Effects of Process Parameters on Microstructure and Properties of Cladding Layers

Literature Overview

This research examines how welding process parameters—including heat input, travel speed, electrode diameter, and interpass temperature—influence the microstructure, hardness, and corrosion resistance of weld overlay layers deposited on carbon steel substrates. The study covers both single-pass and multi-pass cladding scenarios, with particular focus on austenitic stainless steel (304/316) and nickel-based alloy overlays. The work provides valuable insight into the relationship between thermal cycles and the resulting grain morphology, phase distribution, and mechanical integrity of the cladding layer.

Core Technical Analysis

Microstructural Evolution with Heat Input

Heat input is the dominant factor controlling microstructure in weld overlay deposits. At low heat input (<10 kJ/mm), rapid solidification produces fine dendritic structures with high dislocation density, resulting in elevated hardness values (280–320 HV for austenitic 316 overlay). As heat input increases to 20–30 kJ/mm, grain coarsening becomes evident, and secondary phases such as δ-ferrite (in 304-type overlays) or carbide precipitates begin to form at dendrite boundaries. Beyond 35 kJ/mm, excessive grain growth and phase separation significantly degrade both mechanical and corrosion properties.

Phase Composition and Dilution Effects

The dilution rate—defined as the percentage of base metal melted into the overlay—has a profound effect on the final composition and phase structure of the cladding layer. For 304 stainless steel overlay on Q345R carbon steel, dilution rates of 20–30% produce a single-phase austenitic microstructure with adequate corrosion resistance. However, dilution exceeding 40% introduces sufficient carbon and manganese to stabilize ferrite and carbide phases, reducing pitting resistance by up to 60%. The study demonstrates that controlling dilution through layer-by-layer composition analysis (spark-OES at each pass) is a practical quality assurance measure.

Process Parameter Optimization

The study identifies several critical process windows for achieving optimal cladding microstructure:

1. Travel speed: 200–280 mm/min for ESW overlay, balancing deposition rate with adequate solidification cooling rate.
2. Electrode diameter: 6–8 mm for ESW, providing sufficient current capacity without excessive heat concentration.
3. Interpass temperature: Maintained below 250 °C for austenitic overlays and below 150 °C for duplex stainless steel overlays to control grain growth.
4. Backing electrode: Use of low-carbon backing electrodes (such as 304L or 316L) in ESW overlay reduces dilution from the substrate side.

Defect Analysis

Common defects observed at the boundary between overlay and base metal include micro-cracking (due to thermal mismatch), unmelted inclusions from insufficient base metal preparation, and hot cracking in the first pass. The study recommends a minimum base metal preheat of 100 °C for carbon steels above 12 mm thickness to reduce thermal gradients, combined with post-weld stress relief at 620–650 °C for 2 hours per 25 mm of thickness.

Integration with Engineering Standards

The findings align with requirements in NB/T 47014 and ASME IX for qualification of overlay welding procedures. Specifically, the procedure qualification should include a dilution test (per API 934 or ASTM A264) demonstrating that the overlay layer composition remains within specified limits after welding. The hardness gradient across the overlay should be uniform, with no localized hardness exceeding 350 HV for applications subject to chloride stress corrosion cracking. The study's recommendations for multi-pass strategies—starting with a low-dilution bond layer followed by higher-deposition-rate fill passes—directly support compliance with these standards.

This literature provides a solid foundation for understanding how thermal management during overlay welding translates into microstructural control, which ultimately determines the service life of clad components in aggressive environments.