Method for inhibiting surface cracking in rolling process of high-strength titanium alloy thick plate

Abstract

The invention relates to the technical field of titanium alloy rolling processing, and discloses a method for inhibiting surface cracking in the rolling process of a high-strength titanium alloy thick plate, which comprises the following steps: selecting a titanium alloy plate blank, and preheating the plate blank; the preheated plate blank is subjected to surface multi-pass rolling treatment, and the roll gap set in the later-pass rolling treatment is smaller than that in the previous-pass rolling treatment; remelting and heating the plate blank, wherein the heating temperature is higher than the preheating temperature; the plate blank is discharged out of the furnace and subjected to multi-pass rolling, a rolled plate blank is obtained, and the rolling pass rolling reduction is controlled to range from 5 mm to 25 mm; and the rolled plate blank is straightened on line and then air-cooled to the room temperature. According to the method, the surface layer of the plate blank substrate is subjected to structure prefabrication, the surface plasticity is improved, the extensibility in the rolling process is improved, and generation of surface cracks is restrained.

Description

Technical Field

[0001] The invention relates to the technical field of titanium alloy rolling processing, in particular to a method for inhibiting surface cracking during the rolling process of a high-strength titanium alloy thick plate. Background Art

[0002] Titanium alloy materials have been widely used in aerospace, marine engineering and other fields due to their high specific strength and excellent corrosion resistance. In recent years, due to the higher demand for diving depth of underwater equipment, higher index requirements have been put forward for the strength and toughness of materials. Titanium alloy materials will be used on a larger scale in underwater equipment due to their performance advantages. The most widely used titanium alloy material in underwater equipment is titanium alloy thick plate, which is the main material for structural frame and shell. Titanium alloy thick plates are produced by hot rolling. During the rolling and heating process, due to the high activity of titanium, it is easy to react with oxygen, nitrogen, hydrogen, etc. in the air. At the same time, the surface structure is easy to coarsen, the plasticity is reduced, and the surface of the titanium billet is very easy to crack during the subsequent rolling process. In order to solve this problem, the industry often uses the method of applying an anti-oxidation coating or explosively stacking a pure titanium layer on the surface of the titanium alloy billet to avoid the formation of a brittle hard layer during the heating and rolling of the substrate. However, this method has the disadvantages of high cost and long production cycle, which is not conducive to large-scale batch production.

[0003] Therefore, there is a need in the prior art for improving the method of suppressing surface cracking during the rolling process of high-strength titanium alloy thick plates. Summary of the invention

[0004] In view of this, the purpose of an embodiment of the present invention is to propose a method for inhibiting surface cracking during the rolling process of high-strength titanium alloy thick plates, starting from the surface pretreatment of the slab for titanium alloy rolling, the surface layer of the slab matrix is ​​preformed to improve the surface plasticity, improve the elongation during the rolling process, and inhibit the occurrence of surface cracks.

[0005] Based on the above purpose, an embodiment of the present invention provides a method for inhibiting surface cracking during the rolling process of a high-strength titanium alloy thick plate, comprising the following steps: S1 selects a titanium alloy slab and preheats the slab; S2 performs multiple rolling processes on the surface of the preheated slab, and the roll gap setting in the subsequent rolling process is smaller than that in the previous process; S3 heats the slab back into the furnace, and the heating temperature is higher than the preheating temperature; S4 The slab is taken out of the furnace and rolled for multiple passes to obtain the rolled slab, and the reduction of each rolling pass is controlled to be 5~25mm; S5 straightens the rolled slab online and then air cools it to room temperature.

[0006] In some embodiments, in S1, the thickness of the slab ranges from 180 to 240 mm, the width of the slab ranges from 1200 to 1400 mm, and the length of the slab ranges from 2100 to 2400 mm.

[0007] In some embodiments, in S1, the preheating temperature is 850-900°C, and the holding time is 30-50 min.

[0008] In some embodiments, in S2, the first roll gap is set to (T-3)~(T-5) mm, the second roll gap is set to (T-5)~(T-8) mm, and the third roll gap is set to (T-8)~(T-10) mm, where T is the thickness of the slab.

[0009] In some embodiments, the first roll gap is set to (T-5) mm, the second roll gap is set to (T-8) mm, and the third roll gap is set to (T-10) mm.

