KR20130014799A - Welding apparatus with shield box - Google Patents

Abstract

PURPOSE: A welding machine with a shield box is provided to control the impurities of a welded joint and a base material at an identical level, thereby saving manufacturing costs by improving weldability and weld quality regardless of welding methods. CONSTITUTION: A welding machine with a shield box comprises a welding tool and a shield box(30). The welding tool includes a gas nozzle(22). The shield box is connected to the rear of the welding tool in the direction of welding. The shield box is equipped at the upper side of the base material, and prevents the impurities of a welded joint(11) from being mixed. The welding tool is a welding torch part(20). The shield box has a length of 60 to 100mm, width of 20 to 40mm, and a height of 10 to 30mm. The flow rate of a shield gas supplied to the welding torch part is 15 to 20 L/min, the flow rate of the shield gas supplied to the rear of the welding torch part is 15 to 20 L/min, and the flow rate of the shield gas supplied to the rear side of a welding bead is 5 to 10 L/min. The welding tool is a laser head part. The shield box has a length of 100 to 150mm, width of 15 to 30mm, and a height of 10 to 30mm. The flow rate of the shield gas supplied to the laser head part is 15 to 20 L/min, the flow rate of the shield gas supplied to the rear of the laser head part is 100 to 200 L/min, and the flow rate of the shield gas supplied to the rear side of the welding bead is 5 to 10 L/min.

Description

Welding device with shield box {WELDING APPARATUS WITH SHIELD BOX}

The present invention relates to a welding apparatus, and more particularly, to a welding apparatus including a shield box that can prevent the incorporation of impurities such as nitrogen (N), oxygen (O), etc., which are easily introduced into the welding joint.

Recently, the automobile industry has been required to improve fuel efficiency by tightening exhaust gas regulations and reducing vehicle weight. In addition, automobile manufacturers are using ferritic stainless steel having excellent corrosion resistance and heat resistance in place of the existing casting or aluminum plated steel sheet for exhaust system parts.

The converter, which is an exhaust system component, is used for purifying harmful components in exhaust gas generated during combustion of an automobile engine by using a catalyst device. In the past, upper and lower plate materials are press-molded, and catalyst is charged and manufactured by welding. Recently, a method of charging a catalyst into a welded steel pipe and spinning a method for reducing the number of welding works has been proposed. Spinning is a rotary plastic processing method for processing while pushing a welded steel pipe into a rotating roller set according to the shape.

The ferritic stainless steel welded steel pipe for spinning processing is formed by roll bending a sheet material cut to a predetermined size and is made by TIG welding, plasma welding, laser welding, or the like. Although the initial investment cost is higher than TIG welding and plasma welding, the laser welded steel tube uses a high-efficiency laser beam, so the welded joint is narrow, so the quality characteristics are excellent and high-speed production can be expected. TIG welding and plasma welding, which are gas shielded arc welding, have the advantages of low initial installation cost and relatively simple operation compared to laser welding.

Meanwhile, the welded steel pipe needs to remove the tabs TAB attached to both ends of the steel pipe for spinning. At this time, cracks are generated at the welded joint during cutting. In addition, despite the excellent workability of the base material due to cracks in the welded joint during the spinning process, the expansion of application of parts is insufficient due to difficulty in securing the workability of the welded joint. This phenomenon is noticeable when brittle cracking occurs at the welded joint when forming at low processing temperatures in winter or at high processing speeds.

As described above, the use of ferritic stainless steel of medium and high Cr is generally adopted to secure high temperature characteristics of the steel used as the temperature of the exhaust gas increases due to strengthening environmental regulations. It is pointed out as a problem that the weld joint workability further falls.

Various techniques have been proposed to secure the processability of the above-described medium and high Cr ferritic stainless steel pipes, which will be described below.

