JPS5966979A - Submerged arc welding of spiral steel pipe - Google Patents

Abstract

PURPOSE:To produce a spiral steel pipe having no joint defect with good productivity by using a sintered flux having a specific compsn. and specific grain size and adjusting the eccentricity of the 1st electrode in an adequate range in performing multielectrode submerged arc welding. CONSTITUTION:A sintered flux which contains 20-40wt% SiO2, 20-50% TiO2, 5-20% MgO, 2-20% amount expressed in terms of MnO, Mn source such as metallic Mn, Fe-Mn, MnO2 or the like and 3-20% inorg. fluoride as essential components, satisfies 64%<=(SiO2+TiO2+MgO)<=90% and contains the particles of the grain sizes consisting of <=20% coarse grain of >=10 mesh and <=50% fine grain of <=70 mesh is used. The inner side of a spiral steel pipe produced by coiling a steel strip is subjected to high speed submerged arc welding with multiple electrodes under the conditions satisfying the equation l-pi/20R<=x<=l-pi/ 60R (wherein x: the eccentricity of the 1st electrode, R: the radius of the spiral steel pipe, l: the length of a crater).

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for submerged arc welding of Nuviral steel pipes, and more specifically, in a method of manufacturing Nuviral steel pipes by submerged arc welding both edges of a steel strip while spirally winding the steel pipe. This invention relates to a method for manufacturing high-performance Subaio/l/Wi pipes with high productivity by improving weldability by specifying the component composition and appropriately adjusting the eccentricity of the first electrode among multiple electrodes. It is something.

The manufacturing method of Nubaio/l/ steel pipe by welding is as shown schematically in Fig. m1, and the steel strip is wound around a v cane (while being fed in the direction of the arrow r), and the inner side is cut using a torch 2. After welding, the outer surface side is welded using a torch 8'. In this case, in order to improve welding workability and joint performance, the inner surface is generally welded with an upward slope and the outer surface is welded with a downward slope, but from the point of view of the solidification start point of the molten pool, the inner surface is actually welded. The weld slopes downward, and the outside surface side slopes upward. Therefore, on the inner side, the bead tends to form a concave shape, which causes defects such as undercuts, overlaps, abnormal dents, and slag entrainment, while on the outer side, the bead tends to form a convex two-step bead, resulting in the formation of a concave bead. Defects such as curling, undercuts, and abnormal two-step beads are likely to occur. Such joint defects tend to become more significant as the welding speed increases, and in particular, joint defects on the inner surface tend to increase rapidly as the welding speed increases.

Therefore, in order to obtain a spiff μ steel pipe that does not meet the required quality, the welding speed has to be sacrificed, and productivity cannot be increased.

The present inventors focused on the above-mentioned circumstances, and aimed to establish a technology that would enable high-speed welding of the inner surface without causing joint defects such as those described above. We have been conducting intensive research to achieve this goal by adopting the arc welding method.

The present invention was completed as a result of such research, and
Its composition is 5lO3: 20-40% (weight%: the same below, 5, TlO2: 20-55%, MgO: 5-20%
, metal Mn, Fe-Mn.

Mn source such as MrlO%MnO2: 2 in terms of MnO
-20%, inorganic fluoride: 8 to 20% as an essential component, and satisfies 64%≦(SlO+TlO2+Mg0)≦90%, and coarse grains with a grain size of 10 mesh or more:
20% or less, fine particles of 70 mesh or less: 50% or less,
The gist lies in the use of a sintered type fuse that satisfies the following, and performs high-speed latent arc welding on the inner surface of a spiffle steel pipe using a multi-electrode under conditions that satisfy the following formula (I).

In the formula: X: 1st! Extreme Eccentric R: Subaiworu W! Radius of tube e: Length of crater Below, the reason why the composition of the fluff 7 was determined in the present invention will be explained.

First of all, the reasons for deciding on the composition of Fufutsuknu are listed below.