[0010] In some embodiments, in S3, the temperature of the furnace heating is controlled to be 920-960° C., and the holding time is 240-360 min.

[0011] In some embodiments, the titanium alloy slab is TC4 titanium alloy or TA15 titanium alloy.

[0012] In some embodiments, in S4, the thickness of the slab obtained after rolling is 30-50 mm.

[0013] In some embodiments, in S1 and S3, the heating furnaces are roller-hearth heating furnaces.

[0014] In some embodiments, in S4, the rolling speed is 0.1 m / s to 5 m / s.

[0015] The present invention has at least the following beneficial technical effects: The present invention starts with the surface pretreatment of the slab for titanium alloy rolling, preforms the surface layer of the slab matrix, improves the plasticity of the surface, improves the ductility during the rolling process, and inhibits the generation of surface cracks. Compared with the surface coating and composite pure titanium layer methods, the present invention does not require other raw materials or tooling conditions, and can complete the surface prefabrication of the fine-grained layer through easy-to-implement heating and rolling, which has higher economy and surface quality improvement effect. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings in the following description are only some embodiments of the present invention. For ordinary technicians in this field, other embodiments can be obtained based on these drawings without paying creative work.

[0017] Figure 1 A schematic diagram of an embodiment of a method for suppressing surface cracking during the rolling process of a high-strength titanium alloy thick plate provided by the present invention; Figure 2 The fine-grained layer observed on the surface of the high-strength TC4 plate after rolling provided in Example 1 of the present invention; Figure 3 This is a comparison chart of the surface cracking of TA15 titanium alloy thick plate before and after the implementation of the process of Example 2 provided by the present invention. DETAILED DESCRIPTION

[0018] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the embodiments of the present invention are further described in detail below in combination with specific embodiments and with reference to the accompanying drawings.

[0019] The terms "including" and "having" and any variations thereof in the specification and claims of the present invention and the above-mentioned drawings are intended to cover non-exclusive inclusions; the terms "first", "second", etc. in the specification and claims of the present invention or the above-mentioned drawings are used to distinguish different objects rather than to describe a specific order. "Multiple" means two or more, unless otherwise clearly and specifically defined.

[0020] In addition, reference to "embodiments" herein means that a particular feature, structure, or characteristic described in conjunction with the embodiments may be included in at least one embodiment of the present invention. The appearance of the phrase in various places in the specification does not necessarily refer to the same embodiment, nor is it an independent or alternative embodiment that is mutually exclusive with other embodiments. It is explicitly and implicitly understood by those skilled in the art that the embodiments described herein may be combined with other embodiments.

[0021] The present invention is aimed at the rolling production of high-strength titanium alloy thick plates such as TC4 and TA15, with a rolling slab thickness of 260~300mm and a finished plate thickness of ≥30mm. The rolling process of thick high-strength titanium alloy plates has a large absolute reduction, and the surface crack width and depth are larger than the rolling process of thin-gauge plates. It is necessary to reduce the formation of surface cracks through surface treatment or rolling process optimization. The present invention performs surface pretreatment on the rolling slab before rolling, specifically through heating control and small reduction rolling, so that a fine-grained layer with good plasticity is formed on the surface of the slab, and then the slab is heated as a whole and rolled to obtain a high-strength titanium alloy thick plate with a thickness of ≥30mm.

[0022] like Figure 1 The method for inhibiting surface cracking during the rolling process of a high-strength titanium alloy thick plate provided by the present invention comprises the following steps: S1 selects a titanium alloy slab and preheats the slab; S2 performs multiple rolling processes on the surface of the preheated slab, and the roll gap setting in the subsequent rolling process is smaller than that in the previous process; S3 heats the slab back into the furnace, and the heating temperature is higher than the preheating temperature; S4 The slab is taken out of the furnace and rolled for multiple passes to obtain the rolled slab, and the reduction of each rolling pass is controlled to be 5~25mm; S5 straightens the rolled slab online and then air cools it to room temperature.

