CN109848522B

CN109848522B - Ultrasonic-assisted GTAW (gas tungsten arc welding) pulsed arc welding method for duplex stainless steel sheet

Info

Publication number: CN109848522B
Application number: CN201910131056.3A
Authority: CN
Inventors: 谢伟峰; 李梁; 金博; 李浩玄
Original assignee: Northeast Dianli University
Current assignee: Northeast Electric Power University
Priority date: 2019-02-21
Filing date: 2019-02-21
Publication date: 2021-04-27
Anticipated expiration: 2039-02-21
Also published as: CN109848522A

Abstract

A double-phase stainless steel sheet ultrasonic-assisted GTAW pulsed arc welding method is disclosed, wherein the thickness of a double-phase stainless steel sheet is 1.0-2.0 mm, and the method comprises the following steps: an ultrasonic-assisted GTAW pulse arc welding method is adopted, no filler wire is used, the excitation frequency of an ultrasonic power supply is 20kHz, and the maximum output power is 2000W; the welding gun selects a concave spherical acoustic emission end, the radius of the end face of the concave spherical acoustic emission end is 16.5mm, the radius of curvature of the concave spherical acoustic emission end is 27.4mm, and the distance between the concave spherical acoustic emission end and the upper surface of the workpiece is 8-14 mm; the distance from the tip of the tungsten electrode to the bottom surface of the sound emission end is 6.0mm, and the tungsten electrode is protected by argon; the welding current is 60-100A, and the welding speed is 2-2.5 mm/s. The depth-width ratio of the welding seam area is increased, and crystal grains are finer and more uniform; the external ultrasonic field can control the welding heat source and deeply process the metal of the weld pool, and reduce the serious unbalance of the two-phase proportion of austenite and ferrite in a welding seam and a heat affected zone caused by element burning loss, thereby improving the structure and the mechanical property of the joint.

Description

Ultrasonic-assisted GTAW (gas tungsten arc welding) pulsed arc welding method for duplex stainless steel sheet

Technical Field

The invention belongs to the field of special welding, and particularly relates to a ultrasonic-assisted GTAW (gas tungsten arc welding) pulsed arc welding method for a duplex stainless steel sheet.

Background

The microstructure of the duplex stainless steel consists of austenite and martensite or bainite, the ferrite accounts for more than 30% of volume fraction, and the duplex stainless steel integrates the advantages of the austenite stainless steel and the ferrite stainless steel. The duplex stainless steel sheet comprises the following components in percentage by mass: c is more than 0 and less than or equal to 0.085 percent, Si is more than 0 and less than or equal to 1.00 percent, Mn is more than 1.80 percent and less than or equal to 6.00 percent, P is more than 0 and less than or equal to 0.04 percent, S is more than 0 and less than or equal to 0.030 percent, Cr is more than 0 and less than or equal to 22.00 percent, Ni is more than 0 and less than or equal to 3.00 percent, Mo is more than 0.10 and less than or equal to 0.80 percent, N is more than 0 and less than or equal to 0. At present, the method is applied to a plurality of industries such as automobiles, power stations, chemical engineering, pharmacy and the like. The electric arc welding has the advantages of mature technology, simple and convenient operation, easy realization of automation, low cost and the like, and the current duplex stainless steel is mainly connected by the electric arc welding. However, the traditional electric arc has low power density and long heating time, the heat input is difficult to control, the heat affected zone is easily widened, the softening of the joint is aggravated, and the welded joint becomes a weak link of the whole product, and the reasons are mainly as follows: under the action of welding thermal cycle, after ferrite is transformed into austenite, under the action of surface energy of a crystal boundary, large grains are swallowed and small grains are swallowed, so that the grains are easily coarsened; secondly, because the duplex stainless steel is subjected to a special rolling process, a large amount of distortion energy is stored inside, high-energy atoms deviated from an equilibrium position migrate to an equilibrium position with low energy under the action of welding thermal cycle, even if the distortion energy is gradually released to generate deformation recovery and recrystallization, so that the dislocation density is reduced. By combining the characteristics of the duplex stainless steel, it can be seen that the problems of grain coarsening, joint softening and the like of a heat affected zone commonly exist in the duplex stainless steel welding, which are key problems to be solved urgently in the duplex stainless steel welding research process.