Japanese Laid-Open Patent Publication No. 1997-125209 discloses a method of welding a heat-resistant ferritic stainless steel containing Nb and the like by electric resistance welding (ERW), followed by post-heat treatment at a high temperature of 850 to 1000 ° C. and rapidly cooling to 1 ° C./sec or more. Japanese Laid-Open Patent Publication No. 2006-193770 discloses a Vickers hardness HV _W of a welded joint in a ferritic single-phase stainless steel welded steel pipe containing 0.1 to 0.5% of Ti or Nb as one or two kinds by mass. Hardness difference △ HV (= HV _W -HV _M ) between Vickers hardness HV _M and the base metal part ratio between bead width T _W and base material thickness T _M of the welded joint in the range 10 to 40 RT (= T _W / T _M Is 1.05 to 1.3, and after forming and welding (ERW, GTAW), calibration is performed with a deformation amount of 0.5 to 2.0% in the longitudinal direction, and a post-heat treatment method in a temperature range of 700 to 850 ° C is disclosed. In order to reduce the work hardening of steel pipes, it is important to apply annealing heat treatment after welding the pipe. Improved workability of the steel pipe has the effect, but, there are problems such as cost increase and the surface oxidation according to the annealing heat treatment applied.

In addition, Japanese Laid-Open Patent Publication No. 1993-277769 preheats above 250 ° C prior to laser welding of ferritic stainless steel, welds the protruding height of the inner bead to 0.15mm or more, and then reduces the welded joint in the plate thickness direction to improve workability. However, the method of improving the temperature of the preheat processor and laser welding is a low heat input welding method, it is difficult to stably secure the inner bead protrusion height of 0.15 mm or more.

In addition, Japanese Laid-Open Patent Publication No. 1999-256286 discloses a heat-resistant ferritic stainless steel for the purpose of omitting the post-heat treatment of ERW steel pipes, C: 0.02% or less, Si: 0.7-1.0%, Mn: 1.0-1.5%, Cr: 13.5 to 15.5, N: 0.02% or less, Nb: 0.3 to 0.6%, Cu: 0.02 to 0.24%, Al: 0 to 0.03%, and satisfy the relationship of 1.45≥Nb + Si and 1.35≤Nb + 1.2Si Although an annealed welded steel pipe for processing is disclosed, it is difficult to secure sufficient workability for deep processing applications such as bending part expansion pipes.

In addition, Japanese Laid-Open Patent Publication No. 1995-266072 discloses an atmosphere nitrogen concentration near a weld line in order to prevent nitrogen absorption of a stainless steel laser welded joint and improve workability. , the temperature T of the molten metal (℃) and _{[% N] at, log (} [% N] at) ≤ 2log determined by the allowable nitrogen content [% N] _WM of the weld metal _{([% N] WM) -} 2 * (518 / T + 1.068) -2 * (0.046 [% Cr] -0.00028 [% Cr] ² ), but it is difficult to control the process variables in real time in the actual piping process.

The present invention relates to a welding device, to provide a welding device provided with a shield box on the upper side of the welding joint to prevent the mixing of impurities contained in the welding joint.

One side of the present invention is a welding means provided with a gas nozzle; And it is connected to the welding progress direction of the welding means, and provided on the upper side of the base material provides a welding device including a shield box for preventing the mixing of impurities in the welded joint during welding.

The welding means is a welding torch portion, the shield box is preferably length: 60 ~ 100mm, width: 20 ~ 40mm and height: 10 ~ 30mm.

The flow rate of the shield gas supplied to the welding torch unit is 15-20 L / min, the flow rate of the shield gas supplied to the rear of the welding torch unit is 15-20 L / min, and the gas flow rate supplied to the back side of the welding bead is 5 ~. It is preferable that it is 10 L / min.

In addition, the welding means is a laser head portion, the shield box is preferably length: 100 ~ 150mm, width: 15 ~ 30mm and height: 10 ~ 30mm.

The flow rate of the shield gas supplied to the laser head part is 15-20 L / min, the flow rate of the shield gas supplied to the rear of the laser head part is 100-200 L / min, and the gas flow rate supplied to the back side of the welding bead is 5 ~. It is preferable that it is 10 L / min.