[0023] Furthermore, the titanium alloy slabs are TC4 titanium alloy and TA15 titanium alloy. Among them, TC4 titanium alloy is a typical α+β type titanium alloy, the main alloying element is titanium (Ti), and it also contains about 6% aluminum (Al) and 4% vanadium (V). Aluminum plays a major role in solid solution strengthening in titanium alloys, which can improve the strength and heat resistance of the alloy. Vanadium can stabilize the β phase, give the alloy good plasticity and toughness, and can reduce the density of the alloy. TA15 titanium alloy belongs to a near-α type titanium alloy, the main component of which is titanium (Ti), and it also contains about 6.5%-7.5% aluminum (Al), 1.0%-2.5% zirconium (Zr), 1.0%-2.0% molybdenum (Mo) and 0.2%-0.4% tin (Sn). Aluminum also plays a role in solid solution strengthening, and zirconium can refine the grains and improve the strength and toughness of the alloy. Molybdenum can stabilize the β phase and improve the hot working properties of the alloy, and tin also helps to improve the strength and heat resistance of the alloy.

[0024] In some embodiments, in S1, the thickness of the slab ranges from 180 to 240 mm, the width of the slab ranges from 1200 to 1400 mm, and the length of the slab ranges from 2100 to 2400 mm. The preheating temperature is 850 to 900°C, and the holding time is 30 to 50 minutes. In this step, the preheating temperature is set relatively low, and the holding time is short to reduce the formation of the surface oxide layer. The purpose of preheating is to make only the surface layer of the slab with a thickness of 5 to 15 mm reach the set temperature, so as to achieve the goal of only surface deformation and refinement of the surface structure during the rolling process.

[0025] In some embodiments, in S2, the first roll gap is set to (T-3)~(T-5) mm, the second roll gap is set to (T-5)~(T-8) mm, and the third roll gap is set to (T-8)~(T-10) mm, where T is the thickness of the slab. Preferably, the first roll gap is set to (T-5) mm, the second roll gap is set to (T-8) mm, and the third roll gap is set to (T-10) mm. In this step, a rolling method with a small reduction amount and multiple reductions is used to deform the surface preheating layer, so that a fine-grained layer with a thickness of 2~5 mm can be formed on the surface. At the same time, a dense oxide layer will be formed on the surface of the slab, which can effectively inhibit the infiltration of surface gas during the subsequent heating process.

[0026] In some embodiments, in S3, the temperature of the reheating is controlled to be 920-960°C, and the holding time is 240-360 min. In some embodiments, in S1 and S3, the heating furnace is a roller bottom heating furnace.

[0027] In some embodiments, in S4, the thickness of the slab obtained after rolling is 30-50 mm. The rolling speed is 0.1 m / s to 5 m / s. For the rolling of thick plates, the pass reduction is limited, the surface extension deformation of a single pass is reduced, and the excellent plasticity of the surface prefabricated fine-grained layer can effectively inhibit surface cracking.

[0028] Furthermore, in S5, the rolled slab is straightened online. During the rolling process, the titanium alloy thick plate may have some bending deformation. Online straightening can restore the plate to a relatively flat state, avoiding additional stress concentration during the cooling process due to the irregular shape of the plate. For example, if the plate is bent, the contraction of the bent part and other parts is inconsistent during cooling, which is likely to generate stress and cause surface cracking. Straightening can effectively reduce the occurrence of this situation.

[0029] The present invention will be further explained below in conjunction with specific embodiments.

[0030] Example 1 Rolling high iron oxide TC4 thick plate, slab size: thickness 205mm × width 1350mm × length 2200mm, planned rolling plate size thickness 48mm × width 2250mm × length 5600mm; Preheat the slab. After the furnace temperature reaches the temperature, put the slab into the heating furnace. The furnace temperature is controlled at 880℃. When the temperature instrument of the heating furnace shows that the temperature at each position in the furnace reaches and stabilizes at 880℃, start the timing and heat preservation. After the slab is heated for 40 minutes, the surface layer is prefabricated immediately after it is taken out of the furnace. The surface layer of the slab is rolled by a rolling mill. Since only the surface layer temperature reaches the set temperature during the heating process of the slab, only the surface is deformed during the rolling process. The first roll gap is set to 200mm, the second roll gap is set to 197mm, and the third roll gap is set to 195mm. After the treatment is completed, it is air-cooled to room temperature and the edges of the slab are trimmed. The slab after surface prefabrication is returned to the furnace for reheating, and the heating and insulation temperature is controlled at 950°C and the insulation time is 300 minutes; After the holding time is up, the slab is taken out of the furnace for multiple rolling passes. The reduction of each rolling pass is controlled to be 5-25mm. The rolling is performed in a cross-reversing manner in the horizontal and vertical directions. After 9 rolling passes, the thickness of the obtained plate is 48mm. The rolled slab is straightened online and then air-cooled to room temperature; After the plate cooled to room temperature, the surface of the plate was observed and no obvious cracking defects were found. The surface quality was significantly improved. After simple grinding and polishing, the surface quality requirements were met. Figure 2 As shown, by sampling and observing the metallographic structure in the thickness direction of the plate, it can be observed that there is a significant difference between the surface layer structure and the internal structure after rolling. A fine-grained layer with a thickness of about 1 mm can be observed on the surface layer, and the interior is a deformed structure with elongated grains.

