Effect of TiO2 Addition on Microstructure and Properties of High Manganese Steel Surfacing Layers

Literature Overview

This study, published in 2016 in the journal Metal Heat Treatment (Vol. 41, Issue 12, pp. 52-57) by Niu Ben, Yi Yaoyong, Yi Jianglong, Wang Kai, and Liu Hongxi, investigates the influence of titanium dioxide addition on the microstructure and wear performance of high manganese steel surfacing layers. The research was conducted at Kunming University of Science and Technology and the Guangdong Provincial Key Laboratory of Modern Welding Technology at the Chinese-Ukrainian Paton Welding Research Institute in Guangzhou. The work was supported by Guangzhou municipal science research funds and international cooperation projects.

Experimental Design and Methodology

The surfacing experiments were conducted on Q235 carbon steel plates using flux-cored wires with varying TiO2 contents. The high manganese steel composition was modified by adding different amounts of TiO2 and Al, which react during the welding process to form TiAl intermetallic compound particles in situ. The resulting surfacing layers were characterized using scanning electron microscopy (SEM), electron probe microanalysis (EPMA), and X-ray diffraction (XRD). Hardness measurements and wear tests were performed on the deposited metal to evaluate the effect of TiO2 addition on mechanical and tribological properties.

The key experimental variable was the TiO2 content in the flux-cored wire, with the optimal addition identified at 0.53% by mass. At this level, the deposited metal exhibited the best combination of microstructure refinement and wear resistance.

Microstructure Evolution and Hard Phase Formation

The addition of TiO2 and Al to the high manganese steel surfacing system triggers a series of welding metallurgical reactions. During the arc melting process, TiO2 is reduced by Al to form TiAl intermetallic compounds. These reactions occur in the molten pool and continue during solidification, resulting in the formation of fine TiAl particles distributed throughout the austenitic matrix.

The in situ formation of TiAl particles serves as effective nucleation sites for austenite grain refinement. The resulting fine-grained microstructure with a high density of hard particles provides superior wear resistance compared to the baseline composition. The wear mechanism shifts from adhesive wear at low TiO2 levels to abrasive wear at optimal and higher levels, indicating that the hard TiAl particles effectively resist material removal through plowing and cutting mechanisms.

Wear Mechanism Analysis

The transition in wear mechanism from adhesive to abrasive wear is a critical finding. In adhesive wear, material transfer occurs between the surfacing layer and the counterface due to intimate contact and shear at asperity junctions. This mechanism is particularly detrimental in high manganese steel systems because the austenite phase undergoes strain-induced martensitic transformation (TRIP effect) under deformation, which can either enhance or reduce wear resistance depending on the conditions.

At the optimal TiO2 addition of 0.53%, the fine TiAl particles act as barriers to dislocation motion and crack propagation, while also providing a harder surface that resists abrasive wear. The wear tracks and worn surface morphology observed by SEM would show characteristic plowing grooves rather than material smearing and transfer, confirming the shift to abrasive wear dominance.

Engineering Applications and Process Considerations

High manganese steel surfacing layers are widely used in applications requiring high toughness and wear resistance, such as mining equipment, conveyor components, and earth-moving machinery. The TRIP effect in austenitic high manganese steels provides inherent strain hardening under impact and abrasion, making these materials suitable for severe service conditions. The TiO2 addition strategy offers a practical means of further enhancing wear resistance without significantly compromising the toughness advantages of the high manganese system.

From a process standpoint, the use of flux-cored wire with controlled TiO2 and Al additions provides a convenient method for introducing the necessary elements into the surfacing layer. The flux-cored wire process is well-established in industrial surfacing operations and can be adapted to incorporate the TiO2-modified composition with minimal equipment changes.

Study Insights and Reflections

This research demonstrates the effectiveness of in situ particle formation as a microstructure refinement strategy in surfacing metallurgy. The TiO2/Al system is particularly attractive because both elements are readily available and inexpensive, and the resulting TiAl particles are thermodynamically stable under the welding thermal cycle. The optimal TiO2 level of 0.53% is relatively modest, suggesting that the process is robust and not overly sensitive to small compositional variations. The identification of the wear mechanism transition provides valuable insight for predicting service behavior and selecting appropriate surfacing compositions for specific applications.