The application range of the traditional Gas Tungsten Arc Welding (GTAW) is wider, but the production process of the thin-plate GTAW welding is very difficult, mainly because the energy of a free electric arc heat source used by the traditional GTAW welding is more diffused, the energy distribution acting on the surface of a thin-plate workpiece is not uniform, the overall heat input is improved for ensuring penetration, the local heat input is easily overlarge, and the welding deformation and burn-through are caused to occur occasionally and are difficult to control. Compared with common carbon steel welding, when a duplex stainless steel sheet is welded, because a certain amount of alloy elements are contained, the changes of the stress, the strain, the structure and the performance of a welding joint are extremely sensitive to the distribution of welding heat source heat, and the requirement on the control of the welding heat is higher.

Ultrasonic waves have the advantages of high frequency, cavitation effect, easiness in transmission in media and the like, and are widely applied to the fields of material processing, particularly plastic processing and casting. With the continuous and deep research on the mechanism of the influence of the ultrasonic wave on the metal solidification, the ultrasonic wave and the welding process are combined to gradually attract the attention of welding workers, and the research hotspot is developed. However, at present, ultrasonic vibration is directly applied to welding base materials, strong rigid contact fixation is needed, and the tool and equipment are complex. Yangchunli proposes an ultrasonic auxiliary arc welding method, namely an ultrasonic radiation field is formed in an arc region, and a sound field can control electric arcs and realize deep treatment on a molten pool. In a 304 stainless steel ultrasonic-assisted GTAW welding test, the ultrasonic wave has a compression effect on an electric arc, the electric arc pressure is increased, the ultrasonic-assisted GTAW penetration under the same specification can be increased by more than one time, the weld grains are refined, the size of a fusion area is narrowed, the strength of a welding joint is improved by 8%, and the elongation of the joint is improved by more than 10%. However, because the sound radiation capability of the sound source is insufficient, the welding stability needs to be further improved, and the arc heat source is difficult to regulate and control by using sound energy.

Disclosure of Invention

Aiming at the problems that a duplex stainless steel sheet is easy to deform during welding, a joint is sensitive to heat input, the heat input range is narrow and the like, the invention provides an ultrasonic-assisted GTAW pulse arc welding method for the duplex stainless steel sheet, which does not need wire filling, preheating and postweld heat treatment, and controls the welding heat input to keep the proportion of two phases of austenite and ferrite of a welding seam and a heat affected zone within a reasonable range, thereby ensuring the good structure and mechanical property of the welding joint.

The invention adopts the following technical scheme: a duplex stainless steel sheet ultrasonic-assisted GTAW pulsed arc welding method comprises the following steps:

(1) cutting the steel plate by cold shearing, cleaning the surface of a workpiece to be welded before welding, assembling to form an I-shaped groove, and pressing four corners of the welding plate;

(2) welding a workpiece by adopting an ultrasonic-assisted GTAW (gas tungsten arc welding) pulse arc welding method without filling a welding wire, wherein the excitation frequency of an ultrasonic power supply is 20kHz, and the maximum output power of the ultrasonic power supply is 2000W; the ultrasonic-assisted GTAW pulsed arc welding gun adopts a concave spherical acoustic emission end, the end surface radius of the concave spherical acoustic emission end is 16.5mm, the curvature radius of the concave spherical acoustic emission end is 27.4mm, and the vertical distance between the concave spherical acoustic emission end and the upper surface of a workpiece is 8-14 mm; the diameter of the tungsten electrode is 3.2mm, the tungsten electrode penetrates through the central through hole, the distance from the tip of the tungsten electrode to the bottom surface of the sound emission end is 6mm, the protective gas is argon, and the gas flow is 10-15L/min; the welding current is directly connected with 60-100A, and the welding speed is 2.0-2.5 mm/s;

(3) and after welding, removing an oxide layer on the surface of the welding line by adopting acid pickling passivation treatment to form a passivation film, cooling the passivation film to room temperature in air, and taking down the welding plate.

The invention also has the following technical characteristics:

1. the groove gap is not larger than 0.05mm, because no welding wire is added, if the gap is too large, welding cannot be conducted completely, and metal unfused easily occurs.

