Stainless steel and method for improving laser weld penetration of stainless steel plate and suppressing defect generation

Abstract

The present application relates to the technical field of stainless steel laser welding, in particular to a stainless steel and a method for improving the laser welding penetration of stainless steel plates and inhibiting the generation of defects, which comprises the following components in percentage by mass: 0.01-0.03% of C, 0.02-0.03% of S, 0.2-0.3% of N, 3-5% of Mo, 8-10% of Ni, 18-20% of Cr, 1.8-2.4% of Mn, and the balance of Fe.The present application significantly improves the penetration of high-power laser welding of stainless steel by regulating the composition of the stainless steel, while reducing the defects of welding spatter and porosity, and ensuring the quality of the weld.

Description

Technical Field

[0001] This invention relates to the field of stainless steel laser welding technology, and more specifically, to stainless steel and methods for improving the penetration depth of laser welding of stainless steel plates and suppressing the generation of defects. Background Technology

[0002] Stainless steel thick plates are widely used in nuclear power, chemical industry and other fields, and welding is a key technology for connecting related equipment. Traditionally, multi-layer multi-pass electric arc welding is mainly used for welding stainless steel thick plates, but this method has difficulties such as low welding efficiency, large heat input, large welding deformation and poor joint quality.

[0003] Compared to traditional arc welding, laser welding offers advantages such as high energy density, fast welding speed, and low heat input, making it suitable for high-efficiency, high-quality welding of thick plates. However, in the laser welding of stainless steel, as the laser power increases, the weld width increases significantly, while the weld penetration increases relatively slowly. Furthermore, high-power welding of stainless steel generates severe spatter and porosity defects, greatly affecting the weld quality.

[0004] To address the aforementioned shortcomings, existing processes typically employ high-speed side-blowing gas, different beveling techniques, and combined processes with electric arc welding to increase penetration depth within a certain range. However, these methods still struggle to simultaneously resolve issues such as spatter and porosity during welding. Low-vacuum laser welding can significantly improve penetration depth in laser welding of thick stainless steel plates and better control welding defects. However, the workpieces require a vacuum environment, which imposes significant limitations on the dimensions of the welded components.

[0005] It is evident that existing improvement methods primarily address defects such as melting depth, spatter, and porosity in stainless steel by modifying process methods or conditions, rather than improving the composition of the stainless steel.

[0006] In view of this, the present invention is proposed. Summary of the Invention

[0007] The purpose of this invention is to provide stainless steel and a method for improving the penetration depth and suppressing defects in laser welding of stainless steel plates. Embodiments of this invention provide a novel stainless steel that significantly improves the penetration depth in high-power laser welding of stainless steel by controlling its composition, while simultaneously reducing weld spatter and porosity defects, thus ensuring weld quality.

[0008] This invention is implemented as follows: In a first aspect, the present invention provides a stainless steel that improves the penetration depth of laser welding of stainless steel plates and suppresses the generation of defects, wherein the composition by mass percentage is as follows: 0.01-0.03%C, 0.02-0.03%S, 0.2-0.3%N, 3-5%Mo, 8-10%Ni, 18-20%Cr, 1.8-2.4%Mn, with the balance being Fe.

[0009] In an optional embodiment, the S content is 0.02-0.025%.

[0010] In an optional implementation, the N content is 0.25-0.3%.

[0011] In an optional embodiment, the Mo content is 3-4.5%.

[0012] In a second aspect, the present invention provides a method for improving the penetration depth of laser welding of stainless steel plates and suppressing the generation of defects, comprising: performing laser welding using stainless steel that has been described in the foregoing embodiments for improving the penetration depth of laser welding of stainless steel plates and suppressing the generation of defects.

[0013] In an optional embodiment, the thickness of the welded sheet formed from the stainless steel is ≥10mm, preferably 10-100mm.

[0014] In an optional implementation, the laser power is ≥5Kw, preferably 5-50Kw; preferably, the laser beam defocusing amount is ≤0mm.

[0015] In an optional embodiment, the welding speed is ≥1m / min; preferably 1-10m / min.

[0016] In an optional embodiment, the welding shielding gas is an inert gas, preferably argon.

