JPS6032558B2 - Melting type flux for submerged arc welding - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention aims to improve efficiency and save resources in multilayer submerged arc welding, such as circumferential welding of small-diameter extra-thick steel pipes such as steel pipes for pumps and boilers. The present invention also relates to a melting type flux for submerged arc welding that has extremely good slag removability and excellent mechanical performance of weld metal.

Submerged arc welding is a method of welding by covering the arc with flux, and at the end of welding, the surface of the weld bead is covered with flux (slag) that has solidified after being melted, so this slag must be removed after each pass. The difficulty of removing slag (slag removability) greatly affects the number of construction steps during submerged arc welding.

This slag removability generally tends to deteriorate within the joint, especially when the groove is narrow, when the welding heat input is large, and when the temperature between preheating passes is high. A proposal for a welding method that improves the efficiency of welding by improving these problems in terms of welding conditions is found in Tokukankai No. 53-26241. This method limits the current density of the wire and fills the welding area with filler metal (fine steel pieces) according to the amount of welding heat input, and although it is quite effective, it is not possible to use conventional flux. Since this is multilayer welding and the slag removability of the flux itself has not been improved, the groove width has not been narrowed yet. On the other hand, the plate thickness of the main steam pipes of recent ultra-high pressure boilers reaches 1.00 to 150 mm, and submerged arc welding is often used in factory welding. Flux through welding is desired.

Furthermore, in such multi-layer welding, it is considered to reduce the joint cross-sectional area as much as possible in order to shorten welding time and save welding materials, and there is a demand for the development of a flux that can easily remove slag even within such narrow joints. has been done. However, conventional fluxes have a limit in terms of their slag removability, and the joint angle is usually 60% or more for X grooves, and in the case of thick plates, relatively wide U grooves are used for 2 to 3 Currently, layer welding is being carried out in passes.

In addition, in such continuous circumferential welding of 2 to 3 passes per layer, 1
It is necessary to shift the welding position for each circumference, which not only makes operation of the welding device extremely difficult, but also has disadvantages in that the appearance is poor or welding defects are likely to occur. From this perspective,
An attempt to improve the slag removability of the flux itself from the viewpoint of its composition is found in JP-A-52-94836.

This proposal is based on P8 of the Sj02-Mn○ system flux.
However, the basicity of the flux itself is low and the amount of oxygen in the weld metal increases, and the addition of PBO deteriorates the impact rut resistance, so there are problems that it cannot be applied to multilayer welding with more than a few passes. be. Therefore, in circumferential welding, the present inventors have developed a flux that provides a good bead shape even when layer welding is performed in one pass per layer, even within a narrow angle groove or a narrow U-shaped groove, and which is easy to remove slag. For the purpose of developing ``external diameter 355.'' using fluxes of various compositions.
A flux with good slag removability and bead shape was selected by performing one-pass circumferential welding using the submerged arc welding method in a V-groove with a joint angle of 4Qo cut in the circumferential direction of the steel pipe on the 6th side. As a result of investigating the relationship between
Contains a relatively large amount of i and neutral component AI203~
The remainder is occupied by CaF2, Mn○, Ca○, Mg0chi, etc., so to speak, S weight 02 single needle 203-Ti02 flux has a completely new slag removability and bead shape that are far superior to conventional fluxes. I gained knowledge.

In Figure 1, 0 indicates slag peeling, both bead shapes are good, △ indicates either one is defective, and × indicates slag peeling.
This indicates that both the bead shape is defective. The present invention has been made based on the above findings, and is based on the knowledge that Sj02 is more than 20% and less than 25% in weight percentage.
20~40%"Ti0212~25%"CaF24~
A melting type for submerged arc welding characterized by containing 16% or less of Mn, 07% or less of Ca, 09% or less of Ca, and 25% or less of Ba, the total of which is in the range of 13 to 30%. Next, three reasons for limiting each component of the flux of the present invention will be described.

First, Sj02 is an important component that forms slag and regulates basicity, but in this system, if it exceeds 25%, the viscosity of the slag increases and it is difficult to form a uniform pead.
Slag removability deteriorates.

In addition, the amount of oxygen in the 4 weld metal increases and the impact resistance deteriorates. On the other hand, when t is less than 20%, not only does the amount of diffusible hydrogen in the weld metal increase, but also when circumferentially welding small, extremely thick tubes, the viscosity of the slag is insufficient and the slag flows, resulting in incomplete shielding of the weld metal, resulting in bead formation. The shape deteriorates and welding defects such as slag entrainment and blowholes occur frequently.In addition, in this case, it is necessary to increase the amount of expensive Ti02 to maintain the balance with the basic component, which is undesirable from a cost standpoint.N20
3 is an effective component for adjusting the melting point and viscosity without changing the basicity of the flux, but if it exceeds 40%, the melting point and viscosity become too high and the welding process deteriorates.

On the other hand, if it is less than 20%, good beads may not be obtained even though the fire resistance is poor, and the slag removability will be impaired. It increases the slag removability and is an indispensable component for the flux of the present invention. However, if t exceeds 25%, the fluidity of the slag increases too much, impairing the uniformity of the bead shape, and the slag removability actually deteriorates.

