presented data on the effect of heat treatment and prolonged heating of the operational structure and properties of welded joints.
Alpha-alpha-and pseudo alloys
alloys belonging to the first group: alpha-alloys (BT1-00 VT1-0, VT5; BT5-1, 4200) and the pseudo-alpha-alloys (OT4-0, OT4-1, OT4, VT4, OT4-2, AT2, ATZ, AT4, VT20, TC5) are low-alloy (J-stabilizing-forming alloys with elements of $ K <= 0.25. These alloys are well welded by all types of welding and weld strength and Plasticity is approaching the base metal. alloys do not require stabilizing annealing after welding. Since the weld may be present then, the strength of the welded joint is taken into account by a factor of welding weakening equal to 0.9-0.95 of the strength of the base material. With the increase strength of welded joints of these alloys are more susceptible to weld defects (pores, stress concentrators, etc.) and a slight increase in the difference between strength and ductility of the weld and base metal. Technical titanium VT1-00 is made of the purest grades of titanium sponge. It contains fewer impurities such as carbon, iron, silicon, oxygen, than allowed for other titanium alloys. Titanium VT1-00 has low strength characteristics and high plasticity. Well deformed in the hot and cold conditions. Of titanium VT1-00 made virtually all types of semi-finished: aluminum foil, tape, sheet, plate, forgings, stampings, profiles, tubes, wire, etc. Typical mechanical properties of titanium VT1-G0 at room and elevated temperatures are given in Technical Titanium grades 1-00 Tues due to its low strength as a structural material used is limited. When welding with an addition of a filler material used welding wire in titanium VT1-00 and VT1-0. The welded joints of titanium VT1-00, received Td H doped with VT1-00, after partial annealing have the following mechanical properties at room temperature: a * = 0.9, aB base metal; en> = 9.0 kgf * m/sm2 and = 180 ° to the sheet thickness of 1.5 mm and a = 140 ° for a sheet thickness of 3.0 mm.
Technical titanium VT1-0 prepared from unalloyed sponge, somewhat inferior in purity titanium sponge, used for the manufacture of titanium VT1-00. Nevertheless, the content of impurities in titanium VT1-0 is less than in the doped titanium alloys.
The alloy VT1-0 with a smaller ductility compared to the technical titanium VT1-00 has a higher strength and under-wide changes as a structural material. Typical mechanical properties at room and elevated temperatures of titanium VT1-0 are shown in Table. 28. Titan brand BT1-0 is well welded by all types of welding. From Tues 1-0 produce sheets, strips, foils, rods, profiles, tubes, wire, etc. The alloy VT1-0 used in the construction of continuously operating at temperatures ranging from -253 to +150 ° C. The welds are plastic and allow considerable cold deformation [52]. The ductility of the welded joint (bending angle a) is practically not affected by cold work up to 20% (Fig. 64). Heat treatment after welding is not required. Mechanical properties of welded joints of titanium VT1-0, obtained with an addition of H DT, after partial annealing have the following mechanical properties at room temperature: GMT = 0.9, aB base metal; en> = 7 kgf m/sm2, and = 135 ° C for sheet thickness of 1.5 mm and a = 110 ° to the sheet thickness of 3.0 mm. When welding with an addition of a filler material is used for welding wire of VT1-00 and VT1-0. Alloy VT5 is a typical single-phase a-titanium alloy system T1-Al. VT5 alloy forgings are manufactured, stamping, forged and rolled bars and rods, welded rings. The alloy VT5 has moderate strength low ductility. These explained that this alloy does not produce leafy semis. alloy VT5 are well welded by all types of welding applied to titanium. Tensile strength at short-term and long-term tensile strength of the welded joint are equal to 0.9 and 0.9 and aB ^ base material, respectively, at all operating temperatures. As the filler wire is used in titanium VT1-00 alloy, or BT2.