[0017] In an optional implementation, the gas flow rate is ≥20L / min.

[0018] The present invention has the following beneficial effects: By controlling the composition and content of the raw materials used to form stainless steel, the embodiments of the present invention improve the problem of insufficient penetration depth in laser welding of stainless steel plates, and suppress laser defects such as spatter and porosity during the welding process. Attached Figure Description

[0019] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0020] Figure 1This is a result image of stainless steel after laser welding, provided in Embodiment 1 of the present invention; Figure 2 This is a diagram showing the result of laser welding of stainless steel provided in Comparative Example 1 of the present invention; Figure 3 This is a diagram showing the result of laser welding of stainless steel provided in Comparative Example 2 of the present invention; Figure 4 This is a diagram showing the result of laser welding of stainless steel provided in Comparative Example 3 of the present invention. Detailed Implementation

[0021] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased commercially.

[0022] In a first aspect, the present invention provides a stainless steel that improves the penetration depth of laser welding of stainless steel plates and suppresses the generation of defects, wherein the composition by mass percentage is as follows: 0.01-0.03%C, 0.02-0.03%S, 0.2-0.3%N, 3-5%Mo, 8-10%Ni, 18-20%Cr, 1.8-2.4%Mn, with the balance being Fe.

[0023] The stainless steel provided in this invention, through the addition of Mo, can increase the surface tension of the liquid metal, causing the surface tension temperature gradient dσ / dT to change from positive to negative. This leads to convection in the molten pool from the outside to the inside, enhancing the downward flow tendency in the core and contributing to increased weld depth and reduced weld width. However, overall, the improvement in molten pool flow is limited when Mo is added alone. The addition of N can also induce negative convection in the molten pool, but the effect is also limited and does not significantly increase weld depth. However, the simultaneous addition of Mo and N promotes the significant effect of another alloying element, S. When the S content in the alloy composition is relatively high, it also causes convection in the molten pool to move from the outside to the inside. However, excessive S content will reduce the corrosion resistance of stainless steel, so too much S cannot be added to the alloy. The synergistic addition of Mo and N can significantly reduce the threshold of S required to induce a change in the flow direction of the molten pool. Thus, through the synergistic effect of these elements, the flow direction of the molten pool is significantly changed, increasing the weld depth.

[0024] On the other hand, regarding the generation of spatter and porosity, the addition of Mo increases the surface tension of the molten metal at high temperatures and increases the natural frequency of the molten pool metal, while the addition of N increases the damping coefficient of the molten pool and maintains the stability of the master mold. The combined effect of these two elements makes the keyhole more stable and reduces the generation of defects.

[0025] Specifically, carbon can improve the strength and hardness of stainless steel. However, if the carbon content is too high, it will significantly reduce the corrosion resistance and weldability of stainless steel. Therefore, in the embodiments of the present invention, the C content is any value between 0.01%, 0.011%, 0.012%, 0.013%, 0.014%, 0.015%, 0.016%, 0.017%, 0.018%, 0.019%, 0.02%, 0.021%, 0.022%, 0.023%, 0.024%, 0.025%, 0.026%, 0.027%, 0.028%, 0.029%, 0.03%, and 0.01-0.03%.

[0026] Sulfur is a double-edged sword in stainless steel. While it can improve the machinability of stainless steel, excessive sulfur content can negatively impact its ductility and toughness. Specifically, in this application, excessive sulfur content can lead to cracking at the weld joint, while insufficient sulfur content can result in minimal improvement in weld penetration. Therefore, in the embodiments of this invention, the sulfur content is any value between 0.02%, 0.021%, 0.022%, 0.023%, 0.024%, 0.025%, 0.026%, 0.027%, 0.028%, 0.029%, 0.03%, and 0.02-0.03%, preferably between 0.02-0.025%.

[0027] In this embodiment of the invention, the synergistic addition of Mo and N elements can significantly reduce the threshold S required to induce a change in the flow direction of the molten pool. Thus, through the synergistic effect of these elements, the flow direction of the molten pool is significantly altered, increasing the weld penetration. Simultaneously, the addition of Mo increases the high-temperature surface tension of the molten metal, raising the natural frequency of the molten pool, while the addition of N increases the damping coefficient of the molten pool, maintaining the stability of the master mold. These combined effects reduce the generation of defects.

