CN116604149A - Ferrite stainless steel weld line grain refinement method - Google Patents

Abstract

The invention belongs to the field of welding technology, and in particular relates to a ferritic stainless steel weld seam grain refinement method, which adopts hot wire TIG welding equipment for welding. , The wire feeding speed is matched with the welding speed to achieve a periodic short-circuit bursting process between the welding wire and the molten pool. The ferritic stainless steel weld grain refinement method of the present invention can increase the proportion of equiaxed grains in the ferritic stainless steel weld from about 10% of the traditional weld to more than 90%, and the weld microstructure from the traditional one Coarse columnar grains are dominated by equiaxed grains, and the overall grain size has been significantly refined.

Description

Grain refinement method for ferritic stainless steel weld

technical field

The invention belongs to the field of welding technology, and in particular relates to a grain refinement method for ferritic stainless steel welds.

Background technique

Ferritic stainless steel welded pipes are widely used in the field of automobile exhaust systems and heat exchangers. Generally, automatic pipelines using argon arc welding or laser welding are all self-fluxing welding without adding welding materials. Since ferritic stainless steel does not undergo phase transformation in the full temperature range, its self-fluxing weld structure is generally coarse columnar crystals and a small amount of equiaxed crystals in the central area. The two have a competitive growth relationship when the weld solidifies. In the ferritic stainless steel developed in the early stage, such as 430, the weld is almost entirely composed of columnar grains grown by fusion lines, which seriously reduces the plasticity and toughness of the weld. In order to increase the proportion of equiaxed crystals in the weld, elements such as Ti and Nb are added to ferritic stainless steel. These elements play the role of increasing nucleation points during the solidification process of the weld to increase the proportion of equiaxed crystals in the center of the weld. But even so, the proportion of equiaxed grains in ferritic stainless steel welds generally does not exceed 20%.

Contents of the invention

The object of the present invention is to provide a ferritic stainless steel weld grain refinement method for the defects of the prior art.

Specifically, the ferritic stainless steel weld grain refinement method provided by the present invention adopts hot wire TIG welding equipment for welding. Matching with the welding speed, the welding wire and the molten pool form a periodic short-circuit bursting process.

In the above ferritic stainless steel weld grain refinement method, the distance between the point where the welding wire enters the molten pool and the solidification line of the molten pool is 0.5-5 mm.

In the method for refining grains of ferritic stainless steel welds, the welding wire and the tungsten electrode are located on a plane perpendicular to the base material, and the welding wire passes through the centerline of the welding groove.

In the above method for refining grains of ferritic stainless steel welds, the included angle between the welding wire and the base metal is in the range of 30-60°.

In the above ferritic stainless steel weld grain refinement method, during the welding process, the size of the hot wire current is equal to the product of the cross-sectional area of the welding wire and the current density of the hot wire.

In the above method for refining grains of ferritic stainless steel welds, the range of the current density is 80-150A/mm ² .

In the above ferritic stainless steel weld grain refinement method, the wire feeding speed is 0.6-1.4 times of the welding speed during the welding process.

In the method for grain refinement of the ferritic stainless steel weld mentioned above, the welding groove is type I and the gap is 0 mm.

In the above ferritic stainless steel weld grain refinement method, the ferritic stainless steel includes: 409, 429, 430, 436, 439, 441, 443, 444, 445, 446 ferritic stainless steel.

In the method for refining grains of ferritic stainless steel welds, the thickness of the ferritic stainless steel is less than 2 mm.

The technical solution of the present invention has the following beneficial effects:

(1) The ferritic stainless steel weld grain refinement method of the present invention can increase the proportion of equiaxed grains in the ferritic stainless steel weld from about 10% of the traditional weld to more than 90%, and the weld structure from The traditional coarse columnar crystals have changed to equiaxed crystals, and the overall grain size has been significantly refined;

(2) The ferritic stainless steel weld grain refinement method of the present invention is realized by using commercialized hot wire TIG welding equipment. Under the existing conditions of the welded pipeline, only a hot wire feeding mechanism needs to be added, and the transformation low cost;

(3) The ferritic stainless steel weld grain refinement method of the present invention is suitable for ferritic stainless steel with a thickness below 2 mm, using commercial welding equipment, without reducing the original welding efficiency of the pipeline, By changing the use of welding equipment and matching appropriate welding parameters, the purpose of refining the grain size of the weld can be achieved.

Description of drawings

Various other advantages and benefits will become apparent to those of ordinary skill in the art upon reading the following detailed description of the preferred embodiment. The drawings are only for the purpose of illustrating a preferred embodiment and are not to be considered as limiting the invention.

