A processing method for wide-width TC4 cold-rolled strip coils

Abstract

The invention discloses a processing method of a wide TC4 cold-rolled strip coil, comprising the following steps: preparing a slab, explosively compounding the upper and lower surfaces of the slab with a pure titanium layer; heating the slab to 1050-1150°C, controlling the start rolling temperature to 945-955°C, and then performing multiple rough rolling to a 30-45mm head; performing multiple fine continuous rolling to a 3-5mm head for coiling, and the coiling temperature is 840-860°C; performing horizontal continuous atmospheric heat treatment under a temperature condition close to a phase transition point, and then rapidly cooling to room temperature; shot blasting, pickling, and trimming, wherein the trimming process is to heat the coil edge portion to 200-300°C and then perform disc shearing, and then cool the coil edge portion; performing multiple rolling cold rolling to obtain a cold-rolled strip coil with a thickness of 0.5-3.2mm and a width greater than 1000mm, wherein the deformation of a single rolling process is less than 30%; and heat treatment of the finished product. The processing method of the wide TC4 cold-rolled strip coil provided by the present invention has high processing efficiency and high yield rate, and the obtained product performance can meet the national standard requirements and has excellent surface quality.

Description

Technical Field

[0001] The invention relates to the technical field of titanium alloy processing, and in particular to a processing method for a wide TC4 cold-rolled strip coil. Background Art

[0002] TC4 titanium alloy (Ti-6Al-4V) has good room temperature and high temperature mechanical properties, excellent fatigue resistance and crack growth resistance, and is widely used in the manufacture of pressure vessels, rocket engine shells, aircraft skins, ribs and webs, etc. It is an important material for aerospace and aviation defense industries. TC4 titanium alloy is the most used alloy among titanium alloys, and its output accounts for 50% of the total output of titanium alloys and 95% of all titanium alloy processed parts. As a typical α+β type alloy, TC4 titanium alloy contains 6% of α-phase stabilizing element Al and 4% of β-phase stabilizing element V. The phase transition temperature of TC4 titanium alloy is 980-1010℃, and the melting point is about 1667℃. In the annealed state, the alloy contains 7% of β phase. When quenched from the critical quenching temperature Tk (~850℃), about 25% of β phase can be retained. The retained β phase precipitates dispersed α phase during aging, so that the alloy can be strengthened by heat treatment.

[0003] TC4 cold-rolled coils are currently mainly produced by sheet-type processes due to their high product strength and high processing difficulty. During the rolling process, the sheet-type production process can use methods such as cutting width and reversing to improve anisotropy. Although the organization and performance can meet the requirements of relevant standards, the batch production volume is small, and there are generally many fires, many processes, low yield rate, and long production cycle. At present, the coil production process at home and abroad is mainly hot-rolled black belt coils, and there is no relevant report on cold rolling processing, or even processing to thinner wide strips (above 1000mm).

[0004] In view of this, the object of the present invention is to provide a new processing method for wide TC4 cold-rolled strip coil. Summary of the invention

[0005] The technical problem to be solved by the present invention is to provide a processing method for wide TC4 cold-rolled strip coils, which has high processing efficiency and high yield rate, and the obtained product performance can meet the national standard requirements and has excellent surface quality.

[0006] In order to solve the above problems, the technical solution of the present invention is as follows:

[0007] A method for processing a wide TC4 cold-rolled coil comprises the following steps:

[0008] Step S1, slab preparation: slab pretreatment, performing explosion compounding of pure titanium layer on the upper and lower surfaces of the slab, and performing surface treatment on the slab after explosion compounding again;

[0009] Step S2, rough rolling: Heat the slab to 1050 - 1150 °C, control the starting rolling temperature at 945 - 955 °C, and then rough roll it through multiple passes to 30 - 45 mm and cut the head;

[0010] Step S3, finish rolling: Finish continuous tandem rolling through multiple passes to 3 - 5 mm and then wind up, with the winding temperature at 840 - 860 °C;

[0011] Step S4, semi - finished product heat treatment: Conduct horizontal continuous atmospheric heat treatment under conditions close to the phase transition point temperature, and then rapidly cool it to room temperature;

[0012] Step S5, shot peening, pickling, and trimming. The trimming process is to heat the edges of the coil to 200 - 300 °C and then cut with a circular disk shear, and then cool the edges of the coil;

[0013] Step S6, cold rolling: Conduct multi - pass cold rolling to obtain a cold - rolled coil with a thickness of 0.5 - 3.2 mm and a width greater than 1000 mm, where the deformation per single pass is less than 30%;

[0014] Step S7, finished product heat treatment.

