CN105081574B - A Method for Reducing Invar Steel Welding Hot Cracking Tendency by Layered Pulse Laser - Google Patents

Abstract

A method for reducing welding hot cracking tendency of invar steel by layered pulse laser belongs to the technical field of laser welding. The method adopts layered pulse laser to control laser energy, realizes preheating-welding-postwelding heating in each laser period, the preheating laser plays a role in reducing welding temperature gradient, the welding laser realizes the connection of weld metal, and the postwelding heating laser plays a role in reducing the cooling rate of the weld metal after welding. The preheating temperature and range, the welding heat input quantity and the post-welding heat energy are controlled by adjusting the layered laser power and the pulse width to control the layered laser energy, and the welding temperature gradient and the post-welding cooling speed are adjusted by combining the control of the pulse frequency, so that the purpose of reducing the welding stress of invar steel laser welding is achieved, and the problem of invar steel welding hot cracks is solved. The method can greatly improve the welding speed and reduce the welding heat crack tendency of the invar steel. The welding speed can reach 500-800mm/min, and the cooling rate of the welded weld metal is reduced by 50-80 ℃/s.

Description

A Method for Reducing Invar Steel Welding Hot Cracking Tendency by Layered Pulse Laser

technical field

The invention relates to a method for reducing the thermal cracking tendency of invar steel welding by layered pulse laser, and belongs to the technical field of laser welding.

Background technique

Invar steel (Invar steel, also known as Invar steel) is a FeNi36 alloy. Its linear expansion coefficient at room temperature is lower than 1.6×10 ^-6 k ^-1 , which is about one-tenth of that of low-carbon steel, and in a large temperature range The internal change is very small, so it is widely used in precision measuring devices, electronics industry and LNG ships. As the status of natural gas in the energy field becomes more and more important, the LNG ship for long-distance transportation of natural gas has developed rapidly as a difficult and high value-added ship type, and the liquid cargo tank welded by Invar steel film The insulation system shield is the most difficult part to build.

Invar steel has a single-phase austenitic structure and is highly sensitive to hot cracking. The welding hot crack problem seriously affects the welding quality and production efficiency. Invar steel is easy to form hot cracks and reheat cracks during welding, and there are strict requirements on the welding heat input and welding process, even when using tungsten argon arc welding (TIG welding) with relatively concentrated heat and small heat input The problem of thermal cracking has not been solved well, the requirements for welding technology and welding operator level are very strict, and the production efficiency and automation degree are low.

Welding hot cracking refers to cracks generated at high temperature during welding, characterized by cracking along the original austenite grain boundary, and the tendency of welding hot cracking mainly depends on the plasticity and stress of the weld metal when it is in the brittle temperature range of liquid-solid coexistence. Therefore, in order to reduce the tendency of hot cracking, solve the welding hot cracking problem of invar steel and improve production efficiency, there are currently two main methods, one is to improve the plasticity of the weld metal, and the other is to reduce the welding stress.

(1) Filling materials are added to prevent the formation of low-melting eutectic products of S and P at the austenite grain boundary of invar steel, which will cause grain boundary embrittlement, so as to improve the plasticity of the material and reduce the tendency of welding hot cracking. Adding elements such as Mn, Ti, Ca, Nb and C can reduce the welding hot cracking tendency of invar steel, but the added filler material will increase the linear expansion coefficient of the weld, destroy the low expansion performance of invar steel, and affect Low temperature mechanical properties and application value of welded joints;

(2) Reduce welding stress. Strictly control the welding process parameters, reduce the welding heat input, and adopt the solid phase connection method or the high energy beam welding method with highly concentrated heat. Although the friction stir welding method can realize the welding of invar steel, it is difficult to connect the invar steel film with a thickness of only 0.7mm, and the problems such as welding deformation limit its application. Since the laser is a high-energy beam heat source, the welding heat input of laser welding Invar steel is significantly lower than that of argon tungsten arc welding, and a crack-free welded joint can be obtained, but the welding speed is too slow.