Fig. 1-Fig. 4 is welding process of the present invention;

Fig. 5 is the metallographic diagram of the 444 ferritic stainless steel weld joint section welded in embodiment 1;

Fig. 6 is the metallographic diagram of the 441 ferritic stainless steel weld joint section welded in embodiment 2;

Fig. 7 is the metallographic diagram of the 441 ferritic stainless steel weld joint section welded in embodiment 3;

Fig. 8 is the metallographic diagram of the 444 ferritic stainless steel weld joint section welded in comparative example 1;

Fig. 9 is the metallographic diagram of the cross-section of the 441 ferritic stainless steel weld joint welded in comparative example 2;

Fig. 10 is the 441 ferritic stainless steel weld seam surface pictures of comparative example 3 welding;

Fig. 11 is the 441 ferritic stainless steel weld joint section metallographic diagram of comparative example 3 welding;

Fig. 12 is a metallographic diagram of the section of the 441 ferritic stainless steel weld joint welded in Comparative Example 4.

Detailed ways

In order to fully understand the purpose, features and effects of the present invention, the present invention will be described in detail through the following specific embodiments. Process method of the present invention except following content, all the other all adopt the routine method or device of this field. Unless otherwise specified, the following nouns and terms have the meanings commonly understood by those skilled in the art.

When a numerical range is disclosed herein, the said range is considered continuous and includes the minimum and maximum values of the range and every value between such minimum and maximum values. Further, when a range refers to an integer, every integer between the minimum and maximum of the range is included. Furthermore, when multiple ranges are provided to describe a feature or characteristics, the ranges may be combined. In other words, unless otherwise indicated, all ranges disclosed herein are to be understood to include any and all subranges subsumed therein.

The general use of hot wire TIG welding equipment is: the welding wire enters the molten pool in front of the forward direction of the welding torch, a hot wire current is applied between the welding wire and the base metal, and the welding wire is heated by resistance heat to achieve the purpose of efficient wire filling. In order to change the thick columnar grains of ferritic stainless steel welds with a thickness below 2 mm into fine equiaxed grains, the inventor improved the use of hot wire TIG welding equipment through creative work. The welding wire enters the molten pool behind the forward direction of the welding torch, and the area in contact with the molten pool is the mushy area at the front of the solidification front of the tail of the molten pool. The purpose of using the hot wire current is not to heat the welding wire, but to adjust the current value of the hot wire and match the wire feeding speed with the welding speed to achieve a periodic short-circuit bursting process between the welding wire and the molten pool, and the bursting frequency is uniform, at 10Hz above. Oscillations generated by blasting are used to promote nucleation and dendrite dissociation in the mushy zone at the solidification front of the tail of the molten pool, so as to achieve the purpose of refining weld grains. The bursting process is shown in Figure 1-4.

In order to achieve a uniform and stable detonation process, the key parameter ranges used in the present invention are as follows:

In order to ensure that the welding wire enters the mushy area at the solidification front of the tail of the molten pool, the distance between the point where the welding wire enters the molten pool and the solidification line of the molten pool is 0.5-5mm. When the distance between the two is less than 0.5mm, the point where the welding wire enters the molten pool is too close to the solidification line, and the temperature here is close to the solidification point, and poor wire spreading is prone to occur; when the distance between the two is greater than 5mm, the welding wire is too close to the tungsten arc , is easily affected by the arc, and the tiny spatter generated by the short-circuit burst will pollute the tungsten electrode, resulting in arc changes, and the tungsten electrode needs to be replaced if it is seriously polluted. Preferably, the distance between the point where the welding wire enters the molten pool and the solidification line of the molten pool is 1-3mm.

In order to make the position of welding wire filling and short-circuit bursting be located on the center line of the molten pool, and the shape of the obtained weld seam is left-right symmetrical, the invention arranges the welding wire and the tungsten electrode on a plane perpendicular to the base metal, and the welding wire passes through the center of the welding groove Wire.

The angle range between the welding wire and the base metal is 30-60°. When the angle between the welding wire and the base metal is less than 30°, the projected area of the welding wire in the vertical direction is larger, the area in contact with the molten pool is larger, the current density is smaller, and it is difficult to form a stable and uniform short-circuit burst; and when When the range of the included angle is greater than 60°, the wire feeding device will be blocked by the welding torch. Preferably, the included angle between the welding wire and the base metal ranges from 40° to 45°.

Wherein, the hot wire current is determined according to the diameter of the welding wire, and the hot wire current = the cross-sectional area of the welding wire * the current density of the hot wire.

