CN110560894A - High-nitrogen steel composite welding method capable of simultaneously protecting two sides by different protective gases - Google Patents

Abstract

The invention proposes a high-nitrogen steel composite welding method with simultaneous protection on both sides by different shielding gases, which belongs to the field of welding technology. The invention adopts laser-arc welding of high-nitrogen steel plates, and two welding workpieces are placed on a copper plate with a rectangular through groove in a butt joint form, and are fixed together with the copper plate on a workbench. The joint gap of the weldment is formed between two welding workpieces. The laser beam emitted by the laser welding head is coaxial with the gap between the workpieces to be welded, and is irradiated vertically on the front of the workpiece to be welded, and the welding torch is placed on the front of the workpiece to be welded. A 95% Ar+5% CO2 mixed shielding gas output coaxially with the welding torch is provided above the workpiece. The rectangular through slot on the copper plate is located directly below the welding gap, the rectangular through slot faces upwards, nitrogen gas is introduced into both ends of the through slot, and a gas temporary space is formed by the lower surface of the welding workpiece and the rectangular through slot. The nitrogen in the rectangular channel can increase the nitrogen activity outside the molten pool, and inhibit the weld porosity and nitrogen loss. At the same time, Ar+CO2 is used as the upper shielding gas, so that the molten droplets are refined and the welding process is more stable.

Description

A hybrid welding method for high nitrogen steel with simultaneous protection on both sides by different shielding gases

technical field

The invention belongs to the field of welding technology and relates to a laser-arc composite welding method for high nitrogen steel with simultaneous protection on both sides by different shielding gases.

Background technique

High-nitrogen austenitic stainless steel (referred to as high-nitrogen steel), the mass fraction of nitrogen generally exceeds 0.4%, mainly uses nitrogen to partially or completely replace nickel to achieve austenitization, because of its good mechanical properties and corrosion resistance It has received widespread attention and has been widely used in the fields of aviation, weaponry, medical treatment and low temperature industry.

High nitrogen steel is used as a structural material, and its weldability is related to the wide application and promotion of high nitrogen steel. When welding high-nitrogen steel under normal pressure, nitrogen is easy to escape and form nitrogen bubbles in the molten pool. Due to the short solidification time of the molten pool, the bubbles cannot escape from the molten pool in time, and finally form in the weld pool. Nitrogen pores are formed. The formation of nitrogen pores also reduces the content of solid solution nitrogen, resulting in a decrease in joint performance. Therefore, how to take effective measures to suppress the porosity and nitrogen loss of high-nitrogen steel welded joints has become one of the main issues studied by scholars from various countries.

Chinese patent CN106346171A discloses a high-nitrogen steel pressurized welding device and a method for welding high-nitrogen steel by using the device. The welding workpiece is placed in a sealed welding room, and the sealed welding room is connected to a gas mixing room and a vacuum pump through a gas pipeline. Control system shielding gas composition, system total pressure and cooling parameters can achieve fixed nitrogen content in high-nitrogen steel welds, improve the mechanical properties of high-nitrogen steel welds, use the system of the present invention for high-nitrogen steel welding, and the nitrogen content of welds can reach parent More than 95% of the material. But this method is not suitable for the welding of some medium and large components.

Chinese patent CN109128546A discloses a laser spot welding-furnace brazing compound welding method for high-nitrogen steel. This method needs to use laser spot welding to spot-weld and fix the weldment in advance, and then coat the solder paste on the workpiece to be welded. On the surface to be welded, use the brazing process in the furnace to carry out side-to-side welding on positions other than the first step of laser spot welding. When the invention is welded, the nitrogen element of the high-nitrogen steel will not be lost, and pores are not easy to appear, and the mechanical properties of the brazed joint are better. powerful. But this method is loaded down with trivial details technology, and work efficiency is low.

Chinese patent CN105772944A discloses a welding device and a welding method for solving high-nitrogen steel welding pores and improving joint strength. In this invention, the walls of two water-passing copper pipes are placed on both sides of the groove of the weldment, and the excitation coil is placed on the back of the welding workpiece. The laser beam is irradiated vertically on the front of the welding workpiece, and the welding torch is placed on the front of the welding workpiece. bundles, weldment joint gaps, and field coil coaxial lines. The method solves the problems in the prior art that the high nitrogen steel is easy to generate gas, nitrides and the like during the welding process. However, the test device in this invention is complex and requires two numerically controlled workbenches to jointly drive the movement of the workpiece, which is not suitable for mass production in engineering.

