Microstructure and Performance Comparison of Carbon Arc Surfacing and Laser Cladding Fe-Based Alloy Powder Coatings

Literature Overview

This paper by Hu Jiao and colleagues from Liaoning University of Technology provides a comprehensive comparison between carbon arc surfacing (oxy-arc hardfacing) and laser cladding for depositing Fe-05 alloy powder onto Q235 steel substrates. Published in Hot Working Technology in 2017, the study examines microstructure, phase composition, microhardness distribution, and abrasive wear performance of both coating methods, offering valuable guidance for process selection in industrial applications.

Core Technical Findings

Both coating methods produce a similar phase assemblage consisting of a dark matrix phase and white dispersed phases. The matrix is identified as α-(Fe,Cr) solid solution, while the white phases include (Fe,Cr)₇C₃, Cr₂₃C₆, Cr₇C₃, Fe₂B, Fe₃B, Cr₃C₂, CrFeB, and Ni₃Si. However, significant differences exist in microstructure refinement, hardness levels, and wear performance between the two processes.

Comparative Performance Summary

Parameter	Carbon Arc Surfacing	Laser Cladding
Average Microhardness	~750 HV (estimated)	~989 HV
Microstructure Refinement	Moderate	Excellent
Dilution with Substrate	High (30–50%)	Low (5–15%)
Crack Type	Transgranular	Transgranular
Crack Severity	Moderate	Moderate
Wear Resistance	Moderate	Superior
Deposition Efficiency	High	Moderate
Equipment Cost	Low	High
Coating Thickness Capability	>5 mm easily	Typically <3 mm
Geometric Flexibility	High	Limited by laser access

Detailed Metallurgical Analysis

Phase Composition and Distribution

The presence of multiple carbide and boride phases in both coatings reflects the complex thermodynamic equilibrium of the Fe-Cr-B-Ni-Si system. The key differences lie in the distribution and morphology of these phases:

Laser cladding: Rapid solidification rates (10³–10⁴ K/s) produce fine, uniformly distributed hard phases within a refined martensitic matrix. The cellular/dendritic microstructure is significantly finer than in conventional welding.
Carbon arc surfacing: Slower cooling rates (10¹–10² K/s) allow for coarser phase formation and more pronounced segregation. Carbide networks at former liquid-liquid boundaries are more prevalent.

Crack Formation Mechanism

Both processes produce transgranular cracks, which is attributed to the high carbon equivalent of the coating material and the thermal stresses developed during solidification and cooling. The transgranular nature indicates that the cracking is driven by thermal stress rather than by segregation at grain boundaries (which would produce intergranular cracking). This is consistent with the high cooling rate and thermal gradient experienced in both processes.

The carbon arc surfacing process, despite its lower cooling rate, still produces cracks because of the large thermal mass of the deposited material and the significant temperature differential between the hot weld pool and the relatively cool substrate. Laser cladding cracks are driven by the extreme thermal gradient between the small molten pool and the surrounding solidified material.

Engineering Practice Implications

Process Selection Criteria

The choice between carbon arc surfacing and laser cladding should be based on a systematic evaluation of application requirements:

Decision Factor	Favor Carbon Arc	Favor Laser Cladding
Coating thickness >3 mm	✓
Large surface area coverage	✓
Complex geometry	✓
Maximum hardness requirement		✓
Minimum dilution required		✓
Fine microstructure needed		✓
Low equipment budget	✓
High production volume	✓
Precision surface finish		✓

Crack Mitigation Strategies

For both processes, the following measures can reduce crack susceptibility:

Substrate preheating to 200–300°C to reduce thermal gradient
Post-weld heat treatment at 550–600°C for stress relief
Control of interpass temperature below 350°C
Consideration of multi-layer builds with thinner individual layers
Addition of ductile phases (such as retained austenite) through composition modification

Study Insights and Reflections

This comparison study provides engineers with a clear framework for process selection based on performance requirements versus practical constraints. The fundamental trade-off is between deposition efficiency and cost (favoring carbon arc surfacing) versus microstructural refinement and performance (favoring laser cladding).

The finding that both processes produce transgranular cracking is particularly instructive. It demonstrates that the cracking tendency is inherent to the coating composition and the thermal cycle of the process, rather than being specific to one technique. This suggests that composition optimization (such as reducing carbon content or adding ductilizing elements) may be more effective than process modification alone for crack prevention.

The hardness differential of approximately 240 HV between the two processes translates to significant wear life differences in abrasive applications. For applications where coating life is critical and equipment cost is acceptable, laser cladding offers superior performance. However, for many industrial applications—particularly large-scale pipe repair, heavy equipment hardfacing, and field maintenance—carbon arc surfacing remains the practical choice due to its flexibility, lower cost, and proven reliability in production environments. The key is to match the process to the application rather than defaulting to the highest-performance option regardless of cost or practicality constraints.