Research on Stainless Steel Strip Electrode Surfacing on Low Alloy High-Strength Steel Surface

Literature Overview

The paper by Song Tiange, published in 2012 in Hot Working Technology (Vol. 41, No. 9, pp. 191-192), presents research on applying stainless steel surfacing layers to low alloy high-strength steel substrates using the strip electrode surfacing technique. The study originates from Wuxi Vocational and Technical College and addresses the challenge of achieving corrosion-resistant stainless steel surfacing on high-strength structural steels while maintaining adequate metallurgical bonding and avoiding detrimental microstructural phases.

Core Technical Content

The application of stainless steel surfacing to low alloy high-strength steels is a common requirement in industrial applications where structural strength is needed in the base material but corrosion resistance is required at the surface. However, this combination presents significant metallurgical challenges: the high carbon equivalent of the base material can promote hard and brittle phases in the transition zone; the dilution effect can alter the corrosion resistance of the stainless steel deposit; and the formation of delta ferrite in the deposited metal must be controlled to prevent intergranular corrosion and reduce ductility.

Two-Layer Surfacing Strategy

The authors employed a two-layer surfacing approach using stainless steel strip electrodes: a transition layer of 309L composition and a surface layer of 347L composition. The 309L strip (with higher chromium and nickel content) was used for the transition layer because its high alloy content compensates for dilution from the base metal, ensuring that the resulting weld metal retains sufficient chromium and nickel for corrosion resistance. The 347L strip (with niobium stabilization) was used for the surface layer to provide enhanced intergranular corrosion resistance and reduced susceptibility to sensitization.

Optimal Process Parameters

Microstructural Analysis and Delta Ferrite Control

The deposited metal microstructure consists of a duplex austenite-delta ferrite structure. The delta ferrite content was measured to be between 4.5% and 5.5%, which falls within the optimal range of 3-10% recommended for austenitic stainless steel welds. This ferrite content provides adequate resistance to hot cracking during solidification while maintaining good corrosion resistance and ductility. The austenite grain size in the deposited metal was notably refined compared to the base metal, which contributes to improved toughness and fatigue resistance of the surfacing layer.

The transition zone between the 309L transition layer and the base metal was examined for the presence of carbon enrichment layers and the tendency toward M-type embrittlement (tempered martensite embrittlement). The authors confirmed that with the selected 309L composition and controlled heat input, the carbon enrichment layer in the transition zone showed no obvious tendency toward M-type embrittlement, indicating good metallurgical compatibility between the surfacing layer and the base metal.

Mechanical Performance Testing

The surfacing specimens were subjected to transverse and longitudinal side bend tests to evaluate the ductility and bonding strength of the surfacing layer. The transverse bend test evaluates the quality of the weld metal itself, while the longitudinal bend test evaluates the fusion zone and the bonding between the surfacing layer and the base metal. Both tests were performed to ensure that the surfacing layer maintains adequate ductility and bonding strength in all directions, which is critical for components subjected to complex stress states during service.

Engineering Practice Integration

The two-layer strip electrode surfacing approach described in this paper is highly relevant to pipe and fitting manufacturing applications where corrosion-resistant cladding is required on high-strength structural components. Examples include piping systems handling corrosive fluids in oil and gas production, chemical processing plants, and desalination facilities. The use of strip electrode surfacing offers significant productivity advantages over conventional wire electrode methods, making it economical for large surface areas such as pipe interiors, vessel linings, and large fitting surfaces.

Practical Considerations for Pipe Applications

When applying this technology to pipe components, several additional considerations must be addressed: the curvature of the pipe surface affects arc stability and may require specialized equipment; the pipe diameter and wall thickness influence heat dissipation and cooling rates; the internal surfacing of pipes requires consideration of accessibility and inspection after surfacing; and the selection of surfacing materials must account for the specific corrosive environment the pipe will encounter during service. The strip electrode surfacing technique is particularly advantageous for large-diameter pipes where the surface area is substantial and conventional wire electrode methods would be impractical.

Study Insights and Implications

This paper demonstrates a practical and effective approach to applying corrosion-resistant stainless steel surfacing to high-strength structural steels. The two-layer strategy of using 309L for the transition layer and 347L for the surface layer represents a well-established best practice that addresses both metallurgical compatibility and long-term corrosion resistance. The control of delta ferrite content within the optimal range is particularly important for ensuring the long-term durability of the surfacing layer in corrosive environments. For engineers designing surfacing specifications for pipe and fitting applications, this work provides valuable guidance on material selection, process parameter optimization, and quality verification methods that ensure reliable performance in demanding service conditions.