Contents of the invention

The technical solution of the present invention is to provide a high-nitrogen steel composite welding method with simultaneous protection on both sides by different protective gases. By using different protective gases to simultaneously protect the upper and lower surfaces of the welded workpiece, the existing high-nitrogen steel fusion welding technology under normal pressure is solved. Unstable welding quality, seam porosity and nitrogen loss problems, improve joint strength, is a welding method suitable for mass production in engineering. The technical scheme adopted in the present invention is as follows:

A high-nitrogen steel composite welding method with simultaneous protection on both sides by different shielding gases, comprising the following steps:

The welding workbench is installed under the laser welding head, and the two welding workpieces are placed on the copper plate with a rectangular through groove in the form of butt joint, and are fixed on the workbench together with the copper plate. The joint gap of the weldment is formed between the two welding workpieces, and there is a groove on the front of the welding workpiece and the joint gap. The laser beam emitted by the laser welding head is coaxial with the gap between the workpieces to be welded, and is irradiated vertically on the front of the workpiece to be welded, and the welding torch is placed on the front of the workpiece to be welded. A 95% Ar+5% CO2 mixed shielding gas output coaxially with the welding torch is provided above the workpiece, and the gas flow rate is 15-20L/min. The rectangular through slot on the copper plate is located directly below the welding gap, the rectangular through slot faces upwards, nitrogen gas is injected into both ends of the through slot, the gas flow rate is 8-12L/min, and a gas temporary gas flow is formed by the lower surface of the welding workpiece and the rectangular through slot. Leave space.

The present invention is also characterized in that further, the angle between the axis of the welding torch and the axis of the laser beam is 30°.

Further, the power of the laser is 2.0-3.5KW, the defocus of the laser beam is -2mm; the type of welding torch is MIG or MAG; the arc welding current of the welding torch is 180-300A, the arc voltage is 22-28V, and the arc length is 12-15mm; The diameter of the welding wire is Φ1.2mm;

Further, the laser beam emitted by the laser can be any one of the _CO2 gas laser beam, Nd:YAG solid-state laser beam, semiconductor laser beam, disk laser beam or fiber laser beam; the composite welding heat source can be a laser beam -TIG hybrid welding, laser-MIG hybrid welding, laser-MAG hybrid welding, etc.

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

(1) Ar+CO2 is used as the shielding gas above the weldment to refine the welding droplets and increase the transfer frequency of the droplets, so that the welding process is stable and there is no spatter on the surface of the weldment;

(2) N2 is used as a shielding gas under the weldment, which increases the nitrogen activity outside the molten pool, inhibits the transformation of nitrogen to nitrogen in the weld, and then inhibits the formation of nitrogen pores in the weld. At the same time, the larger nitrogen activity outside the molten pool also avoids excessive nitrogen loss in the weld.

(3) The laser-arc composite heat source can eliminate the defects of a single heat source, and has the advantages of increasing the penetration depth, increasing the welding speed, and realizing high-efficiency and high-quality welding;

The present invention adopts a variety of composite welding heat sources, such as laser-TIG, laser-MIG, laser-MAG, etc., and the lasers used include YAG, CO2 lasers, disk lasers, semiconductor lasers, etc.

(4) The device adopted in the present invention is simple, only adds a copper plate with a rectangular slot, the device is easy to manufacture, and the cost is relatively low;

(5) The present invention has the advantages of flexible process, suitable for industrial mass production, and can effectively reduce the porosity of the weld and improve the strength of the welded joint.

Description of drawings

Fig. 1 is the working condition schematic diagram of the present invention;

Fig. 2 is a schematic diagram of a copper plate with a rectangular slot;

Fig. 3 schematic diagram of laser-arc hybrid welding device;

Figure 4 is a schematic diagram of the docking of workpieces to be welded;

Figure 5a is an X-ray flaw detection diagram of a conventional composite welded joint;

Figure 5b is an X-ray flaw detection diagram of a double-sided shielded composite welded joint with different shielding gases;

Figure 6 is a histogram of nitrogen content under different welding methods.