Alloys with alpha + β-structure of the martensitic type This group includes srednelegirovannye p-stabilizing elements yuschimi alloys with Ka = 0.3-0.9, thermally hardened by quenching and aging. The alloys of this group immediately after the welding has reduced weld ductility due to the formation of the joint structure is quite strong martensitic a'-phase. To restore the ductility of welded joints in alloys of this type use a stabilizing heat treatment, which resulted in a 'phase becomes stable in a + p-components. Most welded structures of a + b-martensitic alloys are made with the strength of welded joints of 85-100 kg / mm2. Less commonly, welded construction is subjected to hardening heat treatment on the strength of 105-130 kgf/mm2, and then the joints thicken, and annealed, and the strength balance achieved by the design and provide sufficient the reliability of the welded joint. alloy VT6 - analogue of the widely used overseas alloy Ti-6Al- 4V [2, 121], as well as domestic VT6S alloy. Made in the form of a sheet of alloy plates, bars, forgings, stampings, welded rings. The alloy can be used both in the annealed and thermally hardened in the I (quenching + aging) conditions. Hardening heat treatment the strength of the alloy can be increased by 15-20%. Alloy satisfactorily welded by all kinds of welding used for titanium. Welded joints of VT6 alloy immediately after welding has a number of reduced ductility. To restore the ductility of welded joints requires a stabilizing heat treatment. The strength of welded joints of alloy VT6 made AArDES non-consumable electrode without the additive is, after annealing at 760 - 800 ° C and after quenching from 900 ° C and aging at 500 ° C for 2 h and 105 kgf/mm2 95-100, respectively. Alloy I welded sheet with all titanium alloys. As the filler wire is used in alloys VT1-00, BT1-0, BT2, SPT2, VT6S. VT6 alloy is used for welded parts, for a long time working in the Institute was annealed at temperatures up to 450 ° C, and in the thermally hardened state - with temperatures up to 400 ° C. Alloy VT6S recommended for the manufacture of stamped and welded structures; working for a long time at temperatures up to 400-450 ° C and briefly at temperatures up to 700-750 ° C. The tensile strength of welded joint, fusion welding is not less than 90% of the tensile strength of the base metal. When welding heavy sections of metal use progressive methods of welding, submerged arc welding for example, joints VT6S alloy obtained in this way, of equal strength annealed base metal, and their toughness higher by 1,2-4,0 kgf m/sm2.
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
2:03 AM
Structure and Properties of Welded Joints
weld structure when welding titanium
Consider the effect of different types of welding on the chemical composition, properties and structure of welded joints of different types of titanium alloys. Each specific type of welding alters the structure and the degree of alloying of the weld metal due to different base metal dilution of weld and the additional introduction of the metal electrode, whose composition may differ from that of base metal, as well as due to changes in gas content of the weld metal. Thus, the impact of type of welding on the properties of the weld metal of titanium alloys is determined by several factors: the chemical composition of the metal electrode, which provides the optimum combination of strength and ductility, the ratio percentage of the ground and the electrode metal in various forms of cutting edges, typical for this type of welding structure and phase composition, depending on the thermal cycle of welding and subsequent heat treatment, the possibility of formation of various defects inherent in this type of welding, and influence them (especially the poor penetration and porosity) on the physico-mechanical and operational characteristics, the additional gas saturation of the molten metal gas (nitrogen, oxygen and hydrogen) and the influence of these gases on the various properties and especially the tendency to brittle fracture and the detainee. The influence of these factors increases with increasing strength of the alloys. The choice of a particular type of welding is mainly dependent on the chemical composition of the alloy and the weld thickness.
Welds of a-and pseudo-alloys. In the single-phase and pseudo-alloys, and alloys, for almost the entire range of thicknesses can be welded using different methods of welding in which the formation of the molten weld metal occurs as a direct penetration of the base metal, as well as an additional input electrode filler metal. At the same basic meaning as in welding and pseudo-alloys are the interaction of the molten weld metal with protective environments and the ability to provide the minimum gas saturation of the weld metal. Mechanical properties of cast metal, regardless of thickness similar to those of base metal, and reduction of ductility due to the peculiarities of formation of the cast structure. For these alloys is characterized by a significant amount of die-cast grain, which depends on the value of this type of heat input welding. For all the a-and pseudo-alloys can be used electrode metal of technical titanium VT1-00, BT2 alloy (Ti-ZA1) or an alloy of similar composition to the base metal. In all cases, regardless of changes in the weld cooling rate and fixed-or a'-phase. The nature of the formation of a-or a'-phase in the joints mainly depends on the cooling rate in the range of p wo-MH or a pre-rotation.
At low cooling rates produced a wide and long plate, high cooling rates, and formed melkoigolchataya or a 'phase. By varying the cooling rate can be controlled within certain limits, structural transformations in the weld metal. Thus, the characteristic of the electroslag welding heat input increases, slowing the rate of cooling in the martensite range, leads to the transformation of thin needles of a-phase alloy VT1-0 in the large grains with serrated boundaries. Dispersity of the structural components significantly affect the plastic properties of the weld metal. For these alloys, the change of plasticity, depending on the cooling rate is on a curve with a peak and is associated with a grain size of cast structure and dispersion of a-or a'-phase. Slow cooling of a decrease in ductility of cast metal as a result of increasing the size of the grains. The high cooling rate leads to a decrease in ductility due to the formation or a 'phase.
