CLADDING TECHNOLOGY SHANXI CO., LTDESW Fabrication of Stainless Steel Carbon Steel Clad Plate Microstructure and Properties
Literature Overview
This paper presents a systematic investigation into the microstructure and mechanical properties of stainless steel/carbon steel clad plates fabricated by electroslag welding (ESW). The study covers the entire cross-section from the stainless steel overlay through the transition zone to the carbon steel backing plate, analyzing how the ESW process parameters influence the bond quality, dilution, and final performance. This work is directly relevant to the fabrication of clad-plate pressure vessels, heat exchangers, and chemical processing equipment where corrosion resistance of the overlay is combined with the structural strength of a low-cost carbon steel substrate.
Process Parameters and Their Effects
The study examines the influence of welding current, travel speed, and number of passes on the clad plate quality. ESW is characterized by high deposition rates (typically 3–8 kg/h) and deep penetration, making it suitable for producing thick overlay layers in a single or few passes. However, the high heat input also leads to significant dilution, which is the primary challenge in maintaining the corrosion resistance of the stainless steel overlay.
| Parameter | Low Value Effect | High Value Effect |
|---|---|---|
| Welding current (A) | Lower deposition rate, less dilution, narrower weld | Higher deposition rate, more dilution, wider weld |
| Travel speed (mm/min) | More heat input per unit length, more dilution | Less heat input, less dilution, potential lack of fusion |
| Number of passes | Single thick layer, high dilution at first pass | Multiple thin layers, reduced dilution per pass |
The study finds that using multiple thinner passes (3–5 passes) significantly reduces the dilution ratio compared to a single thick pass, keeping it below 20% and thus maintaining adequate chromium content in the overlay for corrosion resistance.
Microstructure Characterization
Cross-sectional metallography reveals a distinct three-layer structure: the stainless steel overlay (304 or 316 grade), the transition zone (TZ), and the carbon steel base (Q235 or Q345). The overlay exhibits an equiaxed austenitic-ferritic grain structure with grain size typically 50–100 μm. The transition zone, which is 1–3 mm thick, shows a mixed microstructure with increasing carbon steel characteristics toward the base. The carbon steel base remains largely unaffected except for a narrow heat-affected zone (HAZ) of 2–5 mm where grain coarsening occurs due to the high thermal exposure.
The dilution in the transition zone is quantified by chemical analysis, showing chromium content decreasing from 18–20 wt% in the overlay to 0.5–1 wt% in the base over the transition zone width. The carbon content increases correspondingly from near zero in the overlay to 0.2–0.25 wt% in the base. This gradient creates a continuous change in hardness from approximately 200 HV in the overlay to 150–180 HV in the base, with the transition zone showing intermediate values.
Bond Strength and Corrosion Performance
The study reports bond strength values of 280–350 MPa in shear testing, well above the minimum requirements of NB/T 47014 and API 934, which typically specify a minimum bond strength of 205 MPa or 15 ksi. The corrosion resistance of the overlay is evaluated by potentiodynamic polarization in 3.5% NaCl solution, showing that the overlay maintains a passive potential range comparable to solid 304 stainless steel, with a corrosion current density of less than 1 μA/cm². However, the transition zone shows slightly reduced corrosion resistance due to the lower chromium content, which is an inherent limitation of any welded clad plate.
Intergranular corrosion testing of the overlay reveals that the ESW process, due to its slow cooling rate, can promote sensitization if the overlay composition is near the critical chromium level (18–20 wt% Cr with carbon above 0.03%). The study recommends using low-carbon grades (304L or 316L) for the overlay consumable to mitigate this risk.
Engineering Practice and Quality Control
For pressure vessel applications governed by GB/T 150 or ASME VIII Div.1, the clad plate must satisfy specific requirements for bond strength, overlay thickness, and corrosion resistance. This study provides useful data for weld procedure qualification (WPQ) under NB/T 47014 or ASME IX. Key QC measures include: ultrasonic testing (UT) of the bond line for lack of fusion, visual inspection of the overlay surface for undercut or porosity, and hardness testing across the cross-section to verify the dilution profile.
A critical insight from this work is that the transition zone, while unavoidable, can be managed through process control. Engineers should aim for a dilution ratio below 20% for general corrosion service and below 10% for aggressive environments such as sulfuric acid or seawater. The number of ESW passes and the selection of low-carbon stainless consumables are the two most effective levers for achieving this.
Study Insights and Reflections
This literature underscores the fundamental trade-off in welded clad plate fabrication: higher dilution improves bond strength but degrades corrosion resistance. The ESW process, with its high heat input, inherently produces more dilution than lower-heat-input methods such as TIG or PTA cladding. Therefore, ESW is best suited for applications where moderate corrosion resistance is required and cost efficiency is paramount, such as general chemical processing equipment. For severe corrosion environments, PTA or laser cladding with lower dilution may be preferable, even at higher cost. The systematic approach presented in this paper—combining process parameter optimization, microstructure analysis, and property evaluation—provides a replicable methodology for qualifying ESW cladding procedures for specific service conditions.