The welding heat input amount provided from the laser head portion is preferably 1.5 to 6 kW · min / m.

The shield box is preferably provided with a gas nozzle.

The shield box may include a heat resistant part, and may be spaced apart from the base material to be welded with the heat resistant part interposed therebetween.

It is preferable that the intensity | strength of the said heat resistant part is lower than the said base material.

According to one aspect of the present invention, it is possible to control the impurity of the weld joint and the base material at the same level, thereby improving the weldability and welding quality irrespective of the welding method, it is possible to provide a low-cost welded steel pipe.

1 is a schematic view of a gas shielded arc welding apparatus according to one embodiment of the present invention;
Figure 2 is a schematic diagram of a gas shielded arc welding apparatus according to an embodiment of the present invention, a part of which is shown in cross section,
3 is a cross-sectional view of FIG.
4 is a schematic diagram of a laser welding device according to one embodiment of the present invention;
5 is a schematic view of a laser welding device according to an embodiment of the present invention, a part of which is shown in cross section;
6 is a cross-sectional view of FIG. 4.

Hereinafter, the present invention will be described in detail.

The present inventors have endeavored to remove impurities in the weld seam generated when welding stainless steel. In the case of laser welding, the temperature of molten metal increases with the use of a high density heat source compared to the normal arc welding, and the mixing of N and O increases from the atmosphere. The problem of increasing the mixing of N and O from the atmosphere is recognized, and the present invention has been realized by recognizing that this can be solved by the welding apparatus according to the present invention.

First, a welding apparatus which is an aspect of the present invention will be described in detail with reference to the drawings.

As shown in Figures 1 to 3, an arc is generated in the electrode rod 21 provided in the welding torch unit 20, by welding the base material 10 by using the arc. At this time, it is preferable that the shield box 30 is provided above the generated weld joint 11. The shield box 30 is preferably located in the direction opposite to the welding progress direction, and is connected to the welding torch unit 20.

In addition, the welding torch unit 20 includes a gas nozzle 22, and shield gas may be introduced through the gas nozzle 22. The shield gas can improve the stability of the arc and can prevent oxidation of the electrode. If the flow rate is less than 15 L / min, the arc may be unstable and sand bead may occur. On the other hand, if it exceeds 20L / min, the arc is cooled, the penetration characteristics are lowered and bead drooping may occur. In addition, there may be a problem that increases the cost of overuse. Therefore, the flow rate of the shield gas is preferably limited to 15 to 20 L / min. In addition, although inert gas, such as argon and helium, can be used as said shield gas, it is preferable to use argon in consideration of cost.

In addition, the shield box 30 is preferably provided with a gas nozzle 40. The shield gas supplied through the gas nozzle can prevent impurities from penetrating into the weld joint 11, and the shield box 30 can prevent the shield gas from being easily dispersed. If the flow rate is less than 15 L / min, part of the welded joint is oxidized so that the content of impurities (N + O) exceeds the standard value desired by the present invention. On the other hand, if the flow rate exceeds 20 L / min, the electrode Arc shaking may occur in the center, and underfill phenomenon may occur in which the entire surface weld bead sags due to the gas pressure.

The shielding gas flow rate of the weld bead inner surface bead is preferably controlled to 5 ~ 10L / min. When applied at less than 5L / min, the surface of the beads is oxidized due to poor shielding, thereby increasing the content of impurities (N, O). On the other hand, if it exceeds 10L / min, there is a problem that the weld bead in the steel thickness direction caused by the gas pressure occurs.

