JP5334725B2 - Sintered flux for 9% Ni steel submerged arc welding - Google Patents

Description

  The present invention relates to a sintered flux used for submerged arc welding of 9% Ni steel used as a construction material for cryogenic liquid storage tanks such as liquefied natural gas, and in particular can be welded in a vertical welding position, and The present invention relates to a sintered flux for 9% Ni steel submerged arc welding that can be applied to downward and lateral postures, has good slag peelability, and has excellent defect resistance and bead smoothness.

  Conventionally, in welding of 9% Ni steel used as a construction material for a cryogenic liquid storage tank, a coated arc welding method having a relatively low heat input has been applied to prevent hot cracking. Since then, wires with excellent hot cracking resistance have been developed, and the application of submerged arc welding methods to places where downward or lateral posture welding is applied for the purpose of improving the construction efficiency of welded buildings is increasing.

  On the other hand, in the vertical position welding, automatic TIG welding is applied to improve construction efficiency, and partial automatic MAG welding has been promoted. However, in areas where it is difficult to obtain welding gas in field construction, it is still necessary to rely on the coated arc welding method.

  Therefore, in order to improve the construction efficiency in the field where welding gas is not available, there is a demand for the development of a welding material that can apply the submerged arc welding method to vertical welding.

  Conventionally, for submerged arc welding materials of low-temperature steel, when welding is performed in an upright position, the molten metal flows due to gravity during the solidification process, so the bead shape tends to be unstable and convex, and the weld bead There were problems such as the need for smoothing with a grinder.

Therefore, for example, in Patent Document 1, Al ₂ O ₃ : 31 to 60% by mass, CaF ₂ : 10 to 40% by mass, SiO ₂ : 1 to 10% by mass, and Na ₂ O: 0 with respect to the total mass of the flux. 0.1-5% by mass, metal Al: 1-10% by mass, and others are CaCO ₃ , CaO, MgO, metal Mn and a flux for submerged arc welding of low temperature steel which is an inevitable impurity.

  The technology of Patent Document 1 improves arc stability, slag peelability, weld defect resistance, and bead shape in vertical posture welding in addition to downward and horizontal postures by regulating the flux composition within the above range. Is intended.

JP 2009-039761 A

  However, although the technique of the above-mentioned patent document 1 improves the arc stability, slag peelability and weld defect resistance in the vertical posture welding, the smoothness of the weld bead is insufficient. In particular, the submerged arc welding flux of Patent Document 1 has a problem that the shape in the bead longitudinal direction tends to be discontinuous. Therefore, it is hoped to develop a flux for submerged arc welding that can sufficiently satisfy all of the slag peelability, weld defect resistance and bead shape stability (smoothness) in the vertical position welding. It is rare.

  The present invention has been made in view of such a problem, and in addition to the downward and lateral postures, the vertical posture welding also has good slag peelability and weld defect resistance, and has an excellent bead shape. An object of the present invention is to provide a sintered flux for 9% Ni steel submerged arc welding capable of obtaining smoothness.

The sintered flux for 9% Ni steel submerged arc welding according to the present invention is a sintered flux for 9% Ni steel submerged arc welding used in combination with a wire containing Ni: 60% by mass or more per total mass of the wire. The flux composition is Al ₂ O ₃ : 15 to 40% by mass, SiO ₂ : 5 to 35% by mass, ZrO ₂ : 5 to 25% by mass, MgO: 5 to 25% by mass, based on the total mass of the flux. It contains CaCO ₃ : 5 to 25% by mass and metal Al: 1 to 7% by mass, suppresses CaF ₂ to 5% by mass or less, and the balance is metal Fe, Na ₂ O and inevitable impurities. Features.

  Furthermore, it is preferable to contain 0.1 to 5 mass% of metal Ti.

  Moreover, the sintered flux for 9% Ni steel submerged arc welding of the present invention can be used for submerged arc welding in a vertical welding position.

  According to the present invention, it is possible to obtain a sintered flux for 9% Ni steel submerged arc welding having good slag peelability and weld defect resistance and further having excellent bead-shaped smoothness.

