Application of Overlay Welding Technology in Cutting Picks

Literature Overview

This paper, published in Mining Machinery in 2003 by Yao Shuyu, Li Huiqi, and Wu Yuping from Shandong University of Science and Technology and Tai'an Keda Jinna Plasma Technology Co., Ltd., presents a practical application of overlay welding technology to enhance the wear resistance of cutting picks used in mining and tunneling operations. The study demonstrates that high-speed steel wear-resistant electrodes can be applied to cutting pick substrates via overlay welding, achieving metallurgical bonding with high hardness and wear resistance.

Core Technical Approach

Cutting picks are critical consumable components in continuous miners, roadheaders, and tunnel boring machines. They are subjected to extreme impact loading, abrasion against hard rock formations, and repeated shock that leads to rapid wear and failure. The overlay welding approach described in this paper offers a cost-effective alternative to replacement or solid high-speed steel picks.

Process Parameters and Metallurgical Bonding

The overlay welding process achieves metallurgical bonding between the high-speed steel cladding layer and the pick substrate, ensuring structural integrity under impact and abrasion conditions. Key technical considerations include:

Parameter	Typical Range	Engineering Significance
Welding current	120-200 A (SMAW)	Controls dilution and penetration
Arc voltage	22-32 V	Affects bead profile and wetting
Travel speed	2-5 cm/min	Influences cooling rate and microstructure
Preheat temperature	150-300°C	Reduces cracking susceptibility
Cladding thickness	3-8 mm	Balances wear life and cost

Microstructural Characteristics

The high-speed steel cladding layer, typically containing elements such as tungsten, chromium, vanadium, and molybdenum, forms a microstructure rich in hard carbides (MC, M2C, M6C types) dispersed in a tempered martensite matrix. This microstructure provides:

High hardness (typically 58-65 HRC) for abrasion resistance
Good toughness retention at the cladding-substrate interface
Resistance to impact fracture under repeated shock loading
Metallurgical bonding that prevents delamination under cyclic loading

Engineering Practice Implications

The application of overlay welding to cutting picks represents a well-established industrial practice with several advantages over alternative approaches:

Cost reduction: Overlay repair allows multiple re-cladding cycles on the same pick body, extending service life significantly compared to single-use picks.
Material flexibility: Different cladding compositions can be selected for different rock formations (soft coal, hard shale, granite, etc.).
Rapid turnaround: Field repair capability reduces downtime in mining operations.
Metallurgical integrity: Unlike mechanical attachment methods, overlay welding provides cohesive bonding that resists delamination.

Common defects encountered in cutting pick overlay welding include:

Hot cracking in the cladding layer due to high carbon equivalent and rapid cooling
Undercut at the cladding-substrate boundary leading to stress concentration
Incomplete fusion when preheating is insufficient for low-carbon steel substrates
Porosity from contamination or excessive arc voltage

Study Insights and Conclusions

This work demonstrates the practical viability of overlay welding as a wear protection technology for high-impact mining components. The metallurgical bonding achieved through proper process control ensures that the cladding layer functions as an integral part of the component rather than a superficial coating. The approach aligns with established standards such as AWS D10.6 for surfacing welding and ISO 14555 for welding consumables. Engineers should note that the success of overlay welding on cutting picks depends critically on substrate preparation, preheat control, and post-weld heat treatment to relieve residual stresses and optimize the cladding microstructure for the specific service conditions encountered in mining operations.