RU2721977C1 - Welding wire from titanium alloys - Google Patents

Abstract

FIELD: manufacturing technology; chemistry.SUBSTANCE: invention can be used in production of filler materials for arc welding in medium of inert gases of high-strength (α+β) and pseudo-β-titanium alloys intended for use as high-strength structural high-tech material for making shipbuilding, aircraft and space equipment, as well as power plants. Welding wire contains aluminum, vanadium, molybdenum, zirconium, chromium and titanium, as well as limited content of impurities at following ratio of components, wt%: aluminum 3.5–4.5; vanadium 1.5–2.5; molybdenum 1.5–2.5; zirconium 1.0–2.0; chromium 0.5–0.7; carbon not more than 0.05; oxygen not more than 0.12; nitrogen not more than 0.03; hydrogen is not more than 0.003; titanium – the rest.EFFECT: technical result is improved strength characteristics of weld metal (up to 973 MPa) while maintaining plasticity characteristics.1 cl, 3 tbl

Description

The invention relates to the field of metallurgy of titanium-based alloys, in particular to alloys for welding materials, and can be used as a filler wire for arc welding in inert gases of high-strength (α + β) - and pseudo-β-titanium alloys, intended for use as a structural high-strength high-tech material for the manufacture of structures of shipbuilding, aviation and space technology, as well as power plants.

For welding high-strength (α + β) - and pseudo-β-titanium alloys, the most optimal is the use of filler materials belonging to the class of pseudo-α and low alloy (α + β) -titanium alloys.

Known welding wire brand SP15 according to GOST 27265, the following chemical composition, wt. %: aluminum 3.0-5.5; molybdenum 2.0-3.5; vanadium 2.0-3.5; zirconium 1.0-2.0; silicon ≤0.15; iron ≤0.30; carbon ≤0.10; oxygen ≤0.15; nitrogen ≤0.05; hydrogen ≤0.006; the amount of other impurities ≤0.30; titanium - the rest.

A disadvantage of the known filler wire for welding titanium alloys, for example, VT22 alloy, is a decrease in the strength characteristics of the obtained welded joints compared to the base metal [S.M. Gurevich, V.N. Zamkov, N.A. Kushnirenko Welding and heat treatment of VT22 titanium alloy // Automatic welding, 1982, No. 5].

Known welding wires of grades VT20-1sv according to GOST 27265, VT20-2sv according to GOST 27265 and VT20-3sv of the following chemical composition, wt. %:

- VT20-1sv according to GOST 27265 (aluminum 2.0-3.0; molybdenum 0.5-1.5; vanadium 0.5-1.5; zirconium 1.0-2.0; silicon ≤0.10; iron ≤0.15; carbon ≤0.05; oxygen ≤0.12; nitrogen ≤0.04; hydrogen ≤0.003; sum of other impurities ≤0.30; titanium - the rest);

- VT20-2sv according to GOST 27265 (aluminum 3.5-4.5; molybdenum 0.5-1.5; vanadium 0.5-1.5; zirconium 1.0-2.0; silicon ≤0.10; iron ≤0.15; carbon ≤0.05; oxygen ≤0.12; nitrogen ≤0.04; hydrogen ≤0.003; sum of other impurities ≤0.30; titanium - the rest);

- VT20-3sv (patent SU 436717) (aluminum 4.7-5.8; zirconium 2.2-3.5; molybdenum 0.8-1.5; vanadium 1.3-3.2; tin 1-2 %; hydrogen ≤0.003; oxygen ≤0.120; titanium - the rest).

The use of welding wire of the VT20-2sv brand for the manufacture of welded joints of titanium alloys, for example, an alloy of the VT20 brand, leads to a decrease in the temporary resistance of the weld metal with an increase in the thickness of the welded metal. [R.S. Kurochko, N.N. Manuylov, L.A. Gruzdeva, E.A. Borisova Filler wire for welding high-strength titanium alloys // Welding production, 1977, No. 3].

The use of VT20-3sv grade wire for argon-arc welding of titanium alloys, for example, VT22 alloy, reduces the toughness of the weld metal [M.A. Horev, V.I. Lukin, A.V. Ioda, E.S. Silkina et al. Filler materials for welding structural titanium alloys // Light alloy technology, 1990, No. 5].

Known welding wires of grades VT6sv and SPT-2 according to GOST 27265 of the following chemical compositions, wt. %:

- VT6sv (aluminum 3.5-4.5; vanadium 2.5-3.5; silicon ≤0.10; iron ≤0.15; carbon ≤0.05; oxygen ≤0.12; nitrogen ≤0.04 ; hydrogen ≤0.003; sum of other impurities ≤0.30; titanium - the rest);

- SPT-2 (aluminum 3.5-4.5; vanadium 2.5-3.5; zirconium 1.0-2.0; silicon ≤0.10; iron ≤0.15; carbon ≤0.05; oxygen ≤0.12; nitrogen ≤0.04; hydrogen ≤0.003; sum of other impurities ≤0.30; titanium - the rest).