If it is less than 12%, the arc becomes unstable and it becomes difficult to obtain a uniform beat, especially in circumferential welding. However, if i exceeds 6%, the arc becomes unstable, the bead waveform becomes rough, and the slag removability deteriorates.

On the other hand, if it is less than 4%, the shielding is insufficient and bit rough flow holes are likely to occur, and the amount of oxygen in the weld metal increases, resulting in a decrease in impact rice grain properties. Mn0 is generally used as a slag forming agent and is effective in controlling the amount of Mn in the weld metal, but in this system, if it exceeds 7%, the viscosity of the slag decreases, making it difficult to form good beads and deteriorating the slag removability. .

Furthermore, the amount of Mn and oxygen in the weld metal becomes too large, impairing impact toughness. Ca0 is an effective component for adjusting the basicity melting point of slag, but if it exceeds 9%, the arc becomes unstable and the melting point rises too much, making it difficult to obtain uniform beads and deteriorating slag removability.

Like Ca○, Mza0 is used to adjust the basicity and melting point of the slag, but if it exceeds 15%, the amount of diffusible hydrogen in the weld metal increases, causing welding defects such as cracks and bits.

Spot 0 is also used as a basic component to adjust the fluidity and melting point of the slag, but if it exceeds 25%, the amount of diffusible hydrogen in the weld metal increases and causes welding defects.

It is also expensive and undesirable from a cost standpoint. Furthermore, the total amount of one or more basic components of Mno, Cao, Mko, and acid 0 has an appropriate range in terms of balance with the acidic components of Sj02 and Ti02. That is, Mn0, Ca○, Mg○, Ba
If the sum total of one or more types of 0 exceeds 30%, the basicity of the slag becomes too high, the melting point becomes high, the uniformity of the bead deteriorates, and the slag removability is impaired. The amount of diffusible hydrogen in the weld metal also increases. On the other hand, when the slag is 13% full, the viscosity of the slag increases, making it impossible to form uniform beads, deteriorating the slag removability, and increasing the amount of oxygen in the weld metal.
Impact ballability is reduced. In addition to the above components, Zr02 contains 7
%, K20, Na20, Lj20 up to a total of 3% L
B203 can be contained within a range of up to 1%. Next, the effects of the present invention will be explained in more detail based on Examples.

Example 1 Using the flux shown in Table 1 and the WI wire shown in Table 2, 0.5 of an inner diameter of 25 mm and an outer diameter of 35 mm
Continuous circumferential welding of 12 to 13 layers of Mo Kokomachi steel pipes was performed under the welding conditions shown in Table 3, with one pass for each layer, and the welding workability was compared.

Note that the groove shape in this case is as shown in FIG. 2 with a groove angle loo and a U junction with a depth of 4 mm. In addition, for fluxes that have poor slag removability and cannot be continuously welded,
Welding was interrupted every rotation to remove slag. This result is shown in Table 4, where the comparative flux had poor slag removability, poor bead appearance, and welding defects, whereas the inventive flux had extremely excellent slag removability and good bead appearance. No pock marks or defects such as bits were observed.The impact toughness was tested by taking a 2-rib V-notch Charpy test piece (JIS Z31124 test piece) from two holes below the outer surface of the steel pipe. The amount of diffusible hydrogen was measured according to the method specified by JSSC.

For fluxes with poor slag removability and bead appearance, impact tests and diffusible hydrogen content were omitted. Table 1*Z
r02, K20, Na20, Lj20, B203, etc. Table 2 Table 3 Table 4 Suraku Kagunada ◎: Thoroughly natural Isomyo ○: Yasu Iso with full-length attack △
: Difficult to peel ×: Bead shape that cannot be peeled ○: Good △:
Fairly good ×: Rough Example 2 A U-shaped groove joint (welded length approximately 6 m) of SM-5 female wire made of 80 willow plate was made by combining the FI and commercially available flux shown in Table 4 with the W2 wire shown in Table 2. We compared the required time and welding material consumption by performing mass welding.

The results are shown in Table 5. The flux of the present invention has excellent slag removability even in narrow grooves, so compared to conventional commercially available fluxes, both welding man-hours and welding material consumption can be significantly reduced. did it. The welding conditions in this case were all 650A-32V-30c/min, and the groove shape and layering method were as shown in FIG.

Table 5 and above The flux of the present invention exhibits extremely good slag removability even in narrow joints, reduces the number of welding work, and makes it possible to significantly reduce the amount of welding material by narrowing the groove, which has extremely high industrial value. big.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the relationship between slag removability and flux composition, and FIGS. 2 and 3 are diagrams showing the groove shapes of steel pipes and steel plates in Examples 1 and 2. *3 Illustrations Hair Diagram 2 Illustrations

Claims (1)

[Claims] 1 In weight percent, SiO_220% but not more than 25%, Al_2O_320-40%, TiO^212-25
%, contains 24-16% of CaF, and further contains 7% of MnO.
Below, CaO 9% or less, MgO 15% or less, BaO25
% or less, and the total of them is 13~
A melting type flux for submerged arc welding characterized by a flux in the range of 30%.