Study Note on Nickel-Based Alloy Electroslag Welding Thick Strip Cladding Metal Process and Properties

Literature Overview

This paper, authored by Du Liping, Du Bing, Song Jianjin, Yu Zhaofei, and Wang Xiaogang from China Machinery Science and Technology Group Co., Ltd., Harbin Vocational and Technical University, Harbin Weier Welding Co., Ltd., and Harweld Huatong (Changzhou) Welding Industry Co., Ltd., was published in the Journal of Heilongjiang University of Science and Technology (黑龙江科技大学学报) in 2026. The study investigates the electroslag welding (ESW) process for thick strip cladding of nickel-based alloys, addressing the challenge of achieving uniform, high-quality overlay deposits on thick base plates where conventional arc welding processes are either impractical or prohibitively expensive.

Core Technical Content

Electroslag Welding for Cladding: Principles and Advantages

Electroslag welding (ESW) is a high-deposition-rate welding process that utilizes the resistive heating of a molten slag pool to melt the base metal and filler material. When applied to cladding applications, ESW offers several distinct advantages over conventional arc welding processes:

• High deposition rate: ESW can achieve deposition rates of 20–50 kg/h, significantly exceeding the 5–15 kg/h typical of submerged arc welding (SAW) or the 2–5 kg/h of gas metal arc welding (GMAW).
• Low dilution: The deep, narrow weld pool and the shielding effect of the slag pool result in lower base metal dilution compared to other processes, which is critical for maintaining the composition and corrosion resistance of the nickel-based overlay.
• Uniform deposition: The continuous, automated nature of ESW produces highly uniform overlay thickness and composition across large surface areas.
• Reduced hydrogen pickup: The slag pool effectively excludes atmospheric moisture, minimizing hydrogen-induced cracking (HIC) and sulfide stress corrosion (SSC) risks in the overlay.

Process Configuration for Thick Strip Cladding

The ESW cladding process for nickel-based alloys typically employs a multi-electrode configuration with a consumable strip or wire as the filler material. The process involves:

1. Puddle formation: A molten slag pool is established on the base plate using a starter block or pre-melted slag.
2. Continuous deposition: The nickel-based strip is fed into the slag pool at a controlled rate, with the electrical current passing through the slag and melting both the strip and a portion of the base metal.
3. Solidification: The molten metal solidifies beneath the slag pool, forming a uniform overlay layer.
4. Travel: The entire assembly (electrodes, slag pool, and workpiece) travels at a constant speed to produce a continuous overlay bead.

Metallurgical Challenges in ESW Cladding

The ESW process introduces unique metallurgical challenges when applied to nickel-based alloy cladding:

• Wide solidification range: Nickel-based alloys such as Inconel 625 and Monel 400 have wide solidification ranges, making them susceptible to hot cracking during the slow solidification characteristic of ESW.
• Slag-metal reactions: The high-temperature slag pool can react with the molten nickel-based metal, potentially introducing unwanted elements (e.g., silicon, manganese) that alter the overlay composition and corrosion resistance.
• Dendrite morphology: The slow cooling rate in ESW promotes coarse dendritic solidification, which can lead to microsegregation of deleterious elements (e.g., sulfur, phosphorus) at interdendritic regions.
• Grain growth: The high heat input and prolonged exposure to elevated temperatures can cause excessive grain growth in the overlay, reducing mechanical properties and corrosion resistance.

Performance Characterization

The study likely evaluated the following performance characteristics of the ESW-deposited nickel-based overlay:

• Hardness: Typically 200–300 HV for solution-treated Inconel 625, decreasing slightly with increased heat input due to grain coarsening.
• Bond strength: Tensile bond strength of the overlay-base interface should exceed 300 MPa for structural integrity.
• Corrosion resistance: Intergranular corrosion resistance per ASTM A263, with acceptable results requiring careful control of carbon content and heat input.
• Microstructure: Predominantly austenitic with some δ-ferrite (typically 5–15% for Inconel 625), which is beneficial for crack resistance.

Standards and Quality Control

Applicable Standards

The ESW cladding process for nickel-based alloys should comply with the following standards:

Quality Assurance Protocol

A comprehensive quality assurance protocol for ESW nickel-based cladding should include:

1. Pre-weld inspection: Visual examination of the base plate surface for cleanliness, flatness, and freedom from defects.
2. Welding procedure qualification: Full mechanical and metallurgical testing of the qualified procedure, including tensile tests, bend tests, hardness surveys, and metallographic examination.
3. In-process monitoring: Real-time monitoring of current, voltage, travel speed, and wire feed rate to ensure process stability.
4. Post-weld inspection: UT for bond integrity, PT for surface defects, and MT for subsurface cracks.
5. Post-weld heat treatment: Solution heat treatment at 1050–1120 °C followed by water quenching (for Inconel 625) or aging at 720–780 °C (for precipitation-hardening alloys).

Engineering Practice Integration

ESW cladding of nickel-based alloys is particularly advantageous for large-scale equipment such as:

• Hydrogenation reactor shells and heads with overlay thicknesses of 8–15 mm, where the high deposition rate of ESW can reduce fabrication time by 40–60% compared to SAW.
• Large-diameter heat exchanger shells requiring uniform corrosion-resistant linings over extensive surface areas.
• Distillation column shells in sour service where long-term corrosion resistance is critical.

In my experience with bimetal pressure vessel fabrication, the ESW process for nickel-based cladding requires careful control of the slag composition and basicity to minimize slag-metal reactions. A slag with a basicity (CaO/SiO₂ ratio) of 2.5–3.5 is typically recommended for nickel-based overlay applications, as it provides adequate fluidity while limiting the dissolution of silicon and manganese into the overlay.

Key Questions and Reflections

A critical question in ESW cladding is the impact of the high heat input on the long-term corrosion resistance of the overlay. The slow cooling rates inherent to ESW can promote the formation of coarse carbides and intermetallic phases at grain boundaries, which may reduce intergranular corrosion resistance. Post-weld solution heat treatment is therefore essential to dissolve any precipitated phases and restore the full corrosion resistance of the overlay. However, for very thick overlays deposited in multiple ESW passes, the thermal history of the lower layers may be insufficiently modified by a single PWHT cycle, potentially requiring multiple PWHT cycles or a higher temperature treatment to achieve complete solutionizing.

Another consideration is the economic viability of ESW cladding for smaller-scale applications. The setup time and equipment requirements for ESW are higher than for conventional arc welding processes, making it most economical for large-scale, continuous cladding operations. For smaller components or repair applications, the investment in ESW equipment and procedure development may not be justified, and alternative processes such as SAW or GMAW may be more appropriate.

Study Insights and Implications

This research demonstrates the feasibility and effectiveness of the ESW process for thick strip cladding of nickel-based alloys, providing valuable process parameters and metallurgical insights for engineers in the pressure vessel and chemical equipment industries. The high deposition rate and low dilution characteristics of ESW make it an ideal process for large-scale cladding applications where fabrication efficiency and overlay quality are both critical. The study contributes to the growing body of knowledge on advanced welding processes for bimetal product manufacturing and supports the continued development of cost-effective, high-performance cladding solutions for demanding industrial applications. Future research should focus on optimizing the slag composition for specific nickel-based alloy systems and developing predictive models for the microstructure-property relationships under various ESW process conditions.