When the welding power is increased in order to increase the welding speed, due to the high concentration of laser welding energy (the aspect ratio can reach 15: 1), the temperature gradient between the weld seam and the surrounding metal material increases sharply, and the cooling speed of the weld metal after welding Soon, the problem of welding stress became more prominent, and it was easy to form welding hot cracks, which seriously restricted the improvement of welding speed.

It can be seen from the above analysis that in order not to affect the low expansion properties of invar steel, the method of adding alloy elements to improve plasticity cannot be used, and only the method of reducing welding stress can be used to reduce the welding hot cracking tendency of invar steel. Reducing the welding heat input and adopting the high-energy beam welding method is the development direction of high-speed and high-quality welding of Invar steel. However, due to the high-energy beam welding method, the high welding temperature gradient and the fast cooling speed of the weld metal after welding are limited, and the welding speed and production efficiency are difficult. A substantial increase. Reducing the temperature gradient and post-weld cooling rate during laser welding is the key to solving this problem, especially the temperature gradient and cooling rate when the weld metal is in the brittle temperature range where liquid-solid phase coexists during post-weld cooling. In order to solve this problem, a layered pulse laser welding method for invar steel is proposed, which realizes layered control of laser energy in each cycle of pulsed laser, and realizes preheating-welding-post-welding in one laser cycle Heat, preheating laser plays the role of reducing the welding temperature gradient, welding laser realizes the connection of weld metal, post-weld thermal laser plays the role of reducing the cooling rate of weld metal after welding, thereby reducing the welding hot cracking of invar steel tendency.

Contents of the invention

The invention provides a method for reducing the hot cracking tendency of invar steel welding by layered pulse laser. In each cycle of the laser, the laser energy is controlled by a layered pulse laser, and preheating-welding-post-heating is realized in each laser cycle. The preheating laser plays the role of reducing the welding temperature gradient, and the welding laser realizes the welding seam For the connection of metals, the post-weld thermal laser can reduce the cooling rate of the weld metal after welding. By adjusting the layered laser power and pulse width to control the layered laser energy to control the preheating temperature and range, welding heat input and post-weld heat energy, combined with pulse frequency control to adjust the welding temperature gradient and post-weld cooling rate, to achieve The purpose of reducing the welding stress of invar steel laser welding is to solve the problem of thermal cracking of invar steel welding. By this method, the welding speed can be greatly increased and the welding hot cracking tendency of the invar steel can be reduced.

The technical scheme adopted by the present invention is: a method for reducing the hot cracking tendency of invar steel welding by layered pulse laser, and the method adopts the following steps:

(1) Clean the joint surface of the cut invar steel specimen with ethanol, then rinse it with water and dry it with a fan, put it in the fixture of the welding workbench and fix it, and fix it with laser spot welding at the beginning and end of the weld;

(2) Adjust the distance between the height of the laser welding head and the surface of the invar steel specimen to be 80-100mm, the positive defocus of the laser is 3-8mm, and adjust the distance between the shielding gas nozzle and the surface of the invar steel specimen to be 45 degrees at a distance of 10-15mm Corner, protective gas flow 10-15L/min;

(3) Set layered pulse laser, layered pulse laser includes preheating laser, welding laser, post-welding heat laser, preheating laser power is 80-240 watts, pulse width is 0.5-3ms, welding laser power is 300- 550 watts, the pulse width is 2-5ms, the post-welding thermal laser power is 80-240 watts, the pulse width is 0.5-3ms; set the preheating process of the preheating laser, the welding process of the welding laser, and the post-welding thermal laser Cohesion relationship between post-welding and post-heating processes;

(4) Turn on the laser welding machine, the laser pulse frequency is 20-60 Hz, the welding speed is 200-800mm/min, and the diameter of the welding point is adjusted to 0.5mm;

(5) Turn on the CAD drawing function of the automatic operating system of the laser welding machine, and perform welding according to the welding path generated by the computer;

(6) After laser welding, take out the Invar steel welding specimen for performance testing.

The preheating process of the preheating laser, the welding process of the welding laser, and the post-welding post-heating process of the post-weld heat laser are sequentially and continuously performed.