In the figure: 1 working table, 2 copper plate with rectangular slot, 3 laser welding head, 4 welding torch, 5 high nitrogen steel plate, 6 fixture, 7 air inlet hole, 8 rectangular slot, 9 welding wire, 10 groove, 11 welding gap.

Detailed ways

The present invention will be described in detail below in conjunction with the accompanying drawings and specific embodiments.

The present invention is a high-nitrogen steel composite welding method using different shielding gases to simultaneously protect both sides. The welding conditions are shown in Figures 1-4. The high-nitrogen steel plate 5 is placed above the copper plate 2 with a rectangular through groove in a butt joint manner, and the high-nitrogen steel plate 5 and the copper plate 2 are fixed on the workbench 1 by using the clamp 6 . A welding gap 11 is formed between the two high-nitrogen steel plates 5 , and grooves 10 are formed on the front of the welding workpiece and at the welding gap 11 . The rectangular through groove 8 on the copper plate 2 with the rectangular through groove is located directly below the welding gap 11, and the opening of the rectangular through groove faces upward. Before welding, 8-12 L/min nitrogen gas is introduced from the air inlet holes 7 on both sides of the copper plate. Air inlet 7 links to each other with gas bottle by sebific tube, controls the nitrogen flow size by the flow meter on the gas bottle. The laser beam emitted by the laser welding head 3 vertically passes through the welding gap 11 of the two high-nitrogen steel plates 5 , and the welding torch 4 is placed on the front of the high-nitrogen steel plate 5 . The included angle between the axis of the welding torch 4 and the axis of the laser welding head 3 is 30°. During welding, a 95% Ar+5% CO2 mixed shielding gas output coaxially with the welding torch 4 is provided above the high nitrogen steel plate 5 . The type of welding torch 4 is MIG or MAG; the laser is any one of YAG laser, CO2 laser, disk laser and semiconductor laser. In the traditional welding method, the shielding gas only uses 95% Ar+5% CO2 or Ar+N2, which may easily cause problems such as many pores in the weld or unstable welding process. However, in the present invention, nitrogen gas is introduced into the rectangular through groove of the copper plate, which effectively suppresses the formation of nitrogen pores in the weld seam, and also avoids serious nitrogen loss in the weld seam. 95% Ar + 5% CO2 is injected into the protective gas above, which refines the size of welding droplets and makes the welding process more stable.

Example 1 Double-sided shielded welding of 8.0mm thick high-nitrogen steel with different shielding gases

Step 1: Use an angle grinder to remove the oxide film on the surface of two high-nitrogen steel plates with a thickness of 8.0mm, and then use acetone to remove the surface oil stains. The high-nitrogen steel plates are prefabricated with 30° grooves and 3mm blunt edges, and the two high-nitrogen steel plates are prefabricated with welding gaps 0.6mm;

Step 2: Place two high-nitrogen steel plates on top of the copper plate with a rectangular through slot in a butt joint form, and fix the workpiece and the copper plate on the workbench with a clamp.

Step 3: Introduce nitrogen gas with a flow rate of 8L/min into the air intake hole to form a temporary space for nitrogen gas in the rectangular channel.

Step 4: Use laser vertical irradiation welding on the high-nitrogen steel plate, the YAG laser power is 3.0KW, and the laser beam defocus is -2mm; the welding torch is welded on the front of the welding workpiece, and the type of welding torch is MIG; the arc welding current of the welding torch is 220A , The arc voltage is 24.8V, the arc length is 12mm, and the welding speed is 0.8m/min; the welding wire diameter of the welding torch is Φ1.2mm, and the 95%Ar+5%CO2 mixed protective gas output coaxially with the welding torch is provided above the workpiece, and the gas flow rate is 17L /min

Example 2 Different shielding gas double-sided shielded welding 12.0mm thick high nitrogen steel

Step 1: Use an angle grinder to remove the oxide film on the surface of two high-nitrogen steel plates with a thickness of 12.0mm, and then use acetone to remove the surface oil stains. The high-nitrogen steel plates are prefabricated with 30° grooves and 5mm blunt edges, and the welding gap between the two plates of the workpiece to be welded is prefabricated. 0.8mm;

Step 2: Place two high-nitrogen steel plates on top of the copper plate with a rectangular through-slot in a butt joint form, and fix the workpiece high-nitrogen steel plate and copper plate on the workbench with a clamp.