It is a figure which shows the shape and size of a welding base material in case a welding attitude | position is downward, Among them, (a) is a front view, (b) is sectional drawing which shows a groove shape, (c) is lamination | stacking It is a schematic diagram which shows the point. It is a figure which shows the shape and size of a welding preform | base_material in the case where a welding attitude is horizontal, among which (a) is a front view, (b) is sectional drawing which shows a groove shape, (c) is a lamination | stacking procedure It is a schematic diagram which shows. It is a figure which shows the shape and size of a welding preform | base_material in the case where a welding attitude | position is a vertical improvement, (a) is a front view, (b) is sectional drawing which shows a groove shape, (c) is It is a schematic diagram which shows the lamination | stacking point. It is a figure which shows the criteria of the largest uneven | corrugated fluctuation | variation among bead shape evaluation criteria, among which (a) is a front view, (b) is sectional drawing. It is a figure which shows the criterion of the largest width fluctuation | variation among bead shape evaluation criteria.

The inventors have adjusted the flux components in various ways, and by using refractory oxides such as MgO, CaCO ₃ , and ZrO ₂ as main components in addition to Al ₂ O ₃ , the bead shape in the downward and lateral orientations. In addition to being effective for smoothing, it has been found that it is effective for smoothing the bead shape even in the vertical welding position. Furthermore, the present inventors found that CaF ₂ has an effect of making the bead wave finer, but when it is contained in excess of a predetermined amount, the bead shape tends to be discontinuous, and the number of blow holes tends to increase. It was. The present inventors have completed the present invention based on these findings. Hereinafter, the reason for component addition and composition limitation of the sintered flux for 9% Ni steel submerged arc welding according to the present invention will be described.

Al ₂ O ₃ : 15 to 40% by mass
Al ₂ O ₃ in the flux acts as a slag forming agent and is an effective component for increasing the solidification temperature and viscosity of the molten slag. If the Al ₂ O ₃ content in the flux is less than 15% by mass, the bead holding power of the molten slag becomes insufficient in the vertical position welding, and the bead becomes convex or melts off. On the other hand, when Al ₂ O ₃ exceeds 40 mass%, the viscosity of the slag becomes too high and the fluidity becomes poor, so that slag entrainment occurs. Further, when Al ₂ O ₃ exceeds 40% by mass, the bead wave becomes rough and a pock mark is generated in the downward and horizontal postures.

A more preferable range is Al ₂ O ₃ : 20 to 35% by mass. In this range, the bead holding force of the molten slag becomes more appropriate particularly in vertical welding, and the bead shape is stably smoothed, so that a better bead appearance can be obtained.

SiO ₂ : 5 to 35% by mass
SiO ₂ in the flux needs to be 5 to 35% by mass. SiO ₂ in the flux increases the solidification temperature of the molten slag. In addition, the bead holding force is increased in the standing posture, and the bead shape is stabilized. If SiO ₂ is less than 5% by mass, the bead shape becomes unstable due to insufficient bead holding power of the molten slag. On the other hand, when SiO ₂ exceeds 35 mass%, the viscosity of the molten slag becomes too high, the slag peelability is deteriorated, and slag entrainment occurs.

A more preferable range is SiO ₂ : 10 to 25% by mass. In this range, the slag peelability is improved, and particularly in a standing posture, even better slag peelability is obtained, and the bead shape is stably smoothed, so that a good bead appearance can be obtained. it can. In this range, the bead shape at the time of welding in the downward and lateral postures is also stable. The SiO _2, silica sand, other water glass, may also be added a composite oxide such as wollastonite.

ZrO ₂ : 5 to 25% by mass
ZrO ₂ in the flux is an effective component for improving the slag peelability. If ZrO ₂ is less than 5% by mass, this effect cannot be obtained, and the slag removability is poor, for example, the slag is baked on the bead. On the other hand, when ZrO ₂ exceeds 25% by mass, the fluidity of the molten slag is lowered and slag entrainment is likely to occur.

A more preferable range is ZrO ₂ : 10 to 20% by mass. In this range, the slag peelability is improved, and particularly in a standing posture, even better slag peelability is obtained, and the bead shape is stably smoothed, so that a good bead appearance can be obtained. it can.

