Microstructure and Properties of CO2 Surfacing of Iron-Based Alloy with Composite Powders

Literature Overview

This study by Shi Haifang, Zhang Bo, Hu Shiju, and Jiang Xintong investigates the microstructure and wear properties of surfacing layers produced by CO2 shielded arc welding of self-fusing iron-based alloy powder (Fe55) and its composites with tungsten carbide (WC) and silicon carbide (SiC) on 45# steel substrates. Published in Ordnance Materials and Engineering Science (Vol. 34, No. 6, 2011, pp. 64-66), this research addresses the challenge of enhancing the wear resistance of iron-based surfacing alloys through composite reinforcement.

Research Methodology and Sample Design

The authors designed a series of experimental samples to systematically evaluate the effect of composite reinforcement on surfacing layer properties. The base alloy was Fe55 self-fusing iron-based alloy powder, which was blended with different proportions of WC and SiC particles. The optimal formulation was determined to be Fe55 + 15% WC + 6% SiC. All surfacing was performed using CO2 shielded arc welding on 45# steel substrates.

Microstructural Analysis and Phase Identification

The optimal composite surfacing layer (Fe55 + 15% WC + 6% SiC) achieved metallurgical bonding with the 45# steel substrate, indicating good wetting and interfacial reaction. The microstructure consists primarily of martensite and residual austenite, with reinforcement phases including W3Cr12Si5 and Cr3Si. The addition of WC and SiC particles acts as heterogeneous nucleation sites, promoting the formation of these hard intermetallic compounds during solidification.

The XRD analysis confirmed the presence of these reinforcement phases, which are significantly harder than the base Fe55 alloy phases. The W3Cr12Si5 phase is particularly hard and contributes substantially to the overall hardness of the deposit. The Cr3Si phase provides additional hardening through solid solution strengthening and precipitation hardening mechanisms.

The microhardness of 913 HV represents a dramatic improvement over the base Fe55 alloy, which typically achieves around 450 HV. This doubling of hardness translates directly to improved wear resistance, as evidenced by the two-fold increase in wear resistance measured in tribological testing.

Engineering Practice Implications

For engineers working with iron-based surfacing alloys in wear-critical applications, this research provides valuable guidance on composite reinforcement strategies. The key findings are that:

1. The addition of both WC and SiC together produces a synergistic effect that exceeds the improvement from either reinforcement alone.
2. The optimal proportions are 15% WC and 6% SiC by weight, beyond which agglomeration or excessive brittleness may occur.
3. CO2 shielded arc welding is a practical and economical process for depositing these composite alloys.
4. Metallurgical bonding with 45# steel substrates is achievable without special surface preparation.

The practical significance of this work is particularly relevant for applications such as pump impellers, valve seats, and mining equipment components where iron-based surfacing is commonly used but wear life is insufficient. The composite reinforcement approach offers a straightforward method to enhance wear resistance without changing the welding process or substrate material.

Study Insights and Reflections

This research demonstrates the effectiveness of composite powder blending in enhancing the properties of iron-based surfacing alloys. The approach is particularly attractive from a cost perspective because it uses readily available commercial powders and standard welding equipment. The doubling of wear resistance through simple powder blending represents a highly practical solution for extending the service life of wear-critical components. Engineers should note that the optimal reinforcement proportions are specific to the Fe55 base alloy and may need adjustment for other iron-based alloys. The work also highlights the importance of microstructural characterization in understanding the mechanisms of property improvement, as the formation of hard intermetallic phases such as W3Cr12Si5 and Cr3Si is responsible for the dramatic hardness increase rather than simply the presence of the original WC and SiC particles.