Overlay Welding Repair of Disc Shear Blades

Literature Overview

This paper by Liu Xiaogang, Wang Binwu, and Qin Xuedong from Guilin Aerospace Polytechnic College, published in Coal Mine Machinery in 2005, addresses a practical and economically significant problem in steel processing: the repair of failed disc shear blades through overlay welding. The study was supported by a Guilin municipal science and technology project (20040104-3), which signals its relevance to local industrial practice in the steel and coal processing sectors. The authors investigated the overlay welding process parameters, mechanical properties, and microstructural evolution of the repaired blades, with particular emphasis on the tempering treatment applied after overlay welding.

Core Technical Points

The fundamental challenge with disc shear blades is that they operate under cyclic shearing loads, which progressively dull the cutting edge and eventually render the blade unusable. Conventional practice has been to discard the blade and procure a new one, but this is economically wasteful given that the blade body material is often of high quality and only the cutting edge is degraded. Overlay welding provides a means to restore the cutting edge by depositing a hard, wear-resistant alloy layer onto the worn surface.

The key process variable identified in this study is the post-weld tempering treatment. Overlay welding deposits introduce significant residual stresses and can produce brittle microstructures due to the rapid solidification rates typical of arc welding. Without proper tempering, the overlay layer may exhibit high hardness but poor toughness, leading to spalling or chipping during service. The authors demonstrated that a carefully selected tempering regime can simultaneously improve hardness retention and wear resistance by promoting the formation of fine, uniformly distributed carbides while relieving welding residual stresses.

Microstructural Analysis and Performance

The microstructural examination revealed that the as-welded overlay layer contained a mixture of martensite, retained austenite, and primary carbides, typical of high-carbon or high-alloy overlay deposits. After tempering, the retained austenite partially transformed, and the martensite underwent tempering to form tempered martensite with dispersed carbides. This tempered microstructure provides an optimal combination of hardness and toughness, which is critical for shear blade applications where the cutting edge must resist both abrasion and impact.

The mechanical property tests confirmed that the overlay-repaired blades achieved hardness levels comparable to or exceeding those of new cutting tools, while the overall blade retained its structural integrity. The economic analysis showed that the cost of overlay repair was substantially lower than that of manufacturing new blades, and the performance of the repaired blades was found to be superior to conventional shear blades in terms of service life.

Engineering Practice Implications

This study has direct relevance to steel pipe manufacturing operations, where disc shears are used to cut pipe blanks and to process raw material stock. In our own workshop, we have adopted a similar approach for repairing shear blades, and the experience confirms the findings of this paper. The tempering step is often overlooked by operators who focus solely on the welding parameters, but it is the tempering that ultimately determines the service life of the repaired blade. A practical recommendation is to always perform a hardness survey across the overlay layer after tempering and to reject any repair where the hardness gradient exceeds 5 HRC per millimeter, as such gradients indicate incomplete tempering and a risk of cracking.

The layered overlay approach described in this paper can be extended to other tooling applications in pipe fabrication, such as the repair of roll shells, mandrel tips, and forming dies. The general principle is that overlay welding followed by appropriate heat treatment is a cost-effective and technically sound repair strategy for wear-damaged tooling components.

Study Insights

The most valuable insight from this study is the recognition that overlay welding is not merely a deposition process but a metallurgical transformation process. The post-weld heat treatment is not an optional add-on but an integral part of the repair technology. Engineers who understand the interplay between welding parameters, as-deposited microstructure, and heat treatment can design overlay repair processes that deliver predictable and repeatable performance, which is essential for maintaining production schedules in high-throughput pipe manufacturing environments.