, sulfur is effectively fixed to prevent it from volatilizing or separating from titanium. Radial forging and hot rolling processes refine the grains, improve the uniformity of the microstructure, and enhance the machinability. Ultimately, free-cutting discs with excellent machinability and good surface quality are obtained.

[0059] In a preferred embodiment of the present invention, the diameter of the primary water-cooled copper crucible is ≤340mm; the diameter of the secondary water-cooled copper crucible is ≤400mm. In a preferred embodiment of the present invention, the cooling water is cooled using a low-temperature chiller.

[0060] Strict control of crucible size and cooling water temperature is to minimize segregation during solidification and prevent sulfur loss at prolonged high temperatures.

[0061] In a preferred embodiment of the invention, the melting voltage for the two vacuum arc remelting processes is 28–32 V, and the melting current is 2–6 kA. This ensures that the molten pool reaches the edge to obtain an ingot with a good surface finish.

[0062] In a preferred embodiment of the present invention, the outlet water temperature of the vacuum self-consuming melting cooling water is below 15°C.

[0063] In a preferred embodiment of the present invention, the method for controlling the vacuum degree of secondary melting is as follows: after the ingot is loaded into the furnace and the electrodes are welded, the vacuum is evacuated to below 0.5 Pa, the vacuum pump is kept at a stable 0.5 ± 0.1 Pa, the gas charging valve is opened to charge H2S gas to 1.5 Pa, and the vacuum degree of secondary melting is ensured to be between 1 and 2.5 Pa by adjusting the gas charging flow rate of H2S during the melting process.

[0064] Introducing trace amounts of hydrogen sulfide gas helps improve sulfur yield and uniform distribution in the ingot. The mass percentage of sulfur is strictly controlled between 0.06% and 0.12%, and it must form free-machining phases such as Cu₂S with Cu. The introduction of H₂S replenishes the sulfur source, prevents sulfur from volatilizing and being lost at high temperatures in the form of SO₂, and ensures that the sulfur content meets design requirements. By adjusting the vacuum level and H₂S flow rate, the distribution and size of sulfides such as Cu₂S are controlled, segregation is reduced, and free-machining properties are improved (e.g., reducing cutting resistance and improving surface quality).

[0065] In a preferred embodiment of the present invention, a secondary polished ingot is obtained by mechanically peeling off the surface of the smelted ingot. To reduce forging cracking, the secondary ingot must be blanked using a radial forging mill. The present invention employs high-temperature multi-fire secondary radial forging, which can effectively prevent surface cracking of easily cracked titanium alloys during the blanking process.

[0066] In a preferred embodiment of the present invention, the billet cross-sectional dimensions are 140~155mm × 140~155mm, and the billet length is between 4.5m and 5.8m. Optimizing the billet cross-sectional dimensions (140~155mm × 140~155mm) and length (4.5m~5.8m) facilitates subsequent radial forging and hot rolling, reduces processing passes, and improves production efficiency; at the same time, it avoids the risk of uneven temperature or cracking caused by excessively large dimensions, thereby improving the yield.

[0067] In a preferred embodiment of the present invention, during the hot rolling process in step S104, when the cross-sectional diameter of the free-cutting coil is ≤17mm and the rolling speed is greater than 10m / s, the surface of the free-cutting coil is heated by a high-frequency induction heating device with a power of 450~600kW. After heating, the surface temperature is between 900~930℃, ensuring that high-speed rolling does not cause cracking and that the core and surface microstructure are uniform. Surface induction heating is performed when the rolling speed is higher than 10m / s to prevent surface cracking and improve microstructure uniformity.

[0068] The present invention will be further illustrated by the following examples.

[0069] Table 1. Alloy composition of Examples 1-3 (mass fraction / %)

[0070]

[0071] Example 1

[0072] A sulfur-fixing multi-element composite free-machining titanium alloy, belonging to the Ti-Cr-Cu-Mn-Mo-VS system, has a phase composition of α phase + free-machining β phase + sulfides. The mass percentages of each component are shown in Table 1. The sulfur-fixing elements are at their upper limits, with the balance being titanium and unavoidable impurities. The content of any single unavoidable impurity is required to be ≤0.05%, and the sum of the unavoidable impurities is required to be ≤0.1%. This composition yields a relatively high sulfide content, suitable for applications requiring particularly high machinability.