Preferably, the current density is in the range of 80-150A/mm ² . When the current density is less than 80A/mm ² , short-circuit bursting will not occur; when the current density is greater than 150A/mm ² , the short-circuit bursting energy is too large and the splash is large.

As an example, for a solid welding wire of φ1.2mm, the current range of the hot wire is 90-170A. For the solid welding wire of φ0.8mm, the current range of the hot wire is 40-75A.

The wire feeding speed needs to be matched with the welding speed. In the present invention, the wire feeding speed is 0.6-1.4 times of the welding speed, so as to obtain fine and uniform weld seam formation. If the wire feeding speed is too small, the time interval between the short-circuit explosion is too long, the stirring of the molten pool by the explosion oscillation is discontinuous, the weld seam ripple spacing is large and not uniform, and the weld seam is poorly formed; if the wire feeding speed is too high , The amount of welding wire filling is too large, the weld reinforcement is too high, and the weld shape is poor.

The conventional parameters of the welded pipe are adopted, and the groove to be welded has no gap and is extruded by the forming roller table. The I-shaped bevel is easy to prepare, and the steel coil can be slit by a shearing machine without additional processing.

Ferritic stainless steel applicable to the present invention includes but not limited to: 409, 429, 430, 436, 439, 441, 443, 444, 445, 446 and other ferritic stainless steels.

The ferritic stainless steel weld grain refinement method of the present invention can increase the proportion of equiaxed grains in the ferritic stainless steel weld from about 10% of the traditional weld to more than 90%, and the weld structure is changed from the traditional one to coarse Columnar crystals are dominant, and equiaxed crystals are dominant, and the overall grain size has been significantly refined.

Example

The present invention is further illustrated below by means of examples, but the present invention is not limited to the scope of the examples. For the experimental methods not indicating specific conditions in the following examples, follow conventional methods and conditions.

Example 1

In this embodiment, 444 ferritic stainless steel with a thickness of 1.5 mm is used as the test material, processed into two test plates of 100 mm×200 mm, and assembled into a group of welded test plates. The welding groove is type I, and the gap is 0mm. The welding equipment uses Panasonic high-efficiency hot wire TIG welding machine, and the welding material uses ER316L solid welding wire with a diameter of 1.2mm. The distance is 1mm. The welding shielding gas uses 99.999% argon, the flow rate is 10L/min, the welding current is 170A, the welding speed is 1m/min, the hot wire current is 100A, and the wire feeding speed is 0.7m/min. The proportion of equiaxed grains is 100%, and the metallographic phase of the welded joint section is shown in Figure 5.

Example 2

In this embodiment, 441 ferritic stainless steel with a thickness of 1.2 mm is used as the test material, processed into two test plates of 100 mm×200 mm, and assembled into a group of welded test plates. The welding groove is type I, and the gap is 0mm. The welding equipment uses Panasonic high-efficiency hot wire TIG welding machine, and the welding material uses φ0.8mm ER308L solid welding wire. The welding wire is fed in behind, and the angle between the welding wire and the base metal plane is about 40°, and the point where the welding wire enters the molten pool and the solidification line of the molten pool The distance is 1mm. The welding shielding gas uses 99.999% argon, the flow rate is 10L/min, the welding current is 140A, the welding speed is 1m/min, the hot wire current is 67A, and the wire feeding speed is 1m/min. The proportion of equiaxed grains is 92%, and the metallographic phase of the welded joint section is shown in Figure 6.

Example 3

In this embodiment, 441 ferritic stainless steel with a thickness of 1.2 mm is used as the test material, processed into two test plates of 100 mm×200 mm, and assembled into a group of welded test plates. The welding groove is type I, and the gap is 0mm. Welding equipment uses Panasonic high-efficiency hot wire TIG welding machine, welding material uses φ1.2mm ER309L solid welding wire, the welding wire is sent in the rear, the angle between the welding wire and the base metal plane is about 40°, the point where the welding wire enters the molten pool and the solidification line of the molten pool The distance is 1mm. The welding shielding gas uses 99.999% argon, the flow rate is 10L/min, the welding current is 140A, the welding speed is 1m/min, the hot wire current is 150A, and the wire feeding speed is 1m/min. The proportion of equiaxed grains is 96%, and the metallographic phase of the welded joint section is shown in Figure 7.

