Comparative Analysis of Iron-Based Alloy Surfacing Under Transverse and Longitudinal Magnetic Fields

Literature Overview

This paper by Su Yunhai, Li Lecheng, and Liu Zhengjun from Shenyang University of Technology's School of Materials Science and Engineering, published in Welding Journal (Vol. 33, No. 4, 2012, pp. 33-36), investigates the effect of applying DC transverse and DC longitudinal magnetic fields during plasma arc surfacing of an Fe5 self-fusing alloy onto low carbon steel. Funded by the Liaoning Provincial Natural Science Foundation (Grant 20042025), this research explores a relatively novel approach to controlling solidification microstructure through external magnetic field application, with the aim of simultaneously improving hardness and wear resistance of the surfacing layer.

Research Significance

The application of external magnetic fields during welding and surfacing is an emerging technology that offers non-contact, non-consumable control over the solidification process. Unlike conventional approaches that rely on alloy composition modification or process parameter adjustment, magnetic field application can influence:

• Dendrite growth morphology and orientation
• Primary phase nucleation rate and distribution
• Secondary phase precipitation pattern
• Residual stress development during solidification
• Microsegregation patterns in the solidifying weld pool

This research specifically compares two magnetic field orientations — transverse (perpendicular to the weld direction) and longitudinal (parallel to the weld direction) — to determine the differential effects on microstructure and properties.

Experimental Configuration

Surfacing Parameters

Magnetic Field Parameters

Microstructural Analysis

Hard Phase Morphology Under Different Field Conditions

The Fe5 self-fusing alloy contains multiple hard phases — typically Cr₇C₃, Cr₃C, W₂C, and Mo₂C — that provide the wear resistance of the surfacing layer. The magnetic field orientation significantly influences the morphology and distribution of these hard phases:

Without magnetic field: Hard phases form as irregularly shaped particles with random orientation, distributed non-uniformly throughout the dendritic microstructure. The primary phases tend to align with the thermal gradient direction (perpendicular to the surface).

Transverse magnetic field: The Lorentz force (F = J × B) acts on the moving charged particles in the molten pool, creating electromagnetic stirring that disrupts the natural thermal gradient. Hard phases nucleate at a higher rate but form in a disordered, randomly oriented pattern. The increased nucleation rate results in more numerous but smaller hard phase particles, distributed throughout the matrix rather than concentrated at dendrite boundaries.

Longitudinal magnetic field: The magnetic field aligned with the weld direction creates a different force configuration. Hard phases nucleate at an even higher rate and form in a distinctive hexagonal pattern, with the hexagonal axes aligned parallel to the magnetic field direction. This ordered arrangement results from the anisotropic influence of the longitudinal field on the crystal growth direction of the hard phases.

Microstructural Comparison Table

Hardness and Wear Performance

Hardness Results

The transverse magnetic field produces the highest hardness values, attributable to the increased nucleation rate of hard phases and the disruption of the thermal gradient that promotes finer, more uniformly distributed hard phase particles.

Wear Resistance Results