[0073] The preparation method of the above-mentioned sulfur-fixing multi-element composite free-machining titanium alloy is as follows:

[0074] (1) S101. Raw material preparation: After uniformly mixing the raw materials, press them into electrode blocks and weld them into consumable electrodes. The sources of titanium, aluminum, chromium, copper, molybdenum, sulfur, manganese, vanadium, iron, and tin include 0A grade sponge titanium (chemical formula Ti, particle size ≤24.5mm), aluminum pellets (chemical formula Al, particle size ≤15mm), chromium granules (chemical formula Cr, particle size ≤5mm) or aluminum-chromium master alloy (such as Al70Cr, particle size ≤5mm), copper strips (chemical formula Cu, diameter ≤2mm, length ≤15mm), titanium dioxide (chemical formula TiO2, particle size ≤58μm or 250 mesh), and titanium-silicon alloy (chemical formula Ti). 50 Si (particle size ≤ 6 mm) or aluminum-silicon alloys (such as Al) 40 Si, particle size ≤6mm), titanium-molybdenum alloy (chemical formula Ti) 32 Mo (particle size ≤ 8 mm), manganese sulfide (MnS, particle size ≤ 160 μm or 90 mesh), aluminum-vanadium alloy (chemical formula Al)55 V, particle size ≤8mm), titanium-iron alloy (Ti 32 Fe, particle size ≤6mm), titanium-tin alloy (Ti 80 Sn, particle size ≤ 6 mm.

[0075] (2) S102. The raw material is subjected to two vacuum self-consumption melting processes. The melting voltage of the two vacuum self-consumption melting processes is 30±3.5V and the melting current is 3±0.3KA.

[0076] (3) Primary melting: The vacuum degree of primary melting is controlled at 0.1~1.0Pa; corresponding to the smaller current, the diameter of the primary water-cooled copper crucible is 340mm;

[0077] (4) Secondary smelting: Place the ingot after primary smelting into a secondary water-cooled copper crucible; the diameter of the secondary water-cooled copper crucible is 400mm. Adjust the vacuum degree of secondary smelting to 1~2.5Pa by purging with H2S gas; after smelting, cool with low-temperature cooling water, wherein the inlet temperature of the cooling water is controlled at ≤5℃ and the outlet temperature of the cooling water is controlled at ≤15℃; the vacuum degree control method for secondary smelting is as follows: after the ingot is loaded into the furnace and the electrodes are welded, evacuate to below 0.5Pa, maintain the vacuum pump to a stable 0.5±0.1Pa, open the purging valve to purge with H2S gas to 1.5Pa, and ensure that the vacuum degree of secondary smelting is within the range of 1~2.5Pa by adjusting the H2S purging flow rate during the smelting process.

[0078] (5) S103. Ingot forming: After the surface peeling treatment of the ingot after secondary melting, it is radially forged in the temperature range of 1050℃ to obtain a square billet; the billet cross-sectional size is 140×140mm and the billet length is between 4.5m and 5.8m.

[0079] (6) S104. Hot rolling: The billet is heated to 930℃ and then hot rolled to obtain free-cutting coils. When the cross-sectional diameter of the free-cutting coil is ≤17mm and the rolling speed is greater than 10m / s, the surface of the free-cutting coil is heated by a high-frequency induction heating device with a power of 500kW. After heating, the surface temperature is between 900~930℃.

[0080] Example 2

[0081] A sulfur-fixing multi-element composite free-machining titanium alloy, belonging to the Ti-Cr-Cu-Mn-Mo-VS system, has a phase composition of α phase + free-machining β phase + sulfides. The mass percentages of each component are shown in Table 1. The sulfur-fixing elements are taken at their lower limits, with the balance being titanium and unavoidable impurities. The content of any single unavoidable impurity is required to be ≤0.05%, and the sum of the unavoidable impurities is required to be ≤0.1%. This composition results in a lower sulfide content, suitable for applications requiring both high machinability and mechanical properties.