MgO: 5 to 25% by mass
MgO in the flux has an effect of increasing the solidification temperature of the slag, and is an effective component for bead shape stability in the longitudinal direction. This effect cannot be obtained if the amount is less than 5% by mass, and the bead melts off frequently in the standing posture. On the other hand, when MgO exceeds 25 mass%, solidification of slag is completed early, so that the bead shape becomes convex and slag entrainment is likely to occur, and slag releasability is deteriorated.

  A more preferable range is MgO: 10 to 20% by mass. In this range, the slag peelability is improved, and even more excellent slag peelability is obtained particularly in the standing posture, and the bead shape is stably smoothed, so that a good bead appearance can be obtained. .

CaCO ₃ : 5 to 25% by mass
CaCO ₃ in the flux needs to be 5 to 25% by mass. CaCO ₃ is melted decomposition, becomes the CaO and CO ₂ gas, CO ₂ gas is reduced partial pressure of water vapor in the welding arc atmosphere, the effect of reducing the blow hole while reducing the amount of hydrogen in the weld metal . Further, CaO has an effect of increasing the solidification temperature of the molten slag, and the bead shape is stabilized. In a region where CaCO ₃ is less than 5% by mass, the above effect cannot be obtained, and the bead shape is convex. On the other hand, in a region where CaCO ₃ exceeds 25% by mass, the slag peelability is lowered.

A more preferable range is CaCO ₃ : 10 to 20% by mass. In this range, the solidification temperature of the slag further rises and the bead shape is further smoothed and smoothed, so that a good bead appearance can be obtained.

Metal Al: 1 to 7% by mass
Metal Al is a component having the effect of significantly reducing the amount of oxygen in the weld metal and suppressing the generation of blowholes by adding it to the flux as a deoxidizer. When the metal Al is less than 1% by mass with respect to the total weight of the flux, the effect cannot be sufficiently obtained. On the other hand, when it exceeds 7 mass% per flux total weight, slag peelability will deteriorate. Metal Al can be added to the flux by a simple substance or an Fe—Al alloy.

  A more preferable range is metal Al: 2 to 5% by mass. In this range, it is possible to achieve both better slag peelability and further blow hole resistance.

CaF ₂ : 5 mass% or less CaF ₂ is added as an essential component to the conventional flux for submerged arc welding, but in the present invention, CaF ₂ is suppressed to 5 mass% or less. Although CaF ₂ has the effect of stabilizing the arc and making the bead wave finer, it has the effect of lowering the solidification temperature and viscosity of the slag, so the bead shape in the longitudinal direction is unstable, particularly in a vertical position welding. And the beads are easily melted down. Since this tendency appears remarkably when CaF ₂ in the flux exceeds 5 mass%, CaF ₂ needs to be suppressed to 5 mass% or less.

Metal Ti: 0.1 to 5% by mass
Ti raises the solidification temperature of the slag and has the effect of suppressing bead burnout during lateral and vertical welding. If the metal Ti is less than 0.1 mass% with respect to the total weight of the flux, the effect cannot be sufficiently obtained. On the other hand, when metal Ti exceeds 5 mass% per flux total weight, slag peelability will deteriorate. Therefore, when it contains metal Ti, it is 0.1 to 5 mass%. Metal Ti is added as a simple substance or Fe—Ti.

  Hereinafter, the effects of the present invention will be described specifically by way of examples. First, a flux raw material is prepared, water glass is added as a fixing agent to this, granulated, and then sintered to obtain sintered fluxes for submerged arc welding having various chemical compositions shown in Table 1 below. Produced.

  As the base material and the wire, those having chemical compositions shown in Tables 2 and 3 below were used.

  Downward welding was performed under the welding conditions shown in Table 4 below. The shape and size of the weld base material in downward welding are shown in FIG. Fig.1 (a) is a front view which shows the shape and size of a welding base material in case a welding attitude is downward, FIG.1 (b) is sectional drawing which shows a groove shape, FIG.1 (c). FIG. 3 is a schematic diagram showing a lamination procedure.