The disadvantage of the above welding wires when using them as filler material in the process of argon-arc welding of titanium alloys, for example, VT22 alloy, is the insufficient level of strength characteristics of the obtained welded joints [S.M. Gurevich, V.N. Zamkov, N.A. Kushnirenko Welding and heat treatment of VT22 titanium alloy // Automatic welding, 1982, No. 5].

The closest analogue taken as a prototype is a welding wire based on titanium SPT-2 (GOST 27265), which has the highest strength of the above and containing, mass. %: aluminum 3.5-4.5; vanadium 2.5-3.5; zirconium 1.0-2.0; silicon ≤0.10; iron ≤0.15; carbon ≤0.05; oxygen ≤0.12; nitrogen ≤0.04; hydrogen ≤0.003; the amount of other impurities ≤0.30; titanium - the rest.

The technical result of the proposed invention is the creation of a welding wire for arc welding with a non-consumable electrode in an inert gas environment of high-strength titanium (α + β) - and pseudo-β-alloys, which provides an increase in the strength characteristics of the weld metal (up to 973 MPa) while maintaining the ductility characteristics.

The technical result is achieved as a result of the fact that the welding wire based on titanium includes aluminum, vanadium, molybdenum, zirconium, chromium, the rest of the impurities in the following ratio of components, wt. %: aluminum 3.5-4.5; vanadium 1.5-2.5; molybdenum 1.5-2.5; zirconium 1.0-2.0; chrome 0.5-0.7; carbon no more than 0.05; oxygen no more than 0.12; nitrogen not more than 0.03; hydrogen not more than 0.003; titanium - the rest.

The proposed welding wire belongs to the class of low-alloy (α + β) titanic alloys with molybdenum equivalent (Mo _eq) at 4.42% - average value (from 3.4 to 5.44%). The alloy is complexly alloyed with isomorphic (vanadium, molybdenum) and eutectoid (chromium) β-stabilizers, α-stabilizers (aluminum) and a neutral hardener (zirconium).

For the welding wire of the prototype alloy (SPT-2), manufactured in accordance with GOST 27265, the molybdenum equivalent is 1.8-2.5%.

The increase in the molybdenum equivalent value is associated with additional alloying of the proposed welding wire with β-stabilizers (molybdenum, chromium), which leads to positive effects of complex alloying (for example, when welding a new pseudo-β-titanium alloy PT-48, the chemical and structural uniformity and mechanical properties increase different zones of the welded joint, and also increases the tensile strength without reducing the ductility of the weld).

Chromium is an effective hardener in titanium alloys. The content of chromium in the welding wire from 0.5 to 0.7% was selected due to a decrease in segregation of the alloying element during the manufacturing process of the ingot and inside the grain, which contributes to the thermal stability of the titanium welding wire. In addition, the chromium content is limited due to the additional alloying of the alloy with β-stabilizers (chromium and molybdenum), in order to increase the level of mechanical properties of the wire and welded joints.

Joint alloying with chromium and molybdenum ensures the constancy of the total number of β-stabilizers (the central sections of the dendrites are enriched with molybdenum, and the sections adjacent to the boundaries are enriched with chromium) in different zones of the welded joint, thereby increasing the strength and plastic characteristics [Popova MA, Rossina N. G. Popov N.A. The processes of separation of the α ₂ phase in titanium-aluminum alloys. Titan, 2016, No. 4]. In addition, the simultaneous alloying with several β-stabilizing elements allows to obtain a more uniform and dispersed decomposition of the phase components of different zones of the welded joint. Molybdenum in an amount of up to 2.5% increases the strength characteristics of the welded joint. With a further increase in the molybdenum content, a decrease in ductility occurs, which is associated with the formation of a large amount of a supersaturated α'-phase during the thermal welding cycle.

Aluminum increases the tensile strength of the welded joint, but when introduced into the alloy more than 5%, there is a noticeable decrease in ductility and manufacturability in the process of wire drawing. With an increase in the content of aluminum in the alloy, the permissible amount of molybdenum increases, due to its increased solubility in α-titanium.

Vanadium moderately hardens titanium with a slight decrease in its ductility, which is explained by an increase in the content of the stronger β-phase in the α-matrix. The vanadium content relative to the prototype alloy is reduced to 1.5-2.5%, due to the additional alloying of the alloy with β-stabilizers (molybdenum, chromium).