[0028] In the embodiments of the present invention, the nitrogen (N) content is any value between 0.2%, 0.21%, 0.22%, 0.23%, 0.24%, 0.25%, 0.26%, 0.27%, 0.28%, 0.29%, 0.3%, and 0.2-0.3%; preferably 0.25-0.3%. If the N content is too low, the keyhole will be unstable and prone to defects. If the N content is too high, the stainless steel's properties will decrease, for example, its corrosion resistance will decrease, and the weld joint will become more brittle and prone to breakage.

[0029] In the embodiments of the present invention, the Mo content is any value between 3%, 3.1%, 3.2%, 3.3%, 3.4%, 3.5%, 3.6%, 3.7%, 3.8%, 3.9%, 4.0%, 4.1%, 4.2%, 4.3%, 4.4%, 4.5%, 4.6%, 4.7%, 4.8%, 4.9%, 5.0%, and 3-5%, preferably 3-4.5%. If the Mo content is too low, the melting depth will not increase.

[0030] Ni plays a role in stabilizing the austenite crystal structure in stainless steel. In the embodiments of the present invention, the Ni content is any value between 8%, 8.1%, 8.2%, 8.3%, 8.4%, 8.5%, 8.6%, 8.7%, 8.8%, 8.9%, 9%, 9.1%, 9.2%, 9.3%, 9.4%, 9.5%, 9.6%, 9.7%, 9.8%, 9.9%, 10%, and 8-10%.

[0031] In stainless steel, chromium (Cr) forms a dense protective film on the surface, isolating it from air and moisture, thereby reducing corrosion. It also increases the electrode potential of the stainless steel, lowering the probability of corrosion and further enhancing its corrosion resistance. However, excessively low Cr content significantly reduces the corrosion resistance of the stainless steel. In the embodiments of this invention, the Cr content is any value between 18% and 20%, including 18%, 18.1%, 18.2%, 18.3%, 18.4%, 18.5%, 18.6%, 18.7%, 18.8%, 18.9%, 19%, 19.1%, 19.2%, 19.3%, 19.4%, 19.5%, 19.6%, 19.7%, 19.8%, 19.9%, and 20%.

[0032] Mn works synergistically with nickel and nitrogen to ensure that the steel maintains a stable austenitic structure at room temperature, thereby improving the corrosion resistance of stainless steel. Simultaneously, it combines with sulfur to form manganese sulfide, which effectively reduces cutting resistance and improves the machinability of stainless steel. In the embodiments of this invention, the Mn content is any value between 1.8%, 1.9%, 2.0%, 2.1%, 2.2%, 2.3%, 2.4%, and 1.8-2.4%.

[0033] Stainless steel is prepared by selecting corresponding raw materials according to the above element ratios, and then through smelting and casting, hot working, finishing and heat treatment processes. It should be noted that the preparation method of this stainless steel refers to existing smelting methods, and will not be detailed in the embodiments of this invention.

[0034] Furthermore, in a second aspect, the present invention provides a method for improving the penetration depth of laser welding of stainless steel plates and suppressing the generation of defects, comprising: performing laser welding using stainless steel as described in the foregoing embodiments for improving the penetration depth of laser welding of stainless steel plates and suppressing the generation of defects.

[0035] Specifically, the stainless steel plate to be welded is placed at the laser welding station, a welding program is established, and parameters such as laser welding power, speed, defocusing amount, shielding gas flow rate, and welding path are set. The laser welding program is then run to complete the laser welding of the stainless steel.

[0036] The thickness of the welded sheet formed from the stainless steel is ≥10mm, for example, ≥10mm such as 10mm, 20mm, 30mm, 40mm, 50mm, 60mm, 70mm, 80mm, 90mm, 10mm, etc.; preferably 10-100mm.

[0037] Furthermore, the laser power is ≥5 kW, for example, 5 kW, 10 kW, 15 kW, 20 kW, 25 kW, 30 kW, 35 kW, 40 kW, 45 kW, 50 kW, etc.; preferably 5-50 kW. The laser beam defocusing amount is ≤0 mm.