The time interval between the preheating process of the preheating laser and the welding process of the welding laser is 0.5-3ms, and the time interval between the welding process of the welding laser and the post-welding heat process of the post-weld heat laser is 0.5-3ms. 3ms.

The preheating process of the preheating laser and the welding process of the welding laser are carried out continuously, and the time interval between the welding process of the welding laser and the post-weld heat process of the post-weld heat laser is 0.5-3ms.

The time interval between the preheating process of the preheating laser and the welding process of the welding laser is 0.5-3ms, and the welding process of the welding laser and the post-welding heat process of the post-weld heat laser are continuously carried out.

The beneficial effects of the present invention are:

1. Through layered pulse laser energy control, the temperature gradient of the weld metal in the brittle temperature zone can be reduced by 20-55°C/mm;

2. Through layered pulse laser energy control, the cooling rate of the weld metal after welding can be reduced by 50-80°C/s;

3. Through layered pulse laser energy control, the welding speed can reach 500-800mm/min;

4. Through the layered control of laser energy in each pulse period, the preheating before welding, welding and heat after welding are integrated in one pulse period, and the process parameters can be designed according to the needs. The parameter design is convenient and flexible. Wide range of options;

5. No need for other auxiliary equipment, will not increase the cost, and avoid the problem of mutual coordination when multiple devices are used at the same time;

6. The welding temperature gradient and post-weld cooling rate are reduced, thereby reducing the welding hot cracking tendency of Invar steel.

Description of drawings

Figure 1 is a schematic diagram of layered pulsed laser scheme 1.

Fig. 2 is a schematic diagram of scheme 2 of layered pulsed laser.

Fig. 3 is a schematic diagram of scheme 3 of layered pulsed laser.

FIG. 4 is a schematic diagram of scheme 4 of layered pulsed laser.

FIG. 5 is a schematic diagram of layered pulsed laser scheme 5 .

detailed description

The schematic diagram of the technical scheme for reducing the hot cracking tendency of invar steel welding by layered pulse laser is shown in Figure 1-5. In each pulse period, the laser energy is divided into three layers: preheating laser, welding laser and post-welding thermal laser. The specific laser energy layering form can be one of the ones in Figure 1-5, and can be selected according to the need to reduce the temperature gradient and reduce the post-weld cooling rate in practical applications. The difference between the five technical solutions is mainly the connection relationship between the preheating process of the preheating laser, the welding process of the welding laser, and the post-welding post-heating process of the post-weld heat laser, that is, whether there is a time interval or continuous.

Figure 1 represents the layered pulsed laser scheme 1:

(1) Clean the joint surface of the cut invar steel specimen with ethanol, then rinse it with water and blow it dry with a fan, put it into the fixture of the welding workbench, and fix it with laser spot welding at the beginning and end of the weld, To prevent misalignment deformation during welding;

(2) Adjust the distance between the height of the laser welding head and the surface of the invar steel specimen to be 80-100mm, the positive defocus of the laser is 3-8mm, and adjust the distance between the shielding gas nozzle and the surface of the invar steel specimen to be 45 degrees at a distance of 10-15mm Corner, protective gas flow 10-15L/min;

(3) Set layered pulse laser energy separately, preheating laser power 100-240 watts, pulse width 0.5-3ms, welding laser power 300-550 watts, pulse width 2-5ms, post-welding thermal laser power 80-150 watts , the pulse width is 0.5-3ms, there is no time interval between layered pulse lasers, and it is carried out continuously;

(4) Turn on the laser welding machine, the laser pulse frequency is 20-60 Hz, the welding speed is 200-800mm/min, and the diameter of the welding point is adjusted to 0.5mm;

(5) Turn on the CAD drawing function of the automatic operating system of the laser welding machine, and perform welding according to the welding path generated by the computer;

(6) After laser welding, take out the Invar steel welding specimen for performance testing.