[0082] The preparation method of the above-mentioned sulfur-fixing multi-element composite free-machining titanium alloy is as follows:

[0083] (1) S101. Raw material preparation: After uniformly mixing the raw materials, press them into electrode blocks and weld them into consumable electrodes. The sources of titanium, aluminum, chromium, copper, molybdenum, sulfur, manganese, vanadium, iron, and tin include 0A grade sponge titanium (chemical formula Ti, particle size ≤24.5mm), aluminum pellets (chemical formula Al, particle size ≤15mm), chromium granules (chemical formula Cr, particle size ≤5mm) or aluminum-chromium master alloy (such as Al70Cr, particle size ≤5mm), copper strips (chemical formula Cu, diameter ≤2mm, length ≤15mm), titanium dioxide (chemical formula TiO2, particle size ≤58μm or 250 mesh), and titanium-silicon alloy (chemical formula Ti). 50 Si (particle size ≤ 6 mm) or aluminum-silicon alloys (such as Al) 40 Si, particle size ≤6mm), titanium-molybdenum alloy (chemical formula Ti) 32 Mo (particle size ≤ 8 mm), manganese sulfide (MnS, particle size ≤ 160 μm or 90 mesh), aluminum-vanadium alloy (chemical formula Al) 55 V, particle size ≤8mm), titanium-iron alloy (Ti 32 Fe, particle size ≤6mm), titanium-tin alloy (Ti 80 Sn, particle size ≤ 6 mm.

[0084] (2) S102. The raw material is subjected to two vacuum self-consumption melting processes. The melting voltage of the two vacuum self-consumption melting processes is 32±3V and the melting current is 6±0.35KA.

[0085] (3) Primary melting: The vacuum degree of primary melting is controlled at 0.1~1.0Pa; corresponding to a larger melting current, the diameter of the primary water-cooled copper crucible is 300mm;

[0086] (4) Secondary smelting: Place the ingot after primary smelting into a secondary water-cooled copper crucible; the diameter of the secondary water-cooled copper crucible is 380mm. Adjust the vacuum degree of secondary smelting to 1~2.5Pa by purging with H2S gas; after smelting, cool with low-temperature cooling water, wherein the inlet temperature of the cooling water is controlled at ≤5℃ and the outlet temperature of the cooling water is controlled at ≤15℃; the vacuum degree control method for secondary smelting is as follows: after the ingot is loaded into the furnace and the electrodes are welded, evacuate to below 0.5Pa, maintain the vacuum pump to a stable 0.5±0.1Pa, open the purging valve to purge with H2S gas to 1.5Pa, and ensure that the vacuum degree of secondary smelting is within the range of 1~2.5Pa by adjusting the H2S purging flow rate during the smelting process.

[0087] (5) S103. Ingot forming: After the surface peeling treatment of the ingot after secondary melting, it is radially forged in the temperature range of 1100℃ to obtain a square billet; the billet cross-sectional size is 155mm×155mm, and the length of the square billet is between 4.5m and 5.8m.

[0088] (6) S104. Hot rolling: The billet is heated to 940℃ and then hot rolled to obtain free-cutting coils. When the cross-sectional diameter of the free-cutting coil is ≤17mm and the rolling speed is greater than 10m / s, the surface of the free-cutting coil is heated by a high-frequency induction heating device with a power of 600kW. After heating, the surface temperature is between 900~930℃.

[0089] Example 3

[0090] A sulfur-fixing multi-element composite free-machining titanium alloy, belonging to the Ti-Cr-Cu-Mn-Mo-VS system, has a phase composition of α phase + free-machining β phase + sulfides. The mass percentages of each component are shown in Table 1. The proportions of each sulfur-fixing element are taken as the median, with the balance being titanium and unavoidable impurities. The content of any single unavoidable impurity is required to be ≤0.05%, and the sum of the contents of all unavoidable impurities is required to be ≤0.1%. This composition yields a moderate sulfide content, suitable for applications requiring high machinability.