[0038] Furthermore, the welding speed is ≥1m / min; for example, 1 m / min, 2 m / min, 3 m / min, 4 m / min, 5 m / min, 6 m / min, 7 m / min, 8 m / min, 9 m / min, 10 m / min, 15 m / min, etc. ≥1m / min; preferably 1-10m / min.

[0039] Furthermore, the welding shielding gas is an inert gas, such as, but not limited to, argon and nitrogen. The gas flow rate is ≥20 L / min, for example, 20 L / min, 25 L / min, 30 L / min, 35 L / min, 40 L / min, 45 L / min or 50 L / min, etc., ≥20 L / min.

[0040] The features and performance of the present invention will be further described in detail below with reference to embodiments.

[0041] Example 1 This embodiment provides a stainless steel with the following composition: 0.01% C, 0.025% S, 0.3% N, 4.5% Mo, 9.5% Ni, 20% Cr, 2.2% Mn, and the balance being Fe.

[0042] The corresponding stainless steel plates are prepared through the processes of smelting and casting, hot working, finishing and heat treatment.

[0043] This embodiment also provides a method for improving the penetration depth and suppressing defects in laser welding of stainless steel plates, including: Use tools to grind and polish the surface of the stainless steel sheet, and clean the surface oil with reagents such as alcohol and acetone. Dry the sheet and set it aside. Specifically, use a grinding wheel and sandpaper to remove the oxide film from the surface of the stainless steel sheet, and wipe the sheet with acetone and alcohol to remove oil and water. Dry the sheet and set it aside.

[0044] The stainless steel sheet was placed at the laser welding station, and a welding program was established, setting parameters such as laser welding power, speed, defocusing amount, shielding gas flow rate, and welding path. The laser welding program was then run to complete the laser welding of the stainless steel. Specifically, the laser power was 5kW, the welding speed was 1.2m / min, the laser beam defocusing amount was -5mm, the shielding gas was argon, and the gas flow rate was 25L / min.

[0045] The weld surface finish, joint penetration and width, weld spatter, and internal porosity were evaluated after welding. See results below. Figure 1 Where A represents surface forming; B represents back forming; C represents cross-section; and D represents longitudinal section. According to... Figure 1 It can be seen that the stainless steel plate was fully penetrated, with a penetration depth of 10mm and a weld width of 2.6mm. There was very little spatter on the plate surface, and no porosity was generated inside the weld, indicating that the weld quality was relatively high.

[0046] Example 2 This invention provides a stainless steel with the following composition: 0.03% C, 0.02% S, 0.25% N, 5% Mo, 10% Ni, 19% Cr, 1.8% Mn, and the balance being Fe.

[0047] This embodiment also provides a method for improving the penetration depth and suppressing defects in laser welding of stainless steel plates, including: Use a grinding wheel or sandpaper to remove the oxide film from the surface of the stainless steel sheet. Wipe the stainless steel sheet with acetone and alcohol to remove oil and water from the surface of the stainless steel sheet, and then blow it dry for later use.

[0048] The stainless steel sheet was placed at the laser welding station, and a welding program was established, setting parameters such as laser welding power, speed, defocusing amount, shielding gas flow rate, and welding path. The laser welding program was then run to complete the laser welding of the stainless steel. Specifically, the laser power was 50kW, the welding speed was 8m / min, the laser beam defocusing amount was -1mm, the shielding gas was argon, and the gas flow rate was 35L / min.

[0049] Example 3 This invention provides a stainless steel with the following composition: 0.01% C, 0.03% S, 0.2% N, 3% Mo, 8% Ni, 18% Cr, 2.4% Mn, and the balance being Fe.

[0050] This embodiment also provides a method for improving the penetration depth and suppressing defects in laser welding of stainless steel plates, including: Use a grinding wheel or sandpaper to remove the oxide film from the surface of the stainless steel sheet. Wipe the stainless steel sheet with acetone and alcohol to remove oil and water from the surface of the stainless steel sheet, and then blow it dry for later use.

