Wear Resistance of Hard Alloy Surfacing Layer After Heat Treatment

Literature Overview

This study by Liu Yong and colleagues from Luoyang Institute of Technology investigates the wear resistance and corrosion-wear performance of hard alloy surfacing layers after heat treatment. Published in China Surface Engineering (Vol. 15, No. 3, 2002, pp. 17-19), the work compares three surface treatment approaches: B-C-N co-cementation, tungsten carbide-type hard alloy (D707) surfacing, and high carbon high chromium cast iron-type hard alloy (D618) surfacing, all subjected to appropriate heat treatments. The study addresses the practical challenge of combining wear resistance with corrosion resistance in surface engineering applications.

Core Technical Approach

The researchers investigated three surface treatment methods and their corresponding heat treatment cycles:

1. B-C-N co-cementation layer with appropriate heat treatment
2. D707 tungsten carbide-type hard alloy surfacing layer with heat treatment
3. D618 high carbon high chromium cast iron-type hard alloy surfacing layer with heat treatment

The hard alloy surfacing layers were subjected to two heat treatment cycles: 850°C air cooling and 850±5°C oil quenching followed by 400°C tempering. The heat treatment was performed to optimize the microstructure and mechanical properties of the surfacing layers. Corrosion-wear testing was conducted to evaluate the combined effect of wear and corrosion on the surface integrity.

Key Findings and Heat Treatment Effects

The study demonstrates that both D707 and D618 hard alloy surfacing layers, after heat treatment at 850°C air cooling or 850±5°C oil quenching plus 400°C tempering, exhibit high hardness and excellent corrosion-wear resistance. The heat treatment simplifies the surface treatment process compared to multi-step surface engineering approaches.

The D707 tungsten carbide-type hard alloy contains WC particles dispersed in a cobalt or iron-cobalt matrix. The heat treatment at 850°C promotes the dissolution and re-precipitation of carbides, refining the carbide distribution and improving the bonding between the carbides and the matrix. The 400°C tempering treatment relieves residual stresses and improves the toughness of the matrix without significantly reducing the hardness of the WC particles.

The D618 high carbon high chromium cast iron-type hard alloy contains primary chromium carbides (M7C3) in a martensitic matrix. The heat treatment at 850°C promotes the formation of a tempered martensite structure with fine, uniformly distributed carbides. The 400°C tempering further refines the microstructure and improves the corrosion resistance by reducing the residual stresses and minimizing the risk of stress corrosion cracking.

Engineering Practice Implications

The study provides a practical approach to combining wear resistance with corrosion resistance through hard alloy surfacing and heat treatment. In applications where components are exposed to both abrasive and corrosive environments, such as marine equipment, chemical processing vessels, and offshore oil platforms, this approach offers a significant advantage over traditional surface treatment methods.

The simplification of the surface treatment process is a major practical benefit. Traditional approaches to achieving both wear and corrosion resistance often require multiple surface treatment steps, such as hardening followed by passivation or coating. The hard alloy surfacing with heat treatment achieves both properties in a single process step, reducing manufacturing time and cost.

For field repair applications, the hard alloy surfacing approach is particularly attractive because it can be performed with portable welding equipment. The D707 and D618 surfacing alloys are available as consumable electrodes or wires, and the welding process can be adapted to the geometry of the component being repaired.

One practical consideration is the selection between D707 and D618 surfacing alloys. D707, with its WC particles, offers superior abrasion resistance and is suitable for applications dominated by sliding or impact abrasion. D618, with its high chromium content, offers superior corrosion resistance and is suitable for applications where corrosion is a significant concern. Engineers should select the appropriate alloy based on the dominant degradation mechanism in the service environment.

Study Insights

This study demonstrates the effectiveness of hard alloy surfacing combined with heat treatment as a versatile surface engineering approach. The ability to achieve both high hardness and excellent corrosion-wear resistance through a simplified process is a significant advance in practical surface engineering. The comparison with B-C-N co-cementation highlights the process advantages of surfacing over traditional diffusion-based surface treatments.

The heat treatment parameters identified in this study (850°C air cooling or 850±5°C oil quenching plus 400°C tempering) are directly applicable to industrial practice. The air cooling variant is particularly attractive for field applications where quenching media may not be available. The oil quenching variant provides better control over the cooling rate and can produce a more uniform microstructure, but requires additional equipment and handling precautions.

Overall, this study provides a practical and cost-effective solution to the challenge of combining wear and corrosion resistance in surface engineering applications. The hard alloy surfacing approach is particularly well-suited for field repair and maintenance applications, where process simplicity and equipment portability are critical considerations. The findings are directly applicable to the design and optimization of surface treatment processes for components in mining, marine, chemical, and offshore industries.