CN105689919A - Nickel-based alloy welding wire with weld deposit metal capable of being recrystallized - Google Patents

Abstract

The invention belongs to the field of welding materials of ultra-supercritical power stations, in particular to a solid solution strengthening type nickel-based alloy welding wire with high plasticity, which is suitable for welding an superheater/reheater tube of an ultra-supercritical boiler and welding the superheater and the reheater tube with a gas collection header (including a tube connecting seat) of the boiler, and is mainly characterized in that after TIG (tungsten inert gas welding) welding by using the welding wire, weld deposit metal can be recrystallized after postweld heat treatment at 1000 ℃ or above, and dendrite and columnar crystal tissues in the original weld joint are eliminated; the hardness of the welded seam area is 300HV after welding, and the hardness is reduced to 210HV after recrystallization; eliminating the residual stress and component segregation of the welding seam, and basically consistent with the base metal in the structure appearance. The nickel-based alloy welding wire comprises the following chemical components (by weight percent) of Fe less than 3 percent, Cr: 14-18%, Al + Ti is less than or equal to 0.45%, Ti/Al is less than 0.9, Nb: 1.0-1.5%, Mo: 7.0-9.8%, W less than 0.4%, Si less than or equal to 1.0%, Mn: 0.5-1.0%, C is less than or equal to 0.1%, B: 0.003-0.005 percent of Zr, less than or equal to 0.03 percent of Zr, the balance of Ni and the sum of other impurity elements is less than 0.1 percent.

Description

A nickel-based alloy welding wire with recrystallizable weld deposit metal

Technical field:

The invention belongs to the field of welding materials for ultra-supercritical power stations, and in particular relates to a recrystallizable nickel-based alloy welding wire for welding deposited metal.

Background technique:

With the development of thermal power generation technology, the development of 600 ℃ and above ultra-supercritical coal-fired power generation technology has very important strategic significance and practical application value for my country's energy saving, reduction of pollutants and carbon dioxide emissions. The welding of high-temperature materials in power stations has always been a key technical link in the construction and production of power stations. With the continuous improvement of steam parameters, the alloying degree of high-temperature materials used has been continuously improved, and austenitic stainless steel and nickel-based alloys are widely used, making welding technology difficult. Then increase.

In the traditional weld structure, because the deposited metal has no chance of controlled rolling and deformation heat treatment, the directional columnar (dendritic) grains cannot be refined; at the same time, due to the fast cooling rate of the weld, the segregation of alloy elements is serious, Moreover, Nb, V, etc. in the deposited metal are difficult to precipitate as fine carbides and nitrides during the solidification and cooling process, so the comprehensive mechanical properties of the weld are far inferior to those of the base metal, and there is anisotropy. With the prolongation of the service time of welded joints, the mechanical properties (especially toughness) of the welds are significantly attenuated, and the service life is shortened; at the same time, due to the welding residual stress, stress corrosion (SCC) is prone to occur, becoming the weak link of the entire (welded) component, affecting safe operation of the power station.

In view of the problems existing in this type of welding seam, and in the existing domestic welding material system, no such nickel-based alloy welding wire has been found, and no relevant technical reports have been found. The weld deposited metal of this welding material has the following technical requirements: the weld deposited metal is crystallized after welding, and the columnar (dendritic) crystals with obvious direction in the original weld structure are all transformed into equiaxed crystals. , the hardness is reduced from 290 to 310HV to 200 to 220HV, and at the same time, the component segregation and welding residual stress are eliminated to the greatest extent, so that the weld structure is consistent with the base metal.

The solid solution strengthened nickel-based alloy welding material has good thermal stability, and the matrix has no solid phase transformation. The thermal expansion coefficient and plasticity of the material are improved through the action mechanism of the alloying elements on the matrix, so that a large thermal (expansion) stress is generated during the welding process to cause plastic deformation of the deposited metal at high temperature; at the same time, due to the good plasticity of the austenite matrix, Cracking under large welding residual stress and deformation is avoided. Due to the rapid solidification and cooling rate of the weld, the residual deformation of the weld deposit and the distortion of plastic deformation can remain. In the subsequent post-weld heat treatment, the weld deposit occurs above the recrystallization temperature (static) re-crystallize.

