Effect of Low-Frequency Magnetic Field on Microstructure and Properties of Submerged Arc Welding Cladding on Rolls

Literature Overview

This study, published in the journal Chinese Surface Engineering (中国表面工程) in 2011 by Chang Yunlong, Mei Qiang, Zhang Wei, Xia Yuncang, and Xie Tiannan from Shenyang University of Technology and Dalian Heavy Industry Group, investigates the influence of low-frequency magnetic fields on the microstructure and mechanical properties of submerged arc welding (SAW) cladding layers applied to rolls. The research was supported by the Shenyang Talent Special Project (2008030103055) and the Liaoning Provincial Department of Education Key Laboratory Project (2009S072). The work addresses a practical challenge in the manufacturing of wear-resistant rolls used in steel mills and mining equipment, where conventional SAW cladding often produces coarse microstructures with limited hardness uniformity.

Core Technical Points

The application of a low-frequency magnetic field during the SAW cladding process introduces a Lorentz force on the molten pool, which alters the fluid dynamics, heat transfer, and solidification behavior of the weld metal. The authors examined how the magnetic field intensity and frequency affect grain refinement, phase composition, hardness distribution, and wear resistance of the cladding layer.

Microstructure Refinement Mechanism

The low-frequency magnetic field exerts electromagnetic stirring on the molten pool, which breaks up dendritic structures and promotes equiaxed grain formation. This electromagnetic stirring effect is particularly effective at reducing columnar grain growth near the fusion line, which is a common source of cracking and property anisotropy in thick SAW cladding deposits. The magnetic field also influences the growth direction of carbides and intermetallic phases, leading to a more uniform distribution of hard phases throughout the cladding layer.

Key Process Parameters

The magnetic field parameters are selected to ensure sufficient Lorentz force without causing arc instability. A frequency of approximately 100-300 Hz with an intensity of 10-30 mT is typically optimal for achieving significant microstructural refinement without compromising weld quality.

Standards and Inspection Considerations

For SAW cladding applications on rolls, the relevant Chinese standards include NB/T 47014 for qualification testing of welding procedures and JB/T 4730 for non-destructive testing. The cladding layer must meet requirements for bond strength (typically exceeding 15 MPa for shear testing), hardness uniformity (variation within ±5 HRC across the cross-section), and absence of cracks or lack of fusion at the interface. Radiographic testing (RT) per NB/T 47013 and magnetic particle testing (MT) are commonly employed to detect internal and surface defects.

Engineering Practice Integration

In the manufacturing of medium and large-diameter steel mill rolls, SAW cladding is preferred for its high deposition rate and deep penetration. However, the conventional process often produces cladding layers with hardness variations exceeding 8 HRC, leading to uneven wear patterns in service. The introduction of a low-frequency magnetic field during welding can reduce this variation to within 3-4 HRC, significantly improving the service life of the roll. Dalian Heavy Industry Group, as a major manufacturer of heavy-duty equipment, has practical experience in applying this technology to rolls used in hot rolling mills and open-hearth furnaces.

Common Defects and Countermeasures

Study Insights and Reflections

This research demonstrates that external physical field intervention is a promising approach to improving the quality of weld overlay deposits without altering the base materials or consumables. The low-frequency magnetic field method is particularly attractive because it requires no changes to the existing welding equipment beyond the addition of a magnetic field generator, making it relatively easy to implement in production environments. The key insight is that the electromagnetic stirring effect acts as a dynamic grain refiner during solidification, which is fundamentally different from static grain refinement achieved through alloying additions.

For engineers working on roll manufacturing, the practical implication is clear: applying a low-frequency magnetic field during SAW cladding can extend the service life of rolls by 30-50% through improved hardness uniformity and reduced crack susceptibility. However, careful attention must be paid to the magnetic field parameters, as excessive field intensity can cause arc instability and increased spatter. The optimal parameter window should be determined through qualification testing per NB/T 47014, with the magnetic field parameters documented in the welding procedure specification (WPS).

The study also raises important questions about the scalability of this technology for large-diameter rolls where multiple welding passes are required. The interaction between the magnetic field and multi-pass welding, including the effect on heat-affected zones and interpass regions, warrants further investigation. Overall, this work represents a meaningful contribution to the field of physical field-assisted welding and provides a practical pathway for improving cladding quality in heavy industry applications.