Effect of Low-Frequency Magnetic Field on Microstructure and Properties of Submerged Arc Cladding on Roll Surfaces

Literature Overview

This literature addresses the influence of low-frequency magnetic fields on the microstructure and mechanical properties of submerged arc weld overlay deposits applied to roll surfaces. In the steel and paper industries, roll cladding is a critical process for extending service life against abrasive wear, and the application of external magnetic fields during welding is an emerging technique to improve deposit quality. The study investigates how magnetic field parameters interact with the solidification behavior of the cladding layer, providing insights that can enhance the durability and performance of clad rolls in industrial operations.

Mechanism of Magnetic Field Influence

The application of a low-frequency magnetic field during submerged arc welding introduces Lorentz forces on the molten pool, which can alter fluid flow patterns, heat transfer, and solidification morphology. The Lorentz force acts on the electrically conductive molten metal, generating electromagnetic stirring that promotes uniform temperature distribution and reduces thermal gradients. This stirring effect can refine grain structure, reduce columnar grain growth, and minimize segregation of alloying elements at grain boundaries.

The magnetic field also influences the arc behavior and plasma stability. In submerged arc welding, the arc is shielded by a layer of granular flux, and the introduction of a magnetic field can modify the arc shape and energy distribution. This modification can lead to more uniform heat input along the weld path, which is beneficial for achieving consistent overlay properties across the entire cladding area.

Experimental Setup and Process Parameters

The experimental work involved applying magnetic fields of varying strengths and frequencies during the submerged arc cladding process on steel roll substrates. Metallographic examination revealed that the magnetic field significantly refined the microstructure of the overlay layer, with grain size reduction of up to 40 percent compared to deposits produced without magnetic field assistance. The refinement was attributed to the electromagnetic stirring effect, which promoted nucleation and inhibited grain growth during solidification.

Microstructural Analysis and Mechanical Properties

The microstructure of the cladding layer without magnetic field application typically exhibits columnar grains growing from the substrate interface toward the surface. These columnar grains are susceptible to cracking during cooling and are less resistant to wear than equiaxed grains. With the application of a low-frequency magnetic field, the microstructure transitions toward equiaxed morphology, with a more uniform distribution of carbides and alloying elements.

Mechanical testing demonstrated that the magnetic field-assisted cladding layer exhibited improved hardness uniformity and enhanced wear resistance. The hardness distribution across the cross-section was more homogeneous, with reduced soft zones that are typically associated with coarse columnar grains. Wear testing using standard pin-on-disk and dry sliding wear apparatus confirmed that the magnetic field-treated deposits showed 15-25 percent improvement in wear resistance compared to conventionally produced overlays.

Engineering Significance and Practical Considerations

For roll manufacturers and operators, the magnetic field-assisted cladding technique offers a practical means to improve roll durability without changing the base material or welding consumables. The process integration is relatively straightforward, requiring only the addition of a magnetic field generation system around the welding area. However, the equipment cost and the need for process control must be considered in the overall economic evaluation.

The technique is particularly relevant for applications where roll life extension is critical, such as in continuous casting tundish rolls, paper machine felt rolls, and steel mill finishing mills. The improved microstructure and wear resistance can translate into longer service intervals, reduced downtime for re-cladding, and lower total cost of ownership.

Key Questions and Reflections

Several questions arise from this research that merit further investigation. First, the optimal magnetic field parameters for different cladding materials and substrate combinations need to be systematically established. Second, the long-term durability of magnetic field-assisted cladding under actual operating conditions requires validation through extended service testing. Third, the interaction between magnetic field effects and other process variables such as flux composition and welding parameters should be explored to develop comprehensive process maps.

This research demonstrates that electromagnetic stirring is a viable and effective tool for improving submerged arc cladding quality. The fundamental understanding gained from this work can be extended to other welding processes and cladding applications, contributing to the broader field of process engineering in surface modification.