For the alloys of this group is characterized by the fact that the mechanical properties and structure of the weld metal during welding is only marginally affected the entire range of thicknesses and different methods of welding. Annealing after welding stabilizes the structure but does not affect the mechanical properties of the weld, and therefore the heat treatment of welded joints of these types of alloys, including titanium and maintenance is carried out only to reduce the magnitude of internal stresses from the welding process, as well as to reduce the peak concentration of hydrogen in different zones of the welded joint. This is confirmed by the structures of welds that are shown in Fig. 46. Influence of different technological factors on the mechanical properties of weld metal, excluding the effect of alloying elements is convenient to consider the example of alloy BT1-0.
For all types of welding alloy BT1-0 strength of the weld metal is determined by the initial strength of the base-metal and filler wire. If welding is a significant increase in the grain, as well as additional gas saturation of the weld metal, its strength may exceed the original while reducing ductility. The research results presented in this study showed that the welding of alloy VT1-0 non-consumable electrode without the additive increase in the hydrogen content in the main influence on the toughness and the bending angle of the weld metal without altering its hardness. The increase in oxygen and nitrogen strongly influences the strength and ductility when tested in the bending angle. Especially dangerous gas saturation of the surface layers of the seam. Increasing the oxygen content from 0.15 to 0.38% (while 0,02% N) reduces the bending angle of the weld metal in the alloy VT1-0 1.5 mm from 180 to 100 ° C. With increasing thickness of the weld metal and the increase heat input welding depth of the layer with high hardness (contaminated with oxygen and nitrogen) increases, while the hydrogen content in weld metal during welding without the introduction of the filler wire is lower than the base metal due to its desorption and diffusion from the melt in the weld zone . Reduced ductility of the weld metal, associated with oxygen and nitrogen, increases its sensitivity to the influence of the level of hydrogen and a tendency to brittle fracture and the detainee. The data confirm the influence of oxygen and nitrogen on the tendency of the weld metal of alloy VT1-1 to the formation of cracks with increasing hydrogen content.
Thus, the type and technology of welding depends directly on the gas content in the weld metal and, consequently, its mechanical and performance properties. Research has shown that the condition of the protective gas atmosphere in a strong influence on the intensity of the absorption and gas content in the weld metal, depending on the type and mode of welding is the change in the effective thermal capacity of the arc, which leads to a change in the amount of hydrogen supplied to the gas phase, the protective atmosphere.
the source of the saturation of the weld metal hydrogen may be adsorbed, and the moisture, which is at the electrode edges and welded wire. The solubility of hydrogen in the weld pool depends largely on the content of alloying elements in the weld metal. Experimental data on the magnitude of the hydrogen content in weld metal obtained in the studies show that when all the major types of fusion welding in shielding gases argon, the use of the first composition and the electrode wire, held vacuum annealing isoderzhaschey up to 0.0006% N, allows to obtain the weld metal with a lower hydrogen content than the base metal due to its obezvodorazhivaniya and transition of hydrogen in the gas phase. When the automatic submerged arc welding (without additional protection with argon), as well as for ESW, there is additional gas saturation of the weld metal oxygen and hydrogen.
At the same time the implementation of automatic welding in vacuum drastically reduces the gas saturation of the weld metal due to its additional degassing, thus there is decrease in strength and increase ductility weld. Similar processes occur during the degassing electron-beam welding, and the value of reducing the concentration of gases in the weld metal depends primarily on the depth of depression, as well as the heat input welding process and the cooling rate of weld metal. Increasing the concentration of oxygen or nitrogen in the weld metal depends on the amount and the age of the weld pool, which depends on the type and welding conditions and the partial pressures of these gases in a protective atmosphere.
Regardless of the type of alloys for welding of structures is recommended to conduct the process in the cells with a protective atmosphere or to provide a thorough , steady defense throughout the weld zone. For example, in electroslag welding of thick metal of titanium alloys is impossible to completely prevent the molten metal from the effects of atmospheric gases using slag alone, so the additional gas is created by filing a protective atmosphere of argon above the slag bath [ON]. Violation of these conditions leads to significant gas saturation of the weld metal, particularly its surface layers. When welding in a controlled atmosphere, increasing the total gas content in the weld metal slightly, and the hydrogen content in weld metal due to its desorption and diffusion of heat-affected zone, even in decline. Results of the study of the microhardness and gas saturation of welds show that only electron-beam welding in vacuum does not increase the hardness of the seam. All other welding methods lead to an increase in hardness by increasing the amount of gas in the surface layers of the seam.
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
Consider the effect of different types of welding on the chemical composition, properties and structure of welded joints of different types of titanium alloys. Each specific type of welding alters the structure and the degree of alloying of the weld metal due to different base metal dilution of weld and the additional introduction of the metal electrode, whose composition may differ from that of base metal, as well as due to changes in gas content of the weld metal. Thus, the impact of type of welding on the properties of the weld metal of titanium alloys is determined by several factors: the chemical composition of the metal electrode, which provides the optimum combination of strength and ductility, the ratio percentage of the ground and the electrode metal in various forms of cutting edges, typical for this type of welding structure and phase composition, depending on the thermal cycle of welding and subsequent heat treatment, the possibility of formation of various defects inherent in this type of welding, and influence them (especially the poor penetration and porosity) on the physico-mechanical and operational characteristics, the additional gas saturation of the molten metal gas (nitrogen, oxygen and hydrogen) and the influence of these gases on the various properties and especially the tendency to brittle fracture and the detainee. The influence of these factors increases with increasing strength of the alloys. The choice of a particular type of welding is mainly dependent on the chemical composition of the alloy and the weld thickness.
