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Single Pass Arc Welding of Thick Steel Plates

Introduction

Improved productivity continues to be the primary goal for most fabricators. Productivity of arc welding can be improved by adopting welding techniques providing increased penetration and increased deposition rates.  A metal active gas (MAG) welding process variant known as D-Arc® developed by DAIHEN Corporation is a step in this direction. This process is based on MAG welding process principles, but operates with significantly higher currents and wire feed speeds. As a result, establishing adequate heat affected zone (HAZ) properties is quite critical in achieving wider acceptance for the process in the industry. Bearing this in mind, TWI undertook an investigation into the capabilities of D-Arc® welding, and the effect of relatively high heat input associated with this process on hardness and toughness of the resulting welded joints on a range of steel grades.

Objectives

The objective of this investigation was to see if the high metal deposition rates and deep penetration possible with D-Arc® welding could successfully join steel plates of up to 20mm with single pass welding, and without any significant degradation in mechanical properties in the weld and the HAZ.

Approach

Two sets of welding trials were conducted. The first set was aimed at understanding the effect of D-Arc® welding on toughness of the weld metal produced with high strength welding consumables. Welded samples were produced with high strength metal cored wires (E90T and E110T) with pure carbon dioxide shielding, to understand the effect of D-Arc® on the resulting weld metal hardness and toughness. This was then followed by welding trials on medium strength (S355J2 and S460N) structural steel plates of 20mm thickness to understand the effect of high heat input on the HAZ toughness and hardness.

 

Results

The limited number of welding trials and tests carried out in this experimental programme demonstrated the capability of the D-Arc® process to produce full penetration single pass welds on 20mm thick butt joints with backing. The produced welds were without any significant spatter or distortion. The accuracy of the joint preparation and the fit-up of the plates onto the backing support was found to be critical in obtaining a consistent joint. Limited fillet welding trials in the flat welding position showed that fillet welds of up to 20mm throat thickness could be produced in a single pass with the D-Arc® process, although susceptibility to centreline cracking was observed under certain welding conditions.

Charpy impact testing did not show any major reduction in toughness of coarse grained HAZ on S355J2 or S460N steel plates.  Acceptable weld metal toughness also could be achieved with appropriate welding consumables. A hardness survey of the welds did not indicate any abnormal effect of welding on the weld metal or the HAZ hardness.

Conclusions

The ability to provide single pass full penetration butt welds on 20mm thick plates, without significant reduction in HAZ mechanical properties, make the D-Arc® an attractive option for thick section welding with improved productivity.

Figure 1. General Configuration of the D-Arc® welding set-up (Ref: DAIHEN Corporation WST-0021E1.7)
Figure 1. General Configuration of the D-Arc® welding set-up (Ref: DAIHEN Corporation WST-0021E1.7)
Figure 2. Transverse section photomacrograph of a typical butt weld on 20mm plate
Figure 2. Transverse section photomacrograph of a typical butt weld on 20mm plate
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