[0051] The stainless steel sheet was placed at the laser welding station, and a welding program was established, setting parameters such as laser welding power, speed, defocusing amount, shielding gas flow rate, and welding path. The laser welding program was then run to complete the laser welding of the stainless steel. Specifically, the laser power was 35kW, the welding speed was 10m / min, the laser beam defocusing amount was 0mm, the shielding gas was argon, and the gas flow rate was 50L / min.

[0052] Example 4 This invention provides a stainless steel with the following composition: 0.02% C, 0.027% S, 0.22% N, 4% Mo, 9% Ni, 28% Cr, 2% Mn, and the balance being Fe.

[0053] This embodiment also provides a method for improving the penetration depth and suppressing defects in laser welding of stainless steel plates, including: Use a grinding wheel or sandpaper to remove the oxide film from the surface of the stainless steel sheet. Wipe the stainless steel sheet with acetone and alcohol to remove oil and water from the surface of the stainless steel sheet, and then blow it dry for later use.

[0054] The stainless steel sheet was placed at the laser welding station, and a welding program was established, setting parameters such as laser welding power, speed, defocusing amount, shielding gas flow rate, and welding path. The laser welding program was then run to complete the laser welding of the stainless steel. Specifically, the laser power was 15kW, the welding speed was 5m / min, the laser beam defocusing amount was -5mm, the shielding gas was argon, and the gas flow rate was 40L / min.

[0055] Comparative Example 1 This comparative example provides a stainless steel with the following composition: 0.01% C, 0.025% S, 9.5% Ni, 20% Cr, 2.2% Mn, and the balance being Fe.

[0056] The corresponding stainless steel plates are prepared through the processes of smelting and casting, hot working, finishing and heat treatment.

[0057] This comparative example also includes a laser welding method for stainless steel sheets, comprising: Use tools to grind and polish the surface of the stainless steel sheet, and clean the surface oil with reagents such as alcohol and acetone. Dry the sheet and set it aside. Specifically, use a grinding wheel and sandpaper to remove the oxide film from the surface of the stainless steel sheet, and wipe the sheet with acetone and alcohol to remove oil and water. Dry the sheet and set it aside.

[0058] The stainless steel sheet was placed at the laser welding station, and a welding program was established, setting parameters such as laser welding power, speed, defocusing amount, shielding gas flow rate, and welding path. The laser welding program was then run to complete the laser welding of the stainless steel. Specifically, the laser power was 5kW, the welding speed was 1.2m / min, the laser beam defocusing amount was -5mm, the shielding gas was argon, and the gas flow rate was 25L / min.

[0059] The weld surface finish, joint penetration and width, weld spatter, and internal porosity were evaluated after welding. See results below. Figure 2 Where A represents the surface finish; B represents the cross section; and C represents the longitudinal section. According to Figure 2 It can be seen that the stainless steel plate has a penetration depth of 6.6 mm and a penetration width of 4.6 mm. There is significant spatter on the plate surface, and many pores are generated inside the weld, resulting in numerous defects. Comparing Example 1 and Comparative Example 1, it can be seen that without the use of N and Mo, more defects will occur, and the penetration depth will be significantly reduced.

[0060] Comparative Example 2 This comparative example provides a stainless steel with the following composition: 0.01% C, 0.025% S, 0.3% N, 9.5% Ni, 20% Cr, 2.2% Mn, and the balance being Fe.

[0061] The corresponding stainless steel plates are prepared through the processes of smelting and casting, hot working, finishing and heat treatment.

[0062] This comparative example also includes a laser welding method for stainless steel sheets, comprising: Use tools to grind and polish the surface of the stainless steel sheet, and clean the surface oil with reagents such as alcohol and acetone. Dry the sheet and set it aside. Specifically, use a grinding wheel and sandpaper to remove the oxide film from the surface of the stainless steel sheet, and wipe the sheet with acetone and alcohol to remove oil and water. Dry the sheet and set it aside.

[0063] The stainless steel sheet was placed at the laser welding station, and a welding program was established, setting parameters such as laser welding power, speed, defocusing amount, shielding gas flow rate, and welding path. The laser welding program was then run to complete the laser welding of the stainless steel. Specifically, the laser power was 5kW, the welding speed was 1.2m / min, the laser beam defocusing amount was -5mm, the shielding gas was argon, and the gas flow rate was 25L / min.