The plastic deformation of weld deposit metal caused by welding thermal stress exceeds its critical deformation ε _cr of recrystallization and is smaller than its maximum plastic deformation δ _max .

That is, ε _cr < ε _weld < δ _max

The addition of Mn and B elements weakens the Invar characteristic of the alloy and increases the thermal expansion coefficient of the alloy. Both Ti and Al are forming elements of the strengthening phase '(Ni ₃ (Al,Ti)) with an ordered structure. As a solid solution strengthening alloy welding consumable, the content of Ti and Al elements should be reduced as much as possible to avoid post-weld heat treatment. The generation of hot cracks; at the same time, the ratio of Ti/Al should be controlled. When the ratio of Ti/Al is too high, the structural stability at high temperature will be reduced, brittle η (Ni ₃ Ti) phase transformation will occur, and the high temperature plasticity of the alloy will be reduced. Strictly control the content of W and Zr elements to avoid deterioration of weldability.

In addition, rare earth elements will reduce the liquid fluidity of nickel-based alloys and increase the sensitivity of weld crystal cracks, so the chemical composition of welding wire does not contain rare earth elements.

Invention content:

The purpose of the present invention is to provide a welding seam for the existing ultra-supercritical power plant boiler superheater/reheater tube welding joints with large residual stress, serious composition segregation, and obvious solidified (cast) state structure in the weld zone. Deposit metal recrystallizable nickel base alloy welding wire.

In order to achieve the above object, the present invention adopts following technical scheme to realize:

A nickel-based alloy welding wire with recrystallizable weld deposit metal, the nickel-based alloy welding wire is prepared by weight percentage from the following components: Fe<3%, Cr: 14-18%, Al+Ti≤0.45% and Ti/Al<0.9, Nb: 1.0-1.5%, Mo: 7.0-9.8%, W<0.4%, Si≤1.0%, Mn: 0.5-1.0%, C≤0.1%, B: 0.003-0.005%, Zr ≤0.03%, the rest is Ni, and the sum of other impurity elements <0.1%.

The further improvement of the present invention is that the nickel-based alloy welding wire is smelted in a vacuum furnace, and finally formed into a nickel-based alloy welding wire after forging, rolling, cold drawing and annealing.

The further improvement of the present invention is that the specification of the nickel-based alloy welding wire is Φ1.5-2.4mm, the welding process is: manual TIG welding or semi-automatic tungsten inert gas welding TIG welding, welding current intensity: 105-210A, welding arc Voltage: 10.5-18V, welding speed: 100-150mm/min, current type/polarity: direct current DC/positive connection to SP, interlayer temperature not higher than 100°C, shielding gas: Ar, gas flow rate 12-16L/min.

The further improvement of the present invention lies in that, when in use, argon tungsten arc welding is used, and Ar is used as a shielding gas to form weld deposit metal.

The further improvement of the present invention lies in that the weld deposited metal is recrystallized after being heat-treated at 1000-1100° C. for 30-60 minutes and air-cooled.

The further improvement of the present invention lies in that the nickel-based welding wire is suitable for welding superheater and reheater tubes for ultra-supercritical boilers, and welding superheater and reheater tubes and boiler gas headers.

Compared with the prior art, the present invention has the following advantages:

1. Through experiments, the present invention is suitable for welding high-temperature parts of ultra-supercritical power plant boilers. Nickel-based welding wire is suitable for welding superheater and reheater tubes for ultra-supercritical boilers, superheater and reheater tubes and boiler gas collectors Welding of headers (including sockets).

2. When the welding wire of the invention is used for welding, the deposited metal of the weld seam has good high-temperature plasticity and is not easy to produce welding cracks.

3. The welding wire of the present invention can realize the microalloying of the welding seam, and obtain the welding seam meeting the requirements of the standard.

4. When welding with the welding wire of the present invention, after the weld deposited metal is recrystallized (heated) after welding, the solidified columnar crystals and dendrites in the weld zone will transform into equiaxed crystals, eliminating the weld components to the greatest extent. Segregation and welding residual stress, maintaining the consistency with the base metal structure.

