Strip Electroslag Overlay Welding of Inconel 600 on 15CrMo Forging

Literature Overview

This paper published in Petrochemical Equipment Technology (2016, Vol. 37, No. 6, pp. 51-53) by Wang Qingguo from AVIC Liming Jinxi Chemical Machinery Group describes the experimental evaluation and practical application of strip electrode electroslag overlay welding (EESW) of Inconel 600 on 15CrMo forged components. The application context is the transition section inner wall of a coke oven bottom head, where severe thermal and chemical attack demands a high-performance overlay layer. The study is classified under TG455 and addresses a critical industrial need for corrosion-resistant cladding on high-strength alloy substrates.

Core Technical Approach

The 15CrMo forging serves as a high-strength, creep-resistant substrate suitable for elevated-temperature service, while Inconel 600 provides outstanding resistance to oxidizing and reducing corrosive environments. The electroslag welding process is particularly well-suited for thick-section overlay applications because it delivers high deposition rates, deep penetration, and a clean weld pool protected by the slag.

The following table summarizes the key technical parameters and process characteristics:

The electroslag process operates by using a consumable strip electrode and a flux-covered slag pool. The electrode is fed continuously, and the molten slag pool provides both electrical resistance heating and thermal insulation. This results in a stable, controlled weld pool with minimal spatter and gas inclusion.

Process Analysis and Metallurgical Considerations

The metallurgical challenge in this application is the significant difference in composition between the 15CrMo substrate and the Inconel 600 overlay. The first overlay layer will inevitably experience high dilution, potentially forming a brittle martensitic or intermetallic phase in the dilution zone. The authors addressed this through a multi-layer strategy: the initial layers are designed to act as a transition, gradually transitioning the composition from the base metal toward the overlay composition. Subsequent layers achieve progressively lower dilution, approaching the full Inconel 600 composition.

Key metallurgical considerations include:

• Dilution gradient management: The transition layer must be carefully designed to avoid the formation of brittle phases such as sigma phase or intermetallics.
• Thermal cracking susceptibility: Inconel 600 has a narrow solidification range and is susceptible to hot cracking. The electroslag process's low heat input per unit length and controlled cooling rate help mitigate this risk.
• Residual stress: The large thermal gradient between the 15CrMo and Inconel 600 can generate significant residual stresses. Post-weld stress relief is essential.
• Intermetallic compound formation: At the interface, chromium carbides and other intermetallics may form, reducing toughness. The multi-layer approach and appropriate heat treatment minimize this risk.

Engineering Practice Integration

The application to the coke oven bottom head transition section is a demanding industrial scenario. Coke ovens operate at high temperatures (up to 1100 °C in the oven wall) and are exposed to aggressive chemical species including hydrogen sulfide, ammonia, and various organic compounds. The transition section, where the geometry changes from the cylindrical body to the bottom head, is a critical stress concentration zone. The Inconel 600 overlay provides both corrosion resistance and thermal protection at this vulnerable location.

The experimental evaluation described by the authors included mechanical property testing, metallographic examination, and corrosion testing of the overlay weld joint. The results confirmed that the welding procedure was sound and that the overlay layer met the required performance criteria. The successful field application on the actual equipment further validated the procedure, with the equipment operating safely for an extended period without degradation of the overlay layer.

Key Reflections and Study Insights

This paper represents a mature application of electroslag overlay welding technology in the petrochemical industry. The authors' approach of conducting rigorous qualification testing before field application is commendable and aligns with best practices in pressure vessel and heavy equipment repair. The multi-layer strategy for managing dilution is a well-established technique, but its successful implementation requires careful process control and material selection.

In my own engineering experience, the electroslag process for overlay welding demands precise control of the flux composition, electrode feed rate, and welding speed. The slag pool must be maintained at a consistent volume and composition throughout the weld, which requires skilled operator attention or automated feed control. The paper could have benefited from more detailed discussion of the flux composition and its role in controlling dilution and weld pool stability.

The broader implication of this work is that electroslag overlay welding is a viable and cost-effective solution for protecting critical equipment components from severe corrosion environments. The technology bridges the gap between traditional arc welding and more exotic surface engineering techniques such as thermal spraying or laser cladding. For engineers working on high-temperature, high-corrosion applications, this paper provides a valuable reference for process selection and qualification methodology. The successful long-term service of the repaired coke oven confirms that the approach delivers reliable performance in demanding industrial conditions.