[0015] Further, in step S1, cut a pure titanium whole plate with a thickness of 2 - 4 mm, leave margins in both length and width, and conduct explosive cladding of pure titanium layers on the upper and lower surfaces of the slab.

[0016] Further, the surface treatment of the slab after explosive cladding includes steps of polishing, defect inspection, defect point grinding, polishing the large surface, and brushing a high - temperature - resistant coating on the side edges.

[0017] Further, in step S2, through 5 passes of rough rolling, the deformation per pass is successively: 13% → 15% → 17.5% → 21.1% → 30.74%.

[0018] Further, in step S3, through 7 passes of finish rolling, the starting rolling temperature is 900 - 920 °C, and the deformation per pass is successively flat shape → 11.33% → 15.79% → 11.72% → 15% → 19% → 20%.

[0019] Further, in step S4, in the semi - finished product heat treatment process, the running linear speed of the coil is 3 - 4 m / min.

[0020] Further, in step S4, the rapid quenching adopts a three - stage air - cooling method, and the total cooling process time is 2 - 3 min.

[0021] Further, the first - stage air - cooling conducts forced pre - cooling to rapidly reduce the coil temperature to 280 - 320 °C, the second - stage air - cooling reduces the coil temperature to below 80 °C, and the third - stage air - cooling reduces the coil temperature to room temperature.

[0022] Furthermore, the finished product heat treatment process adopts vertical online inert gas protection heat treatment, the heat treatment temperature is 860-880°C, and the annealing speed is 3-6m / min.

[0023] Compared with the prior art, the processing method of wide TC4 cold-rolled strip coil provided by the present invention has the following beneficial effects:

[0024] The processing method of wide TC4 cold-rolled strip coil provided by the present invention realizes coil production, has high processing efficiency and high yield rate, and the obtained product performance can meet the national standard requirements and has excellent surface quality; it can meet the use of ultra-long products and solves the problem of strip raw materials that TC4 foil has always adopted sheet welding and strip rolling. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following briefly introduces the drawings required for use in the description of the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0026] Figure 1 is a thermal simulation curve diagram of the slab in the present invention;

[0027] Figure 2 This is the metallographic structure diagram of the finished coil of the present invention. DETAILED DESCRIPTION

[0028] In order to enable those skilled in the art to better understand the technical solutions in the embodiments of the present invention and to make the above-mentioned objects, features and advantages of the present invention more obvious and understandable, the specific implementation modes of the present invention are further described below.

[0029] It should be noted that the description of these embodiments is used to help understand the present invention, but does not constitute a limitation of the present invention. In addition, the technical features involved in each embodiment of the present invention described below can be combined with each other as long as there is no conflict between them.

[0030] A method for processing a wide TC4 cold-rolled coil, characterized in that it comprises the following steps:

[0031] Step S1, slab preparation: slab pretreatment, performing explosion compounding of pure titanium layer on the upper and lower surfaces of the slab, and performing surface treatment on the slab after explosion compounding again;

[0032] Specifically, the slab pretreatment process is: the slab after forging is planed and milled → polished → defect inspection and marking → defect point grinding → penetrant flaw detection → defect marking → defect point grinding and polishing;

[0033] The explosive cladding process is as follows: Cut a pure titanium whole plate with a thickness of 2 - 4 mm, leaving a margin of 5 mm on each side of the length and width, and perform explosive cladding on the upper and lower surfaces of the slab with pure titanium layers; the thickness of the pure titanium whole plate can be 2 mm, 3 mm or 4 mm, or other thickness values within this range;

[0034] The surface treatment process of the slab after explosive cladding is: polishing → defect inspection → grinding and polishing the defective points, polishing the large surface, and brushing a high-temperature resistant coating on the side edges (let it stand until dry and does not fall off);

[0035] Explosively cladding a pure titanium layer on the surface of the slab and then combining with the surface coating can fully protect the deep oxidation of the slab during the heating process, solve the problem of excessive surface oxidation layer of the slab during heating resulting in surface cracking during the hot rolling process of the strip coil, and thus effectively improve the surface quality of the hot coil.

