CN114029591A

CN114029591A - Active flux suitable for ferrite stainless steel tungsten electrode argon arc welding base metal self-melting welding process

Info

Publication number: CN114029591A
Application number: CN202111144059.4A
Authority: CN
Inventors: 张心保; 吴开明
Original assignee: Zhongneng Huayuan Intelligent Equipment Research And Design Institute Qingdao Co ltd; Caigu Jindai Foshan Metal Composite Material Co ltd; Wuhan University of Science and Engineering WUSE
Current assignee: Zhongneng Huayuan Intelligent Equipment Research And Design Institute Qingdao Co ltd; Caigu Jindai Foshan Metal Composite Material Co ltd; Wuhan University of Science and Engineering WUSE
Priority date: 2021-09-28
Filing date: 2021-09-28
Publication date: 2022-02-11
Anticipated expiration: 2041-09-28
Also published as: CN114029591B

Abstract

The invention provides an active flux suitable for a ferrite stainless steel argon tungsten-arc welding base metal self-melting welding process, which comprises the following components in percentage by mass: SiO 2₂：19.99～29.99％；CaF₂：10.49～14.49％；TiO₂：9.99～14.99％；NaF：7.99～14.99％；ZnF₂：8.79～14.79％；Al₂O₃：3.99～7.99％；Cr₂O₃: 4.49 to 14.49; MgO: 8.99-20.99%. The ferrite stainless steel joint obtained by the active welding flux not only greatly increases the penetration and depth-to-width ratio and has a K value of more than 0.76, but also refines crystal grains and obtains excellent mechanical property and corrosion resistance; eliminate welding forming defects such as air holes, slag inclusion, undercut and weld collapse to a certain extentAnd excellent weld formation is obtained.

Description

Active flux suitable for ferrite stainless steel tungsten electrode argon arc welding base metal self-melting welding process

Technical Field

The invention relates to the technical field of active welding flux, in particular to active welding flux suitable for a ferrite stainless steel argon tungsten-arc welding base metal self-melting welding process.

Background

The ferritic stainless steel is a stainless steel with a structure of a ferritic phase, is an important component of the stainless steel, and has the chemical composition characteristics that the chromium content is 11.5-30%, no nickel or a small amount of nickel is contained, and alloy elements such as titanium, niobium, molybdenum and the like are added, so that the modern ferritic stainless steel has ultralow impurity contents such as C + N, S, P and the like, and has better comprehensive performance. In comparison with austenitic stainless steels, ferritic stainless steels have excellent electrical conductivity, thermal conductivity, low coefficient of thermal expansion, excellent pitting corrosion resistance, thermal fatigue resistance, and the like, and are low in cost, and thus have been increasingly used in many fields in recent years. However, since ferritic stainless steel has a strong dimensional effect and the properties thereof sharply decrease with the thickness of the cross section, it is generally used in applications requiring low mechanical properties with a thin cross-sectional dimension.

In many applications, welding is an important process, however, ferrite grains are easily coarsened after being heated and cannot be refined by heat treatment or mechanical treatment, so that the application of the ferrite stainless steel is greatly limited, and weldability is a bottleneck link of the ferrite stainless steel in practical application.

For many years, welding workers and researchers have attempted to suppress the degree of grain coarsening in ferritic stainless steels during welding by various methods, including reducing the heat input to the weld, using energy density intensive heat sources such as plasma arcs, lasers and compound heat sources, and using processes and methods such as ultrasonic vibration during welding and post-weld rapid cooling, all without achieving a satisfactory grain refinement.

The invention of the argon tungsten-arc welding process with the active welding flux in the 1960 s has been applied to welding materials such as stainless steel, carbon steel, nickel-based alloy, titanium alloy and the like so as to obtain larger penetration and reduce welding deformation under the same welding parameters. The welding composition varies according to the metal to be welded and the technical requirements for the welded joint.

The active welding flux is mainly oxides and fluorides for improving the activity of liquid phase substances, and because various active substances have different influences on a welding pool and the forming effect of a welding seam, the formula of the active welding has stronger pertinence, and the formulas of the active welding of different metal materials are different, so that the expected welding seam forming, microstructure, mechanical property and the like are obtained.