2. The thickness of the duplex stainless steel plate is 1.0-2.0 mm.

3. A high-brightness agglomeration area of arc plasma exists in the ultrasonic-assisted GTAW pulsed arc, the arc plasma jumps up and down at a certain frequency and is in a pulsed state, and the pulse frequency is 510-700 Hz, so that the arc energy is more concentrated, the internal energy is more uniformly distributed, and the fusion depth is increased, the grain is refined, and the like.

The invention has the advantages that: the invention utilizes the ultrasonic-assisted GTAW pulse arc welding duplex stainless steel sheet, and an external ultrasonic field acts on an electric arc and a molten pool simultaneously, not only utilizes the ultrasonic vibration characteristic to realize the deep treatment of molten pool metal, but also utilizes ultrasonic energy to compress the electric arc, controls the heat input of the electric arc, improves the traditional welding heat source, ensures that the ultrasonic-assisted GTAW pulse arc welding process has high efficiency, high quality and controllable properties, slows down the temperature reduction rate of a welding seam from the welding heat source, prolongs the phase transition time of ferrite to austenite in the welding seam and a high-temperature heat affected zone, increases the austenite proportion in the welding seam and the high-temperature heat affected zone, ensures that the two-phase proportion of the austenite and the ferrite is more balanced, ensures the tissue and the mechanical property of a duplex stainless steel welding joint, and has the advantages of simple operation, economy, practicality and beautiful welding seam formation.

Drawings

FIG. 1 is a metallographic view of a weld joint according to example 1 of the present invention;

FIG. 2 is a metallographic comparison of a weld in accordance with example 1 of the present invention;

FIG. 3 is an engineering stress-strain diagram of example 1 of the present invention;

FIG. 4 is a gold phase diagram after electrochemical (3.5 wt.% NaCI solution) polarization for example 1 of the present invention.

Detailed Description

Under the condition of a concave spherical surface acoustic emission end, the directional acoustic pressure of the electric arc from outside to inside reaches the maximum, the acoustic confinement effect is strongest, in an ultrasonic-assisted GTAW welding experiment, a confined pulsed electric arc plasma is found for the first time, the electric arc is compressed after ultrasonic action, a highlight agglomeration region appears inside the electric arc, and the electric arc periodically shakes up and down at a certain frequency, and the phenomenon is found to provide possibility for further realizing regulation and control of the welding electric arc heating power by ultrasonic. The method has great application potential for overcoming the influences of softening, deformation and the like of the welding joint of the duplex stainless steel. The following examples are given to illustrate specific embodiments of the present method.

Example 1

The present embodiment is a welded 2.0mm thick S32101 duplex stainless steel plate, which comprises the following chemical components (mass%): c is more than 0.02 and less than or equal to 0.04 percent, Si is more than 0.20 and less than or equal to 1.00 percent, Mn is more than 4.00 and less than or equal to 6.00 percent, P is more than 0.01 and less than or equal to 0.04 percent, S is more than 0 and less than or equal to 0.03 percent, Cr is more than 19.00 and less than or equal to 22.00 percent, Ni is more than 1.00 and less than or equal to 3.00 percent, Mo is more than 0.10 and less than or equal to 0.80 percent, N is more than 0 and less than or equal to 0.25. Taking an S32101 duplex stainless steel plate with the thickness of 2.0mm, observing the surface to be welded, and requiring flatness without defects such as scratches, dents and the like; if the requirements are not met, the welding surface needs to be polished by sand paper, and the parallelism of the welding surface needs to be noticed during polishing, so that the welding surface cannot be polished into a cambered surface; after polishing, cleaning the area to be welded, thoroughly cleaning the welding surface by using alcohol, cleaning oil stains and the like in the 15mm welding seam area, and after cleaning, carrying out next work after the alcohol is thoroughly volatilized; clamping and pressing an S32101 double-phase stainless steel plate with the thickness of 2.0mm to be welded by using a clamp, wherein the specific splicing mode is that two stainless steel sheets are spliced in parallel, the surface is required to be smooth and has no staggered edge, and the splicing gap at a welding joint is ensured not to be larger than 0.05 mm; welding a workpiece to be welded by adopting an ultrasonic-assisted GTAW (gas tungsten arc welding) pulsed arc welding method without filling a welding wire, wherein the excitation frequency of an ultrasonic power supply is 20kHz, and the maximum output power of the ultrasonic power supply is 2000W; the ultrasonic-assisted GTAW pulsed arc welding gun adopts a concave spherical acoustic emission end, the end surface radius of the concave spherical acoustic emission end is 16.5mm, the curvature radius of the concave spherical acoustic emission end is 27.4mm, and the vertical distance between the concave spherical acoustic emission end and the upper surface of a workpiece is 14 mm; the diameter of the tungsten electrode is 3.2mm, the tungsten electrode penetrates through the central through hole, the distance from the tip of the tungsten electrode to the bottom surface of the sound emission end is 6mm, the protective gas is argon with the purity of 99.99%, and the gas flow is 15L/min; the welding current (direct current positive connection) is 100A, and the welding speed is 2.5 mm/s. Good ventilation is maintained during welding to promote rapid cooling of the weld. And after welding, removing an oxide layer on the surface of the welding line by adopting acid pickling passivation treatment to form a passivation film, cooling to room temperature in air, removing the pressing device, and taking down the welding plate.

