Submerged arc welding is mainly suitable for flat welding position welding. If certain tooling aids are used, fillet welding and horizontal welding position welding can also be realized. The main factors affecting the shape and performance of the weld in submerged arc welding are welding process parameters and process conditions. Below we mainly discuss the situation of the flat welding position.
Influence of welding parameters
The welding process parameters that affect the shape and size of the submerged arc welding seam include welding current, arc voltage, welding speed and wire diameter.
(1) Welding current
When other conditions remain unchanged, the effect of increasing the welding current on the weld penetration (as shown in Figure 1), whether it is a Y-shaped groove or an I-shaped groove, under normal welding conditions, the penetration is proportional to the change of the welding current , that is, the effect is shown in Figure 2. The current is small, the penetration depth is shallow, and the excess height and width are insufficient; the current is too large, the penetration depth is large, and the excess height is too large, which is easy to produce high temperature cracks.
a) I-joint b) Y-joint
(2) Arc voltage
The arc voltage is proportional to the arc length. Under the same arc voltage and welding current, if the selected flux is different and the electric field strength in the arc space is different, the arc length will be different. If other conditions remain unchanged, the effect of changing the arc voltage on the shape of the weld is shown in Figure 3.
The arc voltage is low, the penetration is large, the width of the weld is narrow, and hot cracks are easy to occur: when the arc voltage is high, the width of the weld increases, and the excess height is not enough. During submerged arc welding, the arc voltage is adjusted according to the welding current, that is, a certain welding current must maintain a certain arc length to ensure the stable combustion of the welding arc, so the variation range of the arc voltage is limited.
a) I-joint b) Y-joint
(3) Welding speed
The welding speed has an effect on the penetration depth and width. Usually, the welding speed is small, the welding pool is large, and the weld penetration and width are both larger. That is, the penetration depth and penetration width are inversely proportional to the welding speed, as shown in Figure 4. The effect of welding speed on the shape of the weld section is shown in Figure 5.
The welding speed is too small, the amount of molten metal is large, and the welding seam is poorly formed: when the welding speed is high, the amount of molten metal is insufficient, and undercut is easy to occur. In actual welding, in order to improve productivity, the arc power must be increased while increasing the welding speed to ensure the quality of the weld.
H - penetration depth B - penetration width
Fig. 5 Influence of welding speed on the shape of weld section
a) I-joint b) Y-joint
(4) Welding wire diameter
When the welding current, arc voltage and welding speed are constant, the shape of the welding seam will change due to the different diameter of the welding wire.
The influence of the current density on the shape and size of the weld shown in Table 1 can be seen from the table, other conditions remain unchanged, the penetration depth is inversely proportional to the diameter of the welding wire, but this relationship weakens with the increase of the current density. With the increase of current density, the amount of molten metal in the molten pool continues to increase, and it is difficult for the molten metal to move backward, and the penetration depth increases slowly. The arc voltage should be increased at the same time as the welding current to ensure the quality of the welding seam.
Influence of Process Conditions on Weld Forming
(1) Influence of butt groove shape and clearance
When other conditions are the same, increasing the groove depth and width, the weld penetration increases, the fusion width decreases slightly, and the excess height decreases significantly, as shown in Figure 6. In the butt weld, if the gap size is changed, the shape of the weld can also be adjusted. At the same time, the thickness of the plate and the heat dissipation conditions also have a significant impact on the weld width and excess height, as shown in Table 2.
(2) Influence of wire inclination and workpiece inclination
The inclination direction of the welding wire is divided into two types: forward inclination and backward inclination, as shown in Figure 7. The direction and size of the inclination are different, the effect of the arc on the blowing force and heat of the molten pool is different, and the influence on the welding seam formation is also different. Fig. 7a shows the forward tilt of the welding wire, and Fig. 7b shows the backward tilt of the welding wire. When the welding wire is tilted back within a certain inclination angle, the effect of the arc force on the molten pool metal is weakened, and the liquid metal at the bottom of the molten pool thickens, so the penetration depth decreases. However, the preheating effect of the arc on the base metal in front of the molten pool is strengthened, so the melting width increases. Figure 7c shows the effect of back inclination on the penetration depth and penetration width. In actual work, the forward tilt of the welding wire is only used in some special cases, such as welding the circular seam of small diameter cylindrical workpieces.
There are two cases of upslope welding and downslope welding when the workpiece is inclined welding, and their influences on the weld formation are obviously different, as shown in Figure 8. During uphill welding (Fig. 8a, b), if the inclination β angle is greater than 6° to 12°, the excess height of the weld is too large, undercuts appear on both sides, and the forming is significantly deteriorated. In practice, uphill welding should be avoided. The effect of downhill welding is opposite to that of uphill welding, see Figure 8c, d.
a) Forward tilt b) Backward tilt c) Influence of wire back tilt angle on weld formation
(3) Influence of flux buildup
The height of the submerged arc welding flux is generally 25-40mm, and the arc should be buried around the filament. When using bonded flux or sintered flux, the flux stack height is 20% to 50% higher than that of smelted flux due to its low density. The greater the flux build-up height, the greater the weld height and the shallower the penetration depth.
Influence of Welding Process Conditions on Weld Metal Properties
When the welding conditions change, the dilution rate of the base metal and the flux melting ratio (flux melting amount/welding wire melting amount) all change, which affects the properties of the weld metal, among which the welding current and arc voltage have a greater impact. Figures 9 to 11 show the effects of welding current, arc voltage and welding speed on the flux melting ratio.
Due to the change of the flux melting ratio, the chemical composition and mechanical properties of the weld metal change, especially the addition of alloying elements in the sintered flux has the greatest impact on the chemical composition of the weld metal. Figures 12 to 14 show the effects of various welding conditions on the Mn and Si contents of the weld metal.
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