Annealing of welded joints of titanium alloys consists of heating to the recrystallization temperature or until the phase-transition temperature, holding at a given temperature and subsequent cooling (honey lennogo the furnace, in air or step). Annealing of a-titanium alloys, as a rule, the first joke like that) because it is not associated with phase transformations. On annealing, a + p-titanium alloys in all cases accompanied by a change in the ratio of the content of a-and | 3-phase and should be attributed to the annealing of the second kind. Annealing of the full phase recrystallization for both base metal and weld a titanium-, pseudo-a and a + p-martensitic alloys has not yet found industrial applications as it prevents further improve the physical and mechanical properties. However, currently publishing a series of papers on the application of annealing in p-type region in order to increase the fracture toughness (K1c) semi-finished titanium alloys. For titanium alloys with a + I transition structure and pseudo-Riemannian alloys with phase recrystallization annealing finds industrial application. For welded joints of titanium alloys used full-and part joke. The difference between the partial annealing of the total lies in the fact that the first derivative, is found at lower temperatures and is intended primarily for the partial removal of internal stresses in welded structures, as well as for partial-term stabilization of the structure. Part-time annealing can be used as an intermediate operation in the process of welding of complex design or as the final annealing. The advantage of partial annealing is that it can be done in a furnace with air atmosphere without the need for subsequent removal of slag and contaminated gases, the surface layer of the Me-Full annealing of welded joints would greatly stabilize the structure of the weld and completely remove the residual stresses. Because it is carried out usually at temperatures above 700 ° C, it should be carried out in furnaces with protective atmosphere (argon, helium) or in vacuum furnaces. Titanium alloys with a-structure and pseudo-alloys is almost insensitive to the cooling rate after annealing. Two-phase a + p-type alloys, martensitic (VT16, VTZ-1, VT23, and others) and especially in transition alloys (VT22, VT30, and others), by contrast, are highly sensitive to cooling rate and, therefore, their rate of cooling from the annealing temperature regulated. To do this, apply a joke and then cooled in the furnace at speeds regulated to a certain temperature, and then in air or annealing step, which can be double or isothermal. Double annealing consists of heating to a temperature above the recrystallization temperature and the transformation of metastable phases formed as a result of the thermal cycle of welding, exposure, air cooling and subsequent heating at bo-Lee a low temperature, but sufficient to stabilize the structure formed after the first stage of heat treatment, exposure at this temperature and cooling in air. Isothermal annealing comprises heating to a temperature above the recrystallization temperature and the transformation of metastable phases formed during isothermal cycle of welding, self-control, transfer of alloys in the furnace at a temperature sufficient for transformation of metastable phases in the stable a + p-structure, endurance and cooling in air. When used with subsequent annealing of the alloy in the furnace-cooled (double or isothermal), the temperature at which the cooling air must be so low as to ensure sufficient stability of the a-and p-components in the welded joint is not only to the use of alloy at normal temperatures, but also for its operation at elevated temperatures. Therefore, the annealing regimes for the welded joints of titanium alloys is selected, as a rule, not only to obtain an optimal balance of strength and plasticity characteristics, but also for their thermal stability. Therefore, for titanium alloys depending on their composition, and sometimes on the conditions of welded choose one or another type of annealing. For example, to obtain the specified physical and mechanical properties after welding and annealing of the pseudo-p-alloys (VT15, VT32, and others,) the rate of cooling from the annealing temperature plays no role. However, the stability of the welded joint during the operation at elevated temperatures, it should be a joke, followed by slow cooling at a rate of no more than 2-4 ° C / min.