The alloying of the alloy and the weld with zirconium 1.0-2.0% during welding of high-strength pseudo-β-titanium alloy increases the uniformity of decomposition of the metastable β-phase during aging, reduces the negative effect of segregation of alloying elements on the structure of high-alloy β-alloys in the alloy zone, contributing to more uniform participation of elements in plastic deformation under loading. Zirconium increases thermal stability, corrosion resistance of Ti-Mo alloys, increases hardenability, inhibits the formation of the ω phase at low aging temperatures and reduces oxidation.

Oxygen stabilizes the α-phase, dissolving well in α-titanium, significantly strengthens titanium. Every 0.1% oxygen (by mass) increases the strength properties of titanium by 130 MPa, which is associated with a strong distortion of the α-titanium lattice due to the incorporation of oxygen atoms into octahedral voids. However, during welding, additional oxidation of the weld metal is possible in case of violation of the protection of the welding zone, therefore, in the welding wire, the oxygen content interval is limited to 0.12%.

In the field of low concentrations, carbon increases the strength and yield strength of titanium; at carbon concentrations of more than 0.2%, solid carbides are formed, which reduce toughness and complicate machining. In this regard, the carbon content in the proposed alloy is limited to an interval of 0.05%.

Nitrogen is a harmful impurity in titanium alloys, significantly reducing ductility, and therefore its content in the proposed alloy is regulated in the limit up to 0.03%.

Hydrogen forms a solution of the interstitial type and also belongs to the category of harmful impurities, since it causes hydrogen brittleness of titanium alloys. In the proposed alloy, the hydrogen content is limited to an interval of 0.003%.

Execution Example:

Ingots ∅ 360 × 310 mm in size were made from the proposed titanium alloy by the double vacuum arc remelting method. Next, the ingots were heated to temperatures of 950 ° С-1180 ° С and subsequent rolling to a diameter of 50 mm. The pressed billet was cut into pieces, machined to remove surface defects. After that, the preforms were heated to temperatures of 880 ° С-980 ° С and rolled to a diameter of 8 mm.

The resulting wire blanks (wire rods) underwent multiple drawing to diameters of 2 and 4 mm. After that, the welding wire was etched. The final step in the manufacturing process is vacuum annealing to degass the final product.

As the base metal for studying the properties of welded joints, a PT-48 pseudo-β-titanium alloy (patent RU 2690257 C1) in the form of a plate 100 × 100 × 600 mm in size was chosen. From a plate, plates 20 mm thick were mechanically cut out for the manufacture of welded joints. The plates were welded in the form of butt joints by manual argon-arc welding with filler material (table 1).

Next, the following characteristics of the obtained semi-finished products (wire) and welded joints were determined:

- mechanical characteristics during static tensile testing of the wire at room temperature according to GOST 27265 (temporary resistance and elongation);

- mechanical characteristics during testing of samples cut from weld metal of welded joints, for static tension according to GOST 6996.

Table 2 shows the standard mechanical properties of a wire made from the proposed alloy and prototype alloy. The mechanical properties of the proposed welding wire is higher than the wire of the prototype alloy.

Table 3 presents the strength characteristics of the weld metal of the welded joints obtained by manual argon arc welding using the prototype wire (SPT-2) and the proposed welding wire as filler material.

From table 3 it follows that when using the proposed welding wire as a filler material in the process of argon-arc welding of titanium pseudo-β-alloy compared to the prototype wire (SPT-2), the value of the temporary resistance of the weld metal increased by 250 MPa, the value of yield strength 222 MPa while maintaining the plasticity characteristics at the level of the prototype alloy.

The obtained results on increasing the strength of the weld metal of the welded joints reduce the height of the weld reinforcement, which increases the technical and economic effect in the manufacture of structures, namely, increases the productivity of the process and reduces the consumption of filler material.

In this case, complex alloying of the welding wire with three (β-stabilizing elements (Mo, Cr, V) allows you to get a homogeneous structure in all areas of the welded joint.

The proposed welding wire can be used as a filler material for arc welding in the environment of inert gases of high-strength titanium (α + β) - and pseudo-β-alloys in the environment of inert gases. The weld metal of welded joints obtained using the proposed welding wire has higher values of temporary resistance (973 MPa) while maintaining ductility characteristics compared to weld metal of welded joints made using previously known filler materials.

Claims (2)

Welding wire based on titanium containing aluminum, vanadium, zirconium, titanium and impurities, characterized in that it additionally contains chromium and molybdenum, while the content of carbon, oxygen, nitrogen and hydrogen as impurities is limited in the following ratio of components, wt.% : Aluminum              3.5-4.5 Vanadium              1.5-2.5 Molybdenum              1.5-2.5 Zirconium              1.0-2.0 Chromium                          0.5-0.7 Carbon   no more than 0,05 Oxygen   no more than 0.12 Nitrogen               no more than 0,03 Hydrogen no more than 0,003 Titanium                     rest