In addition, the shield box 30 preferably has a length (horizontal welding direction and horizontal) of 60 to 100 mm, a width (vertical welding direction) of 20 to 40 mm, and a height of 10 to 30 mm. In general, the cooling rate of the welded joint is about 100 ~ 200 ℃ / sec, on the basis of 150 ℃ / second on average, assuming that the temperature of the weld joint is 1600 ℃, the temperature to obtain a good surface quality The cooling time up to 400 ° C. takes about 8 seconds. When the welding speed is 0.32m / min at the maximum, it moves to about 5mm / sec, therefore, the shield box 30 of 40mm length is required for shielding up to 400 ℃. In consideration of welding speed and welding heat input variation, the lower limit of the shield box length is preferably limited to 60 mm, and in the case of exceeding 100 mm, even if a large amount of shield gas is added, the effect is insufficient. It is preferable to limit the width and height of the shield box 30 to the above range for the same reason as the length limitation reason. However, the length, width, and height of the shield box 30 may be reset by the calculation as described above in consideration of the welding speed, the temperature of the welding joint, and the like.

In addition, the shield box 30 is preferably spaced apart from the predetermined distance so as not to contact the base material 10 is located on the upper side of the welded joint (11). The lower portion of the shield box 30 is preferably provided with a heat-resistant portion 31, the heat-resistant portion 31 may be in contact with the base material 10, at this time, the base material 10 is scratched It is preferable that the heat-resistant portion 31 has a low strength as compared with the base material so that the phenomenon of being generated or scratched does not occur. The heat-resistant portion 31 is located in the lower portion of the shield box is not limited in size, width, etc., it is effective only in the characteristics of the portion that can be in contact with the base material.

And, a welding device which is another aspect of the present invention will be described in detail with reference to the drawings.

As shown in Figures 4 to 6, the laser is generated in the laser generating unit 51 provided in the laser head portion 50, by welding the base material 10 by using the laser. At this time, it is preferable that the shield box 30 is provided above the generated weld joint 11. The shield box 30 is preferably located in the direction opposite to the welding progress direction, and is connected to the laser head portion 50.

At this time, it is preferable that the welding heat input amount is controlled to 1.5 to 6 kW · min / m. As the amount of heat input of the welding decreases, the amount of impurity mixed from the outside decreases, thereby improving the shielding property. However, when less than 1.5 kW · min is applied, it is difficult to secure the penetration bead due to insufficient heat input. In addition, when the heat input is excessively applied in excess of 6kW · min, the shielding property is poor, and a hole is generated during welding, and thus, a healthy welded joint cannot be secured.

In addition, the laser head part 50 includes a gas nozzle 52, and shield gas may be introduced through the gas nozzle 52. The shield gas can improve the stability of the laser beam, and can prevent oxidation of the optical system. When the flow rate is less than 15 L / min, beam output may be reduced due to poor shielding, and the optical system may be oxidized to reduce workability. On the other hand, if it exceeds 20L / min, the melted portion is cooled, the penetration characteristics are lowered and bead drooping may occur. In addition, there may be a problem that increases the cost of overuse. Therefore, the flow rate of the shield gas is preferably limited to 15 to 20 L / min. In addition, although the inert gas, such as argon and helium, can be used as said shield gas, it is preferable to use helium in consideration of cost.

In addition, the shield box 30 is preferably provided with a gas nozzle 40. The shield gas supplied through the gas nozzle can prevent impurities from penetrating into the weld joint 11, and the shield box 30 can prevent the shield gas from being easily dispersed. If the flow rate is less than 100 L / min, a part of the welded joint is oxidized so that the content of impurities (N + O) exceeds the standard value desired by the present invention. On the other hand, if the flow rate exceeds 200 L / min, the electrode Arc shaking may occur in the center, and underfill phenomenon may occur in which the entire surface weld bead sags due to the gas pressure. As the shielding gas used at this time, argon is preferably used.

As described above, the shielding flow rate of the inner surface bead of the welded steel pipe is preferably controlled at 5 to 10 L / min for the same reason as the gas shield arc welding apparatus.