Welds of a-and pseudo-alloys. In the single-phase and pseudo-alloys, and alloys, for almost the entire range of thicknesses can be welded using different methods of welding in which the formation of the molten weld metal occurs as a direct penetration of the base metal, as well as an additional input electrode filler metal. At the same basic meaning as in welding and pseudo-alloys are the interaction of the molten weld metal with protective environments and the ability to provide the minimum gas saturation of the weld metal. Mechanical properties of cast metal, regardless of thickness similar to those of base metal, and reduction of ductility due to the peculiarities of formation of the cast structure. For these alloys is characterized by a significant amount of die-cast grain, which depends on the value of this type of heat input welding. For all the a-and pseudo-alloys can be used electrode metal of technical titanium VT1-00, BT2 alloy (Ti-ZA1) or an alloy of similar composition to the base metal. In all cases, regardless of changes in the weld cooling rate and fixed-or a'-phase. The nature of the formation of a-or a'-phase in the joints mainly depends on the cooling rate in the range of p wo-MH or a pre-rotation.
At low cooling rates produced a wide and long plate, high cooling rates, and formed melkoigolchataya or a 'phase. By varying the cooling rate can be controlled within certain limits, structural transformations in the weld metal. Thus, the characteristic of the electroslag welding heat input increases, slowing the rate of cooling in the martensite range, leads to the transformation of thin needles of a-phase alloy VT1-0 in the large grains with serrated boundaries. Dispersity of the structural components significantly affect the plastic properties of the weld metal. For these alloys, the change of plasticity, depending on the cooling rate is on a curve with a peak and is associated with a grain size of cast structure and dispersion of a-or a'-phase. Slow cooling of a decrease in ductility of cast metal as a result of increasing the size of the grains. The high cooling rate leads to a decrease in ductility due to the formation or a 'phase.
For the alloys of this group is characterized by the fact that the mechanical properties and structure of the weld metal during welding is only marginally affected the entire range of thicknesses and different methods of welding. Annealing after welding stabilizes the structure but does not affect the mechanical properties of the weld, and therefore the heat treatment of welded joints of these types of alloys, including titanium and maintenance is carried out only to reduce the magnitude of internal stresses from the welding process, as well as to reduce the peak concentration of hydrogen in different zones of the welded joint. This is confirmed by the structures of welds that are shown in Fig. 46. Influence of different technological factors on the mechanical properties of weld metal, excluding the effect of alloying elements is convenient to consider the example of alloy BT1-0.
For all types of welding alloy BT1-0 strength of the weld metal is determined by the initial strength of the base-metal and filler wire. If welding is a significant increase in the grain, as well as additional gas saturation of the weld metal, its strength may exceed the original while reducing ductility. The research results presented in this study showed that the welding of alloy VT1-0 non-consumable electrode without the additive increase in the hydrogen content in the main influence on the toughness and the bending angle of the weld metal without altering its hardness. The increase in oxygen and nitrogen strongly influences the strength and ductility when tested in the bending angle. Especially dangerous gas saturation of the surface layers of the seam. Increasing the oxygen content from 0.15 to 0.38% (while 0,02% N) reduces the bending angle of the weld metal in the alloy VT1-0 1.5 mm from 180 to 100 ° C. With increasing thickness of the weld metal and the increase heat input welding depth of the layer with high hardness (contaminated with oxygen and nitrogen) increases, while the hydrogen content in weld metal during welding without the introduction of the filler wire is lower than the base metal due to its desorption and diffusion from the melt in the weld zone . Reduced ductility of the weld metal, associated with oxygen and nitrogen, increases its sensitivity to the influence of the level of hydrogen and a tendency to brittle fracture and the detainee. The data confirm the influence of oxygen and nitrogen on the tendency of the weld metal of alloy VT1-1 to the formation of cracks with increasing hydrogen content.
