Submerged Arc Welding TiC Particle Reinforced Composite Coatings Microstructure and Properties

Literature Overview

This study, published in the Chinese Journal of Nonferrous Metals in 2011 by Liu Junhai, Huang Jihua, Liu Junbo, and Song Guixiang from Beijing University of Science and Technology and Weihai Vocational College, investigates the microstructure and mechanical properties of TiC particle reinforced composite coatings produced by submerged arc welding (SAW) overlay. The research was supported by the Shandong Provincial Science and Technology Key Project (2007GG30003003). The work addresses a critical engineering need: producing hardfacing overlays that combine high hardness with adequate toughness for severe abrasive and erosive service conditions.

Core Technical Approach

The researchers employed a composite welding wire technique in which pre-dispersed TiC particles were incorporated into the welding consumable, followed by SAW overlay welding onto a low-carbon steel substrate. The key innovation lies in the controlled dispersion of TiC ceramic particles within the molten weld pool during the SAW process. Unlike conventional hardfacing alloys that rely solely on carbide precipitation during solidification, this approach introduces exogenous TiC particles that survive the thermal cycle and act as primary reinforcement phases.

The SAW process parameters were optimized to ensure adequate heat input for melting the TiC particles without excessive dissolution. Typical parameters for this type of work include:

Parameter	Typical Range	Purpose
Welding current	280–380 A	Ensure complete melting of consumable
Welding voltage	26–32 V	Control arc stability and penetration
Travel speed	200–350 mm/min	Balance dilution and deposition rate
Wire feed speed	150–250 mm/min	Maintain arc length
Shielding flux	Rutile or basic type	Provide shielding and alloying
TiC particle size	10–100 μm	Balance dispersion and dissolution

Microstructural Analysis and Key Findings

Metallographic examination reveals that the overlay microstructure consists of a martensitic matrix with dispersed TiC particles, secondary carbides, and retained austenite. The TiC particles appear as bright angular features distributed throughout the matrix. The critical finding is that the TiC particles undergo partial dissolution during welding, with smaller particles dissolving more readily while larger particles remain intact. This partial dissolution actually benefits the coating properties because dissolved Ti and C atoms promote additional carbide precipitation in the matrix during cooling.

The hardness of the as-welded overlay typically reaches 65–75 HRC, significantly higher than conventional hardfacing alloys which usually achieve 50–60 HRC. The hardness distribution is relatively uniform across the overlay thickness, indicating good particle dispersion. After heat treatment at 600°C for 2 hours, the hardness decreases slightly to approximately 60–68 HRC due to tempering of the martensitic matrix, but the TiC particles remain stable and continue to provide reinforcement.

Wear Resistance Evaluation

Wear testing under dry sliding conditions demonstrates that the TiC particle reinforced overlay exhibits 3–5 times the wear resistance of conventional high-carbon martensitic hardfacing alloys. The wear mechanism transitions from adhesive wear in the base alloy to primarily abrasive wear in the TiC-reinforced composite. The hard TiC particles (approximately 3000 HV) resist micro-cutting by abrasive particles, while the tougher martensitic matrix prevents catastrophic spalling of the particles.

The coefficient of friction is also reduced by approximately 20–30% compared to unmodified hardfacing alloys, which is attributed to the lubricating effect of TiC particles during sliding contact. This dual improvement in wear resistance and friction reduction makes the coating particularly suitable for applications such as coal handling equipment, mining machinery, and slurry pump components.

Engineering Practice Considerations

From a practical fabrication standpoint, several challenges must be addressed when implementing this technology:

Particle dispersion uniformity: Agglomeration of TiC particles in the consumable can lead to localized soft or hard zones in the overlay. Pre-mixing and sieve analysis of the consumable are essential quality control steps.
Crack susceptibility: The high carbon content combined with martensitic transformation increases the risk of cold cracking. Preheating of 150–250°C and controlled cooling rates are recommended for thick sections.
Overlay thickness control: Multi-pass welding is typically required to achieve sufficient overlay thickness (3–8 mm). The dilution rate from the base metal must be monitored, as excessive dilution reduces the TiC content in the final overlay.
Bond strength: The metallurgical bond between the overlay and substrate should exceed 400 MPa for reliable service. Interpass temperature control between 100–250°C helps maintain this bond integrity.

Study Insights and Implications

This research demonstrates that incorporating ceramic reinforcement particles into SAW hardfacing consumables is a viable and cost-effective approach to significantly enhance wear resistance. The technology bridges the gap between conventional hardfacing alloys and expensive thermal spray or laser cladding processes. For engineers designing wear-resistant components, the key takeaway is that particle size selection and welding parameter optimization are the two most critical factors controlling final coating performance. The partial dissolution phenomenon, while seemingly detrimental, actually contributes to a synergistic reinforcement effect that pure particle composites cannot achieve. This insight has direct implications for consumable development and process specification in industrial hardfacing operations.