[0031] Example 2 Rolling TA15 titanium alloy thick plate, slab size: thickness 185mm × width 1300mm × length 2300mm, planned rolling plate size thickness 40mm × width 2150mm × length 6000mm; Preheat the slab. After the furnace temperature reaches the set temperature, put the slab into the heating furnace. The furnace temperature is controlled at 900°C. When the temperature instrument of the heating furnace shows that the temperature at each position in the furnace reaches and stabilizes at 900°C, start the timing and heat preservation. After the slab is heated for 35 minutes, the surface layer is prefabricated immediately after it is taken out of the furnace. The surface layer of the slab is rolled by a rolling mill. Since only the surface layer temperature reaches the set temperature during the heating process of the slab, only the surface is deformed during the rolling process. The first roll gap is set to 180mm, the second roll gap is set to 177mm, and the third roll gap is set to 175mm. After the treatment is completed, it is air-cooled to room temperature and the edges of the slab are trimmed. The slab after surface prefabrication is returned to the furnace for reheating, and the heating and insulation temperature is controlled at 960°C and the insulation time is 240 minutes; After the holding time is up, the slab is taken out of the furnace for multiple rolling passes. The reduction of each rolling pass is controlled to be 5-25mm. The rolling is performed in a cross-reversing manner in the horizontal and vertical directions. After 7 rolling passes, the thickness of the obtained plate is 40mm. The rolled slab is straightened online and then air-cooled to room temperature; After the plate cools to room temperature, Figure 3 As shown, no obvious cracking defects were found on the surface of the plate, but there were micro-cracks on the surface with a depth of less than 0.1 mm and a width of less than 0.2 mm. The surface quality was significantly improved compared with that before the process was implemented (serious surface cracking, large cracks with a depth of more than 1 mm and a width of more than 2 mm). After simple grinding and polishing, the surface quality requirements were met.

[0032] Example 3 Rolling TC4 thick plate of national military standard technical indicators, slab size: thickness 200mm × width 1400mm × length 2300mm, planned rolling plate size thickness 30mm × width 2100mm × length 7500mm; Preheat the slab. After the furnace temperature reaches the temperature, put the slab into the heating furnace. The furnace temperature is controlled at 880℃. When the temperature instrument of the heating furnace shows that the temperature at each position in the furnace reaches and stabilizes at 880℃, start the timing and heat preservation. After the slab is heated for 40 minutes, the surface layer is prefabricated immediately after it is taken out of the furnace. The surface layer of the slab is rolled by a rolling mill. Since only the surface layer temperature reaches the set temperature during the heating process of the slab, only the surface is deformed during the rolling process. The first roll gap is set to 195mm, the second roll gap is set to 192mm, and the third roll gap is set to 190mm. After the treatment is completed, it is air-cooled to room temperature and the edges of the slab are trimmed. The slab after surface prefabrication is returned to the furnace for reheating, and the heating and insulation temperature is controlled at 940°C and the insulation time is 330 minutes; After the holding time is up, the slab is taken out of the furnace for multiple rolling passes. The reduction of each rolling pass is controlled to be 5-25mm. The rolling is performed in a cross-reversing manner in the horizontal and vertical directions. After 11 rolling passes, the thickness of the obtained plate is 30mm. The rolled slab is straightened online and then air-cooled to room temperature; After the plate cooled to room temperature, the surface of the plate was observed and no obvious cracking defects were found. There were micro-cracks on the surface. After simple grinding and polishing, the surface quality requirements were met.

