Ukrainian Electroslag Welding Clad Steel Plate Technology

Literature Overview and Core Thesis

This paper examines the production of clad steel plates using electroslag welding (ESW) overlay technology developed and practiced in Ukraine, specifically the ЭШН (ESW) method for depositing corrosion-resistant overlay layers onto carbon steel or low-alloy steel substrates. The technique leverages the deep, narrow weld pool characteristic of electroslag welding to achieve uniform, dense, and highly metallurgically bonded overlay layers with controlled dilution. The core contribution lies in demonstrating that ESW overlay can produce large-format clad plates with consistent overlay thickness and composition, suitable for pressure vessel fabrication and chemical equipment manufacturing, at lower cost than explosion cladding or roll-bonded alternatives.

Electroslag Welding Overlay Process Description

The ESW overlay process described in the literature involves the following sequence:

1. Substrate preparation: The base plate (typically St3sp, 09Г2С, or 15ХНМФ) is cut to size and beveled at the edge where cladding will be applied. A backing strip is welded to the back to contain the slag pool.
2. Slag flux preparation: A specialized slag composition (typically CaF2-CaO-SiO2-Al2O3 system) is prepared and preheated to 300-400°C to ensure proper slag fluidity and deoxidation during the welding process.
3. ESW overlay execution: The electroslag process deposits the overlay material using a submerged arc electrode (typically wire of the desired cladding composition such as 08Х18Н10Т, 12Х18Н10Т, or nickel-based alloy) with the slag pool covering the weld zone. The process parameters are carefully controlled to maintain a stable slag pool and uniform deposition rate.
4. Multi-pass deposition: Multiple passes are applied to build up the required overlay thickness (typically 3-8 mm), with each pass controlled to maintain composition uniformity and minimize dilution from the base metal.
5. Final machining: The overlay surface is machined to the final thickness and finish specification.

Key Process Parameters

The ESW process offers several advantages over conventional SAW overlay for cladding applications: deeper penetration per pass (reducing the number of passes needed), lower dilution rates due to the slag pool's shielding effect, and the ability to produce very uniform overlay thickness over large plate areas. The slag pool also acts as a natural flux, providing excellent deoxidation and reducing the incidence of porosity and slag inclusions.

Clad Plate Composition and Properties

The literature describes several clad plate configurations:

Mechanical properties of the ESW overlay typically achieve:

• Overlay hardness: 180-220 HV for stainless steel overlays, 150-180 HV for nickel-based overlays
• Bond strength: exceeding 300 MPa in shear testing, well above the minimum requirements of GB/T 150 and ASME VIII Div.1
• Intergranular corrosion resistance: passing ASTM A263/A264 requirements after appropriate heat treatment
• Chemical composition uniformity: chromium content variation within ±1.0% across the overlay thickness

Quality Control and Inspection

The quality assurance program for ESW clad plates involves multiple inspection stages:

1. Visual inspection (VT): Every pass is inspected for surface quality, undercut, and slag inclusion. The overlay surface should be smooth and free of cracks, porosity, and excessive spatter.
2. Radiographic testing (RT): Performed on each pass to detect internal porosity, slag inclusions, and lack of fusion. Acceptance criteria follow NB/T 47013-2 or ASME V Section 12.
3. Ultrasonic testing (UT): Applied to the overlay-substrate interface to detect delamination and lack of bonding. The amplitude method is typically used, with sensitivity calibrated using artificial reflectors.
4. Bond strength testing: Shear tests are performed per ASTM A263 or GB/T 150 requirements. The minimum shear strength must exceed the specified value for the overlay material grade.
5. Metallographic examination: Cross-section samples are examined to verify overlay thickness uniformity, dilution rate, microstructure quality, and absence of microcracks or unmelted particles.

Comparison with Alternative Cladding Methods

The ESW method occupies a favorable position in the cost-performance matrix, offering near-explosion-cladding quality at significantly lower cost, particularly for large-format plates used in pressure vessel fabrication. The main limitation is the requirement for specialized ESW equipment and operator skill, which may not be readily available at all fabrication shops.

Engineering Practice and Standards Compliance

For pressure vessel applications, ESW clad plates must comply with relevant standards:

• GB/T 150.2-2011: Requires minimum overlay thickness of 3 mm for carbon steel clad plates with stainless steel overlay, with bond strength verification per NB/T 47014.
• ASME VIII Div.1 UHA-51: Specifies minimum shear strength of 100 MPa for the overlay-substrate bond, with RT or MT inspection of the overlay.
• ASME IX QW-451: Qualification requirements for ESW overlay processes, including procedure qualification and performance qualification testing.
• NB/T 47014-2011: Chinese qualification standard for weld procedures, including specific requirements for ESW overlay processes.

In practice, the ESW overlay process requires careful control of the slag pool geometry to prevent slag inclusions from being trapped between passes. The use of preheated flux and controlled travel speed are critical to maintaining slag pool stability. Operators must be trained in the specific nuances of ESW overlay, as the process is more sensitive to parameter variations than conventional SAW.

Study Insights and Implications

The Ukrainian ESW overlay technology represents a mature and cost-effective solution for producing clad steel plates for pressure vessel and chemical equipment fabrication. The key insight from this literature is that ESW overlay, when properly executed, can achieve overlay quality comparable to explosion cladding at a fraction of the cost, making it particularly attractive for large-volume production. The dilution control capability of the ESW process—maintaining overlay composition within acceptable limits despite the presence of carbon steel substrate—is a significant advantage over simpler SAW overlay methods. Engineers should note that the process requires significant capital investment in ESW equipment and a trained operator workforce, which may limit its applicability to smaller fabrication shops. Future development should focus on expanding the range of overlay materials compatible with ESW, including nickel-based superalloys and titanium alloys, and on developing automated ESW overlay systems with real-time parameter monitoring and adjustment to further improve consistency and reduce operator dependency.