In addition, the shield box 30 is preferably limited to the length (horizontal welding direction and horizontal) of 100 ~ 150mm, the width (vertical of the welding progress direction) of 15 ~ 30mm, the height of 10 ~ 30mm. In order to cope with the maximum speed of 10m / min, the minimum length is more than 100mm to sufficiently shield the welded joint exposed to high temperature after moving the laser head. If it exceeds 150mm, there is a problem in that the gas supply amount is excessively consumed and the cost is increased. It is preferable to limit the width and height of the shield box 30 to the above range for the same reason as the length limitation reason. However, the length, width, and height of the shield box 30 may be reset by the calculation as described above in consideration of the welding speed, the temperature of the welding joint, and the like.

In addition, the shield box 30 has the same characteristics as the above-described gas shielded arc welding apparatus with respect to the distance from the base material 10 and the heat-resistant portion 31.

Hereinafter, embodiments of the present invention will be described in detail. The following examples are provided for the understanding of the present invention, and the present invention is not limited thereto.

(Example 1)

The ferritic stainless steels having the components shown in Table 1 were manufactured into steel sheets having a thickness of 1.5 mm through hot rolling, cold rolling, and annealing. Using the steel sheet as a base material, a weld steel pipe having an outer diameter of 115.7 mm, a thickness of 1.5 mm, and a length of 600 mm was manufactured by a roll bending method of a TIG welding tube method.

The welding speed was 0.32 m / min, the pure argon gas was used for welding, and the welding current and gas amount were changed. Weldability was evaluated by using external bead, cross-sectional texture test and impact test. The DBTT characteristics of welded joints were investigated by applying the Charpy impact test on 1/4 Sub-size (1.5mm ^t × 10mm ^w × 55mm ^l ) test specimens in the test temperature range of -100 ~ 100 ℃. In the present invention, the test temperature corresponding to 1/2 of the upper limit impact energy was set to DBTT.

Table 2 below shows the results of evaluating the welding characteristics when the shielding method was changed for the lower limit and the upper limit of the appropriate welding current range. At this time, in case of A, only the shielding treatment of the torch portion is performed, and in case of B, the shielding of the torch portion and the welded steel tube backside bead shielding treatment are performed, and C is the torch portion shielding and the welded steel tube backside bead shielding and the torch rear shielding. As for the shield gas flow rate, the torch shield flow rate was 15 L / min, the torch rear shield flow rate was 20 L / min, and the back bead shield flow rate was 5 L / min, respectively.

Through-bead means that the molten part is formed over the entire range in the thickness direction of the steel. Melting occurs when excessive welding heat input is applied. The welding defect is generated by the hole appearance in the weld joint. It was. The occurrence of underfill and bead depression was considered as pass when the weld bead protruded outward from the steel surface in the cross section and failed when beads were formed inside the steel.

division Cr Cu C Mn Mo Nb Ni N P Si S Ti TotalAl Steel grade 1 11.3 - 0.007 0.30 - - 0.09 0.008 0.01 0.45 0.002 0.23 0.050 Steel grade 2 14 0.072 0.0068 0.283 0.02 0.397 0.13 0.0082 0.0237 0.892 0.0020 0.164 0.072 Steel grade 3 19.22 0.479 0.0117 0.302 0.01 0.442 0.19 0.0062 0.0203 0.537 0.0009 - 0.003

(However, the unit of Table 1 is weight%)

