Double-Layer Electroslag Surfacing of Stainless Steel Using Strip Electrode and Flux

Literature Overview

This paper by Sun Jianhong and Ye Donglin (1997) from the Harbin Welding Research Institute describes a novel double-layer electroslag surfacing process for stainless steel components. Published in the journal "Welding" (焊接), Volume 3, pages 12-15, the study leverages the low dilution characteristic of strip electrode electroslag surfacing (below 10%) to produce high-purity stainless steel overlay layers. The authors developed a specialized sintered flux SJ602 and utilized domestic strip electrode submerged arc surfacing equipment with standard Chinese strip electrodes.

Technical Background and Motivation

Electroslag surfacing (ESS) is a specialized welding process that deposits cladding layers by exploiting the high temperature and low cooling rate of the electroslag pool. Unlike conventional submerged arc surfacing, ESS achieves:

• Extremely low dilution: Typically 5-10%, compared to 15-30% for submerged arc surfacing.
• High deposition efficiency: The slag pool acts as a heat reservoir, maintaining the weld pool in a molten state for extended periods.
• Uniform microstructure: Slow cooling promotes equilibrium microstructures with reduced residual stress.
• Thick layer capability: Multiple passes can be deposited with interpass re-melting, producing thick cladding layers in fewer operations.

The motivation for this work was to produce corrosion-resistant stainless steel overlay layers on carbon steel substrates for chemical processing equipment, where the overlay layer must maintain its specified composition despite the presence of a dissimilar base metal.

Process Configuration

Double-Layer Electroslag Surfacing Setup

The "one strip, one flux" (一带一剂) configuration described in this paper involves:

Process Parameters

Flux SJ602 Development

The sintered flux SJ602 is a critical innovation in this process. Its design objectives include:

1. Low iron content: To minimize dilution of the stainless steel overlay by Fe from the slag.
2. High SiO₂ and Al₂O₃ content: To maintain slag viscosity and prevent excessive Fe pickup.
3. Deoxidizing capacity: Silicon and aluminum additions to remove oxygen from the weld pool.
4. Desulfurizing ability: CaF₂ and CaO to reduce sulfur content in the cladding.
5. Stable slag properties: Consistent melting point and viscosity across production batches.

The typical composition of SJ602 would include approximately 35-40% SiO₂, 15-20% CaF₂, 10-15% Al₂O₃, 5-8% MnO, 3-5% Si, and 2-3% Al, with the balance being fluxing agents and stabilizers.

Microstructure and Performance Analysis

Cladding Layer Composition

The low dilution rate (below 10%) ensures that the cladding layer maintains its specified stainless steel composition. For a typical 304 or 316 stainless steel strip electrode, the resulting cladding would contain:

• Cr: ≥ 18% (maintained despite dilution)
• Ni: ≥ 8%
• C: ≤ 0.08%
• Fe: balanced (from dilution and flux)

Microstructural Characteristics

The slow cooling rate in electroslag surfacing (typically 1-10°C/s compared to 50-200°C/s for conventional welding) produces:

• Coarse grain structure in the cladding layer due to high superheat and slow solidification.
• Reduced segregation of alloying elements due to extended solidification time.
• Tempered martensite in the HAZ if the substrate is susceptible to hardening.
• Good metallurgical bond between cladding and substrate with minimal intermetallic compound formation when properly controlled.

Corrosion Resistance

The maintained Cr and Ni content ensures the cladding layer retains its passivation capability. Electrochemical testing would confirm a corrosion potential consistent with the base stainless steel grade, with pitting resistance equivalent to the parent material.

Engineering Applications and Production Implementation

The paper notes that the research results have been applied in production. Typical applications for this type of electroslag surfacing include:

• Chemical reactor linings: Where carbon steel vessels require stainless steel corrosion resistance internally.
• Heat exchanger tube sheets: Dissimilar metal bonding for corrosion service.
• Pump impellers and casing: Repair of worn or corroded surfaces with stainless steel overlay.
• Nuclear industry components: Where radiation resistance and corrosion resistance are required simultaneously (noted by the Northwest Institute for Nuclear Technology affiliation in the related literature).

Key Technical Challenges

Comparison with Alternative Cladding Processes

Study Reflection

This paper represents an important contribution to the domestic (Chinese) welding technology landscape of the 1990s, when the development of indigenous equipment and consumables was a strategic priority. The SJ602 flux represents a materials engineering achievement—its composition was optimized specifically for the electroslag surfacing process to achieve the critical low dilution requirement. For modern engineers, the fundamental principles remain valid: the dilution rate in any cladding process determines the ultimate performance of the overlay, and process parameters must be carefully matched to achieve the desired composition. The double-layer configuration offers an additional advantage in terms of mechanical properties—the first layer provides a transition zone that accommodates thermal expansion mismatch, while the second layer delivers the functional surface properties.

The practical significance of this work extends beyond stainless steel cladding to any application requiring dissimilar metal bonding with composition-sensitive overlay layers, including hard-facing for wear resistance and nickel-based alloy cladding for high-temperature oxidation resistance.