Transfer Coefficients of Alloy Elements in Manual Arc Cladding Electrodes

Literature Overview

Published in Transactions of the Welding Institute of China in 1995, this research by scientists from the Beijing Institute of Metallurgy and University of Science and Technology Beijing addresses a fundamental yet often underappreciated aspect of cladding technology: the transfer efficiency of alloy elements from electrode coating to weld deposit during manual arc cladding (SMAW). Understanding transfer coefficients is essential for accurate prediction of deposit composition, which directly affects mechanical properties, corrosion resistance, and service life of cladding layers.

Core Technical Content

The transfer coefficient (η) for any alloy element is defined as the ratio of the concentration of that element in the weld metal to its concentration in the electrode coating or wire, normalized for dilution effects. The mathematical relationship is expressed as:

η = (C_weld / C_electrode) × (1 - D)

where C_weld is the element concentration in the weld deposit, C_electrode is the concentration in the electrode material, and D is the dilution fraction from base metal.

The study systematically measured transfer coefficients for elements including Mn, Si, Cr, Mo, V, W, Ni, and C using spectrographic analysis of multi-pass cladding deposits deposited on carbon steel and low-alloy steel substrates. The research covered various electrode types including E5015-type basic coated electrodes and specialized cladding electrodes.

Transfer Coefficient Data and Analysis

Alloy Element	Typical Transfer Coefficient (η)	Primary Loss Mechanism	Practical Significance
Mn	0.85-0.95	Oxidation during arc	Affects hardness and hot cracking resistance
Si	0.75-0.90	Oxidation to SiO2 slag	Influences fluidity and slag properties
Cr	0.90-0.98	Minor oxidation	Critical for corrosion resistance prediction
Mo	0.92-0.99	Minimal loss	Reliable for secondary hardening design
V	0.88-0.95	Partial oxidation	Carbide formation prediction
W	0.95-0.99	Negligible loss	Highly predictable composition
Ni	0.95-1.00	Negligible loss	Austenite stabilization prediction
C	0.70-0.85	Decarburization	Affects hardness and martensite formation

Process Parameter Effects on Transfer Coefficients

The research demonstrated that transfer coefficients are not fixed constants but vary with welding parameters:

Current density: Higher current density increases arc temperature, promoting greater oxidation of Mn and Si, reducing their transfer coefficients by 5-10%.
Arc length: Longer arc length increases atmospheric pickup and element oxidation, particularly affecting C and Mn transfer.
Polarity: DCEP (Direct Current Electrode Positive) provides deeper penetration and slightly different transfer behavior compared to DCEN, with electrode-positive polarity showing marginally better transfer of high-vapor-pressure elements.
Electrode coating thickness: Thicker coatings provide more alloying element reserves, partially compensating for losses through sustained alloying during the welding process.

Engineering Application Guidance

For practical cladding operations, the transfer coefficient data enables engineers to:

Back-calculate required electrode composition: If a target deposit composition of 12% Cr is required with an expected dilution of 20%, and the Cr transfer coefficient is 0.95, the electrode must contain approximately 14.7% Cr to compensate for both dilution and transfer losses.
Predict dilution effects accurately: The combined application of transfer coefficients and dilution models allows prediction of final deposit composition within ±1-2% for most elements, which is sufficient for quality assurance purposes.
Optimize multi-pass strategies: In multi-pass cladding, subsequent passes experience lower dilution rates (typically 5-15% for passes beyond the first). This means that transfer coefficient corrections become less significant for later passes, and the final deposit composition converges toward the electrode composition.

Study Reflections

This 1995 publication provides foundational data that remains applicable to modern cladding practice. The methodology employed—systematic spectrographic analysis combined with controlled welding parameter studies—establishes a rigorous approach to composition prediction. In contemporary practice, this knowledge is integrated into welding procedure qualification (WPQ) documentation and is essential for compliance with standards such as ASME IX and NB/T 47014. The study's emphasis on empirical measurement rather than theoretical prediction is particularly valuable, as real-world welding conditions introduce complexities (atmospheric contamination, electrode storage conditions, operator technique) that theoretical models cannot fully capture. Engineers should treat transfer coefficient data as a starting point for qualification testing rather than as absolute design constants.