[0036] Step S2, rough rolling: Heat the slab to 1050 - 1150 °C, control the starting rolling temperature to 945 - 955 °C, and then rough roll it through multiple passes to 30 - 45 mm and cut the head;

[0037] Controlling the temperature before rough rolling ensures the full fragmentation of the coarse structure of the slab and provides a guarantee for the subsequent product performance indicators. In the present invention, thermal simulation tests are carried out to determine the heating temperature of the slab. Specifically, at the end of the slab, slice layers are sawed, wire cut and machined into cylindrical samples, and thermal simulation tests are carried out. The results can be referred to Figure 1 the thermal simulation curve graph of, where Figure 1 (a) represents the thermal simulation curve under the condition of 0.01 s -1 -50%, Figure 1 (b) represents the thermal simulation curve under the condition of 0.1 s -1 -50%, Figure 1 (c) represents the thermal simulation curve under the condition of 1 s -1 -50%, Figure 1 (d) represents the thermal simulation curve under the condition of 10 s -1 -50%. It can be seen from the thermal simulation curve and in combination with the phase transformation point of 960 °C of this ingot number that as the test temperature increases, the deformation resistance decreases, and after exceeding the phase transformation point, the change in the deformation resistance is basically flat. The deformation of this alloy conforms to the change trend of the metal stress-strain curve, and each stage in the plastic deformation is very obvious.

[0038] Combined with the hot rolling mill equipment capacity, and the requirement that the rough rolling start temperature must be below the phase change point, according to the material transfer distance from the furnace outlet to the rough rolling mill entrance, it is finally determined that the heating temperature is 1050-1150℃. After the slab is out of the furnace, it needs to be lifted by the overhead crane to remove the lower pad, and it needs to be transported from the furnace outlet to the mill entrance by rollers. The transfer time is delayed for a long time. Therefore, it is necessary to leave enough temperature drop steps, and 1100℃ is the best. When transported to the mill entrance, remember not to perform high-pressure water / high-pressure air dephosphorization to avoid excessive surface temperature drop during the dephosphorization process, causing the plate shape to warp / down, or even tear after rough rolling.

[0039] Specifically, the rough rolling passes are 4-6 passes, such as 4, 5 or 6 passes, until the slab thickness is 30-45 mm; for example, after 5 rough rolling passes, the deformation amount of each pass is: 13%→15%→17.5%→21.1%→30.74%.

[0040] Step S3, finishing rolling: rolling to 3-5 mm through multiple passes of finishing continuous rolling, and then coiling at a coiling temperature of 840-860°C;

[0041] Specifically, the number of finishing passes may be 6-8, such as 6, 7 or 8; the coiling temperature may be 840°C, 850°C or 860°C, or other temperature values ​​within the range. For example, after 7 finishing passes, the start rolling temperature is 900-920°C, and the deformation of each pass is flat → 11.33% → 15.79% → 11.72% → 15% → 19% → 20%. The coiling temperature is preferably 850°C, under which the yield strength of the coil is about 100Mpa, which is conducive to coiling.

[0042] After rolling, the tail of the hot coil is cut at a higher temperature using a flattening line, and sampling is performed to compare the performance indicators at room temperature with those of sheet rolling. The test results are shown in Table 1:

[0043]

[0044] By controlling the finishing thickness and coiling temperature, the smooth coiling of the high-strength coil can be ensured, and at the same time, the prerequisite for the subsequent uncoiling of the tropical coil can be provided, so as to avoid the problem that the coiling force is too large and the coil temperature is too low, which makes it impossible to coil, or the coil temperature is too high, so that the coiling can be easily coiled, but the structure is coarse, the strength is too high, and the coiling force is greater than the uncoiling force, which makes it impossible to uncoil.

[0045] Step S4, heat treatment of the semi-finished product: horizontal continuous atmospheric heat treatment at a temperature close to the phase transition point, and then rapid cooling to room temperature;

[0046] Specifically, select 950°C close to the phase transition point and perform on-line horizontal continuous atmospheric heat treatment at a running linear speed of 3 - 4 m / min. Adopt the heating method with resistance belts below and electric radiant tubes above to form a loose oxide layer on the surface of the hot coil, which is convenient for subsequent shot peening and crushing, conducive to improving the efficiency of shot peening to remove the oxide scale, and further providing conditions for subsequent pickling to remove deep contamination. Among them, the heat treatment speed can be 3 m / min, 3.5 m / min, or 4 m / min, or other values within this range.

