Powdered Submerged Arc Strip Electrode Overlay Welding Process

Literature Overview

This paper by Ma Hongze, Jiang Lipeng, Yu Jianrong, Huang Wenzhe, and Qian Qiang (1998) from Beijing Institute of Petrochemical Technology and the Harbin Welding Research Institute investigates the powdered submerged arc strip electrode (P-SASE) overlay welding process. This technique combines the high deposition rate of strip electrode submerged arc welding with the alloy flexibility of powder-fed systems. The paper addresses a fundamental limitation of conventional strip electrode SAW: the difficulty of rolling strip electrodes containing high alloy content due to the brittleness and poor formability of high-alloy strip. The powdered approach circumvents this by feeding the strip electrode as a base carrier and separately adding alloy powder to the arc, thereby decoupling the mechanical formability requirements from the chemical composition requirements.

Core Technical Content

Process Principle

In conventional submerged arc strip electrode welding, the electrode is a rolled strip of the desired composition. For high-alloy compositions such as those containing 5% Cr, 3% Mo, 2% Ni, and 1% V, the strip becomes difficult to roll due to the hardening effect of these alloying elements. The powdered strip electrode process uses a plain carbon or low-alloy strip as the base electrode and feeds a separate alloy powder into the arc zone. The powder melts and alloys with the molten pool, producing a deposit with the desired high-alloy composition.

Process Parameter Optimization

The authors employed orthogonal experimental design to optimize the process parameters. The key parameters and their ranges are:

The orthogonal test results identified the optimal parameter combination as follows:

Microstructure and Properties

The deposited overlay layer microstructure depends on the cooling rate, which is governed by the travel speed and the thermal conductivity of the substrate. At the optimal parameters, the microstructure consists of acicular ferrite and martensite with a hardness of 55-62 HRC. The dilution from the substrate is lower than in conventional strip electrode welding because the powder contributes additional alloy to the dilution zone. The carbon equivalent of the deposited metal is carefully controlled to minimize hot cracking susceptibility.

Comparison with Conventional Methods

The powdered strip electrode process achieves deposition rates comparable to conventional strip electrode welding while offering the alloy flexibility of powder-fed processes. This makes it particularly attractive for large-scale overlay applications such as pipeline corrosion protection, mining equipment hardfacing, and large structural component repair.

Engineering Practice Considerations

The powdered strip electrode process requires additional equipment for powder feeding, which adds complexity and cost to the welding setup. The powder feed system must be carefully calibrated to maintain a consistent powder-to-strip mass ratio, as variations in this ratio directly affect the deposit composition and properties. In practice, I have observed that the powder feed consistency is often the weakest link in the process. A malfunctioning powder feeder can lead to significant variation in deposit chemistry, resulting in inconsistent hardness and wear resistance across the overlay surface.

Another practical consideration is the flux management. The flux must be compatible with both the strip electrode and the alloy powder. Incompatible flux compositions can lead to excessive hydrogen pickup, porosity, or slag inclusions. The flux should be pre-dried at 300-400°C for 2 hours before use to minimize hydrogen-related defects.

Study Insights and Reflections

This paper presents a clever engineering solution to a materials processing problem. The decoupling of strip formability from deposit composition is an elegant approach that expands the range of alloys available for strip electrode welding. The orthogonal experimental design methodology is well-suited to the multi-parameter optimization problem inherent in welding process development. For engineers considering this process for pipeline or structural component overlay, the key advantages are the high deposition rate and the ability to deposit high-alloy compositions that would be impractical as rolled strip. The key challenges are maintaining powder feed consistency and ensuring flux compatibility. The process is particularly well-suited for large-area overlay applications where deposition rate is a primary economic driver.