Thus, the type and technology of welding depends directly on the gas content in the weld metal and, consequently, its mechanical and performance properties. Research has shown that the condition of the protective gas atmosphere in a strong influence on the intensity of the absorption and gas content in the weld metal, depending on the type and mode of welding is the change in the effective thermal capacity of the arc, which leads to a change in the amount of hydrogen supplied to the gas phase, the protective atmosphere.
the source of the saturation of the weld metal hydrogen may be adsorbed, and the moisture, which is at the electrode edges and welded wire. The solubility of hydrogen in the weld pool depends largely on the content of alloying elements in the weld metal. Experimental data on the magnitude of the hydrogen content in weld metal obtained in the studies show that when all the major types of fusion welding in shielding gases argon, the use of the first composition and the electrode wire, held vacuum annealing isoderzhaschey up to 0.0006% N, allows to obtain the weld metal with a lower hydrogen content than the base metal due to its obezvodorazhivaniya and transition of hydrogen in the gas phase. When the automatic submerged arc welding (without additional protection with argon), as well as for ESW, there is additional gas saturation of the weld metal oxygen and hydrogen.
At the same time the implementation of automatic welding in vacuum drastically reduces the gas saturation of the weld metal due to its additional degassing, thus there is decrease in strength and increase ductility weld. Similar processes occur during the degassing electron-beam welding, and the value of reducing the concentration of gases in the weld metal depends primarily on the depth of depression, as well as the heat input welding process and the cooling rate of weld metal. Increasing the concentration of oxygen or nitrogen in the weld metal depends on the amount and the age of the weld pool, which depends on the type and welding conditions and the partial pressures of these gases in a protective atmosphere.
Regardless of the type of alloys for welding of structures is recommended to conduct the process in the cells with a protective atmosphere or to provide a thorough , steady defense throughout the weld zone. For example, in electroslag welding of thick metal of titanium alloys is impossible to completely prevent the molten metal from the effects of atmospheric gases using slag alone, so the additional gas is created by filing a protective atmosphere of argon above the slag bath [ON]. Violation of these conditions leads to significant gas saturation of the weld metal, particularly its surface layers. When welding in a controlled atmosphere, increasing the total gas content in the weld metal slightly, and the hydrogen content in weld metal due to its desorption and diffusion of heat-affected zone, even in decline. Results of the study of the microhardness and gas saturation of welds show that only electron-beam welding in vacuum does not increase the hardness of the seam. All other welding methods lead to an increase in hardness by increasing the amount of gas in the surface layers of the seam.
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
1:58 AM
Structure and Properties of Heat Affected Zone
how to change the structure heat affected zone (HAZ)
The length and structure of the heat affected zone (HAZ) is determined by thermal cycle of welding. The main parameters of thermal cycles in the HAZ are wH heating rate in the range of phase transformations, the maximal temperature T max, time spent above the temperature of polymorphic transformation and the rate of cooling Tohl in the range of transformations. The heating rate in the weld zone (OSHZ) is very high, and although it varies depending on several factors, but within narrow limits. The main factor affecting the structure and properties of OSHZ is the cooling rate wohl. When welding titanium swim with a high content of p-stabilizer for large values of wohl OSHZ recorded in the metastable structure. At the same time a significant influence on the final structure also has a residence time of metal OSHZ at a temperature below the temperature of polymorphic transformation. Terms of phase transformations in different parts of the HAZ during welding of titanium alloys in many ways similar to those during quenching from different temperatures. In Fig. 4 is a diagram of a change in the phase composition of titanium alloys depending on the content of p-stabnliziruyuschih elements and the temperature quench. Considered the metastable diagram gives an overview of the kinetics of phase transformations in titanium alloys during continuous cooling at rates of quenching. However, in the weld metal cooling rate in different zones of the welded joint is not the same. It depends on the thickness of the metal, welding conditions, welding and construction work piece, etc. Rapid heating and short residence time of metal with a maximum temperature of heating impede the process of stabilization of high-temperature phase. For the analysis of structure transformations during welding using the diagram depending ki kinetics of transformations on the cooling rate. They help to identify areas of formation of brittle phases and to establish regimes of welding to ensure the receipt of the necessary structures and the need for subsequent heat treatment. Simultaneously with the study of the kinetics of phase transformations in the weld zone of influence depending on building cooling rate in the range of phase transformations on the final mechanical properties and structure. There are several methods for determining these dependencies. In domestic practice, the primary use of the method found IMET-1. The test results of samples are summarized in a chart based on the mechanical properties of various welding parameters, most of the cooling rate. These diagrams define an optimal range of cooling rates (Wopt), in which reduction of the properties in the weld zone compared with the base metal is minimal.