[0047] After heat treatment, quickly cool to room temperature to ensure effective improvement of the hot-rolled structure, which is convenient for subsequent cold rolling and finished product performance. In the present invention, the rapid quenching adopts a three-stage air-cooling method, and the entire cooling process takes 2 - 3 min; among them, the first-stage air-cooling performs forced pre-cooling to quickly reduce the temperature of the coil to 280 - 320°C, the second-stage air-cooling reduces the temperature of the coil to below 80°C, and the third-stage air-cooling reduces the temperature of the coil to room temperature. Among them, the first-stage air-cooling can cool down to 280°C, 290°C, 300°C, 310°C, or 320°C, or other temperature values within this range.

[0048] Step S5, shot peening, pickling, and trimming;

[0049] Specifically, shot peening, pickling, and trimming are carried out on a combined pickling line. Select a relatively high sand falling amount and shot head speed to effectively loosen the oxide scale on the surface of the coil, then remove the residual steel shot ash on the surface through rinsing, and then enter the mixed acid tank for pickling to ensure a single-sided stock removal of 0.03 - 0.05 mm.

[0050] The trimming process is to heat the edge of the coil to 200 - 300°C and then perform circular disc cutting, and then cool the edge of the coil; specifically, an induction heating device is added in front of the original circular disc shear. During the running process of the coil, heat is replenished to the edge in real time to make the temperature of the material within 10 mm of the edge reach 200 - 300°C, and then circular disc cutting is carried out. Due to the high strength of the coiled strip, the warm cutting process is adopted. On the one hand, the method of using temperature to resist its strength is used to solve the problems that in cold trimming, extremely high requirements are imposed on the tool disc material system, the thickness of the coiled strip, and the flatness of the coiled strip. If the hardness of the tool disc is not enough, the material cannot be cut into pieces, and if the hardness of the tool disc is slightly increased by two points, large burrs of edge crushing will occur; on the other hand, the edge of the coiled strip is heated, and after heating, there is no need to uncoil and cut, which can effectively protect the surface quality of the product and can achieve a coiled continuous production method.

[0051] At the same time, to avoid damage to the rubber roller caused by edge preheating, after trimming is completed, an air box is added to cool the edge of the coil to ensure that it passes through the tension rubber roller at room temperature.

[0052] Step S6, cold rolling: performing multiple cold rolling passes to obtain a cold rolled coil with a thickness of 0.3-2 mm and a width greater than 1000 mm, wherein the deformation in a single rolling pass is less than 30%;

[0053] Specifically, adopting small tension, deformation of less than 30% in a single rolling process, and taking no edge cracking as the main control point can fully save the metal loss caused by repeated edge cutting, and at the same time realize a virtuous process cycle;

[0054] After intermediate continuous stress relief heat treatment, the surface is shot blasted and pickled to improve the surface quality, and multiple cold rolling processes are repeated to finally produce cold rolled coils with a thickness of 0.5-3.2mm and a width greater than 1000mm.

[0055] Step S7, heat treatment of finished product;

[0056] Specifically, the finished product heat treatment adopts vertical online inert gas protection heat treatment, the heat treatment temperature is 860-880℃; the annealing speed is 3-6m / min, and after heat treatment, it is cooled to room temperature by rapid multi-stage argon filling cooling. From a microscopic perspective, high-temperature heat treatment and rapid multi-stage argon filling cooling can ensure good organizational and performance requirements, while ensuring uniform heat treatment of the entire coil; from a macroscopic perspective, the weight of the strip is fully utilized to ensure a good plate shape of the finished product, reducing the burden on subsequent finishing processes.

[0057] See also Figure 2 , is the metallographic structure diagram of the finished coil of the present invention (500x metallographic structure after heat treatment at a transverse length of 0.5 mm), which is graded according to GJB / 2505A-2008 and meets the Grade 1 standard, with a primary α phase size of 4.7 um and a primary α content of 75%.

[0058] Through the above process, the finished product coil weight is ≥ 3 tons, and the specification is 0.5-3.2mm×1000mm×C wide TC4 cold-rolled strip coil. The production efficiency is high, the yield rate is high, the product performance meets the requirements of national and American standards, the processing flow is simple, the process is stable, and the surface quality is excellent.

[0059] The processing method of the wide TC4 cold-rolled coil of the present invention is used to produce TC4 cold-rolled coils with a width of δ3.2 mm, δ1.68 mm, and δ0.55 mm, and the annealed properties thereof are tested. The test results are as follows:

[0060] Table 2: Annealing properties of TC4 cold-rolled coils of different thicknesses

[0061] Specification (mm) Rm (MPa) Rp0.2 (MPa) A5(％) 3.2 1000 925 13.5 1.68 1020 910 16 0.35 1090 1000 17.5

[0062] As can be seen from Table 2, after heat treatment, the product performance indicators can all meet the requirements of GB / T3621-2007 (Rm≥895MPa; Rp0.2≥830MPa; A5≥10%).