  Lateral welding was performed under the welding conditions shown in Table 5 below. The shape and size of the weld base material in the transverse welding are shown in FIG. FIG. 2A is a front view showing the shape and size of the weld base material when the welding posture is horizontal, FIG. 2B is a sectional view showing the groove shape, and FIG. It is a schematic diagram which shows the lamination | stacking point.

  Vertical welding was performed under the welding conditions shown in Table 6 below. The shape and size of the weld base material in vertical welding are shown in FIG. FIG. 3A is a front view showing the shape and size of the weld base material when the welding posture is standing up, and FIG. 3B is a cross-sectional view showing the groove shape, and FIG. ) Is a schematic diagram showing a lamination procedure.

  The above evaluation results are shown in Table 7. Submerged arc welding was performed in each of the downward, lateral, and vertical welding postures to determine the bead shape and slag detachability (welding workability), and further, a radioactive transmission test of the welded portion was performed.

  As shown in FIGS. 4 and 5, the bead shape is evaluated by setting the field of view to be 30 × 30 mm at a welding length of 500 mm, changing the height unevenness of the center of the bead except for 50 mm from the crater part and the start part, and the lateral bead. Judgment was made at the position where the width fluctuation was maximum. 4A and 4B are diagrams showing determination criteria for the maximum unevenness, in which (a) is a front view and (b) is a cross-sectional view. FIG. 5 is a criterion for determining the maximum width variation. The positions of the projections and depressions for the unevenness and the lateral width are independent, and the judgment criteria shown in Table 8 are used, and the judgment results of the lower judgment level among the judgment results of the unevenness variation difference and the lateral width variation difference are adopted as the judgment results.

  The slag peelability is ◎ when the slag is completely peeled over the entire length of the bead due to less than 11 hits by the slag hammer. After 10 hits by the slag hammer, the slag is slag Although it remains a little, it was marked with ○ if it could be removed by impact with a slag hammer less than 11 to 20 times, and it was difficult to remove all slag with a slag hammer. The case where the slag could be easily peeled by △ was evaluated as Δ, and the case where the slag could not be completely removed even when the above tool was used was evaluated as ×.

  Moreover, the radioactive penetration test was implemented about the welding part and defect resistance was evaluated using JISZ3106 for the criteria. That is, in the radioactive transmission test, the classification method of the image of the flaw in the transmission test of the welded joint is the first type of round blowhole and similar flaws, entrainment of elongated slug, pipe, poor penetration, poor fusion and this. Similar scratches were classified as type 2, cracks and similar scratches were classified as type 3. For flaws that are difficult to distinguish between type 1 flaws and type 2 flaws, they are categorized independently as type 1 flaws or type 2 flaws, of which the larger classification number is the flaw. And the classification number. The first type of flaw score was determined according to the following method. That is, in the measurement of the number of scratch points of the first type, the plate thickness was 20 mm, so the size of the test visual field was 10 mm × 10 mm. When scratches were found on the boundary line of the test field, measurements were made including the part outside the field of view. The value in Table 9 below was used as the number of flaws in the case of one flaw of the first type depending on the major diameter of the flaw. The number of flaws in the case of two or more flaws was the sum of the number of flaws in each flaw existing in the test visual field.

  The classification of the first type of flaw image was in accordance with Table 10 below. The numerical values in Table 10 indicate the allowable values for the number of flaws within the test field. However, when the major axis of the flaw exceeds 1/2 of the thickness of the base material, it was classified into 4 types.

  The classification of the image of the second type of flaws was according to Table 11 below. The size of the test field is the same as the first type. In addition, even if classified as Class 1, if there was poor penetration or poor fusion, it was classified as Class 2.

  The general classification of flaws was as follows. That is, when there is only one type of flaw, the classification is set as a general classification. When there were two or more types of flaws, the one with the larger classification number was taken as the general classification. However, if the second type of flaws to be classified are mixed in the test field of the first type of flaws, and if the classification by the number of flaws and the classification by the length are both the same, the classification of the mixed part Increased the classification number by one. At this time, the first type was classified into the second type when it exceeded 1/2 of the allowable length of the first type and second type flaws.