Figure 2 represents the layered pulsed laser scheme 2:

(1) Clean the joint surface of the cut invar steel specimen with ethanol, then rinse it with water and blow it dry with a fan, put it into the fixture of the welding workbench, and fix it with laser spot welding at the beginning and end of the weld, To prevent misalignment deformation during welding;

(2) Adjust the distance between the height of the laser welding head and the surface of the invar steel specimen to be 80-100mm, the positive defocus of the laser is 3-8mm, and adjust the distance between the shielding gas nozzle and the surface of the invar steel specimen to be 45 degrees at a distance of 10-15mm Corner, protective gas flow 10-15L/min;

(3) Set layered pulse laser energy respectively, preheating laser power 80-150 watts, pulse width 0.5-3ms, welding laser power 300-550 watts, pulse width 2-5ms, post-welding thermal laser power 100-240 watts , the pulse width is 0.5-3ms, there is no time interval between layered pulse lasers, and it is carried out continuously;

(4) Turn on the laser welding machine, the laser pulse frequency is 20-60 Hz, the welding speed is 200-800mm/min, and the diameter of the welding point is adjusted to 0.5mm;

(5) Turn on the CAD drawing function of the automatic operating system of the laser welding machine, and perform welding according to the welding path generated by the computer;

(6) After laser welding, take out the Invar steel welding specimen for performance testing.

Figure 3 shows the layered pulsed laser scheme 3:

(1) Clean the joint surface of the cut invar steel specimen with ethanol, then rinse it with water and blow it dry with a fan, put it into the fixture of the welding workbench, and fix it with laser spot welding at the beginning and end of the weld, To prevent misalignment deformation during welding;

(2) Adjust the distance between the height of the laser welding head and the surface of the invar steel specimen to be 80-100mm, the positive defocus of the laser is 3-8mm, and adjust the distance between the shielding gas nozzle and the surface of the invar steel specimen to be 45 degrees at a distance of 10-15mm Corner, protective gas flow 10-15L/min;

(3) Turn on the laser welding machine, the laser pulse frequency is 20-60 Hz, the welding speed is 200-800mm/min, and the diameter of the welding point is adjusted to 0.5mm;

(4) Set layered pulse laser energy respectively, preheating laser power 80-150 watts, pulse width 0.5-3ms, welding laser power 300-550 watts, pulse width 2-5ms, post-welding thermal laser power 100-240 watts , pulse width 0.5-3ms. The time interval between the preheating laser and the welding laser is 0.5-3ms, and the time interval between the welding laser and the post-welding heat laser is 0.5-3ms;

(5) Turn on the CAD drawing function of the automatic operating system of the laser welding machine, and perform welding according to the welding path generated by the computer;

(6) After laser welding, take out the Invar steel welding specimen for performance testing.

Figure 4 represents the layered pulsed laser scheme 4:

(1) Clean the joint surface of the cut invar steel specimen with ethanol, then rinse it with water and blow it dry with a fan, put it into the fixture of the welding workbench, and fix it with laser spot welding at the beginning and end of the weld, To prevent misalignment deformation during welding;

(2) Adjust the distance between the height of the laser welding head and the surface of the invar steel specimen to be 80-100mm, the positive defocus of the laser is 3-8mm, and adjust the distance between the shielding gas nozzle and the surface of the invar steel specimen to be 45 degrees at a distance of 10-15mm Corner, protective gas flow 10-15L/min;

(3) Turn on the laser welding machine, the laser pulse frequency is 20-60 Hz, the welding speed is 200-800mm/min, and the diameter of the welding point is adjusted to 0.5mm;

(4) Set layered pulse laser energy respectively, preheating laser power 80-150 watts, pulse width 0.5-3ms, welding laser power 300-550 watts, pulse width 2-5ms, post-welding thermal laser power 100-240 watts , pulse width 0.5-3ms. The time interval between the preheating laser and the welding laser is 0.5-3ms, and there is no time interval between the welding laser and the post-welding heat laser;

(5) Turn on the CAD drawing function of the automatic operating system of the laser welding machine, and perform welding according to the welding path generated by the computer;

(6) After laser welding, take out the Invar steel welding specimen for performance testing.