The research of active welding in China starts late, theoretical research and technology accumulation are less, related documents and technical data are less, and a certain controversial exists about the mechanism of the active welding flux on the aspect of increasing the penetration in China and abroad. However, the effect that the active welding flux can significantly increase the penetration depth and improve the weld forming in the actual welding process is confirmed, and patent formulas of the active welding flux aiming at different materials are also developed at home and abroad, so that better effects are achieved.

The active flux is mainly applied to stainless steel at home and abroad, the penetration depth increase under the same welding condition is realized by adopting the active flux argon tungsten-arc welding process, although the penetration depth can also be obtained by adopting a plasma welding method, the plasma welding equipment is complex, the requirements on welding tool fixtures are high, the occupied area is large, the flexibility is poor, and only a welding joint with a regular shape is suitable, so that the defect is made up to a certain extent by the active flux TIG welding. In recent years, with the rapid development of ferritic stainless steel, the quality is greatly improved, the brands and specifications are more and more, and the application field is more and more extensive, so that the welding process and the weldability of the ferritic stainless steel are more and more valued by welding research workers.

The research work and application of the active flux in the ferrite stainless steel welding at home and abroad are less, the comprehensive performance of the ferrite stainless steel is also obviously improved along with the improvement of metallurgical technology and the improvement of the purity of the ferrite stainless steel, but the weldability is still not substantially improved, and the fundamental reason is that ferrite crystal grains are rapidly coarsened under the action of welding thermal cycle, particularly when a self-melting welding process is adopted to weld a thin plate, a weld joint structure is mainly formed by coarse columnar crystals, the HAZ crystal grains are also obviously coarsened, and the plasticity and toughness of a joint area are poor, so that the later-stage processing and use requirements cannot be met.

The theoretical basis of the active flux penetration increasing mechanism mainly comprises a surface tension temperature gradient theory and an electric arc contraction theory. The theory considers that after the active elements are added, the surface tension temperature gradient of the molten pool is changed from negative temperature gradient to positive temperature gradient, so that the flowing direction of the molten pool is changed, the weld penetration is increased, namely the reversal phenomenon of Marangoni convection in the molten pool is the main reason of the penetration increase. The Marangoni effect (Marangoni coupling) refers to a characteristic that when a liquid film of a liquid is locally thinned due to external disturbance (such as temperature and concentration), a Marangoni flow is formed under the action of surface tension, so that the liquid flows back to a thin liquid surface along an optimal route for restoration.

Under the action of surface tension, the liquid phase substance flows from a region with low surface tension to a region with high surface tension. For pure metals and many alloys, the surface tension gradient increases with decreasing temperature, i.e.

The surface tension of the edge of the welding molten pool is smaller than that of the center, so that high-temperature liquid flows from the center of the molten pool to the edge, and the obtained welding seam is wide and shallow; when the surface of the workpiece has active flux, the direction of this flow changes due to the active elements, such as O, S, F, etc., changing the surface tension gradient from negative to positive, i.e.

Resulting in a deep and narrow weld. Namely, the Marangoni effect changes from negative to positive to cause the formation of the weld.

The arc contraction theory considers that negative ions generated by decomposition of the active agent compress an anode region of the arc, so that the current density of the anode region is increased, the Lorentz force is increased, and the weld penetration is increased.

Combining the two theories, it is believed that the increased arc contraction energy density and the reversed marangoni phenomenon interact, promoting each other. The enhanced arc intensifies the marangoni flow movement of the bath, and the enhanced marangoni flow transfers heat from the surface of the bath at higher temperatures to the depth of the bath at lower temperatures, further constricting the arc. For ferritic stainless steel, the strong marangoni flow plays a role in stirring a molten pool and refining grains to a certain extent.

As is well known, ferritic stainless steel has the advantages of low cost, excellent pitting corrosion resistance and good comprehensive performance, and compared with austenitic stainless steel, the ferritic stainless steel has the advantages of good heat conductivity, good electrical conductivity, small coefficient of thermal expansion and excellent thermal fatigue resistance. Ferritic stainless steel has numerous brands and is generally applied to many fields with thin specifications, such as automobile exhaust systems, water tank containers, pipelines, kitchen utensils and tableware, food machinery and other industries. However, the inherent property of coarsening the crystal grains of the ferrite phase by heating causes coarse crystal grains in the welded joint area, developed columnar crystals, small proportion of isometric crystals and deteriorated performance, so that the application of the stainless steel is greatly limited.