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
The length and structure of the heat affected zone (HAZ) is determined by thermal cycle of welding. The main parameters of thermal cycles in the HAZ are wH heating rate in the range of phase transformations, the maximal temperature T max, time spent above the temperature of polymorphic transformation and the rate of cooling Tohl in the range of transformations. The heating rate in the weld zone (OSHZ) is very high, and although it varies depending on several factors, but within narrow limits. The main factor affecting the structure and properties of OSHZ is the cooling rate wohl. When welding titanium swim with a high content of p-stabilizer for large values of wohl OSHZ recorded in the metastable structure. At the same time a significant influence on the final structure also has a residence time of metal OSHZ at a temperature below the temperature of polymorphic transformation. Terms of phase transformations in different parts of the HAZ during welding of titanium alloys in many ways similar to those during quenching from different temperatures. In Fig. 4 is a diagram of a change in the phase composition of titanium alloys depending on the content of p-stabnliziruyuschih elements and the temperature quench. Considered the metastable diagram gives an overview of the kinetics of phase transformations in titanium alloys during continuous cooling at rates of quenching. However, in the weld metal cooling rate in different zones of the welded joint is not the same. It depends on the thickness of the metal, welding conditions, welding and construction work piece, etc. Rapid heating and short residence time of metal with a maximum temperature of heating impede the process of stabilization of high-temperature phase. For the analysis of structure transformations during welding using the diagram depending ki kinetics of transformations on the cooling rate. They help to identify areas of formation of brittle phases and to establish regimes of welding to ensure the receipt of the necessary structures and the need for subsequent heat treatment. Simultaneously with the study of the kinetics of phase transformations in the weld zone of influence depending on building cooling rate in the range of phase transformations on the final mechanical properties and structure. There are several methods for determining these dependencies. In domestic practice, the primary use of the method found IMET-1. The test results of samples are summarized in a chart based on the mechanical properties of various welding parameters, most of the cooling rate. These diagrams define an optimal range of cooling rates (Wopt), in which reduction of the properties in the weld zone compared with the base metal is minimal.
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
1:55 AM
Effect of Welding on the Structure and Properties of Different Zones of the Welded Joint
introductory article on the subject of welding
A characteristic feature is the presence of titanium polymorphic transformation. This leads to significant changes in the structure and mechanical properties of titanium alloys for welding and structural features of the zone of thermal influence of welding process.
welded joint is determined by the presence of two fundamentally different to each other zones - the weld and heat affected. In the area of weld metal is heated to the melting point and some time in the liquid state. At the same time actively develop the processes of saturation of the metal fumes, grain growth, different types of physical, chemical and structural heterogeneity of Education metastable phases, which significantly alters the properties in comparison with the metal to the welding. After crystallization of the metal in the weld zone acquires a characteristic cast structure.
Most of the famous wrought titanium alloys in the cast state has a lower ductility indices. In such cases, to improve the properties of the metal in the weld zone filler materials are used to manage the chemical composition of the weld.
Zone, which determines the weldability of titanium alloys, is a zone of thermal influence. The most dramatic changes in the structure and properties occur in the area directly adjacent to the weld, where there is a fusion of several grains. The metal in this area is heated to a temperature of TPl (the temperature of melting) to ~ 0.9 TPl. This zone is called the weld. Next is the area where the metal undergoes phase recrystallization. When cooling is metastable phases are fixed. The final structure depends on the temperature and cooling conditions. At the boundary of heat affected zone and base metal is part of recrystallization - the site of the gradual transition to the base metal.
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
A characteristic feature is the presence of titanium polymorphic transformation. This leads to significant changes in the structure and mechanical properties of titanium alloys for welding and structural features of the zone of thermal influence of welding process.
welded joint is determined by the presence of two fundamentally different to each other zones - the weld and heat affected. In the area of weld metal is heated to the melting point and some time in the liquid state. At the same time actively develop the processes of saturation of the metal fumes, grain growth, different types of physical, chemical and structural heterogeneity of Education metastable phases, which significantly alters the properties in comparison with the metal to the welding. After crystallization of the metal in the weld zone acquires a characteristic cast structure.
Most of the famous wrought titanium alloys in the cast state has a lower ductility indices. In such cases, to improve the properties of the metal in the weld zone filler materials are used to manage the chemical composition of the weld.
Zone, which determines the weldability of titanium alloys, is a zone of thermal influence. The most dramatic changes in the structure and properties occur in the area directly adjacent to the weld, where there is a fusion of several grains. The metal in this area is heated to a temperature of TPl (the temperature of melting) to ~ 0.9 TPl. This zone is called the weld. Next is the area where the metal undergoes phase recrystallization. When cooling is metastable phases are fixed. The final structure depends on the temperature and cooling conditions. At the boundary of heat affected zone and base metal is part of recrystallization - the site of the gradual transition to the base metal.
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
1:51 AM
Special Modes of Hardening Heat Treatment of Welded Structures
welded structures made of thermally hardened titanium alloys presents numerous technical difficulties.