[0091] The preparation method of the above-mentioned sulfur-fixing multi-element composite free-machining titanium alloy is as follows:

[0092] (1) S101. Raw material preparation: After uniformly mixing the raw materials, press them into electrode blocks and weld them into consumable electrodes. The titanium source, aluminum source, chromium source, copper source, molybdenum source, sulfur source, manganese source, vanadium source, iron source, and tin source include 0A grade sponge titanium (chemical formula Ti, particle size ≤24.5mm), aluminum granules (chemical formula Al, particle size ≤15mm), chromium granules (chemical formula Cr, particle size ≤5mm) or aluminum-chromium master alloy (such as Al). 70Cr (particle size ≤ 5 mm), copper strips (chemical formula Cu, diameter ≤ 2 mm, length ≤ 15 mm), titanium dioxide (chemical formula TiO2, particle size ≤ 58 μm or 250 mesh), titanium-silicon alloy (chemical formula Ti... 50 Si (particle size ≤ 6 mm) or aluminum-silicon alloys (such as Al) 40 Si, particle size ≤6mm), titanium-molybdenum alloy (chemical formula Ti) 32 Mo (particle size ≤ 8 mm), manganese sulfide (MnS, particle size ≤ 160 μm or 90 mesh), aluminum-vanadium alloy (chemical formula Al) 55 V, particle size ≤8mm), titanium-iron alloy (Ti 32 Fe, particle size ≤6mm), titanium-tin alloy (Ti 80 Sn, particle size ≤ 6 mm.

[0093] (2) S102. The raw material is subjected to two vacuum self-consumption melting processes. The melting voltage of the two vacuum self-consumption melting processes is 30±3V and the melting current is 5±0.4KA.

[0094] (3) First melting: The vacuum degree of the first melting is controlled at 0.1~1.0Pa; the diameter of the water-cooled copper crucible is 340mm;

[0095] (4) Secondary smelting: Place the ingot after primary smelting into a secondary water-cooled copper crucible; the diameter of the secondary water-cooled copper crucible is 400mm. Adjust the vacuum degree of secondary smelting to 1~2.5Pa by purging with H2S gas; after smelting, cool with low-temperature cooling water, wherein the inlet temperature of the cooling water is controlled at ≤5℃ and the outlet temperature of the cooling water is controlled at ≤15℃; the vacuum degree control method for secondary smelting is as follows: after the ingot is loaded into the furnace and the electrodes are welded, evacuate to below 0.5Pa, maintain the vacuum pump to a stable 0.5±0.1Pa, open the purging valve to purge with H2S gas to 1.5Pa, and ensure that the vacuum degree of secondary smelting is within the range of 1~2.5Pa by adjusting the H2S purging flow rate during the smelting process.

[0096] (5) S103. Ingot forming: After the surface peeling treatment of the ingot after secondary melting, it is radially forged in the temperature range of 1050℃ to obtain a square billet; the billet cross-sectional size is 150mm×150mm, and the length of the billet is between 4.5m and 5.8m.

[0097] (6) S104. Hot rolling: The billet is heated to 920℃ and then hot rolled to obtain free-cutting coils. When the cross-sectional diameter of the free-cutting coil is ≤17mm and the rolling speed is greater than 10m / s, the surface of the free-cutting coil is heated by a high-frequency induction heating device with a power of 450kW. After heating, the surface temperature is between 900~930℃.

[0098] Comparative Example

[0099] A titanium alloy has the following mass percentages: Al: 6.0%, V: 4.0%, O: 0.3%; S: 0.06%; Fe: 0.12%; C≤0.03%; N≤0.03%, with the balance being titanium and unavoidable impurities, the content of each individual impurity ≤0.05%, and the sum of the contents of the remaining impurities ≤0.1%. The preparation method of this titanium alloy is as follows:

[0100] (1) S101. Raw material preparation: After uniformly mixing the raw materials, press them into electrode blocks and weld them into consumable electrodes. The titanium source, aluminum source, iron source, sulfur source, vanadium source, and oxygen source include 0A grade sponge titanium (chemical formula Ti, particle size ≤24.5mm), aluminum granules (chemical formula Al, particle size ≤15mm), ferrous sulfide (FeS, particle size ≤160μm or 90 mesh), and aluminum-vanadium alloy (chemical formula Al). 55 V, particle size ≤ 8 mm, titanium dioxide (chemical formula TiO2, particle size ≤ 58 μm or 250 mesh).