Disclosure of Invention

Aiming at the defects of the prior art, the invention provides an active welding flux suitable for a ferrite stainless steel argon tungsten-arc welding base metal self-melting welding process.

The technical scheme of the invention is as follows: an active flux suitable for a ferrite stainless steel argon tungsten-arc welding base metal self-melting welding process comprises the following components in percentage by mass:

the ferritic stainless steel joint obtained by the active flux not only has greatly increased penetration and depth-to-width ratio and K value of more than 0.76, but also has refined grains.

Preferably, the active welding flux also comprises 19-39% of TiC by mass percent.

Preferably, the ω (Cr) is₂O₃) The value of/omega (MgO) ranges between 0.39 and 0.59.

The invention also provides a self-fluxing welding process of a ferrite stainless steel argon tungsten-arc welding base metal by using the active welding flux, which is characterized in that a layer of active welding flux consisting of active chemical substances such as oxide, fluoride and the like and TiC powder is coated in the butt joint area of the I-shaped groove of the ferrite stainless steel sheet, and absolute ethyl alcohol is used as a mixed adhesive to be prepared into a pasty mixture before welding so as to realize A-TIG high-efficiency single-pass fusion penetration welding.

Preferably, the anhydrous ethanol is used for uniformly mixing the active flux and coating the active flux on the area to be welded by using a brush or other coating equipment before welding, the flux is nontoxic, the coating amount is suitable for completely covering the metal surface, the active flux is gasified to form plasma under the action of electric arc in the welding process, the shape of the electric arc is changed, part of the active flux enters a welding molten pool under the action of the electric arc, the surface tension distribution is changed, the flowing state and the intensity of the molten pool are changed, the welding seam formation is improved to a certain extent, the welding defects are avoided, the obtained welding seam structure is also obviously improved, the grain size of columnar crystals is obviously reduced, the proportion of an isometric crystal area in the center is increased, and the comprehensive performance of a welding joint is fundamentally improved.

Preferably, in the welding process, the welding current is 120-150A, the welding voltage is 12-16V, the welding speed is 3-4mm/s, the protective gas is 99.99% pure argon, the diameter of the tungsten electrode is 1.6mm, and the polarity of the power supply is direct current positive.

The invention has the beneficial effects that:

1. the weld joint obtained by the invention has a larger depth-to-width ratio under the same welding current condition, and can realize grain refinement and increase of equiaxial crystal proportion in the central area so as to obtain excellent mechanical property and corrosion resistance;

2. the invention eliminates welding forming defects such as air holes, slag inclusion, undercut, welding seam collapse and the like to a certain extent, in addition, under the action of reversed Marangoni flow, the flow of the molten pool is strengthened, so that the tendency that liquid metal in the molten pool focuses towards a high-temperature area at the center of an arc column is strengthened, meanwhile, the welding seam has certain residual height, thereby obtaining excellent welding seam forming, meanwhile, the fluidity of the molten pool is strengthened, the invention is beneficial to quickly escaping the defects such as air holes, slag inclusion and the like in the molten pool from the surface, and the generation of metallurgical defects is avoided to a certain extent;

3. the crystal grains in the welding joint area are obviously refined, the proportion of the central equiaxed crystal is obviously increased, the effects of improving the welding seam forming and avoiding the defect of the welding seam forming are realized, the active welding flux has no special requirement on the existing TIG welding equipment, the active welding flux is uniformly mixed by absolute ethyl alcohol before welding, and the active welding flux is coated on the welding area by a brush or other coating equipment, and the welding flux has no toxicity;

4. the TiC powder is added, the grain sizes of the welding seam and HAZ are further refined, the performance is further improved, the active welding flux has the effect of increasing the weld penetration, the welding seam is well formed, the depth-to-width ratio K of the welding seam in the prior art is only 0.19, the active welding flux is used for welding, the depth-to-width ratio K of the welding seam is as high as 0.76, and the TiC powder is substantially improved compared with the prior art.