Steel grade Shielding
Way flux
(l / min) welding
electric current
(A) Penetrate
Bead
The presence or absence Entertainment
Occur
The presence or absence Underfill presence Bead
depression
The presence or absence Impurity Level of Weld Joint (ppm) welding
Joint DBTT
(℃)
Remarks Backside shield Torch Rear Shield O N O + N Steel grade 1 - - - - - - - 38 56 94 -68 Base material Steel grade 1 A - - 120 ○ Not occurring Not occurring Not occurring 95 80 175 -25 Comparative Example 1 Steel grade 1 A - - 170 ○ Not occurring Not occurring Not occurring 120 100 220 -10 Comparative Example 2 Steel grade 1 B 5 - 120 ○ Not occurring Not occurring Not occurring 51 52 103 -70 Comparative Example 3 Steel grade 1 B 5 - 170 ○ Not occurring Not occurring Not occurring 74 54 128 -32 Comparative Example 4 Steel grade 1 C 5 20 120 ○ Not occurring Not occurring Not occurring 43 51 94 -67 Inventory 1 Steel grade 1 C 5 20 170 ○ Not occurring Not occurring Not occurring 51 48 99 -40 Inventive Example 2 Steel grade 2 - - - - - - - - 15 88 103 -42 Base material Steel grade 2 A 5 - 120 ○ Not occurring Not occurring Not occurring 140 260 400 40 Comparative Example 5 Steel grade 2 A 5 - 170 ○ Not occurring Not occurring Not occurring 190 180 370 45 Comparative Example 6 Steel grade 2 B 5 - 120 ○ Not occurring Not occurring Not occurring 98 200 298 17 Comparative Example 7 Steel grade 2 B 5 - 170 ○ Not occurring Not occurring Not occurring 110 160 270 33 Comparative Example 8 Steel grade 2 C 5 20 120 ○ Not occurring Not occurring Not occurring 24 87 111 -30 Inventory 3 Steel grade 2 C 5 20 170 ○ Not occurring Not occurring Not occurring 21 84 105 -32 Honorable 4 Steel grade 3 - - - - - - - - 40 63 103 -80 Base material Steel grade 3 A - - 120 ○ Not occurring Not occurring Not occurring 180 200 380 52 Comparative Example 9 Steel grade 3 A - - 170 ○ Not occurring Not occurring Not occurring 260 170 430 58 Comparative Example 10 Steel grade 3 B 5 - 120 ○ Not occurring Not occurring Not occurring 130 220 350 50 Comparative Example 11 Steel grade 3 B 5 - 170 ○ Not occurring Not occurring Not occurring 130 140 270 27 Comparative Example 12 Steel grade 3 C 5 20 120 ○ Not occurring Not occurring Not occurring 41 66 107 -44 Inventory 5 Steel grade 3 C 5 20 170 ○ Not occurring Not occurring Not occurring 36 62 98 -47 Inventory 6

Regardless of the steel type, the shielding methods A, B, and C decrease in the order of N and O, and the DBTT moves to the low temperature side, thereby improving the low temperature toughness and workability of the welded joint. In case of steel grade 1, which is a low Cr type, the DBTT characteristics can be secured by B only shielding treatment.However, in the case of medium and high Cr ferritic stainless steels such as steel grades 2 and 3, only C is applied. It can be seen that the O and N content can be controlled and the DBTT characteristics are greatly improved. In the case of medium and high Cr ferritic stainless steel, O and N in the air can be easily mixed during welding, and it can be confirmed that blocking external air is a necessary factor for securing workability.

(Example 2)

A ferritic stainless steel that satisfies the composition of Steel Grades 1 and 2 of Table 1 was manufactured by hot rolling, cold rolling, and annealing to prepare a steel plate having a thickness of 1.5 mm.

Using the steel sheet as a base material, a weld steel pipe having an outer diameter of 115.7 mm, a thickness of 1.5 mm, and a length of 600 mm was manufactured by a laser welding welding method of a roll bending method. Laser welding has a maximum output of 12kW CO ₂ The laser welding machine was used in a laser output range of 5 to 9 kW and a welding speed of 0.5 to 10 m / min. The flow rate of the helium shield gas supplied to the laser head was 20 L / min, and the rear shield and the inner bead shield gas were welded with varying flow rates using Arcon.

Weldability was evaluated by using external bead, cross-sectional texture test, and impact test. The DBTT characteristics of welded joints were investigated by applying the Charpy impact test on 1/4 Sub-size (1.5mm ^t × 10mm ^w × 55mm ^l ) test specimens in the range of -100 ~ 100 ℃. In the present invention, the test temperature corresponding to 1/2 of the upper limit impact energy was set to DBTT. In addition, the crack susceptibility was evaluated by investigating the weld crack at the welded end of the welded joint in the vertical direction. In addition, the weld heat input, the shielding conditions and the presence of weld defects, the N + O content of the welded joint, and DBTT were evaluated. The results of examining the correlation between the characteristics and crack susceptibility are shown in Table 3 below.