[0101] (2) S102. The raw material is subjected to two vacuum self-consumption melting processes. The melting voltage of the two vacuum self-consumption melting processes is 30±3V and the melting current is 7±0.6KA.

[0102] (3) First melting: The vacuum degree of the first melting is controlled at 1.0~2.0Pa; the diameter of the water-cooled copper crucible is 450mm;

[0103] (4) Secondary smelting: The ingot after primary smelting is placed into a secondary water-cooled copper crucible; the diameter of the secondary water-cooled copper crucible is 650mm. The vacuum degree of secondary smelting is 1~1.5Pa; after smelting, it is cooled by circulating cooling water, wherein the inlet temperature of the cooling water is controlled at ≤25℃ and the outlet temperature of the cooling water is controlled at ≤40℃.

[0104] (5) S103. Ingot forming: After the surface peeling treatment of the ingot after secondary melting, it is radially forged in the temperature range of 1050℃ to obtain a square billet; the billet cross-sectional size is 150mm×150mm, and the length of the billet is between 4.5m and 5.8m.

[0105] (6) S104. Hot rolling: The billet is heated to 940°C and then hot rolled to obtain a free-cutting disc.

[0106] The following methods were used to perform performance tests on the embodiments and comparative examples of this invention:

[0107] (1) Hardness test: The hardness of the examples and comparative examples was tested using a micro Vickers hardness tester. The test standard was GB / T 4340.1-2009 Vickers hardness test for metallic materials. The load was 500 grams. Each sample was tested 4 times, and the average value was taken as the final result.

[0108] (2) Cutting performance test: The testing equipment was a wireless cutting force testing system equipped with Spike® manufactured by Pro-Micro in Germany. The cutting tool was a Φ10 mm 62-degree carbide end mill. The cutting fluid was mineral oil. The rotation speed was 5000 rpm. The milling method was side milling. The tool feed rate was 800 mm / min. The depth of cut was 4 mm, and the side depth of cut was 0.4 mm. Each sample was tested 3 times, and the average value was taken as the final result.

[0109] The performance test results of the examples and comparative examples are shown in Table 2. In Table 2, hardness value 1 represents the hardness value of the first test. Hardness value 2 represents the hardness value of the second test. Hardness value 3 represents the hardness value of the third test. Hardness value 4 represents the hardness value of the fourth test. Bending moment 1 represents the bending moment value of the first test. Bending moment 2 represents the bending moment value of the second test. Bending moment 3 represents the bending moment value of the third test.

[0110] Table 2. Performance test results of the examples and comparative examples

[0111]

[0112] Metallographic photographs of Example 1 and the comparative example after polishing are shown below. Figure 2-3 , Figure 5 As shown, compared with the comparative example, the titanium alloy material in the embodiment introduces a machinable phase that is beneficial to cutting after alloying, thereby improving the machinability of the titanium alloy material.

[0113] Figure 4 The EDS spectrum of the sulfur-fixing multi-element composite free-machining titanium alloy of Example 1 is shown; several points are marked on it, and the alloy composition of each measurement point is shown in Table 3 below. The data in Table 3 represent the mass fractions of Cr, Cu, Mn, Mo, V, and S, calculated as a total of 100%. Table 3 shows the local composition at each point, indicating the presence of Cr, Cu, Mn, Mo, V, and S at each point.

[0114] Table 3. Energy spectrum composition table of Example 1 (mass fraction / %)

[0115]

[0116] The above are exemplary embodiments disclosed in this invention. However, it should be noted that various changes and modifications can be made without departing from the scope of the embodiments of this invention as defined by the claims. Although the elements disclosed in the embodiments of this invention may be described or claimed individually, they may be understood as multiple unless explicitly limited to a singular number.

[0117] Those skilled in the art should understand that the discussion of any of the above embodiments is merely exemplary and is not intended to imply that the scope of the invention (including the claims) is limited to these examples. Within the framework of the invention, technical features of the above embodiments or different embodiments can be combined, and many other variations of different aspects of the invention exist, which are not provided in the details for the sake of brevity. Therefore, any omissions, modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the invention should be included within the protection scope of the invention.

