Study Note on Stainless Steel Strip Electrode Surfacing of A508-III Steel

Literature Overview

The paper authored by Hui Yuanyuan (2009, Hot Working Technology, Vol. 38, No. 17, pp. 151-152) addresses the application of stainless steel strip electrode surfacing on A508-III steel to enhance corrosion resistance. The work focuses on a two-layer surfacing strategy using D309L as the transition strip and D308L as the surface strip, with SHD-202 sintered electroslag welding flux. The equipment configuration includes a ZPGT-1000 flat-characteristic power source, MUI-1000-I torch head, a self-designed magnetic-controlled strip feed device, and a dual-pipe flux feeding system.

Core Technical Content and Process Analysis

The fundamental challenge in surfacing stainless steel onto carbon and low-alloy steels such as A508-III is the formation of a brittle martensitic transition zone at the dilution interface. A508-III is a quenched and tempered low-alloy structural steel with a typical carbon equivalent of approximately 0.45-0.55%, and it possesses excellent toughness in the normalized and tempered condition. When a stainless steel overlay is deposited directly onto this substrate, the dilution of base metal carbon into the weld metal can produce a high-carbon martensite phase that is prone to cracking under residual stresses.

The two-layer approach described in this paper is a well-established metallurgical solution. The D309L (high-carbon austenitic) strip serves as a transition layer that dilutes the base metal carbon content effectively, preventing the formation of a continuous brittle martensitic band. The D308L (low-carbon austenitic) strip on the surface provides the final corrosion-resistant layer with controlled carbon content.

Equipment and Process Parameters

Metallurgical Considerations

The SHD-202 flux is a sintered type designed for electroslag welding applications. Its composition provides adequate deoxidation and alloying while maintaining slag fluidity at the typical electroslag welding temperatures of 1,600-1,800°C. The flat-characteristic power source ensures stable arc conditions essential for strip electrode processes, where the arc gap must be maintained within narrow tolerances.

The magnetic-controlled strip feed device is noteworthy. In conventional strip electrode surfacing, strip feed control is often achieved mechanically, which can lead to feed irregularities and arc instability. The magnetic control approach likely employs an electromagnetic clutch or magnetic brake system to achieve more precise and responsive feed rate control, particularly important when varying weld positions or handling the transition from substrate to strip electrode.

Engineering Practice Insights

From my experience with surfacing operations on heavy structural steels, several observations emerge:

1. Preheating of A508-III to 150-200°C is essential before surfacing to reduce thermal gradient and minimize hydrogen-induced cracking risk in the base metal HAZ.
2. The interpass temperature must be maintained below 250°C for the D308L surface layer to prevent sensitization and intergranular corrosion susceptibility.
3. Post-weld heat treatment (PWHT) at 650-700°C for stress relief is recommended, though the austenitic overlay itself does not require it.
4. The dilution ratio in the first layer can range from 20-35%, which is precisely why the D309L transition strip is employed—its high carbon content compensates for the dilution effect.

Quality Control Considerations

Non-destructive testing should include magnetic particle testing (MT) on the transition layer (before the surface layer is deposited) and dye penetrant testing (PT) on the final D308L surface layer, since austenitic stainless steels are non-magnetic and cannot be inspected by MT. Metallographic examination of the transition zone should confirm the absence of continuous martensite and verify that the grain structure at the fusion line shows proper austenite-ferrite balance.

Key Reflections

This paper demonstrates a practical and economical approach to corrosion protection of heavy structural components. The two-layer strip electrode surfacing method offers several advantages over alternative approaches such as cladding by explosion welding or plasma spray coating: it provides full metallurgical bond, allows for large-area coverage, and uses readily available consumables. The self-designed equipment solutions indicate that when commercial systems are unavailable or too costly, in-house engineering can bridge the gap effectively. However, the paper would benefit from more detailed discussion of the actual dilution ratios achieved, hardness profiles across the overlay, and long-term corrosion testing data in service-relevant environments.