Drawings

FIG. 1 is a macrostructure profile of a weld obtained in example 1 of the present invention, in which FIG. 1(a) is a macrostructure profile of a weld obtained by the method (A-TIG weld) of this example, and FIG. 1(b) is a macrostructure profile of a weld obtained by conventional TIG;

FIG. 2 is a graph of the weld profile and macrostructure of a weld obtained in example 2 of the present invention, in which (a) is the weld profile and (b) is the macrostructure of the weld profile;

fig. 3 is a comparison of the weld texture features 409L obtained in example 3 of the present invention, in which, (a) is a weld texture feature map obtained by a conventional TIG method, and (b) is a weld texture feature map obtained by the method (a-TIG) of this example.

Detailed Description

The following further describes embodiments of the present invention with reference to the accompanying drawings:

example 1

The embodiment provides an active flux suitable for a ferrite stainless steel argon tungsten-arc welding base metal self-melting welding process, which comprises the following components in percentage by mass:

this example forms a weld bead by self-fluxing welding on the surface of a ferritic stainless steel sheet to demonstrate the effect of the active flux on weld formation and texture morphology of the ferritic stainless steel.

Before welding, a proper amount of absolute ethyl alcohol is used for mixing and stirring the materials evenly to prepare suspension liquid which is similar to a paste shape, the suspension liquid is coated on the surface of metal to be welded by a brush, and welding can be carried out after the ethyl alcohol is completely volatilized.

The adopted stainless steel plate is SUS441 ultrapure ferrite stainless steel with the thickness of 5mm, welding process parameters are shown in Table 1, protective gas is 99.99% pure argon, the diameter of a tungsten electrode is 1.6mm, and the polarity of a power supply is direct current positive connection. For comparison, the same process specifications were used to perform ordinary TIG welding to obtain a welded joint.

TABLE 1 welding Process parameters

Taking gold phase sample after welding, grinding and polishing, and then adopting 5g FeCl₃Corrosive agents, prepared from 15ml of hydrochloric acid and 30ml of distilled water, were etched and macroscopic observations were made to investigate the effect on weld formation.

FIG. 1 is a macrostructure profile of a weld obtained by the present example, in which FIG. 1(a) is a macrostructure profile of a weld obtained by the method (A-TIG weld) of the present example, and FIG. 1(b) is a macrostructure profile of a weld obtained by a conventional TIG method; the comparison shows that the weld joint obtained by the A-TIG welding of the embodiment has obvious advantages, the penetration of the weld joint is obviously increased, the columnar crystal size is small, and a large-proportion equiaxed crystal area appears in the center. The structure form is obviously superior to the weld joint structure obtained by the conventional TIG welding, and simultaneously has good mechanical property, in addition, under the action of reversed Marangoni flow, the flow of a molten pool is strengthened, so that the tendency of focusing of liquid-phase metal in the molten pool to a high-temperature area at the center of an arc column is strengthened, and the solidified weld joint has certain residual height, and the weld joint forming has certain beneficial effects on the mechanical property of the weld joint and the defects of undercut prevention and the like. In addition, the enhanced fluidity of the molten pool is beneficial to quickly escaping the defects of air holes, slag inclusion and the like in the molten pool from the surface, and the generation of the metallurgical defects is avoided to a certain extent.

The weld joint obtained by using the active flux formula has excellent weld joint forming and smaller grain size, a larger-proportion central equiaxed crystal area exists, and the penetration of the conventional TIG welding weld joint is 2-3 times that of the conventional TIG welding weld joint under the same process specification.

Example 2

The test conditions in this example were the same as those in example 1, except that TiC powder was added to the reactive flux in an amount of 33% by mass based on the total amount of the flux to obtain a weld structure having finer grains, and SUS441 ultra-pure ferritic stainless steel with a thickness of 5mm was used as the stainless steel plate for the test.

The weld formation and macrostructure results obtained are shown in fig. 2, and compared with fig. 1(a), the weld penetration and the depth-to-width ratio are reduced, but the integral formation is still better than the weld obtained by ordinary TIG welding.

The TiC powder with better electrical conductivity and thermal conductivity is added, so that the compression effect of the active flux on an electric arc is weakened, but the active flux has the effect of increasing Marangoni flow in a molten pool, the TiC powder is favorably and fully dissolved in the molten pool, and the particles have the effect of strongly preventing the coarsening of crystal grains, so that the obtained welding line has finer crystal grains, the columnar crystal size is smaller, the proportion of a central isometric crystal area is larger, the width and the crystal grain size of a welding joint HAZ are greatly reduced, and the structural characteristics ensure that the welding joint has better mechanical property, thereby fundamentally solving the problem that the crystal grains of the welding joint of the ferritic stainless steel are coarse.