Description of drawings:

Figure 1 is an optical microscope topography photo of the welded joint structure of welded IN740H nickel-based alloy (base metal); among them, Fig. 1(a) is an optical microscope topography photo of the welded structure, and Fig. 1(b) is recrystallization after welding Optical microscope topography photos of heat-treated tissues.

Figure 2 is an optical microscope topography photo of the welded joint structure of the welded GH2984 nickel-iron-based alloy (base metal); among them, Fig. 2 (a) is an optical microscope topography photo of the welded structure, and Fig. 2 (b) is the post-weld Optical microscope topography of crystallized heat-treated tissue.

detailed description:

The present invention will be described in further detail below in conjunction with examples.

Example 1:

See Figure 1, use this welding wire (Φ1.5mm) to weld IN740H nickel-based alloy by manual TIG welding, welding current: 140A, welding voltage: 13V, welding speed: 110mm/min, current type/polarity: DC DC/connected to SP, interlayer temperature not higher than 100°C, protective gas: Ar, gas flow rate 13L/min. Heat treatment at 1050℃/1h after welding, the weld microstructure changed from post-weld columnar crystals and dendrites to equiaxed crystals, and no defects such as welding cracks occurred. After welding, the hardness of the weld is 310HV, and the impact toughness is 22kJ; after post-weld heat treatment, the hardness is reduced to 215HV, and the impact toughness is 31kJ.

Example 2:

See Figure 2, use this welding wire (Φ2.4mm) to weld GH2984 nickel-iron-based alloy by manual TIG welding, welding current: 160A, welding voltage: 14V, welding speed: 120mm/min, current type/polarity: Direct current DC/positive connection to SP, interlayer temperature not higher than 100°C, protective gas: Ar, gas flow rate 15L/min. Heat treatment at 1100℃/30min after welding, the weld microstructure changed from post-weld columnar crystals and dendrites to equiaxed crystals, and no defects such as welding cracks occurred. After welding, the hardness of the weld is 300HV, and the impact toughness is 26kJ; after post-weld heat treatment, the hardness is reduced to 210HV, and the impact toughness is 46kJ.

Claims (6)

1. A nickel-based alloy welding wire with recrystallizable weld deposit metal, characterized in that the nickel-based alloy welding wire is prepared from the following components by weight percentage: Fe<3%, Cr: 14-18%, Al +Ti≤0.45% and Ti/Al<0.9, Nb: 1.0-1.5%, Mo: 7.0-9.8%, W<0.4%, Si≤1.0%, Mn: 0.5-1.0%, C≤0.1%, B: 0.003-0.005%, Zr≤0.03%, the rest is Ni, and the sum of other impurity elements <0.1%. 2. The recrystallizable nickel-base alloy welding wire according to claim 1 is characterized in that, the nickel-base alloy welding wire is smelted in a vacuum furnace, after forging, rolling, cold drawing and annealing, finally Form nickel base alloy welding wire. 3. The recrystallizable nickel-based alloy welding wire according to claim 1, characterized in that the specification of the nickel-based alloy welding wire is Φ1.5-2.4 mm, and the welding process is: manual TIG welding or Semi-automatic wire-filled tungsten inert gas welding TIG, welding current intensity: 105-210A, welding arc voltage: 10.5-18V, welding speed: 100-150mm/min, current type/polarity: DC DC/positive SP, interlayer The temperature is not higher than 100°C, the protective gas is Ar, and the gas flow rate is 12-16L/min. 4. The recrystallizable nickel-base alloy welding wire according to claim 1 is characterized in that, when in use, argon tungsten arc welding is used, and Ar is used as shielding gas to form a weld deposit . 5. Use the recrystallizable nickel-based alloy welding wire of weld deposited metal according to claim 4, characterized in that, after the weld deposited metal is heat-treated at 1000-1100° C. for 30-60 minutes, air-cooled, the weld melts Recrystallization of the metallization occurs. 6. according to the recrystallizable nickel-base alloy welding wire of weld deposit metal described in claim 1, it is characterized in that, nickel-base welding wire is suitable for the welding of superheater and reheater pipe of ultra-supercritical boiler, superheater and Welding of reheater tubes and boiler headers.