CLADDING TECHNOLOGY SHANXI CO., LTDMicrostructural Analysis of CO2 Shielded Arc Cladding on Sugarcane Roller Shafts
Literature Overview
This 2002 study published in the Journal of Guangxi University (Natural Science Edition) by Wen Jingxian from the Industrial Testing and Experimental Center of Guangxi University investigates the microstructure and mechanical properties of overlay welds deposited on sugarcane roller shafts using CO2 gas shielded arc welding (GMAW-C). Sugarcane crushing rollers operate under severe conditions of high pressure, abrasive contact with fibrous cane material, and intermittent impact loading. The base material is typically low-carbon steel or low-alloy steel, and the overlay layer must provide enhanced wear resistance while maintaining adequate toughness to resist crack initiation under cyclic loading.
Core Technical Points
The study examines the dilution behavior, phase composition, hardness profile, and microstructural evolution of the overlay layer. CO2 gas shielded welding is a cost-effective and widely available process in industrial settings, making it an attractive choice for field repair and refurbishment of large roller shafts where specialized equipment such as plasma arc or laser cladding systems may not be available.
The key findings include:
- The overlay layer exhibits a martensitic structure with varying degrees of tempering depending on the number of passes and interpass temperature control.
- Dilution from the base metal into the first pass is significant, often exceeding 30%, which reduces the hardness and wear resistance of the initial layers.
- Subsequent passes show progressively lower dilution as the previous overlay layer becomes the effective base for the next pass.
- Hardness in the overlay layer typically ranges from 350 to 480 HV, with the highest values achieved in the uppermost passes where dilution is minimized.
Typical Process Parameters and Microstructural Zones
| Parameter | Typical Value | Engineering Significance |
|---|---|---|
| Shielding gas | 100% CO2 | Low cost, high penetration, moderate arc stability |
| Wire diameter | 1.0–1.6 mm | Balance between deposition rate and heat input |
| Current | 180–260 A | Dependent on wire diameter and travel speed |
| Voltage | 22–28 V | Controls arc length and bead profile |
| Travel speed | 200–400 mm/min | Affects bead overlap and dilution |
| Interpass temperature | < 150°C | Prevents excessive grain growth and softening |
| Preheat temperature | 50–100°C | Reduces hydrogen-induced cracking risk |
Phase Composition and Hardness Distribution
The overlay microstructure typically consists of tempered martensite with retained austenite and carbide precipitates. The type and morphology of carbides depend heavily on the filler metal composition. When using high-carbon or high-alloy filler wires, cementite (Fe3C) and alloy carbides such as (Fe,Cr)7C3 may form, providing enhanced abrasion resistance. However, excessive retained austenite can reduce hardness and dimensional stability during service.
A critical observation from this study is the transition zone between the overlay layer and the base metal. This zone often exhibits a coarse-grained heat-affected zone (HAZ) with reduced toughness. The presence of a soft, ductile transition zone is actually beneficial for fatigue life, as it acts as a crack arrest zone. However, if the transition zone is too thin or too hard, crack initiation from the overlay surface can propagate directly into the base metal.
Hardness Profile Across the Overlay Layer
| Depth from Surface (mm) | Dilution (%) | Hardness (HV) | Dominant Microstructure |
|---|---|---|---|
| 0.0–0.5 | < 5 | 450–480 | Fine tempered martensite + carbides |
| 0.5–1.0 | 10–20 | 400–450 | Tempered martensite |
| 1.0–1.5 | 20–35 | 350–400 | Coarse tempered martensite |
| 1.5–2.0 | 35–50 | 300–350 | Martensite + pearlite transition |
| > 2.0 | > 50 | 200–280 | Base metal HAZ / base metal |
Engineering Practice Implications
For sugarcane roller shaft applications, the following engineering considerations emerge from this study:
- Multi-pass strategy: A minimum of three passes is recommended to ensure adequate dilution control. The first pass serves as a transition layer, and the subsequent passes provide the wear-resistant surface.
- Filler metal selection: High-carbon martensitic wires or austenitic-ferritic wires are commonly used. The choice depends on whether abrasion resistance or impact resistance is prioritized.
- Post-weld heat treatment: Tempering at 500–600°C can relieve residual stresses and reduce hardness slightly while significantly improving toughness. However, this must be balanced against the loss of wear resistance.
- Surface finishing: After welding, the overlay surface should be ground or machined to remove weld ripples and achieve the required dimensional accuracy for roller operation.
Key Reflections
This study highlights the practical value of CO2 GMAW for industrial cladding applications where cost-effectiveness and equipment availability are paramount. The relatively low cost of CO2 gas and the widespread availability of GMAW equipment make this process ideal for large-scale repair operations in sugar mills and similar industries. However, the higher carbon equivalent of CO2 shielding compared to mixed gas (Ar + CO2) increases the risk of hydrogen-induced cracking in high-hardness overlay layers. Proper preheating, low-hydrogen filler metals, and controlled cooling rates are essential to mitigate this risk.
The study also underscores the importance of understanding dilution behavior in multi-pass overlay welding. Engineers must recognize that the first pass is fundamentally different from subsequent passes in terms of composition and properties. Designing overlay schemes that account for this progressive dilution reduction is essential for achieving uniform performance across the entire overlay thickness.
Conclusion
The CO2 gas shielded arc cladding of sugarcane roller shafts represents a classic example of pragmatic engineering solutions for demanding industrial applications. The study provides valuable insights into microstructural evolution, dilution control, and hardness optimization that remain relevant for modern cladding practice. For engineers working on similar applications, the key takeaway is that process simplicity does not preclude high performance, provided that dilution behavior, filler metal selection, and thermal management are carefully controlled.