Claims

1. A method of making a sulfur-fixing, multi-element, composite free-machining titanium alloy, characterized in that, Comprise: S101. Raw material preparation: press the titanium source, aluminum source, chromium source, copper source, molybdenum source, sulfur source, manganese source, vanadium source, iron source and tin source into electrode blocks, and weld to form consumable electrodes; S102. The consumable electrode is subjected to two vacuum consumable smelting: Primary smelting: the consumable electrode is placed into a primary water-cooled copper crucible, and the primary smelting vacuum degree is controlled at 0.1-1.0 Pa; Secondary smelting: the ingot after primary smelting is placed into a secondary water-cooled copper crucible; H2S gas is filled to adjust the secondary smelting vacuum degree to 1-2.5 Pa; after smelting, low-temperature cooling water is used for cooling, wherein the inlet water temperature of the cooling water is controlled at ≤5℃, and the outlet water temperature of the cooling water is controlled at ≤15℃; S103. Ingot forming: after the ingot after secondary smelting is subjected to surface peeling treatment, it is opened up at a temperature interval of 1050-1100℃ by radial forging to obtain a bloom; S104. Hot rolling: the bloom is heated to 920-940℃ and then hot-rolled to obtain a free-cutting disc; The sulfur-fixed multi-element composite free-cutting titanium alloy prepared comprises a base component group and a sulfur-fixing component group; the base component group comprises Ti, S, O, Al, Fe, Sn, C and N; the sulfur-fixing component group comprises Cr, Cu, Mn, Mo and V; the content of component S is 0.06-0.12% by mass fraction; the mass fraction ratio of Cr:Cu:Mn:Mo:V:S is (15-20):(6-8):(4-6):(5-8):(6-10):1; the contents of the remaining components are as follows: O: 0.1-0.2% by mass fraction; Al: 2.00-3.00% by mass fraction; Fe: 0.05-0.15% by mass fraction; Sn: 0.05-0.15% by mass fraction; C≤0.03% by mass fraction; N≤0.03% by mass fraction, and the balance is titanium and unavoidable impurities.

2. The method of claim 1, wherein, The diameter of the primary water-cooled copper crucible is ≤340 mm; and the diameter of the secondary water-cooled copper crucible is ≤400 mm.

3. The method of claim 1, wherein, The outlet water temperature of the cooling water for vacuum consumable smelting is lower than 15℃.

4. The method of claim 1, wherein, The secondary smelting vacuum degree control method is as follows: after the ingot is loaded into the furnace and the electrode is welded, vacuum is drawn to below 0.5 Pa, the vacuum pump is kept pumping to achieve a stable 0.5±0.1 Pa, the gas filling valve is opened to fill H2S gas to 1.5 Pa, and during the smelting process, the H2S gas filling flow rate is adjusted to ensure that the secondary smelting vacuum degree is between 1-2.5 Pa.

5. The method of claim 1, wherein, The bloom has a billet cross-sectional size of 140-155 mm×140-155 mm and a length of 4.5-5.8 m.

6. The method of claim 1, wherein, During the hot rolling process of step S104, the surface of the free-cutting disc is subjected to temperature compensation when the cross-sectional diameter of the free-cutting disc is ≤17 mm and the rolling speed is greater than 10 m / s, and the surface temperature after the temperature compensation is 900-930℃.

7. The method of claim 6, wherein, A high-frequency induction heating device is used to compensate the temperature of the surface of the free-cutting disc, and the power of the high-frequency induction heating device is 450-600 kW.

8. A sulfur-fixed, multi-element, composite free-machining titanium alloy, characterized in that, Prepared by the method according to any one of claims 1-7, wherein the sulfurized multi-element composite free-cutting titanium alloy comprises a base component group and a sulfurized component group; the base component group comprises Ti, S, O, Al, Fe, Sn, C and N; the sulfurized component group comprises Cr, Cu, Mn, Mo and V; wherein the mass percentage of component S is 0.06-0.12%; the mass ratio of Cr:Cu:Mn:Mo:V:S is (15-20):(6-8):(4-6):(5-8):(6-10):1; the mass percentages of the remaining components are O: 0.1-0.2%; Al: 2.00-3.00%; Fe: 0.05-0.15%; Sn: 0.05-0.15%; C≤0.03%; N≤0.03%, and the balance is titanium and unavoidable impurities.

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