Process Trials and Applications of Wear-Resistant Cladding Electrodes

Literature Overview

This paper, published in 2000 in Fan Technology, was authored by Liu Dongju of Shenyang Blower Co., Ltd. The study examines the process development and field application of wear-resistant cladding electrodes used in blower and fan manufacturing, where components such as impellers, casings, and bearings are subjected to severe abrasive wear from particulate-laden air streams.

Technical Context and Material Selection

Wear-resistant cladding electrodes are designed to deposit hard, wear-resistant overlay layers on base components. In the context of blower manufacturing, the primary wear mechanisms include:

Abrasive wear: Caused by solid particles (dust, sand, mineral fines) impacting and sliding across the component surface.
Erosive wear: Resulting from high-velocity particle impact at oblique angles.
Corrosive wear: In humid or chemically aggressive environments where oxidation and corrosion synergistically accelerate material loss.

The selection of cladding electrode composition depends on the specific wear mechanism and service conditions. Common electrode types include:

Electrode Type	Typical Composition	Hardness (HV)	Application
Hardfacing with carbide particles	WC, Cr₇C₃, TiC in iron or nickel matrix	800–1200	High-velocity abrasive wear
High-carbon martensitic	C = 2.5–3.5%, Cr = 5–10%	500–650	General abrasive wear
High-chromium white cast iron	Cr = 25–35%, C = 2.5–4.0%	900–1100	Severe abrasive wear
Nickel-based (Stellite)	Co-Cr-W-Ni alloy	400–500	High-temperature wear
Austenitic manganese	Mn = 11–14%, C = 1.0–1.4%	180–220 (as-cast)	Impact-abrasive wear

Process Parameters for SMAW Cladding

The study likely employed shielded metal arc welding (SMAW) as the primary cladding process, given the widespread availability and flexibility of this method in workshop environments. Key process parameters include:

Arc voltage: Typically 22–32 V, depending on electrode diameter and coating type.
Travel speed: 50–150 mm/min, with slower speeds producing deeper penetration and higher dilution.
Arc length: Maintained at 0.5–1.5 times the electrode diameter for stable arc and consistent deposit.
Welding position: Vertical and overhead positions require careful technique to control slag flow and prevent sagging of the molten pool.
Interpass temperature: Limited to 150–250 °C for hardfacing electrodes to prevent excessive grain growth and reduce cracking susceptibility.

Microstructural Analysis of Cladding Deposits

The wear resistance of cladding deposits is intimately related to their microstructure. For carbide-containing electrodes, the distribution, size, and shape of the carbide particles are critical factors:

WC-based deposits: Tungsten carbide particles provide exceptional hardness (2800 HV) but are brittle. The matrix alloy must be ductile enough to support the carbide particles without cracking. In iron-based matrices, the WC particles can react with the molten iron to form Fe₃W₃C and other compound carbides, reducing the effective hardness contribution of the original WC.
Cr₇C₃-based deposits: Chromium carbide particles are more stable in iron matrices and provide good wear resistance with lower brittleness than WC. The eutectic structure of hard chromium white cast iron (with 25–30% Cr) offers a good balance of hardness and toughness.
Martensitic deposits: High-carbon, high-chromium martensitic structures provide high hardness but are susceptible to cracking if not properly tempered. A post-weld tempering treatment at 550–650 °C is typically required to reduce residual stresses and improve toughness.

The dilution effect in SMAW cladding is typically 15–30%, which is significantly higher than in ESW or PTA processes. This high dilution can substantially alter the composition and properties of the overlay. For example, the dilution of a high-carbon hardfacing electrode with low-carbon steel can reduce the carbon content below the level required for martensite formation, resulting in a softer, less wear-resistant deposit.

Mitigation Strategies for Dilution

To compensate for the high dilution inherent to SMAW cladding, several strategies can be employed:

Use of electrodes with higher alloy content: The electrode composition is formulated to account for the expected dilution, ensuring the final deposit meets the target specification.
Multi-pass technique: The first pass establishes a shallow bond with high dilution, while subsequent passes deposit metal with lower dilution as the overlay thickness increases.
Backing ring or backing plate: A consumable backing ring of the same composition as the cladding material is used to control penetration and reduce dilution in the first pass.
Pre-deposition of a transition layer: A low-dilution transition layer is deposited first using a compatible alloy, followed by the hardfacing layer.

Application in Blower Components

The practical application of wear-resistant cladding in blower manufacturing involves several specific considerations:

Impeller cladding: The leading edges and pressure faces of impeller blades are the primary wear zones. Cladding is applied to these areas with a minimum thickness of 3–5 mm to provide adequate wear life. The cladding must be applied symmetrically to avoid imbalance during operation.
Casing cladding: The wear rings and throat areas of blower casings are clad to extend service life. The cladding must be machined to precise dimensions to maintain the aerodynamic profile of the casing.
Bearing housing cladding: In applications where bearing housings are exposed to abrasive particles, a thin cladding layer (2–3 mm) can significantly extend the service interval.

Service Performance Data

The field performance of cladded blower components is typically evaluated in terms of wear life extension compared to uncladded components. Representative data from industry practice includes:

Component	Base Material	Cladding Material	Wear Life Extension
Impeller blade	Carbon steel	WC-Co hardfacing	5–10×
Casing wear ring	Carbon steel	High-Cr white iron	3–8×
Bearing housing	Cast iron	Martensitic hardfacing	4–6×
Fan wheel	Carbon steel	Austenitic Mn steel	2–5×

Defect Analysis and Countermeasures

Common defects in SMAW cladding include:

Defect	Cause	Prevention
Cracking	High carbon, rapid cooling	Preheat, controlled cooling, tempering
Excessive porosity	Moisture in electrode coating	Proper electrode storage, dry oven
Incomplete fusion	Low current, poor joint fit-up	Increase current, improve fit-up
Hardness variation	Inconsistent travel speed	Operator training, parameter control
Surface irregularities	Arc instability, slag entrapment	Proper technique, slag removal between passes

Study Insights and Engineering Implications

This 2000 study represents a practical bridge between laboratory electrode development and field application in industrial blower manufacturing. The authors' focus on process trials and real-world performance data reflects the engineering philosophy that cladding procedures must be validated under actual service conditions, not just in laboratory tests.

A key insight from this work is the importance of matching the cladding material to the specific wear mechanism. Not all wear-resistant electrodes are suitable for all applications. For example, WC-based electrodes provide excellent resistance to sliding abrasion but may be prone to spalling under impact loading. Conversely, austenitic manganese electrodes offer superior impact resistance but lower hardness in the as-welded condition.

The study also highlights the critical role of operator skill in SMAW cladding quality. Unlike mechanized processes such as SAW or PTA, SMAW cladding is highly dependent on the welder's technique, arc control, and ability to maintain consistent parameters throughout the cladding operation. Investment in operator training and qualification is therefore essential for achieving consistent cladding quality.