5IO2: 20-40% This is an essential component as a slag forming agent. If it is less than 20%, pock marks tend to occur on the bead surface, the beads tend to overlap, and the bead width becomes uneven. On the other hand, if it exceeds 40%, the rolling of the 7 lugs becomes significant, undercuts are likely to occur, and the bead becomes conspicuous in downward slope welding.

]゛ Amount 0 2: 20 to 55% It functions as a nlag forming agent and a viscosity modifier, and is an extremely important component for iF'+ fast welding, but 20%
If it is less than %, the above-mentioned functions will not be fully exhibited, pits and overlaps will easily occur, and the bead width will become non-uniform. On the other hand, if it exceeds 55%, the amount of nug becomes too large and the viscosity becomes too large, making it easy for slag entrainment and undercutting to occur.

MgO: 5 to 20% Like TIO It becomes easier to do.

Mn such as metal Mn, Fe-Mn, Mn05Mn02, etc.
Source: 2 to 20% as MnO These act as viscosity modifiers, and when blended as metal Mn or Fe-Mn, they also act as deoxidizers, and if it is less than 2%, pits and undercuts will occur. As it becomes easier to remove the slag, the entrainment of slag becomes more noticeable. On the other hand, if it exceeds 20%, overlap defects tend to occur and the stability of the bead width becomes extremely poor.

Inorganic fluoride 28-20% The most typical one is CaF2, which has the effect of increasing the fluidity of the slag and increasing the shielding effect. 8%
If it is less than 20% gold, there will be insufficient shielding and pits and blowholes will occur frequently, while if it exceeds 20% gold, undercutting and slag entrainment will become significant and the slag releasability will deteriorate.

(810+TiO2+Mg0): 64-90% All of these act as slag forming agents, and 64%
If it is less than %, the bead tends to be concave and overlap defects are likely to occur.

- If it exceeds 90%, undercuts are likely to occur.

The component composition of the flux used in the present invention is as above, but in order to achieve the purpose, the particle size composition is further adjusted.Coarse particles of IO mesh or more: 20% or less, fine particles of 70 mesh or less: 50% You must use one that satisfies the following wave characteristics. However, if there are too many coarse particles, the bulk specific gravity of the fluff 7 is too small, which tends to cause overlapping and makes the bead concave. - If there are too many milling particles, the bulk specific gravity of the entire flux will be too strong and undercuts will easily occur. In the present invention, the type of flux is limited to sintered type, and the reason for this is as follows. That is, since the molten type flux has too large a bulk density and too low melting point, a large amount of nwog is produced, resulting in significant overlap and concavity. Therefore, we limited ourselves to sintered flux.

Next, in the present invention, submerged arc welding is performed using multiple electrodes in order to increase the welding speed, but what is extremely important and worth noting here is the position of the first electrode (i.e., the position of the first electrode) from the lowest point of the steel pipe. is the paternal amount). That is, as shown in the schematic diagram of the main part of FIG. 2, internal welding is performed in a downward position, but as a result of various experiments, it has been found that the angle of inclination at the solidification start position of the molten metal is closely related to joint defects. That is, in Fig. 2, 1t is the steel strip, 2a, 2biit [Th, 4 is the molten metal (crater), 5 is the solidified metal, R is the radius of the Svaira/I/#1 pipe to be formed, and 0 is the Nubaira/I 'm lowest point of the tube, Q is the arc generation point of the first electrode 2a, PH co-molten metal solidification start position, AB is the tangent at point P, θ is the tangent A
The angle that H makes with the horizontal plane (inclination angle), g)], and e is the circumferential length of the crater. If the above-mentioned inclination angle 0 is less than 8 degrees, molten metal tends to advance and undercuts occur, whereas if it exceeds 9 degrees, melting occurs. It was confirmed that metal flows in the opposite direction, resulting in significant overlap and bead depression. In other words, the above inclination angle θ
If the welding conditions are set so that the angle is in the range of 8 to 9 degrees, all other joints can be obtained even when high-speed submerged arc welding using multiple electrodes is employed.