Comparative example 1

In this embodiment, 444 ferritic stainless steel with a thickness of 1.5 mm is used as the test material, processed into two test plates of 100 mm×200 mm, and assembled into a group of welded test plates. The welding groove is type I, and the gap is 0mm. Welding equipment uses Panasonic high-efficiency hot wire TIG welding machine without filling wire. The welding shielding gas uses 99.999% argon, the flow rate is 10L/min, the welding current is 170A, and the welding speed is 0.7m/min. The proportion of equiaxed grains is 5%, and the metallographic phase of the welded joint section is shown in Figure 8.

Comparative example 2

In this embodiment, 441 ferritic stainless steel with a thickness of 1.2 mm is used as the test material, processed into two test plates of 100 mm×200 mm, and assembled into a group of welded test plates. The welding groove is type I, and the gap is 0mm. Welding equipment uses Panasonic high-efficiency hot wire TIG welding machine without filling wire. The welding shielding gas uses 99.999% argon, the flow rate is 10L/min, the welding current is 140A, the welding speed is 1m/min, and the proportion of equiaxed crystals is 9%. The metallography of the welded joint section is shown in Figure 9.

Comparative example 3

In this embodiment, 441 ferritic stainless steel with a thickness of 1.2 mm is used as the test material, processed into two test plates of 100 mm×200 mm, and assembled into a group of welded test plates. The welding groove is type I, and the gap is 0mm. The welding equipment uses Panasonic high-efficiency hot wire TIG welding machine, and the welding material uses ER309L solid welding wire with a diameter of 1.2mm. The distance is 1mm. The welding shielding gas uses 99.999% argon, the flow rate is 10L/min, the welding current is 140A, the welding speed is 1m/min, the hot wire current is 150A, and the wire feeding speed is 0.3m/min. The weld surface is poorly formed, as shown in Figure 10. The metallographic phase of the welded joint section is shown in Figure 11, and the proportion of equiaxed grains is 40%.

Comparative example 4

In this embodiment, 441 ferritic stainless steel with a thickness of 1.2 mm is used as the test material, processed into two test plates of 100 mm×200 mm, and assembled into a group of welded test plates. The welding groove is type I, and the gap is 0mm. The welding equipment uses Panasonic high-efficiency hot wire TIG welding machine, and the welding material uses ER308L solid welding wire with a diameter of 0.8mm. The distance is 1mm. The welding shielding gas uses 99.999% argon, the flow rate is 10L/min, the welding current is 140A, the welding speed is 1m/min, the hot wire current is 67A, and the wire feeding speed is 1.6m/min. The metallographic phase of the welded joint section is shown in Figure 12. The weld reinforcement is too high, and the proportion of equiaxed grains is 50%.

The present invention has been disclosed above with preferred embodiments, but those skilled in the art should understand that these embodiments are only used to describe the present invention, and should not be construed as limiting the scope of the present invention. It should be noted that all changes and replacements equivalent to these embodiments should be considered as falling within the scope of the claims of the present invention. Therefore, the protection scope of the present invention should be determined by the scope defined in the claims.

Claims (10)

1. A ferrite stainless steel weld grain refining method is characterized in that hot wire TIG welding equipment is adopted for welding, welding wires enter a molten pool behind a welding gun in the welding process, and a periodic short circuit explosion process between the welding wires and the molten pool is achieved by adjusting the current value of the hot wires and matching the wire feeding speed with the welding speed.

2. The ferritic stainless steel weld grain refinement method of claim 1, wherein the distance between the weld wire entry molten pool point and the molten pool solidification line is 0.5-5mm.

3. The method of claim 1, wherein the welding wire and tungsten electrode are positioned on a plane perpendicular to the base material and the welding wire passes through the center line of the welding groove.

4. The ferritic stainless steel weld grain refinement method of claim 1, wherein the welding wire has an included angle with the base material in the range of 30 ° to 60 °.

5. The ferritic stainless steel weld grain refinement method of claim 1, wherein the magnitude of the hot wire current is equal to the product of the wire cross-sectional area and the hot wire current density during welding.

6. The ferritic stainless steel weld grain refinement method according to claim 5, wherein the current density ranges from 80 to 150A/mm ² 。

7. The ferritic stainless steel weld grain refinement method of claim 1, wherein a wire feed speed during welding is 0.6 to 1.4 times a welding speed.

8. The method for refining the ferrite stainless steel weld grains according to claim 1, wherein the welding groove is of an I type and the gap is 0mm.

9. The ferritic stainless steel weld grain refinement method of claim 1, wherein the ferritic stainless steel includes: 409. 429, 430, 436, 439, 441, 443, 444, 445, 446 ferritic stainless steel.

10. The ferritic stainless steel weld grain refinement method according to claim 1, wherein the thickness of the ferritic stainless steel is 2mm or less.