[0063] Comparing the properties of annealed TC4 plates produced in a similar specification sheet form, see Table 3:

[0064] Table 3: Properties of annealed TC4 produced in a similar specification sheet form

[0065] Specification (mm) Rm (MPa) Rp0.2 (MPa) A5(％) 1.6 1080 1060 16 0.4 1060 1020 11

[0066] From the above results, it can be seen that for the wide-width TC4 cold-rolled coil prepared by the present invention, its product indicators fully meet the national standard requirements, are comparable to the properties of TC4 plates produced in a similar specification sheet form, and cover a wide range of product specification series. For the conventional technology that can only produce TC4 plates and foils in a sheet form at present, a new technical idea is proposed.

[0067] The wide-width TC4 coil produced by the present invention meets the requirements of TC4 coils in multiple fields, can improve production efficiency, save processes, and thus achieve a major breakthrough in saving processing costs.

[0068] Each embodiment in this specification is described in a progressive manner. The same or similar parts among the embodiments can be referred to each other, and the key point of each embodiment is to illustrate the differences from other embodiments.

[0069] The above has made a detailed description of the embodiments of the present invention, but the present invention is not limited to the described embodiments. For those skilled in the art, various changes, modifications, substitutions, and variations made to these embodiments without departing from the principle and spirit of the present invention still fall within the protection scope of the present invention.

Claims

1. A processing method for a wide-width TC4 cold-rolled strip coil, characterized in that, It includes the following steps: Step S1, slab preparation: Pretreat the slab, perform explosive cladding of pure titanium layers on the upper and lower surfaces of the slab, and then perform surface treatment on the explosively clad slab again; Step S2, rough rolling: Heat the slab to 1050 - 1150 °C, control the starting rolling temperature at 945 - 955 °C, and then rough roll it through multiple passes to 30 - 45 mm and cut the head; After 5 passes of rough rolling, the reduction per pass is successively: 13% → 15% → 17.5% → 21.1% → 30.74%; Step S3, finish rolling: Finish continuous rolling through multiple passes to 3 - 5 mm and then wind up, with the winding temperature at 840 - 860 °C; After 7 passes of finish rolling, the starting rolling temperature is 900 - 920 °C, and the reduction per pass is successively flat shape → 11.33% → 15.79% → 11.72% → 15% → 19% → 20%; Step S4, semi - finished product heat treatment: Perform horizontal continuous atmospheric heat treatment under conditions close to the phase transition point temperature, and then quickly quench to room temperature; In the semi - finished product heat treatment process, the running linear speed of the coil is 3 - 4 m / min; Step S5, shot blasting, pickling, and trimming. In the trimming process, heat the edge of the coil to 200 - 300 °C and then perform disk cutting, and then cool the edge of the coil; Step S6, cold rolling: Perform multi - pass cold rolling to obtain a cold - rolled coil with a thickness of 0.5 - 3.2 mm and a width greater than 1000 mm, where the reduction per single pass is less than 30%; Step S7, finished product heat treatment; Perform forced pre - cooling with primary air cooling to quickly reduce the coil temperature to 280 - 320 °C, secondary air cooling to reduce the coil temperature to below 80 °C, and tertiary air cooling to reduce the coil temperature to room temperature; The finished product heat treatment process uses vertical on - line inert gas - protected heat treatment, with the heat treatment temperature at 860 - 880 °C and the annealing speed at 3 - 6 m / min.

2. The processing method for a wide-width TC4 cold-rolled strip coil according to claim 1, characterized in that, In step S1, cut a pure titanium whole plate with a thickness of 2 - 4 mm, leave margins in both length and width, and perform explosive cladding of pure titanium layers on the upper and lower surfaces of the slab.

3. The processing method for a wide-width TC4 cold-rolled strip coil according to claim 1, characterized in that, The surface treatment of the explosively clad slab includes steps of polishing, defect inspection, defect point grinding, polishing the large surface, and brushing a high - temperature - resistant coating on the side edges.

4. The processing method for a wide-width TC4 cold-rolled strip coil according to claim 1, characterized in that, In step S4, the quick quenching adopts a three - stage air cooling method, and the total cooling process time is 2 - 3 min.

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