Production of welded structures of heat-hardenable titanium alloys presents numerous technical difficulties. When hardening of large parts or non-rigid structures are considerable leashes, which are very difficult and in some cases can not be eliminated; lengthy welded structures is generally difficult to transfer to the quenching medium, in the process of heating for quenching and transfer to a quenching medium thin sheet structure is oxidized, Even if it be carried out in the heating furnace with protective atmosphere, formed by heating the dross must be removed, which presents some difficulties, and sometimes impossible (eg, etching of structures with lap joints in spot or seam welding), descaling chemical method accompanied by the hydrogenation of thermally hardened alloys, which contain a glycol * ^-tional to the stabilizing elements, the assembly structure by welding of hardened elements, followed by the aging of the whole structure, as a rule, does not provide optimal mechanical and service properties of welded joints because the thermal cycle of welding creates a rather vague state of the seam and the transition zone, which depends on a number of difficult factors considered.
Circumstances above are the main factors hindering the development of thermally hardened alloy sheet in welded structures.
In connection with the above, we were sought special treatment hardening heat treatment of titanium alloys,
allowing to process large welded design in a protective atmosphere. For this purpose are the most promising high-alloy R-stabilizing elements of titanium alloys with a p-phase with increased stability.
Thus, the alloy VT16 with a Ka = 0.8 was found as a hardening effect of the base metal and weld at a certain rate of cooling from the annealing temperature.
With increasing cooling rate up to 4 - 8o C / min and above is observed a continuous increase in tensile strength and lower ductility characteristics of the alloy VT16. When the cooling rates within the 12-17O C / min can increase the strength of alloy VT16 with 85 kgf/mm2 annealed to 105 and above kgf/mm2 after hardening heat treatment of this type. The proposed method of hardening heat treatment was effective in the manufacture of honeycomb structures by welding, brazing and diffusion joining. It was enough to perform the operation of soldering or diffusion annealing, carried out usually at temperatures around 900 ° C and cooled honeycomb in an oven or container at a rate of ~ 15 ° C / min, as its strength (as the base metal and weld) increased to 105 kgf/mm2 and above. With this technological process is easy to protect from oxidation ponds with inert gases or vacuum.
Ratio of strength and ductility in this type of hardening heat treatment is about the same as during quenching and aging.
Hardening mechanism for this kind of heat treatment consists in the fact that in titanium alloys with a + p-structure is determined lennogo composition (with a certain amount of p-phase) at some cooling rates of decay occurs metastabnlnyh phases with the formation of dispersed particles of a-and p-sostavlyayushey, which leads to hardening of the alloy. In this case, the cooling rate of the alloy is such that there is no fixed metastabnlnyh phases, and at the same time is so small that it does not allow to pass to the equilibrium conversion of a + p-states.
Even more interesting way of hardening heat treatment can be applied for processing of alloys supercritical composition. It was found that titanium alloys of supercritical with further increase in the content of p-stabilized-reducing elements of the metastable P-phase can be fixed at very low cooling rates commensurate with the rate of cooling of large industrial furnaces, together with the SADC (4 - 10 ° C / min .) Further isothermal heating of a "hardened" alloy at temperatures of aging leads to the decay of the metastable P-phase and the formation of a dispersed-and P-components, ie, leads to a significant hardening. Obviously, the maximum capacity for hardening heat treatment of this type have titanium alloys with K = 1.6-2.2. At the least, and other titanium alloys can be heat-hardened to perceive this type. Na.etoy basis have developed a way of hardening heat treatment of large welded structures from titanium alloys of supercritical free transfer in the quenching medium. The proposed method is deprived of all the shortcomings of the hardening heat treatment associated with the transfer of cages in a quenching medium. It allows the hardening heat treatment in vacuum furnaces and industrial furnaces with protective atmosphere. So, for example, welded parts or structures of titanium alloy VT32 (Ti-2, 5% Al-8, 5% Mo-8, 5% V-1, 2% Fe-1,2% Cr), treated in a vacuum furnace under the regime: heating at 750 ° C for 1 h, cooling in the furnace at a rate of> = 4 ° C / min to 500 ° C, holding at 500 ° C for 4 h, provided for in the *> = 120 kgf / mm2, bb> = 7%, while in the annealed condition the alloy has s = 82 kgf/mm2 and 65 = 16%. Widespread use of the above-described method of heat treatment found in the manufacture of welded components and structures made of alloy VT22. welded construction of this alloy require stabilizing annealing at 850 ° C, ie, at temperatures limits a + p = p-transformation. After annealing, the alloy has a tensile strength of about 100 kgf/mm2. Hardening heat treatment of the regime: heating at 850 ° C for 1 h, cooling in the oven to 750 ° C, holding 2 h, cooling with furnace to 500 ° C, exposure at 600 ° C for 4 h yields on welded constructions from alloy VT22 = 110 kgf/mm2. For such a heat treatment used vacuum furnaces and furnaces with protective atmosphere to allow thermal processing of finished parts or structures.