Steel grade welding
Heat input
(kWmin / m) Gas flow rate (l / min) Penetrate
Bead
The presence or absence Underfill
The presence or absence Inside
Bead
depression
The presence or absence N + O
(ppm) DBTT
(℃) Shear
Cleavage crack
Incidence
(%) Remarks rear
shield
(Ar) Inner Bead Shield
(Ar) Steel grade 2 - - - - - - 0.0103 -42 0 Base material Steel grade 2 12 - - Penetrate
(Accept) - - - - - Comparative Example 13 Steel grade 2 6 - - Penetrate Not occurring Not occurring 0.103 11 20 Comparative Example 14 Steel grade 2 6 - 5 Penetrate Not occurring Not occurring 0.086 8 10 Comparative Example 15 Steel grade 2 6 - 10 Penetrate Not occurring Not occurring 0.083 8 10 Comparative Example 16 Steel grade 2 6 - 15 Penetrate Not occurring Occur 0.083 - - Comparative Example 17 Steel grade 2 6 50 5 Penetrate Not occurring Not occurring 0.053 -3 10 Comparative Example 18 Steel grade 2 6 100 5 Penetrate Not occurring Not occurring 0.0171 -26 0 Honorable 7 Steel grade 2 1.5 200 5 Penetrate Not occurring Not occurring 0.0121 -30 0 Inventive Example 8 Steel grade 2 1.5 - - Penetrate Not occurring Not occurring 0.025 -20 0 Comparative Example 19 Steel grade 2 1.5 - 5 Penetrate Not occurring Not occurring 0.02 -20 0 Comparative Example 20 Steel grade 2 1.5 100 5 Penetrate Not occurring Not occurring 0.0115 -32 0 Proposition 9 Steel grade 2 One - - Unpenetrating - - - - - Comparative Example 21 Steel grade 3 - - - - - - 0.0103 -80 0 Base material Steel grade 3 6 - - Penetrate Not occurring Not occurring 0.160 85 90 Comparative Example 22 Steel grade 3 6 - 5 Penetrate Not occurring Not occurring 0.096 68 70 Comparative Example 23 Steel grade 3 6 100 5 Penetrate Not occurring Not occurring 0.016 -31 0 Inventory 10 Steel grade 3 1.5 - - Penetrate Not occurring Not occurring 0.063 30 50 Comparative Example 24 Steel grade 3 1.5 - 5 Penetrate Not occurring Not occurring 0.057 10 20 Comparative Example 25 Steel grade 3 1.5 100 5 Penetrate Not occurring Not occurring 0.011 -78 0 Exhibit 11

In Comparative Example 13, the weld heat input was excessively applied at 12 kW · min / m, but the penetration weld joint was secured, but welding of the tubular pipe was difficult due to the melt phenomenon in which holes were generated during welding. Comparative Examples 14 and 19 show that the N + O content increases rapidly, the DBTT temperature rises and the cracking susceptibility increases when the rear shield and the inner bead shielding treatment are not performed. In Comparative Examples 15 to 17, the gas flow rate was changed when only the inner bead was shielded, and it was found that the impact toughness was reduced and the crack susceptibility was high because the N + O content was high regardless of the flow rate increase. In addition, in the case of the gas flow rate 15L / min, the bead shape in which the inner surface beads are recessed in the steel thickness direction due to the high gas pressure was poor. In Comparative Examples 19 and 20, laser welding was performed at low heat input, and the specific DBTT characteristics and crack prevention can be achieved without additional shielding treatment or by shielding only internal beads. Since it is difficult to secure, it was excluded from the present invention. In Comparative Example 21, when a small amount of welding input heat was applied at 1 kW · min / m, it was found that the penetration bead was difficult to be secured, and therefore, it was difficult to be applied to welding a tubular tube. Inventive Examples 7 to 9 correspond to the present invention, by applying the rear shield and the inner bead shielding at the same time, the N + O value is greatly reduced, thereby greatly improving low-temperature toughness of the welded joint and preventing cracking.

