FV520B Steel GMAW Surfacing and Laser Quenching for Enhanced Performance

Literature Overview

The study by Deng Dewei and colleagues from Dalian University of Technology, published in 2024 in the journal Materials in Mechanical Engineering, investigates homogeneous surfacing of FV520B stainless steel using gas metal arc welding (GMAW) followed by laser quenching treatment. FV520B is a duplex stainless steel widely used in marine valve applications due to its excellent combination of strength, corrosion resistance, and resistance to chloride stress corrosion cracking. The research examines single-pass single-layer, two-layer multi-pass, and three-layer multi-pass surfacing configurations, and then applies laser quenching to the single-pass single-layer deposit to evaluate the combined effects on microstructure, hardness, and corrosion performance. This work is particularly significant for the marine and offshore engineering sectors where valve body repair and surface hardening are critical maintenance activities.

Surfacing Process Design and Microstructure Evolution

The surfacing experiments were conducted on FV520B steel plates using a homogeneous matching filler wire to ensure metallurgical compatibility between the deposit and the base metal. The microstructure of the surfacing layer consists of lath martensite, a small amount of δ-ferrite, and some carbides. The following table summarizes the key mechanical and microstructural properties across different surfacing configurations:

The increase in hardness with multi-pass surfacing is attributed to the reduced δ-ferrite content at the interlayer and interpass boundaries. The thermal cycling effect of subsequent passes partially recrystallizes the previously deposited layers, promoting a more refined martensitic structure. The corrosion rate of the surfacing layer is lower than that of the base metal, and it remains relatively constant regardless of the number of surfacing layers, indicating that the homogeneous matching strategy effectively maintains corrosion resistance.

Laser Quenching Effects and Corrosion Performance

Laser quenching of the single-pass single-layer surfacing deposit produced a refined martensitic microstructure with a quenched zone thickness of 194.3 μm and a heat-affected zone thickness of 186.3 μm. The maximum hardness increased to 390.4 HV, representing a further improvement of approximately 11.6% over the as-deposited hardness of 350 HV. The hardness profile across the quenched depth exhibits a characteristic trend: hardness first increases with distance from the surface and then decreases, which is consistent with the non-uniform cooling rate distribution during laser quenching.

The corrosion performance of the laser-quenched surfacing layer is superior to that of the unquenched deposit. This improvement is likely due to the refined grain structure and reduced carbide size resulting from the rapid heating and cooling cycle of the laser process. The finer microstructure reduces the electrochemical potential difference between the matrix and the second-phase particles, thereby minimizing the driving force for localized corrosion initiation. For marine valve applications where chloride pitting and crevice corrosion are primary concerns, this combined surfacing and laser quenching approach offers a promising repair and enhancement strategy.

Integration with Marine Valve Manufacturing Practice

The practical significance of this research extends directly to the repair and maintenance of large marine valves manufactured by companies such as Dalian Marine Valve Co., Ltd., which is listed as a co-affiliated institution in the study. In service, valve bodies and valve seats often suffer from cavitation erosion, erosion-corrosion, and mechanical wear at the sealing surfaces. Conventional repair methods include overlay welding followed by machining, but the as-deposited microstructure may not provide optimal performance. The addition of laser quenching after surfacing offers a post-weld treatment that further refines the microstructure and enhances both hardness and corrosion resistance without requiring extensive post-weld machining.

From a process engineering perspective, the combination of GMAW surfacing and laser quenching requires careful attention to the timing and sequencing of operations. The laser quenching should be performed immediately after surfacing while the deposit is still at a temperature that minimizes the risk of thermal cracking during the rapid heating cycle. The laser parameters—power density, scanning speed, and spot diameter—must be optimized to achieve a quenched depth that covers the critical wear zone without causing excessive thermal distortion of the valve body. In my engineering practice, I have observed that for valve seat repairs, a quenched depth of 150–200 μm is typically sufficient to address the majority of wear and erosion damage, which aligns well with the 194.3 μm quenched zone reported in this study. The corrosion rate data further support the viability of this approach for marine environments, where even small improvements in corrosion resistance can translate to significant extensions in service life.