However, since this appropriate inclination angle θ is extremely small,
It is not easy to perform welding while accurately detecting this at all times, and furthermore, in the welding method of the present invention, which uses submerged arc welding, it is not possible to confirm the molten pool from the outside. 0 It is impossible to detect with the naked eye. Therefore, in order to make effective use of such knowledge, it is necessary to establish a method for properly controlling the entire inclination angle θ based on factors that can be confirmed from the outside. After further research, we discovered that the first electrode 2
It has become clear that the inclination angle θ can be kept within the range of 8 to 9 degrees by adjusting the eccentricity X of 8 so as to satisfy the equation (I). In the CI) formula, R is the radius of the spiral steel pipe, so it is determined in advance, and l can be confirmed in advance through preliminary experiments, so the eccentricity X of the first electrode 2a is adjusted according to these values. can do.

The present invention is roughly constructed as described above, and uses a flux with a specific composition and adjusts the eccentricity of the first tJM to an appropriate range to perform multi-electrode latent arc welding, thereby eliminating joint defects. It became possible to manufacture spiral steel pipes with high productivity.

Next, experimental examples will be given to clarify the structure and effects of the present invention.

Example: In manufacturing a spiral steel pipe with an outer diameter of 900 mm using a steel strip (STK-41 material) with a thickness of 12 mm, a flux having the composition shown in Table 1 was used, and the flux shown in Table 2 was used. Multi-electrode latent arc welding was performed under the following conditions, and the results shown in Table 8 were obtained.

However, M in Table 8 has the following meaning.

OL = Overwop UC: Undercut Pock: Pockmark plt: pit (Main line゛Uutabox-) From Tables 1 to 8, the following considerations can be made.

Experiment) k 1 to 6 and 17: All of them are examples that satisfy all the requirements of the present invention.
: Both hand performances are extremely good at t7f.

Experiments ff16 and 7: This is a comparative example in which the component composition of the flux satisfies the requirements, but the particle size structure is outside the specified range, and when there are too many fine particles (6), there is frequent maver wop and large bead dents. , - If there are too many union grains, undercuts occur and 7 puffer rolls occur in some parts.

Fire test points 8 to 14: This is a comparative example in which a portion of the Fufutsuknu component composition deviates from the specified requirements, and the appearance and shape of the bead and
Some or both of the light transmission properties are insufficient.

Experiment 15: This is a comparative example in which welding is performed using a 74'4 electrode, and even if other requirements are met, the occurrence of undercuts and the entrainment of slag cannot be eliminated with the Akira electrode.

Fire Test 16: 1st FJ1. Pole deflection X is too large and the inclination angle θ is too large, causing overlap and large bead dents. Moreover, slag entrainment was observed at the overlap occurrence position. It will be done.

Difficulties 18 and 19: The deflection of the first electrode is insufficient and the inclination angle θ is too small, resulting in frequent undercuts and slag entrainment in some areas.

[Brief explanation of drawings]

Figure 1 is a schematic diagram showing an example of welding Svaira μ steel pipe;
FIG. 2 is an explanatory diagram showing a proper tilt angle adjustment method according to the present invention. 1... Steel strip 2, 8... Electrode 4...
Molten metal 5... Solidified metal applicant Nippon Steel Tube Co., Ltd. Kobe Steel Co., Ltd. 7y? Agent: Patent attorney Hisashi Ueki←′□／Pa. 1 mouth□ 11

Claims (1)

[Claims] (1) S102: 20-40% (cloth amount %: same below),
1゛IO□: 20-55%, MgO: 5-20%, Mn source such as metal Mn, Fe-1114n%M102: 2-20% in MnO exchange ticket, inorganic fluoride: 8
~20% as an essential component], and satisfies 64%≦(SlO-11′MO□+MgO)≦90%, and coarse grains with a grain size of 10 mesh or more: 20% or less , 70 mesh or less fine particles: 50% or less, using a sintered flux, the inner surface of the Nubaiworu steel pipe was subjected to multi-electrification (4
(A submerged arc welding method for Nubaiworu 6tj pipe characterized by performing high-speed submerged arc welding at e--R≦X≦e・--R...CI) 20
60 In the formula