Example 3

Gas shield arc welding was performed on steel type 3 described in Table 1, and the results of evaluating the N + O content and impact toughness of the welded joint according to the gas flow rate are shown in Table 4 below.

flux
(l / min) welding
electric current
(A) Penetrate
Bead
The presence or absence Entertainment
Occur
The presence or absence Underfill
The presence or absence Bead
depression
The presence or absence Impurity Level of Weld Joint (PPM) welding
Joint DBTT
(℃)
Remarks Backside shield Torch Rear Shield O N O + N 5 25 170 X Not occurring Occur Not occurring - - - - Comparative Example 26 5 20 170 ○ Not occurring Not occurring Not occurring 36 62 98 -47 Inventory 12 5 15 170 ○ Not occurring Not occurring Not occurring 45 60 105 -43 Inventory 13 5 10 170 ○ Not occurring Not occurring Not occurring 125 140 265 25 Comparative Example 27 3 20 170 ○ Not occurring Not occurring Not occurring 84 116 200 -15 Comparative Example 28 10 20 170 ○ Not occurring Not occurring Not occurring 35 63 98 -48 Inventive Example 14 15 20 170 ○ Not occurring Not occurring Occur 38 62 100 - Comparative Example 29

In the case of Comparative Example 26, when the torch rear shield flow rate was excessively applied at 25 L / min, it was difficult to secure the bead through arc cooling. In Comparative Examples 27 and 28, when the back shield and torch rear shield flow rates were applied in a small amount compared to the flow rate to be controlled, it was difficult to secure predetermined DBTT characteristics due to an increase in oxygen and nitrogen contents at the weld joint according to the shielding failure. Inventive Examples 12 to 14 were able to secure low-temperature processability by greatly improving the impurity content and DBTT of the welded joint under the conditions proposed by the present invention.

10: base metal
11: welded joint
20: welding torch
21: electrode
22: gas nozzle (welding torch)
30: Shield Box
31: heat-resistant part
40: gas nozzle (shield box)
50: laser head
51: laser generating unit
52: gas nozzle (laser head part)

Claims (9)

Welding means provided with a gas nozzle; And
And a shield box which is connected to the rear of the welding progress direction of the welding means and is provided on an upper side of the base material to prevent the mixing of impurities in the welded joint during welding.
The method according to claim 1,
The welding means is a welding torch portion, the shield box is a welding device, characterized in that the length: 60 ~ 100㎜, width: 20 ~ 40㎜ and height: 10 ~ 30㎜.
The method according to claim 2,
The flow rate of the shield gas supplied to the welding torch unit is 15-20 L / min, the flow rate of the shield gas supplied to the rear of the welding torch unit is 15-20 L / min, and the gas flow rate supplied to the back side of the welding bead is 5 ~. Welding device, characterized in that 10L / min.
The method according to claim 1,
The welding means is a laser head portion, the shield box is a welding device, characterized in that the length: 100 ~ 150mm, width: 15 ~ 30mm and height: 10 ~ 30mm.
The method of claim 4,
The flow rate of the shield gas supplied to the laser head part is 15-20 L / min, the flow rate of the shield gas supplied to the rear of the laser head part is 100-200 L / min, and the gas flow rate supplied to the back side of the welding bead is 5 ~. Welding device, characterized in that 10L / min.
The method of claim 4,
Welding input heat provided from the laser head portion is characterized in that the welding device is 1.5 ~ 6kW · min / m.
The method according to claim 1,
The shield box is a welding device, characterized in that the gas nozzle is provided.
The method according to claim 1,
The shield box includes a heat resistant portion, the welding apparatus, characterized in that provided with a spaced apart from the base material to be welded through the heat resistant portion.
The method according to claim 8,
Welding strength, characterized in that the heat resistant portion is lower than the base material.

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