  As shown in Table 1 and Table 7 above, since the chemical composition in the flux is appropriately regulated in Examples 1 to 6, the bead shape smoothness and slag peelability during welding are good, and the radiation transmission test In the evaluation, all were judged as 1 type and 1 type.

  In Example 7, the bead shape was slightly unstable as compared with Examples 1 to 6 because the Ti content in the flux was less than the lower limit of the range of the present invention.

  About Example 8, since content of Ti in a flux exceeded the upper limit of the range of the present invention, slag peelability was somewhat inferior.

(Comparative Examples 9 and 10)
On the other hand, in Comparative Example 9, the content of Al ₂ O _{3 in} the flux exceeds the upper limit of the range of the present invention, and the content of SiO ₂ is less than the lower limit of the range of the present invention. In addition to coarsening of the eyes, the bead shape was unstable and slag entrainment occurred in vertical welding.

In Comparative Example 10, since the content of Al ₂ O _{3 in} the flux is less than the lower limit of the range of the present invention and the content of SiO ₂ exceeds the upper limit of the present invention, the bead shape smoothness and slag peelability are In addition to the decrease, slag entrainment occurred.

(Comparative Examples 11 and 12)
In Comparative Example 11, since the content of ZrO _{2 in} the flux exceeds the upper limit of the range of the present invention and the content of CaCO ₃ is less than the lower limit of the range of the present invention, the bead shape smoothness is lowered and slag entrainment occurs. did.

In Comparative Example 12, the content of ZrO _{2 in} the flux is less than the lower limit of the range of the present invention, and the content of CaCO ₃ exceeds the upper limit of the range of the present invention. Declined.

(Comparative Examples 13 and 14)
In Comparative Example 13, the content of MgO in the flux exceeds the upper limit of the range of the present invention, and the content of Al is less than the lower limit of the range of the present invention, so that the bead shape becomes convex and the bead shape smoothness decreases. In vertical welding, slag winding occurred. Moreover, the blowhole resistance decreased.

  In Comparative Example 14, the content of MgO in the flux is less than the lower limit of the range of the present invention, and the Al content exceeds the upper limit of the range of the present invention. As the force decreased, the bead shape smoothness in lateral and vertical welding decreased.

(Comparative Example 15)
In Comparative Example 15, since the Ti content in the flux is less than the lower limit of the present invention range and the CaF ₂ content exceeds the upper limit of the present invention range, the bead shape smoothness is reduced, and vertical welding is performed. Then melted down occurred.

(Comparative Examples 16 and 17)
In Comparative Example 16 and Comparative Example 17, the content of MgO in the flux is less than the lower limit of the more preferable range of the present invention, and the content of CaF ₂ exceeds the upper limit of the present invention range. The bead shape smoothness in the direction welding decreased, and the burnout occurred in the vertical welding.

  As described above in detail, according to the present invention, by appropriately regulating the chemical composition in the sintered flux for 9Ni steel submerged arc welding, it is possible to produce an excellent bead in welding in the downward, lateral and vertical postures. Smoothness, slag peelability and weld defect resistance can be obtained.

Claims (3)

A sintered flux for 9% Ni steel submerged arc welding used in combination with a wire containing Ni: 60% by mass or more per wire total mass, wherein the flux composition is
Al ₂ O ₃ : 15 to 40% by mass,
SiO ₂ : 5 to 35% by mass,
ZrO ₂ : 5 to 25% by mass,
MgO: 5 to 25% by mass,
CaCO ₃ : 5 to 25% by mass,
And 9% Ni steel submerged arc, characterized in that it contains 1 to 7% by mass of metal Al, suppresses CaF ₂ to 5% by mass or less, and the balance is metal Fe, Na ₂ O and inevitable impurities. Sintered flux for welding.   2. The sintered type flux for 9% Ni steel submerged arc welding according to claim 1, comprising metal Ti: 0.1 to 5% by mass.   The sintered type flux for 9% Ni steel submerged arc welding according to claim 1 or 2, which is used for submerged arc welding in a vertical welding posture.

Images