After the welding is completed through the steps, the depth-to-width ratio of the welding seam area is increased, the grain structure of the welding seam is finer and more uniform, the ratio of two phases of austenite and ferrite is balanced, the corrosion resistance of the welding seam is obviously improved, and the mechanical property of a welding joint is improved. The measured self-corrosion potential of the welding seam area is-186 mV, and the self-corrosion current density of the welding seam is 0.364 mu A/cm²As a softening zone, the average hardness 231(HV30) of the weld zone was improved by 19% as compared with that of ordinary GTAW welding, and the weld joint had a tensile strength of 616.57MPa and an elongation of 45.6% and was broken in the heat-affected zone.

Example 2

This example is a welded 1.0mm thick plate of S32101 duplex stainless steel having a chemical composition identical to that of example 1. Taking an S32101 duplex stainless steel plate with the thickness of 1.0mm, observing the surface to be welded, and requiring flatness without defects such as scratches, dents and the like; if the requirements are not met, the welding surface is polished by sand paper, and the parallelism of the welding surface is required to be noticed during polishing, so that the welding surface cannot be polished into a cambered surface; after polishing, cleaning the area to be welded, thoroughly cleaning the welding surface by using alcohol, cleaning oil stains and the like in the welding seam area within 10mm, and performing the next step after the alcohol is thoroughly volatilized; clamping and pressing an S32101 duplex stainless steel plate with the thickness of 1.0mm to be welded by using a clamp, wherein the specific splicing mode is that two stainless steel sheets are spliced in parallel, the surface is required to be smooth without misalignment, and the splicing gap at the welding joint is ensured not to be larger than 0.02 mm; welding a workpiece to be welded by adopting an ultrasonic-assisted GTAW (gas tungsten arc welding) pulse arc welding method without filling a welding wire, wherein the excitation frequency of an ultrasonic power supply is 20kHz, and the maximum output power of the ultrasonic power supply is 2000W; the ultrasonic-assisted GTAW pulsed arc welding gun adopts a concave spherical acoustic emission end, the end surface radius of the concave spherical acoustic emission end is 16.5mm, the curvature radius of the concave spherical acoustic emission end is 27.4mm, and the vertical distance between the concave spherical acoustic emission end and the upper surface of a workpiece is 12 mm; the diameter of the tungsten electrode is 3.2mm, the tungsten electrode penetrates through the central through hole, the distance from the tip of the tungsten electrode to the bottom surface of the sound emission end is 6mm, the protective gas is argon with the purity of 99.99%, and the gas flow is 13L/min; welding current (direct current positive connection) 75A, and welding speed 2.3 mm/s. Good ventilation is maintained during welding to promote rapid cooling of the weld. And after welding, removing an oxide layer on the surface of the welding line by adopting acid pickling passivation treatment to form a passivation film, cooling to room temperature in air, removing the pressing device, and taking down the welding plate.