[0064] The weld surface finish, joint penetration and width, weld spatter, and internal porosity were evaluated after welding. See results below. Figure 3 Where A represents the surface finish; B represents the cross section; and C represents the longitudinal section. According to Figure 3 It can be seen that the penetration depth is 7.2mm, the weld width is 4.9mm, there is a lot of spatter on the surface of the plate, and there are many pores inside the weld, resulting in many defects.

[0065] Comparing Example 1, Comparative Example 1 and Comparative Example 2, it can be seen that if only N is used, the melting depth is improved, but the improvement is not significant, and defects such as porosity still exist.

[0066] Comparative Example 3 This comparative example provides a stainless steel with the following composition: 0.01% C, 0.025% S, 4.5% Mo, 9.5% Ni, 20% Cr, 2.2% Mn, and the balance being Fe.

[0067] The corresponding stainless steel plates are prepared through the processes of smelting and casting, hot working, finishing and heat treatment.

[0068] This comparative example also includes a laser welding method for stainless steel sheets, comprising: Use tools to grind and polish the surface of the stainless steel sheet, and clean the surface oil with reagents such as alcohol and acetone. Dry the sheet and set it aside. Specifically, use a grinding wheel and sandpaper to remove the oxide film from the surface of the stainless steel sheet, and wipe the sheet with acetone and alcohol to remove oil and water. Dry the sheet and set it aside.

[0069] The stainless steel sheet was placed at the laser welding station, and a welding program was established, setting parameters such as laser welding power, speed, defocusing amount, shielding gas flow rate, and welding path. The laser welding program was then run to complete the laser welding of the stainless steel. Specifically, the laser power was 5kW, the welding speed was 1.2m / min, the laser beam defocusing amount was -5mm, the shielding gas was argon, and the gas flow rate was 25L / min.

[0070] The weld surface finish, joint penetration and width, weld spatter, and internal porosity were evaluated after welding. See results below. Figure 4 Where A represents the surface finish; B represents the cross section; and C represents the longitudinal section. According to Figure 4 As can be seen, at this point, the penetration depth is 6.9 mm, the weld width is 5.3 mm, there is significant spatter on the surface of the plate, and many pores are generated inside the weld, resulting in numerous defects.

[0071] Comparing Example 1, Comparative Example 1, and Comparative Example 3, it can be seen that using only the combination of Mo and S does not significantly improve the melting depth and still has defects. However, the synergistic addition of Mo, N, and S significantly improves the melting depth and significantly reduces the melting width, while simultaneously suppressing spatter and porosity.

[0072] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A type of stainless steel that improves the penetration depth of laser welding and suppresses defect formation in stainless steel plates, characterized in that, Its composition by mass percentage is as follows: 0.01-0.03% C, 0.02-0.03% S, 0.2-0.3% N, 3-5% Mo, 8-10% Ni, 18-20% Cr, 1.8-2.4% Mn, with the balance being Fe.

2. The stainless steel according to claim 1, characterized in that, The sulfur content is 0.02-0.025%.

3. The stainless steel according to claim 1, characterized in that, The nitrogen content is 0.25-0.3%.

4. The stainless steel according to claim 1, characterized in that, The Mo content is 3-4.5%.

5. A method for improving the penetration depth and suppressing defect generation in laser welding of stainless steel plates, characterized in that, include: Laser welding is performed using the stainless steel described in claim 1, which improves the penetration depth of laser welding of stainless steel plates and suppresses the generation of defects.

6. The method according to claim 5, characterized in that, The thickness of the welded sheet formed from the stainless steel is ≥10mm, preferably 10-100mm.

7. The method according to claim 5, characterized in that, The laser power is ≥5Kw, preferably 5-50Kw; preferably, the laser beam defocusing amount is ≤0mm.

8. The method according to claim 5, characterized in that, Welding speed ≥ 1 m / min; preferably 1-10 m / min.

9. The method according to claim 5, characterized in that, The welding shielding gas is an inert gas, preferably argon.

10. The method according to claim 9, characterized in that, Gas flow rate ≥ 20 L / min.

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