Wear Resistance Characteristics of High Chromium Molybdenum Alloy Composite Cladding on Deep Plow Blades by CO2 Shielded Metal Arc Welding

Literature Overview

This study, published in the Journal of Inner Mongolia University of Science and Technology (2014), investigates the tribological performance of a composite cladding layer produced by CO2 shielded metal arc welding (SMAW) using high chromium-molybdenum alloy consumables on deep plow blade components. The research was funded by the Jiamusi University Science and Technology Foundation (Project No. L2013-063) and conducted by Jiao Renbao, Yang Hai, Wang Guilian, and Shao Dongwei from the School of Mechanical Engineering, Jiamusi University. The work addresses a critical industrial challenge: extending the service life of agricultural and mining earth-moving tools subjected to severe abrasive wear conditions.

Core Technical Content

The fundamental approach involves depositing a high chromium-molybdenum alloy overlay layer onto the base steel substrate of deep plow blades using a CO2-shielded welding process. The selection of CO2 shielding gas is notable because it offers economic advantages over inert gas shielding while still permitting acceptable deposition rates for field applications. The alloy system leverages the hard carbide-forming capability of chromium combined with the solid solution strengthening effect of molybdenum to achieve a hardened microstructure.

Microstructural Analysis

The composite cladding layer typically exhibits a microstructure composed of martensite matrix with dispersed carbide precipitates. Chromium carbides (Cr7C3, Cr23C6) and molybdenum carbides (Mo2C) form during the solidification and subsequent cooling process. The presence of these hard carbides within a tough martensitic matrix provides the characteristic combination of hardness and fracture resistance required for wear-resistant applications. The hardness of the deposited layer typically reaches 55-62 HRC, significantly exceeding the 25-30 HRC of the base steel substrate.

Wear Mechanism Interpretation

Under abrasive sliding conditions, the wear resistance of the cladding layer is governed by three primary mechanisms: (1) the resistance of hard carbide particles to ploughing and cutting by abrasive particles, (2) the deformation resistance of the matrix phase, and (3) the cohesive strength between the carbide particles and the surrounding matrix. When the matrix is sufficiently hard to prevent plastic deformation around carbide particles, the composite layer demonstrates superior wear life. The molybdenum addition plays a dual role: it increases the hardenability of the matrix and refines the grain structure, thereby reducing the likelihood of intergranular cracking during the cooling cycle.

Process Parameters and Defect Analysis

The primary defects observed in CO2-shielded overlay welding include porosity caused by nitrogen pickup, undercut at the layer-to-layer interface, and excessive dilution leading to hardness reduction. The high oxygen activity of CO2 shielding promotes oxide inclusions, which can act as crack initiation sites. To mitigate these issues, the process employs a multi-pass technique with careful interpass cleaning and controlled heat input.

Engineering Practice Integration

In agricultural machinery manufacturing, deep plow blades operate under cyclic impact loading combined with continuous abrasive contact against soil and rock fragments. The conventional approach of replacing worn blades at 200-400 hours of operation results in significant material waste and downtime. By applying the high chromium-molybdenum composite cladding, service life extensions of 3-5 times have been reported in field trials. The economic viability is further enhanced because the CO2 welding process requires minimal equipment investment compared to gas tungsten arc or plasma arc alternatives.

A critical practical consideration is the preparation of the base material surface. The plow blade, typically manufactured from low-carbon steel or low-alloy steel, must be machined to a flat surface with a groove profile to improve mechanical interlocking. Surface contamination, including rust, oil, and scale, must be removed by grinding to bare metal before overlay application. The resulting cladding layer, with a typical thickness of 3-5 mm, can withstand repeated re-grinding during field maintenance without exposing the base material.

Key Reflections and Study Insights

This research exemplifies the principle of selecting the simplest effective process for a given application. While advanced techniques such as plasma transferred arc welding or laser cladding can produce superior microstructures with lower dilution, the CO2 shielded metal arc welding approach offers a practical compromise between performance, cost, and accessibility. The study reinforces the understanding that overlay welding is fundamentally a dilution-controlled process, and achieving the target hardness requires careful management of the heat input and pass sequencing.

The composite nature of the cladding layer—combining a hard carbide phase with a ductile matrix—reflects a design philosophy applicable across many tribological applications. Engineers should recognize that maximizing hardness alone does not guarantee wear resistance; the fracture toughness of the matrix and the interfacial cohesion between phases are equally critical. This work provides a valuable reference for engineers tasked with developing economical cladding solutions for heavy-duty agricultural and mining equipment.