After the welding is completed through the steps, the depth-to-width ratio of the welding seam area is increased, the grain structure of the welding seam is finer and more uniform, the ratio of two phases of austenite and ferrite is balanced, the corrosion resistance of the welding seam is obviously improved, and the mechanical property of a welding joint is improved. The measured self-corrosion potential of the welding seam area is-154 mV, and the self-corrosion current density of the welding seam is 0.336 mu A/cm²As a softening zone, the average hardness of a weld zone is 222(HV30), which is improved by 22% compared with the common GTAW welding, the tensile strength of a welding joint is 610.82MPa, the elongation is 41.7%, and the welding joint is broken in the weld zone.

Example 3

In this example, a 2.0mm thick DP780 duplex stainless steel plate is welded, which comprises the following chemical components (by mass): c is more than 0 and less than or equal to 0.085 percent, Si is more than 0 and less than or equal to 0.38 percent, Mn is more than 1.80 and less than or equal to 2.08 percent, P is more than 0.004 and less than or equal to 0.011 percent, S is more than 0.002 and less than or equal to 0.016 percent, Cr is more than 0 and less than or equal to 0.326 percent, Ni is more than 0 and less than or equal to 0.008 percent, N is 0.004 percent, Cu is 0.037 percent, and. Taking a DP780 duplex stainless steel plate with the thickness of 2.0mm, observing the surface to be welded of the steel plate, wherein the steel plate is required to be flat and free from defects such as scratches, dents and the like; if the requirements are not met, the welding surface is polished by sand paper, and the parallelism of the welding surface is required to be noticed during polishing, so that the welding surface cannot be polished into a cambered surface; after polishing, cleaning the area to be welded, thoroughly cleaning the welding surface by using alcohol, cleaning oil stains and the like in the 15mm welding seam area, and after cleaning, carrying out next work after the alcohol is thoroughly volatilized; clamping and pressing a DP780 two-phase stainless steel plate with the thickness of 2.0mm to be welded by using a clamp, wherein the specific splicing mode is that two stainless steel sheets are spliced in parallel, the surface is required to be smooth and has no staggered edge, and the splicing gap at a welding seam is ensured not to be larger than 0.05 mm; welding a workpiece by adopting an ultrasonic-assisted GTAW (gas tungsten arc welding) pulse arc welding method without filling a welding wire, wherein the excitation frequency of an ultrasonic power supply is 20kHz, and the maximum output power of the ultrasonic power supply is 2000W; the ultrasonic-assisted GTAW pulsed arc welding gun adopts a concave spherical acoustic emission end, the end surface radius of the concave spherical acoustic emission end is 16.5mm, the curvature radius of the concave spherical acoustic emission end is 27.4mm, and the vertical distance between the concave spherical acoustic emission end and the upper surface of a workpiece is 13 mm; the diameter of the tungsten electrode is 3.2mm, the tungsten electrode penetrates through the central through hole, the distance from the tip of the tungsten electrode to the bottom surface of the sound emission end is 6mm, the protective gas is argon with the purity of 99.99%, and the gas flow is 13L/min; the welding current (direct current positive connection) is 90A, and the welding speed is 2.2 mm/s. Good ventilation is maintained during welding to promote rapid cooling of the weld. And after welding, removing an oxide layer on the surface of the welding line by adopting acid pickling passivation treatment to form a passivation film, cooling to room temperature in air, removing the pressing device, and taking down the welding plate.

After the welding is completed through the steps, the depth-to-width ratio of a welding seam area is increased, the grain structure of the welding seam is finer and more uniform, the ratio of two phases of austenite and ferrite is balanced, the structure and the mechanical property of a welding joint are improved, the average hardness 175(HV0.5) of a heat affected zone serving as a softening zone is measured to be improved by 10% compared with that of a common GTAW welding joint, the tensile strength of the welding joint is 363.45MPa, the elongation is 24.85%, and the welding joint is broken from a base material.

