CLADDING TECHNOLOGY SHANXI CO., LTDSubmerged Arc Strip Electrode Cladding of Stainless Steel on Low Alloy Steel
Overview and Background
Submerged arc welding (SAW) strip electrode overlay is a widely used cladding technique for depositing thick layers of corrosion-resistant or wear-resistant materials on carbon steel and low-alloy steel substrates. This study focuses on the experimental investigation of stainless steel strip electrode cladding on low-alloy steel, with particular attention to process parameter optimization, dilution control, and the evaluation of bond strength and corrosion performance.
The application scenario typically involves large-scale pressure vessels, heat exchangers, and storage tanks where a stainless steel overlay layer is required to provide corrosion resistance while the low-alloy steel base material provides the necessary mechanical strength and structural integrity. The study is relevant to industries such as petrochemical, nuclear power, and marine engineering, where bimetallic components are essential for withstanding aggressive chemical environments.
Core Technical Content
The SAW strip electrode process involves a continuous strip electrode that is fed through a contact tip, with a flux covering the arc and the molten pool. The strip electrode can be made of stainless steel grades such as 308, 309, 310, or 316, depending on the corrosion resistance requirements. The flux acts as a shielding agent and a source of alloying elements, and its composition significantly affects the dilution rate and the final composition of the overlay layer.
The study investigates the effect of key process parameters on the cladding quality:
| Parameter | Low Value | High Value | Effect on Cladding |
|---|---|---|---|
| Welding current | 400 A | 800 A | Higher current increases dilution and deposition rate |
| Travel speed | 100 mm/min | 300 mm/min | Higher speed reduces dilution and heat input |
| Arc voltage | 25 V | 40 V | Higher voltage increases bead width and dilution |
| Flux coverage | Thin | Thick | Thick coverage reduces spatter and improves protection |
| Preheating | None | 200–300 °C | Preheating reduces cracking risk |
The study emphasizes that the dilution rate in SAW strip electrode cladding is typically in the range of 15–35% for the first pass and decreases to 5–15% for subsequent passes. The first pass is critical because it establishes the base of the overlay, and excessive dilution at this stage can compromise the corrosion resistance of the entire cladding layer.
The study also discusses the concept of "dilution reduction" through multi-pass cladding. By applying multiple passes with decreasing dilution rates, the final overlay composition can be brought closer to that of the pure strip electrode material. This is achieved by controlling the heat input per pass and ensuring adequate overlap between passes.
Microstructure and Bond Strength Analysis
The interface between the low-alloy steel base metal and the stainless steel cladding layer is the critical region for bond strength and corrosion resistance. The study reports that the diffusion zone at the interface typically has a width of 100–300 μm, depending on the heat input and the number of passes. The microstructure of this diffusion zone transitions from ferrite in the base metal to austenite-ferrite in the cladding layer, with a gradual change in composition across the interface.
Bond strength testing reveals that the bond strength of the SAW strip electrode cladding typically exceeds 250 MPa, which is well above the minimum requirements specified in standards such as ASTM A263 and EN 10028-7. The study also discusses the effect of post-weld heat treatment on bond strength, noting that a PWHT at 650–700 °C can improve ductility but may slightly reduce the hardness of the overlay layer.
Corrosion testing in simulated industrial environments (e.g., 5% NaCl solution, sulfuric acid, and hydrochloric acid) demonstrates that the multi-pass cladding layer exhibits excellent corrosion resistance, with corrosion rates significantly lower than the unclad base metal. The study confirms that achieving a dilution rate below 15% in the final pass is essential for ensuring adequate corrosion resistance.
Process Optimization and Defect Prevention
The study applies a systematic approach to process optimization, considering the interplay between welding current, travel speed, arc voltage, and flux composition. The optimal parameter window is identified through a combination of experimental trials and theoretical analysis of the heat input and cooling rate.
Common defects in SAW strip electrode cladding include:
| Defect Type | Cause | Countermeasure |
|---|---|---|
| Incomplete bonding | Insufficient heat input, poor surface preparation | Increase current, ensure clean base surface |
| Excessive dilution | High heat input, single-pass cladding | Multi-pass cladding, reduce current, increase speed |
| Flux inclusions | Excessive flux coverage, poor flux quality | Optimize flux thickness, use high-quality flux |
| Cracking | Hydrogen embrittlement, high restraint stress | Preheat, use low-hydrogen flux, PWHT |
| Uneven surface | Inconsistent travel speed, strip misalignment | Stabilize feed mechanism, align strip electrode |
The study recommends a multi-pass cladding strategy with a typical sequence of three to five passes, each with a controlled overlap of 50–70% of the previous pass width. This approach ensures uniform coverage and minimizes the risk of defects.
Study Insights and Reflections
This study provides a comprehensive understanding of the SAW strip electrode cladding process, with particular emphasis on the practical aspects of dilution control and bond strength optimization. The systematic investigation of process parameters and their effects on cladding quality is instructive for engineers who need to develop or optimize cladding procedures for specific applications.
One key insight is that the flux composition plays a more significant role in SAW strip electrode cladding than in conventional SAW. The flux not only shields the molten pool but also contributes alloying elements that affect the dilution rate and the final composition of the overlay. Engineers must carefully select and control the flux composition to achieve the desired overlay properties.
Another important finding is the effectiveness of multi-pass cladding in reducing dilution. This approach is often overlooked in favor of single-pass cladding for simplicity, but the study demonstrates that the additional effort of multi-pass cladding is well justified by the improved corrosion resistance and bond strength.
In conclusion, the SAW strip electrode cladding of stainless steel on low-alloy steel is a mature and reliable technique that, when properly applied, provides excellent corrosion resistance and mechanical integrity. The study serves as a valuable reference for engineers working on bimetallic pressure vessels and other components requiring surface protection in aggressive environments.