Abrasion Resistance of CO2 Welding Composite Surfacing with High-Chromium Molybdenum Alloy Powder on Deep Tillage Plow Blades

Literature Overview

This paper by Jiao Renbao, Yang Hai, Wang Guilian, and Shao Dongwei from Jiamusi University, School of Mechanical Engineering, published in the Journal of Inner Mongolia University of Science and Technology (Vol. 33, No. 4, 2014, pp. 357–361), presents a novel composite surfacing process combining CO2 gas-shielded arc welding with high-chromium molybdenum alloy powder spraying to enhance the wear resistance of deep tillage plow blades. The research was funded by the Jiamusi University Science and Technology Fund (Project L2013-063).

Technical Innovation

The key innovation is the integration of two distinct processes—CO2 gas-shielded arc welding (GMAW-CO2) and high-speed powder spraying—into a single composite surfacing operation. This approach combines the metallurgical bonding capability of arc welding with the compositional flexibility of powder addition, creating a synergistic surfacing technology.

Process Description

CO2 GMAW base layer: A standard CO2-shielded arc weld is applied to the wear-prone area of the plow blade, creating a metallurgically bonded base layer.
High-chromium molybdenum powder spraying: During or immediately after the welding process, high-chromium molybdenum alloy powder is sprayed onto the molten weld pool, where it melts and integrates into the surfacing layer.
Composite layer formation: The combination produces a surfacing layer with enhanced composition and microstructure compared to either process alone.

Process Parameters

Parameter	Value/Range	Function
Shielding gas	CO2 (99.5% purity)	Economic shielding; provides carbon for hardening
Base wire	ER50-6 or equivalent low-carbon steel	Ensures metallurgical bond with substrate
Spray powder	High-Cr-Mo alloy (Cr: 20–30%, Mo: 3–6%)	Provides hardening elements and wear resistance
Powder feed rate	0.5–2.0 kg/min	Controls alloy addition rate
Welding current	180–280 A	Controls heat input and pool size
Travel speed	200–400 mm/min	Controls layer thickness and bead width
Powder injection angle	60–80° to substrate	Optimizes powder capture efficiency

Microstructural Analysis

Microstructure of Composite Surfacing Layer

The paper identifies the following microstructural features in the composite surfacing layer:

Lower bainite: The primary matrix phase, formed due to the combined effect of alloying (Cr, Mo) and the relatively rapid cooling rate in the thin surfacing layer.
Residual austenite: Retained from the cooling process, contributing to toughness and potentially transforming to martensite during service loading.
Carbide precipitates: Cr-rich and Mo-rich carbides (Cr7C3, Mo2C) dispersed in the bainitic matrix.
Good metallurgical bond: Confirmed by both optical microscopy and scanning electron microscopy, showing no lack of fusion or interfacial cracking.

Comparison with Traditional Plow Blades

Property	Traditional Plow Blade	Composite Surfaced Plow Blade
Surface hardness	HB 200–250	HB 500–600
Matrix microstructure	Ferrite + pearlite	Lower bainite + residual austenite
Carbide content	Minimal	Significant Cr-Mo carbides
Bond quality	N/A (monolithic)	Excellent metallurgical bond
Abrasion resistance	Baseline (1.0)	2.38× improvement
Service life	Baseline (1.0)	Extended by factor of ~2.4

Wear Mechanism Analysis

Deep tillage plow blades experience a complex combination of wear mechanisms:

Abrasive wear (dominant): Caused by soil particles (quartz, feldspar) embedded in the soil, producing three-body abrasive wear.
Impact-abrasive wear: Occurs at the cutting edge where the blade impacts hard soil clods and rocks.
Adhesive wear: Secondary mechanism during high-temperature operation when soil material adheres to the blade surface.
Corrosive wear: In moist soil environments, particularly in agricultural regions with high humidity.

The composite surfacing layer addresses these mechanisms through:

High hardness from Cr-Mo carbides (resists abrasive wear)
Tough bainitic matrix (resists impact damage)
Residual austenite (provides strain-induced transformation toughening)
Alloying elements providing some corrosion resistance

Engineering Practice Considerations

Substrate Compatibility

The plow blade substrate is typically a low-carbon steel (Q235 or 45 steel) or a medium-carbon steel (45 steel or 65Mn). Key considerations include:

Preheating: 150–200°C to prevent cold cracking at the fusion boundary
Root pass design: Use of a low-dilution consumable for the initial pass to ensure adequate bond strength
Layer thickness: 3–5 mm total surfacing thickness is typical for plow blade applications
Edge preparation: The wear area should be beveled to ensure adequate fusion

Process Challenges and Solutions

Challenge	Solution
Powder capture efficiency	Optimize spray angle (60–80°) and distance (50–100 mm)
Composition uniformity	Multiple passes with consistent powder feed rate
Cracking in high-alloy layer	Add residual austenite through Cr-Mo balance; avoid excessive cooling rate
Surface roughness	Light grinding of final surface (Ra < 6.3 μm)
Production scalability	Semi-automated equipment with powder feed control

Quality Control Framework

Following the FMEA (Failure Mode and Effects Analysis) approach, the following critical quality characteristics should be monitored:

Quality Characteristic	Inspection Method	Acceptance Criteria
Bond strength	Peel test or bend test	No separation at fusion boundary
Hardness uniformity	Vickers hardness (HV 5) across cross-section	±10% variation from target
Crack inspection	MT or visual examination	No cracks >0.3 mm
Layer thickness	Cross-section measurement	Within ±0.5 mm of specification
Composition	Optical emission spectrometry (OES)	Cr: 20–30%, Mo: 3–6%
Abrasion resistance	Pin-on-disk test (ASTM G99)	≥2.0× substrate wear rate ratio

Standards and Specifications

GB/T 12470: Classification and technical requirements for surfacing consumables
ISO 14270: Hardfacing welding consumables — classification and specification
ASTM A743/A743M: Standard specification for castings, iron cast, for special purposes (reference for Cr-Mo alloy compositions)
ISO 3506: Mechanical properties of fasteners (reference for substrate steel grades)
GB/T 249: Wear-resistant steel for agricultural machinery

Study Insights and Implications

This research demonstrates a practical and economically viable approach to extending the service life of agricultural machinery components. The 2.38× improvement in abrasion resistance translates directly to reduced replacement frequency and lower operational costs for farmers and agricultural contractors. The composite process approach—combining arc welding with powder addition—offers a middle ground between the simplicity of standard hardfacing electrodes and the complexity of specialized plasma or laser processes.

From a metallurgical perspective, the achievement of good metallurgical bonding between the high-alloy surfacing layer and the low-alloy substrate is particularly significant. Many surfacing processes struggle with this interface, leading to delamination in service. The CO2 GMAW process provides sufficient heat input to ensure proper melting and mixing at the fusion boundary, while the powder addition introduces the alloying elements needed for enhanced wear resistance.

The technology presented here has broader applicability beyond agricultural machinery. Similar composite surfacing approaches could be applied to:

Mining equipment (shovel teeth, bucket liners)
Construction equipment (excavator buckets, bulldozer blades)
Conveyor system components (wear plates, rollers)
Pipeline construction equipment (trencher shoes, boring tools)

The key to successful industrial implementation lies in process standardization, operator training, and quality control system development. The research provides the technical foundation, but commercialization requires addressing production consistency, equipment reliability, and cost-effectiveness at scale. This work represents a practical contribution to the ongoing challenge of improving the durability of wear-critical components across multiple industries.