Step 3: Introduce nitrogen gas with a flow rate of 10L/min into the air inlet hole, and form a temporary space for nitrogen gas in the rectangular channel.

Step 4: Use laser vertical irradiation welding above the metal material to be welded. The YAG laser power is 3.8KW, and the laser beam defocus is -2mm; the welding torch is welded on the front of the welding workpiece, and the type of welding torch is MIG; the arc welding current of the welding torch 300A, arc voltage 30V, arc length 14mm, welding speed 0.8m/min; welding torch wire diameter Φ1.2mm, 95% Ar+5% CO2 mixed shielding gas output coaxially with the welding torch is provided above the workpiece, and the gas flow rate is 17L /min.

Referring to Fig. 5, Fig. 5a is an X-ray flaw detection diagram of a conventional composite welded joint; Fig. 5b is an X-ray flaw detection diagram of a composite welded joint protected on both sides by different shielding gases. It can be seen that the quality of the joint obtained by welding with different shielding gases on both sides of the present invention is better, and the internal flaw detection results show that the inside of the welding seam is smoother, free of bubbles, and the welding is stronger.

Referring to Fig. 6, the histogram of nitrogen content under different welding methods, it can be seen that the nitrogen content in the conventional composite welded joint is about 0.4, while the nitrogen content in the gas double-sided shielded composite welded joint proposed by the present invention is about 0.55. The nitrogen content is higher than that in conventional composite welding joints. Therefore, the gas double-sided shielded composite welding method of the present invention increases the nitrogen content of the welding joints, avoids nitrogen loss, and has better effects.

Claims (5)

1. a high-nitrogen steel composite welding method for simultaneously protecting two sides by different protective gases is characterized in that:

Adopting a laser-arc welding high-nitrogen steel plate, adopting Ar + CO2 as protective gas above the high-nitrogen steel plate, placing two welding workpieces on a copper plate with a rectangular through groove in a butt joint mode, and fixing the two welding workpieces on a workbench together with the copper plate;

a joint gap of a weldment is formed between the two welding workpieces; a laser beam emitted by the laser welding head vertically penetrates through a welding gap between the two high-nitrogen steel plates and vertically irradiates the front side of the workpiece to be welded, and the welding gun is arranged on the front side of the workpiece to be welded;

Providing 95% Ar + 5% CO2 mixed protective gas coaxially output with the welding gun above the workpiece, wherein the gas flow is 15-20L/min; the rectangular through groove on the copper plate is positioned right below the welding gap, the opening of the rectangular through groove is upward, nitrogen is introduced into two ends of the through groove, the gas flow is 8-12L/min, and a gas temporary holding space is formed by the lower surface of the welding workpiece and the rectangular through groove.

2. the method for the composite welding of the high-nitrogen steel with the simultaneous protection of the two sides by the different shielding gases as set forth in claim 1, wherein an included angle between the axis of the welding gun and the axis of the laser beam is 30 °.

3. The high-nitrogen steel composite welding method capable of simultaneously protecting two surfaces by different protective gases as claimed in claim 1, characterized in that: the power of the laser is 2.0-4.0KW, and the defocusing amount of the laser beam is-2 mm; the type of welding gun is MIG or MAG; the arc welding current of the welding gun is 180-300A, the arc voltage is 22-30V, and the arc length is 12-15 mm; the diameter of the welding wire of the welding gun is phi 1.2 mm.

4. the high-nitrogen steel composite welding method capable of simultaneously protecting two surfaces by different protective gases as claimed in claim 1, characterized in that: the laser beam emitted by the laser is CO₂A gas laser beam, an Nd-YAG solid laser beam, a semiconductor laser beam, a disc-type laser beam or an optical fiber laser beam.

5. The high-nitrogen steel composite welding method capable of simultaneously protecting two surfaces by different protective gases as claimed in claim 1, characterized in that: the composite welding heat source is laser-TIG composite welding, laser-MIG composite welding or laser-MAG composite welding.