[0033] The above are exemplary embodiments disclosed in the present invention, but it should be noted that various changes and modifications may be made without departing from the scope disclosed in the embodiments of the present invention as defined in the claims. The functions, steps and / or actions of the method claims according to the disclosed embodiments described herein do not need to be performed in any particular order. In addition, although the elements disclosed in the embodiments of the present invention may be described or required in individual form, they may also be understood as multiple unless explicitly limited to the singular.

[0034] It should be understood that, as used herein, the singular forms "a", "an" are intended to include the plural forms as well, unless the context clearly supports an exception. It should also be understood that, as used herein, "and / or" refers to any and all possible combinations including one or more of the associated listed items.

[0035] The serial numbers of the embodiments disclosed in the above embodiments of the present invention are only for description and do not represent the advantages or disadvantages of the embodiments.

[0036] A person skilled in the art should understand that the discussion of any of the above embodiments is only exemplary and is not intended to imply that the scope of the disclosure of the embodiments of the present invention (including the claims) is limited to these examples; under the concept of the embodiments of the present invention, the technical features in the above embodiments or different embodiments can also be combined, and there are many other changes in different aspects of the above embodiments of the present invention, which are not provided in detail for the sake of simplicity. Therefore, any omissions, modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the embodiments of the present invention should be included in the protection scope of the embodiments of the present invention.

Claims

1. A method for inhibiting surface cracking during the rolling process of high-strength titanium alloy thick plates, characterized in that: include: S1 selects a titanium alloy slab and preheats the slab; S2 performs multiple rolling processes on the surface of the preheated slab, and the roll gap setting in the subsequent rolling process is smaller than that in the previous process; S3 heats the slab back into the furnace, and the heating temperature is higher than the preheating temperature; S4 The slab is taken out of the furnace and rolled for multiple passes to obtain the rolled slab, and the reduction of each rolling pass is controlled to be 5~25mm; S5 straightens the rolled slab online and then air cools it to room temperature.

2. The method for suppressing surface cracking during rolling of high-strength titanium alloy thick plates according to claim 1, characterized in that: In S1, the thickness of the slab ranges from 180 to 240 mm, the width of the slab ranges from 1200 to 1400 mm, and the length of the slab ranges from 2100 to 2400 mm.

3. The method for suppressing surface cracking during rolling of high-strength titanium alloy thick plates according to claim 1, characterized in that: In S1, the preheating temperature is 850~900℃, and the holding time is 30~50min.

4. The method for suppressing surface cracking during rolling of high-strength titanium alloy thick plates according to claim 1, characterized in that: In S2, the first roll gap is set to (T-3)~(T-5) mm, the second roll gap is set to (T-5)~(T-8) mm, and the third roll gap is set to (T-8)~(T-10) mm, where T is the slab thickness.

5. The method for suppressing surface cracking during rolling of high-strength titanium alloy thick plates according to claim 4, characterized in that: The first roll gap is set to (T-5) mm, the second roll gap is set to (T-8) mm, and the third roll gap is set to (T-10) mm.

6. The method for suppressing surface cracking during rolling of high-strength titanium alloy thick plates according to claim 1, characterized in that: In S3, the temperature of the reheating furnace is controlled at 920~960℃, and the holding time is 240~360min.

7. The method for suppressing surface cracking during rolling of high-strength titanium alloy thick plates according to claim 1, characterized in that: The titanium alloy slab is TC4 titanium alloy or TA15 titanium alloy.

8. The method for suppressing surface cracking during rolling of high-strength titanium alloy thick plates according to claim 1, characterized in that: In S4, the thickness of the slab obtained after rolling is 30 to 50 mm.

9. The method for suppressing surface cracking during rolling of high-strength titanium alloy thick plates according to claim 1, characterized in that: In S1 and S3, the heating furnaces are both roller-bottom heating furnaces.

10. The method for suppressing surface cracking during rolling of high-strength titanium alloy thick plates according to claim 1, characterized in that: In S4, the rolling speed is 0.1 m / s to 5 m / s.

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