Although some features of the weld, in all cases to apply the general principles of a heat treatment that and the base metal. Dwell time during annealing starts from the moment the heating cages. Obviously, the a-alloys and pseudo-alloys annealed in all cases, followed by cooling in air. These regimes of thermal-mechanical treatment provide welded joints the floor-ing the removal of internal stresses and the optimum the relation of strength and ductility. Weld compounds of this group of alloys, heat-stable, ie can be used at temperatupax working for a long time without significant changes in physical and mechanical properties. The welded joints of titanium alloys with a + p-structure of the martensitic type can in some cases, annealed and then cooled in air, which often provides the optimal values of strength and ductility, since the majority of the annealing temperature of martensitic alloys are below! the critical temperature for this alloy. In this case, the subsequent cooling in air is not accompanied by, the formation of martensite or at least large amounts of it, which provides a welded-| th compound rather good ductility compared to the ductility of the base metal. At the same time, the welded joints of titanium alloys of the martensitic type, operating continuously at temperatures increase the service should be annealed by mode, which provides a sufficiently high stability of the structure, or in the process of welded joints lose their plasticity. Stabilizing annealing regimes weld alloys such as martensitic-tion are given in Table. 7. It should also be noted that compounds of welded titanium alloys VT6 VT6S and adjacent to the p-stabilyziruyuschih content elements to the pseudo-a-alloys do not require stabilizing annealing, since the decay of metastable phases during prolonged heating is not accompanied by significant dispersion hardening of the weld . As for the VT16 alloy, the stabilizing annealing of welded joints of this alloy is needed to maintain the thermal stability of the welded joint during the operation at elevated temperatures and to obtain the optimal relation of strength and ductility of the welded joint in a state after welding and annealing. Titanium alloys with ct + p-structure transition, which is representative of the VT22 alloy are welded joints that require stabilizing schego annealing for optimum mechanical properties, and to improve the thermal stability during long-term operation at elevated temperatures. Stepwise annealing of VT22 alloy can greatly stabilize the structure and properties of its welded joint. Welds pseudorational alloys VT15 and TC6 directly after the weld has a good combination of strength and ductility. Subsequent annealing in air cooling makes it possible to somewhat stabilize the structure of the welds in these alloys, but does not allow for their thermal stability at elevated temperatures during continuous operation. In principle, titanium alloys, pseudo-Riemannian space by a special annealing could stabilize the structure of the weld, but the alloys VT15 and TC6 contain large amounts of evtektoidoobrazuyu schego-element (chromium), and therefore the stabilizing annealing occurs eutectoid metal embrittlement. For example, an experienced titanium alloy having a brand BT32 (Ti-8, 5% Mo-8,5% V-1% Cr - 2.5% A1-1% Fe) and is also a pseudo-Riemannian space-tion alloys, weld can be stabilized by annealing in the regime: heating to 780o C, exposure 1 h, cooling in the furnace at a rate of 2-4 ° C / min to 300 ° C, then in the air. This alloy welded joint after welding has good ductility, which persists even after annealing at the specified mode. However, if this alloy weld immediately after welding tends to prolonged heating to embrittlement, after welding and annealing, it is thermally stable and does not change its properties after prolonged heating. To illustrate the behavior of welded joints of titanium alloys of various types of thermal treatment present some evidence. Mechanical properties of welded joints of alloy OT4 little change as a function of heat treatment. This is explained by the fact "that the a'-phase alloys of this type in their mechanical properties is not very different from the a-phase dispersion hardening of the decay of a 'phase in these alloys is insignificant, and the amount of p-phase is so small that no significant impact the mechanical properties of welded joints. eutectoid transforma-tion of alloys of this type can not be detected under certain lenii-mechanical properties, or when Mr. rentgenostruktur or metallographic analysis. Similarly, for once behave welded joints and other pseudo-a-titanium ... ssh1avol.lri such heat treatment processing. We now consider changes in the structure and properties of welded joints representative a + p-titanium alloys of the martensitic type - VT14 alloy. In titanium alloy VT14 martensitic grades with Kp = 0.35 is already a trend towards a significant influence on the heat treatment, mechanical properties of the weld. In more heavily doped p-stabilizing elements martensitic titanium alloys with K $ = 0.6-0.8 there is a bo-Lee has a significant change in mechanical properties depending on the heat treatment.
See also:
Heat Treatment of Welded Joints of Titanium Alloys
Annealing of Titanium Welded Joints
Hardening Heat Treatment of Titanium Welded Joints
Special Modes of Hardening Heat Treatment of Welded Structures
Effect of Welding on the Structure and Properties of Different Zones of the Welded Joint
Structure and Properties of Heat Affected Zone
Structure and Properties of Welded Joints
Properties and Structure of Welded Joints of Industrial Titanium Alloys
Welding of Titanium
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