Example 4

This example is a welded 1.0mm thick DP780 duplex stainless steel plate having the same chemical composition as example 3. Taking a DP780 duplex stainless steel plate with the thickness of 1.0mm, observing the surface to be welded of the steel plate, and requiring flatness without defects such as scratches, dents and the like; if the requirements are not met, the welding surface is polished by sand paper, and the parallelism of the welding surface is required to be noticed during polishing, so that the welding surface cannot be polished into a cambered surface; after polishing, cleaning the area to be welded, thoroughly cleaning the welding surface by using alcohol, cleaning oil stains and the like in the welding seam area within 10mm, and performing the next step after the alcohol is thoroughly volatilized; clamping and pressing a DP780 duplex stainless steel plate with the thickness of 1.0mm to be welded by using a clamp, wherein the specific splicing mode is that two stainless steel sheets are spliced in parallel, the surface is required to be smooth and has no staggered edge, and the splicing gap at a welding seam is ensured not to be larger than 0.02 mm; welding a workpiece by adopting an ultrasonic-assisted GTAW (gas tungsten arc welding) pulse arc welding method without filling a welding wire, wherein the excitation frequency of an ultrasonic power supply is 20kHz, and the maximum output power of the ultrasonic power supply is 2000W; the ultrasonic-assisted GTAW pulsed arc welding gun adopts a concave spherical acoustic emission end, the end surface radius of the concave spherical acoustic emission end is 16.5mm, the curvature radius of the concave spherical acoustic emission end is 27.4mm, and the vertical distance between the concave spherical acoustic emission end and the upper surface of a workpiece is 10 mm; the diameter of the tungsten electrode is 3.2mm, the tungsten electrode penetrates through the central through hole, the distance from the tip of the tungsten electrode to the bottom surface of the sound emission end is 6mm, the protective gas is argon with the purity of 99.99%, and the gas flow is 10L/min; the welding current (direct current positive connection) is 60A, and the welding speed is 2 mm/s. Good ventilation is maintained during welding to promote rapid cooling of the weld. And after welding, removing an oxide layer on the surface of the welding line by adopting acid pickling passivation treatment to form a passivation film, cooling to room temperature in air, removing the pressing device, and taking down the welding plate.

After the welding is completed through the steps, the depth-to-width ratio of a welding seam area is increased, the grain structure of the welding seam is finer and more uniform, the ratio of two phases of austenite and ferrite is balanced, the structure and the mechanical property of a welding joint are improved, the average hardness of a heat affected zone serving as a softening zone is 158(HV0.5) through measurement, compared with a common GTAW welding joint, the average hardness is improved by 13%, the tensile strength of the welding joint is 358.22MPa, the elongation is 23.57%, and the welding joint is broken from a base material.

The external ultrasonic field can control the welding heat source and deeply process the metal of the weld pool, and reduce the serious unbalance of the two-phase proportion of austenite and ferrite in a welding seam and a heat affected zone caused by element burning loss, thereby improving the structure and the mechanical property of a joint.

Claims

1. A double-phase stainless steel sheet ultrasonic-assisted GTAW pulsed arc welding method is characterized by comprising the following steps:

(1) cutting the steel plate by cold shearing, cleaning the surface of a workpiece to be welded before welding, assembling to form an I-shaped groove, wherein the gap of the groove is not more than 0.05mm, and tightly pressing the four corners of the welding plate;

(2) welding a workpiece by adopting an ultrasonic-assisted GTAW (gas tungsten arc welding) pulse arc welding method without filling a welding wire, wherein the excitation frequency of an ultrasonic power supply is 20kHz, and the maximum output power of the ultrasonic power supply is 2000W; the ultrasonic-assisted GTAW pulsed arc welding gun adopts a concave spherical acoustic emission end, the end surface radius of the concave spherical acoustic emission end is 16.5mm, the curvature radius of the concave spherical acoustic emission end is 27.4mm, and the vertical distance between the concave spherical acoustic emission end and the upper surface of a workpiece is 8-14 mm; the diameter of the tungsten electrode is 3.2mm, the tungsten electrode penetrates through the central through hole, the distance from the tip of the tungsten electrode to the bottom surface of the sound emission end is 6mm, the protective gas is argon, and the gas flow is 10-15L/min; the welding current is directly connected with 60-100A, the welding speed is 2.0-2.5 mm/s, a high-brightness agglomeration area of arc plasma exists in the ultrasonic-assisted GTAW pulsating arc, the arc plasma jumps up and down at a certain frequency and is in a pulsating state, and the pulsating frequency is 510-700 Hz;

2. The ultrasonic-assisted GTAW pulsed arc welding method for duplex stainless steel sheets according to claim 1, wherein: the thickness of the duplex stainless steel plate is 1.0-2.0 mm.