Figure 5 shows the layered pulsed laser scheme 5:

(1) Clean the joint surface of the cut invar steel specimen with ethanol, then rinse it with water and blow it dry with a fan, put it into the fixture of the welding workbench, and fix it with laser spot welding at the beginning and end of the weld, To prevent misalignment deformation during welding;

(2) Adjust the distance between the height of the laser welding head and the surface of the invar steel specimen to be 80-100mm, the positive defocus of the laser is 3-8mm, and adjust the distance between the shielding gas nozzle and the surface of the invar steel specimen to be 45 degrees at a distance of 10-15mm Corner, protective gas flow 10-15L/min;

(3) Turn on the laser welding machine, the laser pulse frequency is 20-60 Hz, the welding speed is 200-800mm/min, and the diameter of the welding point is adjusted to 0.5mm;

(4) Set layered pulse laser energy respectively, preheating laser power 80-150 watts, pulse width 0.5-3ms, welding laser power 300-550 watts, pulse width 2-5ms, post-welding thermal laser power 100-240 watts , pulse width 0.5-3ms. There is no time interval between the preheating laser and the welding laser, and the time interval between the welding laser and the post-welding heat laser is 0.5-3ms;

(5) Turn on the CAD drawing function of the automatic operating system of the laser welding machine, and perform welding according to the welding path generated by the computer;

(6) After laser welding, take out the Invar steel welding specimen for performance testing.

Claims (5)

1. a kind of layering pulse laser reduces the method that invar steel welds hot cracking tendency, it is characterized in that：Methods described adopts following Step：

（1）The invar steel test specimen ethanol purge connection surface of well cutting, then rinsed with water and dried up with fan, put into weldering Connect fixing in the fixture of workbench, fixed with laser spot welding at weld seam initiating terminal and ending；

（2）Adjustment laser welding grease head highness is 80-100mm with the distance of invar steel surface of test piece, and laser positive out of focus 3-8mm are adjusted Whole protection gas jets and become 45 degree of angles, shielding gas flow 10-15L/min with invar steel surface of test piece at 10-15mm；

（3）Setting layering pulse laser, layering pulse laser includes pre- thermal laser, welding laser, thermal laser, pre- heat shock after postwelding Luminous power is 80-240 watt, and pulsewidth is 0.5-3ms, and welding laser power is 300-550 watt, and pulsewidth is 2-5ms, heat shock after postwelding Luminous power is 80-240 watt, and pulsewidth is 0.5-3ms；The warm that pre- thermal laser is set, the welding process welding laser, postwelding Joining relation between thermal process after the postwelding of thermal laser afterwards；

（4）Open laser welder, laser pulse frequency 20-60 hertz, speed of welding 200-800mm/min, adjustment pad is straight Footpath is to 0.5mm；

（5）Open the CAD Plotting Function of laser welder automatic operation system, welded by the path of welding that computer generates；

（6）Take out invar steel welding piece after laser welding and carry out performance test.

2. a kind of layering pulse laser according to claim 1 reduces the method that invar steel welds hot cracking tendency, its feature It is：After the postwelding of thermal laser after the warm of described pre- thermal laser, the welding process of welding laser, postwelding between thermal process it is It is carried out continuously successively.

3. a kind of layering pulse laser according to claim 1 reduces the method that invar steel welds hot cracking tendency, its feature It is：Time interval between the welding process of the warm of described pre- thermal laser and welding laser is 0.5-3ms, welds laser Welding process and postwelding after thermal laser postwelding after time interval between thermal process be 0.5-3ms.

4. a kind of layering pulse laser according to claim 1 reduces the method that invar steel welds hot cracking tendency, its feature It is：It is carried out continuously between the welding process of the warm of described pre- thermal laser and welding laser, the welding of welding laser After the postwelding of thermal laser after process and postwelding, the time interval between thermal process is 0.5-3ms.

5. a kind of layering pulse laser according to claim 1 reduces the method that invar steel welds hot cracking tendency, its feature It is：Time interval between the welding process of the warm of described pre- thermal laser and welding laser is 0.5-3ms, welds laser Welding process and postwelding after thermal laser postwelding after be carried out continuously between thermal process.