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
Production of welded structures of heat-hardenable titanium alloys presents numerous technical difficulties. When hardening of large parts or non-rigid structures are considerable leashes, which are very difficult and in some cases can not be eliminated; lengthy welded structures is generally difficult to transfer to the quenching medium, in the process of heating for quenching and transfer to a quenching medium thin sheet structure is oxidized, Even if it be carried out in the heating furnace with protective atmosphere, formed by heating the dross must be removed, which presents some difficulties, and sometimes impossible (eg, etching of structures with lap joints in spot or seam welding), descaling chemical method accompanied by the hydrogenation of thermally hardened alloys, which contain a glycol * ^-tional to the stabilizing elements, the assembly structure by welding of hardened elements, followed by the aging of the whole structure, as a rule, does not provide optimal mechanical and service properties of welded joints because the thermal cycle of welding creates a rather vague state of the seam and the transition zone, which depends on a number of difficult factors considered.
Circumstances above are the main factors hindering the development of thermally hardened alloy sheet in welded structures.
In connection with the above, we were sought special treatment hardening heat treatment of titanium alloys,
allowing to process large welded design in a protective atmosphere. For this purpose are the most promising high-alloy R-stabilizing elements of titanium alloys with a p-phase with increased stability.
Thus, the alloy VT16 with a Ka = 0.8 was found as a hardening effect of the base metal and weld at a certain rate of cooling from the annealing temperature.
With increasing cooling rate up to 4 - 8o C / min and above is observed a continuous increase in tensile strength and lower ductility characteristics of the alloy VT16. When the cooling rates within the 12-17O C / min can increase the strength of alloy VT16 with 85 kgf/mm2 annealed to 105 and above kgf/mm2 after hardening heat treatment of this type. The proposed method of hardening heat treatment was effective in the manufacture of honeycomb structures by welding, brazing and diffusion joining. It was enough to perform the operation of soldering or diffusion annealing, carried out usually at temperatures around 900 ° C and cooled honeycomb in an oven or container at a rate of ~ 15 ° C / min, as its strength (as the base metal and weld) increased to 105 kgf/mm2 and above. With this technological process is easy to protect from oxidation ponds with inert gases or vacuum.
Ratio of strength and ductility in this type of hardening heat treatment is about the same as during quenching and aging.
Hardening mechanism for this kind of heat treatment consists in the fact that in titanium alloys with a + p-structure is determined lennogo composition (with a certain amount of p-phase) at some cooling rates of decay occurs metastabnlnyh phases with the formation of dispersed particles of a-and p-sostavlyayushey, which leads to hardening of the alloy. In this case, the cooling rate of the alloy is such that there is no fixed metastabnlnyh phases, and at the same time is so small that it does not allow to pass to the equilibrium conversion of a + p-states.
Even more interesting way of hardening heat treatment can be applied for processing of alloys supercritical composition. It was found that titanium alloys of supercritical with further increase in the content of p-stabilized-reducing elements of the metastable P-phase can be fixed at very low cooling rates commensurate with the rate of cooling of large industrial furnaces, together with the SADC (4 - 10 ° C / min .) Further isothermal heating of a "hardened" alloy at temperatures of aging leads to the decay of the metastable P-phase and the formation of a dispersed-and P-components, ie, leads to a significant hardening. Obviously, the maximum capacity for hardening heat treatment of this type have titanium alloys with K = 1.6-2.2. At the least, and other titanium alloys can be heat-hardened to perceive this type. Na.etoy basis have developed a way of hardening heat treatment of large welded structures from titanium alloys of supercritical free transfer in the quenching medium. The proposed method is deprived of all the shortcomings of the hardening heat treatment associated with the transfer of cages in a quenching medium. It allows the hardening heat treatment in vacuum furnaces and industrial furnaces with protective atmosphere. So, for example, welded parts or structures of titanium alloy VT32 (Ti-2, 5% Al-8, 5% Mo-8, 5% V-1, 2% Fe-1,2% Cr), treated in a vacuum furnace under the regime: heating at 750 ° C for 1 h, cooling in the furnace at a rate of> = 4 ° C / min to 500 ° C, holding at 500 ° C for 4 h, provided for in the *> = 120 kgf / mm2, bb> = 7%, while in the annealed condition the alloy has s = 82 kgf/mm2 and 65 = 16%. Widespread use of the above-described method of heat treatment found in the manufacture of welded components and structures made of alloy VT22. welded construction of this alloy require stabilizing annealing at 850 ° C, ie, at temperatures limits a + p = p-transformation. After annealing, the alloy has a tensile strength of about 100 kgf/mm2. Hardening heat treatment of the regime: heating at 850 ° C for 1 h, cooling in the oven to 750 ° C, holding 2 h, cooling with furnace to 500 ° C, exposure at 600 ° C for 4 h yields on welded constructions from alloy VT22
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