In the embodiment, by adding TiC powder into the formula of the active welding flux, although the penetration of the welding seam is increased to a smaller extent, the welding seam with finer grains and the HAZ structure are obtained, and the structure is very favorable for improving the performance of the welded joint. Therefore, the welding process is very suitable for application occasions with relatively low thickness but relatively high requirements on the mechanical property of the welding joint, such as subsequent processing processes of bending, expanding, cross-seam welding and the like of the welding workpiece.

Example 3

The flux formulation used in this example was the same as in example 1, with no TiC powder added, and with absolute ethanol as the solvent, the welding process parameters used were the same as in the example. Except that the stainless steel plate for the test is 409L (00Cr11Ti) ferrite stainless steel with the thickness of 1.5mm, the welding process parameters are welding current 120A, welding speed is 400mm/min, and the flow of protective gas is 10L/min. For comparison, a conventional TIG welding test was performed using the same process.

The macrostructure of the welded joint obtained is shown in fig. 3, and due to the small thickness of the sheet, a completely penetrated weld was obtained for both samples.

The welding seam obtained by the conventional TIG welding is thick columnar crystal, and the width of the welding seam and the width of HAZ are larger; and the coarsening of the crystal grains of the welding seam obtained by A-TIG is obviously inhibited, the width of a coarse crystal area is also obviously reduced, and the texture form is very beneficial to the mechanical property and the forming property of the joint.

Example 4

the foregoing embodiments and description have been presented only to illustrate the principles and preferred embodiments of the invention, and various changes and modifications may be made therein without departing from the spirit and scope of the invention as hereinafter claimed.

Claims

1. The active flux is suitable for a ferrite stainless steel argon tungsten-arc welding base metal self-melting welding process and is characterized by comprising the following components in percentage by mass:

2. The active flux suitable for the ferritic stainless steel argon tungsten-arc welding base metal self-fluxing welding process according to claim 1, wherein: the active welding flux also comprises 19-39% of TiC by mass percent.

3. The active flux suitable for the ferritic stainless steel argon tungsten-arc welding base metal self-fluxing welding process according to claim 1, wherein: the omega (Cr)₂O₃) The value of/omega (MgO) ranges between 0.39 and 0.59.

4. The ferritic stainless steel argon tungsten-arc welding base metal self-fluxing welding process utilizing the active welding flux as described in any one of claims 1-3 is characterized in that a layer of the active welding flux as described in any one of claims 1-3 is coated on an I-shaped groove butt joint area of a ferritic stainless steel sheet, and the active welding flux is prepared into a pasty mixture by taking absolute ethyl alcohol as a mixed adhesive before welding, so that A-TIG high-efficiency single-pass penetration welding is realized.

5. The ferritic stainless steel argon tungsten-arc welding base material self-melting welding process according to claim 4, characterized in that: the method is characterized in that the active welding flux is uniformly mixed by absolute ethyl alcohol before welding, and is coated on an area to be welded by a brush or other coating equipment, the coating amount is suitable for completely covering the metal surface, the active welding flux is gasified to form plasma under the action of electric arc in the welding process, the shape of the electric arc is changed, part of the active welding flux enters a welding pool under the action of the electric arc, so that the surface tension distribution is changed, the flowing state and the intensity of the welding pool are changed, the welding seam formation is improved to a certain extent, the welding defects are avoided, the obtained welding seam structure is also obviously improved, the grain size of columnar crystals is obviously reduced, the proportion of an equiaxed crystal area at the center is increased, and the comprehensive performance of a welding joint is fundamentally improved.

6. The ferritic stainless steel argon tungsten-arc welding base material self-melting welding process according to claim 5, characterized in that: in the welding process, the welding conditions are as follows:

welding current is 120-150A, welding voltage is 12-16V, welding speed is 3-4mm/s, protective gas is 99.99% pure argon, tungsten electrode diameter is 1.6mm, and power polarity is direct current positive connection.